Veterinary Diagnostic Imaging - The Dog and Cat

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Veterinary Diagnostic Imaging: The Dog and Cat Copyright © 2003, Mosby, Inc. All rights reserved.

ISBN 0-323-01205-1

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permissions may be sought directly from Elsevier’s Health Sciences Rights Department in Philadelphia, PA, USA: phone: (+1) 215 238 7869, fax: (+1) 215 238 2239, e-mail: [email protected]. You may also complete your request on-line via the Elsevier Science homepage (http://www.elsevier.com), by selecting ‘Customer Support’ and then ‘Obtaining Permissions.’

NOTICE Veterinary Medicine is an ever-changing field. Standard safety precautions must be followed, but as new research and clinical experience broaden our knowledge, changes in treatment and drug therapy may become necessary or appropriate. Readers are advised to check the most current product information provided by the manufacturer of each drug to be administered to verify the recommended dose, the method and duration of administration, and contraindications. It is the responsibility of the licensed prescriber, relying on experience and knowledge of the patient, to determine dosages and the best treatment for each individual patient. Neither the publisher nor the author assumes any liability for any injury and/or damage to persons or property arising from this publication.

Library of Congress Cataloging-in-Publication Data Farrow, Charles S. Veterinary diagnostic imaging: the dog and cat / Charles S. Farrow. p.; cm. Includes bibliographical references and index. ISBN 0-323-01205-1 (alk. paper) 1. Dogs–Diseases–Diagnosis. 2. Cats–Diseases–Diagnosis. 3. Veterinary diagnostic imaging. I. Title. [DNLM: 1. Dog Diseases–radionuclide imaging. 2. Cat Diseases–radionuclide imaging. 3. Cat Diseases–ultrasonography. 4. Diagnostic Imaging–veterinary. 5. Dog Diseases– ultrasonography. SF 991 F246v 2003] SF991 .F38 2003 636.7¢08960754–dc21 2002041063 Acquisitions Editor: Liz Fathman Developmental Editor: Kristen Mandava Publishing Services Manager: Pat Joiner Project Manager: Rachel E. Dowell Senior Designer: Mark A. Oberkrom Interior Designer: Joan Wendt Cover Design: Studio Montage Printed in China Last digit is the print number: 9

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This book is dedicated to the heroic passengers and aircrew of United Airlines flight 93, who on September 11th, 2001, made their last stand in the sky. May God bless them.

About This Book

First and foremost this is a book about veterinary medical imaging. Although there are smatterings of medicine, surgery, and clinical pathology, you will need to read elsewhere for detailed accountings of such matters.

Content and Credit The backbone of this book has been constituted from the articles published in the American Journal of Veterinary Radiology & Ultrasound from 1963 to the present, nearly all of which are included among the references. In most instances I also included the name of the principal authors in the text (as well as in the chapter references) to properly credit the work and for the convenience of the reader. To provide a contemporary perspective beyond that of the “Journal,” I incorporated selected material from the publications of organizations such as the American Veterinary Medical Association, American Animal Hospital Association, and Journal of Small Animal Practice.

although we will soon have our own in-house MR imager. The majority of these examinations are of the brain and spinal cord, mostly tumors and disks. We rarely perform nuclear medicine, and as a consequence have only limited clinical material. Because radiation therapy is now a specialty in its own right, it has been omitted altogether.

“RDIs”: A Rational Substitute for Roentgen Signs In nearly three decades as a radiologist I have sought to devise a coherent, integrated method for teaching and learning radiographic fundamentals. To this end I have developed a series of radiographic disease indicators, or RDIs, for each radiology subspecialty. These diagnostic building blocks form the basis for radiologic diagnosis, much as words comprise the substance of a sentence. You will be introduced to an appropriate list of RDIs at the beginning of each section, and then see them applied in the subsequent chapters.

Organization

Figures and Captions

Given the anatomic foundation on which all forms of medical imaging are predicated, it is clear that any book on the subject must be organized on a similar basis. Accordingly, Veterinary Medical Imaging is divided into 7 sections: (1) Extremities; (2) Skull, Brain, Eye, and Ear; (3) Spine; (4) Hips and Pelvis; (5) Throat, Neck, and Thorax; (6) Heart; and (7) Abdomen. Each section is in turn divided into chapters—77 in all. To facilitate comprehension, as well as rapid reference, series of facts have been enumerated within individual sentences, presented as bulleted and numbered lists, or tabulated, depending on their number and complexity.

The medical images in a book such as this are in many respects like the actors in a play; they provide a means of expression for the playwright. To this end I tried to present the material in a more “intimate” fashion, incorporating wherever possible both orientation and closeup views, and in the case of the extremities, normal comparison views from the opposite limb. Instead of arrows to identify the salient points in an image, I employed electronic emphasis zones, hopefully making it even easier to appreciate the lesion, while obscuring none of its detail. As an aside, my students refer to this method of pointing out pathology, which I also use in the classroom, as the “electronic hot lamp.” Furthermore, I tried not only to portray a wide variety of disorders, but also to include an ample number of variants, especially of the more commonly encountered diseases such as osteochondritis of the

Imaging Emphasis The emphasis in this book is on radiology and ultrasound, just as in our hospital. Currently we perform MRI and CT examinations out of hours at local hospitals,

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elbow where lesions can range from the obvious, typically shown in most textbooks, and termed “classics,” to the obscure that often only experts can detect. Finally, with respect to captions, I tried to keep them as brief as possible so as not to try the patience of the reader. And to even further expedite the process, I bolded the diagnosis or key point, providing a “diagnosis-at-a-glance.”

Terminology The reader will perhaps note some peculiarities with respect to the anatomic nomenclature, especially in Section 1: The Extremities; these are deliberate and reflect my desire to simplify an increasingly complex (and at times unwieldy) anatomic lexicon. Please read and consider the following proposal, try it out, and be kind enough to let me know what you think—I am open to suggestions. Radiographic Views • Lateral radiographs of the limbs are described as lateral views, or lateral oblique views (as necessary). The term lateromedial is unnecessary since it is understood that the x-ray beam will penetrate the part in this manner. • Dorsopalmar, dorsoplantar, and craniocaudal radiographs will all be termed frontal views, or frontal

oblique views (as required). Changing terminology at the level of the radiocarpal and tibiotarsal joints is both cumbersome and confusing, especially to novices. Because images made from front to back are nearly indistinguishable from those made from back to front—very minor object-film and magnification considerations notwithstanding—there is no need for terms such as palmarodorsal and plantarodorsal. Extremital Anatomy • Shoulder or shoulder joint to replace humeral or scapulohumeral joint. • Elbow or elbow joint to replace cubital or humeroradial/humeroulnar joint. • Radiocarpal joint to replace antibrachiocarpal joint. • Forepaw to replace manus. • Hip or hip joint to replace coxofemoral or coxal joint. • Knee or knee joint to replace stifle or femorotibial joint. • Tibiotarsal joint to replace tarsocrural joint. • Hindpaw to replace pes. For those teaching radiology, to include those explaining medical images to owners, I recommend that whatever terminology is employed, it satisfy the following three criteria: simple, clear, and brief. Charles S. Farrow

Acknowledgment

Many talents are required to write, assemble, and publish a book such as this: author, medical photographer, editor, and compositor, to name only a few. But perhaps most important among this company, and often the most overlooked, is the project manager, the individual who brings everything together, solves problems, listens to excuses, keeps the project on track and on time—and all without hurting anyone’s feelings! Ours is the best, Rachel Dowell. Thanks for everything, Chuck Farrow

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S E C T I O N

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The Extremities

C h a p t e r

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Extremital Radiographic Disease Indicators

The following radiographic abnormalities are reliable indicators of extremital disease, or radiographic disease indicators (RDIs).

❚❚❚ PERIOSTEAL NEW BONE New Bone: The Term One of the common attributes of many different skeletal lesions is the presence of new bone, that is, bone that has developed as a direct or indirect result of an injury, infection, tumor, or some other local or systemic disease. Because the majority of new bone is produced by the periosteum (inner layer), it is often referred to as periosteal new bone or periosteal new bone formation. Most simply, it may be described as bone deposition. Regardless of the term used, the importance lies in what it represents: a response to an abnormal stimulus that is sometimes brief, often repeated, and occasionally sustained. In all cases, it is a stimulus that causes the bone to grow anew, in some instances repairing, and in others strengthening (or defending) it.

Other Related Terms Other terms also deserve mention because of their limitations, ambiguities, or deficiencies rather than for their virtues. Bone reaction: There may be two types: productive or destructive; thus the term bone reaction is ambiguous if not qualified. Sclerosis or sclerotic: Bone that appears excessively white radiographically; this term is often used to describe abnormal subchondral bone. This term is best replaced with increased bone density or opacity. Eburnation or eburnated: Smooth, polished, ivory-like bone surface; this term is often used to describe the articular surfaces of arthritic joints, and implies a complete loss of articular cartilage. This term appears better suited to the sense of touch than that of sight. Increased density: Bone that is radiographically lighter than normal and synonymous with increased opacity. Decreased density: Bone that is radiographically darker than normal and synonymous with decreased opacity. 1

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SECTION I ❚❚❚ The Extremities

Radiodense or radiodensity, radiolucent or radiolucency: The prefix radio- is redundant because it is understood that such observations pertain to a radiograph.

Origins of New Bone New bone may be created from existing bone on either the inner or outer osseous membranes: the endosteum and periosteum, beneath the joint cartilage; the subchondrium, along the joint margins; the periarticular region, on the surface of the epiphysis adjacent to the articular surface; the extraarticular region; and within muscle (myositis ossificans). Bone may also be produced by some primary bone tumors such as osteosarcoma, chondrosarcoma, and fibrosarcoma.

New Bone Stimuli Stress. As first elucidated by Wolf, bone is a highly adaptable and surprisingly labile tissue, which is amply demonstrated by the developing appendicular skeleton.1 For example, the distal ulnar growth plate of a young puppy may be fractured, and as a result, cease to grow. As the inevitable bony curvatures and dislocations develop, the affected long bone cortices begin to change or remodel through caudal and medial thickening and cranial and lateral thinning in the face of the changing force lines and weight distribution. Trabeculae become realigned, and subchondral plates become reinforced in an effort to cope with the new anatomic realities (Figure 1-1). Similar restructuring occurs after part of a bone has been surgically removed. For example, with a femoral head and neck ostectomy, the greater trochanter elongates, tapers, and aligns itself more closely with the

Figure 1-1 • Lateral and frontal views of a deformed midforelimb; the result of an earlier distal ulnar growth plate fracture, subsequent premature physeal closure, and secondary radial bowing.

femoral shaft. Concurrently the acetabulum atrophies and loses density as its mineral content is withdrawn in the absence of articular contact (Figure 1-2). Stress, in the form of weight bearing with related muscular contraction-relaxation, plays a dominant role in fracture healing, gradually incorporating calluses and eliminating angulations, so that in a majority of instances, even in the case of severely comminuted fractures, the damaged bone is largely restored (Figure 1-3). Injury. One needs only to observe a fracture callus to appreciate the potency of injury as a stimulus for new bone formation (Figure 1-4). After the initial repair is achieved, renewal of normal internal and external bone stress initiates, mediates, and maintains the process of bone restoration, often to the extent that the original injury defies recognition some months later. Ischemia, whether or not induced by injury, also stimulates osteogenesis, as exemplified by compartmental syndrome. Infection. Slowly developing, localized osteomyelitis usually allows the affected bone sufficient time to construct a bony perimeter around the lesion, which is termed an involucrum (Figure 1-5). Although substantive, such defensive bulwarks rarely achieve true “containment.” Some authors have termed this type of new bone reactive bone, a loosely mechanistic label that is redundant because all new bone reacts to one or more stimuli.

Figure 1-2 • Close-up frontal view of the proximal femoral stump in a cat 4 years after fracture and surgical removal. The elongated shapes of the greater and lesser trochanters reflect the structural adaptation of these muscular moorings to the removal of the femoral head and neck. The washed-out appearance of the acetabulum is the result of secondary demineralization caused by the removal of the opposing articular surface.

CHAPTER 1 ❚❚❚ Extremital Radiographic Disease Indicators

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A

Figure 1-3 • Full-length frontal view of a healed femoral fracture still encased in a lengthy callus months after the injury. In time, however, most calluses completely disappear by incorporating into the adjacent cortex, thereby restoring the bone to its former appearance.

B Figure 1-4 • A, A thick, smoothly surfaced callus surrounds the distal femur. The callus is the result of a badly comminuted fracture 3 months earlier. B, Lateral (left) and frontal (right) images of a badly displaced, untreated proximal humeral gunshot fracture that has healed end-to-side; like most such fracture calluses, the new bone deposition is asymmetric, reflecting a redistribution of mechanical forces on the limb.

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SECTION I ❚❚❚ The Extremities

Figure 1-5 • Close-up frontal views of the carpi of a dog quilled 6 weeks earlier show a spherical lucency in the bottom center of the right radial carpal bone (left), surrounded by a sclerotic ring (emphasis zone), indicating a localized osteomyelitis; the opposite normal carpus is provided for comparison.

Figure 1-7 • Lateral view of a tibial osteosarcoma shows cloudlike fronds of tumor bone extending outward from the diaphysis.

Soft tissue infections, if severe or chronic enough, cause bone to form beneath the periosteum, often termed periosteal new bone formation, or more simply, periosteal new bone (Figure 1-6). Rarely are bacteria actually residing and replicating in the bone in such instances; rather, the periosteum has been stimulated by the surrounding infection, often with associated thrombosis of portions of the periosteal blood supply.

Figure 1-6 • Frontal view of the distal antibrachium, carpus, and metacarpus show periosteal new bone formation on the outer surfaces of the distal radius, fifth metacarpal bone, and proximal part of the first digit. Moderate regional soft tissue swelling is the result of cellulitis stemming from bite wounds, prompting the described periostitis.

Malignant Bone Lesions. Some tumors are capable of producing bone, including osteosarcoma, chondrosarcoma, and fibrosarcomas (Figure 1-7). Appropriately, such tissue is termed tumor or cancer bone, to distinguish it from defensive bone produced by the host in the case of infection. Unfortunately and in contrast to most bone infections, tumors grow so rapidly that there is usually insufficient time to mount and sustain a defensive bony perimeter, so involucra and sequestra are rarely seen (Figure 1-8). Aging New Bone. In critically evaluating new bone, temporal considerations are often important. For example, is the estimated age of an observed bone deposit consistent with the time elapsed since the presumed injury? Or is an observed new bone deposit a relevant or incidental finding?

