MYELOPATHY, RADICULOPATHY, and PERIPHERAL ENTRAPMENT SYNDROMES
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MYELOPATHY, RADICULOPATHY, and PERIPHERAL ENTRAPMENT SYNDROMES
MYELOPATHY, RADICULOPATHY, and PERIPHERAL ENTRAPMENT SYNDROMES David H. Durrant, D.C., D.A.B.C.N. Neuro-Orthopedic Institute Elgin, Illinois
Jerome M. True, D.C., D.A.B.C.N. University Rehabilitation and Therapeutics Plantation, Florida
With
John W. Blum, Jr., D.C. J. Donald Dishman, D.C., M.Sc., D.A.B.C.N. P. Michael Leahy, D.C., C.C.S.P. Edwin P. Patrick, D.C., F.A.C.O. Clifford M. Shooker, D.C., D.A.B.C.N.
CRC PR E S S Boca Raton London New York Washington, D.C.
Library of Congress Cataloging-in-Publication Data Durrant, David H. Myelopathy, radiculopathy, and peripheral entrapment syndromes / David H. Durrant, Jerome M. True, with John W. Blum, Jr. … [et al.]. p.; cm. Includes bibliographical references and index. ISBN 0-8493-0036-3 (alk. paper) 1. Spinal cord—Diseases. 2. Nerves, Peripheral—Diseases. 3. Entrapment neuropathies. I. True, Jerome M. II. Title. [DNLM: 1. Spinal Diseases—diagnosis. 2. Diagnostic Imaging. 3. Nerve Compression Syndromes. 4. Radiculopathy. 5. Spinal Cord Diseases. 6. Spinal Cord Injuries. WE 725 D965m 2001] RC400 .D87 2001 616.8¢7—dc21 2001035203
This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher. The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from CRC Press LLC for such copying. Direct all inquiries to CRC Press LLC, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe.
Visit the CRC Press Web site at www.crcpress.com © 2002 by CRC Press LLC No claim to original U.S. Government works International Standard Book Number 0-8493-0036-3 Library of Congress Card Number 2001035203 Printed in the United States of America 2 3 4 5 6 7 8 9 0 Printed on acid-free paper
“Many a man has the eyes of a hawk and the vision of a clam.”
— B.J. Palmer, D.C., Ph.C. ( As a Man Thinketh )
Dedication To my loving wife Christine, for her unconditional support and encouragement, which has empowered me to pursue the desires of my heart, and to my beautiful daughter Amanda, who inspires me each day with her abundant love and energy.
To my parents, Richard and Patricia Durrant, for their enduring love and guidance throughout the years, which will forever motivate me to pursue my dreams.
In memory of my friend Jean Ryan, whose courage, independence, and accomplishments, despite her physical limitations, continue to serve as a source of inspiration. — DHD
In Memory of My Father, Martin Austin True “Knowledge comes, but wisdom lingers.” — Alfred, Lord Tennyson And a dedication to my loving wife, for her support, trust and patience. — JMT
Foreword It isn’t often that a textbook appears that so clearly delineates the relationship between neurology and functional musculoskeletal diagnosis. This text represents an extensive diagnostic guide for neurological disorders from the “neck down” to the extremities. It is the first time I have ever seen such a definitive correlation between orthopedic signs/tests and possible neurological involvements. Tables, which assemble and organize information from many studies, permit the practitioner to proceed to an accurate diagnosis in an orderly and efficient way. A few examples I have found beneficial to my own diagnostic procedures are: “Checklist for Assessment of Patient with Spinal Cord Compromise,” “Methods of Quantifying Sensibility,” and “Classification of Spine Lesions by Anatomic Compartment.” The subject of neurology is indeed complex and difficult to retain in our everyday care of patients. Most of us retain a certain level of understanding, but with the
passage of time, details, especially of the neurological variety, begin to escape us. For the Doctor of Chiropractic and all types of physical medicine specialists dealing with the spine and extremity disorders, this textbook provides a complete description and review of what we must understand to adequately treat our patients. The illustrations, tables, and related text are excellent. They are designed so that the practitioner can move easily through them to support daily diagnosis and to help develop a treatment plan. The material covered in this landmark textbook should be part of the core curriculum for all doctors and health care professionals caring for the spine. Those of us in the healing arts owe a debt of gratitude to Doctors Jerry True and David Durrant. They have devoted the last 5 years to assembling and compiling the most recent neurological information in a form accessible and useful to us all. Warren Hammer
Authors’ Foreword It is a pleasure and a great relief to complete a large project, such as the first edition of this text. Countless late nights and early mornings have passed since the initial discussions of the outline topics and framework for this book in 1991 in Orlando, FL. We have met many times per year in Chicago and Fort Lauderdale to organize text, scout for references, and formulate chapter outlines and themes. During the editing process many of the contributing authors received daily phone calls from one or the other of us to discuss refinements or deadlines for their chapters. As any author knows, the contributors have all sacrificed weeks and months of their lives to support this project. Thousands of hours of computer time have gone into creation of the graphics for this text. The meticulous attention to detail should be apparent in our neuroanatomical pathways. The research needed to assemble the illustrations for the neuroanatomical section and the pathway illustrations totaled hundreds of hours per completed illustration, spanning the period between 1989 and 2000. We have made every attempt to accurately illustrate the pathway mechanisms and theories in this book with opinions
currently accepted in the scientific literature. We acknowledge in advance that inadvertent flaws and typos occur in all publications, as well as opposing or contrary views to the status quo. We encourage the reader to direct comments, criticisms, or corrections to the publisher and authors for consideration and review. As a consequence of the exponential growth in monthly scientific periodicals, it is often possible that research is uncovered that supports a different opinion or explains a previously unknown mechanism. Even a cursory review of the top crust of knowledge published each month overwhelms the most voracious data researcher. In an attempt to reach academic consensus, faculty members from many colleges and physicians with specialty interests completed critical reviews of the chapters. We hope that you will find this text clinically valuable and the illustrations skillfully instructive. If we have enlightened the reader and improved his or her clinical expertise, this book has then served our intended purposes. Jerry True David Durrant
Preface “One sees only what one knows.” — Johann Wolfgang von Goethe
The clinician must be able to recognize a condition in order to pursue necessary care. Early recognition requires application of an overview to the outward manifestations of a complex process; localization and diagnosis are required in order to proceed with therapeutic intervention. Of the many texts on clinical neurology, few discuss the potential orthopedic complications associated with nerve injury. This is an important perspective for the developing fields of neurorehabilitation and neuromuscular rehabilitation. The present treatise is meant to serve as a supplement to texts that cover general neurology and orthopedics and to provide an expanded discourse on the pathomechanisms and related presentations of myelopathy, radiculopathy, and peripheral entrapment. With quickly advancing technology in neurology and imaging, interest in, and application of, new methods in the care of spinal disorders have reached an unprecedented level. Great strides have also been made in the early detection and rehabilitation of myelopathy and spinal cord injury. Whether the patient is treated conservatively or surgically, some degree of physical rehabilitation or retraining is often required, and it is therefore imperative that attending clinicians understand patterns of injury and recovery. Additionally, as neurological status may change during the post-traumatic recovery period, follow-up neurological assessment is essential. As life expectancy increases, so will the prevalence of spinal disorders. An increased incidence of myelopathy will be due to degenerative stenosis, vascular disease, and primary and secondary spinal cancer. Intervention will continue to move toward a greater reliance on minimally invasive procedures and rehabilitation, and hence toward a greater emphasis on neurology as it relates to orthopedics (neuro-orthopedics). Early detection and intervention in spinal disorders will become the standard approach, rather than the often-overlooked alternative. The patient with a chronic or complex spinal condition may see a number of independent physicians of various disciplines during the course of care. An integrated approach may be achieved involving a chiropractic physician, pain
specialist, internist, neurosurgeon, and/or orthopedic surgeon. This book is intended to provide “common ground” for physicians who must perform or understand the differential assessment of neurological complications that involve or mimic a spinal condition. It is also intended for the student of clinical neurology and orthopedics, and for the doctor treating neuromusculoskeletal disorders. By reducing the complex field of diagnostic neurology to its common denominators, we hope to introduce the subject in a practical manner and present a concise basis for neurodiagnostic evaluation. The text provides an integrated review of selected anatomy and physiology, clinical localization, classification, and quantification of disorders afflicting the spinal cord, nerve root, and peripheral nerves. It is organized for use as a basic science tool or a quick reference, with abundant tables and graphics included to convey essential and relevant clinical information. Having conducted an indepth review of the literature, we have attempted to reflect current consensus opinion whenever possible. We have also interjected insights and opinions based upon our collective clinical experiences. In addition to recognizing spinal disorders, the clinician must become particularly adept at assessing relatively common patterns of peripheral nerve compromise that may coexist with or mimic spinal presentations. However, this is often not adequately discussed in texts limited to “spinal conditions,” and many general neurology texts are limited in their coverage of both subjects. Combining the topics of spinal and peripheral neurological assessment herein lends itself, for example, to greater understanding of clinical entities such as whole nerve syndrome or double crush syndrome. We have incorporated descriptions of various pathomechanisms in spinal cord and nerve injury and, whenever possible, noted clinically significant timedependent patterns of insult and recovery. There is a vast amount of past and current research data in the fields of neuroanatomy, neurophysiology, and orthopedics that we have not included in this volume. We have carefully chosen what we believe to be relevant information that can be immediately applied to diagnostic and therapeutic approaches to myelopathy and spinal cord injury in clinical practice.
Introduction to Myelopathy and Spinal Cord Injury Myelopathy in its broadest definition includes any pathology involving the spinal cord. Spinal cord injury (SCI) in an empirical sense also includes any condition that causes insult to the cord. However, the term “myelopathy” has customarily been used to describe intrinsic disease processes, whereas SCI has usually referred specifically to a traumatic-onset myelopathy. The most common chronic intrinsic disorders afflicting the cord are the result of degenerative conditions exclusive to the spine — namely, disk derangement, spondylosis, and spinal stenosis. Spinal cord injury from acute trauma involves one or more of the following mechanisms: fracture or dislocation of the spine with impact on the cord; torsional or shear forces on the spine and cord, causing axonal transection; and penetrating injuries that partially or completely sever the cord. The injury may be partial or complete, transient or permanent. There are 7800 new SCIs in the U.S. each year; however, this incidence may be significantly under-reported, because people who instantly die and patients with little residual SCI deficit are not included in the recorded statistics.* Motor vehicle accidents account for the majority of SCI cases, while acts of violence, falls, work injuries, recreational incidents, and athletic injuries constitute the remainder. It is noteworthy that acts of violence have overtaken falls as the second most common source of SCI in the last 4 years; falls overtake motor vehicle accidents as a leading cause of SCI after age 45; and SCI related to acts of violence and sports is less common as age increases.* Other conditions that produce SCI include
infection, immunological disorders, tumor, vascular compromise, herniated intervertebral disk, and degenerative diseases. Monies spent on spinal cord pathology and related conditions will continue to rise, influenced greatly by the large percentage of the population reaching the 65-andabove age group. Of the increasing number of patients with cervical spondylotic myelopathy, many cases will be complicated by cardiovascular disease, impaired glycoregulation, and immunological disorders. Spondylotic myelopathy increases the risk for falls, related injury, and disability, and a higher incidence of cancer in the aged population will also increase the risk for metastatic expansile lesions within the spine. Nevertheless, there is an unprecedented optimism within the scientific community that early diagnosis and intervention in SCI will lead to an improved prognosis and enhanced functional recovery. A vast body of research demonstrates the benefits of exercise and a physical rehabilitative approach to the remodeling characteristics of neurological tissue and the surrounding and supportive tissues of the spine. Advanced imaging techniques allow us to evaluate the anatomic expression of a spinal lesion, its progression, the pattern of recovery, and its relationship to the clinical presentation. Effective management depends upon early identification of the extent and level of neurologic injury, and upon multidisciplinary specialty care of the diverse problems associated with SCI to maximize the potential for tissue recovery and repair.
* National Spinal Cord Injury Association statistics available at http://www.spinalcord.org/resource/Factsheets/factsheet2.html, 2000.
Acknowledgments Any project of this caliber requires delegation, support, negotiation, sacrifice, and donation of considerable time and effort from innumerable sources. The first and most deserving acknowledgment goes to the contributing authors and their support staff. The loved ones, families, and friends of the authors are next on the list of appreciation, because without their understanding, faithful support, and patience during the life-disrupting process of writing a book, the accomplishment and importance of this project would certainly have less merit. We are indebted to Ron Hosek, Ph.D., D.C., M.P.H., for his experience and insight. His scholarly guidance was most valuable. We are also indebted to Ray Conley, D.C., D.A.C.B.R., who deserves credit for his expert review of some of the magnetic resonance (MR) and X-ray images used in this book. Dr. Conley reviewed and qualified over 900 slide images during the initial selection process for the book. Many other individuals have participated and were integral to the completion of this book. These individuals were involved in manuscript preparation, review, editing, photography, computer graphics, and technical advice or troubleshooting. We greatly appreciate the efforts of John Sikes for his energetic assistance. Early in the project John provided a great deal of back-office support and image scanning work to help complete this book. John and Linda Sikes were also invaluable for their help compiling and creating a reference database for the voluminous number of referenced facts. Joleen Riley photographed many of the MRIs that appear in this text and hundreds that were not selected in the final production. Thanks to Lori True for entering text-editing changes and the tedious reference renumbering of many chapters. Thanks to Dan Fortuna for his help compiling research articles and spending many sunny days in the library doing literature searches. Excellent MRI and X-ray case studies were supplied by Richard Leverone, D.C., D.A.C.B.R.; Harold Friedman, M.D.; Ronald Landau, M.D.; James Zelch, M.D.; Brian Mevorah, D.C.; Joseph Kozlowski, M.D., and George Fika, D.C. Bill Atherton D.C., D.A.C.B.R., and Ronald Landau, M.D., generously reviewed MRIs and helped compose figure captions. Thanks to the following: Alex Frost and Kate Herman of BiologyEditors.com, Lisa McCollough and Marce Pollan for reference work and editing; Paul
Ellis, Ph.D., for cadaveric sections and photography; Robert Pearson for anatomical line drawings; Linda Bland, M.D., Greg Page, D.C., D.A.C.N.B., Gloria Y. Niles, D.C., D.A.C.A.N., Marc McRae, M.S., D.C., and Alyson Syrja, D.C., for critical reviews; Phil Serocki and Duwayne Rocus for technical advice that was essential to graphics production; and Gary LaVell, D.C., for general support and computer assistance. We would like to extend thanks to the following colleagues for their supportive words and inspiration: Terry Yochum, D.C., D.A.C.B.R.; Norman Kettner, D.C., D.A.C.B.R.; Arthur Croft, D.C., F.A.C.O.; and Tom Hyde, D.C., D.A.C.B.S.P. An extended apologetic thanks to any and all friends and colleagues whom we forgot to mention. The clinical sciences departments of Canadian Memorial Chiropractic College, Life Chiropractic College West, and New York Chiropractic College; the anatomy department of Logan College of Chiropractic; and the research departments of Life Chiropractic College West, Logan College of Chiropractic, and Cleveland Chiropractic College (KC) all have contributed their support to this book. Thanks to the library departments of National Chiropractic College, New York Chiropractic College, Logan College of Chiropractic, Cleveland Chiropractic College (KC), Life Chiropractic College West, and Palmer Chiropractic College for labored reference searches. A special thanks is extended to Glen Hart for his generosity in hardware troubleshooting and multiple rescues from fatal harddrive crashes who reminds us that “to err is human but to really foul things up requires a computer.” Special appreciation and humble respect goes out to the teachers and mentors who influenced us in the pursuit of lofty goals. First and foremost on this list is Frederick R. Carrick, D.C., Ph.D., D.A.B.C.N., who developed the postgraduate neurology program and the foundation for our neurological training. Great appreciation is extended to our loving wives, Lori True and Christine Durrant, whose devotion and excitement for the completion of this book may exceed our own. Jerome M. True David H. Durrant
Contents Section 1 Myelopathy: Spinal Cord Injury and Selected Clinical Syndromes Chapter 1 Relevant Spinal Cord Anatomy ..........................................................................................................................................3 1.1 Basic Spinal Cord Anatomy ......................................................................................................................................3 1.2 Segmental Spinal Anatomy .......................................................................................................................................5 1.2.1 Regional Neuromere Characteristics.............................................................................................................5 1.2.2 Regional Spinal Canal Characteristics ..........................................................................................................5 1.3 Meninges and Compartments ....................................................................................................................................6 1.3.1 Dura Mater.....................................................................................................................................................6 1.3.2 Arachnoid Mater............................................................................................................................................7 1.3.3 Pia Mater........................................................................................................................................................7 1.3.4 Subarachnoid Space and Cerebrospinal Fluid ..............................................................................................7 1.4 Spinal Vascular Anatomy...........................................................................................................................................8 1.4.1 Extrinsic Spinal Cord Vasculature.................................................................................................................8 1.4.1.1 Radiculomedullary Arteries............................................................................................................8 1.4.1.2 Anterior and Posterior Spinal Arteries ..........................................................................................8 1.4.2 Intraparenchymal Vascular Supply ................................................................................................................9 1.4.3 The Spinal Venous Plexus .............................................................................................................................9 1.5 Cytoarchitectural Organization of Spinal Gray Matter ..........................................................................................10 1.6 Relevant Spinal Cord Pathways ..............................................................................................................................13 1.6.1 Clinically Important Ascending Pathways ..................................................................................................13 1.6.1.1 Posterior Columns ........................................................................................................................13 1.6.1.2 Lateral Spinothalamic Tract .........................................................................................................13 1.6.1.3 Other Ascending Pathways ..........................................................................................................13 1.6.2 Clinically Important Descending Pathways ................................................................................................15 1.6.2.1 Corticospinal Tract .......................................................................................................................15 1.6.2.2 Nonpyramidal Tracts ....................................................................................................................17 1.6.3 Autonomic Pathways ...................................................................................................................................17 1.7 Relevant Spinal Cord Nuclei...................................................................................................................................17 1.8 Anatomy of Spinal-Mediated Myotatic Reflex.......................................................................................................17 References .........................................................................................................................................................................22 Chapter 2 Pathophysiology in Myelopathy and Spinal Cord Injury.................................................................................................23 2.1 Introduction to Pathophysiologic Mechanisms .......................................................................................................23 2.2 Cellular, Ionic, and Biomolecular Mechanisms of Spinal Cord Injury .................................................................23 2.2.1 Free Radical-Mediated Cell Injury..............................................................................................................23 2.2.2 Glutamatergic-Induced Toxicity ..................................................................................................................23 2.2.3 Cation-Mediated Cell Injury .......................................................................................................................24 2.2.4 Programmed Cell Death ..............................................................................................................................24 2.3 Stages of Spinal Cord Injury...................................................................................................................................24 2.4 Spinal Shock ............................................................................................................................................................25 2.5 Spinal Cord Edema..................................................................................................................................................26 2.6 Ischemic Myelopathy...............................................................................................................................................26 2.6.1 Microvascular and Arterial Insufficiency ....................................................................................................27 2.6.1.1 Microvascular Perfusion...............................................................................................................27
2.6.1.2 Tempo of Cord Vascular Insufficiency ........................................................................................27 2.6.1.3 Arterial Insufficiency and Ischemia .............................................................................................27 2.6.2 Spinal Cord Infarction .................................................................................................................................28 2.6.3 Venous Pathology ........................................................................................................................................28 2.7 Myelomalacia...........................................................................................................................................................28 2.8 Cavitation and Gliosis .............................................................................................................................................29 2.9 Spinal Cord Atrophy................................................................................................................................................30 References .........................................................................................................................................................................31 Chapter 3 Physical Mechanisms of Spinal Cord Injury....................................................................................................................35 3.1 Spinal Cord Pathomechanics...................................................................................................................................35 3.2 Types of Spinal Cord Trauma .................................................................................................................................36 3.2.1 Spinal Cord Concussion ..............................................................................................................................37 3.2.2 Spinal Cord Contusion ................................................................................................................................37 3.2.3 Spinal Cord Compression............................................................................................................................37 3.2.4 Penetrating/Transecting Cord Injuries.........................................................................................................38 3.2.5 Tethering and Distraction Injuries...............................................................................................................38 3.3 Vertebral Fracture, Dislocation, and Instability ......................................................................................................38 3.3.1 Causes of Biomechanical Instability...........................................................................................................39 3.3.2 Spinal Fracture and Pathomechanical Intersegmental Motion ...................................................................43 3.3.3 Upper Cervical Fracture Patterns: Fractures of C0–C1–C2 .......................................................................43 3.3.3.1 Posterior Neural Arch Fracture of C1 .........................................................................................43 3.3.3.2 Dens Fracture ...............................................................................................................................43 3.3.3.3 Hangman’s Fracture (Bipedicular Fracture of C2, Traumatic Spondylolisthesis of C2) ...........44 3.3.3.4 Jefferson Fracture of the Atlas (Burst Fracture of C1) ...............................................................44 3.3.4 Cervical Fracture Patterns ...........................................................................................................................44 3.3.4.1 Spinous Process Fracture (Clay Shoveler’s Fracture, Coal Miner’s Fracture) ...........................44 3.3.4.2 Pillar Fracture ...............................................................................................................................44 3.3.4.3 Flexion Teardrop Fracture............................................................................................................45 3.3.4.4 Extension Teardrop Fracture ........................................................................................................45 3.3.5 Fracture Patterns Occurring at any Level of the Spine ..............................................................................46 3.3.5.1 Endplate Burst Fracture ...............................................................................................................46 3.3.5.2 Wedge Fracture (Compression Fracture) .....................................................................................46 3.3.5.3 Chance Fracture............................................................................................................................47 3.3.5.4 Neural Arch Fracture....................................................................................................................48 3.3.6 Spinal Dislocation........................................................................................................................................48 3.3.6.1 Bilateral Cervical Facet Dislocation ............................................................................................48 3.3.6.2 Unilateral Facet Dislocation.........................................................................................................49 3.3.6.3 Spinal Dislocation/Relocation......................................................................................................49 3.4 Spinal Hemorrhage ..................................................................................................................................................49 3.4.1 Subarachnoid Hemorrhage ..........................................................................................................................50 3.4.2 Epidural Hemorrhage ..................................................................................................................................50 3.4.3 Subdural Hemorrhage..................................................................................................................................50 3.4.4 Hematomyelia ..............................................................................................................................................50 3.5 Myelopathy and Disk Herniation ............................................................................................................................50 References .........................................................................................................................................................................53 Chapter 4 Conditions Associated with Myelopathy ..........................................................................................................................55 4.1 Degeneration and Stenosis ......................................................................................................................................55 4.1.1 Spondylotic Myelopathy and Cervical Spondylotic Myelopathy...............................................................55 4.1.1.1 Prevalence.....................................................................................................................................55 4.1.1.2 Pathomechanisms .........................................................................................................................56
4.2
4.3 4.4
4.1.1.3 Clinical Signs and Symptoms and Temporal Pattern of Progression .........................................57 4.1.1.4 Clinical Findings ..........................................................................................................................58 4.1.1.5 Diagnostic Imaging ......................................................................................................................58 4.1.1.6 Differential Considerations ..........................................................................................................59 4.1.2 Ligamentum Flavum Thickening/Buckling.................................................................................................59 4.1.3 Rheumatoid Arthritis and Myelopathy........................................................................................................59 4.1.4 Hypertrophic Spinal Disease .......................................................................................................................60 4.1.4.1 Diffuse Idiopathic Skeletal Hyperostosis.....................................................................................60 4.1.4.2 Ossified Posterior Longitudinal Ligament Syndrome .................................................................61 Expansile Lesions ....................................................................................................................................................62 4.2.1 Syringomyelia ..............................................................................................................................................62 4.2.2 Arachnoid Cyst ............................................................................................................................................64 4.2.3 Epidural Lipomatosis...................................................................................................................................64 4.2.4 Spinal Cord Tumors.....................................................................................................................................64 4.2.4.1 Intramedullary Tumors .................................................................................................................64 4.2.4.1.1 Ependymoma..............................................................................................................64 4.2.4.1.2 Astrocytoma and Oligodendroglioma........................................................................64 4.2.4.1.3 Hemangioblastoma.....................................................................................................66 4.2.4.2 Intradural Extramedullary Tumors...............................................................................................68 4.2.4.2.1 Neural Sheath Tumor .................................................................................................68 4.2.4.2.2 Meningioma ...............................................................................................................68 4.2.4.2.3 Paraganglioma ............................................................................................................69 4.2.4.3 Epidermoid and Dermoid Tumor, and Teratoma ........................................................................70 4.2.4.4 Extradural Tumors........................................................................................................................70 4.2.4.4.1 Lipoma .......................................................................................................................70 4.2.4.4.2 Chordoma ...................................................................................................................70 4.2.4.4.3 Lymphoma..................................................................................................................70 4.2.4.5 Lesions Arising from the Bony Vertebral Column......................................................................70 4.2.4.6 Metastatic Lesions........................................................................................................................70 4.2.5 Epidural Abscess..........................................................................................................................................72 Arteriovenous Malformations..................................................................................................................................72 Noncompressive Myelopathy ..................................................................................................................................76 4.4.1 Postinfectious and Postvaccination Myelitis (Transverse Myelitis) ...........................................................77 4.4.2 Infection .......................................................................................................................................................77 4.4.2.1 Tropical Spastic Paraparesis (Human T-Cell Lymphotrophic Virus I) .......................................77 4.4.2.2 Acquired Immune Deficiency Syndrome ....................................................................................77 4.4.2.3 Lyme Disease ...............................................................................................................................78 4.4.2.4 Tabes Dorsalis (Syphilis) .............................................................................................................78 4.4.3 Spinal Arachnoiditis (Adhesive Arachnoiditis)...........................................................................................78 4.4.4 Toxic Insult ..................................................................................................................................................79 4.4.5 Multiple Sclerosis ........................................................................................................................................79 4.4.6 Radiation Myelopathy .................................................................................................................................79 4.4.7 Decompression Sickness .............................................................................................................................81 4.4.8 Electrical Injury ...........................................................................................................................................81 4.4.9 Metabolic and Nutritional Myelopathies ....................................................................................................81 4.4.9.1 Subacute Combined Degeneration...............................................................................................81 4.4.10 Autoimmune Myelopathy............................................................................................................................81 4.4.11 Paraneoplastic Myelopathy..........................................................................................................................82 4.4.12 Degenerative Neuronal Disorders ...............................................................................................................82 4.4.13 Motor Neuron Disease.................................................................................................................................82 4.4.13.1 Amyotrophic Lateral Sclerosis.....................................................................................................82 4.4.13.2 Spinal Muscular Atrophy .............................................................................................................82 4.4.13.3 Kennedy’s Disease .......................................................................................................................83 4.4.13.4 Familial Spastic Paraplegia ..........................................................................................................83
4.5
Congenital Spinal Anomalies ..................................................................................................................................83 4.5.1 Spina Bifida Aperta: Myelomeningocele ....................................................................................................84 4.5.2 Occult Spinal Dysraphism...........................................................................................................................84 4.5.2.1 Split Cord Malformation..............................................................................................................84 4.5.2.2 Spinal (Dorsal) Dermal Sinus ......................................................................................................85 4.5.2.3 Neuroenteric Cyst.........................................................................................................................86 4.5.3 Caudal Spinal Anomalies ............................................................................................................................87 4.6 Chiari Malformations ..............................................................................................................................................87 4.7 Klippel–Feil Syndrome............................................................................................................................................87 4.8 Scoliosis and Myelopathy .......................................................................................................................................89 References .........................................................................................................................................................................90 Chapter 5 Assessment of Spinal Cord Injury and Myelopathy ........................................................................................................97 5.1 Spasticity, Paresis, Clonus, and Hyperreflexia........................................................................................................97 5.2 Superficial Reflexes and Reflexes of Spinal Automatism ....................................................................................100 5.2.1 Babinski’s Response ..................................................................................................................................102 5.3 Sensory Abnormalities...........................................................................................................................................105 5.3.1 Ataxia.........................................................................................................................................................105 5.4 Spinal Cord Injury Pain.........................................................................................................................................105 5.4.1 Lhermitte’s Sign ........................................................................................................................................105 5.5 Neurogenic Claudication .......................................................................................................................................106 5.6 Sacral Sparing........................................................................................................................................................107 5.7 Autonomic and Other System Considerations......................................................................................................107 5.7.1 Orthostatic Hypotension ............................................................................................................................107 5.7.2 Deep Vein Thrombosis ..............................................................................................................................108 5.7.3 Autonomic Dysreflexia..............................................................................................................................108 5.7.4 Cardiac Complications ..............................................................................................................................109 5.7.5 Respiratory Considerations........................................................................................................................109 5.7.6 Bowel and Bladder Dysfunction ...............................................................................................................109 5.7.7 Sexual Function .........................................................................................................................................110 5.7.8 Skin Complications....................................................................................................................................110 5.7.9 Psychological Considerations....................................................................................................................110 5.7.10 Fever...........................................................................................................................................................111 5.8 Myelopathy and Associated Musculoskeletal Conditions ....................................................................................111 5.8.1 Contractures ...............................................................................................................................................111 5.8.2 Articular Subluxation ................................................................................................................................111 5.8.3 Heterotopic Ossification ............................................................................................................................112 5.8.4 Osteoporosis...............................................................................................................................................112 5.8.5 Neuropathic Arthropathy ...........................................................................................................................112 5.9 Electrodiagnostic Assessment................................................................................................................................112 5.9.1 Somatosensory Evoked Potentials.............................................................................................................113 5.9.2 Motor Evoked Potentials ...........................................................................................................................113 5.9.3 Late Responses ..........................................................................................................................................115 5.9.4 Needle Electromyography .........................................................................................................................115 5.9.5 Sensory Nerve Conduction Studies...........................................................................................................116 5.9.6 Motor Nerve Conduction Studies..............................................................................................................116 5.10 Diagnostic Imaging................................................................................................................................................116 5.10.1 Magnetic Resonance Imaging ...................................................................................................................116 5.10.1.1 Rapid MR Sequencing .............................................................................................................117 5.10.1.2 Turbo Echo MR Sequences .....................................................................................................117 5.10.1.3 Inversion Recovery...................................................................................................................118 5.10.1.4 Contrast Enhancement..............................................................................................................118 5.10.1.5 Kinematic MRI.........................................................................................................................118
5.10.1.6 Functional MRI ........................................................................................................................119 5.10.1.7 Magnetization Transfer ............................................................................................................119 5.10.1.8 Diffusion-Weighted Imaging....................................................................................................119 5.10.1.9 MR Spectroscopy .....................................................................................................................119 5.10.1.10 Three-Dimensional Imaging (Reconstruction) ........................................................................120 5.10.1.11 MR Angiography......................................................................................................................120 5.10.1.12 MR Myelography .....................................................................................................................120 5.10.1.13 Interventional MRI ...................................................................................................................120 5.11 Neurosonography...................................................................................................................................................121 5.11.1 Intraoperative Spinal Sonography .............................................................................................................121 5.12 Computed Tomography .........................................................................................................................................121 5.12.1 CT/Myelography........................................................................................................................................121 5.12.2 Helical CT (Spiral CT)..............................................................................................................................121 5.13 Plain-Film Radiography ........................................................................................................................................121 5.14 Quantitative Considerations in Spinal Cord Imaging ...........................................................................................122 5.14.1 Central Spinal Canal Measurements .........................................................................................................122 5.14.2 Spinal Instability and Vertebral Translation..............................................................................................123 5.14.3 Classifications of Spinal Cord Compression.............................................................................................123 5.14.4 Spinal Cord Cross-Sectional Size and Area .............................................................................................124 5.14.5 Intrinsic Cord Dysmorphism .....................................................................................................................124 5.14.6 Intramedullary Signal Patterns ..................................................................................................................125 5.15 Functional and Laboratory Assessment ................................................................................................................125 5.15.1 Pulmonary Function ..................................................................................................................................125 5.15.2 Cerebrospinal Fluid Evaluation.................................................................................................................126 5.15.3 Amniocentesis............................................................................................................................................126 5.15.4 Blood and Serum Studies ..........................................................................................................................128 5.15.5 Genetic Assessment ...................................................................................................................................128 5.15.6 Bladder Function .......................................................................................................................................129 5.15.6.1 Cystourethrography ....................................................................................................................129 5.15.6.2 Cystometry .................................................................................................................................129 5.15.6.3 Electrodiagnostic Studies of Bladder Function .........................................................................129 5.15.6.4 Uroflowometry............................................................................................................................130 5.15.7 Physical Impairment Assessment ..............................................................................................................130 5.15.7.1 Frankel Classification .................................................................................................................130 5.15.7.2 ASIA/IMSOP Scale....................................................................................................................130 5.15.7.3 Benzel and Larson Scale............................................................................................................130 5.15.7.4 Japanese Orthopedic Association Cervical Myelopathy Score .................................................130 5.15.7.5 Range of Motion (ROM) ...........................................................................................................130 5.15.7.6 Gait .............................................................................................................................................130 5.15.7.7 Muscular Performance ...............................................................................................................132 5.15.7.8 Sensibility ...................................................................................................................................133 5.15.7.9 Balance .......................................................................................................................................133 References .......................................................................................................................................................................133 Chapter 6 Spinal Cord Syndromes and Guide to Neurological Levels ..........................................................................................139 6.1 Vascular Syndromes of the Spinal Cord ...............................................................................................................139 6.1.1 Anterior Spinal Artery Syndrome .............................................................................................................139 6.1.2 Posterior Spinal Artery Syndrome (PSAS) ...............................................................................................139 6.1.3 Radiculomedullary Artery Syndrome (RAS) ............................................................................................139 6.1.4 Central Cord Vascular Syndrome (CCVS)................................................................................................139 6.2 Complete Spinal Cord Transection (Transverse Myelopathy) .............................................................................140 6.3 Central Cord Syndrome.........................................................................................................................................142 6.4 Anterior Cord Syndrome .......................................................................................................................................143
6.5
Posterior Cord Syndrome ......................................................................................................................................143 6.5.1 Posterolateral Cord Syndrome...................................................................................................................144 6.6 Anterior Horn Syndrome (Progressive Muscular Atrophy)..................................................................................145 6.6.1 Polio and Post-Polio Syndrome ................................................................................................................145 6.6.2 Combined Anterior Horn and Pyramidal Tract Disease (Motor Neuron Syndrome) ..............................145 6.7 Multifocal Cord Syndrome....................................................................................................................................146 6.8 Conus Medularis Syndrome ..................................................................................................................................146 6.9 Hemisection Syndrome (Brown–Séquard Syndrome) ..........................................................................................149 6.10 Cervical Medullary Syndrome ..............................................................................................................................149 6.11 Guide to Neurological Levels ...............................................................................................................................151 6.11.1 Cranial-Cervical Lesions (Foramen Magnum Lesions)............................................................................151 6.11.2 Cervical Lesions ........................................................................................................................................152 6.11.2.1 Intact C3 Neurologic Level (C3 Functional Level)...................................................................152 6.11.2.2 Intact C4 Neurologic Level (C4 Functional Level)...................................................................152 6.11.2.3 Intact C5 Neurologic Level (C5 Functional Level)...................................................................152 6.11.2.4 Intact C6 Neurologic Level (C6 Functional Level)...................................................................153 6.11.2.5 Intact C7 Neurologic Level (C7 Functional Level)...................................................................153 6.11.2.6 Intact C8 and T1 Neurologic Levels (C8 and T1 Functional Levels) ......................................153 6.11.3 Thoracic-Intact Lesions (Mid-Thoracic Functional Levels) .....................................................................154 6.11.3.1 Intact T12 Neurologic Level (T12 Functional Level) ...............................................................154 6.11.4 Lumbar Transection Injuries......................................................................................................................154 6.11.4.1 Intact L1 Neurologic Level (L1 Functional Level) ...................................................................154 6.11.4.2 Intact L2 Neurologic Level (L2 Functional Level) ...................................................................154 6.11.4.3 Intact L3 Neurologic Level (L3 Functional Level) ...................................................................154 6.11.4.4 Intact L4 Neurologic Level (L4 Functional Level) ...................................................................154 6.11.4.5 Intact L5 Neurologic Level (L5 Functional Level) ...................................................................155 6.11.5 Sacral Transection Injuries ........................................................................................................................155 6.11.5.1 Intact S1 Neurologic Level (S1 Functional Level) ...................................................................155 6.11.5.2 Intact S2 Neurologic Level and Below......................................................................................155 References .......................................................................................................................................................................157 Section 2 Radiculopathy Chapter 7 Pathomechanisms of Radiculopathy ...............................................................................................................................161 7.1 Spinal Nerve Root Anatomy and Regional Characteristics..................................................................................161 7.1.1 Intervertebral Foramen Anatomy ..............................................................................................................163 7.1.2 Anatomy of the Dural Sleeve and Peripheral Nerve Junction .................................................................165 7.1.3 Blood Supply of the Spinal Nerve Root ...................................................................................................166 7.1.4 The Dorsal Root Ganglia ..........................................................................................................................166 7.1.5 Pathophysiology of Nerve Root Compression..........................................................................................167 7.1.6 Sites of Nerve Root Vulnerability .............................................................................................................168 7.1.7 Pathomechanics Affecting the Nerve Root Complex ...............................................................................169 7.1.8 Nerve Root Double Crush .........................................................................................................................169 7.2 Biochemically Induced Radiculopathy .................................................................................................................170 7.3 Spinal Degeneration and Radiculopathy ...............................................................................................................171 7.3.1 Rostrocaudal Subluxation..........................................................................................................................172 7.4 Fibrosis and Radiculopathy ...................................................................................................................................172 7.4.1 Arachnoiditis and Radiculopathy ..............................................................................................................173 7.5 Acquired Lateral Recess Stenosis and Vascular Stasis.........................................................................................173 7.6 Failed Back Surgery Syndrome.............................................................................................................................175 7.7 Trauma and Radiculopathy....................................................................................................................................176 7.7.1 Nerve Root Avulsion .................................................................................................................................177
7.8
Intervertebral Disk Herniation and Radiculopathy ...............................................................................................177 7.8.1 Experimental Mechanism of Disk Herniation ..........................................................................................177 7.8.2 Conventional Classification of Disk Lesions ............................................................................................178 7.8.2.1 Annular Bulge (Disk Bulge) ......................................................................................................178 7.8.2.2 Disk Protrusion (Herniation)......................................................................................................180 7.8.2.3 Disk Extrusion............................................................................................................................180 7.8.2.4 Free Disk Fragment (Sequestered Disk)....................................................................................182 7.9 Nerve Root Compromise: Expansile Lesions .......................................................................................................183 7.9.1 Schwannoma ..............................................................................................................................................183 7.9.2 Neurofibroma .............................................................................................................................................186 7.9.3 Meningioma ...............................................................................................................................................188 7.9.4 Perineurial Cysts (Tarlov’s Cysts).............................................................................................................189 7.9.5 Synovial Cysts ...........................................................................................................................................189 7.9.6 Metastatic Disease .....................................................................................................................................189 7.10 Vertebral Osteomyelitis and Discitis.....................................................................................................................190 7.11 Spondylolisthesis and Radiculopathy....................................................................................................................190 7.12 Noncompressive Radiculoneuronopathy ...............................................................................................................193 7.12.1 Diabetic Radiculopathy .............................................................................................................................193 7.12.2 Infection .....................................................................................................................................................194 7.12.2.1 Herpes Varicella-Zoster Virus (Shingles)...................................................................................194 7.12.2.2 AIDS-Related Polyradiculopathy...............................................................................................194 7.12.2.3 Lyme Disease .............................................................................................................................194 7.12.3 Coagulopathies...........................................................................................................................................195 References .......................................................................................................................................................................195 Chapter 8 Classic Signs and Symptoms of Radiculopathy.............................................................................................................201 8.1 Sensory Abnormalities...........................................................................................................................................201 8.2 Nerve Root Irritability Signs .................................................................................................................................201 8.3 Reflex Abnormalities .............................................................................................................................................204 8.4 Paresis ....................................................................................................................................................................205 8.5 Muscular Atrophy ..................................................................................................................................................206 8.6 Dysautonomia and Trophic Changes ....................................................................................................................206 8.7 Combined Pain Syndromes: Radicular and Vertebrogenic Pain...........................................................................207 8.7.1 Radiculopathic and Vertebrogenic Symptoms Resembling Visceral Pain................................................209 8.8 Assessment of Radiculopathy ...............................................................................................................................209 8.8.1 Electrodiagnosis and Radiculopathy .........................................................................................................209 8.8.1.1 Needle Electromyographic Evaluation ......................................................................................209 8.8.1.2 Muscles with Segmental Localizing Significance .....................................................................210 8.8.1.3 The Chronology of Electrophysiologic Abnormalities in Radiculopathy.................................210 8.8.1.4 Radiculopathy and Postsurgical EMG Findings........................................................................212 8.8.1.5 Late Reflexes ..............................................................................................................................212 8.8.1.5.1 H-reflex.....................................................................................................................213 8.8.1.5.2 F-wave ......................................................................................................................213 8.8.1.5.3 T-reflex .....................................................................................................................214 8.8.1.6 Nerve Conduction Studies .........................................................................................................215 8.8.1.6.1 Motor Nerve Conduction Studies ............................................................................215 8.8.1.6.2 Sensory Nerve Conduction Studies .........................................................................215 8.8.1.7 Somatosensory and Dermatomal Evoked Potentials .................................................................217 8.8.1.7.1 Mixed Nerve Stimulation.........................................................................................217 8.8.1.7.2 Dermatomal Stimulation ..........................................................................................217 8.8.2 Radiculopathy and Functional Capacity Evaluation.................................................................................218 8.8.3 MRI of Disk, Nerve Root, Venous Plexus, and Muscle...........................................................................220 8.8.3.1 Disk Herniation ..........................................................................................................................220
8.8.3.2 Contrast Enhancement of the Spinal Nerve Root .....................................................................221 8.8.3.3 Enhancement of the Epidural Venous Plexus ............................................................................221 8.8.3.4 MRI of Muscular Atrophy .........................................................................................................222 8.9 Cervical Monoradiculopathy Syndromes ..............................................................................................................223 8.9.1 C1 Radiculopathy ......................................................................................................................................223 8.9.2 C2 Radiculopathy ......................................................................................................................................223 8.9.3 C3 Radiculopathy ......................................................................................................................................224 8.9.4 C4 Radiculopathy ......................................................................................................................................224 8.9.5 C5 Radiculopathy ......................................................................................................................................224 8.9.6 C6 Radiculopathy ......................................................................................................................................229 8.9.7 C7 Radiculopathy ......................................................................................................................................231 8.9.8 C8 Radiculopathy ......................................................................................................................................231 8.10 Thoracic Monoradiculopathy Syndromes .............................................................................................................233 8.10.1 T1 Radiculopathy ......................................................................................................................................233 8.10.2 T2–T12 Radiculopathy ..............................................................................................................................233 8.11 Lumbar and Sacral Monoradiculopathy Syndromes.............................................................................................235 8.11.1 Anatomic Variations of the Lumbosacral Nerve Roots ............................................................................236 8.11.2 L1 Radiculopathy ......................................................................................................................................237 8.11.3 L2 Radiculopathy ......................................................................................................................................238 8.11.4 L3 Radiculopathy ......................................................................................................................................239 8.11.5 L4 Radiculopathy ......................................................................................................................................240 8.11.6 L5 Radiculopathy ......................................................................................................................................242 8.11.7 S1 Radiculopathy.......................................................................................................................................243 8.11.8 S2–S5 Radiculopathy ................................................................................................................................245 8.12 Cauda Equina Syndrome .......................................................................................................................................245 8.12.1 High Lesion within the Cauda Equina......................................................................................................246 References .......................................................................................................................................................................247 Section 3 Peripheral Nerve Entrapment and Compression Neuropathy Chapter 9 Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury ......................................253 9.1 General Organization of Peripheral Nerve Distribution .......................................................................................253 9.1.1 Posterior Primary Divisions ......................................................................................................................253 9.1.2 General Organization of Plexuses .............................................................................................................254 9.2 Cervical Plexus ......................................................................................................................................................254 9.2.1 Cervical Plexus: Sensory Innervation to the Head and Neck ..................................................................254 9.2.2 Cervical Plexus: Sensory Innervation to the Neck and Shoulders...........................................................254 9.2.3 Cervical Plexus in Relationship to Cranial Nerves ..................................................................................254 9.2.4 Motor Fibers within the Cervicobrachial Plexus ......................................................................................255 9.3 Brachial Plexus ......................................................................................................................................................255 9.3.1 Nerves Arising Directly from the Nerve Roots or the Brachial Plexus...................................................256 9.3.2 Nerve Branches Arising from the Upper Trunk .......................................................................................257 9.3.3 Nerves Formed with Contributions from Both the Medial and Lateral Cords ........................................257 9.4 Lumbar Plexus .......................................................................................................................................................257 9.5 Lumbosacral Plexus...............................................................................................................................................259 9.6 Autonomic Nervous System..................................................................................................................................261 9.7 Relevant Anatomy of the Peripheral Nerve ..........................................................................................................261 9.8 Peripheral Nerve Vascularity .................................................................................................................................264 9.9 Biomechanical Characteristics of Peripheral Nerves............................................................................................266 9.10 Classification of Nerve Injuries.............................................................................................................................266 9.10.1 Physiologic Conduction Block ..................................................................................................................266 9.10.2 Neurapraxia................................................................................................................................................266
9.10.3 Axonotmesis ..............................................................................................................................................267 9.10.4 Neurotmesis ...............................................................................................................................................268 9.11 Peripheral Nerve Response to Injury ....................................................................................................................268 9.11.1 Wallerian Degeneration .............................................................................................................................268 9.11.2 Axonal Regeneration .................................................................................................................................269 9.12 Nerve Compression and Related Pathomechanisms.............................................................................................270 9.12.1 Compromised Axonal Transport ...............................................................................................................271 9.12.2 The Double Crush Syndrome or Whole Nerve Syndrome.......................................................................271 9.12.3 Cumulative Trauma Disorder (CTD) ........................................................................................................273 9.13 Myotendinous, Myofascial, and Related Contributions to Entrapment ...............................................................273 9.13.1 Acute Myofascial Injury............................................................................................................................273 9.13.2 Chronic Injuries .........................................................................................................................................273 9.13.2.1 Constant Pressure/Tension Injury ..............................................................................................273 9.13.2.2 Repetitive Injury.........................................................................................................................273 9.13.3 The Cumulative Injury Cycle ....................................................................................................................274 9.13.3.1 Weak and Tight Tissues .............................................................................................................274 9.13.3.2 Friction–Pressure–Tension .........................................................................................................274 9.13.3.3 Decreased Circulation, Edema...................................................................................................274 9.13.4 Inflammation ..............................................................................................................................................275 9.14 Common Predisposing Disorders Associated with Entrapment Neuropathy .......................................................275 9.14.1 General Patterns of Anatomic Distribution...............................................................................................276 9.14.2 Diabetes......................................................................................................................................................277 9.14.3 Uremia........................................................................................................................................................277 9.14.4 Thyroid Disorders......................................................................................................................................277 9.14.5 HIV-1 .........................................................................................................................................................278 9.14.6 Rheumatoid Arthritis .................................................................................................................................278 9.14.7 Respiratory Insufficiency...........................................................................................................................278 References .......................................................................................................................................................................278 Chapter 10 Characteristic Signs and Symptoms of Entrapment.......................................................................................................281 10.1 Assessment of Entrapment Syndromes.................................................................................................................281 10.1.1 History........................................................................................................................................................281 10.1.2 Examination ...............................................................................................................................................281 10.1.3 Nerve Percussion Sign...............................................................................................................................282 10.1.4 Electrodiagnostic Findings ........................................................................................................................283 10.1.5 Entrapment Syndromes Overview.............................................................................................................284 10.2 Proximal Upper Extremity Entrapment ................................................................................................................285 10.2.1 Cervicoaxillary Entrapment Syndromes (Thoracic Outlet Syndrome) ....................................................285 10.2.2 Scalene Entrapment Syndrome .................................................................................................................287 10.2.3 Other Causes of Proximal Plexus Entrapment..........................................................................................288 10.2.3.1 Clinical Signs and Symptoms ....................................................................................................289 10.2.4 Costoclavicular Entrapment Syndrome.....................................................................................................289 10.2.5 Costopectoral Tunnel or Hyperabduction Syndrome................................................................................290 10.2.5.1 Clinical Signs and Symptoms ....................................................................................................290 10.2.6 Axillary Tunnel Entrapment ......................................................................................................................290 10.2.6.1 Electrodiagnostic Evaluation......................................................................................................291 10.2.7 Long Thoracic Nerve Entrapment (Scapular Winging) ............................................................................291 10.2.8 Quadrangular (Quadrilateral) Space Syndrome (Lateral Axillary Hiatus Syndrome) .............................291 10.2.8.1 Clinical Signs and Symptoms ....................................................................................................292 10.2.9 Lateral Antebrachial Symptoms: Lateral Antebrachial Cutaneous Nerve/Musculocutaneous Nerve Entrapment......................................................................................................................................292 10.3 Median Nerve Entrapment Syndromes .................................................................................................................292 10.3.1 Supracondylar Process Syndrome .............................................................................................................292 10.3.1.1 Clinical Signs and Symptoms ....................................................................................................293
10.4
10.5
10.6 10.7
10.3.2 Pronator Teres Muscle Syndrome .............................................................................................................293 10.3.2.1 Clinical Signs and Symptoms ....................................................................................................294 10.3.3 Anterior Interosseous Nerve Syndrome ....................................................................................................295 10.3.3.1 Clinical Signs and Symptoms ....................................................................................................295 10.3.4 Carpal Tunnel Syndrome...........................................................................................................................296 10.3.4.1 Prevalence...................................................................................................................................297 10.3.4.2 Anatomy and Pathomechanics ...................................................................................................297 10.3.4.3 Clinical Signs and Symptoms ....................................................................................................299 10.3.4.4 Electrodiagnostic Evaluation of Carpal Tunnel Syndrome .......................................................301 10.3.4.5 Diagnostic Imaging ....................................................................................................................303 Posterior Upper Extremity Syndromes .................................................................................................................303 10.4.1 Suprascapular Nerve Syndrome ................................................................................................................303 10.4.1.1 Clinical Signs and Symptoms ....................................................................................................304 10.4.2 Lateral Intermuscular Septum/Radial Nerve.............................................................................................305 10.4.3 Brachialis/Brachioradialis/Radial Nerve ...................................................................................................306 10.4.4 Arcade of Frohse/Deep Radial Nerve .......................................................................................................306 10.4.5 Distal Superficial Radial Nerve Entrapment/Cheiralgia Paresthetica.......................................................309 Ulnar Nerve Syndromes ........................................................................................................................................310 10.5.1 Ulnar Nerve Entrapment at the Elbow Cubital Tunnel Syndrome...........................................................310 10.5.1.1 Clinical Signs and Symptoms ....................................................................................................311 10.5.1.2 Electrodiagnostic Evaluation of Ulnar Entrapment at the Elbow .............................................311 10.5.1.3 Diagnostic Imaging ....................................................................................................................311 10.5.2 Guyon’s Canal Syndrome/Ulnar Tunnel Syndrome .................................................................................311 10.5.2.1 Anatomy and Pathomechanics ...................................................................................................311 10.5.2.2 Clinical Signs and Symptoms ....................................................................................................312 Abdominal/Pelvic Entrapment Syndromes ...........................................................................................................314 Lower Extremity Entrapment Syndromes.............................................................................................................317 10.7.1 Psoas Entrapment Syndrome/Iliacus Entrapment Syndrome ...................................................................317 10.7.1.1 Anatomy and Pathomechanics ...................................................................................................317 10.7.1.2 Clinical Signs and Symptoms ....................................................................................................319 10.7.2 Meralgia Paresthetica/Inguinal Tunnel Syndrome (Lateral Femoral Cutaneous Entrapment) ................320 10.7.2.1 Anatomy and Pathomechanics ...................................................................................................320 10.7.2.2 Clinical Signs and Symptoms ....................................................................................................321 10.7.3 Obturator Nerve Entrapment .....................................................................................................................321 10.7.3.1 Anatomy and Pathomechanics ...................................................................................................322 10.7.3.2 Clinical Signs and Symptoms ....................................................................................................322 10.7.4 Iliolumbar–Lumbosacral Ligament Entrapment/Lumbosacral Tunnel Syndrome ...................................322 10.7.4.1 Anatomy and Pathomechanics ...................................................................................................322 10.7.4.2 Clinical Signs and Symptoms ....................................................................................................323 10.7.5 Piriformis Syndrome..................................................................................................................................323 10.7.5.1 Anatomy and Pathomechanics ...................................................................................................323 10.7.5.2 Clinical Signs and Symptoms ....................................................................................................325 10.7.6 Saphenous Nerve Syndrome/Adductor Tunnel Syndrome .......................................................................325 10.7.6.1 Anatomy and Pathomechanics ...................................................................................................325 10.7.6.2 Clinical Signs and Symptoms ....................................................................................................327 10.7.7 Peroneal Tunnel Syndrome/Entrapment at the Knee and Fibular Neck ..................................................327 10.7.7.1 Anatomy and Pathomechanics ...................................................................................................327 10.7.7.2 Clinical Signs and Symptoms ....................................................................................................329 10.7.7.3 Electrodiagnostic Evaluation......................................................................................................329 10.7.8 Anterior Tarsal Tunnel Syndrome/Deep Peroneal Nerve Syndrome........................................................329 10.7.8.1 Anatomy and Pathomechanics ...................................................................................................329 10.7.8.2 Clinical Signs and Symptoms ....................................................................................................330 10.7.9 Medial Tarsal Tunnel Syndrome ...............................................................................................................331 10.7.9.1 Anatomy and Pathomechanics ...................................................................................................331 10.7.9.2 Clinical Signs and Symptoms ....................................................................................................332
10.7.10 Morton’s Neuroma (Metatarsalgia) .........................................................................................................333 10.7.10.1 Anatomy and Pathomechanics ...............................................................................................333 10.7.10.2 Clinical Signs and Symptoms ................................................................................................334 10.8 Summary ................................................................................................................................................................334 References .......................................................................................................................................................................334 Section 4 Appendix ........................................................................................................................................................................341 Index ...............................................................................................................................................................................349
Section 1 Myelopathy: Spinal Cord Injury and Selected Clinical Syndromes
1
Relevant Spinal Cord Anatomy*
The ability to recognize signs and symptoms of acute, subacute, or chronic myelopathy should not be limited to the neurologist or neurosurgeon but should extend to all physicians and physical medicine specialists. The clinician should be familiar with the regional anatomy, risk factors, and early clinical signs. To that end, this chapter reviews relevant regional anatomy, mechanisms of spinovascular insufficiency, infarction, stenotic syndromes, spinal cord injury (SCI), and selected noncompressive myelopathies. Throughout this text, emphasis is placed on assessment. Although the most prevalent spinal syndromes are presented, keep in mind that many incomplete and atypical patterns are seen in clinical practice.
1.1 BASIC SPINAL CORD ANATOMY The spinal cord lies well protected within the spinal canal of the vertebral column. The surrounding vertebrae support the trunk and head and provide a protective covering for the spinal cord throughout intersegmental and global vertebral motion. The column of organized cell bodies and myelinated or unmyelinated axons constituting the spinal cord is somatotopically, longitudinally, and segmentally arranged. In adulthood, the cord averages 42 to 45 cm in length, extending from the medulla oblongata to approximately the L1 vertebral disk level.1 It is generally 25 cm shorter than the 70-cm vertebral column and thus occupies almost two thirds the length of the spinal canal. The adult cord weighs approximately 30 to 35 g and averages 2.5 cm wide. Regions of enlargement occur in the cervical and lumbar areas of the cord, reflecting greater numbers of nerve cell bodies, neurons, and interneurons within the gray matter. These two enlargements correspond to the origin of spinal nerve roots destined for the brachial and lumbar plexuses, which provide innervation to the upper and lower extremities, respectively (see Figure 1.1). The diameter of the cervical enlargement ranges from 9 to 13 mm, and the lumbar enlargement from 8 to 12 mm. By comparison, the normal thoracic cord diameter is approximately 8 to 10 mm.2 The spinal cord terminates in a conical tapering referred to as the conus medularis. At birth, the conus
medularis lies approximately at the level of L3. In adults, the conus normally ends between the T12 and L3 vertebral levels, with the L1–L2 level being the most common site of cord termination. Lumbar and sacral nerve roots originate in the conus, exit, and descend to form the cauda equina. Also extending from the conus is the filum terminale formed from the pia mater, which attaches to the first coccygeal segment. The spinal cord is longitudinally divided by an anterior median fissure and a posterior median sulcus that separate it into right and left symmetric halves. The anterior median fissure is a deep invagination containing the anterior spinal artery; the posterior median sulcus is a shallow midline division of the posterior columns. Nerve roots attach bilaterally to the cord along its dorsal lateral sulcus and ventral lateral sulcus. Each lateral half of the cord is additionally divided into longitudinally organized columns (funiculi) of spinal white matter, consisting of nerve fibers, neuroglia, and blood vessels. This white matter surrounds the central gray portion of the cord. Resembling an “H” on transverse section, the spinal gray matter consists largely of nerve cell bodies in three main categories.3 The first is the internuncial or interneuron: short, small fibers involved in local circuitry between gray matter nerve cells. The second category, motor cells of the cord’s ventral and lateral horns, is in turn subdivided into three subtypes: alpha motor neurons, gamma motor neurons, and preganglionic motor cells of the sympathetic nervous system. The third major category within spinal gray matter is the tract cell; cell bodies of these neurons are involved in relaying sensory information.3 On axial section, the H-shaped gray matter is divided into two symmetric halves representing each side of the body, with a central canal running the entire length of the cord. The anterior portion of the spinal gray matter, or anterior horn, contains nerve cell bodies leading to fibers of the ventral roots. A lateral column, most pronounced in the thoracic region of the cord, contains the preganglionic cells of the autonomic nervous system (ANS). The posterior horn contains the cell bodies of nerves subserving sensory function. Dendritic connections between nerve cell bodies account for the greatest volume of spinal gray matter.4
* This chapter written with John W. Blum.
3
4
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
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FIGURE 1.1 Dorsal view of the spinal cord and dorsal nerve roots in situ, after removal of the neural arches of the vertebrae. (From DeMeyer, W., Neuroanatomy, Hawal, Philadelphia, PA, 1988, p. 99. With permission.)
The surrounding white matter is organized into three columns: dorsal, ventral, and lateral. The dorsal funiculus consists of the fasciculus gracilis, which carries sensory information from the sacral area and lower extremities, and the fasciculus cuneatus, which carries sensory information from the thoracic and cervical region; these are bounded by the dorsal horns of the spinal gray matter. The ventral and lateral funiculi contain both ascending and descending tracts. Of these, the most important descending pathways are the lateral corticospinal tract, vestibulospinal tract, and reticulospinal fibers; the largest ascending tracts in the ventral and lateral funiculi are the anterolateral spinothalamic fibers and the dorsal and ventral spinocerebellar tracts. Nerve fibers of the spinal white matter can be categorized into five groups: (1) afferent fibers from cells in the dorsal root ganglia, which enter through the dorsal root
and may ascend or descend within the cord before synapsing; (2) long ascending fibers derived from nerve cells in the cord, which conduct afferent impulses to supraspinal levels; (3) long descending fibers from supraspinal sources, which synapse within the spinal gray matter; (4) fibers affecting intrasegmental and intersegmental spinal cord processing; and (5) fibers from motor neurons in the ventral and lateral gray columns, which exit the cord into the ventral spinal nerve root. All of these groups, with the exception of the fifth, constitute longitudinal tracts.4 Myelination is formed from glial cells. Schwann cells, normally found in myelinated peripheral nerves, are not found within the brain and central portion of the spinal cord but are found instead in the transitional zone, within a few millimeters distal to the point at which nerve roots traverse away from the spinal cord.
Relevant Spinal Cord Anatomy
1.2 SEGMENTAL SPINAL ANATOMY The spinal cord can be divided into 31 segments or neuromeres, each contributing to one pair of spinal nerve roots. Each of the 31 paired nerve roots, in turn, represents a segmental level that is further defined as the entire region of the body innervated by that root. For clinical purposes, these segments are often further classified: a dermatome is the cutaneous region(s) subserved by a nerve root; a myotome is the skeletal musculature innervated by the motor contributions from a signal nerve root; and an angiotome comprises those blood vessels innervated by the autonomic fibers within a spinal nerve.5 Not every neuromere contributes to each of these segmental categories, and the distribution of segmental autonomic innervation differs significantly from myotome and dermatome innervation. Autonomic nerves contribute to other functions, such as pseudomotor or pyelomotor modulation; this diffuse autonomic distribution contributes to a more complex clinical presentation in nerve root compromise. Each spinal nerve contains contributions from a primarily sensory dorsal root and a primarily motor ventral root. The spinal nerves are segmentally paired as follows: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1–2 coccygeal.6,7 During fetal and infant development, the vertebral column and dura mater lengthen at a more accelerated rate than the neural tube, leaving the terminal end of the cord highly positioned in relation to the most caudal osseous spinal structures. As a result, spinal nerve roots must descend from their cord segments of origin to their levels of exit from the column through intervertebral foramina.1,3,4
1.2.1 REGIONAL NEUROMERE CHARACTERISTICS The cervical cord spans from C1 to T1 and has an average length of 10 cm. The eight cervical segments closely correspond in position to the adjacent cervical vertebrae. The first seven cervical nerve pairs exit through intervertebral foramina above their corresponding vertebrae; the most caudal cervical nerve pair (C8), however, departs the cord below the most caudal cervical vertebra (C7), which allows for the presence of one more cervical nerve root pair than vertebrae. Many of the roots below the C7 vertebral level do not necessarily exit immediately adjacent to their corresponding vertebrae, due to the variability of cord length among individuals and other variables such as cord segmental lengths and level of cord termination. Two enlargements or widenings are found within the spinal cord, one in the cervical and one in the lumbar region. The cervical enlargement commonly extends from cord segments C3 to T1 and represents the increased number of nerve cell bodies originating from C5–T1 that innervate the upper extremities through the brachial plexus. The lumbar enlargement typically spans cord segments L1 to
5
S3 and is located between the T10 and L1 vertebral bodies; these segments subserve the lower extremities through the lumbosacral plexus. The conus medularis lies approximately at the L1–L2 vertebral level in the adult.8 The cauda equina nerve root bundle emerges from the conus medularis, descending as the lumbar and sacral nerve roots. In cervical cord segments, transverse diameter is characteristically greater than sagittal diameter and varies with each descending cervical segment.2,9 White matter is more prevalent in the cervical cord than in any other spinal segment due to the confluence of ascending and descending tracts in this region. The entire diameter of the thoracic cord is smaller than that of the cervical cord; comparatively, the thoracic cord contains a smaller number of neuronal cell bodies and therefore has a smaller ventral horn as well.9 A lateral gray horn is present and is distinguished among thoracic intermediate gray matter, representing the autonomic cell bodies (and their axial projections) that innervate smooth muscle, cardiac muscle, and glandular tissues. Despite containing relatively less white matter than the cervical cord, lumbar spinal segments display large ventral and dorsal horns. The lumbar ventral horns contain a multitude of neuronal cell bodies with axonal projections innervating skeletal muscles of the lower extremities. Lumbar neural segments have roughly the same sagittal and transverse diameter, giving them the most circular appearance in the entire cord.9 The sacral cord is predominantly composed of gray matter with a relative paucity of white matter. Its superiorto-inferior neuromere length is typically short, averaging only 5 mm; other spinal cord segmental lengths vary from 15 mm in the lumbar to 26 mm in the thoracic and 13 mm in the cervical region.4
1.2.2 REGIONAL SPINAL CANAL CHARACTERISTICS Studies of the adult cervical spinal cord lumen have shown that the mean anterior-to-posterior (A-P) and lateral diameter vary, respectively, from 17 mm and 26 mm at C2 to 14 mm and 25 mm at C5.10 In the normal spine at the C1–C2 vertebral level, the cord is positioned within a spinal canal approximately 2.5 times larger and a dural sac 1.5 times larger than the cord itself. The canal then narrows from C3 to C6,11 decreasing to 1.8 times the cord size by C5–C6, with a dural sac only 1.2 times as large as the cord;12 at the C6 vertebral level, the spinal cord fills approximately 75% of the canal.11 The osseous spinal column surrounding the cervical cord is considered the most distinctive region of the spine and characteristically is the most complicated regional articular system in the body.13 Its 37 separate joints enable the most complex movements of any spinal section and therefore assume the greatest risk for pathomechanical
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Posterior spinal arteries Anterior spinal artery Anterior and posterior rootlets
Pia mater Circumferential arteries Radicular artery Arachnoid
Dentate ligaments
Dura mater Dural sleeve Spinal nerve
FIGURE 1.2 Intradural anatomy. (Copyright J.M. True, D.C.)
sequelae, due to the great degree of flexibility, excursion, and exposure to potential physical trauma. There is less risk of compression from vertebral instability in thoracic segments due to the stabilizing effects of the ribcage. The thoracic spinal canal has the smallest diameter spinal lumen.10 The narrowest region extends approximately from vertebral levels T4–T9, with a mean adult A-P diameter of 14 mm and 15 mm laterally at the T6 vertebra. However, this narrowing predisposes the thoracic cord, a region with a less abundant vascular supply than the other cord segments, to greater risk for vascular compromise. The spinal cord from T4–T9 is also more susceptible to stenotic compromise. Rare thoracic disk herniations (1% of all herniated disks) can impose on the narrow canal, compressing the dura mater, subarachnoid space, and the spinal cord.14 In a review of 280 cases, Arce and Dohrmann14 reported that 75% of thoracic disk protrusions occur between T8 and T12 at the caudal end of the thoracic watershed zone. The lumbar and sacral regions of the canal are spacious by comparison, with progressive lateral expansion accommodating the cauda equina as the canal descends. Lumbar A-P canal diameter averages 15 to 25 mm, and any narrowing to less than 12 to 13 mm is considered diagnostic for lumbar stenosis.15 The cross-sectional area of the lumbar canal is at least 77 ± 13 mm2.16
1.3 MENINGES AND COMPARTMENTS Three membranous layers surrounding the spinal cord provide protection and additional support to the neural tissues within. Collectively known as the meninges, these three structural layers are continuations of the meningeal coverings of the brain; from superficial to deep, they are the dura, arachnoid, and pia mater, respectively (Figure 1.2).
1.3.1 DURA MATER The outermost layer of the spinal cord meninges is the dura mater (pachymeninx), a tough fibrous sheath that provides an imposing barrier rarely penetrable by primary bone tumors, metastasis, bacterial infections, or osteomyelitic tuberculosis. The dura mater is primarily comprised of an outermost loosely arranged fibroelastic layer, a middle layer that is largely fibrous tissue, and an inner layer of flattened fibroblasts called the dural border cell layer.17 There is an abundance of collagenous fibers that lie in longitudinal bundles and have redundant properties, being wavy in configuration when shortened, straight and taut when stretched. A continuation of the dural meningeal layer of the brain, the dura mater extends from the foramen magnum to its termination at the second sacral vertebral body. Dural anchoring also occurs at the rim of the foramen magnum, at the posterior vertebral bodies of C2–C3, and to the posterior longitudinal ligament by Hoffmann’s ligaments.4 The dura extends along each nerve root to form a funnel-shaped sleeve within the intervertebral foramen. Sensory innervation of the anterior aspect of the spinal dura mater is greater than the posterolateral aspect of the dura. Innervation to the dura originates from the sinuvertebral nerve of Von Luschka (recurrent meningeal nerve). Branches that innervate the anterior dura may span several vertebral levels, creating considerable innervation overlap from multiple segments.18 The majority of meningeal nerve fibers terminate as free nerve endings with occasional myelinated fibers supplying encapsulated and lamellated receptors.19 Innervation and free nerve endings in the posterior dura are absent or very minimal. The epidural space surrounding the dura mater contains fatty areolar tissue, loose connective tissue, and an
Relevant Spinal Cord Anatomy
extensive venous plexus network separating the spinal dura from the inner vertebral surface.
1.3.2 ARACHNOID MATER The next meningeal layer, the arachnoid mater, is nearly contiguous with the inner surface of the dura mater. Arachnoid tissue is thin, transparent, loosely arranged, and nonvascular.11 The arachnoid membrane is structurally composed of loose, irregular connective tissue with collagen, elastin, and reticular fibers. The arachnoid is composed of an outermost portion (arachnoid barrier cell layer), presenting tightly packed cells, numerous tight junctions, and no extracellular collagen. In view of its numerous tight junctions, the arachnoid barrier cell layer is considered to represent an effective morphological and physiological meningeal barrier between the cerebrospinal fluid in the subarachnoid space and the blood circulation in the dura.17 The spinal arachnoid layer extends from the intracranial arachnoid layer to the S2 vertebral level. Where the nerve roots pass through the dura and enter the IVF, they carry a prolongation of the arachnoid membrane applied to the inner surface of the dural sleeve. This creates a bilaminar tubular funnel-shaped sleeve composed of dura externally and arachnoid internally. The dura blends with the epineurium of the spinal nerve, and the arachnoid blends with the perineurium of the spinal nerve.20 Cerebrospinal fluid (CSF) fills the subarachnoid space, providing biochemical and immunological support and protection to the central nervous system (CNS). During spinal movement, pressure shifts in the CSF and pulsations of the subarachnoid arteries contribute to rostral and caudal movement of the spinal CSF through subarachnoid spaces. The local venous system of the spinal cord absorbs some of the fluid, providing a potential escape route to systemic circulation for CSF metabolites.4 (See Section 1.3.4 for further discussion of CSF.) Inflammation of the arachnoid membrane is termed arachnoiditis. This condition can result in chronic pain and disability. In the strictest sense, arachnoiditis is inflammation of the piaarachnoid membrane. Chronic arachnoid inflammation will induce localized proliferative fibrosis. Fibrosis associated with arachnoiditis can occur in varying degrees, ranging from mild thickening of the membrane to pronounced adhesions severe enough to block the subarachnoid space.
1.3.3 PIA MATER The pia mater, the innermost meningeal membrane, encases the spinal cord and small blood vessels on the cord surface. This thin double layer of connective tissue can be subdivided into the pia-glia and epi-pia. The avascular pia-glia is the deeper layer and adheres directly to the cord, nerve roots, and rootlets. The pia-glia membrane is similar to the
7
ependymal lining, having discontinuous gap junctions that provide bidirectional exchange of solutes between spinal interstitial fluids and the CSF within the subarachnoid space. The epi-pia encases the vascular elements of the pia mater and joins the pia-glia following the nerve roots to the IVF. Two distinguishing structures of the pia mater help to anchor the spinal cord within its osseous confines. First is the bluish-white filum terminale, a slender, fibrous filament of pia that extends approximately 20 cm from the caudal tip of the conus medullaris to the dorsum of the coccyx. Beginning within the dural sac, the filum terminale eventually pierces the dura and arachnoid membranes at the S2 vertebral level to escape extradurally, but retains its dural and arachnoid coverings. This extradural extension is referred to as the coccygeal ligament. The second specialized supportive component of the pia mater is the dentate ligament, a triangular-shaped, serrated epi-pia extending from its base at the lateral margins of the spinal cord to its apex attaching to the dura mater. There are approximately 22 separate dentate ligaments along each side of the cord in the coronal plane.2,6 The dentate ligament stabilizes the spinal cord by cushioning it from constant movement of the dura mater. The most superior dentate ligament attachment, between the vertebral artery and cranial nerve XII (hypoglossal nerve), provides a landmark where the vertebral artery pierces the dura and enters the posterior fossa at the level of the foramen magnum. The most caudal dentate attachment is usually between the T12 and L1 spinal nerves.7 Surgeons rely on their anatomic knowledge of dentate ligament relationships and attachment points to identify important structures during spinal cord surgery. Intraoperative visualization of the dentate ligament provides identification of the ventral nerve roots and also provides a landmark for localizing the spinothalamic and corticospinal tracts: the ligament typically lies dorsal to the spinothalamic tracts and ventral to the corticospinal tracts.
1.3.4 SUBARACHNOID SPACE CEREBROSPINAL FLUID
AND
The choroid plexus lining the lateral ventricles of the brain secretes CSF and contributes the chemical constituents of the fluid through various cellular transport mechanisms. The unidirectional CSF flow within the ventricles eventually enters the cranial subarachnoid space from the caudal fourth ventricle. Subarachnoid flow of CFS then extends around the brain, spinal cord, and the central canal. Within the cord, pressure gradients enable CSF to flow from the subarachnoid space through arachnoid granulations into the venous sinuses of the cranial dura mater; in addition, the venous system of the spinal cord absorbs
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
some CSF into the local circulation.4 This one-way CSF circulation system is thus a filter for removing metabolites and a means for regulating osmotic pressure gradients in the CNS. The 80- to 150-ml total volume of CFS is replaced four to five times daily, and the pressure ranges from 80 to 180 mm water.6 Normal cellular components of CSF include approximately six lymphocytic cells per mL but no red blood cells (RBCs). The slightly alkaline CSF is transparent and contains chloride, sodium, potassium, and magnesium ions. Protein and glucose are also present but at concentrations much less than in plasma. Pathologic processes can alter CSF volumes, pressures, and constituent characteristics, contributing to or producing life-threatening situations. Any increase in CSF volume must be compensated by a shift in blood or brain tissue volumes. Because the rigid osseous boundaries of the brain and spinal column are unyielding, space-occupying lesions within the CSF circulation can elevate CSF pressure, and potentially cause hydrocephalus. Samples of CSF provide useful diagnostic information in conditions such as infectious meningitis, multiple sclerosis (MS), or subarachnoid hemorrhage. Cellular constituents, fluid color, gamma globulin levels, and glucose and protein concentrations can all be analyzed in an effort to determine the etiologic mechanisms of CNS compromise. Microscopic examination of centrifuged CSF sediment provides diagnostic insight to the presence of extramedullary tumors, leukemia (acute lymphocytic leukemia, ALL), lymphoma, various drop metastases, and germ cell tumors.7 (See additional discussion on CSF in Section 5.15.2.)
1.4 SPINAL VASCULAR ANATOMY Through its blood supply, the spinal cord is exposed to systemic influences that include cardiac insufficiency, infection, metabolic abnormalities, and hematogenous seeding of malignancy. Pathology occurring outside the spine can directly or indirectly influence spinal blood supply, and aortic or vertebral arterial disease can result in cord arterial insufficiency. Vascular-induced injury (infarction) is often irreversible and rapid in onset, whereas the signs of insufficiency may emerge over a longer period of time. Spinal blood vessels themselves are susceptible to physical compression. Many of the patients who develop degenerative stenosis — a risk for compressive myelopathy — fall into the same age group at risk for acquiring cardiac and peripheral vascular disease. Some of these individuals may also have a coagulation disorder from disease or from therapeutic intervention (blood thinners). Clinicians who identify cardiac, vertebral, and/or aortic disease should pay particular attention to the possibility of frank myelopathy or a history suggestive of an undiagnosed intermittent myelopathic presentation.
1.4.1 EXTRINSIC SPINAL CORD VASCULATURE The extrinsic spinal cord vasculature receives the greatest portion of its blood supply rostrally from the vertebral artery and caudally from the artery of Adamkiewicz. The largest vascular supply to the anterior portion of the spinal cord comes from arterial feeders from the cervical and lumbar regions; the thoracic region of the spine makes the least vascular contribution to the cord. Comparatively, the posterior paired arterial system of the spinal cord is less vulnerable to vascular insufficiency due to the greater redundancy of blood vessels supplying it. 1.4.1.1 Radiculomedullary Arteries A group of six to nine medullary arteries arises from spinal arteries supplied by the vertebral, deep cervical, intercostal, descending aorta, and common iliac arteries.21 These collateralizing arteries contribute to the anterior spinal artery (ASA) at various levels along the length of the cord. The posterior spinal arteries (PSAs) are similarly augmented by 10 to 20 small-caliber posterior medullary vessels with which they form a plexus.22 The medullary arteries are variable in size and location, traveling to the spinal cord through the intervertebral foramina along with the segmental spinal nerves.23 Radicular arteries that anastomose directly with the ASA vary in diameter and thus differ significantly in perfusion characteristics. The artery of Adamkiewicz (artery of the lumbar enlargement) is the single largest of these radiculomedullary arteries. This artery variably enters the spinal canal on the left side somewhere between the level of cord segments T9 and L2.21,24,25 It usually accompanies the nerve root of L1 or L2, although it has been found to accompany any nerve root from T7 to L3. As the major source of blood flow to the ASA, the artery of Adamkiewicz provides vascular supply to the lower thoracic cord, lumbar cord, and conus medularis. This contribution is thought to supply approximately 50% of the spinal cord in 50% of individuals. Due to the major vascular contribution of the artery of Adamkiewicz, the clinician should always be aware of those disorders that result in hypotension or compression along its course. A large medullary artery is also present at the C5 or C6 level, providing vascular supply to the cervical enlargement. Other medullary arteries, variable in size and number, may be present higher in the cervical spine and in the thoracic spine. 1.4.1.2 Anterior and Posterior Spinal Arteries The spinal cord is supplied by one (unpaired) anterior and two (paired) posterolateral vessels that travel longitudinally along the length of the cord. The ASA supplies approximately two thirds of the anterior and central spinal cord and the PSAs supply the posterior column region.
Relevant Spinal Cord Anatomy
The outer layer of the cord is perfused by the vasa corona, small circumferential vessels intimate with the pia mater (discussed further in Section 1.4.2 below). The primary arterial supply of the cervical cord is the ASA, which is formed by the Y-shaped union of the paired vertebral arteries.26 The ASA commonly originates from the fourth division or intracranial portion of the vertebral artery above the foramen magnum and usually runs uninterrupted along the spinal cord but may vary slightly in its course along the anterior aspect. There are many discrepancies between anatomical descriptions by anatomists. This may be due in part to different preparation techniques or normal variation in the population. As an example, according to Gillilan,27 the ASA is largest in diameter in the lumbar cord and smallest in the thoracic portion of the spinal cord. Whereas, Turnbull,28 reports that the largest diameter of the ASA is in the thoracic cord. The PSAs arise from the posterior cerebellar arteries, and occasionally the vertebral arteries; they also receive contributions from the posterior radicular arteries. Smaller in diameter than the ASA, the PSAs are paired structures that run along the posterolateral aspect of the spinal cord adjacent to the dorsal roots and appear more plexiform on the dorsal cord25 (Figure 1.3).
1.4.2 INTRAPARENCHYMAL VASCULAR SUPPLY The ASA gives rise to approximately 250 to 300 penetrating sulcal vessels throughout the length of the cord21 which perfuse both the right and left anterior two thirds of the spinal white and gray matter (Figure 1.4). The thoracic region has the smallest quantity of sulcal arteries, and thoracic sulcal arteries have the smallest average diameter (0.14 mm) compared to those of the cervical (0.21 mm) and lumbosacral (0.23 mm) regions.26 This contributes to greater risk for hypoperfusion insult within the thoracic cord. The PSAs send their penetrating branches to the dorsal horn and posterior columns, supplying the dorsal third of the white and gray matter of the cord. The ASA and PSAs anastomose together to form an irregular circumferential plexus of arterial vessels referred to as the vasa corona. This fine vascular network, also called the plial arterial plexus, encircles the cord and anastomoses with larger vessels, penetrating and supplying the outer layers of white matter.21 The cervical and lumbar segments receive the greatest blood supply, corresponding to the spinal cord enlargements and the increased metabolic demands from the greater number of neurons located within the cord enlargements.
1.4.3 THE SPINAL VENOUS PLEXUS Venous drainage from the spinal cord is accomplished through a number of medullary veins and an extensive,
9
valveless venous plexus encasing the dural sac (Figure 1.5). The distribution of veins draining the spinal cord is described as intrinsic to the cord, or extrinsic. The intrinsic system has two systems — the central veins and the radial veins. The central veins are prominent, radially oriented vessels that drain blood from the anterior or posterior half of the spinal cord. These vessels exit the cord and join the extrinsic veins on the surface of the cord. The other intrinsic drainage system for the cord is the radial veins or intrinsic veins. These vessels course laterally through the outer edge of the cord, exiting to form the venous vasa corona.21 These spinal intrinsic vessels drain into the anterior and posterior spinal veins. The extrinsic spinal cord venous system consists of an anterior median spinal vein, the posterior spinal vein, posterolateral spinal veins, anterolateral spinal veins, venous vasa corona, medullary veins, and radicular veins. The anterior median spinal vein travels longitudinally from the brainstem to the conus medullaris and may continue as the slender vein of the filum terminale.29 The anterior median spinal vein is always single in the lumbar spine and may be paired in the cervical and thoracic spine. The posterior spinal vein extends the length of the spinal cord, occasionally as high as the medulla. This vessel may be plexiform and quite large over the lumbar and cervical enlargements. The posterolateral and anterolateral veins are longitudinally oriented; however, they are inconsistent and sometimes not apparent. The venous vasa corona collects blood from the outer edge of the cord and channels it to the longitudinal vessels. Medullary veins are numerous and are divided into anterior and posterior groups. The anterior medullary veins drain the anterior half of the cord, and the posterior medullary veins drain the posterior cord. These vessels follow the nerve roots without draining them. Blood from the nerve roots is drained by the radicular veins.29 Medullary veins and radicular veins join within the IVF and exit the dura to converge with the vertebral venous plexus. The largest medullary vein is the great anterior medullary vein, generally located in the left upper lumbar spine, exiting between T11 and L3. The external and internal spinal venous plexus is an extrathecal system that parallels those areas of the cord subserved by the external and internal arteries.25 The internal venous plexus (Batson’s plexus) extends from the coccyx to the foramen magnum and is essentially a continuum of irregular, valveless epidural sinuses. These channels are protected within epidural fat and supported by a network of caliginous fibers, which form a pleomorphic ligament (Hoffmann’s ligament).25 The internal venous plexus lies in the epidural space within the bony vertebral canal. It is also comprised of an anterior and posterior grouping of vessels, which anastomose. The
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
B
A
FIGURE 1.3 Arterial blood supply of the spinal cord showing spinal and radicular arteries. (A) Anterior view. (B) Posterior view. (From Cramer, G.D. and Darby, S.A., Eds., Basic and Clinical Anatomy of the Spine, Spinal Cord, and ANS, Mosby, St. Louis, MO, 1995, p. 67. With permission.)
internal plexus has a single large posterior median vein, paired anterolateral veins, and paired posterolateral veins. The external venous plexus surrounds the vertebral column and channels blood from the vertebral bodies and paravertebral muscles. This venous system is susceptible to compression from any lesions extending from a vertebral body, such as bone spurs or disk protrusion.
1.5 CYTOARCHITECTURAL ORGANIZATION OF SPINAL GRAY MATTER The gray matter of the cord primarily consists of unmyelinated nerve cell bodies. Characteristic layers or laminae of the spinal gray matter are distinguished by relative size,
Relevant Spinal Cord Anatomy
11
Vertebral artery Ascending cervical artery Spinal branch
Anterior spinal artery
Thyrocervical stem
Great radicular artery
Lumbar artery
A
B
Epidural space Spinal dural mater Posterior spinal artery Subarachnoid space Spinal arachnoid Spinal pia mater Denticulate ligament
Anterior spinal artery
FIGURE 1.4 (A) Arterial feeders of spinal arteries. (B) Axial anatomy of the cervical venous plexus. (C) Axial anatomy of the arterial supply to the cervical spinal cord. (From Duus, P., Topical Diagnosis in Neurology, Thieme Medical, Stuttgart, 1989, p. 64. With permission.)
Spinal branch of thyrocervical artery
C
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Epidural venous plexus
Basivertebral v.
Posterior external venous plexus
Anterior external venous plexus
FIGURE 1.5 The vertebral venous plexus system. (Copyright J.M. True, D.C.)
shape, density, and cytological features of the neurons in these regions. This organization, known as the laminae of Rexed, was first described from the observations of Rexed in 1952.30 The layers are consecutively numbered by Roman numerals I through X, beginning with the dorsal horn region and traveling anteriorly to lamina X, which is the remaining gray matter surrounding the central canal (Figure 1.6). Laminae I through IV are the main cutaneous afferent receiving areas and comprise the majority of the posterior horn of the gray matter. Lamina I, II, and V are important for the transmission of pain. Lamina III and IV neurons and interneurons transmit and modulate proprioception and soft touch. Lamina II consists of tightly packed small cells with extensive and highly branched dendrites. This laminar region is named the substantia gelatinosa in reference to the appearance of the cellular layer. This region is believed to be important for receiving and modulating the sensory input that enters the spinal cord. Modulation occurs through the effects of interneuron connections with descending suprasegmental and supraspinal influences. Lamina V receives small-diameter afferents from the skin, muscle, and viscera, and lamina VI receives proprioceptive and some cutaneous afferents.4 Lamina VII, the largest cytoarchitectural region of spinal gray matter, occupies the intermediate zone between the dorsal and ventral horns and much of the space of the ventral horn.3 Lamina VII consists of many cells that function as interneurons, and within the thoracic spine this lamina contains the nucleus thoracicus or Clark’s column. The cell bodies of the sympathetic portion of the autonomic nervous system (ANS) are located within the intermediolateral nucleus from the level of C8 through L3, with their axons exiting the ventral roots from T1 through L3. The preganglion parasympathetic neuronal
!
FIGURE 1.6 Somatotopic representation in the upper cervical cord. (Copyright J.M. True, D.C.)
cell bodies of the spinal cord lie within the lateral intermediate region of the gray matter at the levels of S2, S3, and S4. The preganglionic axons of the parasympathetic nervous system exit the spine via the ventral nerve roots at the S2, S3, and S4 levels, synapsing within peripheral ganglia located near the pelvic viscera. The anteromedial lateral cell column also occurs in lamina VII. Lamina VIII is in the medial aspect of the ventral horn and receives terminations from some descending fiber tracts, including the vestibulospinal and reticulospinal tract. Lamina IX, within the anterior horn, is divided into groups of cell columns. The sizes and positions of these columns vary along the length of the spinal cord, and they consist of alpha motor and gamma motor neurons. The alpha motor neurons innervate extrafusal muscle fibers, whereas the gamma motor neurons innervate small intrafusal fibers of the muscle spindles, which play an important regulatory role in muscle tone and related function. These columns of alpha and gamma motor neurons
Relevant Spinal Cord Anatomy
are somatotopically arranged, with the more ventrally placed neurons supplying extensor groups and the posterior portion of the ventral horn supplying flexor muscle groups in a lateral to medial arrangement. The lateral groups supply the extremities, and medial-placed neurons supply the trunk.1,3,4
1.6 RELEVANT SPINAL CORD PATHWAYS A comprehensive understanding of neuroanatomical pathways of the spinal cord is critical to rendering a timely and accurate diagnosis. There are dozens of ascending and descending pathways, which are beyond the scope of this chapter. We have discussed the pathways in context of those pathway deficits easily identified on clinical examination. Neurological localization of a spinal cord pathway lesion occurs in two primary planes: the longitudinal plane and the transverse plane. Clinical assessment of critical spinal pathways helps to determine whether findings are due to an isolated lesion, multiple lesions, or a diffuse process. The volume of the spinal cord, size of the tracts, and central gray matter configuration of the spinal cord change in a longitudinal fashion characterized by the anatomy of the cervical, thoracic, and lumbar cord levels (Figure 1.7). A select few of the ascending and descending tracts provide a valuable opportunity to clinically localize a spinal lesion due to the unique functions they subserve and their unique decussating characteristics. These tracts are referred to as long tracts and the positive clinical findings as long tract signs.
1.6.1 CLINICALLY IMPORTANT ASCENDING PATHWAYS 1.6.1.1 Posterior Columns The posterior columns of the spinal cord are comprised of the fasciculus gracilis and more laterally positioned fasciculus cuneatus (Figure 1.8). Axons within the posterior columns are somatotopically arranged: fibers from more caudal regions of the body are located medially within the fasciculus gracilis, and fibers from more rostral regions arise within the fasciculus cuneatus. The gracile fasiculus carries fibers from the lower extremity, whereas the cuneate fasiculus carries fibers from the upper extremity. First-order neuron cell bodies lie within the dorsal root ganglia at all spinal levels. The posterior column axons ascend in an uncrossed fashion within the posterior columns, synapsing with second-order neurons within the gracilis and cuneatus nuclei within the medulla. The axons of the second-order pathway ascend rostrally after decussating within the medial lemniscus to synapse within the ventral posterolateral (VPL) nucleus of the thalamus. Third-order neurons within the VPL ascend to the cortex.
13
Axons within the posterior column–medial lemniscus pathway mediate tactile discrimination, form recognition, vibratory stimuli, and joint and muscle position sense (kinesthesia). These fibers also allow for spatial and temporal discrimination of cutaneous stimuli. Clinical evaluation of the integrity of the posterior columns is generally performed by assessment of vibration, position, and static two-point and moving two-point discrimination. Transection of the dorsal column in the spinal cord leads to ipsilateral loss of sensibility. 1.6.1.2 Lateral Spinothalamic Tract The lateral spinothalamic tract arises in a rostral direction within the anterolateral funiculus. The spinothalamic tract contains nonmyelinated and thinly myelinated axons that transmit pain and temperature sensation arising from free nerve endings. The lateral spinothalamic tract receives input from both fast- and slow-conducting pain fibers. First-order neuron cell bodies are located within the dorsal root ganglia at all spinal levels. First-order axons enter the spinal cord along the dorsolateral tract of Lissauer (lateral root entry zone) at the posterior horn and synapse with second-order neurons. Second-order neurons lie within the deeper layers of the posterior horn and give rise to axons that decussate in the ventral white commissure just anterior to the central spinal canal, converging within the lateral funiculus to form the spinothalamic tract. Secondorder neurons ascend contralaterally within the anterolateral funiculus to synapse within the VPL nucleus of the thalamus and within the posterior interlaminar nuclei of the thalamus. Third-order neurons arise within the VPL of the thalamus and project through the posterior limb of the internal capsule arriving at the primary somatosensory cortex (Brodman’s area 1, 2, and 3). The spinothalamic tracts are also somatotopically arranged, with the sacral dermatomes running more laterally and the cervical dermatomes located medially to the lower extremity (Figure 1.9). Spinal cord transection leads to a contralateral loss of pain and temperature sensation. When a central spinal cord lesion, such as syringomyelia, involves the ventral commissure (where second-order neurons cross the midline of the cord to ascend in the spinothalamic tract), there is a bilateral loss of pain and temperature located one to two dermatomal levels below the cord level of interruption. With slowly expanding lesions, there may be a significant delay from the time of symptom onset to correct diagnosis. 1.6.1.3 Other Ascending Pathways There are numerous ascending pathways in the spinal cord that relay or transmit important sensory information to spinal, brainstem, cerebellar, and subcortical neuronal centers. These tracts are largely involved in transmission
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Axial Section Level: 5th Cervical Segment
T
Axial Section Level: 6th Thoracic Segment
Axial Section Level: 5th Lumbar Segment (T12 Vertebral Level)
V
V V
FIGURE 1.7 Anatomical changes over the length of the spine demonstrated in select axial sections. (Copyright J.M. True, D.C.)
of mechanoreceptive kinesthesia for the modulation of fine motor control and posture. Although this sensory information is crucial to normal joint and muscle action, their isolated functions cannot be clinically localized very easily unless the larger tracts are compromised. Ascending
pathways include the dorsal and ventral spinocerebellar, spino-olivary, spinotectal, spinoreticular, spinocervical, and spinovestibular tracts. The spinocerebellar tracts are located in the dorsolateral and ventral cord; they carry afferent information from muscle spindles, Golgi tendon
Relevant Spinal Cord Anatomy
15
Lower extremity 3rd order neurons to somesthetic cortex Upper extremity Ventral posterolateral (VPL) nucleus of thalamus
Medial lemniscus
2nd order neurons to thalamus
Nucleus gracilis Nucleus cuneatus Internal arcuate fibers Internal arcuate fiber decussations Dorsal root ganglion
Fasciculus cuneatus Fasciculus gracilis (Dorsal columns)
Spinocerebellar tract
From lower extremity
70 90 45
25
0 Two point discrimination
Proprioception
Pallesthesia
FIGURE 1.8 Dorsal column and medial lemniscal pathway. (Copyright J.M. True, D.C.)
organs, and discriminative touch receptors to the cerebellum. The spinocerebellar tracts have large input from the lower extremities. The spinoreticular tract provides input to the tegmentum of the brainstem and reticular formation, which influences somatic and visceral reflexes.
1.6.2 CLINICALLY IMPORTANT DESCENDING PATHWAYS 1.6.2.1 Corticospinal Tract Clinically relevant descending pathways are divided between the corticospinal tract (often referred to as the pyramidal
16
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Cortical appreciation of pain
OUCH! Intralaminar nuclei VPL To thalamus
VPM
Periaqueductal gray matter
Trigeminal distribution pain pathway Pons RAS
Sensory nucleus of V
Pons at level of cranial nerve V RAS
V1 V2
Lower medulla
V3 Spinoreticular pathway connections occur throughout all levels of the reticular activating system (RAS) Somatotopic arrangement
RAS
Spinal nucleus ofV cervical level C1-C2 C2 level
Lower limb neurons are located lateral to upperlimb fibers
V3 V2 V1
nd ha unk tr
Spinoreticular tract Spinothalamic tract
le g
Anterolateral fasciculus Nociceptor threshold
Ascends one to two levels before decussating
Anterolateral fasciculus
FIGURE 1.9 Anterolateral nociceptive pathway. (Copyright J.M. True, D.C.)
tract) and nonpyramidal pathways. The cell bodies of the axons comprising the lateral corticospinal tracts lie primarily within layer V of the cerebral cortex. The cell bodies can be found within the premotor cortex (Brodman’s area 6), the primary motor cortex (Brodman’s area 4), and the primary
sensory cortex (Brodman’s areas 3, 1, and 2). The descending fibers of the corticospinal tract strongly influence functions of the distal extremities. The corticospinal tract on each side is comprised of approximately one million fibers, many of them myelinated.31
Relevant Spinal Cord Anatomy
The corticospinal fibers descend within the posterior limb of the internal capsule within the telencephalon. As the descending motor fibers traverse the midbrain they run through the middle portion of the crus cerebri extending through the base of the pons. While descending, approximately 75 to 95% of the corticospinal neurons decussate at the level of the medullary pyramids, converging to form the lateral corticospinal tract located in the dorsal aspect of the lateral funiculus. The distinct pattern of lamination within the corticospinal tract is of great clinical significance (Figure 1.10). Fibers contributing to the lumbar and sacral innervated regions lie within the dorsal lateral aspect of the tract, whereas fibers innervating more caudal and cervical musculature are located more ventromedially, near the central gray matter. Fibers that do not decussate descend ipsilaterally within the anterior corticospinal tract located within the anterior fasciculus. Corticospinal axons descend throughout the length of the spinal cord, synapsing directly on lower motor neurons lying within the anterior gray matter. Noback and colleagues32 propose that approximately 55% of corticospinal fibers project to the cervical region, 20% of the fibers descend to the thoracic region, and the remaining 25% innervate the lumbosacral muscles. Transection of the corticospinal tract causes an ipsilateral spastic paresis, ipsilateral hyperreflexia, and ipsilateral positive Babinski’s sign.
17
The gray rami communicanti contain unmyelinated preganglionic sympathetic fibers and are located at all levels of the spine. White communicanti rami contain myelinated preganglionic fibers and are found at the levels of T1 to L3. The spinal parasympathetic system or sacral outflow arises from the intermediate gray of S2 to S4 levels. These parasympathetic fibers innervate the urinary bladder, anal sphincter, and genitalia (Figures 1.13 and 1.14). The spinal reflex center for micturition is located within the sacral segments and is strongly influenced by descending upper motor neuron (UMN) input. The UMN pathways influencing bowel and bladder function descend within the white matter between the lateral horn and peripheral portion of the spinal cord.34 The bladder is innervated by the sympathetic nervous system arising from the T6 to L3 levels via the hypogastric nerve and plexus. The bladder receives its parasympathetic innervation from the S2 to S4 levels via the pelvic splanchnic nerves. Ascending pathways for bladder and bowel sensation traverse within the peripheral portion of the spinal cord, generally near the location of the sacral fibers within the lateral spinothalamic tract. Vasomotor and sudomotor autonomic UMN pathways descend within the ventrolateral columns of white matter medial to the spinothalamic tract. The efferent pathways synapse at the intermediolateral nuclei prior to emerging to the sympathetic chain ganglia.
1.6.2.2 Nonpyramidal Tracts Nonpyramidal tracts originate within the brainstem and descend to modulate alpha motor neuron function. Large influential nonpyramidal pathways are located within the anterior funiculus of the spinal cord: the reticulospinal tract, vestibulospinal tract, and tectospinal tract. These pathways project to the spinal gray matter, influencing function of axial musculature, muscle tone, reflex activity, posture, and balance.
1.6.3 AUTONOMIC PATHWAYS No anatomically identifiable descending autonomic pathway or tract within the spinal cord exists, although evidence suggests that sympathetic fibers are dispersed within the spinal cord, ultimately projecting to the interomediomedial (IMM) and interomediolateral (IML) neurons of the thoracolumbar cord.33 These descending pathways provide control and regulation of breathing, sweating, urinary bladder control, and blood pressure. The IML and IMM cell columns lie within lamina VII extending from the T1 to L3 cord levels (Figures 1.11 and 1.12). The sympathetic and parasympathetic portions of the ANS are closely integrated by the supraspinal centers forming the central autonomic network (CAN).
1.7 RELEVANT SPINAL CORD NUCLEI A number of motor and sensory nuclei lie within the spinal cord. The ciliospinal center modulates the sympathetic innervation of the eye and is located within the lower end of the cervical enlargement (C8–T2). The nucleus dorsalis of Clarke (C8–L3) is the origin of the dorsal spinocerebellar tract. The interomediolateral cell column (C8–L3) mediates sympathetic functions in the body. The parasympathetic nucleus (S2–S4) is critical to the control of bowel and bladder function. The spinal accessory nucleus (C1–C6) is the origin of the spinal accessory nerve that controls upper trapezius and sternocleidomastoid muscle function. The phrenic nucleus (C3–C6) impacts respiratory efficiency through mediation of diaphragmatic function.
1.8 ANATOMY OF SPINAL-MEDIATED MYOTATIC REFLEX The myotatic reflex is a monosynaptic reflex initiated by muscle and tendinous stretch. The reflex loop is comprised of a sensory or afferent component and a motor or efferent component. Complete interruption of either component of the reflex arc will result in an absent corresponding reflex
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Lower extremity
Motor cortex Trunk Upper extremity
30% of motor fibers originate in the motor cortex (area 4). Another 30% originate in the premotor cortex (area 6). The somatic sensory cortex of parietal lobe contributes the remaining 40% (area 3,1,2).
Internal capsule
Somatotopic arrangement of pyramidal fibers is present from the cortex to cord.
Pyramidal tract
Leg Trunk Arm
Cerebral peduncle
80-85% of pyramidal tract fibers cross in the caudal medulla to become the lateral corticospinal tract. The remaining fibers descend uncrossed as the anterior corticospinal tract.
Pyramidal decussations
Lateral and anterior corticospinal tract
C5 cord Brachial plexus Paraspinals
Uncrossed motor fibers
T6 cord
Sympathetic trunk Intercostal nerves Paraspinals
L5 cord
Lumbosacral plexus Paraspinals
FIGURE 1.10 Corticospinal pathway. (Copyright J.M. True, D.C.)
Relevant Spinal Cord Anatomy
19
Gray rami communicantes (GRC) Dorsal root Intermediolateral cell column
White rami communicantes (WRC) Sympathetic component of sinuvertebral nerve
out GRC Ventral root
T1-T12 Levels
Dorsal ramus
Ventral ramus in WRC
Sympathetic chain ganglia To prevertebral ganglia
FIGURE 1.11 Efferent pathway of the sympathetic nervous system. (Copyright J.M. True, D.C.)
Ventral root
Dorsal root Sinuvertebral nerve Dorsal ramus
Sympathetic chain
Ventral ramus
Dural sleeve Aortic nerve plexus Gray ramus White ramus
Splanchnic nerve
FIGURE 1.12 Sympathetic chain ganglia in the mid-thoracic spine. (Copyright J.M. True, D.C.)
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Descending fiber T10-L2 Sympathetic chain
S2-4
Ganglion in inferior hypogastric plexus Inferior hypogastric plexus
Pudendal n.
Ganglion in inferior hypogastric plexus
Prostatic plexus
Seminal vesicle Prostate
Epididymis
FIGURE 1.13 Innervation of the male reproductive organs. (From Cramer, G.D. and Darby, S.A., Eds. Basic and Clinical Anatomy of the Spine, Spinal Cord, and ANS, Mosby, St. Louis, MO, 1995, p. 338. With permission.)
(areflexia). The efferent limb of the reflex arises from the alpha motor neuron pool of the ventral horn. The resting cell potential of the alpha motor neuron population is influenced by interneuron stimuli within the spinal cord and from descending and segmental influences. These influences affect the magnitude of the reflex response to somatic and external stimuli. The detection of muscle stretch begins when the muscle and muscle spindles are stretched. This causes the primary sensory endings (annulospiral endings) of the spindle cell to fire, transmitting a stimulus to the dorsal horn by group 1A fibers. The greater the stretch of the
spindle cells, the higher the frequency of 1A impulses generated by the annulospiral endings. Activation of the spindle cell occurs with the tap of a reflex hammer or rapid tendon stretch. The reflexive muscle contraction in response to the sensory stimuli is referred to as a muscle stretch reflex (MSR). The most commonly performed MSRs are those of the biceps, brachioradialis, triceps, quadriceps (knee), and gastrocnemius (ankle) muscles. MSR evaluation is helpful in the assessment of myelopathy. Compromise of the lateral corticospinal tract is associated with an ipsilateral increase of the MSR response.
Relevant Spinal Cord Anatomy
21
Thoracolumbar level
T12-L2 Sympathetic chain ganglia
Sacral level
Visceral afferents Sympathetic motor
Parasympathetic motor
Inferior mesenteric ganglion
S2 S3 S4 Somatic motor sensory Pelvic nerves
Pudendal nerve
Detrussor muscle (smooth muscle)
Internal sphincter External sphincter (skeletal muscle)
FIGURE 1.14 Innervation of the bladder. (Copyright J.M. True, D.C.)
REFERENCES 1. Chusid, J.G., Correlative Neuroanatomy and Functional Neurology, 18th ed., Los Altos, CA: Lang Medical Publications, 1982. 2. Carpenter, M., Core Text of Neuroanatomy, 4th ed., Baltimore, MD: Williams & Wilkins, 1991. 3. Barr, M.L. and Kiernan, J.A., The Human Nervous System: An Anatomical Viewpoint, 6th ed., Philadelphia, PA: Lippincott, 1993: 67–87. 4. Williams, P.L. and Warwick, R., Gray’s Anatomy, 37th ed., Edinburgh: Churchill–Livingstone, 1989. 5. Byrne, T.N., Benzel, E.C., and Waxman, S.G., Eds., Diseases of the Spine and Spinal Cord, New York: Oxford University Press, 2000. 6. Cramer, G. and Darby, S., General anatomy of the spinal cord, in Cramer, G. and Darby, S., Eds., Basic and Clinical Anatomy of the Spine, Spinal Cord and ANS, St Louis, MO: Mosby, 1995: 52–71.
7. Greenberg, M., Neuroanatomical basics for surgery on the spine, in Allen, M.B. Jr., and Miller, R.H., Eds, Essentials of Neurosurgery: A Guide to Clinical Practice, New York: McGraw–Hill, 1995: 19–35. 8. Fitzgerald, M., Neuroanatomy, Basic and Applied, London: Bailliere Tindal, 1985. 9. Elliot, H., Cross-sectional diameters and areas of the lumbar spinal cord, Anat. Rec., 93: 287–293, 1945. 10. Dommisse, G.F., The Arteries and Veins of the Human Spinal Cord, New York: Churchill–Livingstone, 1975. 11. Cramer, G. and Darby, S., General characteristics of the spine, in Cramer, G. and Darby, S., Eds., Basic and Clinical Anatomy of the Spine, Spinal Cord, and ANS, St. Louis, MO: Mosby, 1995: 17–51. 12. Wackenheim, A., Roentgen Diagnosis of the Craniovertebral Region, Berlin: Springer-Verlag, 1974: 215–251. 13. Bland, J.H., Disorders of the Cervical Spine: Diagnosis and Medical Management, 2nd ed., Philadelphia, PA: Saunders, 1994: 71–91.
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14. Arce, C. and Dohrmann, G., Thoracic disk herniation: improved diagnosis with computed tomographic scanning and a review of the literature, Surg. Neurol., 23(4): 356–361, 1985. 15. Buehler, M.T., Spinal stenosis, J. Manipulative Physiol. Ther., 1(2):103–112, 1978. 16. Schonstrom, N., Lindahl, S., Willen, J. et al., Dynamic changes in the dimensions of the lumbar spinal canal: an experimental study in vitro, J. Orthoped. Res., 7:115–121, 1988. 17. Vandenabeele, F., Creemers, J., and Lambrichts, I. Ultra structure of the human spinal arachnoid mater and dura mater. J. Anat., Oct. 189 (pt. 2):417–30, 1996. 18. Groen, G., Baljet, B., and Drukker, J., The innervation of the spinal dura mater: anatomy and clinical implications, Acta Neurochir., 92(1–4):39–46, 1988. 19. Fricke, B., Andres, K.H., and Von During, M., Nerve fibers innervating the cranial and spinal meninges: morphology of nerve fiber terminals and their structural integration. Microsc. Res. Tech., Apr. 15, 53(2):96–105, 2001. 20. Sunderland, S. Meningeal–neural relations in the intervertebral foramen. J. Neurosurg., 40:756–763, 1974. 21. Moosy, J., Vascular disease of the spinal cord, Chapter 46 in Joynt, R.J., Ed., Clinical Neurology, Vol. 3, Philadelphia, PA: Lippincott, 1991: 1–17. 22. Oliver, J. and Middleditch, A., Blood supply of the spinal cord and vertebral column, in Oliver, J. and Middleditch, A., Eds., Functional Anatomy of the Spine, Oxford: Butterworth–Heinemann, 1991: 141–160. 23. Flanagan, B. et al., MR imaging of the cervical spine, neural vascular anatomy, Am. J. Neuroradiol., 8:27–32, 1987.
24. Adamkiewicz, A., Die Blutgefasse des menschilchen Ruckenmarkes, II: die Gefasser der Ruckenmarksoberflacke, Sitzungsb. Akad. Wissensch. Wein Math-Naturw., 85:101–130, 1882. 25. Parke, W.W., Applied anatomy of the spine, in Rothman, R.H. and Simeone, F.A., Eds, The Spine, Vol. 1, 3rd ed., Philadelphia, PA: Saunders, 1992: 35–87. 26. Hassler, O., Blood supply to human spinal cord: a microangiographic study, Arch. Neurol., 15:302–307, 1966. 27. Gillilan, L.A., The supply of the human spinal cord, J. Comp. Neurol., 110:75–103, 1958. 28. Turnbull, I.M. Blood supply of the spinal cord, in Vinken, P.J. and Bruyn, G.W. (Eds.) Handbook of Clinical Neurology, Vol. XII. Vascular Diseases of the Nervous System. Amsterdam: North Holland, 478–491, 1972. 29. Sliwa, J.A. and Maclean, I.C. Ischemic myelopathy: a review of spinal vasculature and related clinical syndromes. Arch. Phys. Med. Rehabil., Apr. 73:365–372, 1992. 30. Rexed, B., The cytoarchitectonic organization of the spinal cord in the cat, J. Comp. Neurol., 96:415–495, 1952. 31. Byrne, T.N., Disorders of the spinal cord and cauda equina, Curr. Opin. Neurol. Neurosurg., 6(4):545–548, 1993. 32. Noback, C.R., Strominger, N.L., and Demarest, R.J., The Human Nervous System: Structure and Function, Philadelphia, PA: Williams & Wilkins, 1996. 33. Yadollah, H., Anatomy of the spinal and peripheral autonomic nervous system, in Low, P.A., Ed., Clinical Autonomic Disorders: Evaluation and Management, Boston, MA: Little, Brown, 1993: 17–37. 34. DeMeyer, W., Spinal cord, in DeMeyer, W., Ed., Neuroanatomy, Media, PA: Harwal, 1988: 122–123.
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Pathophysiology in Myelopathy and Spinal Cord Injury
2.1 INTRODUCTION TO PATHOPHYSIOLOGIC MECHANISMS The cascade of biochemical events that follows initial spinal cord trauma may lead to additional neuronal and cellular compromise or death of the patient (Table 2.1). Similar pathophysiologic changes occur in both spinal cord injuries (SCIs) and cervical spondylotic myelopathy.1 Several explanations have emerged to explain the pathophysiology of SCI. The ischemic theory of SCI is a wellresearched mechanism. Compression of the vasculature to the cord is known to produce ischemia and gray matter infarct within minutes.2 The development of intramedullary necrosis follows within the infarcted neuronal tissues.3 Ischemia also develops indirectly following trauma from lipid peroxidation and the release of protaglandins (see more on ischemic mechanisms later in the chapter). In contrast, the neuronal membrane theory proposes that mechanical distortion of the neuronal membrane alters membrane permeability to sodium and thus makes the membrane nonexcitable.4 Direct trauma to long tract pathways may occur with little evidence of cord hemorrhage. Axonal shearing within white matter tracts has been demonstrated in SCI victims without significant injury to the gray matter.5 A free radical theory of neuronal injury proposes activation of reactive oxygen species and lipid peroxidation reactions within regions of tissue damage and ischemia. This process is accelerated following tissue reperfusion. 6 Additional pathophysiologic mechanisms include neuronal apoptosis, neuronal excitotoxic cell death, and cationic-mediated cell injury.7 In practice, many of the mechanisms are interdependent and, in combination, may be responsible for neuronal disruption and degeneration.
2.2 CELLULAR, IONIC, AND BIOMOLECULAR MECHANISMS OF SPINAL CORD INJURY An introduction to the expanding field of cellular, ionic, and biomolecular mechanisms will extend the clinician’s understanding of the mechanisms of tissue injury and recovery. The capacity to prevent, intervene in, and predict the evolution of spinal cord disorders is dependent upon the growing body of knowledge of the most primary elements
of spinal cord function. Novel therapies will incorporate these mechanisms. The hopes for successful pharmaceutical breakthroughs, tissue transplant, and neural regeneration will require further advances in molecular and cellular biology. Responsibilities lie not only with scientists but also with attending clinicians who will direct patients to the therapeutic options available. A lot can be learned about the mechanisms of the central nervous system (CNS) by studying the patterns of tissue recovery.
2.2.1 FREE RADICAL-MEDIATED CELL INJURY Oxygen radicals are highly reactive molecules that are generated during normal metabolism and kept in check by a complex array of cellular defenses. Healthy CNS tissues contain variable concentrations of the antioxidants ascorbic acid, glutathione, ubiquinone, superoxide dismutase, catalase, and alpha-tocopherol.8 The presence of endogenous antioxidants helps to quench excess free radicals, thus reducing the risk for further cell injury. In SCI and tissue injury, whether physical or ischemic, free radical oxygen species are generated in such abundance that normal cellular defense mechanisms are overwhelmed.9 This results in free radical damage and rapid lipid peroxidation of neuronal membranes.9 Membrane phospholipids liberate arachidonic acid, which in turn is metabolized into various groups of vasoactive eicosanoids: thromboxanes, prostaglandins, and leukotrienes. These metabolites play important roles in secondary damage following SCI.10 Arachidonic acid is metabolized by the cyclo-oxygenase pathway to form the prostaglandin or thromboxane groups or through the lipoxygenase pathway to form the leukotriene group of metabolites. The arachidonic acid metabolites leukotriene (LT) C4 and thromboxane B2 elevate in the CSF during the initial phase of SCI to as much as 5 to 9 times normal levels.11 There is little doubt in the scientific community over the production of free radicals and lipid peroxidation following SCI; however, elucidation of the complex interactions and exact biochemicals involved in the process is far from complete.
2.2.2 GLUTAMATERGIC-INDUCED TOXICITY In the CNS, glutamate is an excitatory amino acid that influences the pre- or postsynaptic response through its action on NMDA (N-methyl-D-aspartate) or non-NMDA 23
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TABLE 2.1 Selective Pathophysiologic Mechanisms in SCI • • • • • • • • • •
Free radical-mediated cell injury Cation-mediated cell injury Excitatory amino acids (glutamatergic toxicity) Intracellular-mediated apoptosis Aberrant calcium fluxes Lipid peroxidation Accumulation of arachidonic acid metabolites (eicosanoids) Ischemia/infarction Edema Endogenous opiate receptor activation
receptors. Sources of glutamate include neurons and their supportive glia and terminal portions of descending and ascending spinal cord tracts.12 Cellular insult within the central nervous system injury can lead to increased extracellular levels of glutamate. Impaired intracellular metabolism sensitizes the neuron to potential excitotoxic cell death from the effects of glutamate.13 Glutamate is a secondary mediator of neuronal damage and thus appears to be involved in chronic compressive disorders. Olby and associates14 demonstrated a two- to tenfold increase in glutamate concentration in the lumbar CSF of dogs at intervals of >12 hours after severe, acute thoracolumbar disk herniation injury. Moreover, the severity of the clinical signs was directly related to the glutamate concentration. Dogs with chronic compressive thoracolumbar lesions have a twofold elevation of CSF glutamate concentration, suggesting that excitotoxicity may also be a component of chronic spinal cord compression.
2.2.3 CATION-MEDIATED CELL INJURY Injured tissues and neurons release K+ following injury, which causes voltage-regulated channels to open, allowing an influx of Ca++. With small-tissue injuries, the Ca++ burden is tolerated by the cells because of intrinsic cellular Ca++-binding mechanisms. However, in severely injured cells, Ca++ influx will start an autodestructive cascade that causes the breakdown of membranes and the release of Ca++binding phosphates and phosphatides.8,15 Ca++-activated phospholipase A2 causes the release of arachnidonic acid that is converted to various eicosanoids, some of which are potent vasoconstrictors and edema inducers. The vasoconstriction and tissue swelling help to restrict Ca++ influx to the region; however, the resulting ischemia generates more free radicals that destroy more neuronal membranes.8
2.2.4 PROGRAMMED CELL DEATH Programmed cell death (apoptosis) refers to genetically controlled cellular degeneration that can occur in the absence of acute inflammation. Genes have been identified
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TABLE 2.2 Selective Histopathologic Changes with SCI and Myelopathy • • • • • • • • • •
Demyelination Axonopathy Neuroma Neuronal dropout Gliosis Intramedullary adhesion and tethering Coalescence of microcavitation Cavitation Spinal cord atrophy Surviving neuronal plasticity
that influence CNS apoptosis. Neuronal and glial apoptosis can occur secondary to SCI and spinal cord ischemia.16 Apoptosis serves a number of purposes, which include regulation of the development of cell lines, reduction of cellular redundancy during development, removal of abnormal cells, and regulation of tissue homeostasis.17
2.3 STAGES OF SPINAL CORD INJURY The natural history of SCI can be divided into early, intermediate, and late stages.18 Within the acute phase of SCI, there is disruption of the tissues with subsequent edema, inflammation, and vascular alterations compromising the neurons, myelin, and glial microenvironments. Edema generally occurs within a few minutes and progresses within the ensuing one to two hours after insult. Intraparenchymal edema and swelling of the endothelium results in ischemia, furthering metabolic byproduct accumulation and release and cytokines from injured cells. This initiates a pro-inflammatory cascade contributing to secondary tissue damage. Polymorphonuclear leukocytes and monocytes infiltrate through the vasculature into the damaged parenchyma. The acute lesion is subsequently characterized by traumatic demyelination of the axonal fibers that have not been fully disrupted. Histological changes include axonal irregularities and asymmetric axonal swelling. Magnetic resonance imaging of changes can help qualify the type of tissue changes present. During the intermediate phase of SCI there is a continuation of the inflammatory response. Within 72 hours, macrophages begin to ingest tissue breakdown products. Neuronal degeneration begins to occur distal to the level of axonal injury within descending spinal pathways and also proximally within ascending pathways. The end-stage or late-stage lesion phase follows within six months after injury (Table 2.2). This end stage is characterized by development of multilocular cysts following the removal of debris by white blood cells. The volume of initial intramedullary hemorrhage is relational
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Pathophysiology in Myelopathy and Spinal Cord Injury
to the size and extent of late-injury gliosis. Regeneration of viable neurons in the nerve roots occurs in the late stage. This predominantly occurs at the level of the posterior root ganglia but also occurs at the anterior horn as long as the cell bodies have escaped injury.
2.4 SPINAL SHOCK Central nervous system tissues initially react to trauma in a stereotyped set of responses. In this initial phase, occurring within minutes after injury, neuronal and metabolic activity is rapidly depressed.8 Spinal shock is the term used to describe the initial response that occurs in SCI. Generally, the more severe the SCI and the higher the level of injury within the spinal cord, the greater the severity and duration of the spinal cord shock syndrome. The term “spinal shock” has two primary definitions, the first of which is “hypotension associated with spinal cord injury” and “the transient loss of intrinsic spinal cord reflex activity often lasting several days to several months.”19 Pursuant to the second definition, spinal shock occurs secondary to acute spinal injury or trauma resulting in a pattern of lower motor neuron and autonomic dysfunction occurring days to months after initial onset. This is followed by the development or onset of an upper motor neuron type presentation. Spinal shock is characterized by paralysis of involved skeletal and smooth muscles, areflexia, or flaccid hypotonicity. Generally, there is a complete loss of autonomic function distal to the site of the lesion. This dysautonomia generally results in systemic hypotension, skin hyperemia, and bradycardia due to unopposed vagotonia.20 In cases of mild cord concussion, the somatic motor and sensory components of spinal shock may last an hour or less and have resolved by the time the majority of patients are examined in the trauma center. The reflex autonomic component of spinal shock may last from a few days to a few months depending on the level and severity of SCI. The loss of vasomotor tone contributes to impaired extremity temperature regulation and often edema. Absent sensibility distal to the lesion is also evident. In the majority of SCI with spinal shock, areflexia lasts less than 8 to 9 weeks. A multidisciplinary assessment is necessary in the acute SCI patient because of the associated injuries that occur in 50 to 60% of these cases.21,22 Continual assessment of cardiovascular function, urinary status, blood gases, airway, and ventilation is warranted in the acute spine injury to assure complete stabilization. Poor lung inflation occurs in lower cervical cord injuries from intercostal paralysis, whereas in the high cervical cord injury diaphragmatic paralysis occurs from interruption of the C3–C5 segments and mechanical ventilation is required. Additionally, the polytraumatized patient may have other life-threatening injuries associated with spinal trauma.23 These injuries can endanger ventilation and cardiopulmonary functioning, due to direct trauma
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25
such as lung and cardiac contusions, ribcage fracture, or aortic injury. Head trauma and abdominal bleeding, as well, are serious associated complications that significantly increase the potential for mortality.24 Foley catheterization is required for bladder atony and loss of sphincter control. Gastrointestinal atony occurs, producing distention of the stomach, small intestine, and large intestine; this may result in complications of ulceration, vomiting, constipation, and fecal impaction. Vascular stasis occurs because of a loss of sympathetic tone and muscular paralysis and almost universally results in deep vein thrombosis, requiring the use of anticoagulants. This decreased or absent vasomotor control results in orthostatic hypotension whenever the patient is moved to the upright position (see discussion of orthostatic hypotension later in the chapter). Neurologic localization of the lesion level and determination of lesion severity are often not possible early after injury. As spinal reflexes return, the patient’s complete clinical picture can be better determined. Sensory, motor, and deep tendon reflexes including pathologic reflex testing of the torso and all extremities are crucial localizing adjuncts. Magnetic resonance imaging (MRI) and computed tomography (CT) are both integral for correlating the level of actual cord trauma. Any patient with SCI should also be assumed to have some degree of postconcussional injury, thus cranial nerves are also assessed along with level of consciousness. During spinal shock the patient demonstrates a hypotensive crisis. In triage, hemorrhagic shock must be differentiated from neurogenic shock. An injury above the T6–T8 level is generally associated with a neurogenictype shock. Bradycardia and hypotension follow spinal cord trauma above the T6 level. This is a result of the interrupted sympathetic outflow to the heart and peripheral vasculature. A quick screen is to increase the return flow to the heart by elevating the legs: lack of response to this maneuver indicates the need for immediate pharmacologic intervention.25-27 Secondary injury to the spinal cord may be minimized with efforts that maintain a normal blood pressure.28 Hypovolemia is not the true problem with the neurogenic shock patient; rather, the acute pathology lies with distribution of the intravascular volume. Therefore, attempting triage with fluids can result in pulmonary edema. The hemorrhagic hypotensive patient needs compressive attention to flowing wounds and special consideration to increasing intravascular volume via intravenous measures. After the period of spinal shock, characteristic upper motor neuron signs such as hyperreflexia are often found to be exaggerated.29,30 For example, the Babinski response, which typically involves dorsiflexion of the great toe and fanning of the remaining toes, may develop into an amplified flexion response involving the hip, knee, and foot upon minimal stimulation of the sole of the foot. This is
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termed the withdrawal reflex or flexion spinal defense reflex. Simple withdrawal responses to plantar stimulation may develop into more complex flexor spasms including abdominal contraction and defecation, referred to as a mass reflex. Stimulation of one leg may cause flexion of that extremity and extension of the other leg: This is the crossed extensor reflex. There may also be heightened muscle stretch reflexes (MSRs) with the onset of some degree of clonus (see the additional discussion of hyperreflexia and clonus in Section 5.2). Some researchers propose that this heightened period of activity following spinal shock may be secondary to interneuronal crossinnervation and other neuroplastic changes involving the spinal cord.31 In the period following spinal shock there may be exaggerated impairment of thermoregulatory sweating below the level of injury paralleling the other heightened responses. This inhibition of the sympathetic nervous system may contribute to the reflexive hypertension seen in autonomic dysreflexia (see additional discussion in Section 5.7). The acutely injured spinal cord patient needs immediate attention in a trauma center specializing in SCI patients. Since progressive secondary injury occurs within minutes to hours following trauma, any measures that prevent additional damage to the spinal cord must be attempted. By inhibiting the cascade of microvascular events occurring post-traumatically, it is assumed that the progressive damage to the cord that occurs during spinal cord shock and reperfusion may be halted or inhibited.
Several processes occur simultaneously, that facilitate progressive efflux of water, sodium, and chloride ions from the capillaries into the extracellular space. Tissue hypoxia or anoxia elicits capillary membrane permeability. The release of histamine, bradykinin, acetylcholine, and other synaptic transmitters contributes to an increase in capillary permeability.34-37 The early edematous process induces increasing water concentrations in the extracellular spaces, which then shift to the intracellular compartments within the initial 48 to 72 hours after injury.34-37 Hemorrhagic insult to the spinal cord gray matter following trauma causes edematous accumulation at the site of injury beginning in the gray matter and spreading centrifugally into the white matter.38-41 Central nervous system edema is associated with increased tissue pressure as well as compression of arterioles, capillaries, and veins, resulting in decreased local blood flow.38 Increased tissue pressure may contribute to the observed sequelae of intravascular sludging, stasis, and resultant ischemia.42 Neural tissue is thus compromised by direct mechanical insult and hemorrhage as well as edematous compression of the swelling spinal cord. As the cord swells, pressure against the constrictive meningeal envelope increases. Unchecked edema in the cord will cause degeneration of the unmyelinated fibers in the white matter. This degeneration is a result of increasing tissue pressure and decreasing local vascular flow. The degree of functional deficit may be associated with the extent of intramedullary microvascular alterations and edema.43
2.5 SPINAL CORD EDEMA
2.6 ISCHEMIC MYELOPATHY
This condition is best described as swelling of the spinal cord due to an influx of hydrophobic metabolites and water into the neural tissue. Significant evidence suggests that inflammatory mediators can cause progressive tissue damage within both central and peripheral nervous system tissues. The increased pressure and pro-inflammatory state within and around the neural tissue contribute to the clinical presentation. The two primary causes of edema in the spinal cord are spinal cord ischemia or anoxia and proinflammatory chemical substances liberated as a result of injury.32 Any direct insult to the neural tissue usually damages the corresponding vasculature, altering microcirculatory dynamics and producing edematous perfusion. Numerous inflammatory mediators accumulate in the acutely injured spinal cord. These mediators include bradykinin, prostaglandins, leukotrienes, platelet-activating factor, substance P, and serotonin. Increased concentrations of prostaglandin E2 have been reported to promote vasodilatation and plasma exudation in parallel with the development of spinal cord edema.33 Substance P is a potent vasodilator, increasing capillary permeability and tissue edema.
Any pathologic process that compromises the limited sources of the arterial supply to the spinal cord may result in infarction or ischemia of the cord. Those patients at greater risk are the elderly patients with known diabetes, atherosclerosis, hypotension, hypertension, and dysautonomia. The elderly patient has additional potential risk secondary to multilevel spondylosis and lateral stenosis. Patients with thoraco-abdominal aortic aneurysm are at risk for spontaneous spinal cord ischemia. Occlusion of an intercostal artery supplying a medullary artery of the thoracic cord is presumably a mechanism of ischemic myelopathy secondary to aortic aneurysm.44 The spinal cord is at risk of arterial infarction from additional causes, including hypotension, angiography, vertebral artery occlusion or dissection, syphilis, sickle cell anemia, polycythemia, leukemia, spinal trauma, decompression sickness, and disk herniation.45 The tempo of neurologic deficit varies with the degree of ischemia and local neuronal metabolic synaptic demands. Ischemic myelopathy may be transient, progressive, and in some cases sudden and debilitating with subsequent organ and/or motor dysfunction. Motor symptoms typically predominate.
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2.6.1 MICROVASCULAR AND ARTERIAL INSUFFICIENCY 2.6.1.1 Microvascular Perfusion The gray matter of the brain and spinal cord requires greater vascular perfusion than the white matter regions. Blood flow to the gray matter is approximately fivefold that of the white matter.46 Comparatively, blood flow to the spinal cord is approximately two thirds to one half that of the brain when equal volumes of respective tissues are examined. Areas of increased synaptic density have the highest oxygen demand and consequently the capillary density in these regions is proportionately increased. Due to its metabolic demands and requirement for perfusion, the gray matter of the spinal cord may be particularly vulnerable to ischemic injury.47 Because of the high density of neuronal cell bodies in the spinal gray matter, compromise can lead to devastating consequences. If the intercostal and lumbar arteries become occluded or compromised as a result of ischemia due to aneurysm, damage to the spinal cord is quite severe.48 Experimentally, the gray matter of the lumbosacral cord undergoes profound histological alterations after thoracic cord ligation.49 The microvasculature of the gray matter of the spinal cord is sensitive to trauma.50 The white matter of the spinal cord is also susceptible to ischemia and axonal shearing; however, the gray matter is more sensitive to hypoxic and ischemic changes.42,48,51,52 Neural damage may occur within minutes to hours after ischemia and cord trauma. Systemic factors that impair the microvascular delivery of oxygen and various nutrients to the spinal cord include segmental arterial hypotension, segmental venous hypertension, increased blood viscosity, erythrocyte aggregation (rouleau and/or sludging), impaired erythrocyte deformability, platelet membrane instability, elevated levels of total fibrinogen, and cardiac insufficiency. Arteriosclerotic lesions of the spinal arteries within the intradural compartment are rare in contrast to arteriosclerotic lesions of the extradural arteries. Moderate fluctuations of systemic blood pressure have a minimal effect on regional and total spinal cord blood flow due to constant autoregulation by intrinsic spinal cord mechanisms.47 Many researchers have demonstrated stenotic lesions in the aorta and extradural vessels. Singh and associates53 described four patients, all of whom had local lesions in the area of the artery of Adamkiewicz and subsequently developed infarcts of the lumbar cord after hypotension was induced. Segmental hypotension and related hypoperfusion along a radicular artery or its branches often results from a thrombotic or atheromatous occlusion at the mouth of these arteries within the aorta. Focal lesions can then give rise to a shower of emboli that migrate and lodge in smaller spinal vessels, contributing to segmental hypotension, intravascular stasis and potential spinal cord infarct.
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To maintain normal function, the cord, spinal nerve root, and peripheral fibers must receive a continuous and adequate supply of nutrients.54 2.6.1.2 Tempo of Cord Vascular Insufficiency Terms utilized to describe the tempo of brain vascular disease are also applicable to the spinal cord. Focal ischemia of the CNS has at least three distinct patterns: (1) transient ischemia attack (TIA) with rapid recovery, (2) stroke in evolution (SIE) progressing slowly, and (3) complete infarction with tissue necrosis. A stroke in evolution may involve varying degrees of hemorrhagic and occlusive etiologies. A wide range of neurological deficits can accompany each of these categories. As previously discussed, the central gray matter of the spinal cord is particularly vulnerable to hypoxic and ischemic compromise. Spinal hypotension secondary to localized dissection of the ascending aorta can result in gray matter necrosis. Gray matter ischemic necrosis can occur in the absence of known structural compromise of the spinal cord vasculature.55 Dohrmann and colleagues42 determined that within 30 to 60 minutes of insult, the blood flow to the gray matter is markedly decreased, with the white matter remaining relatively unaffected in the early stage of compromise. Post-traumatic focal reductions of blood flow occur secondary to constriction and narrowing of the arteries.56 Tissue injury can occur secondary to parenchymal reperfusion, resulting in free-radical generation and subsequent lipid perioxidation, thereby accelerating membrane destruction.6 This reperfusion injury following return of blood flow in CNS ischemia can possibly be reduced or prevented by maintaining adequate serum vitamin E levels prior to the ischemic event.57 High superoxide dismutase levels prior to spinal cord ischemia have also been demonstrated to reduce free-radical damage from reperfusion.6 Ischemic myelopathic infarction results in neuronal atrophy, spongy changes, and cavities or lacunae in the anterior gray matter of the cord. DeJerine’s syndrome of intermittent spinal cord claudication may occur, involving progressive lower extremity motor weakness and pain while walking that promptly disappears with rest. This can occur if blood flow to the spinal cord gray matter is reduced to a level insufficient to meet the CNS metabolic demands. Further vascular occlusion and ischemia then occur as platelets promote thrombus formation, eventually leading to a rapid loss of vascular autoregulation.3,58 2.6.1.3 Arterial Insufficiency and Ischemia Watershed or border regions are areas particularly vulnerable to ischemia due to their location at a distal end of an arterial supply (Table 2.3). In the longitudinal plane, the
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2.6.2 SPINAL CORD INFARCTION TABLE 2.3 Features of Vascular Watershed Zones • A region perfused by tributaries from more than one large artery • A collaterized border zone • Regions highly susceptible to systematic hypotension
irregular augmentation of the anterior and posterior spinal arterial system results in regions of poorly collateralized blood supply in the upper thoracic cord. A border zone of potential ischemia also exists within the cord parenchyma in the transverse plane, at the point where the pial vasa corona meets the distribution of the anterior spinal artery (ASA) and posterior spinal artery (PSA) throughout the spinal cord.59 The watershed regions can be classified into two primary categories. The first category is the anatomic watershed zone. The anatomic region has a reduced number of physical collateral vascular channels or networks. There may be decreased capillation and/or a small number of feeder arteries. Regions of the spinal cord characteristically fall into this category, although there is a significant degree of variability between individuals. The intraspinal anatomic watershed zones occurring between anterior and posterior spinal arteries and the vasa corona territories are extremely vulnerable to systemic hypotension. Common causes of systemic hypotension include dehydration, dysautonomia, hypoalbuminemia, extraspinal arterial atherosclerosis, and cardiac insufficiency with impaired left ventricular output. The second category of watershed zones is acquired. This category encompasses acquired occlusive, compressive, and hemorrhagic vascular syndromes. Occlusive etiologies include embolic obstruction and focal thrombus formation. Compressive vascular mechanisms can occur secondary to space-occupying lesions such as disk herniations or tumors. However, chronic mild impairment of arterial blood supply and ischemia often leads to some compensatory capillary development within the watershed region, thereby evading early clinical detection. Hemorrhagic mechanisms include trauma and stroke. Blunt trauma to the artery of Adamkiewicz or to the anterior spinal artery can result in a clinical entity known as anterior spinal artery syndrome.60 This can also occur secondary to intra-arterial occlusion, hypotension, or extravascular compression. The anatomical spinal cord watershed zones include the T4–T9 segments and the L1 segment. Perfusion of the T4–T9 region of the spinal cord is dependent upon the descending ASA from the cervical region, the ascending ASA supplied from the artery of Adamkiewicz, and the anterior radiculomedullary branches of the intercostal arteries for vascular perfusion. This region typically has insufficient anastomotic connections to prevent cord ischemia in the event of loss of any primary feeder supply (Figure 2.1).
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Spinal cord infarction resulting from impaired delivery of oxygen and nutrients or the impaired removal of metabolic waste products to cord parenchyma produces a localized area of ischemic necrosis (ischemic myelomalacia). Patients on blood anticoagulants may be at greater than normal risk for spontaneous epidural or intradural and/or intraparenchymal hemorrhagic diathesis. Four primary factors predispose tissue to ischemic necrosis: (1) the general status of the blood and cardiovascular system, (2) the anatomical pattern of the vascular supply to the region, (3) the rate of intravascular occlusion, and (4) tissue-specific vulnerability to ischemia. Slowly developing vascular insufficiency is often more innocuous clinically than rapidly induced ischemia secondary to the development of increased collateral circulation. Physical blood vessel compression, torsion, and elongation can cause rapid onset tissue ischemia. The intrinsic spinal cord vessels are exceptionally vulnerable to rapid intermittent compression, torsion, and elongation as a result of changes in posture and pathomechanical dynamics within the degenerative spine.