CHAPTER 1 ❚❚❚ Extremital Radiographic Disease Indicators

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Potential conclusions that may be reached from estimates of new bone age include: • Clinical relevancy • Historical compatibility • Lesion activity or inactivity

Morphologic Observations Configuration. The amount of observed new bone may be great or small, and its shape quite variable. It may be flat and closely applied to the outer cortical surface over a wide area, or it may project outwardly at a sharp angle from a narrow base, the latter situation termed an osteophyte. Margination. The surface of new bone deposits ranges from thick to thin, and from smooth to rough— features that are often reliable indicators of new bone maturity. Density. Like margination, new bone density can be used to estimate the maturity of new bone. In general, the denser the new bone, the older it is.

A

Estimating the Age of New Bone Deposits Immature New Bone. Immature new bone initially resembles fine strands of newly planted grass emerging from the cortical surface, or alternatively, the tips of the bristles of a paintbrush seen in profile. In a week or so, the new bone begins to assume a denser, rougher looking surface. Bone with this appearance has usually been produced within the past month or so (Figures 1-9 and 1-10). Developing New Bone. Developing new bone can assume a variety of appearances, ranging from even layering to interrupted, variably-sized bony mounds (Figures 1-11 and 1-12); at other times, a series of individual blocks of bone forms at right angles to the cortex, forming what is sometimes referred to as a palisade. New bone of this type is usually between 1 and 3 months old.

B Figure 1-8 • A, Close-up frontal view of a distal fibular osteosarcoma shows a mixed, productive destructive lesion. B, A month later the tumor has broken out of the fibula and is producing clouds of tumor bone in the adjacent soft tissues.

Mature New Bone. In its advanced stages of development, new bone more closely resembles the bone surface on which it resides. It usually appears smoothly surfaced and quite dense, often appearing more as a lump in the underlying bone, than a bony add-on. Such deposits are very difficult to precisely age because they may be as little as a few months old, or alternatively, years in duration (Figures 1-13 and 1-14). Unlike exterior bone deposits, interior (medullary or endosteal) bone deposits are difficult to evaluate because discrete margins are difficult or impossible to profile. Fortunately however, most such lesions are caused by panosteitis (Figure 1-15), a condition characteristically found in young German Shepherds being presented for lameness.

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SECTION I ❚❚❚ The Extremities

A

B

Figure 1-9 • Single lateral oblique views of right (A) and left (B) tarsi of a cat injured approximately 1 week prior show similar injuries bilaterally: badly displaced fractures of the distal tibial growth plate and distal fibular body. The left calcaneus has a detached apophysis. New bone deposition on the distal fibular fragments supports the fact that this is not an acute injury.

Figure 1-10 • Lateral view of the mid-forelimb of a cat containing an intravenous line shows recently formed periosteal new bone on the cranial surface of the radius (emphasis zone).

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Figure 1-11 • Lateral close-up of the proximal humerus shows recently formed metaphyseal new bone and a faint lucent band just below the growth plate, the characteristic features of metaphyseal osteopathy.

Figure 1-13 • Frontal close-up of the distal humerus shows a large, dense, smoothly surfaced bone deposit, the result of a previous fracture.

Caution: Growing long bones, especially early in their development, often exhibit roughened metaphyses, termed cutback zones (Figure 1-16). This is normal and usually persists for only a few weeks, depending on the time required to attain skeletal maturing.

❚❚❚ JOINT BODIES (INTRAARTICULAR BONE FRAGMENTS) As used in this context, “loose” usually refers to small bone fragments or joint bodies that appear separated from the normal osseous elements of the joint, although such bodies may be fixed in position by soft tissue. Caution: Care must be taken not to mistake normal sesamoids for loose joint bodies (Figure 1-17). Figure 1-12 • Close-up lateral view of the infected carpus of a dog shows a large chunk of new bone (intermediate duration) on the craniodistal aspect of the radius, in addition to smaller deposits on the carpal bones and proximal metacarpus. Numerous small areas of bone destruction are also present, especially in the distal radius and caudal carpus. Joint swelling is pronounced.

Loose intraarticular bodies are most often seen in the humeral, cubital, and genual joints of the dog. In the case of the dog’s shoulder, most joint bodies located in the caudal pouch are presumed to have originated from the caudal aspect of the humeral head, second-

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SECTION I ❚❚❚ The Extremities

Figure 1-14 • Lateral (A) and frontal (B) views of an old femoral fracture in a cat. A single wire band deeply imbedded in the callus is all that remains of the original implants.

A B

Figure 1-15 • Immature German Shepherd: lateral close-up of the elbow shows a patch of new bone in the interior of the proximal ulnar shaft (emphasis zone) typical of panosteitis.

Figure 1-16 • Close-up frontal view of the distal radius and ulna shows normally prominent metaphyseal cutback zones resembling periosteal new bone.

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Figure 1-18 • Close-up lateral view of a cat’s shoulder shows a large conforming joint body lying over the caudal aspect of the humeral head, presumed to be the result of an old injury. Figure 1-17 • Lateral close-up of the stifle of a dog that tore its cranial cruciate ligament 7 weeks earlier. The genual joint has developed a characteristic arthritic pattern consisting of osteophytes on the proximal trochlea, distal patella, and proximal tibia, in addition to being swollen. The small circular bone just proximal to the fibula is the popliteal sesamoid, which is not a joint body related to the dog’s damaged knee.

ary to osteochondritis. Humeral joint bodies in cats are more likely to be the result of a previous injury or immunoarthritis (Figure 1-18). Occasionally, osteochondritis occurs in unusual locations, suggesting trauma. Fortunately most such findings are present bilaterally, thereby decreasing the probability of injury compared with osteochondritis (Figure 1-19), whereas other findings are clearly incidental (Figure 1-20). Alternatively, these bony objects may represent synovial osteochondromatosis, a proliferative disease of undifferentiated synovial stem cells in which cartilage flaps or vascularized cartilage fragments are transformed into bone through the process of enchondral ossification (Figure 1-21).2 Bodies located cranial to the humeral tubercles are more problematic because they may be osteochondral fragments or regional dystrophic calcification (Figure 1-22). In the stifle, small, centrally located calcified bodies are most likely to have originated from avulsion of the cranial cruciate ligament (Figure 1-23, A, B). In older cats, loose joint bodies are most likely to be found in the cubital, antibrachial carpal, genual, and tarsocrural joints.3 The most probable cause of such bodies, especially if present bilaterally, is osteochondromatosis. Both dogs and cats may incur loose joint bodies as a result of articular or avulsion fractures, particularly when associated with dislocation.

❚❚❚ PERIARTICULAR OSTEOPHYTES Variably-sized triangular bone deposits on the articular margin of a joint are known as periarticular osteophytes and are generally considered to be the most characteristic feature of osteoarthritis (Figures 1-24 and 1-25).

❚❚❚ EXTRAARTICULAR OSTEOPHYTES Small bone deposits located adjacent to the articular margin are known as periarticular osteophytes. When present in a single joint, periarticular osteophytes are most likely to be the result of previous trauma (Figure 1-26), but when present bilaterally are more likely to be associated with osteochondritis or immunoarthritis (Figure 1-27).

❚❚❚ ENTHESIOPHYTES Enthesiophytes are often anatomically indiscernible from osteophytes, both possessing a roughly triangular appearance and bonelike density. Location distinguishes the osteophyte from the enthesiophyte because unlike osteophytes, enthesiophytes are formed within the origin or insertion of a tendon or ligament. Recall that osteophytes, the premier RDI of osteoarthritis, are characteristically found along the articular margin of one or more bones in a particular joint. Accordingly, they are termed periarticular osteo-

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SECTION I ❚❚❚ The Extremities

A

B

Figure 1-19 • Unusual osteochondritis: close-up frontal views (A, B) of the radiocarpal joints of a young Golden Retriever show multiple bone fragments alongside large irregular defects in the distal radius.

or around a joint, provided they are in the known location of a tendon or ligament because this is where they are formed. Clearly, declaring a periarticular bone deposit to be an enthesiophyte, rather than an osteophyte, is highly speculative business. Even if an enthesiophyte is identified with confidence, establishing its clinical importance can be quite difficult because many enthesiophytes are innocuous. For example, a painless enthesiophyte at the origin of the short radial ligament (frontal projection) is present in 14 percent of racing Greyhounds.4

❚❚❚ LOCALIZED BONE LOSS Aggressive Lesions Figure 1-20 • Close-up flexed lateral view of 8-month-old German Shepherd shows a small triangular bone fragment just above the center of the anconeal ridge. Because a similar fragment was also present in the opposite elbow, but more importantly that the dog was sound, final diagnosis was postponed pending future radiographic examination. Possible explanations for the described fragment can be found in the text.

phytes. Bone deposits that are similar in appearance and estimated to be in close proximity to the joint capsule are termed extraarticular osteophytes, and are the principal RDI of immunoarthritis. Enthesiophytes, unlike periarticular and extraarticular osteophytes, may be located anywhere within

Aggressive appearing bone lesions often prove to be cancerous. When located in the proximal or distal metaphysis, they are most probably primary bone tumors (Figure 1-28), whereas those found in the diaphysis are more likely metastases. Occasionally, aggressive appearing fungal infections occur in the shafts of long bones and resemble secondary bone tumors. Some advanced bone tumors so consume the bone that determining their origin is impossible (Figures 1-29 and 1-30). Although difficult to precisely define, the term aggressive is in wide clinical use. Most often, the term refers to a poorly marginated, primarily destructive lesion that often involves the marrow and an adjacent cortex. Accompanying plumes of calcification extendText continued on p. 15

CHAPTER 1 ❚❚❚ Extremital Radiographic Disease Indicators

A

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B

Figure 1-21 • Close-up frontal (A) and lateral (B) views of a cat’s elbow show numerous periarticular and extraarticular bone deposits, the result of synovial osteochondromatosis. As in most such cases, this was an incidental finding in an older cat.

Figure 1-22 • Close-up skyline view of the proximal tuberal groove shows focal bone deposits, which have been associated with tenosynovitis.

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SECTION I ❚❚❚ The Extremities

B

A

Figure 1-23 • Close-up recumbent (A) and standing lateral (B) views of the arthritic stifle of a dog that previously ruptured its cranial cruciate ligament. Note the dislocation (subluxation) apparent in the standing film but not in the conventional projection.

Figure 1-24 • Osteochondritis: close-up frontal view of an arthritic elbow in a middle-aged Labrador Retriever shows a characteristically beaked medial coronoid process.

Figure 1-25 • Long-standing instability caused by a third-degree cranial cruciate sprain 7 years earlier has resulted in severe osteoarthritis and a spectacular bone spur on the caudal aspect of the tibia.

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Figure 1-26 • Close-up frontal view of a severely arthritic stifle shows osteophytes in both the periarticular and extraarticular regions; the uneven joint width suggests instability and miniscal injury/degeneration.

A

B Figure 1-28 • A, Close-up ventrodorsal view of proximal femur in

Figure 1-27 • Frontal view of a dog’s carpus shows a large extraarticular osteophyte on the lateral aspect of the distal radius just below the physeal growth scar (emphasis zone), which is the result of chronic immunoarthritis.

an older dog shows a roughly spherical region of metaphyseal bone loss, surrounded laterally and distally by areas of new bone deposition and cortical disruption consistent with a moderately advanced primary bone tumor (fibrosarcoma). B, Close-up frontal view of the distal radius of a dog with an early primary bone tumor (osteosarcoma) shows new bone deposition on the exterior surface and mild destruction of the interior (emphasis zone).

B

A

C

Figure 1-29 • A, Ventrodorsal view of the pelvis and upper hind limbs of a dog with a secondary bone tumor in the midshaft of its right femur (emphasis zone). B, A full-length, close-up frontal view of the tumor reveals its predominantly destructive nature. C, A close-up lateral view shows a centrally located pathologic fracture (ragged dark line in the center of the emphasis zone).

A

B

Figure 1-30 • A, Close-up ventrodorsal view of pelvis, hips, and upper hind limbs of a dog with a primary bone tumor (osteosarcoma). B, Close-up view of the tumor, which shows the impossibility of determining exactly where it began.

CHAPTER 1 ❚❚❚ Extremital Radiographic Disease Indicators

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Figure 1-32 • Lateral oblique close-up view of the carpus shows the accessory carpal bone enveloped in a cloud of new bone, the result of a rare parosteal sarcoma.

Figure 1-31 • Close-up xerogram shows classic localized bone infection in the lateral aspect of the distal ulna, featuring a (1) sequestrum, (2) cloaca, (3) involucrum, and (4) new bone along the outer perimeter of the lesion.

ing outwardly into the surrounding muscle (tumor bone) further signal potential malignancy.

Nonaggressive Lesions Nonaggressive bone lesions, usually infections, are those that have a well-defined margin and are usually found in the diaphysis (Figure 1-31). Unfortunately, some malignant bone lesions initially appear this way, only later adopting the aggressive features of a malignancy.

❚❚❚ LOCALIZED BONE DEPOSITION Localized bone deposits, as already described, can form for a myriad of reasons, but are most often the result of a previous injury, infection, or tumor (Figure 1-32).

❚❚❚ METAPHYSEAL LYSIS Metaphyseal lysis is most commonly encountered after growth plate fractures (Figure 1-33, A-D). Metaphyseal osteopathy, which is also termed hypertrophic osteodystrophy (Figure 1-34), and some hematogenous infections (“puppy strangles”) may also produce lucent metaphyseal bands but are far less common.

❚❚❚ OSTEOPENIA Posttraumatic osteoporosis is a common sequela to many mid and distal long bone fractures and can be particularly pronounced in young dogs. Often mistakenly termed disuse osteoporosis, posttraumatic osteoporosis always develops distal to the fracture and/or dislocation (Figure 1-35, A, B), whereas disuse osteoporosis (a comparative rarity) involves the entire limb. Once the fracture forms a solid callus and the bone once again becomes rigid, bone density rapidly returns to normal. Chronic carpal and tarsal sprains, with or without fracture or fracture-dislocation, are also subject to mineral depletion caused by posttraumatic osteoporosis, which often leaves the bones faint and hollow looking (Figure 1-36).

❚❚❚ DISLOCATION (SUBLUXATION, LUXATION) Dislocations, which are also termed luxations or subluxations depending on the amount of articular displacement, are almost always accompanied by ligament injuries, such as injury to the collaterals in the elbow, the cruciates in the knee, and the teres in the hip. If untreated, dislocation may predispose to reinjury and eventually result in arthritis. Some dislocations relocate shortly after they occur, often defying radiographic diagnosis, unless stress or postural films are made. Occasionally, dogs may be born with dislocation of the elbow, which is nearly always bilateral, or suffer a traumatic dislocation as young puppies. In the

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SECTION I ❚❚❚ The Extremities

A

B

C

D

Figure 1-33 • Close-up frontal (A) and lateral (B) views of nondisplaced distal radial and ulnar growth plate fractures in a kitten show widened, irregular physes with a vague band of mineral depletion in the adjacent metaphyses. Views of the opposite carpus are provided for comparison (C, D).

CHAPTER 1 ❚❚❚ Extremital Radiographic Disease Indicators

Figure 1-34 • Radiolucent bands paralleling the growth plates of

17

A

the distal radius and ulna are the hallmark of metaphyseal osteopathy, as well as subacute growth plate fractures.

latter instance, and especially after a few months of remodeling, it can be very difficult to separate congenital from traumatic causes. Radiographically, most dislocations feature malalignment and varying degrees of articular overlap. As a result, the cartilage space may appear abnormally widened, narrowed, uneven, misshapen, or invisible. In some instances one or more small extraarticular bone fragments indicate the presence of avulsion fractures, potential clues as to which ligaments may have been injured (Figures 1-37 and 1-38).

❚❚❚ LIMB DEFORMITY (ANGULAR LIMB DEFORMITY) Most unilateral limb deformities in dogs result from injury, either to growth plates, in which case the deformity is of a secondary nature, or to the bones or joints directly. Figure 1-39 shows a severely bowed lower forelimb caused by a badly comminuted radial fracture (currently classified as a malunion). Bilateral limb curvatures, deficits, and deformities are more likely to be the result of congenital or developmental disorders.

❚❚❚ SOFT TISSUE SWELLING Soft tissue swelling, or more accurately (from a radiographic perspective) increased soft tissue area (and

B Figure 1-35 • Frontal (A) and lateral oblique (B) views of the carpus of a young kitten show the regional mineral depletion (posttraumatic osteoporosis) characteristic of a chronic carpal injury (sprain, fracture, and dislocation).

often density), is a nonspecific finding that is typically interpreted in the current clinical context: cellulitis, when present with puncture wounds (Figure 1-40), hemorrhage when associated with fracture, and so forth.

18

SECTION I ❚❚❚ The Extremities

Figure 1-36 • Severe posttraumatic osteoporosis of the tarsal bones of a cat (medial oblique projection).

A

B

Figure 1-37 • Lateral (A) and frontal (B) close-up views of a sprain, fracture, and dislocation of a cat’s elbow.

CHAPTER 1 ❚❚❚ Extremital Radiographic Disease Indicators

A

B

19

Figure 1-39 • Limb deformity.

Figure 1-38 • Frontal standing (A) and close-up (B) views of chronic sprain, fracture, and dislocation of a dog’s radiocarpal joint.

A

B

C

Figure 1-40 • Full-length lateral (A) and frontal (B) views of the mid-forelimb of a cat show uniform swelling, the result of numerous bite wounds. C, Lateral thigh region of a dog shows massive soft tissue swelling, which developed over a period of 4 months, the result of a leiomyosarcoma.

20

SECTION I ❚❚❚ The Extremities

References 1. Wolf J: The law of transformation of bone. Berlin, 1892, Hirshwald Verlag. 2. Edinger DT, Manley PA: J Small Anim Pract 39:397, 1998.

3. Hardie EM, Roe SC, Martin FR: Radiographic evidence of degenerative joint disease in geriatric cats: 100 cases (1994-1997), J Am Vet Med Assoc 220:628, 2002. 4. Guilliand MJ: Enthesiopathy of the short radial ligaments in racing greyhounds. J Small Anim Pract 39:227, 1998.

C h a p t e r

2

Extremital Injury

❚❚❚ MUSCLE BRUISES AND HEMATOMAS Bruise Varying degrees of bruising accompany most serious injuries in animals. Radiographically, bruising appears as a nonspecific soft tissue swelling that reflects deep or superficial hemorrhage and edema. Unlike a hematoma, which is often relatively localized and well marginated, bruising is diffuse and poorly delineated. Sonographically, an acute bruise often appears as a diffuse, ill-defined area of decreased echogenicity within the injured muscle. Within just a few days, however, the only remaining distinguishing feature may be a relative increase in overall muscle size compared with the opposite limb. Severe muscle swelling often results in spreading and distortion of the parallel white bands (striae) that characterize normal muscle.1

Hematoma Hematomas may be either intramuscular or intermuscular; the former is the more serious injury. Tearing of the muscle body in association with arterial rupture constitutes the optimal conditions for the formation of an intramuscular hematoma (Figure 2-1). Residual scarring or fatty infiltration can cause chronic pain and weakness with varying degrees of associated disability. Occasionally, a large, rapidly developing hematoma exerts enough pressure on the surrounding tissues to cause ischemia, anoxia, and, if the pressure is not relieved, eventual necrosis. This is termed a compartment or compartmental syndrome. Sonographically observed lesions compatible with hemorrhagic compartmentalization typically appear, depending mostly on duration, as discrete, oval, or circular anechoic; hypoechoic; or mixed echoic objects located in displaced, damaged, or otherwise abnormal muscle. In my experience, intramuscular hematomas often are located near a large, sonographically visible, artery (with or without a visible attachment to the hematoma).

In one reported case of compartmental syndrome, a large fluid-filled capsule containing a hematoma was removed from the thigh of a dog. Sonographically, the lesion was characterized by alternating light and dark rings radiating outwardly from a centrally located blood vessel.2 Hematomas also can form on the muscle exterior, either on the fascial sheath or in the large intermuscular septa. In these locations, especially higher in the leg, hematomas tend to migrate distally (especially with exercise) and in the process disperse over a wider area, making sonographic identification more difficult. On a positive note, however, the wider distribution of the migrating hematoma tends to relieve potentially dangerous pressure effects. Thus, an intermuscular hematoma is a decidedly less serious injury than a formed intramuscular hemorrhage and usually heals uneventfully. Sonographically, a hematoma can assume a variety of appearances. Initially, a hematoma usually appears anechoic and well demarcated (Figure 2-2). In the next few days, the hematoma gradually becomes more echoic and textured (Figure 2-3). Between 1 and 2 weeks later, most hematomas shrink and become hyperechoic. Afew disappear altogether. Although the sonographic progression of hematomas is predictable (dark to light), the rate at which these changes take place varies widely among individuals. Accordingly, hematomas can be difficult to age with any accuracy.3

Compartmental Syndrome (Compartment Syndrome) Compartmental syndrome is a term usually given to acute hemorrhage confined to a closed space or, more accurately, a potential space (typically, the space between a bone and adjacent fascia); as a result, it compresses surrounding nerves and blood vessels. People with this condition describe it as very painful and often associated with numbness in the distal part of the affected limb. As far as I can determine, this is a rare condition in pets or, alternatively, it is rarely recognized. 21

22

SECTION I ❚❚❚ The Extremities

Figure 2-2 • Sonogram shows relatively transparent appearance of a fresh intramuscular hematoma (24 hours old).

A

B Figure 2-1 • A, Sonogram shows a large intramuscular hematoma in the medial thigh region of a dog recently hit by a car. B, Close-up sonogram of medial thigh region shows two oval hematomas immediately to the right of the ruptured femoral artery (small black rectangle). A blood-filled muscle in the belly lies on the far lower right, depicted by widely spaced, parallel white lines.

Figure 2-3 • Progress sonogram of same lesion shown in Figure 2-2 (1 week later) shows increased echogenicity, the result of clotting and serum resorption, which are characteristics of a subacute hematoma.

Soft Tissue Gas Somewhat expanding the traditional definition of compartment syndrome, Williams and co-workers described a false aneurysm of a femoral artery that caused turgidity of the thigh region in a dog following repeated injuries sustained over 6 months.4 Sonographically, a cross-sectional view of the lesion and surrounding muscle resembled an intestinal intussusception: alternating light and dark concentric rings. Femoral arteriography showed contrast leakage confined to a small area around the distal aspect of the opacified femoral artery. During subsequent surgery, the leakage site proved to be a large, fluid-filled capsule, formed by the fascia of the semimembranosus and semitendinosus muscles, which communicated with the adjacent femoral artery through a 2-cm tear.

Soft tissue gas is usually the result of atmospheric contamination, made possible by one or more deep bite wounds or lacerations. The gas may accumulate in small pockets deep within the muscle (Figure 2-4) or as dark bands lying just beneath the skin or outlining deeper muscles and tendons (Figure 2-5, A). Alternatively, soft tissue gas may appear as a series of closely approximated but poorly defined pockets or bubbles located between a bone and nearby tendon, a pattern often found with bite wounds in the hock region (Figure 2-5, B, C).

Soft Tissue Calcification Soft tissue calcification occasionally is identified in extremital films of dogs and cats, nearly always incidentally. Presumably, most such deposits are dys-

CHAPTER 2 ❚❚❚ Extremital Injury

23

❚❚❚ STRAINS, TENDINITIS, AND BURSITIS Background

Figure 2-4 • Close-up frontal view of the stifle region of a dog shows multiple gas pockets deep in the severely swollen muscle medial to the genual joint (and superimposed on the distal femur), the result of multiple deep bite wounds sustained in a recent dogfight.

trophic, the result of a previous injury, although corroborating histories are often lacking. Extremital dystrophic calcification is most apt to be found near the apophyseal attachment of a tendon; for example, the proximal calcaneus (Figures 2-6, A, B and 2-7 A, B) and olecranon (Figure 2-8). Patterns vary, ranging from discrete calcific bands to amorphous foci, with the latter often displaying a linear arrangement. Tumoral calcinosis, a benign lesion typically appearing as a calcific cluster alongside the shoulder, elbow, stifle, or hock, has a highly distinctive appearance (Figure 2-9) that is not likely to be confused with other sources of soft tissue calcification. Rarely, a torn muscle will become partially ossified, a debilitating condition known as myositis ossificans.

High-density Foreign Bodies High-density extremital foreign bodies are usually readily apparent on radiographs: bullets, buckshot, air gun pellets (Figure 2-10), BBs, fishhooks, and needles, for example. Glass and gravel also are often visible, but they do not tend to penetrate as deeply and typically are found just beneath the skin or contaminating the surface of open road wounds.

In dogs (and less commonly in cats), complete tearing of a muscle belly, musculotendinous junction, muscle origin, or tendinous insertion is usually the result of a single trauma (as opposed to the overuse injuries so common in humans). Third-degree strain (large internal tears) and complete rupture also have been reported in a dog, occurring as a consequence of steroid-induced myopathy (triamcinolone).5 Avulsion fracture at the origin of the long digital extensor tendon has been described in dogs, both with and without a visible femoral fragment. Such injuries can occur without a history of known trauma, usually in large-breed puppies 5 to 8 months old. With subacute or chronic damage, the only indication of long digital extensor tendon injury may be a deeper and more lucent fossa. If a vascularized fragment of fossa is present, it may grow, becoming larger than the fossa from which it originated.6 Fitch and co-workers described a chronically detached long digital extensor tendon in a dog. Their report featured radiographic, computed tomographic (CT), and magnetic resonance images (MRIs) of the injury.7 Occasionally, following tearing, avulsion, or rupture, damaged muscle tissue changes to bone, a condition known as myositis ossificans.8 Little is known about this disease in dogs and cats, but in athletes such injuries can reduce performance substantially. Long and Nyland described the normal sonographic appearance of the canine shoulder, illustrating the utility of their findings with a number of case examples, including synovitis, bicipital bursitis, bicipital and supraspinous tendinitis, strained biceps, and dystrophic calcification.9

Imaging Findings Indirect mechanical stimulation, for example, that resulting from the prolonged licking of a skin wound (or a resultant lick granuloma), can cause fluid to accumulate in the tendon sheath (Figure 2-11). In my experience, there are no consistently reliable sonographic indicators of tendonitis in the dog.

❚❚❚ MAJOR TEARS, LACERATIONS, AND TRAUMA-RELATED INFECTIONS AND ABSCESSES Severe muscle tears (third-degree strains) often are associated with intramuscular bleeding (Figure 2-12), which can lead to compression-induced intramuscular or extramuscular ischemia. Hemorrhage resulting from deep muscle lacerations, although potentially

24

SECTION I ❚❚❚ The Extremities

B

A

C

Figure 2-5 • A, Full-length view of the crus of a dog recently cut by a barbed-wired fence shows large bands of gas beneath the skin and traces the gastrocnemius muscle and swollen Achilles tendon. B, Close-up view of distal half of mid-hindlimb shows bands of gas located between the tibial shaft and Achilles tendon. C, Opposite normal leg is provided for comparison.

CHAPTER 2 ❚❚❚ Extremital Injury

A

B

Figure 2-6 • Lateral close-up (A) and ultraclose (B) views of the proximal tarsus show the bony aftermath of a torn Achilles tendon: calcaneal remodeling, dystrophic calcification, and a thickened tendon.

A

B

Figure 2-7 • Close-up lateral (A) and frontal (B) views of the distal triceps field show soft tissue calcification consistent with an old injury.

25

26

SECTION I ❚❚❚ The Extremities

Figure 2-8 • Flexed lateral close-up of the elbow shows a band of calcification lying just beyond the edge of the medial epicondyle consistent with an old injury. Figure 2-10 • Lateral view of the soft tissue of the mid-hindlimb shows an air gun pellet just under the skin.

Figure 2-11 • Sonogram shows tendon sheath distended by fluid.

Figure 2-9 • Close-up frontal oblique view of tarsus shows a cluster of small and medium-sized calcifications lateral to the fourth tarsal bone characteristic of tumoral calcinosis.

debilitating, usually dissipates into the adjacent deep fascial planes and thus is not likely to cause intramuscular or extramuscular ischemia. Rupture or severe tearing of the Achilles tendon can be diagnosed physically, but lesser injuries or heavily scarred injuries usually require ultrasound, CT, or magnetography (Figure 2-13). Untreated deep puncture wounds, which typically close almost immediately, often become infected and may abscess (Figure 2-14, A, B). Ultrasound is required for diagnosis because radiographs, even using soft tissue technique, are unlikely to reveal more than nonspecific soft tissue swelling. Where sub-

CHAPTER 2 ❚❚❚ Extremital Injury

27

A Figure 2-12 • Sonogram shows freshly torn inner thigh muscle containing a large hematoma.

B Figure 2-14 • Long (A) and cross-sectional (B) views of a cylindrically shaped muscle abscess containing a foreign body (small, bright object).

denly and forcefully, the securing ligaments may stretch, tear, internally separate, or tear away from their bony moorings. Sprains are quantitatively described as first-, second-, and third-degree, depending on their severity; alternatively, they are characterized qualitatively as mild, moderate, or severe.

Carpal Sprains Figure 2-13 • Computed tomogram of the hock shows a ruptured Achilles tendon about 2 inches proximal to the calcaneus (as seen in the midsagittal plane).

stantial drainage is present or the abscess has been recently probed, one or more small gas pockets may be present.