2.6.3 VENOUS PATHOLOGY Reports of venous spinal cord infarction in the literature are relatively rare. Although venous infarction involves the central elements of the spinal cord, the location of compromise varies. Fibrocartilaginous emboli from disk herniations can occur in the presence of degenerative disk disease. Vascular sepsis can contribute to venous thrombosis and infarction. The limited number of references to spinal cord venous infarction in the literature suggests that it is an uncommon phenomenon. Increased risk for venous infarction has been associated with dural arteriovenous or radiculomeningeal vascular malformations concurrent with hypercoagulable states, sepsis and conditions producing fibrocartilaginous emboli.44,61
2.7 MYELOMALACIA In a study by Fieschi et al.,62 necroscopy was performed on the spinal cord of ten elderly athersclerotic subjects who had died from ischemic brain lesions. In five out of ten subjects, small regions of recent spinal cord softening were evident. The longitudinal extensions of the lesions were greater than their transverse, suggesting the role of gravity on the column of blood. The lesions were often located within the center or at the base of the anterior horns of gray matter usually in the lower cervical and middle dorsal tract.62 In all of these cases, the lesions consisted of rarefaction of tissue with loss of neurons and spongy dissolution. There was nearly always sclerosis of the peri- and intraspinal arterial network.62 Systemic cardiovascular
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RELATIVE A-P CANAL DIAMETER
29
RELATIVE BLOOD SUPPLY
MAXIMAL
T4
THORACIC DISK HERNIATIONS
T4
THE CRITICAL ZONE
MINIMAL
T9
T9
MEDIUM
CONTRECOUP
FIGURE 2.1 Thoracic spine “critical zone.” Considerations of limited canal space, modest blood supply, and disk herniation in thoracic disk disease and clinical instability. (Adapted from White III, A.A., and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 413. With permission.)
disease and the high degree of atherosclerosis contribute to the risk for cord softening. Jellinger and Neumayer63 give an informative correlation of ischemic myelopathic syndromes and pathologic findings. These authors report 21 cases consisting of mixed upper and lower motor neuron paresis syndromes associated with general arteriosclerosis and severe aortic atheroma, all verifiable during necropsy. Mannen64 reported circumscribed ischemic lesions within the gray matter of the spinal cord in 8.3% of unselected elderly subjects; he observed 25 small circumscribed softenings of the gray matter, particularly in the anterior horns, during systematic examination of macroscopic sections of the spinal cords of 300 deceased elderly people. The most frequent location of ischemic damage occurred at the levels of C5 and C6. Most of the specimens came from persons reportedly asymptomatic throughout their lives.64
2.8 CAVITATION AND GLIOSIS Spinal cord injury leads to a complex cascade of events that may result in both cavitation and scarring of spinal cord parenchyma. Post-traumatic spinal cord inflammation is an active process that involves astrocyte morphological changes, mobilization of microglia, excitotoxicity,
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and the release of numerous chemicals. The inflammatory process itself can induce secondary neuronal injury. The loss of intramedullary cellular elements within and around the zone of compromise results in varying patterns of cavitation. Cavitation refers to a void previously occupied by tissue. Spinal trauma and/or infarction can initiate the formation of multifocal regions of microcavitation that may coalesce over time to form a larger region of complex cavitation (Figure 2.2). In vivo experimentation has confirmed that a CNS inflammatory process can initiate secondary tissue damage, progressive cavitation, and glial scarring.65 Hematomyelia is frequently followed by cavitation. Barnett66 suggests that such cavities may result from minor to moderate spine trauma. In vitro experimentation has revealed that the process of cavitation further leads to astrocyte abandonment of neuronal processes, neurite stretching, and secondary injury.65 The cavitating disruption of the neural environment provides a physical and chemical barrier to any potential neuronal regeneration– reinnervation process. Delayed cystic degeneration in the spinal cord may occur adjacent to the region or regions of initial insult and progress over many years.67-69 The formation of excessive gliotic tissue (reactive gliosis) even in the absence of cavitation within the CNS becomes a major obstacle to CNS axonal regeneration.70 Patchy gliosis may
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Enlargement of cystic cavity over months to years
Cystic cavity
Petechial hemorrhage Gliotic tissue
Gradual cystic enlargement
Coalescence of cysts FIGURE 2.2 Enlargement of cystic cavity over months to years. (Copyright J.M. True, D.C.)
occur longitudinally secondary to degeneration of fiber tracts.69 Many studies have demonstrated that in the acutely injured spinal cord growth factors and inflammatory cytokines are released which may potentiate the neuronal repair process. An injured axon may sprout neurites that attempt to cross the injury site. If a microcyst or large single cyst forms it will likely fill with spinal fluid and may progress in size over time. The cystic formation is often lined with ependymal cells and there may be dense packets of astrocytes and glial scar (Figure 2.3).71 This complex barrier can make it nearly impossible for neuronal extensions to cross the injury site. Additionally, the release of chemical substances during the CNS post-injury process may inhibit axonal growth within and around the injury site. The loss of cellular elements within the spinal cord results in spinal cord atrophy, which may be readily evident on MR imaging.65
2.9 SPINAL CORD ATROPHY Numerous histopathologic changes occur with SCI and chronic myelopathy (see Table 2.2). Parenchymal atrophy is a late effect of SCI. Spinal cord atrophy may develop with cervical spondylotic myelopathy and myelopathy associated with ossification of the posterior longitudinal ligament. Following cord trauma, microglial ameboid cells and macrophages release enzymes, phagocytose myelin, and clean up cellular debris. Approximately 30% of the area
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FIGURE 2.3 Large cystic cavity. (Copyright J.M. True, D.C.)
of the injured cord region may be occupied by macrophages a week later, as seen in studies of the cat.72 These cells may persist for many years after an SCI. The experimentally injured cat cord indicates that central cystic cavities may form and be heavily populated with microglial cells and small clumps of macrophage cells.73 These phagocytic cells shrink as the glial scar forms and cord atrophy develops. The oligodendrocyte is associated with remyelination; this cell will proliferate to help remyelinate viable axons. In contrast, if type 1 astrocytes, rather than oligodendrocytes, proliferate in the post-injured cord, remyelination is inhibited. Astrocyte infiltration and mitosis is stimulated by fibroblast growth factor. The astrocyte is the major cell type of the gliotic scar that fills in the extracellular space remaining after nerve fiber degeneration. The change in shape of the atrophic cord following compression or injury may clinically correlate with the neurological presentation. There are very few scientific studies that correlate the diagnostic imaging appearance of the cord with severity of symptoms. Even fewer studies have anatomical correlation of autopsy findings with the patient’s clinical symptoms recorded before death. Gray matter atrophy contributes to the greatest degree of loss in cord axial area when the MRI appearance of the cord is flattened or crescent shaped (Figure 2.4). These patients may have predominant segmental motor loss. When the axial appearance is small and triangular, the damage is more severe and involves the white and gray matter. In these cases, the posterior columns and pyramidal tracts are involved in addition to the anterior horns.74 These patients will have spastic paresis and ataxia.
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Normal cervical cord
Boomerang or crescent appearance on axial MRI: Atrophy of the central gray predominates
Triangular appearance on axial MRI: Atrophy of white and gray matter FIGURE 2.4 The morphological appearance of cord atrophy on axial imaging. Normal cervical cord; boomerang or crescent appearance on axial MRI, with predominant atrophy of the central gray matter; and triangular appearance on axial MRI, with atrophy of white and gray matter. (Copyright J.M. True, D.C.)
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42. Dohrmann, G., Wick, K., and Bucy, P., Spinal cord blood flow patterns in experimental traumatic paraplegia, J. Neurosurg., 38:52–58, 1973. 43. Reed, J., Allen, W.E., and Dohrmann, G.J., Effect of Mannitol on the traumatized spinal cord, microangiography, blood flow patterns and electrophysiology, Spine, 4(5):391–397, 1979. 44. Mawad, M., Rivera, V., Crawford, S. et al., Spinal cord ischemia after resection of thoracoabdominal aortic aneurysm: MR findings in 24 patients, Am. J. Neuroradiol., 11:987–991, 1990. 45. Mikulis, D., Ogilvy, C., McKee, A. et al., Spinal cord infarction and fibrocartilaginous emboli, Am. J. Neuroradiol., 13:155–160, 1992. 46. Ireland, W., Fletcher, T., and Bingham, C., Quantification of microvasculature in the canine spinal cord, Anat. Rec., 200:102–113, 1981. 47. Marcus, M., Heistad, D., Ehrhardt, J., and Abbounb, F., Regulation of total and regional spinal cord blood flow, Circ. Res., 41(1):128–134, 1977. 48. Thompson, G., Dissecting aortic aneurysm with infarction of the spinal cord, Brain, 79:111–118, 1956. 49. Turnball, I., Blood supply of the spinal cord, normal and pathological considerations, Clin. Neurosurg., 20:56– 84, 1973. 50. White, R., Pathology of spinal cord injury in experimental lesions, Clin. Orthoped., 112:16–26, 1975. 51. Collins, W., Piepmeier, J., and Ogle, E., The spinal cord injury problem — a review, Cent. Nerv. Syst. Trauma, 3:317–331, 1986. 52. Gelfan, S. and Tarlov, I., Differential vulnerability of spinal cord structures to anoxia, J. Neurophysiol., 18:170–188, 1955. 53. Singh, U., Silver, J.R., and Welply, N.C., Hypotensive infarction of the spinal cord, Paraplegia., 32(5):314– 322, 1994. 54. Lundborg, G., Nerve Injury and Repair, Edinburgh: Churchill–Livingstone, 1988. 55. Blumbergs, P. and Byrne, E., Hypotensive central infarction of the spinal cord, J. Neurol. Neurosurg. Psychiatry, 43:751–753, 1980. 56. Fried, L. and Goodkin, R., Microangiographic observations of the experimentally traumatized spinal cord, J. Neurosurg., 35:709–714, 1971. 57. Yoshida, M., Shima, K., Taniguchi, Y., Temaki, T., and Tanaka, T., Hypertrophied ligamentum flavum in lumbar spinal canal stenosis. Pathogenesis and morphologic and immunohistochemical observation, Spine, 17(11):1353– 1360, 1992. 58. Senter, H. and Venes, J., Loss of autoregulation and posttraumatic ischemia following experimental spinal cord trauma, J. Neurosurg., 50:198–206, 1979. 59. Moosy, J., Vascular disease of the spinal cord, in Joynt, R.J., Ed., Clinical Neurology, Vol. 3, Philadelphia, PA: J Lippincott, 1991: 1–17. 60. Sliwa, J.A. and Maclean, I.C., Ischemic myelopathy: a review of spinal vasculature and related clinical syndromes, Arch. Phys. Med. Rehabil., 73(4):365–372, 1992.
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61. Naiman, J., Donohue, W., and Prichard, J., Fatal nucleus pulposus embolism of spinal cord after trauma, Neurol. Minneapolis, 11:83–87, 1961. 62. Fieschi, C., Gottlieb, A., and Carolis, V.D., Ischemic lacunae in the spinal cord of arteriosclerotic subjects, J. Neurol. Neurosurg. Psychiatry, 33:138–146, 1970. 63. Jellinger, K. and Neumayer, E., Myelopathy progressive d’origine vascular: contribution anatomoclinique aux syndromes d’une hypovascularisation chronique de la moelle, Acta Neurol. Psychiatry, (62):944–956, 1962. 64. Mannen, T., The vascular lesions in the spinal cord of the aged, Clin. Neurol. Jpn., 3:47–63, 1963. 65. Fitch, M.T., Doller, C., Combs, C.K., Landreth, J.E., and Silver, J., Cellular and molecular mechanisms of glial scarring and progressive cavitation: in vivo and in vitro analysis of inflammation-induced secondary injury after CNS trauma, J. Neurosci., 19(19):8182–8198, 1999. 66. Barnett, H.J.M., Syringomyelia consequent on minor to moderate trauma, in Barnett, H.J.M., Foster, J.B., and Hudgson, P., Eds., Syringomyelia, Philadelphia, PA: Saunders, 1973: 179–243.
Black process 45.0° 150.0 LPI
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67. Klawans, H.L., Delayed traumatic syringomyelia, Dis. Nerv. Syst., 29(8):525–528, 1968. 68. Nurick, S., Russell, J.A., and Deck, M.D.F., Cystic degeneration of the spinal cord following spinal cord injury, Brain, 93(1):211–222, 1970. 69. Yashon, D., Pathology and pathogenesis, in Yashon, D., Ed., Spinal Injury, New York: Appleton–Century Crofts, 1986: 71–103. 70. Nieto-Sampedro, M., Neurite outgrowth inhibitors in gliotic tissue, Adv. Exp. Med. Biol., 468:207–224, 1999. 71. McDonald, J.W., Repairing the damaged spinal cord, Sci. Am., 281(3):64–73, 1999. 72. Blight, A.R., Delayed myelination macrophage invasion: a candidate for secondary cell damage in spinal cord injury, Cent. Nerv. Sys. Trauma, 2:299–315, 1985. 73. Blight, A.R., Macrophages and inflammatory damage in spinal cord injury, J. Neurotrauma, 9(S1):83–91, 1992. 74. Kameyama, T., Ando, T., Yanagi, T., and Hashizume, Y., Neuroimaging and pathology of the spinal cord in compressive cervical myelopathy, Rinsho Byori, 43(9):886– 90, 1995.
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3
Physical Mechanisms of Spinal Cord Injury*
3.1 SPINAL CORD PATHOMECHANICS The spinal cord moves in relation to the spinal canal, and spinal column movement influences spinal cord dynamics; however, the amplitude of cord translation is restricted by structural anchoring of the cord to the spinal column. The primary anchoring elements of the spinal cord consist of the dentate ligaments and filum terminale. Any condition that places abnormal tension on the spinal cord can potentially lead to neurological insult and related signs and symptoms. Aberrations of posture, particularly within the sagittal plane, can have direct and indirect effects on neuronal pathways and centers within the central nervous system (CNS), specifically the spinal cord.1 In the study of spinal biomechanics, investigations of spinal cord biomechanics are rare. The intrinsic viscoelastic properties of medullary tissue include plasticity and elasticity. Medullary tissue can be mechanically deformed in almost any direction without significant opposing resistance as long as it is not tractioned, but as soon as traction forces are introduced the medullary tissue retracts elastically.2 Breig2 discovered that during cervical canal shortening (as in dorsal extension) the cervical medullary tissue relaxes and takes on plastic characteristics, telescoping into large undulated folds and reducing strain upon CNS structures. During forward head or trunk flexion, lengthening of the spinal canal and medullary tissue produces longitudinal strain along the entire cord and nerve roots. The capacity for elastic deformation allows for changes in length and curvature of the spinal canal during spinal column movement without significant axial cord displacement. The entire spinal cord will change in length from 4.5 to 7.5 cm during changes in maximum positions of lordosis and kyphosis as measured from the dorsal mesencephalon to the conus medullaris.2 Similarly, on lateral flexion, the canal is lengthened on the convex side and shortened on the concave.1 During cervical flexion, the spinal cord translates anteriorly toward the vertebral bodies and, in extension, toward the posterior elements. Research has demonstrated that maximum cord elongation takes place in the lumbar region, some elongation occurs in the thoracic, and minimal elongation occurs within the cervical region.3
Flexion
Extension
Not Analogous
Analogous
FIGURE 3.1 Adjustment of spinal cord and nerve roots to axial deformation during flexion and extension. (Adapted from White, A.A., III, and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 282. With permission.)
The characteristics of spinal cord elasticity allow the cord to match the length of the spinal canal during movement. As the canal and column reach maximum length during flexion, the physiologic elastic tension of the cord is also at its maximum. Then, near the end of elongation a slight elastic resistance is evident, causing a sudden stiffening and stubborn resistance to further deformation, thus negating the flexible behavior of the cord. The spinal cord tissue also displays plastic deformation characteristics with axial compressive forces by formation into folds having a slight tendency for recovery. This folding during shortening and subsequent unfolding during elongation, similar to that of an accordion, begins with the initial movement of the cord (Figure 3.1). The first phase of cord movement represents the structural properties of the cord, whereas the second phase represents the material properties of the cord.2 Lateral flexion of the spinal column is reported to contribute to ipsilateral relaxation of the pons-cord tract while placing greater tensile stresses upon the contralateral side.4 Maiman and colleagues5 demonstrated a relational coupled motion between the spinal cord and spinal column in an experimental spinal cord injury (SCI) study performed on cats. This coupling ratio of cord motion to spine motion varies with the amount of loading and varies by location
* This chapter written with Edwin P. Patrick.
35
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
A
B
FIGURE 3.2 Postsurgical changes following fusion at C5–C6, C6–C7, and C7–T1. There is evidence of post-traumatic transection of the surgical spinal cord at the (A) C6–C7 and (B) C7–T1 levels. (Spin echo parasagittal T1 and fast spin echo parasagittal C2 midline sagittal sections.) (Courtesy of George W. Fika, D.C.)
within the spine. This ratio of movement is of great significance when traumatic displacement of the spine exceeds the reserve space of the spinal canal or fibroproliferative pathology restricts spinal cord compliance and elasticity. Histologic and microangiographic studies have demonstrated that nerve fibers, blood vessels, and supportive tissues can be injured secondary to tensile or stretch injury across a regional mass effect.2 Research suggests that as little as 20 to 25% compression of the spinal cord will increase axial tension on neural and vascular elements within the spinal cord.6 This can result in disruption and distortion of neural and vascular elements contributing to intramedullary ischemia and infarction with permanent neurological impairment.
3.2 TYPES OF SPINAL CORD TRAUMA Compression of the spinal cord is one of the most prevalent etiologies of neurologic dysfunction associated
with degenerative spine disease and trauma. Spinal cord compression associated with degenerative spondylosis usually results from cord compression by an osteophyte, hypertrophic dorsal lateral facet, hypertrophic or buckled ligamentum flavum, and/or disk herniation. In the case of SCI, the most common cause of cord compression is from vertebral element dislocation and/or fracture. Traumatic cord stretching can also contribute to acute spinal trauma (Figure 3.2).7 The mechanism by which an epidural mass contributes to SCI is complex and multifactorial. Space-occupying lesions within the epidural region often compress the epidural venous plexus, resulting in venous engorgement, and also contribute to arterial insufficiency with diminished arterial pulsation.8 Physical compression of Batson’s plexus results in venous congestion. This results in impaired venous drainage from the spinal cord and increases the risk for cord edema. Mechanical compression of spinal axons may interfere with axonal transport and
Physical Mechanisms of Spinal Cord Injury
subsequently compromise nerve impulse transmission. It has been well established that compression of myelinated fiber tracts results in damage to the myelin.9-11 The larger myelinated fibers within the tracts are more susceptible to physical compromise. Neurological tissue requires oxygen and other nutrients in order to maintain function. Alterations in oxygen levels occur following abnormal pressure or force delivered to the spinal cord, particularly longitudinal tension.12 Yamada et al.13 used both human and animal studies in an attempt to clarify the effect of traction on the filum terminale and lumbosacral cord and its relationship to the pathophysiology of the tethered cord syndrome. The underlying mechanism of this disorder is found to involve derangement of neural tissue metabolism caused by longitudinal tensile-type stress. Mechanical tension applied to the spinal cord reduces its cross-sectional area and places a transverse-type stress across the vessels, possibly reducing their cross-sectional area as well.4 Increased pressure applied to the cord results in reduced afferent and efferent impulse conduction along with increased damage to neural and supporting tissues.14 Pathologic tension applied to the cord may result in increased medullary cord pressures, reduced blood flow, and subsequent reduction of spinal cord perfusion. Additionally, tension applied directly to neural tissue results in impaired oxidative metabolism in the mitochondria.4 Other studies have found that any change in metabolic efficiency of the cellular mitochondria contributes to progressive neuronal dysfunction.15 Vascular hypoperfusion results in altered cellular biosynthesis, impaired neurotransmitter metabolism, ineffective ionic pumps, and inefficient axoplasmic transport. As mentioned previously, in cases of significant spinal cord pathomechanics, there is evidence to suggest that impaired blood flow to both the spinal cord and meningeal complex may occur.16 There are four mechanisms associated with neuroelement distortion-related injury: (1) Extrinsic neurovascular compression, (2) simple distraction, (3) tethering of the neuroelements over extrinsic masses on the sagittal plane (the sagittal bowstring effect), and (4) tethering of the neuroelements of extrinsic masses in the coronal plane (the coronal bowstring effect).17 These pathomechanical mechanisms should be considered in the evaluation of a patient with a distraction injury and spinal cord compromise. An example of coronal tethering occurs when an epidural mass such as a disk herniation or spondylotic bar displaces the cervical cord and deforms the dura. Consequently, this may result in transference of tensile stresses to the spinal cord from the dura via the dentate ligaments, thus increasing the risk of further compromise during neck flexion.18 Spinal cord injury is classified by the type of injury sustained, such as a closed spinal trauma vs. a penetrating type injury, as well as by the segmental cord level of the
37
TABLE 3.1 Criteria for Spinal Cord Concussion 1. Spinal trauma immediately preceding onset of neurological deficits 2. Neurological deficits consistent with spinal cord level of injury 3. Complete neurological recovery within 72 hours of injury Based on data from: Zwimpfer, T.J. and Bernstein, M., Spinal cord concussion, J. Neurosurg., 72(6):894-900, 1990.
injury. The mechanical forces in closed spinal trauma that produce the injury are compression, shear, distraction, and torsion.
3.2.1 SPINAL CORD CONCUSSION The term “spinal cord concussion” is used to describe an immediate transverse lesion of the spinal cord resulting from indirect trauma, such as that secondary to transmission of an impact shockwave to the cord. The trauma usually occurs in the absence of vertebral fracture or dislocation; however, patients commonly have preexisting pathology that causes hypermobility or narrowing of the spinal canal.19 Characteristically, there is immediate impairment of sensory and motor function distal to the lesion. The initial clinical presentation is not easily differentiated from the presentation of spinal shock. The unique feature of spinal concussion is the relatively rapid return of spinal cord functions in a few hours or days, most often within 48 to 72 hours (Table 3.1). By definition, there are no permanent structural abnormalities. There may be reversible spinal cord edema and reversible intracellular and nerve fiber changes.
3.2.2 SPINAL CORD CONTUSION The term “spinal cord contusion” is used to describe trauma of spinal cord tissue secondary to direct insult or hemorrhage. Petechial hemorrhages, predominantly within gray matter, often result in focal spinal dysfunction, and permanent structural pathology may occur. Spinal cord contusion may also be due to vertebral fracture, vertebral dislocation, or intervertebral disk herniation. Diagnostic imaging may not reveal the extent of direct trauma in cases of transient vertebral dislocation or other direct insult with spontaneous reduction. The initial clinical presentation usually involves total paraplegia. The pattern of neurological recovery depends on the degree of tissue injury, and recovery may or may not be complete. A rapid return of sensory function is generally a good prognostic indicator for the recovery of some motor function
3.2.3 SPINAL CORD COMPRESSION The term “spinal cord compression” is used to describe mechanical deformation of the spinal cord by an adjacent
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 3.2 Signs and Symptoms Associated with Tethered Cord Syndrome • • • • • • •
Diffuse leg pain Anorectal pain Progressive lower extremity sensorimotor deficits Bowel and bladder dysfunction Back pain Gait disturbance Club foot
structure or tissue. This may be secondary to disk pathology, hypertrophic changes, osteophytosis, vertebral fracture, vertebral dislocation, hematoma, arteriovenous malformation, tumor, or lipomatosis. One of the most common causes of debilitating spinal cord compression is traumatic vertebral fracture–dislocation; the most common degenerative etiology is spondylosis with spinal stenosis. Another common cause of spinal cord compression is intervertebral disk herniation. When disk herniation occurs with spinal stenosis, there is a greater potential for significant cord compression. Spinal cord compression may manifest as partial or complete loss of spinal function but may also occur in the absence of abnormal clinical manifestations.
3.2.4 PENETRATING/TRANSECTING CORD INJURIES Penetrating or transecting cord injuries are usually from a gunshot or knife wound. Axonal shearing in white matter (long tracts) may occur with cord traction injuries from ballistic neck trauma. Bone fragments from comminuted fractures may lacerate the spinal cord, as well. Gunshot injuries to the cord are often more devastating than stab wounds. The degree of tissue damage is greater in missile wounds because of the high kinetic energy of the bullet that is transferred through the spine and cord.20 There is an expanding conical-shaped, fluid-pressure shockwave that follows the projectile; consequently, there is a concussive force injury as well as the penetrating component of the bullet. The patient has a complete loss of function of the severed pathways below the cord laceration.
3.2.5 TETHERING
AND
DISTRACTION INJURIES
Pathologic spinal cord tension is referred to as tethering, and when accompanied by clinical signs and symptoms it is referred to as a tethered cord syndrome (TCS) (Table 3.2). TCS is usually first identified in children and adolescents.21 Initial symptom onset occurs less often in adults.22-24 When it does occur, it is usually the result of predisposing cord tension factors such as spondylotic stenosis or trauma. Signs and symptoms of TCS include progressive lower extremity motor and sensory changes,
TABLE 3.3 Causes of Spinal Cord Tethering • • • • • • • •
Tight filum terminale Diastematomyelia Myelomeningeocele Traction lesions Spinal (bony) dysraphisms Adhesions/fibroproliferation Lumbosacral lipoma Cord herniation through dura
back pain, anorectal pain, gait disturbances, incontinence, leg pain, and scoliosis.21,22,25 Clubfoot may also occur in TCS.21 Conditions that lead to cord tethering may be congenital and/or acquired, with the most common tethering lesions being thickened filum terminale, intradural lipoma, and fibrous adhesions (Figure 3.3).22 Other conditions associated with spinal cord tethering are listed in Table 3.3. The tip of the conus medullaris generally lies within the region of T12–L1. A short filum terminale may draw the conus to levels below the L1 vertebral body. The location of the conus in relationship to the spine is commonly identified on sagittal magnetic resonance imaging (MRI) acquisitions. The absence of a low conus on MRI does not preclude the possibility of TCS, for TCS has been identified in patients who present the conus in a “normal” position.26 Phase-contrast MR may be used to assess longitudinal movement of the spinal cord27 and in some cases can help to ascertain the degree of impaired cord kinetics. Markedly diminished cord motion in children has been associated with a lack of significant postoperative improvement.27 Spinal cord tethering contributes to impairment of oxidative metabolism and electrophysiologic impairment of the lumbosacral cord.3,28 Shortened H-reflex and bulbocavernosus latencies may be recorded when the conus is found lower in the lumbar canal.29 Early diagnosis and intervention are imperative to the successful management of TCS. (See additional information in Section 4.6.)
3.3 VERTEBRAL FRACTURE, DISLOCATION, AND INSTABILITY Blunt trauma to the spine can produce SCI from shear force, compression, or tensile injury to the cord or vasculature. Any rapid reduction in the diameter of the spinal canal and the space available for the cord can result in myelopathy; vertebral fracture, instability, dislocation, and subluxation all have this potential to dynamically alter central canal geometry (Figures 3.4 and 3.5). Spinal cord injury can occur secondary to stretch or concussive forces even in the absence of spinal fracture or obvious dislocation. This is referred to as SCIWORA syndrome (SCI
Physical Mechanisms of Spinal Cord Injury
39
FIGURE 3.3 Cord and root tethering patterns. (Copyright J.M. True, D.C.)
FIGURE 3.4 Burst fracture at C5 with retropulsion of bone fragments into the spinal cord. (Courtesy of E. Shick, M.S. Copyright MedicalVisions.com. With permission.)
without radiographic abnormality) and tends to be more common in children due to greater connective tissue elasticity and spinal column flexibility;30 patients with SCIWORA may not develop obvious neurological complications for days or weeks after the original trauma. The rapid
change in canal diameter causing an SCI may not be apparent in a post-injury imaging study — for example, although a spondylotic bar may contuse the spinal cord during an acceleration/deceleration injury, the post-injury image of the canal at the level of insult may appear to be only mildly narrow. Numerous attempts have been made to classify relationships between bony spinal elements and the spinal cord as a means of fracture assessment.31-33 Meyer et al.34 constructed and described a vertebral fracture classification system including five variables that can result in altered central canal geometry. The first component, a score (1 – 3) of damaged longitudinal columns, describes the loss of vertical support and vertebral stability. The second component is the presence of vertebral listhesis, with lateral or sagittal translation as a subset of this category. The third is the degree of angulation or curvature created by vertebral body collapse in the case of compression fractures. The fourth component is the extent of spinal canal obliteration measured as a percentage of compromise, and the fifth is the percentage of loss of vertebral height from compression. These five variables are scored and assigned a fracture category of type A, B, or C.34 This classification system simplifies the ability to communicate the severity of the fracture by identifying the relationship between canal compromise and neurologic injury.
3.3.1 CAUSES
OF
BIOMECHANICAL INSTABILITY
It is important not only to detect biomechanical instability, but also to understand its etiology, as the course of progression can be more clearly defined if the exact cause has been determined. A three-dimensional coordinate
40
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
FIGURE 3.5 Fracture dislocation of the thoracic spine at T5 on T6. A comminuted fracture of T6 is causing transection of the spinal cord at that level. (Courtesy of E. Shick, M.S. Copyright MedicalVisions.com. With permission.)
+Y Axis Translation +YAxis Rotation
Z
X
+XAxis Translation +X Axis Rotation
+Z Axis Rotation +Z AxisTranslation
Y
FIGURE 3.6 Right-handed Cartesian coordinate system denoting spinal motion segment position, coupled motions, or the direction of forces acting on the motion segment. This figure depicts positive axis rotation and translation. (Copyright David H. Durrant, D.C.)
system has been proposed to reference movement of a spinal motion segment (Figure 3.6). Biomechanical spinal instabilities arise from a variety of causes (see, for instance, Table 3.3). These instabilities can be classified as either primary or secondary instabilities. Primary instabilities are the direct result of damage to the posterior column and are usually associated with trauma. Secondary instabilities, which develop over a period of time as a result of damage or disease, can initiate in any of the columns. Biomechanical instability most commonly occurs secondary to acute trauma, surgical procedures, or cumulative degenerative changes in the spine 35 (Figures 3.7 through 3.9). Acute trauma may produce biomechanical instability by disruption of ligamentous support structures or by fracture with comminution. The degree of biomechanical instability secondary to fracture is not only dependent on the severity of the fracture, but also on the vertebral element and spinal area involved. A three-column model for spine stability has been utilized. The spine is broken into three anatomic configurations along the sagittal plane: the anterior, middle, and posterior columns. If the fracture does not compromise the space available for the cord or the exiting nerve root,
Physical Mechanisms of Spinal Cord Injury
41
FIGURE 3.8 Lateral radiograph of the cervical spine demonstrating prominent anterior listhesis of vertebra C4 with respect to C5. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
FIGURE 3.7 Lateral X-ray of the cervical spine demonstrating anterior listhesis of vertebra C3 with respect to C4. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
there will be little immediate neurological consequence; if the fracture has the potential to heal without deformity, fragmentation, or significant biomechanical alteration, there may be no future consequences of neurological dysfunction. White and Panjabi have proposed a checklist for clinical instability of the cervical, thoracic, and thoracolumbar spine (Tables 3.4 to 3.6).36 Post-traumatic disruption of either all of the anterior or all of the posterior soft tissue elements can lead to obvious and potentially serious pathomechanical intersegmental motion. Incomplete disruption may lead to intermittent episodes of severe catching pain; however, without radiographic evidence of displacement, the clinician’s diagnostic acumen is often challenged. Postsurgical complications due to failed interbody fusion can result in pseudoarthrosis and potential cord compression; failed fusion may require a second fusion procedure to correct excessive intersegmental motion. Successful fusion at one level may create secondary effects from increased compensatory range of motion at adjacent vertebral segments. Biomechanical instability with resulting neurologic compromise has also been associated with many arthritic
TABLE 3.4 Checklist for the Diagnosis of Clinical Instability in the Thoracic and Thoracolumbar Spine Element Anterior elements destroyed or unable to function Posterior elements destroyed or unable to function Disruptions of costovertebral articulations Radiographic criteria Sagittal plane displacement > 2.5 mm (2 pts.) Relative sagittal plane angulation > 5° (2 pts.) Spinal cord or cauda equina damage Dangerous loading anticipated
Point Value 2 2 1 4
2 1
Note: Total of 5 or more = unstable. Source: From White, A.A., III, and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 335. With permission.
disorders. Quadriplegia or death may result from atlantoaxial subluxation that occurs as a complication of several arthritides.37 Rheumatoid arthritis is the most common causal disorder, but atlantoaxial subluxation may also occur with ankylosing spondylitis and in association with psoriatic arthritis.38 Transverse atlantal ligament laxity and eventual lysis can occur secondary to regional hyperemia. The sero-negative arthropathies can also induce destructive joint changes by hypertrophic bone formations. Joints ankylosed by the sero-negative arthropathies are susceptible
42
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 3.5 Checklist for the Diagnosis of Clinical Instability in the Lumbar Spine
TABLE 3.6 Checklist for the Diagnosis of Clinical Instability in the Middle and Lower Cervical Spine
Element
Element
Anterior elements destroyed or unable to function Posterior elements destroyed or unable to function Radiographic criteria A. Flexion/extension X-rays 1. Sagittal plane translation > 4.5 mm (2 pts.) 2. Sagittal plane rotation >15° at L1–L2, L2–L3, and L3–L4 (2 pts.) >20° at L4–L5 (2 pts.) >25° at L5–S1 (2 pts.) or B. Resting X-rays 1. Sagittal plane translation > 4.5 mm or 15% (2 pts.) 2. Relative sagittal plane angulation > 22° (2 pts.) Cauda equina damage Dangerous loading anticipated
Point Value 2 2 4
3 1
Note: Total of 5 or more = unstable. Source: From White, A.A., III, and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 352. With permission.
Point Value
Anterior elements destroyed or unable to function Posterior elements destroyed or unable to function Positive stretch test Radiographic criteria A. Flexion/extension X-rays 1. Sagittal plane translation > 3.5 mm or 20% (2 pts.) 2. Sagittal plane rotation > 20° (2 pts.) or B. Resting X-rays 1. Sagittal plane displacement > 3.5 mm or 20% (2 pts.) 2. Relative sagittal plane angulation > 11° (2 pts.) Abnormal disk narrowing Developmentally narrow spinal canal 1. Sagittal diameter < 13 mm or 2. Pavlov’s ratio < 0.8 Spinal cord damage Nerve root damage Dangerous loading anticipated
2 2 2 4
1 1
2 1 1
Note: Total of 5 or more = unstable. Source: From White, A.A., III, and Panjabi, M.M., Clinical Biomechanics of the Spine, Lippincott, Philadelphia, PA, 1990, p. 314. With permission.
FIGURE 3.9 Lateral flexion radiograph of the cervical spine demonstrating anterior listhesis of vertebra C6 with respect to C7. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
to fracture or dislocation resulting in significant pathomechanical intersegmental motion, neurological sequelae, and a mortality rate of twice that observed with similar fractures in a normal spine.39 Any sudden development of mobility in a previously immobile spinal segment should raise the clinician’s level of suspicion. The “chin on chest” deformity seen in ankylosing spondylitis40 is caused by a complete dislocation of C1 on C2. Any systemic infection that causes joint destruction, such as tuberculosis, is an obvious precursor to biomechanical instability. Articular and periarticular denervation can lead to neuropathic arthropathy, also referred to as Charcot’s joint. Charcot’s joint changes can occur in the spine. The usual predilection is the lumbar spine. Subluxation and dislocation proceed to destruction and malalignment of articular surfaces and to characteristic disorganization in the neuropathic joint. Lytic destruction from primary or metastatic cancer can also create gross disruption of the spinal segment, altering segmental ranges of motion and thus increasing risk for development of cord compression. Osteoporosis increases the risk for acquiring a compression fracture. This must be differentiated from a pathological fracture due to other causes. MR assessment can help improve the accuracy of the differential workup.
Physical Mechanisms of Spinal Cord Injury
TABLE 3.7 Conditions Associated with Atlantoaxial Instability and Compressive Myelopathy • • • • • • • • •
Down syndrome Rheumatoid arthritis Os odontoidium Odontoid fracture Marfan’s syndrome I-cell disease (mucolipidosis II) Transverse ligament rupture Morquio’s syndrome Atlantodental hypertrophic osteoarthropathy
43
smaller supportive elements of the neck. Upper cervical fractures with SCI are not compatible with life when immediate acute respiratory support is not available. The pattern of fracture seen in subaxial cervical injury is dependent on the complex relationship between the predisposing state (underlying pathology in the region) and the vector and magnitude of force. For example, axial compression may produce a burst fracture; however, adding a flexion component to the vector will produce a flexion tear-drop fracture or a wedge fracture. The individual with underlying osteoporosis will be more susceptible to fractures. 3.3.3.1 Posterior Neural Arch Fracture of C1
“Glacial instability” is a term distinguishing chronic biomechanical instability, describing the gradually developing progressive angulation, translation, or rotational deformity that may manifest secondary to a slow breakdown of supportive elements associated with degenerative processes.41 In contrast to acute biomechanical instability, substantial external forces do not cause immediate movement or progression of the deformity;42 rather, the etiologies of glacial instability include trauma, congenital defect, tumor, spondylosis, and infection (Table 3.7).
3.3.2 SPINAL FRACTURE AND PATHOMECHANICAL INTERSEGMENTAL MOTION It is helpful to understand that different regions of the spine react differently to trauma and disease. Cervical spine fractures have a greater potential for biomechanical instability than thoracic or lumbar spine fractures because the vertebrae are smaller and the bulk of the protective muscles and supportive soft tissues is not as great as in the rest of the spine. This also renders the cervical spinal cord more susceptible to injury — this is particularly evident in the suboccipital spine. Due to the stabilizing capacity of the ribcage, the vast majority of thoracic spine fractures are unaccompanied by the serious neurological consequences of biomechanical instability. However, spinal cord compression may occur with extensive compression, ligament rupture, or vertebral fragmentation43 (as associated with Figure 3.5). Fractures of the lumbar and lumbosacral spine may result in spondylolisthesis and cauda equina compression, in the lower lumbar spine.
3.3.3 UPPER CERVICAL FRACTURE PATTERNS: FRACTURES OF C0–C1–C2 Fractures of the upper cervical spine are common with ballistic trauma involving the head and neck. This fracture pattern occurs because of the flexibility of the cervical spine and relative biomechanical instability created by the large size and weight of the head in relationship to the
This, the most common fracture of the atlas, is an extension injury that involves the posterior arch.44 The mechanism of injury includes compression of the arch between the occiput and the large spinous process of the axis. It is usually a stable fracture, as the arch that has been fractured is usually displaced posteriorly and the fragment does not compromise the space available for the cord; the anterior ring, with the intact transverse atlantal ligament, provides stability for the axis. This fracture is best visualized on the lateral cervical spine radiograph and can be identified by computerized tomography or lateral tomogram (Figure 3.10). 3.3.3.2 Dens Fracture Dens fracture has been classified into three subtypes45 based on the location of the fracture line. Type I fractures involving only the tip of the dens, can be described as avulsion fractures, with a radiographic appearance of an obliquely oriented fracture across the tip. These are considered stable as long as the body of the dens is still restrained by the transverse atlantal ligament. Type II fractures are the most common, occurring at the junction of the body of the axis and the base of the dens; the radiographic representation is a transverse fracture along the base. These are typically unstable, as they can produce a primary biomechanical instability resulting from the architectural bone damage or a secondary biomechanical instability resulting from the ineffectiveness of the transverse atlantal ligament. There is a 36% chance of non-union in cases of type II dens fracture.45 Radiographically, type III fractures show a fracture line extending into the body of the axis; these are usually stable,46 as there is no cord compromise, and they usually heal without incident. The anteroposterior (AP) open mouth radiograph will usually demonstrate a dens fracture. In cases of significant sagittal displacement, the fracture will also be visualized on the lateral cervical spine radiograph. Tomograms or computed tomography will further define the fracture line.
44
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
likely to be the result of a head-on motor vehicle accident in which sudden hyperextension/deceleration occurs as the chin or head hits the steering wheel or windshield, resulting in upper cervical hyperextension. Such sudden, excessive axial compression in conjunction with hyperextension can result in fracture/dislocation of the neural arch with sudden transection of the spinal cord; this is considered an unstable spinal fracture due to major disruption of the restraint mechanisms. Best visualized on the lateral cervical spine radiograph, it is not a difficult radiographic diagnosis when the displacement is apparent. 3.3.3.4 Jefferson Fracture of the Atlas (Burst Fracture of C1) This fracture is caused by a vertical compression of the lateral masses of the atlas by the occipital condyles. The usual mechanism of injury is a blow to the vertex of the skull. This results in bilateral fractures of the anterior and posterior arches. This forces the lateral masses laterally, usually tearing the transverse atlantal ligament. This is considered an unstable spinal fracture secondary to major bony disruption and compromise of the transverse atlantal ligament. This fracture is best viewed on the AP openmouth view of C1 (Figure 3.11). Greater than 7 mm of total displacement of the lateral masses of C1 on C2 is indicative of biomechanical instability.47
3.3.4 CERVICAL FRACTURE PATTERNS FIGURE 3.10 Lateral X-ray of the cervical spine demonstrating a fracture through the neural arch of the atlas. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
FIGURE 3.11 Open mouth view of the C1–C2 articulation demonstrating lateral instability. Note the left lateral displacement of the C1 vertebral body with respect to the lateral mass of C2. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
3.3.3.3 Hangman’s Fracture (Bipedicular Fracture of C2, Traumatic Spondylolisthesis of C2) Hangman’s fracture refers to a bilateral fracture of the pedicles of the axis caused by sudden hyperextension of the head and neck due to a sudden deceleration from high speed. Despite the derivation of the name from a method of capital punishment, in this country this injury is more
3.3.4.1 Spinous Process Fracture (Clay Shoveler’s Fracture, Coal Miner’s Fracture) The spinous fracture is a flexion injury. The usual mechanism is for a sudden flexion of the cervical spine to avulse the tip of the spinous fracture. A neurological deficit typically does not occur with this fracture; therefore, it is a stable fracture. C7 is most often involved, but it can involve other vertebrae. This fracture is best viewed on the lateral cervical radiograph. The fracture margins are rough and serrated and the fractured tip is usually displaced caudally, which is helpful in differentiating this fracture from a nonunion of a secondary growth center (Figure 3.12).48 3.3.4.2 Pillar Fracture Injury to the cervical pillars typically involves a degree of lateral flexion or rotation. Typically, pillar fractures are unilateral. This is usually a stable fracture; however, a pillar fracture can be unstable depending upon the magnitude of the fracture. Secondary instabilities due to restraint mechanism disruptions can develop. Radiographically, this fracture is best viewed on the cervical pillar view. Bone scintigraphy may be necessary to confirm less obvious pillar fractures. Compression fractures of the pillars also
Physical Mechanisms of Spinal Cord Injury
45
A
FIGURE 3.12 Lateral postmortem view of a cervical spine demonstrating anterior listhesis of vertebra C2 with respect to C3. There is a fracture through the spinous process of C3. (Courtesy of J.P. Ellis, Ph.D.)
occur, altering the articular surface and damaging the subchondral capillary bed. 3.3.4.3 Flexion Teardrop Fracture Flexion teardrop fracture–dislocation is the most severe and unstable injury of the lower cervical spine (Figures 3.13 to 3.15).49 The mechanism of injury is compression and shear force to the anterior border of the cervical vertebra, crushing the vertebral body and fracturing a triangular or teardrop-shaped fragment from its anterior side. A combination of injuries is associated with this fracture: 1. 2. 3. 4. 5.
Posterior subluxation of the vertebral body Fracture of the posterior elements Disruption of the ligamentum flavum Compromise of the spinal cord Rupture or avulsion of the anterior longitudinal ligament
Flexion teardrop fracture is sometimes associated with an acute anterior cord syndrome with complete motor paralysis and loss of pain and temperature sensations (anterior column loss) along with continued ability to perceive position, vibration, and motion (posterior column sparing). Central canal damage is caused by the combination of forward dislocation of the vertebral body,
FIGURE 3.13 Bilateral perched facets of vertebra C4 on C5 and a flexion teardrop fracture of C5 at the anterior inferior vertebral margin. (Courtesy of E. Shick, M.S. Copyright MedicalVisions.com. With permission.)
fracture–dislocation of the posterior elements and complete disruption of supportive soft–tissue structures that contribute to the stability of this segment. This fracture complex is best demonstrated on the lateral cervical spine radiograph (Figure 3.16). 3.3.4.4 Extension Teardrop Fracture The extension teardrop fracture is an avulsion fracture of the anterior–inferior body of the cervical vertebra. This is caused by a forceful extension producing sufficient force on the anterior longitudinal ligament to avulse away a portion of the anterior–inferior vertebral body. The fragment is usually triangular or teardrop shaped. This fracture may be stable or unstable. Stability of an extension teardrop cervical spine fracture is dependent upon the direction of spinal motion. When this fractured spine is flexed, the intact posterior restraint mechanisms prevent excessive segmental mobility. Cervical flexion does not create any potentially dangerous complications in this type of fracture; therefore, in cervical flexion, this fracture is considered to be stable. However, because of the damage to the anterior longitudinal ligament restraints, this injury can produce secondary biomechanical instability during extension, and thus is considered an unstable spinal fracture in extension.
46
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
FIGURE 3.15 C7 flexion teardrop fracture with perivertebral soft-tissue swelling causing airway compromise. Note the anterior listhesis of the C6 vertebral body with respect to C7. (Fast spin echo parasagittal T2-weighted midline sagittal image.) FIGURE 3.14 Lateral radiograph of the cervical spine demonstrating a flexion teardrop fracture involving the anterior–inferior margin of the C3 vertebral body with associated perivertebral soft tissue swelling. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
3.3.5 FRACTURE PATTERNS OCCURRING AT ANY LEVEL OF THE SPINE The pain associated with a fracture may mimic the pain arising from intervertebral disk pathology or from the capsular region. The presence of a spinal fracture may render the region biomechanically unstable, thus increasing the risk for neurologic insult. With a history of trauma or abrupt onset spinal pain, the possibility of fracture should always be considered. 3.3.5.1 Endplate Burst Fracture The endplate burst fracture is a fracture of the vertebral endplates. A vertical compressive force creating an implosion effect of the nucleus pulposus on the vertebral endplates causes this spinal fracture. The nucleus pulposus herniates through the endplates with a sufficient force to cause an actual “bursting” of the cancellous vertebral body. Typically, these fractures compress the anterior and middle columns while sparing the posterior column.33
The integrity of the posterior column, not the middle column, is a better indicator of burst fracture stability.50 A burst fracture is considered stable if there is not any disruption of the posterior restraint elements or displacement of vertebral body fragments into the spinal canal. The clinician must be aware of the possibility of the initial trauma producing a posterior displacement of a free fragment from the vertebral body into the spinal canal. Transient spinal cord compression may occur as a result of posterior fragments and/or the fluid shockwave striking the cord. The fragments may relocate back to their normal vertebral boundaries in a rebound fashion after a crushing blow. Consequently, acute spinal shock may be present without any evidence of fracture displacement. AP and lateral radiographs of the region will usually demonstrate these types of fractures; on the AP view, a vertical fracture line or an increased interpedicular space is a characteristic finding. Computed tomography may be necessary to visualize fragments compressing the thecal sac (see Figure 3.4). 3.3.5.2 Wedge Fracture (Compression Fracture) The wedge or compression fracture is a flexion or lateral flexion injury and is not a difficult diagnostic challenge.
Physical Mechanisms of Spinal Cord Injury
47
B
A
FIGURE 3.16 (A) Lateral neutral radiograph of the cervical spine demonstrating a flexion teardrop fracture of vertebra C7. This injury is unstable due to disruption of the ligaments throughout the posterior elements. (B) Lateral spot view radiograph of the cervical spine through C6–C7. This close-up more clearly delineates the teardrop fracture through the anterosuperior corner of C7 and demonstrates the spinous process widening between C6 and C7. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
The mechanism of injury is an hyperflexion of the superior vertebral segment upon the inferior vertebral segment. There is a measurable decrease in vertical anterior vertebral body height compared to posterior vertebral body height. It is important to determine the degree of vertebral body compression because the greater the percentage of body height lost the greater the probability that there has been disruption of the opposing restraint mechanisms (i.e., ligaments, capsular structures, and muscular attachments). Understanding the amount of flexion required to create the degree of compression can give the clinician an insight into the amount of posterior restraint stress at the moment of injury. In this type of fracture, it is not the vertebral body compression that causes biomechanical instability; it is damage to the posterior vertebral restraint mechanisms that leads to the signs of secondary instability. This is considered a stable fracture unless there is a displaced or separated fracture fragment or there is a significant degree of wedging. The wedge fracture is the most common fracture in the lumbar spine.51 Compression fractures can usually be viewed on the lateral radiograph, although a minimum of
25 to 30% compression is required for conclusive X-ray appreciation and diagnosis (Figure 3.17).52 A computerized tomogram with 3D reconstruction may be needed to appreciate the full extent of the fracture (Figure 3.18). 3.3.5.3 Chance Fracture The Chance fracture results from a shearing flexion mechanism. This has also been called the lap seatbelt fracture or the fulcrum fracture. Chance first described this fracture in 194853 as an obliquely horizontal fracture of the spinous process and the neural arch, extending through the superior portion of the vertebral body. A more complete description includes a horizontal splitting of the spine and the neural arch, ending with an upward curvilinear fracture that usually reaches the upper surface of the body just anterior to the neural foramen.48 This fracture is more common in the upper lumbar spine. The lateral lumbar radiograph ordinarily demonstrates this fracture. Computed tomography may be necessary to fully define the fracture lines.
48
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
C FIGURE 3.16 (C) Sagittal T2-weighted image of the cervical spine. Disruption of the ligaments between C6 and C7 is evident because of the hyperintense signal between the spinous processes. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
3.3.5.4 Neural Arch Fracture Acute fractures of the pars interarticularis are usually the result of extreme hyperextension mechanisms. Best seen on the oblique view, the fracture line is an irregular, vertically oriented radiolucency. Because this fracture is usually unilateral, it does not have the tendency to result in neurological compromise.
3.3.6 SPINAL DISLOCATION Unreduced spinal dislocations in the cervical spine are usually seen by emergency personnel in trauma centers and often significantly compromise the central canal. Dislocations in the thoracic or lumbar spine are not common. The mechanism of spinal dislocations is usually a combination of flexion, extension, rotation, or translation. When dislocation is apparent, there will usually be an accompanying fracture or fractures of the vertebral body or posterior elements. These spinal fractures can be of various magnitudes from a small fleck fracture of a facet to a body or arch fracture of the vertebra. Facet dislocations without fractures have a significantly higher association with cord
FIGURE 3.17 Lateral radiograph of the thoracolumbar spine demonstrating a central compression fracture. (Courtesy of Richard Leverone, D.C., D.A.B.C.R.)
syndromes than do rotational facet injuries with fractures.54 Because spinal dislocation is a failure of all three columns,33 these conditions are mechanically unstable. Two types of cervical dislocates are described below. 3.3.6.1 Bilateral Cervical Facet Dislocation In bilateral facet dislocation, the superior facets are dislocated anteriorly to the inferior facets at the intervertebral foramen. The superior facets can displace into the intervertebral foramen and compromise the nerve roots. The central canal is compromised by the posterior arch producing an anterior cord syndrome, unless there is a fracture of the neural arch allowing the posterior elements to be displaced posteriorly. This injury severely disrupts the posterior restraint mechanisms, the anular fibers of the disk, and frequently the anterior longitudinal ligament. This injury is unstable and even X-ray examination should proceed cautiously. A lateral cervical radiograph will demonstrate the characteristic displacement of the superior facets into the neural foramen. A cross-table lateral view allows for the least movement of the patient’s spine and
Physical Mechanisms of Spinal Cord Injury
49
Compression fracture line through posterior aspect of centrum
L4 TP fracture
FIGURE 3.18 Three-dimensional (reconstructed 3-D) CAT scan demonstrating compression fracture of the L5 body and L4 transverse process. (TVP).
is the radiograph of first choice when a bilateral facet dislocate is suspected. 3.3.6.2 Unilateral Facet Dislocation By definition, this is the anterior perching of one of the superior facets in relation to the inferior facet at the intervertebral foramen, and there is certainly compromise of the affected intervertebral foramen on the side of facet dislocate. The central canal is usually not affected because this is a rotational injury. Although there is major disruption of the ligamentous and capsular constraints of the dislocated facet joint, the posterior joint restraints and anular fibers can be spared. The anular fibers are more likely to become involved in dislocates of the lower segments of the cervical spine.55 A unilateral facet dislocate is usually considered a stable injury. The characteristic appearance of the perched facet is best demonstrated on the oblique radiograph. 3.3.6.3 Spinal Dislocation/Relocation In this type of injury, the spinal segment dislocates as a result of a traumatic force, resulting in the disruption of spinal restraint mechanisms; then, either from an opposite force or spontaneously, the spinal dislocation repositions to its normal anatomic position. The disruption of the restraint mechanisms has already been complete, however, which makes this injury unstable even though standard static radiographic studies may appear normal. Clinical findings along with spinal stress radiographs should supply
TABLE 3.8 Conditions Associated with Acute Back Pain and Rapidly Evolving Myelopathy: Spinal Hematoma and Differential Considerations • • • • • •
Acute and subacute transverse myelitis Spinal cord infarction Spinal abscess Acute large disk herniation Neoplasm Spinal fracture or dislocation
the clinician with sufficient evidence to identify the unstable spinal segment.
3.4 SPINAL HEMORRHAGE Spinal hemorrhage can occur within the epidural space, subarachnoid space, or spinal cord parenchyma. Spinal hemorrhage may occur secondary to coagulopathy, anticoagulant therapy, medical intervention, trauma, or vascular malformation. Hemorrhage can lead to neurological compression if the hematoma is confined to a compartmentalized region. Spinal hematomas typically are associated with acute-onset, well-localized spinal pain and a rapidly progressing myelopathy (Table 3.8). Emergency intervention is required to decompress the spinal cord. Recovery from paraplegia secondary to compressive hematoma is dependent on the length of time from onset
50
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 3.9 Common Causes of Spontaneous Spinal Subarachnoid Hemorrhage • • • • • • •
Arteriovenous malformations Neoplasm Infectious meningitis Coagulopathy Extreme physical exertion Lumbar puncture Collagen vascular disease
of symptoms to surgical intervention and the extent of spinal cord damage.
3.4.1 SUBARACHNOID HEMORRHAGE Most cases of subarachnoid hemorrhage occur secondary to trauma. A few conditions result in spontaneous subarachnoid hemorrhage, the most common of which is spinal arteriovenous malformations (AVM) (Table 3.9).56 This condition is frequently associated with sudden severe neck or back pain and may be equated with a stabbing knife-type pain. The pain tends to be more severe than pain associated with epidural or subdural hematoma. Evolving subarachnoid hemorrhage may result in radicular, myelopathic, and intracranial symptoms. The cerebrospinal fluid (CSF) study usually reveals blood. Subarachnoid hemorrhage may occur simultaneously with a subdural hematoma, thus increasing the risk for a devastating mass effect upon the adjacent spinal cord.
3.4.2 EPIDURAL HEMORRHAGE Individuals with an underlying coagulopathy or those on anticoagulant therapy are more prone to suffer a bleeding diathesis such as an epidural or subdural hemorrhage with trauma. Epidural hematomas can occur secondary to epidural anesthesia and spinal puncture with the concurrent use of low-molecular-weight heparin.57 The development of a spinal epidural hematoma is characterized by acute spinal pain followed by signs of rapidly progressing myelopathy typically occurring within minutes or hours. Spinal epidural hematomas occur more frequently in the thoracic and thoracolumbar regions. Epidural hematomas commonly develop within the posterior epidural space and may span multiple segments.58 Evaluation of the CSF is variable, sometimes demonstrating blood or an elevated protein level. MRI has become the assessment method of choice for spinal hematoma.59
3.4.3 SUBDURAL HEMORRHAGE Spinal subdural hematomas occur less frequently than epidural hematoma, and they are usually related to trauma.
The epidural predilection may be secondary to greater blood vessel caliber and prevalence within the epidural space.60 The clinical presentation usually involves acuteonset back pain in the absence of radicular symptoms. Like epidural hematomas, the clinical signs and symptoms of myelopathy frequently evolve within minutes or days after the bleeding ensues. A chronic spinal subdural hematoma may result in a less obvious clinical picture and is more apt to mimic the presentation of spondylosis and disk pathology.61 CSF assessment may demonstrate blood if there is an associated subarachnoid hemorrhage. A subdural hematoma may contribute to a spinal fluid block (filling defect), rendering a CSF study more challenging. MRI is the imaging method of choice and should always be considered before myelography.
3.4.4 HEMATOMYELIA “Hematomyelia” is a term used to describe bleeding within the parenchyma of the spinal cord. Hematomyelia often occurs as the result of trauma. The pattern of bleeding usually follows a longitudinal course. The clinical presentation is often abrupt with some progression over the following 1 to 2 days. The most common site of posttraumatic hematomyelia is at the lower cervical cord. The clinical findings are similar to an incomplete hemimyelopathy. The cerebrospinal fluid may be blood stained, although this is not a pathognomonic finding required for diagnosis. Intraspinal microhemorrhages may occur secondary to small ruptures along the walls of the muscular venules.62-65 Spontaneous hematomyelia should alert the attending clinician to the possibility of an arteriovenous malformation or coagulopathy. Hemorrhage secondary to spinal arteriovenous malformations may be microscopic and cumulative, leading to a slow, progressive neurologic decline in clinical presentation.
3.5 MYELOPATHY AND DISK HERNIATION Disk herniation may be classified into one of three general categories based on consistency: (1) soft herniation, (2) mixed soft–calcific herniation (disk-spur complex), and (3) calcified herniation. The soft herniation is more apt to be relatively recent and therefore has the propensity to become larger. It is less rigid than the other categories, allowing for slightly greater physical adaptation within the spinal canal during movement. The calcific disk is rigid and more apt to slowly progress in size with time. Trauma is usually integral to onset of symptoms in any of the three categories. Intervertebral disk herniation, extrusion, or sequestration can contribute to the onset of myelopathy. This may occur secondary to direct mechanical insult to neural elements and/or from an associated interruption of blood supply to the spinal cord (Figure 3.19). Signs and symptoms may be abrupt in onset or may occur gradually,
Physical Mechanisms of Spinal Cord Injury
51
Disk-spur complex
FIGURE 3.19 Anterior spinal cord compression with and without anterior spinal artery (ASA) compression.
paralleling the temporal pattern of spondylotic stenosis. A midline disk herniation exposes the anterior spinal artery (ASA) to compressive forces and is more apt to lead to a pure medullary syndrome. Intervertebral disk hernation may cause altered venous flow and venous stasis with dilatation, which may contribute to a mass effect. Depending on the size and location of disk herniation, it may result in a pure radiculopathy syndrome, pure medullary syndrome, or myeloradiculopathy (Figures 3.20 and 3.21).66 A large cervical disk herniation can cause a Brown– Séquard syndrome.67 With upper cervical disk herniation at C2–C3, radiculopathic symptoms may outweigh cord signs.68 Other signs and symptoms associated with highlevel cervical disk compression of the cord include nonspecific neck and shoulder pain, cervical radiculopathy in a level different than expected, and variable myelopathy characterized by impairment of motor and sensory function more in the upper extremities than lower extremities and mostly starting following trauma. MRI of myelopathy secondary
FIGURE 3.20 Prominent degenerative changes throughout the cervical spine, most pronounced at the C5–C6 and C6–C7 levels where there is intervertebral disk-space narrowing and degenerative endplate change. Mild retrolisthesis at C5–C6 secondary to a degenerative process. Diffuse disk bulges at C3–C4, C5– C6, C6–C7, and C7–T1, with resultant ventral cord compression at C5–C6, C6–C7, and C7–T1. Also demonstrated is facet hypertrophy at the C5–C6, C6–C7, and C7–T1 levels, resulting in dorsal encroachment upon the thecal sac and dorsal cord compression. (Parasagittal fast spin echo T2-weighted image right parasagittal section.)
to disk herniation may be associated with a focal region of high T2-weighted signal intensity not demonstrated on T1 weighting (Figure 3.22). A region of abnormal intramedullary MR signal may lie directly adjacent to, slightly above, or below a disk herniation. The presence of abnormal cord signal at the level of disk pathology without evidence of direct compression of the spinal cord should raise the index of suspicion of a retracted disk herniation, migrated sequestered fragment, or dynamic spinal stenosis with cumulative cord insult. Myelopathy may occur as the result of multisegmental disk herniation contributing to a watershed region of vascular insufficiency.
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Cord compression with deformation
FIGURE 3.21 The same patient as in Figure 3.20. Pronounced focal right paracentral disk herniation with resulting right paracentral cord compression. (Parasagittal fast spin echo T2-weighted image to the right of the midline.)
)
*
FIGURE 3.22 (A) Parasagittal T2-weighted image demonstrating cord compression from C4–C5 HNP. (B) Gradient echo axial image of large right paracentral disk herniation, deforming the ventral cord.
Physical Mechanisms of Spinal Cord Injury
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38. Katz, W.A., Rheumatic Diseases: Diagnosis and Management, Philadelphia, PA: Lippincott, 1977. 39. Wade, W., Saltzstein, R., and Maiman, D., Spinal fractures complicating ankylosing spondylitis, Arch. Phys. Med. Rehabil., 70(5):398–401, 1989. 40. Turek, S.L., Orthopedics Principles & Their Application, 4th ed., Philadelphia, PA: Lippincott, 1984. 41. Benzel, E.C., Biomechanics of Spine Stabilization, New York: McGraw–Hill, 1995. 42. Benzel, E.C., Biomechanics of lumbar and lumbosacral spine fracture, in Rea, G.L. and Miller, C.A., Eds., Spinal Trauma, Current Evaluation and Management, Neurosurgical Topics, American Association of Neurological Surgeons (AANS) Publications Committee, Chicago, IL, 1993: 165–195. 43. Gehweiler, J.A., Jr., Daffner, R.H., and Osborne, R.L., Jr., Relevant signs of stable and unstable thoracolumbar vertebral column trauma, Skeletal Radiol., 7:179–183, 1981. 44. Sherk, H.H. and Nicholson, J.T., Fractures of the atlas, J. Bone Joint Surg. Am., 52:1017–1024, 1970. 45. Anderson, D. and D’Alonzo, R.T., Fractures of the odontoid process of the axis, J. Bone Joint Surg. Am., 56:1663–1674, 1974. 46. Felson, B., Fractures, Semin. Roentgenol., 13(1–2), 1978. 47. Rea, G.L. and Miller, C.A., Spinal Trauma, Current Evaluation and Management, Neurosurgical Topics, American Association of Neurological Surgeons (AANS) Publications Committee, Chicago, IL, 1993: 807. 48. Yochum, T.R. and Rowe, L.J., Essentials of Skeletal Radiology, Vol. 1, Baltimore, MD: Williams & Wilkins, 1987. 49. Schneider, R.C. and Kahn, E.A., Chronic neurological sequela of acute trauma to the spine and spinal cord, J. Bone Joint Surg., 38(A):985–997, 1956. 50. James, K.S., Wenger, K.H., Schlegel, J.D., and Dunn, H.K., Biomechanical evaluation of the stability of thoracolumbar burst fractures, Spine, 19(15):1731–1740, 1994. 51. Schinz, H.R. et al., Roentgen Diagnostics, Vol. 2, 2nd ed., New York: Grune & Stratton, 1967. 52. Gehweiler, J.A., Jr., Osborne, R.L., Jr., and Bader, R.F., The Radiology of Vertebral Trauma, Philadelphia, PA: Saunders, 1980. 53. Chance, G.Q., Note on type of flexion fracture of spine, Br. J. Radiol., 21:452–453, 1948.
54. Shanmuganathan, K., Mirvis, S.E., and Levine, A.M., Rotational injury of cervical facets: CT analysis of fracture patterns with implications for management and neurologic outcome, Am. J. Roentgenol., 163(5):1165– 1169, 1994. 55. Braakman, R. and Vinken, P.J., Unilateral facet interlocking in the lower cervical spine, J. Bone Joint Surg. Br., 49:249–257, 1967. 56. Swann, K.W., Ropper, A.H., New, P.J.F., and Poletti, C.E., Spontaneous spinal subarachnoid hemorrhage and subdural hematoma: report of two cases, J. Neurosurg., 61:975–980, 1984. 57. Lumpkin, M., Reports of epidural or spinal hematomas with the concurrent use of low molecular weight heparin and spinal/epidural anesthesia or spinal puncture, FDA Public Advisory, Dec. 15, 1997. 58. Mattle, H., Sieb, J.P., Rohner, M., and Munenthaler, M., Non-traumatic spinal epidural and subdural hematomas, Neurology, 37(8):1351–1356, 1987. 59. Holtas, S., Heiling, M., and Lonntoft, M., Spontaneous spinal epidural hematoma: findings at MR imaging and clinical correlation, Radiology, 199(2):409–413, 1996. 60. Edelson, R.N., Chernik, N.L., and Posner, J.B., Spinal subdural hematomas complicating lumbar puncture. occurrence in thrombocytopenic patients, Arch. Neurol., 31(2):134–137, 1974. 61. Khosla, V.K., Kak, V.K., and Mathuriya, S.N., Chronic spinal subdural hematomas: report of two cases. J. Neurosurg., 63(4):636–639, 1985. 62. Balentine, J., Pathology of experimental spinal cord trauma, I, Lab Invest., 39:236–253, 1978. 63. Balentine, J., Pathology of experimental spinal cord trauma, II, Lab Invest., 39:254–266, 1978. 64. Dohrmann, G. and Bucy, P., The microvasculature in transitory traumatic paraplegia: an electron microscopic study in the monkey, Neurosurgery, 35:263–271, 1971. 65. Dohrmann, G. and Bucy, P., Transitory traumatic paraplegia: electron microscopy of early alterations in myelinated nerve fibers, J. Neurosurg., 36:407–415, 1972. 66. Bucciero, A., Vizioli, L., and Cerillo, A., Soft cervical disk herniation: an analysis of 187 cases, J. Neurosurg. Sci., 42(3):125–130, 1998. 67. Rumana, C.S. and Baskin, D.S., Brown–Séquard syndrome produced by cervical disk herniation: case report and literature review, Surg. Neurol., 45(4):359–361, 1996. 68. Chen, T.Y., The clinical presentation of uppermost cervical disk protrusion, Spine, 25(4):439–442, 2000.
4
Conditions Associated with Myelopathy
4.1 DEGENERATION AND STENOSIS “Spinal stenosis” is a term used to describe narrowing of the neural foramina lateral recess and/or central canal within the vertebral column. Spinal stenosis can be classified into four primary categories. The first of these categories is congenital stenosis, which is developmental and present from birth. The second category refers to an acquired spinal stenosis secondary to injury, disk herniation, spondylosis, or diseases that produce proliferation and remodeling of tissues which compromise the spinal canal (Figure 4.1). The third category is dynamic or functional spinal stenosis. This refers to an alteration of structural relationships within and/or adjacent to the lateral foramina or central spinal canal with positionally induced narrowing during periods of movement. The fourth category is complex stenosis, which refers to a combined presentation with characteristics of two or more of the above categories. Complex spinal stenosis is often associated with the greatest potential for risk to neighboring neural and vascular elements. Degenerative disk disease is one of the most common conditions leading to spinal stenosis.1 The progression of spondylosis can be categorized by radiographic and clinical findings: stage I, cervical disk disease; stage II, spondylosis; stage III, spondylosis with restricted motion; and stage IV, cervical spondylotic myelopathy.2 These stages reflect the temporal pattern of progression. The advancing sequence of pathologic events surrounding spondylosis and the development of spinal stenosis involves morphological changes of the anatomic structures adjacent to the spinal canal. There may be a congenital predisposition to developing clinically significant spinal stenosis. The different variations of spinal canal configuration generally fall into one of the following four categories: (1) oval, (2) triangular, (3) trefoil, or (4) deltoid. An example of congenital lateral stenosis is the short pedicle syndrome. The involved pedicles are typically thick and short in their anteroposterior projection. This developmental anomaly renders the adjacent intervertebral foramen smaller in diameter and area than neighboring foramen. Pedicogenic stenosis also contributes to narrowing of the central spinal canal. Reduced coronal diameter can occur with developmental reduction in interpendicular distance. Common examples of acquired spinal stenosis include facet arthropathy, scoliosis, spondylolithesis, trauma,
intervertebral disk bulge, protrusion, extrusion, and/or free fragment migration. Bony stenosis should be differentiated from other causes. Less commonly, acquired central or lateral canal stenosis can occur secondary to cyst, tumor, or postoperative scar. Early stenosis is often asymptomatic. One study demonstrated lumbar stenosis ranging from 4% to 28% of computed tomography (CT) or magnetic resonance imaging (MRI) scans of asymptomatic subjects.3 Most patients are asymptomatic until the third decade or later and then develop symptoms following a mild vertebral injury. As previously discussed, extreme hyperflexion or hyperextension of the cervical spine exposes the spinal cord to mechanical and microvascular trauma in the normal dimensioned canal. Patients with reduced spinal canal size are at increased risk for spinal cord contusion, compression, and spinal cord injury (SCI) subsequent to trauma.4 One of the most common forms of pathomechanical insult that occurs within the narrowed spinal canal is the pincer effect. The spinal cord is vulnerable to the pincer effect in the presence of disk herniation, spondylosis, vertebral listhesis, thickened or buckled ligaments, and postsurgical hypomobility at adjacent segments (Figure 4.2).
4.1.1 SPONDYLOTIC MYELOPATHY AND CERVICAL SPONDYLOTIC MYELOPATHY 4.1.1.1 Prevalence Spondylotic myelopathy can occur at any level of the spinal cord where the spinal canal is narrowed, although it most commonly afflicts the cervical spine. Significant spondylotic stenosis often occurs with bony canal encroachment superimposed under a congenitally narrowed canal. Cervical spondylotic myelopathy (CSM) was recognized as a distinct clinical entity as early as the 1950s by Brain.5 Clarke and Robinson6 also recognized CSM as a condition distinct from myelopathy due to cervical disk herniation. In the patient population over 50 years old, CSM is the most common cause for spinal cord pathology and spinal cord dysfunction encountered in practice.7 CSM remains the most serious complication of cervical spondylosis. Cervical spondylotic myelopathy may coexist with multisegmental levels of spinal stenosis,8 usually occurring in the patient over age 60, with an average of three lesions per individual.9 Epstein et al.10 estimated that 5% 55
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Right paracentral cord compression
Disk-spur complex
A
B
FIGURE 4.1 (A) Large right paracentral disk-osteophyte complex causing right paracentral spinal cord compression. Diffuse disk bulge at C3–C4 resulting in ventral cord compression. (Parasagittal gradient echo T2-weighted right parasagittal image.) (B) In the same patient, right paracentral spinal cord compression and exiting right nerve root impingement secondary to the disk–osteophyte complex. (Axial gradient echo T2-weighted image through the C3–C4 level.) (Courtesy of Ronald Landau, M.D.)
4.1.1.2 Pathomechanisms
Buckling of ligamentum flavum
Disk herniation
Instability
Spondylosis
Compression at superior edge of vertebra below anterolisthesis
FIGURE 4.2 The “pincher effect” occurs with anterolisthesis, ligamentum flavum hypertrophy, disk herniation, and osteophytic spurs in the spinal canal. (Copyright J.M. True, D.C.)
of patients with cervical stenosis also have lumbar stenosis, which may result in a challenging diagnostic workup. Multilevel spondylotic stenosis can result in a mixed and seemingly contradictory clinical presentation of upper and lower motor neuron dysfunction in the same patient.
Spinal cord compression secondary to spondylosis and central spinal stenosis can also compromise intramedullary blood flow, leading to ischemia and/or infarction (Table 4.1). There are four primary elements which contribute to the development of cervical myelopathy in the presence of advancing cervical spondylosis: (1) circumferential stenotic narrowing of the central spinal canal; (2) development of focal projections into the canal (spondylotic ridges, bars and spurs, or disk herniation); (3) impaired patency or integrity of intrinsic spinal or radicular circulation; and (4) chronic block of CSF flow. The pre-morbid size of the central canal is a major predisposing factor to the development of spondylotic myelopathy. Larger spinal canals have significant reserve space and can therefore tolerate greater degrees of spondylotic intrusion. The posterolateral white matter is vulnerable to the negative effects of spinal cord compression, particularly the corticospinal tract.11 Voskuhl et al.12 proposed the presence of a watershed zone in the region of the funiculus cuneatus, medial spinothalamic, and corticospinal tracts, thus rendering the regions susceptible to ischemic and hypoxic injury.12,13 Autopsies performed on individuals with CSM have commonly revealed relative preservation of the anterior columns, marked gray matter atrophy, degeneration in the lateral and posterior funiculi, and thin myelinated fibers within the white matter suggestive of a demyelinative–remyelinative process.11,14 Degeneration of the medial portion of the posterior columns is usually only noted in cases of severe cord compression.11
Conditions Associated with Myelopathy
57
TABLE 4.1 Cervical Spondylotic Myelopathy (CSM): Potential Causes for Spinal Cord Vascular Insult • • • • • • •
Intermittent or persistent compressive occlusion of the anterior spinal artery (ASA) Anterior spinal cord compression with compromise of sulcul and terminal branches of ASA Intramedulary vascular stasis secondary to tethering of the spinal cord against anterior osteophytes complicated by tension of dentate ligaments Possible reduction of intramedullary collateralization due to multilevel spondylosis and related central canal stenosis Compression of venous channels associated with anterior spinal cord compression Intramedulary capillary venous stasis and edema with absent cord pulsation Cumulative spinal cord ischemia with infarction
4.1.1.3 Clinical Signs and Symptoms and Temporal Pattern of Progression During the early onset of CSM, the presentation may be subtle with the possibility of being overlooked in the presence of more obvious radiculopathic signs and symptoms. Symptom magnification may occur secondary to superimposed injury such as a vehicular injury. CSM usually develops in a gradual and slowly progressive fashion with the duration of symptoms usually ranging from one week to a few years (Table 4.2). In some cases, signs and symptoms of CSM may develop over a few decades. The myelopathic findings may eventually appear to stabilize due to the somewhat self-limiting nature of spondylosis and the reduction of segmental spinal mobility, which occurs with advancing spondylosis (Table 4.3). The most common early complaints of individuals with CSM include insidious-onset, painless paresis characterized by leg stiffness, incoordination, and/or weakness. Paresis may begin in one leg progressing to involve the opposite leg and/or to the ipsilateral arm. The history may be remarkable for falls, frequent episodes of tripping with near falls, and difficulty navigating unlevel ground due to unsteadiness. Leg weakness predominantly involves the small muscles of the foot and distal leg. This often leads to varying degrees of dorsiflexion paresis or foot scuffing. Clearance of the foot during the swing phase of gait becomes even more difficult with lower extremity spasticity. It is not uncommon for these patients to blame their difficulty walking and related symptoms on “old age.” The pattern of gait commonly seen is a broad-based, cautious, dysrhythmic, short stride. The initial sensory complaints predominate in the upper extremities, whereas initial motor compromise usually predominates in the lower extremities. Progressive leg weakness is often followed by the progression of sensory complaints. Early sensory complaints frequently consist of reported patchy numbness, pain, and/or dysesthesia involving the arms or hands with the latter presentation predominating. This characteristically progresses to involve a large diffuse portion of the limb. Upper extremity paresis or clumsiness may be present early in the progression of the disorder although the patients are often unaware of it. Patients over 65 years of age with cervical
TABLE 4.2 Historical Signs and Symptoms Suggestive of Mild to Moderate (Incomplete) Compressive Myelopathy • • • • • • • • • • • • • • • • •
Intermittent extremity shocklike sensations Brief episodes of nonfocal extremity muscle twitching or tightness Intermittent gait “incoordination” or “weakness” Extremity clumsiness with spine pain Multifocal lower extremity temperature dysethesia Intermittent bowel and/or bladder urgency Periodic nonfocal extremity paresthesia with clumsiness Inability to adequately perform complex motor tasks Back pain with radiation during spinal flexion or extension Exertional muscle weakness, tightness, or clumsiness Frequent falls Difficulty ambulating in the dark Progressive avoidance of tasks requiring balance Fear of stairs Wide-based stance Short, cautious steps during ambulation Looking at feet to improve gait
TABLE 4.3 Common Etiology Leading to Spinal Cord Compression in the Elderly • • • •
Spondylosis Falls Fracture Neoplasm
spondylotic myelopathy may present with unilateral or bilateral deltoid paresis or paralysis. 15 Ebara and associates16 characterized a “myelopathy hand” with wasting of the hand muscles similar to that seen in amyotrophy. The numb, clumsy hand is a characteristic feature of upper cervical myelopathy (C1–C5) (Table 4.4). Cervical spondylosis may lead to intermittent or persistent neck discomfort and stiffness. Facet hypertrophy and capsular pain arising from the mid- to lower cervical region can lead to referred pain to the scapular regions. Limited cervical range of motion can place a greater burden
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 4.4 Relevant Features of Numb Clumsy Hand Syndrome Secondary to High Cervical Myelopathy • Lesion usually between C3–C5 • High cervical compromise of funiculus cuneatus supplying the C6–C8 segments • Finger and hand dysesthesia • Hand stereoanesthesia • Intrinsic hand atrophy • Occipital and/or cervical pain • Late-onset spasticity • Late-onset gait pathology • Mimics lower cervical radiculopathy • Mimics plexopathy • Mimics shoulder pathology
on the lumbar region, thereby contributing to low back pain. Low back pain may also occur from spasticity involving paralumbar and gluteal muscles. Bladder symptoms are rarely severe or the primary presenting complaint.17 Urinary urgency is one of the most common bladder symptoms. Patients with moderate to severe stenotic myelopathy may present with neurogenic or spastic bladder, depending on the level of compression. They may have episodes of urinary and fecal incontinence along with ataxic gait. 4.1.1.4 Clinical Findings Global and segmental cervical active cervical range of motion is typically reduced secondary to soft-tissue changes and disk stiffening associated with spondylosis. The levels adjacent to regions of moderate to severe spondylosis may exhibit compensatory hypermobility on flexion–extension radiographs. Cervical spondylosis may lead to dynamic cord compromise and resultant L’hermittes phenomena during neck movement. This is characterized by a brief, shocklike sensation traversing the spine and extremities. It may occur unilaterally or bilaterally. A position of cervical rotation combined with extension may elicit radicular complaints and L’hermittes phenomena due to central and lateral stenosis (myeloradiculopathy). The toes are often upgoing in response to plantar stimulation, representing a positive Babinski’s response. Multilevel cervical spondylosis with lateral stenosis may present with reduced or absent upper extremity muscle stretch reflexes (MSRs) with preservation or magnification of lower extremity MSRs. In rare cases, the patellar MSR may be the only hyperreflexive MSR due to multilevel cervical radiculopathy and peripheral neuropathy (lower motor neuron lesions) in the elderly patient with CSM. A normal jaw MSR helps rule out more cephalad compromise of the descending corticospinal tract. Abdominal reflexes
FIGURE 4.3 Sagittal T2-weighted image of the cervical spine in a patient with cervical spondylotic myelopathy. Note the marked spinal canal narrowing in the sagittal dimension, especially at C4 and C5. There is also some high signal intensity within the cord, consistent with injury at this level from the narrow canal.
may be diminished with CSM but do not correlate well with degree of lower extremity spasticity.18 Chiles et al.19 retrospectively reviewed the presenting symptoms of his preoperative CSM patients. The most common symptoms were deterioration of hand use (75%), upper extremity sensory complaints (82.9%), and gait difficulties (80.3%). Moderate to severe CSM may be characterized by one of the following presentations: (1) spastic tetraparesis with numbness and extremity hyperreflexia; (2) spastic paraparesis with lesion below C6; (3) spastic tetraparesis, mild or moderate, with deltoid muscle paresis; (4) amyotrophic myelopathic hand with mild long tract signs; or (5) central cord syndrome secondary to cervical spondylosis and trauma.20 4.1.1.5 Diagnostic Imaging Quantitative measurements of the cervical spinal canal on plain X-ray can be helpful indicators of congenital narrowing or acquired stenosis. Plain X-ray does not always accurately reflect osteophytic projection into the central canal that could otherwise be seen on advanced neuroimaging procedures such as CT or MRI. MRI remains the procedure of choice for assessing the effects of spondylosis on the spinal cord. MRI provides the most sensitive means of measuring acute and chronic cord changes secondary to stenosis (Figure 4.3). There is relatively good correlation between clinical severity of CSM and the presence of a region of high T2-weighted MR signal intensity within the cervical cord of symptomatic patients.21-23 Postcontrast imaging should be considered when noncontrast studies are equivocal. Computed tomography and myelography (CTM) have limited use in the evaluation of
Conditions Associated with Myelopathy
CSM. CT can help differentiate bony lesions from soft tissue mass effects such as disk herniation or tumor. CT can also provide an accurate measurement of the spinal cord transverse area, which has been associated with levels of clinical severity (see Section 5.14). 4.1.1.6 Differential Considerations The lower extremity changes characteristic of CSM can occur secondary to myelopathy at other levels. A careful examination should be performed to identify the level of cord involvement. Mid- to lower lumbar spinal stenosis will not typically result in compressive myelopathy, because the conus is rarely located below the level of L1. Conditions that may mimic CSM include thoracic disk herniation, thoracic spondylotic myelopathy, demyelinative disease, primary lateral sclerosis, spinal tumor, and subacute combined degeneration. These conditions can coexist.
4.1.2 LIGAMENTUM FLAVUM THICKENING/BUCKLING In the adult, the ligamenta flava consist of yellow elastin fibers (80%), type I collagen fibers (20%) interspersed between the elastic fibers, and a few spindle-shaped fibrocytes. Magnetic resonance imaging provides a method for examination of spinal ligaments.10 The higher signal intensity of the ligamentum flavum vs. the posterior longitudinal ligament, on T1-weighted or gradient echo images, occurs due to the high elastin content.24,25 The ligamentum flavum extends far laterally to blend with the fibrous joint capsule along the roof of the lateral recess and intervertebral canal, subsequently, minimal thickening or hypertrophy may cause dorsal compression.26 Thickening of the ligamentum flavum can be identified in both the axial and the sagittal MR planes of acquisition.24 The average thickness of the ligamentum flavum in the lumbar spine is 3 mm.27 Degenerative disk disease results in a loss of vertical disk height (rostrocaudal subluxation) between contiguous spinal motion segments. This decrease in height causes the posterior segment ligaments to infold or buckle.28 Fukuyama et al.29 demonstrated a higher incidence of ligamentum flavum thickening in patients with degenerative spine conditions. Buckling of a thickened or hypertrophied ligament flavum can lead to greater spinal canal compromise.30 Ligamentum hypertrophy occurs as a result of increased mechanical stress in the region. Ligamentous encroachment of the posterolateral aspect of the spinal cord may coexist with degenerative changes occurring within the anterior aspect of the canal, such as tenting of the posterior longitudinal ligament with vertebral disk herniation.
4.1.3 RHEUMATOID ARTHRITIS
AND
MYELOPATHY
Rheumatoid arthritis (RA) is a chronic systemically mediated inflammatory condition associated with progressive
59
damage to synovially lined joints with a loss of cartilage, bony erosion, and ligamentous degeneration. It may involve axial and/or extra-axial joints, although the distal interphalangeal, sacroiliac, and lumbar joints are rarely involved.31 The condition usually afflicts the hand first. Symptoms include articular and periarticular swelling, tenderness, limited range of motion, and morning stiffness. Onset may be slow or rapid. Many other signs and symptoms — such as fatigue, fever, nodules, vasculitis, hematological abnormalities, malaise, and weight loss — may also be associated with RA. Rheumatoid arthritis has been associated with a number of spinal complications which include discitis,32 vertebral body erosion,33 ligamentous erosion,34,35 vertebral instability,34,35 and spinal cord compression.35 Many forms of cervical subluxation can occur. Degenerative and erosive changes associated with RA of the cervical spine usually occur along the subcranial region,36 but this consequence of RA only leads to instability and neurological complications in a small percentage of patients.37 Early in the development of cervical subluxation, symptoms may be limited to neck pain and stiffness. The neurological manifestations include intermittent sensory disturbances, radiculopathy, myelopathy, quadriplegia, and, in rare cases, sudden death. The most common radiographic changes characteristic of RA in the upper cervical spine include atlantoaxial subluxation (AAS), cranial settling (CS), subaxial subluxation (SAS),34,36 periodontoid pannus,34 and atlantoaxial kyphosis.35 RA often results in atlantoaxial instability (AAI) which occurs secondary to weakening, softening, and rupture of cervicocranial junction ligaments.35 AAI is associated with a cumulative inflammatory tissue injury-repair cycle leading to the development of fibrovascular granulation tissue referred to as pannus (Figures 4.4 and 4.5). Erosion of bone occurs where hyperplastic and inflammatory synovium contacts the unprotected interface between joint cartilage and bone. The histologic character and invasive properties of pannus are unique to RA. Pannus can expand and place the cord at risk due to direct physical compression. AAI contributes to the progressive development of AAS often accompanied by an irreducible atlantoaxial kyphosis.35 Cranial settling may then develop accompanied by SAS. Cranial settling is characterized by vertical migration of the odontoid process, which can potentially damage the upper cervical cord and brainstem within the foramen magnum. The combination of pannus formation and excessive vertebral translation associated with instability may contribute to spinal cord compression. Atlantoaxial instability may contribute to the development of pannus. Evidence for this presumption stems from the observation that surgical stabilization of AAI has been associated with rapid reduction of pannus.38 A limited neutral view radiographic study of the cervical spine without flexion and extension views has limited
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 4.5 Radiographic Measurements in the Assessment of Rheumatoid Arthritis Anterior atlantodens interval Posterior atlantodens interval Atlantoaxial subluxation
FIGURE 4.4 Abnormal soft tissue surrounding the odontoid process of the dens and involving the atlas, representing pannus secondary to rheumatoid arthritis. Note the ventral cord compression with cord deformity. (Midline parasagittal spin echo T1-weighted image through the brain and upper cervical spine.) (Courtesy of Ronald Landau, M.D.)
FIGURE 4.5 Lateral X-ray of the upper cervical spine demonstrating an increased atlantodental interval (ADI), and erosion of the odontoid process of the dens. These abnormalities are secondary to rheumatoid arthritis, causing atlantoaxial instability.
clinical utility in the examination for AAS in the rheumatoid patient. Kauppi and Neva39 reported that radiographic evaluation limited to neutral position views failed to confirm a diagnosis of AAS in 48% of their cases and failed
<14 mm <14 mm >9 mm
to represent the severity of involvement in 66%. They found that the addition of lateral flexion and extension views greatly increased sensitivity.39 This concept has been applied to MRI of the cervical spine. Dynamic MRI has demonstrated that C1–C2 motion initiates earlier than C2–C3 motion in patients with RA.40 Cine MRI of the cervical spine in patients with rheumatoid arthritis can help assess for dynamic narrowing, although statistically significant cord compression at the atlantoaxial level and below C2 is typically evident only in those patients who demonstrate some degree of compromise of the subarachnoid space on neutral MR views.41 MRI evidence of subarachnoid space encroachment on neutral MRI views of the upper cervical spine raises the suspicion for potential neurological compromise. The most useful radiographic measurements are the anterior atlantodens interval (ADI), posterior atlantodens interval (PADI), and the evaluation of vertical settling (Table 4.5).34 A PADI of less than 14 mm has correlated well with the severity of paralysis secondary to cervical myelopathy42 and has been referred to as the most reliable screening tool and predictor of progressive neurological compromise.43 Thin-slice CT with three-dimensional CT reconstruction can be helpful in the assessment of cranial settling,44 as well as other stages of segmental pathology. Three-dimensional reformatting allows detailed assessment of the degree of odontoid positioning within the foramen magnum. Isolated sensory disturbances are one of the most common early clinical presentations arising from upper cervical changes due to rheumatoid arthritis. These symptoms may falsely be attributed to multifocal peripheral mononeuropathy. Once the myelopathic features become readily evident, there are typically multiple neurological deficits.42 The serum levels of C-reactive protein, the quantity of joints with erosion, and the carpal height ratio closely correlate with the degree of cervical subluxation.45
4.1.4 HYPERTROPHIC SPINAL DISEASE 4.1.4.1 Diffuse Idiopathic Skeletal Hyperostosis Diffuse idiopathic skeletal hyperostosis (DISH), also known as Forestier’s or ankylosing hyperostosis, is a relatively common hyperostotic disorder afflicting middle-aged and elderly people. DISH afflicts men more than woman at a ratio of approximately 2:1.46 Additional risk factors include diabetes,
Conditions Associated with Myelopathy
increased alcohol intake, and dietary deficiencies of calcium, carotene, and vitamins C and E.47 DISH is an axial and extraaxial disorder characterized by ligamentous calcification and ossification. In DISH there is a predisposition to lay down bone within soft tissues, hence the alternative use of the description “ossifying diathesis.” The extraosseous calcification typically occurs in ligamentous and tendonous regions with a multisegmental spinal predisposition. Problems occur when the exuberant bone deposition effaces other tissues, causing dysphagia, cervical myelopathy, or a myeloradicular syndrome. Quadriplegia may occur in rare cases when there is compression of the anterior spinal artery in the cervical spine. Ligamentous hyperostosis may be dramatic, ranging from 1 to 20 mm in thickness, typically projecting with a flame-shaped configuration. Calcification and thickening of portions of the anterior longitudinal ligament are often present, and occasionally the lateral spinal ligaments or ligamentum flavum. ALL calcification often begins along the mid-portion of the vertebral body, eventually extending in a bridgelike configuration across the intervertebral disk space. Calcification of the posterior longitudinal ligament may also occur which may contribute to spinal stenosis. The common level of spinal involvement is the lower thoracic region, especially between T7 and T11.48 In the cervical spine, DISH occurs more frequently in the lower segments, consistent with the predilection to early spondylosis. Lumbar involvement is most common at the upper three levels. The radiographic criteria for DISH are (1) flowing ossification of at least four adjacent vertebral segments, (2) relatively normal disk height, and (3) absence of apophyseal or sacroiliac joint ankylosis.48,49 There is generally no reported predilection to DISH, but spinal stenosis can occur with or without myelopathy secondary to ossification of the posterior longitudinal ligament (OPLL) or ligamentum flavum. Early clinical features include intermittent discomfort and stiffness of the involved region. 4.1.4.2 Ossified Posterior Longitudinal Ligament Syndrome Ossified posterior longitudinal ligament (OPLL) syndrome is another condition that can result in myelopathy. There is significant predilection for the Japanese population.50,51 OPLL occurs most commonly in the cervical spine, followed by the thoracic then lumbar spines.52 The ossification pattern of the posterior longitudinal ligament can be placed in one of four categories: (1) segmental type traversing a spinal motion segment, (2) continuous over several adjacent vertebrae, (3) combined segmental and continuous, and (4) focal over an individual disk space.53 In one study, the average number of vertebral bodies involved was three.54 The risk for spinal cord compression tends to be greater with multisegmental OPLL.55
61
Multisegmental OPLL leads to greater risk for spinal cord arterial insufficiency secondary to the larger area of blood vessel compromise. The anterior spinal artery is particularly vulnerable to OPLL due to their anatomic relationship. Central spinal stenosis secondary to OPLL can result in compression of the epidural venous plexus, spinal cord displacement, spinal cord compression, gray matter infarction, and demyelination of the posterior and lateral columns.56 Spinal cord compression secondary to OPLL has been shown to result in greater compromise of intramedullary gray matter than white matter.57,58 Ossified posterior longitudinal ligament syndrome may remain subclinical. If clinical signs and symptoms do manifest, they are often insidious in onset. Many patients with OPLL have mild subjective complaints of neck pain and hand numbness. OPLL has been reported to contribute to over 20% of the cases of cervical myelopathy in the U.S.59 Myelopathic features often begin to develop when the posterior longitudinal ligament occupies greater than 30 to 60% of the spinal canal.49,58,60 The clinical presentation may be unmasked or magnified by trauma. The neurological sequelae of OPLL can be classified into three major categories: (1) spinal cord signs manifesting with lower extremity motor and sensory changes, (2) segmental signs manifested by predominate upper extremity motor and sensory disturbances, (3) cervicobrachialgia without neurological deficits.58 The individual may initially complain of leg dysesthesia, clumsiness, and difficulty walking secondary to ataxia and lower extremity paraparesis. If spinal pain does occur it usually resembles common pain of vertebrogenic origin. There is often an absence of coexistent posterior disk protrusion possibly due to greater restraining forces by the posterior longitudinal ligament secondary to inherent stiffening of the involved spinal motion segment. The radiographic signs of OPLL are distinct. A dense linear radiopaque hyperostosis along the posterior border of the vertebral bodies is typical. This commonly appears to be 1 to 5 mm thick. There may be a radiolucent zone between the OPLL and the vertebral body secondary to sparing of subligamentous tissues and space. Some individuals may present with some of the radiographic features of DISH, suggesting an overlapping pathogenesis. CT and/or MRI should be utilized to assess for high-grade spinal stenosis and myelopathy. MRI is the imaging of choice to assess the relationship of the posterior longitudinal ligament to the spinal cord. The characteristic MRI feature of OPLL is a band of low signal on all pulse sequences lying between the vertebral body marrow and the dura. Differential considerations for the low signal band include posterior longitudinal ligament hypertrophy, hemosiderin deposition, flowing cerebrospinal fluid (CSF) or calcified meningioma.
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FIGURE 4.6 Immense syrinx extending throughout the cervical spinal cord, from C3 to the T2–T3 level. Dilation of the syrinx contributes to expansion of the spinal cord. (Parasagittal spin echo T1- and T2-weighted images.) (Courtesy of George W. Fika, D.C.)
radiographic study does not preclude the coexistence of an underlying (radiographically latent) expansile lesion at the same level.
4.2.1 SYRINGOMYELIA
FIGURE 4.7 Axial T2-weighted image through the level of C2. This image confirms that the small fluid-filled space is in the center of the cord, consistent with a syrinx.
4.2 EXPANSILE LESIONS A space-occupying lesion can develop within any portion of the neuroaxis. The bony confines of the spinal canal contain and deflect the pressure of the expanding mass longitudinally and horizontally into the spinal cord. An expansile lesion may mimic more common degenerative changes such as disk pathology and/or bone spurs. The presence of spondylosis or degenerative changes on a
Syringomyelia refers to dilation of the central canal of the spinal cord or formation of abnormal tubular cystic cavities within the spinal cord (Figure 4.6). Hydromyelia is characterized by distention of the ependymal-lined central canal of the spinal cord, whereas syringomyelia is pathologically characterized by CSF dissection through the ependymal lining, forming a central tubular cavity. The two conditions often coincide; hence, the term “hydrosyringomyelia” is often used. Syringomyelia may be congenital or acquired. The cystic changes can occur at any location in the cord although they most commonly occur within the cervical cord.61 If the tubular cystic cavity extends to the medulla, the lesion is referred to as syringobulbia. One of the most frequently reported features of syringomyelia is cavitation next to or within the central portion of the gray matter of the cord (Figure 4.7). Portions of the cystic formation may be lined with gliotic tissue. The diverse etiology of syrinx formation suggests a complex pathological mechanism. The pathogenesis of syringomyelia has been debated and many theories proposed. Three primary theories have many proposed contributing mechanisms. The dysraphic theory proposes that
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TABLE 4.6 Syringomyelia: MRI Features
TABLE 4.7 Syringomyelia: Clinical Features
• Focal cord enlargement • Central or slightly eccentric fluid-filled tubular cavity isointense with cerebrospinal fluid • Metameric haustrations • Occasional septations • Frequent ring of high T2-weighted signal
• • • • • • •
a defect in neural tube closure predisposes the development of a syrinx.62,63 The hydrodynamic theory proposes a disturbance of CSF outflow from the third ventricle,64 a “presyrinx” condition associated with alteration of CSF flow,65,66 and Valsalva contribution to syrinx expansion.65 The degeneration theory encompasses different mechanisms that include disturbed blood supply,67 blockage of perivascular spaces,68 microhemorrhage with tissue atrophy (autolysis),69 and physical tissue compromise.70 Syringomyelia may be communicating or noncommunicating. A communicating syrinx is structurally contiguous with the fourth ventricle and may be associated with hydrocephalous. Most syrinxes are noncommunicating and may occur secondary to conditions such as infection processes, vascular anomalies, tumors, compressive lesions, and trauma. A noncommunicating syrinx may also occur with Chiari I and Chiari II malformations. Post-traumatic syrinxes have been identified at all levels of the spine.61 Syringomyelia is divided into five primary categories: (1) communicating syringomyelia, (2) syringomyelia as sequel to arachnoiditis confined to the spine, (3) syringomyelia associated with spinal cord tumors, (4) syringomyelia as a late sequelae to trauma, and (5) idiopathic syringomyelia.71 The expanding syrinx typically initially compromises decussating fibers of the lateral spinothalamic tract with further expansion leading to compromise of the adjacent gray matter and posterior columns (Table 4.6). Three distinct cavity patterns have been identified using axial MR acquisitions:72 (1) symmetrically enlarged central cavities, (2) central cavities that expand paracentrally in one or more focal area, and (3) eccentric cavities (frequently irregular) (Figure 4.8). Symmetric central cavities were found to be less often associated with clinical symptoms.72 Central cavities with paracentral expansion are more often associated with symptoms than central cavities with a symmetric presentation. Eccentric cavities were found to resemble extracanicular syringes and typically occurred with disorders that injure spinal cord tissue such as physical trauma, infarction, meningitis/arachnoiditis, disk herniation, spondylosis, radiation necrosis, and transverse myelitis.72 Syringomyelia usually is a progressive spinal disorder (Table 4.7). The expanding cavitation within the spinal
Bilateral pain and temperature disturbances Sensory disassociation Muscle atrophy Muscle weakness Mixed lower motor neuron lesions and upper motor neuron lesions Lower extremity spastic paraparesis Hand and leg stiffness
Central
Central with paracentral expansion
Eccentric FIGURE 4.8 Syrinx locations. (Copyright J.M. True, D.C.)
cord contributes to clinical sensory dissociation with impaired pain and temperature and relatively good preservation of light touch and kinesthesia. Compromise of crossing fibers of the spinothalamic tract is one of the earliest clinical features of central cord cavitation. Progressive intramedullary cavity expansion can lead to compromise of the anterior horn cell region, resulting in a lower motor neuron presentation in the upper extremity. Lateral expansion resulting in corticospinal tract compromise leads to varying degrees of lower extremity spastic paraparesis.
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Dysautonomia may occur secondary to compromise of spinal sympathetic fibers. Magnetic resonance imaging remains the best imaging method for detecting and following syringomyelia.
4.2.2 ARACHNOID CYST Intradural arachnoid cysts are rare and often asymptomatic lesions. They occur more frequently in the thoracic spine region, often arising posterior to the spinal cord (Figure 4.9). Arachnoid cysts are simply outpocket extensions of the arachnoid membrane, thus allowing for communication with the subarachnoid space. The spinal cord can herniate into large arachnoid cysts.73 Arachnoid cysts opacify with intrathecal contrast enhancement. Noncontrast MR studies reveal a signal pattern that is characteristically isointense with the CSF therefore making the cyst more difficult to visualize. Pulsatile erosion of the intervertebral foramen (IVF) and spinal canal may occur (Figure 4.10). Intermittant signs of cord compression develop following increases in cyst turgor pressure. Trauma can initiate neurological symptoms in a previously asymptomatic arachnoid cyst.74 Plain radiography, plain tomography, and contrastenhanced CT scans usually fail to reveal evidence of arachnoid cysts.75 One of the first CT or MRI indicators of an arachnoid cyst may be displacement and compression of the spinal cord. Cine magnetic resonance imaging (CMRI) may detect asynchronous (asynchronous rebound phenomena) CSF dynamics within the cystic region and may help ascertain the complexity of multiloculated cysts.76 CMRI may be more sensitive for assessing the intradural location of an arachnoid cyst than conventional MRI.
4.2.3 EPIDURAL LIPOMATOSIS Lipomatosis refers to excessive deposition and proliferation of unencapsulated fat within the epidural space. This can result in clinically significant central spinal stenosis. Epidural lipomatosis (EL) is usually more significant in the thoracic spine in part due to the smaller central canal. EL may occur secondary to exogenous or endogenous hypercortisolemia. It is a relatively common sequelae of adrenocorticotropic hormone (ACTH) syndrome. EL also tends to be more prevalent in the morbidly obese patient. Neuroimaging such at CT or MR reveals a voluminous quantity of extradural fat and circumferential reduction of the subarachnoid space.
4.2.4 SPINAL CORD TUMORS Neoplastic expansile lesions can cause spinal cord compromise. The most common form of bone tumor is cancer by metastasis. The spine is the most common location for metastatic spread, which exposes the nerve root and spinal
cord to compromise. The temporal pattern of evolving myelopathy depends on the location, type of lesion, and local vascular characteristics (see Table 4.8 and Figure 4.11). For example, some ependymomas develop slowly over months to years, whereas an epidural lymphoma may progress over days to weeks. Intramedullary tumors often consist of neoplasms arising from ectodermal tissues such as ependymoma or gliomas. Extramedullary–intradural tumors are usually histologically benign, arising from the meninges or nerve sheath. Metastatic leptomeningeal spread can also occur. However, leptomeningeal metastasis often produces multifocal neurological symptoms involving the brain, cranial nerves, spinal roots, and signs of meningeal irritation. Epidural tumors are often metastatic with extension within the spinal canal. Occurring less frequently than metastasis, primary extradural tumors may arise from adjacent osseous structures of the spinal column. 4.2.4.1 Intramedullary Tumors 4.2.4.1.1 Ependymoma Spinal ependymomas are slow-growing neoplasms that arise from glial tissue, specifically the ependymal cells that line the central canal. They are frequently found within the ventriculus terminalis of the filum terminale and within the cervical cord. Ependymomas represent one of the most common intramedullary tumors in adults.77 Myxopapillary ependymomas represent a subtype that has been found to occur more frequently within the conus medullaris or filum terminale. Ependymomas have been associated with neurofibromatosis.78 Ependymomas are solid tumors associated with symmetric spinal cord expansion. There may be adjacent bone erosion. There may be microhemorrhage and cystic formation along the margins of the expanding tumor, contributing to more well-defined borders than the astrocytoma. The cysts usually lie caudal or rostral to the tumor. Most ependymomas are isointense to the spinal cord on T1WI. They are typically hyperintense on T2WI surrounded by a thin band of hypointensity. They generally enhance with contrast, helping to differentiate it from a syrinx. Ependymomas tend to enhance with a more homogenous appearance than do astrocytomas.79 There may be calcification, which may be revealed in gradient recalled echo sequences.80 4.2.4.1.2 Astrocytoma and oligodendroglioma Astrocytoma is a relatively benign tumor that arises from within the spinal cord parenchyma. Oligodendrogliomas resemble astrocytomas but occur with much less frequency. Most spinal astrocytomas are of low-grade malignancy; they are slow to develop and if not completely removed will ultimately cause the death of the patient.81
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FIGURE 4.9 MRI series of an intradural arachnoid cyst. (A) Thoracic arachnoid cyst extending through the intervertebral foramen (IVF) of T7–T9. (Left parasagittal T1 spin echo pulse sequence, postcontrast study.) (B) T2-weighted image demonstrates the CSFfilled lesion. (C) Axial T6–T7 level demonstrates outpouching of the arachnoid cyst. (Courtesy of George W. Fika, D.C.)
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Intradural arachnoid cyst
IVF enlargement from pulsatile erosion
TABLE 4.8 Classification of Spine Lesions by Anatomic Compartment • Extradural masses Location: outside thecal sac Tissues: osseous spine, epidural space, disk, paraspinal soft tissues Examples: herniated disk, spondylitic spurs, fractures, metastases Classic myelogram appearance: thecal sac extrinsically compressed; if block, interface between lesion and contrast column is poorly defined with “feathered” appearance at level of obstruction • Intradural extramedullary masses Location: inside thecal sac but outside cord Tissues: nerve roots, leptomeninges, CSF spaces Examples: nerve sheath tumors, meningiomas Classic myelogram appearance: intradural filling defect outlined by sharp meniscus of contrast; spinal cord deviated away from mass; ipsilateral subarachnoid space enlarged up to mass • Intramedullary masses Location: inside spinal cord Tissues: cord parenchyma, pia Examples: astrocytoma, hydrosyringomyelia Classic myelogram appearance: diffuse, multisegmental, smoothly enlarged cord with gradual subarachnoid space effacement Source: Osborne, A., Neuroradiology, Mosby, St. Louis, MO, 1993. With permission.
FIGURE 4.10 Intradural arachnoid cyst in the mid-thoracic spine. Cord compression occurs from increased cerebrospinal fluid (CSF) pressure created by the contained swelling cyst. (Copyright J.M. True, D.C.)
Anaplastic astrocytomas and glioblastoma multiforme are rare. Astrocytomas are the most common intramedullary tumor occurring in children and second most common tumor in adults following ependymoma. They may occur in a multifocal pattern with greatest predilection for the cervical region. Intramedullary astrocytomas cause diffuse expansion into the surrounding spinal cord region. This may result in obliteration of the subdural space with extension of the elongated tumor mass more than 3 to 5 vertebral segments. The expansile astrocytoma may be associated with cystic and/or syrinx formation. Tumoral cysts, unlike common benign syrinxes, usually lie in an eccentric location within the spinal cord. Because of the insidious nature of the tumor, many patients are diagnosed many months or years after initial symptoms appear.81 The early symptoms usually include a long-standing history of neck or back pain, slowly developing ataxia, and sensory disturbances. As the long tract signs intensify, the patient will become paraplegic if the tumor is allowed to progress. Astrocytomas tend to be isointense to hypointense on T1WI and hyperintense on T2WI. There is usually good postcontrast enhancement. MRI may reveal associated
cysts and syrinx formation. It is difficult to differentiate a low-grade astrocytoma from a high-grade malignant astrocytoma with MR unless there is MRI evidence of leptomeningeal spread at the time of imaging.82 4.2.4.1.3 Hemangioblastoma Hemangioblastoma are usually singular intramedullary tumors occurring in the posterior part of the cord, with a small percent exhibiting extramedullary extension. They are neoplasms comprised of densely arranged blood vessels and stromal cells. MR assessment is characterized by dilated and tortuous arterial tributaries and plial veins. Clinically, they are very difficult to differentiate from arteriovenous malformations because both appear as an expanding mass lesion that may hemorrhage or cause ischemic neurological symptoms.83 These lesions may remain clinically silent throughout life only to be discovered after MRI of the spine. Dynamic three-dimensional contrast-enhanced MR angiography demonstrates a dense vascular mass and can help differentiate hemangioblastoma from arteriovenous malformations and spinal dural arteriovenous fistulas.84 Routine angiography usually demonstrates tumor blush. There is usually diffuse cord expansion, edema, and hyperintense signal on T2WI with frequent signal voids. The tumor nodule usually enhances.
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A
Intradural extramedullary Arachnoid cyst Nerve sheath tumors Meningioma Ependymoma Lymphoma Drop metastasis Dermoid cyst Sarcoid tumor
Extradural Metastases Arachnoiditis Disc herniation Disc extrusion Facet synovial cyst Hemangioma Lymphoma Meningocele Abscess Epidural lipomatosis Osteoblastoma Aneurysmal bone cyst Spondylosis and stenosis Displaced vertebral fracture
Intramedullary Ependymoma Astrocytoma Arteriovenous malformation Syringohydromyelia Multiple sclerosis Cord ischemia and infarct Viral myelitis Lipoma Metastasis Hemangioblastoma Schwannoma Paraganglioma B
FIGURE 4.11 (A) Various sites of intraspinal tumor origin. (B) Tumor and myelopathy differentials by anatomical region. (Copyright J.M. True, D.C.)
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FIGURE 4.12 Tumors with an hourglass or dumbbell appearance on axial imaging are commonly neurofibromas, schwannomas, or meningiomas. (Copyright J.M. True, D.C.)
4.2.4.2 Intradural Extramedullary Tumors 4.2.4.2.1 Neural sheath tumor The category of nerve sheath tumors encompasses the following conditions: schwannomas, neuroma, neurilemoma, perineural fibroblastoma, and neurofibroma. These tumors generally arise from the nerve sheath of the nerve root or peripheral nerve. They may arise from the nerve root at any level of the spine. The two primary classifications of nerve sheath tumors are schwannoma and neurofibroma. Both are histologically unique although the terms may occasionally be inaccurately interchanged. Neurofibromas are histologically characterized by the presence of Schwann cells and fibroblasts. They are usually fusiform in appearance and are more commonly seen in association with neurofibromatosis type 1 (NF-1). Schwannomas, on the other hand, are lobulated mass lesions primarily comprised of Schwann cells. They may be isolated or multifocal in occurrence. Nerve sheath tumors are usually benign, but a small percentage undergo malignant transformation. Malignant nerve sheath tumors often acquire some of the histological characteristics of the schwannoma and neurofibroma and are more apt to infiltrate the adjacent neural structures. Most nerve sheath tumors arise from the sensory portion of the nerve root occupying an intradural extramedullary location. A small percentage may develop both intradural and extradural extensions or may be limited to an extradural location.85 Nerve sheath tumors that arise within the intervertebral foramen often expand and extend through the IVF, assuming a dumbbell or hourglass shape (Figure 4.12). Extension into the central spinal canal usually occurs from a lateral or posterolateral direction. This may result in gradual progressive spinal cord displacement with eventual compression. Nerve root symptoms typically precede myelopathic features whereas primary intramedullary lesions are
more likely to expand in a more painless fashion. The nerve root pain associated with this type of expansile intraforaminal lesion tends to be worse at night. When spinal cord compression does occur, it usually involves an incomplete hemicord or Brown–Séquard-type presentation. One of the earliest myelopathic-related complaints may be perceived temperature aberrations in the lower extremities secondary to compromise of the spinothalamic pathway. Spinal radiographic studies may reveal a large eroded intervertebral foramen with thinning of the pedicles (Figures 4.13 to 4.15). A limited cervical radiographic study without oblique views may not reveal these characteristic bony changes. Schwannomas and neurofibromas have a similar general foramen appearance with MR imaging. Nerve sheath tumors are well-circumscribed tumors, which usually enhance in a homogenous fashion on T1-weighted acquisitions following application of paramagnetic contrast. Schwannomas are more apt to have cystic degeneration, whereas neurofibromas are more apt to have a nonenhancing focus, which is dark on T2-weighted imaging. Larger tumors are more apt to demonstrate a more heterogeneous pattern of enhancement. MR imaging may reveal cord compression with less than expected myelopathic features. It is uncommon for a schwannoma to arise from an intramedullary location, particularly in the absence of neurofibromatosis (von Recklinghausen’s disease), although intramedullary schwannomas have been discovered and reported as isolated case studies.86-88 Spinal tumors in NF-1 are usually intraforaminal, often extending into the central spinal canal, whereas nerve sheath tumors (schwannomas) associated with NF-2 are more likely to develop in an intraspinal intradural location.89 4.2.4.2.2 Meningioma Meningiomas are relatively common spinal neoplasms accounting for as much as one fourth to one third of intraspinal expansile lesions.90,91 Spinal meningiomas are usually benign tumors, which progress slowly. The most common type of meningioma occurs as a globoid tumor that arises from meningothelial cells within the arachnoid membrane adjacent to the nerve root. The tumor is typically nodular and well circumscribed and is adherent to the dura. The four histological types of meningiomas are (1) meningothelial, (2) psammomatous, (3) fibroblastic, and (4) angiomatous.92 Meningiomas usually are found in an intradural extramedullary tumor although epidural location may occur.91 The tumor may expand through the nerve root sleeve and IVF, resulting in an extradural and occasionally extraspinal extension. This produces the classic dumbbell-shaped tumor. Spinal meningiomas usually afflict individuals over 40 years of age with a reported female to male predominance ranging from 4:193 to as high as 10:1.90 They occur more commonly in the thoracic spine followed by the cervical spine.94 A relatively high reoccurrence rate of 10 to 20% has been reported after surgical resection.95
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A
B
FIGURE 4.14 A and B. Large lobulated enhancing mass that extends along the nerve root, expanding the right neural foramen, in the same patient as in Figure 4.13. Note the associated mass effect upon the lateral right aspect of the spinal cord with cord deformity, as well as the homogeneous tissue enhancement following the administration of gadolinium. The presentation is consistent with a schwannoma at the C2 neuroforamen. (Coronal spin echo T1-weighted image through the cervical spine following administration of gadolinium.)
FIGURE 4.13 Oblique radiograph of the cervical spine demonstrating marked bony expansion of the right neural foramen at the C2–C3 level. This erosion was not evident on lateral radiograph. (The same patient is shown in Figures 4.13 through 4.15.)
Patients often initially complain of radicular pain accompanied by a long history of back pain. As the lesion expands, it may displace and eventually compress the spinal cord, leading to myeloradiculopathic features. These patients’ symptoms are frequently misdiagnosed as resulting from spondylosis or spinal stenosis, until cord compression signs appear or a diagnosis is made from appropriate diagnostic imaging. The MRI appearance of meningioma is similar to schwannoma. They are usually isointense with the spinal cord on T1-weighted imaging and isotense to CSF on T2weighted studies. The low signal changes are readily apparent when compared to the surrounding hyperintense CSF signal. Calcification may occur and will contribute to low T2-weighted signal changes. Meningiomas usually enhance with a homogeneous appearance and may present with an enhancing dural extension.96 Computerized tomography may demonstrate a well-marginated duralbased lesion with considerable surrounding peritumor edema.97
FIGURE 4.15 Postcontrast enhancing lobulated mass compatible with a schwannoma, causing spinal cord compression and cord deviation towards the left. (Axial spin echo T1-weighted image through the C2–C3 level following gadolinium enhancement.)
4.2.4.2.3 Paraganglioma Paraganglioma is an uncommon tumor which arises from the autonomic nervous system (ANS)-associated paraganglia, often arising within the cauda equina and
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filum terminale.90 They are usually slow-growing, benign tumors which can arise anywhere along the spine. They can transform into aggressive tumors.98 Malignant paragangliomas rarely metastasize to the spine.99 Paragangliomas may occur in an extraspinal location such as the carotid body, adrenal medulla, and para-aortic regions. They are generally well-circumscribed masses which are typically isointense with the spinal cord on T1WI and isointense to hyperintense on T2WI. They may appear somewhat inhomogeneous and are often associated with recurrent microhemorrhage. Paragangliomas are highly vascular tumors which usually give rise to homogeneous contrast enhancement.100,101 4.2.4.3 Epidermoid and Dermoid Tumor, and Teratoma This classification of tumors is exceptionally rare and represents neoplasms of congenital origin. They are slowly expanding lesions which usually arise within the lumbar region. They frequently arise within the region of the conus medullaris and are associated with early saddle dysesthesia and bowel and bladder disturbances. Epidermoid tumors may arise within an intramedullary, extramedullary, or extradural location. There are two primary classifications of epidermoid cyst: (1) the congenital cyst frequently associated with bone or skin malformations, and (2) the iatrogenic cyst occurring due to lumbar puncture.102 The more common epidermoid tumors are cystic characteristically comprised of epithelium and features of skin such as hair follicles, sebum, and sweat glands. T1WI imaging usually reveals tumor hypointensity with heterogenicity. MR imaging with T1-weighted enhancement with gadoliniumDTPA (diethylenetriamine pentaacetic acid) often demonstrates the rim morphology of the epidermoid tumor.103 4.2.4.4 Extradural Tumors 4.2.4.4.1 Lipoma This benign fatty tumor may occur at any level of the spine but tends to be more prevalent in the lumbar region. Lipomas tend to be slowly expansile lesions, which can reach a relatively large size before detection. They may be associated with a cutaneous angioma or fibrofatty communication through a spina bifida. Large congenital lipomas can cause progressive defects including nerve root tethering, filum terminale tethering, and/or spinal cord tethering.104 The patient may develop a subcutaneous extension, which becomes palpable during the latter course of development. 4.2.4.4.2 Chordoma Chordomas are malignant tumors that arise from intraosseous notochordal remnants within the vertebral column. They can occur anywhere along the midline of the spinal column but typically arise from the sacrum or coccyx. They are commonly associated with multisegmental
focal tissue invasion and destruction, rarely metastasizing. They have been classified into two primary categories: (1) typical chordomas and (2) chondroid chordomas. The expanding lesion often compromises bowel and/or bladder function. It may be palpated during a rectal examination. MRI reveals most chordomas to have an inhomogeneous appearance with low signal intensity on T1WI and hyperintensity on T2WI, excelling that of the CSF. 4.2.4.4.3 Lymphoma Lymphoma is the most common malignancy found in the epidural space.105 Lymphoma can afflict the spine and soft tissue within the epidural region. Primary spinal involvement is rare but metastasis to the epidural region is relatively common, particularly in individuals who are immunocompromised. 101 Most cases are associated with nonHodgkin’s lymphoma (NHL). NHL may cause bone destruction and hyperostosis. In NHL, plain-film and CT imaging may demonstrate poorly defined destructive bone changes with an adjacent soft-tissue mass; MRI characteristically reveals signal hypointensity on T1WI, demonstrating inhomogeneous multifocal regions of hyperintensity on T2WI. 4.2.4.5 Lesions Arising from the Bony Vertebral Column Any lesion that restricts the dimensions of the central spinal canal can potentially result in myelopathy. Numerous benign and malignant expansile lesions can arise from the vertebral complex. Malignant lesions include sarcoma, osteosarcoma, chondrosarcoma, and fibrosarcoma. Benign lesions include hemangioma, osteoid osteoma, aneurysmal bone cyst, giant cell tumor, and osteochondromas. A small percentage of hemangiomas within the vertebral body may expand, cause pathologic fracture, and contribute to spinal cord compression. 4.2.4.6 Metastatic Lesions One of the most common neoplastic extradural lesions is metastasis.106 In adults, approximately half of all spinal metastasis leading to an epidural expansile lesion arises from the breast, lung, or prostate regions spread by a hematogenous route.83,106 Malignant spread can occur by direct extension of malignancies from the pelvis, retroperitoneum, lungs, cervical region, and posterior aspect of the mediastinum or from hematogenous seeding. It has been proposed that as many as 5 to 10% of cancer patients may develop neurological deficits secondary to metastatic spread to the epidural region of the spine.107 Most metastatic tumors within the spine do not arise from the parenchyma but compromise the spinal cord from the epidural space. Therefore, myelopathy usually occurs secondary to the consequences of spinal cord compression rather than invasion of the cord parenchyma. The clinical presentation
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2a
2b
3a
3b 1c 1b FIGURE 4.16 Pathophysiology of leptomeningeal metastases. This schematic illustration of the spinal canal depicts the mechanisms of tumor cell entry into the spinal subarachnoid space. The tumor may invade the vertebral body (1a) and grow along vertebral veins (1b) into the subarachnoid space (1c). The tumor may invade peripheral nerves or nerve roots outside the vertebral canal (2a) and grow along the nerve sheath into the spinal canal to seed the leptomeninges (2b). The tumor can invade blood vessels outside the CNS (3a) and traverse subarachnoid veins into the subarachnoid space (3b). (From Posner, J.B., Neurologic Complications of Cancer, Oxford University Press, New York, 1995. With permission.)
associated with spinal cord compression is often characterized by relatively rapid evolution of myelopathic signs and symptoms. Direct intraparenchymal destruction would likely lead to aggressive clinical progression. If the spinal parenchyma is directly invaded, it is usually secondary to hematogenous spread to the interior of the spinal cord.108,109 If spinal cord compression secondary to metastasis is left untreated, it will eventually progress to weakness and eventually paralysis. Metastatic cells may reach the spine through (1) extension from a vertebral metastasis, (2) invasion through the intervertebral foramen, or (3) direct hematogenous seeding to the epidural space (Figure 4.16).110 Once metastatic cells reach the epidural space, they may expand to compress the spinal cord near its primary entry site or they may migrate within the epidural space, compromising the spinal cord at a more distal location. If the lesion arises from the vertebral body, it is more likely to result in anterior spinal cord compression, whereas if it arises from the pedicle or through the IVF, it is more likely to cause lateral cord compression. Patients with spinal tumors occasionally present with signs and symptoms of intracranial disease;111 however, this is not a common manifestation of spinal tumors. Michowiz and associates112,113 found 53 cases of papilledema coexistent with spinal lesions. In each reported case, the papilledema resolved with surgical decompression of the spinal lesion. The majority of spinal tumors producing increased intracranial pressure and papilledema have been
ependymomas and ependymoblastomas.114 Most of these spinal tumors have been noted within the lower spinal canal. Elevated intracranial pressure increases the risk for ventriculomegaly. This, in turn, can contribute to dementia, which may be reversible upon reduction of CSF pressures. Lesions of the high cervical spine rarely produce lower cranial nerve symptoms and signs. When they do occur, it typically involves the trigeminal nucleus with some degree of sensory aberrancy on the face and cranial nerve 11 and 12 involvement. Vertigo and nystagmus are occasionally seen. Usually, the cranial nerve deficit is overshadowed by the symptoms of spinal cord compression. Magnetic resonance imaging is the best single modality for imaging spinal tumors due to its unsurpassed capacity to differentiate soft tissue and the demarcation between cerebrospinal fluid and neural tissue. Plain-film radiography is generally insensitive for the detection of spinal tumors unless the tumor has produced bony erosion or destruction. MRI has generally replaced CT as the gold standard for evaluating the spinal cord and epidural region. MRI provides multiplanar imaging, which does not require time-consuming reconstruction. The use of contrast agents with MRI helps further differentiate tumor blood flow, metabolic and parenchymal characteristics. New MR techniques allow for assessment of CSF flow dynamics, giving a higher yield of information than the myelogram. CT may occasionally be used to complement MRI of spinal cord tumors. For example, CT imaging provides excellent spatial resolution for the appraisal of
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tumors arising from bone and bony element destruction. Tumors can usually be distinguished from arteriovenous malformations (AVMs) by the presence of a mass effect, bony erosion, and cystic changes. Some tumors may have associated enlargement of intradural blood vessels due to the demand for increased blood flow. Spinal tumors with enlarged vessels include hemangioblastoma, paraganglioma, and angioblastic meningioma.115 Magnetic resonance angiography (MRA) can be used to help differentiate the extent of vascularity of the tumor and surrounding tissues.
4.2.5 EPIDURAL ABSCESS Early diagnosis and treatment of a spinal epidural abscess is critical for a favorable outcome. An epidural abscess is a rare disorder that results from spread of an infection to the extradural space. The most common organism is Staphylococcus aureus; however, any abscess-forming pyogenic organism or combination of organisms may be found. An acute epidural abscess may arise from hematogenous seeding from a distant site such as a cutaneous, periodontal, urinary tract, or pulmonary source. It may also result from a primary infection within the region of the spine or retroperitoneal space. Intravenous drug abuse is major risk factor for spinal infection. Predisposing factors include cancer, diabetes, and immunosuppression. Infectious seeding of the vertebral body can lead to osteomyelitis and infectious extension to the epidural space. Spinal surgery, diagnostic procedures, and minimally invasive intervention requiring needle puncture can expose the spinal region to pathogens and epidural abscess formation. An acute abscess is primarily comprised of inflammatory and purulent exudates, whereas a chronic abscess contains more granulomatous tissue. Chronic abscess formation may result from discitis and/or osteomyelitis. Both acute and chronic abscesses can produce a mass effect that will compress the spinal cord and mimic more common space-occupying pathology such as disk herniation or tumor. Abscess formation can promote the development of epidural venous thrombophlebitis and/or regional arterial obstruction contributing to spinal cord infarction. Patients with progressive acute or chronic abscess development may pass through the following four stages: (1) localized back pain that becomes severe, (2) radicular pain, (3) motor weakness and sphincter disturbance, and (4) paralysis.83,116 The patient with an acute abscess is often acutely ill, febrile with signs of systemic infection. The signs and symptoms may rapidly progress within hours or days. The pain associated with chronic abscess development may persist for weeks or months, sometimes in the absence of fever prior to the onset of neurological deficits or dysfunction. Onset of cord signs may be abrupt or gradual depending on the type and location of the infection. Whenever abrupt onset paraparesis develops, an
epidural abscess should be considered. Clinical evaluation may reveal a positive percussion sign over the involved region of the spine. Segmental spinal palpation may elicit a reactive paraspinal spasm. Diagnostic confusion with other disorders may occur when the onset of the radicular complaints, severe back pain, and motor weakness slowly develops. With rapid-developing abscesses, the initial diagnostic appearance is similar to meningitis or transverse myelitis. In addition to long tract signs, the patient may exhibit nuchal rigidity, fever, headache, chills, sweating, delerium, and convulsions. A CSF puncture is avoided in the region of abscess because of the risk for meningeal spread. CSF pressure may be normal or raised, and it characteristically demonstrates modest pleocytosis, normal glucose, and high protein content. There may be a dynamic CSF block or positive Queckenstedt test. Rapid clinical progression and positive CSF findings warrant immediate neuroimaging and intervention. MRI is extremely helpful in identifying the mass effect. In subtle cases, the use of gadolinium can be useful117 to help differentiate epidural granulation tissue from a pus-filled abscess. An abscess typically enhances along its periphery, whereas granulation tissue enhances homogenously due to its vascular characteristics. An MR signal void within a suspected abscess suggests a gas-forming organism.118 MRI may reveal extraspinal extension of infection or a path of cellulitis leading to the abscess location. Intervention for an acute abscess usually requires emergency laminectomy, lesion drainage, and antibiotic treatment. The prognosis for recovery is dependent on the virulence of the organism, its susceptibility to antibiotics, and the severity of cord damage.
4.3 ARTERIOVENOUS MALFORMATIONS Vascular malformations of the spine and spinal cord are uncommon lesions, approximately one tenth as common as cerebral arteriovenous malformations.119 Most of the vascular malformations within the spine are arteriovenous malformations or arteriovenous fistulae (AVFs). Cavernous angiomas and capillary telangiectasia are relatively less common. Abnormalities of spinal vasculature can lead to ischemic changes within the cord and may contribute to a mass effect compromising adjacent neural elements. One of the more common vascular abnormalities is the arteriovenous malformation. This refers to a variation in the pattern of vessel diameter, vessel density per area, regional blood flow characteristics, and structural transition between the arterial and venous systems. It is characterized by a true nidus of pathological vessels transitional between feeder arteries and draining veins.120 Some AVMs will be unnoticed symptomatically, whereas others will result in a progressive insult to neural elements. An AVM could result in a catastrophic spinal cord hemorrhage.
Conditions Associated with Myelopathy
TABLE 4.9 Arteriovenous Malformations: Clinical Features • • • • • • • • • • • •
More prevalent in men Usually occurs between 2nd and 4th decades Prevalent at thoracolumbar junction Usually sudden or subacute onset Possible focal spinal pain Possible radicular pain Rapid signs of incomplete or transverse myelopathy Often early urinary impairment Episodic or “stuttering” course Progressive steplike progression Partial or complete clinical remissions Signs and symptoms attributable to same spinal level
TABLE 4.10 Spinal Arteriovenous Malformation Classificationsa Type Type Type Type a
I: II: III: IV:
Dural arteriovenous fistula (AVF) Intramedullary glomus type Intramedullary juvenile type Intradural, extramedullary (perimedulary)
Types according to Anson, J.A. and Spetzler, R.F.179
TABLE 4.11 Arteriovenous Malformations: Potential Complications • • • • •
“Water hammer” effect of cord Direct neural compression Spontaneous thrombosis Venous hypertension Spinal cord ischemia and infarction
Pain is a frequent sign of spinal AVMs due to their more common dorsal location (Table 4.9).119 There are four primary classifications of spinal AVMs (Table 4.10). Type I is the dural arterialvenous fistula (AVF). This has been referred to as the “long coiled venous malformation”119 and represents the most common spinal vascular malformation (Figure 4.17). The AVF is typically a slow-flow shunt transitioning between the proximal portion of the nerve root sleeve dura and the adjacent spina dura. It is usually found along the dorsal aspect of the lower thoracic cord and conus medullaris. The AVF arterial feeder is frequently an isolated dural branch of the intervertebral artery,121 whereas a medullary vein usually provides the venous outflow in a retrograde
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direction to the coronal venous plexus.122 This can result in dilation, elongation, and tortuosity of the vessels. The intrathecal venous system is typically valveless; therefore, elevated intravenous pressure may transmit through sulcal tributaries into the spinal cord. This can further contribute to elevated intramedullary venous pressures, resulting in congestion, hypertension, and cord edema. Intramedullary venous hypertension can lead to intramedullary arterial insufficiency and related ischemia (Table 4.11). The majority of AVFs occur in men and develop within the lower half of the spinal column.123 Individuals with AVFs often have a gradual onset of paraparesis and/or sphincter dysfunction accompanied by back pain or radiculopathy. The incidence of AVF hemorrhage is low, whereas the incidence of hemorrhage with AVMs is considerably higher.122,124,125 Arteriovenous fistuale can further be subclassified into intramedullary glomus malformation (type II; Figure 4.18), juvenile AVMs (type III; Figure 4.19), and perimedullary AVMs (type IV). The glomus-type AVM commonly has a relatively compact intramedullary vascular plexus (nidus) supplied by well-identified arterial feeders from the anterior and/or posterior circulation. The glomus malformation has relatively high intra-AVM pressures. Juvenile-typeAVMs are the least common AVM. This rare vascular malformation has a morphologically complex intramedullary nidus. This AVM may have extensive extramedullary and, sometimes, extraspinal extension. The juvenile-type AVM will often encompass the spinal canal and penetrate and disrupt spinal cord tissue, making intervention difficult. Type IV AVMs are intradural extramedullary AVMs often referred to as perimedullary AVFs. The three subclassifications of type IV AVMs are based on the size of the arterial feeder and draining vein and the magnitude of blood flow through the shunt (Figure 4.20). Perimedullary AVFs lie outside the spinal cord and pia mater and are commonly located within the region of the conus medullaris. They are anastomotic with the anterior spinal artery and often demonstrate a simple direct arterial–venous shunt near the pia that is sometimes accompanied by a venous varix, arterial ectasia, or arterial aneurysm. Most perimedullary AVFs lie within the anterior and lower portions of the spinal cord,123 frequently located in the region of the conus medullaris.126 Acute or subacute neurological deterioration without evidence of hemorrhage in a patient with a spinal arteriovenous (AV) malformation has been referred to as Foix–Alajouanine syndrome.127 Intradural AVMs can cause myelopathy as a direct result of hemorrhage or by contributing to compression-induced ischemia, as most likely occurs in Foix-Alajouanine syndrome. This may occur by one or more of the following mechanisms: (1) arterial insufficiency secondary to vascular steal, (2) venous hypertension, or (3) compression of the spinal cord
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
A
B
FIGURE 4.17 (A) Diagram of a type I-A arteriovenous malformation (AVM) illustrates the single dural feeder supplying the cluster of small vessels at the dural root sleeve that forms the fistula. The fistula flows into an enlarged efferent intradural vein that drains into the dilated coronal plexus of the spinal cord. (B) The type I-B arteriovenous malformation has additional feeders at adjacent levels that communicate with the dural nidus via small vessels running within or beneath the dura. (From Anson, J.A. and Spetzler, R.F., Classification of spinal arteriovenous malformations and implications for treatment, BNI Q., 8(2), 2–8, 1992. With permission of Barrow Neurological Institute.)
FIGURE 4.18 Diagram of a type II arteriovenous malformation (AVM) shows the characteristic compact nidus within the spinal cord parenchyma. The AVM is supplied by branches of the spinal arteries. (From Anson, J.A. and Spetzler, R.F., Classification of spinal arteriovenous malformations and implications for treatment, BNI Q., 8(2), 2–8, 1992. With permission of Barrow Neurological Institute.)
Conditions Associated with Myelopathy
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A
B
FIGURE 4.19 (A) Diagram of a type III arteriovenous malformation (AVM) demonstrates the extensive involvement of the complex AVM, which is diffuse and extends into the spinal cord, the intra- and extradural spaces, and even the bone. The AVM is supplied by all spinal arteries at multiple levels. (From Spetzler, R.F., Zabramski, J.M., Flom, R.A., Management of juvenile spinal AVMs by embolization and operative excision. Case report. JNS, Vol. 70 p. 628–632, 1989. With permission.) (B) Diagram of the type IV arteriovenous malformation shows the direct fistula between the anterior spinal artery and an adjacent vein. Type IV AVMs are typically located anterior to the spinal cord, as shown here. They may, however, be dorsal to the spinal cord and supplied by the posterior spinal artery. (From Anson, J.A. and Spetzler, R.F., Classification of spinal arteriovenous malformations and implications for treatment, BNI Q., 8(2), 2–8, 1992. With permission of Barrow Neurological Institute.)
IV-A
IV-B
IV-C
FIGURE 4.20 The three subtypes of type IV arteriovenous malformations are classified on the basis of size of the arterial feeder and draining vein and the degree of increased flow through the shunt. (From Anson, J.A. and Spetzler, R.F., Classification of spinal arteriovenous malformations and implications for treatment, BNI Q., 8(2), 2–8, 1992. With permission of Barrow Neurological Institute.)
by a venous or arterial aneurysm.123 An elongated ectopic vessel or intertwined group of vessels in the absence of focal aneurysm may also contribute to a mass effect compromising the spinal cord. The natural history of AVMs varies greatly between individuals. AVMs can cause recurrent hemorrhages, progressive SCI, and related disability.
The cavernous angioma is a mulberry-type lesion characterized by low-flow often supplied by delicate, thinwalled vessels (Table 4.12). The lesions are typically small, ranging in size from 5 to 25 mm.123 Another unique, frequent feature is the surrounding rim of hemosiderin and gliosis suggestive of recurrent microhemorrhages. The use of MRI has provided a sensitive window for viewing these
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TABLE 4.12 Cavernous Angiomas: MRI Characteristics • Reduced perimetric T2-weighted signal (hemosiderin) • Reduced signal void (slow-flow) • Punctate pattern of increased T1- and T2-weighted signal (microhemorrhages) • Mixed high and low signal intensity (target pattern)
TABLE 4.13 Dural Arteriovenous Malformations: MRI Characteristics • • • • •
Area of focal cord expansion Central area of high or low T1-weighted signal intensity Increased T2-weighted signal intensity Common gadolinium-DTPA enhancement on T1 weighting Postcontrast enhancement of coronal venous plexus
relatively small lesions, which may be relatively undetected by myelography, arteriography, and computerized tomography. Cavernous angiomas may be isolated in their occurrence or may be multifocal such as in the case of familial multiple cavernous angiomatosis.128,129 The clinical presentation is variable, although it is often associated with brief episodes of overlapping myelopathic features due to a cycle of recurrent microhemorrhages. Capillary telangiectasias and venous malformations are sometimes found incidentally on autopsy but are rarely identified on advanced imaging studies.126 If AVM is suspected or confirmed, an aggressive assessment should be considered. Aminoff and Logue found that within 6 years of the onset of symptoms related to AVMs most patients become severely disabled or crippled.130 In another study of intramedullary AVMs, hemorrhagic onset occurred in 50% of cases.131 Ancillary investigation for AVMs may reveal an increased cell and protein content in the cerebrospinal fluid. Myelography may reveal tortuous varicosities on the surface of the spinal cord. MRI is the primary method for noninvasive evaluation of AVM. Spinal MR supplemented with MR angiography allows for assessment of vascularity and the spinal cord parenchyma. The technique of MRA has been extremely valuable for the assessment of intracranial vessels and continues to hold promise relative to spinal vascular evaluation (Tables 4.13 and 4.14). MRA has been used to evaluate the flow patterns in spinal vessels following surgery and embolization of intradural and extradural vascular malformations.132 Spinal intradural vessels as small as 1 mm have been detected and displayed with postcontrast MRA.133 MRA has been utilized to detect enlarged tortuous veins of the coronal plexus.133 Further developments in dynamic MR imaging, postcontrast
TABLE 4.14 Intradural Arteriovenous Malformations: MRI Characteristics • • • • • •
Serpentine flow void on T1-weighted images Focal expansion of spinal cord May be regions of cord parenchyma atrophy Intramedullary nidus on sagittal and axial acquisitions Possible globular flow void (aneurysm) Possible increased T1-weighted signal (subacute hemorrhage)
acquisitions, and spatial resolution will enhance the evaluation of vascular malformations, watershed regions, blood supply to tumors, and vascular changes secondary to mass effects within the spinal column.
4.4 NONCOMPRESSIVE MYELOPATHY Many diseases and disorders cause intrinsic or intramedullary tissue injury and degeneration. The general categories of noncompressive myelopathy are postinfectious myelitis, demyelinating myelitis, infectious myelitis, toxic myelitis, myelopathy secondary to physical agents, metabolic and nutritional myelopathy, paraneoplastic myelopathy, and myelopathy secondary to fibroproliferative and vascular disease. Most of the disorders that fall into these categories have abrupt-onset clinical presentations. The workup of a suspected noncompressive myelopathy should be expedited immediately; myelitis usually evolves over a few hours to a few days, and timely intervention is critical. Rapid-onset myelopathy without imaging evidence of cord compression or a mass effect is commonly referred to as acute or subacute transverse myelitis. The term “acute transverse myelopathy” (ATM) has been defined as “an acute intramedullary dysfunction of the spinal cord, either ascending or static, involving both halves of the cord, often over a considerable length, and appearing without previous neurological disease.”134 This pattern of involvement and progression can occur secondary to many different etiologies. Myelopathy is therefore not a true disease but a clinical syndrome with characteristic pattern of progression with a diversity of causes. In the past, spinal cord imaging was limited and did not offer the soft-tissue resolution now available with MRI, which can reveal intramedullary soft-tissue changes such as edema, low-grade gliosis, and microhemorrhage during early phases of myelitis. The advent of new MR imaging protocol and contrast agents has further assisted the diagnostic process. MRI provides a noninvasive method for identifying treatable conditions that may mimic ATM, such as disk herniation, abscesses, hematoma, and other compressive etiologies. Most of the ATMs regardless of etiology have similar appearances with MR imaging. During the acute phase, the MR study
Conditions Associated with Myelopathy
may appear normal in as many as half of the cases.135 Common abnormal MR findings in ATM include focal cord enlargement on T1-weighted imaging and poorly demarcated focal hyperintensities on T2-weighted imaging. 136 As the condition progresses, the region of T2-weighted hyperintensities enlarges in size. Due to the vast array of potential etiologies, only a few of the more common presentations of noncompressive myelopathy are discussed.
4.4.1 POSTINFECTIOUS AND POSTVACCINATION MYELITIS (TRANSVERSE MYELITIS) Exposure to infectious and antigenic agents in some individuals can cause acute CNS disease such as meningitis and encephalitis or stimulate an autoimmune cascade that results in compromise of neurological elements of the spinal cord. Acute transverse myelitis presents as rapid extremity weakness followed by flaccid paralysis and sensory loss with occasional sphincteric dysfunction. A history of infectious illness is found in 30 to 40% of patients within a few weeks prior to onset.137 Postinfectious and postvaccination autoimmune disorders tend to have a predilection for the white matter of the spinal cord. Collectively the autoimmune disorders are the most common cause for transverse myelitis. Though transverse myelitis may be caused by one of more than a dozen different etiological agents and conditions, the immune reaction, inflammatory response, pattern of tissue injury, and clinical presentation are similar. It has been proposed that transverse myelitis may occur due to an autoimmune response to a CNS antigen such as myelin basic protein,138 or due to the proinflammatory effects of circulating immune complexes.139 Because of the systemic autoimmune response, tissue compromise may not be limited to the spinal cord but may also involve the brain. Histopathological studies have demonstrated the following constellation of findings in the spinal cord: microhemorrhage, perivascular exudates, edema, and infiltration by inflammatory cells. Tissue necrosis and coalescing areas of demyelination are not uncommon. Any level of the spinal cord may be involved and involvement may not be limited to one region. However, the midthoracic spinal cord is frequently the level of initial involvement. It is of obvious importance that any antecedent history of infection or vaccination be considered. Generally, the development of spinal shock following an abrupt clinical onset indicates greater tissue damage and a less favorable recovery. If neurological improvement has not occurred within three months, further clinical recovery is unlikely.137 Routine blood assessments may be unremarkable, as the causative agent is often no longer present. The CSF may demonstrate mild lymphocytic pleocytosis, elevated protein levels, elevated IgG, or the presence of oligoclonal bands.
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4.4.2 INFECTION Spinal cord infection is most commonly viral. Viral infections generally have a predilection for the gray matter, often sparing white matter. This anatomical predilection helps to differentiate viral myelitis from other etiologies, as neoplastic or non-neoplastic spinal cord compression often initially involves the white matter. Poliomyelitis compromises the anterior horn cells leading to a lower motor neuron lesion, whereas herpes zoster infection compromises posterior horn cells leading to sensory abnormalities. 4.4.2.1 Tropical Spastic Paraparesis (Human T-Cell Lymphotrophic Virus I) Human T-cell lymphotrophic virus I (HTLV I), commonly referred to as tropical spastic paraparesis, is known to produce myelopathy and, unlike most viral presentations, may involve the white matter. HTLV I is a relatively rare disease often identified in individuals of Afro-Asian origin. HTLV I presents somewhat like multiple sclerosis (MS) although this condition is extremely rare in this ethnic group. The MR features are similar to those seen in MS. The clinical presentation is characterized by leg weakness, spastic paresis, ataxia, back pain, bladder dysfunction, and hyperreflexia. This infection has been reported in Japan and at higher prevalence in the Caribbean islands, particularly Jamaica. Its transmission is similar to that of human immunodeficiency virus (HIV), through blood products and semen. 4.4.2.2 Acquired Immune Deficiency Syndrome The human immunodeficiency virus produces myelopathy through two primary mechanisms: direct effects of the virus on the CNS and opportunistic infections secondary to immunosuppression. Myelopathy commonly coexists with encephalopathy. Compressive myelopathy may also occur secondary to acquired immunodeficiency syndrome (AIDS) from an expanding infectious abscess or neoplasm. AIDS dementia complex, vacuolar myelopathy, aseptic meningitis, and possibly a form of Guillain–Barré syndrome are neurologic disorders linked directly to fullblown AIDS. Spinal cord involvement in AIDS is characteristically associated with progressive spastic paraparesis combined with the presentation of peripheral neuropathy. The majority of symptoms are associated with degeneration of the posterolateral columns. Often encountered are varying degrees of extremity dysesthesia, pyramidal weakness, and upgoing toes to plantar stimulation. This presentation is somewhat similar to that of subacute combined degeneration. Memory loss, ataxia, aphasia, and progressive paraparesis with rapid deterioration and death are the direct neurological manifestations of advancing HIV infection. AIDS-related CNS syndromes or indirect infections that may further compound AIDS myelopathy
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include cytomegalovirus (CMV), progressive multifocal leukoencephalopathy (PML), and herpes simplex virus (HSV). 4.4.2.3 Lyme Disease Lyme disease has been recognized as a cause for a variety of neurological presentations including myelopathy.140 The infective organism is the spirochete Borrelia burgdorferi and the vector is the ixodid tick. The disease is generally not fatal but can lead to significant disability. The cutaneous stigma of the disorder is a characteristic erythematous rash, with central clearing, erythema migrans, extending out from the center of the initial wound. One of the most common clinical manifestations is facial weakness.141 Three stages of Lyme disease have been categorized. The first stage begins after the initial infection and is characterized by flu-like symptoms and slowly expanding skin lesions referred to as erythema migrans. The second stage generally begins within a few weeks to a few months and may involve joint pain and neurological and heart complications. On rare occasions, acute transverse myelitis may develop during the second stage.142 Other signs of neurological involvement include meningitis, cranial neuritis, radiculitis, and/or peripheral neuropathy.142 The condition may occur in the form of a fluctuating meningoencephalitis with intermittent bouts of headache, nausea, stiff neck, and vomiting. The third stage may begin within a few months to years after initial infectious insult. The infected person may complain of polyarthralgia although the spinal cord signs and symptoms may still predominate. Encephalopathy and encephalomyelitis may occur during the late stages of Lyme disease. A demyelinating disorder resembling multiple sclerosis and a variety of neuropsychiatric syndromes have also been identified during the third stage of involvement.143 CSF samples should be taken to detect presence of intrathecal B. burgdorferi antibodies. Serum Lyme tests performed are: the western blot and enzyme linked immunosorbent assay (ELISA) tests. 4.4.2.4 Tabes Dorsalis (Syphilis) Another spirochete that can invade the CNS is Treponema pallidum, which causes syphilis. This organism can seed the CNS during the second stage of syphilis. The third stage is characterized by meningovascular pathology, then by parenchymal manifestations. The neurological involvement in the second and third stages is referred to as neurosyphilis. Clinical syndromes associated with the spinal cord are syphilitic meningomyelitis, syphilitic pachymeningitis, syphilitic spastic paraplegia, and syphilitic myotrophy.144 In the later stages of syphilis, SCI includes degeneration and atrophy of the dorsal funiculi of the cord. This presentation is referred to as tabes dorsalis and represents the parenchymal form of the disease. Tabes dorsalis
has become rare due to improved epidemiological control and effective treatment of syphilis. Tabes may occur within 10 to 20 years after the initial infection. Histologically, tabes dorsalis is characterized by leptomeningeal thickening, posterior column gliosis, and insult to the posterior nerve roots.144 Tabes dorsalis is clinically characterized by lancing leg pain, dense lower extremity sensory loss, impotence, areflexia, muscle hypotonia, bladder hypotonia incontinence, and neuropathic arthropathy (Charcot’s joints). During the late stages of tabes, the individual may have total loss of lower extremity position sense. This typically results in a compensatory ataxic-high steppage gait. The individual may be found to frequently rely on visual cues and may frequently gaze downward while walking. During the latter stages of the disease, the Romberg test is commonly positive to the damage to the dorsal columns. The Romberg test is an effective measure of posterior column function. Most patients with tabes dorsalis will present with an Argyll Robertson pupil (pupillary constriction with accommodation but not with light stimuli) and varying degrees of optic atrophy. Cerebrospinal fluid studies are abnormal in most cases of active disease, demonstrating the presence of syphilitic reagin and antibodies. An increase in CSF lymphocytes, gamma globulin, and protein will generally be evident. Normal CSF glucose levels are expected. Blood testing can be performed to assess for reagin and treponemal antibodies via VDRL and FTA-ABS.
4.4.3 SPINAL ARACHNOIDITIS (ADHESIVE ARACHNOIDITIS) Spinal arachnoiditis is a relatively uncommon disorder characterized by inflammation, fibrosis, and thickening of the leptomeninges resulting in nerve root and/or spinal cord signs and symptoms.145 The clinical presentation is usually that of a multifocal disease process. Adhesive arachnoiditis is not an isolated entity but the result of a broad spectrum of pathologic and physiologic conditions. Adhesions may form between the arachnoid and the dura secondary to connective tissue proliferation. Fibroproliferative changes may also be more circumscribed extending along the neuraxis.146 Severe fibroproliferation and membranous thickening can contribute to spinal cord compression and mimic the clinical presentation of a spinal cord tumor. This generally occurs with greater prevalence in thoracic spine. The patient with arachnoiditis develops a progressive myelopathy with spasticity and ataxia. Syringomyelia secondary to arachnoid adhesions (SSAA) may also contribute to the development of myelopathy. Thick arachnoid adhesions can occlude the subarachnoid space, altering CSF dynamics and facilitating the development of syringomyelia and/or extramedullary arachnoid cysts.147 The majority of SSAA are found in the thoracic cord.147
Conditions Associated with Myelopathy
The causes for fibroproliferation between the arachnoid and dural membranes are numerous and include infections such as syphilis and tuberculosis, nontraumatic hemorrhage, trauma, and spinal surgery. Arachnoiditis may also occur secondary to injections of substances into the subarachnoid space. Arachnoiditis may be a contributing factor to spinal pain in the failed back syndrome (FBS). Spinal arachnoiditis is often associated with pain due to pain fibers within the dura, and the recurrent cycle of microstretch injury occurring between the dural and arachnoid membranes. The vascular supply of nerve roots is abundant within the subarachnoid space, rendering the nerve roots vulnerable to secondary compromise from arachnoid adhesions.148 Postoperative myelographic findings of arachnoiditis include blunting of nerve root sleeves, nerve root fusion, and irregularities around the thecal margins.149 The MR features of arachnoiditis include intradural fibrosis, nodular cordlike intradural mass, nerve root adherence, nerve root retraction, CSF block, and spinal cord compression.150
4.4.4 TOXIC INSULT In most cases of toxic myelitis there is systemic involvement with widespread injury to the viscera. The signs and symptoms of myelitis may be overshadowed due to the magnitude of the overall presentation. Myeloneuropathic symptoms have been reported with exposure to various toxic agents. Common examples include methotrexate and cis-platinum, both used in chemotherapy; orthocresyl phosphate and the industrial solvent, Chymopapain, used in chemonucleolysis; anesthetic and myelographic agents used in the 1960s and ’70s; and chronic nitrous oxide inhalation.
4.4.5 MULTIPLE SCLEROSIS Multiple sclerosis is one of the most frequent causes of asymmetric paraparesis with sensory ataxia and hyperreflexia. It is a major cause of spinal cord disease in North America and Europe, with about 1.1 million patients affected worldwide and an estimated 400,000 affected in the U.S.151 MS is twice as common in women and is generally first diagnosed when patients are in their 20s or 30s. Early during the course of the disease, the clinical presentation may be similar to spinal cord compression. It then evolves becoming clinically consistent with multifocal CNS pathology. Five categories of MS are recognized in clinical practice. The most common form is relapsing-remitting (RR). These patients have periods of exacerbation and remission in the course of the disease. This form affects the majority of MS patients. With each exacerbation, the disease may progressively intensify; however, the disease does not progress during periods of remission. In the remission
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phase, the patients’ symptoms may completely disappear or substantially reduce. The next form is primary progressive (PP). These patients have a steady progression of the disease with occasional rapid decline. Although the speed of decline may slow down briefly, there are no periods of remission. The secondary progressive (SP) form is thought to develop from the relapsing-remitting type of MS. These patients begin with years of on-and-off symptoms only to rapidly progress on a path of continuous decline. Progressive relapsing describes the MS patient with steady neurological decline and episodes of rapid progression. Benign MS describes a nonprogressive form of the disease that results in minimal disability for the patient. Sensory loss and dysesthesias are often the first clinical signs. Progression of the disease is variable with frequent relapses and remissions. It is characterized by recurrent sensory and motor deficits that cannot be explained by an isolated ablative CNS lesion. The most common presentations include extremity numbness, weakness, monocular visual loss, diplopia, ataxia, and nystagmus. The presentations do not typically occur simultaneously. Multiple sclerosis can compromise the spinal cord, brainstem, cerebrum, cerebellum, and optic nerves, with the spinal cord being a common site of affliction. The spinal cord was considered the site of injury responsible for the initial presentation in over one half of patients evaluated in one study.152 Plaque occurs more often in the cervical cord than other levels,153 and tends to occur within the region of the lateral columns (Figure 4.21).154 Neural compromise is primarily due to demyelination, although some degree of axonal compromise has also been identified.155 Many patients with spinal evidence of MS have involvement of other areas of the CNS. The most common region of involvement is the periventricular area of the brain. Sclerotic foci are not always visible to traditional neuroimaging during the earliest stages of the disease. In some cases, the lesions are incidentally discovered during neuroimaging. The first clinical episode may occur without warning. Eventually the condition progresses with the patient becoming handicapped. The diagnosis of MS should not be made without MRI evidence of white matter plaques and abnormally delayed brainstem-evoked and visual-evoked potentials, along with a CSF study demonstrating oligoclonal bands. Lyme disease, B12 deficiency, HTLV 1, and AIDS should be considered in the differential diagnosis of MS.
4.4.6 RADIATION MYELOPATHY Radiation has been identified as a potential source of CNS injury and myelopathy. The spinal cord is exposed to potentially detrimental radiation effects when it lies within the center of the field of radiation during radiation treatment of carcinoma. Radiation-induced myelopathy is
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A
B
FIGURE 4.21 (A) Abnormal linear longitudinally oriented high signal intensity within the cervical spinal cord extending from C2 through C4–C5, representing a demyelinative plaque in a patient with multiple sclerosis. (Parasagittal gradient echo T2-weighted image midline sagittal section.) (B) Abnormally bright T2-weighted signal at the level of the C4 vertebral body within the left side of the spinal cord, compatible with a demyelinative plaque from multiple sclerosis. (Axial gradient echo T2-weighted image.) (Courtesy of Ronald Landau, M.D.)
associated with long-term effects of radiation damage to the spinal cord typically following cancer treatment. Necrosis of tissue within the CNS in the region of maximal radiation exposure occurs slowly and is cumulative, occurring over a few months to five years. Prolonged survival with cancer treatments increases the possibility of experiencing symptoms associated with radiation myelopathy. In some cases, the symptoms of radiation myelopathy can be similar to those of a transverse myelopathy. The neurological decline and damage from progressive radiation myelopathy is usually irreversible.156 The most common reason for radiation exposure is the treatment of cancer. Radiation myelopathy is becoming more prevalent due to the aging population, early detection of cancer, and advancement of nonsurgical treatment of cancer. Radiation myelopathy has been classified into four general categories: transient myelopathy, chronic progressive radiation myelopathy, lower motor neuron dysfunction, and acute transverse myelopathy. Transient myelopathy is characterized by positive L’hermitte’s sign and subjective sensory complaints. The presentation is usually dominated by spinothalamic symptoms.141 The individual may perceive temperature aberrations involving the extremities. There are no objective neurologic deficits. This has been estimated to occur with approximately 15% frequency in the treatment of cancer with standard mantle irradiation.157 The risk for transient radiation myelopathy increases with the total dosage applied. Based on the clinical presentation, the radiation damage is likely limited to reversible demyelination of white matter within the ascending tracts of the spinal cord.
Chronic progressive radiation myelopathy is the most common form of severe irradiation induced myelopathy. The myelopathic presentation is often diverse beginning with intermittent subjective disturbances but eventually progressing after a latent period to involve spastic lower extremity paresis and sphincter disturbances. An incomplete hemi-cord presentation may occur. Progressive neurological deterioration usually develops over a few months to a few years. Spontaneous recovery is not common. MRI has been beneficial for diagnosis of this type of iatrogenic myelopathy, demonstrating either cord swelling early in development or severe cord atrophy.158,159 The third classification of radiation myelopathy, the lower motor neuron presentation, is rare but may occur with greater spinal cord damage. The stage is characterized by painless amyotrophy and weakness predominately involving the lower extremities. This stage often develops a few months after intense radiation exposure to the spinal cord.160 There is generally sparing of sensory abnormalities and sphincter disturbances. The muscle atrophy, fasciculations, and weakness are similar to those seen with motor neuron disease, although there are characteristically no upper motor neuron findings with radiation myelopathy. The fourth classification, radiation-induced acute transverse myelitis, is extremely rare and is associated with the acute development of paraplegia or quadriplegia following irradiation. The ATM occurs secondary to radiation-induced damage of the intrinsic spinal cord blood supply with resultant hemorrhage and related parenchymal damage.161
Conditions Associated with Myelopathy
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4.4.7 DECOMPRESSION SICKNESS
4.4.9.1 Subacute Combined Degeneration
Injury to the spinal cord can occur secondary to rapid alteration of atmospheric pressure. The greatest exposure to this type of barotrauma occurs during scuba diving.162 Rapid decompression leads to intravascular coalescing of nitrogen bubbles with subsequent occlusion of spinal cord blood supply. This contributes to infarction following embolization and petechial hemorrhage. The signs and symptoms tend to occur abruptly consistent with a vascular etiology. Spinal cord injury occurs with greater prevalence within the thoracic region. MRI has proved to be reliable in the detection of pathologic changes of spinal cord decompression sickness that were previously undetectable by other neuroimaging methods and also has proved to be useful in the follow-up during therapeutic hyperbaric recompressions.163 The rise in popularity of recreational scuba diving in North America and the Caribbean Islands has increased the incidence of decompression injury. Immediate hyperbaric chamber recompression is essential to avoid further neurological damage.164
Subacute combined degeneration (SCD) is clinically characterized by progressive sensory disturbances of the lower extremities. Distal peripheral nerve compromise usually precedes damage to the spinal cord.141 The white matter of the lateral and posterior columns undergoes degenerative and demyelinative changes. Similar changes take place in the brain. The peripheral nerves may also demonstrate clinical and electrophysiologic signs of demyelination and axonal degeneration.166 The early clinical manifestations of SCD include distal extremity paresthesia, reduced kinesthesia and vibration sense, and extremity weakness. One of the first clinical manifestations of spinal cord involvement is upgoing toes to plantar stimulation (positive Babinski). Later presentations may include a combined spastic–ataxic gait, upgoing toes to plantar stimulation, and a positive Romberg sign. In severe cases, paraplegia may occur. Neuropsychiatric findings may also develop along with other cerebral deficits including visual deficits.167 The search for B12 deficiency should be included in the workup of suspected demyelinating disorders. Erythrocyte macrocytosis may precede the neurological manifestations of the disorder. The condition should be suspected with mean corpuscular volume (MCV) exceeding 95 µm3 on a CBC (normal 82 to 92 µm3). Serum cobalamin levels can be normal despite the presence of tissue deficiency.168 As many as 25% of patients with CNS damage due to cobalamin deficiency do not show hematological abnormalities.141 Cobalamin is a necessary cofactor in the conversion of methymalonic acid and homocysteine; therefore, serum elevation of these levels can serve as an indicator of tissue cobalamin deficiency. Early diagnosis is critical to ensure timely intervention prior to irreversible neurological injury. The condition should be excluded in all patients with myelopathy and in those patients who present with peripheral extremity paresthesia and absent distal MSRs. The nutritional myelopathies have generally been classified into three categories: (1) posterolateral myelopathy manifesting primarily as an ataxic syndrome, (2) anterolateral myelopathy presenting as a spastic syndrome, and (3) combined ataxia and spastic syndrome.169
4.4.8 ELECTRICAL INJURY Electrical injury from a lightning strike or high-voltage line often results in severe acute CNS pathology with development of spinal cord and brain edema. The current sufficient to cause CNS damage may be fatal. The onset of signs and symptoms may be acute or delayed. The most common site of injury is the cervical spinal cord because of the frequency of hand contact in electrical injury. The current travels from one hand to the other, passing through the cervical region. This can cause severe cervical injury leading to quadriparesis.165 Acute electrical injury may occur secondary to ischemia or directly from heat-related insult to the tissues. Gray and white matter regions can be injured. After electrical injury, focal regions of spinal cord may develop myelomalacia and gliosis with residual symptoms. On occasion, electrical injury to the spinal cord may result in a delayed progressive spinal cord syndrome mimicking the presentation of amyotrophic lateral sclerosis (ALS).165
4.4.9 METABOLIC
AND
NUTRITIONAL MYELOPATHIES
Metabolic and nutritional myelopathies may develop secondary to extreme vitamin deficiencies or liver disease. One of the most common disorders within this category is subacute combined degeneration occurring secondary to B12 (cobalamin) deficiency. It is always important to consider this easily treatable disorder in the evaluation of patients with myelopathy. Causes of the condition include partial gastric resection, blind loop syndrome, and Crohn’s disease or other disorders of the gastrointestinal tract. Strict vegetarians are more prone to develop B12 deficiency.
4.4.10 AUTOIMMUNE MYELOPATHY The spinal cord has a rich blood supply and therefore is susceptible to a variety of disorders that fall into the autoimmune category. Some of the more common autoimmune disorders with potential to afflict the spinal cord are Sjögren’s syndrome, systemic lupus erythematosus, rheumatoid arthritis, and Wegener’s granulomatosis. In most cases there is clinical and/or laboratory evidence of systemic vasculitis.
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4.4.11 PARANEOPLASTIC MYELOPATHY
4.4.13 MOTOR NEURON DISEASE
Paraneoplastic syndromes can afflict any portion of the nervous system. Paraneoplastic myelopathy refers to spinal cord pathology, in individuals with malignancy, due to a poorly defined remote effect of the cancer at the level of the cord. The development of a paraneoplastic syndrome is a rare complication of cancer. It may present in individuals who fall into one of three general categories: (1) individuals not known to have cancer (most common), (2) individuals with known cancer, and (3) individuals in remission after treatment of cancer. Paraneoplastic myelopathy should be considered in cancer patients who develop clinical features of myelopathy in the absence of other readily identifiable etiologies. In as many as 50% of cases, signs and symptoms associated with the paraneoplastic syndrome precede the recognition and diagnosis of cancer.110 The etiology of most paraneoplastic syndromes is unknown but the following mechanisms have been proposed: toxic substance release by tumor,170,171 competition for vital nutrients,172 opportunistic viral infection,173 and an immunological mechanism initiated by the exposure of onconeural antigens,174 which has most recently been considered as the primary contributing factor. Well-identified antibodies associated with paraneoplastic syndromes include Anti-Yo, Anti-Hu, Anti-Ri, Anti-retinol, AntiNMJ, and Hodgkins.110 The condition is clinically characterized by a rapidly developing ascending sensorimotor myelopathy. The course is typically aggressive and rapidly progressive, often resulting in death within a few months.175 Pathological examination of the cord has demonstrated relatively symmetric necrosis of gray and white matter176 involving both myelin and axons.175 An initial predilection for the thoracic spinal cord175 may be due to the large area of this region and greater exposure to the offending stimuli.
“The hallmark of motor neuron disease is wasting and weakness in the presence of preserved or brisk reflexes.”141 Motor neuron diseases are associated with degeneration of the ventral horn cells and the upper motor neurons. The clinical presentation may be varied, with some individuals manifesting with an overwhelming lower motor neuron presentation or a predominant upper motor neuron presentation or a mix of upper and lower motor neuron features.
4.4.12 DEGENERATIVE NEURONAL DISORDERS Several disorders associated with chronic progressive neuronal degeneration may involve the spinal cord. These conditions should be considered in the differential workup of the patient suspected of having significant spinal cord compression. Some of the disorders that fall within this category are genetic, requiring that a careful family history be obtained. If the patient has a genetic disorder, there may be an early history of motor involvement with clumsiness and/or incoordination. The clinical presentations of these disorders are generally similar and usually include an absence of pain during early development. There may be early development of a high foot arch (pes cavus) and scoliosis. These signs may precede progressive muscular signs of symptoms. The patient may develop peripheral nerve and brain involvement.
4.4.13.1 Amyotrophic Lateral Sclerosis Amyotrophic lateral sclerosis (ALS) is clinically characterized by coexistent upper and lower motor neuron findings. ALS is the most common motor neuron disease. Approximately 5% of ALS cases are inherited as an autosomal trait.177 The hands are usually affected first, demonstrating weakness, cramping, atrophy, and fasciculations. This is commonly followed by a similar pattern of muscular involvement of the shoulder girdle. Insidious onset lower extremity spastic paraparesis may begin to parallel upper extremity progression. The clinical triad of ALS is (1) atrophy of hands and forearm, (2) mild lower extremity spasticity, and (3) generalized hyperreflexia in the absence of sensory abnormalities.177 The smallest muscles of the distal extremities are typically the first to be associated with physical disability. In the case of the lower extremities this may manifest as early dorsiflexion fatigue or foot drop. During the evolution of ALS, bulbar symptoms set in, characterized by dysarthria, dysphagia, and dysphonia. The tongue may present with atrophic changes in combination with fasciculations. A spastic bulbar paralysis (pseudobulbar palsy) may develop. During the course of the disease evaluation, the lower extremity presentation may simulate cervical spondylotic myelopathy (CSM); here, the important differential consideration is the segmental sensory deficit often associated with CSM-related radiculopathy vs. the preserved or facilitated MSR accompanying weakness in all but the late stages of ALS. With ALS, muscular fasciculations will not be limited to segmentally innervated muscles (myotome) but will occur in a diffuse fashion. Rarely, ALS may initially present like a segmental lesion (radiculopathy) with focal limb atrophy and weakness. Needle electromyographic and nerve conduction assessment provides overwhelming evidence of widespread motor neuronal involvement and is therefore a helpful test. The disease is rapidly progressive, typically leading to death within 2 to 5 years. 4.4.13.2 Spinal Muscular Atrophy Spinal muscular atrophy (SMA) is characterized by progressive muscle weakness due to a loss of motor neurons within the spinal cord and nuclei of the brainstem. There
Conditions Associated with Myelopathy
are many different classifications of SMA, each based on various inclusionary criteria such as age of onset, method of inheritance, clinical presentation, electrodiagnostic findings, degree of physical impairment, and life expectancy. The three basic categories of infantile/juvenile SMA are SMA I, commonly referred to Werdnig–Hoffman syndrome; type II; and type III, often referred to as Kugelberg–Welander disease. Type I SMA usually manifests by 5 years of age and results in profound physical impairment and a life span often less than 2 years. SMA type II is a milder more intermediate form with a common age of onset ranging from 3 to 24 months. Some individuals with SMA type II will reach adulthood; however, their symptoms are usually severe and they usually require assisted ambulation. Type III has the best prognosis and is often characterized by a normal life span. The signs and symptoms of SMA type III usually present between the ages of 3 and 30. An adult form of SMA is categorized as type IV, which is usually chronic in nature and often manifests between 20 and 60 years of age. Advances in genetic mapping will help improve the diagnosis and classification of the various types of this disorder. SMA remains one of the most common autosomal recessive genetic disorders resulting in infant death. 4.4.13.3 Kennedy’s Disease Kennedy’s disease is a rare X-linked, recessive, bulbospinal neuronopathy. It usually manifests between the third and fourth decades of life. Kennedy’s disease is characterized by adult-onset muscle weakness typically occurring in a limb-girdle distribution. The absence of upper motor neuron findings helps to differentiate this disorder from early to intermediate stages of ALS. The first complaints of impaired muscle performance may involve difficulty climbing stairs, rising from a sitting position, and performing overhead activities. Other distinguishing clinical features of Kennedy’s disease include: (1) facial weakness, (2) facial twitching or fasiculations, (3) tongue paresis and atrophy, (4) fine postural hand tremor, (5) hypo- or areflexia, and (6) absent or low-amplitude sensory nerve action potentials.178 4.4.13.4 Familial Spastic Paraplegia Familial spastic paraplegia represents a subtype of motor neuron disease. It is relatively rare and may be inherited as a dominant or recessive gene. It more commonly affects men. It tends to manifest between 5 and 17 years of age. The classic form of familial spastic paraplegia is associated with mild pyramidal pathway degeneration, usually limited to Betz cells, other cortical motor neurons, and the corticospinal spinal tracts. Variant forms of spastic paraplegia may be associated with optic changes, polyneuropathy, extra-pyramidal disease, and cerebellar signs and
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symptoms. The condition is typically characterized by spastic paraparesis rather than paraplegia, afflicting the legs more often than the arms. The disease often develops with the onset of leg stiffness secondary to spasticity. Individuals usually have adequate muscular power, although they are unable to efficiently ambulate. The spasticity predominantly involves the extensor muscles, resulting in rigid legs, plantar flexed feet, and a tendency toward hip abduction. The patient has a challenge walking because both legs are typically involved. The individuals often appear as though they are going to topple forward. Unlike compensatory steppage gait of foot drop, the degree of extensor stiffness renders it more difficult to clear the foot during the swing phase of gait. Subsequently, the legs often appear to be dragged. The extremity muscle stretch response is often brisk but may be masked due to the severity of muscle hypertonicity/spasticity. Babinski response is typically positive. The individual may develop blisters or callous formation along the tip of the great toe due to the prominent extensor response while ambulating. Sensory findings are usually normal, although there may be a mild diminution of sensory perception as a late feature of the disease, which may be associated with aging. Superficial abdominal reflexes usually remain intact and bowel and bladder functions preserved, in contrast with spastic paraparesis associated with spondylotic myelopathy or other compressive etiologies. Familial spastic paraparesis is not associated with a reduced life span, although it may progress, disabling the individual, requiring him or her to become wheelchair bound later in life. Many individuals are able to perform most of the normal activities of daily living with some difficulty.
4.5 CONGENITAL SPINAL ANOMALIES There are numerous congenital anomalies of the spine and spinal cord. The diversity of congenital conditions affecting the spine has made it difficult to classify the disorders in a logical (concise) framework. The majority of congenital anomalies of the spinal cord are due to defects in neural tube closure or development and are collectively referred to as spinal dysraphic disorders. Spinal dysraphism is relatively common in some populations in North America. For example, myelomeningocele occurs with a frequency of 1 to 2 cases per 1000 live births.179 Neural tube defects are generally categorized by location. They can be designated by location of occurrence as cranial or caudal types, or a combination of both regions. The most commonly discussed neural tube defects include anencephaly, craniorachischisis, encephalocele, myelomeningocele, and meningocele. This section will only cover the anomalies which primarily affect the spine and spinal cord. Spinal malformations can be divided into three primary categories: (1) spina bifida aperta, (2) occult spinal dysraphism, and (3) caudal spinal anomalies.180 The Chiari
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
malformations are included in the following discussion of dysraphic anomalies, because of the associated spinal manifestations.
4.5.1 SPINA BIFIDA APERTA: MYELOMENINGOCELE Spina bifida aperta is a birth defect that results in portions of the nervous system and/or meninges protruding through an unclosed opening in the distal spine. The term meningocele refers to meningeal exposure without accompanying neural tissues. Myelomeningocele represents a more significant defect given that neural tissues meninges protrude above the border of the skin in the lower spine. Myelomeningocele represents one of the most common birth defects involving the spine and neural elements. It is obvious at birth and is characterized by the herniation of a malformed spinal cord defect, involving the bony spinal canal and overlying skin. A myelomeningocele usually results in long-term disability. The exact etiology of the myelodysplasia is not known. Myelomeningocele may occur due to failure of the neural tube to close or due to reopening of the neural tube during gestational development. Fetal ultrasound at 8 to 22 weeks can be helpful in the assessment of the intact spinal column. The intrauterine diagnosis of myelomeningocele can usually be made between 16 and 21 weeks gestation with a level II (highresolution) ultrasound imaging study. A serum maternal triple screen procedure comprised of measurements of human chorionic gonadotropin, estriol, and alpha fetoprotein can help identify risk for neural tube defects based on lab criteria. High levels of alpha-fetoprotein during triple screen testing are associated with a greater likelihood of a neural tube defect. False positive lab findings do occur. The majority of infants with lumbosacral myelomeningocele have an associated Chiari II malformation. Many infants born with myelomeningocele also present with hydrocephalus, which may develop after birth. Other associated deformities include scoliosis, clubfeet, extremity contractures, and propensity for hip dislocation. Surgical closure of the defect is attempted usually within 48 hours of birth. There are many postsurgical complications, such as spinal cord tethering, infection, and spinal cord ischemia. Bladder and bowel incontinence or other difficulties almost always require the child to have an assisted urinary and bowel management program. Ambulation is generally possible only if the defect occurs below the S1 level.
secondary to tethering of the spinal cord. Spina bifida occulta may be associated with a hypertrophied filum terminale, short filum terminale, neuroenteric cyst, diastomyelia, and spinal lipomas. There are generally no visible cystic masses or exposed neural tissue. Bony spina bifida occulta at the L5 or S1 level is a relatively common radiologic finding in children and adults. It is the mildest form of spinal dysraphism and is not directly associated with significant neurologic signs or symptoms. A number of cutaneous manifestations may suggest spinal dysraphism. These cutaneous abnormalities generally lie over the midline of the spine and are often found in the lumbosacral region. The focal “hair patch” is usually somewhat symmetric, often diamond shaped lying between the midline of the lower lumbar or thoracic regions. Cutaneous changes overlying the cervical or thoracic region tend to involve smaller patches of silky hair rather than thick, coarse hair like that seen in the lumbar region. Cutaneous stigmata may not lie directly over a spinal malformation. The underlying anomaly may occur anywhere along the spine. Subcutaneous lipomas lying at or near the midline of the spine suggest the possibility of an underlying intradural lipoma. It is prudent to ask patients if they have ever had any cutaneous lesions removed from the spinal region. Cutaneous hemangiomas are more common in the lumbosacral region and are associated with increased frequency of underlying spinal dysraphism. A subcutaneous sinus should also raise the index of suspicion for dysraphism. When a child with spinal dysraphism begins to walk, there are often severe gait abnormalities, sometimes associated with congenital leg length inequality. Myelopathy is often associated with a combination of upper and lower neuron findings. The sensory loss is usually patchy. The characteristic clinical finding is a high arch or pes cavus foot with claw toes. The child usually develops an abnormal voiding pattern with frequent urinary tract infections. If there are increasing episodes of urinary incontinence in an otherwise toilet-trained child, the possibility of spinal dysraphism should be investigated. The most characteristic finding on MRI is a hypertrophied filum terminale, which may cause tethering of the spinal cord. When the conus medullaris lies at the level of L2-3 or below, the possibility of a tethered cord syndrome should be raised. The following are examples of occult spinal dysraphism: split cord malformation, dorsal dermal sinus, and neuroenteric cyst, all of which are discussed further. 4.5.2.1 Split Cord Malformation
4.5.2 OCCULT SPINAL DYSRAPHISM Developmental defects of the spine and spinal cord with intact covering of skin are referred to as occult spinal dysraphism. Overlying cutaneous signs may be subtle. Symptoms may not develop until later childhood or adulthood
Split cord malformation refers to congenital separation of the spinal cord into two halves, which can extend for varying lengths. Pang et al.181 proposed that the term split cord malformation (SCM) be applied to double cord syndromes. SCM can occur anywhere along the spine and
Conditions Associated with Myelopathy
can be placed into one of two subcategories, which are type (I) diastematomyelia and type (II) diplomyelia.1 Diastematomyelia represents a rare form of occult spinal dysraphism. Diastematomyelia refers to splitting of the spinal cord, with each half transfixed within the sagittal plane by a dural sheathed septum or spur-like projection comprised of fibrous, bony, or fibrocartilaginous tissue. The septal cleft occurs between the spinal levels of T9 and S1 in 85% of cases.182 Splitting of the spinal cord may be partial or complete. There may be multiple septa. Near the level of the septa, each hemicord is wrapped with its own dura, which coalesce to form one dural tube above and below the septa. The overall diameter of the spinal canal at the level of the septa tends to be reduced, although the transverse diameter tends to be greater than expected. The increased interpedicular distance may be helpful in the identification of the level of diastematomyelia. At the level of diastematomyelia there may be an absent disk or anomalous vertebral development such as hemivertebrae, block vertebrae, or butterfly vertebrae. Scoliotic deformities may also be seen. Diplomyelia refers to two separate spinal cords residing within one dural sac with a nonrigid fibrous median septal barrier. In diplomyelia, each half of the spinal cord has paired nerve roots at each level, whereas in diastematomyelia, each half of the spinal cord has only laterally positioned nerve roots. With diplomyelia there are usually no associated bony abnormalities at the level of the split, but there may be spina bifida occulta in the lumbosacral region. Numerous theories have been proposed relative to the etiology of the split cord syndrome. In 1992, Pang et al.181 proposed a unified theory of embryogenesis, stating that all variants of split cord malformation occur due to the same basic mechanism, which involves the formation of adhesions between the ectoderm and endoderm, the development of an accessory neuroenteric canal, and a sequelae which results in bisection of the developing notochord with the formation of two hemineural plates. Subsequently, diastematomyelia and diplomyelia likely represent varying degrees of the same embryologic abnormality rather than representing two completely distinct entities. Cutaneous stigmata may overlie the region of split cord malformation. Spinal cutaneous stigmata are found over the spine in 50 to 75% of patients with diastematomyelia.183 Cutaneous manifestations may involve a region of abnormal pigmentation, hypertrichosis (tuft of hair), subcutaneous lipoma, dermal sinus, or cutaneous dimpling. Hypertrichosis is one of the more common cutaneous findings. Additionally, neuroenteric cysts may accompany a split cord syndrome. Asymptomatic individuals may never develop associated signs or symptoms. Patients with diastematomyelia may present with scoliosis, a neurogenic bladder, gait impairment, muscular atrophy, varying degrees of spastic
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paraparesis and sphincter control. There may be increased back pain and other signs and symptoms with physical exertion secondary to limited movement of the spine with a septum, particularly during anteflexion. Signs and symptoms may develop after an injury such as a fall. Infants and children with SCM are often admitted to the hospital with a constellation of neuromuscular signs and symptoms, which include motor weakness, sensory and deep tendon reflex changes. Clinical signs may include pes cavus (neurogenic high arch) with claw deformation of the toes. Clubfoot occurs in almost half of all individuals with diastematomyelia.184 Abnormal urodynamic changes with low pressure hyperreflexia is evident in a large percentage of patients.185 Radiographic assessment of the patient with a split cord syndrome may reveal increased interpedicular distance, the actual septum, vertebral body malformations, and spina bifida. MR imaging often reveals the septa with clear cord separation, and is extremely valuable for detecting an associated syringomyelic cavity and low-lying conus. An MRI CNS survey should be performed on patients with SCM to evaluate the entire spinal cord and brain for the presence of additional congenital malformations. CT may be diagnostically advantageous if there is a severe scoliosis and may be done in conjunction with MR imaging. 4.5.2.2 Spinal (Dorsal) Dermal Sinus A dermal sinus refers to a midline tract arising from the skin surface near the spine, lined with epithelium, and coursing in a subdermal fashion. It arises from a developmental neural tube defect. It may arise from failure of the cutaneous ectoderm to separate from the neuro-ectoderm during embryonic closure of the neural tube.186 The dermal sinus usually occurs at one or both ends of the neural tube, often involving the lumbosacral region, although it can occur anywhere along the spine or occiput. The spinal sinus tract characteristically courses in a cephalad (cranialward) direction, helping to differentiate it from other forms of dermal pathology. The dermal sinus is usually identified during early infancy or childhood, although may initially be identified later in life. The dermal sinus is typically small in diameter, being 1 to 2 mm. The cutaneous opening of the sinus (ostium) may be surrounded by cutaneous stigmata such as hyperpigmentation, post-wine discoloration, hairy nevus, capillary angioma, dimpling of the skin, or patch of hair. A dimpling presentation is more common at the sacral region. A dermal sinus may terminate at varying subcutaneous depths. It may extend over a significant distance, terminating several spinal segments away from the cutaneous ostium. The neural (ectoderma) level involved often corresponds to the dermatomal level of the cutaneous defect.187 A dermal sinus can reach varying depths, ending
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
within extraspinal or intraspinal tissues. The sinus tract may reach or attach to the dura, enter the subdural or subarachnoid space, or attach to neural elements. A dermal sinus may extend to the dural tube through bony defects or by traversing around normal vertebrae. A focal region of widening along the course of a dermal tract is referred to as an epidermoid cyst if lined with stratified squamous epithelium, or a dermoid cyst if lined with dermis containing skin appendages such as sebaceous glands and hair follicles. Epidermoid cysts are very uncommon, accounting for between 0.5 and 1.0% of all spinal tumors and up to 10% of intraspinal tumors in children.188 Epidermoid cysts may be acquired or congenital. Congenital epidermoid cysts are more commonly found in the region of the conus or cauda equina.189 Acquired epidermoid cysts are more often found in the lumbar region,190 and may occur as a late complication of lumbar puncture191 with seeding of a distal region with epidermal cells. The mass effects of a dermoid or epidermoid tumor may contribute to symptoms. The dermal sinus often appears benign and is asymptomatic until an infection is acquired, which can lead to severe consequences such as meningitis, peri-thecal abscess, or intrathecal abscess if there is dural or subdural extension of the sinus tract. A deep infection may occur in the absence of superficial (cutaneous) signs of infection. Recurrent bacterial or chemical meningitis may occur.192 Intrathecal extension may present as a tethered spinal cord with intradural tumor. A sinus tract should never be probed or injected with contrast media. Physical manipulation of the sinus tract opening may help identify the course of the sinus. A sinus traversing in a caudal direction is less likely to open to the dura than a sinus tract traversing cranialward and may represent a pilonidal sinus, which is acquired. Physical assessment should include careful inspection for pus or purulent discharge at the sinus opening. Progressive infection could cause irritation and/or infection within the tract and involve tissues at the distal portion of the tract, resulting in aseptic or septic meningitis. The examination should be focused on anal and urinary sphincteric function and those neurological functions associated with the known or suspected level of compromise. Symptoms associated with dermoid or epidermoid cysts may include progressive back pain, gait abnormalities, radicular pain, and persistent hamstring tightness or spasms. Diagnostic ultrasound may help clarify the extent of the sinus and help identify cysts or other mass effects within or along the course of the dermal sinus. After birth, MRI remains the most reliable form of assessment. Sagittal MR acquisitions may help identify the course of the sinus tract and any associated anomalies such as lipomas or epidermoid tumors within the spinal canal. Myelomalacia, septic or aseptic transverse myelitis are also readily
apparent on MR imaging. The filum terminale should be scrutinized for anomalous development and the distal end of the cord identified to ascertain the risk for cord tethering. Although X-rays and CT studies may reveal associated bony anomalies of the spine, they are not often helpful in the assessment of a dermal sinus tract. Radiographic assessment is an important part of the presurgical workup, particularly when laminectomy may be required. 4.5.2.3 Neuroenteric Cyst Neuroenteric cysts, also referred to as enterogenous cysts, are extremely rare, and represent congenital non-neoplastic intradural cysts. They are most commonly found in the cervico-thoracic region lying midline and anterior to the spinal cord.180,193 They are less frequently found anterior to the cervical spinal cord and rarely occur in the lower lumbar region. They usually lie intradurally but may also develop in an intramedullary location. They are often associated with developmental vertebral anomalies. There is always some degree of spinal cord compression, particularly when the cyst is found in the thoracic region due to the smaller central canal diameter of the thoracic spine. The neuroenteric cyst represents persistent communication between the embryonic endoderm and ectoderm.194 The cysts are fluid-containing masses that are usually well circumscribed and thin-walled with a lining that resembles gastrointestinal or respiratory epithelium.195 A spinal neuroenteric cyst may have a fistulous extension or fibrous connection to the gastrointestinal tract secondary to incomplete separation of notochord from the primitive gut. There could be fistulous extension to the respiratory system. French196 reported that approximately one half of the patients with neuroenteric cysts had coexistent mediastinal enteric cysts in direct communication with the intraspinal cyst via an anterior developmental defect within the vertebral body. The neuroenteric cyst is commonly detected during the first decade of life. Common clinical presentations are focal spinal pain with or without compressive myelopathy, meningitis, or symptoms associated with a mediastinal mass.194 Fistulous communication with viscera, the thoracic or abdominal cavity increases the risk for acquiring meningitis and infectious myelopathy. If the respiratory system is involved, there may be mild to severe cardiorespiratory complications. MR is the imaging method of choice for the initial evaluation in cases of suspected neuroenteric cyst. CT or CT/myelography will usually represent a well-demarcated low-density mass, whereas MRI usually reveals a T1-weighted isotense or mildly hyperintense signal when compared to CSF. Primary differential considerations include arachnoid cyst, epidermoid cyst, dermoid cyst, and an inflammatory cyst.
Conditions Associated with Myelopathy
4.5.3 CAUDAL SPINAL ANOMALIES The category of caudal spinal anomalies comprises a variety of abnormal embryonic developmental disorders. Dysraphic conditions of this type include genitourinary and anorectal malformations, terminal myelocystocele, sacral agenesis, and anterior sacral meningocele. These defects do not represent a complete listing of the caudal spinal anomalies. This discussion will only review myelocystocele and sacral agenesis. There are five primary types of sacral agenesis with nine subtypes, ranging from total absence of the sacrum to incomplete development of the sacrum or the coccyx. Concurrent deformities include heart defects, kidney agenesis, kidney malformation, clubfeet, and pelvic organ malformation. Terminal myelocystoceles constitute approximately 5% of skin-covered lumbosacral masses and are especially common in patients with cloacal exstrophy.197 Pathologically, terminal myelocystocele consists of a closed form of a neural tube defect having the following characteristics: (a) a skin-covered lumbosacral spina bifida; (b) an arachnoid-lined meningocele that is directly continuous with the spinal subarachnoid space; and (c) a low-lying, hydromyelic spinal cord that traverses the meningocele and then expands into a large terminal cyst. The terminal cyst bulges into the extra-arachnoid compartment caudal to the meningocele and forms a distal sac that does not communicate with the subarachnoid space. The terminal cyst is lined by ependyma and dysplastic glia, is directly continuous with the dilated central canal of the cord, and probably represents a ballooned terminal ventricle. This form of neural tube defect is associated with significant caudal cell mass abnormalities. These patients often have anomalies of the lower spine, pelvis, genitalia, bowel, bladder, kidney, and abdominal wall.198 Impairment of lower extremity function is usually severe, if not corrected shortly after birth.
4.6 CHIARI MALFORMATIONS The Chiari malformations represent a group of central nervous system developmental anomalies primarily afflicting the posterior fossa. The clinical complaints may include headache, sensory changes, difficulty swallowing, vertigo, ataxia, imbalance, or hearing loss. Specific conditions associated with the Chiari malformations include cranial nerve palsy, nystagmus, syringomyelia, scoliosis, and hydrocephalus. Chiari malformations deserve mention in a chapter on myelopathy, as the spinal cord is often involved. Spinal cord involvement may include hydromyelia, syringomyelia, compression, and/or herniation. There are four primary classifications of Chiari malformation. Their only commonality is that they all involve the cerebellum.199 Type I malformation
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is the most common, a distinct entity not likely related to types II and III. Types II and III can overlap in their characteristic features, rendering precise delineation challenging. Chiari I malformation is sometimes referred to as congenital tonsil ectopia, as the cerebellar tonsils lie below the neuroforamen magnum (Figure 4.22). The cerebellar tonsils may extend into the upper cervical spinal canal and lie adjacent to the posterior aspect of the spinal cord and medulla. In Chiari I the 4th ventricle usually appears normal. The cerebellar tonsils tend to descend in a caudal direction with advancing age. At 10 years of age, the criterion for tonsillar ectopia is 6 mm. Within the 2nd and 3rd decade, the criterion for tonsillar ectopia is reduced to 5 mm, and between the 4th and 5th decades, a criterion of 4 mm is customary. Tonsillar ectopia may contribute to spinal cord compression, resulting in long tract signs and symptoms. Tonsillar ectopia may also present with a constellation of signs and symptoms mimicking that of multiple sclerosis. Most patients with tonsillar ectopia are asymptomatic and are identified as the result of an incidental MRI finding. In a high percentage of cases, Chiari I malformation may be associated with syringomyelia, hydromyelia, or syringohydromyelia. The medulla may be compressed due to the presence of ectopic cerebellar tonsils. There may be medullary signs and symptoms. Chiari II malformation is a much more complex anomaly involving the spine, spinal cord, dura, brain, and skull. Chiari II is frequently associated with myelomeningocele and hydrocephalus. It consists of herniation of the tonsils and all of the contents of the posterior fossa into the foramen magnum.200 This herniation involves the brainstem, 4th ventricle, and cerebellar vermis. The patient may demonstrate neurologic signs of lower brainstem and cranial nerve involvement. Chiari III and IV malformations are rare. Patients with Chiari III malformation usually have an encephalocele (external sac containing brainstem and posterior fossa contents); thus, the cerebellum and brainstem are descending into the spine and into an external sac. This is usually present in combination with the features of Chiari II malformation. Chiari IV malformation involves complex cerebellar hypoplasia and dysplasia. This type of deformity has many similarities to Dandy–Walker syndrome. The Chiari malformations represent a complex set of developmental abnormalities that are beyond the scope of this section.
4.7 KLIPPEL–FEIL SYNDROME Klippel–Feil syndrome is associated with the congenital fusion of two or more vertebrae. The condition is associated with failure of normal segmentation of the somites during 3 through 8 weeks’ gestation. The bony fusion may
88
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
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FIGURE 4.22 Chiari I malformation: nerve involvement, clinical signs, and typical congenital anomalies. (Copyright J.M. True, D.C.)
occur to varying degrees limited to the vertebral body or involving the anterior and posterior elements. There is frequent hypoplastic development of the associated cervical vertebrae and intervertebral disk. The vertebral bodies may appear flattened, and the intervertebral disk volume reduced. Hemivertebrae may occur. The neuroforamen of the abnormal segments is often smaller than normal. Patients with an unstable fusion pattern, craniocervical anomalies, or an associated spinal stenosis are at higher risk of developing neurologic sequelae.201 Klippel–Feil syndrome is rare and often asymptomatic. The development of symptoms may follow superimposed disease such as spondylosis or injury to the anomalous region. The condition may be detected during routine radiographic assessment for spinal pain. Klippel–Feil syndrome may be associated with spontaneous and progressive neurologic sequelae after relatively minor neck trauma. The neurologic symptoms may resemble a spondylotic myelopathy. Klippel–Feil may be detected in conjunction with other congenital malformations, such as basilar impression, atlanto-occipital fusion, torticollis, facial asymmetry, webbing of the neck, Sprengel’s deformity, scoliosis, and
cleft or high arch palate.202 The most common associated condition is scoliosis, which often occurs due to asymmetric vertebral development. Klippel–Feil may present with the following triad: a shortened neck (brevicollis), limited neck mobility, and low neckline. This triad is complete in 52% of individuals with the disease.202 Limited neck mobility is generally more evident in rotation, although the limitation may not be readily evident unless three or more vertebrae are involved. X-ray will reveal multiple block vertebrae (two or more) involving the cervical and, less commonly, the thoracic spine. Radiographic assessment with flexion–extension views may reveal supra-adjacent or infraadjacent compensatory vertebral hypermobility. Symptoms are more likely to arise from mobile segments. Disk herniation is associated with the deformity in young adults and adolescents.203 Chronic segmental hypermobility may lead to accelerated spondylosis, which could progress to involve central or lateral spinal stenosis, compressing the cord or nerve roots. There is increased risk for acquiring more advanced degenerative facet arthropathy and associated segmental instability.
Conditions Associated with Myelopathy
4.8 SCOLIOSIS AND MYELOPATHY The term scoliosis refers to lateral deviation of the spine from the midsagittal position. Abnormal spinal curvature may be congenital or acquired. A high percentage of children with a congenital scoliosis have spinal cord tethering and other anomalous findings.204 Scoliosis is the most common spinal deformity, and the most prevalent type of scoliosis is idiopathic, referring to no recognizable etiology. The congenital scoliosis types have the most significant neurological complications and will be the focus of this discussion. There are many classifications and topics related to scoliosis that exceed the focus of this book and chapter; therefore, the following represents a brief but relevant overview of the subject. Scoliotic curvatures are described by the region of the spine and by the side of convexity. It should be further designated whether there are rotatory changes and by the number of lateral curvatures. Scoliosis can be classified based upon whether they are structural or nonstructural (functional). A structural scoliosis is characterized by a lateral curvature which is fixed and does not completely reduce during recumbent bending. The fixed nature of the scoliosis may be revealed by lateral bending X-ray views or views taken while the patient is hanging by hands in a vertical position. A functional scoliosis is not caused by abnormal bony development and thus reduces or corrects during recumbent lateral bending. Scoliosis may be associated with underlying occult spinal dysraphism and other congenital anomalies. A rapidly progressive scoliosis or acute changes in spinal lordosis and kyphosis in an infant or child are suggestive of spinal cord tethering or another spinal dysraphic condition. Additionally, patients with a surgically repaired myelomeningocele may require follow-up surgical decompression of spinal cord tethering with progressive scoliosis, which develops from associated scar tissue around the distal spinal structures. Severe degenerative arthropathy may result in vertebral instability, contributing to scoliosis and central canal stenosis. Primary or secondary scoliosis occurring in a region of high-grade central stenosis may further render the spinal cord vulnerable to compressive forces. Spinal cord tethering secondary to an acquired stenosis exposes the spinal cord to compression. Scoliosis associated with neuromuscular diseases is unique, characterized by: (1) large progressive curves during prenatal to childhood period; (2) early onset of curve stiffness; (3) curve progression during adulthood; (4) long curves with pelvic obliquity and increased prevalence and
89
degree of complications.204 Because of these factors, scoliotic deformities associated with neuromuscular disease remain one of the most challenging spinal deformities to manage. Neuromuscular scoliosis may occur secondary to myelopathy and various forms of motor neuron disease. Attempts have been made to classify neuromuscular scoliosis into one of three major categories: (I) upper motor neuropathy, (II) lower motor neuropathy, and (III) myopathic. Neuromuscular scoliosis should be further classified as progressive or nonprogressive under each category I–III.204 The neuromuscular-type scoliosis occurs with high frequency in patients with Friedreich’s ataxia,205 possibly due to disrupted equilibrium, chronic ataxia, muscular atrophy, and muscular imbalance. It is generally progressive and associated with pelvic obliquity. The spinal deformities associated with poliomyelitis tend to have long C-shaped curvatures. Children with myelomeningocele (MM) often have a scoliosis and thoracic hyperkyphosis. The scoliotic deformities associated with MM tend to be extremely complex secondary to muscle spasticity, muscle weakness, absent posterior spinal elements, and congenital scoliosis.204 The scoliosis seen in patients with spinal muscular atrophy (SMA) tends to be of the characteristic neuromuscular type with a long C-type curve, a thoracolumbar apex, and oblique pelvic configuration.206 Paralytic scoliosis may occur secondary to pyramidal tract compromise of intracranial or spinal origin. An example is the rapid onset scoliosis which occurs secondary to a profound right-to-left muscular imbalance associated with hemiparesis secondary to hemimyelopathy. Paralytic scoliosis is often associated with marked pelvic obliquity, creating a significant challenge for the patient to sit upright in a chair or wheelchair without special bracing. It is also associated with accentuating A-P curvatures with acquired hyperlordotic and hyperkyphotic deformities. Paralytic scoliosis may be of a progressive, collapsing nature, requiring surgical correction or elaborate bracing. There are many potential complications associated with progressive or severe scoliosis which include cardiopulmonary changes, impaired respiratory capacity, degenerative facet arthropathy, degenerative discopathy, accelerated spondylosis, curvature progression, joint dysfunction syndromes, muscular fatigue, myelopathy, and radiculopathy. The latter two possibilities may occur secondary to spatial compromise of the central and/or lateral spinal canals. A severe rotary scoliosis can contribute to increased dural tension and increase the risk for spinal cord or nerve root tethering. There may also be greater tension placed upon dentate ligaments.
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5
Assessment of Spinal Cord Injury and Myelopathy
The evaluation of the individual with suspected myelopathy may occur in an emergency setting or during the course of a normal office visit (Tables 5.1 and 5.2). The assessment may be for acute spinal cord injury (SCI) or for the evaluation of late sequelae (Tables 5.3 and 5.4). It may be performed to rule out myelopathy due to stenosis, a systemic disorder, or other medical conditions. In all situations where myelopathy is suspected, the clinician should perform a detailed history and a comprehensive evaluation not limited to just the spine or area of regional complaint (Table 5.5).
5.1 SPASTICITY, PARESIS, CLONUS, AND HYPERREFLEXIA The corticospinal and corticobulbar tracts are collectively referred to as upper motor neuron or pyramidal pathways. The corticospinal tract provides descending motor contributions that converge upon the alpha and gamma motor neuron pools within the anterior horn. As their names imply, the fiber tracts originate in the cerebral cortex and traverse the brainstem and spinal cord to reach the anterior horn, where they synapse with the final common motor pathway to peripheral end organs. The lateral corticospinal tracts have a laminar somatotopic relationship: as a general rule, motor fibers that innervate the upper extremity are located medially and fibers innervating the distal lower extremities are located laterally. Therefore, lateral compromise of the spinal cord will initially result in clinical deficits of the distal portion of the involved lower extremity. Complete transection of the spinal cord at C8 or below will lead to paraplegia. Myelopathic compromise of the corticospinal tract results in a pyramidal tract syndrome that impairs the integration and activation of purposeful movements. Spastic paralysis, spastic paresis, hyperreflexia, and clonus are classic signs of an upper motor neuron lesion. Intact motor pathways modulate many spinal cord reflex arcs and interneurons controlling muscle action. A loss of descending motor control drives intramedullary reflex thresholds lower by creating a release phenomenon that appears when the shielding of the motoneurons from cortically generated voluntary movement is abolished, allowing indirect reflex connections and pathways to dominate.1 This results in pathologic (facilitated) spinal reflexive responses and spasticity below the level of the spinal
cord lesion. At the segmental level of spinal cord compromise lesion, a lower motor neuron presentation is typically evident. This is associated with muscle stretch reflex (MSR) hyporeflexia, atrophy, fasciculations, hypotonus, and paresis. Some atypical signs and symptoms have been associated with compressive myelopathy. With pyramidal insult, the loss of skilled voluntary movement is greatest involving the distal extremity musculature. There may be relative sparing of proximal muscle groups and the ability for gross extremity movement. “Synkinesia” is the term to describe the coarse limb movement that occurs when attempting to perform fine distal functions. The patient with myelopathy should be asked to rapidly tap the ball of his or her foot against the examiner’s hand. Difficulty or clumsiness with rapid fine movements is referred to as dysdiadochokinesia. Four categories of extremity paresis or paralysis occur as the result of SCI. Monoparesis refers to weakness of one limb. Hemiparesis refers to the weakness of the ipsilateral arm and leg. Paraparesis refers to weakness of the lower extremities. Quadriparesis is synonymous with tetraparesis, which refers to weakness of all four extremities. When referring to paralysis, these syndromes are referred to as monoplegia, hemiplegia, paraplegia, and quadriplegia respectively. Bulbar paralysis or paresis refers to compromise of the muscles innervated by motor nuclei of the brainstem (Figure 5.1). The segmental hyperfacilitation seen in pyramidal tract disease contributes to increased muscular tonus, MSR hyperreflexia, and clonus. A clonus response is a series of abnormal rhythmic involuntary contractions after the brisk passive stretch of a muscle or tendon; true clonus has a regular rate and rhythm. Most commonly observed at the ankle after a quick stretch of the gastrocnemius, clonus may also be observed at the patella after stretch of the quadriceps, and at the wrist or fingers after rapid passive extension. Occasionally, clonus may occur with slight foot stimulation or from slightly stretching the gastrocnemius when resting the foot. Varying degrees of clonus may occur. Clonus may be sustained or unsustained. Sustained clonus is often associated with more severe compromise of the corticospinal tract. Transient unsustained clonus may not always be secondary to disease of the central nervous system (CNS). It may occur in any condition that physiologically lowers the synaptic thresholds of the monosynaptic MSR. Some 97
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TABLE 5.1 Spinal Cord Injury: Considerations for Onsite Emergency Evaluation
TABLE 5.4 Spinal Cord Injury: Potential Late Complications
Airway assessment Breathing assessment Circulation assessment Disability assessment Exposure assessment
• • • • • • • • • • • • • • • • • • •
TABLE 5.2 “Spinal Clues” To Aid in the Diagnosis of Acute Spinal Cord Injury • • • • • • • • • • • • •
Hypotension and bradycardia occur in spinal shock Paradoxical respiration Low body temperature and high skin temperature Priapism Bilateral paralysis of arms and legs, especially flaccid Bilateral paralysis of either arms only or arms more than legs, especially flaccid Bilateral paralysis of legs, especially flaccid Lack of response to painful stimuli Detection of an anatomic level in response to painful stimuli Painful stimulation produces only head movement or facial grimacing Sweating level Horner’s syndrome Brown–Séquard syndrome
TABLE 5.3 Acute Spinal Cord Injury: Potential Complications • • • • • • • • • • • • • • •
Hypoventilation with hypoxia Bradycardia Atelectasis Pulmonary infection Pulmonary embolism Deep venous thrombosis Coagulopathy Orthostatic hypotension Autonomic dysreflexia (hypertension) Paralytic illeus Gastrointestinal bleeding Fecal impaction Atonic bladder Progressive SCI Denial, anger, depression
medications or adverse drug interactions may produce muscular hypertonicity and clonus. Hysterical states may increase muscular responses. A clonus response that is poorly sustained with an irregular rate and variable excursion
Segmental (vertebral) dysfunction Disk degeneration and herniation Osteoarthrosis Spinal stenosis Syringomyelia Progressive myelopathy Progressive radiculopathy Nerve root neuroma Chronic pain Adverse neuroplasticity Decubitus ulcers Atelectesis Pneumonia Pulmonary embolism Deep vein thrombosis Gastrointestinal bleeding Paralytic illeus Fecal impaction Atonic bladder
may be referred to as pseudoclonus. Altered serum electrolyte concentrations may produce pseudoclonus. A grading scale from 0 to 4 is used when clinically evaluating the muscle stretch response (Table 5.6). MSR hyperactivity is characterized by a decrease in the reflex threshold, magnification of the range of movement, increased speed of response, prolonged muscular contraction, and a broadened reflexogenous zone. A smaller stimulus intensity is required to elicit a reflexive response. Occasionally, in the severe SCI patient, a physical stimulus will provoke coarse hyperreflexive responses as seen with spinal automatism. The clinical presentation is often obvious with moderate to severe cervical myelopathy. The findings usually involve hyperreflexia below the level of the lesion and some degree of lower extremity spasticity, often accompanied by paresis and a Babinski sign. In patients presenting with cervical spondylotic myelopathy, upper and lower motor neuron findings are frequently present. At the site of the compressive lesion it is common to have associated segmental lower motor neuron signs from injury to the descending or exiting nerve root. This results in segmental flaccid paresis, hyporeflexia, and diminished sensation. Spondylotic myelopathy will induce upper motor neuron signs below the level of the lesion. These patients display some degree of hyperreflexia, clonus, and spastic paresis. A grading scale for muscular spasticity has been proposed (Table 5.7). In the elderly patient with cord compromise, peripheral neuropathy and age-related axonal drop-out may also be present. This will result in a reduced hyperreflexive response. The Babinski’s response may also be reduced in magnitude.
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1.) Motor cortex
TABLE 5.5 Checklist for Assessment of the Patient with Spinal Cord Compromise • Cervical spinal canal configuration Torg ratio (canal to body ratio by X-ray): < .80 Sagittal canal diameter : < 8 mm — severe Sagittal canal diameter : < 11 mm — moderate Sagittal canal diameter : < 13 mm — mild • Spinal cord morphology Effacement Displacement without deformation Deformation Class I compression < 1/5 A-P cord diameter Class II compression < 1/3 A-P cord diameter Class III compression > 1/3 A-P cord diameter Compression with abnormal spinal cord signal T1 hypointensity, T2 hyperintensity of cord — moderate T1 hyperintensity, T2 hyperintensity of cord — severe Deformed H-sign • Electrodiagnostic considerations Absolute prolongation of spinal cord conduction time Sensory (SEP) Motor (MEP) Relative prolongation of spinal cord conduction time F-wave amplitude 5% or greater than CMAP amplitude Decreased motor unit recruitment with slow firing rate on EMG • Clinical Findings Grading of spasticity Clonus 2–5 beats >5 beats unsustained Sustained Babinski Extension response of great toe Extension of toes with fanning Atonic or neurogenic bladder MSR hyperreflexia Extremity ataxia Nonsegmental sensory loss
TABLE 5.6 Grading of Muscle Stretch Reflexes: Deep Tendon Reflexes 0 1 2 3 4
Absent Diminished Average (normal) Exaggerated Brisk with clonus
Areflexia Hyporeflexia Average Hyperreflexia Hyperreflexia
The upper cervical cord can be difficult to assess clinically for the localization of myelopathic signs. A variety of clinical procedures can be utilized to evaluate the presence of an upper motor neuron lesion presentation involving
2.) Pyramidal tract
4.) Anterior horn
3.) Lateral and anterior corticospinal tracts
5.) Peripheral nerve or root
6.) Myoneural junction 7.) Myofascial 8.) Myopathic
FIGURE 5.1 Sites where potential compromise will result in muscle weakness. (Copyright J.M. True, D.C.)
the upper extremities (Figure 5.2). The scapulohumeral reflex described by Shimizu et al.2 is a C1–C4 innervated MSR that may be beneficial for localizing high cervical cord lesions. The test is performed by having the patient sitting comfortably, with arms hanging limp at the patient’s side. The examiner taps the spine of the scapula and the acromion process with a large reflex hammer (Babinski hammer) and observes response of the arm and shoulder. If there is elevation of the scapula and/or abduction of the humerus, the reflex is considered hyperactive. Two of the most reproducible pathological signs of the upper extremities are the Hoffmann’s and Tromner’s signs. The Hoffmann maneuver is performed by supporting the patient’s hand with the wrist slightly dorsiflexed and relaxed. The fingers should be slightly flexed. The middle finger should be fully extended with the distal phalanx firmly held between the examiner’s index finger and thumb. The examiner should then nip or snap the nail
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TABLE 5.7 Scale for Grading Motor Strength and Spasticity Grade Description 0 1
1+
2 3 4
No increase in muscle tone Slight increase in muscle tone, manifested by a catch-andrelease or by minimal resistance at the end of the range of motion (ROM) when the affected part(s) is moved in flexion or extension Slight increase in muscle tone, manifested by a catch, followed by minimal resistance throughout the remainder (less than half) of the ROM More marked increase in muscle tone through most of the ROM, but affected part(s) easily moved Considerable increase in muscle tone; passive movement difficult Affected part(s) rigid in flexion or extension
Source: Based on Ashworth, B., Preliminary trial of carisoprodol in multiple sclerosis, Practitioner, 192, 540, 1964. With permission.
patient’s relaxed hand. The examiner should grasp the middle phalanx of the third digit. With the middle finger of his or her other hand, the examiner should tap the volar surface of the distal phalanx. The sign is considered positive using the same criteria as the Hoffmann’s sign. A positive Hoffmann’s or Tromner’s sign is suggestive of a corticospinal lesion at or above the fifth or sixth cervical level, but an isolated Hoffmann’s or Tromner’s sign in the absence of other myelopathic signs or symptoms does not confirm a spinal lesion. The examiner should always attempt to correlate with additional long tract signs, diagnostic imaging, and lab work if necessary. Denno and Meadows3 described a Hoffmann’s sign with an additional dynamic component performed by having the patient flex and extend his or her head and neck multiple times to tolerance. These researchers called this test a dynamic Hoffmann’s sign vs. a static Hoffmann’s sign when the neck was not moved. The dynamic Hoffmann’s test may help to elicit upper motor neuron lesion signs in patients with a negative static Hoffmann’s sign and thus increase the sensitivity of the clinical neurological exam.
5.2 SUPERFICIAL REFLEXES AND REFLEXES OF SPINAL AUTOMATISM
Jaw reflex (Brainstem)
Scapulohumeral reflex (Shimizu) (C1-C4 or C5)
BLIND ZONE
Biceps reflex (C5, C6)
FIGURE 5.2 Neurologic lesions high in the cervical cord are difficult to isolate by hyperactive reflex centers, unless the clinician evaluates the scapulohumeral reflex (Shimizu). (Adapted from Shimizu, T., Shimada, H., and Shirakura, K., Scapulohumeral reflex (Shimizu): its clinical significance and testing maneuver, Spine, 18, 2182–2190, 1993. With permission.)
of the patient’s middle finger, inducing brisk forcible flexion of the finger. If this maneuver is followed by flexion of the index finger and adduction of the thumb, the response is referred to as the Hoffmann’s sign. If only one finger responds, this is referred to as an equivocal sign. The Tromner maneuver is an alternative way to evoke a similar response. The examiner should again hold the
Superficial reflexes are those reflexes that respond to stimulation of the skin or mucous membranes. Threshold stimulation can usually be evoked with a cutaneous stimulus such as a stroke with a blunt or sharp object. For this reason, superficial reflexes are often referred to as cutaneomuscular reflexes. Common superficial and pathological reflexes that are easy to evaluate include the abdominal, gluteal, cremasteric, scapulohumoral, and Hoffmann’s responses (Figure 5.3). Unlike the MSR, these responses have an ascending reflex arc extending to the cerebral cortex, a spinal reflex arc, and a descending cortical contribution via the corticospinal tract; thus, a corticospinal tract lesion may interrupt those descending influences to the anterior horn, and a skin stimulus will subsequently result in decreased or absent muscular response caudal to the level of the lesion. If the level of cord compromise is distal to the decussation of the medullary pyramids, loss of the superficial reflex response will be apparent on the ipsilateral side. The dissociation of muscle stretch and superficial reflexes is an important clinical presentation in the workup of the potential myelopathic patient. Distal to the segmental level of corticospinal tract compromise there will be an ipsilateral exaggeration of the MSR and a diminution or absence of the superficial reflexes (Figure 5.3). Occasionally, the abdominal reflexes are preserved in the presence of corticospinal tract disease. This may occur with familial spastic paraparesis and with some transverse spinal cord lesions. Many spinal cord lesions are incomplete; consequently, evocative positioning or combined maneuvers
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Cremasteric reflex. The examiner strokes the medial thigh, the testicle normally elevates on the same side of stimulation.
Abdominal reflex. The examiner strokes the abdomen in all quadrants, the umbilicus normally deviates to the direction of quadrant tested.
Abnormal response: Absence of testicular elevation.
Abnormal response: Absence of umbilical movement in any quadrant.
Examiner touches anus. In the normal patient, the sphincter contracts.
Anal wink reflex
S3 S4 S5
Anal contraction
Abnormal response: Absence of anal contraction FIGURE 5.3A Superficial reflexes: abdominal, anal wink, and cremasteric. (Copyright J.M. True, D.C.)
may be required to elicit the latent abnormal response. Repetition may progressively facilitate the superficial response, providing additional insight as to whether dissociation of the reflexes truly exists.
The superficial reflexes can be exaggerated in a variety of conditions. Hysteria may result in facilitation of the MSR and the superficial response. The superficial reflexes may be exaggerated with parkinsonism and in other
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Scapulohumeral Reflex (Shimizu) Examiner taps spine of scapula or acromion.
Abnormal response: arm abducts or moves, or scapula elevates.
TABLE 5.8 Variations of Toe Response to Plantar Stimulation in the Myelopathic Patient • • • •
Hoffmann's Reflex or Sign Examiner pinches or flicks the patient’s finger tip
Unilateral unresponsive toes Upgoing toes without fanning Isolated extension of big toe Slow tonic upgoing toes with fanning of toes (+ Babinski’s sign)
The crossed extensor reflex is associated with partial or incomplete spinal cord lesions. Stimulation of the leg or foot produces flexion of the same extremity and extension of the contralateral extremity. In severe spinal injury, after the initial episode of spinal shock has subsided, a more exaggerated flexion spinal automatism may occur, called the mass reflex. This spinal reflex occurs following distention of the bladder or from stimulation of the feet or legs. Contraction of the abdomen, sweating, and piloerection below the level of the lesion, along with evacuation of the bowels and bladder and hip flexion, are associated with the mass reflex.
5.2.1 BABINSKI’S RESPONSE
An abnormal response is present if the patient’s index finger and thumb flex. FIGURE 5.3B Pathological superficial reflexes: scapulohumeral (SHR) (Shimizu), and Hoffmann. (Copyright J.M. True, D.C.)
extrapyramidal disorders. The examiner must always investigate other potential signs and symptoms to help confirm or eliminate the possibility of myelopathy. In the SCI patient, a variable degree of spinal automatism is usually present. These spinal-mediated defense reflexes occur as the result of loss of descending inhibitory control of muscle action, following spinal injuries or lesions. The flexion withdraw reflex is the most commonly observed spinal automatism. This reflex process is identical to Babinski’s sign, only more pronounced.4 In complete or near-complete spinal cord lesions, the flexion withdraw reflex can be elicited by stimulating the foot, leg, or toes. The reflex produces varying degrees of hip and knee flexion, dorsiflexion of the ankle, and dorsiflexion of the great toe with fanning of the small toes. The reflex may be reproduced from any type of stimulation, such as pinching, stroking, deep pressure, and, in some patients, by light touch of the extremity.
In the normal individual, stimulation of the plantar surface of the foot by stroking with a blunt pointed object produces a downward twitch of the toes, clinically referred to as downgoing toes. The smaller toes usually respond with a greater degree of flexion than the great toe, and the response is usually brisk. It is important to compare the right and left responses when examining a patient with suspected myelopathy, as a significant side-to-side difference may be an initial sign of an early or subtle lesion (Table 5.8). The plantar reflex is innervated by the fourth lumbar through the second sacral segments via the tibial nerve; thus, lumbosacral polyradiculopathy, lower extremity polyneuropathy, or tibial mononeuropathy will lead to a diminished plantar response on the involved side, but the toes should not be upgoing. Compromise of the corticospinal tract, however, leads to an inversion of the normal downgoing toe response. Stimulation of the sole of the foot will result in dorsiflexion of the great toe and fanning of the toes (Figure 5.4). The extension response of the big toe is typically quite evident. The extension and fanning of the toes is the Babinski’s sign. The extension response may be followed by a flexion response. A variety of extensor or Babinski’s responses may occur. The response is dependent upon a number of variables that include the degree of stimulation and severity of corticospinal tract compromise. Variations include isolated extension of the big toe and extension of the big toe with simultaneous plantar flexion of the small toes. Occasionally, plantar stimulation may be followed by an exaggerated proximal
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Normal response: Examiner strokes sole of foot in the depicted pattern. Toes normally twitch in flexion.
Babinski’s sign present: The patient’s toes fan apart or the great toe extends.
Abnormal response
Ankle clonus response: Examiner pulls up on the patient’s foot brisklydorsiflexing the foot.
Abnormal response: The foot reflexively plantar flexes with multiple down beat contractions.
FIGURE 5.4 Pathological signs of pyramidal tract compromise. Babinski and clonus. (Copyright J.M. True, D.C.)
response with ipsilateral dorsiflexion of the foot and flexion of the knee and hip. With an incomplete corticospinal tract lesion a Babinski’s response may or may not be evident. Having the patient turn his or her head to the side opposite plantar stimulation can occasionally reinforce a Babinski’s sign. This protocol may be helpful in the evaluation of an otherwise latent response. Additionally, pseudo-Babinski’s responses may occur in the absence of corticospinal tract disease. Plantar hyperesthesia can lead to an exaggerated response. In the presence of a true Babinski’s sign there is palpable tonic or clonic contraction of the hamstring muscles. This does
not occur in the presence of a pseudo-Babinski’s sign. The examiner may need to palpate the hamstring muscle groups while performing plantar stimulation. With lesions of the primary motor region of the cortex and the premotor area, there may be a greater extensor response of the toes to plantar stimulation. If the ipsilateral basal ganglia and corticospinal tract are compromised, there may not be a toe extensor response; therefore, an intact basal ganglia appears to be important to the extensor response. Toe extensor responses are normally seen in newborn infants until 18 to 24 months of age. A positive Babinski’s sign is often paralleled by the reduction of
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(A)
(B)
Jaw jerk unchanged
Upper extremity intact Site of cord transection
10
Biceps jerk unchanged Motor and sensory level at T10
-
-
+
+
Most intercostal muscles intact
Superficial abdominal reflexes absent in lower quadrants Sensory loss up to T10 dermatomal level
Lower body paralyzed (paraplegic) Knee jerk 3+ Ankle jerk 3+ Babinski's signs
FIGURE 5.5 Spinal cord, vertebral, and clinical levels. (A) Note the disproportion between the spinal cord and spinal column; below the cervical region, the cord segments are progressively rostral to the vertebral segments. This cord ends at approximately L1–L2 (usually T12–L2). The site of a lesion transecting the spinal cord is shown at cord segment T10. Note that sacral vertebral segments are fused; the roots exit via foramina, not interspaces. (B) A clinical level at T10 with motor, sensory, and reflex markers indicated. After initial spinal shock, deep tendon reflexes in the legs are hyperactive and extensor plantar signs (Babinski’s signs) are present. Superficial abdominal reflexes are present in the two upper quadrants (above T10, marked by the umbilicus) but absent in the two lower quadrants. Descending sympathetic and parasympathetic pathways in the cord (not shown) are also disrupted (but descending sympathetic fibers leaving the cord above T10 to enter the sympathetic chain are preserved). (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, 1993, p. 256. With permission.)
rapid or skilled movements of the foot. A Babinski’s sign can occur in the absence of disease, examples include stages of deep sleep, during deep anesthesia, and in occasional severe states of drug abuse or intoxication. The Babinski’s sign has often been referred to as one of the most important signs in clinical neurology.4 It can be used to indicate the presence of disease along the corticospinal system extending from the cortex through the descending pathways to the anterior horn. Additional maneuvers can be performed to elicit an extensor response in the presence of corticospinal tract disease. Common maneuvers include Chaddock’s sign, which is evoked by stimulating the lateral aspect of the foot; Oppenheim’s sign, elicited upon applying heavy stroking pressure along
the anterior surface of the tibia, and Gordon’s sign, elicited when squeezing the gastrocnemius in the patient with pyramidal disease. The clinician should always evaluate for paresis or paralysis of foot and toe dorsiflexors prior to the evaluation of plantar responses. A loss of the ability to dorsiflex the toes can mask what would be a positive Babinski’s sign. Common causes for a loss of dorsiflexion include an ipsilateral L4 and L5 polyradiculopathy and/or a peroneal mononeuropathy. The examiner should always refer to questionable findings by describing the response characteristics. This becomes extremely important if there is deterioration or improvement in the response of the patient with mild pyramidal tract disease (Figure 5.5).
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5.3 SENSORY ABNORMALITIES In the spinal cord, the sensations of pain and joint position sense are carried in different fiber tracts and are physically separated; therefore, a solitary lesion may only involve one sensory tract. However, complete transverse spinal cord lesion will eradicate all sensory modalities below the level of the lesion. When an SCI is unilateral, the sensory loss is often dissociated. Sensory dissociation refers to the loss of some modalities with sparing of others. For example, sensory dissociation occurs in the presence of a lateralizing spinal cord lesion. The laterally expanding mass produces an ipsilateral loss of vibratory perception and kinesthesia due to posterior column and spinocerebellar tract interruption. Additionally, contralateral loss of pain and temperature sensation occurs one to two dermatomal levels below the actual cord level of the lesion because the spinothalamic tract crosses one to two levels higher than the level of dorsal root entry to the cord. Anterior spinal cord syndromes often result in a bilateral loss or diminishment of pain and temperature perception with the preservation of posterior column modalities such as kinesthesia and vibratory perception. An expansile lesion within the central portion of the spinal cord initially compromises the crossed spinothalamic fibers, resulting in impaired pain and temperature perception, initially preserving the corticospinal tracts and the posterior columns. A central intramedullary lesion may expand to eventually compromise these regions but the initial presentation is instead one of sensory dissociation. Posterior spinal cord compromise will result in initial sparing of pain and temperature with impairment of kinesthesia and vibratory perception. The sensory presentation characteristic of a hemimyelopathy usually includes the preservation of touch, but the loss of proprioception, vibration, pain, and temperature sensation below the level of the lesion.5 An expanding lesion in the cervical spine may result in a rising sensory level deficit, which may initially mimic a polyneuropathy (Figure 5.6).
5.3.1 ATAXIA Injury to sensory pathways of the central nervous system leads to a loss of limb awareness, loss of joint position awareness, and a loss of the ability to efficiently modulate voluntary and involuntary muscular activity. The term “ataxia” refers to the degradation of movement and impaired control of movement secondary to sensory compromise. The patient with a spinal ataxic gait will demonstrate a toe-out, wide-based stance; choppy overcompensated leg movement during ambulation; and a tendency to tap the foot (double tap sign). The patient compensates for the decreased sensibility by greater visual scanning of the environment. The degree of ataxia can be magnified by having mildly ataxic patients close their eyes while
TABLE 5.9 Disorders Associated with Central Nervous System Pain • • • • • • •
Central post-stroke pain Epilepsy Parkinson’s disease Multiple sclerosis Spinal cord injury Syringomyelia Syringobulbia
attempting to walk a straight line or while running the heel down the shin. These patients use visual cues as compensation for the decreased sensory (proprioceptive) input from the skin and musculoskeletal tissues.
5.4 SPINAL CORD INJURY PAIN Pain is exceedingly common following SCI (Table 5.9). Patients with cervical-level SCI frequently have neck pain radiating into the shoulders. These pains are a combination of nociceptive and neuropathic pain production. Pain in the acutely injured patient is primarily nociceptive pain from direct injury to pain afferents. Acute injury pain occurs from damage to the vertebral column, nerve roots, and soft tissues. During rehabilitation, nociceptive pain frequently occurs from poorly fitting orthoses or halo fixators as well as concomitant disk and musculoskeletal injury. One of the consequences of SCI is the development of central pain. This type of pain is neuropathic and does not involve the activation of peripheral nociceptors. Central pain is a common effect of injury to the spinal cord and brain.6 The majority of central pain states seen in clinical practice occur following SCI. The incidence of central pain is highest following cord injury and lowest following stroke. A lesion producing neuropathic pain mechanisms may be located anywhere in the CNS, from the spinal cord dorsal horn to the cerebral afferent processing of the spinothalamic pathways including spinoreticulobulbothalamic and spinomesencephalic projections.
5.4.1 LHERMITTE’S SIGN Lhermitte’s sign is one of many presentations that suggest myelopathy (Table 5.10). The Lhermitte’s sign is the report of an electric shocklike or painful perception into the extremities or along the spine during antiflexion of the cervical spine. The Lhermitte’s sign often occurs in the presence of focal traumatic or demyelinative disorders involving the spinal cord (Table 5.11). Neoplastic disease compromising the spinal cord may also contribute to a Lhermitte’s sign. The mechanical stretching of the irritated spinal cord and thecal membranes facilitates axonal discharge and
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(A) Expanding lesion at C4
4
(B) Rising sensory levels Sensory level at cord level of lesion (C4) T2 levels extend on to arms Next, an obvious sensory level on the trunk (T7)
Area of abnormal sensation rises to L1
Initial dorsal column symptoms and signs simulate polyneuropathy from the frontal aspect
FIGURE 5.6 Rising clinical sensory levels due to an expanding cord lesion. (A) Spinal cord and column showing C4 location of cord lesion. (B) Clinical progression is shown sequentially, from distal to more proximal sensory symptoms and signs. Distal involvement might be mistaken for a polyneuropathy (from the anterior aspect), but note the asymmetry. The medially placed C4 lesion in the posterior columns at first affects only those fibers (fasciculus gracilis) that come from the lowest lumbosacral segments and has yet to involve fibers originating from higher dermatomes. As the lesion expands at the C4 level to involve more and more of the posterior column fibers, the clinical level ascends to L1, to T7, then to T2, and finally to the level of the spinal cord lesion (C4). (In reality, the rising sensory levels usually are not so well demarcated nor so symmetrical, and do not “jump” from one level to another.) Other long tract signs, as well as segmental signs at the level of the lesion, may also be noted in some cases. (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, 1993, p. 312. With permission.)
ephaptic transmission. Cervical flexion combined with a Valsalva maneuver or a supine straight leg raise may help elicit a “slump maneuver” Lhermitte’s sign. Dysesthesia occurring in the legs with cervical flexion is strongly suggestive of cervical myelopathy. Arachnoiditis, multiple sclerosis, and cervical radiculopathy are a few of the more common disorders that can produce a Lhermitte’s sign.
5.5 NEUROGENIC CLAUDICATION Neurogenic claudication of spinal cord origin should be distinguished from claudication secondary to peripheral arterial disease. Neurogenic claudication is characterized by progressive paresis of the lower extremities occurring during exertion. The symptoms are generally relieved by rest. During the early stage of spinal neurogenic claudication, the
lower extremity weakness may be unilateral, progressing to become bilateral. Progressive paresis during exertion is often accompanied by sensory complaints of paresthesia or dysesthesia. Unlike the claudication secondary to cauda equina impairment or arterial insufficiency, neurogenic spinal cord claudication tends to be less painful. As the condition progresses, a lower level of physical exertion is required to induce symptoms. An identifying feature of neurogenic claudication of spinal cord origin is the change in the postexercise from pre-exercise neurologic examination. After a brief period of exercise there may be muscular spasticity and hyperreflexia of the lower extremities, which may not have been noted prior to exercise. This has been referred to by Verbiest as “Afternoon Babinski’s.”7 The lower cervical spine is the most common site of myelopathy resulting in neurogenic claudication. It is not uncommon for the patient
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TABLE 5.10 Correlative Signs of Myelopathy
TABLE 5.12 Autonomic Dysregulation in Myelopathy
• • • • •
• • • • • • • •
• • • • • • •
Inverted radial reflex Finger escape sign Deficient repetitive hand closing Hoffmann’s sign Hoffmann’s sign (dynamic Hoffmann’s sign) during cervical flexion or extension Lhermitte’s response Disassociated MSR (hyporeflexia + hyperreflexia) Ataxic gait Spastic paresis Diminished or absent superficial abdominal reflexes Babinski’s response Impaired fine motor control
TABLE 5.11 Myelopathic Conditions Associated with Lhermitte’s Sign • • • • • • • • •
Multiple sclerosis Cervical spondylosis Cervical disk herniation Spinal metastasis Subacute combined degeneration cis-Platin therapy Cervical radiation therapy Post-traumatic syndrome Herpes zoster
to have corresponding upper extremity radiculopathic signs and symptoms with a history and examination suggestive of neurogenic claudication. When neurogenic claudication arises from the thoracic region, it is usually the lower region.
5.6 SACRAL SPARING In patients with confirmed cord injury, the most reliable indicator of the return of spinal cord function is sacral sparing. Injuries that involve the central aspect of the lower cord in the lumbar enlargement region may not injure axons of the sacral-innervated structures. Sacral sparing suggests a partial lesion and a greater possibility of the return of bladder function, bowel function, and lower extremity muscle strength. In the nontraumatic patient, sacral sparing occurs with intramedullary lower cord tumors. Tests to evaluate sacral sparing include anal and sphincter reflex, flexion strength of the hallux, and perianal sensibility to pinprick. In concordance with Comarr’s findings,8,9 Katoh et al.10 found that in the longterm evaluation of cervical SCI patients, those with preservation of pinprick sensation between the level of the injury and the sacral dermatomes shortly after injury
Urinary sphincter dysfunction Rectal sphincter dysfunction Trophic skin changes Vasomotor instability Sexual dysfunction Anhidrosis Impaired temperature control Autonomic dysreflexia Hypertension Bradycardia Seizures
recovered the most motor function, with 75% of the patients regaining the ability to walk. This pattern of sensory sparing predicted a statistically significant better motor outcome than other patterns of sensory sparing.
5.7 AUTONOMIC AND OTHER SYSTEM CONSIDERATIONS The autonomic nervous system (ANS) plays an intricate role in the control and modulation of the cardiovascular system. Myelopathy can lead to altered autonomic regulation (Table 5.12). Complex neuronal connections from higher CNS centers such as the forebrain, hypothalamus, and brainstem send descending influence to the spinal cord to modulate sympathetic and parasympathetic outflow. These higher CNS centers are influenced by peripheral chemoreceptors and baroreceptors located within the carotid arteries, carotid sinus, aortic arch, renal vasculature, and cardiac chamber walls. Circulatory homeostasis requires a balance between the sympathetic and parasympathetic systems. A loss of the delicate autonomic balance alters peripheral vasotone directly through innervation loss and indirectly from a myriad of neurohormonal shifts. The sympathetic nervous system has a strong influence on peripheral vascular resistance via its extension from the interomediolateral cell column of the thoracic spinal cord. Postganglionic sympathetic fibers can mediate vasoconstriction or vasodilation.
5.7.1 ORTHOSTATIC HYPOTENSION Orthostatic hypotension is a common dysautonomia that occurs following SCI above T5–T6 levels. Reduced cardiac output and peripheral vasoconstrictor tone results in a significant drop in blood pressure when the patient is moved, usually from a recumbent position; this reduced output is consequential to a reduction in cardiac return from poor peripheral vascular resistance. The symptoms of hypotension include dizziness, positional syncope, lightheadedness, nausea, and fatigue. Orthostatic hypotension
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tends to be worse during the initial post-injury period of spinal shock. Neurogenic shock can be differentiated from hypovolemic shock by the presence of compensatory tachycardia in the latter. Severe hypotension within minutes or hours after SCI can contribute to further cord injury as the result of arterial insufficiency and spinal cord parenchymal infarction. During the months following acute SCI, the signs and symptoms associated with orthostatic hypotension may improve secondary to the returning function of some necessary compensatory mechanisms.11
5.7.2 DEEP VEIN THROMBOSIS The patient who has suffered acute SCI is at risk for acquiring deep venous thrombosis (DVT) secondary to the drop in peripheral vascular resistance, impaired sympathetic regulation, diminished venous return, reduced cardiac output, and increased coagulability. DVT occurs with significant prevalence in SCI, warranting consideration of prophylactic intervention12 to prevent pulmonary embolism (PE) and pulmonary impairment or death. The individual with chronic myelopathy and associated physical impairment is also at risk for acquiring DVT. This increased risk is primarily due to decreased physical activity and subsequent venous stasis. It occurs most commonly in the lower extremities. The presence of DVT will cause a delay or modification of rehabilitative intervention and places the individual at risk for pulmonary emboli, which may cause respiratory impairment or death. The risk is greatest in quadriplegia patients who already have impaired respiratory function. The possibility of PE should be assessed with a lung scan and/or ventilation–perfusion study. Close serial clinical evaluation of the patient with myelopathy is required, as the patient may be deafferentated and therefore unable to perceive the pain and tissue changes associated with DVT. DVT usually occurs in the lower extremities; because the paralyzed patient will be unable to easily observe the distal extremities, assistence may be required. The high-level quadriplegic patient may not experience chest pain following pulmonary emboli and therefore may not receive prompt medical attention. Depending upon the level of spinal cord involvement, an individual may experience PE pain in the shoulder region that could be mistaken for pain of primary orthopedic etiology. The clinician should carefully assess for rubor, regional hyperthermia, edema, and circumferential enlargement of the limb; all such findings are suggestive of diminished venous return. A circumferential increase in the extremity of as little as 1 to 2 cm should lead the clinician to suspect DVT. These findings may be accompanied by acute pain in the region of DVT. The presence of venous stasis and sustained dermal pressure increases the risk for a decubitus lesion. If DVT is suspected, prompt assessment should ensue. The diagnostic approach may involve a coagulation profile, ultrasonic venography, magnetic resonance
TABLE 5.13 Autonomic Dysreflexia: Emergency Management Algorithm Check blood pressure: Taken every 3 minutes in both arms during autonomic dysreflexia attack and for 2 hours after the attack is resolved. Remove noxious stimuli: Investigate below level of injury. Check bladder: Look for distention and catheterize bladder (anesthetize using 2% Lidocaine jelly). Look for obstructions and clear or replace catheter line. Look for UA infection or other genitourinary disorder. Check bowel: Anesthetize rectum using 2% Lidocaine jelly. Examine for impaction and remove. Check skin: Look for insect bites, tight clothing, pressure ulcers, etc. Assess environment: Check bed and wheelchair cushion for comfort. Avoid rapid changes in temperature. Check for upset gastrointestinal tract: Look for poor food combining, gas, dysbiosis, gastritis, enteritis. Avoid rapid tube feeding and food that is too hot or too cold. Female-specific: Evaluate for menstrual cramping, vaginitis, uterine contractions. Male-specific: Evaluate for reflexogenic erection or genital constriction. Look for catheter problems or constriction. Admit patient for hospitalization: Take this step if blood pressure is uncontrolled or the source of irritation is not found. Source: Based on Stover, S. UAB Model Spinal Cord Injury Care System, Spain Rehabilitation Center, Birmingham, AL, 1999. NIDRR, Office of Special Education and Rehabilitative Services, U.S. Dept. of Education, Washington, D.C.
angiography, impedance plethysmography, or radionuclide scanning.
5.7.3 AUTONOMIC DYSREFLEXIA Spinal cord injuries occurring above the T6 level can result in a serious complication referred to as autonomic dysreflexia (AD), a potentially devastating reaction that, if left untreated, can lead to stroke or death (Table 5.13). The presenting symptoms of autonomic dysreflexia are generally diverse and constitutional. They include a pounding headache, cutis anserina, paresthesia, shivering, flushing and sweating above the level of injury, nasal congestion, desire to void, anxiety, malaise, and nausea.13 Hypertension, bradycardia, bronchospasm, and seizures are lifethreatening signs in AD associated with death or serious morbidity. The main objective sign to monitor in AD is blood pressure. A large increase in blood pressure above 170 systolic requires hospitalization if the source of irritation or exacerbation is not found. Seemingly innocuous stimuli as well as noxious stimuli may produce the overactive sympathetic response, causing a rapid rise in blood pressure with other autonomic signs and symptoms. One of the primary goals should be to find and quickly eliminate or reduce the promoting stimuli. Whenever a patient with SCI above the level of T8 presents with a resting
Assessment of Spinal Cord Injury and Myelopathy
diastolic or systolic pressure 20 mmHg greater than baseline, autonomic hyperreflexia should be considered.14 AD results from impaired modulation of sympathetic activity and/or a loss of descending regulatory influences from the cardiovascular regulatory centers within the medulla. The afferent stimuli leading to a segmentally facilitated response at the spinal cord level usually arise from the viscera. The most common etiologies are defecation, distention of the bowel or bladder, gall bladder disease, and urinary tract infection. Cutaneous sores or lesions creating noxious stimuli may stimulate the syndrome. In the female patient, this may be mediated by fibroid uterine disease.
5.7.4 CARDIAC COMPLICATIONS The patient with acute SCI may require tracheal intervention; this can lead to vagal stimulation mediated by tracheal stimulation and physiological suppression of function, which may cause an autonomically mediated slowing of the heart rate. Bradycardia below 60 BPM will result in decreased pulmonary perfusion, increasing the risk for systemic hypoxia. Extreme bradycardia may lead to cardiac arrest. Electrocardiographic monitoring, pulse volume recording, and pulse oximetry help to identify this potentially life-threatening condition. The individual with paralysis, like the sedentary individual without SCI, is prone to deconditioning and developing hyperlipidemia, elevated low-density lipoprotein (LDL), and a drop in the level of protective high-density lipoprotein (HDL) due to limited physical activity. This change in the blood lipid patterns increases the risk for acquiring coronary artery disease (CAD). The loss of skeletal muscle mass may contribute to impaired glycoregulation and hyperglycemia, thus increasing the risk for tissue glycosylation and related vascular pathology. Cardiac irregularity may occur secondary to the dysautonomic state. Diminished sympathetic influence can lead to a relative state of hyperparasympatheticonia. This may lead to supraventricular or ventricular arrhythmias. Ambulatory electrocardiography may reveal abnormal heart rate variation (R-R intervals) and arrhythmia.15
5.7.5 RESPIRATORY CONSIDERATIONS Cervical or upper thoracic spinal cord SCI influences respiratory control and efficiency; transverse or complete SCI at these levels results in paralysis of respiratory muscles. Many muscles contribute to inspiration, whereas expiration is primarily a passive process that occurs when the intercostal and diaphragmatic muscles relax, returning the diaphragm to its dome shape rising within the chest cavity (Table 5.14). Normal abdominal muscle tone helps to contain the viscera and maintain abdominal and subdiaphragmatic pressures that assist the expiratory excursion of the diaphragm.
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TABLE 5.14 Respiratory Muscles: Innervation Levels Muscle
Cord Level
Action
Diaphragm Sternocleidomastoid Trapezius Scalene Serratus anterior Pectoralis major Erector spinae Intercostal
C2–C4 Acc. N. and C2 Acc. N. and C3–C4 C2–C7 C5–C7 C5–T1 Segmentally dependent T1–T12
Diaphragm excursion Elevates sternum Stabilizes scapula Raises ribs Raises ribs Raises ribs Extends spinal column Segmentally dependent
The greatest degree of respiratory impairment occurs secondary to diaphragmatic paralysis, for it contributes to approximately three quarters of the tidal volume when supine and two thirds of the tidal volume when sitting.16 The most important accessory muscles of respiration are the sternocleidomastoid muscles (SCM), which elevate the sternum, allowing for greater ribcage expansion. After spinal cord compromise, an aggressive rehabilitative approach should be applied to all respiratory muscles that have a corresponding functional spinal cord level. Respiratory impairment will result in increased risk for atelectasis, respiratory infection, and systemic hypoxia. The primary cause of death in acute SCI is respiratory insufficiency.17
5.7.6 BOWEL
AND
BLADDER DYSFUNCTION
Abnormal patterns of micturition and bowel function are common features of moderate to severe spinal cord disease or injury. Disturbances of the bowel and bladder occur in myelopathy due to the loss of suprasegmental facilitatory and inhibitory influences from the pontomesencephalic tegmentum via the reticulospinal tract. Corticospinal pathways also contribute inhibitory influences. Acute spinal cord lesions often result in a state of shock that may be associated with inhibition of the bladder wall, resulting in urinary retention and overflow incontinence. The bladder should not be allowed to retain more than 400 to 500 mL of urine in order to reduce the risk for infection, renal compromise, and autonomic hyperreflexia. As the state of spinal shock resolves and lower extremity muscular spasticity develops, the bladder often becomes spastic, resulting in automaticity and incontinence. This is referred to as the neurogenic bladder or spinal bladder. The patient with myelopathy will not appreciate the degree of bladder fullness, and a rise in intravesical pressure often induces a rapid, reflexively driven emptying of the bladder. The patient can often stimulate the exaggerated bladder response by tapping the abdomen or stroking the inner thigh. This stimulates reflexive detrussor contraction and sphincter relaxation with subsequent emptying of the bladder.
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It is important to note that voluntary micturition is not lost with unilateral spinal cord lesions.18 This is why some patients with spondylotic myelopathy and incomplete cord syndromes do not present with a neurogenic bladder. If the spinal cord is compromised in the region of the conus medularis, a lower motor neuron bladder condition may result. A lower motor neuron lesion results in a flaccid bladder that will distend to the point of overflow incontinence. Sustained urinary retention may result in a medical emergency. A similar pathologic mechanism and presentation in SCI occurs relative to the bowel, producing atony and impaction. The anatomical pathways subserving the bowel are similar to that of the bladder. Parasympathetic innervation occurs at S3–S5. Spinal shock often results in paralytic ileus, and in some cases the colon may progressively dilate to become a neurogenic megacolon. The dilated colon contributes to the risk for fecal impaction and diverticuli. The clinical assessment of the patient with suspected ileus should include careful auscultation of the abdomen, for the patient may not experience any visceral sensation. The anal reflex generally remains intact unless there is a complete transverse cord lesion. Sphincter control of the bowel is lost with SCI. A lower motor neuron lesion (LMNL) occurs when the anterior horn cells of S3–S5 within the conus medullaris or the S3–S5 nerve roots are injured. This LMNL presents with impaired peristalsis, atony, and a flaccid anal sphincter. The loss of anal sphincter tone and control leads to fecal incontinence. Significant bowel or bladder disease may develop without any sensation of pain. The SCI patient should be evaluated for GI or pelvic disease on a frequent basis because of the absence of early subjective indicators of visceral disease.
few of these individuals were able to experience ejaculation or orgasm. In contrast, Comarr8,9 noted that in 150 males with SCI 82% were able to obtain erections; only 1% could ejaculate and have an orgasm. Preservation of pinprick sensation in the sacral dermatomes is a more significant prognostic indicator for the SCI male to recover function of erection and ejaculation than preservation of light touch, perception, or retained volitional motor function of the pelvic muscles. The clinical presence of a bulbocavernosus reflex and/or anal sphincter tone suggests that the individual has retained upper motor neuron sexual function. An individual with an incomplete spinal cord lesion may have normal sexual function. Atrophy of the testicles is relatively common following spinal trauma and can be noted as early as 3 to 4 months after an injury; male SCI patients are often sterile, which in part may be secondary to abnormal temperature regulation. Spinal cord injury above L1 in women generally results in a limited ability to achieve orgasm but fertility is not affected. Female paraplegics who are still menstruating are able to conceive and give natural birth to children. Ohry et al.20 reported that women who suffered an SCI had no significant change in their sex hormone levels when compared to non-spinal-injured women. This aspect of female sexual function typically remains unchanged after an SCI. In complete cord transectional lesions, there is loss of vaginal sensation; however, there may be some emotional satisfaction from intercourse. Women with SCI may attain a state of heightened arousal secondary to tactile stimuli above the sensory level of injury. Few paraplegic women are able to experience orgasms.
5.7.7 SEXUAL FUNCTION
The individual with SCI will lose some sensation below the level of the segmental compromise. This will lead to a reduction or loss of the ability to perceive injury to the skin, thus increasing the likelihood of progressive skin damage. Muscular paresis or paralysis accompanying spinal insult leads to sustained postures and risk for pressure necrosis of cutaneous and subcutaneous tissues. This breakdown of the skin is referred to as a decubitus ulcer. A weight-shifting program must be initiated in order to reduce the risk for complicated skin lesions. The goal of intervention is to prevent skin breakdown, increase tissue tolerance for pressure, and improve skin hygiene.
An ablative injury to the spinal cord above the level of L1 impairs the capacity for voluntary erections in the male subject. There are two primary categories of erection: psychogenic and reflex. A psychogenic erection occurs as the result of descending messages from the brain initiated by voluntary, visual, or auditory arousal. Reflex erection occurs secondary to direct physical contact to the penis or other erogenous areas. The nerves that control the erection arise from the S2–S4 segments of the spinal cord within the conus. Spinal cord insult above these segments impairs the ability to have a psychogenically induced erection, although some of these patients may obtain an erection with physical stimulation. The ejaculatory capacity varies greatly between SCI patients. The ejaculatory process is mediated by multiple spinal segments, and it is usually impaired to some degree with myelopathy. Jochheim and Wahle19 reported that 30 to 75% of SCI male patients with spastic paralysis were unable to obtain an erection. Very
5.7.8 SKIN COMPLICATIONS
5.7.9 PSYCHOLOGICAL CONSIDERATIONS The individual who suffers a SCI experiences a foreverlife-changing experience. He or she will have to learn to adapt to physical and nonphysical limitations. This is often a long and arduous road to travel. Immediately after the injury there is often a period of grief and denial relative
Assessment of Spinal Cord Injury and Myelopathy
to both the severity and chronicity of their presentation. The individual’s hopes and short-term goals may not be realistic. Many have a difficult time conceptualizing the potential permanency of their limitations. As they progress through physical rehabilitation, the physical limitations are realized and greater attention is focused on the ramifications of the spinal injury. In some cases, the degree of disability may be magnified. Realization of the permanency and degree of limitations often precedes moderate to severe depression. The individual may begin to manifest negative behavior towards their therapist, doctors, friends, and family members. The period of initial depression may extend from a few weeks to more than a year. During this time, psychological support is necessary. The support may be limited to a social worker, psychologist, or in some cases psychiatric attention. A team approach may be required to improve the coping skills and enhance the motivation level of the patient with SCI. Underlying psychiatric illness may become manifest or magnified by the onset of myelopathy. Individuals must be motivated to capitalize on the functions they have and must be shown that they can improve their status.
5.7.10 FEVER Spinal cord injury may result in elevated body temperature secondary to numerous etiologies, which include infection and impaired physiologic temperature regulation due to the SCI. The injured patient may be unable to experience symptoms associated with an infection due to the level of SCI placing a greater demand on the expertise of the attending health care team. An undetected infection in an SCI patient can lead to significant complications or death. Respiratory infections are more common during the immediate post-injury period and can contribute to a febrile state. Two to four weeks after SCI, urinary tract infections become a more common cause for temperature elevation. An infected decubitus lesion is not an uncommon cause for a febrile state. Some individuals with spinal cord injury may experience persistent elevation of their body temperature secondary to impairment of physiologic temperature-regulating capacity. The development of a persistent or spiking fever in a patient with SCI should prompt a diligent search for an infectious or otherwise treatable etiology. The workup for infection should include CBC with differential, urinalysis, blood culture, and chest X-ray if necessary. The SCI patient may develop spinal osteomyelitis associated with post-traumatic spinal surgery, requiring appropriate work-up. Radioisotope tagging may be required to identify a potential region of infection within the chest or abdomen. If a fever of unknown origin persists 4 to 6 weeks after the initial workup, the assessment should be repeated prior to assuming the fever is secondary to
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TABLE 5.15 Factors Limiting Joint Range of Motion in Patients with Myelopathy • • • • • • • • • • •
Joint subluxation Adhesive capsulitis Contractures Muscle hypertonicity Spasticity Pain Joint deformity Heterotrophic ossification Neuropathic arthropathy Degenerative joint disease Paralysis/paresis
impaired thermoregulatory mechanisms in the absence of other pathology. The fever associated with SCI-related disruption of temperature regulation mechanisms often improves over time.
5.8 MYELOPATHY AND ASSOCIATED MUSCULOSKELETAL CONDITIONS The workup of the individual with myelopathy is ongoing, due to potential complications and musculoskeletal consequences. It is important that the rehabilitative approach be tailored to the individual’s unique musculoskeletal presentation. No two myelopathic presentations will be exactly the same due to varying degrees of SCI and predisposing peripheral musculoskeletal states. Unidentified progressive musculoskeletal complications will impact the individual’s capacity to participate in physical rehabilitation, subsequently reducing the potential for recovery (Table 5.15).
5.8.1 CONTRACTURES Chronic limb or joint immobilization can lead to physiologic shortening of supportive and contractile tissues, resulting in contractures. Additional causes of contractures include chronic spasticity, unopposed pull of agonist muscle, paralysis, and bodily positioning. The presence of contracture contributes to disability by greatly impairing the ability to perform activities of daily living (ADLs). Risk for contractures can be significantly reduced by implementing periodic assisted range of motion (ROM) exercises, applying various forms of traction, and utilizing specialized beds.
5.8.2 ARTICULAR SUBLUXATION The shoulder is vulnerable to subluxation due to its anatomic configuration and dependence upon surrounding
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
muscles for stability. Individuals with high SCI (above C5) lose the shoulder-stabilizing functions of the deltoid and rotator cuff muscles. Paralysis of periscapular muscles further contributes to shoulder pathomechanics and alteration of the angle of the glenoid fossa. The glenoid fossa tends to take on a lateral and downward angle.14 Paralysis of the supraspinatus muscle contributes to translation and subsequently subluxation of the humeral head. An intact C5 level offers some stabilization to the shoulder, reducing the risk for subluxation.
5.8.3 HETEROTOPIC OSSIFICATION Heterotopic ossification (HO) refers to the formation of bone in abnormal areas, usually within connective tissue between muscle and tendon planes. A relatively common complication of SCI, HO may involve axial and extraaxial joints and tends to occur more frequently around the hip, followed by the knees, shoulders, and elbows. Usually appearing within 1 to 4 months after injury, HO can sometimes take several years to develop.21 Heterotopic bone formation occurring a year or more after SCI may result from tissue injury secondary to infection. During the early stages of HO, the condition may be clinically silent. Progressive HO is often associated with an inflammatory response, edema, focal hyperthermia, and pain affecting the involved joint. The hips are the most frequently involved joint often afflicted within the flexor or adductor areas. The differential considerations are many and include thrombophlebitis, deep venous thrombosis, cellulitis, joint sepsis, osteomyelitis, and fracture. The workup often requires venography and a bone scan. A bone scan can demonstrate HO 7 to 10 days earlier than a plain X-ray. The three-phase bone scan provides the earliest detection. A classification system has been developed differentiating between myositis ossificans and HO.21
5.8.4 OSTEOPOROSIS A common complication of SCI is osteoporosis. This often occurs as the result of immobilization secondary to paresis or paralysis. Osteoporosis results from the rate of bone resorption exceeding that of bone deposition due to inadequent physical loads. The bone loss tends to progress more rapidly during the first year after SCI. The presence of osteoporosis increases the risk for trabecular failure and fracture. Bone injury may occur due to strong involuntary muscle contractions.
5.8.5 NEUROPATHIC ARTHROPATHY Any condition that compromises sensory and neuroregulatory feedback from articular and periarticular structures may contribute to the development of the neuropathic joint. Myelopathic conditions that have been associated with neurosensory deficits and neurogenic arthropathy
include spinal trauma with paraplegia,22-24 tabes dorsalis,25 and syringomyelia.26-28 Syringomyelia may contribute to the development of neuropathic arthropathy (NA) due to compromise of decussating fibers of the spinothalamic tract. Cervical syringomyelia in rare instances may lead to the triad of syringomyelia tardia, paraplegia, and neuropathic arthrosis of the shoulder.29 The shoulder may be susceptible to NA due to the propensity for glenohumeral instability and related cumulative trauma with deafferentation. The sequence of pathological features that characterize NA include deafferentation, distention of the involved joint space due to effusion, ligamentous laxity, biomechanical instability, cumulative destruction of articular cartilage, and hypertrophic and atrophic remodeling of the bony architecture. Severe deafferentation of an articular complex results in impairment of autonomic regulation, poorly mediated periarticular muscle tone, and a loss of reflexive muscular protection, rendering the joint susceptible to cumulative microtrauma. There are three primary radiographic patterns: (1) atrophic, (2) hypertrophic, and (3) a mixed appearance.30
5.9 ELECTRODIAGNOSTIC ASSESSMENT Electrodiagnostic studies such as electromyography, nerve conduction studies, and somatosensory evoked-potential studies are an extension of the clinical examination and should be correlated with information gathered in the history, physical examination, and imaging work-up. Electrodiagnostic testing can be used to evaluate physiologic function of the nerves of the central and peripheral nervous system. A normal electrophysiologic study does not always exclude the possibility that minimal to mild nerve damage has occurred. The primary reasons for performing electrodiagnostic testing include confirming or excluding neurological compromise, localizing neurologic compromise, and determining the extent of neurologic injury. Electrodiagnostic tests often utilized to provide quantitative information after SCI include the compound motor unit action potential (CMAP, or M-response), sensory nerve action potential (SNAP), segmental responses (Hreflex or F-wave), needle electromyography (NEMG), somatosensory evoked potential (SEP), motor evoked potential (MEP), and NEMG in conjunction with bladder function studies. A discussion of bladder studies is found in Section 5.15.3.3. Timing of electrodiagnostic evaluation must be considered in order to avoid false-negative results. Acute injury of spinal cord axons can result in immediate compromise of SEP and MEP latencies and amplitudes. Consequently, these two procedures are good for acute and subacute monitoring of SCI. Muscle membrane instability secondary to denervation may not manifest for 2 to 6 weeks although the needle EMG may reveal reduced motor-unit firing rates and reduced motor-unit recruitment density immediately. The CMAP or M-response may not
Assessment of Spinal Cord Injury and Myelopathy
SSEP tests integrity of the posterior column
From upper extremity
MEP tests integrity of the corticospinal pathway
From lower extremity
To segmental muscles
FIGURE 5.7 Motor evoked potentials test the corticospinal pathway, from cortex to peripheral muscle end organ. (Copyright J.M. True, D.C.)
reflect axonal loss for 5 to 10 days after the onset of myosynaptic degradation and muscle degeneration. After an acute spinal injury, T-reflexes may be absent for many weeks to months.
5.9.1 SOMATOSENSORY EVOKED POTENTIALS Somatosensory evoked potentials test the largest myelinated fibers of the medial lemniscal system, the group 1A muscle afferent fibers and the group II afferent fibers. The SEP response is generated via electrical stimulation of the peripheral mixed nerve and recorded from various locations along the course of the nerve from periphery, spinal cord, and cerebral cortex. Thus, SEPs have the potential to detect CNS pathology involving the posterior columns (Figure 5.7). They have excellent correlation for vibration and joint position sense loss; however, the SEP study is poor for exact localization and it does not specify the nature of the pathology producing the neurophysiologic deficit. SEP studies are commonly used in the intensive care unit or operating room for diagnosis, monitoring, and establishing a prognosis in SCI and cervical spondylotic myelopathy (CSM).31,32 Within general neurological practice, they are also used for the correlation and diagnosis of CSM or posterior column disease.33-39 The most important information recorded from evoked potential studies is the latency, which refers to the time of stimulus to the onset of the recorded waveform. This value varies according to the nerve studied. Latencies vary considerably between upper and lower extremity stimulation, because of the length-dependent variable of nerve conduction: the longer the nerve length, the longer the latency of the response. Both animal and human studies suggest that the SEP components are dependent upon the integrity of posterior column medial-lemniscal pathways.
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Somatosensory evoked potential evaluation can be helpful for the assessment of suspected myelopathy in the patient with impaired vibration or joint position sense. SEP evaluation may help localize a spinal lesion, but the findings will not reveal the type of compromise present. Noel and Desmedt35 reported that sural nerve SEPs were often abnormal in patients with compressive cervical myelopathy. They also report that lower extremity sural testing was more sensitive than upper extremity SEP evaluation. Some researchers report a higher detection rate of CSM using tibial SEPs.34,36,39 It has been suggested that lower extremity SEP procedures may uncover silent myelopathy even in the absence of gross myelopathic clinical findings.34,35 Yu and Jones39 found that SEP studies were occasionally more sensitive than their clinical examination. Snowden et al.37 found dermatomal evoked potentials (DEP) to be a more sensitive indicator of spinal stenosis than needle electromyography (Figure 5.8). Focal compromise of the spinal cord will usually be associated with slowing between two spine recording sites. Diffuse myelopathy or multiple sclerosis often leads to an absent scalp potential. Upper extremity SEP studies can be helpful in the localization of cervical myelopathy. A poor cervical response can be expected with a cord lesion at C6 or C7 to median stimulation. Ulnar stimulation with high cervical recording can provide a good screen of peripheral to central conduction across the cervical cord.40 High cervical lesions, which spare the recording of cervical potentials from a lower level, are often associated with attenuation of scalp responses. Somatosensory evoked potential abnormalities may be present in patients with a number of spinal disorders, including intrinsic expansile cord lesions such as syringomyelia. Abnormal SEPs have been reported in patients with multiple sclerosis, hereditary spinocerebellar degeneration, subacute combined degeneration, and hereditary spastic paraplegia. The SEP study should be considered a valuable part of the myelopathic risk profile.
5.9.2 MOTOR EVOKED POTENTIALS Motor evoked potentials can be obtained by stimulating the neural pathways over the cortex or over the spine. The former is often referred to as transcortical magnetic stimulation. MEP assessment can be used to evoke the central and peripheral motor pathway allowing for measurement of the motor conduction time from the cerebral cortex to the muscle or from the spine to designated muscles. Motor evoked potentials are usually recorded at extremity muscles. MEP assessment can lead to the measurement of central motor conduction time (CMCT). Chokroverty et al.41 and Jarrat42 reported that some patients with cervical myelopathy demonstrated abnormal central conduction characteristics after transcortical stimulation. Other conditions associated with prolonged
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
DEP Lesion Differentials
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FIGURE 5.8 Somatosensory evoked potentials test the posterior columns by stimulating the peripheral nervous system or extremity mixed nerves and recording the impulse at various locations as it ascends to the cortex. (Copyright J.M. True, D.C.)
CMCT include myelopathy associated with rheumatoid arthritis, cervical stenosis, post-traumatic syringomyelia, and complete and incomplete thoracic cord injuries.
MEP abnormalities often do not improve after surgical intervention for CSM and are more likely to improve after shunting for syringomyelia.43
Assessment of Spinal Cord Injury and Myelopathy
115
3. Stimulation of alpha motoneurons producing an efferent volley F-wave
2. Antidromic conduction
4. Orthodromic conduction
1. Stimulation at the wrist
5. Recording from the distal innervated muscle
FIGURE 5.9 The F-wave is valuable for evaluation of cord injury because the central component of the test depends on activation of intact alpha motor neurons. (Copyright J.M. True, D.C.)
Transcortical stimulation (TCS) and F-waves have been used to serially study the postsurgical neurological improvement of myelopathy from disk herniation. This study44 demonstrated that functional motor improvement was accompanied by an increase in spinal cord motor conduction velocity in patients with mild neurological impairment after surgery, whereas no definite change was seen in patients with moderate or severe neurological impairment. TCS has been evaluated in incomplete SCI; however, one study found no correlation between the TCS data and clinical assessment beyond the initial recovery period.45
5.9.3 LATE RESPONSES The three general types of late reflexes beneficial for evaluation of central neuronal integrity are the F-wave, Hreflex, and the T-reflex. Obtaining baseline segmental responses can be used to help monitor myelopathic changes. Useful measurements include minimal H-reflex and F-wave latencies, F-wave chronodispersion, F-wave persistence, and H/M and F/M amplitude ratios.46 The Fwave response is a late response that occurs following the compound motor action potential. It is a recurrent discharge of antidromically activated alpha motor neurons (Figure 5.9). The F-wave can be used to assess the effects of supraspinal and segmental influences on the central state of the alpha motor neuron population within the spinal cord. F-waves are often absent in patients with spinal shock, reduced in persistence in patients with acute SCI without spinal shock, and normal in persistence in patients with chronic SCI.47 During spinal shock, the loss of tendon tap reflexes and flaccid muscle tone were associated with a low persistence of F-waves and loss of flexor reflexes, whereas H-reflexes were readily elicitable. During the transition to spasticity, the reappearance of tendon tap reflexes and muscle tone and the occurrence of spasms were associated with the recovery of F-waves and flexor reflex excitability.48,49 The F-wave amplitude may be increased in patients with chronic myelopathy due to compromised descending
inhibitory influences. A reproducible, abnormally large amplitude F-wave may occur ipsilateral to the side of myelopathy. The F-waves are typically larger in amplitude than the uninvolved side coinciding with the side of muscular spasticity.50,51 Serial F-wave studies may occasionally be helpful in the assessment of therapeutic efficacy in the myelopathic patient. H-reflexes are often absent or markedly suppressed in patients with spinal shock within 24 hours of injury; however, the response will usually recover to normal amplitudes within several days post-injury. This recovery will occur despite the fact that the F-wave response will be absent for several weeks post-injury. The H-reflex can be used to monitor the development of hyperactive muscle stretch reflexes after the onset of myelopathy and associated upper motor neuron (UMN) weakness. Deep tendon reflexes (T-reflexes) are also proportionally more depressed in spinal shock than H-reflexes. The H-reflex will be elicitable for days or weeks before the development of clinical reflexes.47 The maximum H-reflex amplitude can be placed over the M-wave amplitude (H/M ratio) in order to calculate the magnitude of the spinal motoneuronal response that responds through reflexive stimuli. H/M ratio increases parallel to the development of muscular spasticity.52 Similar findings have been reported using a F/M ratio.51 The T-reflex is another valuable late reflex study to record from a patient with suspected or confirmed myelopathy. In a study by Karandreas et al.,53 pathological Treflexes were found in 73.1% of the patients, while EMG — which was the next more effective method — was positive in 38.5% of the cases. Eight pathologically delayed T-waves were recorded from muscles with clinically normal or even exaggerated reflexes.
5.9.4 NEEDLE ELECTROMYOGRAPHY A pure upper motor neuron lesion characteristically presents with normal insertional activity, an absence of fibrillation potentials, and normal-appearing motor unit action potential morphology. Insertional activity in the muscle
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may be decreased if there is profound motor loss. At the level of the segmental lesion there may be compromise of the alpha motor neuron pool, thus creating a lower motor neuron lesion. This may result in muscle denervation changes. Acute and subacute EMG changes are characterized by insertional instability and spontaneous discharges such as sharp waves and fibrillations. Chronic muscle denervation changes are characterized by large or prolonged-duration polyphasic motor unit action potentials and reduced recruitment density. Electromyogram changes corresponding to spinal segments below the level of compromised gray matter will present with a pattern of corticospinal loss. Myelopathic compromise of the corticospinal tract results in diminished descending input to the alpha motor neuron pool. This loss of UMN drive subsequently contributes to a slight delay in motor unit response, a reduction of motor unit recruitment (firing) density, and slowed motor unit firing rate. Excited motor units fire slower than expected for the degree of contraction and voluntary effort. This stands in contrast to the characteristic rapid motor-unit-firing pattern of lower motor neuron involvement such as radiculopathy. Fasciculation potentials without evidence of other LMNL electromyographic characteristics may appear in the lower extremities with cervical myelopathy. Lower extremity fasciculations have been abated with cervical surgical decompression procedures.54,55 Fasciculations are likely to occur secondary to the loss of suprasegmental inhibitory influences. Mild passive muscle stretch performed during needle recording may increase the occurrence of spontaneous fasciculations or a cramp discharge in the presence of mild spasticity.
5.9.5 SENSORY NERVE CONDUCTION STUDIES Sensory nerve conduction evaluation can help determine whether there is a preganglionic or postganglionic sensory lesion. Postganglionic injury resulting in sensory axonopathy will lead to a reduction of the sensory nerve action potential amplitude and area under the waveform. In contrast, a lesion proximal to the dorsal root ganglia (DRG) will spare the distal axons, therefore preserving the distal SNAP.
5.9.6 MOTOR NERVE CONDUCTION STUDIES Evaluation of the compound motor unit action potential can provide insight relative to the degree of lower motor neuron (LMN) compromise with the anterior horn after SCI or chronic compressive myelopathy. Reduced CMAP amplitude and decreased area suggest a loss of motor axons, although muscle atrophy can also result in similar CMAP appearances. Needle electromyography can help differentiate the presence of disuse vs. denervation atrophy of a muscle. Collateral motor axon sprouting from spared axons and related muscle fiber reinnervation can contribute to some recovery of CMAP amplitude. It has
TABLE 5.16 Possible Magnetic Resonance Findings in Acute Spinal Cord Injury • • • • • • • • • • • • • • • •
Vertebral subluxation Vertebral dislocation Vertebral lithesis Ligamentous avulsion Vertebral fracture Bone edema Disk herniation, extrusion, and sequestration Extradural hematoma Intradural hematoma Intramuscular hematoma Intramedullary hemorrhage Intramedullary edema Intramedullary cavitation Cord enlargement Cord compression Cord transection
been estimated that a motor axon can reinnervate neighboring denervated muscle fibers, increasing the size of the motor unit as much as two- to fourfold.56
5.10 DIAGNOSTIC IMAGING The goal of imaging is to evaluate anatomy and tissue function without utilizing invasive and potentially harmful techniques whenever possible. There are three primary goals in imaging of the spinal lesion: (1) localization, (2) characterization, and (3) assessment of secondary compromise and potential compromise. Effective imaging requires magnification of the inherent differences between tissues by using methods that provide contrasting information. This information may be anatomic, biomechanical, or biochemical in nature. Numerous imaging modalities, protocols, and techniques are now available, each providing a unique window into the body (Table 5.16). Rapidly advancing technology brings us closer to the physiology, biochemistry, and assessment of the dynamic properties of tissue at the microstructural level. Several of the existing and potential applications of imaging in the assessment of SCI, myelitis, and chronic myelopathy are described below; this discussion is meant to provide a brief introduction, and the reader is referred to neuroradiology texts for a more detailed treatment of the methods available.
5.10.1 MAGNETIC RESONANCE IMAGING Magnetic resonance imaging (MRI) is a noninvasive and relatively safe technology. The signal used in MRI arises primarily from protons within the body’s water, although other constituents are involved as well. Energy given off
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Canal to Body Ratio = 1:1
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A
B
AP Canal Diameter 13 - 22 mm
D
C A A- 1 mm Epidural Space B- 1 mm Dura/Arachnoid C- At Least 1 mm Subarachnoid Space D- 8-9 mm AP Cord Width
FIGURE 5.10 MRI measurements for the determination of available cord space within the spinal canal. Measurements A, B, and C should be assessed circumferentially around the cord. (Copyright J.M. True, D.C.)
TABLE 5.17 Conditions Associated with Spinal Cord Enlargement
TABLE 5.18 Contraindications in Magnetic Resonance Imaging
• • • • • • • •
• Relative Claustrophobia Surgical staples • Absolute Pacemaker or other implanted device Confirmed orbital ferromagnetic fragments Ferromagnetic vascular clips Intracranial vascular clips
Intramedullary tumor Spinal cord infarction Syringomyelia Viral and bacterial infections Multiple sclerosis Intramedullary hemorrhage Intramedullary edema Radiation myelopathy
by the changing spin cycles of tissue protons is influenced by the application of radiofrequencies and pulsed magnetic fields. Each tissue has a unique signal pattern dependent upon the type, quantity, and density of molecular elements. During the MR study, the signals are recorded and encoded to create a multiplanar or dimensional rendering of tissue relationships. Tissues can be identified based on a three-dimensional function of density in addition to their T1 and T2 MR-specific relaxation properties. The major differences between MR and computed tomography (CT) imaging are that in MRI (1) images have complex values of amplitude and phase for each pixel, (2) tissue signals are noninstantaneous and can be constructed over time, (3) image contrast reflects three mechanisms (T1, T2, and density), and (4) Fourier transform data are directly acquired. Magnetic resonance imaging is also the initial test of choice for evaluating the spinal cord because it provides excellent soft-tissue resolution and characterization of tissue properties. MRI can be used to assess the size and volume of the spinal cord (Figure 5.10, Table 5.17). MRI is more sensitive than either myelography or CT in the assessment of intrinsic spinal cord lesions57 and extramedullary pathology. MRI and CT should be considered complementary studies due to the moderate degree of concordance in the differentiation of
disk and osseous pathology.58 Many specialized protocols can be applied in MR imaging, some of which are listed below. MRI is contraindicated in patients with the conditions shown in Table 5.18. 5.10.1.1 Rapid MR Sequencing Echo planar imaging (EPI) has many applications for CNS evaluation, particularly in the brain. EPI protocol allows for more rapid information to generate an image than other common forms of imaging. EPI can literally acquire T2-weighted images within 2 to 3 seconds. Ultra-fast EPI is so quick that it can effectively be used to evaluate physiology; subsequently, it is used to perform functionalactivation MR studies. 5.10.1.2 Turbo Echo MR Sequences Turbospin echo (TSE) sequences are a type of T2-weighted imaging useful for the evaluation of spondylosis and degenerative spinal conditions, because this technique reduces involuntary motion artifact and requires a relatively short acquisition time. Contrast resolution is generally higher with TSE than SE when evaluating intrinsic spinal cord lesions, therefore, TSE protocol should be considered when evaluating for intrinsic spinal cord conditions.59 Its
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TABLE 5.19 Properties of Magnetic Resonance Contrast Agent Gd-DTPA
TABLE 5.20 Indications for Use of Magnetic Resonance Contrast Agents
• • • • • • •
• • • • • • • • • •
Helps differentiate disk from scar Helps classify tumors Serial evaluation of reparative process Detects vertebral endplate leaks Reveals altered blood/cord barrier Demonstrates region of aggressive tumor activity Improves detection of vascularized granulation tissue
detailed delineation of spinal anatomy allows for grading of spinal stenosis and evaluation of myelopathy.60 5.10.1.3 Inversion Recovery The use of inversion recovery sequences with a short T1-time suppresses signals arising from fat. This provides good contrast for bone edema after spinal injury that may otherwise be difficult to see. The presence of acute or subacute bone edema suggests the possibility of spinal fracture, risk for vertebral instability, and risk for SCI and raises the possibility of post-traumatic vertebral dislocation with spontaneous reduction. 5.10.1.4 Contrast Enhancement Gadolinium (gadolinium diethylenetriamine pentaacetic acid, Gd-DTPA) is the most widely utilized contrast agent for neuroimaging (Table 5.19). Gd-DTPA is administered by intravenous injection and is primarily a T1-shortening agent that enhances the properties of various tissues and their vascular states (Table 5.20). It has become an invaluable tool in imaging the central nervous system due to its ability to pass through a breakdown in the blood-brain and blood-spine barrier. The properties of Gd-DTPA allow for the enhancement of highly vascularized tissue, helping to differentiate epidural scar from disk, vascularized tumor from normal surrounding tissue, and regions of acute inflammation. It is particularly helpful in the assessment of the postoperative back. Pre- and postcontrast image comparisons are required. 5.10.1.5 Kinematic MRI Kinematic MRI or cine MRI provides useful information about the relationship of pathology to the spine in various positions. This protocol should only be considered an adjunctive part of a routine MRI study of the region in question. This study simulates some of the normal daily movements and therefore may help explain intermittent neurological presentations. It may be particularly helpful in the evaluation of dynamic stenosis, vertebral instability, subluxation, and the work-up for ligamentous injury.
Tumor Infection Infarction Suspected fibrosis Differentiating scar vs. disk Arteriovenous malformation Postsurgical status Post-traumatic lesions Suspected metastatic disease Demyelinative disease
Kinematic MRI may help identify whether a region of high signal intensity within the spinal cord might be related to repeated microtrauma secondary to dynamic stenosis. The procedure can occasionally document an unstable disk protrusion that changes in size during spinal translation. Kinematic MRI has been used to demonstrate abnormal fluid flow and spinal cord compression by a spinal arachnoid cyst.61 Dynamic MRI has been helpful in the assessment of rheumatoid arthritis with upper cervical instability.62 Flexion/extension MRI of the cervical spine is useful for evaluating the patient at risk for spinal cord compression secondary to vertebral instability and to help determine candidacy for decompression and arthrodesis.63 Kinematic MRI studies of the cervical spine have demonstrated significant changes in spine and cord length during flexion and extension.64 When comparing flexion to extension, the cervical spinal canal and spinal cord have been shown to lengthen as much as 12 mm (cord) and 28 mm (canal).64 Flexion/extension MRI of the cervical spine is useful for evaluating the patient at risk for spinal cord compression secondary to vertebral instability to help determine candidacy for decompression and arthrodesis.62 Dynamic MRI of the cervical spinal cord has demonstrated linear elongation of 6 to 10% of its normal resting length along the anterior and posterior surfaces with average displacement of 1 to 3 mm.65 The greatest translation during cervical cord flexion occurs along the posterior surface of the cord. The information obtained with kinematic cervical MRI may change therapeutic management60 and is important in planning stabilizing operations for the cervical spine.62 For the purpose of assessing the potential of kinematic MRI, four classifications of pathology have been proposed: stage I, cervical disk disease; stage II, spondylosis; stage III, spondylosis and restricted motion; and stage IV, cervical spondylotic myelopathy.60 In one study, the use of kinematic MRI changed the course of surgical management in stages III and IV.60 With significant spinal cord compression, movement (translation) of the cord is
Assessment of Spinal Cord Injury and Myelopathy
diminished. Follow up on post-operative cases has demonstrated good recovery of spinal cord and CSF motion.66 5.10.1.6 Functional MRI Functional magnetic resonance imaging (fMRI), primarily utilized for brain assessment, identifies focal regions of increased neuronal-cellular activity activated by the performance of isolated physical or cognitive tasks. The technique applies blood-oxygen-level-dependent (BOLD) imaging to detect changes in MR contrast associated with changes in tissue oxygen concentration. BOLD imaging is effective because of the magnetic properties of hemoglobin. When oxygen binds to iron (oxyhemoglobin), the magnetic properties of iron are suppressed. When oxygen is not bound to iron (deoxyhemoglobin), the magnetic properties of hemoglobin are enhanced. Oxyhemoglobin is diamagnetic and deoxyhemoglobin paramagnetic. This acquired difference in magnetic characteristics of hemoglobin while passing through the tissue allows for differentiating regions of greater deoxygenated vs. oxygenated hemoglobin. This results in the ability to generate an image delineating regions of increased cellular metabolism and increased oxygen uptake. High-field fMRI therefore provides a noninvasive method for identifying regions of activated tissue. This technique holds great promise for the evaluation of the spinal cord. In fact, fMRI has recently been used to demonstrate spinal cord motor activation associated with unilateral handclosing tasks.67,68 5.10.1.7 Magnetization Transfer Magnetization transfer (MT) in MR imaging refers to the relaxation properties between two interactive populations of protons: free mobile water protons and protons with restricted mobility in semisolid macromolecular pools.69 This property combined with new technology has proved a unique contrast mechanism in tissue imaging different from other commonly used protocols. This protocol was applied to MRI in order to improve contrast between stationary and moving fluids. MT improved the contrast between background neural tissue and the circulating blood. The MT protocol has been applied to spinal imaging, allowing for improved cord-to-CSF contrast and creating a myelogram-like effect. Disk material creates moderate MT suppression, creating improved contrast between disk material and CSF.70 MT provides a new basis for contrasting between different tissues within the brain and spine. It provides a window into the behavior of tissue that will help to study the stages, degree, and evolution of tissue injury, remodeling, and repair. Emerging quantitative MT imaging has been used to characterize pathologic tissue and to quantify the biochemical attributes and quantity of myelin comprising white matter.71,72
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5.10.1.8 Diffusion-Weighted Imaging New MR techniques and protocols are being developed in an attempt to further distinguish unique structural characteristics of tissues and their function in health and disease. Water within tissues diffuses across different planes in a translational motion. MR imaging of this mechanism provides a new method for characterizing tissues at the microscopic level. Values are assigned to water-diffusion properties and lead to the generation of an MR image. When diffusion occurs equally in all directions, it is referred to as isotropic. When it occurs in a specific direction or an asymmetric pattern, it is referred to as anisotropic. Isotropic diffusion is more likely to take place in tissues that lack an ordered microarchitecture. An ordered microarchitecture is more apt to influence water diffusion, leading to greater anisotropy. Factors that influence diffusion properties include connective tissue density, cell packing density, membrane fluidity, intracellular organelle arrangement, nerve fiber density, degree of myelination, viscosity, temperature, and blood flow to the region. MR diffusion imaging techniques actually measure apparent diffusion coefficients because the vast array of tissue variables renders pure assessment impossible. Biochemical and tissue micoarchitectural changes with tissue injury or disease will alter the pattern of water diffusion. This pattern can be demonstrated by using this specialized MR technique. Diffusion imaging of the brain has been used to help classify the potential for neurological recovery vs. irreversible tissue damage after ischemia or infarction.73 Advancing knowledge about water-diffusion characteristics within the human spinal cord will provide valuable insight about the nature of spinal cord pathology. The requirement for higher resolution and the effects of motion have made the prospect of diffusion-weighted imaging challenging in the assessment of the spinal cord.74,75 Diffusion imaging is helpful in the assessment of white matter damage76 and will continue to impact the evaluation of stroke, multiple sclerosis, amyotrophic lateral sclerosis, head injury, and SCI.77 Diffusion-weighted echo planar imaging (DW-EPI) improves delineation between gray and white matter.78 The application of DW-EPI provides greater insight about the evolution of ischemic, compressive, and demyelinating disorders. It may also provide delineation of specific spinal tract compromise in the future. 5.10.1.9 MR Spectroscopy Magnetic resonance spectroscopy (MRS) of the CNS has been primarily restricted to the brain and brainstem due to technical limitations. The MR spectroscopy protocol can be added to routine MR assessment of the brain and brainstem with MR spectra can be obtained in a relatively short period of time. Numerous metabolites have been
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identified based on their spectral signature. MRS may be utilized to visualize tumor metabolite signatures within the vicinity of the spine. MR spectroscopy provides the ability to obtain additional information about tissue characterization and chemical shift patterns. Advances in MR technology with improved filtering techniques and spatial and temporal resolution hold great promise for the use of MRI spectroscopy in the assessment of SCI and disease. Brain MRS has become a form of noninvasive biopsy able to detect changes in the chemical environment within and around lesions. It helps to delineate the true biochemical zone of pathology that may lie outside the confines of structural pathology. Phosphorus-31 MR spectroscopy is of value in assessing malignant changes of the vertebral column through marked elevation of the tumor marker phosphomonoester (PME).79 Animal studies have demonstrated the potential role of phosphorus-31 nuclear magnetic resonance spectroscopy in the evaluation of changes in spinal cord myelin80 and cellular bioenergetics secondary to trauma and ischemia.81 5.10.1.10
Three-Dimensional Imaging (Reconstruction)
Advanced imaging procedures with good spatial resolution such as MRI, CT, and high-resolution ultrasonography acquire datasets that can be manipulated to provide three-dimensional renditions of the surface and intrinsic anatomy of the spinal column, spinal cord, and nerve roots. Sectional anatomy can be viewed, allowing for teaching, improved clinical correlation, procedural planning, postoperative follow-up, and for use for near-realtime computer-assisted intervention. Clinical application of three-dimensional imaging has helped bridge the gap of communication between the radiologist and attending clinician. It has also broadened the field of interventional radiology. The application of three-dimensional imaging is rapidly advancing the potential of CT, MRI, and ultrasonography and creating a form of virtual endoscopy that allows for “fly throughs and fly bys” using tissue datasets. Computed tomography reconstruction has been used for more than a decade to aid the assessment of spinal disorders.82 Three-dimensional surface reconstruction with CT can provide accurate reconstruction of complex spinal column fractures and the relationship to the spinal cord.83 The datasets can also be manipulated to drive technology capable of fabricating physical models of the anatomy in question. MR three-dimensional imaging can provide for volumetric evaluation of tumor size and configuration. Volume-rendered imaging provides the capacity for creating dimensional projection that goes beyond the computer screen and may involve holography and other forms of stereoscopic displays.