❚❚❚ SPRAINS AND DISLOCATIONS Background Ligaments serve to set limits on normal joint movement. When these limits are exceeded, especially sud-

Overview. As one might expect, much has been published on the subject of carpal sprain in racing Greyhounds, including accounts of specific injuries, for example, the short radial collateral ligament.10 Severe carpal sprains may require surgical restoration of one or more torn ligaments. Where this is not possible, usually in chronic cases in which the damaged ligaments have become so badly frayed that reattachment is impossible, it may be necessary to immobilize the joint permanently by using a compression plate. This is sometimes erroneously termed fusing the joint; however, in most instances, the implants, not bony ankylosis, are preventing movement.11 Johnson documented the radiographic progress of grafted and nongrafted experimental carpal arthrode-

28

SECTION I ❚❚❚ The Extremities

A

B

Figure 2-15 • Lateral (A) and frontal (B) close-up views of a severely sprained carpus treated by prolonged casting and custom-built splintage. A year later, there is obvious swelling, especially of the radiocarpal joint, and some chronic appearing new bone on the face of the distal radius; however, the dog uses the leg normally.

sis in dogs and, predictably, the grafted carpi fused first.12 Nordberg and Johnson described the appearance of normal frozen canine carpi using a 1.5 T magnet and a human wrist coil. T2 gradient echoes provided the best combination of bone and ligament detail.13 Establishing the Degree of Carpal Injury. The severity of a carpal sprain injury is determined by using a combination of physical and radiographic abnormalities, listed in Table 2-1.14 Examples of Carpal Sprains and Diagnostic Tactics. Many carpal sprains can be successfully treated by prolonged external support, leaving only a cool, firm swelling as testament to the original injury (Figure 2-15, A, B). Intercarpal dislocation, especially if slight, can be difficult to detect without the aid of normal comparison films from the opposite carpus (Figure 2-16, A, B). Four views of a suspected carpal injury (frontal, lateral, and a pair of obliques) often make diagnosis easier, faster, and more accurate (Figure 2-17, A-D), especially when there are small, hard-to-see, minimally displaced fractures. A complete and accurate radiographic diagnosis of a serious carpal injury informs the prognosis, particularly with respect to potential long-term

consequences, such as osteoarthritis (Figure 2-18, A-C), disability (Figure 2-19, A, B), chronic pain, joint bodies (Figure 2-20, A, B), severe osteopenia (Figure 2-21, A-D), and traumatic capsulitis (Figure 2-22, A, B).

Elbow Sprains Most third-degree elbow sprains are associated with complete dislocation of the cubital joint (Figure 2-23, A-C). Somewhat surprisingly, O’Brian and co-workers showed that nonsurgical reduction, without collateral ligament repair, is as effective as open reduction with ligament repair, as long as the repair is done promptly. If not, posttraumatic osteoarthritis is likely to develop regardless of the method of reduction used.15 Arthriticfree healing of fracture–dislocations of the elbow (Figure 2-24) depends on both prompt surgical reduction and restoration (apposition and alignment) of disrupted articular surfaces.

Dislocated Shoulder Strictly speaking, there are no shoulder ligaments, although the humeral joint capsule functionally acts in such a capacity. Nonreduced scapulohumeral dislocations often lead to arthritis, joint bodies, pain, and severe forelimb disability (Figure 2-25, A-C).

CHAPTER 2 ❚❚❚ Extremital Injury

29

B

A

Figure 2-16 • A, Frontal close-up view of carpus shows swelling and proximal row displacement characteristic of an acute sprain–fracture–dislocation. B, Frontal view of the opposite carpus is included for comparison.

Table 2-1 • FACTORS THAT DETERMINE THE SEVERITY OF A CARPAL SPRAIN INJURY Abnormalities

Mild (First-degree) Sprain

Moderate (Second-degree) Sprain

Severe (Third-degree) Sprain

Physical

Minimal lameness Mild to moderate regional soft tissue swelling, which may be confined to the intracapsular location

Obvious lameness Obvious swelling Frank pain on palpation Pain readily elicited on minimal manipulation

Severe lameness often resulting in non–weight-bearing of the affected limb. Gross swelling that may extend well into the proximal metacarpus and the digits of the affected paw. Extreme pain on palpation and manipulation; frequently accompanied by crepitus or abnormal mobility

Radiographic

Minimal recognizable regional soft tissue swelling No bony lesions No apparent instability; stress films fail to identify spatial derangement

Prominent regional soft tissue swelling; usually both intracapsular and extracapsular in origin. Bony lesions rarely present. No apparent instability; stress radiographs may demonstrate spatial derangement

Gross regional soft tissue swelling. Bony lesions frequently present. Avulsion fractures are common and are often associated with subluxation. Instability often apparent and readily demonstrable with stress radiographs

Stifle Sprains The stifle is the most commonly sprained joint in the dog, followed by the carpus. In general, sprains heal slowly and are subject to reinjury, especially if normal activity is resumed prematurely. If during healing an injured ligament becomes elongated, it usually heals that way, causing the associated joint eventually to become arthritic, presumably because of intermittent incongruency related to instability. As to sprains to the genual joint, traditional belief has long held that there are two types of injury: one, the result of acute trauma; the other, the consequence

of chronic degeneration (presumably sustained over several years).16 This “either-or” explanation is probably an oversimplification, as recently suggested by Duval and co-workers.17 In the case of traumatic injury to the stifle, isolated cranial cruciate tears or avulsions are most common; however, multiple ligament injuries can occur, usually in young athletic dogs or as a result of being hit by a car. The cranial and caudal cruciate and lateral collateral ligament are most often sprained or ruptured.18 Isolated caudal cruciate injuries are exceptional.19 Occasionally, the bony mooring of the cranial cruciate detaches from the distal femur, leaving the ligament Text continued on p. 34

30

SECTION I ❚❚❚ The Extremities

B

A

C

D

Figure 2-17 • Four close-up views: frontal (A), lateral (B), medial oblique (C), and lateral oblique (D) of subacute carpal sprain–fracture– dislocations in a dog illustrate the diagnostic value of four views.

CHAPTER 2 ❚❚❚ Extremital Injury

B

A

C Figure 2-18 • A, Frontal view of an acute carpal sprain showing only mild to moderate swelling. The wavy, dark band traversing the distal ulnar metaphysis is edge enhancement or Mach band, caused by a congenital exostosis on the adjacent surface of the radius. Frontal (B) and lateral oblique (C) films made a year later show characteristic extraarticular new bone deposits on the cranial and medial surfaces of the distal radius and on various bones in the proximal carpal row.

31

32

SECTION I ❚❚❚ The Extremities

A

B

Figure 2-19 • Frontal (A) and lateral (B) views of a chronically unstable carpus sprained 7 years earlier. Although no films were made originally, the current arthritic pattern clearly suggests that the carpometacarpal joints were likely dislocated (and probably fractured as well).

B

A Figure 2-20 • When sprains are initially undiagnosed, untreated, or neglected, the only later indication of the injury may be one or two small bone fragments resembling normal sesamoids, and varying degrees of joint swelling, usually firm and cool (A, B).

CHAPTER 2 ❚❚❚ Extremital Injury

A

B

C

D

Figure 2-21 • Lateral (A) and frontal (B) views of the carpus and proximal metacarpus show chronic bone deposition over much of the face of the proximal metacarpus, causing it to appear abnormally white. Carpometacarpal swelling and severe regional osteopenia complete the picture. These changes are the result of a chronic sprain–fracture–dislocation. Also of note is the fact that another consultant diagnosed this as rheumatoid arthritis. C, D, The dog’s normal opposite carpus is provided for comparison.

33

34

SECTION I ❚❚❚ The Extremities

A A

B Figure 2-22 • Occasionally, particularly with severe capsular tearing

B

and excessive scarring, the capacity of the radiocarpal joint is reduced to the extent that there is insufficient synovial fluid to nourish the articular cartilage, a condition known as traumatic capsulitis. This volumetric difference can be appreciated best arthrographically by comparing the injured (A) with the uninjured joint (B).

stretched but intact. In such instances, it is often possible radiographically to identify a small intercondylar bone fragment and varying degrees of tibial dislocation.20 Partial cruciate tears (second-degree sprains) are less common than complete tears or avulsions (third-degree sprains), but when they do occur, they can potentially cause osteoarthritis, similar to that seen with more severe knee injuries. In my experience, the incidence of single and multiple ligament injuries in cats is much lower than in dogs. Some of the worst stifle trauma I have seen in cats has been the result of car accidents, mangling by large dogs, and various forms of entrapment.

Meniscal Injuries Medial meniscal injuries have been reported in nearly half of dogs with second- and third-degree cruciate

C Figure 2-23 • A, Dislocated elbow is readily seen in the closeup frontal view. B, It is somewhat harder to appreciate when viewed from the side. C, A comparable view of the opposite uninjured elbow is included for comparison.

CHAPTER 2 ❚❚❚ Extremital Injury

35

A

Figure 2-24 • Lateral view of the elbow region of a cat shows a displaced short oblique fracture of the proximal ulnar shaft and a dislocated radius. The beak-like bony projection ventral to the humeral condyle is the medial coronoid process, which may be mistaken for a fracture fragment.

sprains.21 In one elaborate classification, meniscal tears were divided into seven types according to location, orientation, and extent of the sprain:

B

Type 1: Folded caudal horn, which features an upward and forward folding of the caudal edge Type 2: Single longitudinal tear Type 3: Multiple longitudinal tears Type 4: Surface abrasions (termed by the authors as fibrillations) and a variety of partial-thickness tears Type 5: Axial-fringe tear Type 6: Bucket-handle tear Type 7: Transverse tear along inner margin

Imaging Findings Experimental Destabilization of the Canine Genual Joint. Experimental creation of osteoarthritis in the knees of dogs by severing the cranial cruciate ligament produces the following radiographic abnormalities (in order of appearance) 22: • Regional muscle atrophy • Joint swelling • Spurring on medial aspect of tibia, proximal aspect of patella, and lateral fabella • Spurring on the lateral aspect of the trochlear ridge, the caudal aspect of the tibia, and the distal aspect of the patella • Firm convex swelling centered over a medial collateral ligament

C Figure 2-25 • Ventrodorsal (A) and lateral (B) close-ups of a chronically dislocated shoulder in a cat show numerous spherical densities, most likely representing vitalized bone or cartilage fragments. C, See opposite shoulder for comparison.

36

SECTION I ❚❚❚ The Extremities

A A

B Figure 2-26 • A, Close-up lateral view of a stifle sprained 2 weeks earlier shows a partial dislocation, marked swelling, but as yet no osteoarthritis. B, The opposite genual joint is provided for comparison.

Using MRI (low-field strength imager), Baird and coworkers reported the development of a medium-sized, cyst-like lesion in the medial aspect of the proximal tibia within 3 months following cutting of the cranial cruciate ligament in healthy dogs.23 Naturally Occurring Cruciate Sprains in Dogs. Overall, the lateral view of the stifle is the most informative, especially in the detection of intraarticular swelling, which is often the only radiographic indication of an acute cruciate sprain (Figure 2-26, A, B). Partial dislocation occasionally is seen in recumbent images

B Figure 2-27 • Close-up lateral (A) and frontal (B) views of a young retriever’s stifle, sprained 2 months earlier, show marked joint swelling and early osteoarthritis.

but in most instances cannot be identified without the aid of postural (dog standing with a horizontally directed x-ray beam) or stress films. After 1 or 2 months, most seriously injured stifles begin to show signs of osteoarthritis in the form of triangular bone deposits located at the lower pole of the patella, on the proximal aspect of the femoral trochlea, along the outer surfaces of the femoral epiphysis, and on the ventral margins of the fabellae (Figure 2-27, A, B). In some dogs, the extensor fossa (as seen in lateral projection) begins to deepen, resembling a fracture bed (Figure 2-28, A). For most dogs,

CHAPTER 2 ❚❚❚ Extremital Injury

37

sesamoid in association with rupture of the cranial cruciate ligament, a radiographic abnormality also associated with avulsion of the popliteus muscle.25 In my experience, however, the standing lateral, even if the dog is only partially weightbearing, is still the most sensitive means of radiographically detecting dislocation of the stifle. Caution: Most standing projections differ from comparable recumbent views, and the standing knee is no exception (Figure 2-28, B).

A

B Figure 2-28 • A, Close-up lateral view of a stifle sprained 6 weeks earlier shows swelling and early osteoarthritis, but no dislocation. B, Close-up lateral view of the stifle of a healthy dog in standing position. Note the near-vertical position of the femur, the caudally sloped proximal tibia, and the cranially positioned articular contact point of the distal femoral epiphysis.

even those treated surgically, the resultant osteoarthritis is progressive, eventually leading to loss of articular cartilage and varying degrees of pain and disability. DeRoosten and van Bree devised a compression stress maneuver that can aid in the radiographic detection of cranial cruciate sprains.24 These same authors also reported the distal displacement of the popliteal

Intercondylar Stenosis. Montgomery and co-workers described a method of radiographing the intercondylar fossa, a postural projection they term the tunnel view (horizontally directed x-ray beam; dog in lateral recumbency). They contend that this projection is capable of detecting what they term “fossal stenosis,” a somewhat ambiguous term referring to the development of multiple inwardly projecting osteophytes following severe cruciate injuries, which may potentially encroach on the cruciate ligaments and limit joint extension. The authors contend that such information is important in planning reconstructive knee surgery. The amount of “stenosis” is described as a ratio (notch width index), calculated by dividing the width of the intercondyloid fossa by the width of the distal femur (epicondyle to epicondyle). The authors repeatedly cautioned that an accurate projection angle is critical because off-angle views result in false-positive diagnoses. The reported notch width index in normal Greyhounds was 0.25.26 The same group compared femoral fossa measurements made using CT with those obtained using conventional radiography. They concluded that CT images were more accurate in normal, arthritic, and unstable genual joints.27 Ultrasound. Reed and co-workers described the normal sonographic anatomy of the canine stifle.28 Regularly seen structures included (1) patellar tendon, (2) medial and lateral menisci, (3) cranial cruciate ligament, and (4) articular cartilage of the femoral condyle. The caudal cruciate ligament was seen in only two of four dogs; the collateral and meniscal ligaments could not be identified. The average weight of the dogs examined was 55 pounds. Kramer and co-workers described the sonographic appearance of both normal and abnormal canine stifles. Using a standardized examination protocol (patterned after one used by physician–sonologists), the authors claim to have diagnosed a wide variety of disorders, including the following: (1) tumors and nonneoplastic masses, (2) osteochondritis of the lateral femoral condyle, (3) ruptured cranial cruciate ligament, (4) meniscal injury, (5) nonspecific trauma, (6) degenerative joint disease, (7) patellar ligament sprain, and (8) patellar dislocation.29 Magnetic Resonance Imaging. Widmer and coworkers were among the first to discuss the appli-

38

SECTION I ❚❚❚ The Extremities

B A

C

D

Figure 2-29 • Close-up lateral (A) and frontal (B) views of a dog that tore its medial gastrocnemius muscle, resulting in dislocation of the associated fabella. Note how the degree of displacement varies with positioning. The opposite stifle is included for comparison (C, D).

cability of MRI to canine stifle injuries.30 Later, Widmer compared the relative sensitivities of radiography and magnetography in detecting the early signs of osteoarthritis in the stifles of healthy experimental dogs that had their cranial cruciate ligaments severed.31 Baird and co-workers also described the normal canine stifle using a lowfield MRI (0.064 T), including matched anatomic specimens.32 Magnetic Resonance Arthrography. Banfield and Morrison reported the use of magnetic resonance

arthrography in a small group of 11 military dogs suspected of having stifle injuries.33 Observed pathology included sprains and rupture of the cranial cruciate ligament, meniscal tears, medial collateral ligament injury, and synovitis. Optimal imaging planes are tabulated in Box 2-1. Fabella Injuries. Injuries to one or both fabellae are rare compared with cruciate sprains. Most are characterized by either displacement (Figure 2-29, A-D) or fragmentation and callus formation (Figure 2-30, A, B).