5.10.1.11
MR Angiography
Magnetic resonance imaging is the primary method for noninvasive assessment of patients suspected to have a spinal cord lesion. Pathological conditions of the spinal vasculature often results in morphological and hemodynamic changes which include: (1) increased size of vessels, (2) increased vessel tortuousity, (3) vascular occlusion, and (4) altered intravascular flow dynamics. These gross deviations of normal vascular characteristics provide an opportunity to apply available MR methods to quantify and characterize vascular pathology. Postcontrast MR angiography (MRA) complements the routine MRI evaluation by improving the detection and display of normal and abnormal intradural vessels84 although there are limitations relative to the delineation of spinal veins vs. arteries. Spinal intradural vessels as small as 1-mm diameter have been detected on postcontrast MRA images.84 The use of MRA improves the detection and dynamic assessment of vascular malformations and vascularized tumors and the detection of arterial and venous occlusive disease. MRA can also be used to screen for dural arteriovenous fistulas. The addition of three-dimensional acquisitions and phase display helps differentiate feeder arteries of spinal vascular lesions.85 Fast three-dimensional contrast-enhanced MRA will visualize arterial branches that correlate well with digital subtraction angiography.86 In the future, gadolinium-enhanced three-dimensional MRA may achieve enough spatial and temporal resolution to differentiate spinal arteries from spinal veins, helping to clarify the nature of vascular lesions.84 The combined use of MRA and diffusion imaging in the future will allow for improved characterization of intramedullary arterial insufficiency and infarction. 5.10.1.12
MR Myelography
Magnetic resonance imaging of cerebrospinal fluid dynamics and cord motion can help differentiate pathomechanisms associated with different lesions. It is particularly helpful in assessing the dynamics of CSF spaces, cystic lesions, and the biomechanics of a tethered cord.66 Spinal cord velocity curves can be evaluated with phasecontrast MRI, providing valuable insight into the evaluation of tethering and spinal dysraphism.87 5.10.1.13
Interventional MRI
Advancing MR technology is leading this imaging modality into the interventional setting. MRI is capable of providing rapid multiplanar acquisitions during operative procedures. The development of specialized open magnets provides a greater opportunity for easy access to the patient by multiple people. Special technological modifications are required for the use of MRI in this setting, some of which have already been applied. MR imaging
Assessment of Spinal Cord Injury and Myelopathy
can provide a real-time window of anatomy during interventional procedures. There is also the added benefit of performing image-guided stereotaxic procedures, which reduces reliance on pre-operative films. The potential applications of interventional MRI include interventional disk procedures as well as image-guided biopsies, surgical spinal procedures, and positioning for arthrodesis placement.
5.11 NEUROSONOGRAPHY Many methods can be utilized to image the spine and spinal cord. Ultrasound is portable, noninvasive, and relatively inexpensive. New-generation equipment provides superior spatial and contrast resolution without known biological side effects and offers the option of full-thickness tissue imaging. There is no associated ionizing radiation, and image acquisitions can be obtained in multiple planes. Ultrasonography has emerged as a valuable option for assessing infants, particularly those with occult dysraphic lesions, and for performing intraoperative imaging. The creation of a surgical window provides an opportunity for the induction of a sonographic beam to investigate the integrity of underlying and surrounding tissues. Intraoperative spinal sonography (IOSS) can help direct the surgeon to the shortest route to a spinal lesion, subsequently limiting the degree of tissue compromise.
5.11.1 INTRAOPERATIVE SPINAL SONOGRAPHY Ultrasonography provides a method for intraoperative evaluation of spinal cord pathology,88 specifically in the localization of intrinsic tumors, abscesses, vascular malformations, hematomas, and syrinx formations. Ultrasound imaging can be performed at low cost and without ionizing radiation. Intrinsic spinal cord pathology can be localized and characterized without cord manipulation or incision. Intrinsic lesions of the spinal cord can be identified by the following criteria: (1) expansion of the spinal cord, (2) obliteration of the central echo complex, (3) abnormal cord echogenicity, and (4) abnormal spinal cord pulsation.89 The technique is used to direct the neurosurgeon to the spinal lesion using the shortest and potentially safest route which helps to limit tissue damage. The procedure is usually performed with the patient prone with entry through a laminectomy or laminotomy site. It is often performed throughout the procedure to identify operative progress.
5.12 COMPUTED TOMOGRAPHY 5.12.1 CT/MYELOGRAPHY If a patient is unable to undergo a spinal MRI, computed tomography (CT) with myelography provides a viable alternative. CT/myelography should be considered in those patients with contraindications to MRI. Myelography
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TABLE 5.21 Spinal Mass Effects: Myelographic Features • • • • •
Non-filling of nerve root sleeve Extradural filling defect Flattening of the spinal cord Multiple indentations Obstruction of contrast flow
has some associated risk; therefore, its use should be limited. CT and myelography should generally be performed together to improve the sensitivity and specificity of the test. Post-myelographic CT scan provides a higher yield of information than isolated CT evaluation.90 CT/myelography should be considered when MRI findings are disconcordant with the clinical presentation and a spinal lesion is still suspected. Computed tomography/myelography provides an accurate method for assessing the relationship of the spinal nerve root to adjacent bone and surrounding cerebrospinal fluid (Table 5.21). When a physical mass is large enough to block the flow of CSF, a cutoff or column-filling defect becomes apparent on myelography. A dynamic (variable position) myelogram can help identify significant positional central or lateral stenosis with CSF cutoff. However, it is difficult to determine the extent of an intradural lesion such as syringomyelia and distal pathology if a complete myelographic block is present.90
5.12.2 HELICAL CT (SPIRAL CT) Computed tomography remains a superior method of imaging for bone and soft-tissue pathology associated with calcific changes. Thin-slice CT is a valuable method of assessment for failed spinal fusion. The development of helical techniques has revolutionized the science and application of CT. This protocol provides quicker and sharper axial images and utilizes an overlapping imaging sequence91 to reduce radiation exposure as compared to conventional CT, while increasing the field of view. Faster scan times also decrease patient discomfort, anxiety, and movement artifact, therefore rendering a more detailed image. Greater coverage of a region can be performed in a short period of time, so helical CT is an important addition to a trauma center. The procedure is so efficient that rapid whole-body helical CT scanning can be performed on patients who have sustained multifocal trauma, often within minutes.
5.13 PLAIN-FILM RADIOGRAPHY Plain-film radiography is valuable as a cost-effective method of initially evaluating the structural and biomechanical
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TABLE 5.22 Classification of Intersegmental Motion Patterns Parmobility • Normal Type I: Intersegmental motion within the average (mean) for population studied • Abnormal Type II: Normal intersegmental motion associated with pain at the same segmental level or within biomechanically connected structures Hypomobility • Normal Type I: Reduced intersegmental motion within normal ranges without evidence of pain or spondylosis • Pathomechanical Type II: Abnormally reduced intersegmental motion; associated with pain, reactive myospasm, and/or spondylosis Type III: Immobilization; complete loss of intersegmental motion; may or may not be associated with pain or neurological findings Hypermobility • Normal Type I: Excessive intersegmental motion without evidence of pain or spondylosis • Pathomechanical Type II: Excessive intersegmental motion in the tissue-damaging range with 2–3.5 mm, 1–2.5 mm (thoracic), or 3–4.5 mm (lumbar) of translation in the sagittal plane (one direction) and/or angular displacement <11°; may or may not be associated with pain, reactive myospasm, and other symptoms Type III: Biomechanical instability, excessive intersegmental motion in the sagittal plane (one direction), with translation of 3.5 mm or greater (cervical), 2.5 or greater (thoracic), or 4.5 or greater (lumbar) and/or angular displacement >11°; often associated with pain or neurological findings Parakinetic mobility • Normal Type I: Intersegmental motion occurring in a direction or pattern other than that expected, without evidence of pain or spondylosis • Pathomechanical Type II: Abnormal intersegmental-coupled motion or excursion pattern in the tissue-deforming or -damaging range that occurs in an unexpected direction or pattern; may or may not be associated with pain, reactive myospasm, and other symptoms Type III: Biomechanical instability; excessive intersegmental motion in an unexpected direction or pattern in the sagittal plane, with translation of 3.5 mm or greater (cervical), 2.5 or greater (thoracic), or 4.5 or greater (lumbar) and/or angular displacement >11°; often associated with pain or neurological findings Note: This table defines the types of motion that are seen at the intersegmental level. The type II and III pathomechanical motions may further be qualified by temporal characteristics using the terms acute, glacial (slowly progressive), and chronic. Type II and III measurement criteria are based on mid- and lower cervical spine flexion and extension positional radiographs taken at 72-inch source-image distance. Rotary and lateral motions can also be considered in type II and III pathomechanical mobility patterns, although these ranges are not reported. Source: True, Durrant.
integrity of the osseous elements of the spine. It is a valuable front-line method for the evaluation of fractures, dislocations, congenital bony malformations, segmental function, and postural considerations. The plain-film study can also help determine the risk for positional or dynamic central and/or lateral spinal stenosis in a weight-bearing position. Visualization of the spine by plain film should include lateral, anteroposterior, and open-mouth views including the C1 through the T1 vertebra. Oblique views are beneficial for dislocation and fracture visualization. Also unique to the radiographic work-up is the ability to evaluate segmental biomechanics. Segmental movement may fall into one of the following categories: (1) normal (par mobility); (2) hypomobility, including immobilization; (3) hypermobility, including instability; and (4) parakinetic mobility (Table 5.22). This portion of the assessment can be performed using flexion and extension views. On rare occasions, lateral-bending views may also be taken. If a fracture is suspected, the X-ray work-up should be supplemented with conventional or helical CT. If SCI is suspected, the study should be correlated with MR imaging.
5.14 QUANTITATIVE CONSIDERATIONS IN SPINAL CORD IMAGING It is important to evaluate the size, configuration, and signal characteristics of the spinal canal and spinal cord when reviewing advanced neuroimaging studies. Special attention should be given to the region of the spinal cord adjacent to areas of acquired stenosis. There is variation in spinal column size between individual cords;92 therefore, it can be helpful to compare morphometric information from the suspected segmental level of involvement to an uninvolved segmental level.
5.14.1 CENTRAL SPINAL CANAL MEASUREMENTS Reserve space around the spinal cord is necessary to ensure adequate blood supply and biomechanics. The transverse area of the spinal canal is generally smaller in patients with myelopathy when compared to normal individuals.93 The spinal cord becomes particularly vulnerable to compression secondary to disk herniation or other mass effect within a developmentally narrowed central spinal canal.94 A narrow cervical canal is an unfavorable finding in patients who have suffered flexionextension injury.95 The sagittal diameter of the cervical, thoracic, and lumbar spinal canal can be quantitatively measured on MRI or CT as well as plain-film radiography (Figure 5.11). There is generally good correlation between the sagittal diameter of the spondylotic cervical spinal canal and the development of myelopathic sign and symptoms. A sagittal measurement of the cervical spinal canal can be made on a plain-film radiograph measuring from the posterior surface
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Average Diameter of the Spinal Canal at Four Different Levels
C5
Mean Lumen Diameters
T7
AP-14 mm Lat.-25 mm
AP -14 mm Lat -15 mm
T11
AP -16.5 mm Lat -19.3 mm
L5
AP -12 mm Lat -24 mm
FIGURE 5.11 The narrow zone of the spinal canal extends from approximately T4 to T9 vertebral levels. The narrowest region of the spinal canal is at the T6 level. The wide lateral diameter of the lumbosacral canal easily accommodates the cauda equina. (Copyright J.M. True, D.C.)
of the vertebral body to the closest surface of the spinolaminar junction at the same vertebral level; however, this method may be somewhat inaccurate due to radiographic magnification. Cervical mid-sagittal diameter between 10 and 13 mm is a premyelopathic condition due to the limited tolerance for hypertrophic bony changes projecting more than 2 mm.96 A cervical sagittal canal measurement of 12 or less is considered a critical factor in the development of cervical spondylotic myelopathy on plain films.97,98 The normal cervical canal diameter ranges from 17 to 18 mm at C3– C7. An alternative method of measurement is the application of the ratio between the sagittal measurement of the canal and the vertebral body referred to as the canal/body ratio or Torg–Pavlov ratio.99 A spinal canal/body ratio of less than 0.80 on a lateral cervical spine roentgenogram is indicative of cervical spinal canal stenosis.100
5.14.2 SPINAL INSTABILITY AND VERTEBRAL TRANSLATION Segmental vertebral hypermobility in conjunction with central stenosis increases the risk for cord and supportive vascular microcontusion during movement. The degree of vertebral translation or instability can be determined on positional radiographic views or kinematic MRI. Injury to the ascending and descending tracts of the spinal cord generally is more devastating than focal injury to the cellular elements of the gray horn. Injury to the white matter may compromise ascending or descending pathways that control function below the level of compromise, thus the clinical deficit has the potential to be more complex and incapacitating than the segmental effects of anterior horn insult.101
5.14.3 CLASSIFICATIONS OF SPINAL CORD COMPRESSION Nagata et al.102 described four classifications of spinal cord compression assessed with T1-weighted sagittal MRI acquisitions of the cervical spine. In Class 0, there is no
FIGURE 5.12 Classifications of spinal cord compression visualized on T2-weighted MRI, sagittal acquisition. (Copyright J.M. True, D.C.)
compression. In Class 1, the cord is slightly compressed. In Class 2, the cord width is compressed by less than one third, and in Class 3 the cord width is decreased by one third or more (Figure 5.12). These researchers found that the greater the degree of cord compression, the greater the severity of myelopathy and clinical sequelae. The spinal cord may be displaced within the spinal canal without obvious compression, which may lead to abnormal tension patterns within the cord (Table 5.23).
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TABLE 5.23 Magnetic Resonance Imaging Appearance with Increasing Levels of Mechanical Spinal Cord Compression
Cervical Cord
Cord Square 2 Area (mm)
2
>75 mm 1. Cord deviation without deformation 2. Cord deviation with deformation 3. Cord deviation without cord deformation with adjacent focal cord MR signal abnormality 4. Cord deviation with deformation and adjacent abnormal MR signal 5. Cord deformation, abnormal signal and focal enlargement
Normal
2
50 mm
Moderate Compression
2
40 mm Severe Compression
A–B=11.9
FIGURE 5.14 A reduced square area of the spinal cord correlates with severity of myelopathic symptoms. (Copyright J.M. True, D.C.)
C–D-7.2
E–F=12.0
G–H=13.6
FIGURE 5.13 Quantitative measurements of the cervical spinal canal at various levels. Central canal stenosis at C5–C6 is due to prominent disk bulging. (Parasagittal fast spin echo T2weighted midline sagittal image.)
cord area by greater than 30% as compared to adjacent regions or a transverse cord area of less than 60 mm2 depicted by CT has been associated with increased prevalence of myelopathic symptoms.104 Nagata et al.102 correlated MRI cord appearance with myelopathic presentation. These researchers suggest that a cross-sectional cervical cord area less than 50 mm2 carries a high risk of myelopathic symptoms and loss of functional capacity (Figure 5.14). A transverse cord area less than 40 mm2 is a poor prognostic finding, and surgery in these patients is often indicated;105 unfortunately, cord area of less than 30 mm2 has been associated with a poor response to surgery.106
5.14.4 SPINAL CORD CROSS-SECTIONAL SIZE AND AREA
5.14.5 INTRINSIC CORD DYSMORPHISM
The spinal cord cross-section and sagittal images can be evaluated on MR (Figure 5.13). The normal cervical spinal cord measures approximately 8.5 to 11.5 mm in diameter. Small cord diameter (atrophy) may occur secondary to neuronal and support element dropout due to injury. An enlarged cord may occur secondary to a focal or diffuse expanding intramedullary lesion. Ono and associates103 devised the anteroposterior (AP) compression ratio (the ratio of the AP canal diameter to the lateral cord diameter) and effectively correlated it with the severity of spinal cord compromise. A reduction of the cross-sectional spinal
The ability to evaluate and provide calculations in digitized images also offers additional advantages as part of a positional spinal MRI study. High-field, 1.5-Tesla MRI can readily demonstrate the central “H” configuration of the normal spinal gray matter on axial specialized T2 gradient echo pulse sequences; thus, distortions of the central gray can be quantified to correlate with myelopathic symptoms.107 Distortion of the “H” configuration suggests greater likelihood for microvascular and neural compromise as well as gray matter atrophy of the spinal cord (Figures 5.15 and 5.16).
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FIGURE 5.15 The distorted H-sign. (Copyright J.M. True, D.C.)
Cord compression with deformation
FIGURE 5.17 Posterior bony spur at C5–C6 with corresponding ventral cord compression. The associated abnormal signal changes within the cervical spinal cord at this level are compatible with myelomalacia. (Parasagittal fast spin echo T2-weighted midline sagittal image.) FIGURE 5.16 Spinal cord compression with a distorted H-sign. (Axial fast spin echo T2-weighted image through the C2–C3 level.) (Same patient as in Figures 3.21 and 3.22.)
and low-intensity signal on T1WI with a poor prognosis for clinical recovery. This may indicate more severe cord pathology such as severe necrotic, spongiform, or myelomalacic changes.111
5.14.6 INTRAMEDULLARY SIGNAL PATTERNS Spinal cord injury may be associated with abnormal signal changes within the spinal cord. The relationship between increased intramedullary signal intensity and histologic findings has been reported by many researchers.101,108 Takahashi108 was one of the first researchers to report a focal region of abnormal high-intensity signal within a chronically compressed region of the spinal cord. Linear high-intensity signal regions on T2-weighted images (T2WI) have been associated with clinical evidence of extensive anterior horn cell compromise and radiographic evidence of cavitation.101 It has been postulated that focal high T2-weighted signals within the spinal cord represent inflammation, edema, vascular ischemia, myelomalacia, and/or gliosis (Figure 5.17). Some of these signal aberrancies resolve after decompressive surgical intervention;109 however, Kulkanari et al.110 reported good correlation between regions of high-intensity signal on T2WI
5.15 FUNCTIONAL AND LABORATORY ASSESSMENT The majority of back complaints are mechanical in nature. Laboratory evaluation can be used to help identify the cause of nonmechanical back pain and conditions that render the spinal cord vulnerable to compression or other forms of neurological compromise. Functional assessment forms the basis of diagnosis and is critical to evaluation of the progression or rehabilitation of impairment.
5.15.1 PULMONARY FUNCTION Cervical or thoracic SCI results in varying degrees of respiratory impairment. Pulmonary function tests provide quantifiable discrimination between degrees of impairment.112 Additionally, these tests are practical and cost effective, providing valuable data to follow the patient with
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acute, subacute, or chronic myelopathy. More advanced methods of measurement are available. The five primary reasons for performing a pulmonary function profile are (1) to assess the need for acute intervention, (2) to determine the degree of neurologic and related pulmonary impairment, (3) to help identify the type of respiratory or physical therapy required, (4) to assess the ability to move secretions, and (5) to serve as a baseline for outcome assessment. The normal respiratory rate (RR) at rest falls between 12 and 14 breaths per minute. The RR in patients with myelopathy or SCI with respiratory impairment will increase in an attempt to compensate for their reduced lung expansion and vital capacity. The ability to inflate the lungs is also impaired, thus chest wall excursion is reduced. Vital capacity is defined as the maximum amount of air that can be forcibly exhaled after maximum inhalation. A greater vital capacity increases the patient’s ability to clear and expel airway secretions. A greater vital capacity also improves the ability to inflate the alveoli, reducing the risk for atelectasis. Reduced vital capacity will cause a reduction of the SaO2 unless there is an adequate compensatory increase in the RR. The vital capacity can be quantified by utilizing a hand-held spirometer. The average normal vital capacity is approximately 4500 mL.113 A vital capacity of 800 mL is enough to maintain respiration without mechanical support.14 A vital capacity of approximately 1500 mL is required to have an effective functional cough to clear lung secretions.114 Peak expiratory flow (PEF) tests the patient’s ability to properly ventilate and expel pulmonary secretions. PEF represents the greatest flow that can be achieved during forceful exhalation. The amount of arterial oxygen saturation in the body can be measured by pulse oximetry. The oximeter sensor is usually a finger cuff or clip placed over the distal end of a digit. The normal arterial oxygen saturation (SaO2) is 97% or greater. Increasing SaO2 values is consistent with improved functional respiratory capacity.112
5.15.2 CEREBROSPINAL FLUID EVALUATION The CSF surrounding the brain and spinal cord performs four major functions: (1) physical support and protection, (2) method of excretion, (3) provision of controlled chemical environment, and (4) intra- and extracerebral transport.115 Cerebrospinal fluid assessment should only be considered when a biochemical, serology, or cytology assay of the spinal fluid might provide clinically relevant insight that would change the course of care. The laboratory investigation of CSF is indicated for suspicions of CNS infection, immunological disorders, subarachnoid bleeding, meningeal carcinoma, and MS. Cytology may be helpful in assessment for neoplastic cells (Table 5.24). Normal CSF from a patient without infection has low protein, no phagocytic cells or inflammatory by-products.
In patients with bacterial meningitis, the classic CSF findings are leukocytic pleocytosis, increased protein, decreased glucose, and increased intrathecal pressure. The most common organisms producing bacterial meningitis in neonates are Group B streptococci and Gram-negative enteric bacilli. In children and adults, Streptococcus pneumoniae or Neisseria meningitides are the organisms most frequently responsible for bacterial meningitis. Viral meningitis may be caused from any one of dozens of DNA or RNA viruses. Some of the more common etiologic viruses are herpes simplex virus, influenza type A or B, HIV, Epstein–Barr virus, and St. Louis encephalitis virus. A spinal fluid tap is strongly contraindicated in the presence of known or suspected increased intracranial pressure. Relative contraindications include headache, unconsciousness, local sepsis, suspected spinal cord compression, and neck stiffness. Neuroimaging should be performed prior to most CSF studies. A lumbar puncture, usually at the interspace of the L3 to L4 vertebrae or below, is performed to obtain CSF fluid that is then usually apportioned for (1) chemistry and serology, (2) bacteriology, and (3) microscopy. Practical biochemical tests of interest are glucose, total protein, and specific protein assays. The CSF glucose concentration is usually about two thirds the level of the plasma. A decrease in CSF glucose levels may occur secondary to (1) a disorder in carriermediated transport of glucose into CSF, (2) active metabolism of glucose by cells or organisms, and (3) increased metabolism by the CNS.115 A low CSF glucose level may occur with meningeal metastasis or primary carcinoma. A decreased level of CSF protein may occur due to (1) decreased dialysis from plasma, (2) leakage of CSF, or (3) increased protein removal.115 An increased level of total protein is one of the most useful nonspecific indicators of a pathologic state. An increase in protein may occur due to the one of the following reasons: (1) lysis of blood from a traumatic tap, 2) increased permeability of the epithelial membranes, (3) increased production by CNS tissue, (4) obstruction, or (5) decreased rate of removal.115 Electrophoretic separation of protein subtypes can be helpful in the evaluation of immune-mediated spinal cord disease and in cases of CSF total protein elevation. Electrophoretic separation may demonstrate banding of the IgG proteins, referred to as oligoclonal banding, and often occurs in the presence of inflammatory disorders such as multiple sclerosis, HTLV-1, HIV, or Lyme disease. These types of gamma globulins may stimulate immunocompetent cell lines.
5.15.3 AMNIOCENTESIS Amniocentesis refers to sampling of the amniotic fluid during pregnancy. Many congenital anomalies with neurological consequences can be prenatally detected. Biochemical assessment of amniotic fluid may be performed
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TABLE 5.24 Cerebrospinal Fluid Abnormalities. CSF Abnormalities in Various Conditions Affecting the Spinal Cord CSF Appearance
Pressure (mm hg)
Protein (mg/dl)
Glucose (mg/dl)
Normal Acute bacterial meningitis
Clear Cloudy
100–200 Decreased
20–45 Increased
50–80 Decreased
< 6 Lymphocytes Increased (PMN or mono)
Amyotrophic lateral sclerosis Aseptic (viral) meningitis
Clear
Mild increase
Normal
Increased
Clear or cloudy
Normal or increased Normal or increased
Increased
Normal
Culture, virus specific antibodies, polymerase chain reaction (PCR)
Diabetes
Clear
Increased
Increased
Fungal meningitis
Clear or cloudy
Increased
Increased (50–400) Increased
Increased (mononuclear), lymphocytic pleocytosis Normal
Decreased
Culture, antigen detection and serology
Guillain–Barre Syndrome
Clear or cloudy
Normal
Increased
Normal
Hepatic disease
Clear or xanthochromic Bloody or xanthochromic Clear or cloudy
Normal or increased Increased
Increased
Normal
Increased (monocytes), leukocytic pleocytosis Normal or increased (lymphocytes) Normal
Increased
Increased
Increased
Normal or decreased Normal
Normal to increased Normal to mildy increased Increased
Increased (24–1200) Increased
Normal
Normal or increased
Normal or decreased
Condition
Hemorrhage HTLV-1
Meningeal carcinomatosis Multiple sclerosis
Clear or cloudy Clear or cloudy
Decreased
Neoplasm
Clear or xanthochromic
Subarachnoid hemorrhage Tuberculous meningitis
Bloody or xanthochromic Cloudy
Increased
Increased
Increased
Increased
Normal or decreased Decreased
Neuroborreliosis
Clear or cloudy
Increased
Increased (100)
Normal or decreased
Neurosyphilis
Clear or cloudy
Normal or increased
Increased
Normal
Increased (50–200) Increased
Mild decrease (30–40) Normal
Neurosarcoidosis Paraneoplastic
Clear or cloudy
Normal or increased
Cytology
Increased (RBC) Increased (WBC or mononuclear) Increased (PMN) Increased (WBC)
Additional CSF Tests
Culture, Gram’s stain, polymerase chain reaction (PCR) Neurofilament
Rule-out active infection
Glutamine
Increased IgG specific antibodies, oligoclonal bands Beta-Glucuronidase
Oligoclonal bands, increased IgG index, myelin basic protein Normal or increased Neuron specific enolase (lymphocytes/ (NSE), carcinembryonic mononuclear) antigen (CEA) Increased (RBC and WBC) Increased Culture, PCR (PMN-early) (lymphs-late) Increased Lyme antibodies, (monocytes) oligoclonal bands, fibronectin Increased VDRL (monocytes) Increased Angiotension converting (monocytes) enzyme (ACE) Increased Antibodies (many others) (WBC’s 8–20) AniYo Anti-Hu
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in high-risk patients to test for chromosomal abnormalities, neural tube defects, gestational development, fetal pulmonary development, and presence of hemolytic disease. The confirmation or suspicion of congenital maldevelopment on fetal ultrasound indicates the need for amniocentesis. Amniotic fluid specimens are usually taken between the gestation period of 14 to 21 weeks. The sample is assessed for fetal cells, which can then be used for chromosomal and intracellular enzyme evaluation. Tests used to screen for neural tube defects include alphafetoprotein (AFP) and CNS-specific acetylcholinesterase (ACE). When both ACE and AFP are elevated, there is a higher probability that neural tube defect is present. AFP assessment does not provide an absolute marker for neural tube defects but has been associated with increased prevalence. The sensitivity of AFP is improved when performed along with other serum tests. The maternal triple screen is a common profile consisting of AFP, estriol, and human chorion gonadotropin (HCG) levels.
5.15.4 BLOOD
AND
SERUM STUDIES
Blood and serum studies can be useful in the workup of a patient with suspected acute myelopathy, particularly transverse myelitis or meningitis. An elevated white blood cell count (WBC) is indicative of an acute inflammatory state or the response to a local or systemic infection. The white blood cell types and quantities provide further insight relative to the degree and stage of the infection. An elevated erythrocyte mean cell volume (macrocytosis) can be one of the earliest indicators of B12 and/or folate deficiency, increasing the risk for subacute combined degeneration The fluidity of the blood is dependent on normal quantities of platelets, normal ratio and interaction of proteins of the fibrinolytic system. When there is risk for hemorrhagic stroke, hematomyelia, or impaired clotting due to coumadin, clotting factors should be monitored. Spinal subdural hematoma may occur following lumbar puncture in patients on blood thinners or with platelet counts below 40,000 mm3. Prothrombin time, activated partial thromboplastin time, plasma fibrinogen, and tests for defective platelet function are usually performed in the evaluation of the hemorrhagic patient. Serum assessment of triglycerides, cholesterol, and their subtype lipids can help ascertain risk for peripheral vascular disease. Chronic elevation of LDL, especially when accompanied by a concomitant reduction of the HDL fraction of cholesterol, increases the risk for acquiring obstructive arterial disease. Obstructive disease within the thoracic and abdominal aorta increases the susceptibility of the spine to hypotension secondary to compromise of arterial feeders from the aorta, such as the large artery of Adamkiewicz. Elevated cholesterol accompanied by other cardiovascular risk factors should warrant further
cardiac and peripheral arterial assessment, particularly in the patient who may be undergoing major abdominal or chest surgery. A drop in systemic blood pressure in a patient with aortic disease may result in spinal cord injury. A serum metabolic profile helps to provide an indication of overall health. Disease states such as hepatitis, diabetes, and uremia, although unrelated to SCI, can hamper the healing and rehabilitation process. The metabolic profile can also be used to assess the risk for or presence of infectious complications after SCI, particularly involving the pulmonary system and urinary tract. A blood culture and Gram’s stain should be performed to rule out septicemia in the patient with suspected infectious myelitis. In cases of suspected or known transverse myelitis or meningitis, both blood and CSF cultures should be performed. With aseptic meningitis, in addition to direct culture of the virus, enzyme linked immunosorbent assay (ELISA), Western blot, or polymerase chain reaction (PCR), and virus specific antibody testing are methods used to identify different viruses that may also be present in the serum as well as CSF. Systemic inflammatory markers such as C-reactive protein (CRP) are helpful in the initial assessment and follow-up of the patients with infectious or postinfectious myelopathy. Plasma pH, CO2, and serum acid–base relationships should be evaluated in the SCI patient with known or suspected respiratory impairment. Acidosis due to hypoventilation should be monitored in patients with respiratory insufficiency due to SCI. Respiratory acidosis occurs secondary to pulmonary CO2 retention, which results in an excess of H2CO3. This causes a drop in the plasma pH, hence the term respiratory acidosis. Undiagnosed post-traumatic urinary infection with pyelonephritis may cause renal acidosis, complicating the acidosis due to hypoventilation. If metastasis or paraneoplastic syndrome is suspected, serum tumor markers may be useful. They can be used to screen the patient with possible disease, used for adjunctive disease staging, and used to detect disease recurrence. Most serum tumor markers cannot be used to confirm the diagnosis of cancer but they will raise the probability of its presence. Common serum tumor markers are carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), and human chorionic gonadotropin (beta-HCG).
5.15.5 GENETIC ASSESSMENT Some inherited disorders escape detection by more conventional laboratory measures such as serum and CSF biochemical assays. Recent advances in molecular genetics make it possible to determine the precise location of genes which cause or contribute to neurological disease states. The mapped gene location provides for accurate hereditary diagnosis.
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TABLE 5.25 Cystourethrographic Presentations Lesion Site
Electromyogram
Cystogram
Clinical
Complete supraconus myelopathy Incomplete supraconus myelopathy
Detrusor sphincter dyssynergy Normal sphincter
Detrusor hyperreflexia Detrusor hyperreflexia
Lesion of the conus medullaris
Decreased activity
Detrusor areflexia
Spontaneous voiding; incomplete voiding Increased urinary frequency; painful urge; urge incontinence Urinary retention
Each human cell contains 46 chromosomes arranged into 23 pairs, 22 autosomes plus the sex chromosomes X and Y. This chromosomal arrangement is referred to as the human genome. The primary infrastructure of the chromosome is a continuous DNA double strand consisting of approximately 50 to 200 million base pairs in length, dependent upon the size of the chromosome. The gene is comprised of a series of base pairs. The chromosome represents a discrete unit of the genome containing a complex array of genes composed up to an average length of a few thousand base pairs. The gene further represents the basic unit of inheritance, comprised of a nucleic acid arrangement capable of encoding proteins for the synthesis and modulation of other structures. An abnormal gene, gene sequence, or gene interaction may be inherited or acquired through a mutation, which represents an alteration of its nucleic acid sequence. Many common conditions are known to arise from the complex interaction between environmental and genetic mechanisms. Linkage mapping, linkage analysis, gene isolation, and positional cloning represent some of the techniques for identifying and isolating gene locations. Through these and other methods, genetic testing has identified the chromosomal location and mutant gene characteristics for a number of neurological disorders. In some cases, a genetic diagnosis is possible, whereas in other cases, it remains suggestive. Some of the diseases identified by genetic testing are Friedreich’s ataxia; spinal muscular atrophy, types 1, 2, and 3; familial amyotrophic lateral sclerosis; and neurofibromatosis type I and II. An extensive discussion of genetic markers extends beyond the scope of this chapter and book.
5.15.6 BLADDER FUNCTION 5.15.6.1 Cystourethrography Spinal cord injury and disease can cause urinary bladder dysfunction. Functional evaluation of the urinary bladder and related peripheral mechanisms can help differentiate whether the urinary presentation is directly related to spinal cord compromise or secondary to coexistent cauda equina syndrome, peripheral neuropathy, autonomic neuropathy, or intrinsic bladder pathology (Table 5.25).
5.15.6.2 Cystometry Cystometry refers to the testing of bladder function. Carefully performed cystometry can provide valuable insight about detrusor muscle function. In the patient with SCI or myelopathy due to other causes, cystometry can help to evaluate (1) bladder wall sensation, (2) motility of the bladder, (3) sphincter integrity, (4) response to filling pressures, and (5) neurological response. Cystometry can be performed with sterile water insufflation. Sterile water is instilled into the empty bladder at a rate of 1 mL/sec. In the normal bladder, the first desire to void occurs after about 175 to 250 mL of water has been introduced.116 Normally, at this filling pressure, there are no signs of detrusor contraction. An intravesicle pressure elevation in excess of 15 cm H2O is considered to represent a detrusor contraction.117 The following observations and recordings are critical to cystometric assessment: (1) perception of temperature, (2) perception of filling pressure, (3) pressure at the time of experiencing the urge to void, (4) pressure at the time of painful distention, (5) pressure at the time of voiding, and (6) quality and character of the urinary stream. Ambulatory cystometry can be performed. It is more commonly used to assess stress incontinence in women but could be used to assess urge incontinence in the patient with suspected spinal cord dysfunction. 5.15.6.3 Electrodiagnostic Studies of Bladder Function Electromyography of the pelvic basin muscles or monitoring the activity of the internal and external sphincters is often done in conjunction with cystourethrography. Electromyographic measurement of the function of the urogenital diaphragm and levator ani muscle during cystometry can provide further quantifiable information about neurological and muscular integrity. Interruption of spinal or supraspinal pathways to the bladder results in detrusor overactivity. Electromyographic assessment of the detrusor sphincter can help determine whether there is sphincter dyssynergy. This is characterized during cystometry by inability to voluntarily suppress the detrusor reflex contraction and early involuntary voiding with low intravesicle pressure. This will help to ascertain the severity of
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the neurogenic bladder condition and to assess risk for intravesicle urinary retention. Increased urinary retention or incomplete voiding increases the risk for acquiring a urinary tract infection, which could stimulate a state of autonomic hyperreflexia and lead to infectious complications. Cortical evoked potentials are reported to be of value for (1) differentiating between intraspinal and extraspinal lesions of the afferent pathways of the detrusor if the etiology is unknown, (2) differentiating between neurogenic and myogenic damage to the urinary bladder, and (3) selecting patients not suitable for intravesical electrotherapy for bladder rehabilitation. The findings of a cortical evoked potential study should be correlated with pudendal somatosensory evoked potentials and clinical symptomatology.118 5.15.6.4 Uroflowometry Urethral function can also be assessed by uroflowometry, a procedure requiring the patient to void into a flowmeter unit providing for the calculation of average flow rate, maximum flow rate, time to peak flow, and urinary volume voided.117 This test can be used to evaluate detrusordyssynergy and pathology along the course of the urethra.
5.15.7 PHYSICAL IMPAIRMENT ASSESSMENT Spinal cord compromise, whether acute or chronic, results in varying degrees of functional impairment. The pattern of impairment is dependent upon the (1) duration of compromise, (2) cause of injury, (3) location of insult, (4) degree of tissue damage, and (5) capacity for recovery. It is important to evaluate baseline neurological and related orthopedic impairment in order to efficiently plan and effectively initiate a therapeutic and rehabilitative approach. Periodic quantitative follow-up assessments should be used whenever possible in order to better evaluate therapeutic outcome and to become aware of progressive impairment early. The use of quantitative measurements of function can also be extremely motivating for myelopathic patients if there is even small incremental improvement in any aspect of their physical performance. Impairment scales can also be used to assess the status of the patient. Some of these scales are presented below. 5.15.7.1 Frankel Classification The first goal in the assessment of the patient with myelopathy is to localize the level of neurologic injury and baseline simple clinical findings below the intact level. This should include emphasis on sensory and motor assessment. It is important to use a method of assessment that has significant inter-observer reliability and can be easily used for reevaluation. The Frankel scale was one of the first such methods for classifying clinical neurological deficits.119
5.15.7.2 ASIA/IMSOP Scale The Frankel scale, however, lacks some specificity with reference to the extent of neurological deficit and dysfunction. The American Spinal Injury Association (ASIA) and the International Medical Society of Paraplegia (IMSOP) have published a modified scale referred to as the International Standards for Neurologic and Functional Classification of Spinal Cord Injury.120 This classification method provides a measure of assessment of the segmental level of injury on either side of the body, which is important in the evaluation of an incomplete SCI (Figure 5.18). 5.15.7.3 Benzel and Larson Scale The more incomplete the myelopathy, the better the prognosis. Benzel and Larson121 proposed a neurological grading scale for SCI that expands the Frankel scale, allowing more precise quantification of the patient with an incomplete myelopathy. This scale was initially applied to patients with thoracic and lumbar spine injuries. 5.15.7.4 Japanese Orthopedic Association Cervical Myelopathy Score This scale is based on a regression score where patients with the worst myelopathic symptoms have the lowest numerical score. This scale is based on functional capacity assessment of hand dexterity and ambulation along with the extent of sensory deficits and sphincter dysfunction. Patients with larger degrees of cord compression tend to have lower Japanese Orthopedic Association (JOA) scores (Table 5.26).102 5.15.7.5 Range of Motion (ROM) Range of motion (ROM) is easy to evaluate and an important measure of physical capacity. Dual inclinometry is the best way to measure ROM because it provides digital quantification and allows determination of the range based upon movement at two points, which is more accurate, especially in the spinal cord patient with spasticity. ROM measurements can be used as a baseline for joint movement to assess functional range (1) with contracture, (2) with muscle hypertonicity, (3) with reactive spasticity or clonus, or (4) with pain limitation, as well as for orthopedic-joint assessment with normal musculotendinous status. ROM can be evaluated passively with the assistance of the examiner or actively with voluntary effort on behalf of the patient. 5.15.7.6 Gait Ambulation in SCI is not possible without stabilization of the trunk, hip, and knee. SCI above the L3 cord level is not conducive to functional independent ambulation. Even
FIGURE 5.18 (From American Spinal Injury Association. Copyright 2000. Used with permission.)
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TABLE 5.26 Japanese Orthopaedic Association Criteria for Assessment of Cervical Myelopathy • Motor dysfunction of the upper extremity Score 0 = Unable to feed oneself 1 = Unable to handle chopsticks, able to eat with a spoon 2 = Handle chopsticks with slight difficulty 3 = None • Motor dysfunction of the lower extremity Score 0 = Unable to walk 1 = Walk on flat floor with walking aid 2 = Up and/or down stairs with hand rail 3 = None • Sensory deficit A. Upper extremity Score 0 = Severe sensory loss or pain 1 = Mild sensory loss 2 = None B. Lower extremity; same as A C. Trunk; same as A • Sphincter dysfunction Score 0 = Unable to void 1 = Marked difficulty in micturition (retention, strangury) 2 = Difficulty in micturition (dysuria, hesitation) 3 = None Source: From Nagata, K. et al., Clinical value of magnetic resonance imaging for cervical myelopathy, Spine, 15, 1089, 1990. With permission.
gait patterns in L3–L4 lumbar cord injuries may involve considerable abnormality of gait. The ataxia and spasticity in the lower extremities of lumbosacral level hemiplegics make ambulation challenging. Gait requires integrated supraspinal neurological control of the muscles of locomotion with maintenance of postural tone. The pattern of gait and the method of assistance required depend upon the level and degree of SCI. This is discussed in more detail in Section 6.11.3. In patients with incomplete lower cord injuries, there will be diminished kinesthetic perception and spasticity. This gait pattern is termed spastic ataxia. Patients with spondylotic myelopathy or with posterior column compromise may only demonstrate ataxia and slow speed in gait. CSM patients usually demonstrate reduced gait velocity and step length, prolonged double support, increased step width, and reduced ankle joint extension during treadmill walking.122 Knee and hip motion is generally unaffected. In mild or subtle cases of myelopathy, the degree of ataxia can be magnified with gait evaluation on a treadmill. Changes in cervical position may induce a functional stenosis producing changes in gait patterns
and stability. Too often gait evaluation is limited to walking a short distance in a small examination room often not exceeding 10 to 12 feet in length at a slow pace. Subtle myelopathic symptoms may be amplified by having the patient maintain some degree of cervical flexion or extension. Patients with ataxia are very unstable and require vigilant supervision during evocative maneuvers. It is recommended that spotters be present at the patient’s side or use of a safety harness to ensure safety during treadmill gait evaluation. Additionally, the demonstration or facilitation of pathologic reflexes and/or subjective neurologic perceptions in the asymptomatic patient during sustained cervical positions would be highly suggestive of functional stenosis.3 5.15.7.7 Muscular Performance The evaluation of muscular performance is important in the patient with some preservation of muscle function at the level of SCI or below. A number of physical parameters can be measured, the most important being strength, power, endurance, muscle activation patterns, and torque. The most practical parameters to measure are strength, endurance, and muscle activation patterns. Strength is defined as the ability of a muscle or group of muscles to exert force.123 Force exertion is an essential component of functional capacity. Strength testing falls into one of two categories, either static or dynamic. Static testing is a method in which force is measured without limb (joint) movement. Dynamic testing requires movement of the joint and muscle(s) against resistance. Dynamic testing can further be subcategorized into isotonic and isokinetic testing. Isotonic testing allows for dynamic assessment with fixed resistance and variable velocity. Isokinetic testing is a dynamic assessment of an individual’s ability to apply force at constant rate of speed. Isotonic testing comes closer to simulating normal activities, although isokinetic testing provides a more accurate method of measuring change. The assessment of muscular strength can be placed into three primary categories: (1) isolated, (2) regional, and (3) kinetic chain. Assessment of isolated muscular evaluation is important for testing segmental (nerve root) neuromuscular integrity and to allow for more accurate reevaluation. Isolated muscle testing also allows a complex movement to be broken down into its muscular subcomponents. One or more paretic muscles may render a joint mechanically unstable during complex tasks where the agonist is otherwise strong. Regional strength assessment refers to the evaluation of muscles required to perform a task placing primary demand on one joint. An example would be shoulder assessment. This is important for testing the capacity to perform isolated “normal tasks.” Kinetic chain evaluation
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TABLE 5.27 Methods of Quantifying Sensibility Method
Primary Cord Pathway Device
Moving 2-pt. discrimination Static 2-pt. discrimination Pressure Digit/joint kinesthesia Barognosis Vibration Temperature Pain
Dorsolateral pathway Dorsolateral pathway Dorsolateral pathway Dorsolateral pathway Dorsolateral pathway Dorsolateral pathway Anterolateral pathway Anterolateral pathway
requires observation and testing of many muscles and joints to complete a task, such as the muscle groups required for transfers from a wheelchair to bed. 5.15.7.8 Sensibility The approach to measuring sensibility can be twofold. The goal of the first approach should be to localize the spinal level of involvement and the specific tracts compromised. The latter approach is to test specific sensory modalities. This method of assessment can be followed by more quantifiable protocol to help determine changes in sensibility (Table 5.27). 5.15.7.9 Balance Balance is maintained through three primary mechanisms: (1) sensory input, (2) motor output, and (3) CNS integration. Sensory input is comprised of information obtained from visual input and vestibular, skin, joint, and muscle receptors. The neuromuscular apparatus responds in order to maintain equilibrium. The CNS integrates the input and modulates the musculoskeletal response. The patient with myelopathy will have some degree of compromise of all three components. This may contribute to imbalance while standing, walking, sitting, or lying. Balance can be measured in a given position or while performing a task. Balance may be qualitatively assessed or measured quantitatively through many available devices.
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6
Spinal Cord Syndromes and Guide to Neurological Levels
The degree of spinal cord injury (SCI) can be determined based on the clinical evaluation of function below the level of injury. If no sensory or motor function below the level of injury is detectable, the SCI would be classified as “complete.” However, many patients with SCI or myelopathy have incomplete patterns of neurological compromise. Because of the consistent arrangement and location of ascending and descending spinal cord pathways and segmental-level neuronal cell bodies, predictable neurologic syndromes occur with injury to a given region.
6.1 VASCULAR SYNDROMES OF THE SPINAL CORD Vascular syndromes are potential emergencies requiring astute recognition. We have simplified the presentations so that they might be recognized.
6.1.1 ANTERIOR SPINAL ARTERY SYNDROME Anterior spinal artery syndrome (ASAS) refers to the signs and symptoms associated with SCI that occur secondary to anterior spinal artery occlusion or hypotension. ASAS is a severe ischemic event in the distribution of the anterior spinal artery (Table 6.1). This region of vascular supply includes the anterior funiculi, anterior horns, base of the dorsal horns, anteromedial aspect of the lateral funiculi, and the periependymal regions (Figure 6.1). Occlusion of the anterior spinal artery results in an abruptonset, complex presentation (Table 6.2). The patient may describe lancing pain in a girdle-like distribution, rapid onset paralysis, impaired bowel and bladder control, sexual dysfunction, and a dissociated loss of pain and temperature sensation below the level of the lesion. Thermoanesthesia and analgesia often occur secondary to ischemic or infarctive changes within the spinothalamic tracts. A segmental loss of muscle function may develop within minutes or hours corresponding to the level of the lesion. There is a sparing of vibratory perception, position sense, and light touch because the posterior columns have a separate blood supply from the posterior spinal arteries (Figure 6.2).
6.1.2 POSTERIOR SPINAL ARTERY SYNDROME (PSAS) Posterior spinal artery syndrome (PSAS) is less common than ASA syndrome. The paired posterior spinal arteries allow for more extensive collateral flow, reducing the risk
for spinal cord arterial insufficiency. The area of the spinal cord perfused by the posterior vascular network is smaller than the area subserved by the ASA and its branches. This syndrome presentation is less complex than ASAS (Table 6.3). The PSAS results from ischemic insult to the fasiculus cuneatus, fasiculus gracilus, and posterior spinocerebellar tract. Vibratory perception and position sense are usually the first modalities lost. There is often a reduction or loss of associated segmental muscle stretch reflexes. Gait in these patients is ataxic and cautious. A positive Romberg sign is present with poor coordination.
6.1.3 RADICULOMEDULLARY ARTERY SYNDROME (RAS) Compromise of the radiculomedullary artery at the intervertebral foramen may contribute to spinal cord arterial insufficiency. Spondylosis and osteophytic narrowing of the intervertebral foramen (IVF) can result in encroachment of the arterial supply. The radiculomedullary arteries are not found at every vertebral level. Multilevel radiculomedullary compromise within the IVF may result in a pathologic watershed zone within the spinal cord. The signs of RAS are variable depending on the pattern of intramedullary insufficiency.
6.1.4 CENTRAL CORD VASCULAR SYNDROME (CCVS) The central cord vascular syndrome (CCVS) is one of the most common cervical cord syndromes, more common in male patients of middle and older age groups who have preexisting cervical spondylosis and stenosis. A CCVS is characterized by flaccid motor deficits of the distal upper extremities often accompanied by dysesthesia. Usually sensation from the sacral region is spared because the outer periphery of the cord is unaffected. A central cord syndrome may occur secondary to aortic disease and hypotension. Herrick and Mills1 report two cases of central spinal cord infarction that primarily involved the gray matter. A CCVS may be difficult to differentiate from an ASAS. Systemic hypotension may lead to severe impairment of perfusion through a watershed zone occurring between the territory perfused by AS and PS arteries.2 The CCVS presents very similar to ASAS due to compromise of the anterior horn and anterior commissure. 139
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Posterior spinal artery
Anterior sulcal (sulcocommissural) artery
The anterior spinal artery supplies the anterior 2/3 of the cord. This includes the central gray matter and lateral columns of the spinal cord. The posterior spinal and circumferential arteries supply the remaining 1/3 of the cord. A compressive lesion or thrombosis within the anterior artery produces paresthesias, pain, spastic paresis, flaccid paralysis and bowel and bladder dysfunction. The posterior columns are usually spared, leaving proprioception and vibration intact.
Posterior spinal distribution Circumferential branches
Anterior spinal artery located within sulcus
Anterior sulcal distribution
Circumferential distribution
Posterior spinal artery
FIGURE 6.1 Intramedullary arterial supply to the spinal cord. (Copyright J.M. True, D.C.)
TABLE 6.1 Selective Causes of Ischemia and Infarction within the Distribution of the Anterior Spinal Arterya • • • • • • • • • • • a
Intervertebral disk herniation Complications of discectomy Ballistic trauma to the spine Angiography Surgical complications of aortoiliac disease Complications of surgery Polyarteritis Sickle cell anemia Giant cell arteritis Syphilis Arteriosclerosis Not listed in order of prevalence.
6.2 COMPLETE SPINAL CORD TRANSECTION (TRANSVERSE MYELOPATHY) Transverse myelopathy results in complete interruption of all ascending and descending tracts at the level of the lesion. This results in a loss of motor, sensory, autonomic, and reflex functions.
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TABLE 6.2 Anterior Spinal Artery Syndrome • • • • • • •
Radicular and ascending leg pain Sensory level for pain and temperature Sudden progressive paraplegia Flaccidity (acute), spasticity (late) Areflexia (acute), hyperreflexia with Babinski’s sign (late) Sparing of touch, vibration, and temperature Urinary and fecal incontinence (uncommon)
TABLE 6.3 Posterior Spinal Artery Syndrome • • • •
Suspended global anesthesia Regional tendon and cutaneous reflex loss Dorsal column sensory level Sparing of anterior cord functions
Radicular pain, radicular paresthesia, and/or focal pain over the spine may have localizing significance. Focal pain may be elicited through spinal percussion and/or palpatory techniques. Hypoalgesia or anesthesia below the
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Spinal cord (T7) Posterior spinal arteries Territory of the posterior spinal artery
Posterior columns
Lateral corticospinal tract
Territory of the anteriorspinal artery
Lateral spinothalamic tract Anterior spinothalamic tract Anterior spinal artery
Motor loss below T7 (paraplegic) T7 level Segmental sensory loss
Loss of pain-temperature sensation
Several segments of cord infarction
FIGURE 6.2 Anterior spinal artery territory and syndrome. The anterior spinal artery (with its collateral supply) irrigates the anterior two thirds of the cord (diagonal hatching). All segmental functions are affected in the infarcted cord levels. Deficits in pain–temperature sensation occur below the sensory level, due to interruption of all ascending information in the spinothalamic tracts bilaterally. The posterior columns (and posterolateral columns), serving vibration and some aspects of fine touch and joint position sense, are preserved. The lateral corticospinal tract involvement causes paraplegia. (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, Oxford, 1993, p. 307. With permission.)
level of the lesion often provides important localizing significance. With a complete transverse lesion, all sensory modalities below the level of compromise will be absent. Paraplegia or tetraplegia occurs below the level of a complete transverse lesion. All unattended lesions above the level of C3 are fatal due to respiratory failure secondary to paralysis of diaphragmatic and accessory respiratory muscles. Acute SCI with transverse myelopathy results in a period of spinal shock. After recovery from spinal shock, hypertonicity and spasticity develop below the level of the lesion. The toes are upgoing (Babinski’s response) to plantar stimulation, and there is a loss of superficial reflexes
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and the cremasteric response. At the level of the transverse lesion lower motor neuron findings include flaccid paresis, hyporeflexia, fasciculations, and atrophy. The specific location of a transverse myelopathy in the thoracic region can sometimes be difficult to assess solely by clinical examination. Transverse myelopathy may result in urinary and rectal dysfunction with incontinence. Initially atonic, and later hyperreflexive, rectal and bladder sphincteric dysfunction occurs. Stimulation of the perineum often produces a reflex contraction of the spastic bladder with subsequent involuntary partial voiding. Constipation with risk for fecal impaction occurs as a result of the atonic bowel presentation. Voluntary control of the bladder is not possible
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TABLE 6.4 Central Cord Syndrome: Clinical Characteristics • • • •
Bandlike thermoanesthesia or thermodysesthesia Bandlike analgesia or hypoalgesia Preservation of light touch Dissociated sensory loss
with a complete transverse myelopathy because of the loss of descending influences. Anhidrosis and trophic skin changes may be seen below the level of the transverse lesion. There is sexual dysfunction with impotence.
6.3 CENTRAL CORD SYNDROME The acute central cord syndrome is characterized by a disproportionate loss of motor power in the upper extremities vs. the lower extremities with varying degrees of sensory involvement. Patients with a central cord syndrome may be capable of substantial recovery unless there is persistent spinal cord compression. A chronic central cord syndrome can occur secondary to lesions that compromise the central portion of the spinal cord, such as syringomyelia, hydromyelia, and intramedullary spinal cord tumors. A central cord syndrome within the cervical region is usually associated with severe hand paresis, which is disproportionate to pyramidal long tract signs in the lower extremities. The hands are often the last region to recover. Post-traumatic central cord compromise can occur in the absence of spinal fracture or dislocation with severe hyperextension. An acute central spinal cord syndrome can occur secondary to ballistic cervical injuries. Weakness in the arms is usually the predominant motor finding. There may be a patchy hypoesthesia of the extremities involving the segmental level below the lesion. The signs and symptoms are often temporary and may be secondary to high-velocity stretch injury to neurons within the central gray matter and corticospinal tracts within the cervical enlargement. A post-traumatic cervical syrinx may be noted incidentally upon cervical MRI evaluation. One of the earliest manifestations of a central cord syndrome results from insult to the spinothalamic fibers crossing in the midline (Table 6.4; Figure 6.3). These fibers convey pain and temperature sensibility. Injury to decussating spinothalamic fibers in this region results in a disassociated sensory clinical presentation due to preservation of the posterior column fibers. Damage to the crossing fibers will produce a loss of pain and temperature perception in a suspended vestlike pattern. With a true midline lesion there will be a relatively symmetric crossover
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spinothalamic deficit. With small paramedian lesions, sensory dissociation will be present, but the degree of thermohypoesthesia and hypoalgesia may be asymmetric. The clinical presentation and region of sensory loss will expand consistent with the expansile evolution of the lesion. In a small study, Quencer and colleagues3 evaluated the magnetic resonance imaging (MRI) appearance of spinal cords from patients with acute traumatic central cord syndrome. All patients exhibited hyperintense signal within the parenchyma of the cervical spinal cord on gradient echo MRI, representing cord edema. None showed MRI features characteristic of hemorrhage on T1-weighted spin echo or T2-weighted gradient echo studies. Gross and histological examination of the necropsy specimens showed no evidence of blood or blood products within the cord parenchyma: the primary finding was diffuse disruption of axons, especially within the lateral columns of the cervical cord in the region occupied by the corticospinal tracts. An interesting observation in this study was that the central gray matter was found to be intact.3 These researchers noted that patients with preexisting cervical stenosis or spondylosis were more likely to have a predominant white matter injury with little evidence for intraparenchymal hemorrhage following acute cervical trauma. With enlargement and dorsal migration of a central cord lesion, the posterior columns may be involved, resulting in superimposition of diminished vibratory and kinesthetic loss. Extreme anterolateral migration of a central lesion may compromise the spinothalamic tract. This results in impairment of pain and temperature perception below the level of the lesion. If anterolateral lesion migration is predominantly ipsilateral, the degree of clinical pain and temperature loss will be greater contralateral to the side of the lesion. Medial to lateral progression of a central cord lesion will initially spare sacral pain and temperature sensibility. Pure anterior horn lesions are characterized by segmental flaccid paresis, atrophy, and hyporeflexia. Extensive lateral involvement with a central cord syndrome can include compromise of the corticospinal tracts resulting in spastic paresis or paralysis below the segmental level of the lesion. Clinical characteristics of upper motor neuron lesion (UMNL) include hyperreflexia, spasticity, and pathologic reflex responses such as upgoing toes to plantar stimulation in adults. Sparing of autonomic functions occurs in the presence of small central spinal cord lesions. Extreme lateral extension of a central cord lesion may result in compromise of the intermediolateral cell column. If this occurs at the C8–T2 neurologic levels, it can result in an ipsilateral Horner’s syndrome (miosis, lid ptosis, and ipsilateral facial anhidrosis). Lateral mass expansion with extensive damage to the lateral horns will contribute to extremity trophic changes.
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(A) Cervical cord Lesion (cavity)
143 Posterior columns (vibration, aspects of fine touch, and joint position sense) Corticospinal tract
Segmental gray matter damage
2nd order pain-temperature fiber (B)
Spinothalamic tract Anterior white (pain-temperature) commissure (crossing spinothalamic tract fibers) Loss of pain-temperature sensation (damage to crossing fibers); also multisegmental motor deficits
FIGURE 6.3 Syringomyelia. (A) In a representative section of the cervical cord, the lesion (a central cavity) involves the anterior white commissure (just ventral to the central canal) through which the second-order fibers of the pain–temperature pathway cross. (B) Pain–temperature sensation is lost only at (or slightly below) each segment of damage from the syringomyelic cavity, but is not lost from lower parts of the body since the spinothalamic tracts themselves are unaffected. Lower motor neuron deficits are also variably present in each affected segment because of damage to the anterior horns of the spinal cord. Compare with the anterior spinal artery syndrome. (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, Oxford, 1993, p. 308. With permission.)
6.4 ANTERIOR CORD SYNDROME The second most common cervical syndrome is the anterior cord syndrome (ACS). Schneider4 originally described the anterior cord syndrome following acute cervical trauma. ACS is often associated with cervical flexion and extension injury that may be accompanied by vertebral fracture, dislocation, or disk herniation. ACS occurs when the anterior portion of the spinal cord is compromised through direct trauma or ischemia. By definition, there is sparing of the posterior columns with preservation of proprioception, light touch, and position sense (Table 6.5). Mild cases of ACS may be associated with retention of some motor function
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due to sparing of descending fibers within the lateral corticospinal tracts. The prognosis for anterior cord syndrome is usually not as good as with the central cord syndrome.
6.5 POSTERIOR CORD SYNDROME A pure posterior cord syndrome (PCS) is rare, characterized by selective compromise of the posterior columns (Figure 6.4). This typically occurs secondary to neurosyphilis or an expansile extradural lesion lying within the posterior cervical canal. An expansile lesion may initially present as a PCS, eventually developing into a posterolateral
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A
B
FIGURE 6.4 (A) Posterior cord (column) syndrome. (B) Axial T2 weighted cervical spine image demonstrating bilateral posterior column high-intensity signal. This patient has confirmed pernicious anemia.
TABLE 6.5 Anterior Cord Syndrome: Clinical Characteristics • • • •
Preservation of proprioception Preservation of vibratory perception Diminished or loss of pain and temperature sensation below lesion Complete or incomplete motor loss
TABLE 6.6 Posterior Cord (Column) Syndrome: Clinical Characteristics • • • • • • •
Impaired vibration sense Abnormal position sense Loss of deep pressure perception Diminished tactile localization Sensory gait ataxia Tactile and postural hallucinations Spared pain and temperature perception
cord syndrome. The primary differential evaluation of posterior column presentation should include tabes dorsalis, central spinal canal stenosis, and demyelinative disease such as multiple sclerosis. The characteristic sensory presentation of PCS includes a loss of proprioception and discriminative sensation distal to the lesion (Table 6.6). There is often a positive Romberg sign and sensory ataxia; during the Romberg maneuver, the loss of balance increases dramatically with closing of the eyes. Patients with sensory ataxia will attempt to observe their feet during ambulation, using visual cues to help correct for loss of kinesthesia. The clinician may occasionally observe a double tap sign during gait, reflecting the individual’s attempt to increase afferentation.
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TABLE 6.7 Syndrome of Posterolateral Columns (Subacute Combined Degeneration): Clinical Characteristics • Distal extremity paresthesia • Sensory ataxia • Hyperreflexia (superimposed peripheral neuropathy may cause hyporeflexia) • Muscular spasticity • Bilateral toe extensor signs (Babinski’s) • Impaired proprioception and vibratory sense • Sparing of pain and temperature sensibility
Posterior column compromise may lead to truncal ataxia, secondary to impaired proprioception and postural perception. Some degree of truncal and extremity disuse muscle atrophy and paresis usually occurs secondary to involuntary and voluntary limitation of physical activity. Patients with moderate to severe posterior column compromise often present with diminished or absent patellar and Achilles muscle stretch reflexes (MSRs). Individuals may also complain of urinary incontinence.
6.5.1 POSTEROLATERAL CORD SYNDROME The posterior spinocerebellar tract, fasciculus cuneatus, and fasciculus gracilis may be compromised in a number of conditions. Contributing conditions include vitamin B12 deficiency with subacute combined degeneration, vacuolar myelopathy secondary to autoimmune deficiency syndrome (AIDS), and cervical spondylosis with ligamentum flava buckling and hypertrophy. Many patients with posterior column lesions initially complain of distal extremity paresthesia, sensory ataxia, and loss of proprioceptive functions (Table 6.7; Figure 6.5). The patient may report diminished distal extremity vibratory perception during examination in the early stages of compromise. As the condition progresses,
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FIGURE 6.5 Posterolateral cord syndrome.
loss of vibratory perception intensifies and impaired joint position sense becomes more apparent, but, with early detection, most conditions will not progress to this level of severity. If posterolateral cord syndrome is suspected, the clinician should always evaluate for subtle or progressive sensory disturbances. Subacute combined degeneration spares the spinothalamic tract, preserving pain and temperature sensation. In the absence of obvious long tract signs, peripheral neuropathy should also be considered in the differential diagnosis of lower extremity sensory loss. Autonomic centers or pathways are not typically involved with posterolateral compromise.
6.6 ANTERIOR HORN SYNDROME (PROGRESSIVE MUSCULAR ATROPHY) Several diseases selectively compromise the motor cells of the anterior horn (Figure 6.6). Diseases that selectively afflict the anterior horn lead to progressive muscular atrophy. Prior to development of the polio vaccine, the most common cause for acute anterior horn syndrome was poliomyelitis. Less common is an acute syndrome secondary to other enteroviruses. Lymphoma, on rare occasions, has been associated with subacute motor neuronopathy involving the anterior horn. A few forms of inherited spinal muscular atrophy may present as an isolated anterior horn syndrome. In a pure anterior horn syndrome, sensation is normal, due to sparing of the sensory tracts and fibers. A lower motor neuron presentation occurs at the segmental level of insult. The clinical findings include flaccid paresis/paralysis, atrophy, hypotonus, and hyporeflexia within affected segmental levels. Additional findings may include axial and extra-axial fasciculations. With selective anterior horn compromise there is sparing of the autonomic tract or fibers (Table 6.8).
6.6.1 POLIO
AND
POST-POLIO SYNDROME
Poliomyelitis is an extremely rare viral disease caused by a picornavirus that is transmitted initially through the gastrointestinal system. Spinal cord infection results in aggressive degeneration of the anterior horn and alpha motor neurons. Involvement is not limited to the spinal cord, as areas of the brain and brainstem may also be
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FIGURE 6.6 Anterior horn cord syndrome.
TABLE 6.8 Anterior Horn Syndrome: Clinical Characteristics • • • • •
Diffuse weakness (LMNL) Muscular atrophy Reduced muscle tone Muscle fasciculations Hyporeflexia or areflexia
afflicted. Some infected individuals only experience minor illness with a sore throat, vomiting, malaise, abdominal pain, and mild headache. Others go on to suffer devastating motor neuron loss with associated lower motor neuron features. After the initial illness, some neurological recovery might occur during the ensuing 4 to 8 years, likely due to partial anterior horn cell recovery and collateral sprouting.5 As many as 25 to 60% of patients afflicted with polio may acquire additional signs and symptoms 25 to 50 years after the initial infection.6 The post-polio syndrome (PPS) is characterized by predominant musculoskeletal symptoms and post-polio progressive muscular atrophy. There may be new onset of joint pain, muscle pain, and acquired pathomechanical lesions such as scoliosis. There may be progressive impairment of bulbar and spinal involvement including muscles not previously affected. The specific etiology of post-polio syndrome has not been determined but it has been proposed that surviving motor neurons with extensive collateral sprouts may become compromised secondary to metabolic and/or age-related changes leading to critical axonal dropout and muscular impairment.5 The diagnosis of PPS can be made assuming the following criteria are met: (1) history of poliomyelitis with 15 years of functional stability; (2) residual asymmetric muscular atrophy, hypotonia, paresis, and areflexia; (3) new onset of neuromuscular symptoms to include paresis and atrophy; and (4) exclusion of other possible etiologies.7
6.6.2 COMBINED ANTERIOR HORN AND PYRAMIDAL TRACT DISEASE (MOTOR NEURON SYNDROME) Combined anterior horn and pyramidal tract disease syndrome is often referred to as amyotrophic lateral sclerosis
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Irregular intramedullary lesions
FIGURE 6.7 Combined anterior horn and pyramidal tract cord syndrome.
TABLE 6.9 Spinal Motor Neuron Disease: Clinical Characteristicsa • Upper motor neuron lesion (UMNL) Spastic paresis Extensor plantar responses Hyperreflexia • Lower motor neuron lesion (LMNL) Muscular atrophy Flaccid paresis Fasciculations a
Combined upper and lower motor neuron signs.
(ALS) (Figure 6.7). ALS is a terminal progressive disease with features similar to spastic paraplegia and the spinal muscular atrophies. Damage to the anterior horns will result in flaccid paresis, whereas coexistent compromise of the pyramidal tracts produces spastic paresis. In ALS, spinal presentations usually predominate in the early stages, eventually progressing to bulbar paralysis. The disorder is most predominant in males.8 Early clinical signs are often unilateral and limited to the distal extremities. ALS can progress to compromise any striated muscle and occasionally spares the pelvic floor sphincters and external ocular muscles. Sensory perception is characteristically spared. ALS develops into a complex presentation of combined upper and lower motor neuron disease (Table 6.9). This presentation often coexists within the same extremity. The individual may present with hand atrophy and evidence of spasticity after passive extension of the fingers. MSR hyporeflexia secondary to anterior horn insult may appear normal with coexistence of upper motor neuron mechanisms from impaired pyramidal fibers. Upper motor neuron presentations include spasticity, hyperreflexia, and spastic paresis, whereas the lower motor neuron presentations include flaccid paresis, hyporeflexia, hypotonus, and fasciculations. Lower extremity muscle stretch reflexes are usually hyperreflexive during most of this disease process. Bulbar deficits, when present, may cause a rapid decline in the condition. These deficits may manifest as explosive dysarthria, difficulty swallowing,
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FIGURE 6.8 Multifocal cord syndrome.
glossal spasticity, and loss of vital capacity. ALS causes death by respiratory paralysis, cardiac failure, or suffocation from aspiration of food or liquids due to loss of swallowing control.
6.7 MULTIFOCAL CORD SYNDROME The multifocal cord syndrome does not follow any of the classic presentations of the other syndromes described in this chapter. The more common etiologies for multifocal cord syndrome include multilevel stenosis and/or multifocal demylinative disease. There may be increased vulnerability secondary to metabolic influences such as diabetes. Demyelinative lesions do not characteristically occur within watershed regions; therefore, the presentation is not characteristic of vascular syndromes. Demyelinative changes can occur anywhere throughout the spinal cord (Figure 6.8). Multifocal stenosis can lead to multisegmental lower motor neuron paresis with superimposed upper motor neuron and other long tract signs (myeloradiculopathy).
6.8 CONUS MEDULARIS SYNDROME The distal end of the spinal cord tapers to a conical shaped tip referred to as the conus medullaris. The conus contains the segments (neuromeres) for the lumbar and sacral regions and generally lies posterior to the L1 vertebral body or at the L1–L2 disk interspace. Most of the lumbar cord neuromeres lie within the conus adjacent to the T12 vertebral body, and most of the sacral cord segments lie opposite the L1 vertebral body.
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A
B
C
FIGURE 6.9 (A) Distal spinal cord neoplasm visualized in the axial plane, demonstrating marked cord expansion encompassing the entire spinal canal. (Axial spin echo T1-weighted image through the conus medullaris following gadolinium enhancement.) (B, C) Round enhancing mass contained within the conus medullaris, confirmed as a myxopapillary adenoma. Note expansion of the distal spinal cord. There is also a central nonenhancing area representing focal cystic degeneration. (Parasagittal spin echo T1-weighted image following gadolinium enhancement; parasagittal spin echo T2-weighted image.) These two images are to the right of the midline. (Courtesy Dr. Mary Ann Hordesky–Storr, D.C.)
TABLE 6.10 Epiconus Syndrome: Clinical Characteristics • • • • •
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Loss of bladder control Loss of perianal muscle control Absent bulbocavernosis reflex Absent anal wink reflex Flaccid paresis of lower extremity
A conus syndrome may arise from intraparenchymal or extraparenchymal pathology (Figure 6.9). The conus is susceptible to injury at the T11–12 and T12–L1 levels due to greater segmental movement as compared to the more immobile thoracic region. Injury to the upper portion of the conus medullaris may result in a combined upper and lower motor neuron presentation often preceded by initial flaccid paralysis of the legs, bladder, and anal sphincter (Figure 6.10; Table 6.10). This is often followed by muscular atrophy, muscle spasticity, positive Babinski’s response, and
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A. Lower cord A Lower cord lesion
Distal ipsilateral lower extremity spastic hemiparesis
(hemisection)
Contralateral loss of pain and temperature below level of lesion
B
High radicular and lateral conus lesion
Ipsilateral loss of light touch and kinesthesia below level of lesion Ipsilateral lower extremity hyperreflexia below level of lesion Ipsilateral positive Babinbski
C D B. Lateral conus
Midline distal conus/epiconus lesion
Ipsilateral lower extremity muscle hypertonicity below level of lesion Ipsilateral segmental sensory and paresis
Midline cauda equina lesion
C. Distal conus
D. Cauda equina Prominent radicular pain
Ipsilateral segmental flaccid muscle paresis/paralysis
Motor findings are usually not severe
Ipsilateral segmental sensory loss
Rarely severe pain
No dissociated sensory loss
Bilateral perineal pain
Bowel/bladder function
Infrasegmental ipsilateral hyperreflexia Infrasegmental ipsilateral spastic hemiparesis/paralysis Ipsilateral positive Babinski May have reflex neurogenic bladder with large lesion
Epiconus: absent achilles MSR Conus: Intact patellar and achilles MSRs. May be hyperreflexive Saddle anesthesia is a late sign Early and marked urinary and fecal incontinence
Patellar and achilles MSRs may be absent Late onset sphincter disturbance Saddle distribution of sensory loss
May develop a motor paralytic bladder Bilateral lower extremity flaccid paresis/paralysis
May develop an autonomous bladder in severe cases
FIGURE 6.10 Localizing patterns in lesions of the lower cord, conus medullaris, and cauda equina. (Copyright J.M. True, D.C.)
hyperreflexia. The sensory presentation is variable, and sensory sparing may be limited to perianal sensation. In more severe cases of conus medullaris insult, bowel and bladder deficits may be profound. Compromise limited to the distal tip of the conus may spare the greater portion of descending pyramidal fibers, thus raising the possibility that long tract signs may be minimally present or nonexistent. An extraparenchymal lesion arising from the region of the distal conus may result in a unilateral or bilateral lower motor neuron presentation due to polyradiculopathy, bladder impairment, and perineal and perianal sensory disturbances.
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Injury to the conus or epiconus may also injure the cauda equina. Neurological compromise within the conus generally has the same prognosis as spinal cord compromise at more rostral levels. A high lumbar disk herniation may result in compression of the conus medullaris (Figure 6.11). Compromise of the cauda equina has a much better prognosis than SCI due to the greater capacity for neurologic recovery of the descending nerve roots. Urodynamic assessment is an important part of the differential workup of any patient with a neurologically significant lesion at the thoracolumbar vertebral level.9
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FIGURE 6.11 A high lumbar disk herniation is rare; however, it may produce cord or conus medullaris compression as well as spinal nerve root compression. (Copyright J.M. True, D.C.)
TABLE 6.11 Hemisection Cord Syndrome (Brown–Séquard): Clinical Characteristics • Ipsilateral loss of vibratory perception • Segmental lower motor neuron signs at the level of the lesion • Ipsilateral loss of proprioception (position sense) (below level of lesion) • Contralateral loss of pain and temperature sensibility (one or two segments below level of lesions) • Ipsilateral motor loss with spastic paresis • Inability to walk • Loss of normal bowel and bladder function
6.9 HEMISECTION SYNDROME (BROWN–SÉQUARD SYNDROME) A Brown–Séquard syndrome refers to injury to the lateral half (hemisection) of the spinal cord. This syndrome is characterized by ipsilateral motor deficits, ipsilateral proprioceptive loss, diminished ipsilateral vibratory perception, and contralateral loss of pain and temperature sensation. In mild cases there may be sparing of sphincter function (Table 6.11). A number of different mechanisms have been found to contribute to the hemisection syndrome. The most common cause is observed with hyperextension injuries and facet and compression fractures, including those studied by Braakman and Penning.10 The Brown–Séquard syndrome occurs most often after cervical injuries and less frequently after thoracic cord injuries. Large or expansile extramedullary lesions can compress the spinal cord, resulting in a Brown–Séquard syndrome. Spinal cord hemisection may be incomplete with some sparing of descending and ascending nerve fibers.
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Hemimyelopathy occurs more commonly from posttraumatic concussions or contusions as well as due to an expansile lesion. Initially, the presentation may be subtle. Patients taking anticoagulants may suffer post-traumatic or spontaneous hemimyelopathy secondary to hematomyelia and/or epidural hematoma. Additional causes of Brown–Séquard syndrome include vertebral fracture-dislocations, severe spondylosis with projective exostosis, migration of disk or bone fragments, hematoma, or metastasis. Interruption of the crossed ipsilateral spinothalamic tract and spinothalamic projections results in contralateral loss of pain and temperature (Figure 6.12). The contralateral sensory loss occurs one to two segments below the level of cord compromise due to the descent of the spinothalamic fibers as they decussate. This anatomic arrangement results in preservation of ipsilateral spinothalamic sensibility (pain and temperature) below the level of the lesion. Contralateral pain and temperature loss with contralateral preservation of posterior column sensation creates a disassociated sensory loss distal to the SCI. There is ipsilateral loss of deep sensibility that includes joint position sense, two-point discrimination, and vibratory loss secondary to ipsilateral compromise of the posterior columns. Ipsilateral interruption of the dorsal spinocerebellar tract contributes to positional disorientation and abnormal kinesthesia. Compromise of the ipsilateral descending corticospinal tracts will lead to spastic paresis or paralysis below the segmental level of the lesion. Motor functions contralateral to the lesion are spared. An acute hemicord syndrome may initially present with ipsilateral hypotonicity and hyporeflexia below the segmental level secondary to spinal shock. After recovery from spinal shock, ipsilateral MSR hyperreflexia, ipsilateral muscle spasticity, and Babinski’s responses develop below the involved segmental level. Ipsilateral compromise of the vasomotor fibers of the lateral columns contributes to dysautonomia presenting cutaneous hyperemia and absent or impaired sweat secretion. The lesion that causes the Brown–Séquard syndrome may also injure the anterior horn cells and associated nerve root or roots. This will result in segmental flaccid paresis or paralysis, muscle atrophy, and hyporeflexia. Segmental anesthesia and analgesia may be present if sensory portions of the nerve root are injured.
6.10 CERVICAL MEDULLARY SYNDROME Injury to the upper cervical cord may involve the medulla. Cervical medullary syndrome describes those syndromes involving injury to the upper cervical cord and lower brainstem. Lesions in the region of the foramen magnum are usually associated with a complex sensory and motor presentation. Compromise of cranial nerves IX–XII may occur. There is often suboccipital pain in the distribution of the C2 nerve root. Cerviocogenic headaches may accompany neck stiffness and reactive paracervical myospasm.
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FIGURE 6.12 Brown–Séquard syndrome. Principal deficits resulting from a right hemitransectional lesion of the spinal cord, shown here at T4 cord level. (A) Dissociated sensory loss, with deficit (shaded) or “dorsal column” modalities (vibration, some aspects of fine touch, and joint position sense) ipsilaterally below the lesion and spinothalamic (pain–temperature) deficit (shown by hatching) contralateral and almost up to the level of the lesion. Corticospinal motor deficits occur ipsilaterally below the lesion. All segmental functions are affected ipsilaterally at the level of the lesion. (B) In this highly simplified schema, “dorsal column” modalities are conveyed by first order neuronal fibers that enter the right side of the cord at each segment and would ascend in the right (ipsilateral) dorsal column without synapse until the medulla, if not blocked by the T4 lesion represented in (D). (C) The second order neuronal pain–temperature fibers cross just above their segmental level of origin to form the right lateral spinothalamic tract. (D) The position of the three main ascending and descending tracts are seen in the cross-section of the cord at T4 (lesion shaded). (From Glick, T.H., Neurologic Skills: Examination and Diagnosis, Blackwell Scientific, Oxford, 1993, p. 271. With permission.)
Lesions extending into the region of the foramen magnum may be associated with a downbeat nystagmus, cerebellar ataxia, and cerebrospinal fluid (CSF) block with increased intracranial pressure. Clinical features of the cervical medullary syndrome include respiratory insufficiency or arrest, systemic hypotension, varying degrees of quadriparesis or quadriplegia, long tract sensory findings, bladder dysfunction, and lower cranial nerve involvement (Table 6.12). Hypoesthesia may extend from from C1–C4. There may be hemifacial sensory loss. It is critical to evaluate cranial nerve function in all potential cases of cervical medullary syndrome. The assessment of facial sensibility will help determine whether there is involvement of the trigeminal
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TABLE 6.12 Cervicomedullary Syndrome: Clinical Characteristics • • • • •
Respiratory insufficiency or arrest Arterial hypotension Varying degrees of tetraparesis Facial sensory loss Greater arm than leg weakness
nerve or the nucleus of the spinal tract of V, which extends as caudal as the C3 segment. The patient may complain of a perioral distribution of sensory disturbance or loss,
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suggesting injury to the lower medulla or upper cervical cord. Cervical medullary compromise can mimic a central cord syndrome due to the greater weakness of the arm than the leg. Compromise of the C1–C4 segments of the spinal cord may include insult to the spinal accessory nerve, cranial nerve XI. This nerve innervates the sternocleidomastoid (SCM) muscle and the upper portion of the trapezius muscle. Nerve damage will result in abnormal head position, trapezius, and SCM muscle atrophy and paresis. This will result in difficulty or inability to elevate the ipsilateral shoulder and difficulty rotating the head and neck towards the side opposite the lesion.
6.11 GUIDE TO NEUROLOGICAL LEVELS Classification of SCI using the “intact functional level” is one of the most clinically relevant systems for predicting outcome and physical rehabilitation requirements. The intact functional level classification scheme is based on the features observed with complete transection injury at a particular level, although incomplete patterns are more commonly seen in clinical practice. Polytraumatized patients often have complex neurological injuries including head trauma as well as cord and root findings. Patients with noncompressive myelopathy may exhibit a multifocal cord presentation or a combination of myelopathy and polyradiculopathy. A review of neurological levels provides a basis for diagnosis, therapeutic planning, and taking steps to improve the patient’s capacity to perform activities of daily living.
6.11.1 CRANIAL-CERVICAL LESIONS (FORAMEN MAGNUM LESIONS) Etiologies of foramen magnum lesions include tumors, multiple sclerosis (MS), Arnold–Chiari malformation, atlantoaxial dislocation, syringomyelia, and other congenital anomalies of the cervical cranial junction. This region can be a diagnostic challenge for the attending clinician as the symptoms are often vague and intermittent. Patients with Arnold–Chiari malformation type I without meningocele may present with progressive cerebellar dysfunction due to compromise of the cerebellar tonsils within the foramen magnum. This type I presentation may be characterized by increased intracranial pressure, myelopathy, upper cervical syringomyelia, and lower cranial nerve dysfunction. Many foramen magnum lesions are treatable; therefore, early diagnosis and intervention are important. Congenital anomalies of the cranial cervical junction are often asymptomatic. A lesion within the foramen magnum may contribute to suboccipital or upper neck pain that is often increased with cervical movement in various positions. Pain may radiate into the shoulders or
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proximal arm on the involved side. The pattern of pain is not unlike that of spondylosis. In many cases, spondylosis of mid- and lower cervical regions may coexist with the foramen magnum level lesion. Tumors at the foramen magnum constitute approximately 1% of all intracranial and intraspinal tumors.11 The cranial nerve signs and symptoms may include hemifacial dysesthesia, dysarthria, dysphonia, and dysphasia. Motor involvement generally presents as an upper motor neuron lesion with spastic weakness. Corticospinal tracts may be compromised by extramedullary intradural neurofibromas or meningiomas. Spastic paresis generally begins in the ipsilateral arm followed in order by weakness of the ipsilateral and contralateral leg. Foramen magnum tumors may occasionally cause signs of lower motor neuron weakness, atrophy, and reduced MSRs within the upper extremities and hands.12 Paresthesia associated with lesion at the foramen magnum often occurs along the ulnar aspect of the forearm and hand, but the mechanism whereby the upper motor neuron weakness and sensory loss occur in the same upper extremity has not been fully explained. The sensory abnormalities tend to be disassociated; therefore, patients suffering from hypoalgesia have preserved tactile sensation. When L’hermitte’s sign is frequently positive, the patient may exhibit some degree of vibratory abnormality over the clavicle or region of the acromion process.12 A relatively common cause of cervical-cranial abnormality resulting in myelopathy is that of atlantoaxial dislocation. This may occur secondary to hypoplasia of the odontoid process or incompetence of the transverse ligament. Some of the disorders associated with atlantoaxial instability and subsequent dislocation include congenital anomalies of the region, basilar impression, congenital scoliosis, neurofibromatosis, and rheumatoid arthritis. Metastatic cancer may be rarely seen at the dens. Atlantoaxial subluxation may result in physical spinal cord compression. This generally occurs when the sagittal diameter of the spinal canal is less than 14 mm, but physical compression of the spinal cord has been reported to occur occasionally at 15 to 17 mm.13 These upper cervical spine canal measurements where spinal cord compression occurs are larger than lower cervical spine measurements reported to occur between 10 and 13 mm.14 The mechanism of neural injury in many cases of atlantoaxial subluxation is compression of the medullary cervical junction by the odontoid process. (See Section 3.3.2.) The symptoms of atlantoaxial instability often are intermittent and involve weakness of an upper motor neuron type and some degree of wasting of the muscles of the upper extremities. Ataxia, dizziness, and lower cranial nerve symptoms are not uncommon. The presentation may mimic demyelinative disease.
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6.11.2 CERVICAL LESIONS Neoplasms involving the upper cervical spine have signs and symptoms that mimic lesions of the cranial-cervical region arising at the foramen magnum. The first cervical root does not have a sensory dermatomal distribution, but the second cervical root does innervate the posterior aspect of the scalp, explaining the pattern of radicular pain. In the presence of neoplasms involving the cervical spine, simple neck movements may result in pain radiating along the back of the head accompanied by dysesthesia. The descending tract of the trigeminal nerve may also be compromised, producing paresthesia or numbness in the face or loss of the corneal reflex.15 Fatality associated with high cervical transectional lesions, if not instantaneous, usually ensues within a matter of hours or days. Respiration becomes the critical factor when the motor neurons become disconnected from the respiratory center, inducing respiratory paralysis. Even incomplete transection creates problems, as respiration becomes depressed and insufficient due to spinal shock. Mortality increases after the initial injury because of the high risk of complications secondary to pneumonia. Autonomic functions are lost below the lesion. Bladder tonus and bowel function are lost as is sweating and piloerection. The lower extremities become edematous in response to impaired vasomotor tone and temperature regulation. With high spinal cord transection, determining which neurologic level is intact and functional is paramount. For the sake of the following discussion, a neurologic level is considered intact if its corresponding nerve root is intact and functional; thus, a neurologically intact C2 level will have a functional C2 nerve root while all segments caudally are completely dysfunctional. The presentations listed below may be incomplete. 6.11.2.1 Intact C3 Neurologic Level (C3 Functional Level) The presentation of the intact C3 neurologic level after cervical transection injury includes complete absence of upper extremity sensibility and loss of sensation caudal to approximately 3 inches above the nipple line along the anterior chest wall. The patient is completely tetraplegic. Deep tendon reflexes may be initially absent due to spinal shock but become brisk to exaggerated, with pathologic reflexes when the spinal shock dissipates. The patient is devoid of independent respiratory function due to disruption of diaphragmatic innervation and will require artificial respiratory assistance for the duration of life. Tracheostomy is necessary along with respiratory physiotherapy to clear lung secretions. Voluntary bowel and bladder function is nonexistent, requiring complete assistance. The mortality rate is very high due to respiratory complications.
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6.11.2.2 Intact C4 Neurologic Level (C4 Functional Level) A functional C4 neurologic level varies slightly from the C3 presentation. Hyperreflexia of deep tendon reflexes are deficits in the upper extremities beginning several inches lower on the mid-portion of the anterior chest wall. Motor findings include upper extremity spastic paralysis, but shoulder shrug function remains intact. The patient has respiratory insufficiency. The respiratory impairment is not complete, as the C4 neurologic level provides primary innervation to the diaphragm, but respiratory function remains depressed due to denervation of intercostal and abdominal muscles. C4 is the highest cervical functional level compatible with independent respiration. However, respiratory complications are common, and regular cough assistance is necessary to prevent pneumonia. Patients with functional C4 level generally have good head and neck control and can subsequently use a mouth stick. They are also capable of utilizing chin switches, breath control, eyebrow motion, and tongue switching for wheelchair or computer control. All activities of daily living require assistance. A mechanical lift for bed and toilet transfers is required. The patient is catheterized and the rectum must be manually cleared with assistance. 6.11.2.3 Intact C5 Neurologic Level (C5 Functional Level) The intact C5 neurologic level has a significantly different presentation than C4 with some upper extremity function preserved. Sensibility is intact along the lateral aspect of the arm from the shoulder to the elbow crease and along the upper anterior chest region. The biceps MSR is intact but may be absent during spinal shock, becoming brisk as spinal shock resolves. This first cord level subservient to the brachial plexus allows a functional but paretic deltoid muscle with mild biceps participation. Intact shoulder movement includes flexion, extension, and abduction with mild sparing of elbow flexion. The respiratory reserve remains depressed. As with all cord lesions above T10, the patient is unable to elicit a strong cough and will need assistance. A patient with a C5 functional level has a lesion just caudal to the C5 myotomal segment. The individual generally has full innervation of the trapezius, sternocleidomastoid, and upper cervical paraspinal musculature. The patient has intact rhomboids, deltoids, and major muscles of the rotator cuff, although these may be mildly paretic due to the contribution from the level of C6. These innervated muscles of the shoulder provide for scapular retraction and weak protraction, glenohumeral abduction, internal and external shoulder rotation. Elbow flexion is possible but is often mildly paretic due to the loss of C6
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nerve contribution. There is generally little to no elbow and wrist extension or hand function. Sensation is typically intact over the deltoid region and radial aspect of the thumb. This individual needs assistance in order to perform a prehensive pinch, often requiring electric hand splints with head, shoulder, and chin controls. The individual with a C5 functional level may require mobile arm supports. This individual generally has difficulty changing positions. Endurance is generally low because of reduced respiratory reserve. Bowel and bladder function requires assistance. These patients are not capable of independent transfers without a sliding board and subsequently are confined to a motorized wheelchair or bed. 6.11.2.4 Intact C6 Neurologic Level (C6 Functional Level) The C6 functional level represents one of the most common levels of quadriplegia. Over 50% of spinal cord injuries occur at the C6 level or slightly lower. The C6 neurologic level contributes to the brachial plexus and as a result the clinical picture begins to change significantly as some hand movement returns. Sensation of the lateral upper extremity extending distal to the thumb, index finger, and a portion of the middle finger is preserved. The biceps and brachioradialis muscle functions are intact; therefore, elbow flexion and supination are possible. With an intact C6 level, the supraspinatus and rotator cuff complex is fully innervated and strong. There is generally good stability and biomechanics at the glenohumeral joint. The serratus anterior, latissimus dorsi, and pectoralis major muscles receive partial innervation and are subsequently mildly paretic. The wrist extensor group receives partial innervation but remains paretic as the extensor carpi radialis muscle receives C7 innervation. The C6 intact individual will retain some function of pronation; however, forearm pronation and wrist extension remain paretic. Muscles distal to the proximal arm and shoulder are spastic, paretic, or paralyzed. Respiration is mildly depressed. There is a complete absence of voluntary finger extension or flexor power. This individual typically requires hand devices in order to enable prehension. Preservation of elbow flexors gives the individual the power to sit up independently or to assist with of this maneuver. There is greater capability of rolling over in bed. A strong individual with a functional C6 level may be able to independently transfer to a wheelchair. This individual is capable of feeding himself with hand-assistant devices and may contribute to toilet and dressing activities. This individual is capable of using elbow flexors and shoulder abductors and flexors to help guide a wheelchair. With extension of the wrist, typically the thumb and fingers approximate each other in a grasping motion. As the wrist is dropped in a flexion position, tightness of the finger extension
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muscles provides passive release. Hand splints can help enhance this mechanism. 6.11.2.5 Intact C7 Neurologic Level (C7 Functional Level) Impaired paretic grasp function allows additional motor tasks in the patient with an intact C7 neurologic level. Sensory sparing is not precise at this level but will contribute sensation to the middle digit. Triceps, biceps, and brachioradialis muscle stretch reflexes are normal. Clinical motor representation from C7 includes elbow extension, wrist flexion, and long finger extension. The intact C7 level patient gains three important motor functions: forearm extension using the triceps, finger extension, and finger flexion. Occasionally, these functions may be absent due to individual variations in anatomy between the C7 and C8 levels. A patient can generally lift his body, as he can stabilize his arm at the triceps and has a greater capability of shoulder girdle depression. Subacromial degeneration is common from continually lifting themselves during transfers. The patient has the advantage of grasp and release afforded by activated finger extensors and flexors. Fine motor dexterity of the hands is impaired, as the intrinsic muscles of the hand are innervated from C8–T1 levels. The C7 quadriplegic typically is confined to a wheelchair and transfers well between bed, wheelchair, car, and toilet following successful rehabilitation. Occasionally, C6-spared and C7-spared quadriplegics can drive a car with the proper enabling devices. 6.11.2.6 Intact C8 and T1 Neurologic Levels (C8 and T1 Functional Levels) The quadriplegic with intact C8 level muscles is able to grasp objects, thus making it possible for these patients to manage many activities of daily living. Proximal upper extremity sensibility sensation is normal to the upper extremity except along the proximal medial arm several inches below the elbow to the axillary region. Upper extremity reflexes are intact. Patients with intact C8 neurologic functions have preservation of finger flexion as well as extension but lack interossei function. They are able to voluntarily grasp and release but develop a clawhand-type deformity. Fine control grasp is difficult. Finger abduction is impaired, and adduction is present with a lost ability to perform pinch maneuvers. With sparing of T1 and C8 levels, there is full innervation of the upper extremity musculature, including the intrinsic muscles of the hand. This individual has normal strength, fine motor capacity, and dexterity of grasp and release as well as normal proximal muscular potential. This individual has not regained trunk stability. The T1 patient may be independent in bed activities and is able to transfer to and from a wheelchair or car without assistance.
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This individual can drive an automobile given appropriate hand controls. The individual with C8 and T1 functional levels can often be independent in most household activities with wheelchair access. Work is also possible with minimal assistance if the work area is set up for wheelchair access.
6.11.3 THORACIC-INTACT LESIONS (MID-THORACIC FUNCTIONAL LEVELS) The patient with neurologic levels intact above T2 has complete upper extremity strength and an intact brachial plexus. This patient’s motor loss is a paraplegic pattern. Sensation rostral to the mid-chest region is intact along with upper extremity sensibility. Upper extremity MSRs are normal. Trunk stability remains problematic, and there is total or partial lower extremity paralysis depending on the degree of cord damage. Sensibility assessment is the most accurate method to determine the level of neurologic involvement; sensory dermatomal landmarks contribute to localization of the lesion level. Motor function should be attempted. The intercostal, paraspinal, and abdominal muscles are segmentally innervated. Beevor’s sign during performance of a half sit-up is also a sign of abdominal muscle denervation. When the cord lesion is below T6, the patient retains significant trunk control compared to the patient with a high thoracic lesion. The T6 level individual has functional innervation of long muscles of the upper and mid-back and may use the intercostals for respiration. Respiratory reserve and endurance are therefore improved. This individual is typically independent in most phases of self-care. Full leg bracing becomes possible and the individual may be able to stabilize the upper extremities adequately to apply braces while recumbent. The individual with a functional mid-thoracic level typically can transfer independently to and from a wheelchair because of strong (innervated) upper extremities. Assistance is often not required. In conjunction with long leg braces and lower trunk stabilization, this individual is able to stand erect for a long period of time. Ambulation requires help and is not functional. The lower thoracic intact patient has increased wheelchair control and can negotiate the street environment or participate in wheelchair sports. 6.11.3.1 Intact T12 Neurologic Level (T12 Functional Level) The individual with sparing of T12 function has use of the rectus abdominus and oblique muscles of the abdomen and all muscles of the thorax which provides good trunk stabilization and respiratory ability. The low back and hip musculature are not innervated. This individual may utilize bilateral long leg braces with spine stabilization for household ambulation.
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6.11.4 LUMBAR TRANSECTION INJURIES 6.11.4.1 Intact L1 Neurologic Level (L1 Functional Level) A complete lumbar transection injury results in spastic paralysis of the lower extremities after spinal shock. Voluntary control of the bowel and bladder function is nonexistent in upper lumbar lesions. Although the bladder may be less hyperreflexic and store more urine, patients must be routinely catheterized if the reflexive sphincter tone cannot be overcome by manual maneuvers. There is increased anal sphincter tone with hyperreflexia, and defecation requires anal dilation, hard Valsalva straining, and frequent manual extraction. Lumbar transection with an intact L1 neurologic level is characterized by absent sensation below the L1 dermatomal sensory band. Paralysis or paresis is present in all the muscles of the lower extremity. There may be some slight hip flexion ability. The cremasteric reflex is diminished or absent. Achilles, hamstring, and patellar reflexes are exaggerated. 6.11.4.2 Intact L2 Neurologic Level (L2 Functional Level) An intact L2 neurologic level is associated with strong hip flexion and paretic leg adduction. The quadriceps are paretic, resulting in severe lower extremity disability even with partial innervation. The unopposed iliopsoas and adductor action results in a lower extremity deformation with a predominant flexion and adducted presentation. Sensation is absent below the L2 dermatome. The patellar and Achilles MSRs become hyperreflexive after resolution of spinal shock. Ambulation is possible for some motivated patients, although most patients find ambulation tedious with leg braces and prefer a wheelchair. 6.11.4.3 Intact L3 Neurologic Level (L3 Functional Level) The intact L3 neurologic level patient has increased quadriceps power as compared to an L2 level patient. However, knee stabilization requires a knee–ankle foot orthoses. The iliopsoas and the adductor muscles are fully functional. Paretic knee extension is possible and the hip may become flexed, adducted, and externally rotated. Sensation is intact including and above the L3 dermatome. The bladder is hyperreflexive. 6.11.4.4 Intact L4 Neurologic Level (L4 Functional Level) In the intact L4 level paraplegic, strong quadriceps muscle function allows stabilization of the knee. Foot–ankle dorsiflexion and inversion are preserved. Sensation along the
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medial aspect of the lower leg and foot is preserved. The patellar reflex is normal. As spinal shock dissipates the Achilles MSRs become hyperresponsive. The patient with an intact L4 level retains significant functional muscle action of the quadratus musculature, lower erector spinae, quadriceps, and hip flexors. The major stabilizers of the hips remain absent and the ankles are unstable. Long leg bracing is not necessary because of the stabilization of the knee. Frail ankles typically need to be supported by an ankle-stabilizing orthotic, (ankle–foot orthoses, A.F.O.). These patients occasionally require bilateral canes or crutches due to destabilization of the hip from the lack of hip extension. Canes with support above the wrists will provide greater assistance.
6.11.5 SACRAL TRANSECTION INJURIES
6.11.4.5 Intact L5 Neurologic Level (L5 Functional Level) The neurologically intact L5 level leaves only the lateral side and plantar surfaces of the foot and sometimes the back of the leg void of sensation in the lower extremities. The Achilles tendon reflex becomes hyperreflexive after spinal shock resolves. The gluteus medius muscle receives partial innervation but the paretic gluteus maximus muscle results in hip flexion deformity. The neurologically intact medial hamstring muscle allows paretic knee flexion but the lateral hamstrings remain paralyzed. A dorsiflexion deformity of the foot may occur, characterized by dorsiflexion and inversion of the foot with unopposed plantar flexion and eversion. Incontinence is common because of poor sphincter tone. Manual extraction of feces is necessary if the patient is unable to evacuate by straining. In male patients, erection is not possible without a prosthetic implant.
Bowel and bladder incontinence is the major functional concern of the S2-level patient. Sexual function in upper sacral levels is impaired with impotence common in complete cord lesions at this level. The extent of bulbocavernosus and superficial anal reflex loss is dependent upon the degree of compromise below S2. Complete anesthesia or diminished sensation in the anal–scrotal–perineal regions is typical. The individual will be unable to contract the bladder (autonomous bladder) with a rise in urinary retention and elevated intravesical pressure which results in overflow incontinence. Intermittent catheterization may be required to reduce the risk of lower urinary tract infection if the patient is unable to successfully void using manual assistance. Any maneuvers that increase intraabdominal pressure may contribute to urinary and fecal incontinence requiring the use of incontinence pads or underwear. Ambulation and lower extremity muscle stretch reflexes are preserved (Figure 6.13).
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6.11.5.1 Intact S1 Neurologic Level (S1 Functional Level) In the intact S1 level, there is loss of bowel and bladder function. Poor sphincter control is common, and episodes of incontinence may occur. The perianal region is anesthetic and is the only analgesic region of the lower body. The Achilles reflex will be normal or depressed based upon small S2 representation. The gluteus maximus will display mild paresis, as do the soleus and gastrocnemius muscles. Toe clawing may occur due to intrinsic foot muscle paresis. These patients are fully ambulatory, and only a few patients need ankle bracing or a cane. 6.11.5.2 Intact S2 Neurologic Level and Below
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FIGURE 6.13 Summary diagram of spinal cord injury functional classification, vertebral level, cord level function, and functional capacity. (Copyright J.M. True, D.C.)
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REFERENCES 1. Herrick, M. and Mills, P., Infarction of the spinal cord: two cases of selective gray matter involvement secondary to asymptomatic aortic disease, Arch. Neurol., 24(3):228–241, 1971. 2. Hogan, E. and Romanul, F., Spinal cord infarction occurring during insertion of aortic graft, Neurology, 16(1):67–74, 1966. 3. Quencer, R.M., Bunge, R.P., Egnor, M. et al., Acute traumatic central cord syndrome: MRI-pathological correlations, Neuroradiology, 34(2):85–94, 1992. 4. Schneider, R.D., A syndrome in acute cervical injuries for which early operation is indicated, J. Neurosurg., 8:360–367, 1951. 5. Dimitru, D., Central nervous system disorders, in Dimitru, D., Ed., Electrodiagnostic Medicine, St. Louis, MO: Mosby, 1995: 481–482. 6. Chetwynd, J., Botting, C., and Hogan, D., Post-polio syndrome in New Zealand: a survey of 700 polio survivors, N.Z. Med. J., 106:406–408, 1993. 7. Dalakas, M.C. and Hallet, M., The post-polio syndrome, in Flum, F., Ed., Advances in Contemporary Neurology, Philadelphia, PA: F.A. Davis, 1988: 51–94. 8. Mumenthaler, M., Degenerative and heredodegenerative diseases principally involving the spinal cord, in Neurology, Stuttgart: Georg Thieme Verlag, 1983: 254–261.
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9. Pesce, F., Castellano, V., Finazzi Argo, E., Giannantoni, A., Tamburro, F., and Vespasiani, G.. Voiding dysfunction in patients with spinal cord lesions at the thoracolumbar vertebral junction, Spinal Cord, 35(1):37–39, 1997. 10. Braakman, R. and Penning, L., Injuries of the cervical spine, in Vinknpg, A. and Bruyng, W., Eds., Handbook of Clinical Neurology, New York: Elsevier, 1976: 25, 227–380. 11. Adams, R.D. and Victor, M., Pain in the back, neck and extremities, in Adams, R.D. and Victor, M., Eds., Principles of Neurology, New York: McGraw–Hill, 1985: 149–172. 12. McCray, D.L., The significance of abnormalities of the cervical spine, Am. J. Radiol., 84:3–25, 1960. 13. Greenberg, A.D., Atlanto-axial dislocations, Brain, 91:655–684, 1968. 14. Wolfe, B.S., Kilnony, M., and Malice, L., The sagittal diameter of the bony cervical spinal canal and significant cervical spondylosis, J. Mt. Sinai Hosp., 23:283–292, 1965. 15. DeMayer, W., Anatomy and neurology of the spinal cord, in Joynt, R.J., Ed., Clinical Neurology, Vol. 3, Philadelphia, PA: Lippincott, 1991: 16.
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Section 2 Radiculopathy
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Pathomechanisms of Radiculopathy
Radiculopathy is a peripheral neurologic syndrome resulting from mechanical injury and chemical irritation of the spinal nerve roots. Mechanical injury to the nerve root occurs with compression, traction, or frictional forces. Chemical irritation occurs as a response to nerve root ischemia, vascular stasis, or nerve root exposure to inflammatory components released during tissue injury. The classic signs associated with radiculopathy include neck or back pain with spasm, mild to moderate peripheral numbness, shooting pain, or extremity weakness in the distribution of a nerve root. Radiculopathy is often seen in the post-trauma patient with intervertebral disk herniation. Direct compression of the nerve root is not necessary to produce radiculopathic symptoms. A radicular pattern of pain or deficit will frequently occur with any condition that produces inflammation in the nerve root area. Osteophytic projections, degenerative disk disease, and lateral recess stenosis are common etiologies of radiculopathy in the degenerative spine. Localization of the neurologic deficit requires an understanding of the segmental innervation patterns in the body and extremities. There is considerable overlap of innervation from contiguous spinal levels to the skin, muscles, and skeleton, so that deficit localization is sometimes difficult. Occasionally, multiple nerve roots are involved, further complicating the localization process. Confirmation of subtle or multilevel radiculopathy is based on the anatomic and functional correlatives between diagnostic imaging and examination findings. Common correlative procedures include positive orthopedic tension or compression signs, neurologic indicators (reflex changes, motor fatigue, sensory deficits, or pain patterns), electrodiagnostic findings, and diagnostic imaging findings, including magnetic resonance (MR), computed tomography (CT), and plain films. This chapter covers the relevant anatomy of the nerve root, the pathological processes, and the most common differential conditions seen with radiculopathy.
7.1 SPINAL NERVE ROOT ANATOMY AND REGIONAL CHARACTERISTICS Spinal nerve roots represent the anatomic and functional link between the peripheral and central nervous systems. Thirty-one pairs of nerve roots exit the spinal column. The first pair of cervical nerve roots exits the spine between the atlas and occiput, and the last sacral and coccygeal pairs of nerve roots pass through the sacral hiatus. The
remaining 28 pairs of nerve roots traverse the intervertebral foramen (IVF) formed by the pedicle arches of the superior and inferior contiguous vertebrae, the zygapophyseal structures to the posterior, and the intervertebral disk to the anterior. Early in embryonic development, the spinal cord and spinal column are of similar lengths. As development proceeds, however, the longitudinal growth of the vertebral column exceeds that of the spinal cord, and consequently the spinal cord usually terminates at the level of T12–L1. This tapered termination of the cord is referred to as the conus medullaris. The cervical nerve roots descend the equivalent of one neuromere (segmental cord level) before horizontally traversing their respective neural foramina. Thus, the C5–C6 disk will compress the C6 nerve root. This arrangement of nerve roots exiting above the respective numbered vertebrae changes at the thoracic level as a result of the anatomic configuration of the eight cervical nerve roots and seven cervical vertebrae (Figure 7.1). The thoracic and lumbar spinal roots exit below their respective vertebrae. Accordingly, the L4–L5 lateral disk will compress the L4 nerve root. Because the spinal cord ends at the T12–L1 level, the lumbar and sacral nerve roots must travel a longer vertical path before exiting their respective neural foramina. The descending nerve roots travel a long course within the spinal canal and are therefore susceptible to central stenotic syndromes. The length of the nerve roots from the spinal cord to the foramina in the human lumbosacral spine varies from about 60 mm at the L1 level to about 170 mm at the S1 level.1 Nerve cell bodies of the motor axons exist within the spinal cord gray matter of the anterior horn. These populations of motor neuron cell bodies in the anterior gray matter of the cord are classified as alpha and gamma groups. Motor rootlets converge from clusters of motoneuron axons and exit the ventrolateral surface of the spinal cord. Ventral rootlets and their projections comprise primarily efferent motor axons and a small percentage of afferent axons. These rootlets join to form the ventral root and travel in an anterolateral direction to converge with the dorsal root within the lateral recess (Figure 7.2). Sensory input from peripheral and axial receptors enters the dorsal aspect of the cord through a configuration of nerve fibers called the dorsal rootlets. The cell bodies of sensory axons are not found within the gray matter of the dorsal horn of the spinal cord; rather, they are located within the dorsal root ganglia (DRG) distal to the spinal cord within the IVF.2 161
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Vertebral Level
Root Level C1
C1
C2 C3
C2 Cervical Spine
C3
C4
C4 C5
C5
Cervical enlargement
C6
C6
C7
C7 T1
C8
T2 T1
T3 T2
T4
The spinal cord has 31 pairs of spinal nerves segmentally innervating the body. The first cervical nerve exits the spinal canal above the first cervical vertebra. There are eight cervical nerves with seven cervical vertebra. The first thoracic nerve exits below the first thoracic segment. The thoracic and lumbar spine have the same corresponding number of spinal nerves as number of vertebrae.
T3 T5 Thoracic Spine
T4 T5
T6
T6 T7
T7
T8
T8
T9
T9
T10
T10 T11
T11
T12
Lumbar enlargement T12
L1 Cord termination L1-L2 level Lumbar Spine
L2
L1
Conus medularis
L3 L2 L4 L3 L5
L4
Sacral Spine
S1
L5
S2 S3 S4 S5 Coccygeal nerves
FIGURE 7.1 Anatomical relationships of the spine and nerve roots. (Copyright J.M. True, D.C.)
The anterior and posterior rootlets merge just distal to the DRG to form the spinal nerve. Dorsal root fibers comprise the largest volume of the spinal nerve (Figure 7.3). At the point where the convergence occurs,
the sensory and motor nerve components are no longer separate. The commingled rootlets interweave in a fascicular pattern to form the mixed spinal nerve. The spinal nerve is usually only a few millimeters long and then
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Recurrent meningeal n.
Spinal nerve
Dural sleeve
Ventral root CSF
Dorsal root Epidural venous plexus
FIGURE 7.2 Anatomy of the lateral recess in the cervical spine. (Copyright J.M. True, D.C.)
The cross-sectional appearance of the nerve roots just proximal to the formation of a mixed spinal nerve. Dorsal root (sensory portion)
Ventral root (motor portion)
Motor axons Sensory axons
TABLE 7.2 Structures Innervated by the Medial Branch of the Dorsal Rami • Zygapophyseal joints at level of exit and segment below • Deep back muscles that arise from the spinous process and lamina (level specific) • Spinal ligaments: ligamentum flavum, supraspinatus, and intertransverse ligament • Interspinous ligament (root level specific) • Periosteum of vertebral arch
Spinal nerve
FIGURE 7.3 Within the spinal nerve, sensory and motor fibers become interweaved in a fascicular pattern. (Copyright J.M. True, D.C.)
TABLE 7.1 Structures Innervated by the Lateral Branch of the Dorsal Rami • • • •
Erector spinae Skin overlying the spine Skin of the upper buttock and top of hip Splenis capitus and cervicis muscles (cervical region)
divides into the ventral and dorsal rami. In the cervical and lumbosacral spine, the ventral rami course anterior to the spine and intermingle to form the plexes and major nerves of the extremitites. In the thoracic spine, the ventral rami form the intercostal nerves. The dorsal rami are much smaller than the ventral rami. The dorsal rami branch into two or three branches that supply innervation to the muscles, ligaments, zygapophyseal joints, and skin overlying the spine (Tables 7.1 to 7.4; Figures 7.4 and 7.5).
TABLE 7.3 Structures Innervated by the Recurrent Meningeal Nerve • • • • • •
Posterior annular fibers Posterior longitudinal ligament Periosteum of vertebral bodies Epidural and basivertebral veins Epidural adipose tissue Anterior dura mater
7.1.1 INTERVERTEBRAL FORAMEN ANATOMY The primary contents of the IVF include the spinal nerve, the DRG, connective tissue, fat, the radicular artery, the radicular vein, and two to four recurrent meningeal nerves (Figure 7.6). This group of structures is referred to as the nerve root complex (Table 7.5).3 The nerve root typically occupies approximately one quarter to one third of the volume of the IVF. This can be readily observed on sagittal MR images. The nerve-to-IVF
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
1.
4. 6.
5.
7.
2.
8.
9.
10. 3. 1. Branches to anterior vertebral body and anterior longitudinal ligament
12. 11.
2. Sinuvertebral nerve
7. Ventral ramus 8. Dorsal ramus
3. Branch to ligamentum flavum and apophyseal joint
9. Lateral branch of dorsal ramus
4. Paraspinal sympathetic ganglion
10. Medial branch of dorsal ramus
5. Branch to posterior longitudinal ligament and vertebral body
11. Ascending articular branch
6. Gray and white rami communicans
12. Descending articular branch
FIGURE 7.4 Axial view of peripheral nerve anatomy of the spine. (Copyright J.M. True, D.C.)
TABLE 7.4 Structures Innervated by Nerves Associated with the Sympathetic Trunk and Gray Rami Communicans • • • •
Posterolateral intervertebral disk Anterior disk Anterior longitudinal ligament Periosteum of the anterior and lateral vertebral bodies
ratio will vary in the presence of pathologic osseous and soft-tissue foraminal stenosis. Nerve root distension or enlargement will contribute to an abnormal nerve-to-IVF ratio. The most common causes of an abnormal ratio include spondylosis and lateral disk herniation. In the lumbar spine, IVF area decreases in volume from levels L1 to L5, whereas the circumference of the traversing lumbar nerve roots increases.4 The L5 IVF is smaller in diameter than the lumbar levels above it, yet the diameter of the L5 nerve root is the largest of the lumbar roots. This change in nerve-to-IVF ratio predisposes the L5–S1 region to lateral stenotic syndromes and radiculopathy.5 The nerve-to-IVF ratio may also be reduced by the presence of transforaminal ligaments. Bogduk and Twomey5 refer to transforaminal ligaments as false ligaments that probably represent thickenings of the ventral
TABLE 7.5 Contents of the IVF • • • • •
Mixed spinal nerve root Dural sleeve Branches of radiculomedullary artery Two to four recurrent meningeal nerve branches Veins that communicate between the internal and external venous plexuses • Dorsal root ganglia (when laterally located)
portion of the intertransverse ligament. These narrow bands of collagen fibers are found attaching to the lateral IVF margins but are not always present. The nerve root may be compromised by ossification of this ligament or when the ligament reduces the available space for a normal nerve-to-IVF ratio. The extent to which compartmentalization of the IVF by a transforaminal ligament contributes to the development of radiculopathy is unknown. A small study of cervical IVF anatomy demonstrated that nerve root compression occurred at the entrance zone of the intervertebral foramina. In the anterior aspect of the IVF, compression of the nerve roots was caused by protruding discs and osteophytes of the uncovertebral region, whereas the superior articular process, the ligamentum flavum, and the periradicular fibrous tissues affected the nerve posteriorly.6
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9
Spinal nerve
11
3 4
8
1.- Branch to anterior longitudinal ligament 2.- Branches to lateral aspect of IVD 3.- Branches to IVD from gray rami 4.- Branches to IVD from ventral rami 5.- Medial branch of dorsal rami 6.- Lateral branch of dorsal rami 7.- Descending articular branch 8.- Ascending articular branch 9.- Sympathetic trunk 10.- White rami communicantes 11.- Gray rami communicantes 12.- Lumbar splanchnic nerves 13.- Ventral ramus 14.- Dorsal ramus 15.- Extradural root anastomoses (variable)
Anterior longitudinal ligament
10
9 1
15
5
10
2
7
11
12
14
8 6
Innervation to disc
2 13
5 14
4
2
1
6 5
12
13
12
6
FIGURE 7.5 Lateral view of peripheral nerve anatomy of the spine. (Copyright J.M. True, D.C.)
Spinal nerve Ligamentum flavum Posterior longitudinal ligament
Radicular artery Transforaminal ligament (variable) Superior facet
Sinuvertebral nerve
Intraforaminal venous plexus
Intervertebral disk
Intraforaminal adipose tissue FIGURE 7.6 Intervertebral foramen anatomy. (Copyright J.M. True, D.C.)
7.1.2 ANATOMY OF THE DURAL SLEEVE PERIPHERAL NERVE JUNCTION
AND
The nerve roots exit the thecal sac through dural openings surrounded by thick, membranous, funnel-shaped dural extensions referred to as nerve root sleeves or epiradicular
sheathes.7 The dural sleeve is an extension of the arachnoid mater and dura mater; it encloses the nerve root and cerebrospinal fluid (CSF), tapering to merge with the epineurium of the spinal nerve.5 The greatest portion of the spinal nerve root is intradural. The subarachnoid space and CSF extend along the length of the dural sleeve. The
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Arachnoid Dura mater Pia mater Dorsal root ganglion Rami communicans
Dorsal root Ventral root Subarachnoid space
Ventral ramus
Cauda equina
Dorsal ramus
Sinuvertebral nerve
FIGURE 7.7 Lumbar spinal nerve and surrounding anatomy. (Copyright J.M. True, D.C.)
dura and dural sleeve are both pain sensitive and chemosensitive.8 This may have clinical relevance for those patients who develop radicular-like symptoms after dural sleeve encroachment without actual nerve root compression (Figure 7.7). Like the peripheral nerves, the nerve root is encapsulated by endoneurium. The structures within the endoneurium include sensory and motor axons, collagen fibers, blood vessels, and a population of fibroblasts. In peripheral nerves, the perineurium acts as a diffusion barrier to macromolecules.9 The perineurium separates into two layers, and only part of it continues in the nerve root sheath. The nerve root lacks both the epineurium and the perineurium of the peripheral nerve.10 This creates an increased permeability within the endoneurial vasculature of nerve roots and the DRG to plasma proteins compared with the endoneurial vessels of peripheral nerves.11 Consequently, the nerve root is more vulnerable to inflammatory chemicals than the peripheral nerve. The monocollagen content of the nerve root is approximately one fifth that found within the peripheral nerves.12 Because the nerve root has a lower collagen content than the peripheral nerve, the nerve root is less capable of resisting deformation stressors. Also, the proximal spinal nerve root has extraneural supportive cells resembling those in the central nervous system. These supportive cells are not found in peripheral nerves. The proximal portions of the nerve root contain microglial cells, oligodendrocytes, and astrocytes. A few millimeters distal to the proximal nerve root is an area
referred to as the dome-shaped junction. Schwann cells distal to this junction are consistent with the microanatomy of the peripheral nervous system.
7.1.3 BLOOD SUPPLY
OF THE
SPINAL NERVE ROOT
The two primary nutrient pathways to the spinal nerve root occur through vascular supply and diffusion from the CSF.13,14 The blood supply to the vertebrae and the nerve roots arise from the segmental artery. The segmental artery gives off a dorsal branch, which further branches to supply the vertebral arch, with an additional branch supplying the posterior vertebral body, and a smaller longitudinally oriented arterial branch that supplies the nerve root. The artery that supplies the posterior intervertebral body perforates the posterior longitudinal ligament. The longitudinal radicular artery provides several collateral radicular arteries, which may lie anterior and posterior to the nerve root, branching to provide perforating interfascicular arteries. The interfascicular arteries are redundant, often coiled in appearance, allowing for nerve root translation and stretch, without compromising blood flow to the nerve root. The interfascicular arteries supply precapillary arterioles, which in turn supply intraneuronal capillaries. Nerve roots receive their blood supply from both ends. The nerve root has adequate vasculature to prevent a watershed zone in most cases of slow onset compression;15 however, a large intradural or extradural lesion may reduce the blood supply to the nerve root and inhibit CSF flow to the nerve root sleeve, thus reducing nutrient delivery.
7.1.4 THE DORSAL ROOT GANGLIA The subarachnoid space ends in the region of the DRG, so the shock-absorbing property of CSF around the spinal nerve is not substantial. The surrounding membranes of the DRG comprise the distal leptomeninges, which become the perineurium and epineurium of the peripheral nervous system. Dense connective tissue encapsulation of the DRG increases the risk of pathologic compartmentalization. Increased compartmental pressure within a CSF will contribute to peripheral dysesthesias and spinal radicular pain syndromes. Furthermore, the DRG is sensitive to mechanical pressure, and neural discharge will occur after minimal traction or external compression. The neurons of the DRG often become spontaneously active as a result of a direct lesion to their peripheral processes.16 The dorsal nerve root does not produce a sustained neural discharge after acute mechanical injury unless preexisting chronic nerve compromise is present, but when the DRG is involved, sustained neural discharge is easily elicited.17 The blood supply of the DRG differs from that of other portions of the nerve root in that the DRG has a rich microvascular supply.11 For this reason, the capillary bed
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167
Dura mater
Arachnoid
Pia mater
Dorsal root ganglion
Internal or subarticular
Sublaminar or intraforaminal
Lateral or extraforaminal
FIGURE 7.8 Variable positions of the dorsal root ganglion within the IVF. (Copyright J.M. True, D.C.)
TABLE 7.6 Factors Increasing Nerve Root Injury to Compression Forces
Sublaminar space
Intraspinal Extraforaminal
DRG
Intraforaminal space
FIGURE 7.9 The dorsal root ganglia is exposed to greater risk of compression when it is located in more medial positions within the intervertebral foramen and spinal canal. (Copyright J.M. True, D.C.)
may expose the DRG neurons to sensitizing chemicals from systemic or metabolic influences and exudative edema. Sensory fibers from the periphery enter the DRG in a dermatomal laminar pattern with organization of the fibers by the diameter size of the nerve fiber. In the peripheral nerve, fibers of different diameters are arranged in a random fascicular fashion. At the DRG, large fiber afferents begin to migrate posteromedially, and small unmyelinated fibers distribute themselves anterolaterally. The DRG is usually found within the IVF, but it can be located within the spinal canal, lateral to the neural foramina or in the medial subarticular aspect of the IVF (Figure 7.8).18
• • • • • • • •
Absence of perineurium in the subarachnoid space Conditions causing poor vascular perfusion to root and spinal nerve Narrowed intervertebral foramen from stenosis or osteophytosis Rapid-onset compression Sustained compression Perineural fibrosis Metabolic disease Presence of proinflammatory biochemicals
The DRG is vulnerable to physical insult within the medial third of the IVF particularly from posterolateral disk herniation and osteophytic spurs (Figure 7.9).
7.1.5 PATHOPHYSIOLOGY OF NERVE ROOT COMPRESSION A nerve fiber begins physically deforming when the external pressure exceeds the intraneuronal hydrostatic pressure. Electrophysiologic conduction block occurs at different degrees of external pressure, depending on the axon diameter. A complete compression block of the peripheral nerve occurs at the nerve trunk when approximately 150-mmHg pressure is applied.19 Spinal nerve roots have demonstrated conduction block at only 30 mmHg of pressure.19 When compression of the nerve root complex occurs, direct mechanical effects include conduction block, interruption of axonal flow, and vascular sequelae that include hypoxia and metabolic byproduct accumulation, which compromise impulse propagation (Table 7.6). Nerve root compression contributes to a loss of impulse propagation via impairment of axonal transport.20
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Anoxia and hypoxia may compromise fast and slow anterograde axonal transport as well as retrograde axonal transport.21,22 Axonal transport is required for the replenishment of neurotransmitter complexes. Axonal transport may be impaired in various pathologic conditions such as ischemia, compression, infection, immunologic cascades, and axonal degeneration and regeneration.23 Moderate to severe compression of a nerve root complex may induce direct pathomechanical effects on the nerve fibers, such as deformation of the nodes of Ranvier and invagination of the paranodal myelin sheaths.24 Neurologic function is highly dependent on the availability of oxygen. A classic study of the frog nerve by Grundfest22 showed that a nerve can function under high external loads as long as there is a high concentration of available oxygen. Even at normal extraneural pressure levels, if the intraneural oxygen level decreases, the nerve will become more susceptible to compressive loads. Conversely, even with an adequate systemic circulatory capacity to make oxygen available to the nerve root complex, focal vascular insufficiency within the complex will render it hypoxic. The combination of vascular insufficiency and diminished arterial oxygen saturation will result in greater susceptibility to intraneural hypoxia. Nerve root compression often results in impairment of intraneural blood flow.25 The endoneurial vessels of nerve roots, in particular the DRG, are more permeable to plasma proteins than the endoneurial vessels of peripheral nerves.5,11,26 Physical deformation of the nerve root increases the permeability of the microvasculature, leading to the formation of edema within the intraneuronal environment.27,28 Large-diameter nerve fibers within the nerve roots are more susceptible to compression and deformation than small-diameter fibers.29 Mild mechanical compromise of the nerve root complex can result in selective sensory and motor presentations limited to the large-diameter fibers. Focal demyelination of large myelinated fibers without axonopathy results in neural impulses firing in a dysynchronous volley. Olmarker et al.30 have shown that compression of the nerve root complex, even at low pressures (e.g., 5 to 10 mmHg), may induce short-term changes within the intraneural microcirculation. Initially, the intraneural venous blood flow is compromised. The intravenous pressures result in retrograde stasis within the intraneural capillary beds and a breakdown of the capillary junctions. This contributes to exudation and extravascular intraneural edema formation. Rapid spinal nerve root compression influences the degree of clinical deficit and recovery characteristics. Rapid-onset compression (between 0.05 and 0.10 sec) causes a more pronounced effect than slow-onset compression (over a 20-sec interval) with similar level pressures.31 Rapid-onset as well as sustained compressive
TABLE 7.7 Effects of Chronic Nerve Root Compression • • • • • • • •
Altered intraneural blood flow Increased intraneural permeability to macromolecules Impaired axonal transport Intraneural edema Fibroblast invasion Intraneural fibrosis and compartmentalization Impaired nutrient delivery Perineural fibrosis with recurrent microstretch injuries
insult results in pronounced intraneural edema, impaired vascular flow, conductive changes, and reduced capacity for nerve conduction recovery.13,31 This is an important consideration relative to intermittent and slow-onset compression syndromes compared with rapid-onset disk herniation and spine injuries after motor vehicle collisions. The magnitude of compression is also important in the development of symptoms. Changes in spinal nerve root conduction occur at pressures between 15 and 75 mmHg. Motor conduction velocity recovers more rapidly than sensory conduction when nerve root compression pressures reach 100 to 200 mmHg.32 Spinal nerve root compression can be present without overt symptoms.33 In such cases, however, there is invariably an absence of trauma, but the presence of a longstanding condition, such as osteophytosis or lateral recess stenosis, producing a slow-onset of compression (Table 7.7).
7.1.6 SITES
OF
NERVE ROOT VULNERABILITY
The spine contains many osteoligamentous spaces that accommodate and protect delicate neurovascular structures. These spaces include the central vertebral canal, the IVF, and the foramen transversarium. The morphologic relationships of these osteoligamentous spaces differ in various intravertebral and intervertebral locations (Table 7.8). The spatial relationship of the nervous tissue to osseous and nonosseous elements of the spinal canal and the IVF is an important consideration in the development of radicular compression.7 The dynamic properties of these spaces are strongly dependent on the anatomic characteristics and relationships of the tissues making up their margins. The dynamics of the intervertebral motion segment affect the relative instantaneous size and volume of the intrinsic osteoligamentous canals and foramina. The volume of the IVF increases slightly during flexion and decreases during extension. These changes are more pronounced in the cervical spine. Yoo and colleagues34 found that, in the neutral position and at extremes of flexion and extension in the cervical spine, 20º of axial rotation produced a decrease in the mean size of the foramen on the ipsilateral side and an increase on the contralateral side. Compared with the measurement at
Pathomechanisms of Radiculopathy
TABLE 7.8 Causes of Neurovascular Compression within the Intervertebral Foramen • • • • • • • • • • • • • •
Osteoligamentous hypertrophic stenosis Transforaminal ligament compartmentalization Combined stenosis (disk, facet, ligament, etc.) Intervertebral pathomechanics and dynamic stenosis Degenerative disk disease and rostrocaudal subluxation Venous dilation Intraforaminal and intraneural fibrosis Pedicogenic stenosis Vertebral expansion or collapse Isolated foraminal soft-tissue mass Intraspinal soft-tissue mass involving one or more foramina Paraspinal soft-tissue mass involving one or more foramina Intraforaminal foreign body or enlarged nerve root Intervertebral disk bulge or protrusion
neutral position, 30º of extension caused a 13.2% decrease in the cervical foraminal dimensions, and 30º of flexion caused a 10.6% increase.34 This IVF narrowing explains one of the mechanisms involved in reproducing radicular pain with Spurling’s clinical maneuver. This orthopedic test is performed by turning the patient’s head to the side of complaint and extending it backward with gradual downward pressure. A controlled downward blow to the vertex of the head can also be used to reproduce symptoms. During forward flexion in the lumbar spine, the spinal cord and nerve roots of the cauda equina move anteriorly. These same structures move posteriorly when the patient assumes a supine position and during lumbar extension. Lateral lumbar translation results in lateral deviation of these structures. The lumbar and sacral nerve roots are exposed to compressive insult at multiple locations prior to exiting the spine. These nerve roots are vulnerable as they descend through the central spinal canal (central zone) and traverse the lateral zone. The lateral zone is comprised of three primary divisions, which are the subarticular, foraminal, and extraforaminal divisions. Physical compression of a nerve root may occur in the central zone and within any one of the divisions of the lateral zone. The nerve root is more vulnerable to compression within the lateral zone than the central zone (central canal) secondary to less reserve space and due to the greater propensity for space-occupying pathology in the lateral zone. More common causes of nerve root compression in the lateral zone include paracentral or far lateral intervertebral disk pathology, subarticular stenosis, facet cyst, nerve root entrapment with lytic spondylolisthesis, capsular hypertrophy, and rostrocaudal subluxation associated with degenerative disk disease.
169
7.1.7 PATHOMECHANICS AFFECTING ROOT COMPLEX
THE
NERVE
Breig35 demonstrated that when the spine moves there is no significant axial displacement of the spinal nerve root relative to the canal. During extension, however, the nerve root increases in cross-sectional diameter, and consequently there is a slackening and widening of the nerve root sleeve. During forward flexion, the dural sleeves and nerve roots were found to straighten gradually. This adaptability of the nerve roots greatly reduces friction between the nerve roots and their adjacent sheaths during movement. Severe fibrotic adherence of the nerve roots and their perineural structures results in excessive traction at the nerve root attachment to the spinal cord. Some of the signs and symptoms of radiculopathy develop from irritation created by immobilization of the nerve root and dural sleeve. Because the dura mater is mechanosensitive, traction of the dura over a space-occupying lesion, such as a herniated disk or osteophyte, may result in pain originating from the dura.36 The nerve root near a disk herniation is sensitive to mechanical deformation, as observed in patients under epidural anesthesia during laminectomy and disk excision.37 For patients with paresthesia secondary to neuroforaminal compression, extension-induced narrowing may magnify symptoms. Concomitant adduction of the painful arm and contralateral lateral flexion may cause stretching of the nerve root within the narrowed foramen, thereby worsening symptoms. Conversely, shoulder abduction and cervical flexion may lessen symptoms. Nerve root tension signs are common in cervical and lumbosacral radiculopathy. Cervical motions that reduce foramen size also tend to elicit symptoms associated with neuropathology at the IVF.34 In lumbosacral radiculopathies, a positive straight leg raise test is highly correlative to nerve root compression. See Section 8.2 for an expanded discussion of nerve root irritability.
7.1.8 NERVE ROOT DOUBLE CRUSH The term double crush refers to compressive insult of a single nerve root in two distinct locations. The term double crush may also be used to describe compression of two adjacent nerve roots by a single source, although this should more correctly be referred to as polyradiculopathy describing the site of compressive etiology so as not to be confused with the pathophysiology associated with multifocal compromise along the same axon. Multifocal compression may render the nerve root more vulnerable to axonpathy secondary to greater impairment of axonal transport, retrograde axonal transport, and the general synthesis and trafficking of neuronal proteins. When a nerve root is compromised at two or more locations, it is possible that
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the resulting radiculopathy will be more refractory to treatment. If lumbosacral roots are compressed at multiple locations, a greater amount of tethering will occur, increasing the possibility of greater root injury following trauma. One of the most common causes of double crush insult to the nerve root occurs when the descending lumbar nerve root is compressed within the central canal (central zone) by the disk above the level of root exit, combined with compression from subarticular stenosis in the lateral zone of the IVF. The second example occurs when the nerve root is compressed both in the lateral zone by subarticular stenosis and by a far lateral (extraforaminal) disk protrusion or osteophytic projection. A third example of double crush occurs in the lower lumbar spine when two levels of disk herniation compress the same descending root. When considering moderate or severe lumbar stenosis, there are many possibilities for double crush of the cauda equina and exiting nerve roots. MR imaging and MR myelography are extremely helpful for the assessment of nerve root double crush, using appropriate scan techniques. Conventional myelography is not as sensitive as MRI for identifying nerve root double crush. For example, conventional myelography may reveal a subarticular nerve root cutoff (CSF block), and the CSF block thereby masks coexistent extraforaminal nerve root compression.
7.2 BIOCHEMICALLY INDUCED RADICULOPATHY Inflammatory substances arising from a degenerative or herniated nucleus pulposus may spread and contact the nerve root, inducing a chemical radiculitis. This inflammatory process promotes edema and membrane damage to axons in the nerve root.38-43 A study by Kayama and colleagues in dogs demonstrated significant loss of conduction velocity across the nerve root area 7 days after incision of the annulus without herniation.38 This incision caused leakage of nucleus pulposus material into the epidural space. Nerve conduction in the incision group was 13 ± 14 m/sec compared with 73 ± 5 m/sec in the control group. Similar reductions in nerve root conduction times were seen when preparations of nucleus pulposus cells were applied to the cauda equina of pigs.44 Another study in dogs demonstrated that nerve root injury occurring with exposure to nucleus pulposus material reverses in approximately 2 months.45 A loss of blood flow to the nerve root preceded and was related to the observed changes in motor nerve conduction velocity during the 2-month recovery.46 These experiments suggest that a biochemical or membrane-bound substance causes the radiculopathy without physical nerve root compression. In our experience, many patients present with signs and symptoms of radiculopathy in the absence of direct nerve root compression.
2. Distention of Mass Disk
1. Mass of HNP
3. Inflammatory interface
Nerve root
FIGURE 7.10 Three factors that may contribute to the production of leg pain (sciatica) with lumbar disk herniation are (1) the mass of the ruptured discal material, (2) intradiscal distention secondary to water–proteoglycan content within the mass, and (3) the inflammatory interface between the disk fragment and nerve root. (From McCulloch, J.A. Essentials of Spinal Microsurgery, Lippincott-Raven, Philadelphia, PA, 1998. With permission.)
Biochemically induced degradation of the nerve root is a plausible mechanism for the production of radiculopathic signs in acute cases. Some researchers report that involvement of inflammatory mediators in radiculopathy only explains a part of the pathophysiologic mechanism of acute radiculopathic symptoms, and these mediators are not found in chronic disk lesions (Figures 7.10 and 7.11).47 One substance thought to be responsible for the production of symptoms is the enzyme phospholipase A2, which has been shown to be a significant inflammatory substance found in markedly high levels in herniated disk material.38,42,48-50 Other biochemicals directly or indirectly associated with nerve root inflammation include phospholipase A2; prostaglandin E2; leukotrienes; nitric oxide; immunoglobulins; proinflammatory cytokines, such as interleukin (IL)-1a, IL-1b, and IL-6; tumor necrosis factor alpha (TNF-a) and autoimmune reaction (macrophages expressing IL-1b, intercellular adhesion molecules); and metallo-proteinases.47,51 Phospholipase A2 is the enzyme responsible for the rate-limiting step in the liberation of arachidonic acid from cell membranes at the site of inflammation. Arachidonic acid leads to the production of chemical mediators of inflammation and nociceptive activation, such as prostaglandins and leukotrienes. Variable concentrations of phospholipase A2 in the region of disk injury may account for the lack of correlation between the extent of intervertebral disk herniation or degeneration seen on MR imaging and the level of pain reported by the patient. The most probable mechanism responsible for this connection between phospholipase A2 and radiculitis is the direct enzymatic effects of phospholipase A2 on the phospholipids of the neural components, effects on the microcirculation, and chemical sensitization of nociceptors within the annulus or surrounding tissues by secondary phospholipase A2-mediated inflammatory byproducts.48,50 The algesic
Pathomechanisms of Radiculopathy
Nerve root
171
Dorsal root ganglion Disk herniation Apophyseal trauma
Pathomechanical dysfunction
7.3 SPINAL DEGENERATION AND RADICULOPATHY
Venous congestion Inflammatogenic metabolites
Inflammatory response
Fibrous infiltration disrupted axoplasmic flow
Trophic nerve and cell changes
Electrophysiological changes
by the immune system, resulting in an autoimmune inflammatory response.48,52 Antigen–antibody complexes have been found in the pericellular capsule of herniated disk material but not in healthy disks or residual disk material.53 One study has indicated that the predominant inflammatory cells surrounding herniated nucleus pulposus material in both acute and chronic radiculopathies are macrophages.54 Macrophages are the only inflammatory cells that have clinical relevance in disk tissue inflammation.
Metabolic changes
Sympathetic influence
Synaptic sensitization of dorsal horn
Mechanosensitization of peripheral nerve fibers
Radicular Pain! FIGURE 7.11 Proposed mechanism of radicular pain pathogenesis. (Modified from Hasue, M., Pain in the nerve root, Spine, 18(14), 1056, 1993. With permission.)
and sensitizing potential of phospholipase A2 on A-delta and C fibers directly activates the nociceptors to fire or lowers the threshold of these nociceptors to firing via mechanical stimulation. As previously discussed, this sensitization of the nerve root and DRG is in part responsible for the production of radicular pain. In the absence of degeneration or injury, the nucleus pulposus is contained by the annulus and thus is sheltered from the immune system. Consequently, with disk herniation or annular tear, the nuclear material is not recognized
Spondylosis and posterolateral exostosis are common causes of IVF stenosis, lateral recess stenosis, or central spinal canal stenosis. Routine radiographs or CT scans often demonstrate disk-spur complexes or isolated osteophytosis. Osteophytic changes are more prevalent within particular segmental levels of the spine. The levels of the cervical spine most frequently affected are C5–C6 and C6–C7. In the thoracic spine, the T8 level is most vulnerable. In the lumbar spine, the L4–L5 and L5–S1 levels are the regions most often involved.55 The larger the osteophytic bar or projection, the greater the potential for a mass effect on neural structures and their blood supply. The osteoarthritic spine is particularly vulnerable to trauma.55 The four general classifications of compression syndromes associated with spondylosis are lateral or radicular syndrome, medial or spinal syndrome, combined medial– lateral syndrome or myeloradiculopathy, and vascular syndromes.56 Lateral recess stenosis has four subcategories: (1) lateral stenosis from hypertrophic enlargement of the superior facet, (2) subarticular stenosis, (3) dynamic stenosis that occurs from increased intersegmental motion or clinical instability, and (4) fixed stenosis that occurs when degeneration and stenosis are severe.57 Osteophytosis is more prevalent where Sharpey’s fibers attach to the vertebral body.58 This transitional region of bone and periosteum is usually several millimeters from the discovertebral junction. In this region, osteophytes generally begin as clawlike, horizontal, calcific projections off the vertebral body. As the spur develops, it begins to project in a vertical or inferior direction, forming an osseous bar as both vertebral margins fuse. Progressive osteophytosis results in an expansile mass effect on neighboring neurovascular tissues. Posterior or posterolateral projections are often visualized on MR images as tenting of the posterior longitudinal ligament (PLL). Ligamentous tenting may be a significant source of chronic pain because of the irritation to the free nerve endings in the PLL.59 Spondylotic myelopathy and radiculopathy can occur when osteophytic projections progress to the point of compressing both vascular and neural elements within the IVF, the lateral recess, and the central spinal canal (Figure 7.12).
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
A
B
FIGURE 7.12 (A) Midline sagittal fast spin-echo T2-weighted image and (B) axial fast spin echo T2-weighted image through L4– L5. There is pronounced posterior element hypertrophy at the L3–L4 and L4–L5 levels. Posterior element hypertrophy, ligamentum flavum hypertrophy, and disk protrusion contribute to a near complete obliteration of the spinal canal at L4–L5.
7.3.1 ROSTROCAUDAL SUBLUXATION The intervertebral disk probably reflects aging more than any other musculoskeletal tissue. Degenerative changes within the fibrocartilaginous matrix of the intervertebral disk lead to concentric and radial tears of the annulus along with loss of disk hydration. A loss of intervertebral disk volume and associated reduction of vertical height of the disk leads to IVF narrowing and increased physical loading upon the facet joints. The loss of intervertebral disk height and approximation of adjacent vertebral bodies represents one of the most common structural abnormalities of the spine. This is referred to as rostrocaudal subluxation (RCS). Reduced dimensions of the intervertebral foramen will in more severe cases result in physical and vascular compromise of the nerve root complex. This loss of intervertebral disk height is often associated with a degenerative cycle leading to facet arthropathy, ligamentous hypertrophy, spinal motion segment pathomechanics, spondylosis, and subsequent central and/or lateral stenosis. RCS most often occurs in the lower lumbar spine, predominantly at the L4-5 and L5-S1 levels and in the cervical spine at C5-6 and C6-7. Rostrocaudal subluxation may be asymptomatic in some individuals and become symptomatic following trivial trauma. RCS resulting in IVF narrowing predisposes the nerve root complex to greater injury in vehicular trauma. The combination of degenerative disk changes and loss of vertical disk height often results in some degree of laxity of the ligamentum flavum. This laxity produces a buckling (sometimes referred to as hypertrophy) of the ligamentum flavum into the foramen or the posterolateral aspect of the spinal canal. Osteophytic projections and
ligamentum flavum hypertrophy contribute to a complex acquired stenosis and higher risk for radicular compromise. See more on ligamentum flavum hypertrophy in Section 4.1.2. RSC is easily identified on lateral view X-rays by the approximation of adjacent vertebral bodies caused by a loss of intervertebral disk height. RSC is identified on MRI by loss of intervertebral disk volume and height, varying degrees of intervertebral disk bulging, loss of IVF dimension, and decreased intradiscal signal on T2-weighted imaging. There is diminished delineation between the inner annular–nuclear complex and the annular outer fibers on T-2 weighted acquisitions due to dehydration and desiccation of the disk.
7.4 FIBROSIS AND RADICULOPATHY During spinal movement, the nerve roots slide within their dural sleeves. Compressive lesions that deform the nerve root, its adjacent sleeve, or the surrounding vasculature induce edema formation, which in turn may lead to fibroblast invasion and fibrosis in the nerve root and IVF. Fibrotic adhesions between the nerve root and dural sleeve inhibit this sliding motion and compromise the elasticity of the nerve root and dural sleeve. In this situation, the nerve root and dural sleeve are subjected to abnormal tensions that induce the cyclic development of inflammation. Inflamed nerve roots are in turn sensitized to compression or traction 60 and cause pain syndromes (Figure 7.13).17 When fibrotic tissue compartmentalizes the peridural space in the region of the descending or exiting nerve root, the nerve root is immobilized and susceptible to compression from acute or recurrent disk
Pathomechanisms of Radiculopathy
Nerve
Mass effect
Blockage or Reduction
Ischemia Nerve endings activated or sensitized
Bradykinin Potassium Histamine
Inflammation Entrapment Adhesion
Fibroproliferation FIGURE 7.13 Common pathomechanisms of radicular pain. (Copyright J.M. True, D.C.)
pathology. If a nerve root cannot move out of the path of a mass effect, it is rendered more susceptible to compression and is also at risk for traction-type injuries because of loss of elasticity. The elastic limit of a normal nerve root is approximately 15% of its resting length, and any stress beyond 21% of its resting length may bring about complete failure.61 Mild compressive lesions may only slightly decrease the extent of movement between the nerve root sleeve and nerve root. A chronic compressive lesion may induce fibrotic adherence and mechanical approximation that severely impairs nerve root movement.62,63 This results in nerve root traction microinjuries against the pedicles, vertebral arches, and/or posterior vertebral body projections. Fibrosis of the nerve root sleeve results in cumulative microinjury and a vicious cycle of scar-tissue formation. Painless extremity movement is dependent on normal biomechanics within the IVF and nerve root elasticity. A loss of neural elasticity can lead to traction-induced nociception and microavulsion of scar tissue, stimulating an inflammatory cascade.
7.4.1 ARACHNOIDITIS
AND
RADICULOPATHY
The CSF flow through the subarachnoid space is critical to the health of the nerve root. Blood vessels physically course through the subarachnoid space to the nerve root complex, and CSF extends into the subarachnoid space within the dural sleeve. Any inflammatory or physical
173
obstruction of vascular or CSF circulation within the subarachnoid space will compromise the nerve root. Inflammatory changes can occur at the pia-arachnoid complex in the absence of an epidural mass effect. The inflammatory cascade may be initiated or perpetuated by septic or aseptic stimuli. This may involve exposure to an infectious, biochemically or iatrogenic chemically induced antigenic response. (See Section 7.2, Biochemically Induced Radiculopathy.) Arachnoiditis refers to an inflammatory process afflicting the arachnoid lining of the spinal cord, thecal sac, or nerve roots. It may be associated with discomfort, severe incapacitating pain, and neurological disability. The arachnoid membrane is an avascular membrane; it is highly fenestrated and lies along the inner aspect of the dura mater. There are varying degrees of arachnoiditis that will contribute to radiculopathy. These are arachnoiditis, adhesive arachnoiditis and calcific arachnoiditis. During the early stage of radiculitis there is inflammation of the pia-arachnoid membranes associated with hyperemia and nerve root swelling. In response, there is fibrinous exudation and deposition of collagenous fibrils or strands between the nerve root and the pia-arachnoid membranes. This may lead to minor subarachnoidal adhesions, which may be resorbed or physically broken loose with normal activities. With progressive arachnoiditis, there will be profound fibroproliferation with thicker fibrotic bridging adhering the nerve roots to the pia-arachnoid complex. This process represents the progression to adhesive arachnoiditis. This cascade of events can result in progressive severe scarring, axonopathy, nerve root atrophy, and adhesive attachment of the nerve root and to the surrounding leptomeninges. Dense scar tissue can result in an intrathecal mass effect with constriction and subsequent compression of the nerve root as well as obstruction of CSF flow. This associated CSF block will not likely be evident upon routine MR imaging but may be revealed with MR myelography or selective root myelography. Severe chronic progression of arachnoiditis may lead to calcification of dense scar tissue with further progression of radiculopathy.
7.5 ACQUIRED LATERAL RECESS STENOSIS AND VASCULAR STASIS A reduction in the central spinal canal or IVF diameter often produces vascular stasis. A study by Cooper and colleagues63 demonstrated clear evidence of vascular congestion and fibrosis within the microvasculature, intraneural and perineural tissues in patients undergoing decompressive disk surgery; there was an absence of similar findings in control cadaver spines. Degenerative disk disease with osteophytic proliferation and disk herniation can lead to compression of the dural veins and dilation of
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Anterior and posterior recurrent meningeal nerve Radiculomedullary artery and vein
Posterior (P)
Anterior (A)
A A
Connective tissue and fat
Spinal nerve
Normal IVF
A
P
Zygapophyseal arthrosis
A
P
P
P
Moderate/severe
Posterolateral disk herniation
Uncinate arthrosis
A
P
A
Retrolisthesis
Loss of disk height
A
P
Severe
P
A
P
Extreme
Progressive spondylitic obliteration of the IVF FIGURE 7.14 Pathological IVF variations of the cervical spine. (Copyright J.M. True, D.C.)
adjacent noncompressed veins. The risk of intra-arachnoid and intradural exudation substantially increases in this situation. Chronic intraneural ischemia will result in intraneural fibrosis.64 Pain, paresthesia, sensory deficits, and motor weakness are clinical manifestations of neural ischemia with or without mechanical deformation of the nerve root. The veins in the IVF are extremely vulnerable to mechanical compression. The IVF is dynamic and constantly changing in dimension secondary to coupled movement of the vertebral motion segment. During foraminal dynamics, the mean cervical foraminal measurement at 30º of flexion increases approximately 24.7% compared with the measurement at 30º of extension.34 The veins are positionally compromised during extremes of extension but typically not long enough to induce a progressive ischemic or inflammatory cascade. Many pathologic considerations contribute to IVF stenosis and lateral recess stenosis, as illustrated in Figure 7.14. The normal IVF is approximately two thirds larger than the nerve root complex. An adequate nerve-
to-IVF ratio allows for normal movement without nerve root compromise. Certain congenital configurations of the IVF can predispose an individual to an acquired stenosis and radicular compromise. A study of 160 cadaver lumbar foramina by Hoyland and colleagues62 demonstrated that, concurrent with IVF compromise, there is often distortion of the large venous plexus within the foramen. In eight of the cadaver specimens with distortion of the venous plexus, there was an absence of direct nerve compression. The investigators further described the pathologic changes within and around the nerve root complex of the IVF as including intraneural fibrosis, edema of the nerve roots, and focal demyelination (Figure 7.15). They reported that the most severe neural changes secondary to compression resulted from dilation of foraminal veins. Basement membrane thickening was also reported, suggesting endothelial cell compromise secondary to vascular changes within the thickened fibrous sheath. It therefore appears that venous obstruction is an important pathogenic mechanism in the development of perineural and intraneural fibrosis.63
Pathomechanisms of Radiculopathy
175
FIGURE 7.15 A lateral disk protrusion may compress the venous plexus within the lower portion of the neural foramen, producing venous stasis, dilatation, and local tissue ischemia. A chronic process may lead to perineural fibrosis and nerve fiber atrophy. (Copyright J.M. True, D.C.)
7.6 FAILED BACK SURGERY SYNDROME
Conservative
Surgical
Spine pain
Extremity pain
Palsy
Increasing severity FIGURE 7.16 Generalized linear relationship between radicular signs and symptoms and treatment options. (From Tsuji, H., Comprehensive Atlas of Lumbar Spine Surgery, Saunders, Philadelphia, PA, 1991. With permission.)
Other researchers also have reported the effects of venous stasis after IVF stenosis. Watanabe and Parke65 concluded that the venous side of the radiculomedullary circulation is the most vulnerable component to compression. Yoshizawa and colleagues66 recently concluded from their experimental studies that there is a vascular “watershed area” near the base of the dural sleeve. Sunderland67 concluded that venous congestion and retrograde stasis in intraneural capillaries represent an important pathophysiologic mechanism in nerve compression syndromes. Moderate to severe venous congestion could theoretically reduce the space available for the nerve root in the IVF.68
There is a general linear relationship between the need for surgery and the severity of symptoms (Figure 7.16). However, postsurgical complications and undesirable outcomes are at greater risk of occurring with poor patient selection. Postsurgical stenosis and fibrosis in the central spinal canal and IVF are of great concern. Some medications and contrast agents are inflammogenic. Proinflammatory chemicals include therapeutic and diagnostic pharmaceutical agents and some contrast media, especially legacy myelographic agents. Additionally, epidural fibrosis will occur secondary to infection, ischemia, bleeding, thrombosis, and immunologic reaction to surgical sponges and glove powder. Severe iatrogenic fibrosis can result in acquired stenosis and contribute to progressive pathomechanics between central and peripheral neural elements. Pretherapeutic considerations should include evaluation of systemic risk for abnormal fibrinolytic activity and habitual patterns, such as smoking, that may increase the risk for epidural fibrosis and altered collagen cross-linking. Common factors contributing to failed back surgery syndrome (FBSS) include recurrent disk herniation (12–16%), lateral (58%) or central (7–14%) spinal stenosis, arachnoiditis (6–16%), and epidural fibrosis (6–8%).69 FBSS has also been reported to result from poor surgical selection or technique and peridural fibrosis.70 A nerve root entrapped by fibrosis is rendered more susceptible to recurrent or residual disk herniation. Surgical disruption of granulation tissue may lead to increased postsurgical fibrosis. The clinical signs and symptoms secondary to intervertebral disk herniation, extrusion, or sequestration may respond to surgical decompression, but the prognosis
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
for postsurgical recovery from fibrotic debridement is poor. A large percentage of failed back surgery patients with continued pain may also be the result of chemically mediated pain mechanisms. According to Saal,42 “Management of chemically mediated pain by surgical removal of the disk is analogous to excision of a painful sensory nerve. Not only is this ineffective, but it frequently intensifies the pain, by creating a neuropathic pain pattern.”
Stenosis of Iateral recess and IVF
Fibrotic adhesion of nerve root preventing normal nerve root glide DRG
7.7 TRAUMA AND RADICULOPATHY IVF
Spinal trauma may lead to nerve root injury secondary to avulsion, contusion, stretch, and/or compressive injury. Nerve root contusion and stretch injuries represent transient physical pathomechanisms. Compressive insult may be transient or may persist after the original trauma. Signs of root compression may occur as a result of neural injury anywhere from the rootlets on the spinal cord to the spinal nerve in the distal portion of the IVF. Common causes of persistent post-traumatic nerve root compression include hematoma, disk herniation, displaced vertebral fracture, or vertebral dislocation. Any condition that distorts and narrows the dimensions of the IVF may result in nerve root compromise. Unilateral facet dislocation, vertebral body fracture, and ligamentous disruption with a shift of bony elements may produce transient, partial, or complete occlusion of the IVF or cause a traction injury of the nerve root. Preexisting spondylosis with spurring or spinal stenosis due to other causes may infringe on the reserve space surrounding the neural elements, increasing the risk for concussive and stretch injury of the nerve root (Figure 7.17). Perineural fibrosis and postsurgical scarring may adhere the nerve root sleeve to the surrounding tissues, predisposing the nerve root to tensile strain injury from reduced gliding capacity of the nerve during vertebral motion. Patients with chronic radiculopathy may have significant fibroproliferation within the lateral recess and IVF which lowers the threshold for subsequent nerve root injury and aggravated symptoms. Individuals with ankylosing spondylitis are prone to fractures.71,72 This may be due to greater focal stress placed upon select bony regions due to the general spinal rigidity created by the ankylosis. The greater risk for fracture in ankylosing spondylitis is associated with an increased risk for associated nerve root injury. Diminished bone strength increases the risk for acquiring reduced IVF dimensions secondary to fracture. The World Health Organization (WHO) has classified bone density characteristics into the following four primary categories: (1) normal, (2) osteopenic, (3) osteoporotic without fractures, and (4) severely osteoporotic.73 Low bone mineral density and reduced trabecular density are associated with increased risk for acquiring a fracture due to loss of subcortical bony support.74 During the aging process, trabecular bone loss
Osteophytic spur
Pedicle Nerve root
Osteophytic projections into the nerve root
Traction of neural elements
Spondylolisthesis
FIGURE 7.17 Degenerative factors that increase the risk for nerve root injury and tethering. (Copyright J.M. True, D.C.)
is similar between men and women although women commonly acquire greater loss of trabecular connectivity.75 Whiplash injury is a common pseudomechanistic term that describes a constellation of symptoms following injury sustained in a motor vehicle accident (MVA). Considerable debate can be found in the scientific literature regarding the very definition of whiplash, including its mechanism of onset, prevalence, extent of related injuries, and how to name this complex trauma disorder.76-78 Injuries to the body result from rapid acceleration or deceleration forces transmitted through the head, neck, and body within a few hundred milliseconds after vehicle impact.80 Rear-end collisions are responsible for approximately 85% of reported whiplash injuries.76 MVAs are one of the most frequent causes of radiculopathy. Although more than one third of patients acutely complain of paresthesias following an MVA, neurogenic thoracic outlet syndrome is more commonly the cause than cervical radiculopathy.81 Symptoms associated with whiplash can be classified in a loose time frame of acute and late whiplash syndromes. Patients with cervical spondylosis are more likely to present with late-onset abnormal clinical findings after whiplash injury.82 Osteophytosis and bony hypertrophic changes which narrow the IVF may contribute to contusion and/or avulsive injury to the nerve root. After vertebral trauma, plain radiographic studies should be performed in
Pathomechanisms of Radiculopathy
any patient with reduced range of motion (ROM) or lateralizing pain symptoms. Oblique projections and flexion– extension plain films are essential for evaluating the posttraumatic patient with mild radicular symptoms. The diagnostic yield, however, may be low in cases with transient IVF occlusion or nerve root traction injuries. Flexion–extension X-rays should not be performed on acutely injured patients if fracture or biomechanical instability is suspected. Spiral (helical) CT or magnetic resonance imaging (MRI) is suggested for the patient with moderate to severe acute injury, with peripheral neurological symptoms. CT scanning is indicated in more severe spine trauma because of its greater capacity to detect occult fractures. However, injury to the spinal cord, nerve root, or smaller nerves intrinsic to the spinal column may occur in the absence of bony changes, thus may be underestimated on radiographic studies. The magnitude of soft-tissue trauma is therefore best assessed with MRI, which is superior for the evaluation of spinal cord and nerve root trauma.83 MRI is also superior to conventional plain-film radiography for the acute assessment of prevertebral or paravertebral hemorrhage or edema, spinal cord edema, ligamentous injury, acute disk pathology, and spinal cord compression.84
7.7.1 NERVE ROOT AVULSION Significant neural element injury can occur with spinal trauma with or without associated bony injury. Traction insult applied to the shoulder and/or neck may result in cervical nerve root avulsion and avulsion of elements of the brachial plexus. The two injuries may occur in the same instance. A penetrating injury from a foreign object may also lead to nerve root avulsion. If nerve root avulsion occurs in the region of the neuroforamen and the dural sleeve is stretched but intact, it often results in the formation of a pseudomeningocele. This CSF-filled lesion can be detected by myelography, CT, or MRI. The ventral nerve root is more vulnerable to traction-induced avulsion than the posterior nerve root because it is significantly thinner and traverses a slightly greater vertical course.61 The posterior root is more resistant to stretch due to the thick dural sheath and convergence of the posterior roots into the dorsal root ganglia, which provides additional stability.61,85 Complete structural separation of the nerve root results in an intravertebral and preganglionic lesion associated with profound segmental weakness, impaired dermatomal sensibility, and severe diffuse radiating pain. Because of the magnitude of trauma sustained in nerve root avulsion, the clinical presentation may be complex due to coexistent diffuse plexopathy, cervical injury, and limb fractures. Isolated ventral root avulsion will lead to considerable sparing of dermatomal sensibility. Incomplete sensory and motor root avulsion will contribute to a less distinct presentation. Severe traumatic plexopathies are often associated with nerve root avulsion.86 The C8 and T1 levels are
177
TABLE 7.9 Predisposing Factors to Disk Derangement • • • • • • • • • • • •
Excessive loading pressure Increased intradiscal expansion pressure Intradiscal degeneration Endplate microfractures and sclerosis leading to closure Impaired nutrient delivery to the disk Subchondral trabecular failure Coalescence of annular tears Excessive shearing forces Cumulative microtrauma Macrotrauma Facet tropism Segmental dysfunction
the most common levels of root avulsion due to limited connective tissue anchoring to the transverse processes.85 Careful assessment of intrinsic hand function should always be performed in suspected cases of nerve root avulsion. Magnetic resonance imaging is a valuable method for assessing the post-traumatic nerve root status, although the clinician should be aware that volume averaging and 4–5 mm slice thickness may occasionally result in falsepositive or false-negative MR interpretations. The sensitivity of MRI can be improved with the use of gadolinium enhancement, which provides a method of investigating the spinal cord surface at the root entry zone (injury site) and the integrity of intradural nerve root stump (injury site).87 The area of post-traumatic neural avulsion is likely to enhance. CT myelography offers the benefit of thinslice acquisitions of 1 to 3 mm, providing a sensitive preoperative indicator of complete or partial nerve root avulsion in post-traumatic injuries.88
7.8 INTERVERTEBRAL DISK HERNIATION AND RADICULOPATHY Disk herniation is well documented as one of the most common etiologies of radiculopathy.36,89-93 For example, in a study by Modic and colleagues,91 72% of patients with acute radiculopathy had a herniated nucleus pulposus. Direct correlation among the size of the disk lesion, clinical presentation, and treatment outcome is not always clear.91 Many patients older than 60 years may have one or more relatively asymptomatic herniations. It should be noted, however, that intermittent pain and loss of functional capacity accompany virtually all relatively asymptomatic herniations (Table 7.9).
7.8.1 EXPERIMENTAL MECHANISM OF DISK HERNIATION A normal intervertebral disk has a high capacity for accepting axial loads. Many studies have been performed
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
In combination
Anterolateral flexion
Axial compressive blow
Annular failure Nuclear extrusion
FIGURE 7.18 Physical mechanisms contributing to annular disruption. (Copyright J.M. True, D.C.)
on the behavior of the disk under variable stressors. One of these showed that the normal intervertebral disk loses about 0.6 mm of vertical height and bulges approximately 0.34 mm in a radialward direction under a compressive axial load of 1700 N.94 This study determined that the disk withstands a maximum compressive force of 7000 N before failure; by comparison, the maximum force needed to produce failure of the endplate was 2500 N.94 These findings indicate that compression alone does not produce disk prolapse in the experimentally prepared spine. Adams and Hutton90 were able to experimentally produce disk herniation in a two-vertebrae specimen by applying sudden compression to the specimen with simultaneous lateral and full forward flexion. The disk prolapse occurred on the open disk wedge side opposite the side of lateral flexion. Clinically, disk herniation is often seen after a lifting injury or motor vehicle accident in which lateral flexion and forward flexion positions of the spine occur at the time of traumatic compression or shear (Figure 7.18).
7.8.2 CONVENTIONAL CLASSIFICATION LESIONS
OF
DISK
The classification of disk herniations is often confusing and imprecise. The term disk herniation implies that a rupture or tear of annular fibers occurs allowing the migration of nuclear material beyond the vertebral margin. The nuclear material may protrude out and cause a distention of the outer annulus fibrosis or rupture through the annulus and extrude behind the posterior longitudinal ligament. Additionally, in cases with a greater degree of extrusion, the nuclear material may become separated from the disk of origin and migrate into the epidural space or lateral recess as a free fragment. The confusion in describing the previously mentioned lesions stems from the limited resolution of diagnostic imaging technology and the poor
standardization of terminology. This resolution inadequacy is most problematic in confirming small-to-moderate sized subannular herniations and confirming whether an extrusion has separated from the disk as a free fragment. The second problem is the plethora of terms used to describe a disk herniation. Some of the terms encountered are disk herniation, protrusion, extrusion, nuclear extrusion, prolapse, bulging disk, slipped disk, ruptured disk, and sequestered disk. We have classified disk lesions into four main groups based on their appearance on MR imaging. They are annular bulge; protrusion (herniation); extrusion; and free disk fragment (sequestration). These categories can be applied to the description of disk lesions throughout the spine. The next consideration in describing a disk lesion is whether the herniation is contained by the annulus or uncontained and in a subligamentous position under the posterior longitudinal ligament (PLL). When disk material has migrated around or through the PLL, it is called transligamentous extrusion. The sizes of disk herniations are categorized as small, moderate, and large. The location of the disk herniation in relation to midline spinal anatomy should be described. The majority of disk lesions involve herniation in a central posterior or posterolateral direction. Herniations that occur in a lateral direction or through the anterior portion of the intervertebral disk are not as common. The pathoanatomical relationship of the herniation to the adjacent neural and spinal elements should be evaluated and described. Compression of the nerve root or spinal cord is described as mild, moderate, and severe. Effacement of the thecal sac, nerve root, or cord is also clinically significant because of compression of the surrounding vasculature and contact with the inflammatory interface of discal material. 7.8.2.1 Annular Bulge (Disk Bulge) The term annular bulge should be reserved for describing symmetric annular extension beyond the posterior margin of the vertebral body without evidence of internal concentric annular fiber disruption (Figure 7.19a). An annular bulge does not often directly contact the nerve root. The disk bulge may be accompanied by a loss of intradiscal proteoglycans and water content with a resultant loss of vertical disk height and laxity of annular fibers. There will often be some loss of cross-sectional IVF area. Two important criteria for identifying an annular bulge are broadbased annular extension and a symmetrically enlarged margin. Large disk bulges are often secondary to radial tears of the annulus.95 A short-based focal disk extension is more typical of internal annular derangement and nuclear migration. This type of bulge often represents a small disk herniation and may easily progress to a larger degree of nuclear protrusion because of a loss of the containing annular fibers. Degeneration will predispose annular
Pathomechanisms of Radiculopathy
179
Axial
Sagittal
Contained
Diffuse annular bulge
Intradiscal mass displacement Focal disk bulge or focal protrusion with annular fiber disruption
Subtotal annular disruption Disk herniation or protrusion (Intra-annular protrusion)
Uncontained
Disk extrusion (subligamentous)
Transligamentous disk extrusion
Disk extrusion with sequestration
FIGURE 7.19A Classifications of disk injury. Although degenerative disk disease is sometimes included as a classification of disk lesion, its role in disk injury is more of a predisposing factor to disk herniation resulting from internal derangement. (Copyright J.M. True, D.C.)
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Radial tear to outer annular edge
Concentric annular tears
FIGURE 7.19B Predisposing intradiscal factors that increase the risk for complete annular failure during trauma. (Copyright J.M. True, D.C.)
fibers to failure following trauma (Figure 7.19b). The abnormality of the bulging annulus has been well documented by Yu and colleagues,96 who saw radial tears in 84% of disks bulging more than 2.5 mm (Figure 7.20). Discontinuity of the annulus, such as a radial tear, results in a nonuniform stress pattern that increases the risk of structural failure at the boundary.97
2.5 mm FIGURE 7.20 Radial tears of the annulus fibrosis are usually present when a disk bulge or protrusion extends more than 2.5 mm beyond the outer vertebral margin. (After Yu et al.95)
Sinuvertebral nerve Disk herniation
PLL
Spinal nerve
Dura mater
Anterior root
IVF
Posterior root
FIGURE 7.21 The sinuvertebral nerve is vulnerable to disk herniation due to its anterior position within the spinal canal. Sinuvertebral nerve compromise may result in discogenic pain without spinal nerve root effacement. (Copyright J.M. True, D.C.)
7.8.2.2 Disk Protrusion (Herniation) A disk herniation represents a rupture of nuclear material through a defect in the annulus, producing a focal extension of the disk or asymmetric, broad-based extension of the disk margin.98 The term disk protrusion is synonymous with the term subannular contained nuclear herniation. A portion of nuclear material may eccentrically migrate through compromised internal annular fibers without extruding beyond the outer annular fibers. This produces an abrupt, asymmetric extension beyond the vertebral margin without the degree of gradual tapering typically observed with an annular bulge. The protruding subannular disk material often migrates in a caudal direction. Intervertebral disk herniations result in some degree of central canal or foraminal occlusion. Therefore, when thecal sac effacement is present, compression of the epidural venous plexus and sinuvertebral nerve is possible (Figures 7.21 and 7.22). Lateral disk herniations may compress the intraforaminal venous plexus or segmental artery (Figure 7.23). These symptom-producing pathomechanisms should always be a consideration in rapid-onset disk herniation, with or without nerve root compression. 7.8.2.3 Disk Extrusion The classification of an extruded disk is applied when portions of the nucleus pulposus fibrocartilage and endplate cartilage have migrated through compromised outer
Pathomechanisms of Radiculopathy
181
L4-5 disk herniation
Thecal sac
L5
A
B FIGURE 7.22 (A) Cadaveric depiction of an L4–L5 disk herniation effacing the thecal sac. (Courtesy of J. Paul Ellis, Ph.D.) (B) Photomicrotome of a lumbar intervertebral disk. The arrow demarks a midline posterior disk herniation. The abbreviation RL denotes a rim lesion. (Courtesy of Shiwei Yu, M.D.)
Venous plexus congestion may occur with thecal sac effacement. Chronic compression produces engorgement and dilation of local venous tributaries, which can contribute to the development of inflammation and fibrous infiltration secondary to venous stasis.
Internal vertebral venous plexus congestion
Reduced venous drainage through IVF FIGURE 7.23 Intervertebral disk herniation compromising the epidural venous plexus.
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
FIGURE 7.24 Intervertebral disk herniation with tenting of the posterior longitudinal ligament. (Parasagittal T1- and T2-weighted images).
larger subligamentous extrusion will cause a tenting of the PLL (Figure 7.24). Extruded nuclear material can migrate superiorward or inferiorward as a result of the high-pressure containment of the PLL (Figure 7.25). Disk extrusion material, when moderate to large in size, may migrate around or through the PLL or follow the dural sleeve into the IVF. This is characteristic of an uncontained disk herniation. Depending on location, a moderate- to large-sized extrusion may also compress the root, cord, or both and cause a myeloradiculopathy. Disk extrusion increases the risk of the release of inflammogenic compounds into the nerve root environment, as previously described. Subligamentous tenting or deformation of the PLL may contribute to a chronic low back pain syndrome. This is based on the fact that the PLL contains an extensive webwork of free nerve endings supplied from the sinuvertebral nerves (Figure 7.26).59 7.8.2.4 Free Disk Fragment (Sequestered Disk)
FIGURE 7.25 Parasagittal T1-weighted image through the cervical spine demonstrating a subligamentous C5–C6 intervertebral disk herniation.
annular fibers. Disk extrusions are also qualified by their size, being described as small, moderate, and large. This type of herniation may be subligamentous or transligamentous depending on whether the extrusion is under the PLL or extends around or through the PLL. A moderate-sized or
The term free disk fragment refers to the extra-annular separation and migration of a piece of nuclear material, which is no longer contiguous with the parent nucleus.98 This is often referred to as a sequestered disk herniation (Figure 7.27). Occasionally, a free fragment migrates behind the midportion of the body of the adjacent vertebra, making it difficult to determine the disk of origin without scrutiny. A free disk fragment may be subligamentous between the vertebral body and PLL or migrate to a transligamentous position in the epidural space. A migrated free fragment may compromise the ipsilateral lateral recess or IVF above or below the level of injury, causing
Pathomechanisms of Radiculopathy
183
The distribution of the left lumbar sinuvertebral nerve (SVN) is represented by this figure. The pedicle has been transected and the neural arch and dural sac removed to reveal the nerve in the floor of the vertebral canal.
A
PLL
SVN D IVD A Pedicle Gray rami Ventral ramus
a
SVN D DRG
FIGURE 7.26 Innervation of the posterior longitudinal ligament. (From Bogduk, N., The innervation of the lumbar spine, Spine, 8(3):287, 1983. With permission.)
significant nerve root compression. Disk fragments migrate in a superior (42%) or inferior (40%) direction from the donor disk, with the displaced disk components most frequently (94%) becoming lodged into the right or left half of the anterior epidural space, rarely straddling the midline.99 An intradural disk extrusion can occur, although it is not common. Cauda equina syndromes are common with intradural migration of an extruded lumbar disk fragment Table 7.10.100 MR imaging is very sensitive to free fragment when the scan slice is optimal. In these cases, MR imaging is not always able to determine if a free fragment is present.101
7.9 NERVE ROOT COMPROMISE: EXPANSILE LESIONS Benign cysts and tumors may perfectly simulate radiculopathy from a herniated disk. The patient’s symptoms will be reproduced with neuro-orthopedic maneuvers that compress the tumor against the nerve root or traction the nerve root across the mass. The presence of radiographic abnormality such as IVF erosion is a hallmark
indicator of a schwannoma, neurofibroma, or other expansile lesion. MRI is the best procedure for noninvasive diagnosis of tumors and cysts. Patients with benign spinal tumors may be treated conservatively for years before symptoms accentuate to a red-flag level of obvious neurological compression. In one study, the duration of symptoms prior to diagnosis of a sacral area tumor ranged from 1 month to 9 years (Table 7.11).102
7.9.1 SCHWANNOMA Schwannomas are benign nerve sheath tumors that commonly occur singularly in otherwise normal individuals. Schwannomas are one of the most common benign tumors to afflict the nerve root and occur with greatest prevalence in the thoracic spine, although they can occur along any spinal nerve.103 They are encapsulated tumors that arise in an eccentric fashion from Schwann cells of the peripheral nerve. In the spine, they usually occur as intradural extramedullary lesions and on rare occasions may acquire an extradural extension, most commonly arising from the sensory portion of the nerve root. Schwannomas usually present as intraforamenal masses, which expand in size
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FIGURE 7.27 (A) Axial spin echo T1-weighted image following gadolinium enhancement through the L4–L5 interspace. The image demonstrates a free disk fragment within the right lateral recess. There is an enhancing rim of granulation tissue surrounding the free disk fragment. The patient has undergone partial microdiscectomy and hemilaminectomy at this level. (B) Parasagittal spin echo T1-weighted image of the same patient, demonstrating fragmented free-floating disk material within the right lateral portion of the spinal canal.
TABLE 7.11 Nerve Sheath Tumors
TABLE 7.10 Common Findings Associated with Intervertebral Disk Pathology • • • • • • • • • • • •
Annular tears Rim lesions Nuclear migration Disk desiccation or annular fiber degradation with rostrocaudal subluxation Discogenic inflammation or infection Osteophytosis at the annular rim Sharpey’s fiber disruption Release of proinflammatory phospholipase A2 and metallo-proteins following disk injury Endplate herniation (Schmorl’s node) Facet imbrication and segmental dysfunction Facet arthrosis and hypertrophy Foraminal encroachment
• Most commonly occurs as an intradural/extramedullary mass. • Types: Schwannoma, neurofibroma Ganglioneuroma, neurofibrosarcoma (rare) • Primarily seen in middle-aged adults. • Variable location: Intradural/extramedullary (70% to 75%) “Dumbbell” (15%) Extradural (15%) Intramedullary (<1%) • Multiple lesions common with neurofibromatosis. • Clinical symptoms can mimic disk herniation. • Imaging findings: Enlarged neural foramen common; Ca rare 75% isointense, 25% hyperintense on T1-weighted image >90% hyperintense on T2-weighted image (“target” appearance common) Virtually 100% enhance Source: Osbourne, A. Diagnostic Neuroradiology: An Atlas/Text, St. Louis, MO: Mosby, 1993, p. 897. With permission.
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The tumor’s growth is contained by the foramen causing the characteristic dumbbell shape.
FIGURE 7.28 The dumbbell or hourglass tumor characteristically describes the morphological appearance of a schwannoma, neurofibroma, or meningioma as it expands intraspinally and extraspinally through the IVF. (Copyright J.M. True, D.C.)
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FIGURE 7.29 (A) Axial T1-weighted image through the thoracic spine demonstrating a large soft-tissue mass surrounding the left nerve root which widens the neural foramen. (B) Axial T2-weighted image of the thoracic spine of the patient shown in Figure 7.30a. This postcontrast image reveals the hypertintensity characteristic of a tumor such as a neurofibroma or schwannoma.
and eventually displace and compress the adjacent nerve root. They do not characteristically invade the originating spinal nerve root.104 A large schwannoma may extend into the spinal canal and displace and compress the spinal cord, although they rarely occur as isolated intramedullary tumors. Expansion from the IVF leads to the development of a dumbbell or hourglass configuration as the tumor conforms to the lower resistance outside the rigid boundaries of the IVF (Figure 7.28). Appearance of a dumbbell-shaped mass in the thoracic spine is highly suggestive of neurofibroma, schwannoma, or meningioma (Figure 7.29). Schwannomas usually occur as isolated lesions with the exception of approximately 5% of cases, which occur in neurofibromatosis, type 2 (NF-2).105,106 The term
“schwannomatosis” has recently been applied to classify the occurrence of multifocal schwannomas not otherwise associated with NF-2.107 Isolated schwannomas tend to be more prevalent in older individuals, usually occurring in the fifth and sixth decades, and are extremely rare in children with the exception of those occurring in association with NF-2.108 Malignant transformation of schwannomas is rare. Schwannomas are generally slow-developing expansile lesions, which characteristically grow to a relatively large size prior to being associated with radiculopathy. Radiculopathy occurs secondary to crowding of the IVF. The clinical presentation often mimics radiculopathy due to more common causes such as far lateral disk herniation, uncovertebral
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FIGURE 7.30 (A) Oblique radiograph of the cervical spine demonstrates marked bony erosion with expansion of the right neural foramen at the C2–C3 level. Erosion of the pedicle and scalloping of the posterior bony elements are apparent. (B) Coronal spin echo T1-weighted image of the cervical spine following the administration of gadolinium. This image demonstrates a large lobulated enhancing mass, which extends along the nerve root and expands the right neural foramen. There is a mass effect upon the right lateral aspect of the spinal cord with subsequent spinal cord deformity. There is intense homogenous enhancement of the extra-spinal lesion following the administration of gadolinium, consistent with a schwannoma.
hypertrophy in the cervical spine, spondylolisthesis, and degenerative spondylosis. Schwannomas have been reported to cause thoracic outlet-type symptoms following extension from the C7 root.109 Schwannomas of the cauda equina can mimic the common complaints of low back pain. Because of the mobility of the nerve roots and the relatively wide lumbar canal, tumors arising in the region of the conus medullaris can become larger than most other spinal tumors. General differentiating features of neurological compromise secondary to a cauda equina schwannoma vs. disk pathology include increased back pain while lying recumbent, polyradiculopathy, and a refractory response to conservative intervention.110 The first sign of a schwannoma as a cause for back and extremity pain can be bony erosion and resorption within the IVF due to the expansile lesion. Bony erosion of the IVF in the cervical spine may be evident on oblique views (Figure 7.30a). Lateral radiographic views in the lumbar spine will often reveal the associated bony changes. This finding may be seen during the incidental work-up for trauma or neck symptoms due to other causes. Hyperostosis and bony sclerosis are rare. The schwannomas generally appear hypointense– isointense on T1-weighted MR images and hyperintense on T2-weighted images. 111 Schwannomas typically
enhance on MRI following contrast administration, whereas disk herniations do not enhance (Figure 7.30b). They tend to be slightly more vascular than other forms of neuromas. Microcystic changes may be evident and tend to be more prevalent in spinal tumors than in intracranial lesions.112 Macrocystic changes are less common.113 Focal regions of low T2-weighted signal intensity may represent intratumoral hemorrhage, a dense cellular region, or collagen deposition.112 Cystic changes help to differentiate the tumor from neurofibromas and meningiomas, which are less apt to demonstrate intratumoral cysts.106 This is more likely to occur with a more chronic lesion. Tumor extension can be classified as intradural intra-arachnoid, intraforaminal extra-arachnoid, and extraforaminal.114 CT myelography may demonstrate nerve root cutoff, the extent of bony enlargement of the IVF, and thinning of the adjacent pedicles. The CT study will help determine the risk for acquired intersegmental instability secondary to bony changes.
7.9.2 NEUROFIBROMA Neurofibromas are a form of nerve sheath tumor. Like schwannomas, they are neurogenic tumors that arise from the sensory portion of the nerve root and present
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FIGURE 7.31 (A) Axial CT soft-tissue window slice through the L3 level. A large soft-tissue density has eroded the right pedicle and enlarged the right neural foramen. This is characteristic of a neurofibroma. (Courtesy of George W. Fika, D.C.) (B) Axial T1weighted image through the L3 level of the same patient. The large mass is again seen markedly enlarging the right neural foramen and displacing the thecal sac. (Courtesy of George W. Fika, D.C.) (C) Sagittal T1-weighted MRI through the lumbar spine of the same patient. The tumor is again seen markedly eroding the posterior vertebral bodies and enlarging the neural foramen. (Courtesy of George W. Fika, D.C.)
as an intraforaminal, intradural, extramedullary lesion. Intraspinal neurofibromas are rare and usually are associated with neurofibromatosis, type 1 (NF-1) (von Recklinghausen’s disease).103,106 NF-1 is a genetic disease with a wide range of neurological manifestations; it has more profound complications when the disorder manifests during childhood. These complications include symptomatic optic pathway tumors, cerebral gliomas, symptomatic aqueductal stenosis, and spinal cord compression. The predominant neurological features in adults with NF-1 are chronic pain and malignant peripheral nerve sheath tumors.115 Thus, neurofibromas associated with NF-1 represent a more aggressive lesion than schwannomas. Neoplastic schwann cells infiltrate the adjacent nerve root and may become life-threatening. The radiculopathic signs and symptoms may occur
abruptly due to the more aggressive nature of this nerve sheath tumor. Schwannomas and neurofibromas generally have a similar radiographic appearance. IVF erosion and expansion are usually present. Arising from the spinal nerve, the tumor commonly produces a dumbbell or hourglass shape because of the bony constrictions of the IVF (Figure 7.31). The neurofibroma is a solid tumor and therefore has a slightly more homogenous MR appearance. It generally appears hypointense–isointense on T1-weighted imaging and hyperintense on T2-weighted imaging. Unlike schwannomas, neurofibromas do not characteristically present with cystic changes and may present with a “target appearance” with a central nonenhancing region that is hypointense on T2-weighted imaging (Figure 7.32).116,117
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FIGURE 7.32 (A) Oblique X-ray of the lumbar spine demonstrating marked bony expansion of the right neural foramen secondary to a neurofibroma. (B) Axial spin echo T1-weighted image through the L5–S1 level revealing a large, round mass markedly expanding the right neural foramen. There is a mass effect upon the right lateral recess at this level. This presentation represents a neurofibroma. (C) Right parasagittal spin echo T1-weighted image at L5–S1 demonstrating a large, round mass, which follows the course of the exiting right nerve root, compatible with neurofibroma.
7.9.3 MENINGIOMA Meningiomas are relatively common spinal neoplasms accounting for as much as one fourth to one third of intraspinal expansile lesions.104,118 Spinal meningiomas
are slow growing and almost always benign. Meningiomas may occur within the spinal canal as an intradural extramedullary tumor or epidural location, although they may occur adjacent to nerve roots and occasionally
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The most common location of the cyst occurs on the extradural components of sacral or coccygeal nerve roots. They may occasionally be found on nerve roots in other areas of the spine (Figure 7.33). Although most are asymptomatic, they occasionally cause low back pain, sciatic radicular pain, and sacrococcygeal pain. Sensory and motor deficits in the lower extremities imitate lumbar or lumbosacral disk herniation. Urinary dysfunction may occur with large lesions in the sacral canal. Symptoms occur because the expanding cyst impinges upon adjacent nerve roots. The cysts are described as thin walled and CSF filled. They are formed in a space between the endoneurium and the perineurium. Microscopically, the cyst walls consist of peripheral nerve fibers or ganglionic cells covered with meningeal epithelium.123 Erosion of the surrounding bone or IVF may occur because of the pulsatile action of CSF flow. The MR appearance of a perineurial cystic lesion is that of an intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images comparable with CSF.120 FIGURE 7.33 Right lumbar parasagittal (A) spin echo T1weighted and (B) fast spin echo T2-weighted images demonstrating a round, cystic lesion expanding the right neural foramen at the T11–T12 level compatible with a perineural cyst.
extend through the IVF, producing a classic dumbbell lesion. Meningiomas occur more commonly in the thoracic spine, followed by their occurrence in the cervical spine.111 Radicular pain may occur early on the side of the tumor. This may be accompanied by years of focal back pain before MRI confirms the diagnosis. As the lesion expands, signs of cord compression will become obvious. The appearance of meningiomas on MRI is very similar to schwannomas. They are usually isointense to the spinal cord on T1-weighted imaging and are also of low signal intensity as compared to CSF on T2-weighted imaging. The low signal changes are readily apparent when compared to the surrounding hyperintense CSF signal. Because they develop slowly, calcification may occur and will contribute to low T2-weighted signal changes.
7.9.4 PERINEURIAL CYSTS (TARLOV’S CYSTS) Perineurial cysts are reported in the literature to occur in a wide range of prevalence. Paulsen et al.119 reported that lumbosacral perineurial cysts were common lesions, occurring with a prevalence of 4.6% The researchers reviewed 500 sequential lumbosacral spine MRIs and found 23 patients with perineurial cysts; however, only five patients (1%) were symptomatic from the cysts.119 Most researchers report the prevalence to be rare, although the majority of published studies are single case reports.120-122 All case reports and reviews agree that perineurial cysts are usually asymptomatic.
7.9.5 SYNOVIAL CYSTS Facet cysts can cause direct compression of the nerve root or posterolateral aspect of the spinal cord, depending on their size and location. Synovial cysts are rare and occur most frequently at the L4–L5 and L5–S1 levels.124,125 Tissue studies have demonstrated that facet synovial cysts contain various components, including loose fibrous connective tissue, dense fibrous connective tissue, a hyperplastic synovial membrane, and fine calcifications.126 Facet cysts may contain serous fluid and, occasionally, blood. Facet cysts are sometimes mistaken for a tumor within the neural foramen. Facet joint arthrography can be helpful in both diagnosis and treatment of synovial cysts,127 although arthrography is not often required given the availability of MRI. Additional diagnostic considerations having MR appearance similar to synovial cysts include a large or migrated free disk fragment or a cystic nerve root tumor.
7.9.6 METASTATIC DISEASE Spinal metastasis rarely causes radicular symptoms without also causing cord compression. Symptoms associated with metastatic tumor spread usually begin when the nerve root or neurovascular structures within the IVF and cord are compressed or infiltrated by cancer. Hematogenous spread to the nerve root is less common than direct compression by an expanding tumor mass from the vertebral body or lamina.128 Early symptoms may be indistinguishable from radiculopathy or severe far lateral IVF stenosis. Symptoms may result from bony destruction or vertebral collapse, compression of the nerve root by tumor expansion, or from direct metastatic invasion of the nerve
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root. With solitary metastasis, depending on the level and spinal structure invaded, cervical spinal tumors produce neck pain, with diffuse radiation into the shoulder and arm. Lumbar tumors produce diffuse back pain with weakness in the distribution of the lumbar root. Metastatic bony destruction almost universally causes significant pain except in spinal cord injury and patients with congenital insensitivity to pain. Vertebral collapse is a late effect of metastasis. Patients with leptomeningeal metastasis usually have multifocal complex neurological presentations because the CNS is affected at multiple locations (Figure 7.34). Patients with leptomeningeal metastasis often have complex neurological symptoms involving the brain, cranial nerves, and spinal roots, with occasional signs of meningeal irritation.103,128 Leptomeningeal metastases frequently result in a multifocal neurologic presentation. The patient may present with headaches and ataxia with involvement of the brain, or cranial nerve deficits such as diplopia or dysphagia. Back pain, weakness, and absent reflexes are a few of the signs of leptomeningeal metastasis to the roots and the spine. Metastasis may also cause brachial or lumbosacral plexopathy or, in rare cases, isolated peripheral nerve involvement. The most common brachial plexus metastasis occurs from an apical lung tumor (Pancoast tumor) or lymph node metastasis from breast cancer.128 Lower brachial plexus invasion produces C8–T1 deficits; paresthesia, numbness, and weakness in the distal ulnar innervated structures; occasional Horner’s syndrome; and ipsilateral miosis, ptosis, hypohydrosis, paralysis of orbital muscle, and vasodilatation in the ipsilateral half of the face.129
7.10 VERTEBRAL OSTEOMYELITIS AND DISCITIS Infectious organisms can reside and proliferate within tissues of the spinal column. Pyogenic infections of the spinal column usually afflict the vertebral body and/or the intervertebral disk. Coexistent infection of both regions is referred to as spondylodiscitis (Figure 7.35). The source of infection may be secondary to hematogenous seeding or direct inoculation from a foreign body or surgical intervention. Children are more prone to develop discitis, whereas adults are more likely to develop osteomyelitis.130 Juvenile discitis occurs more frequently in girls under 2 years of age, with staphylococcus being the most common infectious etiology. Osteomyelitis occurs more often in men over 50 years old. Pyogenic infection is characterized by infiltration of polymorphonuclear leukocytes, vasodilatation, edema, and fibrin deposition. During the acute inflammatory process, the local release of lytic enzymes can degrade supportive connective tissue. The loss of supportive tissue integrity promotes further spread of the infectious organism and
weakening of involved structures. Under axial loads, the weakened supportive tissues may give way, resulting in an expansile lesion comprised of abscess and degraded disk or osseous matrix. Progressive osteomyelitis and/or discitis can result in an expansile lesion, which may compromise the adjacent nerve root and/or spinal cord. Disk protrusion and fragmentation can occur in combination with disk space infections, resulting in migration of discal material as a consequence of the infectious process.131 This can lead to infection, inflammation, and compressive insult to the adjacent nerve root. Magnetic resonance imaging is the most sensitive imaging technique for the detection of discitis, although the MRI findings typically lag behind acute tissue destruction in the acute phase and tissue repair during the recovery phase. Due to this imaging lag, historical, clinical, and laboratory correlation is critical. Sequential MRI studies are often required to gauge the therapeutic response. Comparison of pre- and post-contrast spin echo T1-weighted imaging increases the sensitivity of detecting infectious changes.132 Gadolinium enhancement can increase or persist after symptom resolution.133 Acute MRI changes are characterized by increased signal intensity on T2-weighted images and decreased signal intensity on T1-weighted images. The healing phase is characterized on MRI by reduced intervertebral disk height (rostrocaudal subluxation), decreased intradiscal and endplate subchondral T2-weighted signal intensity, and resultant fibrous or bony fusion of vertebral bodies. Laboratory methods of diagnosis include C-reactive protein, serum sedimentation rate, and a complete blood count with differential. It is usually important to culture the organism following needle biopsy and to test for antibiotic sensitivity. If the patient with infectious spondylodiscitis demonstrates signs of spinal cord and/or nerve root involvement, surgical decompression and debridement may become a neurosurgical emergency.
7.11 SPONDYLOLISTHESIS AND RADICULOPATHY Radiculopathy and spondylolisthesis are relatively uncommon, as compared to nerve root compression from disk herniation in the lumbar spine. However, in cases of spondylotic spondylolisthesis, radiculopathy occurs in 60 to 70% of patients.134 Spondylolisthesis refers to the anterior displacement or listhesis of a vertebral body in relationship to the vertebral body immediately below. The term listhesis refers to slippage or displacement without reference to direction. Spondylolisthesis may occur without a defect in the neural arch or secondary to a defect in the neural arch. If there is a defect in the neural arch, the term spondylotic spondylolisthesis should be applied. With an intact neural arch, the term non-spondylotic spondylolisthesis should be
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FIGURE 7.34 (A) Sagittal T1-weighted image of the lumbar spine. Notice the absence of the normal high signal intensity of the vertebral body at L2 and the “check mark” fracture of the superior endplate. There is also an area of marrow replacement at the posterior aspect of T11. These findings are most consistent with metastatic disease. (B) Sagittal spin echo T1-weighted image with contrast of the lumbar spine. This image is the same as that in (A) with the addition of contrast media. Notice how the metastasis enhances and becomes isointense to the normal vertebral bodies. Also, there is protrusion of the mass into the spinal canal. (C) Axial spin echo T1-weighted image with contrast at the level of L2. This image is of the same patient seen in the previous two views. The mass obliterates the posterolateral third of L2 and extends through the pedicle into the posterior elements, narrowing both the intervertebral foramen and spinal canal.
used. Spondylolisthesis is relatively common and usually involves the 4th or 5th lumbar vertebrae. Consequently, the radiculopathic symptoms may reflect L4, L5, or S1
nerve root involvement. The most common root involved is the L5 root. Cervical spondylolisthesis is rare, but when present, it is often found at the C6 level. Cervical
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B FIGURE 7.35 (A) Lateral radiograph of the lumbosacral junction demonstrating destruction of the inferior endplate of L5 and the superior endplate of S1 secondary to osteomyelitis and discitis. (B) Sagittal fat-suppressed T1-weighted image of the lumbosacral junction demonstrating diffuse high signal intensity of L5 and S1 secondary to an inflammatory process. (C) Sagittal T2-weighted image of the lumbosacral junction of the same patient. The infection is associated with hypertintensity on T2-weighted images and is seen extending into the spinal canal. (Courtesy of Shiwei Yu, M.D.)
spondylolisthesis is commonly associated with spina bifida occulta, suggesting a congenital predisposition. There are many opinions relative to the etiology, clinical significance,
therapeutic options, and prognosis with spondylolisthesis. The cause of spondylolisthesis remains controversial. The most commonly reported symptoms associated with
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degenerative spondylolisthesis and lateral stenosis are neurogenic claudication and radiculopathy.135 There are five pathoetiologic classifications of spondylolisthesis as follows:135a Type I: Dysplastic. The dysplastic type refers to spondylolisthesis with a congenital abnormality involving the neural arch inclusive of hypoplasia. Type II: Isthmic. Refers to physical compromise of the pars interarticularis. (a) Stress or fatigue fracture, or (b) elongated intact pars, or (c) an acute fracture of the pars. Type III: Degenerative (pseudo-spondylolisthesis): This form of spondylolisthesis occurs secondary to chronic degenerative arthrosis at the facet joints and diskovertebral articulations in the absence of a pars separation. Degenerative changes of the facet joint complex can cause laxity and subsequent anterolothesis of the vertebral complex. Type IV: Traumatic type refers to spondylolisthesis secondary to fracture of a portion of the neural arch other than the pars interarticularis. Type V: Pathologic. This category is characterized by the presence of generalized or localized bone disease such as metastatic bone destruction, severe osteoporosis, and Paget’s disease. The diagnosis of radiculopathy and spondylolisthesis often presents a challenge to the attending clinician. Spondylolisthesis can be found in asymptomatic individuals as well as symptomatic patients with concurrent radiculopathy produced from other mechanisms. Paradoxically, patients with severe spondylolisthesis may not report back pain, and patients with relatively less severe spondylolisthesis may have severe back-related complaints. One of the most common complaints associated with spondylolisthesis is a deep dull, aching discomfort or pain focal to the region of spondylolysis. Neurologic evaluation of the lower extremities may be unremarkable unless neurogenic claudication or radiculopathy is present (see Figure 8.19). Loss of Achilles reflexes and weakness in anterior tibial muscles are common in degenerative non-spondylotic spondylolisthesis.136 The pain associated with spondylolisthesis may be a combination of sclerotomal and radicular etiology. Radiculopathic symptoms in spondylotic spondylolisthesis result from a combination of the tethering effect on the nerve roots, compression of the roots from a ligamentum flavum process, impingement of the nerve roots within the foramen, or symptom production from an associated disk herniation and inflammation. In degenerative spondylolisthesis where the neural arch is intact, compression of the cauda equina occurs from a pincer effect caused by dislocation of the intervertebral body and intrusion of the neural arch into the spinal canal. This may produce a
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complete or partial CSF block on conventional myelography or MR myelography in addition to nerve root compromise.136 In cases of spondylotic spondylolisthesis, root compression in the IVF has been demonstrated to occur from a ligamentum flavum process. The ligament flavum process is a bony fixed process that lies on the internal inferior aspect of the laminar arch, associated with the ligamentum flavum and area of lysis. This bony process protrudes into the IVF and was found to be the cause of root compression in the majority of spondylotic spondylolisthesis patients studied.134 Distortion and swelling of the posterior disk margin (pseudo-disk) occur in spondylolisthesis, which also may be a source of radiculopathic symptom production. Anterolisthesis of the vertebral segment causes a pseudo-disk herniation appearance on MR sagittal or axial images, due to deformation of the posterior annular fibers causing a bulging of the intervertebral disk into the anterior portion of the adjacent spinal canal and neuroforamen. A complete lumbar radiographic study should be performed to rule out spondylolysis of the posterior arch. If a recent fracture of the posterior (neural) arch is suspected, but not seen on routine x-rays, a bone scan is indicated. Single positron emission computed tomography (SPECT) imaging with multiplanar acquisitions can be utilized to evaluate for bone remodeling (increased bone activity secondary to varying levels of trabecular failure or fracture). MRI assessment may demonstrate interruption of the cortical margins of the pars interarticularis, confirming spondylolysis. T-2 weighted images and inversion recovery (fat suppression) technique may reveal regions of high signal in the pars or an area of defect, suggesting bone marrow inflammation/edema compatible with a traumatic separation. Sagittal MR images are critical in the evaluation of the volume and contents of intervertebral foramen. The lumbar nerve root can often be visualized on sagittal views. The intervertebral foramen should be compared to supra-adjacent and infra-adjacent levels. The nerve/IVF ratio should be conceptualized. The MRI may reveal an abnormal nerve root appearance, such as flattening, edematous enlargement, or focal high signal within the nerve root at the level of the spondylolisthesis. In patients with spondylotic spondylolisthesis, evidence of neuroforaminal impingement of the nerve root is often correlative to the segmental level of radiculopathy.137
7.12 NONCOMPRESSIVE RADICULONEURONOPATHY 7.12.1 DIABETIC RADICULOPATHY Diabetic radiculopathy or diabetic polyradiculopathy is a rare complication of diabetes that occurs in middle-aged diabetic patients. This condition is also referred to as
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diabetic proximal neuropathy, diabetic femoral neuropathy, diabetic myelopathy, diabetic plexopathy, diabetic myopathy, Bruns–Garland syndrome, and diabetic amyotrophy.138 This severe, debilitating neuropathy begins with symptoms located unilaterally and focally in the leg, thigh, or buttock and spreads to involve other regions of the same extremity.139 Anterior thigh pain is the most common initial symptom. Pain may be severe and is usually unrelieved by overthe-counter medication. Proximal leg, thigh, or hip weakness develops over a period of weeks to months. The condition often expands to involve the opposite side because of multifocal involvement of lumbosacral roots, plexus, and peripheral nerves (i.e., diabetic lumbosacral radiculoplexus neuropathy). Although motor, sensory, and autonomic fibers are all involved, motor weakness predominates and sensory loss is usually mild. Hyporeflexia or areflexia of the quadriceps muscle stretch reflex is commonly seen. Bowel and bladder involvement is rare. The clinical picture can resemble that of high lumbar disk herniation.140 Another rare complication of uncontrolled type 2 diabetes is thoracic polyradiculopathy. A patient presenting with abdominal pain and paraspinal denervation may have thoracic polyradiculopathy caused by an underlying type 2 diabetes.141 These patients will present with radicular symptoms in the flank or diffuse abdominal pain that is often worse at night and aggravated by light pressure. Thoracic segments T6–T12 are most commonly affected.142 Pain may be unilateral or bilateral and is often accompanied by weight loss. Cutaneous sensory abnormalities are common, and localized abdominal wall paresis with protrusion may occur.142,143
7.12.2 INFECTION 7.12.2.1 Herpes Varicella-Zoster Virus (Shingles) Herpes zoster is a dorsal root-specific disease most commonly affecting the thoracic roots. The trigeminal nerves are the next most frequently affected. With thoracic involvement, symptoms begin as a deep burning pain in the flank or ribs and precede the classic appearance of cutaneous vesicular eruption. The disease tends to be confused initially with radiculopathy or other conditions. Within 3 weeks of the initial symptoms, there is a cutaneous eruption of small clusters of vesicles that follow a dermatomal distribution.144 Motor loss is rare because the disease has a predilection for the dorsal root ganglia. Herpes zoster has also been reported to mimic radiculopathy of the distal extremities. Segmental zoster paresis (SZP) is the focal, asymmetrical, neurogenic weakness that may occur in a limb affected by cutaneous herpes zoster. The appearance of paresis occurs in conjunction with the appearance of vesicular eruption. These patients are generally over 60 years of age. With cervical or lumbar involvement, C5,6,7 or L2,3,4 innervated mus-
cles are the most common segments affected. In addition to this radiculopathic-type involvement, peripheral nerves may also occasionally become involved and manifest as mononeuropathies of the median, ulnar, long thoracic, recurrent laryngeal, and phrenic nerves.145 Severe herpes zoster infection may produce neurogenic bladder, diaphragmatic paralysis, or an ascending paralysis similar to Guillain–Barré syndrome.144 7.12.2.2 AIDS-Related Polyradiculopathy Cytomegalovirus (CMV) has been implicated in the production of polyradicular signs and symptoms in AIDS patients,146,147 and herpes zoster may also be involved in production of AIDS-related polyneuropathy. This rare complication of AIDS should be considered in HIV patients with myeloradicular-type symptoms. AIDS polyradiculopathy is predominantly a motor axonal neuropathy most commonly affecting the lumbosacral roots and cord.148 A retrospective study suggested that in as many as 13% of the cases reviewed, CMV polyradiculopathy was the first manifestation of AIDS.146 MRI may demonstrate enhancement of the pial lining of the conus medullaris, cauda equina, and lumbar nerve roots following contrast enhancement.6 7.12.2.3 Lyme Disease Lyme disease is found throughout the world almost anywhere ticks are present. The disease is caused by the spirochete Borrelia burgdorferi and transmitted by the tick genus Ixodes. In most of North America, the most common vector tick is Ixodes dammini.149 The initial disease begins a few days to a few weeks after a bite from a disease-carrying tick. The disease progresses in three stages.149,150 The first stage follows an acute bite, which develops into a clinically characteristic red macule or papule that slowly expands over 3 to 4 weeks and tends to clear centrally. This identifiable lesion is called erythema migrans. The second stage follows, with systemic infection spreading to the muscles, joints, heart, and nervous system. Signs of a constitutional viral infection progress: fever, fatigue, headache, neck stiffness, and swollen glands. Neurological symptoms develop in stage 2 of the disease. The patient often develops meningitis-type symptoms that fluctuate between moderate/severe and mild/nonexistent over a period of several weeks. Approximately 50% patients with stage 2 disease will develop peripheral nerve involvement resembling radiculitis. These symptoms include severe radicular pain, spine pain, paresthesias, motor weakness, and depressed tendon responses. Stage 3 is the late phase of infection. Serious neurological signs predominate such as ataxia, seizures, paraparesis, quadriparesis, and other signs of encephalomyelitis. Without a history of tick bite or the suggestive triad
Pathomechanisms of Radiculopathy
of (1) meningitis, (2) radiculoneuritis, and (3) facial palsies, the diagnosis is often difficult because of the pleiomorphism of neurological manifestations. These can be localized or diffuse, with central involvement, meningitis, or peripheral manifestations.150 Lyme disease should be in the differential diagnosis when atypical radicular symptoms occur in conjunction with mild meningitis and arthalgic pain. A history of tick bite or erythema migrans with insidious onset polyradiculoneuritis are clear indications of the disease.149
7.12.3 COAGULOPATHIES Bleeding disorders may result in nerve root or cord hemorrhage. Hemophilia is the most common. Excessive Coumadin® medication should be considered as a risk and a possible etiology for hemorrhage following musculoskeletal trauma.
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141. Hayes, F.J., Redmond, J.M., and McKenna, M.J., Thoracic polyradiculopathy: abdominal wall swelling and sensory symptoms in diabetes mellitus, Ir. Med. J., 87:150–151, 1994. 142. Chaudhuri, K.R., Wren, D.R., Werring, D., and Watkins, P.J., Unilateral abdominal muscle herniation with pain: a distinctive variant of diabetic radiculopathy, Diabet. Med., 14:803–807, 1997. 143. Longstreth, G.F., Diabetic thoracic polyradiculopathy: ten patients with abdominal pain, Am. J. Gastroenterol., 92:502–505, 1997. 144. Baringer, R.J. and Townsend, J.J., Herpesvirus infection of the peripheral nervous system, in Dyck, P.J. and Thomas, P.K., Eds., Peripheral Neuropathy, 3rd ed., Philadelphia, PA: Saunders, 1993: 1333–1342. 145. Merchut, M.P. and Gruener, G., Segmental zoster paresis of limbs, Electromyogr. Clin. Neurophysiol., 36:369– 375, 1996. 146. Anders, H.J. and Goebel, F.D., Cytomegalovirus polyradiculopathy in patients with AIDS, Clin. Infect. Dis., 27:345–352, 1998. 147. Wolf, D.G. and Spector, S.A., Diagnosis of human cytomegalovirus central nervous system disease in AIDS patients by DNA amplification from cerebrospinal fluid, J. Infect. Dis., 166:1412–1415, 1992. 148. Corral, I., Quereda, C., Casado, J.L., Cobo, J., Navas, E., Perez-Elias, M.J., Pintado, V., Fortun, J., and Guerrero, A., Acute polyradiculopathies in HIV-infected patients, J. Neurol., 1244(8):499–504, 1997. 149. Reik, L., Peripheral neuropathy in Lyme disease, in Dyck, P.J. and Thomas, P.K., Eds., Peripheral Neuropathy, 3rd ed., Philadelphia, PA: Saunders, 1993: 1401–1411. 150. Lecomte, F., Mihout, B., and Humbert, G., Neurological manifestations of Lyme disease and treatments, Biomed. Pharmacother., 43:409–413, 1989.
8
Classic Signs and Symptoms of Radiculopathy
Many clinical signs such as foot drop or sciatic pain with antalgia point to the diagnosis of radiculopathy. However, confirmation of the cause of radiculopathy may be perplexing except when magnetic resonance imaging (MRI) demonstrates a moderate- to large-sized disk herniation compressing the same level nerve root as clinically expected. Diagnostically, complex conditions involving multiroot symptoms, intermittent root compression, or biochemically induced radiculopathies are often difficult to confirm without additional diagnostic investigation. The most commonly reported symptoms of radiculopathy are pain, tingling, numbness, and weakness. Although patients most often complain of sensory symptoms, these symptoms are not as clinically significant as motor loss. When paresis is present, it is highly probable that electrodiagnostic studies will be abnormal (Figure 8.1).1 This chapter discusses the common signs and symptoms of radiculopathy and the concomitant pain patterns that occur with or mimic radiculopathy. The pathogenesis and clinical significance of these signs are individually reviewed. Section 8.8, Assessment of Radiculopathy, reviews the clinical importance and utility of tests such as electromyography, nerve conduction studies, somatosensory evoked potentials, and MRI, which is an important tool for anatomical localization of root level compression. A brief review of important MRI characteristics of the disk and nerve root is presented. The remainder of the chapter is devoted to localization of monoradicular syndromes. This clinically valuable section discusses each spinal nerve root level and the signs and symptoms associated with each radiculopathic presentation.
8.1 SENSORY ABNORMALITIES Patients with radiculopathy commonly describe sensory symptoms such as pain, paresthesia (tingling), or numbness in a segmental distribution corresponding to the level of involvement. These segmental levels of sensory innervation are called dermatomes (Figure 8.2). The sensory evaluation should include comparative pin prick, twopoint discrimination, pallesthetic (vibratory) perception, and joint position sense (Table 8.1). Sensory symptoms associated with radiculopathy result from a combination of neurapraxic and axonotmestic damage to the nerve root. The decreased dermatomal sensation associated with radiculopathy is a result of
conduction block or loss of axon continuity in the sensory nerves of the nerve root. When the patient describes a region of numbness, there is usually a decreased perception of pin prick or vibratory sensation; however, severe numbness is usually associated with a peripheral nerve lesion or neuropathy (Figure 8.3). The region of hypesthesia will usually follow a dermatomal pattern, whereas the paresthesia and perceived pain may appear diffuse or nondermatomal. This type of pain, sclerotomal pain, occurs when there is root level involvement of afferent fibers originating from segmental muscles and deep tissue structures. The mechanism of pain production is not clearly understood. Compression of the intraneural microcirculation is thought to be part of the pathophysiologic process. It should be noted that the epineural circulation provides 50% of the blood flow to the local nerve fiber.2 Ischemia to the nerve root may occur in disk lesions without direct nerve root compromise, producing a painful dysesthesia. This occurs with compression of the radicular artery in the lateral recess. The shooting pain associated with radiculopathy may be a result of hypersensitivity and spontaneous activity of the regenerating axons in the root and spinal nerve. When nerve root compression results in axonotmesis, the proximal axon sends out sprouts in an attempt to reinnervate the distal end organ. Axonal sprouts that fail to regenerate may form mechanosensitive and chemosensitive neuromas in the area of axonal damage. The presence of neuromas, changes in vascular permeability, increased sensitivity to neuropeptides, and other trophic effects of nerve root compression result in spontaneous nerve root firing,3 which causes the characteristic pain of radiculopathy described by patients as a shooting pain or “electric pain” into the extremities (Figure 8.4). These spontaneous, ectopically generated sensory symptoms are a type of neuropathic pain.
8.2 NERVE ROOT IRRITABILITY SIGNS Neuro-orthopedic tests that compress or stretch an irritated nerve root are a routine part of the clinical examination. These maneuvers are designed to reproduce the patient’s radiculopathic symptoms. In mild to moderate cases of radiculopathy, nerve root sensitivity to mechanical stimulation may be one of the earliest signs of radiculopathy. Nerve root irritability signs can often be elicited before the clinical appearance of sensory deficits, reflex changes, 201
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Perineural fibrosis Disk herniation
Uncinate process/vertebral exostosis
Zone of inflammation Perineural edema
Intraneural edema
Hypertrophy of the ligamentum flavum Synovial cyst
Facet arthrosis exostosis
Spinal infection, tumor or metastasis are ominous conditions that may result in a rapid neurological decline.
FIGURE 8.1 Pathologies contributing to compressive root and spinal nerve syndromes. (Copyright J.M. True, D.C.)
TABLE 8.1 Dermatomal Landmarks Thumb Middle finger Little finger Breast nipple Umbilicus Medial knee Medial ankle Web space great toe Little toe/lat. foot
C6 C7 C8 T4 T10 L3 L4 L5 S1
or muscular paresis in mild to moderate radiculopathy. In cases of chronic symptomatic radiculopathy associated with spondylosis, nerve root tension signs are consistently present, with varying degrees of sensory, motor, or reflex abnormalities. The nerve root and nerve root sleeve slides within the intervertebral foramen during movement of the spine and extremities. For example, the straight leg raise maneuver translates the lumbar nerve roots approximately 2 to 5 mm at the level of the intervertebral foramen (IVF).4 This movement is constrained by direct compression of the nerve root and by the secondary reflexive spasm of muscles that guard against further stretch of an irritated nerve membrane. In a review of 2000 patients with surgically demonstrated disk herniations, Spangfort5 found that the straight leg raise tension sign was positive in 90% of cases (Figure 8.5).
In the upper extremity the most common neuro-orthopedic tests for nerve irritability are variations of the foraminal compression test, shoulder depressor test, Bikele’s sign, and Bakody’s sign. In the lower extremity, variations of the straight leg raise, Kemp’s test, and femoral stretch are important (Table 8.2). The application of additional tension to a traditional clinical maneuver may magnify a subclinical presentation. This can be accomplished in the upper extremity by extending the arm, extending the wrist, and laterally flexing the neck to the opposite side. In the lower extremity, a straight leg raise and passive foot dorsiflexion, also called Braggard’s maneuver, can be performed. To stretch and challenge the middle to lower cervical nerve root levels, Adson’s maneuver should be performed with the arm in less than 40º of abduction. Conversely, a patient’s radiculopathic presentation may be alleviated by putting the extremity in a position that decreases tension on the nerve root. For example, elbow flexion reduces tension on the midcervical nerve roots and arm abduction also relieves root tension. It is common with middle to lower cervical radiculopathies for the patient to hold the arm against the body or elevated with shoulder abduction and elbow flexion to reduce pain into the extremity; this is known as Bakody’s sign. A differential diagnosis of plexopathy must also be considered when other indicators of radiculopathy are not present. Evocative maneuvers such as cervical extension with ipsilateral rotation can magnify radiculopathic clinical presentations by reducing available foraminal space,
Classic Signs and Symptoms of Radiculopathy
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C2 C2 C3
C4 C3
C5
T2
T2
T3 T4 T5 T6 T7 T8 T9 T10 T11 T12
T1 C6
C5
C4
T1 C6 C8 Palm
C8 Palm
S3
L1 L1
C7
L2
C8
Dorsum
C7
L2
L3
L3
C6 L4
L2
C8
Dorsum
C6
C7
S4-5
C7
S2
L4
L5
L3
S2
L5 L4
Key Sensory Points S1
L5
S1
L5 S1
S1
FIGURE 8.2 Dermatomes: segmental innervation of the skin. (From American Spinal Injury Association. Copyright 2000. Used with permission.)
Skin C1 C1 C2 C3 C4 C5 C6 C7
C2 C3 C4 C5
C6 C7
C6
C7
C8
Peripheral nerve
C8 FIGURE 8.3 Simplified schematic of plurisegmental sensory innervation to the upper extremity. Multilevel cutaneous innervation renders it more difficult to isolate a sensory deficit when a single nerve root is involved. (Copyright J.M. True, D.C.)
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Motion of the neck or extremity may produce the lancinating pain sensation associated with radiculopathy
TABLE 8.2 Nerve Root Irritability Signs • Upper Extremity Bikele’s sign Bakody’s sign Foraminal compression Shoulder depression Soto hall Valsalva’s maneuver Déjérine’s sign • Lower extremity Straight leg raise and variations Braggard’s sign Lindner’s sign Turyn’s sign
FIGURE 8.4 Motion of the neck or upper extremity may produce lancinating pain secondary to radiculopathy. (Copyright J.M. True, D.C.)
90 60 Axial MRI L
R I S K
FL EX I
Nerve root compression from lower lumbar HNP should be suspected when straight leg raising below 50 produces radiation of pain in to the posterior thigh or leg.
Y LIT BI
R
L O W
30
Absence of a radicular component on SLR does not exclude the possibility of disc herniation.
Hip and Sacroiliac syndromes in absence of radicular pain 0
FIGURE 8.5 The supine straight leg raise. (Copyright J.M. True, D.C.)
which leads to pain, nerve root compression, and subsequent neural injury.6 Thus, changes in cervical spine position can produce microstretch injury of the nerve root in the foramen as well as direct compression of the nerve root.
8.3 REFLEX ABNORMALITIES Muscle stretch reflexes (MSRs), also referred to as deep tendon reflexes (DTRs) and monosynaptic reflexes, have significant clinical relevance in the evaluation of radiculopathy. The MSR is an involuntary response elicited by stimulation of the tendon (usually a brisk tap of the tendon using a reflex hammer). Because the MSR is an involuntary and readily reproducible response, it is one of the most objective indicators of neurological involvement.
The MSR is generated from the stimulation of specialized receptors called muscle spindle cells that are very sensitive to stretch. These small encapsulated receptors are located throughout skeletal muscles. The muscle spindle cell in conjunction with another receptor, the Golgi tendon organ, acts as a transducer that provides mechanoreceptive (proprioceptive) feedback information to the central nervous system concerning dynamic and passive muscle length and tension. The spindle cell receptors fire in response to rapid stretching from the tendon hammer tap, and this produces an initial afferent volley that in turn synapses with motor neurons of the anterior horn to reproduce the reflexive muscle contraction (Figure 8.6). The normal MSR is dependent on (1) an intact afferent limb (carried by group Ia sensory nerves), (2) a functional synapse in the spinal cord, (3) an
Classic Signs and Symptoms of Radiculopathy
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To thalamus, basal ganglia and cerebellum
Renshaw neuron
1
CJM T19 9
Tendon and muscle are stretched by reflex hammer
5
Muscle spindle cell fires 1A afferent fiber
The 1A afferent fiber synapses directly to an alpha-motoneuron inducing it to fire. The 1A afferent fiber also connects polysynaptically with antagonist musculature and inhibitory Renshaw neurons.
2
Agonist muscle reflexively contracts in response to stretch Antagonist muscle contracts to break the acceleration of agonist muscle.
FIGURE 8.6 The monosynaptic muscle stretch reflex. (Copyright J.M. True, D.C.)
TABLE 8.3 Grading of Muscle Stretch Reflexes, (Deep Tendon Reflexes) 0 1 2 3 4
Absent Diminished Average (normal) Exaggerated Brisk with clonus
intact alpha motor neuron, (4) an intact motor nerve, (5) a functional synapse at the myoneural junction, and (6) an adequately healthy muscle. The MSR is graded by the intensity of observed response on a scale of zero to four (Table 8.3). The most common deep tendon reflexes and methods of elicitation are listed in Table 8.4. The afferent limb of the reflex arc is more susceptible than the efferent limb with respect to sensitivity of the MSR to detect a disorder within any of the components of the reflex. Polyneuropathies cause significant suppression of the MSR. Reflexes are usually suppressed in moderate cases of
radiculopathy and are only absent in chronic or severe root compromise. The reflex response may still be elicited in severe monoradiculopathy because of the multisegmental innervation to most muscles. Accentuated reflexes occur with upper motor neuron lesions such as cord compression or other pyramidal tract disease.
8.4 PARESIS Motor weakness may occur with radiculopathy because the ventral nerve root is first to be compressed due to its vulnerable position in the lateral recess. The distal muscles supplied from the ventral root of one vertebral level are collectively called a myotome. Paresis of extremity muscles innervated by a given myotome helps to diagnostically localize the vertebral level of radiculopathy. In cases of moderate to severe radiculopathy, significant myotomal weakness is usually present. Functional capacity or performance muscle testing may be the most accurate noninvasive tests for quantifying a nerve root deficit. Needle electromyography (EMG), however, is the gold standard for quantifying and localizing radiculopathy,
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TABLE 8.4 Deep Tendon Reflexes Upper Extremity
Stimulation Site
Scapulohumeral C5–C6 Pectoral C5–T1 Biceps C5–C6 Brachioradialis C5–C6 Triceps C7–C8 Finger flexor C8–T1
Tendon tap on the medial border of the scapula Tendon tap on the proximal tendon insertion Tendon tap on the distal biceps tendon Tendon tap on the brachioradialis tendon Tendon tap on the distal triceps tendon Tendon tap on the examiner’s fingers resting on the palmer surface of the patient’s flexed fingers
Lower Extremity
Stimulation Site
Patellar L3–L4 Tendon tap on the infrapatellar quadriceps tendon Hamstring (biceps femoris) L4–S1 Tendon tap on the biceps femoris tendon proximal to fibular head insertion Achilles S1–S2 Tendon tap on the Achilles tendon just above the calcaneal insertion
especially in subacute presentations after 3 to 6 weeks post-onset. When evaluating muscular performance, the clinician must always attempt to fatigue those muscles that are innervated by a suspected level of radicular involvement. The smallest muscle groups innervated by a radicular level should be used as an initial screen for pathology. The viable motor units of the partially denervated larger muscles are more capable of compensation; consequently, these muscles may appear normal in strength during routine physical assessment. Paresis can be evaluated by resisted muscle contraction in the primary planes of joint movement. Paresis secondary to lumbar monoradiculopathy will often be subtle as a result of multisegmental innervation from adjacent radicular levels. For this reason, paresis occurs rather than paralysis. Paresis is typically first identified by the patient’s inability to complete a full arc of joint movement against resistance before complete fatigue and failure.
8.5 MUSCULAR ATROPHY Denervation due to nerve root compression secondary to disk herniation is reflected by atrophic changes of muscle fibers.7 Segmental denervation results in a loss of motor axons, producing a dispersed atrophic pattern in those muscles innervated by the spinal root level. The majority of skeletal muscles are innervated by more than one radicular level; therefore, isolated compromise of a single nerve root will not lead to extensive atrophy. Monoradiculopathies, themselves, are often incomplete, making it difficult to assess muscular wasting using circumferential limb measurements during the physical examination because the side-to-side difference may be relatively small (Figure 8.7). Muscular performance studies will contribute more to the objective assessment of a
Normal
Atrophic
FIGURE 8.7 Gastrocnemius muscle denervation atrophy associated with an S1 radiculopathy. (Copyright J.M. True, D.C.)
mild to moderate monoradicular syndrome and influence treatment decisions more than any other test. MR imaging of muscular atrophy due to denervation is currently only performed on an academic basis, but as protocols improve its use may become more common. Radicular compromise results in a loss of motor fibers from the dorsal primary rami, resulting in corresponding atrophy of the intrinsic paraspinal musculature. Sparing of the paraspinal intrinsic musculature is a differential consideration in the diagnosis of a peripheral nerve lesion. This pattern becomes important during needle EMG evaluation.
8.6 DYSAUTONOMIA AND TROPHIC CHANGES No sympathetic branches exit the spinal cord above the T2 and below the L2 radicular levels.8,9 The most common sites of monoradiculopathy are between C5–C8 and
Classic Signs and Symptoms of Radiculopathy
207
FIGURE 8.8 Sources of spinal pain producing radicular and pseudoradicular symptoms. Additional differential considerations include arachnoiditis, tumors, cysts, osteomyelitis, cancer, and osteoporosis. (Copyright J.M. True, D.C.)
L4–S1 and do not result in overt sympathetic compromise; therefore, the absence of sympathetic signs and symptoms, such as impaired perspiration or microvascular changes, constitutes an important differential consideration in the evaluation of plexus and peripheral nerve lesions. Moderate to severe nerve root presentations are often multiphasic and may contribute to complex regional pain syndromes. These sequelae include autonomic dysfunction, trophic changes, cutaneous and myalgic hyperalgesia, and a decrease in muscle tone. Peripheral nerve lesions result in a greater ablation of sympathetic function than radiculopathy. Palpation and observation of the skin may reveal the peau d’orange effect, pilomotor erection, sweating, trophic changes, tenderness, and hyperesthesia indicative of denervation supersensitivity (autonomic nervous system dysfunction). These signs may involve the dermatome, myotome, or sclerotome with disk derangement.8,10 A pilomotor effect secondary to a radiculopathy may become evident with exposure of the skin to cool air. This has been referred to as cutis anserina (“gooseflesh”) in the dermatomes of affected segmental levels secondary to cervical spondylosis and disk herniation.11
8.7 COMBINED PAIN SYNDROMES: RADICULAR AND VERTEBROGENIC PAIN The source of pain in nerve root syndromes is often complex. The patient’s pain may come from localized injury
to tissues surrounding the nerve root, such as the facet joint or the outer disk. Injury to intrinsic skeletal structures (periosteum, facet joints, ligaments, and spinal intrinsic muscles) produces a deep referral of diffuse pain, distal to the area of injury. This poorly localized pain is called vertebrogenic pain or sclerotomal pain. The referral of pain distal to the skeletal injury site is thought to occur from convergence of pain fibers on the same second-order neurons in the dorsal horn that project pain from both the injury location and the distal referral site. Nociceptive and sclerotogenous pain may coexist with a radicular pattern of pain to create a combined pain syndrome. Pain arising from intrinsic spinal motion segment structures often has a referral pattern that is diffuse and only generally localized to a segmental level. Intervertebral joint pain or a facet syndrome can produce a pseudoradicular syndrome, resulting in sclerotogenous or vertebrogenic referred pain. Examples of various spinal pathology capable of producing somatic referred pain are illustrated in Figure 8.8. Conventional localizing signs for nerve root involvement are late to appear and often absent in patients with vertebrogenic pain. Incomplete radicular nerve compression often leads to nonclassic findings on physical examination.12 Also, radicular pain is sometimes difficult to differentiate from sclerotogenous pain when multiple roots or different pain-producing structures are involved. For example, in a study of subjects with documented cervical spine disorders, Frykholm13 found that stimulation of the cervical dorsal root produced pain within a dermatomal distribution but that stimulation of the ventral
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Myotomal
Dermatomal
Sclerotomal
FIGURE 8.9 Monoradiculopathy may result in variable patterns of pain, dysesthesia, paresis, and autonomic disturbances due to the wide distribution of segmental innervation in the upper extremity. This example demonstrates segmental distribution of the C6 nerve root. (Copyright J.M. True, D.C.)
B
A
L1-2 C2-3
L2-3
C3-4
L3-4
C4-5 C5 -6 C8-T1
C6-7
L4-5 L5-S1
FIGURE 8.10 The sclerotomal or vertebrogenic referral pain pattern generated from irritation or injury to capsular and pericapsular tissues does not follow a dermatomal pattern. This diffuse pattern is variable between patients and may occur with or without radiculopathy. (A) Posterior cervical sclerotomal pattern. (B) Posterior lumbar sclerotomal pattern. (Copyright J.M. True, D.C.)
root produced a more diffuse pain in the neck, shoulder, and upper arm (Figure 8.9). Sensory involvement may produce a range of symptoms from mild paresthesia, to severe pain, or near complete dermatomal anesthesia. Studies by Smyth and Wright14 indicated that the length of the “pain band” is proportional to the size of the herniation imposed on the nerve root. An example of this is a small lumbar disk herniation that results in radiating pain to the thigh. A larger disk herniation with a greater degree of nerve root compression may result in radicular pain extending farther down the leg to the foot. Consideration should also be given to the likelihood that larger amounts of disk material produce larger inflammatory responses and thus contribute to greater symptom production. Vertebrogenic pain referring to the lower extremities from irritation to lumbar skeletal structures is
highly variable. Because of this variability, interpretation of the source of pain from the pattern of referral is very difficult. Vertebrogenic pain may refer to the inguinal region when the upper lumbar spine is the source of pain. In the lower lumbar spine, pain will extend into the buttock, over the greater trochanter, down the back of the thigh to the knee, and sometimes down the posterior or outer calf to the ankle. Rarely does sclerotogenous or referred pain reach the foot or toes.15 In the cervical spine, sclerotogenous pain may refer to pain in the back of the skull, the top of the shoulder, between the shoulder blades, and in the upper arm (Figure 8.10).16 Additionally, patients with diffuse chronic back pain may have associated intraspinal adhesions that contribute to pain production. As suggested by Parke and Watanabe,17 mechanical disruption of adhesions and the associated
Classic Signs and Symptoms of Radiculopathy
perivascular nociceptive fibers may be another source of discogenic pain. In that study, adhesions between the ventral dura and the posterior longitudinal ligament PLL were found in 16% of the specimens at the L3–L4 level, 40% were found at the L4–L5 level, and 36% were found at the L5–S1 level.17 Microscopic evaluation of the adhesions demonstrated disruption of neurovascular bundles containing branches of the sinuvertebral nerve where they coursed between the adherent dura and the posterior longitudinal ligament (PLL). The investigators assumed that forced separation of these adhesions during disk herniation and elevation of the PLL probably would amplify the degree and extent of nociceptor activation and contribute to low back pain.17 Additionally, dural connections between dorsal nerve roots and the intradural membrane have been documented.18 This may create abnormal tethering patterns in nerve roots exposed to compression and result in atypical radicular deficits or pain patterns.
8.7.1 RADICULOPATHIC AND VERTEBROGENIC SYMPTOMS RESEMBLING VISCERAL PAIN Cervicogenic angina or pseudoangina is a clinical entity that mimics angina pectoris associated with heart disease. Noncardiac angina results from irritation of the lower cervical roots (C6 and C7), which produces pectoralis pain. Several important factors differentiate pseudoangina from angina of cardiac origin. In pseudoangina, shock, fever, elevated sedimentation rate, and isoenzyme changes are not present, and the electrocardiogram is normal. Pseudoangina may be aggravated by neck movement,11 whereas cardiogenic angina is increased with exertion. Intercostal radicular pain will also produce pain in the anterior chest.19 Spinal pathology may mimic gallbladder disease, gastrointestinal disease, renal disease, and disturbances in bowel, bladder, gynecologic, or sexual function.20 Visceral disease typically does not produce segmental paresis or cause loss of deep tendon reflexes. Visceral referred pain is usually deep and diffuse, whereas primary somatic pain can be localized by mechanical provocation. The only exceptions are chronic visceral pain that has resulted in the production of trigger points or spasm and organic disease that directly compresses or infiltrates the nervous system. As a general rule of thumb, referred pain is not worsened by palpation.21
8.8 ASSESSMENT OF RADICULOPATHY The diagnosis of radiculopathy requires correlation of findings from different components of the evaluation process. These examination components may include the patient’s history, the clinical examination, blood testing, cerebrospinal fluid (CSF) assessment, electrodiagnostics, functional testing, and diagnostic imaging. Each of these components of the evaluation provides unique information
209
that helps confirm or reject diagnostic suspicions. The electrodiagnostic evaluation provides an objective physiologic measure of neurological integrity and function, whereas advanced imaging such as MRI provides excellent anatomic detail with reasonably high sensitivity but low specificity to nerve function and clinical symptoms. Functional assessment can evaluate segmental muscular performance more specifically as well as physical attributes such as power, endurance, fatigability, and closed kinetic chain strength. Functional assessment may also include quantitative testing such as functional capacity, coordination, and gait analysis. Utilization of the methods available can provide an invaluable, cost-effective measure of therapeutic outcome and prognostic insight for neurologic and related orthopedic recovery.
8.8.1 ELECTRODIAGNOSIS
AND
RADICULOPATHY
Physical compromise of the nerve root may result in structural nerve damage, impairment of intraneural blood flow, disrupted axonal transport, and the development of intraneural edema. These changes lead to neurophysiologic features, many of which can be quantified by electrodiagnostic testing. Some electrodiagnostic changes characteristically occur during the early phase of nerve injury, during the late or chronic phase, or may be limited to the recovery process. Pathology occurring at the same segmental level in different individuals can lead to diverse clinical and electrodiagnostic presentations due to anatomical variations within the nerve root and regional anatomy. Sensory presentations occur more frequently than sensorimotor or pure motor root involvement, thus accounting for some of the false-negative needle EMG studies in symptomatic patients. Most radiculopathies are relatively mild or incomplete, resulting in a small percentage of motor units being denervated. This limits the diagnostic utility of needle electromyography. 8.8.1.1 Needle Electromyographic Evaluation Electromyography is a classic and important electrodiagnostic method for assessing patients with suspected radiculopathy. The diagnosis of radiculopathy requires that abnormal EMG patterns be present in two or more extremity muscles innervated by two different peripheral nerves supplied by the same segmental level. Abnormal paraspinal potentials will help confirm the segmental level of radiculopathy (Table 8.5). Moderate to severe nerve root insult often results in some degree of motor axonopathy. Radiculopathy involving only the dorsal root is not detectable on needle EMG. Acute or subacute nerve injury is characterized during the EMG evaluation by the presence of muscle denervation supersensitivity.22 Denervation supersensitivity develops in part from the hypersensitization of muscle fibers to
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 8.5 EMG Indicators of Nerve Root Pathology • Abnormal EMG activity in two separate muscles with same segmental level innervation • Abnormal EMG activity in paraspinal muscles • Spontaneous activity: sharp waves, fibrillations, fasciculations • Prolonged insertional activity • Altered morphology of motor unit action potential Complex/dispersed, increased amplitude, irregular/prolonged • Poor recruitment • Rapid firing rate
acetylcholine and circulating neuropeptides. This produces spontaneous activation of motor units, which can be observed on needle EMG evaluation. Muscle denervation supersensitivity also leads to prolonged or increased needle insertional activity. Spontaneous activity, if reproducible in at least two muscles supplied by different nerves with the same segmental origin, indicates a high probability of radiculopathy or other lower motor neuron disease. These changes may not be detected in all patients with radiculopathy and also may not be evident until 2 to 6 weeks following acute nerve (motor axon) injury. Spontaneous potentials may manifest as fibrillations, positive sharp waves, fasciculations, and other discharge patterns. Fibrillation potentials are small-amplitude discharges with a characteristic diphasic or triphasic waveform. They fire in a regular temporal pattern originating from a single motor unit. Positive sharp waves are an abnormal discharge with a characteristic downward spike and slow return to baseline negativity (positivity is displayed as a downward deflection on EMG). Fasciculations refer to fine, irregular twitchings of muscle fiber groups that may be visible or palpable. During the clinical examination, fasciculations may be observed in a muscle at rest or may be evoked on muscle percussion. It should be noted that fibrillations, positive sharp waves, and fasciculations also occur in conditions other than radiculopathy. Chronic muscle denervation with incomplete reinnervation is characterized by reduced motor unit recruitment density, fast motor unit firing rate, and large motor units. This is represented by large, often polyphasic motor unit action potentials on EMG examination. Nerve root injury may be limited to disruption of the myelin and sparing of the axons, resulting in a normal EMG study with clinical evidence of intermittent dysesthesia and/or episodic muscle weakness. Injuries resulting in nerve demyelination will cause desychronization of nerve impulse propagation with diminishment of the corresponding muscle stretch reflexes. Paraspinal muscles should be evaluated with needle EMG in cases of suspected radiculopathy. The presence of abnormal paraspinal and extremity findings signifies radiculopathy, although the absence of paraspinal abnormalities
does not exclude radiculopathy. This absence may occur secondarily to the sparing of fibers of the primary dorsal rami or due to the earlier reinnervation of paraspinal muscles. Paraspinal abnormalities may also occur in the absence of abnormal extremity changes if nerve compromise is limited to the muscular territory innervated by the dorsal primary rami. The multifidus muscle is monosegmentally innervated; however, it lies beneath other muscle layers and therefore can be a challenge to isolate during EMG evaluation (Figure 8.11). The more accessible superficial paraspinal muscles are plurisegmentally innervated, making them less suitable for localizing nerve root involvement. Denervation results in a decreased number of motor units capable of contraction. In an effort to maintain muscular function, the central nervous system responds by causing the remaining motor units to fire at a faster rate. This may help improve muscle performance in the presence of denervation. However, the fast firing rates results in early fatigue of the intact motor unit, which becomes evident during muscle endurance (functional capacity) testing. 8.8.1.2 Muscles with Segmental Localizing Significance In the upper extremity, the rhomboid muscle groups only receive innervation from the C5 radicular level. The anterior deltoid is predominately innervated by C5. Motor innervation from the C7 level does not extend to the intrinsic hand muscles. The hand muscles are innervated by C8 and predominately T1 levels. Significant L5 contribution below the ankle is found in the extensor digitorum brevis (EDB) muscle. The EDB will often be atrophic with an ipsilateral chronic L5 radiculopathy. The gastrocnemius and soleus are important S1 muscles. There is no S2 representation within the paraspinal muscle groups. Therefore, S2-level EMG sampling must be performed in the gluteus maximus, the soleus muscle, and the intrinsic muscles of the foot (Table 8.6). 8.8.1.3 The Chronology of Electrophysiologic Abnormalities in Radiculopathy Spontaneous potentials in the form of fibrillations, sharp waves, and fasciculations may become evident within 2 to 6 weeks after radicular motor axonopathy. A number of electrophysiologic findings may be present from the onset of radicular insult. If needle EMG sampling is warranted during the initial 2- to 6-week window, the examiner should carefully evaluate the motor recruitment interval and look for early polyphasic motor unit action potentials (MUAPs). These are large MUAPs with multiple peaks that cross the baseline, changing phase or polarity five or more times. A reduced number of recruited
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211
Psoas major
Iliocostalis lumborum
Quadratus lumborum
Multifidus
Latissimus dorsi
Semispinalis lumborum
1.5-2cm
Longissimus thoracis
FIGURE 8.11 General location of needle electrode placement in the multifidus muscle of the lumbar spine. (Copyright J.M. True, D.C.)
TABLE 8.6 Minimal Screen Needle Electromyographic Examination Upper Extremity
Lower Extremity
Muscle
Root Level
Muscle
Root Level
Cervical paraspinal muscles Deltoid Biceps brachii Triceps Extensor carpi radialis Flexor carpi radialis Pronator teres Thenar muscles Dorsal interossei Hypothenar muscles
C4–T2 C5, C6 C5, C6 C6, C7, C8 C6, C7, C8 C6, C7, C8 C6, C7 C8, T1 C8, T1 C8, T1
Lumbosacral paraspinal muscles Quadriceps femoris Gluteus medius Tibialis anterior Peroneus longus Medial gastrocnemius Lateral gastrocnemius Extensor hallucis longus
L1–S1 L2, L3, L4 L4, L5, S1 L4, L5, S1 L5, S1 S1, S2 L5, S1, S2 L5, S1
Note: Additional muscles should be investigated should the diagnosis be unclear. In the paraspinal regions, the root level designations refer to the bony level that should be examined (i.e., the multifidi muscle layer). Source: Dumitru, D., Electrodiagnostic Medicine, Hanley & Belfus, Philadelphia, PA, 1995. With permission.
motor units secondary to axonopathy results in muscle weakness (paresis). In an attempt to improve functional strength, a good voluntary effort on the part of the patient will result in an increased firing frequency (rate) of intact motor units. This can be noted on needle EMG sampling, represented by an increased firing rate and reduced recruitment density. The early presence of polyphasic muscle unit potentials in the
absence of denervation supersensitivity may be due to ephaptic transmission from adjacent motor axons. Approximately 1 week after the onset of radicular injury, needle EMG sampling may reveal occasional positive (sharp) waves in the paraspinal muscles. Within 12 to 14 days, sharp waves may become evident in proximal limb muscles, and fibrillation potentials often begin to appear in the involved paraspinal muscle groups. A mild
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Distal peripheral muscles reinnervate last due to length of nerve segment
Paraspinals reinnervate first Temporal electromyographic signs of reinnervation
Normal MUAP
Polyphasic MUAP
Large dispersed Large MUAP MUAP following collateral reinnervation
FIGURE 8.12 Electrodiagnostic signs of muscle reinnervation. (Copyright J.M. True, D.C.)
radiculopathy may be missed on routine EMG sampling during this period. In ongoing radiculopathy, a complex electrophysiologic presentation develops over a time span of 18 to 21 weeks. During this period, electrophysiologic confirmation of radiculopathy is usually obvious. Denervation supersensitivity may be present with an associated increase in insertional activity and spontaneous potential frequency. Motor recruitment is reduced, and there is an increase in the firing pattern. Reinnervation patterns may become evident 4 to 6 weeks after radicular compromise. Reinnervation changes are dependent on axonal repair and collateral innervation at the level of the radiculopathy. EMG characteristics of reinnervation include large polyphasic MUAPs or MUAPs with multiple turns or serration. If incomplete reinnervation takes place, the total number of viable motor units within the muscle will be reduced, but the size of each viable motor unit will be larger. Consequently, the EMG will demonstrate large motor units with increased area, prolonged duration, and larger amplitude. Reinnervation contributes to reorganization of the compound motor unit action potential (CMAP). If recovery is nearly full with reinnervation, the CMAP will return to its pretraumatic normal morphologic appearance. Complete motor unit reorganization can take many months or even years (Figure 8.12).
8.8.1.4 Radiculopathy and Postsurgical EMG Findings Ascribing significance to postlaminectomy paraspinal EMG findings can be difficult. Spontaneous potentials in the form of fibrillations and sharp waves may be present on needle sampling of the paraspinal muscles in the region of the postsurgical scar. EMG findings at least 3 cm lateral to the scar may be diagnostic. Investigation of the levels innervated by the primary anterior rami is more important in the postsurgical assessment for reinnervation. A poor reinnervation pattern may be indicative of residual or recurrent radicular pathology. 8.8.1.5 Late Reflexes Late reflexes are electrical conduction responses that involve a central spinal cord-mediated component in production of the response. The most common are the Hreflex, F-wave, and the tendon reflex, or T-reflex. They have significant value in the investigation of radiculopathy because these tests are some of the few electrophysiologic tests that assess the proximal portion of the nerve root. Late reflexes are not able to specifically localize a proximal pathology because general demyelination plexopathy and peripheral entrapment may produce abnormal responses. The information derived from the late reflex is
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213
IVF
L4
The H-reflex is normal with an isolated lesion involving L4 or L5 roots, because the response is elicited predominately from S1 fibers in the posterior tibial nerve to the gastroc/soleus muscle. A delayed H-reflex would be expected when a lesion occurs in the S1 nerve root, sacral plexus or lower spinal cord.
L5
Lesion
Either lesion will produce a delayed H-reflex
S1 Lesion
Other differentials to consider with a delayed response are the presence of polyneuropathy, cauda equina involvement and root anomalies. H-reflex
FIGURE 8.13 The H-reflex as a diagnostic indicator of an S1-level lesion. (Copyright J.M. True, D.C.)
an indicator of pathology and is used in conjunction with other tests and clinical findings to help localize the source of the patient’s pathology. 8.8.1.5.1 H-reflex An H-reflex can be recorded from many muscles in the body; however, in only two muscles is the H-reflex reliably reproduced. These clinically relevant reflexes involve recording at the gastrocnemius–soleus muscles (S1), following stimulation of the posterior tibial nerve at the knee and recording at the flexor carpi radialis muscle (C6 and C7), following stimulation of the median nerve at the wrist. The depolarization response travels both up and down the nerve. The H-reflex is believed to represent a monosynaptic response to firing of large peripheral myelinated sensory axons.23 The tibial H-reflex is the electrophysiologic measurement of the Achilles muscle stretch reflex (MSR). When the wave of depolarization reaches the dorsal root, it enters the dorsal horn and makes an excitatory connection to alpha motor neurons, causing the motor neurons to fire. The response travels back down the nerve and stimulates the gastrocnemius-soleus muscle. This in turn is recorded with instrumentation. The amplitude of the H-reflex by itself is not a reliable indicator of pathology. The H-reflex latency is assessed by measuring from the onset of the stimulus to the initial waveform deviation from the baseline in any direction. The latency value of the H-reflex is the most reliable and reproducible indicator of pathology derived from this test (Figure 8.13). The normal H-reflex value is length dependent, thus taller patients have longer latencies. Generally, the top end latency value is below 32 ms. An H-reflex nomogram should be used in order to predict the normal latency taking into account leg length. An absolute unilateral latency delay of the H-reflex suggests compromise somewhere along its anatomic course and does not always indicate S1 radiculopathy. The finding must always be
correlated with the clinical presentation and the remaining electrodiagnostic findings. Side-to-side latency delays of greater than 1.0 to 1.5 msec (<60 years old) and greater than 1.8 msec (60 to 88 years old) remain valid criteria for S1 radiculopathy. An absent bilateral H-reflex in the elderly may be somewhat inconclusive because of agerelated degeneration. However, spinal stenosis and/or polyneuropathy are also seen with greater frequency in the symptomatic elderly patient and should be investigated when a delayed H-reflex is present. The amplitude should also be considered as a possible criterion for identifying pathology. An H-reflex amplitude decrease of greater than 50% on the involved side remains a possible indicator of pathology but does not represent an absolute criterion. Additional research into the clinical relevance of side-toside amplitude variation is still required. Contraction of the gastrocnemius-soleus complex during H-reflex assessment may magnify an otherwise-suppressed H-reflex amplitude. This maneuver should be performed bilaterally for accurate comparison. An H-reflex study can be used to evaluate for S1 radiculopathy when abnormal needle EMG findings are not evident or to differentiate an L5 radiculopathy from an S1 lesion.24 Moderate to severe abnormality of the tibial H-reflex often correlates with a reduction of the Achilles MSR, gastrocnemius–soleus paresis, and fatigability of repetitive plantar flexion against resistance. Follow-up Hreflex studies may be used to assess therapeutic outcome and rule out progressive radiculopathy. The H-reflex does not always parallel clinical improvement and will not always represent the extent of clinical recovery. 8.8.1.5.2 F-wave The F-wave is recorded in similar fashion to the H-reflex; however, the underlying mechanisms are different. The F-wave is not propagated through the dorsal horn or a monosynaptic reflex. The F-wave results from antidromic
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Ventral root compression
Multilevel stenosis, fibrotic entrapment and traction injuries
Central delay, alpha motoneuron hyperexcitability, and degeneration
Brachial plexus entrapment, trauma, lesions, and demyelinating plexopathies Peripheral mononeuropathy or polyneuropathies Carpal tunnel syndrome will produce a false delay in the median f-wave value. The delay is apparent in the initial motor response (distal latency).
FIGURE 8.14 Conditions that may alter the F-wave response. (Copyright J.M. True, D.C.)
activation of alpha motoneurons through the ventral roots (Figure 8.14), thus the F-wave response enters and exits the ventral roots. The second difference is the variability of the response. F-waves vary in amplitude, latency, and morphology, depending on the group of motoneurons activated with each electrical stimulus. Unlike the H-reflex, F-wave responses can usually be elicited from almost every muscle in the body. F-wave studies have limited utility in the evaluation of isolated radiculopathy, particularly when the radiculopathy is mild. This limitation is due to the underlying physiology of the response. Most muscles are innervated by more than one nerve root level; therefore, isolated injury to a given nerve root is usually partial or incomplete. Stimulation of a peripheral nerve will evoke antidromic firing of remaining motor axons at the involved level and corresponding alpha motor neurons at adjacent segmental levels, leading to preservation of the F-wave latency. Multiple F-wave indices and parameters have been proposed in an attempt to increase sensitivity and specificity of the test.25-27 Various parameters include F-wave minimum/maximum ratio, F-wave average latency (mean), Fwave amplitude, chronodispersion, F-wave duration, and Fwave persistence. F-wave amplitude should be less than 5% of the distal CMAP amplitude response.28 Chronodispersion refers to the spread between the minimum and maximum Fwave values. F-wave persistence refers to the F-wave response to peripheral nerve stimulation. Normally, stimulation of the peripheral nerve elicits an F-wave approximately 90 to 100% of the time,29 following
a minimum of 8 to 15 stimulations used for each nerve studied. If the F-wave occurs less frequently, this is referred to as reduced or poor persistence and is suggestive of peripheral axonopathy and/or anterior horn disease. The impairment of F-wave persistence may be accompanied by diminished F-wave amplitude, further suggesting a loss of viable motor axons or alpha motor neurons along the neuroaxis. F-wave studies are most reliable when in the presence of an ipsilateral polyradiculopathy involving two or more contiguous levels (Figure 8.15). The F-wave stimulus enters the spinal cord at multiple nerve root levels; thus, multiple segmental levels supplying a given muscle will be compromised. The most frequent F-response abnormality in L5–S1 radiculopathies is a prolonged maximum/minimum latency range rather than abnormalities of minimal latency or persistence.26,27 With chronic unilateral pathology, the difference in interside latency is the most reliable indicator of pathology. 8.8.1.5.3 T-reflex The tendon reflex study is accomplished by stimulating a tendon with a specially designed reflex hammer that simultaneously triggers recording of the electrical reflex contraction of the contracting muscle.30 The tendon percussion activates spindle cells in the muscle belly to fire 1a afferents to the dorsal horn which in turn synapse with ipsilateral alpha motor neurons, which produce the classic efferent leg of the monosynaptic response. It is interesting that the tendon reflex has a longer central latency than the H-reflex, which is also considered to be the equivalent to
Classic Signs and Symptoms of Radiculopathy
TIME(MS)
215
of demyelination. Isolated latency prolongation usually represents an abnormal state of myelin causing desynchronization of nerve fiber depolarization or a loss of fastconducting, large-diameter myelinated axons. A reduction of evoked waveform amplitude and area is most consistent with axonopathy. Some lesions such as nerve root injury will contribute to varying degrees of combined demyelination and axonopathy. Axonopathy generally corresponds to more profound clinical deficits.
64.17 74.58
F waves
0
50
100
FIGURE 8.15 F-wave changes in polyradiculopathy secondary to multilevel lateral stenosis. A significant delay is present in the posterior tibial nerve. Normal values are below 56 ms. This patient was in the 64 to 74 ms range.
the monosynaptic reflex response.31 Thus, the current understanding of the reflex and synaptic connections occurring with the monosynaptic reflex probably needs revision.30 The T-reflex is not commonly used in clinical practice, probably because of the lack of clinical research and the relative unavailability of a tendon trigger hammer and appropriate software in the commercial electrodiagnostic instrument market. Most of the clinically applicable research is based on the T-reflex and its use in myelopathy evaluation. At the present, clinical protocols for the Treflex in diagnosis of radiculopathy are scant; however, its use in cervical myelopathy is promising. In one study, the T-reflex demonstrated a higher sensitivity for detecting pathology than EMG. The researchers found pathological tendon reflexes in 73.1% of patients with cervical myelopathy, while EMG, which was the next more effective method, was positive in 38.5% of cases. Eight pathologically delayed T-waves were recorded from muscles with clinically normal or even exaggerated reflexes.32 8.8.1.6 Nerve Conduction Studies Nerve conduction studies (NCS) or nerve conduction velocity (NCV) primarily evaluate large myelinated nerve fibers. Electrical stimulation is delivered to a nerve at various locations along the course of the nerve and the response is recorded from a corresponding muscle in motor studies or from a distant portion of the nerve in sensory studies. The recorded electrophysiological response helps objectively document the pathophysiological process, such as the extent of axonal loss or degree
8.8.1.6.1 Motor nerve conduction studies The CMAP refers to measurement of the electrical response that is recorded from a selected muscle after peripheral nerve or nerve root stimulation (Figure 8.16). The motor neuron cell body lies proximal to the nerve root. Thus, radiculopathy due to any cause can lead to peripheral axonopathy and Wallerian degeneration. Diminished CMAP amplitude is consistent with a loss of motor axons. With mild single-level radiculopathy, there may be no detectable change in the CMAP due to the significant number of remaining motor axons supplying the muscle being tested. With moderate to severe isolated radiculopathy, a corresponding detectable decrease in the CMAP may occur, representing a greater loss of contributing motor axons. Adjacent polyradiculopathy such as that which occurs secondary to spinal stenosis, diabetes, an expansile lesion, or disk herniation is more likely to lead to reduced CMAP amplitude or an absent CMAP response.33 Reduced amplitude of the CMAP may be seen as early as 1 to 6 weeks after the onset of severe multilevel radicular injury (Figure 8.17). 8.8.1.6.2 Sensory nerve conduction studies The sensory nerve action potential (SNAP) refers to measurement of the electrical response recorded over a nerve distant to the site of electrical stimulation. Like CMAP, the speed of nerve conduction and the magnitude of the response can be recorded after electrical stimulation. The sensory nerve cell body resides within the dorsal root ganglion (DRG), which usually lies within the intervertebral foramen distal to the site of nerve root injury within the spinal canal or lateral recess. This anatomic relationship contributes to sparing of the peripheral sensory axons from Wallerian degeneration with compressive radiculopathy; therefore, the SNAP findings are usually normal. In rare cases, the DRG lies in a more proximal location such as the lateral recess, rendering the sensory cell bodies of the peripheral nerve vulnerable to injury with radiculopathy. DRG compromise injury will contribute to a reduction of SNAP amplitude with a loss of axons and/or conduction block. This is not always detectable for the same reasons a CMAP amplitude reduction is not always measurable. A number of sensory studies can be considered in the evaluation of radiculopathy. For example,
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Determination of median nerve conduction velocity Direction of depolarization
Distal stimulation Reference Recording S1
Median motor NCV recorded at Abductor Pollicis Brevis
-+
-+
S2 Proximal stimulation Distance = 36cm
S2
Amplitude 10mv
S1
Amplitude 10mv
4.0 ms Latency
10 ms Latency
Distance divided by difference in latency (S2-S1) = Conduction velocity (Cv) Distance = 36cm or .36 meters (D) S2 (10.0ms) - S1 (4.0ms) = 6ms or .006 sec (∆T)
D = Cv T
.36 meters .006 seconds = 60 m/s
FIGURE 8.16 In monoradiculopathy, abnormalities of nerve conduction are typically only seen with moderate to severe nerve root lesions causing significant axonal loss. (Copyright J.M. True, D.C.)
Action Potential Morphology Lesion location
E D
A
CMAP Distal
SNAP Distal
Normal
Ventral root Reduced amplitude
A
Dorsal root ganglion
C
B
Dorsal root (preganglionic)
C
Ventral-dorsal root compromise
Normal
Normal
Normal Reduced amplitude
B
D E
Single level spinal nerve
Multi-level spinal nerves
Reduced amplitude
Reduced amplitude
Reduced amplitude
Reduced amplitude
FIGURE 8.17 Peripheral sensory and motor nerve conduction changes associated with neurological compromise at the level of the spine. (Copyright J.M. True, D.C.)
preservation of the sural nerve action potential can help to differentiate lumbosacral radiculopathy from sciatic mononeuropathy and/or polyneuropathy. Generalized
SNAP abnormalities are suggestive of peripheral nerve disease (polyneuropathy). Radiculopathy and peripheral neuropathy may coexist.
Classic Signs and Symptoms of Radiculopathy
8.8.1.7 Somatosensory and Dermatomal Evoked Potentials In general, the conventional somatosensory evoked potential (SEP or SSEP) study involves electrical stimulation of the largest myelinated fibers in the periphery and recording the evoked response from specific locations along the nerve pathway to the cortex. Evoked potential testing is valuable for the evaluation of persistent sensory symptoms. The sensory response can be recorded along the ascending pathways in the spine and cortex. The SEP study enables the examiner to evaluate nerves and pathways not otherwise accessible to conventional testing such as EMG and NCV. The distal peripheral mixed nerves of the brachial and lumbosacral plexuses are easy to depolarize and evoke an electrical potential in response to electrical stimulation. These electrical potentials travel to the cord and contralateral cortex within predictable time frames or latencies. There are a number of theoretical advantages of utilizing SEPs for the evaluation of suspected radiculopathy. Early radiculopathy often manifests with sensory disturbances in the absence of motor or reflexive change. Needle electromyography does not provide any direct measurement of indication for sensory fiber integrity within the nerve root. Sensory nerve conduction studies in most cases do not provide any direct measurement of sensory integrity proximal to the dorsal root and thus fail to detect nerve root (sensory) injury within the spinal canal, lateral recess, and proximal portion of the neuroforamen. The H-reflex provides a measurement of sensory and motor integrity but is limited to C6–C7 and S1 root assessment. The performance of SEPs is based on the premise that sensory axonopathy, sensory axon demyelination, or conduction block within the nerve root should alter measurable parameters of conduction such as the latency, amplitude, and morphology of the evoked waveform. The potential measurement of sensory radiculopathy is not limited by the 7- to 14-day delay often required for needle electromyographic diagnosis. Considerable controversy surrounds the use of SEPs in the evaluation of radiculopathy. The sensitivity and specificity of the SEP are often low in single-root radiculopathy; however, sensitivity for detecting a problem improves with multiroot pathology, chronic root compression, and myeloradiculopathy. The specificity for radiculopathy is low, because numerous conditions also produce an abnormal response (e.g., plexopathy, MS, and cord compression). The latency of the SEP reflects a long peripheral and central course of nerve transmission (several meters) compared with the relatively small distance associated with nerve root lesions (a few millimeters). Focal conduction block or demyelination insufficient to impact the overall latency may be undetected with conventional SEP protocols.34 Mild sensory axonopathy may be masked by central amplification, which occurs within
217
the subcortical region of the brain, possibly at the level of the thalamus. Central neuroplastic changes, which likely occur with chronic radiculopathy, may also lead to central amplification secondary to cortical overlap of dermatomal responses. Relatively wide normal standards of deviation for amplitude and latency measurements render the diagnosis of radiculopathy by SEP somewhat challenging. The nerve root may be assessed using mixed nerve stimulation, segmental stimulation, and/or dermatomal stimulation (DSEP) (Figure 8.18). 8.8.1.7.1 Mixed nerve stimulation Mixed nerve stimulation requires the stimulation of a mixed peripheral nerve (sensory and motor) associated with multilevel nerve root contributions. This method is of little diagnostic significance in the evaluation of unisegmental radiculopathy. It can sometimes be helpful for the evaluation of adjoining polyradiculopathy secondary to spinal stenosis. Numerous factors influence mixed nerve SEP responses such as a peripheral nerve lesion, polyneuropathy, myelopathy, or a supratentorial lesion along the subserving pathways. 8.8.1.7.2 Dermatomal stimulation Applying repetitive cutaneous stimulation within a designated single dermatomal predominant region is referred to as a dermatomal evoked potential (DEP) study. Recording over the spine and cortical regions can be performed, although the spinal potentials are often too small to reproduce. Assessment is therefore usually limited to the latency of the response recorded from periphery to cortex. Some controversy remains over the sensitivity of DEPs in detecting root level pathology, with some studies reporting misleading or doubtful benefits33,35,36 and other studies demonstrating equal or higher sensitivity than EMG.37-41 For example, one small study found correlation of DEP abnormalities and radiculopathy in up to 83.3% of subjects studied, whereas EMG findings correlated with the level of radiculopathy in about 62.5% of the same subjects.39 DEPs have been reported to be the only noninvasive test that can be used to demonstrate radicular compromise at all levels of the spine, including the intercostal root levels.41 The DEP findings should be compared to normal standards for the tested root level and should also be evaluated relative to adjacent and contralateral nerve root responses. A delayed response is not specific for radiculopathy as other conditions such as peripheral nerve injury, diffuse plexopathy, myelopathy, or cortical disease, also produce abnormal DEPs (Figure 8.19). Criteria for an abnormal study include absolute latency prolongation, relative side-to-side latency asymmetry greater than 3.0 msec, and relative side-to-side amplitude decrease greater than 50%. The DEP morphology will vary considerably, although prolonged duration should be correlated with other more acceptable criteria.
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Differential considerations in somatosensory evoked potential interpretation Decreased amplitude
1. C Central pathway pa pathology
Normal interpeak latencies
Desynchronized or absent response
1.
2.
Erbs
Erbs
N13 N13 Prolonged interpeak latencies
2. Root lesion
N19
N19
Central pathway disorders such as multiple sclerosis or myelopathy have the most pronounced effects on SSEP latencies and morphology. 3. Focal plexus demyelination
Mixed nerve SSEP interpeak and absolute latencies are usually normal with single root lesions.
3. 4. Distal peripheral lesion Prolonged interpeak latencies
Erbs Patients with peripheral focal lesions typically demonstrate normal SSEP studies. However, prolonged absolute latencies with normal interpeak latencies may occur
N13 N19
Erbs N13 N19
Prolonged interpeak latencies Erbs - N13 and Erbs - N19. Absolute values for individual peaks may be within normal ranges, However side to side asymmetries may be present.
Normal interpeaks 4.
Temporal dispersion
Decreased amplitude
Median SSEP
C5
Ulnar SSEP
C6
C5-C6 C8
C7
Common stimulation sites for upper extremity somatosensory and dermatomal evoked potentials.
FIGURE 8.18 Upper extremity somatosensory evoked potential findings relative to lesion location. (Copyright J.M. True, D.C.)
8.8.2 RADICULOPATHY AND FUNCTIONAL CAPACITY EVALUATION Diseases or disorders that compromise the spinal nerve root can result in segmental muscle impairment secondary to skeletal muscle denervation, and loss of muscle kinesthetic sense. In radiculopathy involving an extremity, there
is often a loss of strength, power, endurance, and muscular control. Extremity musculoskeletal impairment has a strong relationship to overall function, particularly in older adults. Functional capacity evaluation (FCE) refers to the assessment of an individual’s physical performance for the purpose of quantifying various parameters, such as
Classic Signs and Symptoms of Radiculopathy
219
L4
B
A
P45
Right side P37 P45 P37
Left side
L4 DEP
C
R- P37 = 45.78ms
0
L- P37 = 53.43ms
50
100
FIGURE 8.19 (A) Lateral radiograph of the lumbar spine depicting a grade II spondylolytic spondylolisthesis at L4–L5 in a patient with left L4 radiculopathy. (B) Sagittal lumbar MR acquisition of the same patient. Note desiccation of the L4–L5 intervertebral disk and anterolisthesis of L4 upon L5 which tractions the thecal sac and distorts the neural foramen. (C) The above lumbar DEP findings demonstrate a significant left-sided latency delay involving the L4 root level associated with the grade II spondylolisthesis at L4–L5 referred to in (A) and (B).
range of motion, endurance, strength, power, and coordination. It is used to help identify location of injury, degree of injury, the capacity and limitations of physical potential. The goals of the FCE include the following: to document the extent of deficit or functional level and to develop a rehabilitative plan around the detected functional deficits. It is imperative to evaluate a patient’s progress based upon his or her own functional baseline rather than spending too much time comparing to “normal” charts. Published
comparative data may be difficult to apply due to inconsistent variables and unique attributes of the patient’s injury and coexistent pathology. FCE parameters that may be measured include: 1. 2. 3. 4.
Range of motion Strength Endurance Aerobic capacity
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
5. Functional unit integration (complex task): failure to perform a task may occur due to a breakdown in one or more elements or segments of the task or because all elements are functioning but not in a uniform or time-dependent way. 6. Psychosocial testing 7. Effort validity (consistency) 8. Sensibility 9. Coordination 10. Compensatory potential 11. Functional pain threshold 12. Reaction time 13. Kinesthesia/barognosis Functional evaluation can be obtained by clinical exam or in combination with a dynamometer capable of performing isometric, isokinetic (concentric and eccentric), and isotonic measurements. Dynamometry can be extremely accurate when adequate calibration, gravity correction, and patient positioning are standardized and recorded. Various software-interpreted protocols are available that will assess consistency of effort between testing trials. There are a variety of specialty attachments for isokinetic and isometric dynamometers that test specific joint functions, such as plantar flexion and dorsiflexion strength or grip and pinch strength. These attachments can be used to create unique/custom test conditions. Examples of attachments include ball knobs for closed hand grip activity (C7-T1), flat knobs for open grasp activities (C7-T1), pinch and grip attachments (C7-8), shoulder flexion and extension attachments (C5-6), elbow flexion (C5-6) and extension (C7-8) attachments, and wrist flexion (C7) and extension (C6) attachments. More unique attachments for the dynamometer include screwdriver handles, ladder box for rope pulling, stirrup handles to test push and pull activities, a turret handle to simulate machine operation, and a steering wheel to assess an important ADL. Quantitative dynamometry can be used to evaluate moments of peak acceleration and deceleration in denervated muscles for assessment of joint stability. Maximum torque, velocity, and power can be measured. Induced acceleration analysis (IAA) can be used in the evaluation of gait to evaluate the contributions of the hip, knee, and ankle to the gait cycle. Joints that are commonly tested using dynamometry include the ankle, knee, hip, trunk, shoulder, elbow, and wrist. A number of manufacturers make available functional balance testing platforms, which can help assess the consequences of altered lower extremity proprioception and lower extremity weakness. Static and dynamic force platforms can be used to evaluate postural stability and sit-tostand function. Denervation-related fatigue of distal postural muscles may cause increased ankle instability, therefore compromising balance. Joint angular motions during repetitive sit-to-stand maneuvers can be quantified to help
TABLE 8.7 Imaging Procedures for Radiculopathy Magnetic resonance imaging (MRI) with multiple acquisition techniques Spiral computed tomography (CT) MR myelography Contrast MRI Myelogram/CT Plain film X-rays Isotope bone scan Myelogram
assess hip and knee extensor function in individuals with mid-lumbar radiculopathy.
8.8.3 MRI OF DISK, NERVE ROOT, VENOUS PLEXUS, AND MUSCLE 8.8.3.1 Disk Herniation Magnetic resonance imaging is the preferred imaging modality for suspected soft-tissue compression of the nerve root. The hierarchy of imaging techniques used for clinical correlation of radiculopathy is shown in Table 8.7. Intervertebral disk herniations are usually visualized on sagittal and axial MR images. However, techniques that use a 3–5-mm slice thickness may occasionally miss a small disk lesion. The MR evaluation of small disk herniations in the IVF may require the use of three-dimensional volume sequences with partitions of 2 mm or less and/or reconstruction in other planes.42 Sagittal imaging is important in the evaluation of deformities of the thecal sac. Sagittal views visualize the posterior annular fibers and may demonstrate discontinuity not otherwise verified on axial views. Sagittal views also provide a composite look at the IVF in the lumbar spine. On these views, it is often possible to see the exiting nerve root in cross-section. In the presence of a lateral disk, the intraforaminal relationship between the nerve root and disk can often be appreciated. Axial slices are preferable if there is displacement of the epidural fat without an obvious disk. The morphologic appearance and migratory path of a disk herniation are often best noted on contiguous axial images. Careful correlative review of the sagittal studies should follow (Figure 8.20). The PLL is an important anatomic landmark in the MR evaluation of disk lesions. The outer annulus–PLL complex can usually be seen as an area of decreased signal relative to the inner annulus–nucleus pulposus. This characteristic low signal of the interface between the posterior annular fibers and the PLL is best visualized on gradient echo images. This difference of tissue interface helps in characterizing the type of herniation (bulge, herniation, extrusion, or free fragment). Extruded nuclear material can sometimes be seen associated with high signal on gradient echo studies.43 T2-weighted MR scans help define annular
Classic Signs and Symptoms of Radiculopathy
1
221
2
FIGURE 8.20A Examples of cervical disk pathology resulting in root compression. (1) Right paracentral disk herniation at C6-7 compressing the exiting nerve root. (T2 gradient medic technique through the C6-7 level.) (Courtesy Joseph Kozlowski, M.D.) (2) Right paracentral spinal cord compression and exiting right nerve root impingement secondary to the disk–osteophyte complex. (Axial gradient echo T2-weighted image through the C3-C4 level.) (Courtesy Ronald Landau, M.D.)
disruption without herniation by the identification of highsignal material within the annulus.44 T2-weighted images may demonstrate an area of increased signal intensity within the annulus fibrosus at the site of the acute tear.45 This has been termed a high-intensity zone (HIZ) and is thought to represent an area of secondary inflammation following annular tear. The lumbar disk HIZ observed on MRI in patients with low back pain has been shown to correlate with painful internal disk disruption in over 80% of the cases.46-48 Even though the HIZ is commonly observed in patients with low back and leg pain, there is some debate as to the overall sensitivity of the HIZ sign for annular tear or predicting back pain and its clinical significance.49,50 Additionally, annular tears may be difficult to visualize if MR resolution or scan slices are not optimal. The MR differential considerations in the diagnosis of intervertebral disk herniation or extrusion include both normal and pathologic variants. Examples of common normal variants include a large nerve root sleeve (referred to as dural ectasia), conjoined nerve roots, approximated nerve roots, and perineural cysts. Examples of common pathologic disorders confused with disk herniations include epidural and/or intradural fibrosis, tumors (e.g., neurofibromas or schwannomas), and bony exostosis. MR imaging with gadolinium (Gd-DTPA) can occasionally be useful in the evaluation of disk herniation and the differentiation of epidural scar tissue. A large focal disk herniation compressing the adjacent epidural venous plexus may produce high signal intensity in the epidural venous structures surrounding the disk space.42 8.8.3.2 Contrast Enhancement of the Spinal Nerve Root Capillary leakage within the spinal nerve root is occasionally demonstrated with Gd-DTPA enhancement. Enhancement
of the nerve root is classifiable into three categories: grade 0 (no enhancement), grade 1 (enhancement restricted to a focal region in the dural sleeve), and grade 2 (diffuse and homogeneous enhancement).51 Enhancement of the compromised nerve root and sleeve typically occurs along the caudal edge of the disk herniation. MR imaging with GdDTPA may also demonstrate enhancement of the symptomatic nerve roots in a patient with a disk herniation. The degree of enhancement reflects the severity of sciatica.51 Jinkins52 and Jinkins and Runge53 concluded that enhancement of the compromised blood–nerve barrier serves as a marker for nerve root pathology in the unoperated lumbosacral spine. 8.8.3.3 Enhancement of the Epidural Venous Plexus Compression of the epidural venous plexus is common with paracentral or central intervertebral disk herniations. Consequently, compression of the epidural plexus raises intravenous pressure in the tributaries around the site of compression and, in severe cases, increases the intravenous pressure within Batson’s system, including subchondral tributaries. The use of Gd-DTPA contrast during the MR evaluation can aid indirectly in the evaluation of epidural venous plexus compression. Enhancement of the epidural veins can occur for up to 40 minutes after administration of the agent. If a compressive mass effect on the epidural venous plexus occurs, it may be accompanied by adjacent venous dilatation and venous stasis with pooling.53 This pooling suggests possible increased venous pressure within the intraneural environment.42 A common focal region for enhancement is seen within the basivertebral vein as it enters the midposterior
222
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
1
2
3
4
FIGURE 8.20B Examples of lumbar disk herniation resulting in root compression. (1 and 2) Right lateral disk extrusion producing displacement and compression of the S1 root. (Axial gradient echo images through the L5-S1 level.) (3 and 4). Parasagittal images of the lumbar spine demonstrating disk extrusion with displacement of the descending nerve root. (Parasagittal T2 weighted images of the lumbar spine.)
aspect of the vertebral body. This is often quite evident as bright signal against the bone and is usually considered a normal variant. 8.8.3.4 MRI of Muscular Atrophy MR imaging of end organ (muscular) atrophy is seldom performed because it is considered equivocal or “academic” at best. In cases of a moderate to severe radiculopathy or polyradiculopathy, a correlative region of paraspinal and
extremity muscular atrophy will often be evident on MR images. The axial image may demonstrate increased marbling, a loss of muscular volume, and decreased T2-weighted signal intensity. The MR findings can be correlated with needle electromyographic sampling to help confirm whether the paraspinal atrophy is based on disuse or denervation. Magnetic resonance protocols for muscular compartment cross-sectional studies and atrophic assessment need to be refined.54,55 These MR studies serve as an adjunct
Classic Signs and Symptoms of Radiculopathy
223
C1
Motor: Head flexion and rotation Lateral flexion Fixation and steadying the neck Extension Clinical exam: Flexion—chin on chest, active, passive, against resistance Extension—chin on chest, active, passive, against resistance Rotation—chin on chest, active, passive, against resistance Lateral flexion—chin on chest, active, passive, against resistance Observe contraction Muscles, palpate for size and cervical power* Reflexes: Jaw jerk—5th cranial nerve (separate lesion above and below foramen magnum) Head retraction reflex—5th cranial nerve 8 cervical nerves: one appraises only weakness of movements, not individual muscles *Note: all cervical muscles supplied by branches of all 8 cervical nerves
FIGURE 8.21 Clinical findings in the evaluation of the C1 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 21. With permission.)
for the correlation of the MR radicular lesion, nerve root level, and end organ (muscular) involvement.
8.9 CERVICAL MONORADICULOPATHY SYNDROMES
and cervicis, multifidi, intertransversari, rotatores, semispinalis, and infrahyoid muscles. As a result of the multilevel innervation of most of these muscles, an isolated C1 motor presentation is subtle and therefore clinically difficult to identify (Figure 8.21).56
8.9.1 C1 RADICULOPATHY
8.9.2 C2 RADICULOPATHY
The C1 nerve root does not contain a dorsal sensory contribution. Accordingly, a lesion involving the C1 nerve root only produces a motor deficit. The C1 nerve root innervates many of the muscles that support the head, stabilize the neck, and assist in neck flexion and extension. These muscles in the suboccipital region include the longus capiti, oblique capiti, rectus capiti, longissimus capitis
The C2 nerve root has both sensory and motor components. The sensory signs and symptoms of a C2 radiculopathy are typically localized to the posterior scalp region. This pattern of loss is best localized with a careful pinprick evaluation. The levels of muscle innervation from the C2 level are similar to those from the C1 level. The differential identification of a C2 monoradiculopathy is best performed
224
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 8.8 Common Clinical Findings in Cervical Radiculopathy Vertebral Level
Root
Pain Pattern (Sclerotogenous)
Sensory Paresthesia and Deficits
Motor Weakness and Atrophy
Relevant Reflex
Supraclavicular region Clavicular region Anterior aspect of shoulder Lateral forearm and thumb Dorsum of arm and forearm; dorsal and palmar aspect of 2nd and 3rd digits Medial arm; dorsal and palmar aspect of 4th and 5th digits
Trapezius Supraspinatus, deltoid biceps
None Biceps
Biceps, brachioradialis Triceps, finger extensors
Biceps, brachioradialis Triceps
Finger flexors, grip
Flexor digitorum
C3–C4 C4–C5
C4 C5
Back of neck, top of shoulder Top of shoulder, proximal arm
C5–C6 C6–C7
C6 C7
Anterior arm, scapula Posterior arm and wrist
C7–T1
C8
Elbow, hand, and wrist
with sensory studies. The C2 nerve root contributes to innervation of the sternocleidomastoid muscles through the spinal accessory nerve and therefore contributes to head rotation and flexion. Sternocleidomastoid muscle paresis will not be obvious with an isolated C2 presentation (Figure 8.22).56
8.9.3 C3 RADICULOPATHY It is unusual to have a C3 radiculopathy secondary to a disk lesion or spondylosis (Figure 8.23). Intraforaminal stenosis rarely occurs at the C2–C3 level. This is because movement is limited at the C2–C3 level. This reduced movement decreases the risk of disk injuries and chronic degenerative changes, which are more prevalent in the lower cervical spine (Table 8.8). Paresis after C3 nerve root injury is clinically difficult to detect because of plurisegmental innervation. Diaphragmatic weakness may be present if the C3 contribution to diaphragm innervation is significant. A C3 radiculopathy may produce mild paresis of the scalene and levator scapulae muscles of the neck. Scalene paresis and subsequent first and second rib pathomechanics may increase susceptibility to neurogenic thoracic outlet syndrome. The patient with C3 radiculopathy may demonstrate diminished sensation to pin prick in the occipital region, the posterior auricular regions, or the upper neck. A small study demonstrated that most patients with C2–C3 herniation have central herniations. When the herniation is large enough to compress the cord, variable radicular symptoms usually predominate over myelopathic symptoms. The presentation may be characterized by suboccipital pain, loss of hand dexterity, and paresthesia over the face and unilateral lateral arm.57 Headaches are also observed with upper cervical pathomechanics. Headaches of cervical origin are thought to result from irritation of roots C1, C2, or C3. Convergence of C3-level pain fibers with secondorder neurons of the descending sensory tract of cranial nerve V is one proposed mechanism for the referred pain of vertebrogenic headaches.58
8.9.4 C4 RADICULOPATHY C4 radiculopathy is rare, but it is more common than the more rostral radiculopathies. C4 radiculopathies often contribute to otherwise unexplained neck and shoulder pain. As with C3 radiculopathy, motor deficit with an isolated C4 radiculopathy is difficult to detect because of the multisegmental innervation of the cervical musculature. The C4 level contributes to innervation of the diaphragm. Declining serial pulmonary function studies or delayed phrenic nerve conduction latencies may indicate diaphragmatic paresis secondary to C3 or C4 radiculopathy. Numbness is not commonly reported with a C4 radiculopathy. When C4 radiculopathy occurs, it is often associated with pain at the base of the neck extending into the middle and posterior shoulder regions to the level of the scapulae. Cervical hyperextension may induce pain or magnify existing pain to the shoulder. A reproducible decrease in paresthesia or dysesthesia in the shoulder region after upper cervical anteflexion suggests a radiculopathic contribution. C4 radiculopathy may result in acute, subacute, or chronic scalenius anticus and levator scapulae myofasciitis. This pattern of muscle paresis may contribute to thoracic outlet entrapment (Figure 8.24). Needle EMG is of limited utility in the diagnosis of a C4 radiculopathy. Cervical MRI and myelography are the best methods of confirmation. The diagnosis of a C4 radiculopathy requires proper correlation among diagnostic imaging, pulmonary function measurements, phrenic nerve conduction studies, and the dermatomal sensory deficit evaluation.