CHAPTER 2 ❚❚❚ Extremital Injury

A

39

B

Figure 2-30 • Close-up lateral (A) and frontal (B) views of the stifle show lateral fabella enveloped in bone, presumed to be the result of a former injury.

B o x

2 - 1

Optimal Imaging Planes for the Individual Elements of the Canine Stifle Stifle Structure

Optimal Imaging Plane

Articular cartilage

Sagittal (if 3DFSPGR sequence can be performed) Sagittal oblique (oriented along the cranial crutiate ligament) Dorsal plane

Cruciate ligaments Medial and lateral collateral Ligaments Patella and patella pendon

Sagittal

along the margins of the tarsocrural joint. Secondary lesions may develop in the proximal intertarsal joint, usually taking the form of one or more angular osteophytes along the leading edges of the talus and calcaneus. These findings are best seen in the lateral projection. Some sprains, especially those involving the tarsometatarsal joint, do little to change the radiographic appearance of the surrounding bones. In such cases, circumstantial evidence potentially may be obtained by performing stress radiography in the hope of showing dislocation. In some instances, it is also possible to show small corner fractures that are not evident in the initial nonstress images.

❚❚❚ SOFT TISSUE FOREIGN BODIES Tarsal Sprains Tarsal sprains range from the obvious, where there is an associated, displaced malleolar fracture, to the subtle, where there is little or no radiographic indication of the injury. Most serious tarsocrural sprains feature the combination of joint swelling, dislocation, and malleolar fracture. Mild to moderate sprains, however, although often very painful, typically result in tarsocrural swelling but no fracture or displacement. Not all severe tarsocrural sprains are diagnosed at the time of occurrence, but some are diagnosed later by their characteristic arthritic pattern (Figure 2-31, A, B), a pattern shared by osteochondritis of the talar ridge. Specifics include prominent periarticular lipping of the cranial and caudal aspects of the distal tibia, widening of the tarsocrural joint, and bone deposition

Currently, the most prevalent noninjurious foreign body in dogs is the microchip. Although most such chips appear to remain where they were initially placed, Burk and Eich reported the migration of a microchip from the soft tissues between the scapulae (where it was originally implanted) to the midcaudal aspect of the right brachium.34 Barrett described a variety of soft tissue foreign bodies in dogs, along with abnormal calcifications and gas pockets resulting from different causes.35 Shah and co-workers described the radiographic and sonographic appearances of a variety of foreign bodies (BB pellet, nail, steel wire, rock, gravel, glass, pencil lead, plastic, and wood) that were experimentally implanted in muscle.36 Table 2-2 indicates the imaging features of these objects.

40

SECTION I ❚❚❚ The Extremities

B

A

Figure 2-31 • Close-up frontal (A) and lateral (B) views of the tarsus of a dog badly sprained 1 year ago. Although treated immediately with casting, osteoarthritis developed within 3 months, primarily at the levels of the tarsocrural and proximal intertarsal joints.

Depending on clinical circumstances, in particular any operant diagnostic bias, an object located on the skin surface, such as small tumor, chunk of dirt or mud, or even an engorged tick, can be mistaken for an interior lesion, including a foreign body.37

❚❚❚ FRACTURES The following are the essential elements of fracture description: • Whether the fracture fragments are displaced or nondisplaced • The configuration of the fracture (fracture type) • Which bone or bones are broken • Where in a particular bone the fracture has occurred: shaft, metaphysis, growth plate (in skeletally immature animals), or epiphysis For example: There is a displaced, transverse fracture of the distal radial body. For another example: There is a nondisplaced, oblique fracture of the distal tibial metaphysis. Supplementary observations, such as the presence of fissures and joint or growth plate involvement, are

mentioned as necessary. Figures 2-32 to 2-34 further exemplify how fractures are described.

Fracture Types Apophyseal Fracture. An apophysis is an accessory growth center that requires intermittent traction to develop properly, in contrast to epiphyses, which require intermittent compression to thrive. Examples of apophyses are the greater and lesser trochanters of the femur, the tibial tuberosity, the proximal calcaneus, and the olecranon. Proximal displacement and associated growth plate widening characterize apophyseal fractures. Like many epiphyseal fractures, apophyseal fractures are often subtle, requiring opposite side comparison films to distinguish physeal variation from bona fide injury (Figure 2-35, A, B). Articular Fracture. An articular fracture enters one or more joints (Figure 2-36). Such injuries can lead to osteoarthritis if the affected articular surface is not restored. This is especially true if there is concurrent sprain, which further compromises joint congruency. In immature dogs and cats, articular fractures occur most often in the distal humerus and femur (Figures

CHAPTER 2 ❚❚❚ Extremital Injury

41

Table 2-2 • RADIOGRAPHIC AND SONOGRAPHIC FEATURES OF SOFT TISSUE FOREIGN BODIES IN DOGS Object Type

Object Size

Surface Echo Strength

BB Pellet

Nail

2 mm 5 mm 1 cm 2 mm 5 mm 1 cm 2 mm 5 mm 1 cm 2 cm

Strong Strong Strong Strong Strong Strong Strong Strong Strong Strong

Pencil lead 0.25 mm

2 mm 5 mm 1 cm

Pencil lead 1 mm Plastic

2 mm 5 mm 1 cm 2 mm 5 mm 1 cm 2 mm 5 mm 1 cm 2 mm 5 mm 1 cm 2 mm 5 mm 1 cm

Moderate Moderate Moderate to good Good Good Good Strong Strong Strong Strong Strong Strong Strong Strong Strong Moderate Moderate Strong

Glass

Gravel

Rock

Steel wire

Wood

Presence of Acoustic Shadow Comet-tail artifact Yes Yes Yes Yes Yes Yes Comet-tail artifact Poor Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

2-37 to 2-39). Mature pets, on the other hand, are more likely to sustain articular fractures in the carpus and tarsus. Avulsion Fracture. Avulsion fractures occur near joints at the sites of ligament or tendon attachments and, as such, always should be considered potentially destabilizing (Figure 2-40). In most instances, the resultant fracture fragment is very small, which sometimes leads to the shortsighted dismissal of the injury as, “. . . just a chip” (Figure 2-41, A, B). If there is doubt about the integrity of a contiguous joint, stress radiography may resolve the question, but only if it is carried out in a pain-free manner. Avulsion fractures of the cranial cruciate ligament are usually quite small and in some instances nearly invisible. Occasionally, however, avulsion fractures of the tibia (with the attached cruciate ligament) are large enough that they can be surgically reduced.38 Normal sesamoids sometimes are mistaken for avulsion fractures or other kinds of joint disease. This type of diagnostic error can be avoided by knowing where the sesamoids are normally located (Table 2-3).

Presence of Reverberation Artifact

Presence of Radiographic Visibility

Yes Yes Yes No No No No No No Yes

Good Good Good Moderate Moderate Moderate Moderate Good Good Good

No No No

Invisible Invisible Invisible

No No No No No No No No No Yes Yes Yes No No No

Poor Moderate Moderate Invisible Invisible Invisible Moderate Good Good Good Good Good Invisible Invisible Invisible

Chisel Fracture. A chisel fracture typically is found in the cortex and may be of full or partial depth. Such fractures often involve bones that lie close to the skin surface, relatively unprotected by muscle. As the name chisel implies, these fractures usually are caused by sharp-edged objects that strike the bone obliquely, producing a bony “shaving” (Figure 2-42). Closed Fracture. A closed fracture is “closed” to potential outside microbial contamination by virtue of an intact surrounding skin. Other factors being equal, a closed fracture is much less likely to become infected than one that is open to the atmosphere. Comminuted Fracture. A comminuted fracture is composed of three or more fragments and often is associated with malalignment and disapposition (Figure 2-43). Compression Fracture. A compression fracture is one in which the bone is made to cave in on itself, making it appear smaller than normal. Compression fractures are most common in the thoracolumbar and lumbar spinal regions of dogs and cats (Figure 2-44). Text continued on p. 46

42

SECTION I ❚❚❚ The Extremities

A

B

C

Figure 2-32 • Long lateral (A) and frontal views (B) of a dog with a displaced, comminuted midshaft tibial fracture. Because of its distinctive triangular shape, the large central piece is known as a butterfly fragment (C).

CHAPTER 2 ❚❚❚ Extremital Injury

Figure 2-33 • Ventrodorsal view of the pelvis, hips, femurs,

43

A

and stifles in a cat recently hit by a car show a displaced, comminuted fracture of the right femur and a dislocated left genual joint.

Figure 2-34 • Close-up lateral view of a displaced comminuted fracture of the humeral shaft shows an arthritic elbow, most probably the result of osteochondritis of the coronoid process.

B Figure 2-35 • Close-up lateral (A) and frontal (B) views of an avulsion fracture of the tibial apophysis, a shearing-type fracture of the tibial epiphysis, and a displaced transverse proximal shaft fracture of the fibula. Intraarticular and extraarticular swelling are marked.

44

SECTION I ❚❚❚ The Extremities

A

Figure 2-36 • Close-up lateral view of the humeral joint shows a displaced articular fracture of the cranial aspect of the glenoid immediately caudal to the tubercle.

B

C Figure 2-38 • Frontal (A) and lateral (B) views of the elbow of a kitten show a displaced articular fracture of the medial half of the distal humeral epiphysis and associated medial epicondyle. A frontal view of the normal opposite elbow is provided for comparison (C).

Figure 2-37 • Frontal long-bone survey of a forelimb in an immature dog shows a displaced articular fracture of the distal humerus. The fracture travels diagonally through the medial side of the metaphysis, the central part of the growth plate, and the lateral aspect of the epiphysis into the elbow joint.

CHAPTER 2 ❚❚❚ Extremital Injury

A

45

B

Figure 2-39 • Lateral (A) and frontal (B) views of a displaced, comminuted articular fracture of the medial aspect of the femoral epiphysis (with secondary displacement of the medial fabella) in an immature dog.

Table 2-3 • LOCATIONS OF FORE AND HINDLIMB SESAMOID BONES IN THE DOG Body Area Forelimb

Sesamoid Bone

Location

Elbow

Within tendon of origin of supinator muscle on craniolateral aspect of proximal radius

Carpus

Within tendon of insertion of abductor pollicis longus muscle on medial aspect of the proximal metacarpus

Metacarpophalangeal joints

Single sesamoid within tendons of insertion of common digital extensor muscle and interosseous muscles on dorsal aspect of metacarpophalangeal joints Paired sesamoids within tendons of insertion of interosseous muscles on palmar aspect of the distal interphalangeal joints Single cartilaginous nodules on the dorsal aspect of the proximal interphalangeal joints and palmar aspect of the distal interphalangeal joints

Hindlimb

Stifle

Single sesamoid (patella) within insertion of the quadriceps femoris muscle in trochlear groove of the distal femur Paired sesamoids (fabellae) within medial and lateral tendons of origin of gastrocnemius muscle proximal to the caudal aspects of the medial and lateral femoral condyles Single sesamoid within tendon of origin of popliteus muscle distal to the lateral femoral condyle on the lateral aspect of the joint

Tarsometatarsal joints

Medial (intraarticular) and lateral sesamoid bones within the fibrocartilage plate on the plantar aspect of the tarsometatarsal joints

Metatarsophalangeal joints

Single sesamoid within tendons of insertion of common digital extensor muscle and interosseous muscles on dorsal aspect of metacarpophalangeal joints Paired sesamoids within tendons of insertion of interosseous muscles on palmar aspect of the distal interphalangeal joints Single cartilaginous nodules on the dorsal aspect of the proximal interphalangeal joints and palmar aspect of the distal interphalangeal joints

Modified from Mahoney PN, Lamb CR: Articular, periarticular and juxtaarticular calcified bodies in the dog and cat: a radiologic review. Vet Radiol Ultrasound 37:3, 1996.

46

SECTION I ❚❚❚ The Extremities

A Figure 2-40 • Close-up frontal view of the elbow of a dog recently hit by a car shows a subtotal, latch-type avulsion fracture of the medial epicondyle (emphasis zone).

Corner Fracture (Chip Fracture). A corner fracture is one in which a bone fragment breaks free from the outer articular margin of a joint. The resultant corner fragment is characterized by a right angle (Figure 2-45). Crush Fracture. Crush fractures are often seen in series, for example, two or more of the metacarpal or metatarsal bones. Most result from heavy objects being dropped on one of the lower limbs or by having one of the legs slammed in a door. Dogs occasionally get a paw caught in a steel trap, in which case the entire row of metacarpals or metatarsals are broken in the same place (Figure 2-46, A, B). Depression Fracture. A depression fracture occurs when a portion of a bony perimeter is driven into an adjacent cavity. Cranial and facial fractures are often of this type, with portions of the maxilla being driven into the nasal cavity or the frontal bone being displaced into the underlying sinus (Figure 2-47).

B Figure 2-41 • Close-up lateral (A) and frontal (B) views of the stifle of a dog that recently fell off a balcony show a swollen joint and a small avulsion fracture from the proximal part of the patella.

Diastatic Fracture. A diastatic fracture results when fibrous junctions, such as the sacroiliac joint or pubic symphysis, are torn apart (Figure 2-48). Expression Fracture. This relatively rare fracture type occurs when the fracturing force causes bone fragments to be displaced outwardly. Flat bones of the face, skull, scapula, and pelvis are most often involved. Fault-line Fracture. Radial carpal bone fractures are typically the result of injury and usually are associated with some degree of dislocation; however, Li and col-

Figure 2-42 • Close-up lateral view of the olecranon shows a chisel fracture caudally (emphasis zone).

CHAPTER 2 ❚❚❚ Extremital Injury

leagues reported radial carpal bone fractures in 15 dogs without known trauma. They speculated that these fractures occur along a pair of “fault lines,” potential points of structural weakness, located equidistant between the three ossification centers of the radial carpal bone.39 Greenstick Fracture. Greenstick injury occurs in immature long bones and is characterized by an indistinct or nearly invisible fracture line and the separation of only one cortex (Figure 2-49).

Growth Plate Fracture (Physeal Fracture, Epiphyseal Fracture). Growth plates come in a variety of sizes and shapes. Some, like that in the distal femur, are composed of a cluster of four individual cleats and sockets, roughly arranged in a square (Figure 2-50, A). By contrast, the growth plate in the distal radius is composed of a single large, billowy element (Figure 2-50, B), whereas that in the distal ulna is distinctly conical (Figure 2-50, C). Growth plate fractures must not be confused with accessory growth centers, which can be highly variable, especially in young puppies, where the growth plate is growing, changing in shape, assuming new positions, and fusing to adjacent bones (Figure 2-51, A-C). Structurally weaker than the flanking bone, the cartilaginous growth plate is susceptible to injury. Traditionally, growth-plate injuries have been radiographically described using a surgical classification developed by pediatric orthopedists (Salter and Harris); this classification focuses on prognosis relative to the specific type of fracture. In radiology, however, the focus is entirely anatomic (Box 2-2).

B o x

2 - 2

Salter-Harris Classification of Growth Plate Fractures Type I

Type II Type III

Type IV Type V

Figure 2-43 • Lateral view of a severely displaced, comminuted fracture in a dog.

Figure 2-44 • Lateral view of the thoracolumbar spinal region of a dog with a broken back shows shortening and distortion of L1, the characteristic features of a vertebral compression fracture.

47

A transversely oriented fracture, which results in entire growth plate and epiphysis being detached from adjacent metaphysis. Like type I, but also includes a small attached, triangle-shaped, metaphyseal fragment. A vertically oriented fracture that results in part of the growth plate and underlying epiphysis being detached from adjacent metaphysis. Like type III, but also includes a large metaphyseal fragment. An impaction type fracture in which the growth plate is crushed between the epiphysis and metaphysis. This injury may only be inferred from clinical signs since it is radiographically invisible.

48

SECTION I ❚❚❚ The Extremities

Numeric classification schemes, such as that by Salter and Harris, can be difficult to remember, both in their own right and also because they conflict with other medical schema. In an effort to overcome such problems, I devised a briefer, hopefully more intuitive method of growth-plate fracture description that focuses on the actual injury, in particular, the fractured epiphysis (Box 2-3). A crushed growth plate is not considered because it cannot be diagnosed radiographically.

B o x

2 - 3

Simplified, Nonnumeric Classification of Growth Plate Fractures

Figure 2-45 • Close-up lateral view of canine tarsus shows a displaced corner fracture of the fourth tarsal bone and sprain–fracture–dislocation of the tarsometatarsal joints.

Complete epiphyseal separation without metaphyseal fragment Complete epiphyseal separation with metaphyseal fragment Partial epiphyseal separation without metaphyseal fragment Partial epiphyseal separation with metaphyseal fragment

B

A Figure 2-46 • Lateral (A) and frontal (B) views of the front paw of a cat show displaced short oblique fractures of the second and third metacarpal bones in the context of severe soft tissue swelling related to the crushing nature of the injury.

CHAPTER 2 ❚❚❚ Extremital Injury

49

Figure 2-47 • Close-up ventrodorsal view of the facial region shows depression fracture of right zygoma (left) that has fused to the adjacent mandible, which was also broken, preventing the mouth from opening.

Figure 2-49 • Full-length frontal view of the radius and ulna of a dog shows a greenstick fracture in the medial aspect of the central radial body (left).

Distal Humeral Growth Plate Fracture. Untreated or unsuccessfully treated distal humeral growth plate fractures are likely to cause arthritis and varying degrees of limb deformity if not treated effectively.40 Figure 2-52, A-D shows examples of growth plate fractures. Gunshot Fracture. As the name indicates, gunshot fractures are caused by bullets, slugs, and, less often, buckshot. In the case of joints, it is important to determine whether there are any intraarticular fragments, which can cause harm beyond the obvious wounding capacity of such missiles. Figures 2-53 to 2-57 show various examples of gunshot injuries in dogs and cats. Hairline Fracture. A hairline fracture is one in which the fragments are only minimally displaced, such that the break is little wider than a hair (Figure 2-58, A, B). Figure 2-48 • Close-up ventrodorsal view of the pelvis and hips shows displaced right sacroiliac diastatic fracture, dislocated right hip, and displaced fractures of the left pubis and left central ischium.

Impacted or Impaction Fracture. In an impacted fracture, the bone fragments are driven into one another, with or without a visible radiolucent fracture line (Figure 2-59, A-C). Incomplete Fracture. An incomplete fracture is one that is typically transverse or oblique and is characterized by a partially visible fracture line but no overt fragment displacement (Figure 2-60).

50

SECTION I ❚❚❚ The Extremities

A

C

B

Figure 2-50 • A, Close-up view of opened distal femoral growth plate of a dog (caudal perspective) shows two of four cleat and socket pairs. B, Close-up view of distal radial growth plate of a dog (caudal perspective) shows a billowy type growth plate. C, Close-up view of distal ulnar growth plate (caudal perspective) shows conical type of growth plate.

A

B

C

Figure 2-51 • Close-up lateral views of the elbow of a puppy at 1 (A), 2 (B), and 3 (C) months of age.

CHAPTER 2 ❚❚❚ Extremital Injury

51

A Figure 2-52 • A, Lateral oblique views of right and left stifles of a 4-month-old Basset Hound puppy recently hit by a car; the distal femoral and proximal tibial growth plates are fractured bilaterally. Appearances vary as a result of differences in projection angles. Continued

52

SECTION I ❚❚❚ The Extremities

B

C

D Figure 2-52 • cont’d B, Close-up lateral view of the genual joint shows badly displaced distal femoral growth plate fracture (SH II [Salter-Harris], based on metaphyseal fragment attached to femoral epiphysis). C, Close-up, flexed ventrodorsal view of the coxal joints shows a displaced proximal femoral growth plate fracture. D, Close-up lateral and frontal views of the shoulder joint show displaced growth plate fractures of the humeral head and greater tubercle.

CHAPTER 2 ❚❚❚ Extremital Injury

53

Figure 2-53 • Flexed ventrodorsal view of the left hip of a dog recently shot with a high-powered rifle shows a shattered proximal femoral shaft seen against a backdrop of dozens of bone and lead fragments. A plume of gas can be seen extending from the wound site deeply into the thigh, attesting to the open nature of the wound.

A Insufficiency Fracture. Insufficiency fracture is another name for a pathologic fracture, an injury that occurs in diseased bone (Figure 2-61). Letter Fractures. Letter fractures are named for their resemblance to some of the letters of the alphabet; specifically, T, Y, and V. They typically occur in the distal humerus of immature animals and involve the growth plate. Even more importantly, these fractures extend into one or both elbow joints (Figure 2-62). Longitudinal Fracture. A longitudinal fracture is one that lies parallel to the long axis of the bone (Figure 2-63). Oblique Fracture. An oblique fracture slants across the long axis of the bone (Figure 2-64). Open Fracture. An open fracture is one that has broken through the skin and thus is presumed potentially infected; most contain gas (Figure 2-65, A, B). Pathologic Fracture. A pathologic fracture is one that occurs in diseased, structurally weakened bone; accordingly, these injuries are also known as insufficiency fractures. Whereas most pathologic fractures occur in cancerous bone, they also can take place at the site of a bone cyst, in bacterial or fungal osteomyelitis, or in bones that have undergone extensive mineral depletion as a result of nutritional secondary hyperparathyroidism.41-42 Spiral shaft and transverse metaphyseal configurations are the most common. Contrary to popular opinion, posttraumatic osteoporosis (less precisely termed osteopenia), which temporarily follows

B Figure 2-54 • Ventrodorsal (A) and lateral (B) close-up views of the scapula of a cat show flecks of lead along the medial surface proximally, the result of a glancing gunshot wound.

fracture repair, rarely leads to pathologic fracture (Figure 2-66, A, B). Segmental Fracture. Two or more complete separations in a single bone are termed a segmental or, less commonly, a multiple fracture (Figure 2-67). Sesamoid Fracture. Two-piece sesamoid fractures occur most often in the feet of sled and racing dogs. These injuries need to be differentiated from the fragmenting form of osteochondritis, especially in Rott-

54

SECTION I ❚❚❚ The Extremities

A A

B Figure 2-55 • Lateral (A) and frontal (B) close-ups of the distal humerus of a dog shattered by a gunshot. There is also a displaced fracture of the olecranon that enters the elbow joint, as do many of the humeral fractures.

B Figure 2-56 • Lateral (A) and frontal oblique (B) views of the

weilers, and benign congenital fragmentation, termed bipartite (two-piece) and tripartite (three-piece) sesamoids (Figure 2-68, A, B).43 Simple Fracture. A simple fracture comprises a single break, usually transverse or oblique, resulting in two fragments (Figure 2-69). Spiral Fracture. A spiral fracture is one that turns through the long axis of the bone, describing a full or partial spiral (Figure 2-70). Stress Fracture. Stress fractures (also referred to as march fractures, as in soldiers marching) are rare injuries in dogs, arising from repeated stresses on bone, usually

elbow region of a cat show a shattered distal humerus, the result of a gunshot.

in the context of overtraining or overwork. As with people, stress fractures are most likely to affect young dogs. Bilateral stress fractures have been reported in the distal ulna of a Great Dane puppy.44 Transverse Fracture. A transverse fracture is one that breaks across the shaft perpendicular to the long axis of a bone (Figure 2-71). Talar Neck Fractures. Talar neck fractures are more common in cats than in dogs.45 In most such cases, there

A

B

Figure 2-57 • Lateral (A) and frontal (B) close-up views of a malunion gunshot fracture of the distal femur. Note the intraarticular and extraarticular migratory patterns of the smaller lead fragments, which trace the trochlear and gastrocnemius contours in the lateral projection.

A

Figure 2-58 • A, Close-up lateral view of the elbow joint shows hairline fractures (emphasis zone) passing through the olecranon and anconeal process into the humeroulnar joint. B, Close-up lateral views of the midbodies of the radius and ulna show transverse and oblique hairline fractures, respectively (emphasis zone).

B

56

A

SECTION I ❚❚❚ The Extremities

B

C

Figure 2-59 • A, Close-up frontal view of the tarsus of a dog shows multiple impaction fractions located on the lateral aspect of the tarsocrural and proximal intertarsal joints. Close-up lateral (B) and frontal (C) views of the distal radius and ulna show a displaced biplanar impaction fracture of the radial epiphysis and a mildly displaced, oblique, greenstick fracture of the ulnar shaft.

CHAPTER 2 ❚❚❚ Extremital Injury

57

Figure 2-61 • Close-up lateral view of the distal radius and ulna shows insufficiency (pathologic) fractures of both the radial and ulnar epiphyses as a result of an osteosarcoma.

Figure 2-60 • Close-up view of an incomplete fracture in the cranial cortex of the radial body (emphasis zone).

Figure 2-62 • Close-up frontal view of the humerus in a puppy shows a displaced Y-fracture involving the metaphysis, growth plate, and epiphysis. Distally, the fracture enters the far corner of the humeroradial joint (left).

58

SECTION I ❚❚❚ The Extremities

Figure 2-63 • Close-up frontal view of a badly displaced longitudinal fracture of the lateral aspect of the calcaneal body. The fracture is also articular by virtue of its entering the proximal intertarsal joint.

are additional fractures and dislocations. At least four views of the tarsus—lateral, frontal, and a pair of frontal obliques—are necessary to determine the full extent of the injury.

Traumatic Amputation Cats seeking the warmth of an automobile engine compartment on a cold winter day may be caught unawares when the car is restarted, often resulting in serious injury, including amputation (Figure 2-72).

Fracture Classification Using Electronic Databases Fracture descriptions stored in computerized databases need to be as precise as possible to facilitate accurate retrieval. They also must be designed with computer input foremost in mind. Such electronic classification schemes typically use anatomic location and fracture complexity to create an alphanumeric code that can be entered and retrieved by standard computer databases. Although maintaining data input in such systems is time consuming and thus quite costly, electronic data-

Figure 2-64 • Lateral oblique view of the metatarsus shows multiple displaced short oblique fractures of the proximal metatarsal bodies.

bases are necessary in large facilities, such as group specialty practices and teaching hospitals. One such method, known as the Unger system, has been tested in a veterinary teaching hospital and is said to be effective.46

Fracture Repair Before discussing the radiographic evaluation of fracture healing, a few words (and examples) on the subject of fracture repair. First, the principles: 1. The closer the fracture fragments are approximated, and the less they move during callus formation, the more rapidly the fracture heals. 2. The better the blood supply, the better the healing.

CHAPTER 2 ❚❚❚ Extremital Injury

A

A

B Figure 2-66 • Lateral (A) and frontal (B) close-up views of a

B Figure 2-65 • A, Full-length frontal view of a badly comminuted humeral fracture in which many of the fragments are being traced by gas, indicating the open nature of the injury. B, Closeup frontal view of a stifle of a dog, recently bitten by another dog, shows numerous gas pockets and a chisel-type fracture lying just beyond the lateral margin of the medial condyle (emphasis zone).

displaced pathologic fracture through a suspected metastatic bone tumor located in the distal aspect of the body of the tibia (emphasis zones).

59

60

SECTION I ❚❚❚ The Extremities

A

Figure 2-67 • Close-up frontal view of a refractured radius/ulna in a dog shows a segmental fracture of the middle and distal aspects of the ulnar body and an oblique fracture of the distal radial body.

B Figure 2-68 • A, Close-up frontal view of the left paw of a dog with a comminuted sesamoid fracture, an uneven cartilage space, and a new bone deposit on the inside edge of the underlying first phalanx. These findings are consistent with a former third-degree sprain of the second metacarpophalangeal joint and sesamoid fracture–displacement. B, Close-up frontal view of the forepaw of a dog shows a fracture–dislocation of the seventh caudal metacarpal sesamoid.

CHAPTER 2 ❚❚❚ Extremital Injury

61

Figure 2-69 • Full-length view of dog’s femur shows displaced simple oblique fracture of the femoral midshaft.

Figure 2-71 • Lateral oblique view of the scapula shows a displaced transverse fracture through the midbody. Vertically oriented cracks (fissures) are present in both the proximal and distal fragments.

Figure 2-70 • Full-length frontal view of a dog’s tibia (and fibula) shows a minimally displaced, long uneven spiral fracture.