8.9.5 C5 RADICULOPATHY The primary C5 sensory distribution is across the top of the shoulder to a midpoint along the lateral aspect of the upper arm. This is sometimes referred to as the epaulet pattern. The patient with a C5 radiculopathy often complains of localized shoulder pain and numbness that may be misdiagnosed as a mechanical, inflammatory, or internal
Classic Signs and Symptoms of Radiculopathy
225
C2
Motor: Trapezius: extension and pull to one side (Cr XI) Sternocleidomastoid-Flex and rotate (Cr XI) Head flexion and rotation Lateral Flexion Fixation and steadying neck Extension Clinical exam: Extend neck Draw to one side Flexion Extension Lateral Flexion Rotation Shrug Active Passive Against resistance Observe muscle contraction Palpate for size and power, tone, volume, contour, compare with opposite side, may be slight scapular droop and winging Trapezius function Torticollis present Reflexes: Sternocleidomastoid reflex—tap muscle at its clavicular end, muscle contracts. (Innervated Cr XI and C1, C2C3) Sensory: Posterior scalp Anterolateral neck Posterior anterior and inferior external ear *Note: all cervical muscles supplied by branches of all 8 cervical nerves
FIGURE 8.22 Clinical findings in the evaluation of the C2 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 23. With permission.)
derangement of the shoulder. Pain may also radiate into the medial border of the scapula or top of the shoulder. A C5 radiculopathy can mimic subacromial impingement of the rotator cuff as well as induce subacromial impingement from altered shoulder muscle contraction. Paresis of the major and minor rhomboid muscles impairs the
patient’s capacity for elevation, medial adduction, and medial rotation of the scapula. Denervation of the shoulder girdle and rotator cuff will produce subacromial pathomechanics and subsequent subacromial tendinopathy. Hence, C5 radiculopathy and shoulder impingement often coexist. This is a common presentation in the older patient with
226
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
C3
Motor: Active, passive, against resistance Head and neck flexion Extension Lateral flexion Rotation Reflexes: None See C1 and C2 Sensory: Posterior neck Anterolateral neck Posterior neck Region of clavicle
*All cervical muscles supplied by branches of all 8 cervical nerves: one appraises only weakness of movements, not individual muscles.
FIGURE 8.23 Clinical findings in the evaluation of the C3 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 25. With permission.)
spondylosis at the C4–C5 level. Coexisting subacromial spurring often occurs in the patient with osteoarthritis, paralleling the degenerative changes found in the cervical spine. The C5 differential evaluation should include a comprehensive regional shoulder examination. C5 radiculopathic pain typically does not intensify with internal or external rotation of the humerus. Primary shoulder pathology is characterized by pain and tenderness intrinsic to the shoulder area that is reproduced on orthopedic testing. The principal muscles with C5 innervation are the deltoids. The deltoid has three planes of action: forward elevation, abduction, and extension. The anterior and middle divisions of the deltoid are easiest to evaluate. When anterior deltoid strength is tested, both arms should be at a forward elevation in the range of 40 to 70º to isolate the
muscle. Paresis of the deltoid muscle without significant neck pain suggests axillary nerve involvement or, in patients older than 60 years, spondylosis with IVF stenosis. The C5 level also contributes to the innervation of the rhomboid, supraspinatus, infraspinatus, teres minor, biceps brachii, coracobrachialis, brachialis, brachioradialis, and supinator muscles. Other muscles receiving a small C5 contribution are the scalenes, serratus anterior, levator scapulae, latissimus dorsi, teres major, subscapularis, and pectoralis major and minor (Figure 8.25). A progressive C5 radiculopathy can lead to severe paresis and atrophy of the deltoid, rhomboids, supraspinatus, and infraspinatus muscles. This can be both devastating and disabling. Simple daily tasks such as eating, combing the hair, and getting dressed may become difficult. A
Classic Signs and Symptoms of Radiculopathy
227
3
C4
%
C 4
&
C5
'
C 6
2
C 7
1
C8
0
T1
! ! ! ! ! * !# ! * !!! ! *
+ *
/ !
* * ! *
! " # $ % &'
( ) # # ! #
* # ! ! & '* +
! ! ! ( + (! ! !
, ! ! #+ # - . + /
! ! *
FIGURE 8.24 Clinical findings in the evaluation of the C4 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 27. With permission.)
228
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
C5
upper trunk middle trunk suprascapular n. lateral cord posterior cord subscapular ns. musculocutaneous n. axillary n. radial n. median n. ulnar n. medial cord lower trunk Compare with normal side—active, passive, against resistance Adduction arm from behind to front (anterior thoracic nerve) Forward thrust shoulders (long thoracic nerve) Levator scapula (dorsal scapular nerve) Medial adduction and elevation (dorsal scapular nerve) of scapula Adduction of arm (suprascapular nerve) Abduction of arm (axillary nerve) Flexion of forearm (musculocutaneous nerve) Clinical exam: Shoulder: Flexion, extension, adduction, abduction Medial and lateral rotation Observe contraction, size, power, tone, volume and contour of muscle Range motion: fatigue time Contracture; flexibility Deformity Reflexes: Deltoid reflex: tap junction of upper and middle third lateral aspect humerus: contraction and abduction upper arm; C5C6 axillary nerve. Pectoralis reflex: arms midposition abduction; place index finger under pectoralis major tendon near crest greater tubercle humerus; tap finger; adductor and medial rotation arm of shoulder: C5T1 lateral and medial anterior thoracic nerve. Clavicle reflex: In hyper-reflexic state, tap lateral aspect clavicle causes extensive contraction various muscle groups upper extremity; C5T1. Nonspecific: useful compare the two sides: indicates gross spread of reflex response. Biceps reflex: arm relaxed midposition: tap bicep tendon through examiner’s thumb: biceps contraction and supination. C5C6 musculocutaneous nerve. Brachioradialis reflex (radial periosteal or supination reflex): tap styioid process radius with arm in semiflexion and semipronation: flexion of forearm and supination, sometimes flexion fingers associated. C5C6 Radial nerve: In pyramidal tract in midcervical cord lesion may see contraction of flexors of finger and hands without flexion and supination of the forearm (inversion radial reflex). Sensory: Anterior aspect shoulder, arm and forearm to wrist: lateral to ventral axial line: small area low posterior neck. Motor:
FIGURE 8.25 Clinical findings in the evaluation of the C5 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 29. With permission.)
Classic Signs and Symptoms of Radiculopathy
C5 nerve root lesion will also mildly compromise forearm flexion and supination. No significant reflex is discernible from the deltoid muscles. The biceps muscle is therefore the most common MSR evaluated for its C5 contribution. The biceps muscle is innervated by both C5 and C6 nerve root levels. The brachioradialis muscle and its associated MSR occasionally have a small C5 contribution. Biceps muscular performance and the biceps MSR may appear normal with an isolated C5 nerve root lesion. The biceps MSR is rarely absent and often presents as mild hyporeflexia. The biceps MSR response only needs to be slightly less than expected to indicate a possible C5 radiculopathy. It is therefore critical that a side-to-side comparison be performed.
8.9.6 C6 RADICULOPATHY With cervical-level monoradiculopathies, C6 radiculopathy is one of the most common levels of involvement. A C6 level radicular syndrome is seen more frequently than a C5 syndrome. The characteristic sensory presentation of a C6 radiculopathy is often described as a radiating pain or dysesthesia along the neck and across the biceps muscle to the lateral aspect of the forearm. This abnormal sensory experience often involves both the dorsal and volar surfaces of the hand, including the region between the thumb and index finger. The pain may be described as involving only the tips of the thumb and index finger. Pain may also radiate to the anterior chest, mimicking the pain of angina pectoris. The correlation of electrocardiographic and EMG findings can be critical in the differential evaluation of true angina from pseudoangina. The sensory presentation of a C6 radiculopathy often involves the first and second digits of the hand; therefore, it is also important to differentiate this sensory presentation from that of a peripheral median neuropathy, which typically involves the first, second, and third digits. Hand weakness from a median entrapment neuropathy below the elbow may be misdiagnosed as a C6 radiculopathy in a patient with concurrent neck pain. Median neuropathy spares biceps and brachioradialis functions but causes thenar muscle group weakness. Radiculopathy is usually aggravated by neck motion, whereas a distal median nerve entrapment is unaffected by neck maneuvers. Needle EMG will differentiate radiculopathy from median nerve entrapment by demonstrating denervation signs involving C6-innervated muscles that are outside the median nerve territory. A radial nerve lesion can mimic a C6 sensory and motor presentation at the hand and wrist. The biceps MSR and biceps strength are unaffected by radial nerve compromise; radial nerve entrapment at the shoulder may coexist with C6 radiculopathy.
229
A C6 radiculopathy contributes to paresis of the biceps and brachioradialis muscles. This will result in paresis of supinatory actions of the forearm. The patient may not be aware of the loss of strength until the weakness becomes moderate to severe. A repetition-based muscular assessment may amplify a subtle denervation; an isolated repetition may not detect mild paresis. Isometric or isokinetic instrumented evaluation of forearm and wrist supination, flexion, and extension can be used to quantify the degree of C6 level paresis. Muscle fatigue patterns correlate well with the extent of radiculopathy (Figure 8.26). The wrist extensor muscle groups are primarily innervated by the C6 and C7 nerve root levels. The posterior compartment muscles of the forearm should therefore be evaluated in suspected C6 radiculopathy. The radial nerve conveys C6 fibers to the wrist extensor muscle groups, which include the extensor carpi radialis longus (C5–C7) and brevis (C5–C7) and the extensor carpi ulnaris (C7–C8). In the presence of C6 denervation and normal C7 innervation, the wrist will often deviate to the ulnar side during active wrist extension. This will be accompanied by a mild extension paresis. The ulnar deviation of the hand is secondary to preservation of the extensor carpi ulnaris muscle fibers innervated by C7 and C8. This pathomechanical observation can aid the differential evaluation. Chronic ulnar deviation from unopposed C7 forearm functions will increase the risk for degenerative joint disease in the wrist and elbow. Pathomechanically induced myotendinopathies and some entrapments occur with overuse and excessive traction on nerves traveling through osteoligamentous tunnels. Many patients with chronic tennis elbow or carpal tunnel syndrome unresponsive to treatment frequently have an underlying cervical radiculopathy or spondylosis perpetuating their condition.11,59 These patients usually do not improve until both areas are treated. Cervical spondyloarthropathy or spondylosis is common at the C5–C6 and C6–C7 vertebral levels in patients older than 50 years. The disk–spur complex formed by degenerative changes and disk herniation narrows the lateral recess and spinal canal, placing the nervous system at risk for compression.11 This central canal and lateral recess stenosis may produce a combined C6 radiculopathy and compressive myelopathy. In the early stages of myeloradiculopathy, myelopathic signs and symptoms may not be obvious. Common findings with C5–C6 vertebral level cord and root compression are diminished biceps and brachioradialis MSRs with a brisk or hyperreflexive triceps MSR. A tap to the brachioradialis tendon may elicit a brisk contraction of the finger flexors, which are innervated by C7 and C8 segmental levels. The anterior horn cells and descending motor tracts controlling the C5–C6 innervated muscles are located two
230
Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
C6
upper trunk middle trunk suprascapular n. lateral cord posterior cord subscapular ns. musculocutaneous n. axillary n. radial n. median n. lower trunk
medial cord
ulnar n.
Motor: Wrist extension, C5—6 radial nerve Medial rotation arm, C5—8 subscapular nerve Adduction of arm front to back, C5—8 subscapular nerve Adduction arm Flexion forearm C6—7 musculocutaneus nerve Pronation of forearm, C6—7 median verve Radial flexion hand, C6—7 Flexion terminal phalanx thumb, C6—C7 median nerve Abduction medtacarpal thumb, C6—C7 median nerve Flexion proximal phalanx thumb, C6—C7 median nerve Clinical exam: Carry out above anatomic movement, active passive and against resistance. Observe for contour, weakness, range of motion, contraction, size tone, volume of muscle. Reflexes: Pronator reflex: tap styioid process, ulna or postero-inferior surface of ulna with forearm semiflexed and wrist semipronated: forearm pronates and wrist adducts. Pronator feres and quadratus muscle C6—T1 reflex exaggerated in pyramidal tract lesion. Brachioradialis (radial periosteal or supinator reflex): tap styloid process radius: forearm flexion and supination, C5—6 radial nerve. Wrist extension reflex: Tap extensor tendon of the wrist with forearm pronated and wrist hanging down: contraction of extensor muscles and extension of the wrist, C6—C8 radial nerve. Wrist flexion reflex: Tap flexor tendons of wrist on volar surface of forearm at or above transverse carpal ligament, hand supinated, fingers flexed: flexor muscles contract hand and finger: C6—C8 median, ulnar nerves. Sensory: Anterior and posterior areas of upper arm, forearm, lateral to ventral axial line. Anterior an posterior area of thumb. Small area posterior neck and shoulder at C6 level.
FIGURE 8.26 Clinical findings in the evaluation of the C6 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 31. With permission.)
Classic Signs and Symptoms of Radiculopathy
to three segments rostral to the C5–C6 disk and are not affected by a disk herniation or stenosis in the same vertebral level. Thus, cord and root compression from a C5–C6 disk or stenosis produces a segmental radiculopathy at the C6 root level and an upper motor lesion at the C7–C8 level (and below).
8.9.7 C7 RADICULOPATHY Intervertebral disk herniations commonly occur at the C6–C7 level. The C7 root is one of the levels most often involved in radiculopathy. The C6–C7 vertebral level is also one of the most frequently involved levels in cervical spondylosis. Consequently, spondylosis with discopathy is the most common etiology of radiculopathy seen in the elderly population. Clinical isolation of a C7 sensory presentation is difficult. The middle finger is predominantly supplied from C7 with some overlapping of C6 and C8 contributions. Typically, the patient with a C7 radiculopathy will complain of radiating pain across the back of the shoulder. The pain may progress to migrate along the triceps and down the posterolateral aspect of the forearm to the middle finger or dorsal web space of the thumb and second finger; the pain may involve the third finger as well. One important consideration in the differential between a C7 and C6 radiculopathy is that C6 root presentations rarely involve paresthesia of the middle finger. The patient with a mild C7 radiculopathy may complain that the arm feels tired rather than report obvious weakness. The primary actions of muscles innervated from C7 are forearm extension, wrist flexion, and finger extension. The majority of wrist flexion power derives from contraction of the flexor carpi radialis (C6–C7). The flexor carpi ulnaris receives innervation from the C7 and C8 levels. The triceps muscle, the largest muscle of the arm, is innervated by C7 and C8, although characteristically its chief nerve supply is from the C7 level. Despite its large size, weakness is not always evident because gravity assists triceps performance. An important clinical factor indicating a C7 radiculopathy is the loss or diminishment of the triceps MSR and sparing of the C6 innervated biceps and brachioradialis MSRs. Radial nerve palsy or entrapment may mimic C7 radiculopathy, but triceps MSR is usually spared (Figure 8.27). The most important muscles to evaluate, therefore, are the triceps, flexor carpi radialis, extensor digitorum communis, and extensor indicis proprius. Secondary muscles to evaluate with a C7 innervation component are the pectoralis major, serratus anterior, pronator teres, and supinator. The C7 innervated muscles that contribute to pronation are the pronator teres, flexor carpi radialis, palmaris longus, and pronator quadratus. Supination is largely controlled by the biceps muscle, but the supinator is supplied by C6–C7 from the radial nerve.
231
Computerized or instrumented evaluation of repetitive flexion and extension of the elbow and wrist can be important in the differential evaluation of a C6 and C7 radiculopathic presentation. C7 radiculopathy is often attended by some paresis involving the pectoralis major muscle. Because of multilevel innervation, the patient is often unaware of perceptible weakness in this region. A common method for evaluating coupled functions of the triceps and pectoralis major is to have the patient perform a push-up on the floor or against the wall. The patient will often demonstrate rapid fatigue or inability to support the affected side, which indicates C7-level weakness.
8.9.8 C8 RADICULOPATHY Disk herniation at the C7–T1 level accounts for the majority of C8 radiculopathies. C8 radiculopathy has the poorest prognosis relative to strength recovery because this nerve root supplies most of the small muscles of the hand, including the interossei and lumbricals. C8 radiculopathy often leads to paresis of the flexor carpi ulnaris, flexor digitorum superficialis and flexor digitorum profundus. Therefore, a timely diagnostic and therapeutic plan should be implemented with suspected C8 root involvement because of the potential for disabling paresis of the intrinsic hand muscles. The patient with a lesion at the C7–T1 vertebral level typically reports progressive difficulty using his or her hands, similar to the dysgraphia seen in Parkinson’s disease. The patient often complains that he or she cannot operate simple devices, such as a pen or pencil, spray bottles, or scissors; removing the caps or tops of jars and bottles may also be difficult. C8 nerve root pain may be less severe than that arising from other cervical root levels because the C8 nerve root contains more motor than sensory fibers compared to other nerve roots. The C8 muscle evaluation is simple to perform in the clinical setting. The motor evaluation involves resistive testing of hand grip, finger pinch, adduction, and abduction strength. Difficulty arises in differentiating a C8 radiculopathy from a lower trunk brachial plexus lesion and some cases of neurogenic thoracic outlet syndrome. Also, needle EMG and nerve conduction studies are critical for distinguishing radiculopathy from ulnar neuropathy. A needle EMG study of the C8 innervated paraspinals will usually confirm root level involvement in acute lesions. Chronic radiculopathies are often difficult to differentiate from more distal lesions because motor unit reorganization and reinnervation in the paraspinal muscles occur faster than in the peripheral muscles. The possibility of Pancoast tumor should be investigated in patients with a history of smoking and the diagnosis of C8 or T1 radiculopathy or brachial plexopathy.60 Differential diagnostic considerations also include breast carcinoma and other pathologies affecting the sternocostovertebral space.
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C7
upper trunk middle trunk suprascapular n. lateral cord posterior cord subscapular ns. musculocutaneous n. axillary n. radial n. median n. lower trunk
medial cord
ulnar n.
Motor: Adduction arm, C6—7 musculocutaneus nerve Flexion forearm, C6—7 musculocutaneus nerve Flexion hand, C7—T1 median nerve Flexion middle phalanx, index and middle fingers, C7—T1 median verve Flexion terminal phalanx index and middle fingers, C7—T1 median nerve Flexion proximal phalanx and extension of 2 distal phalanges, index, middle, ring & little, C6—C7 median nerve Ulnar flexion of hand, C7—T1 ulnar nerve Clinical examination: Carry out above anatomic movement, active passive and against resistance. Observe for contour, weakness, range of motion, contraction, size tone, volume of muscle. Reflexes: Triceps reflex: Tap triceps tendon just above insertion in olectanon process ulna, arm midway between flexion and extension: contraction triceps muscle, extension of forearm on the arm; C6—8 radial nerve, center flexion of forearm indicates damage to area of triceps reflex, eg: lesion C7—C8 cervical segment, flexion unopposed by biceps. Thumb reflex: Tap tendons flexor pollicis langus: flexion distal phalanx thumb, C6—T1 median verve. Finger flexion reflex: Hand in partial supination, resting on table, fingers flexed; examiner places his middle and index fingers on volar surface phalanges patient’s four fingers; taps his fingers lightly: response is flexion of patient’s four fingers and distal phalanx, thumb—C6—T1 median and ulnar nerves. Sensory: Dorsum arm and forearm; dorsal and palmar aspects 2nd and 3rd digits; small area posterior neck and shoulder at this level.
FIGURE 8.27 Clinical findings in the evaluation of the C7 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 33. With permission.)
Dysesthesia secondary to a C8 radiculopathy is often confined to below the wrist. Careful evaluation of the comparative perceptions of sensation between the thumb and second finger to the fourth and fifth fingers is important. The C8 level sensory deficits are usually described as numbness along the ring and fifth fingers frequently
without mention of neck pain. The medial portion of the fourth finger is innervated by the ulnar nerve, and the lateral portion is innervated by the median nerve. Multiple reflexes in the upper extremity have a C8 component, but none is purely attributable to the C8 root. Finger flexion MSR (C8–T1), thumb flexion MSR
Classic Signs and Symptoms of Radiculopathy
(C7–T1), and latissimus dorsi MSR (C6–C8) can be difficult to elicit and are nonspecific in the evaluation of C8 radiculopathy. These reflexes may be depressed but are rarely absent (Figure 8.28). Occasionally, the patient with a C8 radiculopathy will have an accompanying ipsilateral Horner’s syndrome as a result of pathology affecting sympathetic fibers destined for the superior cervical ganglia.
8.10 THORACIC MONORADICULOPATHY SYNDROMES Thoracic disk herniations may be dismissed as insignificant by some clinicians in the absence of high-grade spinal stenosis. This perspective is probably based on the rare incidence of the disorder and the limited therapeutic options rather than its potential for ominous consequences. The thoracic spinal canal is relatively narrow, limiting the reserve space for the spinal cord and its blood supply. However, even in the absence of myelopathy or objective radicular deficits, disk pathology may contribute to vertebrogenic pain and a significant vertebral subluxation complex. Most thoracic spine herniations are centrally or paracentrally located, which places the spinal cord at greater risk for compression than the nerve roots. Disk herniations occur more frequently in the lower thoracic region. Consequently, the cord or descending nerve roots may be compressed. There is a reported case of lower thoracic disk herniation mimicking acute lumbosacral radiculopathy.61 Spondyloarthropathy may contribute to thoracic radiculopathy.
8.10.1 T1 RADICULOPATHY T1 radiculopathy occurs at the T1–T2 disk level. Radiculopathy at this level is uncommon because of the relative immobility created by the junction of the first rib and the spine. Sensory deficits and paresthesia associated with T1 radiculopathy involve the medial aspect of the proximal arm. T1 motor involvement is limited to the hand. T1 paresis involves the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, lumbricals, interossei, and abductor digiti minimi. The muscles most commonly evaluated are the interossei and abductor digiti minimi. The abductor digiti minimi is easy to isolate and evaluate. The finger flexion MSR may be depressed with a T1 radiculopathy (Figure 8.29). Compromise of the sympathetic fibers destined for the supraclavicular ganglia may occur with T1 nerve root compression, producing an ipsilateral Horner’s syndrome. As previously mentioned, this can also occur with C8 radiculopathy because of sympathetic nerve contributions to the chain ganglia traveling with the C8 root. Apical lung pathology should be a primary differential consideration in the assessment of a patient with a C8 or T1 radiculopathy (Table 8.9).
233
8.10.2 T2–T12 RADICULOPATHY Generally, lesions affecting the thoracic nerve roots are somewhat challenging to diagnose because the thoracic and abdominal muscles are difficult to examine. There are no observable MSRs arising from the T2–T9 nerve root levels. The clinical diagnosis is thus based predominantly on sensory signs and symptoms correlated with diagnostic imaging. Gradual signs of spinal cord compression that progress over many months or years are possible, thus periodic examination of neurological status in thoracic disk herniation is suggested. Isolated root pain, such as burning paresthesia or shooting pain between the ribs, is an unusual clinical finding. The patient often complains of midline back pain and paresthesia in the distribution of the posterior primary rami. The lateral branches of the posterior primary rami in the lower thoracic spine may descend several vertebral levels before reaching its cutaneous distribution. Consequently, the sensory deficit and pain pattern of a T10 radiculopathy may extend to a few inches above the iliac crest. Sensory loss is difficult to evaluate in the mid- and upper thoracic region because of the small area of segmental distribution and dermatomal overlap. Dermatomal evoked potentials have been reported to be an accurate and reliable method for noninvasive diagnosis of thoracic radiculopathy.41 Dreyfuss62 supports the use of somatosensory evoked potentials for the evaluation of intercostal nerves at rib interspace levels 3, 5, 7, and 9. These noninvasive tests have an obvious safety advantage over nerve conduction techniques that use needle electromyographic stimulation of the intercostal nerve, which is rarely performed because of the unacceptable risk of pneumothorax. The clinical examination should include maneuvers that increase intraspinal pressure or induce mechanical stretching of the thoracic dorsal root. An example is the performance of a sustained Valsalva maneuver coupled with thoracic lateral bending. Thoracic radiculopathy with axonopathy results in intercostal muscle paresis and atrophy. When paresis is severe, a retraction of the costal interspace occurs during inspiration and a bulging of the interspace during expiration. Costal interspace bulging intensifies with the performance of Valsalva maneuvers. Paresis and occasional atrophy of segmental erector spinae muscles will also occur. In slender patients, atrophy of the short rotators and multifidi may create a small depression next to the spine. With multilevel thoracic radiculopathy, the depression area may be accentuated with ipsilateral resisted lateral flexion and posterior trunk rotation. Observation of abdominal and costal movement is important in the examination for thoracic radiculopathy. Lower thoracic and upper lumbar nerve root lesions may result in excessive protrusion of the abdomen during inspiration. The abdominal muscles may be severely paretic or paralyzed unilaterally within a quadrant. The umbilicus
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C8
upper trunk middle trunk suprascapular n. lateral cord posterior cord subscapular ns. musculocutaneous n. axillary n. radial n. median n. lower trunk
medial cord
ulnar n.
Motor: Flexion proximal phalanx and extension of 3 distal phalanges ring and little fingers. C8—T1 ulnar nerve Flexion terminal phalanx, ring and little fingers, C8—T1 ulnar nerve Adduction metacarpal thumb, C8—T1 ulnar nerve Abduction little finger Opposition of little finger, C8—T1 ulnar nerve Flexion of little finger, C8—T1 ulnar nerve Flexion proximal phalanx, C8—T1 ulnar nerve, extension of two distal phalanges adduct and abduct fingers Ulnar extension of hand, C6—C8 radial nerve Extension index finger and hand Extension phalanges little finger Extension of hand, C6—C8 radial nerve Clinical examination: Carry out above anatomic movements, active, passive and against resistance; assess power, range of motion, size , volume, contactures and tone. Reflexes: Pronation reflex-see above Wrist extension reflex-see above Wrist flexion reflex-see above Finger flexion reflex-see above Sensory: Ulnar aspect arm, forearm and palmar and dorsal aspect of 4th, 5th digits; small area posterior neck and shoulder at this level.
FIGURE 8.28 Clinical findings in the evaluation of the C8 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 35. With permission.)
Classic Signs and Symptoms of Radiculopathy
235
FIGURE 8.29 Clinical findings in the evaluation of the T1 root. (From Bland, J., Disorders of the Cervical Spine, W.B. Saunders, Philadelphia, PA, 1994, 37. With permission.)
will pull toward the uninvolved side during inspiration unopposed by the contralateral muscle impairment. Resisted head elevation and associated abdominal contraction will occasionally result in umbilical movement toward the uninvolved quadrant. With a lesion below the T10 level there may be bilateral lower abdominal muscle paresis producing midline elevation of the umbilicus when the patient attempts to do a sit-up. This is referred to as Beevor’s sign,56,63 and results from weakness of the lower abdominals and preservation of muscle strength in the upper abdominals (Figure 8.30).
8.11 LUMBAR AND SACRAL MONORADICULOPATHY SYNDROMES Approximately 95% of lumbar herniated nucleus pulposus radicular syndromes occur at L4–L5 or L5–S1.64 In a retrospective study of patients treated for lumbar root syndromes, Kramer65 noted that 54.2% of patients with monoradiculopathy of the lower two lumbar segments had involvement of the S1 nerve root (L5–S1 level), 43.8% had involvement of the L5 nerve root (L4–L5 level), and
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TABLE 8.9 Common Clinical Findings in Thoracic Radiculopathy Vertebral Level
Root(s)
Pain Pattern (Sclerotogenous)
Sensory Paresthesia and Deficits
Motor Weakness and Atrophy
Relevant Reflex
T1–T2
T1
Corresponding costovertebral region, elbow, wrist, and hand
Proximal medial arm
None
T3–T6 T7–T12
Corresponding costovertebral region Corresponding costovertebral region
Upper transthoracic region Lower transthoracic, abdominal region
Intrinsic hand interossei, lumbricales, adductor, abductor, and opponens pollicis Intercostal muscles, abdominal muscles Intercostal muscles, abdominal muscles
T3–T6 T7–T12
None Abdominal
T2-T12 Clinical Findings - T2 - T12 Medial and lateral branches of posterior primary rami
Sensory Anterior rami: skin overlying Intercostal space, lateral and anterior torso Posterior rami: skin next to spine and a few inches lateral. In the lower T-spine posterior primary branches descend to the iliac crest
T10 Root (example)
Motor Segmental level erector spinae Intercostal muscles Abdominal muscles (T9-T12)
Reflex Superficial abdominal (T10-T12)
Perceived Pain Pain under shoulder blade (upper T-spine) Midline back pain Flank pain, hip and buttock (lower T-spine) Abdominal wall pain Intercostal pain
Lateral cutaneous branch of intercostal nerve
Lateral cutaneous branch of posterior primary rami
FIGURE 8.30 General clinical findings in the evaluation of the thoracic roots. (Copyright J.M. True, D.C.)
only 1.0% had involvement of the L4 nerve root (L3–L4 level). The remaining patients had involvement of one of the upper lumbar roots. The patient with an acute lower lumbar radiculopathy often demonstrates a distinct postural deformity referred to as lumbar antalgia. The patient will be flexed slightly forward, often with severe paraspinal hypertonicity and loss of lumbar lordosis (Table 8.10).
8.11.1 ANATOMIC VARIATIONS OF THE LUMBOSACRAL NERVE ROOTS Attention must be directed to the possibility of anomalous nerve root anatomy when lumbosacral radicular symptoms are being assessed, especially when the neurologic findings do not correlate with electrophysiologic studies and findings on MR imaging. This lack of correlation with clinical presentation and pathoanatomy
may be a result of an extra nerve root called the furcal nerve, plurisegmental overlapping of peripheral innervation, a more cranial or caudal origin of a root, intradural anastomosis between spinal nerve roots, or conjoined nerve roots, where two segmental levels exit the same spinal IVF.66,67 As an example of the last of these variations, 17 of 5000 patients studied postoperatively were found to have conjoined roots complicating the presurgical diagnosis.68 An anatomic and clinical study of the furcal nerve indicated that this nerve, when present, most commonly arises at the L4 root level in most dissections (93%) and it has its own anterior and posterior root fibers and DRG. This confirms that the furcal nerve is an independent nerve root. Lower extremity neurologic symptoms suggestive of two roots being involved are frequently due to furcal nerve compression.69
Classic Signs and Symptoms of Radiculopathy
237
TABLE 8.10 Common Clinical Findings in Lumbosacral Radiculopathy Vertebral Level
Root(s)
Pain Pattern (Sclerotogenous)
Sensory Paresthesia and Deficits
Motor Weakness and Atrophy
Relevant Reflex
Groin and inquinal region
Slight contribution to psoas major
Cremasteric
Proximal anterolateral thigh Mid-anterolateral thigh Anterior knee, medial foot, medial aspect of great toe Anterior leg distal to knee, dorsum of foot
Quadriceps, adductors Quadriceps, adductors Quadriceps, adductors
Patellar Patellar Patellar
Anterolateral compartment lower leg, tibialis anterior, extensor digitorum brevis, extensor hallucis longus, gluteus Gastrocnemius, soleus, flexor hallucis brevis Anal sphincter (S2–S4)
Tibialis posterior Biceps femoris
L1–L2
L1
L2–L3 L3–L4 L4–L5
L2 L3 L4
Anterior hip, lateral thigh; iliac region Iliac region Pubic region, lateral thigh Thigh and knee regions
L5–S1
L5
Hip, femur, and knee regions
S1–S2
S1
S2
S2
Ischium, periosteum of lateral foot Lateral ankle
Epispinal
Lateral margin of foot and little toe Perianal (S2–S4)
Achilles Anal (S2–S4)
L4
rootlets
L5
Epiconus
S1
Conus
Rootlet descends with fibers from unrelated level
FIGURE 8.31 Anomalous innervation resulting from epispinal rootlets. (Copyright J.M. True, D.C.)
Variation in ventral root contribution to the spinal nerve has also been demonstrated. Parke and Watanabe70 found epispinal rootlets from the L2–S2 levels that traveled along the surface of the spinal cord to join with ventral roots of another spinal level caudal to the level of origination (Figure 8.31). Atypical neurological symptoms may occur from five different causes: (1) two roots compressed by a single lesion, (2) two independent lesions, (3) two nerve roots traversing the same foramen,
FIGURE 8.32 Anomalies of the lumbar nerve roots. (From Bogduk, N. and Twomey, L. T., Clinical Anatomy of the Lumbar Spine and Sacrum, J. A. Majors, New York, 1997. With permission.)
(4) presence of the furcal nerve, and (5) epispinal rootlets descending along the cord to join a lower segmental level before being compressed (Figure 8.32). Significant advances in MR imaging resolution are needed to help identify and resolve these innervation anomalies in cases of diagnostic uncertainty.
8.11.2 L1 RADICULOPATHY The sensory deficits and paresthesia of an L1 radiculopathy localize to the inguinal and groin regions. A painful hyperesthetic area may extend from the high lumbar region to the groin region; pain may be described as a shooting pain or a deep, clenching ache into the groin. There is also a contribution to the lateral femoral cutaneous nerve of the
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L1 L1 Root Clinical Findings - L1 Root Sensory Inguinal area Scrotum/labia Pubis region Upper medial thigh
Iliohypogastric nerve (T12-L1) Ilioinguinal nerve (L1)
Motor Cremasteric muscle Internal oblique Transverse abdominus
Genitofemoral nerve (L1-L2)
Reflex Cremasteric
Perceived Pain Referred pain may resemble ureter or kidney disease Pain in groin region Pain in inguinal region Vague abdominal pain
FIGURE 8.33 Clinical findings in the evaluation of the L1 root. (Copyright J.M. True, D.C.)
thigh. This level of innervation does not cross the midline of the thigh. The sensory presentation is often the only useful sign in the clinical examination. No characteristic reflexive changes are evident with a high lumbar radiculopathy. The motor presentation is usually negative, although there may be mild lower abdominal paresis involving the internal oblique and transversus abdominus muscles. The L1 contribution to the abdominal muscles is impossible to isolate by clinical examination alone, and weakness may only be evident as rapid onset of fatigue during abdominal exertion. The diagnosis is confirmed by sensory findings correlated with MR findings (Figure 8.33). On clinical testing, the supine straight leg raise is typically negative. A magnification of symptoms may occur with a reverse straight leg raise, also referred to as the femoral stretch maneuver. This extremely important test helps to differentiate groin- and perineal-region pain of lumbar origin from that of local pelvic pathology. Discogenic pain or vertebral instability at this level results in pronounced localized paraspinal guarding in the dorsolumbar spine. Reactive guarding and pain in the dorsolumbar spine can be accentuated by resistive testing of the psoas muscle with the leg extended. The patient will be unable to hold the leg extended when discopathy or pathomechanics is present in the upper lumbar spine.
8.11.3 L2 RADICULOPATHY L2 radiculopathic sensory disturbances are similar to those of the L1 presentation, although it is often attended by migration over the anterior thigh region. The motor evaluation characteristically reveals some degree of paresis involving the pectineus muscle (thigh adduction), iliopsoas muscle (thigh flexion), sartorius (thigh flexion/eversion), and quadriceps (knee extension). An L2 radiculopathy may also lead to paresis of internal rotation of the lower extremity. Paretic adduction will contribute to a change in the axis of rotation about the hip. Abnormal acetabalar loading occurs with chronic L2 radiculopathy, predisposing the hip to early degenerative change. The cremasteric reflexes are primarily L2 modulated and are often depressed in the L2 radiculopathic patient. A depressed cremasteric response with a normal abdominal superficial response is further suggestive of radicular compromise. The examiner must carefully compare the cremasteric response bilaterally. The absence of both the abdominal and the cremasteric superficial responses is consistent with an upper motor neuron lesion. Differential consideration includes uncontrolled diabetes; the clinical picture of diabetic amyotrophy can resemble that of high lumbar disk herniation with radiculopathy (Figure 8.34).71
Classic Signs and Symptoms of Radiculopathy
239
L2 Clinical Findings - L2 Root
L2 Root
Sensory Lateral thigh Middle thigh Scrotum/labia Upper anterior thigh
Genitofemoral nerve (L1-L2) Lateral femoral cutaneous nerve (L2-L3)
Motor Cremasteric muscle Quadriceps Adductor magnus and longus Iliopsoas
Femoral nerve (L2-L3-L4)
Reflex
Obturator nerve (L2-L3-L4)
Cremasteric
Perceived Pain Referred pain may resemble ureter or kidney disease Medial or lateral thigh pain Groin region pain
FIGURE 8.34 Clinical findings in the evaluation of the L2 root. (Copyright J.M. True, D.C.)
TABLE 8.11 Lumbar/Sacral Radiculopathies and Gait Patterns Level
Function
Gait Pattern
L2 or 3 L2, L3, or L4 L4
Hip flexion Knee extension Foot dorsiflexion/foot inversion
L5 S1
Foot eversion/dorsiflexion Plantar flexion
Difficult ambulation; trunk and abdominal compensation required; unable to walk up stairs Reduced knee stability; may have ability to ambulate with cane or knee supports Foot drop May require orthosis or crutches Mild foot drop; reduced ankle stability during stance (may require ankle brace) Impaired push-off Inability to run
8.11.4 L3 RADICULOPATHY Radiculopathy at this level, like the other upper lumbar root syndromes, is rare. Femoral nerve symptoms generally predominate in an L3 radiculopathic syndrome. The sensory signs and symptoms typically reported involve the lower anterior thigh and the medial aspect of the knee. The patellar MSR is often depressed, although it is not typically absent because the quadriceps muscles are innervated by the L2–L4 roots. Femoral neuropathy is more likely to produce an absent patellar response because all the segmental levels of the nerve are affected. The L3 radiculopathic presentation often involves a greater degree of paresis of lower extremity adduction than
abduction and a greater degree of paresis involving knee extension than knee flexion (Table 8.11). Knee extension can be evaluated with repetitive squatting, sitting kneeextension maneuvers, or stair-stepping onto a simple bench. Ablation of the L3 root will rarely cause more than one third of the quadricep muscles to atrophy. Compensatory hypertrophy of the remaining quadriceps may mask atrophy. The primary muscles evaluated during the clinical examination of L3 are the iliopsoas (L2–L4), quadriceps (L2–L4), and adductor groups (L2–L4) (Figure 8.35). Isolated paresis of the quadriceps without similar weakness of the adductor muscles is suggestive of peripheral femoral
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
L3 Clinical Findings - L3 Root
Sensory
L3 Root
Lateral thigh Middle anterior thigh Distal anterior thigh Inner thigh
Motor
Quadriceps Adductor magnus and longus Iliopsoas
Reflex
Quadriceps
Lateral femoral cutaneous nerve (L2-L3 ) Femoral nerve (L2-L3 -L4) Obturator nerve (L2-L3 -L4)
Perceived Pain
Distal thigh region pain Pain in knee region
FIGURE 8.35 Clinical findings in the evaluation of the L3 root. (Copyright J.M. True, D.C.)
nerve neuropathy. Severe paresis or paralysis of the knee extensors (quadriceps femoris groups) will result in knee hyperextension during gait. With bilateral knee extensor paresis, both legs will hyperextend at the knees during gait. The patient will hyperextend the knee to prevent buckling of the knees during the normal transfer of weight onto the bearing extremity. This compensatory postural attitude requires much less muscular work. The supine straight leg test is usually normal, but the reverse (prone) straight leg raise, or femoral stretch test, often produces anterior thigh pain. The assumption of a hyperlordotic lumbar position occasionally affords lower extremity relief by reducing tension across the L3 nerve root.
8.11.5 L4 RADICULOPATHY After the L5–S1 motion segment, the L4–L5 vertebral motion segment has the greatest degree of motion within the lumbar spine. This greater excursion predisposes these two levels to larger forces and increased risk of intervertebral disk herniation. Consequently, L4 and L5 radiculopathic presentations are the two most common levels at which herniated nucleus pulposus occurs. Most sensory disturbances associated with an L4 radiculopathy involve the local knee region and the medial aspect of the lower leg. The L4 nerve root innervates the medial side of the lower leg above the ankle in 88% of individuals.72 The painful or dysesthetic region usually
involves the thigh lateral to the region supplied by the third lumbar level. The L4 pain band extends across the knee and down to the anteromedial aspect of the lower leg and foot. The pain associated with L4 radiculopathy can mimic knee pathology. The patellar tendon reflex is diminished, although rarely absent, with an isolated L4 radiculopathy. In the absence of patellar MSR, the clinician should consider a coexistent L3 radiculopathic contribution (polyradiculopathy) or femoral neuropathy. Involvement of the fourth and/or the third lumbar nerve root may result in a decreased or absent patellar tendon reflex, but a far lateral L4–L5 disk herniation often results in a decreased patellar tendon response.73 If the patellar MSR is completely absent, the examiner must consider the following differential possibilities: examiner error, primary muscle disease, hypothyroidism, knee pathology with extreme guarding, severe stenosis, anterior horn disease, femoral neuropathy, lumbar polyradiculopathy, or a normal variant. In addition, knee surgery will commonly produce an aberrant patellar reflex. Normal variants will present symmetrically. An abnormal L4 MSR should only be considered a normal variant in the absence of other signs and after a thorough, otherwise unremarkable work-up. A diminished or absent patellar MSR should be reevaluated with the patient performing a reinforcement maneuver. This can be performed by having the patient clench the
Classic Signs and Symptoms of Radiculopathy
241
L4 Clinical Findings - L4 Root Sensory Distal anterior thigh Distal inner thigh Medial leg Medial ankle
Femoral nerve (L2-L3-L4 )
L4 Root
Motor Quadriceps femoris Adductor magnus and minimus Gracilis Iliopsoas Tibialis anterior Gluteus medius/minimus Tensor fascia lata Extensor hallucis longus Extensor digitorum brevis
Obturator nerve (L2-L3-L4 ) Superior Gluteal nerve (L4 -L5-S1) Common peroneal nerve (L4 -L5-S1-S2)
Reflex Quadriceps
Perceived Pain
Tibial nerve (L4 -L5-S1-S2-S3)
Distal thigh pain Pain in knee region Pain along medial leg Ankle pain
FIGURE 8.36 Clinical findings in the evaluation of the L4 root. (Copyright J.M. True, D.C.)
teeth or clasp the hands and isometrically attempt to pull them apart as the examiner taps the patellar tendon. The presence of a patellar MSR on this maneuver suggests reflexive dampening or sluggishness rather than true axonopathy. The tibialis anterior (L4–L5) is the most clinically significant muscle innervated from the L4 root. This muscle is innervated by the deep peroneal nerve. Its actions include inversion and dorsiflexion of the foot. A chronic denervating L4 radiculopathy will lead to excessive pronation and paresis of foot dorsiflexion. Extension strength of the large toe will be preserved because the extensor hallicis longis (L4–L5–S1) is primarily innervated by the L5 root. Excessive pronation secondary to anterior tibialis weakness predisposes the individual to a chronic patellofemoral syndrome due to alteration of the Q angle of the patellar tendon. Chronic patellar pathomechanics increases wear-and-tear microtrauma to the undersurface of the patella, promoting the development of chondromalacia patellae. A chronic L4 monoradiculopathy will contribute to quadriceps atrophy, although it will not be as pronounced as the atrophy that occurs secondary to an L3 radiculopathy. L4 paresis involves the quadriceps (leg extension), sartorius (thigh flexion and inversion), and tibialis anterior (foot dorsiflexion and inversion). An L4 radiculopathy will contribute to paresis of hip flexion secondary to denervation of the psoas major, iliacus, sartorius, adductor longus,
adductor brevis and rectus femoris, adductor magnus, and tensor fascia lata. The majority of the hip extensor muscles are primarily innervated by the L5 and S1 radicular levels. Earlier fatigue of hip flexion compared with hip extension is clinically significant for L4 root syndrome. Additionally, L4 radiculopathy will contribute to greater paresis of dorsiflexor muscles while sparing plantar flexion in the lower extremity (Figure 8.36). Gait analysis is an important component of the evaluation of the patient with possible L4 radiculopathy Table 8.11. Anterior muscle weakness of the lower extremity results in an identifiable L4 pathologic gait pattern. The patient will commonly present with foot drop and a compensatory steppage gait. Mild foot drop may not manifest during the cursory clinical evaluation; however, a greater demand must be put on the L4 muscle group for the foot drop to become apparent. The patient should be asked to walk on his or her heels with the feet inverted. This maneuver will isolate and load the predominately L4-innervated tibialis anterior muscle. The predominantly L5-innervated peroneal muscles will assist heel walking with the foot in neutral dorsiflexion. Subtle L4-related dorsiflexor weakness may only appear after extended heel walking with foot inversion. Prolonged walking on a treadmill will magnify the foot drop and the compensatory steppage gait. The patient and the examiner may appreciate the sound of the foot scuffing
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L1 Conus medullaris
L1 nerve
L2 Cauda equina
L2 nerve L3 L3 nerve
L4 central herniation or L5 posterolateral herniation
L4 L4 nerve L5 S1
L5 radiculopathy S1 nerve
FIGURE 8.37 Location and direction of disk herniation determines which spinal roots are predominately affected. The above example demonstrates how the L5 nerve root may be compromised by a paracentral L4–L5 or lateral L5–S1 disk protrusion. (Copyright J.M. True, D.C.)
or slapping on the treadmill during the study. An elevation of the front of the treadmill or increased speed will place an additional demand upon foot dorsiflexion.
8.11.6 L5 RADICULOPATHY The L5 nerve root innervates the lateral side of the large toe on the dorsum of the foot in 82% of individuals.72 It is particularly vulnerable to stenosis or compression in the lateral recess and IVF. This is because the nerve root diameter of L5 is the largest of the lumbar nerves and the L5 IVF is the smallest foramen of the lumbar spine. Consequently, less space is available for the nerve root to slide or move away from a compressive structure or lesion.74,75 Furthermore, the L5–S1 vertebral level is a common site for degenerative disk disease and related disk herniation. The L5 root may be compressed by a centrally located L4 disk herniation (Figure 8.37) or in cases of spondylolisthesis where traction of the thecal sac has occurred (Figure 8.19). The sensory presentation or radicular pain band characteristic of an L5 radiculopathy involves a region extending from the low back to the posterolateral thigh. When
greater nerve root compression or inflammation is present, pain and paresthesia extend below the knee and across the anterior lower leg to the lateral malleolus and top of the foot. Sensory deficits are found along the dorsal and medial aspects of the foot and the web space of the large toe. Motor and sensory evaluation of the large toe can help differentiate L5 radicular involvement from S1 involvement. With an L5 lesion, hypoesthesia will often be limited to the dorsal aspect of the foot or the web space of the great toe. The most diagnostically significant motor weakness is large toe dorsiflexion.76 Motor paresis secondary to L5 radiculopathy typically involves the gluteus medius, gluteus minimis, tensor fascia lata, semimembranosus, semitendinosus, extensor hallucis longus, tibialis posterior, and tibialis anterior. A common L5 presentation includes paresis of large toe extension, a positive supine straight leg raise test at less than 50°, and sparing of the patellar and Achilles MSRs. During supine straight leg raise, the greatest degree of nerve root translation occurs through the IVF at the L5 and S1 levels;77 therefore, a positive straight leg raise test correlates well with either L5 or S1 radiculopathy. No clinically distinct reflexes are supplied solely by the L5 root. The posterior tibialis and biceps femoris MSRs are commonly associated with the L5 root. The posterior tibialis muscle MSR (L5–S1) is difficult to elicit routinely. The biceps femoris MSR (L5, S1, S2) can be evaluated and compared bilaterally. Decreased responses may be seen with L5 nerve root pathology. Assessment of a subtle L5 root lesion requires sideto-side comparison of foot dorsiflexion (primarily L4–L5). The extensor hallucis longus (L5–S1) is innervated predominantly by L5.76 It is a small muscle that is easy to isolate, and small muscles are easier to overpower and fatigue. Repetitive resisted extension of the large toe may be more apt to induce fatigue as compared with the uninvolved limb. The examiner’s thumb should not cross the proximal interphalangeal joint during testing, which would also recruit the extensor digitorum brevis (S1) and longus (L5–S1). This simple mistake may cause overestimation of extensor hallucis longus strength and thereby mask L5 paresis. Dorsiflexion paresis (foot drop) results in a compensatory steppage gait, thus increasing the workload of the hip flexors of the involved side. This can contribute to chronic hip flexor myofasciitis and tendonitis. Impaired foot and ankle control results in inefficient shock absorption exposing proximal joints to greater physical trauma. Chronic steppage gait places additional stress on the lumbopelvic region, predisposing to low back pain syndromes. Treadmill assessment on an incline will magnify steppage gait (See Table 8.11; Figure 8.38). Proximally innervated large hip extensor muscles should be evaluated for paresis, although these large and powerful muscles are innervated by L4, L5 and S1; therefore, obvious
Classic Signs and Symptoms of Radiculopathy
243
L5 Clinical Findings - L5 Root Sensory Anterior leg Anterolateral ankle Top (dorsum) of foot Web space of great toe
Motor Hamstrings Tibialis anterior Tibialis posterior Gluteus maximus Gluteus medius\minimus Piriformis Tensor fascia lata Extensor hallucis longus Extensor digitorum longus and brevis Peroneus longus and brevis
Reflex Hamstring Tibialis posterior
Perceived Pain Lateral leg pain Pain along lateral ankle Hip and buttock pain
L5 Root
Superior Gluteal nerve (L4-L5 -S1) Inferior Gluteal nerve (L4-L5 -S1) Common peroneal nerve (L4-L5 -S1-S2) Tibial nerve (L4-L5 -S1-S2-S3)
FIGURE 8.38 Clinical findings in the evaluation of the L5 root. (Copyright J.M. True, D.C.)
atrophy and weakness may not be present. Most hip flexor muscles are primary innervated by L4, whereas hip extensor muscles are primarily innervated by the L5 nerve root. L5 radiculopathic lesions therefore result in earlier fatigue of hip extension than hip flexion. This may manifest during gait evaluation as a shorter hip extension component during stride. L5 radiculopathy may contribute to a lateral pelvic tilt secondary to hip abductor weakness. With marked weakness of the gluteus medius, the patient will have an obvious limp from shifting the body weight laterally toward the side of the weak hip. This is referred to as a Trendelenburg gait. Pathomechanical stresses are placed on the ipsilateral hip joint and adjacent soft tissues. As a consequence, ipsilateral trochanteric bursitis is relatively common. Chronic hip abduction paresis increases pathologic loading of the femoral acetabular joints and lumbar facets increasing the risk of early degenerative changes.
8.11.7 S1 RADICULOPATHY S1 lesions are among the most frequent causes of sciatic pain syndromes (Table 8.12). S1 monoradiculopathy may produce sciatic pain in the absence of low back complaints. Typically, the patient with an S1 radiculopathy
complains of pain that radiates along the back of the thigh to the leg and lateral aspect of the foot. Common associated symptoms include calf cramping, calf pain, “pins and needles” sensations involving the foot, and “electric” jolts of pain along the posterior thigh and buttock. The S1 nerve root innervates the lateral side of the foot and the little toe in 83% of individuals.72 S1 sensory deficits and paresthesia commonly involve the little toe, the lateral foot, and the sole of the foot. S1 muscle paresis involves many muscles throughout the lower extremity. The most clinically significant muscles evaluated in S1 root syndromes are the gastrocnemius and soleus. Moderate to severe S1 radiculopathy contributes to impaired hip extension and knee flexion due to denervation of the gluteus maximus (L5–S2) and biceps femoris (L4–S2) muscles. Chronic hip instability increases the risk for falling, exposure to cumulative joint microtrauma, and degenerative joint disease (DJD) (Figure 8.39). The Achilles MSR is usually depressed or absent with S1 radiculopathy. Mild S1 lesions typically result in Achilles hyporeflexia. A complete absence of the Achilles MSR may occur secondary to S1 radiculopathy, peripheral neuropathy, polyradiculopathy involving both S1 and S2 levels, hip surgery, and lumbosacral canal stenosis. Bilateral Achilles MSR hyporeflexia is relatively common in the
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
S1
Clinical Findings - S1 Root Sensory Posterior thigh Posterior leg Lateral side of foot Bottom of foot
Motor Hamstrings Gastrocnemius\soleus Gluteus maximus Gluteus medius\minimus Piriformis Tensor fascia lata Flexor digitorum longus and brevis Extensor hallucis longus and brevis Extensor digitorum brevis Abductor hallucis
Reflex Hamstring Achilles
Perceived Pain Pain in buttock Posterior thigh pain Pain along back of knee Pain in back of heel or bottom of foot
Superior Gluteal nerve (L4-L5-S1)
S1 Root
Inferior Gluteal nerve (L4-L5-S1) Common peroneal nerve (L4-L5-S1-S2) Tibial nerve (L4-L5-S1-S2-S3)
FIGURE 8.39 Clinical findings in the evaluation of the S1 root. (Copyright J.M. True, D.C.)
TABLE 8.12 Differential Diagnosis of Sciatica • Intraspinal Causes Proximal to disk Conus and cauda equina lesions (e.g., neurofibroma, ependymoma) Disk level Herniated nucleus pulposus Stenosis (canal or recess) Infection: osteomyelitis or discitis (with nerve root pressure) Inflammation: arachnoiditis Neoplasm: benign or malignant with nerve root pressure) • Extraspinal Causes Pelvis Cardiovascular conditions (e.g., peripheral vascular disease) Gynecologic conditions Orthopedic conditions (e.g., osteoarthritis of hip) Sacroiliac joint disease Neoplasms (invading or compressing lumbosacral plexus) Peripheral nerve lesions Neuropathy (diabetic, tumor, alcohol) Local sciatic nerve conditions (trauma, tumor) Inflammation (herpes zoster) Source: Glick, T.H., Neurologic Skills, Blackwell Scientific, Oxford, 1991. With permission.
older population. Hakelius and Hindmarsh73 noted that the incidence of disk herniation among patients in whom the Achilles reflex was absent was higher than among those in whom this reflex was simply diminished. The H-reflex is a common electrodiagnostic procedure which correlates well with the Achilles tendon reflex response.78 The peroneal muscles have a significant S1 contribution. The function of the peroneus longus and brevis muscles can be evaluated simultaneously by having the patient walk on the medial borders of the feet while everting the feet. The gastrocnemius–soleus complex can be evaluated by having the patient perform 20 repetitive toe raises while weight bearing. This may be performed with one or both feet. Plantar flexion paresis will result in early muscle fatigue and degradation of plantar flexion range of motion with eventual loss of the ability to successfully plantarflex the foot. S1 denervation results in greater fatigue and paresis of plantar flexion than dorsiflexion. On occasion, pseudohypertrophy or unilateral calf enlargement may occur on the side of S1 denervation secondary to fatty replacement and connective tissue proliferation. Usually with a chronic S1 radiculopathy, there will be a relative diminishment of midcalf circumference of the involved limb.
Classic Signs and Symptoms of Radiculopathy
245
!
FIGURE 8.40 Various pathological changes compromising the cauda equina. (Copyright J.M. True, D.C.)
8.11.8 S2–S5 RADICULOPATHY Patients with middle to lower sacral radiculopathy often report sensory disturbances involving the calf, posterior thigh, genital, and perianal regions. Sensory and sphincteric abnormalites in the perineal and perirectal regions are not associated with lumbar radiculopathies except when large central herniations compress the sacral roots. With a sacral radiculopathy, the external anal sphincter may fail to contract in response to pricking of the skin or mucous membrane, referred to as absence of the anal wink response. Bowel and bladder control is often dysfunctional, but the degree of impairment is dependent on the severity of the lesion. Sacral polyradiculopathy may lead to a bladder hypotony. Intraforaminal tumors, pelvic masses, and prostate enlargement should be included in the differential diagnosis. Without diagnostic imaging correlation of a space-occupying lesion or disk herniation causing S2–S4 radiculopathy, it is nearly impossible to distinguish a pudendal nerve injury from an S2–S4 radiculopathy using electrodiagnosis alone.
8.12 CAUDA EQUINA SYNDROME Lesions of the cauda equina often contribute to pain in a lumbosacral radicular distribution (Figure 8.40). The reported pain may be unilateral or bilateral. A sustained Valsalva maneuver will occasionally increase the pain intensity. A large space-occupying lesion in the cauda equina can lead to lower extremity hypotonia, areflexia, paresis, or paralysis. Muscle groups commonly involved include the gluteal muscles, posterior thigh muscles, and anterolateral
Severe spinal canal narrowing
FIGURE 8.41 Fast spin echo parasagittal T2-weighted image of the lumbar spine demonstrating a grade I spondylolisthesis at L3–L4. Also noted is a central disk herniation with extruded disk material extending posterior to the L3 vertebral body and congenital narrowing of the spinal canal secondary to short pedicles. These findings all contribute to near complete obliteration of the central spinal canal. (Courtesy Ronald Landau, M.D.)
muscles of the lower leg. In the early stages, symptoms may be limited to intermittent low back pain and neurogenic claudication. In severe cases, a lower motor neuron paraplegia may occur (Figures 8.41 and 8.42).
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
A Presurgical sagittal T2 weighted image
C
B
Postsurgical laminectomy
FIGURE 8.42 (A) Fast spin echo parasagittal T2-weighted midline image demonstrating a pronounced central disk herniation nearly obliterating the spinal canal. (B) Axial fast spin echo T2-weighted image at L5–S1 of the same patient. This axial acquisition demonstrates a pronounced disk herniation, which extends into the spinal canal, compromising the cauda equina. (C) Axial fast spin echo T2-weighted image at L5–S1 depicting the postsurgical hemilaminectomy.
The sensory evaluation usually reveals an asymmetric hypoalgesia in the saddle region. This typically involves the perineal, anal, and genital regions. Dysesthesia may extend along the anterolateral aspect of the leg. Urinary and rectal sphincteric changes are similar to those seen with a lesion of the conus medularis. Lesions of the cauda equina typically associate with early lower extremity symptoms progressing to sphincteric dysfunction, whereas lesions of the conus medularis often present with early sphincter dysfunction and progress to involve the lower extremities.
8.12.1 HIGH LESION
WITHIN THE
CAUDA EQUINA
The nerve roots making up the cauda equina descend along the conus medularis and are generally organized into anterolateral and dorsolateral bundles. This bundling leads to increased susceptibility to polyradiculopathy if a mass effect should occur. The upper portion of the cauda equina within the central lumbar canal tends to reside along the posterior third of the thecal sac, assuming a crescent appearance. Posterior aggregation increases nerve root susceptibility to a mass effect from buckling
of the ligamentum flavum or spinal canal stenosis. With nerve root adhesion, the nerves of the cauda equina are also extremely vulnerable to compression from a midline disk lesion. In the absence of nerve root adhesion, there is normally adequate reserve capacity for compensatory deviation of the nerve root bundle anteriorward in the canal. A pincer stenosis arising from coexisting anterior and posterior canal stenosis creates a loss of reserve space and increases the risk of a compressive cauda equina syndrome. The nerve roots of the cauda equina, although well vascularized, are not impervious to insult from vascular insufficiency. A vulnerable region of vascularity, susceptible to compression has been identified at the junction of the proximal and middle cauda equina nerve roots.79 Spinal stenosis or a space-occupying lesion in this location could result in neural ischemia, with the signs and symptoms being based on the cauda equina nerve roots affected. A large, high, midline cauda equina lesion, such as an ependymoma, will often result in a lumbar polyradiculopathy involving the L2, L3, and L4 segments. This will result in significant quadriceps paresis and patellar
Classic Signs and Symptoms of Radiculopathy
hyporeflexia. High to middle cauda equina compromise will lead to an absent or severely diminished patellar and hamstring MSR response. Often a significant degree of atrophic change proximal to the knee secondary to axonopathy is present. The patient often complains of great difficulty climbing stairs.
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49. Ito, M., Incorvaia, K.M., Yu, S.F., Fredrickson, B.E., Yuan, H.A., and Rosenbaum, A.E., Predictive signs of discogenic lumbar pain on magnetic resonance imaging with discography correlation, Spine, 23:1252–1258, 1998. 50. Smith, B.M., Hurwitz, E.L., Solsberg, D., Rubinstein, D., Corenman, D.S., Dwyer, A.P., and Kleiner, J., Interobserver reliability of detecting lumbar intervertebral disk high-intensity zone on magnetic resonance imaging and association of high-intensity zone with pain and annular disruption, Spine, 23:2074–2080, 1998. 51. Toyone, T., Takahashi, K., Kitahara, H., Yamagata, M., Murakami, M., and Moriya, H., Visualisation of symptomatic nerve roots: prospective study of contrastenhanced MRI in patients with lumbar disk herniation, J. Bone Joint Surg. Br., 75:529–533, 1993. 52. Jinkins, J., MR of enhancing nerve roots in the unoperated lumbosacral spine, Am. J. Neuroradiol., 14:193–202, 1993. 53. Jinkins, J.R. and Runge, V.M., The use of MR contrast agents in the evaluation of disease of the spine, Top. Magn. Reson. Imaging, 7:168–180, 1995. 54. Carter, G.T. and Fritz, R.C., Electromyographic and lower extremity short time to inversion recovery: magnetic resonance imaging findings in lumbar radiculopathy, Muscle Nerve, 20:1191–1193, 1997. 55. Sallomi, D., Janzen, D.L., Munk, P.L., Connell, D.G., and Tirman, P.F., Muscle denervation patterns in upper nerve injuries: MR imaging findings and anatomic basis, Am. J. Roentgenol., 171:779–784, 1998. 56. Brazis, P.W., Masdeu, J.C., and Biller, J., Localization in Clinical Neurology, 2nd ed., Boston, MA: Little, Brown, 1990. 57. Chen, T.Y., The clinical presentation of uppermost cervical disk protrusion, Spine, 25:439–442, 2000. 58. Bogduk, N., The anatomical basis for cervicogenic headache, J. Manip. Physiol. Ther., 15:67–70, 1992. 59. Gunn, C. and Milbrandt, W.E., Tennis elbow and the cervical spine, Can. Med. Assoc J., 114:803–809, 1976. 60. Vargo, M.M. and Flood, K.M., Pancoast tumor presenting as cervical radiculopathy, Arch. Phys. Med. Rehabil., 71:606–609, 1990. 61. Lyu, R.K., Chang, H.S., Tang, L.M., and Chen, S.T., Thoracic disk herniation mimicking acute lumbar disk disease, Spine, 24:416–418, 1999. 62. Dreyfuss, D.D., Intercostal somatosensory evoked potentials; a new technique, Am. J. Phys. Med. Rehabil., 72:144–150, 1993. 63. Hoppenfeld, S., Orthopaedic Neurology: A Diagnostic Guide to Neurological Levels, Philadelphia, PA: Lippincott, 1977. 64. Deyo, R.A., Loeser, J.D., and Bigos, S.J., Herniated lumbar intervertebral disk, Ann. Intern. Med., 112:598–603, 1990. 65. Kramer, J., Clinical syndromes, in Kramer, J., Ed., Intervertebral Disk Diseases: Causes, Diagnosis, Treatment and Prophylaxis, New York: Thieme Medical, 170–198, 1990. 66. Chotigavanich, C. and Sawangnatra, S., Anomalies of the lumbosacral nerve roots: an anatomic investigation, Clin. Orthoped., (278):46–50, 1992.
Classic Signs and Symptoms of Radiculopathy
67. Maiuri, F. and Gambardella, A., Anomalies of the lumbosacral nerve roots, Neurol. Res., 11:130–135, 1989. 68. Prestar, F.J., Anomalies and malformations of lumbar spinal nerve roots, Minim. Invasive Neurosurg., 39:133– 137, 1996. 69. Kikuchi, S., Hasue, M., Nishyama, K., and Ito, T., Anatomic features of the furcal nerve and its clinical significance, Spine, 11:1002–1007, 1986. 70. Parke, W. and Watanabe, R., Lumbosacral intersegmental epispinal axons and ectopic ventral nerve rootlets, J. Neurosurg., 67:269–277, 1987. 71. Naftulin, S., Fast, A., and Thomas, M., Diabetic lumbar radiculopathy: sciatica without disk herniation, Spine, 18:2419–2422, 1993. 72. Nitta, H., Tamima, T., Surgiyama, H., and Morama, A., Study on dermatomes by means of selective lumbar spinal nerve block, Spine, 18:1782–1786, 1993. 73. Hakelius, A. and Hindmarsh, J., The significance of neurological signs and myelographic findings in the diagnosis of lumbar root compression, Acta Orthoped. Scand., 43:239–246, 1972.
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74. Hasue, M., Kikuchi, S., Sakuyama, Y., and Ito, T., Anatomic study of the interrelationship between lumbosacral nerve roots and their surrounding tissues, Spine, 8:50–58, 1983. 75. Bogduk, N. and Twomey, L.T., Clinical Anatomy of the Lumbar Spine and Sacrum, New York: J.A. Majors, 1997. 76. Madden, P.J. and Lazaro, R., Drooping of the big toe: another diagnostic marker for L-5 radiculopathy, South. Med. J., 90:209–210, 1997. 77. Falconer, M., McGeorge, M., and Begg, A., Observations on the cause and mechanism of symptom-production in sciatica and low-back pain, J. Neurol. Neurosurg. Psychiatry, 11:13–26, 1948. 78. Wilbourn, A., The value and limitations of electromyographic examination in the diagnosis of lumbosacral radiculopathy, in Hardy, R., Ed., Lumbar Disc Disease, New York: Raven, 1982: 65–109. 79. Cramer, G., The lumbar region, in Cramer, G. and Darby, S., Eds., Basic and Clinical Anatomy of the Spine, Spinal Cord, and ANS, St Louis, MO: Mosby, 1995: 177–221.
Section 3 Peripheral Nerve Entrapment and Compression Neuropathy
9
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury*
The peripheral nervous system is susceptible to injury at various locations in the body where neurovascular components pass through narrowed anatomical spaces. Generally, the boundaries of these spaces are formed by a combination of osseous, ligamentous, muscular, or fibrous tissues. A peripheral entrapment may occur due to compression, adhesion, or traction of a nerve or its vasculature within these confining anatomical tunnels. The peripheral nerve has an integral vascular complex. For our purposes in considering entrapment, when we speak of the peripheral nerve, we consider not only the neuronal functions, but also the vascular component incorporated within and around the nerve. Intermittent pressure on the nerve may then produce transient symptoms such as paresthesia or numbness. Chronic nerve compression may produce symptoms of diffuse pain, numbness, paresthesia, and paresis. Some entrapment neuropathies or “tunnel syndromes” are easily recognized by clinical evaluation and electrodiagnostics, as frequently is the case with carpal tunnel syndrome. Diagnosis may also be particularly difficult when the tunnel syndrome mimics other possible compressive etiology or when there is an underlying metabolic or other pathologic disorder contributing to the syndrome. This chapter will discuss peripheral nerve anatomy and physiology, pathophysiology as it relates to compression, and pathomechanisms that predispose the nerves to entrapment.
9.1 GENERAL ORGANIZATION OF PERIPHERAL NERVE DISTRIBUTION The neurons that make up peripheral nerves have their cell bodies contained within or near the spinal cord in the anterior horn (skeletal motor), lateral horn (autonomic motor), and dorsal root ganglia (sensory). Cranial nerves have cell bodies in analogous areas of the brainstem (with the exceptions of the olfactory nerve and the retinal visual receptors). Axons emerge from the spinal cord as anterior and posterior rootlets that coalesce to form the nerve root. The nerve roots exit through intervertebral foramina.
Nerve roots are organized segmentally. Injury or involvement of these roots leads to signs and symptoms that are expressed in either a dermatomal or myotomal pattern. In all regions of the spine, the nerve roots divide into an anterior primary division and a posterior primary division. The posterior primary divisions course to spinal segmental distributions. They divide into medial branches (generally sensory) and lateral branches (mainly motor). In the cervicothoracic, lumbar, and sacral regions of the spine, the anterior primary divisions of the nerve roots intermix in plexes. Branches from the plexes ultimately form named peripheral nerves. In contrast to the posterior primary divisions (which maintain the segmental orientation), the named peripheral nerves branching from the plexuses have distributions that may further contain several dermatomal or myotomal distributions. Only in the thoracic spine is this segmental organization of anterior rami maintained as the nerve roots become segmental peripheral nerves traveling in the intercostal zones. The peripheral nerve sensory and motor distributions are different from dermatomes or myotomes. Clinical testing of sensation and motor function will help differentiate a peripheral nerve distribution from a radicular distribution.
9.1.1 POSTERIOR PRIMARY DIVISIONS The medial branches of the posterior primary divisions of the cervical spine innervate the posterior aspect of the skull and the cervical spine in descending order beginning with the C2 root. The medial branch of the C2 posterior primary division forms the greater occipital nerve supplying the base of the skull and the upper cervical skin. The medial branch of the C3 posterior primary division forms the third occipital nerve supplying the cervical skin to the base of the skull (scalp). The medial branches of the C4–C5 posterior primary divisions supply skin of the lower cervical region into the shoulders. Medial branches of the C6–C8 posterior primary divisions supply motor fibers to the deep multifidus musculature. The lateral branches of the posterior primary divisions of the cervical spine supply erector spinae musculature of the cervical spine. The C2 lateral branches of the posterior
* This chapter written with Clifford M. Shooker, J. Donald Dishman, and P. Michael Leahy.
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primary divisions innervate more lateral upper cervical musculature including the obliquus capitis inferior, splenius, and longissimus capitis. C3 lateral branches of the posterior primary divisions provide fibers to the semispinalis capitis, while fibers from the C4–C8 lateral branches of posterior primary nerve root divisions innervate the other long erectors. The C1 posterior division forms the suboccipital nerve providing innervation to the suboccipital triangle. The C2 posterior primary division also supplies innervation to the obliquus capitis inferior as discussed above. The C1 nerve root lacks a dermatomal representation. Continuing down the spine, posterior primary divisions of the nerve roots generally supply one to three segmental levels of the intrinsic muscles and ligaments of the spine. A narrow area of skin on each side of the spine represents the sensory distribution of the medial branch of the posterior primary divisions.
9.1.2 GENERAL ORGANIZATION
OF
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PLEXUSES
The four main plexuses to consider relative to the peripheral nervous system (aside from autonomic plexuses) are cervical, brachial, lumbar, and sacral. The cervical plexus supplies innervation to the cervical spine, shoulder region, and posterior aspect of the cranium. The brachial plexus supplies innervation to the upper extremity. The lumbar plexus provides innervation to the anterior abdomen and pelvis, thigh (except posterior), and medial leg/foot, while the sacral plexus provides innervation to the buttock and other regions of the lower extremity.
9.2 CERVICAL PLEXUS The sensory distribution of the cervical plexus supplies the anterior neck, between the lower scalp and the upper chest (Figure 9.1).
9.2.1 CERVICAL PLEXUS: SENSORY INNERVATION TO THE HEAD AND NECK The cervical plexus includes fibers of the anterior primary divisions of C1–C4. The nerve roots from the C2–C3 levels send fibers to the posterior scalp and the upper cervical spine via three named branches: (1) the lesser occipital nerve, (2) the greater auricular nerve, (3) the cervical cutaneous nerve. The lesser occipital nerve supplies the mastoid region and part of the auricle. The distribution is anterior to that of the C2 posterior primary division, which also supplies the scalp as the greater occipital nerve. The greater auricular nerve has a distribution that extends from the mastoid process to the ear and skin over the posterior aspect of the mandible. The cervical cutaneous nerve has a distribution to the skin of the cervical spine.
FIGURE 9.1 The cervical plexus is formed by ventral rami of C1–C4 supplying motor and sensory innervation to the cervical/cranial region. (Copyright J.M. True, D.C.)
9.2.2 CERVICAL PLEXUS: SENSORY INNERVATION TO THE NECK AND SHOULDERS C3–C4 fibers blend together to form supraclavicular nerves. These nerves supply the lower aspect of the cervical spine and the skin over and anterior to the upper trapezius down to about the level of rib 3. Depending on your reference source, these may be called anterior, middle, and posterior supraclavicular nerves or (to more accurately reflect the sensory distribution) medial, intermediate, and lateral branches of the supraclavicular nerves.
9.2.3 CERVICAL PLEXUS IN RELATIONSHIP TO CRANIAL NERVES Both cervical and cranial nerve fibers provide innervation to the muscles of the anterior cervical spine including musculature of the hyoid bone. Communication occurs between fibers of the C1 anterior primary division and cranial nerve X (the vagus nerve). Communication also occurs between C1–C2 anterior primary divisions and cranial nerve XII (the hypoglossal nerve). In addition to supplying hyoid musculature (via the descendens hypoglossal branch), these nerves send fibers to the dura mater of the posterior skull via a recurrent meningeal branch. Cranial nerve XI (spinal accessory nerve) provides innervation to the upper
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
trapezius and the upper sternocleidomastoid. The cervical plexus also innervates these muscles with a branch of C2 to the lower sternocleidomastoid and branches of C3–C4 to the lower trapezius. Other branches of the cervical plexus communicate with the descendens hypoglossi. Fibers from roots C1–C3 form the descendens cervicalis, providing innervation to the omohyoid muscle. The descendens cervicalis joins with the descendens hypoglossi as it supplies the geniohyoid, thyrohyoid, sternohyoid, and sternothyroid muscles. The joining of C1 fibers of the descendens hypoglossi with the C1–C3 fibers of the descendens cervicalis creates a loop between these two motor fibers called the ansa cervicalis (or ansa hypoglossi). The descendens hypoglossi is the superior root of the ansa cervicalis; the descendens cervicalis is the inferior root. Other muscular branches of the cervical plexus include motor distribution of C1 to the suboccipital triangle. (Both anterior and posterior primary divisions of C1 supply these muscles.) C1–C4 supplies motor branches to the longus capitis and the longus colli.
9.2.4 MOTOR FIBERS WITHIN THE CERVICOBRACHIAL PLEXUS Some cervical plexus fibers provide motor innervation in conjunction with the brachial plexus. The C1–C4 contribution to the longus colli joins C5–C8 fibers from the brachial plexus. C3–C4 supplies motor innervation to the upper scalene musculature, whereas the lower portion of the scalenes are innervated by C5–C8 roots of the brachial plexus. C3–C5 fibers join together to form the dorsal scapular nerve. The dorsal scapular nerve innervates the levator scapula and rhomboids; the C5 contribution is from the brachial plexus. In a similar manner C3–C5 blends cervical and brachial plexus fibers to form the phrenic nerve.
9.3 BRACHIAL PLEXUS Anterior primary division fibers of the C5–T1 spinal levels form the brachial plexus. As they course laterally away from the cervical spine, these roots form three trunks. Each trunk splits into divisions, and the divisions redistribute as cords. The cords ultimately form the major peripheral nerve branches (Figure 9.2). Trunks are formed in the proximal portion of the brachial plexus from the anterior primary division of the cervical roots. These are named upper, middle and lower trunks. The middle trunk is formed by the middle nerve root C7; C5–C6 merge to form the upper trunk, and C8–T1 merge to form the lower trunk. The next level of organization of the brachial plexus is termed division. Each of the three trunks (upper, middle, and lower) divides into anterior and posterior divisions.
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With some exceptions the anterior divisions supply the anterior upper extremity, while the posterior divisions supply the posterior upper extremity. The next level of organization of the brachial plexus is termed cord. The three anterior divisions redistribute fibers forming the lateral and medial cords. The posterior divisions of all three trunks merge to form the posterior cord, which will generally supply the posterior aspect of the upper extremity. The anterior divisions of the upper two trunks join together to form the lateral cord. The anterior division of the lower trunk extends to become the medial cord. The lateral cord will supply sensation of the lateral aspect of the anterior upper extremity and the medial cord will supply the medial aspect. Upper extremity sensory innervation may be approximately divided into medial and lateral regions of the anterior part of the extremity. These are differentiated from the posterior aspect of the extremity. Branches of the lateral cord include the musculocutaneous nerve and a contribution to the median nerve. Branches of the medial cord include the ulnar nerve and a contribution to the median nerve. Branches of the posterior cord include the radial nerve, the axillary nerve, the subscapular nerves, and the thoracodorsal nerve. Anatomic variation may lead to slightly different segmental contributions for the individual nerves. As such, the segmental distributions below should be considered general guidelines. The median nerve (C5–T1) most commonly supplies sensation to the lateral three digits and the lateral half of the fourth digit of the hand, the underlying thenar eminence musculature (with the exception of the adductor and extensor pollicis), pronators of the forearm, the lateral aspect of the long flexors of the wrist and hand, and the first two lumbricals. The median nerve has an anterior interosseous branch in the forearm that supplies motor innervation to the flexor pollicis longus, flexor digitorum profundus, and pronator quadratus (Figure 9.3). The ulnar nerve (C7–T1) generally supplies sensation to the small finger and the medial half of the fourth digit of the hand, underlying hypothenar eminence, intrinsic muscles of the hand (except lumbricals 1 to 2), and the more medial long flexors of the wrist and hand. The other medial cord branches are the medial brachial cutaneous and medial antebrachial cutaneous nerves. These may also branch directly from the ulnar nerve (Figure 9.4). The radial nerve (C5–C8) supplies extensors of the upper extremity including the triceps, anconeus, extensor compartment of the forearm, and the supinator muscle. Posterior cord fibers also supply sensation to the posterior aspect of the extremity by the posterior brachial cutaneous and the posterior antebrachial cutaneous nerves. The radial nerve divides into a deep and superficial branch in the forearm. The superficial branch supplies sensation to the hand; the deep branch supplies the extensor musculature
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Five ventral rami
Three trunks: (1) superior, (2) middle, (3 )inferior
Three posterior divisions
Three cords: (1) lateral, (2) posterior, (3) medial
Three anterior divisions C5 C6 C7 C8 T1
The radial nerve is a direct extension of the posterior cord of the brachial plexus.
1 2 3
1 2 3
Musculocutaneous n. Axillary n.
Median n.
Ulnar n.
FIGURE 9.2 The brachial plexus is formed by ventral rami of C5–T1. These form the superior, middle, and inferior trunks that divide into anterior and posterior divisions. The divisions ultimately form the medial, lateral, and posterior cords that branch into the main nerves of the upper extremity. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 1984. With permission.)
of the forearm. Terminating as the posterior interosseous nerve, the deep branch supplies sensory innervation to the ligaments and capsule of the wrist (Figure 9.5). The musculocutaneous nerve (C5–C6) supplies flexors of the brachium including coracobrachialis, biceps, and brachialis. This nerve is aptly named in that the “musculo” distribution from the nerve is proximal and regionally separate from the “cutaneous” distribution. The cutaneous distribution of the musculocutaneous nerve supplies the lateral forearm via the lateral antebrachial cutaneous nerve (Figure 9.6). The axillary nerve (C5–C6) arises from the posterior cord of the brachial plexus. A small articular branch to the glenohumeral capsule may arise from the axillary nerve before it passes to the posterior shoulder. The axillary nerve passes through the quadrilateral space and divides into a superior and inferior branch (also referred to as anterior and posterior branch). The superior branch travels with the circumflex artery around the humeral neck to innervate the deltoid muscle extending to the anterior muscle. Small branches may be given off that innervate the skin overlying the anterior and lateral shoulder. The inferior
branch supplies the teres minor muscle (Figure 9.7). The largest sensory component of the nerve arises from the inferior branch, which forms the lateral brachial cutaneous nerve. The overlying skin of the mid/lower shoulder region is supplied via the lateral brachial cutaneous nerve. The thoracodorsal nerve (C5–C7) innnervates the latissimus dorsi. The subscapular nerves (upper and lower) (C5–C7) supply the subscapularis and teres major, respectively.
9.3.1 NERVES ARISING DIRECTLY FROM THE NERVE ROOTS OR THE BRACHIAL PLEXUS With the exception of the serratus anterior, the muscles served by these nerves receive innervation from both the cervical plexus and the brachial plexus. These are muscles of the cervical spine and respiratory muscles including the scalenes, longus colli, levator scapula, rhomboids, diaphragm, and serratus anterior. The brachial plexus contributes C5–C8 fibers to the nerve to the scalenes. These fibers join the C3–C4 contribution to the scalenes from the cervical plexus. C5–C8
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
257
Ulnar nerve
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FIGURE 9.3 The median nerve supplies sensory innervation to the lateral anterior hand, and motor supply to flexor muscles, pronators, and thenar eminence muscles. (Copyright J.M. True, D.C.)
fibers of the brachial plexus also contribute to the nerve to the longus colli. These fibers join the C1–C4 contribution to the longus colli from the cervical plexus. C5 fibers of the brachial plexus contribute to the dorsal scapular nerve to supply the levator scapula and rhomboid muscles. These muscles also receive C3–C4 contribution from the cervical plexus. C5 fibers of the brachial plexus also join C3–C4 fibers that form the phrenic nerve to innervate the diaphragm. The contribution of the brachial plexus to the phrenic nerve is called the accessory phrenic nerve. The long thoracic nerve is made up of branches of the C5–C7 ventral rami. It does not receive any contribution from the cervical plexus. The nerve crosses the middle scalene, traveling caudally and laterally to descend through the axilla. The long thoracic nerve lays on top of the serratus anterior along the lateral chest. It innervates the serratus anterior, sending branches to each of the digitations. The serratus anterior stabilizes the scapula against the rib cage; paresis of the serratus anterior causes winging of the scapula.
9.3.2 NERVE BRANCHES ARISING UPPER TRUNK
FROM THE
These supply shoulder musculature with C5–C6 fibers. The suprascapular nerve is formed from C5–C6 fibers emanating from the upper trunk. This nerve supplies innervation to the supraspinatus and infraspinatus muscles.
1. Flexor digitorum profundus 2. Flexor carpi ulnaris 3. Palmaris brevis 4. Flexor digiti minimi 5. Opponens digiti minimi 6. Abductor digiti minimi 7. Lumbricals III and IV 8. Palmar and dorsal interossei 9. Adductor pollicis 10. Deep head of the flexor pollicis brevis
1
2
Palmar cutaneous n. 10 9 8
3
Dorsal cutaneous n. 4 5 6 7
Digital nerves
FIGURE 9.4 The ulnar nerve forms the medial cutaneous nerves of the arm and forearm as well as supplying sensation of the medial hand. It also supplies motor innervation to forearm flexors, the hypothenar eminence, and the intrinsic muscles of the hand. (Copyright J.M. True, D.C.)
Upper trunk fibers also send a branch to innervate the subclavius muscle.
9.3.3 NERVES FORMED WITH CONTRIBUTIONS FROM BOTH THE MEDIAL AND LATERAL CORDS In addition to the median nerve, the pectoral nerves (medial and lateral) also contain C5–T1 fibers.
9.4 LUMBAR PLEXUS The lumbar plexus is comprised of L1–L4 fibers. Branches of the plexus supply the anterior aspect of the abdomen and pelvis along with the bulk of the thigh; they do not innervate the posterior thigh. One branch continues below the knee, along the medial aspect of the leg into the foot. L1 fibers of the lumbar plexus descend along the anterior aspect of the lower abdomen as the iliohypogastric and ilioinguinal nerves. These supply the lower abdomen and continue into the inguinal region. L1–L2 sensory fibers of the genitofemoral nerve extend to the genitalia and the upper medial thigh. The genitofemoral nerve supplies motor innervation to the cremaster muscle (Figure 9.8). L1–L3 fibers form the nerve to the psoas, piercing the psoas to travel along the anterior aspect of the muscle. It may continue to supply the iliacus (or the iliacus may receive a distinct branch). Three other branches of the lumbar plexus supply the bulk of the thigh. The lateral thigh is supplied by L2–L3 fibers of the lateral femoral cutaneous nerve. The anterior
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Radial nerve Spiral groove 1. Triceps 2. Posterior cutaneous nerve of arm 3. Brachioradialis 4. Extensor carpi radialis longus 5. Extensor carpi radialis brevis 6. Anconeus 7. Extensor carpi ulnaris 8. Supinator
1 2
3 4 6
5
7 8
9. Extensor digitorum 10. Extensor digiti minimi 11. Extensor indicis 12. Extensor pollicis longus 13. Extensor pollicis brevis 14. Abductor pollicis longus
9 10 11 12 13
Superficial radial n. 14
Dorsal digital nerves
FIGURE 9.5 The radial nerve forms the posterior cutaneous nerves of the arm and forearm as well as supplying sensory innervation to the posterior lateral hand, and motor supply to the extensor compartment of the forearm, supinator, and abductor pollicis longus. (Copyright J.M. True, D.C.)
Musculocutaneous nerve
Biceps
Coracobrachialis
Brachialis
Articular branch
Axillary nerve
Axillary n. Nerve to deltoid
2 1 3
Inferior division Nerve to teres minor
Superior division Lateral brachial cutaneous n.
4
1. Articular branch 2. Lateral antebrachial cutaneous 3. Posterior branch of the lateral antebrachial cutaneous 4. Anterior branch of the lateral anterior cutaneous
FIGURE 9.6 The musculocutaneous nerve arises from the lateral cord of the brachial plexus. The musculocutaneous supplies motor innervation to the anterior arm and sensation to the lateral forearm. (Copyright J.M. True, D.C.)
FIGURE 9.7 The axillary nerve passes posteriorly through the quadrilateral space and divides into a superior and inferior division. The superior branch of the axillary nerve continues around the neck of the humerus with the circumflex artery. (Copyright J.M. True, D.C.)
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
259
L2 L3 L4
Obturator nerve
1. Obturator externus 2. Adductor brevis 3. Adductor longus 4. Adductor magnus 5. Gracilis
1 2
L1
3
Iliohypogastric n.
4 L2
Ilioinguinal n. Genitofemoral n. Lateral femoral cutaneous n.
L3
5 Cutaneous branch
L4
Femoral n. Obturator n.
FIGURE 9.8 The lumbar plexus supplies innervation to the anterior abdomen, pelvis, bulk of the thigh (except posterior structures), and medial leg/foot. (Copyright J.M. True, D.C.)
FIGURE 9.9 The obturator nerve supplies sensation to the medial thigh and motor innervation to the adductors and obturator externus. (Copyright J.M. True, D.C.)
thigh is supplied by the femoral nerve, and the medial thigh is supplied by the obturator nerve; both the femoral and obturator nerves are formed with L2–L4 fibers of the lumbar plexus. The femoral nerve supplies the underlying quadriceps, sartorius, and pectineus musculature; the obturator nerve supplies the adductor musculature (as well as the obturator externus). The sensory distribution of the femoral nerve continues below the knee along the medial aspect of the leg with L4 fibers of the saphenous nerve. Only the L2–L4 branches of the lumbar plexus divide into anterior and posterior divisions (analogous to the brachial plexus anterior and posterior divisions). Anterior divisions of the L2–L4 branches form the obturator nerve. The posterior divisions form the lateral femoral cutaneous nerve and the femoral nerves. The analogy to the brachial plexus is a loose one in that neither the lateral femoral cutaneous nerve nor the femoral nerves supply the posterior extremity (Figures 9.9 to 9.11).
medial leg and foot, which are supplied by the saphenous nerve). Analogous to the brachial plexus, the lumbosacral plexus divides into anterior and posterior divisions (Figure 9.12). The largest division of the lumbosacral plexus is the sciatic nerve. It receives L4–S3 fibers from both the anterior and posterior divisions of the sacral plexus roots. The nerve courses down the posterior aspect of the thigh and the extremity to supply the bulk of the lower extremity below the knee. Motor innervation begins above the knee as the sciatic nerve supplies the hamstring musculature; it also innervates the adductor magnus and the popliteus. The large sciatic nerve contains two divisions: the posterior tibial (posterior division fibers) and the common peroneal nerves (anterior division fibers). These may divide in the thigh but are functionally and anatomically separated at the popliteal fossa (Figure 9.13). The tibial nerve descends in the area of the popliteal fossa, supplying the flexors of the calf and ankle along with the long flexors of the toes. Its sensory distribution includes the skin over the posterior calf and the sole of the foot. This nerve continues in the foot as the medial and lateral plantar nerves, after sending a calcaneal branch to the heel (Figure 9.14). The common peroneal nerve wraps around the lateral aspect of the lower extremity to divide into a deep and
9.5 LUMBOSACRAL PLEXUS The lumbosacral plexus contains fibers of the L4–S4 nerve roots. The lumbosacral plexus supplies the remainder of the lower extremity including the buttock, posterior thigh, and bulk of the leg and foot (with the exception of the
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
The lateral femoral cutaneous nerve arises from the posterior portion of the lumbar plexus, picking up fibers from spinal levels L2 and L3
L2 L3 L4 1 2
Femoral nerve
Inguinal ligament
3 4
It then penetrates the psoas and crosses the iliacus muscle.
It reaches its most likely site of entrapment as it passes into the thigh under the lateral portion of the inguinal ligament.
6 5 8
7
1. Iliacus 2. Psoas 3. Sartorius 4. Pectineus
Quadriceps femoris muscle 5. Rectus femoris 6. Vastus intermedius 7. Vastus medialis 8. Vastus lateralis Saphenous n.
The anterior branch innervates the anterolateral thigh from about 10 cm below the anterior superior iliac spine to the knee. It is distributed only to the skin and fascia.
FIGURE 9.10 The lateral femoral cutaneous nerve supplies sensation to the lateral thigh. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 1984. With permission.)
superficial portion. The superficial portion runs along the lateral aspect of the leg innervating the peroneal muscles in addition to the skin overlying them. It supplies sensation to the majority of the dorsal foot. The deep peroneal nerve runs along the anterior aspect of the leg, supplying the extensors of the foot and ankle (including tibialis anterior), but it does not supply the overlying skin (which is mainly supplied by the superficial peroneal nerve). The deep peroneal nerve has a sensory distribution confined to a variable portion of the dorsal aspect of the medial two digits and their web spaces (Figure 9.15). The sural nerve is formed by contributions of both the tibial nerve and common peroneal nerve. This purely sensory nerve provides innervation to the distal aspect of the lateral leg and foot. The posterior femoral cutaneous nerve leaves the pelvis through the greater sciatic notch running alongside the
FIGURE 9.11 The femoral nerve supplies sensation to the anterior thigh and medial leg (via the saphenous nerve) and motor innervation to the sartorius, pectineus, and quadriceps. (Copyright J.M. True, D.C.)
sciatic nerve. This is a sensory nerve comprised of fibers of S1–S3 that innervate the skin of the posterior thigh. Nerves to the gluteal musculature are the superior (L4–S1) and inferior (L5–S2) gluteal nerves. These are named relative to their relationship to the piriformis muscle. The superior gluteal nerve passes above the piriformis to supply the tensor fascia lata (TFL) and the gluteus medius and minimus. The inferior gluteal nerve passes below the piriformis to supply the gluteus maximus. In contrast, the overlying skin is supplied by clunial nerves arising from posterior primary rami of the same segments and the inferior clunial nerve with S2–S3 fibers. S1–S2 fibers of the posterior division of the sacral plexus supply the piriformis as a distinct nerve to the piriformis. The other external rotators are supplied by branches of the anterior divisions including the quadratus femoris, gemelli, and obturator internus. Obturator externus receives lumbar plexus innervation via the obturator nerve. The sciatic plexus also has anterior and posterior divisions of the nerve roots. Somewhat conversely, given their cutaneous distributions, the anterior divisions form the tibial contribution to the sciatic nerve. The posterior division forms the peroneal contribution. The posterior divisions also go to form the posterior femoral cutaneous nerve, gluteal nerves, the nerve to the piriformis, and clunial nerves. S2–S4 fibers form the pudendal nerve joining the pudendal plexus to pelvic organs including the genitalia.
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
261
L5
S1
Superior gluteal n. Common peroneal n. Inferior gluteal n.
S3
Tibial n.
S2
S4
Posterior femoral cutaneous n. S5 Pudendal n. Coccygeal roots
FIGURE 9.12 The lumbosacral plexus supplies the posterior thigh and bulk of the leg below the knee with the exception of the medial aspect. (Copyright J.M. True, D.C.)
The pudendal plexus also provides branches to the coccygeus, levator ani, and anal sphincter.
9.6 AUTONOMIC NERVOUS SYSTEM No discussion of the peripheral nervous system would be complete without mention of the autonomic nervous system. This visceral efferent system has its primary cell bodies in the lateral horn of the spinal cord either at T1–L1(2) (sympathetic) or S2–S4 and brainstem analogs (parasympathetic). These fibers send myelinated white rami communicantes to a ganglion either anterior to the spine (prevertebral ganglia of the sympathetic system) or near the target organ (parasympathetic). Gray ramus communicantes travel between the ganglion and the target tissue. Prevertebral ganglia include the three cervical chain ganglia (superior, middle, and anterior), segmental thoracic ganglia, and varying numbers of lumbar ganglia. Fibers carrying autonomic motor innervation to target tissues will travel in conjunction with sensory fibers of the shared segmental level. Sensory innervation to the anterior aspect of the intervertebral disk is carried in association with autonomic fibers; however, the autonomic nervous system is defined as a purely efferent system; the sensory
FIGURE 9.13 The sciatic nerve supplies the hamstrings as well as continuing as the tibial and common peroneal nerve; these two nerves send branches that merge to form the sural nerve. (Copyright J.M. True, D.C.)
fibers traveling with it are not autonomic. For this reason, there are anatomic and reflexogenic relationships between disk injury at one segmental level and other levels of the spine. In the lumbar spine, discogenic pain from L4–S1 runs with fibers of the prevertebral ganglia entering the spine at the L1–L2 intervertebral foramen (IVF) level, creating pain referrals other than would be expected from dermatomal relationships.
9.7 RELEVANT ANATOMY OF THE PERIPHERAL NERVE Peripheral nerves are comprised of bundles of axons and supportive tissues. A neuron of the peripheral nerve is an individual cell comprised of a cell body, dendrites, and an axon. Variable numbers of dendrites extend from a cell body to receive stimuli from other neurons. An axon extends from the cell body to run within the peripheral nerve trunk. The axon transmits the electrical impulse of
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
A. Medial plantar nerve 1. Proper plantar digital n. 2. Common plantar digital n.
3. Flexor hallucis brevis 4. Lumbricals 1 & 2 5. Abductor hallucis
6. Flexor digitorum brevis
1
2
! " # $ # $ %
7
3 4 8 9 10 5 6
11
12
Sural nerve
13 A B
B. Lateral plantar nerve 7. Proper plantar digital n. 8. Common plantar n. 9. Abductor hallucis
2
1
10. Lumbricals 3 & 4
1. Lateral calcaneal
11. Interossei
2. Terminal branch of sural n. (lateral dorsal cutaneous)
12. Quadratus plantae 13. Abductor digiti minimi
FIGURE 9.14 The tibial nerve supplies sensory innervation to the calf and (via the plantar nerves) the sole of the foot. It supplies motor innervation to the muscles of the calf and intrinsic muscles of the plantar foot and a contribution to the sural nerve. (Copyright J.M. True, D.C.)
the action potential along its length and releases neurotransmitters to communicate with other cells. Axons of peripheral nerves form the longest component of communication between the central nervous system (CNS) and the periphery. The cell bodies forming the basis of the peripheral nerve are found either in the spinal cord gray matter or the dorsal root ganglion. Cell bodies contain the bulk of the metabolic machinery for the neuron. Ribosomes and associated endoplasmic reticulum within the cell body form proteins, including neurotransmitters and neurotrophins.
Neurotransmitters may be transported along the axon as discrete molecules or packaged in vesicles by the Golgi apparatus of the cell body. The axon contains neurofilaments and neurotubules forming the cytoarchitecture of the axon. These assist in axoplasmic transport of the neurotransmitters. The axon also contains axoplasm (analogous to the cytoplasm of the cell body) and mitochondria interspersed along its length. Impulse transmission between cells is accomplished by synaptic vesicle release of neurotransmitters at the terminal bouton of the presynaptic cell. After crossing the synapse, neurotransmitters are taken up by
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
Common peroneal nerve Superficial peroneal nerve
263
Motor distribution of the deep peroneal nerve Tibialis anterior Extensor digitorum longus
Deep peroneal nerve
Extensor hallucis longus Peroneus tertius Extensor digitorum brevis
The superficial peroneal nerve innervates the peroneus longus and brevis; it provides sensory supply for the dorsum of the foot and the lower anterolateral leg.
Sensory innervation is limited to the dorsal web space between toes 1 and 2.
FIGURE 9.15 The peroneal nerve supplies the peroneal muscles by the superficial peroneal branch and anterior compartment of the leg (and extensor digitorum brevis) by the deep peroneal branch. The superficial peroneal nerve supplies sensation of the lateral leg and dorsal foot; the deep branch supplies the web space between toes one and two. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med. 20(6), 1984. With permission.)
the postsynaptic cell membrane eliciting an excitatory postsynaptic potential, driving the postsynaptic cell towards threshold of depolarization. Intracellular organelles, vesicles, and chemical compounds are moved both proximal and distal along the axon through active transport mechanisms. This bidirectional streaming of intracellular compounds and components is termed anterograde (away from the cell body) and retrograde (towards the cell body) axonal transport or axoplasmic transport. Purposes of axoplasmic transport include intracellular production of neurotransmitter substances and neurotrophins, modulation of neuronal cell metabolism, turnover of vesicle membranes, and regulation of organelle function. Additionally, demands placed on the neuron influence plastic changes in the synapse that are supported by axoplasmic transport. Plastic changes may include a greater quantum of neurotransmitter release, greater synaptic surface area, and/or new synaptic connections. Anterograde transport is differentiated by two broad categories based on the speed of axoplasmic flow. These two components are termed fast and slow axonal transport. Fast and slow axonal transport differs both in the substances and structures conveyed as well as the mechanisms involved in their movement. Fast transport occurs at an approximate rate of 50 to 400 mm/day.1 Fast anterograde transport is extremely dependent on an adequate supply of oxygen; it is rapidly impaired by ischemic insult.2 Fast anterograde transport is primarily responsible for the movement of larger membranous organelles and vesicles.
The second component is slow anterograde axoplasmic transport, which occurs at the approximate rate of 1 to 5 mm/day. Slow transport conveys smaller molecular structures and the cytoplasmic building blocks of intraneuronal elements such as subunit proteins of microtubules and neurofilaments.3 The movement of the microtrabecular lattice and cytoplasmic matrix (in which cytoskeletal proteins, neurofilaments, and microtubules are embedded) is also thought to occur by slow axonal transport mechanisms.1 Retrograde transport serves to return membranous organelles, metabolic byproducts, and chemical constituents from the axonal microenvironment back to the cell body and nucleus.2 The speed of retrograde transport is approximately 3 to 6 mm/day, which is slightly faster than slow anterograde transport. The fast component of retrograde transport moves biochemicals and smallmolecular-weight recycled materials. Fast retrograde transport may move molecular materials in the axon up to 300 mm/day. Individual axons may be myelinated or unmyelinated. Schwann cells wrap around axons, creating a multilaminar myelin covering that insulates the fibers. The coverings are separated by clefts called nodes of Ranvier. Nodes of Ranvier are found in 1- to 2-mm intervals.4 Along with providing a mechanical barrier, the nodular pattern of myelination allows for fast conduction of electrical impulses from node to node, increasing the speed of neuronal transmission. The thicker the myelin sheath, the more rapid the conduction of impulses.
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Blood vessel
Unmyelinated fibers mostly autonomic
Fat
Myelinated segmented fibers, motor or sensory
Endoneurium Perineurium Epineurium
Endoneurium
Nucleus of a Myelin sheath Schwann Ranvier’s node cell
Axon
FIGURE 9.16 Microanatomy of the nerve and myelinated axon. (From Duus, P., Topical Diagnosis in Neurology, Thieme Medical, New York, 1989, pp. 3–4. With permission.)
Peripheral nerves are formed from bundles of axons and may be composed purely of motor fibers or sensory fibers, or a combination of both (mixed). Mixed nerves will subdivide into smaller branches containing purely motor or sensory fibers as they course to target tissues. The major component of the peripheral nerve is connective tissue; nerves also contain blood vessels and support cells. Individual axons (extensions of individual cells) — and their Schwann cell sheaths in the case of myelinated axons — are surrounded by a thin tubule of collagen fibers, the endoneurium. Groups of axons within the nerve are called fascicles. Fascicles are surrounded by perineurium. The peripheral nerve, itself, is comprised of groups of fascicles surrounded by epineurium. Individual peripheral nerves may contain fibers from a number of nerve roots (Figure 9.16).
9.8 PERIPHERAL NERVE VASCULARITY Peripheral nerves have a dual, functionally independent vascular supply from both extrinsic and intrinsic systems. The
extrinsic system consists of a regional network of arteries, arterioles, and venules supplying the nerve that penetrates to the epineurial plexus. The intrinsic (or intraneural) system includes vascular plexuses within each of the three connective tissue layers (epineurial plexus, perineurial plexus, and endoneurial plexus) and communicating vessels. The endoneurial component (of the intrinsic system) extends along the length of the nerve and consists mainly of capillaries within the fascicles. It is not clear whether involvement of either the intrinsic or extrinsic system alone can cause reduction in nerve blood flow as a result of the extensive anastomoses between them (Figure 9.17).5 The length of the peripheral axon from the cell body renders it dependent on the nerve microenvironment for its blood supply, oxygenation, and nutrition and for the removal of toxic metabolic products. Peripheral nerves are vulnerable to vascular insufficiency and changes in osmotic pressures or blood composition. Limited control mechanisms exist regarding the vascular supply to peripheral nerves. The endoneurial vascular plexus
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
265
Extrinsic artery Mesoneurium
Epineurial arteriole
Perineurial sleeve around capillary Perineurium Endoneurial vessels (Tight junctions) Capillary loop Epineurial vessels FIGURE 9.17 Schematic diagram of the vascular supply to the peripheral nerve. (From Lundborg, G., The intrinsic vascularization of human peripheral nerves: structural and functional aspects, J. Hand Surg., 4(1):34, 1979. With permission.)
seems to have limited ability to adapt to changes in blood flow. Endoneurial arterioles have poorly developed smooth muscle.6 In contrast to the epineurial and perineural vascular plexuses, the endoneurial vessels do not have an adrenergic nerve plexus around them. Epineurial vessels have a dense perivascular plexus of serotoninergic, peptidergic, and noradrenergic nerves.7 The major neurotransmitter for the mammalian peripheral nerve vasculature is norepinephrine;7 it is absent in the endoneurium but has been identified in the microvasculature of epineurium.8 Reductions in nerve blood flow have been demonstrated with sympathetic stimulation, while chemical sympathectomy has been shown to increase peripheral nerve blood flow. The autonomic regulatory mechanisms of the epineurial and perineurial plexuses are then absent (or minimal) in the endoneurial plexus; it is poorly equipped to autoregulate blood flow. This is consistent with the observation that autoregulation of regional blood flow within mammalian peripheral nerve is limited or totally absent.9 Intercapillary distances within peripheral nerves are greater than those within brain and muscle. Nerve capillaries tend to be larger than those of the brain and muscles, approaching the size of venules; their size may also increase their vulnerability to changes in perfusion pressure and blood volume.5 This further hampers the ability to autoregulate endoneurial blood dynamics. The limitation of intrinsic regulatory mechanisms and the comparatively greater intercapillary distances may create a propensity for endoneurial edema. Systemic changes such as those seen with diabetes further compromise microvasculature, which creates further risk. Edema may contribute to axonal ischemia. Reduction of adenosine
triphosphate (ATP) production may result, leading to loss of sodium pump efficiency, reduced axoplasmic transport, and a resultant reduction in the ability of the axon to transmit information. The microcirculation of the nerve is vulnerable to compression and stretching, either of which can lead to local obstruction of venous return, which leads to increased pressure within the region of entrapment contributing to ischemia. Additionally, venous stasis may cause accumulation of toxic metabolic by-products. Severe ischemia of peripheral nerve results in reperfusion injury, conduction block, and blood–nerve barrier disruption.10 Ischemic changes can damage nerve fibers directly and indirectly. Sunderland describes three stages of intraneural ischemia. Initially, endoneural edema results in increased intraneural pressure. Capillary damage will further contribute to edema with breakdown of the blood–nerve barrier. Subsequent decreased arterial blood flow will lead to further compromise and fibrotic change.11 Hasegawa12 demonstrated abnormalities in conduction and blood flow in rabbit sciatic nerves when the nerve sustained 11.8% elongation. Although blood flow was not completely arrested, it was further observed that the blood–nerve barrier was disrupted after 6 to 12 hours, endoneurial edema developed after 48 hours, and extensive degeneration of nerve fibers was noted after 5 days. Complete neural ischemia has been demonstrated in rabbit lower extremity nerves with longitudinal stretching of the nerve in the range of 15% of its in vivo length.13,14 Mechanical deformation has long been accepted as a cause of altered neuronal function although the reported ranges in the past have been conflicting.15
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The anatomy and physiology of the peripheral nerve include adaptive factors that confer limited resistance to ischemia. Anastomosis between the intrinsic and extrinsic vascular systems provides resistance to ischemia.16 Resistance to ischemia is also afforded by a high basal nerve blood flow relative to metabolic requirements and adaptive ability to use anaerobic metabolism. Additionally, the peripheral nerve will reduce its metabolic demands under hypoxic conditions. Perineurium provides a blood–nerve barrier for the peripheral nerve; this barrier helps to maintain homeostasis in the endoneurial environment. The existence of a blood–nerve barrier composed of the endothelium of endoneurial vessels has been established.17 Endoneurial cells contain tight junctions that render the intraneurial microvasculature essentially impermeable to circulating proteins. Although adaptive mechanisms exist, the vascular supply of the nerve is vulnerable to both intrinsic and extrinsic factors. The unique physical makeup and the length of the axon make it dependent on vascular integrity. When considering neuropathies, the microcirculation of the intraneural environment must be considered.
9.9 BIOMECHANICAL CHARACTERISTICS OF PERIPHERAL NERVES The flexibility of the peripheral nerves allows them to bend with the extremities, although they have limited elastic property and are susceptible to stretch injury. The perineurium provides the greatest resistance to tensile loading, whereas the epineurium provides the greatest resistance to compression.18 In the early stages of nerve compression, it is the peripheral fascicles that are affected most while the central fascicles may appear normal.19 Myelinated nerves are more vulnerable to the effects of compression.20 The biomechanical properties of peripheral nerves are affected by perineural and intraneural fibroproliferation (scar tissue), which reduces elasticity of the nerve.18
9.10 CLASSIFICATION OF NERVE INJURIES Peripheral nerve injury as a consequence of incremental pressure, stretching, or frictional trauma is classified by the extent of physical damage to the nerve fiber. In early nerve compression, the patient may present with other than classical findings on physical examination. Signs and symptoms may be partial and intermittent, thus requiring a more insightful examination. A reversible loss of nerve function occurs when the nerve is subjected to a short period of oxygen deprivation or ischemia. This temporary alteration of sensation or loss of motor function may occur with any sustained pressure or constriction of neurovascular structures in the nerve. This reversible physiologic conduction block occurs without damage to the nerve fiber, hence it can be
TABLE 9.1 Complications of Peripheral Nerve Injury • • • • • • • • • •
Shrinkage of endoneurial tubes Disruption of endoneurial tubes Perineural fibrosis Intraneural fibrosis Disorganization of guiding elements Axonal misdirection Synaptic degeneration Transneuronal degeneration Neuronal cell death End-organ atrophy
differentiated from true injury to the nerve. Any injury to the myelin sheath or nerve fiber, or loss of nerve continuity, produces a potential long-term neurophysiological deficit. Nerve injuries fall into three general categories: neurapraxia, axonotmesis, and neurotmesis. Seddon21 first proposed this three-level pathohistological classification of nerve injury in 1943. Sunderland11 (in 1978) expanded the classification of nerve injury to five degrees of increasing severity, essentially by subdividing neurotmesis. The Sunderland classification is preferable for describing the actual pathohistological extent of injury. From a practical and clinical perspective, only three levels of injury can easily be differentiated. Seddon’s classification of nerve injury is the most common nerve injury model used in clinical practice. Neurapraxia and axonotmesis represent the two main categories of peripheral nerve injury that are most often associated with compression neuropathies and tunnel syndromes.21 However, in the clinical setting, entrapment neuropathies demonstrate a variable mixture of acute, chronic, axonotmestic, and neurapraxic changes (Table 9.1; Figure 9.18).22
9.10.1 PHYSIOLOGIC CONDUCTION BLOCK The neurological symptoms resulting from physiologic conduction block are transient and represent a subclinical injury state. The symptoms produced following a brief loss of blood supply to the nerve are described as a “pins and needles” sensation in the extremities. Examples of the reversible physiologic block occur with prolonged leg crossing or sleeping on one’s arm. However, frequent reproducible paresthesia and numbness that occurs during simple activities such as using one’s arms overhead or typing on a keyboard suggests early entrapment pathology requiring diagnostic investigation.
9.10.2 NEURAPRAXIA Neurapraxia refers to a focal block in nerve conduction that results from a compressive deformation of the axon without loss of axon continuity or Wallerian degeneration.
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
Sunderland Grades
1
267
5
2
Complete transection
Compression
Epineurium
Perineurium
Endoneurium
Seddon Grades
Neurapraxia
Neurapraxia
Neurotmesis
Axonotmesis Neurotmesis
Axonotmesis
Schwann cell
Axis cylinder
Sunderland Grades Conduction block Loss of axon continuity Intact endoneurium Loss of axon continuity Disrupted endoneurium Intact perineurium Loss of axon continuity Disrupted endoneurium Disrupted perineurium Intact epineurium Complete nerve transection
1 2 3
4 5
FIGURE 9.18 Classifications of nerve injury and conduction block based upon myelinated motor nerve. (Copyright 1998 David H. Durrant. With permission.)
Demyelination and distortion of the myelin sheaths comprising the nodes of Ranvier or paranodal regions may occur with acute or sustained compression. The Sunderland injury classification refers to this as a first-degree nerve injury. The most common finding seen with neurapraxia is motor paresis and dyspallesthesia secondary to compression and focal demyelination of large myelinated fibers. Sliding two-point discrimination may also demonstrate subtle findings. The paresis may be secondary to a conduction block and a loss of synchronous motor unit activation. The classic example of this injury is Saturday night paralysis, or radial nerve compression at the spiral groove. This is a conduction block lesion producing short-term injury to the nerve that lasts from days to weeks and occasionally months or longer. The neurapraxic lesion is more severe than the “rapidly reversible physiologic block,” or physiological block as described earlier. In the presence of a complete neurapraxia, needle electromyography (EMG) will be negative for fibrillations, sharp waves, fasciculations, or other spontaneous activity because of motor axon preservation. However, when the conduction block is complete, the nerve will be unresponsive to electrophysiologic stimulation within the region of block.
9.10.3 AXONOTMESIS The term “axonotmesis” refers to a conduction block secondary to the loss of axonal continuity with preservation of the outer connective tissue (epineurium, perineurium, and endoneurium) and myelin wrappings of the axon itself. Wallerian degeneration of the distal segment follows, with complete loss of excitability of the distal segment and the appearance of spontaneous activity in denervated muscles. Axonotmesis is synonymous with Sunderland’s seconddegree nerve injury. When the endoneurial tubes remain intact, they serve as a guiding pathway for regenerating axonal sprouts, and reinnervation is more probable. A near to complete reinnervation may occur if the insulting influences are removed or resolved in the early stages of an axonotmestic injury. When traumatic axonotmesis has occurred, an immediate conduction block will occur at the site of injury. Axonotmesis secondary to metabolic influences may assume a more gradual course of dysfunction.23 Wallerian degeneration will typically occur within 3 to 5 days distal to the site of axon compromise. For a few days after the onset of axonotmesis, the distal axons may remain excitable. During this period the electrophysiological response of the nerve above and below the lesion appears similar
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
to neurapraxia.24 However, as Wallerian degeneration develops in axonotmestic nerves, the compound action potential sharply drops in amplitude, which indicates axonal loss and axonotmesis. In acute partial axonotmesis, spontaneous activity will begin after 10 to 14 days in the denervated musculature. Fibrillation, positive sharp waves, and reduced voluntary activation of motor units are evident on electromyography. Reduced distal amplitudes on nerve conduction studies will be present until reinnervation is established. During the recovery period after Wallerian degeneration, variable ranges of axon regeneration may occur, depending on the particular nerve, type of injury, and location. Generally, peripheral nerve axons regenerate at the approximate rate of 1 mm per day, 1 cm per week, and 2.5 to 3 cm per month.23 Therefore, regeneration may take months to years before maximum recovery status can be determined.
boundaries and the inability of axonal sprouts to find their pathway due to connective tissue disorganization. When reinnervation does take place, there is a greater risk for misdirected axonal sprouting and neuroma formation. Cross-reinnervation of receptor types and muscular end organs is more likely to occur after neurotmesis,19,23 creating discriminative and coordinative challenges for the patient (Figure 9.19). Reinnervation characteristics during the recovery period help distinguish neurotmesis from axonotmesis. However, due to Wallerian degeneration, the initial electrophysiologic presentations of axonotmesis and neurotmesis are identical. Excessive intraneural and perineural scarring after severe trauma creates a structural impediment that further inhibits reinnervation. Neurotmesis represents the most serious level of peripheral nerve injury, and often the patient requires surgical intervention. Typically, neurologic recovery is poor at best, even after surgery.
9.10.4 NEUROTMESIS
9.11 PERIPHERAL NERVE RESPONSE TO INJURY
Neurotmesis refers to a total block in nerve conduction resulting from loss of axonal continuity or complete axonal transection. Both the axon and the surrounding sheaths are disrupted. This loss in continuity of the protective sheaths surrounding the axon significantly and adversely impacts the likelihood of axonal regeneration and reinnervation of target tissues. This type of nerve injury occurs from a penetrating, crushing, or avulsing trauma. Sunderland expands on Seddon’s definition of neurotmesis, essentially by creating three subclassifications of neurotmesis.11 These are differentiated according to which supportive sheaths within the peripheral nerve are involved. Sunderland’s third-degree nerve injury refers to a loss of axonal and endoneurial continuity with preservation of the perineurium and epineurium. In the absence of the endoneurial tube to guide axonal regeneration, nerve regeneration in third-degree injury is imperfect, resulting in permanent end-organ deficits. The fourthdegree nerve injury refers to a loss of continuity of the axon, endoneurium, and perineurium with only the epineurium (outermost layer of the peripheral nerve) remaining intact. Useful recovery of nerve function in fourth-degree injury nerves is unlikely. Sunderland’s grade-five nerve injury describes complete nerve transection, where there is loss of continuity of the axon and all three supportive sheaths. Since neurotmesis is associated with an immediate traumatic event such as laceration or amputation, rather than a slow constricting process, it does not occur in entrapment. However, neurotmesis may be more likely to occur to an entrapped nerve or nerves infiltrated by fibrotic change that are subjected to traumatic tensile, compressive, or shear-type forces. Neurotmesis is associated with a poor prognosis for reinnervation due to the disruption of anatomic neural
9.11.1 WALLERIAN DEGENERATION When neural lesions involve crushing, cold, concussion, or compressive mechanisms, the endoneurial tubes may remain intact. With an intact endoneurial tube, potential improves for the axon to regrow across the damaged section.25 However, loss of axonal continuity from nerve transection or crush of a peripheral nerve leads to a degenerative process in the distal nerve stump. This predictable pattern is referred to as Wallerian degeneration. Retrograde chromatolytic changes involving the cell body may occur with severe injury to the axon. As an initial response to transection, the severed axonal ends retract secondary to the elastic properties of endoneurium.25 Within 2 hours after nerve injury, endoneurial edema and hyperemia occur as a result of mechanical compromise of surrounding capillaries and tissues.25,26 Synaptic transmission fails within hours. Myelin particles and cellular debris are removed from the injury site by hematogenous macrophages recruited to the distal stump region. Mast cells also support the inflammatory process. Within several hours the axon begins to swell.25 Severing of the axon causes loss of large amounts of axoplasmic volume; consequently, the cell body has to prepare for replacement of the lost axoplasm. Changes include swelling of the cell body, displacement of the nucleus to the periphery, and disappearance of basophilic material or Nissl substance from the cytoplasm. These changes reflect retrograde chromatolysis.27 With severe enough injury, the cell body cannot recover and the neuron dies. Within 19 hours, intra-axonal osmophilic particles and vacuoles accumulate. These are believed to represent endoplasmic reticulum and mitochondrial changes.25 Within 24 hours,
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
269
Average probability of reinnervation
Greatest probability of reinnervation
Pacinian corpuscle
Meissner’s corpuscle
One axon per receptor Multiple axons per receptor
Any neuropathy with reinnervation
Lowest probability of reinnervation
Merkel’s cells Multiple receptors per axon
FIGURE 9.19 The probability of mechanoreceptor reinnervation following Wallerian degeneration is dependent on multiple variables, one of which is the axon-to-receptor innervation ratio. A receptor with multiple axons per corpuscle will reinnervate and to a greater extent than a single axon subserving multiple receptors in the same reinnervating region. An altered neuroreceptive field may occur as a result of the loss of perception to the specific sensation carried by the mechanoreceptor pool. (Copyright J.M. True, D.C.)
multiple sprouts (neurites) occur from a single, severed axon. Myelin retracts at the nodes of Ranvier initially from the site of the lesion and then continues to retract distally. This process occurs faster in larger fibers.25 Within 72 hours after crush injury, Schwann cells and macrophages digest myelin and axonal remnants, preparing the endoneurial sheath for regeneration of proximal axons.25 The distal portions of the neurites develop an area of swelling from which several microspikes or filopodia arise; this region is termed the “growth cone.” The filopodia are constantly moving, apparently exploring the local microenvironment.27 They reach out for contact with the appropriate substrate, preferably fibronectin and laminin, both components of the basal laminae of Schwann cells.28 The subsequent organization of the axonal sprouts, in particular their orderly outgrowth in minifascicles towards a distant distal stump, does not occur unless Schwann cells are present. Schwann cells proliferate and comigrate with the regenerating axons (beginning adjacent to the severed nerve ends) in an attempt to bridge the gap four days’ post-injury.29,30 The axon may take days to degenerate. Consequently, electrophysiologic responses from the axon may be elicited for days post-injury. After 10 days, the entire axon distal to the lesion is converted into myelin ovoids.25 Fragments of myelin and axonal fragments are completely removed by 35 days by Schwann cells and macrophages.
9.11.2 AXONAL REGENERATION Within 2 to 4 weeks, Schwann cells and cellular debris align into tubes. These tubes form the bands of Bunger.25 Schwann cells of the bands of Bunger express surface molecules that guide regenerating axonal fibers. The number of cells in the newly formed tubes is greater than that normally present within the endoneurial tube. The endoneurial tube will shrink to a 10-micron diameter and await the return of the axon. The window of reinnervation is approximately 1 to 1.5 years. Should the axon fail to enter the tube within that time frame, connective tissue engulfs the endoneurial tube, reducing it to half the cross-sectional area. Significant disorganization of the neurites may occur. They may proliferate into connective tissue forming a painful neuroma and/or innervate inappropriate tissues (Table 9.2).11 Repair is more likely to succeed with crush injuries or with transection if there is a very short (less than 0.5 cm) interstump gap to cross. Repairs are more likely to fail if the interstump gap is long (greater than 1 cm) and associated with soft-tissue damage.29 Several factors guide the growth of the neurite. Target cells may exert a trophic influence. Nerve regeneration may be influenced by contact guidance and by neurotropism (chemotaxis). Neurite-promoting factors may be bound to the surface of cells or tissue structures. They may be humoral or may be confined to the medium within the microenvironment.
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TABLE 9.2 Types of Neuromas • Neuroma incontinuity Interruption of axoplasm in a portion of fibers in a large nerve Nerve compression/crush Ischemic injury • Neurite outgrowth Injury to basal lamina of Schwann fields Injury to perineurium of nerve bundle or misguided regeneration Physical obstruction to regeneration path
The instruction to the Schwann cell to form myelin is based on a genetic code located in the cell body of the corresponding neuron; each neuron is coded as to its destiny as myelinated or unmyelinated. The instruction to the Schwann cell to form myelin requires a direct axon–Schwann cell contact.31 The new myelin segments formed following reinnervation are shorter and thinner than the original myelin layer. Sunderland has reported regeneration as occurring between 1 and 1.5 mm per day.11 More recent reports describe the rate of regeneration as 3 to 4 mm/day after crush and 2 to 3 mm/day after sectioning a nerve.30 The closer the injury is to the cell body, the faster it can regenerate; there may be differences in regeneration rates specific to individual nerves. Muscle fibers undergo atrophy several weeks after denervation; this underscores the importance of early treatment that considers the time frame necessary for reinnervation. Therapeutic algorithms must factor in the days preceding onset of the growth cone, then factor in the axonal regrowth rate (as low as 1 mm per day). They should also consider factors that may complicate regeneration (e.g., the presence of systemic disease). Division of the distance from the injury site to the target organ by the regeneration rate gives a target range for potential recovery. Electrodiagnostic study is appropriate to monitor reinnervation. Regrowth of nerve fibers occurs with high specificity; axons of anterior horn cells preferentially reinnervate muscle. With reinnervation, motor fibers may reconnect to neuromuscular junctions at the original endplates and also send axonal projections to adjacent muscle fibers so that a group of neighboring muscle fibers may receive innervation from the same axon; this is termed “collateral innervation.” This leads to changes in the size of motor units and resultant changes in EMG voluntary recruitment and motor unit action potential (MUAP) morphology (Figure 9.20). Cutaneous sensation is more likely to recover from denervation than motor function. Sensations carried in small afferent fibers (pain, touch, and temperature) are more likely to recover after denervation than sensations carried by large myelinated fibers (discriminate touch,
vibration, and kinesthesis). Regrowth of sensory fibers may be followed by Tinel’s sign. Consider that distal migration of Tinel’s sign may be a sign of C-fiber regeneration, which may be a sign of incomplete reinnervation.32 Strictly interpreted, Tinel’s sign is a sign of neural regeneration. Commonly used, it is a sign of nerve irritability. Causalgia (complex regional pain syndrome II; CRPS II) is an intense, constant, burning pain and is known to occur after peripheral nerve injury. The slightest movement of the affected extremities may cause severe neuropathic pain. CRPS II pain is commonly a dysesthetic or lancinating type of pain. Changes in the autonomic function to the affected extremities may be apparent with causalgia. Although it is the result of an initial peripheral injury, both central and peripheral mechanisms foster its development.
9.12 NERVE COMPRESSION AND RELATED PATHOMECHANISMS Constriction, compression, or stretching of neurovascular structures may be the result of myofascial banding, fibrous adhesions, osteophytes, or any space-occupying lesion. Both mechanical pressure and the resultant ischemia have been demonstrated to contribute to pathologic processes occurring in the entrapped nerve.11,33 Adequate oxygenation delivered to the nerve via the intrinsic microvasculature and extrinsic vascular plexus is essential for peripheral nerve function. If pressure progresses without intervention, the resultant forces ultimately produce ischemia, focal demyelination in the region of the compression, conduction block, and Wallerian degeneration.34 The pathomechanical forces exerted on the myelin sheath produce thinning and irregularities in myelin deposition. Traumatic pressures also damage the blood–nerve barrier, increasing intraneural permeability to degradative macromolecules.35 Compressive insult may be intermittent and transient, or consistent and chronic. Sufficient mechanical pressure and ischemia result in terminal axon infarction and subsequent Wallerian degeneration. Szabo and Sharkey report that cyclic compression effects on nerve conduction are equivalent to the effects of constant compression at the average applied pressure.36 The duration of compression is also of importance for the production of nerve injury as well as the level of compressive force.37 Ischemia occurs by way of direct pressure reducing blood flow to the nerve or by indirect pressure generated by an obstructed venous return. In addition to the obvious mechanism of nerve entrapment through an anatomically narrowed passageway, other factors may increase the vulnerability of a nerve to compression. Peripheral nerves have an increased susceptibility to compression when coupled with metabolic abnormality, chronic nutritional deficiency, vascular insufficiency, toxic exposure, or compression in another area of the nerve.
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
Normal motor units
Segmental demyelination
Axonal degeneration
Reinnervation
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Myopathy
Neuron cell body
Myelin
Axon Myocytes
FIGURE 9.20 Normal and abnormal motor units. Segmental demyelination: Random internodes of myelin are injured and are remyelinated by multiple Schwann cells, while the axon and myocytes remain intact. Axonal degeneration: The axon and its myelin sheath undergo anterograde degeneration, with resulting denervation atrophy of the muscle fibers within its motor unit. Reinnervation: Sprouting of adjacent uninjured motor axons leads to fiber type grouping of myocytes, while the injured axon attempts axonal sprouting. Myopathy: Scattered myocytes of adjacent motor units are small (degenerated or regenerated), whereas the neurons and nerve fibers are normal. (From Cotran, R.S. et al., Robbins Pathologic Basis of Disease, W.B. Saunders, Philadelphia, PA, 1994, p. 1274. With permission.)
Terminal bouton
Ischemia Ionic imbalance Constricting pressure Venous congestion Metabolic disease Edema Axon
Neurotransmitter vesicles
FIGURE 9.21 Pathologies that inhibit axoplasmic flow, depolarization, and synaptic discharge. (Copyright J.M. True, D.C.)
indirect, secondary to cardiorespiratory insufficiency, anemia, or a deficiency in chemical substrates required for intraneural metabolism. Axonal transport may be impaired without a paralleling degree of compromise to the gross structural integrity of the myelin sheath or the cell membrane. Experimental compression of a peripheral nerve at pressures as low as 20 to 30 mmHg for 2 to 8 hours was found to inhibit both anterograde and retrograde axonal transport.2 A loss of axonal transport mechanisms will result in a clinical presentation similar to synaptic fatigue, progressing to axonal block. If the compromise of axonal transport is chronic and severe enough it can lead to degeneration of the axon (Figure 9.21).
9.12.1 COMPROMISED AXONAL TRANSPORT
9.12.2 THE DOUBLE CRUSH SYNDROME WHOLE NERVE SYNDROME
Axoplasmic transport is an energy-dependent process. Loss of nutrients to the nerve cell from circulatory impairment can slow or inactivate the axonal transport system.35 Circulatory impairment may be direct in the form of intravascular occlusion, hemorrhage, or mechanical compression of supplying vessels. Circulatory impairment may be
The double crush nerve compression hypothesis has been investigated by many researchers.38-44 Other protocols have failed to support the existence of double crush;45,46 this may reflect limited capability to assess the phenomenon. The original theory by Upton and McComas44 suggested that impaired axonal transport of intraneural elements following
OR
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TABLE 9.3 Predisposing Etiology for Peripheral Nerve Compression and Entrapment •
• • • • • • • • • •
Small anatomical tunnel Congenital: Klippel–Feil syndrome, fibrotendinous banding, ligamentous constriction, anatomical variation, cervical rib Acquired: Traumatic, myofascial, osteodegenerative, postsurgical, tumor, edema Metabolic Diabetes mellitus, hypothyroidism, hyperthyroidism, amyloidosis, renal failure Neurovascular Insufficiency, deconditioning, compression, vasculitis, complex regional pain syndrome Toxic Pharmaceutical agents, occupational/environmental toxins, toxic metals Infection Staphylococcus, Candida albicans, viruses, diphtheria, leprosy Nutritional Chronic vitamin C, B12, or B6, or magnesium deficiency Trauma Cervical acceleration–deceleration (CAD) syndrome, cumulative trauma disorder (CTD), penetrating wounds, blunt injury Neuromuscular Altered muscle tone: upper motor neuron spasticity, fibromyalgia Loss of tissue elasticity Age (in combination with other factors), scleroderma Proliferative conditions Paget’s disease, diffuse idiopathic skeletal hyperostosis (DISH) Inflammatory Rheumatoid arthritis
compression may render other portions of the nerve more susceptible to the adverse effects of compression. Mechanisms of double crush syndrome as reported by Osterman18 include: 1. Impaired axoplasmic flow resulting in architectural changes in the axon 2. Edema compromising intraneural circulation 3. Increased sensitivity of an otherwise impaired nerve to entrapment (diabetic neuropathy, renal failure, etc.) 4. Altered neural elasticity because of fibrotic changes 5. Other connective tissue abnormalities Dellon and Mackinnon39 have expanded the description of the double crush syndrome to include compromise along (1) multiple anatomic regions along a nerve, (2) multiple anatomic structures across a peripheral nerve within an anatomic region, (3) mononeuropathy superimposed on a neuropathy, and (4) a combination of the prior factors.39 Leahy et al.47 report that the term “whole nerve syndrome” is appropriate to describe increased susceptibility to pressure observed along any point of an entrapped nerve regardless of the site of entrapment. The reverse double crush syndrome theory describes the increased incidence of proximal nerve compression that follows a primary distal lesion.40,41,44 A large retrospective study by Hurst
et al.40 reported an increased prevalence of carpal tunnel syndrome (CTS) occurring bilaterally in patients who have coexistent cervical spondylosis with nerve root compression. It is not uncommon for a clinician to halt the examination process after concluding that radiculopathy was confirmed by the presence of disk herniation on MR imaging or, similarly, that CTS is the only source of the patient’s symptoms demonstrated by electrodiagnosis. The double crush syndrome may be one of the reasons that patients with clear-cut CTS fail to improve following carpal tunnel surgery.22 Simpson and Fern9 consider the contribution of metabolic neuropathies associated with double crush including uremia, diabetes mellitis, alcohol neuropathy, and B6 deficiency in their review of double crush syndromes. The clinician should always be alert to the possibility of coexistent peripheral entrapment neuropathy and radiculopathy simply due to their statistical prevalence.48 The astute clinician will also consider other factors predisposing multifactorial causes of neuropathic presentation. Table 9.3 summarizes the pathological factors that directly or indirectly increase the probability of entrapment. The frequency of CTS and radiculopathy suggests that C6–C7 radiculopathy and median neuropathy at the carpal tunnel would be the most common double crush syndrome. Thoracic outlet syndrome, C8–T1 radiculopathy, and ulnar compromise at the elbow may be the next most commonly encountered double crush presentation. Osterman18 considers double crush in the lower extremities
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
to be rare. He suggests that lumbar radiculopathy and peroneal palsy or tarsal tunnel syndrome would be the most likely combinations in the lower extremity.
9.12.3 CUMULATIVE TRAUMA DISORDER (CTD) Cumulative trauma disorder (CTD) or repetitive strain injury refers to the cumulative effects of multiple injuries to a given tissue or injuries to a number of tissues. Tissue injury generally results in histological changes that are maintained after the healing process is over. Following acute injury to tissues, a cascade of vasoactive amines and nociceptor-sensitizing substances is released in the vicinity of the injury. The complex processes that occur posttrauma precipitate the local deposition of leukocytes and fibrinogen.49 The healing process often results in deposition of nonfunctional scar tissue and strictures in the involved area of the nerve. For example, consider a mechanism that would explain the onset of CTS. Injury to the tendons surrounding the carpal tunnel leads to the development of fibrosis and scar tissue. The additional tissue takes up space and reduces the elasticity of the involved tissues and the mobility of the nerve. This creates direct pressure effects on the nerve and reduces intraneural vascular perfusion from compression of the microcirculation about the median nerve. The development of fibrosis and scar tissue may be a sequel of an acute injury, repetitive injuries, or constant pressure/tension injuries, or a combination thereof (i.e., cumulative trauma). When considering peripheral nerve entrapment, the interrelationships of the mechanisms described below must be considered as a basic mechanism contributing to the pathogenesis of nerve injury.
9.13 MYOTENDINOUS, MYOFASCIAL, AND RELATED CONTRIBUTIONS TO ENTRAPMENT 9.13.1 ACUTE MYOFASCIAL INJURY Acute injury involves the disruption of tissues either on a microscopic or macroscopic level. When microscopic insult occurs, injury to soft tissue is often difficult to objectify. In addition to the histological effects of tissue repair, acute injury may have the highest level of experienced pain and thus trigger the pain–spasm cycle. This may become self-perpetuating as protective postures become more permanent, combining with the histological changes to limit tissue extensibility. Novak et al.50 report three major influences of posture relative to entrapment: (1) directly increasing pressure on nerves at entrapment sites, (2) placing muscles in shortened positions so that adaptive muscle shortening may then secondarily compress nerves, and (3) placing some muscles in elongated and weakened positions, resulting in other muscles being
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overused, thus creating the cycle of muscle imbalance. Central potentiation of nociceptive reflexes further complicates the process and limits muscle extensibility. Muscular overuse and direct trauma to the muscles surrounding a neurovascular space may cause injury to the nerve by shear or crush forces. Hammer51 separates muscle injury into four categories: (1) exercise-induced injuries, (2) muscle strains, (3) muscle contusions, and (4) ischemic injury. Muscle injuries brought on by exercise are typically reversible with relatively minor ultrastructural damage. A complete repair usually occurs within days.52-54 Muscle strain injuries are more severe and often involve a partial or complete tear at the musculotendinous junction.55 Post-traumatic scar tissues develop as a result of the fiber disruption, hemorrhage, and inflammation.56 Muscle contusions characteristically heal via muscle regeneration and dense fibrous tissue invasion. Ischemic muscle injuries often heal well if vascular perfusion is reintroduced quickly and the myofibers are not disrupted. Prolonged circulatory deprivation to the myofibers will result in fiber discontinuity, cellular death, and fibrous tissue infiltration.57,58
9.13.2 CHRONIC INJURIES 9.13.2.1 Constant Pressure/Tension Injury Constant pressure and tension in injured tissues decreases circulation and compromises recovery.59 Abnormal retention of intracellular calcium, fibroblast proliferation, poor collagen repair, and altered cellular metabolism represent only a few of the sequelae of chronic exposure to pressure or tension forces. Perineural mechanical compression may induce edema formation within and around the nerve tissue resulting in fibroproliferation. This proliferative fibrous accumulation is implicated in entrapment syndromes and microstretch injury in perineural tissues.60 9.13.2.2 Repetitive Injury Repetitive motion injuries occur when the motion (or the additive effects of the motions) are sufficient to trigger the histological effects of tissue injuries described above. If repetitive injuries can be represented by a waveform, the potential for tissue insult becomes proportional to the area under the waveform (or the total force sustained by the tissues). This area would be directly proportional to: (1) number of waves (the number of hits, repetitive movements, or other traumas), (2) amplitude of the waves (forcefulness of impact or motion) and (3) wavelength of the wave (duration of impact or motion). Figure 9.22 illustrates the findings of Higgs et al.61 that jobs requiring the highest repetition with the least rest per cycle had the highest impairment ratings. In addition, the repetitive forces may directly affect the nerve. As discussed above, the effect of cyclic compression
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Symptomatic Injury Threshold
A.