Figure 2-72 • Frontal view of a cat’s paw in which the distal half of the second digit was amputated by an automobile cooling fan at the level of the midproximal phalanx.

62

SECTION I ❚❚❚ The Extremities

A

B

Figure 2-73 • Close-up lateral views of displaced longitudinal midshaft radial and ulnar fractures before (A) and after (B) 1 month of casting. As expected in such cases, healing is slow, especially distally, where movement was maximal.

Splints and Casts. Splints and casts do a poor job of immobilizing displaced fractures. The result is that fractures repaired in this way take longer to heal and form large calluses than fractures treated by other means (Figures 2-73 to 2-75). Casts are inexpensive, however, and they preserve the uninjured regional blood supply. Pinning and Wiring. Pins and wire loops in the case of comminuted fractures or those requiring counter traction do a better job than casts and splints in approximating and immobilizing fracture fragments but usually allow varying degrees of axial rotation that prolong healing (Figure 2-76, A-C). External bars attached to pins inserted into the fracture fragments help reduce rotation, but they are heavy, awkward, and often uncomfortable. Fractures treated in this fashion are also often slow to heal, callous heavily, and often result in bone loss immediately surrounding one or more of the pins (Figures 2-77, A-D and 2-78, A-D). Some fractures are now being treated with large pins that contain holes through which transcortical screws can be placed to prevent fragment rotation. Based on the cases I have seen thus far, healing is generally pro-

tracted compared with plates or conventional pins or with pin and wire combinations. As most veterinarians are now aware, improperly applied circlage wires can retard, and in some instances even prevent, fracture healing. Generally speaking, overly thin wire loops and half loops are ineffective, and an excessive number of closely approximated loops can delay callus formation. External Bars. Transcortical pins, mounted on external bars, with or without circlage wires, often move back and fourth like small seesaws, creating small lucent bands between the pin surface and the adjacent bone, especially at exit points. Pin infections can create a similar appearance but usually are associated with lameness (Figures 2-78, A-D and 2-79, A, B). Plates and Screws. Among the various surgical devices designed to repair fractures, bone plates achieve the greatest degree of fragment rigidity; as such, the associated calluses are typically small and in some instances nonexistent. Because of greater stability, fractures that

CHAPTER 2 ❚❚❚ Extremital Injury

B

A

63

C

Figure 2-74 • Frontal and lateral views of mid-forelimb (A) show an incomplete fracture of the central radial diaphysis and a minimally displaced transverse fracture of the distal ulna. Following a month of casting (B, C) only a portion of the radial fracture line is visible, and the ulnar fracture has disappeared altogether.

are plated heal faster than those that are not plated. Additionally, severely comminuted femoral fractures that are treated with a bridging plate heal more rapidly than comparable fractures treated with a combination of fragment reconstruction and plating.47 Figure 2-80 shows a partially healed tibial fracture fixed with a plate and screws.

Fracture Healing Fracture Union. The restoration of a fractured bone depends most on vascularization (and revascularization) of the injury site. When a fracture is cast, pinned, or plated, the purpose is to prevent the bone fragments from moving, which facilitates revascularization, providing the optimal environment for callus development. The following of certain events occurring in and around the fracture site will in most instances lead to healing: hematoma formation, localized inflammation, callus development, bony consolidation, and bony remodeling.48

Radiographic Indications of Fracture Healing (Bony Union). Based on serial radiography, fracture healing is assessed using the following changes in the appearance of the fractured bone: • Fracture line or lines initially widen, then narrow, become faint, and finally disappear. • Fragment margins gradually smooth and become less distinct. • Fragments gradually draw closer together before disappearing altogether. • Callus gradually fills the gap between fragments, eventually uniting them. The bone first becomes a single entity and then is gradually restored to its original appearance (or at least a close proximity). The radiographic judgment of healing always must be rendered on an individual case-by-case basis, made in the context of: (1) the location and severity of the fracture, (2) the duration of injury, (3) the method of repair, and (4) the progress of the injury over time (as seen in sequential

64

SECTION I ❚❚❚ The Extremities

A

B

C

Figure 2-75 • Frontal close-up views of a displaced distal radial shaft fracture at admission (A), 3 weeks (B), and 6 weeks (C) after casting. The fracture is now strong enough to bear weight without further support.

A

B

C

Figure 2-76 • A, Close-up view of the elbow of a dog shows a dark, wedge-shaped band crossing the proximal ulna and entering the humeroulnar joint consistent with a displaced articular fracture. B, One month later, the fracture remains clearly visible. C, Two months later, the fracture line has become faint and is likely healed enough to allow removal of the implants.

CHAPTER 2 ❚❚❚ Extremital Injury

65

C A

D

B

Figure 2-77 • Lateral (A) and frontal oblique (B) views of a cat’s femur, seen against a backdrop of massive swelling, show a displaced long oblique fracture of the proximal femoral shaft. An immediate postoperative film (C) shows anatomic reduction, achieved with an intramedullary pin and circlage wires. Six weeks later, the fracture appears healed without evidence of an external callus, attesting to the degree of surgical rigidity obtained (D).

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SECTION I ❚❚❚ The Extremities

B A

C

D

Figure 2-78 • A, B, Paired nonstandard views of the pelvis, hips, and left femur of a cat recently hit by a car show a severely displaced, comminuted fracture of the left femur and an avulsion of the left ischium. C, D, Progress films made 7 weeks later reveal that the fracture has healed well enough to remove the pins and external support bar.

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67

A

Figure 2-80 • Close-up frontal view of a partially healed tibial fracture in a dog. This fracture was repaired with a bone plate.

B Figure 2-79 • A, Comminuted tibial fracture 2 months following repair shows a pair of radiolucent lines along the edges of the uppermost pin (emphasis zone). B, These lines flare at the exit points, the result of a mild pin tract infection and associated pin cycling.

postoperative radiographic examinations. Pertinent radiographic reports also should be reviewed before arriving at a final decision. This process is exemplified in Figure 2-81, A-H. Soft Tissue Viability and Fracture Healing. Arteriography and venography provide the greatest degree of vascular detail in damaged soft tissues and are the optimal means of assessing viability. Subtraction angiography provides an even better view of small vessels by removing potentially confusing background anatomy; however, angiography is time consuming, expensive, requires general anesthesia, involves vascular surgery, and most importantly may further injure an already compromised blood supply.

Although not as anatomically precise, Doppler ultrasound, in the form of a vascular pressure tracing, usually indicates whether blood flow is present, which in the case of a potentially devascularized fracture or freeze injury may be all that is needed. Doppler is safe, fast, inexpensive, and poses no danger to a tenuous blood supply. Doppler has been used to determine the likelihood of fracture healing.49 The Orthopedic Imperative. Without exception, all fracture reductions, regardless of the method of repair, must be radiographed immediately after completing the procedure. Fracture repairs also should be checked radiographically before the animal is discharged home in cases of unusually long postoperative hospitalization because not all implant dislocations can be detected by physical examination (Figure 2-82). Delayed Fracture Healing When Is Union Considered Delayed? There is no precise definition of delayed healing; it is not a

68

SECTION I ❚❚❚ The Extremities

A–D

E–H Figure 2-81 • Close-up lateral (A-D) and frontal (E-H) views of a fractured distal tibial growth plate in a puppy treated by casting and then checked 2 and 4 weeks later.

quantitative entity but rather a statement regarding the accuracy of an earlier prediction. For example, when an animal breaks its leg, the bone is cast, pinned, or plated, and a predication is made as to how long it will take to heal. If the fracture exceeds the predicted healing time, it is designated a delayed union. If it heals faster than predicted, the doctor is considered skilled, but no specific term is used to mark the event. The best way to monitor the progress of a healing fracture is to recheck it on a regular basis. My preference is to do so at monthly intervals beginning 30 days after the immediate postoperative radiographs are made, unless it appears that the fracture has become infected or that the implants have broken or become detached, in which case I recheck it immediately. Radiographic Indications of Delayed Union. The experienced veterinarian initially predicts healing time based on a number of variables, including the bone involved, severity of injury, method of repair, and skill and experience of the surgeon. Thereafter, estimated healing time is based on progress rechecks. Inexperienced veterinarians are almost entirely dependent on the opinions of colleagues and the relevant veterinary literature. Some veterinarians seem

reluctant to use the term delayed union, contending that it suggests incompetence; others avoid the issue entirely by making no predictions. To reiterate, by describing the healing of a fracture as delayed, all that one is saying is that the fracture is taking longer to heal than originally predicted. Possible reasons for delayed union include (1) instability; (2) devascularization; (3) comminution, disapposition, or malalignment; (4) misapplied or inappropriate surgical implants; (5) broken or dislocated implants; (6) infection; and (7) reoperation (surgical revision). Figure 2-83 shows an example of a delayed union related to implant dislocation. Nonhealing Fracture: Nonunion. A nonunion fracture is one that does not heal, although not everyone can agree on when this should be: 4 weeks, 8 weeks, or 16 weeks. Most of us appear inclined to delay as long as possible before uttering the dreaded “N” word. On a more practical note, reluctance to acknowledge the presence of a nonunion often needlessly delays corrective treatment. The problem has been at least partially remedied by Heppenstall, a physician–orthopedist, who proposed that any fracture that fails to show any radiographic improvement for at least 3 months should be considered a nonunion and treated as such. I strongly support this def-

CHAPTER 2 ❚❚❚ Extremital Injury

69

A A

B Figure 2-83 • A, Immediate postoperative ventrodorsal view of

B Figure 2-82 • A, Discharge ventrodorsal view of the pelvis of a dog recently operated on to improve the position of its left acetabulum, subluxated as a result of hip dysplasia, shows unsuspected implant dislocation (emphasis zone). B, Close-up view shows that the screws have pulled out of both the ilial and sacral fragments, eliminating surgical stability.

the pelvis shows plating of the right ilium and a tandem screw reduction of a left sacroiliac fracture–dislocation. B, A close-up of the right ilium made a month later shows that most of the bone screws have partially pulled out and that the plate has bent. Even though the caudal ilial fragment has become badly displaced, a callus has begun to form. Based on the described implant and fragment dislocations, a delayed union is inevitable.

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SECTION I ❚❚❚ The Extremities

Figure 2-84 • Lateral view of femur 4 months following fracture and attempted pin repair shows a hypertrophic nonunion (partially covered by marker).

inition of nonunion, as I have stated in previous publications. The classic clinical signs of a nonunion are (1) lameness, (2) palpable pain, and (3) fragment mobility. If these signs are noted, there is no need to wait 3 months for radiographic confirmation (Figures 2-81, A-H). Bear in mind that this is a working definition. The medullary blood supply of a suspected nonunion can be evaluated using osteomedullography, a form of angiography in which a bone biopsy needle is used to inject contrast solution into the distal part of fracture.50 If the contrast crosses the fragment gap moving distally to proximally, an intramedullary blood supply exists, along with the potential for a bony callus. Causes of Nonunion. The causes of nonunion are often the same as for delayed union except they are usually of greater magnitude and are more sustained. They include the following: • • • •

Inappropriate repair Incorrect repair Instability Devascularization

Figure 2-85 • Close-up lateral view of 1-month-old puppy, untreated radial and ulnar midshaft fractures shows complete malalignment of the radial fracture, with little or no bridging callus. In the context of pain, lameness, and palpable fragment motion, the fracture was judged to be a nonunion.

• Infection • Implant misapplication I have omitted the term implant failure (breakage, dislocation) from the preceding list because it is so unusual and replaced it with implant misapplication, which in my experience is far more common, especially in the case of inexperienced surgeons. Radiographic Indications of Nonunion. Radiographic signs suggesting nonunion usually include one or more of the following: • • • • •

Absence of a bridging callus Increased density and smoothness of fragment ends Fragment motion Pseudoarthrosis formation Smoothness and thickening of fragment margins

Figures 2-84 to 2-93 exemplify various types of nonunions. Abnormally Healed Fracture: Malunion. Malunion is another word that some veterinarians seem reluctant to use, at least in their medical records. In fact, there is nothing derogatory about the term; it merely indicates that the bone has yet to be re-

C

A

B

D

Figure 2-86 • Lateral (A) and flexed ventrodorsal (B) close-up views of a complete mid-calcaneal fracture 4 months after attempted repair show nonunion as indicated by the clear gap between bone fragments at the level of the distalmost wire. Three months later, following implant removal, the nonunion has been replaced by a malunion (C, D).

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SECTION I ❚❚❚ The Extremities

mities are based. Using the radius and ulna as examples, they described the complexity of synchronous growth and how even small disturbances in this collaborative skeletal development—in the form of a comparatively minor vascular injury to the distal ulnar physis—could later lead to striking physical and radiographic abnormalities.52 Carrig and Morgan used radiation to damage deliberately the distal ulnar growth plates of 10-week-old Beagle puppies to retard the longitudinal growth of the ulna and thus upset the dynamic balance between ulnar and radial development. They described the resultant limb deformity, catalogued the associated radiographic changes, euthanized the dogs, and studied their bones.53 A related publication using the same material focused on the radiologic and pathologic aspects of radiation-induced distal ulnar growth plate injury.54 In a later experiment, Carrig and colleagues showed that the distal ulnar growth plate could sustain a minor injury without perceptible limb deformity.55

Imaging Findings

Figure 2-87 • Frontal and lateral views of a failed radial repair (attempted 5 months earlier) show nonunions of both the distal radius and ulna. Posttraumatic osteoporosis is evident in all bones distal to the fracture sites.

stored to its preinjury form. More importantly, nonarticular malunion fractures rarely lead to pain, discomfort, or serious disability, nor do most cause arthritis. Figures 2-94 to 2-99 show a variety of malunions.

Regeneration Anderson and Muhlbauer described a case of a 6month-old Great Dane that appeared to partially regenerate a digit following fracture and successful repair.51

❚❚❚ LIMB DEFORMITY SECONDARY TO GROWTH-PLATE FRACTURE AND EARLY CLOSURE Background Riser and Shirer were among the first to set out the principles on which growth-plate–induced limb defor-

Injuries to the distal radial or ulnar growth plates typically cause the most serious limb deformities in dogs. Of equal or greater importance, however, are the related dislocations that develop in the elbow, which can eventually lead to osteoarthritis. Injuries to the distal radial physis can cause shortening, making it appear as if the radial head is pulling away from the humeroradial joint. Meanwhile, the ulna, which is attempting to grow normally, seems to be pushing the distal humerus proximally and, in the process, dislocating the humeroulnar joint. A damaged distal ulnar growth plate likewise causes shortening but with the reverse effects to the elbow joints: the radial appears to be pushing proximally, and the ulnar seems to be pulling distally. Injuries to the proximal radial growth physis resemble those to the distal growth plate but with less deformity and articular dislocation because the proximal radial physis contributes less to axial growth than the distal physis. Injuries to the proximal ulnar growth plate can lead to underdevelopment of the olecranon but usually little else. Recall that the olecranon is an apophysis, not an epiphysis, and as such it makes only a minor contribution to bone length. Figures 2-100 to 2-110 exemplify these and other types of growth-plate injuries.