Amount of Tissue Insult
Amount of Tissue Insult
Recovery Cycle
Injury Cycle
Frequency of Insult
Insufficient Tissue Recovery Between Injury Cycles
B.
Tissue Damage Accumulates
Injury Cycle
Frequency of Insult
FIGURE 9.22 Pathogenesis of the cumulative trauma disorder. (A) Normal; injury cycle is below the threshold for symptomatic injury. The area under the curve is directly proportional to the time or frequency of the tissue deformation. The time between the waves represents the potential for the tissues to adapt to the forces without triggering the inflammatory response or damaging the tissue. (B) If the next wave (or trauma) occurs before complete tissue recovery or tissue adaptation, then the effect of the next wave is cumulative and symptomatic injury may result. (Copyright J.M. True, D.C.)
9.13.3 THE CUMULATIVE INJURY CYCLE Gravity line 115
70-99
Left untreated, sequelae of injury may contribute to a selfperpetuating cycle of pain, tissue dysfunction, and inflammation. While they are not necessarily present in a linear fashion, the complex interrelationships may be considered as the cumulative injury cycle (CIC). Consider the following components as they may interrelate. 9.13.3.1 Weak and Tight Tissues
90-110 90
Repetitive muscular effort tends to result in a muscle remaining abnormally contracted or tightened. When a muscle is abnormally tight, it tends to weaken. Conversely, when a muscle is weak, it tends to be tight.62 The surrounding supportive soft-tissue structures may also be shortened and tight. 9.13.3.2 Friction–Pressure–Tension
FIGURE 9.23 The proper visual angle of monitor to eye field; a monitor refresh rate set above 75 hz, a properly adjusted ergonomic chair, and healthy workstation environment all contribute to work productivity and reduced cumulative trauma. (Copyright J.M. True, D.C.)
on nerve conduction may be equivalent to those of constant compression at the average applied pressure.36 When fibrous tissue surrounds or invades the interfacing tissues of a neurovascular tunnel, the potential for entrapment neuropathy increases (Figure 9.23).
As a consequence of weak and tight tissues, the internal forces acting on these tissues increase. Friction, force pressure, or tension can exist independently or in combination. If one or more of these factors reaches a threshold, for tissue damage, an acute injury with subsequent inflammation can occur, even without the addition of external forces. The resultant changes may reduce the threshold to provoke the inflammatory process, provoking repetitive injury. 9.13.3.3 Decreased Circulation, Edema Increased interstitial fluid pressure may lead to decreased postcapillary venous blood flow and, subsequently, increased hydrostatic pressure. The effect of increased force on tissues results in decreased local blood flow.63
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
9.13.4 INFLAMMATION In discussing the etiology and pathogenesis of tissue trauma, the potential role of the inflammatory process must be considered. Chemical mediators of inflammation released at the site of tissue injury act as vasodilators and also enhance vascular permeability. These mediators, which include bradykinin, histamine, and arachidonic acid metabolites, have been demonstrated to contribute to local inflammatory edema.64 In addition, a noninflammatory edema may also occur as a result of increased forces that tend to move fluids from the intravascular compartment into the interstitial fluid (i.e., increases in hydrostatic pressure, reduced plasma osmotic pressure, and/or lymphatic obstruction).65 Causes of increased hydrostatic pressure that may lead to edema include thrombosis, increased external pressure, and inactivity of extremities. Factors that may cause reduced plasma osmotic pressure are systemic in etiology and most likely are not directly involved in the pathogenesis of focal peripheral neuropathies. Examples include malnutrition, renal dysfunction, and liver cirrhosis; however, these systemic factors may indeed predispose a peripheral nerve to compression as a result of pressure that otherwise would not produce a neuropathy in a healthy individual. The limited autoregulatory capacity of the endoneurial vascular plexus makes it a focus for intraneural edematogenesis. Lymphatic obstruction, such as that occurring with neoplasia or as a consequence of surgery or irradiation, may contribute to the edema observed in nerve compression syndromes. Regardless of the etiology of the edema, the resultant local increases in interstitial fluid pressure act to contribute to the pain/symptomatology of peripheral nerve entrapment. In addition to edema, the local inflammatory response has been documented to elicit the release of chemical mediators of pain. The eicosanoids, derived from the metabolism of arachidonic acid, have been investigated for their inflammatory potential.66 In particular, prostaglandin I2 (PGI2) has been examined for its algesic properties. PGI2 has been demonstrated to elicit a painful response from joints and skin and to stimulate a nocioceptive response when applied in situ to rat sciatic nerves.67 Cells involved in the synthesis of prostaglandins include macrophages, chondrocytes, and fibroblasts. A role for PGI2 as well as other eicosanoids (including thromboxane, leukotrienes, and lipoxins) in the pathogenesis of peripheral nerve entrapment syndromes requires further investigation. Conditions that contribute to microangiopathy of vasa nervorum may render the peripheral nerve vulnerable to mechanical insult. Microangiopathy may result in reduced blood flow within the endoneurial environment. Finally, chronic inflammation, as a result of intermittent tissue irritation, may lead to persistent tissue destruction.68 The body attempts to repair tissue damage by
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replacing nonregenerated parenchymal cells with connective tissue, which in time produces fibrosis and scarring. This tissue destruction is believed to play a role in the pathogenesis of peripheral nerve entrapment syndromes. Chemical mediators of inflammation, particularly those released by macrophages and fibroblasts at the site of tissue injury, contribute to the process of healing by fibrosis. These mediators include chemotactic factors, growth factors, and cytokines.69
9.14 COMMON PREDISPOSING DISORDERS ASSOCIATED WITH ENTRAPMENT NEUROPATHY Many categories and causes of peripheral neuropathy are beyond the scope of this chapter. The following discussion is limited to predisposing disorders that are more common. Multifocal neuropathies with systemic predisposition may be generally classified by: (1) the associated disease process or etiology, (2) the fiber type affected, (3) the anatomic pattern of neurologic deficit, or (4) by the underlying pathological mechanism behind the neuropathy. Although these neuropathies are a separate class of disorders from entrapment neuropathies, a brief overview is warranted because of their prevalence in the general population and the increased frequency of entrapment syndromes resulting from the various predisposing disorders. Mechanisms involved in the pathogenesis of peripheral neuropathies are debated. The numerous pathophysiologic processes that contribute to the etiology of peripheral neuropathies are summarized in Table 9.4. These broad etiologic categories contribute to the development of neuropathy via axonal degeneration, the development of myelin abnormalities or a combination of both. Axonal degeneration or axonopathy results in attenuation of the compound motor unit action potential (CMAP) or the sensory nerve action potential (SNAP) amplitude with a loss of area under the waveform. Abnormalities in myelin will alter the ability of the axon to function and will be associated with slow depolarization of the neural membrane. This is characterized on electrodiagnostic testing by temporal dispersion of the compound action potential waveform. Pathogenesis of noncompressive neuropathy is complex and many disorders involve several contributory mechanisms. Disruption of neuronal function may result from disturbances in membrane ion gates or macromolecule transport. Interference with the delivery or production of energy substrates may also cause peripheral neuropathy. Insufficient neurotransmitter transport or uptake may lead to neuropathic syndromes. Toxic accumulation disorders may have direct effects on metabolic pathways within the neuron and may contribute to microvascular insufficiency of the neuron and surrounding tissues. Metabolic and toxic
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TABLE 9.4 Nonentrapment Neuropathies • Vascular Vasculitis Hemorrhage Arteriovenous malformation/aneurysm Ischemia • Neurotoxicity Metabolic Industrial Heavy metal Pharmacologic • Neoplastic • Chronic respiratory insufficiency • Renal insufficiency • Nutritional deficiencies Vitamin E Vitamin B6 Vitamin B12 Vitamin B1 • Inflammatory • Infectious • Immunologic Antigen/antibody complexes Immunoglobulins binding to myelin-associated glycoproteins or ganglioside GM1 Membrane gradient disruption Membrane macromolecule transport inhibition • Deposits of systemic diseases Amyloidosis Xanthomatous swellings of cirrhosis • Postinfection syndromes Guillain–Barré • Trauma (Nerve Transection) • Neuralgic amyotrophy/idiopathic lumbosacral plexitis/acute brachial • Iatrogenic Mechanical Medication/toxicity Postoperative Malpositioning Direct trauma to peripheral nerves during surgery • Radiation induced • Metabolic Diabetic neuropathy Endocrine • Hereditary • Thermal injury
neuropathies cause neuronopathy through various mechanisms; for example, neuropathy secondary to diabetes can occur due to sorbitol accumulation, tissue glycosolation, hyperglycemia, vasculopathy, and poor autonomic control. Obtaining a thorough patient history is critical. The patient may reveal a family history of an inheritable or predisposing metabolic disorder. There may be a history of malnutrition or a malabsorption syndrome such as
regional enteritis. The possibility of digestive malabsorption should always be considered following surgical resection of any portion of the stomach or small intestines. The patient’s occupation may involve exposure to toxic substances. The historical pattern of alcohol ingestion is important, for chronic alcoholism is one of the most common causes of peripheral neuropathy in the U.S.
9.14.1 GENERAL PATTERNS OF ANATOMIC DISTRIBUTION The most common presentation of peripheral neuropathy occurs in a distal symmetric pattern often referred to as a “stocking-glove” configuration. This may involve varying degrees of sensory compromise including near anesthesia, paresthesia, hypoalgesia, and dysesthesia. Anatomical localization of polyneuropathy is the initial part of the clinical work-up, whereas ascertaining the underlying causative disorder is more challenging. The work-up often requires extensive laboratory investigation to help identify the primary etiology. Commonly, in metabolic and systemic type polyneuropathies there is a length-dependent relationship of clinical involvement. The distal lower extremities tend to be affected first. As a general guideline consider the following patterns. Clinical signs and symptoms involving the hands usually occur when the polyneuropathy has progressed to the level of the knees in the lower extremities. Once the neuropathy in the distal upper extremity progresses to the elbow, truncal paresthesias may follow. In contrast, proximal symmetric patterns of peripheral neuropathy may be seen in HIV-1/AIDS, lymphoma, Lyme disease, and diabetes mellitus. Peripheral neuropathies may also follow an asymmetric pattern and involve single peripheral nerves along different regions or multiple nerves. This is commonly referred to as mononeuritis multiplex. Some asymmetric patterns of peripheral neuropathy are easily confused with entrapment neuropathies and can be challenging to diagnose. Mononeuritis multiplex may be seen in conditions involving tissue deposits (e.g., sarcoidosis, amyloidosis) or with focal destructive inflammatory changes (arthritides such as rheumatoid arthritis). Distribution of neuropathy suggesting multiple peripheral nerves suggests mononeuritis multiplex. There can be proximal patterns of neuropathy as well as disease processes that primarily affect the nerves of the upper limbs. Examples include Guillain-Barré, acute intermittent porphyria, hereditary proximal motor neuropathies, and in rare cases chronic progressive inflammatory demyelinating polyneuropathy. Other classifications of peripheral neuropathy describe the nerve fiber predilection, such as motor neuropathies, sensory neuropathies, or small fiber or autonomic neuropathy. A motor neuropathic pattern is seen
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
more commonly in Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, and neuropathies associated with porphyria, lead, and diphtheria. There are also hereditary neuropathies with specific motor or sensory predilections. Predominantly sensory involvement is more common in diabetes mellitus, B12 deficiency, hereditary sensory neuropathy, and leprosy. Autonomic changes are associated as a predominant and early feature in amyloid neuropathy, diabetic neuropathy, familial dysautonomia, and pandysautonomia.
9.14.2 DIABETES Symptomatic peripheral neuropathy is the most common complication of diabetes mellitus, affecting up to 62% of Americans with diabetes.70 Neurologic complications occur equally in both type I and type II diabetes mellitus and with other various forms of acquired diabetes.71 Peripheral neuropathy associated with diabetes mellitus is usually associated with a distal symmetric pattern. Small-fiber degeneration and autonomic neuropathy are not uncommon. Proposed pathomechanisms for diabetic neuropathy include those metabolic changes that lead to endoneural edema and compromise of the vasa nervorum, rendering the peripheral nerves more susceptible to compression.72 Other causes of diabetic neuropathy include reduced myoinositol uptake by nerves. This compromises the ability to maintain the membrane potential and reduces amino acid uptake. These processes may lead to structural changes of the neuron itself. Sorbitol accumulation in the nerve and microvasculature of the nerve may occur (this is similar to the mechanism of diabetic cataract formation and may relate to neuropathy). Entrapment neuropathy is a fairly common complication associated with diabetes. In the upper extremity, compression of the median nerve within the carpal tunnel or ulnar nerve compression at the cubital tunnel are the most common entrapments, occurring with a higher than normal frequency in the diabetic. In the lower extremity, the most commonly entrapped nerve is the common peroneal at the fibular neck. Additionally, meralgia paresthetica occurs with greater prevalence in the diabetic. Diabetic neuropathy can also present as a proximal pattern of pain, paresthesia, and paresis. Proximal diabetic neuropathy, also referred to as Bruns–Garland syndrome, diabetic polyradiculopathy, or diabetic amyotrophy. The onset is usually abrupt and begins as severe unilateral hip/thigh pain followed by asymmetric weakness and wasting affecting the legs. This variant is commonly seen in unregulated diabetics over 50 years old. The syndrome affects both proximal and distal muscle groups.72
9.14.3 UREMIA Renal insufficiency and failure have been associated with neuropathy. Neuropathy associated with renal insufficiency
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is significantly more common in men than women. The neuropathy associated with renal disease is characterized by a distal symmetric polyneuropathy typically manifesting in the lower extremities. It is often associated with autonomic dysfunction. The rate of occurrence increases in proportion to the duration of renal failure. Renalinduced neuropathy occurs more commonly in males. Early in the course of the disease, electrodiagnostic assessment may reveal sural nerve compromise. An abnormal H-reflex may be the only conduction abnormality. Strikingly, renal dialysis may improve uremic polyneuropathy but will not necessarily be associated with improved nerve conduction velocity. In contrast, renal transplantation (in the nondiabetic population) not only produces striking reversal of clinical findings but also is associated with significant improvement of electrodiagnostic abnormalities.73 CNS abnormalities may be associated with uremic syndromes. Causes of uremic neuropathy have been hypothesized to relate to the accumulation of systemic toxins; however, no specific toxins have been identified.73 Presumably, these toxins would be molecules that are less likely to cross the dialysis membranes, which may explain the difference in response to dialysis as opposed to transplantation discussed above. CNS, peripheral, and autonomic neuropathies are frequently seen in dialysis patients, suggesting other mechanisms, perhaps edema/ischemia of the endoneurial environment secondary to altered osmotic pressures based on solute content.
9.14.4 THYROID DISORDERS A small study by Khedr et al.74 concluded that the CNS is more vulnerable to the effect of hypothyroidism than the peripheral nervous system (PNS). However, within this study of hypothyroid patients, 52% had PNS involvement. In patients with PNS involvement, entrapment neuropathy was the most common (35%) pathologic finding. Axonal neuropathy was recorded in 9%, and myopathy was recorded in another 9%. The central nervous system was affected in 78% of the cases. The authors suggested performing electrophysiological studies in hypothyroid patients, even in the asymptomatic ones, early in the course of disease in order to detect the extent of nervous system involvement.74 Another study in newly diagnosed hypothyroid patients found that 79% had neuromuscular complaints, 38% had clinical weakness (manual muscle strength testing) in one or more muscle groups, 42% had electrodiagnostic signs of sensorimotor axonal neuropathy, and 29% of these patients had carpal tunnel syndrome.75 Hyperthyroid disease contributes to the development of a sensory–motor axonopathy early in the course of the disease; however, this only occurs in 20% of the hyperthyroid patients. Specific distinguishing features of a neuropathy associated with hyperthyroid have not been determined. In the absence of having features
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distinguishing it from acute idiopathic polyneuritis, neuropathy associated with hyperthyroid is not a clearly defined entity.
9.14.5 HIV-1 Because of the rapidly rising numbers of HIV-1 infected individuals in the U.S. and the world and the lengthened survival of infected patients, HIV-1-associated neurological disorders may become one of the most common disorders seen by neurologists.76 Neuropathy associated with HIV-1 may have a variety of mechanisms consistent with the myriad of associated disease processes occurring in the immunocompromised patient. HIV-related neuropathy may be associated with direct viral-induced compromise, opportunistic infection (herpes zoster or cytomegalovirus), the effect of malignancy (most commonly lymphoma), malnutrition, metabolic derangement, and iatrogenic causes from neurotoxic medications. In the late stages of AIDS, severe weight loss decreases the volume of cushioning tissues and thus increases the vulnerability of the nerve to compressive neuropathy. The neurological presentation varies with the severity of the systemic disease and level of immunodeficiency as related to the cell count of receptor molecule CD4+-expressing cells, mainly the CD4+ T-lymphocyte. Mononeuritis multiplex and acute inflammatory demyelinating polyradiculopathy are seen in early HIV-1 disease, whereas distal symmetric polyneuropathy and progressive polyneuropathy are seen in late stages of the disease.76
9.14.6 RHEUMATOID ARTHRITIS Most entrapment neuropathies in rheumatoid arthritis (RA) are caused by direct compression of the nerve by the inflammatory soft-tissue swelling and pannus in the region of osteoligamentous neurovascular tunnels. The most common locations for entrapment are the median nerve in the carpal tunnel, the ulnar nerve at the elbow, the posterior tibial nerve in the popliteal space, and the common peroneal nerve as it traverses across the tibiofibular articulation and fibular head.77 Associated with rheumatoid arthritis is a vasculitis that affects small arteries and venules. Associated neuropathy in rheumatoid arthritis may begin as a mild distal symmetric sensorimotor polyneuropathy. Vasculitic changes of rheumatoid arthritis may develop into a systemic arteritis whose primary clinical manifestation may be a neuropathy. In advanced cases, RA vasculitis may progress to more widespread organ involvement.78 Multiple mononeuropathies may present secondary to RA. In addition, infiltration of inflammatory cells into peripheral nerve itself may lead to neuropathic changes associated with rheumatoid arthritis.
9.14.7 RESPIRATORY INSUFFICIENCY Respiratory insufficiency has been associated with a mild, often subclinical peripheral neuropathy. The mild involvement has been questioned as having significance. Correlation with cigarette smokers was suggested in a review of 23 patients with chronic obstructive pulmonary disease (COPD).79 Almitrine, a medication used to increase ventilation and oxygenation, has been associated with neurotoxicity, although there is controversy as to the relative contributions of toxicity as opposed to that of the respiratory insufficiency. Hypoxia may affect intraneuronal metabolism directly. Circulating byproducts of anaerobic metabolism may have secondary effects contributing to neuropathy.
REFERENCES 1. Peters, A., The Fine Structure of the Nervous System: Neurons and their Supporting Cells, 3rd ed., New York: Oxford University Press, 1991: 126–130. 2. Dahlin, L.B. and McLean, W.G., Effects of graded experimental compression on slow and fast axonal transport in rabbit vagus nerve, J. Neurol. Sci., 72:19–30, 1986. 3. Ochs, S., Trophic functions of the neuron: mechanisms of neurotrophic interaction. Systems of material transport in nerve fibers (axoplasmic transport) related to nerve function and trophic control, Ann. NY Acad. Sci., 228:202–223, 1974. 4. Duus, P., Topical Diagnosis in Neurology: Anatomy–Physiology–Signs–Symptoms, New York: Thieme Medical, 1989. 5. McManis, P.G., Low, P.A., and Lagerlund, T.D., Microenvironment of nerve: Blood flow and ischemia, in Dyke, P.J. and Thomas, P.K., Eds., Peripheral Neuropathy, Philadelphia, PA: Saunders, 1993: 453–473. 6. Bell, M.A. and Weddell, A.G., A descriptive study of the blood vessels of the sciatic nerve in the rat, man and other mammals, Brain, 107(Pt 3):871–898, 1984. 7. Rechthand, E., Hervonen, A., Sato, S., and Rapoport, S.I., Distribution of adrenergic innervation of blood vessels in peripheral nerve, Brain Res., 374:185–189, 1986. 8. Rechthand, E., Smith, Q.R., Latker, C.H., and Rapoport, S.I., Altered blood–nerve barrier to small molecules in experimental diabetes mellitus, J. Neuropathol. Exp. Neurol., 46:302–314, 1987. 9. Simpson, R.L. and Fern, S.A., Multiple compression neuropathies and the double-crush syndrome, Orthoped. Clin. North Am., 27:381–388, 1996. 10. Schmelzer, J.D., Zochodne, D.W., and Low, P.A., Ischemic and reperfusion injury of rat peripheral nerve, Proc. Natl Acad. Sci. USA, 86:1639–1642, 1989. 11. Sunderland, S., Nerve and Nerve Injuries, 2nd ed., New York: Churchill-Livingstone, 1978. 12. Hasegawa, T., An experimental study on elongation injury of peripheral nerve, Nippon Seikei Gakkai Zasshi, 66:1184–1193, 1992.
Relevant Anatomy, Pathophysiology, and Predisposing Factors for Peripheral Nerve Injury
13. Lundborg, G. and Rydevik, B., Effects of stretching the tibial nerve of the rabbit: a preliminary study of the intraneural circulation and the barrier function of the perinuerium, J. Bone Joint Surg. Br., 55:390–401, 1973. 14. Ogata, K. and Naito, M., Blood flow of peripheral nerve effects of dissection, stretching and compression, J. Hand Surg. Br., 11:10–14, 1986. 15. Kwan, M.K. and Woo, S.L.-Y., Biomechanical properties of peripheral nerve, in Gelberman, R.H., Ed., Operative Nerve Repair and Reconstruction, Philadelphia, PA: Lippincott, 1991: 1211–1229. 16. Lundborg, G. and Branemark, P.I., Microvascular structure and function of peripheral nerves: vital microscopic studies of the tibial nerve in the rabbit, Adv. Microcirc., 1:66–68, 1968. 17. Lundborg, G., Structure and function of the intraneural microvessels as related to trauma, edema formation, and nerve function, J. Bone Joint Surg. Am., 57:938–948, 1975. 18. Osterman, L., Double crush and multiple compression neuropathy, in Gelberman, R.H., Ed., Operative Nerve Repair and Reconstruction, Philadelphia, PA: Lippincott, 1991: 1211–1229. 19. MacKinnon, S.E. and Dellon, A.L., Experimental study of chronic nerve compression, Hand Clin., 2:639–650, 1986. 20. Dellon, A.L., Evaluation of Sensibility and Reeducation of Sensation of the Hand, Baltimore, MD: Lucas, 1988. 21. Seddon, H.J., Three types of nerve injury, Brain, 66:239–288, 1943. 22. Dawson, D.M., Hallett, M., and Millender, L.H., Entrapment Neuropathies, Boston, MA: Little, Brown, 1990. 23. Sabin, T.B., Classification of peripheral neuropathy: the long and the short of it, Muscle Nerve, 9:711–719, 1986. 24. Kimura, J., Electrodiagnosis in Diseases of Nerve and Muscle: Principles and Practice, 2nd ed., Philadelphia, PA: F.A. Davis, 1989. 25. Dumitru, D., Reaction of the peripheral nervous system to injury, in Dumitru, D., Ed., Electrodiagnostic Medicine, Philadelphia, PA: Hanley & Belfus, 1995: 341–384. 26. Mellick, R.S. and Cavanagh, J.B., Changes in blood vessel permeability during degeneration and regeneration in peripheral nerves, Brain, 91:141–160, 1968. 27. Lundborg, G. and Danielsen, N., Injury degeneration and regeneration, in Gelberman, R.H., Ed., Operative Nerve Repair and Reconstruction, Philadelphia, PA: Lippincott, 1991: 109–131. 28. Rogers, S.L., Letourneau, P.C., Palm, S.L., McCarthy, J., and Furcht, L.T., Neurite extension by peripheral and central nervous system neurons in response to substratum bound fibronectin and laminin, Dev. Biol., 98:212–220, 1983. 29. Hall, S.M., Regeneration in the peripheral nervous system, Neuropathol. Appl. Neurobiol., 15:513–529, 1989. 30. Stoll, G. and Muller, H.W., Nerve injury, axonal degeneration and neural regeneration: basic insights, Brain Pathol., 9:313–325, 1999.
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31. Politis, M.J. and Spencer, P.S., A method to separate spatially the temporal sequence of axon–Schwann cell interaction during nerve regeneration, J. Neuro-Cytol., 10:221–232, 1981. 32. Cole, G.P. and Smith, J.R., Surgery of peripheral nerves, in Allen, M.B. and Miller, R.H., Eds., Essentials of Neurosurgery: A Guide to Clinical Practice, New York: McGraw-Hill, 1995: 419–436. 33. Rydevik, B. and Lundborg, G.N., The effects of gradual compression on intraneural blood flow: an in vivo study on rabbit tibial nerve, J. Hand Surg. Am., 45:953–966, 1963. 34. Szabo, R.M., Nerve Compression Syndromes: Diagnosis and Treatment, Thorofare, NJ: Slack, 1989. 35. Lundborg, G. and Dahlin, L.B., The pathophysiology of nerve compression, Hand Clin., 8:215–227, 1992. 36. Szabo, R.M. and Sharkey, N.A., Response of peripheral nerve to cyclic compression in a laboratory rat model, J. Orthoped. Res., 11:828–833, 1993. 37. Dahlin, L.B., Danielsen, N., Ehira, T., Lundborg, G., and Rydevik, B., Mechanical effects of compression of peripheral nerves, J. Biomech Eng., 108:120–122, 1986. 38. Dahlin, L.B., Aspects of pathophysiology of nerve entrapments and nerve compression injuries, Neurosurg. Clin. North Am., 2:21–29, 1991. 39. Dellon, A.L. and Mackinnon, S.E., Chronic nerve compression model for the double crush hypothesis, Ann. Plast. Surg., 26:259–264, 1991. 40. Hurst, L.C., Weissberg, D., and Carroll, R.E., The relationship of the double crush to the carpal tunnel syndrome (an analysis of 1000 cases of carpal syndrome), J. Hand Surg. Br., 10:202–204, 1985. 41. Lundborg, G. and Dahlin, L.B., Anatomy, function and pathophysiology of peripheral nerves and nerve compression, Hand Clin., 12:185–193, 1996. 42. Nemoto, K., Matsumoto, N., Tazaki, K., Horiuchi, Y., Uchinishi, K., and Mori, Y., An experimental study on the “double crush” hypothesis, J. Hand Surg., 12:552–559, 1987. 43. Olmarker, K. and Rydevik, B., Single- vs. double-level nerve root compression: an experimental study on the porcine cauda equina with analysis of nerve impulse conduction properties, Clin. Orthoped. Related Res., 279:35–39, 1992. 44. Upton, A.R.M. and McComas, A.J., The double crush in nerve entrapment syndromes, Lancet, 2:359–362, 1973. 45. Bednarik, J., Kadanka, Z., and Vohanka, S., Median nerve mononeuropathy in spondylotic cervical myelopathy: double crush syndrome?, J. Neurol., 246:544–551, 1999. 46. Richardson, J.K., Forman, G.M., and Riley, B., An electrophysiological exploration of the double crush hypothesis, Muscle Nerve, 22:71–77, 1999. 47. Leahy, P.M. and Mock, L.E., Myofascial release technique and mechanical compromise of the upper extremity, Chiropr Sports Med., 6:139–150, 1992.
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48. Mariano, K.A., McDougle, M.A., and Tanksley, G.W., Double crush syndrome: chiropractic care of an entrapment neuropathy, J. Manip. Physiol. Ther., 14:262–265, 1991. 49. Scarpelli, D.G. and Chiga, M., Cell injury and errors of metabolism, in Anderson, W.A.D. and Kissane, J.M., Eds., Pathology, 7th ed., St. Louis, MO: Mosby, 1977: 90–147. 50. Novak, C.B. and Mackinnon, S.E., Repetitive use and static postures: a source of nerve compression and pain, J. Hand Ther., 10:151–159, 1997. 51. Hammer, W., Functional Soft Tissue Examination and Treatment by Manual Methods: New Perspectives, Gaithersburg, MD: Aspen, 1999: 22–25. 52. Friden, J., Muscle soreness after exercise: implications of morphological changes, Int. J. Sports Med., 5:57–66, 1984. 53. Friden, J., Sjostrom, M., and Ekblom, B., Myofibrillar damage following intense eccentric exercise in man, Int. J. Sports Med., 4:170–176, 1983. 54. Newham, D., Jones, D., and Clorkson, P., Repeated high force eccentric exercise: effects and muscle pain and damage, J. Appl. Physiol., 63:1381–1386, 1987. 55. Garret, W. and Tidball, J., Myotendinous junction: structure, function and failure, in Woo, S.L.-Y. and Buckwalter, J., Eds., Injury and Repair of Musculoskeletal Soft Tissues, Park Ridge, IL: American Academy of Orthopaedic Surgeons, 1988. 56. Nikolaou, P.K., Macdonald, B.L., Glisson, R.R., Seaber, A.V., and Garrett, W.E., Jr., Biomechanical and histologic evaluation of muscle after controlled strain injury, Am. J. Sports Med., 15:9–14, 1987. 57. Jarvinen, M., Healing of a crush injury in rat striated muscle. 4. Effect of early mobilization and immobilization on the tensile properties of gastrocnemius muscle, Acta Pathol. Microbiol. Scand., 142:47–56, 1976. 58. Lehto, M., Jarvinen, M., and Nelimorkka, O., Scar formation after skeletal muscle injury: a histological and autoradiographical study in rats, Arch. Orthoped. Trauma Surg., 104:366–370, 1986. 59. Dawes, K.E. and Peacock, A.J., Characterization of fibroblast mitogens and chemoattractants produced by endothelial cells exposed to hypoxia, Am. J. Respir. Cell Molec. Biol., 10:552–559, 1994. 60. Millesi, H., Zoch, G., and Reihsner, R., Mechanical properties of peripheral nerves, Clin. Orthoped., 314:76–83, 1995. 61. Higgs, P., Young, V.L., Seaton, M., Edwards, D., and Feely, C., Upper extremity impairment in workers performing repetitive tasks, Plast. Reconstr. Surg., 90:614–620, 1992. 62. Janda, V., Muscle Function Testing, London: Butterworths, 1983. 63. Cotran, R.S., Kumar, V., and Robbins, S.L., Pathologic Basis of Disease, Philadelphia, PA: Saunders, 1994. 64. Majno, G. and Palade, G.. Studies on inflammation. I. The effect of histamine and serotonin on vascular permeability: an electron microscopic study, J. Biophys. Biochem. Cytol., 11:571, 1961.
65. Braunwald, E., Pathophysiology of heart failure, in Braunwald, E., Ed., A Textbook of Cardiovascular Medicine, 4th ed., Philadelphia, PA: Saunders, 1992: 393–418. 66. Zurier, R., Prostaglandins, leukotrienes, and related compounds, in Kelley, W., Ed., Inflammation, 2nd ed., New York: Raven, 1992: 103–121. 67. Robertson, J.T., Huffmon, G.V., III, Thomas, L.B., Leffler, C.W., Gunter, B.C., and White, R.P., Prostaglandin production after experimental discectomy, Spine, 21:1731–1736, 1996. 68. Johnston, R., Monocytes and macrophages, in Lachman, P., Ed., Critical Aspects of Immunology, 5th ed., London: Blackwell, 1993: 457–480. 69. Roberts, A., McCune, B.K., and Sporn, M.B., TGF-beta: regulation of extracellualr matrix, Kidney Int., 41:557, 1992. 70. Wunderlich, R.P., Peters, E.J., Bosma, J., and Armstrong, D.G., Pathophysiology and treatment of painful diabetic neuropathy of the lower extremity, South. Med. J., 1998 Oct;91(10):894–8. 71. Vinik, A.I., Diagnosis and management of diabetic neuropathy, Clin. Geriatr Med., 1999 May:15(2):293– 320. 72. Mendell, J.R., Diabetic Neuropathy, Peripheral Neuropathy Course #441. American Academy of Neurology Annual Meeting, San Diego, CA, May 9, 1992. 73. Asbury, A.K., Neuropathies with Renal Failure, Hepatic Disorders, Chronic Respiratory Insufficiency, and Critical Illness, Peripheral Neuropathy Course #441, American Academy of Neurology Annual Meeting, San Diego, CA, May 9, 1992: 23–30. 74. Khedr, E.M., El Toony, L.F., Tarkhan, M.N., and Abdella, G., Peripheral and central nervous system alterations in hypothyroidism: electrophysiological findings, Neuropsychobiology, 41(2):88–94, 2000. 75. Duyff, R.F., Van den Bosch, J., Laman, D.M., van Loon, B.J., and Linssen, W.H., Neuromuscular findings in thyroid dysfunction: a prospective clinical and electrodiagnostic study, J. Neurol. Neurosurg. Psychiatry, 68(6):750–755, 2000. 76. Belman, A.L., Preston, T., and Milazzo, M., Human immunodeficiency virus and acquired immunodeficiency syndrome, in Goetz, C.G., and Pappart, E.J., Eds., Texbook of Clinical Neurology, Philadelphia, PA: Saunders, 1999: 895–898. 77. Hazes, J.M.W. and Cats, A., Rheumatoid arthritis management: end-stage and complications, in Klippel, J.H. and Dieppe, P.A., Rhematology, London: Mosby Yearbook, 1994: 3.14.7 78. Chalk, C.H., Dyck, P.J., and Conn, D.L., Vasculitic neuropathy, in Dyke, P.J. and Thomas, P.K., Eds. Peripheral Neuropathy, Philadelphia, PA: Saunders, 1993: 1424–1436. 79. Faden, A., Mendoza, E., and Flynn, F., Sub-clinical neuropathy associated with chronic obstructive pulmonary disease: possible pathophysiological role of smoking, Arch. Neurol., 38:639, 1981.
10
Characteristic Signs and Symptoms of Entrapment*
The presence of diffuse dysesthetic pain, paresis, or paresthesia dictates that all differential diagnoses must be eliminated before focal or multifocal entrapment may be accurately implicated. Vertebrogenic pain, myofascial pain, and disk compression often produce pseudoradicular and radicular complaints. Visceral or organic pathology may refer pain into the extremities. These symptoms may occur as a result of a primary pathology or in conjunction with entrapment, thus further obscuring the actual etiology of the complaint. The vast majority of chronic tunnel syndromes exhibit sensory, motor, and autonomic nerve involvement.1 In general, varying percentages of these three types of fibers are present in all mixed nerves. Nerves with a predominance of sensory or motor fibers may demonstrate exclusive motor or sensory signs/symptoms. Examples include deficits such as exhibited in anterior interosseous syndrome (motor) and lateral femoral cutaneous (sensory) neuropathy. Diffuse pain in the extremity, at rest or during activity, is the most common presenting complaint in early entrapment neuropathy. Patients may describe the initial complaint as a deep ache, burning paresthesia, numbness, or tingling that occurs proximal and/or distal to the lesion site. Sensory deficits, when present, will follow the cutaneous distribution of the nerve.
10.1 ASSESSMENT OF ENTRAPMENT SYNDROMES Assessment of peripheral entrapment in the clinical setting requires detailed understanding of the surrounding anatomy, consideration of mechanical challenges to the pathways, and functional evaluation of the nerves. Electrodiagnosis is a necessary component of the clinical examination for localization, quantification, and differentiation of an entrapment neuropathy from other disorders.
10.1.1 HISTORY History taking is an integral part of the process for assessing peripheral entrapment. The patient history provides the doctor with information surrounding the type and quality of symptoms, the chronology of the neurological complaint, family history, and potentially pertinent social and occupational status. Standard history-taking protocols
should be applied with particular attention to key provocative and relieving factors. In cases of suspected cumulative trauma, the patient should demonstrate repetitive motions required for the occupation. Occupations that are most apt to result in peripheral nerve entrapment include those involving repetitive handwork, shock waves from hammering, and vibration from power tools. In the extremity, presenting symptoms may involve medial, lateral, or posterior aspect of the extremity. However, symptoms may also be described in a diffuse pattern that involves the whole extremity. Patients may be unable to verbalize the location, yet when asked to run their hand along the involved area they often circumscribe the particular anatomic distribution of the peripheral nerve. Patterns of involvement provide clues to the localization of the entrapped nerve. Combinations of these regions may suggest more proximal pathology (see Figures 10.1 to 10.5).
10.1.2 EXAMINATION The two components of the clinical examination are assessment of neurological function and various orthopedic maneuvers designed to mechanically challenge the region and provoke or relieve symptoms. In mixed nerves, sensory signs usually predominate and are the first to appear during entrapment; generally, they initially involve large-diameter axonal functions (dorsal column sensations). In nerve entrapment with a motor fiber predominance, patients commonly report a deep diffuse ache (Table 10.1). Paresis in most entrapment pathologies occurs much later than sensory deficits.1 Pain and dysesthesia may occur both proximal and distal to sites of entrapment, perplexing the localization process. Evaluation of neurological function includes assessment of sensory deficits, relevant reflexes, and motor strength. Sensory deficits should be assessed by pinprick, two-point discrimination, tuning fork, and joint position sensibility. Discriminative pressure sensation can be evaluated with tools such as Semmes–Weinstein® monofilaments or the Dellon DiskCriminator® moving two-point discrimination test for hand sensibility. Careful attention to the subtlety of autonomic innervation is important. Alterations in trophic function may be indictors of entrapment. Edema, inflammation, or
* This chapter written with J. Donald Dishman and Clifford M. Shooker.
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Upper lateral brachial cutaneous Intercostobrachial nerve Medial cutaneous nerve of arm Posterior cutaneous nerve of arm
Posterior cutaneous nerve of arm
Medial cutaneous nerve of forearm Lateral cutaneous nerve of forearm
Lateral cutaneous nerve of forearm Posterior cutaneous nerve of forearm Radial nerve
Radial nerve Ulnar nerve Median nerve
Ulnar nerve
Median nerve
FIGURE 10.1 Cutaneous innervation of the upper extremity. With some exceptions, the cutaneous distribution of the upper extremity can be grossly considered in medial/lateral and posterior distributions continuing from the corresponding cord of the brachial plexus. (Copyright J.M. True, D.C.)
changes in skin texture may occur in severe cases with autonomic involvement. Reflexes may be depressed or absent distal to a nerve entrapment. Side-to-side asymmetry is clinically significant when relevant reflexes are affected. Motor deficits may be apparent when repetitive strength testing is performed. However, pronounced paresis or atrophy usually does not occur unless the lesion is quite severe or very chronic. Nerve entrapments caused by a narrowed myofascial tunnel may often be symptomatically reproduced, by contracting or stretching the muscle forming or bordering the tunnel. Mechanical challenge to the suspected entrapped nerve can be accomplished by one or more of the following physical methods: by the examiner applying pressure to deform the nerve (such as with Tinel’s sign or nerve percussion tests), by creating stretch of the nerve (e.g., with the elbow flexion maneuver), or by putting surrounding musculoligamentous tissues in a position of stretch combined with contraction in order to compress the nerve (Phalen’s test for the carpal tunnel). Integration of findings from the clinical examination should provide reasonable localization of the involvement. The course of treatment may be set and closely monitored. The results of a trial of treatment should be considered as part of the differential diagnostic assessment. Post-treatment improvement and a reduced ability to reproduce symptoms should be viewed as diagnostic confirmation of the source of entrapment. Clinical improvement substantiates
the working diagnosis and current treatment plan, whereas failure to improve or declining status indicates need for reconsideration of the original hypothesis, implementing a different trial of treatment, and possible further diagnostic study.
10.1.3 NERVE PERCUSSION SIGN An injured or compressed nerve becomes sensitive to mechanical forces and has a lowered threshold for depolarization. As a consequence, lightly tapping along the course of a peripheral nerve in the vicinity of an entrapment reproduces the patient’s paresthesia and sensory complaints. This finding is called a positive nerve percussion sign or positive Tinel’s sign. The nerve becomes hypersensitive and susceptible to mechanical depolarization through a variety of pathomechanisms. This mechanical irritability may develop from: (1) tissue injury and macrophage action causing inflammatory metabolites to accumulate in the nerve and entrapment vicinity, (2) sympathetic nervous system action on the local vasculature following increased sensitivity to endogenous and exogenous catecholamines, and (3) most importantly, axonal sprouts and neuromas arising from attempted proximal axon regeneration. Neuroma formation may occur at the site of chronic compression. The neuroma forms on the distal end of an injured axon from the clustered axonal sprouts that grow
Characteristic Signs and Symptoms of Entrapment
Femoral branches of genitofemoral nerve
Anterior cutaneous branches of T12
Femoral branches of genitofemoral nerve
283
Superior, middle and inferior clunial nerves Iliohypogastric nerve
Lateral femoral cutaneous nerve (L2-L3)
Ilioinguinal nerve
Anterior cutaneous branches of femoral nerve (L2-L4)
Obturator nerve (L2-L4)
Lateral cutaneous nerve of calf (L5-S1) Saphenous nerve (L3-4)
Superficial peroneal nerve
Iliohypogastric nerve (T12-L1) Posterior cutaneous nerve of thigh (S1-S3)
Lateral femoral cutaneous nerve (L2-L3)
Lateral cutaneous nerve of calf (L5-S1)
Superficial peroneal nerve
Medial plantar nerve Sural nerve (S1)
Deep peroneal nerve (L5)
Terminal branch of sural nerve (S1)
FIGURE 10.2 Cutaneous innervation of the lower extremity. The cutaneous distribution of the lower extremity has four divisions in the thigh (medial, lateral, anterior, posterior) and continues in the leg with medial, lateral, and posterior distributions. The sural nerve and deep peroneal nerves form exceptions to the rule. (Copyright J.M. True, D.C.)
after a failed attempt at regeneration. These small clustered bundles of axon sprouts have unstable membranes that are sensitive to ectopic depolarization.2 Collateral sprouting may also involve nearby intact nerves.3 These sprouting terminals exhibit both mechanical and chemical sensitivity. The nerve percussion sign is the result of crossed after-discharges in the sprouting terminals.4 Lightly tapping a normal nerve may be uncomfortable but generally should not produce paresthesias or pain. Although there is debate within the field regarding the significance of Tinel’s sign in an otherwise normal individual, the finding should be closely considered, particularly in the context of double crush or whole nerve mechanisms discussed previously.
10.1.4 ELECTRODIAGNOSTIC FINDINGS The earliest electrodiagnostic sign of entrapment is a loss of amplitude of the nerve action potential seen during a nerve conduction study. When there is a 50% or more loss of action potential amplitude, the pathological response is denoted as a focal conduction block. This loss of amplitude is recorded when the nerve is electrically stimulated on one side of the entrapment site and a reduced response is recorded on the other side of the lesion (Figure 10.6). To isolate the specific location of the conduction block, serial stimulations are delivered to the nerve above and
below the suspected lesion. The examiner advances stimulation slowly along the course of the nerve until the site of the lesion is demonstrated by a distinguishing loss of amplitude. Axonotmesis or Wallerian degeneration occurs in significant entrapments and the loss of axons impacts the electrical response of the nerve. The resulting axonopathy causes the compound motor unit action potential (CMAP) elicited on nerve conduction to be reduced in amplitude (Figure 10.7). Distal axonopathy also occurs with multifocal neuropathies such as metabolic neuropathies associated with diabetes or hypothyroidism. There are many diseases and conditions that are associated with an increased risk of entrapments (see Table 9.3). Needle electromyography (EMG) is valuable for evaluating the extent of motor fiber loss within a nerve territory and the degree of reinnervation following Wallerian degeneration. Spontaneous muscle activity is occasionally demonstrated in chronic focal entrapment. Due to the slow progression of most entrapment pathology, spontaneous discharges consistent with rapid denervation are not routinely encountered. In rapid-onset compression or acute traumatic partial nerve injuries, EMG evidence of spontaneous activity will be present within 2 weeks. This spontaneous activity subsides after a few weeks as collateral nerve fibers reinnervate the muscle. EMG also provides valuable data for differential diagnosis in cases that may
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Median
Median Ulnar
Superficial radial
Superficial radial
Lateral antebrachial l cutaneous
Ulnar
Peripheral nerve distribution
C7
C6
C7
C8 C6
C8
T1
Dermatomal innervation FIGURE 10.3 There is considerable variation in the distribution and segmental overlap of the peripheral nervous system. These figures are generalized and not absolute. (Copyright J.M. True, D.C.)
be complicated by cervical radiculopathy or other concurrent pathologies. Chronic entrapment with resultant axonotmesis will produce delays in late responses (Fwave), increase distal latency values, and cause an amplitude loss in sensory and compound motor nerve conduction studies.5 Additionally, an entrapment syndrome may produce a mild prolongation during evoked potential studies. These electrodiagnostic findings should be clinically correlated with the neurologic and orthopedic examination to establish the definitive diagnosis. Although electrodiagnostic testing is arguably the “gold standard” for localization of entrapment in superficially accessible nerves, it may not be of much help other than for exclusionary purposes in some of the proximal entrapment syndromes. In addition, the value of close clinical examination in association with electrodiagnostic study cannot be overstated. The clinical examination alone may be equivalent or better than the diagnostic sensitivity of electrodiagnosis, when considering specific entrapment syndromes such as pronator teres syndrome or carpal tunnel syndrome (CTS).6
10.1.5 ENTRAPMENT SYNDROMES OVERVIEW The following section reviews selected entrapment syndromes. As reviewed above, sensory symptoms will commonly predominate in mixed nerves. The sensory orientation of the patients’ complaints in the extremities will generally follow along one side or within an anatomical compartment. For this reason, the syndromes have been organized in a rostral-to-caudal fashion or, whenever possible, according to the cutaneous distribution of the involved nerve. This section begins with a discussion of the broad category of cervicoaxillary entrapments (thoracic outlet), which may produce symptoms in any part of the distal upper extremity. The median nerve syndromes are discussed next, followed by the radial nerve and ulnar nerve syndromes. Pelvic and abdominal entrapments are discussed briefly, followed by the lower extremity entrapment syndromes. Within each section, the entrapment syndromes are organized from proximal to distal.
Characteristic Signs and Symptoms of Entrapment
285
Anterior
Posterior
Femoral n.
Superior and inferior gluteal n.
Inguinal ligament
Axillary nerve
Obturator n. Musculocutaneous nerve
Sciatic n.
Ant. branch Post. branch
Tibial n. Common peroneal n.
Radial nerve
Medial and lateral plantar n. (from tibial n.)
Common peroneal n.
Deep peroneal n.
Median nerve Ulnar nerve
FIGURE 10.4 Motor innervation of the upper extremity. The axillary nerve innervates two muscles of the shoulder, and the musculocutaneous nerve innervates flexors of the shoulder and elbow. The radial nerve innervates extensors of the shoulder, elbow, wrist, fingers, the forearm, and the supinator. The median nerve innervates the lateral part of the long flexors of the forearm, the pronators, and the thenar eminence. The ulnar nerve innervates the medial part of the long flexors of the forearm, the hypothenar eminence, and the intrinsic muscles of the hand. (Copyright J.M. True, D.C.)
10.2 PROXIMAL UPPER EXTREMITY ENTRAPMENT 10.2.1 CERVICOAXILLARY ENTRAPMENT SYNDROMES (THORACIC OUTLET SYNDROME) Commonly, clinicians refer to compressive neuropathies in the region of the brachial plexus as thoracic outlet syndrome (TOS). The term “thoracic outlet syndrome” was coined by Peete et al. in 1956 to encompass all the forms and causes of neurovascular compression in the base of the neck (cited in Reference 7). To the anatomist, TOS refers to an anatomical opening also known as the inferior thoracic aperture. This opening enters the abdominal region, bordered by the lower costal elements.8 In contrast, the clinician often refers to the area of the scalene triangle or scalene aperture as the thoracic outlet. Obviously,
FIGURE 10.5 Motor innervation of the lower extremity. (Copyright J.M. True, D.C.)
anatomists and clinicians are referring to two different locations when speaking of the thoracic outlet. Ranney9 addresses this issue in an anatomical review and proposes that the collective term “cervicoaxillary syndrome” (CAS) be employed as more anatomically correct and appropriate for the purpose of organizing these entities into one named category or terminology scheme. Simply clustering the brachial plexus entrapments together as TOS is a nondescript and anatomically incorrect classification scheme. However, because of the wide usage and recognition of TOS, it is unlikely that the anatomically correct CAS descriptor will ever displace TOS as a description of these syndromes. Symptom production occurs from compression and/or traction forces created by osteoligamenteous or myotendofascial (also referred to as osseous and soft tissue) anomalies in the cervicoaxillary region. These two groups of anomalies causing TOS comprise virtually all cases of neurogenic TOS, with the exception of rare cases resulting from tumors or metastic invasion of the plexus. Four symptom patterns have been described: upper plexus, lower plexus, vascular, and mixed.10 As a result, symptom patterns may include both or either neural and vascular components. However, the neurogenic type of TOS represents the greatest proportion of patients with TOS. When vascular occlusion or thrombosis is present, vascular patency studies are necessary, such as arteriovenous doppler for less severe conditions and venography or angiography for the moderate to severe cases.
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TABLE 10.1 Key Muscles for Screening Tests of the Major Peripheral Nerves Root Innervation
Peripheral Nerve
Key Muscle in Action
Median
Opponens (opposition of the thumb); short abductor of the thumb (abductor pollicis brevis, APB); flexor of distal phalanx, index finger Abduction of the fifth finger; (abductor digiti minimi) First dorsal interosseous-adduction of thumb and index finger Extensors of the thumb (extensor pollicis longus) Radial extensors of the wrist (extensor carpi radialis) Triceps (forearm extension) Biceps (forearm flexion and supination) Deltoid (arm abduction, tested in abducted position) Quadriceps (extension of leg at knee) Adductor group (adduction of thigh) Gastrocnemius (plantar flexion of foot) Posterior tibial muscle (inversion of foot) Anterior tibial muscle (dorsiflexion of foot) Extensor hallucis longus (extension of great toe) Peroneal group (eversion of foot)
Ulnar Radial
Musculocutaneous Axillary Femoral Obturator Sciatic: posterior tibial nerve Common peroneal anterior tibial nerve (deep peroneal) Superficial peroneal
C8, T1
C7, C8, T1 C8, T1 C7, C8 C6, C7, C8 C7, C8 C5, C6 C5, (C6) (L2), L3, L4 L2, L3, L4 L5, S1, S2 L5, S1 L4, L5, (S1) L5, (S1) (L4), L5, S1
Source: Glick, T.H., Neurologic Skills Examination and Diagnosis, Blackwell Scientific, Boston, MA, 1991, p. 370. With permission.
Stimulation 1 above lesion
Stimulation 2 distal to lesion
+-
+-
Recording and reference electrodes
Peripheral nerve
4mv
1 Above lesion Area 20mv\sec
Conduction block with demyelination
Reduced amplitude Mild dispersion of waveform
+
2 Below lesion Area 50mv\sec 10mv
Normal waveform No dispersion
FIGURE 10.6 Electrophysiologic response of the median nerve with conduction block. When a conduction block is present, there is a 50% or greater drop in amplitude following stimulation of the nerve above the lesion. (Copyright J.M. True, D.C.)
Diagnostic imaging and electrodiagnostic examination are essential in most cases because of the differential pathologies with similar symptoms to this disorder. Plain film radiographs of the neck and shoulder region should be performed. Magnetic resonance imaging (MRI) of the cervical spine is appropriate when paresthesia or paresis is progressive. Where available, the brachial plexus can be visualized with specialized phase-array MRI coils. The roots and trunks of the brachial plexus in normal patients are isointense to muscle on T1-weighted images and slightly hyperintense on short tau inversion recovery
(STIR) technique. The divisions, cords, and peripheral nerves arising from the cords are normally isointense to muscle in all pulse sequences. Demonstration of T2weighted hyperintensity, with or without neural enlargement, indicates plexus abnormality.11 Neurophysiologic studies include electromyography, nerve conduction velocity, F-wave studies, and somatosensory evoked potentials. The results of these tests are usually imprecise for exact localization of the plexus compression; however, in combination with other clinical findings they help to establish a diagnosis (see Table 10.2; Figure 10.8).
Characteristic Signs and Symptoms of Entrapment
287
Stimulation 1
Stimulation 2
+-
+Peripheral nerve
3mv
Axonal degeneration
1 Proximal Area 30mv\sec
Reduced amplitude Moderate dispersion Prolonged latency
Sensory loss +
2 Distal Area 30mv\sec 3mv
Reduced amplitude Less dispersion than proximal Prolonged latency
FIGURE 10.7 Electrophysiologic response from stimulation of the median nerve with distal axonopathy. (Copyright J.M. True, D.C.)
TABLE 10.2 Examination Parameters for Thoracic Outlet Syndrome • • • • • • • • • • • • • • • • • • •
Cervical range of motion (consider coupled contralateral flexion/ipsilateral the rotation — Adson’s sign) Shoulder ranges into extension (Eden’s, Wright’s) Tinel’s sign: supraclavicular, costoclavicular, ulnar groove, carpal tunnel, tunnel of Guyon, pronator teres, brachioradialis Phalen’s sign Carpal tunnel compression test Roos test (90 degree abduction/external rotation [90AER]) Cervical/upper thoracic palpation Cervical compression Shoulder depression/reverse Bakody’s sign Regional shoulder examination Regional upper quarter examination/palpation for syndrome provocation Upper extremity motor testing Upper extremity sensory testing Vascular evaluation: auscultate for bruits and pulses in proximal/distal supply Breast examination Lung examination Diagnostic imaging: post-trauma, bony changes or degeneration, space-occupying lesion Upper extremity somatosensory evoked potential (SEP) and nerve conduction velocity (NCV) exam with F-waves Needle EMG (more for differential diagnosis of cervical radiculopathy)
Note: The basic goal will be to demonstrate symptom provocation with stress to TOS tissues to identify those tissues, to qualify/quantify motor and sensory deficits, and to rule out pathology, radiculopathy, or other sources of entrapment neuropathy.
10.2.2 SCALENE ENTRAPMENT SYNDROME The brachial plexus is vulnerable to compression in the scalene triangle. Most commonly, fibers of the lower plexus (lower trunk) are involved. This causes symptoms of numbness or paresthesia into the C8–T1 dermatomal distribution. Upper plexus symptoms, when present, will produce lateral hand paresthesia in a C5–6 distribution. Hypertrophy of the scalenes can lead to a reduction in the size of the aperture and thus produce direct compression as can other space-occupying lesions. The anterior and middle scalene muscles form a triangle in the anterolateral
aspect of the neck and have multiple bands of fibers that originate from the transverse processes of the C4–C6 to insert on the first rib. The posterior scalene attaches to the posterior aspect of the transverse foramen and inserts on the anteromedial portion of the second rib. Bilateral contraction of the scalene musculature results in flexion of the cervical spine. Unilateral scalene contraction predisposes to ipsilateral lateral flexion of the cervical spine coupled with contralateral rotation. The secondary action of the scalenes is to assist with inspiration by elevation of the first and second rib. There is considerable controversy regarding the frequency
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Compression in the scalene triangle region occurs from multiple causes. Fibrous banding adhesing nerve roots to the scalenes, scalene hypertrophy, nerve roots piercing the anterior scalene, cervical ribs and congenital or otherwise narrowed scalene triangle.
Entrapment/traction of the peripheral nerves of the brachial plexus can occur from fibrous attachment of the sheath to the shoulder capsule and subscapularis tendon in the axilla. The humeral head may compress the brachial plexus in cases of degenerative shoulder pathology and glenohumeral instability.
The brachial plexus sheath is tractioned by the action of the scalenes, in the presence of fibrous adhesion. This commonly compromises the inferior trunk and ulnar nerve fibers.
Compression and tractioning effects may occur between the space formed by the teres major, coracobrachialis, and latissimus dorsi
Coracoid process Subscapularis
Axillary sheath Teres major
CJ .T RUE,D C
Latissimus dorsi
Pectoralis minor Infraclavicular entrapment may occur under the costopectoral space formed between the coracoid process, pectoralis minor and the rib cage
The sternocostovertebral space is the most proximal region where compression occurs. Apical lung tumors may compress the lower trunk.
FIGURE 10.8 Anatomic regions capable of producing cervicoaxillary symptoms. (Copyright 2000 J.M. True, D.C.)
TABLE 10.3 TOS: Anterior/Middle Scalene Syndrome Clinical Signs and Symptoms
Possible Etiologies
Numbness in fingers, hand and forearm (commonly medial distribution) Intrinsic hand atrophy and paresis Hypertrophied or taut scalene muscles Positive Adson’s sign (scalene stretch) Distal upper extremity ischemic changes Raynaud’s type phenomena Subclavian artery bruit Finger ulcerations
Cervical rib Elongated transverse process Presence of scalenus minimus Fibrous bands Scalene muscle hypertrophy Anterior/middle scalene muscle spasm Poor posture Prolonged overhead work Cervical biomechanical fault
of scalene entrapment syndrome because of the lack of radiographic or other objective evidence specific to localizing the scalenes as the causative factor (Table 10.3).
10.2.3 OTHER CAUSES OF PROXIMAL PLEXUS ENTRAPMENT Various pathologies that may contribute to brachial plexus compression and entrapment include fibrotic induration
about the plexus, a large callous on the clavicle following fracture, blunt impact or acceleration–deceleration trauma, infections, and apical lung tumors. Elongated C7 transverse process or cervical ribs may involve the C8 nerve root. Additionally, several common anatomical variations of the brachial plexus exist in which the plexus penetrates the scalene muscle or fibrous banding passes over the plexus in a variety of combinations.8 Roos7 has identified ten different soft tissue anomalies in the cervicoaxillary
Characteristic Signs and Symptoms of Entrapment
FIGURE 10.9 Anatomic example of deep cervical fascia (A) arching over and adhering to the ventral primary rami forming the brachial plexus. (Courtesy of J. Paul Ellis, Ph.D.)
region capable of producing lower plexus entrapment, in addition to seven anomalies in upper plexus involvement (Figure 10.9). Magnetic resonance imaging of the brachial plexus is considered to be the technique of choice for studying traumatic or tumor involvement of the brachial plexus.11,12 Magnetic resonance angiography for TOS is diagnostically comparable to angiography when a vascular component is present.13 Although many cervicoaxillary anomalies are well described in the literature, most can only be confirmed after surgical exploration.14 10.2.3.1 Clinical Signs and Symptoms Paresthesia and pain in the hand, finger, arm, and forearm are the most common complaints associated with mild scalene entrapment syndromes. In late stages, the patient may encounter progressive motor weakness and vascular insufficiency. Additionally, a decrease in grip strength with associated atrophy of the intrinsic hand muscles may occur. Clumsiness and loss of fine motor control of the fingers may also occur. Supraclavicular region TOS commonly affects the lower trunk of the brachial plexus (C8–T1) and gives rise to medial pattern paresthesia and ulnar pattern paresis. Some researchers have proposed that the apex of the scalene triangle may also frequently compress the upper brachial plexus roots.9 The 90-degree abduction external rotation (90° AER) test (also referred to as an elevated arm stress test [E.A.S.T.], or Roos test) of the shoulder is reported as a reliable method for evaluating thoracic outlet syndrome.7,15-16 This test may
289
be helpful in differentiating radicular findings from those secondary to a neurogenic thoracic outlet syndrome. The procedure is performed by having the patient abduct his or her arm to approximately 90°, followed by assuming a position of full external rotation of the glenohumeral joint. The patient should then be asked to slowly flex and extend the fingers, although this portion of the test is not always required to reproduce symptoms. The test is considered positive if this sequence of events leads to neurogenic or vascular claudication of the tested extremity in less then 3 minutes. Sanders and Haug15 found high sensitivity with the 90° AER, reproducing symptoms of paresthesia, pain, weakness, or fatigue in over 90% of the patients with TOS. This maneuver is a better test for assessing neurogenic cervicoaxillary compression than Adson’s maneuver or costoclavicular and hyperabduction maneuvers. Gergoudis and Barnes17 recorded the upper extremity pulses in 130 normal patients while performing Adson’s, costoclavicular compression, and hyperabduction maneuvers. They found that 53% of their patients had a positive Adson’s test and one or more of these maneuvers were positive in 60% of the patients examined. Because obliteration of the radial pulse occurs in such a high percentage of normal patients, interpretation can be difficult with Adson’s or hyperabduction maneuvers. Auscultation may reveal a supraclavicular bruit in the presence of pulse obliteration with Adson’s representing subclavian involvement. When arterial TOS is present, a loss of pulse and mild ischemia of the hand occurs. When venous TOS is present, the hand becomes cyanotic with distention of forearm veins.7 The 90° AER should be the preferential orthopedic test for clinical correlation of CAS along with tenderness of scalene musculature and other neurological indicators such as Tinel’s sign at the supraclavicular fossa and elbow.15 An increase of symptoms following scalene stretch or scalene contraction is referred to as the neck tilting test and suggests the scalenes as a causative factor.
10.2.4 COSTOCLAVICULAR ENTRAPMENT SYNDROME The brachial plexus and subclavian artery exit the thoracic outlet and are vulnerable to compression as they pass over the first rib and under the clavicle. The subclavian vein passes medial to the anterior scalene insertion on the first rib. The subclavian vein may also be involved in other compression syndromes due to anatomical constriction of the aperture or hypertrophy of the subclavius muscle. The lower trunk of the brachial plexus may be tractioned over the first rib as it elevates during deep inspiration. Additionally, traction force acting upon the axillary sheath as a result of hypertonic muscles in the axilla may also affect the lower plexus.
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 10.4 TOS: Costoclavicular Syndrome Clinical Signs and Symptoms
Possible Etiologies
Numbness in fingers, hand, and forearm Arm and hand pain Greater vascular complications than anterior scalene syndrome Hand edema secondary to venous compromise Diminished radial pulse with elevation of chest and pulling shoulders posteriorly
Congenital fibrous bands Poor posture Clavicular callus Respiratory pathology (tumor) with deep inhalation Post-clavicular or rib fracture with malalignment Sternoclavicular biomechanical fault
TABLE 10.5 TOS: Costopectoral Space Syndrome Clinical Signs and Symptoms
Possible Etiologies
Pain and paresthesia in fingers, later in hands Neurological symptoms may be absent Positional paresthesia and pain Successful positional adaptation by patient Increased symptoms with arm abduction Transitory hand ischemia and edema
Hypertrophic pectoralis minor tendon Chondroepitrochlearis muscle arising from pectoralis major muscle Prolonged hyperabduction of arm Scar tissue in costopectoral space Prolonged overhead arm activity
Vascular symptoms may or may not be present, but they may be produced or reproduced mechanically as a result of provocative maneuvers such as depression of the shoulder girdle. Falconer and Weddel18 have previously described the possibility of vascular symptomatology as the distinctive feature that may differentiate costoclavicular syndrome from scalene syndrome. Roos and Owens19 have attributed the majority of cases to congenital anatomical or functional anomalies. In general, the clinical presentations of costoclavicular syndrome appear similar to the symptoms encountered in the scalene syndrome, but perhaps more frequently with an additional component of vascular symptomatology (Table 10.4).1
10.2.5 COSTOPECTORAL TUNNEL OR HYPERABDUCTION SYNDROME The brachial plexus, subclavian artery, and vein pass through a narrow tunnel formed by the pectoralis minor muscle, coracoid process, and thoracic wall. A tractioning effect on the brachial plexus can occur during hyperabduction of the upper extremity, encouraging an overuse syndrome, or as a result of hypertrophy of the pectoralis minor muscle. First described in 1945, this tractioning of the brachial plexus was initially termed hyperabduction syndrome as a result of the mechanism of compression of the neurovascular bundle.20 Vascular symptom severity may be of sufficient magnitude to produce Raynaud-like symptoms into the distal upper extremities.21
10.2.5.1 Clinical Signs and Symptoms Patients presenting with hyperabduction syndrome often complain of intermittent paresthesias and pain. Activities of daily living or occupations involving elevation of the arm and shoulders frequently produce or exacerbate the complaint. A dermatomal pattern of paresthesia is variable; clinically, the patient may exhibit signs of radial nerve palsy, carpal tunnel syndrome, or ulnar paresthesia. A Tinel’s sign may be elicited in the coracopectoral region. Elevation of the symptomatic arm over the head while draping the forearm across the top of the head often reproduces the primary complaint. This maneuver is called the reverse Bakody sign. As a differential consideration, the same maneuver (Bakody sign) may reduce symptoms of a C5–C6 radiculopathy by minimizing traction on the nerve roots. The most common pattern of paresthesia reproduced is in an ulnar distribution. Symptom reproduction occurs from traction of the irritated brachial plexus under the coracoid process (Table 10.5).
10.2.6 AXILLARY TUNNEL ENTRAPMENT Axillary tunnel entrapment may occur if the axillary sheath becomes fixed to the subscapularis muscle, humerus, or glenohumeral capsule. Reflexogenic contracture of muscles forming the posterior wall of the axilla may produce compression in the axillary sheath and its contents following injury to the thoracic spine. Injuries to the subscapularis that result in adhesions between the subscapularis, the axillary
Characteristic Signs and Symptoms of Entrapment
291
TABLE 10.6 Long Thoracic Nerve (C5–C7) Compression Clinical Signs and Symptoms
Possible Etiologies
Paresis of shoulder abduction and elevation Vague shoulder weakness and pain Trouble with overhead tasks Winging of scapula Positive wall pushaway test Abnormal scapular movement Sup. angle displaced medially Inf. angle displaced laterally Difficulty raising arm up straight
Tight bandage Poorly adjusted crutches Tight plaster cast Blow to shoulder Borrelia burgdorferi infection Axillary surgery
sheath, and cords of the brachial plexus may also be a mechanism of symptom production. With this type of lesion, the patient presents with altered texture and hypertonicity in the subscapularis. Additionally, the clinician may identify palpable adhesions or traction on the medial cord of the brachial plexus. If left unmanaged, all three cords may become involved in the syndrome. This mechanism could provide a plausible theory as to why ulnar nerve symptoms usually develop initially, with subsequent multiple peripheral nerve symptoms developing later in the course of the disorder. 10.2.6.1 Electrodiagnostic Evaluation Evoked potentials across the brachial plexus with recording in Erb’s fossa may sometimes provide diagnostic localizing insight for cervicoaxillary syndromes. Reduced evoked potential amplitude or delayed latency of the Erb’s response is clinically significant. Side-to-side comparisons of amplitude and peak latency should be made. Amplitude reduced by 50% or peak latency delayed more than 1.5 milliseconds as compared to the other side are indicators of neuropathology. Nerve conduction studies and F-waves should also be performed. Reduced amplitudes seen in distal ulnar sensory and motor nerve action potentials are signs of chronic axonopathy of the lower plexus/medial cord; however, the distal median nerve response is frequently normal. In addition, reduced amplitude of the medial antebrachial cutaneous sensory nerve action potential (SNAP) has been described.22 F-wave studies of the ulnar and median nerves have value for the correlation of plexus lesions with clinical findings; however, F-waves alone are not specifically localizing for TOS. Reduced F-wave production, prolonged F-wave duration, and F-wave onset delay are some of the criteria used to determine abnormality.
10.2.7 LONG THORACIC NERVE ENTRAPMENT (SCAPULAR WINGING) The long thoracic nerve is formed from branches of the C5–C7 roots, proximal to the brachial plexus. The upper two roots may pierce the scalenes medius muscle, making the C5 and C6 roots vulnerable to entrapment. The nerve runs over the external surface of the serratus anterior. Entrapment may result from compression of the long thoracic nerve against the second rib.23 This purely motor nerve provides innervation to the serratus anterior muscle, which stabilizes the scapula to the posterior thorax. Weakness of the serratus anterior as a result of impingement may lead to “winging” of the scapula. Long thoracic nerve palsy has been reported as a lesion associated with sports activity.24 In one case report, restriction from the activity (volleyball) led to resolution within 6 months (Table 10.6).25
10.2.8 QUADRANGULAR (QUADRILATERAL) SPACE SYNDROME (LATERAL AXILLARY HIATUS SYNDROME) The quadrilateral space is formed by the teres minor and major muscles (forming horizontal borders), along with the shaft of the humerus and the long head of the triceps (forming vertical borders of the space). First described in 1955, quadrangular space syndrome has been observed following humeral and scapular fractures and as a sequel to shoulder dislocation.26 Some clinicians have also attributed this condition to hypertrophy of the teres muscles.27 Fibrous bands entrapping the nerve have also been described.28 The axillary nerve can become entrapped in the quadrangular space as a result of these mechanisms. Additionally, traumatic injuries to the rotator cuff muscles may lead to this condition.
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 10.7 Lateral Axillary Nerve (C5, C6) Hiatus Syndrome Clinical Signs and Symptoms
Possible Etiologies
Lateral shoulder and proximal arm paresthesia Deltoid paresis and atrophy Shoulder abduction paresis Compensatory use of supraspinatus and biceps Tenderness over quadrilateral space Pain with internal shoulder rotation Abnormal scapulohumeral rhythm
Fracture of humerus Fracture of scapula Shoulder dislocation Shoulder abduction narrowing the hiatus Teres muscle hypertrophy Fibrous band Throwing injury
10.2.8.1 Clinical Signs and Symptoms Pain or paresthesia originating from the quadrangular space and extending down the posterolateral upper arm towards the elbow represent the most frequently reported symptoms. The patient may frequently experience difficulty providing an exact location of the symptoms. Weakness of shoulder abduction is a result of impingement on the motor branch to the deltoid. Compensatory hypertrophy of the supraspinatus may result from deltoid weakness. Teres minor weakness and atrophy may develop from impingement of its motor branch from the axillary nerve. This syndrome may also occur as a secondary, compensatory finding in deltoid atrophy patients, usually due to the compensatory hypertrophy of the teres muscles. Subclavian angiography may demonstrate reduced flow in the posterior humeral circumflex artery during concomitant abduction and external rotation.28 In reporting on surgical management of five presentations of quadrilateral space syndrome with history of trauma, Francel et al. suggest that arteriography of the posterior circumflex humeral artery was not necessary to diagnose axillary nerve entrapment in the quadrilateral space. Diagnosis was made on the basis of (1) tenderness over the quadrilateral space, (2) paresthesia over the lateral shoulder and upper posterior arm, and (3) deltoid weakness associated with decreased shoulder abduction (Table 10.7).29
10.2.9 LATERAL ANTEBRACHIAL SYMPTOMS: LATERAL ANTEBRACHIAL CUTANEOUS NERVE/MUSCULOCUTANEOUS NERVE ENTRAPMENT The lateral antebrachial or lateral antebrachial cutaneous nerve, as it is often called, is a terminal sensory branch of the musculocutaneous nerve. The musculocutaneous nerve is one of the least likely nerves in the upper extremity to be subjected to entrapment neuropathy.30 However, the lateral antebrachial cutaneous branch has a tendency to become compressed in the region of the elbow. As the musculocutaneous nerve extends distally down toward the
elbow, it emerges superficially and anterolaterally to the coracobrachialis muscle. It may pierce the coracobrachialis, rendering it vulnerable to compression. The nerve is surrounded by the biceps and brachialis muscles, to which it supplies motor branches; hypertrophic changes (particularly in heavy weightlifters) may compress it here.24 Ultimately, the nerve emerges near the lateral elbow crease in the vicinity of the biceps tendon, just medial to the brachioradialis muscle. The lateral antebrachial cutaneous nerve is most susceptible to compression at this region. The biceps tendon is stretched with extension and pronation of the elbow which tightens it. Contact with the nerve may give rise to compression. Antalgic posture may include elbow flexion with supination. Symptoms of lateral antebrachial cutaneous nerve entrapment include point tenderness lateral to the biceps tendon at the elbow crease and hypesthesia of the radial foream. The mechanism of injury usually involves forceful and repetitive elbow use, especially pronation or supination during extreme elbow extension.30 Tennis players, in an attempt to execute an overhead smash, can injure the nerve, making the diagnosis of lateral antebrachial cutaneous nerve compression even more challenging since a main differential must include lateral epicondylitis, or tennis elbow (Tables 10.8 and 10.9).
10.3 MEDIAN NERVE ENTRAPMENT SYNDROMES 10.3.1 SUPRACONDYLAR PROCESS SYNDROME The supracondylar process is an anomalous osseous formation that occurs proximal to the medial epicondyle of the humerus. The ligament of Struthers, if present, projects from the supracondylar process to the medial epicondyle, creating a tunnel in the general region.1 As the median nerve courses distally through this region, it is exposed to the possibility of focal entrapment. The brachial artery is adjacent to the median nerve and thus may also be affected within the tunnel. The proximity of the ulnar nerve also presents risk.
Characteristic Signs and Symptoms of Entrapment
293
TABLE 10.8 Musculocutaneous Nerve (C5–C7) Syndrome in Shoulder Region Clinical Signs and Symptoms
Possible Etiologies
Biceps muscle atrophy Paresthesia or hypesthesia along lateral forearm Diminished or absent biceps deep tendon reflex Typically, no pain Diminished biceps muscle tone
Hypertrophy of coracobrachialis Repetitive work with flexed shoulder and elbow with pronated forearm Stretch injury
TABLE 10.9 Musculocutaneous Nerve (C5–C7) Syndrome at Elbow Clinical Signs and Symptoms
Possible Etiologies
May mimic lateral epicondylitis Anterolateral elbow pain Lateral wrist and forearm pain and hypesthesia Pain with elbow extension and forearm pronation Reduced pain with forearm supination
Compression by biceps aponeurosis Hypertrophied coracobrachialis muscle Excessive use of a screwdriver Trauma to elbow with forced extension coupled with forearm pronation
10.3.1.1 Clinical Signs and Symptoms Patterns depend on the structures involved. Pain, diminished muscle strength, and hypesthesias/paresthesia may be present. The site of median nerve entrapment occurs on the humerus prior to branching; therefore, all structures innervated by the median nerve may be involved. Nocturnal pattern may be associated. A Tinel’s sign may be elicited upon deep palpation of the supracondylar tunnel region. Signs of reduced arterial insufficiency (pallor, pallesthesia, coldness, and reduced pulses) suggest brachial artery impingement. The process is located approximately 5 cm proximal to the medial epicondyle, and it may be possible for the clinician to directly palpate the process in some thin patients. Typically, the patient describes the pain as a deep ache in the forearm, and occasionally, in the hand. Early symptoms may mimic those of CTS, and a thorough examination is required to offer definitive diagnosis; involvement of the long wrist and finger flexors of the forearm are differential clues from more distal median (or ulnar, if involved) entrapment (Figure 10.10). A complete median lesion will cause a flaccid paralysis called a benediction hand. Nerve conduction velocity studies across the region, as well as electromyography of the distally innervated muscles, may provide clinically useful information in the management of supracondylar process syndrome. Radiographs may demonstrate the process and tunnel, particularly with calcification of the ligament. The course of the median nerve should also be considered relative to fracture of the supracondylar region. Supracondylar fracture of the
Weak with proximal and distal lesion Weak with proximal lesion
FIGURE 10.10 Flaccid paralysis caused by median motor nerve pathology causing a “benediction hand” appearance. Median motor paresis will weaken finger flexion of the lateral three digits and thumb functions with the exception of adduction and extension. (From Duus, P., Topical Diagnosis in Neurology, Thieme Medical, New York, 1989, p. 42. With permission.)
humerus may lead to entrapment of the median nerve by callus deposition or post-traumatic calcification of the ligament (Table 10.10).
10.3.2 PRONATOR TERES MUSCLE SYNDROME The median nerve traverses the elbow region and subsequently courses between the two heads of the pronator teres muscle. The nerve then projects through a fibrotendinous
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 10.10 Supracondylar Process Syndrome (Median Nerve, C6–T1) Clinical Signs and Symptoms
Possible Etiologies
Pain and paresthesia along median distribution Radiating pin to forearm, thumb, and first three digits Increased nocturnal pain Paresis of thumb opposition Diminished flexion of first three digits Positive Tinel’s sign in region of supracondylar process Possible compromise of ulnar nerve Reduction of radial pulse by elbow extension
Fracture of supracondylar process Brachial artery ischemia Prolonged intravenous infusions with arm fixed in extension and supination
TABLE 10.11 Pronator Teres Muscle Syndrome (Median Nerve, C6–T1) Clinical Signs and Symptoms
Possible Etiologies
Pain and paresthesia in median nerve distribution Impaired thumb, index finger, and middle finger flexion Sensory disturbances over the proximal palm Resisted forearm pronation with pain and paresthesia Tinel’s sign over pronator muscle
Fibrous band Scarred lacertus fibrosus Anomalous head of pronator teres Nerve perforating the pronator teres Sustained forearm supination/elbow extension Post-traumatic Volkmann’s contracture Pronator muscle hypertrophy
arch formed by the flexor digitorum superficialis (FDS) muscle to run between the FDS and flexor digitorum profundus. The course of the nerve through the heads of the pronator teres can be highly variable. In over 15% of the population, the nerve will either pass through the humeral or ulnar head of the pronator teres.31 It is more common in women than men.32 Various etiologies of pronator teres muscle syndrome have been suggested and include fibrous banding or hypertrophy of the pronator teres and constriction at the fibrous arch of the flexor digitorum superficialis. However, all of these etiologies share a common pathogenesis: mechanical compression of the median nerve. Some investigators have noted a propensity for this condition to occur in the occupational setting, specifically in workers who perform repetitive, forceful pronation and supination.33 Stal et al.32 described the syndrome in female “machine milkers,” suggesting an association of entrapment from the action of statically loading the hands along with the action of strong downward pulling while twisting the wrist. Direct trauma and myofascial inflammation have also been implicated in the pathogenesis of this syndrome. In that a compartment syndrome of the ventral forearm may also affect the
median nerve, it should be considered as a differential cause of median entrapment in the forearm.34 10.3.2.1 Clinical Signs and Symptoms A Tinel’s sign or a positive percussion test may be elicited in the region of the pronator teres. The patient may describe a deep ache in the forearm with numbness and pain in the thumb as well as in the second and third digits. A sensory deficit may be demonstrated in the median innervated digits and palm; however, this sensory finding is quite variable and may not be consistently encountered. Reproduction or amplification of symptoms as a result of dynamic pronation of the forearm or forced extension in combination with supination indicates pronator teres syndrome. Gainor35 reported ten presentations of pronator teres entrapment surgically decompressed, all of whom developed paresthesias preoperatively in the hand after 30 seconds or less of manual compression of the median nerve at or near the pronator muscle. Only one patient had a positive electromyographic result, suggesting the reliability of the clinical test over electrodiagnostic studies for this entrapment (Table 10.11).
Characteristic Signs and Symptoms of Entrapment
295
Biceps brachii Median n. Lacertus fibrosis
Anterior interosseous n.
Adductor pollicis
Sublimis arch Flexor digitorum sublimus
Ulnar n.
Flexor pollicis longus
Flexor pollicis longus
Pronator quadratus
Anterior interosseous n.
FIGURE 10.11 Course of the median nerve and its anterior interosseous branch. (From Liveson, J.A., Peripheral Neurology, F.A. Davis, Philadelphia, PA, 1991, p. 25. With permission.)
10.3.3 ANTERIOR INTEROSSEOUS NERVE SYNDROME The anterior interosseous nerve, a pure motor branch of the median nerve, innervates the flexor digitorum profundus, pronator quadratus, and flexor pollicis longus muscles. Anatomically, the nerve tends to initially follow the midline course of the median nerve; after branching, it runs more lateral to the median nerve and dives deeper into the fascia of the flexor digitorum superficialis to travel along the region of the interosseous membrane, from which it derives its name. The nerve continues between the flexor pollicis longus and the flexor digitorum profundus muscles. At its terminal point distally, the nerve ends, innervating the pronator quadratus muscle (Figure 10.11). Entrapment of the nerve was first described by Kiloh and Nevin in 1952.36 Entrapment has been suggested to occur as a result of many etiologies and remains somewhat controversial. Common theoretical mechanisms include forearm fracture, fibrous adhesions, and dialysis
FIGURE 10.12 Comparison of “thumb pinch” performed in the presence of ulnar and anterior interosseous lesions. With an ulnar nerve lesion, thumb flexion will be substituted for thumb adduction demonstrating the classic Froment’s pinch sign. (From Liveson, J.A., Peripheral Neurology, F.A. Davis, Philadelphia, PA, 1991, p. 25. With permission.)
shunts implanted within the region, all of which have been implicated in the genesis of ischemic neuropathy of the anterior interosseous nerve. Fracture of the forearm and pressure exerted by the edge of a cast may also contribute to the pathogenesis of this condition. Debate is ongoing as to whether the fascia of the flexor digitorum superficialis may compress the nerve. Recovery has been reported to be spontaneous in the majority of patients within 6 months to a year.1 10.3.3.1 Clinical Signs and Symptoms The patient presents with a deep diffuse ache in the forearm and weakness of distal finger flexion. A Tinel’s sign may be produced in the mid-forearm region. Muscle weakness is the primary indicator of the interosseous nerve syndrome, as the nerve is thought to be purely motor in function. Classically, the patient demonstrates an inability to flex the distal interphalangeal joint and the inability to hold a grip with the tip of the index fingers against the thumb; the distal interphalangeal joint collapses (pinch sign) (Figure 10.12). The flexor pollicis longus muscle
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TABLE 10.12 Anterior Interosseous Syndrome/Syndrome of Kiloh and Nevin (Median Nerve, C6–T1) Clinical Signs and Symptoms
Possible Etiologies
Inability to pinch between thumb and 2nd digit Positive “pinch sign” (lost distal phalangeal flexion) Impaired flexion of terminal phalanges of thumb and 2nd digit Unable to make “OK” sign Weakness of FPL, PQ, and median-innervated FDP (lateral half) Sparing of 3rd to 5th digits Diminished or lost ability to write Inability to clench fist Occasional weakness of pronator quadratus muscles Diffuse ache along proximal third of forearm Forearm and elbow pain Typically, no sensory loss
Fibrous anomalies of the FPL and flexor digitorum superficialis Intratruncal fascicular compression Forearm fractures Post-traumatic injury or thrombosis of antebrachial vessels Vascular anomalies Dialysis shunts Tight forearm band treatment Use of sling for A-C dislocation
FPL: PQ: FDP: AC:
flexor pollicis longus pronator quadratus flexor digitorum profundus acromio-clavicular
may also exhibit paresis. The thumb may not flex across the closed fist. Difficulty with grip and handwriting may be presenting signs. Weakness of the pronator quadratus can be isolated by testing muscle strength with the elbow flexed (approximating the pronator teres). Sensory deficits are not present. Changes viewed with diagnostic ultrasound have been described, including loss of muscle bulk, increased reflectivity, and lack of active contraction of affected muscles. Decreased perfusion on Doppler sonography has been imaged. Dynamic imaging and Doppler changes viewed post-exercise may help identify muscles involved.37 Magnetic resonance imaging has also been described.38 Eversmann suggests that many patients have vague symptoms for many months or even years prior to confirming the diagnosis of either pronator syndrome or anterior interosseous syndrome of the forearm but that prompt predictable recovery within 8 to 12 weeks after surgical exploration may be expected. He suggests that continued postsurgical symptomatology is due to either (1) extremely severe median nerve injury secondary to pronator syndrome with prolonged recovery and distal nerve axomnetic recovery into the hand, or (2) sensory nerve dysesthesia of the small sensory nerves on the proximal volar surface of the forearm.39 The first point illustrates the importance of prompt effective intervention for these syndromes (Table 10.12).
10.3.4 CARPAL TUNNEL SYNDROME The wrist as a site of entrapment of the median nerve is the most common peripheral nerve lesion affecting modern society.40 The signs and symptoms associated with median nerve compromise at the wrist are referred to as carpal tunnel syndrome (CTS). CTS is a commonly misdiagnosed entrapment syndrome which may account for failed carpal tunnel surgical release, particularly with atypical presentations.41 Repetitive stress trauma, classically illustrated by data entry and assembly workers, has been reported as the most common etiologic mechanism leading to CTS.42 Some sources have noted a disproportionate number of cases occurring in poultry and meat-packing workers.43 Experimental studies have demonstrated that certain forearm, hand, and finger postures; repetitive activity; and mild to moderate hand loads can temporarily or chronically increase carpal tunnel pressure to levels which threaten nerve viability.44 Therefore, any occupation in which the worker experiences repetitive use of the hands may predispose an individual to development of CTS. Carpal tunnel pressure has been shown to increase during use of the computer mouse in some individuals; consequently, prolonged mouse use may increase the risk of acquiring CTS.45 Additional occupations with a high morbidity rate for CTS include construction work requiring the use of a hammer and those occupations involving continuous exposure to vibration forces.
Characteristic Signs and Symptoms of Entrapment
297
10.3.4.1 Prevalence Carpal tunnel syndrome is second only to back pain as the most common occupational injury.46 The syndrome commonly afflicts people 30 to 60 years of age. It occurs with a female-to-male prevalence of 3–5:1, and greater than 50% of cases occur bilaterally.47 Carpal tunnel release is one of the most common hand operations performed in the U.S.48,49
Palmar digital nerves
Branches to lumbricals I and II
10.3.4.2 Anatomy and Pathomechanics The median nerve in the hand innervates the abductor pollicis brevis, the lumbrical muscles of the first and second digits, and the opponens pollicis. Sensory innervation to the palmar thumb and the second and third digits is provided by the median nerve. Additionally, the median nerve also supplies the radial one half of the palmar fourth digit, distal one half of the dorsum of the second and third digits, and the radial aspect of the distal one half of the fourth digit. The median nerve courses distally along the forearm (contained medially and laterally by the tendons of the palmaris longus and flexor carpi radialis muscles) where it becomes superficial, accessible to stimulation during electrodiagnostic studies. As the median nerve projects distally, it passes into the hand through the carpal tunnel. Anatomically, the tunnel is a fibro-osseous canal. The roof is formed by the transverse carpal ligament, which extends from the pisiform and the hook of the hamate (ulnar side) to the tubercle of the scaphoid and crest of the trapezium (radial side) (Figure 10.13). The bony carpus and their ligaments form the floor and walls of the carpal tunnel. The sides are formed from the tubercles of the scaphoid and trapezium on the radial side, and the pisiform and hamate on the ulnar side. The size of the canal varies, with common measurements of 2 to 5 cm in length, and 2 to 3 cm in width. The tunnel tends to converge and become somewhat more narrow as it courses distally. Nine tendons, which serve as finger flexors, along with the more volar median nerve, pass underneath the flexor retinaculum at the level of the tunnel. A common synovial sheath surrounds all tendons except the flexor pollicis longus tendon (Figure 10.14). The median nerve tends to be the first overtly symptomatic structure compromised during stenosis or increased pressure in the canal. During flexion and extension of the wrist the median nerve can translate up to 20 mm while being positioned adjacent to or against the transverse carpal ligament.50 Greater flattening of the median nerve is evidenced during flexion than extension. Friction occurs between the flexor tendons, the median nerve, and the transverse carpal ligament. Any condition that results in a reduction of available space within the carpal tunnel or increased pressure within the tunnel will
Flexor pollicis brevis, superficial head
Common palmar digital nerves
Abductor pollicis brevis
Palmar cutaneous branch of the median nerve
Flexor retinaculum
Median nerve
FIGURE 10.13 The cutaneous and motor distribution of the median nerve in the hand. (Copyright 2000 J.M. True, D.C.)
increase friction. Repetitive or sustained flexion and extension of the wrist may lead to stenosis and increased pressure within the canal. Conditions that may contribute to CTS include inflammatory flexor tenosynovitis, hypertrophic tenosynovitis, neurinoma, lipoma, ganglia, hemangioma, rheumatoid arthritis, calcium or gouty tophus deposition, amyloidosis, rheumatoid arthritis, diabetes, renal insuffiency myxedema, extracellular fluid shifts associated with pregnancy, post-traumatic scarring, vitamin B6 deficiency, hypothyroidism, and hypoproteinemia (Table 10.13). Carpal tunnel syndrome fracture and/or dislocation of carpal bones or the carpometacarpal joint complex can contribute to CTS. Flexor tenosynovitis is the most frequent etiology of median nerve compression within the carpal tunnel (Table 10.14). Many studies have quantified the normal and pathological pressures within the carpal tunnel. In the normal population, mean intracanal pressure is thought to be about 2.5 mm Hg.51 In patients with electrodiagnostically confirmed CTS, the mean pressure was determined to be 32 mm Hg. Further research has revealed that positional extremes of flexion and extension of the wrist produce recordings of 31 mm Hg and 30 mm Hg for the normal population. Likewise, positional intracanal pressure
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Ulnar artery
Flexor retinaculum
Ulnar nerve
Median nerve
Flexor carpi ulnaris
Flexor pollicis longus
Flexor digitorum profundus Flexor digitorum superficialis Flexor carpi radialis Pisiform Digital synovial sheath Triquetrium
Scaphoid
Hamate
Capitate
FIGURE 10.14 Carpal tunnel contents and bordering structures. (From Pecina, M. et al., Tunnel Syndromes, CRC Press, Boca Raton, FL, 1996. With permission.)
TABLE 10.13 Carpal Tunnel Syndrome (Median Nerve, C6–T1) Clinical Signs and Symptoms
Possible Etiologies
Nocturnal hand pain and numbness Shaking of hand may alleviate symptoms Sensory abnormality over palmar surface of thumb, 2nd, 3rd and lateral half of 4th digit Sensory splitting of 4th digit (spares medial half) Diminished sensation along radial palm Sparing of proximal palmar sensation Wrist pain with resisted 2nd and 3rd digit flexion Abnormal moving 2-point discrimination over palmar aspect of thumb to 3rd digits Impaired sensation over dorsal aspect of terminal phalanges of 2nd, 3rd, and lateral aspect of 4th digit Thenar hypotrophy or atrophy Difficulty grasping and pinching Impaired repetitive finger motion Clinical sparing of opponens pollicis Positive Phalen’s and/or reverse Phalen’s test Positive Tinel’s sign over median nerve at wrist Positive Phalen’s + digital compression of median nerve Carpal compression test Mild hand reflex sympathetic dystrophy (RSD)
Rheumatoid arthritis Degenerative joint disease Flexor tenosynovitis Dermatomyositis Palmar lipomas Repetitive wrist/digit action Wrist/carpal fractures Colles fracture Fracture of capitate or hamate Carpal subluxation Congenital bony stenosis Tuberculosis Renal insufficiency Paraproteinemia Hyperparathyroidism Hypothyroidism/myxedema Pregnancy Diabetes mellitus Obesity Amyloidosis Psoriasis Hemophilia Anticoagulant therapy Multiple myeloma Blood dyscrasias
Characteristic Signs and Symptoms of Entrapment
299
A
C
B
Schema of digital distribution of median nerve branches: Note that only the radial half of the 4th finger is supplied (in most individuals).
Sensory map of the volar surface of the hand: Approximate areas of median nerve (A) and ulnar nerve (B) supply
Sensory map of the dorsum of the hand: Median nerve (A), ulnar nerve (B), and radial nerve (C) areas
FIGURE 10.15 Carpal tunnel sensory symptoms. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 34–35, 1984. With permission.)
TABLE 10.14 Neurological Disorders with Presentations Similar to Carpal Tunnel Syndrome • • • • • • • • •
Pronator entrapment syndrome Cervical radiculopathy Incomplete upper plexopathy Mononeuritis multiplex Spondylotic myelopathy Motor neuron disease Syringomyelia Polyneuropathy Multiple sclerosis
recordings in a CTS patient population revealed findings of 94 and 110 mm Hg as a result of flexion and extension. This finding is significant considering that pressure greater than 50 mm Hg in the carpal tunnel produces a complete conduction block for sensory and motor responses, with sensory deficits appearing before motor loss.52 Flexion of the metacarpophalangeal joints with the wrist in different positions contributes to a reduction of intracanal pressures confirming the importance of both wrist and finger positions.53 Clearly, the CTS patient must be instructed to avoid maximum flexion and extension of the wrist during activities. 10.3.4.3 Clinical Signs and Symptoms Individuals with carpal tunnel usually complain of sensory abnormalities of the hand, specifically involving the palmar aspect of the first through fourth digits. In one series of 1059 involved wrists, 42.5% had all five fingers involved.54 However, variations in median innervation do occur and thus should be considered as well as concurrent ulnar
involvement when patients only demonstrate sensory loss in digits 1 through 5 (Figure 10.15). Sensory complaints may range from hyperesthesia to complete anesthesia. The patient may report an increase of numbness, tingling, and dysesthesia intensity at night and commonly being awakened from sleep. Historically, this hallmark phenomenon has been called brachialgia paresthetica nocturna (Figure 10.16). Subjective swelling of the hand correlates with a more acute presentation and poor response to splinting.55 Raynaud’s phenomenon can independently coexist with CTS, although it has been noted to occur in conjunction with CTS in a higher frequency than would be expected in the general population.56 There are similar overlapping symptoms with Raynaud’s phenomenon and CTS; however, the neurological association between these two disorders is unknown (Figure 10.17). Findings of the initial physical examination may be unremarkable, but the clinician should be aware of screening maneuvers that are specific to the carpal tunnel. A symptom-oriented hand diagram can be extremely helpful in the initial hand work-up. The early or mild CTS presentation is usually limited to sensory complaints, while more severe cases often involve abductor pollicis brevis weakness and atrophy. The thenar muscles are easily evaluated in the clinical exam for CTS (Figure 10.18). The patient typically experiences pain and/or paresthesia with performance of direct compression, Phalen’s (Figure 10.19), and reverse Phalen’s (Wormser’s sign) maneuvers, presumably as a result of elevated intracarpal pressure. Phalen’s test combined with digital compression of the median nerve may improve the sensitivity of detecting CTS. A maneuver described by LaBan et al.,57 known as the tethered median nerve stress test, has proven useful in the evaluation of the CTS patient. However, it has also been criticized due to its low predictive value relative to
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Characteristic symptoms include tingling, burning, numbness, and weakness, that may be disabling.
Nocturnal pain and paresthesias are early findings. Activities requiring wrist flexion or extension aggravate symptoms, and positions of the hands during sleep may contribute to nocturnal distress.
FIGURE 10.16 Classic symptomatology of carpal tunnel syndrome. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 34–35, 1984. With permission.)
Raynaud’s phenomenon is associated with: Carpal tunnel syndrome Cervical spondylotic myelopathy Thoracic outlet syndrome Occupational use of vibrational tools Connective tissue disease (RA, scleroderma) Certain medications (beta blockers, cyclosporine, methysergide, and others) Case study drawn during acrocyanotic phase in 80 y/o female with cervical spondylotic myelopathy.
FIGURE 10.17 Raynaud’s phenomenon may be associated with peripheral nerve entrapment. (Copyright J.M. True, D.C.)
electrodiagnostically confirmed CTS in symptomatic patients.58 Tinel’s sign may also be elicited directly over the median nerve at the wrist. This is a non-specific sign but it is frequently present in CTS (Figure 10.20). There is a conspicuous loss of two-point discrimination and vibratory sense (pallesthesia) as the disorder progresses (Figure 10.21). These tests are simple and quick to perform using a 128-Hz tuning fork for vibratory sense and a bent paper clip or other two-point discriminating device. The use of Semmes–Weinstein monofilaments and static and moving two-point discrimination provides a quantitative measure of sensibility, which can help evaluate the initial patient or post-therapeutic outcomes. Semmes–Weinstein monofilaments are flexible probes that bend at specific pressures when pushed against the skin or digits. They are sensitive indicators of early carpal tunnel syndrome, because the CTS patient will not feel the filament pressures usually perceived by the normal
patient. As the condition progresses, the severity of sensory complaints often increases. Clinical detection of sensory splitting of the palmar aspect of the fourth digit can be a valuable indicator of peripheral mononeuropathy because the radial half is innervated by the median nerve and the ulnar half by the ulnar nerve. Carpal tunnel syndrome spares the superficial palmar branch of the median nerve (which branches prior to the carpal tunnel) and does not involve the median innervated muscles of the forearm. Impaired hand and digit sensibility secondary to CTS can contribute to diminished coordination and inefficient handgrip, resulting in higher grip exertion and progressive CTS.59 Carpal tunnel syndrome can occur in conjunction with C5–C6 or C6–C7 radiculopathy or proximal entrapment. Upton and McComas60 in 1973 proposed that the impairment of axonal flow at more than one site across a nerve may summate or potentiate additional areas along the
Characteristic Signs and Symptoms of Entrapment
Weakness of the abductor pollicis brevis will result in decreased ability to abduct the thumb. (Note: Advanced cases may show atrophy of the thenar eminence.)
301
Weakness of the opponens pollicis is demonstrated by a decreased ability to move the palmar surface of the thumb toward the ulnar side of the hand.
FIGURE 10.18 Median neuropathy will cause weakness of specific thenar eminence muscles. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
FIGURE 10.19 The reproduction of symptoms by passive, sustained flexion of the wrist is called the Phalen’s test. The more severe the case, the more rapidly are the typical pain and numbness produced. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
nerve to multifocal neuropathy. This is referred to as a double crush syndrome and should be considered in those CTS patients who also report cervical spine or supraclavicular fossa pain. Perhaps the only objective confirmation of the condition can be achieved when an electrophysiologic examination demonstrates two distinct lesions. 10.3.4.4 Electrodiagnostic Evaluation of Carpal Tunnel Syndrome The most sensitive and reliable electrophysiologic indicator of CTS is prolongation of distal latencies across the transverse carpal ligament.61 Sensory nerve conduction studies with distal sensory peak latencies greater than 3.5 msec from wrist to digit or motor conduction studies
FIGURE 10.20 Percussion of an irritated median nerve over the transverse carpal ligament may cause dysesthesias in the nerve’s distribution. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
with onset greater than 3.7 msec to the abductor pollicis brevis (APB) muscle indicate the presence of a carpal tunnel condition or median neuropathy.62 Distal CMAP amplitude less than 5000 µV or distal SNAP amplitude less than 10 µV also indicates a peripheral neuropathy or CTS. When the median innervation pattern includes splitting of the fourth digit, sensory conduction studies of the fourth finger have greater sensitivity for the detection of CTS than the first, second, or third digits.63 Clinical twopoint discrimination correlates well with distal sensory latencies. Isolated electrophysiological abnormalities of median motor fibers are rare, usually being preceded by sensory abnormalities.64 The median-to-ulnar (intraside) sensory nerve amplitude ratio (MUSAR) increases the specificity for diagnosing CTS while reducing the risk for false positives (Figures 10.22 and 10.23).65
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
FIGURE 10.21 (A) Early in carpal tunnel syndrome there is decreased vibratory sense and two-point acuity in median innervated digits. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.) (B) Two-point discrimination in the distal palmar digits should not exceed 2 to 4 mm of separation between the probe ends.
Amplitude in microvolts (µV)
1.8 ms Latency
Direction of depolarization
Recording Reference
-+
Median sensory fibers
8 cm Bar electrode FIGURE 10.22 Carpal tunnel study using orthodromic palmar stimulation of the median nerve. (Copyright 2000 J.M. True, D.C.)
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# $ " " " %" " " $
FIGURE 10.23 Evaluation of the distal median motor nerve across the wrist. (Copyright 2000 J.M. True, D.C.)
Characteristic Signs and Symptoms of Entrapment
303
TABLE 10.15 Magnetic Resonance Imaging Criteria in Carpal Tunnel Syndrome
TABLE 10.16 Carpal Tunnel Syndrome Magnetic Resonance Considerations and Criteria
• Early CTS Isolated prestenotic and intracarpal nerve swelling Absence of significant nerve flattening Diffuse increased intraneural signal distal to level of radius • Advanced CTS Retrograde nerve swelling to the distal radius Poor demarcation of nerve Fasciculated intraneural signal pattern
• • • • • •
Needle electromyography is a valuable modality for assessing abductor pollicis brevis muscle denervation and ruling out a mimicking or contributory cervical radiculopathy. Spontaneous activity as a result of denervation may be demonstrated in an examination of the APB muscle. This electromyographic finding is usually only seen in severe, late-stage syndromes. Motor unit number estimate (MUNE) testing and consideration of motor unit potential morphology have been suggested for consideration of “silent” loss of motor units in mild to moderate CTS to screen for predisposition to functional impairment of the hand, which requires more active diagnostic and therapeutic intervention.66 Electrodiagnostic findings should not always be the sole criteria for screening for CTS or for developing a therapeutic plan. When electrodiagnostic findings suggest a more severe involvement than is elicited during the clinical exam, MR imaging may help determine the mechanism of CTS.67 10.3.4.5 Diagnostic Imaging Similar to CT, magnetic resonance (MR) has the ability to portray cross-sectional anatomy of the wrist. MR provides better soft-tissue resolution and the added benefit of multiplanar sagittal and coronal MR acquisitions, which allow for detailed investigation of the carpal tunnel region and its contents.68 A small surface coil can improve softtissue resolution within the carpal tunnel. MR imaging reveals morphological information about the median nerve that can be used to identify the severity and duration of compromise.69 Numerous MR criteria have been proposed for the diagnosis of CTS (Tables 10.15 and 10.16). The most significant MR criteria in patients with CTS is nerve enlargement within or proximal to the carpal tunnel and palmar bowing of the flexor retinaculum only at the level of the hamate (Figure 10.24).70 Osseous pathology causing CTS may be detected on X-ray or computed tomography (CT). Fractures of the wrist, dislocation of the navicular–lunate articulation, and tumor or cyst erosion can be radiographically identified. The risk for CTS increases when the cross-sectional diameter of the
a b
Enlargement of nerve at level of pisiforma Flattening of nerve at level of hamatea Palmar bowing of flexor retinaculum at level of hamateb Increased intraneural T2-weighted signal (acute)a Decreased intraneural T2-weighted signal (chronic)a Increased flattening ratioa Brody and Stoller. Healy C., 1990.
FIGURE 10.24 Cross-sectional MRI of the carpal tunnel. Axial fast spin echo T2-weighted image through the level of the metacarpal base. This image shows enlargement of the median nerve between the flexor tendons and the palmer aponeurosis in a chronic carpal tunnel syndrome patient.
carpal tunnel is less than 16 mm in men and 12 mm in women. Sonography can be used to evaluate for CTS.71,72 The ultrasound characteristics of the median nerve and carpal tunnel dimensions can help elucidate the diagnosis. Tumors and cysts in the carpal tunnel are clearly delineated by sonography. Sonographic evidence of increased cross-sectional area of the median nerve larger than 0.09 cm2 is highly predictive for CTS.
10.4 POSTERIOR UPPER EXTREMITY SYNDROMES 10.4.1 SUPRASCAPULAR NERVE SYNDROME The suprascapular nerve is formed by C5–C6 roots of the upper trunk of the brachial plexus. Carrying motor innervation to the supraspinatus and the infraspinatus, it runs under the transverse scapular ligament through the scapular notch.
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Suprascapular nerve and artery Superior transverse scapular ligament
Acromion process
Spine of scapula Scapular notch
Coracoid process
Branch to supraspinatus
Branch to infraspinatus Inferior transverse scapular ligament (variable) (ligamentum spinoglenoidale)
FIGURE 10.25 Suprascapular nerve anatomy and entrapment sites. The suprascapular nerve travels with its corresponding artery to innervate the supraspinatus and infraspinatus. Notice the suprascapular artery passes over the superior transverse scapular ligament. (Copyright 2000 J.M. True, D.C.)
Aside from anomaly, the associated vasculature generally runs over the superior transverse scapular ligament (which bridges the notch), leaving the suprascapular nerve to run independently below the ligament. Although it does not have a cutaneous distribution, sensory branches from the nerve supply the acromioclavicular joint and the subacromial bursa. After innervating the supraspinatus muscle, the neurovascular bundle wraps around the lateral aspect of the spine of the scapula to enter the infraspinous fossa. A connective tissue band that may exist in as many as 50% of individuals (inferior transverse scapular ligament or ligamentum spinoglenoidale) creates a fibrous roof over the osseous groove that may compress the nerve.1 Isolated involvement of the infraspinatus suggests spinoglenoid notch compression (Figure 10.25).73 Supraglenoid ganglion cysts are common and may entrap the suprascapular nerve; these can be imaged with MRI.74 MRI may also be useful for assessing stage of paralysis.75 Entrapment of the suprascapular nerve at the spinoglenoid notch is usually a painless syndrome that is frequently observed in volleyball players.76 Protraction and abduction may pull the nerve against the walls of the tunnel. Given the mobility of the scapula and proximity to the infraspinatus tendon, the suprascapular nerve must adapt to shoulder motions. Fracture, bony growth, softtissue proliferation, or muscular tensions may contribute to narrowing of the foramen. Repetitive shoulder motion may mechanically irritate the nerve as it glides through
the tunnel. Combination adduction across the body with internal rotation of the shoulder may tighten the spinoglenoid ligament and tense the nerve, thus provoking pain.1,73 Antoniadis et al.77 reported 28 cases of suprascapular nerve entrapment (including one bilateral) treated by surgical decompression of the nerve, including five with a history of trauma and three in which ganglion cyst was the origin of the nerve lesion. Sixteen cases were considered related to athletic activities (including eight professional volleyball players). One case involved “prolonged wearing of a rucksack.”78 Cadaveric study of 79 shoulders from 41 cadavers showed variations including a “V” shape of the suprascapular notch in 23% and partial or complete ossification of the superior transverse scapular ligament or multiple bands in 23%. Inferior transverse scapular ligament was identified in 14%. One ganglion cyst was identified.79 10.4.1.1 Clinical Signs and Symptoms Posterior shoulder pain along the upper trapezius with a nocturnal pattern with aggravation by shoulder movement (consider repetitive overhead activities such as hair care) are expected. Both scapulocostal and dorsal scapular nerve syndromes should be considered as differentials (see Tables 10.17 through 10.19). Pain over the suprascapular notch suggests suprascapular nerve involvement. In 27 patients, Antoniadis et al.77 reported one with sensory deficit
Characteristic Signs and Symptoms of Entrapment
305
TABLE 10.17 Scapulocostal Syndrome Clinical Signs and Symptoms
Possible Etiologies
Neck pain Upper arm and chest pain Shoulder-girdle spasm No sensory deficit No muscle atrophy No motor paralysis Focal medial scapular border pain Scapular elevation off chest wall with forward stretch
Poor posture Prolonged shoulder immobilization Rib stress fracture Shoulder subluxation Humeral fracture Rotator cuff injury Deconditioned muscle girdle Poor thoracoscapulohumeral coupled motion
TABLE 10.18 Dorsal Scapular Nerve (C5–C7) Syndrome Clinical Signs and Symptoms
Possible Etiologies
Abnormal shoulder motion Mild scapular winging in resting position Elevation of medial and inferior border of scapula Reduced capacity to adduct scapula Rhomboid muscle atrophy No sensory deficit
Hypertrophied scalenus anterior muscle Direct trauma
TABLE 10.19 Suprascapular Nerve (C5–C6) Syndrome Clinical Signs and Symptoms
Possible etiologies
Posterior shoulder pain Acromioclavicular pain Focal pain over scapular notch Increased nocturnal pain Positive crossed-arm adduction test Supraspinatus and infraspinatus atrophy Paresis of shoulder abduction and external rotation Reduced vibratory perception at A-C joint
Ganglionic cyst Scapular fracture Arthrodesed shoulder Repetitive overhead activity Sleeping with arm overhead Hypertrophied transverse scapular ligament Nerve crushed from resting weight bar on shoulders during squat exercises
over the posterior portion of the shoulder; cutaneous deficits are not expected. Lesion of the suprascapular nerve may mimic rotator cuff tear with pain and weakness of the rotator cuff.24 Because of innervation to the joint, pallesthesia of the acromioclavicular joint is an indicator of suprascapular nerve involvement.1 Electromyographic evidence of denervation in the infraspinatus and supraspinatus may develop.77 Atrophic changes in the supraspinatus and infraspinatus may develop with compensatory action by the deltoid and teres minor, respectively. Atrophic changes may not entirely reverse even after surgical release in spite of relief of pain;
surgical intervention prior to more severe atrophic change may lead to a better prognosis relative to atrophic changes.80
10.4.2 LATERAL INTERMUSCULAR SEPTUM/RADIAL NERVE The radial nerve passes through the lateral intermuscular septum as it courses from the posterior brachium to the elbow (Figure 10.26). In one case study, the septum was implicated as a cause of progressive radial palsy 3 months post-humeral shaft fracture.81 When fibrosis of the triceps occurs, tension may be exerted upon the nerve and cause
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
The radial nerve passes through the axilla into the arm, lying at first medial to the humerus and anterior to the long head of the triceps.
Glenohumeral dislocation Compression by crutches or arm-over-chair positions
After passing between the long and medial heads of the triceps, it winds around the back of the humerus in the spiral groove, to lie laterally as it descends to the humeral condyle.
Humeral fracture or compression callus
“Saturday night palsy”
It passes into the forearm anterior to the lateral humeral condyle (between the brachioradialis and brachialis muscles). Dislocation of radial head At this point it divides into its terminal branches: a deep (motor) branch and a superficial (cutaneous) branch.
Contusions, lacerations
Colles’ fracture
FIGURE 10.26 Radial nerve anatomy and potential sources of compression or injury. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 34–35, 1984. With permission.)
radial nerve symptoms distal to this area.1 Fibrous arches of the lateral or long head of the triceps muscle may also entrap the nerve (Figure 10.27).82 Radial nerve symptoms may include the classic “wrist drop” presentation, a result of the action of the unopposed wrist flexors (Figure 10.28). Weakness of elbow extension may be associated (Table 10.20).
10.4.3 BRACHIALIS/BRACHIORADIALIS/ RADIAL NERVE The radial nerve enters the forearm running between the brachialis and brachioradialis. Adhesions between these flexors may traction the nerve.83 Provocative maneuvers include extension of the elbow or resisted coupled flexion/
pronation. Symptoms of deep and superficial radial nerve entrapment, including pain upon palpation of the suspected lesion site, may result.30 Both motor signs of wrist/finger extension weakness and weakness of supination may be present. Sensory involvement of the dorsal forearm and radial three digits (sparing the distal phalanges) may result from involvement of the superficial branch (Figure 10.29).
10.4.4 ARCADE
OF
FROHSE/DEEP RADIAL NERVE
As it courses between the brachialis and brachioradialis, the radial nerve divides into a deep and superficial branch. The deep branch may be affected by the fibrous edge of
Characteristic Signs and Symptoms of Entrapment
307
TABLE 10.20 Radial Nerve (C4–T1) Syndrome (Upper Arm) Clinical Signs and Symptoms
Possible Etiologies
Paresis or of elbow flexion (in pronation), wrist and finger extension, supination Dorsal hand numbness or pain Lateral epicondylar region (muscular) pain
High-riding crutches Tumors/callus Arm over chair (Saturday night paralysis) Anomalous muscle or connective tissue Axillary nodes/edema/tumor
Deltoid
Radial n. Long head of triceps
Lateral head of triceps
Radial n. (In groove)
Lateral head of triceps
Brachialis
Brachioradialis
Lateral view of arm
B
A
FIGURE 10.27 (A) Course of the radial nerve in the region of the radial groove. (B) Radial nerve piercing the lateral head of the triceps (*), a possible site of entrapment. (From Liveson, J.A., Peripheral Neurology, F.A. Davis, Philadelphia, PA, 1991, p. 34. With permission.)
the extensor carpi radialis brevis.83 The arcade of Frohse is formed by the edge of the fascia, which is formed by the proximal aspect of the supinator muscle. The deep branch of the radial nerve passes under this edge and then travels between the layers of the supinator. Spasm of the muscles of the lateral elbow and fibrosis may trap the
radial nerve as it passes under the arcade. Fibrous bands of the supinator may also entrap the nerve.83 Sources of compression may also include the anterior and posterior interosseous vessels and the septum between the extensor carpi ulnaris and extensor digitorum minimi.84 Compression between the brachioradialis and extensor carpi
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Weakness
Motor findings The radial nerve innervates the major extensors of the elbow, wrist, and fingers, as well as the brachioradialis, supinator, and abductor pollicis longus. In axillary lesions, weakness and atrophy of the triceps and brachioradialis may accompany involvement of the hand and finger extensors.
Sensory findings Because of cutaneous overlap from other nerves, findings of sensory loss in the posterior forearm are minor. In the hand, only a small area on the dorsal aspect is apt to be involved, between the thumb and index finger.
The cardinal feature of damage to the nerve at any level is wrist drop.
FIGURE 10.28 Radial nerve lesion. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 34–35, 1984. With permission.)
Brachial artery
Radial nerve Superficial radial nerve
Medial epicondyle Fibrous bands over radial head and capsule
Radial recurrent artery (Leash of Henry)
1 Joint capsule
2
3 Margin of ECRB Ulnar artery
4 Arcade of Frohse Posterior interosseous nerve
FIGURE 10.29 The radial nerve has four potential sites of entrapment in the elbow. (From Scuderi, G.R. and McMann, P.D., Sports Medicine: Principles of Primary Care, Mosby, St. Louis, MO, 1996, p. 253.)
Characteristic Signs and Symptoms of Entrapment
Radial n.
Superficial radial n. Supinator
Posterior interosseous n.
309
of the arcade of Frohse have been described.87 Posterior interosseous nerve entrapment is a rare complication of rheumatoid arthritis.88 Surgical exploration of the radial tunnel may be necessary in entrapments recalcitrant to conservative treatment (Figure 10.30). Clinical studies have indicated that approximately 5% of patients with lateral epicondylitis also concurrently suffer from RTS.89 Other reports suggest a higher correlation, even to the point of suggesting that radial nerve compression is a specific form of tennis elbow by virtue of the anatomical relationships and the frequency of association.90 Electrodiagnostic studies of the radial nerve tend to reveal a relative paucity of information in comparison to median and ulnar nerve studies.30 Thus, confirmation of the diagnosis by nerve conduction poses a challenge to the clinician. Barnum et al.83 suggest that the pain centered over the tunnel is the dominant clinical finding and that muscle weakness is clinically uncommon. They report that provocation of pain with middle finger extension and resisted supination tests and relief of symptoms following a radial tunnel anesthetic block help diagnose RTS. Local pain in the region and pain distal to the epicondyle are associated. Wrist and finger extensor weakness are associated. In that the superficial branch supplies sensory function, there are no sensory deficits specific to deep branch compression within the radial tunnel (Table 10.21).
10.4.5 DISTAL SUPERFICIAL RADIAL NERVE ENTRAPMENT/CHEIRALGIA PARESTHETICA
FIGURE 10.30 Course of the posterior interosseous branch of the radial nerve. (From Liveson, J.A., Peripheral Neurology, F.A. Davis, Philadelphia, PA, 1991, p. 35. With permission.)
radialis longus proximal to the wrist has been noted.85 Spasm-induced compression of the deep radial nerve may be confused with the local pain pattern that is also found in lateral epicondylitis. Like lateral epicondylitis (tennis elbow), entrapment of the posterior interosseous branch is common in tennis players.24 The etiology of this syndrome is thought to stem from chronic microtrauma or occupational stress. Investigations have revealed that active supination places significant pressure upon the edge of the supinator muscle.86 This chronic pressure or compression can lead to radial tunnel syndrome (RTS). Anatomic variations in the length of the nerve between anatomic landmarks, branch points, the relationship to the recurrent radial artery, and the texture
The superficial radial nerve is a purely sensory branch. It branches as the radial nerve runs between the brachialis and brachioradialis superficial to the supinator. It crosses superficial to the lateral fibers of pronator teres and then cuts under the distal aspect of the brachioradialis to run along the dorsal radial forearm. At the point where the superficial radial nerve passes through the fascial bands of the distal radio-ulnar joint, an entrapment may occur which is frequently misdiagnosed as de Quervain’s tenosynovitis. It often occurs concurrently with de Quervain’s tenosynovitis, making differentiation difficult. Some texts refer to this syndrome as cheiralgia paresthetica, despite a consensus that the terminology is antiquated. The condition may be caused or exacerbated by tension or fibrosis of the brachioradialis muscle, which increases tension in the fascia. Massey et al. reported two presentations secondary to handcuff placement.91 Other reports of compression at the wrist caused by casts, tight cuffs, and watchstraps are included in the literature.1 A Tinel’s sign may be elicited at the point at which the nerve exits the fascia. The patient may complain of numbness, tingling, and paresthesia on the radial and dorsal portion of the hand. The symptoms appear to be exacerbated by movement. The etiology of the syndrome may
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 10.21 Supinator Syndrome: Radial Nerve (C6–C7) Posterior Interosseous Branch Clinical Signs and Symptoms
Possible Etiologies
Deep posterior forearm pain Progressive fist weakness Pain with manual compression distal to the lateral humeral epicondyle May develop wrist drop paresis Symptom aggravation by “wringing linen” motion May mimic lateral epicondylitis No sensory deficits
Repetitive stretching over Frohse’s arcade Radial head subluxation Distal humeral fracture Bursitis Rheumatoid arthritis Monteggia fracture Fibromas/lipomas/ganglion
TABLE 10.22 Syndrome of the Superficial Branch of the Radial Nerve (C6–C7) (Cheiralgia Paresthetica) Clinical Signs and Symptoms
Possible Etiologies
Dorsal–medial hand paresthesia (burning) Sensory abnormalities along the dorsal wrist, thumb, and web space Nocturnal pain Mild cutaneous trophic changes Positive Tinel’s sign No forearm or hand atrophy No weakness
Compressive plaster cast Tight watch strap Tight cuffs Intravenous infusion in forearm or wrist Wrist osteoarthropathy Split tendon of brachioradialis muscle Palmar ganglion
be related to chronic use of screwdrivers, writing instruments, or keyboards (Table 10.22).92
10.5 ULNAR NERVE SYNDROMES 10.5.1 ULNAR NERVE ENTRAPMENT AT CUBITAL TUNNEL SYNDROME
THE
ELBOW
Cubital tunnel syndrome has been described as the second most common compressive neuropathy.93 The ulnar nerve runs deep to the medial head of the triceps and is vulnerable to compression there (Figure 10.31). The ulnar nerve is then susceptible to compression or stretch injuries as it passes between the medial epicondyle of the humerus and the olecranon process of the ulna, as it travels through the ulnar groove, and as it enters the flexor carpi ulnaris. The ulnar nerve superficially traverses the ulnar groove and cubital tunnel, having only subcutaneous fat and skin as covering at the ulnar groove. The floor of the cubital tunnel is formed by the medial collateral ligament of the elbow. The roof is bounded by the triangular-shaped arcuate ligament which connects the medial epicondyle to the olecranon process. The walls of the cubital tunnel are formed by the two heads of the flexor carpi ulnaris muscle (Figure 10.32).
The ulnar nerve is vulnerable to compression and entrapment in the ulnar groove from resting the elbows on a table for an extended period, fracture deformation, excessive stretch upon the nerve, or compression from ganglia and synovial cysts.33 The ulnar predilection of rheumatoid arthritis may affect the nerve there. With a greater carrying angle at the elbow (valgus), women may be more vulnerable to narrowing of the ulnar cubital tunnel. Ulnar neuritis at the elbow is common in baseball pitchers.24 The nerve may also be displaced within the tunnel during elbow flexion, tensing it against the medial epicondyle. Repetitive stress trauma has also been implicated in the cubital tunnel syndrome. When the nerve becomes attached to the flexor carpi ulnaris or medial triceps and the elbow is flexed, the resulting traction from both sides of the cubital tunnel may cause a flattening of the nerve within the tunnel. This will lead to signs and symptoms of compression. Dynamic ultrasonography of 200 normal elbows has shown movement to the tip of the medial epicondyle (27%) and anterior displacement of the ulnar nerve (20%) during flexion. Of some interest is that the diameters of the hypermobile nerves were significantly larger than those that were less mobile.94 A provocative
Characteristic Signs and Symptoms of Entrapment
Note the anatomic vulnerability of the ulnar nerve to repetitive, often overlooked, trauma.
311
patient may complain of pain and paresthesia of the fourth and fifth digits, as well as the volar surface of the hand. Large afferent fiber loss, exhibited by deficits of two-point discrimination and pallesthesia in the fourth and fifth digits, is usually evident early in ulnar neuropathy presentations. In chronic cases, motor deficits can be demonstrated in the intrinsic muscles of the hand, including abduction of the small finger (adductor digiti minimi) and finger adduction/abduction (interossei) (Figure 10.34, Tables 10.23 and 10.24). A claw hand deformity occurs with complete or longstanding ulnar lesions proximal to the wrist (Figure 10.35). If median neuropathy occurs in the same extremity as ulnar compression, an ape hand deformity may result (Figure 10.36). 10.5.1.2 Electrodiagnostic Evaluation of Ulnar Entrapment at the Elbow
A shallow ulnar groove may worsen chronic trauma. During elbow flexion, the nerve is displaced and “flicks” over the medial epicondyle.
FIGURE 10.31 Simple repetitive actions may result in ulnar nerve palsy. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
test designed to narrow the tunnel has been proposed by Buehler and Thayer.95 This maneuver simply entails instructing the patient to rapidly and actively flex the elbow in an effort to reproduce the ulnar compression symptoms. 10.5.1.1 Clinical Signs and Symptoms Patients with ulnar neuropathy at the elbow usually present with paresthesia and pain in the region of the ulnar nerve distribution (Figure 10.33). Typically, this includes sensory deficits of the fourth and fifth digits, as well as paresis of grip strength. Injury to the medial antebrachial cutaneous branch may also result.93 Ulnar entrapment at the elbow may also produce functional deficits of the flexor carpi ulnaris and the medial half of flexor digitorum profundus muscles. A nerve percussion sign and nerve stretch sign are readily produced over the ulnar groove if entrapment has occurred. The patient may describe diffuse pain in the elbow and medial forearm. Additionally, the
Classification of the extent of ulnar entrapment is rated from mild to severe (Table 10.25). Mild ulnar nerve entrapment primarily exhibits sensory signs. However, even in the mild category, abnormalities in the F-wave study may be present. Moderate ulnar neuropathy at the elbow demonstrates abnormalities in ulnar nerve compound motor action potential latency and amplitude. Patients with severe entrapment also demonstrate denervation of ulnar innervated muscles. EMG is of value in the differential diagnosis of cubital tunnel compression from C8–T1 radiculopathy.5 Anterior transposition of the nerve may be necessary to adequately decompress the nerve when significant compression is present.96 Because of their close anatomic proximity, needle electrode conduction studies with placement specific to the entrapment locations may be useful in differentiating ulnar groove from cubital tunnel syndrome.97 10.5.1.3 Diagnostic Imaging Morphologic changes in the ulnar nerve have been evaluated with high-resolution ultrasound imaging.98 Such imaging may prove useful for screening.
10.5.2 GUYON’S CANAL SYNDROME/ULNAR TUNNEL SYNDROME 10.5.2.1 Anatomy and Pathomechanics Like the median nerve, the ulnar nerve is also susceptible to compression as it enters the wrist. The ulnar tunnel (Guyon’s canal) is a fibro-osseous tunnel found at the level of the proximal carpals on the ulnar border of the hand. The tunnel is formed by the transverse carpal pisohamate ligament, the tendon of the flexor carpi ulnaris muscle, and the pisiform and hamate bones. The height of the tunnel ranges from 8 to 15 mm.1 The ulnar nerve has a dorsal branch that divides proximal to the tunnel, arching
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
Arcade of Struthers and medial intermuscular septum
Aoneurosis of flexor carpi ulnaris
Common site for direct trauma and repetitive compression Cubital tunnel Ulnar nerve
FIGURE 10.32 Four potential sites of ulnar entrapment or compression. (Copyright 2000 J.M. True, D.C.)
Typical ulnar sensory deficit. The ulnar nerve also conveys sensation from the medial 11/2 fingers, as well as from the medial aspects of the palm and back of hand.
FIGURE 10.33 Ulnar sensory distribution. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
over it; thus, it is not compressed in the tunnel of Guyon, and this should be considered relative to symptom patterns with nerve percussion maneuvers. The tunnel contains the palmar branch of the ulnar nerve and ulnar artery and vein; the palmar branch divides into superficial and deep palmar branches that pass through the tunnel. This aids differentiation of ulnar compression at the elbow, which would also affect the dorsal branch. The superficial division of the palmar branch innervates the palmaris brevis muscle, palmar fifth digit, and ulnar aspect of the fourth digit. Similarly, the deep branch innervates the hypothenar muscles, the two most lateral lumbricals, the interossei, the adductor pollicis, and the deep head of the flexor pollicis brevis. With this understanding of ulnar anatomy, one can appreciate that compression of the superficial branch produces both sensory and motor signs, while entrapment of the deep branch exhibits purely motor signs (Figure 10.37). Although less common than CTS, ulnar tunnel syndrome can occur as a result of various mechanisms. The most common etiologies of the syndrome include traumatic compression and anatomical anomalies. Ulnar nerve
compression occurs when repetitive pressure is exerted over the hypothenar eminence by a tool or from the use of the heel of the hand as a hammer.99 Ulnar nerve palsy at the wrist is seen among bicyclists.24 Nonoccupational etiologies include congenital, inflammatory, neoplastic, vascular, metabolic, degenerative, and traumatic disorders. Fracture of the hook of the hamate, ganglia, hypertrophy of the flexor carpi ulnaris muscle, ulnar artery aneurysms, and pisiform bursitis represent only a few of the specific conditions that may lead to ulnar tunnel syndrome. The ulnar nerve may be affected in association with the systemic conditions discussed for the carpal tunnel. 10.5.2.2 Clinical Signs and Symptoms Patients will initially complain of pain that arises from, or is exacerbated by, wrist extension. Associated sensory signs such as numbness, tingling, and paresthesia may be exhibited along the ulnar distribution. The symptoms may be reported as being worse at night, and usually the fourth and fifth digits are affected. Motor symptoms include grip strength deficits and hypothenar atrophy. The patient may
Characteristic Signs and Symptoms of Entrapment
The patient with an ulnar nerve lesion cannot oppose the pads of the thumb and little finger because of hypothenar muscle involvement.
313
Other findings in the fully developed case may include: Hollowing between the metacarpal bones Flattening of the hypothenar eminence “Claw” hand Inability to fan fingers and bring them together Incomplete flexion of the ring and little fingers upon attempts to make a fist
The fingertips can, however, be brought together using any uninvolved flexors (false test).
FIGURE 10.34 Clinical findings in ulnar palsy. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
TABLE 10.23 Sulcus Ulnaris Syndrome (Ulnar Groove; Ulnar Nerve, C8–T1) Clinical Signs and Symptoms
Possible Etiologies
Paresthesia and dysesthesia in ulnar distribution Occasional proximal arm and shoulder pain Possible Tinel’s sign over the sulcus Hypothenar atrophy and paresis Early muscle atrophy at web of 1st and 2nd digits (adductor pollicis) May acquire a claw hand appearance
Rheumatoid arthritis Degenerative joint disease Post-traumatic cubitus–valgus Prolonged leaning on elbow Supracondylar fracture Elbow dislocation Callus formation Tophaceous gout Epitrochleoanconeous muscle Repetitive use injury
also exhibit a propensity to hyperextend the metacarpophalangeal joint of the thumb, “signe de Jeanne.” Many of the very same evaluation procedures used in carpal tunnel cases are also employed in the work-up of the suspected ulnar tunnel syndrome patient. As in CTS, performing the Phalen’s or reversed Phalen’s test may reproduce the complaint, but the symptoms will usually be confined to the fourth and fifth digits in the ulnar tunnel syndrome patient. A Tinel’s sign may be elicited directly over the ulnar tunnel. Vascular patency to the hand can be assessed by performing Allen’s test.
Electrophysiologic studies consisting of sensory and motor conduction and EMG of associated ulnar innervated hand muscles may also prove beneficial in evaluation of the Guyon tunnel patient. An increase in distal sensory latency across the tunnel greater than 3 msec or a side-to-side difference greater than 1 msec is indicative of pathology.100 Fibrillation potentials and positive sharp waves may occasionally be seen during the EMG examination of hand intrinsics. When the proper coil and imaging technique is used, MRI of the wrist depicts the anatomy of the tunnel of
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 10.24 Flexor Carpi Ulnaris Muscle Syndrome/Cubital Tunnel Syndrome (Ulnar Nerve, C8–T1) Clinical Signs and Symptoms
Possible Etiologies
Gradual onset ulnar paresthesia, pain and muscle weakness, “tardy ulnar nerve palsy” Froment’s paper sign: look for a substitution of thumb flexion for thumb adduction Dysfunction of adductor pollicis muscle Positive elbow flexion test + ulnar Often negative Tinel’s sign at elbow May mimic medial epicondylitis Intrinsic hand atrophy with sparing of abductor pollicis brevis Paresis of small finger abduction Impaired precision movement Weakness first affecting 1st dorsal interosseous Sensory symptoms precede weakness Loss of grip power Difficulty crossing fingers
Prolonged elbow flexion Compression by deep aponeurosis of flexor carpi ulnaris muscle Proliferative elbow synovitis Elbow DJD with osteophytosis Perineural cysts Variations of anconeous muscle Lipomas Ganglions Frequent hand use with flexed elbow
Atrophy of hand intrinsics
FIGURE 10.35 Ulnar neuropathy will cause weakness of hypothenar eminence muscles. In severe cases, intrinsic muscle atrophy may occur, causing the classic “claw hand” appearance. (From Duus, P., Topical Diagnosis in Neurology, Thieme Medical, New York, 1989, p. 42. With permission.)
Guyon in sufficient detail for MR to be useful in the evaluation of patients with ulnar neuropathy.101 MRI of the ulnar tunnel is particularly beneficial when the entrapment is caused by tumor, fracture, cyst, or degeneration (Tables 10.26 through 10.29).
10.6 ABDOMINAL/PELVIC ENTRAPMENT SYNDROMES Entrapments of nerves in the pelvic cavity or retroperitoneal space are extremely difficult to diagnose when a
Atrophy of hypothenar and thenar eminences
FIGURE 10.36 A complete lesion of the ulnar and median nerves producing an “ape hand” deformity. (From Duus, P., Topical Diagnosis in Neurology, Thieme Medical, New York, 1989, p. 42. With permission.)
narrowed tunnel is the cause of nerve compression. When the source of compression is pelvic or retroperitoneal neoplasm, the problem is more ominous than myofascial entrapment; however, it is much easier to identify on MRI. A space-occupying lesion such as tumor or abscess may be found in the kidney, ureter, intestines, psoas muscle, or retroperitoneal space. The differential diagnosis of neoplasm should be investigated in all cases of suspected abdominal/pelvic entrapment (Figure 10.38). Compression of the intercostal nerves and/or the three divisions of the lumbar plexus innervating the abdominal wall and the anterior pelvis/genitals can, in part, be differentiated by their descending dermatomal patterns of innervation.
Characteristic Signs and Symptoms of Entrapment
315
TABLE 10.25 Staging of Ulnar Nerve Compression at the Elbow • Mild Sensory: Intermittent paresthesias; vibratory perception increased Motor: Subjective weakness, clumsiness, or loss of coordination Test: Elbow flexion test or Tinel’s sign may be positive • Moderate Sensory: Intermittent paresthesias; vibratory perception normal or decreased Motor: Measurable weakness in pinch or grip strength Test: Elbow flexion test or Tinel’s sign are positive; finger crossing may be abnormal • Severe Sensory: Persistent paresthesias; vibratory perception decreased; abnormal two-point discrimination (static ≥ 6 mm, moving two-point discrimination ≥ 4 mm) Motor: Measurable weakness in pinch and grip, plus muscle atrophy Test: Positive elbow flexion test or positive Tinel’s sign may be present; finger crossing usually abnormal Source: Dellon, A.L., Review of treatment results for ulnar nerve entrapment at the elbow, J. Hand Surg. Am., 14, 689, 1989. With permission.
Digital nerves
1. Compression of the superficial branch will result in a sensory loss in digits 4 and 5 2. Compression of the deep branch will result in a pure motor deficit
Motor branches to hand intrinsics
3. Compression proximal to the bifurcation will result in motor and sensory deficits
Superficial branch of the ulnar nerve
1. 2.
Hook of the hamate 3.
Deep branch of the ulnar nerve Pisiform Dorsal ulnar cutaneous n. Ulnar nerve
FIGURE 10.37 Ulnar nerve compression may occur at three sites at the wrist. (Copyright 2000 J.M. True, D.C.)
Entrapment patterns in the abdominal area may involve the T6–T12 intercostal nerves, iliohypogastric nerve, ilioinguinal nerve, or the genitofemoral nerve. The genitofemoral nerve will be further discussed below in relationship to the lower extremity. We include the pudendal nerve syndrome here because of the proximity to the genitofemoral distribution. Recall that the pudendal nerve branches
from the sacral plexus, but the genitofemoral distribution is from the lumbar plexus. Even though iliolumbar tunnel syndrome occurs in the vicinity of the anterolateral lumbosacral spine, it has been categorized in the posterior thigh section because of the predominant sensory pattern following the L5 root and posterior thigh (Tables 10.30 through 10.34).
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 10.26 Ulnar Tunnel Syndrome (Tunnel of Guyon; Ulnar Nerve, C8–T1) Clinical Signs and Symptoms
Possible Etiologies
Possible hypothenar atrophy Paresis of finger abduction Difficulty with hand grasp Sensory abnormality over palmar aspect of medial 4th and 5th digits (dorsal is spared) Positive Wormser’s (reverse Phalen’s sign) with 4th and 5th digit dysesthesia Positive Tinels’ sign over ulnar tunnel Sparing of flexor carpi ulnaris and flexor digitorum profundus (digits 3, 4) Mumenthaler’s sign (palmaris brevis paresis)
Fracture of hook of hamate Bipartate hamulus Prolonged bike riding with racing handlebars Fourth finger fllexor tendon anomaly Degenerative arthritis/ganglion Occupational-related external compression Pisotriquetral joint arthritis Rheumatoid arthritis Aberrant muscles Ulnar artery aneurysm Lipoma
TABLE 10.27 Syndrome of Deep Branch of Ulnar Nerve (C8–T1) Clinical Signs and Symptoms
Possible Etiologies
Poorly localized hand pain No sensory deficit Atrophy of 1st dorsal interossei Atrophy of medial two lumbricals, deep head of flexor pollicis brevis, and adductor pollicis muscles Carpal fractures/dislocations
Ganglion cysts Anomalous muscles Intraneural cysts Giant cell tumor Hand edema Fibrous band Ulnar artery disease
TABLE 10.28 Syndrome of the Tendinous Arch of the Adductor Pollicis Muscle (Ulnar Nerve, C7–T1) Clinical Signs and Symptoms
Possible Etiologies
Blunt midpalmar pain No paresthesia Isolated paresis and atrophy of 1st dorsal interossei and adductor pollicis brevis muscles Pain to compression at base of 3rd metacarpal bone
Repetitive mid-palm trauma Prolonged gripping Pathology of 3rd metacarpal bone Compression by arch of adductor pollicis Tumors
TABLE 10.29 Collateral Digital Nerve Syndrome (Median or Ulnar Nerves, C6–C7–C8) Clinical Signs and Symptoms
Possible Etiologies
Sensory abnormalities limited to fingers Pressure and discomfort between metacarpal heads Pain with finger hyperextension or adduction Positive metacarpal compression with digit paresthesia
Inflammation of tendon sheaths Rheumatoid arthritis Hyperextension injury of finger Digital nerve aneurysm
Characteristic Signs and Symptoms of Entrapment
317
Areas of L/S Plexus Vulnerability in the Pelvic Cavity
Iliohypogastric
1.
1. Lateral femoral cutaneous nerve neuropathy may result from: a. Direct trauma: Seat belt trauma, tight clothing b. Retroperitoneal tumor/hematoma c. Iliopsoas infection 2. Femoral nerve compression can result from multiple causes: a. Post surgical adhesion b. Pelvic tumors (abdominal or osseous) c. Psoas or retroperitoneal hematoma d. Traumatic hip hyperextension 3. The iliolumbar ligament may compress the 5th lumbar root. 4. Foraminal stenosisor tumor may compress the sacral roots. 5. Sciatic nerve compression may occur with: a. Malignant infiltration (bowel/prostate) b. Bony exostosis of pelvic ring or sacrum c. Vascular compression (iliac artery or vein) d. Chronic constipation 6. Obturator nerve injury or compression may result from: a. Complications of hip or genitourological surgery b. Intrapelvic/retroperitoneal tumors and masses c. Secondary to obstetrical and birthing trauma d. Pelvic fracture 3. 4.
2.
6.
5.
Pudendal n.
FIGURE 10.38 Areas of lumbosacral plexus vulnerability in the abdominal and pelvic cavity. (Copyright 2000 J.M. True, D.C.)
10.7 LOWER EXTREMITY ENTRAPMENT SYNDROMES 10.7.1 PSOAS ENTRAPMENT SYNDROME/ILIACUS ENTRAPMENT SYNDROME The neurovascular bundle of the femoral region, along with the iliopsoas muscle, pass directly beneath the inguinal ligament as they travel distally from the pelvis into the lower extremity. At this site, the femoral, lateral femoral cutaneous, and genitofemoral nerves are susceptible to entrapment. 10.7.1.1 Anatomy and Pathomechanics The femoral nerve originates from the L2–L4 nerve roots. The nerve courses caudally between the iliacus and psoas muscles and innervates them. The psoas muscle may be innervated directly by the L2–L4 nerve roots. The femoral nerve then combines with the tendon of the iliopsoas as they pass underneath the inguinal ligament. A superficial branch supplies cutaneous innervation to the anterior
thigh, while the deep branch innervates the quadriceps musculature. In addition, the deep branch gives rise to the saphenous nerve, which provides cutaneous sensation to the medial thigh, leg, and foot. The genitofemoral nerve, however, divides much more proximally than the femoral nerve. The genitofemoral divides either directly within or on the psoas muscle. It bifurcates and becomes the genital and femoral branches. The genital branch travels out of the abdomen over the inguinal ligament. It then proceeds to innervate the scrotum or labia and provides for sensation to the superior anteromedial thigh. The femoral branch passes below the inguinal ligament as it exits the pelvis. It supplies cutaneous innervation to a small patch along the superior anteromedial thigh, just slightly lateral to the region supplied by the genital branch. It should be of interest to clinicians to note that only the femoral branch passes below the ligament; thus, the genital branch is rarely compressed in this region.102 The femoral nerve and its proximal branches lie deep within the pelvic basin. Within this region, the nerve is often insulted secondary to surgical procedures. Nerve
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Myelopathy, Radiculopathy, and Peripheral Entrapment Syndromes
TABLE 10.30 Syndrome of Rectus Abdominis Muscle (Intercostal Nerves, T6–T12) Clinical Signs and Symptoms
Possible Etiologies
Acute burning in region of rectus abdominus Increased abdominal wall pain with Valsalva-type maneuvers Diminished region of abdominal muscle tone Reduced sensation, loss of vibratory sense and 2-point discrimination
Increased volume of abdominal cavity Pregnancy Heavy physical activity Muscle hyperactivity
TABLE 10.31 Iliohypogastricus Syndrome (Iliohypogastric Nerve, T12–L1) Clinical Signs and Symptoms
Possible Etiologies
Inguinal paresthesia Inguinal dysesthesia or pain aggravated by hip extension Ambulation with mild lumbar anteflexion to reduce nerve tension No motor deficit Pain and/or paresthesia over outer buttock and hip
Tumors Hemorrhage Pregnancy Scar/fibroproliferation Blunt abdominal trauma Hip or pelvic surgery
TABLE 10.32 Ilioinguinal Syndrome (Ilioinguinal Nerve, L1 possible contribution of L2) Clinical Signs and Symptoms
Possible Etiologies
Inguinal and/or hip region pain Increased pain with increased abdominal wall tension (standing straight) Inguinal pain reproduced with pressure applied to region of anterior superior ilial spine (ASIS) Hypesthesia and dysesthesia along distribution of ilioinguinal nerve (along inguinal ligament) Abdominal muscle weakness and atrophy Difficulty arising from a supine position Protusion of abdomen above inguinal ligament during abdominal muscle contraction Negligible motor findings Development of inguinal hernia
Urogenital pathology Renal pathology Inguinal hernia Systemic sclerosis Retroperitoneal pathology
damage following nephrectomy and appendectomy is not uncommon. Additionally, the psoas may undergo spasm as a result of trauma or biomechanical dysfunction, resulting in femoral compression within the confines of the muscle itself. Arteriovenous malformations, aneurysms,
Hip osteoarthritis Prolonged coughing Spermatic cord pathology Prolonged or recurrent stretching Heavy weightlifting
muscle tumors, and hernias have been reported as probable etiologies of this syndrome.1 Iliopsoas hematoma from high-energy sports may compress the nerve.24 Poor venipuncture technique in the femoral triangle may injure the femoral nerve.
Characteristic Signs and Symptoms of Entrapment
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TABLE 10.33 Genitofemoral Nerve (L1–L2) Syndrome Clinical Signs and Symptoms
Possible Etiologies
Inguinal, scrotal (labia), and medial thigh pain Sensory deficits over femoral triangle Increased pain with hip extension or rotation Pain radiation with pressure over deep inguinal canal Absent cremasteric reflex
Postsurgical scars Psoas abcess Tight clothing Bicycling
TABLE 10.34 Pudendal Nerve (S2–S4) Syndrome Clinical Signs and Symptoms
Possible Etiologies
Pain and hypesthesia in perineal region Difficulty with bowel and bladder function Impotence
Perineal tear associated with vaginal delivery Pelvic surgery or tumor
TABLE 10.35 Iliacus Muscle Syndrome (Femoral Nerve, L2–L4) Clinical Signs and Symptoms
Possible Etiologies
Sensory disturbance in anterior thigh and medial leg/foot Difficulty standing from a sitting position Difficulty extending the knee with sparing hip flexion (paresis of inferior type) Hypotrophy of anterior thigh compartment Hip extension increases pain With exception of hip extension other hip movements are painless Diminished or absent patellar reflex (DTR)
Pelvic surgery Pelvic hematomas Hernias Arteriovenous malformations Retroperitoneal sarcoma Subperiosteal hematoma Femoral vessel catheterization Complications form anterior lumbar interbody fusion Prolonged immobilization of the hip
10.7.1.2 Clinical Signs and Symptoms Clinical symptoms of lower extremity entrapment syndromes may vary, depending on the level of the femoral lesion. If the suspected lesion is high along the proximal psoas, the patient may exhibit difficulty with the swing phase of gait as a result of paresis of the iliopsoas muscle group. Circumduction may be substituted for flexion. This class of femoral entrapment lesion is often referred to as the superior type. Conversely, patients with a lesion within the iliacus tunnel will exhibit a propensity for knee extensor weakness, termed the inferior type of entrapment; this spares the branches to the iliopsoas, which diverge more proximally.
These patients may have trouble standing up due to paresis of the quadriceps. Several signs and symptoms may be encountered within the broad class of femoral lesions. Common examination findings include loss of or diminished patellar and cremasteric reflexes. The patient will report sensory disturbances within the femoral and saphenous distributions and rapid fatigue or paresis of the knee extensors. These findings tend to eliminate lumbar radiculopathy from the differential diagnosis; typically, a dermatomal or segmental sensory loss would be expected in radiculopathy as opposed to a plurisegmental distribution consistent with a peripheral nerve. Provocative maneuvers that apply tension to the nerve, such as hip extension, tend to exacerbate the complaints (Tables 10.35 and 10.36; Figure 10.39).
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TABLE 10.36 Femoral Nerve (L2–L4) Syndrome Clinical Signs and Symptoms
Possible Etiologies
Paresis of hip flexion Paresis of knee extension Reduced or absent patellar muscle stretch reflex Variable sensory loss over thigh/medial leg Positive reverse straight leg raise (SLR)
Vertebral tumors Diabetes Vascular disease Intrapelvic tumors Inguinal canal pathology
Femoral nerve Iliopectineal compression Hernia Tumor Surgery complication
Obturator nerve Lateral femoral cutaneous nerve Chronic stretching Increased abdominal pressure Seat belt injury Hyperextension of trunk or thigh
Obturator tunnel Chronic adductor spasm Pelvic hematoma Hip surgery complications
Saphenous nerve Vastoadductor membrane tunnel Direct trauma Biomechanical irritation Genu varum Knee surgery
FIGURE 10.39 Anterior and medial thigh entrapment pathologies. (Copyright 2000 J.M. True, D.C.)
10.7.2 MERALGIA PARESTHETICA/INGUINAL TUNNEL SYNDROME (LATERAL FEMORAL CUTANEOUS ENTRAPMENT) The femoral nerve and some of its branches travel directly beneath the inguinal ligament. The lateral femoral cutaneous nerve, originating from the lumbar plexus, also passes through the inguinal tunnel. Unlike the femoral nerve, the lateral femoral cutaneous nerve passes laterally under the inguinal ligament. Like the femoral nerve, the lateral femoral cutaneous nerve can be compressed underneath the inguinal ligament, resulting in a syndrome known as lateral femoral cutaneous neuralgia. 10.7.2.1 Anatomy and Pathomechanics The lateral femoral cutaneous nerve, a pure sensory nerve, arises from the L2 and L3 nerve roots. It courses posterior
to the psoas and lies anterior to the iliacus. The nerve then crosses the iliac region laterally through a small tunnel formed by the fascia of the iliacus. It further travels towards the anterior superior iliac spine and then passes under the inguinal ligament. As it exits from under the ligament, the lateral femoral cutaneous nerve undergoes up to a 90° bend. In exiting the pelvis, the nerve must pass through two separate and distinct anatomical tunnels and course under the inguinal ligament as well as through a fibrous tunnel within the fascia lata. In addition, it may pierce the sartorius muscle. Compression can occur at either or both regions. As the nerve pierces the fascia lata of the thigh, it provides for cutaneous sensory innervation to the anterolateral thigh. A small sensory branch runs posterior under the tensor fascia lata to contribute to gluteal cutaneous sensation (Figure 10.40). The lateral femoral cutaneous nerve tends to be susceptible to compression and traction forces in the following
Characteristic Signs and Symptoms of Entrapment
Lateral femoral cutaneous nerve compression results in a characteristic area of sensory disturbance, marked by burning pain, formication, and numbness. Relieved by sitting, the symptoms are aggravated by thigh extension and abduction or by prolonged standing and walking. Sensory testing will demarcate an area with diminished touch and pin awareness.
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TABLE 10.37 Meralgia Paresthetica (Lateral Femoral Cutaneous Nerve, L2–L3) Clinical Signs and Symptoms
Possible Etiologies
Anterolateral thigh pain, paresthesia, and burning Sensitive to clothing contact and leg extension Positive reverse SLR Trophic skin changes over nerve distribution Focal pressure applied over inguinal ligament may increase symptoms No motor signs
Scoliosis Leg length inequality Trunk hyperextension Leg hyperextension Prolonged standing Acute or chronic stretching Tight clothing Tight waist belt or strap Gun or tool belt
10.7.2.2 Clinical Signs and Symptoms
Pain may be elicited by pressure with the finger over the inguinal ligament just medial to the anterior superior iliac spine. Important: Suspect a radiculopathy if the presentation of meralgia paresthetica is associated with motor findings, reflex changes, or pain in the back.
FIGURE 10.40 Sensory distribution of lateral femoral cutaneous neuropathy. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
three regions: (1) as it passes underneath the psoas muscle, (2) as it courses under the inguinal ligament and (3) as it exits the fascia lata. Leg extension and constant standing tend to produce an irritation of the nerve. Fibrotic thickening of the nerve tissues surrounding the nerve as it exits the inguinal canal may also be a mechanism of chronic compression.1 Additional mechanisms of nerve compression include the pressure caused by pendulous abdomens of obese persons and excessive abdominal stress due to pregnancy. Some clinicians have postulated that pathomechanical changes in posture as a result of scoliosis and leg length inequality may apply undue stress on the nerve, leading to meralgia paresthetica.103 Tight or constricting clothing may also contribute. One case seen in a police officer was caused by chronic compression of the nerve by his gun holster, distal to the inguinal canal (clinical experience, Dr. True, 1998). Seatbelt injury and iliac crest bone-graft harvesting have also been reported as etiologies.104
Most often, patients with inguinal tunnel syndrome reports a burning and shooting pain over the lateral thigh. They may also note paresthesia along the cutaneous distribution of the nerve. As the nerve is purely sensory, no motor deficit or diminishment of reflex occurs (unless there is associated femoral entrapment). Pain tends to be reproduced or exacerbated by hip extension. Similarly, hip flexion tends to produce attenuation of the symptoms. Meralgia paresthetica is observed unilaterally in 90% of reported cases.105 The syndrome has also been documented to occur in males at a ratio of 3:1 compared to females. Local point tenderness overlying the lateral aspect of the inguinal ligament is a characteristic examination finding. Both the lateral femoral cutaneous nerve and the femoral nerve may be involved in the syndrome, depending upon the etiology. A large retroperitoneal or pelvic mass could be of sufficient size to compress both nerves. In this scenario, signs of motor deficits of muscles innervated by the femoral nerve may be present. However, motor deficits are not present in lateral femoral cutaneous syndrome. Differential diagnosis must include radiculopathy as a result of a high lumbar disk lesion and plexopathy (Table 10.37).
10.7.3 OBTURATOR NERVE ENTRAPMENT The obturator nerve exits the pelvis and enters the thigh through an anatomic tunnel, the fibroosseous obturator tunnel. Although uncommonly encountered in clinical practice, this syndrome should be considered when a differentiation of medial thigh pain and sensory deficits is required.46 Obturator tunnel syndrome is likely to be encountered in association with a femoral nerve lesion as a result of an upper lumbar plexus lesion.
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TABLE 10.38 Obturator Tunnel Syndrome (Obturator Nerve, L2–L4) Clinical Signs and Symptoms
Possible Etiologies
Pain extending from symphysis pubis to knee Medial thigh hypesthesia Possible posteriomedial knee pain Leg adductor paresis Medial thigh muscle atrophy Adductor muscle group pain and spasms Circumduction gait (involved leg)
Pelvic fractures Coagulopathy and pelvic hematomas Retroperitoneal mass Intrapelvic tumors Pregnancy Total hip arthroplasty Bone osteophytes Tissue edema Osteitis pubis
10.7.3.1 Anatomy and Pathomechanics The obturator nerve is derived from the L2, L3, and L4 nerve roots. The nerve travels below the psoas muscle and along the anterior margin of the sacroiliac joint as it courses inferiorly to emerge from the pelvis. The obturator tunnel is formed by the obturator sulcus of the pubic bone and the internal and external obturator muscles in the roof and floor of the tunnel. The obturator artery, veins, and lymph nodes are also contained within the tunnel, along with the obturator nerve. The obturator nerve branches as it travels out of the canal. The anterior branch innervates the gracilis, adductor brevis and longus, and pectineus muscles. The posterior branch provides innervation exclusively to the adductor brevis and magnus muscles. The terminal division of the anterior branch of the obturator nerve supplies sensory innervation to the medial thigh. The obturator nerve is also responsible for sensory innervation of the joint and cutaneous medial aspect of the knee.1 Due to the location and path of the nerve, it is susceptible to compression both in the pelvis and in the tunnel. In the pelvis, the nerve can be compromised by pelvic fractures, hematomas, retroperitoneal masses, or even a normal pregnancy. Lesions can occur as a result of surgery in the region, such as hip arthroplasty and genitourinary procedures. Minor hemorrhage due to anticoagulation disorders occasionally compromises the nerve within the canal. Soft-tissue inflammation as a result of direct trauma may also lead to obturator tunnel syndrome. 10.7.3.2 Clinical Signs and Symptoms Patients presenting with obturator tunnel syndrome typically complain primarily of deficits and pain along the medial aspect of the thigh. Patients often describe the pain as nonlocalized, extending from the region of the pubic symphysis distally to the knee. Some clinicians have reported pain complaints as distal as the calf.46 Less commonly, adductor
paresis may develop as a sequel to chronic compression. The adductors receive partial innervation from the femoral and sciatic nerves; thus, total paresis or palsy are unlikely. If paresis of the adductors is present, the patient typically exhibits a characteristic circumduction gait during the swing phase through the unopposed abduction action associated with hip flexion (Table 10.38).
10.7.4 ILIOLUMBAR–LUMBOSACRAL LIGAMENT ENTRAPMENT/LUMBOSACRAL TUNNEL SYNDROME Since compression of the L5 nerve root is a commonly encountered clinical entity, the clinician must investigate all possible etiologies of compression. The most common causes include a herniated lumbar nucleus pulposus and spinal canal stenosis. When present, lumbosacral tunnel syndrome is a difficult diagnosis to confirm. Advanced MRI techniques such as MR neurography may provide more exacting differentiation. Degenerative spondylosis with osteophytic spurring is the most common cause of iliolumbar tunnel narrowing. This pathomechanism of spinal nerve compression should be considered in cases of lower back and leg pain not explained by other more common etiology (Figure 10.41). 10.7.4.1 Anatomy and Pathomechanics The iliolumbar tunnel is a fibro-osseous canal formed by the iliolumbar ligament as it passes over the L5 anterior ramus connecting the L5 vertebra with the sacrum and ilium. The iliolumbar ligament originates on the fifth lumbar vertebra and travels inferolaterally to attach to the alla of the sacrum and a portion of the ilium. The ligament’s presence and morphology tend to be variable.106 The most common origination is upon the body and transverse process of the L5 vertebra, followed by the body exclusively and the transverse process. The actual tunnel is formed
Characteristic Signs and Symptoms of Entrapment
Iliolumbar ligament
L5 vertebra
L5 root
Entrapment site
FIGURE 10.41 L5 entrapment by the iliolumbar ligament. (Copyright 2000 J.M. True, D.C.)
anteriorly by the iliolumbar ligament and posteriorly by the osseous alla of the sacrum. Stenosis of the tunnel can occur as a result of osteophyte formation on L5 or S1 or hypertrophic changes of the ligament and vascular entities, such as aneurysms and venous congestion. Because the branches of the iliolumbar arteries and veins pass through the iliolumbar tunnel, any inflammation in the region can lead to edema and focal compression of the nerve or vessels. Regional osseous neoplasia and pelvic fractures are also potential causes of the iliolumbar tunnel syndrome. 10.7.4.2 Clinical Signs and Symptoms The patient exhibits the classic signs of L5 nerve root compression; however, usually there is a conspicuous absence of back pain. Principally, patients tend to report sensory deficits and pain along the L5 dermatome. Typically, few motor deficits are exhibited. The primary differentials include the etiologies of L5 radiculopathy. Sparing of the posterior division of the L5 root is a possible differential consideration to L5 radiculopathy (Table 10.39).
10.7.5 PIRIFORMIS SYNDROME Low back pain with associated lower extremity pain is one of the most commonly encountered neurological syndromes. The piriformis syndrome is a relatively uncommon cause of sciatic pain that occurs when the sciatic nerve is compressed within or under the piriformis muscle. The diagnosis of piriformis syndrome is often overlooked
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as a cause of sciatica, leg, or buttock pain. This leads to frequent misdiagnosis, mismanagement, and delay in the proper diagnosis and treatment of this extrapelvic entrapment syndrome. The piriformis syndrome was first discussed as a clinical entity by Yeoman in 1928.107 There is still controversy as to whether the syndrome exists.108 McCrory and Bell suggest the term “deep gluteal syndrome” to encompass compression of structures other than the sciatic nerve as the diagnosis has been ascribed to various causes of buttock/posterior thigh symptoms.109 10.7.5.1 Anatomy and Pathomechanics The piriformis muscle and sciatic nerve have a variable anatomical relationship in the sciatic notch region. This is problematic for accurate localization and diagnosis of the entrapment or injury site. The strap-like piriformis muscle functions primarily as an external rotator and abductor of the thigh. It also provides an abductor force to the flexed thigh. The secondary action of the piriformis contributes to extension of the thigh.110 When the femur is fixed, the muscle tends to produce lateral rotation of the pelvis away from the side of contraction with posterior translation of the pelvis. The piriformis muscle receives innervation directly from the sacral plexus, originating from the L5–S2 nerve roots. The anatomy of the muscle and its interrelationship with nerves in the region are complex and highly variable. Additionally, the anatomical tunnels or foramina formed by the traversing piriformis muscle vary among individuals. The clinician should have knowledge of the most common anatomic variables that may contribute to the etiology of piriformis syndrome (Figure 10.42). The sacrospinal and sacrotuberous ligaments connect the ischium to the sacrum. These two ligaments contribute to the formation of two pelvic foramina through which several important structures pass. The ligaments create the greater and lesser sciatic foramen. Most of the structures that travel from the gluteal region to the pelvis pass through the greater foramen. Some anatomists refer to this foramen as the Gibraltar of the gluteus.1 The piriformis divides the greater foramen into the suprapiriform and infrapiriform regions. Several blood vessels, as well as the superior gluteal nerve (which innervates the gluteus minimus and medius), travel through the suprapiriform region of the greater foramen. The infrapiriformis portion of the greater foramen, which is bounded superiorly by the piriformis muscle, allows for the passage of two separate neurovascular bundles that are referred to as the medial and lateral neurovascular groups. The medial group primarily contains the pudendal nerve and associated vessels. The voluminous lateral group, in addition to the inferior gluteal vessels, contains the sciatic, inferior gluteal, and posterior femoral cutaneous nerves. The sciatic nerve subsequently divides distally into the tibial and
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TABLE 10.39 Lumbosacral Tunnel Syndrome (L5) Clinical Signs and Symptoms
Possible Etiologies
Hypoesthesia in L5 dermatomal distribution Pain in L5 dermatomal distribution Typically, no weakness or muscle atrophy Pain increases with walking Sclerotomal pain in hip
Marginal osteophytes at L5 and S1 Ligamentous thickening Intrinsic and extrinsic neural tumors Sacral and lumbar pathomechanics Tumors of the sacrum, ilium, or spine
Sciatic nerve L4, L5, S1, S2
Sciatic foramen
The sciatic nerve has peroneal and tibial divisions
Etiologies
Anatomical variations of the sciatic foramen
Direct and indirect trauma Chronic repetitive trauma (wallet sciatica) Inflammation of bursa, muscle or tendon Local ischemia Myofascial band between biceps femoris and adductor magnus Complications of hip surgery
1.) Sacrotuberous and sacrospinal ligament size and attachments 2.) Suprapiriformis and infrapiriformis division relationship to sciatic nerve 3.) Nerve courses through muscle belly
FIGURE 10.42 Entrapment pathologies of the posterior thigh. (Copyright 2000 J.M. True, D.C.)
common peroneal nerves. The location of the sciatic division is subject to a high degree of anatomical variation. Pecina has noted that 26.5% of these nerves divide intrapelvically, 4.6% post-foraminally, and 11.5% at the inferior margin of the gluteus maximus, with the remainder dividing throughout the thigh (Figure 10.43).1 The anatomy of the piriformis muscle and its interrelationship to the regional nerves plays a role in the
pathogenesis of the syndrome. Hypertrophy of the piriformis muscle results in a narrowing of the foramen and therefore presents a greater risk for nerve compression. Many researchers attribute piriformis muscle syndrome to irritation of the sciatic nerve as the main etiology of the disorder.107 It has been postulated that post-traumatic spasm of the muscle produces focal compression of the nerve. If the sciatic nerve passes through the two tendinous
Characteristic Signs and Symptoms of Entrapment
FIGURE 10.43 The variable sites of sciatic bifurcation into the common peroneal and tibial nerves. (From Pecina, M. et al., Tunnel Syndromes, CRC Press, Boca Raton, 1996. With permission.)
attachments of the piriformis, a resultant entrapment can occur during internal rotation. The internal rotation movement stretches the muscle, producing a decrease in the space through which the nerve passes. Another possible mechanism discussed by several authors implicates pathology and the pathomechanics of the sacroiliac joint as the primary causative factors in piriformis syndrome.107,111 Blunt trauma to the pelvis or buttock muscles can result in piriformis injury producing inflammation and scar tissue formation, eliciting the syndrome.1,112 In approximately 50% of the population, a synovial bursa underlies the piriformis muscle. Inflammation of the subpiriform bursa may provide a plausible explanation of the pathogenesis of the syndrome in some patients. The posterior thigh is innervated by the posterior femoral cutaneous nerve, which runs with the sciatic and may explain the posterior thigh component of sciatica. 10.7.5.2 Clinical Signs and Symptoms The piriformis syndrome patient usually presents with symptoms consistent with lumbar radiculopathy without significant back pain. The chief differential diagnosis in the elderly is spinal stenosis. In patients with back pain, the common differentials are discogenic referred pain, or L5–S1 radiculopathy. Comparatively greater involvement of the peroneal division is evidenced, which raises the possibility of peroneal neuropathy as a differential.113 The patient usually presents with pain and paresthesia along the course of the sciatic nerve. Deep pain, described as an ache, may be reported in the region of the gluteus. Straight leg raising produces pain at about 25 degrees. Passive stretching of the piriformis as a result of internal rotation of the thigh tends to exacerbate focal gluteal pain and numbness into the leg or top of the foot. Passive external
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rotation relieves the symptoms. Sciatic notch tenderness is invariably present. Tardy motor paresis of the piriformis may also be present in the syndrome. Vascular and autonomic concomitants may be associated. To further localize the lesion, the clinician may wish to palpate the piriformis via the rectum in order to reproduce the patient’s symptoms. In retrospective review, Durrani and Winnie114 reported reproduction of sciatica with either pelvic or rectal examination as present in 100% of 26 patients described. A rectal examination can also provide additional diagnostic information, such as pelvic or rectal pathology. Sacroiliac joint mechanical dysfunction may be associated with piriformis syndrome, or it may be responsible for initiation of the syndrome. The clinician must rule out lumbar radiculopathy, sacroiliac dysfunction, pelvic or rectal pathology, and anatomic variations resulting in nerve compression (Tables 10.40 through 10.42).
10.7.6 SAPHENOUS NERVE SYNDROME/ADDUCTOR TUNNEL SYNDROME The saphenous nerve passes through the adductor canal as it courses superficially to innervate the medial leg and foot. It not uncommon for the saphenous nerve to become compressed in the region of the adductor canal. 10.7.6.1 Anatomy and Pathomechanics The femoral nerve gives rise to the saphenous nerve in the anteromedial thigh. Along with the femoral artery and veins, the nerve travels through the adductor canal. This tunnel is often referred to as the subsartorial canal, or Hunter’s canal. The walls of the canal are formed by the intersection of the vastus medialis and adductor longus muscles. The vastoadductor membrane forms the roof of the tunnel. After the nerve passes through the canal, it divides into two branches. The infrapatellar branch turns at the knee to supply sensory innervation to the medial aspect of the knee and overlying skin. The descending branch is responsible for sensory innervation to the cutaneous medial leg and foot.1 The most common etiology of the syndrome is direct trauma in the region of the nerve, such as that caused by sports such as soccer or football. Surgical trauma has also been documented to produce lesions of the saphenous nerve. In fact, knee surgery (one of the most common orthopedic surgical procedures) is thought to produce a relatively high rate of incidence of this disorder.115 Femoral arteriography, a commonly performed diagnostic procedure, may also lead to saphenous nerve syndrome. Functional pathomechanical disorders of the knee, such as genu varum, may chronically stretch the nerve and induce the disorder.
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TABLE 10.40 Piriformis Muscle Syndrome (Sciatic Nerve, L4–S2) Clinical Signs and Symptoms
Possible Etiologies
Sensory disturbance in posterior thigh and leg, sparing the medial anterior leg/foot Sacral/gluteal pain with no lumbosacral pain Trophic changes Positive SLR at 25 degrees Increased pain with internal rotation of hip Decreased pain with external rotation of hip Piriformis muscle spasm and myalgia (further appreciated with rectal exam) Pain at sciatic notch to palpation Palpable mass over piriformis muscle May have diminished patellar and Achilles muscle stretch reflexes Foot drop Possible atrophy of hamstring and muscles below knee Sparing of knee extension
Piriformis spasm Piriformis hypertrophy Sacroiliac disease Fibrous adhesions Anomalous course of nerve relative to piriformis (e.g., piercing it) Inflammation of synovial bursa Prolonged direct compression Trochanteric disease
TABLE 10.41 Gluteal Nerve Syndromes (Superior and Inferior Gluteal Nerves, L4–S1) Clinical Signs and Symptoms
Possible Etiologies
Trendelenberg sign Difficulty climbing stairs Difficulty with step test Difficulty hopping on one leg Paresis of hip extension (inferior gluteal) Paresis of thigh abduction and medial rotation (superior gluteal) No sensory signs
Pelvic fractures Upper femur fracture Intramuscular injections Prolonged hip traction Hip surgery Coagulopathy and hematoma Blunt trauma Prolonged sitting Piriformis muscle hypertrophy Labor pressure with gravid uterus
TABLE 10.42 Cutaneous Posterior Femoral Nerve Syndrome (Sacral Plexus, S2–S3) Clinical Signs and Symptoms
Possible Etiologies
Sensory abnormality along the posterior surface of the thigh Sensory abnormalities distal gluteal region, posterior perineum, labia major/scrotum
Piriformis hypertrophy Narrowing of foramen infrapiriforme Piriformis spasm
Characteristic Signs and Symptoms of Entrapment
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TABLE 10.43 Saphenous Nerve (L4) Syndrome (Gonyalgia Paresthetica) Clinical Signs and Symptoms
Possible Etiologies
Persistent medial leg pain during activity Magnified pain with pressure applied to adductor canal (vastus medialis obliqus/ adductor longus) Hyperalgesia and hyperesthesia in the infrapatellar region Medial leg pain with resisted leg adduction Pain with knee hyperextension with altered gait (maintaining flexion) Progressive medial foot pain with activity (especially walking/climbing)
Femoral arteriography Thrombophebitis Entrapment by pes anserine bursitis Direct trauma Knee surgery (palsy/poor leg positioning) Compression by vasto-adductor membrane Obstructive vascular disease Genu varum
10.7.6.2 Clinical Signs and Symptoms The chief complaint of patients with this syndrome is medial leg pain that is omnipresent when walking. Sensory examination findings typically reveal hyperesthesia and hyperalgesia along the infrapatellar region. In contrast, they may also report hypesthesia and hypalgesia of the medial leg and foot. Active extension of the leg tends to exacerbate the pain, forcing the patient to walk with an altered gait. Some researchers have documented a high incidence of secondary metatarsalgia as a result of antalgically altered gait biomechanics.103 Saphenous nerve lesions may be misdiagnosed as medial meniscus lesions of the knee, resulting in the erroneous performance of surgical procedures. The clinician must be aware that the primary differential is intrinsic knee joint derangement. Locally applied manual pressure over the adductor tunnel can aid in the evaluation of this syndrome (Table 10.43).
10.7.7 PERONEAL TUNNEL SYNDROME/ENTRAPMENT AT THE KNEE AND FIBULAR NECK The peroneal nerve often becomes entrapped within the region of the popliteal fossa and proximal fibula resulting in peroneal tunnel syndrome (PTS). This nerve compression syndrome is one of the most commonly encountered lower extremity mononeuropathies.46 The nerve may also be compressed as it wraps around the neck of the fibula held against the bone in a fibrous tunnel (Figure 10.44). The common or deep peroneal is susceptible to compression at the fibular neck (Figure 10.45). 10.7.7.1 Anatomy and Pathomechanics The common peroneal nerve branches off of the sciatic nerve as it courses along the posterior aspect of the thigh. The division occurs in the most proximal and lateral portion
Common peroneal n. Tendinous arch of the peroneus longus muscle Site of entrapment Deep branch of the peroneal n. Superficial branch of the peroneal n. FIGURE 10.44 Compression of the common peroneal nerve by the peroneus longus tendon involves both the superficial and deep peroneal branches. (Copyright J.M. True, D.C.)
of the popliteal fossa; variants include branching more proximally. The nerve travels from the midline in a slightly lateral trajectory, where it continues distally along the medial margin of the biceps femoris tendon. It subsequently lies superficial to the lateral head of the gastrocnemius. (See Figure 10.43.) From this point, the common peroneal nerve encircles the fibular neck as it begins its descent into the leg, deep to the peroneous longus muscle. The common peroneal nerve bifurcates into the superficial and deep peroneal nerves. In some frequently encountered anatomical variations, the common peroneal nerve branches into superficial and deep divisions as it passes through the tendinous arch of the peroneus longus muscle. Additionally, it is common to observe that the fibular collateral ligament is morphologically continuous with the tendinous portion of the peroneus longus. (Vijayashankar, N., personal communication,
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B A
A B
The common or deep peroneal nerves are frequently compressed at the neck of the fibula, often by habitual sitting with one thigh crossed over the other. More common in the setting of rapid weight loss, the lesion is characterized by a foot drop.
FIGURE 10.45 The common peroneal is one of the most frequent entrapped nerves in the lower extremity, often due to habitual sitting with one leg crossed over the other. More common in the setting of rapid weight loss, the lesion is characterized by a foot drop. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
1996.) These sites will occasionally be the focus of nerve compression. The superficial branch of the common peroneal nerve proceeds distally, bounded by the fibula and the peroneus longus, lying on the anterior intermuscular septum. The common peroneal nerve innervates the peroneus muscles. At the juncture of the middle and distal one third of the tibia, the superficial peroneal nerve pierces the crural fascia. Once the nerve exits the fascia it divides into two very superficial secondary branches, the medial and intermediate dorsal cutaneous nerves. These terminal branches of the superficial peroneal nerve provide cutaneous sensation of the anterolateral aspect of the distal lower leg and the dorsal surface of the first through fourth toes. Compartment syndromes may affect the deep or superficial peroneal nerves.24 Chronic lateral compartment syndrome occurs in young athletes. It is a relatively rare cause of entrapment involving the superficial peroneal nerve.116 Classically speaking, compression of the superficial peroneal nerve is described as a separate and distinct entity;117 however, the authors have elected to include the syndrome within the general category of peroneal entrapments. The deep branch of the common peroneal nerve passes through the anterior intermuscular septum, travels in tandem
In deep peroneal involvement, weakness is limited to dorsiflexion of the foot and toes (A). Lesions of the common peroneal nerve produce additional weakness of the foot evertors. In advanced cases, look for atrophy of the anterior tibial muscles (B).
In deep peroneal lesions, dysfunction of the dorsal digital cutaneous branch (A) produces a characteristic sensory deficit in the 1st web space (B). A wider field of anesthesia occurs with common peroneal nerve involvement.
FIGURE 10.46 Clinical considerations with deep peroneal nerve compression. (From Rapoport, S., Common peripheral nerve injuries, Hospital Med., 20(6), 35, 1984. With permission.)
with the tibialis anterior and extensor digitorum longus, and innervates those muscles. As the nerve courses distally, it lies between the tibialis anterior and extensor hallucis longus muscles, providing innervation to those muscles. The deep branch of the common peroneal nerve enters the foot as it passes under the cruciform ligament, and provides cutaneous sensation between the first and second toes (Figure 10.46). Nerve compression can occur in a multitude of locations and result from a variety of mechanisms. Commonly, a simple contusion or chronic compressive force applied to the region of the fibular head can elicit the syndrome. The “dashboard contusion” commonly observed in those involved in motor vehicle accidents is known to produce peroneal irritation at the fibular head. In fact, simply resting a leg against the console or dashboard in a vehicle may result in compression of the peroneal nerve and a transient syndrome. Improperly fitting orthopedic casts can also irritate the nerve at this site. Synovial cysts and ganglia may also compress the peroneal nerve in the region of the popliteal fossa. Repetitive motion, such as running or industrial activity, may lead to chronic irritation of the nerve at the region of the fibula. Systemic or metabolic disorders, such as diabetic neuropathy, frequently involve the peroneal nerve and may contribute to compression syndromes.
Characteristic Signs and Symptoms of Entrapment
329
TABLE 10.44 Popliteal Entrapment Syndrome (Tibial Nerve, L4–S3; Popliteal Artery/Vein) Clinical Signs and Symptoms
Possible Etiologies
Intermittent distal leg cramping Lower extremity claudication Distal lower extremity ischemic changes Diminished dorsalis pedis pulse with maximal plantar flexion or dorsiflexion with extended knee
Myotendinous anomalies Neurovascular compression by soleus and plantaris muscle Transverse fibrous bands Positional myofascial compression Thrombosis/aneurysm of popliteal artery
10.7.7.2 Clinical Signs and Symptoms Patients may exhibit both motor and sensory deficits as a result of peroneal tunnel syndrome. Foot drop may be the primary motor sign. If both the superficial and deep branches are involved, paresthesia about the lateral leg and dorsal foot including the area between the first two toes may be present. The deep branch supplies the space between the first two toes. Frank pain is not common in PTS. Peroneal palsy may occur as a result either of an acute insult or a chronic compressive lesion. In considering various differentials, the presence of pain in the sciatic notch along with posterior thigh pain suggests more proximal involvement. Another differential is L5 root involvement. Diabetes mellitus predisposes a peripheral nerve to compression. Peroneal nerve palsy is one of the more common lesions encountered in the diabetic neuropathy patient. Laboratory findings of hyperglycemia, coupled with the electrodiagnostic findings of multinerve amplitude loss and conduction slowing, will aid in determining the presence of diabetic neuropathy. 10.7.7.3 Electrodiagnostic Evaluation Electrophysiologic evaluation of peroneal nerve focal compression demyelination is a very common and simple procedure and is one of the most commonly utilized protocols in electrodiagnostic medicine. Active (recording) electrodes are applied cutaneously over the extensor digitorum brevis muscle, and sites above and below the fibular neck are subsequently stimulated. A reproducible drop in amplitude with widening of the waveform base above the fibular neck is indicative of focal conduction block.5 The extensor digitorum brevis, tibialis anterior, and extensor hallucis muscles are all studied electromyographically in the electrophysiologic examination of the peroneal nerve. Chronic lesions of the peroneal nerve produce frequent EMG abnormalities. If complete denervation has occurred in the extensor digitorum brevis, the clinician should perform motor conduction studies of the tibialis anterior muscle. In general,
focal conduction slowing across the fibular neck coupled with loss of amplitude represents the hallmark electrodiagnostic findings of peroneal compression syndrome. EMG abnormalities in the paraspinal musculature would indicate another, perhaps nonassociated pathology or a concurrent pathology (Tables 10.44 to 10.47).
10.7.8 ANTERIOR TARSAL TUNNEL SYNDROME/DEEP PERONEAL NERVE SYNDROME The deep peroneal nerve travels under the extensor retinaculum as it passes into the foot. At this site, the nerve can become entrapped, leading to a syndrome with the potential to produce both sensory and motor deficits. 10.7.8.1 Anatomy and Pathomechanics The anterior tarsal tunnel is an anatomical canal that lies under the fascia of the dorsal foot. A thickening of the fascia forms a “Y”-shaped retinaculum over the extensor tendons. The dorsalis pedis vessels also runs under the retinaculum. The deep peroneal nerve joins with these structures in the tunnel after it has innervated all of the ankle and toe extensors, with the exception of the extensor digitorum brevis muscle. As a result, the extensor digitorum brevis muscle is the only muscle that reflects the motor distribution of anterior tarsal compression. Distal to the tunnel, the nerve further divides into a medial and lateral branch. The lateral branch innervates the tarsal and metatarsal joints, while the medial branch provides for sensory innervation to the space between the first and second toes. A multitude of etiologies exist that may result in anterior tarsal tunnel syndrome (TTS). The anatomy of the tunnel contributes to the syndrome, as the tightly banded retinaculum contains soft-tissue structures compressed against a bony surface. This close relationship coupled with the mobile, weight-bearing ankle joint represents the major etiology of the syndrome. Excessive and chronic dorsiflexion, such as that forced by the wearing of women’s high-heeled shoes, has been attributed to many cases of the disorder.118
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TABLE 10.45 Peroneal Tunnel Syndrome (Common Peroneal Nerve, L4–S2) Clinical Signs and Symptoms
Possible Etiologies
Sensory abnormalites along the anterolateral aspect of the leg below the knee and along the top of the foot Possible radiation of pain to thigh Increased pain with pressure over tunnel Dorsiflexion paresis and foot drop Weakness of foot inversion Increased pain with passive foot inversion Neurotrophic bony changes in the foot (neuropathic arthropathy)
Tight, short leg cast: knee hyperextension Fibular fractures Arthroplasty of knee valgus Synovial cysts Repetitive foot inversion and pronation Nerve stretch Crossed legs
TABLE 10.46 Superficial Peroneal Nerve (L5) Syndrome (Mononeuralgia) Clinical Signs and Symptoms
Possible Etiologies
Pain and/or paresthesia along lateral leg/dorsum of foot Production of pain or paresthesia over dorsum of the foot with resisted dorsiflexion and eversion, passive plantar flexion and eversion, stretching of the nerve with percussion, or compression pressure over tunnel
Muscular hernia Tight boots Repetitive compression at foot Traumatic compression Surgical trauma Scarring of fascial borders over tunnel
TABLE 10.47 Sural Nerve (S1–S2) Syndrome Clinical Signs and Symptoms
Possible Etiologies
Positive Tinel’s sign Pain, paresthesia, and/or burning along the lateral of the foot
Compression against crural fascia Traction injury Baker’s cyst Scar/fibrosis Thrombophlebitis Ankle/pedal edema Tight boots Nerve biopsy
Tight and constricting shoes can also contribute to anterior TTS. Direct trauma leading to local edema has also been observed in many cases. Any enlargement of the osseous base of the tunnel or the other contents of the tunnel will predispose to compression. Chronic prolonged stretching of the deep peroneal nerve on the dorsum of the foot may cause anterior TTS.119 Aside from the tarsal tunnel, entrapment of the deep peroneal nerve by the extensor hallucis brevis has also been reported.120
10.7.8.2 Clinical Signs and Symptoms Sensory complaints presented by patients with anterior TTS involve the web space between the first and second toes. Motor deficits are limited to paresis of the extensor digitorum brevis. With motor involvement, the patient may report nonspecific pain within the foot in addition to paresis. Trophic changes such as osteopenia of the metatarsal bones may also appear concurrent with motor fiber
Characteristic Signs and Symptoms of Entrapment
331
TABLE 10.48 Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve, L5–S1) Clinical Signs and Symptoms
Possible Etiologies
Burning pain localizing to dorsal web between great and 2nd toes Blunt forefoot pain Nocturnal exacerbation Positive Tinel’s over deep peroneal nerve at inferior extensor retinaculum Abnormal extensor digitorum brevis muscle function Increased pain with ankle plantar flexion Metatarsal osteopenia
Talonavicular joint osteophytes Tight shoe laces Synovial pseudocysts Ankle arthrosis with osteophytes Ganglions Prolonged stretching from high-heeled shoes Direct contusion Pes cavus Aneurysm
lesions.1 There has been a report of reflex sympathetic dystrophy in a 10-year-old child associated with deep peroneal nerve entrapment by the retinaculum.121 To attempt to isolate the function of the extensor digitorum brevis, toe extension is tested in a position of forced dorsiflexion so as to limit the action of the long toe extensors. Electrodiagnostic evaluation of anterior tarsal tunnel syndrome usually reveals an increased deep peroneal latency across the canal upon performance of nerve conduction studies; conduction studies may also exhibit amplitude loss.119 EMG examination of the extensor digitorum brevis may reveal findings of denervation (Table 10.48).
10.7.9 MEDIAL TARSAL TUNNEL SYNDROME Many clinicians inadvertently refer to the medial tarsal tunnel syndrome as simply tarsal tunnel syndrome. The term does not differentiate the anterior tarsal tunnel. Although the deep peroneal nerve can become compressed by the extensor retinaculum, this discussion refers to entrapment of the posterior tibial nerve within the most medial aspect of the tarsal canal (Figure 10.47). 10.7.9.1 Anatomy and Pathomechanics Many anatomists consider the tarsal tunnel to be the hilum of the plantar foot, because all of the neurovascular structures that supply the plantar region pass through the tunnel. The posterior tibial nerve passes through the medial tarsal tunnel as it courses distally into the foot. The medial tarsal tunnel is formed by the distal tibia and the medial malleous. The groove, or depression, formed by the junction of these osseous structures is covered by the flexor retinaculum of the foot. The so-called “tarsal tunnel” is actually comprised of two smaller sections, or tunnels, within the larger tunnel — the upper and lower portions of the tarsal tunnel. The upper portion of the tunnel contains the medial plantar nerve and artery; the
lower portion of the tunnel contains the lateral plantar nerve and artery. The tibial nerve gives rise to several branches, the first branch being the medial calcaneal nerve. This branch supplies cutaneous sensation to the heel of the foot. The medial calcaneal nerve arises from the tibial nerve before it passes under the flexor retinaculum. Thus, compression within the ankle rarely compromises the medial calcaneal nerve. Some clinicians have reported a compression of this nerve branch against the edge of the retinaculum, which may lead to sensory deficits of the heel.122 As the tibial nerve continues distally and enters the tunnel, the nerve branches into the medial and lateral plantar branches. The medial plantar nerve innervates the abductor hallucis muscle, while the lateral plantar nerve innervates the abductor digiti quinti muscle. The medial plantar nerve innervates the skin overlying the medial three and a half toes, and the lateral plantar nerve innervates the lateral one and a half toes. The tarsal tunnel also contains flexor tendons of tibialis posterior, flexor digitorum longus, and flexor hallucis longus. The cause of nerve compression neuropathy within the tarsal tunnel may be varied, but the common factor shared by the diverse mechanisms is that they all produce compression of the neurovascular bundle at or near the tarsal tunnel. The upper section of the tunnel is narrower, making it more susceptible to compressive forces. Medial TTS tends to compromise the medial plantar nerve and artery more often than their lateral homologues. A decrease in the tunnel’s volume can occur as a result of autoimmune and inflammatory disease. Some of the inflammatory disorders known to produce medial TTS include rheumatoid arthritis, gout, dermatomyositis, scleroderma, sarcoidosis, and amyloidosis. The subsequent soft tissue changes in the canal can lead to medial TTS. Trauma may fracture or dislocate the talus or medial malleolus, provoking nerve compression within the tunnel.123
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Tibialis posterior tendon Flexor digitorum longus tendon Posterior tibial nerve
Medial tarsal tunnel Medial calcaneal branches
Medial plantar nerve
Lateral plantar nerve
FIGURE 10.47 Medial tarsal tunnel compression may spare the posterior calcaneal branches. (Copyright 2000 J.M. True, D.C.)
Pathomechanical causes, such as varus and valgus deformities, can also contribute to medial TTS.124 Pressure changes within the tarsal tunnel with full eversion have been demonstrated to increase up to 16-fold and in inversion, eightfold, suggesting that the positioning may aggravate medial TTS.125 In describing eight cases of lateral plantar neuropathy, Oh et al.126 considered the course of the lateral plantar nerve through the abductor tunnel at the instep as the most common site of injury. Metabolic and hormonal factors may also produce TTS. Diabetes, pregnancy, myxedema, and acromegaly have all been implicated in the etiology of the syndrome.1 Space-occupying lesions, such as a ganglia or lipoma, may compromise the tunnel with resultant nerve compression. Nagaoka and Satou127 described 30 presentations of medial TTS caused by ganglia (mostly originating from the talocalcaneal joint) in which impalpable swellings were detected by ultrasonography. Vascular etiologies of the disorder are relatively common. Venous stasis as a result of extended periods of standing has been shown to cause the syndrome.1 Kopell and Thompson103 have even reported several cases of idiopathic tarsal tunnel syndrome. It is common among runners and mountain climbers.24 10.7.9.2 Clinical Signs and Symptoms Sensory symptoms are more common in the distribution of the medial plantar nerve. This area includes the medial aspect of the plantar surface and the first through third toes. The symptoms are exacerbated by extended periods of standing or walking. A nocturnal pattern is possible.
Pain of the sole of the foot is a common presenting symptom; provocation of sensory involvement with Tinel’s percussion over the tunnel has been reported.128 Some individuals may experience proximal radiation of pain such that they may be diagnosed with sciatic neuropathy or lumbar radiculopathy. Hypesthesia and loss of two-point discrimination may be present as early signs, as they often are in any nerve compression syndrome. Objective findings are usually difficult to appreciate. Since the foot is not utilized for fine manipulative tasks, any progressive motor deficit may go unnoticed for quite an extended time. The motor examination should consist of evaluation of the strength of the abductor hallucis and abductor digiti quinti muscles. Many patients will note exacerbation of pain upon forced eversion and dorsiflexion of the foot. Autonomic effects of nerve compression, such as local anhydrosis, may be observed. To properly diagnose this condition, one must perform a complete physical, radiographic, and electrodiagnostic examination. Radiographic views of the calcaneus may aid in evaluating the patency of the osseous canal. The electrophysiologic examination may reveal increased distal latency as well as decreased amplitude with tibial studies. Some have suggested a high degree of correlation between increased duration of evoked potentials and the presence of TTS.129 Although surgical release is an option, in their report of three cases of TTS, Calzada-Sierra et al.128 suggest that “initially conservative treatment is indicated in all cases,” describing successful outcome with rest, B-complex, and anti-inflammatory analgesics in two out of three presentations. The observed increases in pressure within the tarsal
Characteristic Signs and Symptoms of Entrapment
333
TABLE 10.49 Tarsal Tunnel Syndrome (Tibial Nerve, S1–S2) Clinical Signs and Symptoms
Possible Etiologies
Pain and/or paresthesia along medial plantar surface of foot great, 2nd and 3rd toes Predominant toe sensory disturbances May spare the heel Hypesthesia and impaired 2-point discrimination Magnification of symptoms with walking and pronation Positive Tinel’s sign posterior to medial malleolus Reduced foot sweating Retromalleolar or submalleolar swelling Pain with toe abduction Increased pain and dysesthesia with passive eversion and dorsiflexion Usually no difficulty standing or walking due to weakness
Autoimmune disease Pronation syndrome Varus heels Tendonitis Medial malleolar fracture Varicose veins Rheumatoid arthritis Hyperlipidemia Diabetes Edema Ankylosing spondylitis Pregnancy Peripheral vascular disease Ganglionic cyst
TABLE 10.50 Morton’s Metatarsalgia/Neuroma (Medial and Lateral Plantar Nerves, S1–S2) Clinical Signs and Symptoms
Possible Etiologies
Hypoesthesia or analgesia over involved Trigger point at metatarsal heads Often pain between 3rd and 4th metatarsal heads Increased pain with compression of metatarsal heads Increased pain with walking Increased forefoot pain with toe hyperextension
Pregnancy Osteochondritis Rheumatic inflammatory disease Pronation Prolonged crouching Flexion contractures of hip and knee Splay foot Poor-fitting shoes
tunnel with inversion/eversion suggest the necessity of considering the biomechanics of the foot/ankle complex for medial TTS presentations; neutral immobilization has led to improvement in some patients (Table 10.49).
10.7.10 MORTON’S NEUROMA (METATARSALGIA) Interdigital neuroma, more classically referred to as Morton’s neuroma or Morton’s metatarsalgia is one of the most common nerve disorders affecting the foot. It is associated with the development of a neuroma secondary to injury to one of the interdigital nerves of the foot. It is most likely a mechanically induced degenerative neuropathy, which occurs with a predilection for middle-aged women. Morton’s neuroma may develop after isolated physical trauma or cumulative microtrauma to the interdigital nerve.130
10.7.10.1 Anatomy and Pathomechanics The interdigital neuroma most commonly occurs between the 3rd and 4th toes. The predilection for the 3rd interdigital nerve is associated with excessive motion between the 3rd and 4th metatarsals, the large 3rd and 4th metatarsal heads approximating the nerve, chronic tethering of the interdigital nerve, the stout 3rd transverse intermetatarsal ligament overlying the 3rd interdigital nerve, and excessive weight-bearing stress placed on the forefoot, particularly due to pointed and high-heeled shoes.131 The primary differential considerations include medial tarsal tunnel syndrome, rheumatoid arthritis with nodule, metatarsal stress fracture, and metatarsal–phalangeal synovitis (Table 10.50).
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10.7.10.2 Clinical Signs and Symptoms The condition is characterized by intermittent seizing or agonizing pain initiated by weight-bearing during walking or running. The pain is usually intermittent, radiating to the distal forefoot and toes. The most reliable orthopedic test is perfomed by squeezing the forefoot (metatarsals) thus eliciting focal forefoot and radiating pain. Pain may also be produced with deep interdigital palpation or single leg hop, causing increased loading of the involved forefoot. Sonographic evaluation of the forefoot has been found valuable for the detection of interdigital neuromas,132,133 although sonography poorly differentiates between neuroma tissue and mucoid degeneration in surrounding loose connective tissues; its sensitivity for detecting web space abnormality is 95%.134 MRI is an effective tool for the evaluation of interdigital neuromas; the application of gadopentetate-enhancement may improve diagnostic sensitivity and specificity in some cases.135
10.8 SUMMARY In summary, peripheral nerve compression syndromes present a commonly encountered disorder in daily clinical practice. A thorough basis of the involved anatomy is a prerequisite to the appreciation of these syndromes. A selected few of the more common upper and lower extremity syndromes have been highlighted in this chapter. It is the sincere desire of the authors that the reader will be sparked to further investigate the intricacies of the diagnosis and management of those patients suffering from peripheral nerve compression syndromes. Most, if not all, of the commonly encountered syndromes are responsive to conservative therapeutic measures if recognized and managed early in their development.
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Section 4 Appendix
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Appendix TABLE 1 Clinical Considerations with Neurological Compromise below the Level of the Foramen Magnum Neurological Level
Motor Findings
Sensory Findings
Posterior column
Ataxic motor control
Numbness Tingling Loss of touch Loss of vibratory sensibility Ataxia Positive Romberg Dysmetria
Corticospinal tract
Spastic weakness (Greater distal) Distal clonus Muscle spasticity Spastic gait Loss or impairment of voluntary movement
Lateral spinothalamic tract Ventral commissure
Sensory horn or root
Motor horn or root
Ataxic motor control
Contralateral loss of pain and temperature at and below the lesion Bilateral loss of pain and temperature at and below the lesion Diminished segmental touch, temperature, and pain Numbness Tingling Diminished position and vibratory sense Broad based gait ataxia accentuated by closing eyes Radicular pain
Reduced muscle tone
Diminished or absent segmental MSR
Flaccid neurogenic bladder if S2, S3, or S4 involved Trophic changes
Loss of anal reflex if S2, S3, Vasomotor change if lateral or S4 involved horn involved Reduced segmental MSR Flaccid neurogenic bladder if S2, S3, or S4 involved No pathological cutaneous reflexes
Reduced muscle tone
Muscle atrophy Muscle fasciculations
Spastic neurogenic bladder
Babinski’s sign Hoffmann’s sign Tromner’s sign Loss of superficial abdominal and cremasteric reflexes
Myotomal muscle atrophy
Muscle fasciculations Muscle weakness
Autonomic Findings Flaccid neurogenic bladder
Increased MSRs
Myotomal weakness
Peripheral nerve
Reflexive Findings
Pain
Diminished or absent MSR
Trophic and vasomotor changes
Paresthesia Nonsegmental combined sensory loss Diminished vibratory and position sense Nerve tenderness Tinel’s sign
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TABLE 1 (continued) Clinical Considerations with Neurological Compromise below the Level of the Foramen Magnum Neurological Level
Motor Findings
Sensory Findings
Reflexive Findings
Sympathetic ganglion
Neuromuscular junction
Autonomic Findings Horner’s syndrome Hypertension Vasomotor changes Dermographia Anhidrosis Trophic changes
Progressive weakness (often greater proximal) Myasthenia gravis or Pain secondary to diffuse botulism may be severe and weakness and overuse of involve cranial nerve muscles innervated muscles or cause respiratory arrest Muscle atrophy Rapid variable level fatigue Contractures Coarse fasciculation in myokymia
Reduction or absence of MSRs
TABLE 2 Common Neuro-orthopedic Tests and Signs Orthopedic tests are classically reported as positive or negative and are dependent upon a reproduction of the patient’s symptomatology. However, many of the standard orthopedic tests that classically identify pathology in a specific soft-tissue structure such as a myotendinous sprain or a bursitis, may also have significance for neurological interpretation. Therefore, as clinicians we should not limit our interpretation of orthopedic tests to a contractile vs. non-contractile tissue diagnosis or bone/joint structure and function. Often, there are many underlying reasons for why the test is positive that may be a secondary component from nerve irritation, denervation, or weakness. An excellent example is the shoulder impingement sign, caused from C5-6 radiculopathy and denervation of the rotator cuff muscles. In the following table, we have tried to outline orthopedic and neurological considerations for some of the standard tests. Our approach to interpretation is nonconventional in many of the tests listed. We suggest that the reader consult standard orthopedic references for the traditional or complete interpretive differentials. For space purposes, we have not elaborated on the customarily reported indictors or soft-tissue diagnostic impression. This appendix, of course, is by no means an all-inclusive list. Orthopedic Sign/Test 90° AbductionExternal Rotation Test (Roos Test) or EAST (Elevated Arm Stress Test) Adson’s Test
Black process 45.0° 150.0 LPI
Orthopedic Procedure
Classical Orthopedic Significance*
Possible Neurological Involvement and (Mechanism)
While seated, the patient abducts arms to 90° and Reproduction of extremity Compression of the brachial plexus in the externally rotates the shoulder joints, in a “surrender pain, paresthesia, cervicoaxillary region. position.” numbness, or weakness. Neurologic symptoms may be found with The patient may also simultaneously rapidly open and Absence of radial pulse may or without vascular deficit. close the hands. This position may be held for up to also occur. 3 minutes. While seated, the patient turns the head to the side of Absence of radial pulse. complaint; he or she takes a long deep breath and slightly extends the head. The ipsilateral arm is extended and externally rotated. The examiner palpates the radial pulse. The patient may also rotate the head to the opposite side for a modified test.
Occurs with cervicoaxillary neurovascular compression of the brachial plexus and subclavian artery. (Scalene muscle spasm or cervical rib.)
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TABLE 2 (continued) Common Neuro-orthopedic Tests and Signs Orthopedic Sign/Test Babinski Sign
Bakody Sign
Bench Step Test
Braggard’s Test
Calf Circumference Test Cervical Distraction Test Clarke’s Sign
Cozens Test
Elbow Flexion Test Ely’s Test
Erichsen’s Test
Fajersztajn’s Test
Foraminal Compression Test Froment’s Paper Sign
Black process 45.0° 150.0 LPI
Orthopedic Procedure
Classical Orthopedic Significance*
Possible Neurological Involvement and (Mechanism)
The examiner strokes the bottom of the foot with a blunt object, along the lateral sole from the heel to the base of great toe in a sweeping arc.
Up going toes. Spinal cord compromise. Up going toes with splaying Upper motor neuron lesion. of the toes indicates a more serious response. While seated, patient actively places palm of involved Reduced radiating arm pain. Decreased traction on compressed upper extremity on top of head or a position of the shoulder roots of the cervical spine. at 90° with abduction-external rotation of the arm. Have the patient actively elevate the arm above the head. The patient is asked to arise onto a 6- to 12-inch bench Weakness or unilateral Hip extensor (L5) and knee extensor (L4) step one leg at a time for 10 to 30 repetitions. Can fatigue. weakness results in more pronounced use alternate stepping. difficulty. If the Lasegue or SLR tests are positive, the examiner Magnification of radicular Increased stretch of irritated or compressed should lower the leg just below the point of initiating symptoms lower lumbar roots. radiating leg pain. The examiner quickly and passively moves the ipsilateral foot into dorsiflexion While the patient is supine, a circumferential Reduced circumference. Tibial neuropathy. measurement is made 6 inches from the midline of Sciatic neuropathy the patella. S1 or S2 radiculopathy (muscle denervation and atrophy). The examiner manually applies axialward traction to Reduction of arm or hand Decompression of cervical roots. the cervical spine. symptoms. With the patient supine and the knees extended, the Retropatellar pain or Femoral neuropathy examiner places the web of one hand along the inability to maintain L2, L3, or L4 radiculopathy superior portion of the patella and exerts downward contraction of the (quadriceps denervation, patellar pressure while the patient is asked to contract the quadriceps because of pain. pathomechanics, and patellar ipsilateral quadriceps muscle. chondromalacia). The patient clenches fist and simultaneously Lancinating lateral elbow Radial neuropathy or entrapment. dorsiflexes hand while in a pronated position. pain. C6-C8 radiculopathy Examiner attempts to flex hand against patient’s (wrist extensor paresis with forearm resistance. muscle dyssynergy). Patient is asked to fully flex the elbow and to hold it Numbness or tingling in an Ulnar neuropathy. for 1 minute. ulnar distribution. Possible C8 or T1 radiculopathy (double crush syndrome). With the patient prone, the heel is brought toward the Radiating anterior thigh or Femoral neuropathy buttock. After flexion of the knee, the thigh is leg pain. L2, L3, or L4 radiculopathy extended. (stretch of irritated nerve or nerve root). With the patient lying prone, the examiner places his Sacroiliac pain. Gluteal neuropathy. or her hands over the ilia and provides a rapid thrust L5 and/or S1 radiculopathy lateral to medial. (pelvic destabilization, abnormal gait, and sacroiliac disease). With the patient supine, the examiner passively Leg pain on contralateral L4-S2 radiculopathy elevates the leg on the asymptomatic side while side. (tractioning of compromised nerve root). holding the foot in dorsiflexion. With the patient seated, the examiner laterally flexes Radiating arm pain. Arm or Nerve root compression the patient’s head while applying a downward hand numbness or tingling. (IVF nerve root pathology). pressure. A sheet of paper is placed between the 1st and 2nd Inability to hold paper Ulnar neuropathy. digits, and the patient is asked to adduct the fingers, without bending the thumb. Possible C8 orT1 radiculopathy preventing the examiner from removing the paper. (double crush).
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TABLE 2 (continued) Common Neuro-orthopedic Tests and Signs Orthopedic Sign/Test
Orthopedic Procedure
Classical Orthopedic Significance*
Gaenslen’s Test
With the patient lying supine, the examiner flexes the Sacroiliac pain. thigh and knee of the uninvolved side and then pushes the opposite leg–hip into extension.
Golfer’s Elbow Test
The seated patient flexes the elbow and supinates the hand. The patient then attempts to extend the elbow against resistance.
Heel Walk Test
While weight bearing, the patient is asked to walk on his or her heels.
Iliac Compression With the patient lying on his or her side, the examiner Test places his or her hands over the superior ilia and applies pressure toward the table. Kemp’s Test Knee–Shoulder Test
While seated or standing, the patient is supported and taken into a position of extension and rotation. With the patient supine, the knee and hip are passively flexed by the examiner in an attempt to bring the knee to the opposite elbow.
Gluteal neuropathy. L5 and/or S1 radiculopathy (pelvic destabilization, abnormal gait and sacroiliac disease). Medial elbow pain. Median neuropathy. Ulnar neuropathy. C6-C8 radiculopathy (wrist flexor paresis with forearm muscle dyssynergy). Inability to perform multiple L4 and/or L5 radiculopathy repetitions from anterior (anterior tibialis muscle denervation). tibialis weakness. Sacroiliac pain. Gluteal neuropathy. L5 and/or S1 radiculopathy (pelvic destabilization, abnormal gait, and sacroiliac sprain, fracture or disease). Radiating leg pain. Compression of compromised nerve root (dynamic lateral stenosis). Sacroiliac pain. Gluteal neuropathy. L5 and/or S1 radiculopathy (pelvic destabilization, abnormal gait, and sacroiliac sprain or inflammation). Sacroiliac or acetabular Gluteal neuropathy. pain. L5 and/or S1 radiculopathy (pelvic destabilization, abnormal gait, and sacroiliac sprain or inflammation). Radiating leg pain. L4-S2 radiculopathy (stretch of compromised nerve root).
Laguerre’s Test
With the patient supine, the examiner flexes, abducts, and laterally rotates the hip. Additional pressure is applied at the end of the ROM. Pelvis is stabilized.
Lasegue Test
While the patient is supine, the examiner flexes the patient’s hip and knee to approximately 90°, then slowly attempts to straighten the leg by extending the knee. With the patient sitting, the examiner passively flexes Spine and extremity the patient’s head. dysesthetic symptoms.
Lhermitte’s Sign
Lindner’s Sign Maximum Cervical Compression Test McMurray Sign
With the patient supine, the examiner passively flexes Lumbar spine and radiating the cervical spine, taking the chin toward the chest. leg pain. While seated, the patient is asked to rotate the head Radiating arm pain. Arm or and extend the neck. hand numbness or tingling.
With the patient supine, the examiner flexes the thigh Painful click. and knee until the heel approaches the buttock. The examiner then internally rotates the leg while extending and adducting the knee.
One-Legged Toe Raises
The patient is asked to perform 10 to 20 repetitive toe Weakness. raises on one leg at a time with body weight.
Patella Ballottement Test
With the patient supine and the knee flexed or extended to a position of comfort, the examiner applies a rapid tap to the anterior portion of the patella.
Black process 45.0° 150.0 LPI
Possible Neurological Involvement and (Mechanism)
Floating patella.
Physical irritation of the spinal cord, nerve root, dural membrane, or arachnoid membrane. Stretch of CNS neurons. Lumbar or sacral radiculopathy (stretch of irritated nerve root). Root compression from IVF pathology.
Femoral neuropathy. L2-4 radiculopathy (quadriceps denervation with chronic knee pathomechanics resulting in injury to medial meniscus). S1 or S2 radiculopathy (gastrocnemius and/or soleus muscle denervation). Femoral neuropathy L2, L3, or L4 radiculopathy (quadriceps denervation, abnormal knee loading, and intra-articular swelling).
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TABLE 2 (continued) Common Neuro-orthopedic Tests and Signs Orthopedic Sign/Test
Orthopedic Procedure
Classical Orthopedic Significance*
Fabere–Patrick’s Test
With the patient supine, the examiner holds the ankle Hip pain. and flexes the ipsilateral knee. The thigh is then flexed, externally rotated, and extended.
Shoulder Depression Test
While the patient is seated, the patient’s neck is laterally flexed to the side opposite the shoulder tested; the examiner applies downward pressure to the ipsilateral shoulder. With patient supine, the examiner raises a leg to a point just below eliciting radiating leg pain. The examiner then passively dorsiflexes the great toe. With the patient sitting, he or she is asked to slump forward.
Possible Neurological Involvement and (Mechanism)
Gluteal neuropathy L4-S1 radiculopathy (muscle denervation, pelvic and hip instability with coxa pathology). Peroneal Nerve Physical tap applied over the common peroneal nerve Numbness or tingling along Ectopic discharge from irritated nerve fibers Percussion Sign at the peroneal tunnel along the fibular neck. the distal peroneal nerve. or neuromas. Phalen’s Test While seated, patient places the hands back to back, Numbness or tingling in Median neuropathy. (Wrist Flexion elevates the hands to the level of the sternum and is median distribution. Possible C5-C8 contribution Test) to hold for at least 60 seconds. (CTS or double crush syndrome). Prone Knee With the patient prone and the hips in a neutral Low back and radiating L2 and/or L3 radiculopathy Bending Test position of rotation, the heels are brought toward the thigh pain. (stretch of irritated nerve root). buttocks. Quick Test The patient is asked to move from a standing position Hip pain, knee pain, or L2-S1 radiculopathy to a squatting position while on toes. The patient is difficulty arising due to (muscle denervation with paresis of hip then asked to bounce a few times and arise. weakness or inability to extensors, knee extensors, or plantarfully squat. flexors) Repetitive Grip Quantitative grip testing is performed using a device Weakness. C5-T1 involvement Test such as a dynamometer. Five repetitions are used, (muscle denervation). with greater than 15% deficit from side to side on the last repetitions being considered positive. Reverse Phalen’s While seated, patient is to place palms of hands Numbness or tingling in Median neuropathy. Test (Prayer Test) together with the wrists in an extended position and median distribution. Possible C5-C8 contribution to hold for at least 60 seconds. (CTS or double crush syndrome). Romberg’s Sign Patient instructed to stand with feet together, first with Swaying and losing one’s Proprioceptive loss from posterior column the eyes open and then with the eyes closed. balance when the eyes are compromise or other causes of sensory closed. ataxia. Sacroiliac With the patient side lying, the patient is asked to Sacroiliac pain. Unilateral Gluteal neuropathy. Resistedactively abduct the superior leg. The examiner hip weakness. L5 and/or S1 radiculopathy Abduction Test applies pressure to the abducted leg in an attempt to (pelvic destabilization, abnormal gait with return it to a neutral position. sacroiliac strain or subluxation). Supine SLR Test With the patient lying supine, the leg is passively Radiating leg pain. L4-S2 radiculopathy elevated. (stretch of compromised nerve root). Scalene Triangle Examiner briskly taps along the scalene triangle with Reproduction of paresthesia Ectopic discharge from irritated nerve root Percussion Test fingertip. or radicular complaints. trunk or brachial plexus.
Sicard’s Test
Sitting Lumbar Slump Test
Sitting SLR (Kick) Test Soto–Hall Test
Black process 45.0° 150.0 LPI
While sitting, the patient is asked to actively straighten a leg. While supine, the patient’s neck is passively flexed, moving the chin toward chest.
Radiating arm pain or paresthesia.
Stretching of the nerve roots, adhesion of nerve roots, or foraminal stenosis.
Radiating leg pain.
L4-S2 radiculopathy (stretch of compromised nerve root).
Low back and/or leg pain.
L4-S2 radiculopathy. (stretch and/or compression of compromised nerve root). Meningeal irritation will also cause a positive response. L4-S2 radiculopathy (stretch of compromised nerve root). Localized neck pathology, such as discogenic injury, fracture, spondylosis, or ligament injury. When meningeal irritation is present, transverse myelitis or meningitis may be in early stage of development.
Radiating leg pain. Sharp increase of neck pain when localized or signs of meningeal irritation and CNS involvement when meningitis is present.
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TABLE 2 (continued) Common Neuro-orthopedic Tests and Signs Orthopedic Sign/Test
Orthopedic Procedure
Speed’s (Biceps) Test
With patient’s forearm supinated and elbow extended, Bicipital tendon pain. examiner resists shoulder flexion.
Spurling’s Test
While seated, the patient is asked to laterally flex and rotate the neck while the examiner applies a quick pulse of downward pressure to the top of the head. Ask the patient to make a circle with the thumb and index finger. The fingertips should touch. Then, try to break the circle while the patient resists.
Thumb and Index Circle Test
Tibial Nerve Physical tap applied over the tibial nerve at the tarsal Percussion Sign tunnel along the medial ankle. Tinel’s Sign The median nerve is physically tapped anywhere (Median Nerve at along its course. Wrist) Toe Walk Test While weight bearing, the patient is asked to walk on his or her toes.
Classical Orthopedic Significance*
Possible Neurological Involvement and (Mechanism)
Possible C5-C6 radiculopathy (muscle denervation and/or muscle dyssynergy with shoulder dysfunction with proximal long head bicipital tendonitis). Radiating arm pain. Arm or Compression of compromised cervical hand numbness or tingling. nerve roots (cervical spondylosis and disc disease). The inability to make a Median neuropathy. Ulnar neuropathy. circle by pinching the thumb and index finger is median nerve weakness. Inability to resist the circle being pulled open is ulnar weakness. Numbness or tingling along Ectopic discharge from irritated nerve fibers the distal tibial nerve. or neuromas . Numbness or tingling Ectopic discharge from irritated nerve fibers reproduced in median or neuromas at the flexor retinaculum. nerve distribution. Inability to perform multiple S1 and/or S2 radiculopathy repetitions from (gastrocnemius and/or soleus muscle gastrocnemius/ denervation). soleus weakness. Unilateral foot drop Deep peroneal neuropathy. considered positive. L4 or L5 radiculopathy (tibialis anterior and extensor digitorum longus muscle denervation). The gluteal fold will drop Superior or inferior gluteal neuropathy. below the level of the L5 and/or S1 radiculopathy contralateral side. (hip abductor and/or extensor muscle denervation).
Treadmill Foot Drop Test
The patient is asked to walk on a treadmill with a 5° incline for 5 minutes at a comfortable speed.
Trendelenburg’s Test
With the patient standing, the patient is asked to actively flex one hip and knee resulting in standing on one foot.
Turyn’s Test
With the patient lying supine, the examiner dorsiflexes Sciatic or gluteal pain. the great toe.
Ulnar Nerve Percussion Sign (Elbow) Valsalva Test
Examiner taps along the medial elbow between the Numbness or tingling in an olecranon process and the lateral epicondyle with a ulnar distribution. reflex hammer. The patient should breathe in deeply, hold it, and bear Increased pain or down. neurological complaints.
Yeoman’s Test
With the patient lying prone, the examiner flexes the knee and reaches under the thigh to extend the hip. Opposite SI region is stabilized by the examiner’s opposite hand.
Sacroiliac pain.
Sciatic neuropathy. L4-S1 radiculopathy (stretch of irritated peripheral nerve, lumbar or upper sacral nerve root). Ectopic discharge from irritated nerve fibers or neuromas. Spinal cord compression, neurovascular compromise or nerve root irritation. Test may also appear positive with other conditions, such as discopathy. Gluteal neuropathy. L5 and/or S1 radiculopathy (pelvic destabilization, abnormal gait, and injury to anterior sacral ligaments).
∗ Orthopedic tests are reported as positive or negative, whereas, orthopedic signs are reported as present or absent.
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347
TABLE 3A Upper Extremity Motor Innervation Muscle
Peripheral Nerve
Trapezius
Accessory
Levator scapulae
C3, C4 nerve roots Dorsal scapular Long thoracic Thoracodorsal Subscapular Subscapular Dorsal scapular Dorsal scapular Suprascapular Suprascapular Axillary Axillary Musculocutaneous Musculocutaneous Musculocutaneous Lateral pectoral Medial pectoral Radial Radial Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial: Posterior interosseous Radial Radial Median: Anterior interosseous Median: Anterior interosseous Median: Anterior interosseous: lateral two digits Ulnar: medial two digits Median Median Median Median Median: superficial head Ulnar Ulnar Ulnar Ulnar Ulnar Ulnar Ulnar Median: first and second; Ulnar: third and fourth
Serratus anterior Latissimus dorsi Teres major Subscapularis Rhomboid major Rhomboid minor Supraspinatus Infraspinatus Teres minor Deltoid Coracobrachialis Biceps brachii Brachialis Pectoralis major Pectoralis minor Brachioradialis Triceps Supinator Extensor digitorum communis Extensor indices Extensor carpi ulnaris Extensor carpi radialis brevis Abductor pollicis longus Extensor pollicis longus Extensor pollicis brevis Extensor digiti minimi Extensor indices Abductor pollicis longus Extensor carpi radialis longus Anconeus Flexor pollicis longus Pronator quadratus Flexor digitorum profundus
Flexor carpi radialis Pronator teres Opponens pollicis Abductor pollicis brevis Flexor pollicis brevis Flexor carpi ulnaris Flexor digiti minimi Abductor digiti minimi Dorsal interossei Palmar interossei Adductor pollicis Opponens digiti minimi Lumbricals
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Root level (Dominant root supply in bold ) Cranial nerve XI C2, C3, C4 C3, C4, C5 C5, C6, C7, C8 C6, C7, C8 C5, C6, C7 C5, C6, C7 C4, C5 C4, C5 C4, C5, C6 C4, C5, C6 C5, C6 C5, C6 C6, C7 C5, C6 C5, C6 C5, C6, C7 C6, C7, C8, T1 C5, C6 C6, C7, C8 C5, C6, C7 C7, C8 C7, C8 C7, C8 C6, C7, C8 C7, C8 C7, C8 C7, C8 C7, C8 C7, C8 C7, C8 C6, C7, C8 C7, C8 C7, C8 C8, T1 C7, C8, T1 C8, T1 C6, C7 C5, C6, C7 C8, T1 C8, T1 C8, T1 C7, C8 C8, T1 C8, T1 C8, T1 C8, T1 C8, T1 C8, T1 C8, T1 C8, T1
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TABLE 3B Lower Extremity Motor Innervation
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Muscle
Peripheral Nerve
Root level (Dominant root supply in bold )
Psoas Gluteus maximus Gluteus medius Gluteus minimus Tensor fasciae latae Obturator externus Adductor brevis Adductor longus Gracilis Iliacus Pectineus Rectus femoris Sartorius Vastus intermedius Vastus lateralis Vastus medialis Adductor magnus Biceps femoris Semimembranosus Semimembranosus Gemellus inferior Gemellus superior Obturator internus Piriformis Quadratus femoris Gastrocnemius Soleus Popliteus Peroneus brevis Peroneus longus Peroneus tertius Extensor digitorum longus Extensor hallucis longus Tibialis anterior Tibialis posterior Plantaris Flexor digitorum longus Flexor digitorum brevis Flexor hallucis longus Flexor hallucis brevis Flexor digiti minimi brevis Abductor digiti minimi Abductor hallucis Dorsal interossei Plantar interossei Lumbricals
Ant. rami L1-L3 Inferior gluteal Superior gluteal Superior gluteal Superior gluteal Obturator Obturator Obturator Obturator Femoral Femoral Femoral Femoral Femoral Femoral Femoral Sciatic Sciatic Sciatic Sciatic N. to quadratus femoris N. to obturator internus N. to obturator internus L5, S1, S2 N. to quadratus femoris Tibial Tibial Tibial Superficial peroneal Superficial peroneal Deep peroneal Deep peroneal Deep peroneal Deep peroneal Tibial Tibial Tibial Tibial Tibial Tibial Tibial Tibial Tibial Tibial Tibial Tibial
L1, L2, L3 L5, S1, S2 L4, L5, S1 L4, L5, S1 L4, L5 L3, L4 L2, L3 L2, L3, L4 L2, L3 L2, L3 L2, L3 L2, L3, L4 L2, L3, L4 L2, L3, L4 L2, L3, L4 L2, L3, L4 L2, L3, L4, L5 L5, S1, S2 L5, S1, S2 L5, S1, S2 L5, S1 L5, S1 L5, S1 L5, S1, S2 L5, S1 S1, S2 S1, S2 L4, L5, S1 L5, S1, S2 L5, S1, S2 L5, S1 L5, S1 L5, S1 L4, L5 L4, L5, S1 S1, S2 L5, S1, S2 L5, S1, S2 S1, S2 S1, S2 S1, S2 S1, S2, S3 S2, S3 S2, S3 S2, S3 S2, S3
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Index A Abdominal/pelvic entrapment syndromes, 314–316 Abduction external rotation (AER) test, 287 Abscess, epidural, 72 Adhesive (spinal) arachnoiditis, 78–79 Adson’s maneuver, 287 AIDS/HIV, 77–78, 144 as predisposing to entrapment, 278 radiculopathy in, 194 Amniocentesis, 126–128 Amyotrophic lateral sclerosis (ALS), 82, 145–146 Anaplastic astrocytoma, 66 Anatomic distribution, of peripheral neuropathy, 276–277 Anatomy dorsal root ganglia, 166–167 dural sleeve, 165–166 gray matter, 10–13 meninges and compartments, 6–8 arachnoid mater, 7 dura mater, 6–7 pia mater, 7 subarachnoid space and cerebrospinal fluid, 7–8 nerve root, 161–167, see also Radiculopathy, anatomical considerations peripheral nerve junction, 165–166 peripheral nervous system, 253–266, see also Peripheral nerves; Plexuses autonomic nervous system, 261 biomechanical characteristics, 266 brachial plexus, 255–257 cervical plexus, 254–255 general organization, 253–254 lumbar plexus, 257–259 lumbosacral plexus, 259–261 peripheral nerves, 261–264 vascularity, 264–266 spinal cord basic, 3–4 regional neuromeres, 5 regional spinal canal, 5–6 segmental, 5–6 spinal cord nuclei, 17 spinal cord pathways, 13–17 autonomic pathways, 17 clinically important ascending, 13–15 lateral spinothalamic tract, 13 other, 13–15 posterior columns, 13 clinically important descending, 15–17 corticospinal tract, 15–17 nonpyramidal tracts, 17 spinal-mediated myotatic reflex, 17–21
vascular of spine, 8–10 extrinsic, 8–9 anterior and posterior spinal arteries, 8–9 radiculomedullary arteries, 8 intraparenchymal, 9 spinal venous plexus, 9–10 Angina, cervicogenic (pseudo), 209 Angiography, magnetic resonance (MRA), 120 Angioma, cavernous, 72, 75–77 Ankylosing (diffuse idiopathic) hyperostosis, 60–61 Ankylosing spondylitis, 176 Annular bulge (disk bulge), 178–180 Anterior atlantodens interval (ADI), 60 Anterior cord syndrome, 143 Anterior horn/pyramidal tract disease (motor neuron syndrome), 145–146 Anterior horn syndrome (progressive muscular atrophy), 145–146
Anterior interosseous nerve syndrome, 295–296 Anterior spinal artery, 8–9 Anterior spinal artery syndrome (ASAS), 139 Anterior tarsal tunnel syndrome, 331–333 Anterior tarsal tunnel syndrome/deep peroneal nerve syndrome, 329–331 Apoptosis (programmed cell death), 24 Arachnoid cyst, 64 Arachnoiditis radiculopathy and, 173 spinal (adhesive), 78–79 Arachnoid mater anatomy, 7 Arcade or Frohse/deep radial nerve entrapment syndrome, 306–309
Arnold–Chiari malformation, 151 Arterial insufficiency, 27–28 cerebral edema and, 27–28 Arteriosclerosis, of spinal arteries, 27 Artery (arteries), see also Vascular spinal cord syndromes anterior spinal, 8–9 posterior spinal, 8–9 radiculomedullary, 8 of spinal nerve roots, 166 Arthritis biomechanical instability in, 41–42 rheumatoid, 59–60, 278 Arthropathy, neuropathic (Charcot’s joint), 43–44, 112 Articular subluxation, 111–112 assessment of, 111–112 Ascending spinal cord pathways, 13–15 ASIA/MSOP scale, 130 Assessment diagnostic imaging, 116–121, see also Imaging and specific modalities computed tomography (CT scan), 121
349
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magnetic resonance imaging (MRI), 116–121 neurosonography, 121 plain-film radiography, 121–122 quantitative considerations in spinal cord imaging, 122–125 central spinal canal measurements, 122–123 classification of spinal cord compression, 123–124 intramedullary signal patterns, 125 intrinsic cord dysmorphism, 124 spinal cord cross-sectional size and area, 124 spinal instability and vertebral translation, 123 electrodiagnostic techniques, 112–116, see also Electrodiagnostics late responses, 115 motor evoked potentials, 113–115 motor nerve conduction studies, 116 needle electromyography (EMG), 115–116 in radiculopathy, 209–217 needle electromyography (EMG), 209–215 nerve conduction studies, 215–216 somatosensory and dermatomal evoked potentials, 217 sensory nerve conduction studies, 116 somatosensory evoked potentials, 113, 217 functional and laboratory assessment, 125–133 amniocentesis, 126–128 bladder function, 129–130 cystometry, 129 cystourethrography, 129 electrodiagnostic studies, 129–130 uroflowometry, 130 blood and serum studies, 128 cerebrospinal fluid (CSF) evaluation, 126, 127 genetic assessment, 128–129 physical impairment, 130–133 ASIA/MSOP scale, 130 balance, 133 Benzel and Larson scale, 130 Frankel classification, 130 gait, 130–132 Japanese Orthopedic Association Cervical Myelopathy Score, 130 muscular performance, 132–133 range of motion (ROM), 130 sensibility, 133 pulmonary function, 125–126 of myelopathy and associated musculoskeletal conditions, 111–116
articular subluxation, 111–112 contractures, 112 neuropathic arthropathy, 112 osteoporosis, 112 of radiculopathy, 209–223 functional capacity evaluation, 218–219 magnetic resonance imaging (MRI), 219–223 of spinal cord injury, 97–137 autonomic and other system considerations, 107–111 autonomic dysreflexia, 108–109 bowel and bladder dysfunction, 109–110 cardiac complications, 109 deep vein thrombosis (DVT), 108 orthostatic hypotension, 107–108
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psychological considerations, 110–111 respiratory considerations, 109 sexual function, 110 skin complications, 110 Babinski’s response, 25–26, 81, 102–104, 149 fever, 111 neurogenic claudication, 106–107 pain, 104–105 disorders associated with, 104 Lhermitte’s sign, 104–105 reflexes, 100–104 sacral sparing, 107 sensory abnormalities, 104 spasticity, clonus, and hyperreflexia, 97–100 superficial, 100–101 Astrocytoma, 64–66 Ataxia, 104 Atlas fractures, 43–45, see also Fracture, cervical Atrophy muscle in radiculopathy, 206 spinal cord, 30–31 spinal muscular (SMA), 82–83 Autoimmune myelopathy, 81 Autonomic and other system assessment, 107–111 autonomic dysreflexia, 108–109 bowel and bladder dysfunction, 109–110 cardiac complications, 109 deep vein thrombosis (DVT), 108 orthostatic hypotension, 107–108 psychological considerations, 110–111 respiratory considerations, 109 sexual function, 110 skin complications, 110 Autonomic dysreflexia, 108–109 Autonomic nervous system, 261 Autonomic pathways, 17 Avulsion, nerve root, 177 Axillary nerve, 256 Axillary tunnel entrapment, 290–291 Axonal regeneration, 269–270 Axonotmesis, 267–268
B Babinski’s response, 25–26, 102–104 in hemisection (Brown–Séquard) syndrome, 149 in subacute combined degeneration, 81 Bakody’s sign, 202 Balance assessment, 133 Bands of Bunger, 269 Barotrauma, 81 Benzel and Larson scale, 130 Bilateral cervical facet dislocation, 48–49 Biochemical radiculopathy, 170–171 Biomechanical characteristics, of peripheral nerves, 266 Biomechanical instability, 39–43 in acute trauma, 40–41 in arthritic disorders, 41–42 Bipedicular fracture of C2 (hangman’s fracture, traumatic spondylolisthesis of C2), 44
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Bladder dysfunction, 109–110, 141–142, 155 Bladder function assessment, 129–130 Blood and serum studies, 128 Blood supply, of spinal nerve roots, 166 Borrelia burgdorferi, 78, 194–195 Bowel dysfunction, 109–110, 141–142, 155 Brachialis/brachioradialis/radial nerve entrapment, 306–309 Brachial plexus nerve branches arising from upper trunk, 257 nerves arising directly from nerve roots or plexus, 256–257 nerves comprising, 255–256 nerves formed from medial and lateral cords, 257 Braggard’s maneuver, 202 Brown–Séquard syndrome, 148, 149 Bruns–Garland syndrome, 277 Bunger, bands of, 269 Burst fracture of C1 (Jefferson fracture of atlas), 44
C Capillary telangiectasia, 72 Cardiac complications, of spinal cord injury, 109 Ca2+–related pathogenesis, 24 Carpal tunnel syndrome, 272–273, 296–303 Cation-mediated cell injury, 24 Cauda equina syndrome, 246–247 Caudal spinal anomalies, 87 Causalgia, 270 Cavernous angioma, 72, 75–77 Cavitation and gliosis, 29–30 Central cord syndrome, 142 Central cord vascular syndrome (CCVS), 139 Central spinal canal measurements, 122–123 Cerebrospinal fluid (CSF), 7–8 Cerebrospinal fluid (CSF) evaluation, 126, 127 Cervical evaluation, problems of, 99 Cervical facet dislocation bilateral, 48–49 unilateral, 48–49 Cervical lesions, 152–154 intact C3 neurologic (C3 functional) level, 152 intact C4 neurologic (C4 functional) level, 152 intact C5 neurologic (C5 functional) level, 152–153 intact C6 neurologic (C6 functional) level, 153 intact C7 neurologic (C7 functional) level, 153 intact C8/T1 neurologic (C8/T1 functional) levels, 153–154 Cervical plexus, 254–255 motor fibers within cervicobrachial plexus, 255 in relationship to cranial nerves, 254–255 sensory innervation to head and neck, 254 to neck and shoulders, 254 Cervical radiculopathies, 223–233 C1, 223 C2, 223–224 C3, 224 C4, 224 C5, 224–229 C6, 229–231
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C7, 231 C8, 233 Cervical spinal fractures, 43–45, see also under Fracture(s) Cervical spondylotic myelopathy, 55–59, see also Spondylotic myelopathy Cervicoaxillary (thoracic outlet syndrome), 285–287 Cervicogenic (pseudo) angina, 209 Cervicomedullary syndrome, 148–151 Chance (lap seatbelt, fulcrum) fracture, 47 Charcot’s joint (neuropathic arthropathy), 43–44, 112 Cheiralgia paresthetica (distal superficial radial nerve entrapment), 309–310 Chemical radiculitis, 170–171 Chiari malformations, 84, 87 Chordoma, 70 Claudication, neurogenic, 106–197 Claw hand deformity, 311 Clay shoveler’s fracture (spinous process fracture, coal miner’s fracture), 44 Clonus, assessment, 97–100 Coagulopathies, radiculopathy in, 193 Coal miner’s fracture (spinous process fracture, clay shoveler’s fracture), 44 Cobalamin deficiency, 81, 144 Combined anterior horn/pyramidal tract disease (motor neuron syndrome), 145–146 Common peroneal nerve, 259–260 Complete spinal cord transection (transverse myelopathy), 140–142
Complex regional pain syndrome II (causalgia), 270 Compound motor action potential (CMAP), 112–113, 215, 275, see also Electrodiagnostics; Electromyography (EMG) Compression classification of, 123–124 epidural mass in, 36–37 mechanisms of, 37–38 Compression neuropathy, peripheral nerve, see Entrapment Compressive myelopathy, see Myelopathy, in degeneration and stenosis Compressive radiculopathy, 167–193 acquired lateral recess stenosis and vascular stasis, 173–175 disk herniation, 177–183, see also Disk herniation expansile lesions, 183–190, see also Expansile lesions and specific lesions failed back surgery syndrome, 175–176 fibrosis in, 172–173 nerve root double crush, 169–170, 301 osteomyelitis and discitis, 190 sites of nerve root vulnerability, 168–169 spinal degeneration, 171–172 spondylolisthesis, 190–193 trauma, 176–177 Computed tomography (CT scan), 121 CT/myelography, 121 helical (spiral), 121 Conduction block, physiologic, 266 Congenital spinal anomalies caudal, 87 occult spinal dysraphism, 84–86
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neuroenteric cyst, 86 spinal (dorsal) dermal sinus, 85–86 split cord malformation, 84–85 spina bifida aperta (myelomeningocele), 84, 89 Contractures, 111 assessment of, 112 Contrast enhancement MRI, 118 Contusion, mechanisms of, 37 Conus medularis syndrome, 146–148 Corticospinal tract, 15–17 Costoclavicular entrapment syndrome, 289–290 Costopectoral tunnel (hyperabduction) syndrome, 290 Coupling, of spine and cord motion, 35–36 Cranial-cervical (foramen magnum) lesions, 151 Cranial nerves, cervical plexus in relationship to, 254–255 Critical zone of thoracic spine, 28, 29 Crossed extensor reflex, 26 Cubital tunnel syndrome (entrapment at elbow), 310–311 Cumulative injury cycle, 274 Cumulative trauma disorder (CTD), 273 Cutaneous complications, 110 Cutaneous stigmata, 85 Cyst(s) arachnoid, 64 neuroenteric, 86 perineural (Tarlov’s), 189 supraglenoid ganglion, 304 synovial, 189 Cystic enlargement, 29, 30 Cystometry, 129 Cystourethrography, 129 Cytoarchitecture of gray matter, 10–13
D Dandy–Walker syndrome, 87 Decompression sickness, 81 Deep tendon (muscle stretch) reflexes, 26, 204–205 Deep vein thrombosis (DVT), 108 Degenerative disease hypertrophic spinal disease, 60–61 diffuse idiopathic skeletal hyperostosis, 60–61 ossified posterior longitudinal ligament syndrome, 61 ligamentum flavium thickening/buckling, 59 radiculopathy related to, 171–172 rheumatoid arthritis, 59–60 Degenerative neuronal disorders, 82 DeJerine’s syndrome, 27 Dens fracture, 43–44 Depression, 110–111 Dermal sinus, 85–86 Dermatomal evoked potentials, in radiculopathy, 217 Dermatomes, 5, 201 Dermoid tumor, 70 Descending spinal cord pathways, 15–17 corticospinal tract, 15–17 nonpyramidal tracts, 17 Diabetes mellitus, as predisposing to entrapment, 277
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Diabetic radiculopathy, 193–194 Diastematomyelia, 85 Diffuse idiopathic skeletal hyperostosis (DISH), 60–61 Diplomyelia, 85 Discitis, radiculopathy related to, 190 Disk herniation, 50–53, 148, 177–183 classification of, 178–183 annular bulge (disk bulge), 178–180 disk extrusion, 180–182 disk protrusion (herniation), 180 free disk fragment (sequestered disk herniation), 182–183 experimental mechanisms of, 177–178 magnetic resonance imaging (MRI) in, 220–221 Dislocation, 48–49 bilateral cervical facet dislocation, 48–49 spinal dislocation/relocation, 49 unilateral facet dislocation, 49 Distal superficial radial nerve entrapment/cheiralgia paresthetica, 309–310 Distraction injuries, 38 Dorsal root ganglia anatomy, 166–167 Dorsal scapular nerve syndrome, 305 Double crush insult, 169–170, 271–272, 301 Dural sleeve anatomy, 165–166 Dura mater anatomy, 6–7 Dysautonomia and trophic changes, in radiculopathy, 206–207 Dysmorphism, intrinsic cord, 124 Dysraphism, occult spinal, 84–86 Dysreflexia, autonomic, 108–109
E Edema, spinal cord, 26 Electrical injury, 81 Electrodiagnostics, 112–116 of bladder function, 129–130 in entrapment, 283–284 late responses, 115 motor evoked potentials, 113–115 motor nerve conduction studies, 116, 215–216 needle electromyography (EMG), 115–116, 209–215 in radiculopathy, 209–217 needle electromyography, 209–215 nerve conduction studies, 215–216 somatosensory and dermatomal evoked potentials, 217 sensory nerve conduction studies, 116 somatosensory evoked potentials, 113, 217 Electromyography (EMG), 115–116 chronology of abnormalities in radiculopathy, 210–212 in entrapment, 283–284 late reflexes, 212–215 muscles with segmental localizing significance, 210 pelvic basin, 129–130 postsurgical findings, 212 in radiculopathy, 209–215 Elevated arm stress test (EAST), 287 Emboli, pulmonary, 108 Entrapment, see also Entrapment syndromes
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anatomical considerations, 253–266, see also Peripheral nerves; Plexuses autonomic nervous system, 261 biomechanical characteristics, 266 brachial plexus, 255–257 cervical plexus, 254–255 general organization of peripheral nerves and plexuses, 253–254
lumbar plexus, 257–259 lumbosacral plexus, 259–261 peripheral nerve anatomy, 261–264 peripheral nerve vascularity, 264–266 assessment, 281–284 electrodiagnostic findings, 283–284 examination, 281–282 history, 281 nerve percussion sign, 282–283 classification of nerve injuries, 266–268 axonotmesis, 267–268 neurapraxia, 266–267 neurotmesis, 268 physiologic conduction block, 266 clinical signs and symptoms, see Entrapment syndromes common disorders predisposing to, 275–278 AIDS/HIV, 278 diabetes mellitus, 277 general patterns of anatomic distribution, 276–277 respiratory insufficiency, 278 rheumatoid arthritis, 278 thyroid disorders, 277–278 uremia, 277 myotendinous, myofascial, and related contributions, 273–275 acute myofascial injury, 273 chronic injuries, 273–274 cumulative injury cycle, 274 inflammation, 275 pathophysiology, 268–275 compromised axonal transport, 271 cumulative trauma disorder (CTD), 273 double crush syndrome, 271–272 peripheral nerve response to injury, 268–270 whole nerve syndrome, 272–273 Entrapment syndromes, 284–334 abdominal/pelvic, 314–316 lower extremity, 317–334 anterior tarsal tunnel syndrome/deep peroneal nerve syndrome, 329–331 iliolumbar–lumbosacral ligament entrapment/lumbosacral tunnel syndrome, 322–323 medial tarsal tunnel syndrome, 331–333 meralgia paresthetica/inguinal tunnel syndrome (lateral femoral cutaneous syndrome), 320–321 Morton’s neuroma (metatarsalgia), 333–334 obturator nerve entrapment, 321–322 peroneal tunnel syndrome/entrapment at knee and fibular neck, 327–329 piriformis syndrome, 323–325 psoas entrapment/iliacus entrapment syndrome, 317–319 saphenous nerve syndrome/adductor tunnel syndrome, 325–327
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median nerve, 292–303 anterior interosseous nerve syndrome, 295–296 carpal tunnel syndrome, 296–303 pronator teres muscle syndrome, 293–295 supracondylar process syndrome, 292–293 posterior upper extremity, 303–310 brachialis/brachioradialis/radial nerve, 306–309 distal superficial radial nerve entrapment/cheiralgia paresthetica, 309–310 lateral intermuscular septum/radial nerve, 305–306 suprascapular nerve syndrome, 303–305 proximal upper extremity, 284–292 axillary tunnel entrapment, 290–291 cervicoaxillary (thoracic outlet syndrome), 285–287 costoclavicular entrapment syndrome, 289–290 costopectoral tunnel (hyperabduction) syndrome, 290 lateral antebrachial syndromes, 292 long thoracic nerve entrapment (scapular winging), 291 quadrangular (quadrilateral) space syndrome (lateral hiatus syndrome), 291–292 scalene entrapment syndrome, 287–289 ulnar nerve, 310–314 cubital tunnel syndrome (entrapment at elbow), 310–311 Guyon’s canal/ulnar nerve tunnel syndrome, 311–314 Ependymoma, 64 myxopapillary, 64 Epiconus syndrome, 146–146 Epidermoid and dermoid tumor, teratoma, 70 Epidural abscess, 72 Epidural hemorrhage, 50 Epidural lipomatosis, 64 Expansile lesions, 152 cysts arachnoid, 64 neuroenteric, 86 perineural (Tarlov’s), 189 synovial, 189 epidermoid and dermoid tumor, teratoma, 70 epidural abscess, 72 epidural lipomatosis, 64 extradural tumors, 70 chordoma, 70 lipoma, 70 lymphoma, 70 intradural extramedullary tumors, 67–70 meningioma, 68–70, 189–190 neural sheath tumor, 68, 183–188 intramedullary tumors, 64–67 astrocytoma and oligodendroglioma, 64–66 ependymoma, 64 hemangioblastoma, 66 metastatic, 70–72, 189–190 radiculopathy related to, 183–190 meningioma, 188–189 metastatic disease, 189–190 neurofibroma, 186–187 perineural (Tarlov’s) cysts, 189 schwannoma, 183–186 synovial cysts, 189
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spinal cord tumors, 64 syringomyelia, 62–64 of vertebral origin, 70 Extension teardrop fracture, 45 Extradural tumors, 70 chordoma, 70 lipoma, 70 lymphoma, 70
F Facet dislocation, cervical, 48–49 Failed back surgery syndrome, 175–176 Familial spastic paraplegia, 83 Femoral cutaneous nerve, 260 Fever, 111 Fibrosis iatrogenic (failed back surgery syndrome), 175–176 radiculopathy and, 172–173 Filopodia, 269 Fistulae, arteriovenous, 72–77 Flexion teardrop fracture, 45 Flexor tenosynovitis, 297 Foix–Alajouanine syndrome, 73–75 Foramen, intervertebral, anatomy, 163–164 Foramen magnum, clinical considerations with neurologic compromise below, 341–342 Foramen magnum (cranial-cervical) lesions, 151–152 Forestier’s (diffuse idiopathic) hyperostosis, 60–61 Fracture(s), 43–48 classification systems for, 39 dens, 43–44 hangman’s (bipedicular fracture of C2, traumatic spondylolisthesis of C2), 44 Jefferson of atlas (burst of C1), 44 pathomechanical intersegmental motion and, 44 patterns at any level of spine, 46–48 Chance (lap seatbelt, fulcrum) fracture, 47 endplate burst fracture, 46 neural arch fracture, 48 wedge (compression) fracture, 46–47 patterns of cervical, 44–46 extension teardrop fracture, 45 flexion teardrop fracture, 45 pillar fracture, 44–45 spinous process fracture (clay shoveler’s, coal miner’s), 44 posterior neural arch of C1, 43 upper cervical, 43 Frankel classification, 130 Free radical-mediated cell injury, 23 Frohse (arcade) /deep radial nerve entrapment syndrome, 306–309
Fulcrum (Chance, lap seatbelt) fracture, 47 Functional and laboratory assessment, 125–133 amniocentesis, 126–128 bladder function, 129–130 cystometry, 129 cystourethrography, 129 electrodiagnostic studies, 129–130
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uroflowometry, 130 blood and serum studies, 128 cerebrospinal fluid (CSF) evaluation, 126, 127 genetic assessment, 128–129 physical impairment, 130–133 ASIA/MSOP scale, 130 balance, 133 Benzel and Larson scale, 130 Frankel classification, 130 gait, 130–132 Japanese Orthopedic Association Cervical Myelopathy Score, 130 muscular performance, 132–133 range of motion (ROM), 130 sensibility, 133 pulmonary function, 125–126 Functional capacity evaluation, in radiculopathy, 218–219 Functional MRI, 119 F-wave EMG studies, 115, 213–214
G Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) contrast enhancement MRI, 118, 221 Gait assessment, 130–132 Ganglia, dorsal root, anatomy, 166–167 Genetic assessment, 128–129 Genitofemoral nerve syndrome, 319 Glacial instability, 43 Glioblastoma multiforme, 66 Gliosis and cavitation, 29–30 Glove-stocking configuration, 276 Glutaminergic-induced toxicity, 23–24 Gluteal nerve, 260 Gluteal nerve syndromes, 326 Gonyalgia paresthetica (saphenous nerve syndrome), 327 Gray matter, cytoarchitecture of, 10–13 Growth cone region, 269 Guyon’s canal/ulnar nerve tunnel syndrome, 311–314
H Hangman’s fracture (bipedicular fracture of C2, traumatic spondylolisthesis of C2), 44 Helical (spiral) computed tomography, 121 Hemangioblastoma, 66 Hematomyelia, 29–30, 50 Hemimyelopathy, 149 Hemiparesis, 97 Hemisection (Brown–Séquard) syndrome, 149, 150 Hemorrhage, 49–50 epidural, 50 hematomyelia and, 29–30, 50 subarachnoid, 50 subdural, 50 Herpes varicella-zoster (shingles), 194 Heterotopic ossification, 112 Hoffman’s sign, 99–100 H-reflex EMG studies, 115, 213, 277
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Human T-cell lymphotrophic virus I (tropical spastic paraparesis, HTLV-1), 77 Hyperabduction (costopectoral tunnel) syndrome, 290 Hyperostosis, diffuse idiopathic skeletal (DISH), 60–61 Hyperreflexia assessment, 97–100 in spinal shock, 25–26 Hyperthyroidism, peripheral neuropathy in, 277–278 Hypertrophic spinal disease, 60–61 diffuse idiopathic skeletal hyperostosis, 60–61 ossified posterior longitudinal ligament syndrome, 61 Hypoperfusion, in compression, 37 Hypotension central cord vascular syndrome and, 139 orthostatic, 107–108 Hypothyroidism, peripheral neuropathy in, 277
I Iatrogenic fibrosis (failed back surgery syndrome), 175–176
Idiopathic skeletal hyperostosis, diffuse (DISH), 60–61 Iliacus muscle syndrome, 319 Iliohypogastricus syndrome, 318 Ilioinguinal syndrome, 318 Iliolumbar–lumbosacral ligament entrapment/lumbosacral tunnel syndrome, 322–323 Imaging, 116–121 in carpal tunnel syndrome, 303 computed tomography (CT scan), 121 magnetic resonance angiography (MRA), 120 magnetic resonance imaging (MRI), 116–121 in central cord syndrome, 142 contrast enhancement of spinal nerve root, 221 in disk herniation, 220–221 enhancement of epidural venous plexus, 221–222 of muscular atrophy, 222–223 magnetic resonance myelography, 120 magnetic resonance spectroscopy (MRS), 119–120 neurosonography, 121 plain-film radiography, 121–122 quantitative considerations in spinal cord imaging, 122–125 central spinal canal measurements, 122–123 classification of spinal cord compression, 123–124 intramedullary signal patterns, 125 intrinsic cord dysmorphism, 124 spinal cord cross-sectional size and area, 124 spinal instability and vertebral translation, 123 in spinal stenosis, 58–59 Infarction, 28, 139–140 Infection, 77–78 Infection(s), 77–78 AIDS/HIV, 77–78, 194 biomechanical instability and, 42 Lyme disease, 78, 194–195 poliomyelitis, 145 radiculopathy in, 194–195 AIDS/HIV, 194 herpes varicella-zoster (shingles), 194 Lyme disease, 194–195
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tabes dorsalis (syphilis), 78 tropical spastic paraparesis (human T-cell lymphotrophic virus I), 77 Inflammation in entrapment neuropathy, 275 as predisposing to entrapment, 275 Inguinal referred pain, 208 Inguinal tunnel syndrome (lateral femoral cutaneous syndrome), 320–321 Instability biomechanical, 39–43 glacial, 43 Intersegmental motion patterns, classification of, 122 Interventional MRI, 120–121 Intervertebral disk herniation, 50–53, 178–183, see also Disk herniation Intervertebral foramen, anatomy, 163–164 Intradural extramedullary tumors, 67–70 meningioma, 68–70 neural sheath tumor, 68 Intramedullary tumors, 64–67 astrocytoma and oligodendroglioma, 64–66 ependymoma, 64 hemangioblastoma, 66 Intraoperative spinal sonography, 121 Intraparenchymal vascular anatomy, 9 Intrinsic cord dysmorphism, 124 Inversion recovery MRI, 118 Ischemia, 139–140 Ischemic myelopathy, 26–28 microvascular and arterial insufficiency, 27–28 spinal cord infarction, 28 venous infarction, 28
J Japanese Orthopedic Association Cervical Myelopathy Score, 130 Jefferson fracture of atlas (burst of C1), 44 Junction, peripheral nerve, anatomy, 165–166 Juvenile arteriovenous malformations, 73
K Kennedy’s disease, 83 Kinematic MRI, 118–119 Klippel–Feil syndrome, 87–88
L Laboratory assessment, 125–133, see also Functional and laboratory assessment Lap seatbelt (Chance, fulcrum) fracture, 47 Lateral antebrachial syndromes, 292 Lateral hiatus (quadrangular/quadrilateral space) syndrome, 291–292 Lateral intermuscular septum/radial nerve entrapment, 305–306 Lateral recess stenosis, 171–175
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Lateral spinothalamic tract, 13 Late responses assessment, 115 Lhermitte’s sign, 105–106 Ligamentum flavium thickening/buckling, 59 Ligamentus hyperostosis, 61 Lipoma, 70 Lipomatosis, epidural, 64 Long thoracic nerve entrapment (scapular winging), 291 Low back pain, 323–325 Lower extremity, chart of innervation, 348 Lower extremity entrapment syndromes, 317–334, see also under Entrapment syndromes Lower motor neuron lesions, 110 Lumbar disk herniation, 148, see also Disk herniation Lumbar plexus, 257–259 Lumbar transection injuries, 154–155 intact L1 neurologic (L1 functional) level, 154 intact L2 neurologic (L2 functional) level, 154 intact L3 neurologic (L3 functional) level, 154 intact L4 neurologic (L4 functional) level, 154–155 intact L5 neurologic (L5 functional) level, 155 Lumbosacral monoradiculopathy, 235–245 anatomic variants of lumbosacral nerve roots, 236–237 L1, 237–238 L2, 238 L3, 239–240 L4, 240–242 L5, 242–246 S1, 246 S2–S5, 246 Lumbosacral plexus, 259–261 Lyme disease, 78, 194–195 Lymphoma, 70, 145
M Magnetic resonance angiography (MRA), 120 Magnetic resonance imaging (MRI), 116–121 in carpal tunnel syndrome, 303 contrast enhancement, 118 of spinal nerve root, 221 in discitis, 190 in disk herniation, 220–221 enhancement of epidural venous plexus, 221–222 functional, 119 interventional, 120–121 inversion recovery, 118 kinematic, 118–119 magnetic resonance angiography (MRA), 120 magnetic resonance myelography, 120 magnetic resonance spectroscopy (MRS), 119–120 magnetization transfer, 119 of muscular atrophy, 222–223 in nerve root avulsion, 177 in radiculopathy, 219–223 rapid-sequence, 117 in tethered cord syndrome, 38 three-dimensional, 120 turbo echo, 117–118
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Magnetic resonance myelography, 120 Magnetic resonance spectroscopy (MRS), 119–120 Magnetization transfer MRI, 119 Maneuvers, Braggard’s, 202 Medial tarsal tunnel syndrome, 331–333 Median nerve, 255 Median nerve entrapment syndromes, 292–303, see also under Entrapment syndromes Meninges and compartments, anatomy, 6–8 arachnoid mater, 7 dura mater, 6–7 pia mater, 7 subarachnoid space and cerebrospinal fluid, 7–8 Meningioma, 68–70, 188–189 Meralgia paresthetica/inguinal tunnel syndrome (lateral femoral cutaneous syndrome), 320–321 Metabolic and nutritional myelopathy, 81 Metabolic neuropathies, 81 Metastatic neoplasms, 189–190, see also Expansile lesions Metastatic neoplasms, 70–72 Microvascular insufficiency, 27–28 Microvascular perfusion, 27 Monoparesis, 97 Morton’s neuroma (metatarsalgia), 333–334 Motion patterns, intersegmental, classification of, 122 Motor evoked potentials, 113–115 Motor fibers, of cervical plexus, 255 Motor neuron disease, 82–83 amyotrophic lateral sclerosis (ALS), 82, 145–146 Kennedy’s disease, 83 spinal muscular atrophy (SMA), 82–83 Motor neuron syndrome (combined anterior horn/pyramidal tract disease), 145–146 Multifocal cord syndrome, 146 Multiple sclerosis, 79, 151 Muscle stretch reflexes (MSRs), 98, 204–205 in spinal shock, 26 Muscular atrophy, in radiculopathy, 206 Muscular performance assessment, 132–133 Musculocutaneous nerve, 256 Myelocystocele, terminal, 87 Myelography computed tomographic (CT), 121 magnetic resonance, 120 Myelomalacia, 28–29 Myelomeningocele (spina bifida aperta), 84, 89 Myelopathy, see also specific subtopics and conditions in arteriovenous malformations, 72–76 assessment, 111–116 articular subluxation, 111–112 contractures, 112 neuropathic arthropathy, 112 osteoporosis, 112 Chiari malformations, 87 in congenital spinal anomalies, 83–87 caudal spinal anomalies, 87 occult spinal dysraphism, 84–86 neuroenteric cyst, 86 spinal (dorsal) dermal sinus, 85–86 split cord malformation, 84–85
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spina bifida aperta (myelomeningocele), 84, 89 in degenerative disease and stenosis, 55–62 hypertrophic spinal disease, 60–61 diffuse idiopathic skeletal hyperostosis, 60–61 ossified posterior longitudinal ligament syndrome, 61 ligamentum flavium thickening/buckling, 59 rheumatoid arthritis, 59–60 spondylotic and cervical spondylotic myelopathy, 55–59 in expansile lesions, 62–72 arachnoid cyst, 64 epidermoid and dermoid tumor, teratoma, 70 epidural abscess, 72 epidural lipomatosis, 64 extradural tumors, 70 chordoma, 70 lipoma, 70 lymphoma, 70 intradural extramedullary tumors, 67–70 meningioma, 68–70 neural sheath tumor, 68 intramedullary tumors, 64–67 astrocytoma and oligodendroglioma, 64–66 ependymoma, 64 hemangioblastoma, 66 metastatic, 70–72 spinal cord tumors, 64 syringomyelia, 62–64 of vertebral origin, 70 ischemic, 26–28 Klippel–Feil syndrome, 87–88 noncompressive, 76–83 autoimmune myelopathy, 81 decompression sickness, 81 degenerative neuronal disorders, 82 electrical injury, 81 familial spastic paraplegia, 83 infection, 77–78 AIDS/HIV, 77–78 Lyme disease, 78 tabes dorsalis (syphilis), 78 tropical spastic paraparesis (human T-cell lymphotrophic virus I), 77 metabolic and nutritional, 81 motor neuron disease, 82–83 amyotrophic lateral sclerosis (ALS), 82, 145–146 Kennedy’s disease, 83 spinal muscular atrophy (SMA), 82–83 multiple sclerosis, 79 paraneoplastic myelopathy, 82 postinfectious and postvaccination myelitis (transverse myelitis), 77 radiation myelopathy, 79–80 spinal arachnoiditis (adhesive arachnoiditis), 78–79 subacute combined degeneration, 81 toxic insult, 79 pathophysiology, 23–33, see also Pathophysiology scoliosis and, 89 transverse (complete spinal cord transection), 140–142 Myotatic reflex, 17–21 Myxopapillary ependymoma, 64
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N Needle electromyography, see Electromyography (EMG) Nerve(s) axillary, 256 common peroneal, 259–260 femoral cutaneous, 260 gluteal, 260 median, 255 musculocutaneous, 256 pudendal, 260–261 radial, 255–256 sciatic, 259 sural, 260 thoracic, 257 thoracodorsal, 256 tibial, 259 ulnar, 255 Nerve conduction studies motor nerve, 215 in radiculopathy, 215–216 sensory nerve, 215–216 Nerve injuries, classification of, 266–268 axonotmesis, 267–268 neurapraxia, 266–267 neurotmesis, 268 physiologic conduction block, 266 Nerve percussion sign, 282–283 Nerve roots anatomy, 161–167, see also Radiculopathy, anatomical considerations double crush insult to, 169–170 pathomechanics affecting, 169 sites of vulnerability, 168–169 Nerve root avulsion, 177 Nerve root irritability signs, 201–204 Neural sheath tumor, 68 Neurapraxia, 266–267 Neurilemoma, 68 Neuroenteric cyst, 86 Neurofibroma, 68, 186–187 Neurogenic bladder, 109–110, 155 Neurogenic claudication, 106–107 Neurogenic versus hemorrhagic shock, 25 Neurological levels, 151–155 cervical lesions, 152–154 intact C3 neurologic (C3 functional) level, 152 intact C4 neurologic (C4 functional) level, 152 intact C5 neurologic (C5 functional) level, 152–153 intact C6 neurologic (C6 functional) level, 153 intact C7 neurologic (C7 functional) level, 153 intact C8/T1 neurologic (C8/T1 functional) levels, 153–154 cranial-cervical (foramen magnum) lesions, 151 lumbar transection injuries, 154–155 intact L1 neurologic (L1 functional) level, 154 intact L2 neurologic (L2 functional) level, 154 intact L3 neurologic (L3 functional) level, 154 intact L4 neurologic (L4 functional) level, 154–155 intact L5 neurologic (L5 functional) level, 155 sacral transection injuries, 155
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intact S1 neurologic (S1 functional) level, 155 intact S2 neurologic level and below, 155 thoracic-intact lesions (mid-thoracic functional levels), 154 intact T12 (T12 functional) level, 154 Neuroma, 68 Morton’s (metatarsalgia), 333–334 Neuromuscular scoliosis, 89 Neuro-orthopedic tests and signs, 342–346 Neuropathic arthropathy (Charcot’s joint), 43–44, 112 Neurosonography, 121 Neurotmesis, 268 NMDA receptors, 23–24 Noncompressive myelopathy autoimmune myelopathy, 81 decompression sickness, 81 degenerative neuronal disorders, 82 electrical injury, 81 familial spastic paraplegia, 83 infection, 77–78 AIDS/HIV, 77–78 Lyme disease, 78 tabes dorsalis (syphilis), 78 tropical spastic paraparesis (human T-cell lymphotrophic virus I), 77 metabolic and nutritional, 81 motor neuron disease, 82–83 amyotrophic lateral sclerosis (ALS), 82, 145–146 Kennedy’s disease, 83 spinal muscular atrophy (SMA), 82–83 multiple sclerosis, 79 paraneoplastic myelopathy, 82 postinfectious and postvaccination myelitis (transverse myelitis), 77 radiation myelopathy, 79–80 spinal arachnoiditis (adhesive arachnoiditis), 78–79 subacute combined degeneration, 81 toxic insult, 79 Noncompressive radiculopathy, 193–195 in coagulopathies, 193 diabetic radiculopathy/polyradiculopathy, 193–194 infection, 194–195 Nonpyramidal tracts, 17 Nuclei, spinal cord, 17 Nutritional myelopathies, 81
O Obturator nerve entrapment, 321–322 Occult spinal dysraphism, 84–86 neuroenteric cyst, 86 spinal (dorsal) dermal sinus, 85–86 split cord malformation, 84–85 Oligodendroglioma, 64–66 Orthostatic hypotension, 107–108 Ossification, heterotopic, 112 Ossified posterior longitudinal ligament syndrome, 61 Osteomyelitis, radiculopathy related to, 190 Osteophytosis, 171–172 Osteoporosis, assessment of, 112
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Oxygen radicals, 23
P Pain cervicogenic (pseudo) angina, 209 combined radicular/vertebrogenic pain syndromes, 207–209 complex regional pain syndrome II (causalgia), 270 false visceral, 209 inguinal referred, 208 mechanisms of, 201 vertebrogenic (sclerotomal), 207 Pain assessment, 104–105 disorders associated with, 104 Lhermitte’s sign, 104–105 Pain band, 208 Pallesthesia, in carpal tunnel syndrome, 300 Paralytic scoliosis, 89 Paraneoplastic myelopathy, 82 Paraparesis, 97 tropical spastic (human T-cell lymphotrophic virus I, HTLV1), 77 Paraplegia, 141 familial spastic, 83 Paresis assessment, 97–100 in entrapment syndromes, 281 in radiculopathy, 205–206 Pathomechanics, of spinal cord injury, 35–36 Pathophysiology, 23–33, see also Physical mechanisms of injury cavitation and gliosis, 29–30 cellular, ionic, and biomolecular mechanisms, 23–24 cation-mediated cell injury, 24 free radical-mediated cell injury, 23 glutaminergic-induced toxicity, 23–24 programmed cell death (apoptosis), 24 ischemic myelopathy, 26–28 microvascular and arterial insufficiency, 27–28 spinal cord infarction, 28 venous infarction, 28 myelomalacia, 28–29 spinal cord atrophy, 30–31 spinal cord edema, 26 spinal shock, 25–26 stages of spinal cord injury, 24–25 Peau d’orange effect, diagnostic significance, 207 Pelvic basin electromyography, 129–130 Perfusion, microvascular, 27 Perineural (Tarlov’s) cysts, 189 Perineural fibroblastoma, 68 Peripheral nerve entrapment, see Entrapment Peripheral nerve junction, anatomy, 165–166 Peripheral nerves, see also Entrapment anatomy, 261–264 autonomic nervous system, 261 biomechanical characteristics, 266 brachial plexus, 255–257 nerve branches arising from upper trunk, 257 nerves arising directly from nerve roots or plexus, 256–257
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nerves comprising, 255–256 nerves formed from medial and lateral cords, 257 cervical plexus, 254–255 motor fibers within cervicobrachial plexus, 255 in relationship to cranial nerves, 254–255 sensory innervation to head and neck, 254 sensory innervation to neck and shoulders, 254 classification of nerve injuries, 266–268, see also Nerve injuries general organization, 253–254 of plexuses, 254 posterior primary divisions, 253–254 lumbar plexus, 257–259 lumbosacral plexus, 259–261 response to injury, 268–270 axonal regeneration, 269–270 Wallerian degeneration, 268–269 screening tests for, 286 vascularity, 264–266 Peroneal tunnel syndrome/entrapment at knee and fibular neck, 327–330 Phalen’s test, 282 Phospholipase A2, in chemical radiculitis, 170–171 Physical impairment assessment, 130–133 ASIA/MSOP scale, 130 balance, 133 Benzel and Larson scale, 130 Frankel classification, 130 gait, 130–132 Japanese Orthopedic Association Cervical Myelopathy Score, 130 muscular performance, 132–133 range of motion (ROM), 130 sensibility, 133 Physical mechanisms of injury, 35–55 disk herniation as, 50–53 pathomechanics, 35–36 spinal cord, 36–38 compression, 37–38 concussion, 37 contusion, 37 penetrating/transecting injuries, 38 tethering and distraction injuries, 38 spinal hemorrhage and, 49–50, see also Hemorrhage vertebral, 38–49 causes of biomechanical instability, 39–43 dislocation, 48–49, see also Dislocation and specific types fracture, 43–48, see also Fracture(s) and specific types Physiologic conduction block, 266 Pia mater, anatomy, 7 Pillar fracture, 44–45 Pilomotor effect, diagnostic significance, 207 Piriformis syndrome, 323–325 Plain-film radiography, 121–122 Plexus brachial, 255–257 nerve branches arising from upper trunk, 257 nerves arising directly from nerve roots or plexus, 256–257 nerves comprising, 255–256 nerves formed from medial and lateral cords, 257
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cervical, 254–255 motor fibers within cervicobrachial plexus, 255 in relationship to cranial nerves, 254–255 sensory innervation to head and neck, 254 sensory innervation to neck and shoulders, 254 lumbar, 257–259 lumbosacral, 259–261 sacral, 260 sciatic, 260 Poliomyelitis and post-polio syndrome, 146 Popliteal entrapment syndrome, 329 Positive nerve percussion (Tinel’s) sign, 270, 282, 294, 309 Posterior atlantodens interval (PADI), 60 Posterior columns, 13 Posterior cord syndrome, 143–145 posterolateral cord syndrome, 144–145 Posterior neural arch fracture of C1, 43 Posterior spinal artery, 8–9 Posterior spinal artery syndrome (PSAS), 139 Posterior upper extremity entrapment syndromes, 303–310, see also under Entrapment syndromes Postinfectious and postvaccination myelitis (transverse myelitis), 77 Programmed cell death (apoptosis), 24 Pronator teres muscle syndrome, 293–295 Proprioception, loss of, 144–145 Prostaglandin E2, 26 Prostaglandin I2, in entrapment neuropathy, 275 Proximal upper extremity entrapment syndromes, 284–292, see also under Entrapment syndromes Psoas entrapment/iliacus entrapment syndrome, 317–319 Psychological considerations, 110–111 Pudendal nerve, 260–261 Pudendal nerve syndrome, 319 Pulmonary emboli, 108 Pulmonary function assessment, 125–126
Q Quadrangular (quadrilateral) space syndrome (lateral hiatus syndrome), 291–292 Quadriparesis, 97 Quantitative considerations in spinal cord imaging, 122–125 central spinal canal measurements, 122–123 classification of spinal cord compression, 123–124 intramedullary signal patterns, 125 intrinsic cord dysmorphism, 124 spinal cord cross-sectional size and area, 124 spinal instability and vertebral translation, 123
R Radial nerve, 255–256 Radiation myelopathy, 79–80 Radiculomedullary arteries, 8 Radiculomedullary artery syndrome (RAS), 139 Radiculopathy anatomical considerations, 161–167 blood supply, 166
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dorsal root ganglia, 166–167 dural sleeve and peripheral nerve junction, 165–166 intervertebral foramen, 163–165 assessment, 209–223 electrodiagnostics, 209–217 needle electromyography (EMG), 209–215 nerve conduction studies, 215–216 somatosensory and dermatomal evoked potentials, 217 functional capacity evaluation, 218–219 magnetic resonance imaging (MRI), 219–223 cauda equina syndrome, 246–247 cervical syndromes, 223–233 C1, 223 C2, 223–224 C3, 224 C4, 224 C5, 224–229 C6, 229–231 C7, 231 C8, 233 lumbar and sacral monoradiculopathy, 235–245 anatomic variants of lumbosacral nerve roots, 236–237 L1, 237–238 L2, 238 L3, 239–240 L4, 240–242 L5, 242–246 S1, 246 S2–S5, 246 noncompressive, in coagulopathies, 193 pathophysiologic mechanisms biochemical, 170–171 compressive, 167–193 acquired lateral recess stenosis and vascular stasis, 173–175 disk herniation, 177–183, see also Disk herniation expansile lesions, 183–190, see also Expansile lesions and specific lesions failed back surgery syndrome, 175–176 fibrosis in, 172–173 nerve root double crush, 169–170 osteomyelitis and discitis, 190 pathomechanics affecting nerve root complex, 169 sites of nerve root vulnerability, 168–169 spinal degeneration, 171–172 spondylolisthesis, 190–193 trauma, 176–177 noncompressive, 193–195 diabetic radiculopathy/polyradiculopathy, 193–194 infection, 194–195 signs and symptoms, 201–249 combined radicular/vertebrogenic pain syndromes, 207–209 dysautonomia and trophic changes, 206–207 muscular atrophy, 206 nerve root irritability signs, 201–204 paresis, 205–206 reflex abnormalities, 204–205 sensory abnormalities, 201 thoracic monoradiculopathy, 233–235 T1, 233 T2–T12, 233–235
Radiography, plain-film, 121–122, see also Imaging Range of motion (ROM) assessment, 130 Rapid-sequence MRI, 117 Raynaud’s phenomenon, 299 Reflex abnormalities, in radiculopathy, 204–205 Reflexes, see also Electromyography (EMG) assessment, 100–104 Babinski’s response, 102–104 in spinal shock, 25–26 superficial reflexes, 100–101 crossed extensor, 26 late, 212–215 muscle stretch (MSRs, deep tendon reflexes), 26, 204–205 Reperfusion injury, 27 Repetitive motion injury, 273–274 Repetitive stress injury, 310–311 Respiratory impairment, 109 Rheumatoid arthritis, 41–42, 59–60, 278 Romberg sign, 144 Rostrocaudal subluxation, 172
S Sacral plexus, 260 Sacral sparing, 107 Sacral transection injuries, 155 intact S1 neurologic (S1 functional) level, 155 intact S2 neurologic level and below, 155 Saphenous nerve syndrome (gonyalgia paresthetica), 327 Saphenous nerve syndrome/adductor tunnel syndrome, 325–327 Scalene entrapment syndrome, 287–289 Scapular winging (long thoracic nerve entrapment), 291 Schwannoma, 68, 183–186 Sciatic nerve, 259 piriformis syndrome, 323–325 Sciatic plexus, 260 SCIWORA syndrome (spinal cord injury without radiographic abnormality), 39 Sclerosis, amyotrophic lateral (ALS), 82, 145–146 Scoliosis, 89 Seatbelt (Chance, fulcrum) fracture, 47 Segmental anatomy of spinal cord, 5–6 Sensibility assessment, 133 Sensory abnormalities assessment, 104 in radiculopathy, 201 Sensory innervation of head and neck, 254 of neck and shoulders, 254 Sensory nerve action potential (SNAP), 112, 215, 275, see also Electrodiagnostics; Electromyography (EMG) Sequestered disk herniation (free disk fragment), 182–183 Sexual function, 110 Shock hemorrhagic versus neurogenic, 25 spinal, 25–26, 109 Signs Bakody’s, 202 common neuro-orthopedic, 342–346, see also specific signs
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Lhermitte’s, 105–106 nerve percussion, 282–283 nerve root irritability, 201–204 neuro-orthopedic, 342–346 Romberg, 144 Tinel’s (nerve percussion), 270, 282, 294, 309 Trommer’s, 99–100 Skin complications, 110 Somatosensory evoked potentials, 113 in radiculopathy, 217 Space, subarachnoid, 7–8 Spasticity, clonus, and hyperreflexia assessment, 97–100 Spectroscopy, magnetic resonance (MRS), 119–120 Spina bifida aperta (myelomeningocele), 84, 89 Spinal accessory nerve (cranial nerve XI), 150 Spinal arachnoiditis (adhesive arachnoiditis), 78–79 Spinal automatism, reflexes of, 100–102 Spinal cord, elasticity of, 35 Spinal cord atrophy, 30–31 Spinal cord compression, see Compression Spinal cord concussion, 37 Spinal cord contusion, 37 Spinal cord edema, 26 Spinal cord injury, see also Spinal cord syndromes assessment, 97–137 autonomic and other system considerations, 107–111 autonomic dysreflexia, 108–109 bowel and bladder dysfunction, 109–110 cardiac complications, 109 deep vein thrombosis (DVT), 108 orthostatic hypotension, 107–108 psychological considerations, 110–111 respiratory considerations, 109 sexual function, 110 skin complications, 110 Babinski’s response, 25–26, 81, 102–104, 149 fever, 111 neurogenic claudication, 106–107 pain, 104–105 disorders associated with, 104 Lhermitte’s sign, 104–105 reflexes, 100–104 sacral sparing, 107 sensory abnormalities, 104 spasticity, clonus, and hyperreflexia, 97–100 superficial, 100–101 Spinal cord pathways, anatomy, 13–17 autonomic pathways, 17 clinically important ascending, 13–15 lateral spinothalamic tract, 13 other, 13–15 posterior columns, 13 clinically important descending, 15–17 corticospinal tract, 15–17 nonpyramidal tracts, 17 Spinal cord syndromes, 139–157, see also Neurological levels anterior cord syndrome, 143 anterior horn syndrome (progressive muscular atrophy), 145– 146
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combined anterior horn/pyramidal tract disease (motor neuron syndrome), 145–146 polio and post-polio syndrome, 146 central cord syndrome, 142 cervicomedullary syndrome, 148–151 complete spinal cord transections (transverse myelopathy), 140–142 conus medularis syndrome, 146–148 hemisection (Brown–Séquard) syndrome, 148, 149 multifocal cord syndrome, 146 posterior cord syndrome, 143–145 posterolateral cord syndrome, 144–145 vascular, 139–140 anterior spinal artery syndrome (ASAS), 139 central cord vascular syndrome (CCVS), 139 posterior spinal artery syndrome (PSAS), 139 radiculomedullary artery syndrome (RAS), 139 Spinal cord tumors, 64 Spinal (dorsal) dermal sinus, 85–86 Spinal instability, imaging considerations in, 123 Spinal muscular atrophy (SMA), 82–83 Spinal shock, 25–26, 109, 141 Spinal stenosis, 55–59, see also Spondolytic myelopathy Spinal venous plexus, 9–10 Spinothalamic tract, lateral, 13 Spinous process fracture (clay shoveler’s, coal miner’s), 44 Spiral (helical) computed tomography, 121 Split cord malformation, 84–85 Spondylitis, ankylosing, 176 Spondylolisthesis radiculopathy related to, 190–193 traumatic of C2 (hangman’s fracture, bipedicular fracture of C2), 44 Spondylotic myelopathy, 55–59 clinical signs, symptoms, and pattern of progression, 57–58 clinical findings, 58 diagnostic imaging, 58–59 differential considerations pathomechanisms, 56–57 prevalence, 55–56 Stages of spinal cord injury, 24–25 Stenosis, lateral recess, 171–175 Stocking-glove configuration, 276 Straight leg raise test, 202 Stroke in evolution (SIE), 27 Subacute combined degeneration, 81 Subarachnoid hemorrhage, 50 Subarachnoid space, 7–8 Subdural hemorrhage, 50 Subluxation articular, 111–112 rostrocaudal, 172 Substance P, 26 Superficial peroneal nerve syndrome (mononeuralgia), 330 Superficial reflexes, 100–102 Supracondylar process syndrome, 292–293 Supraglenoid ganglion cysts, 304 Suprascapular nerve syndrome, 303–305 Sural nerve, 260 Sural nerve syndrome, 330
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Synovial cysts, 189 Syphilis (tabes dorsalis), 78 Syringomyelia, 62–64
Treponema pallidum, 78 Trommer’s sign, 99–100 Tropical spastic paraparesis (human T-cell lymphotrophic
T
Tumors, see Expansile lesions and specific lesions Turbo echo MRI, 117–118
virus I), 77
Tabes dorsalis (syphilis), 78 Tarlov’s (perineural) cysts, 189 Tarsal tunnel syndrome, 331–333 Teardrop fracture extension, 45 flexion, 45 Telangiectasia, capillary, 72 Teratoma, 70 Terminal myelocystocele, 87 Tests abduction external rotation (AER), 287 common neuro-orthopedic tests and signs, 342–346 elevated arm stress test (EAST), 287 peripheral nerve screening, 286 Phalen’s, 282 straight leg raise, 202 Tethered cord syndrome, 37, 38 Tetraplegia, 141 Thoracic-intact lesions (mid-thoracic functional levels), 154 intact T12 (T12 functional) level, 154 Thoracic monoradiculopathy, 233–235 T1, 233 T2–T12, 233–235 Thoracic nerve, 257 Thoracic outlet (cervicoaxillary) syndrome, 285–287 Thoracic spine, critical zone of, 28, 29 Thoracodorsal nerve, 256 Three-dimensional MRI, 120 Thrombosis, deep vein (DVT), 108 Thyroid disorders, as predisposing to entrapment, 277–278 Tibial nerve, 259 Tinel’s (nerve percussion) sign, 270, 282, 294, 309 Toxic insult, 79 Tract corticospinal, 15–17 lateral spinothalamic, 13 nonpyramidal, 17 Transient ischemic attack (TIA), 27 Transverse myelitis (postinfectious and postvaccination myelitis), 77 Transverse myelopathy (complete spinal cord transection), 140–142
Trauma, see also Physical mechanisms of injury radiculopathy related to, 176–177 types of, 36–38 compression, 37–38 concussion, 37 contusion, 37 penetrating/transecting injuries, 38 tethering and distraction injuries, 38 Traumatic spondylolisthesis of C2 (hangman’s fracture, bipedicular fracture of C2), 44 T-reflex EMG studies, 115, 214–215
Black process 45.0° 150.0 LPI
U Ulnar nerve, 255 Ulnar nerve entrapment syndromes, 310–314, see also under Entrapment syndromes Ulnar nerve tunnel (Guyon’s canal) syndrome, 311–314 Ultrasound in carpal tunnel syndrome, 303 imaging applications, 121 Unilateral cervical facet dislocation, 48–49 Upper extremity, chart of innervation, 347 Upper motor neuron lesions, 142 Uremia, as predisposing to entrapment, 277 Uroflowometry, 130
V Vascular anatomy of spine, 8–10 extrinsic, 8–9 anterior and posterior spinal arteries, 8–9 radiculomedullary arteries, 8 intraparenchymal, 9 spinal venous plexus, 9–10 Vascularity, of peripheral nerves, 264–266 Vascular malformations, 72–77 Vascular spinal cord syndromes, 139–140 anterior spinal artery syndrome (ASAS), 139 central cord vascular syndrome (CCVS), 139 posterior spinal artery syndrome (PSAS), 139 radiculomedullary artery syndrome (RAS), 139 Vascular watershed (border) zones, 27–28 Vasculitis, in rheumatoid arthritis, 278 Venous spinal cord infarction, 28 Vertebrae, 38–49, see also Biomechanical instability; Dislocation; Fracture(s) causes of biomechanical instability, 39–43 dislocation, 48–49 fracture, 43–48, see also Fracture and specific types tumors of, 70 Vertebrogenic (sclerotomal) pain, 207 Visceral pain, radiculopathic/vertebrogenic, 209 Vitamin B12 deficiency, 81, 144 Vitamin E, in preventing reperfusion injury, 27
W Wallerian degeneration, 268–269 Watershed (border) vascular zones, 27–28 Whiplash injury, 176–177 White matter, 3 Whole nerve syndrome, 271–272
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