❚❚❚ SUGGESTED READING For an overview of the sonographic appearance of extremital soft tissue injuries in pets, I recommend the following paper by Kramer and colleagues: “Sonography of the Musculoskeletal System in Dogs and Cats,” in Veterinary Radiology & Ultrasound 38:139, 1997. Text continued on p. 91

A

B

C

D

Figure 2-88 • Full-length lateral (A) and frontal (B) views of the radius and ulna of a dog that broke its leg 3 months earlier and was treated by casting. C, Close-up frontal view shows a nonpurposeful callus, one that develops around the fragment ends but fails to bridge the fracture gap. D, Nonunions such as this are often re-treated surgically by removing the bone ends, inserting a cancellous bone graft, and plating the fracture.

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SECTION I ❚❚❚ The Extremities

A

B

Figure 2-89 • Lateral (A) and frontal (B) close-up views of an ulnar nonunion operated on 6 months earlier. The cubital joint is arthritic because of an ununited anconeal process.

CHAPTER 2 ❚❚❚ Extremital Injury

75

C

A

B

D

Figure 2-90 • Lateral (A) and frontal (B) views before and after (C, D) pin removal of a femoral shaft fracture in a cat repaired with a large threaded intramedullary pin and a single wire loop. For the present at least, the circlage wire is inhibiting growth of the central portion of the callus, preventing it from bridging the fracture (nonunion).

76

SECTION I ❚❚❚ The Extremities

A

B

Figure 2-91 • A, Lateral view of the elbow of a middle-aged Irish Setter shows a nonunion fracture of the anconeal process, which was initially misdiagnosed as osteochondritis. B, Fortunately, the dog had been radiographed a year earlier for an unrelated problem, which provided a comparison view.

Figure 2-92 • Lateral view of a previously fractured distal femur shows a false joint (pseudoarthrosis), the result of a diaphyseal nonunion (hypertrophic type).

Figure 2-93 • Close-up frontal view of the stifle shows a nonunion fracture in the proximal half of the patella. Stress radiography conducted with the dog unconscious failed to show any fragment movement, indicating a rigid fibrous union.

CHAPTER 2 ❚❚❚ Extremital Injury

Figure 2-94 • Close-up lateral and full-length views of femoral malunion 2 years after surgery show abnormal angulations in both standard imaging planes, but as yet there is no osteoarthritis.

77

78

SECTION I ❚❚❚ The Extremities

B

A

C

D

Figure 2-95 • Close-up lateral (A) and frontal (B) views of an untreated femoral growth plate fracture in an immature dog about 3 weeks after the injury; films made a year later show severe malunion but no osteoarthritis (C, D).

CHAPTER 2 ❚❚❚ Extremital Injury

79

A Figure 2-96 • Lateral view of the tarsus of a cat shows a side-to-side malunion of the fifth metacarpal bone.

B

D

C Figure 2-97 • Full-length (A, C) and close-up (B, D) frontal and lateral views of a mid and lower forelimb show medial bowing at the level of the distal radius caused by a previous fracture.

80

SECTION I ❚❚❚ The Extremities

Figure 2-98 • Flexed lateral view of the elbow shows what at first glance appears to be osteochondritis of the coronoid but in reality is a healed articular fracture of the distal humerus with posttraumatic osteoarthritis.

A

A

B

C

D

B

Figure 2-99 • Lateral (A) and frontal (B) views show shortening, deformity, and outward distal rotation of the radius and ulna of a cat caused by an injury sustained as a kitten. Malunions are potentially most harmful when they occur before skeletal maturation because of their potentially deleterious effects on remaining bone and joint development.

Figure 2-100 • Postoperative films taken at 1 week (A, B) and 8 weeks (C, D) of a distal femoral growth plate fracture illustrating how some imperfectly reduced fractures of this type may self-correct over time, especially in the frontal plane.

CHAPTER 2 ❚❚❚ Extremital Injury

81

A

E D

C

B Figure 2-101 • Lateral (A) and frontal (B) views of the tibia and fibula in a cat recently struck by a car show badly displaced growth plate fractures at both ends of the tibia and distal end of the fibula. A frontal view of the uninjured opposite limb is included for comparison (C). Progress films made some months later (D, E) show shortening and deformity of the crus secondary to a combination of proximal and distal tibial malunions, and a distal fibular nonunion. The tarsocrural joint exemplifies posttraumatic osteoarthritis.

82

SECTION I ❚❚❚ The Extremities

B

A

C

D

Figure 2-102 • Close-up lateral (A), frontal (B), and frontal oblique (C) projections of the stifle of a cat show detachment and vertical splitting of the femoral epiphysis as a result of a growth plate fracture. Immediate postoperative images show near-anatomic reduction (D).

CHAPTER 2 ❚❚❚ Extremital Injury

E

F

G Figure 2-102 • cont’d Immediate postoperative images show near-anatomic reduction (E); later progress films show malunion and a small articular defect in the center of the lateral half of the femoral condyle (F, G).

83

84

SECTION I ❚❚❚ The Extremities

A

C

D

B Figure 2-103 • Full-length frontal (A), tarsocrural close-up (B), and lateral (C, D) views of the middle and distal portions of the hindlimb of an immature dog show multiple deformities (particularly of the genual joint and tibial tuberosity) caused by a previous injury. Normal opposite limb is provided for comparison.

CHAPTER 2 ❚❚❚ Extremital Injury

A

B

85

C

Figure 2-104 • Close-up lateral (A), frontal (B), medial oblique (C) views of a deformed tarsus of a cat, who, according to its owner, had been injured previously. Continued

86

D

SECTION I ❚❚❚ The Extremities

E

F

Figure 2-104 • cont‘d Lateral oblique (D) view of a deformed tarsus in a cat who, according to its owner, had been injured previously. Lateral and frontal views of the opposite tarsus are included for comparison (E, F)

CHAPTER 2 ❚❚❚ Extremital Injury

A

B

C

D

Figure 2-105 • Full-length lateral (A) and frontal (B) views of hindlimb in a 6-month-old Golden Retriever, deformed as a result of a previous proximal tibial growth plate fracture. The normal opposite limb is provided for comparison (C, D).

87

Figure 2-106 • Postural film (standing frontal view) of the tarsocrural joints of a dog thought to have sustained a distal tibial growth plate injury 6 weeks earlier. The combination of deviation, deformity, and swelling of the left tarsocrural joint (right) supports this diagnosis.

A

B

C

D

Figure 2-107 • Full-length and close-up lateral (A, B) and frontal views (C, D) of previously injured mid-forelimb show (1) upward dislocation of the articular portion of the proximal ulna, (2) downward dislocation of the articular portion of the proximal radius, (3) overall radial shortening, and (4) deformity or deviation (laterally) of the distal radius.

CHAPTER 2 ❚❚❚ Extremital Injury

E

89

F

Figure 2-107 • cont’d These findings are most likely the result of a distal radial growth plate fracture, secondary physeal closure, and reduced radial growth. Comparable views of the normal opposite limb are provided for comparison (E, F).

A

B

Figure 2-108 • A, Close-up lateral view of the distal radius and ulna of an immature dog injured 2 months earlier shows a large “sequestrum” in the center of a deformed and deviated radial metaphysis. B, The opposite limb is provided for comparison.

90

SECTION I ❚❚❚ The Extremities

B A

C

D

Figure 2-109 • A, Limb and joint deformities: ventrodorsal view of pelvis, hips, and upper hindlimbs of a young adult Borzoi injured as a puppy shows (1) left femoral deformity, (2) subluxation and arthritis of the left hip and stifle, and (3) lateral patella dislocation. Close-ups of the hips (B) and stifle (C, D) reveal further detail.

CHAPTER 2 ❚❚❚ Extremital Injury

Figure 2-110 • Limb deformity: Frontal view of the lower forelimbs (postural film made with dog standing and a horizontally directed x-ray beam) shows curvature of the distal radius and ulna and outward deviation of the paws (valgus deformity), the result of asymmetric physeal growth.

References 1. Fornage BD: Muscular trauma. In Fornage BD, ed: Musculoskeletal Ultrasound, New York, 1995, Churchill Livingstone. 2. Williams J, Bailey MQ, et al: Compartmental syndrome in a Labrador retriever. Vet Radiol Ultrasound 34:244, 1993. 3. Farrow CS: Musculoskeletal system. In Green RW, ed: Small Animal Ultrasound, Philadelphia, 1996, LippincottRaven. 4. Williams J, Bailey MQ, et al: Compartmental syndrome in a Labrador retriever. Vet Radiol Ultrasound 34:244, 1993. 5. Rewerts JM, Grooters AM, et al: Atraumatic rupture of the gastrocnemius muscle after corticosteroid administration in a dog. J Am Vet Med Assoc 210:655, 1997. 6. Salmeri KR: Radiographic diagnosis. Vet Rad 31:132, 1990. 7. Fitch RB, Wilson ER, et al: Radiographic, computed tomographic and magnetic resonance imaging evaluation of a chronic long digital extensor tendon avulsion in a dog. Vet Radiol Ultrasound 38:177, 1997. 8. Mahoney PN, Lamb CR: Articular, periarticular and juxtaarticular calcified bodies in the dog and cat: a radiologic review. Vet Radiol Ultrasound 37:3, 1996. 9. Long CD, Nyland TG: Ultrasonographic evaluation of the canine shoulder joint. Vet Radiol Ultrasound 40:372, 1999. 10. Guillard MJ, Mayo AK: Sprain of the short radial collateral ligament in a racing greyhound. J Small Anim Pract 41:169, 2000. 11. Denny HR, Barr RS: Partial carpal and pancarpal arthrodesis in the dog: a review of 50 cases. J Small Anim Pract 32:329, 1991. 12. Johnson KA: A radiographic study of the effects of autologous cancellous bone grafts on bone healing after carpal arthrodesis in the dog. Vet Rad 22:177, 1981. 13. Nordberg CC, Johnson KA: Magnetic resonance imaging of normal canine carpal ligaments. Vet Radiol Ultrasound 40:128, 1998. 14. Farrow CS: Carpal sprain injury in the dog. J Am Vet Rad Soc 18:38, 1977.

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15. O’Brian MG, Boudrieau RJ, Clark GN: Traumatic luxation of the cubital joint (elbow) in dogs: 44 cases (19781988). J Am Vet Med Assoc 201:1760, 1992. 16. Whitehair JG, Vasseur PB, Willits NH: Epidemiology of cranial cruciate ligament rupture in dogs. J Am Vet Med Assoc 203:1016, 1993. 17. Duval JM, Budsberg SC, et al: Breed, sex, and body weight as risk factors for rupture of the cranial crutiate ligament in young dogs. J Am Vet Med Assoc 215:811, 1999. 18. Bruce WJ: Multiple ligamentous injuries of the canine stifle joint: a study of 12 cases. J Small Anim Pract 39:333, 1998. 19. Soderstrom MJ, Rochat MC, Drost WT: Avulsion fracture of the caudal cruciate ligament. Vet Radiol Ultrasound 39:536, 1998. 20. Williams J, Fitch RB, Lemarie RJ: Partial avulsion of the origin of the cranial cruciate ligament in a 4-year-old dog. Vet Radiol Ultrasound 38:380, 1997. 21. Bennet D, May C: Meniscal damage associated with cruciate disease in the dog. J Small Anim Pract 32:111, 1999. 22. Lewis DD, Goring RL, et al: A comparison of diagnostic methods used in the evaluation of early degenerative joint disease in the dog. J Am Anim Hosp Assoc 23:305, 1987. 23. Baird DK, Hathcock JT, et al: Low-field magnetic resonance imaging of early subchondral cyst-like lesions in induced cranial cruciate ligament deficient dogs. Vet Radiol Ultrasound 39:167, 1998. 24. DeRooster H, vanBree H: Use of compression stress radiography for the detection of partial tears of the canine cranial cruciate ligament. J Small Anim Pract 40:573, 1999. 25. DeRooster H, vanBree H: Popliteal sesamoid displacement associated with cruciate rupture in a dog. J Small Anim Pract 40:316, 1999. 26. Montgomery RD, Fitch RB, et al: Radiographic imaging of the canine intercondyloid fossa. Vet Radiol Ultrasound 36:276, 1995. 27. Fitch RB, Hathcock JT, et al: Radiographic and computed tomographic evaluation of the canine intercondylar fossa in normal stifles and after notchplasty in stable and unstable stifles. Vet Radiol Ultrasound 37:266, 1996. 28. Reed AL, Payne JT, Constantinescu GM: Ultrasonographic anatomy of the normal canine stifle. Vet Radiol Ultrasound 36:315, 1995. 29. Kramer M, Stengel H, et al: Sonography of the canine stifle. Vet Radiol Ultrasound 40:282, 1999. 30. Widmer WR, Buckwalter KA, et al: Principles of magnetic resonance imaging and application to the stifle joint in dogs. J Am Vet Med Assoc 198:1914, 1991. 31. Widmer WR, Buckwalter KA, et al: Radiographic and magnetic resonance imaging of the stifle joint in experimental osteoarthritis of dogs. Vet Radiol Ultrasound 35:371, 1994. 32. Baird DK, Hathcock JT, et al: Low-field magnetic resonance imaging of the canine stifle joint: normal anatomy. Vet Radiol Ultrasound 39:87, 1998. 33. Banfield CM, Morrison WB: Magnetic resonance arthrography of the canine stifle joint: technique and applications in eleven military dogs. Vet Radiol Ultrasound 41:200, 2000. 34. Burk RL, Eich DW: Letter to the editor. J Am Vet Med Assoc 206:1838, 1995.

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35. Barrett RB: Radiography in trauma of the musculotendinous soft tissues of dogs and cats. J Am Vet Rad Soc 12:5, 1971. 36. Shah ZR, Crass JR, et al: Ultrasonic detection of foreign bodies in soft tissues using turkey muscle as a model. Vet Radiol Ultrasound 33:94, 1992. 37. Britt LG, Barbee DD, et al: Engorged ticks appearing as distinct radiographic opacities. Vet Radiol Ultrasound 41:145, 2000. 38. Huss B, Lattimer JC: What is your diagnosis? J Am Vet Med Assoc 204:1017, 1994. 39. Li A, Bennett D, et al: Radial carpal bone fractures in 15 dogs. J Small Anim Pract 41:74, 2000. 40. Cook JL, Jordan RC: What is your diagnosis? J Am Vet Med Assoc 210:329, 1997. 41. Boulay JP, Wallace LJ, Lipowitz AJ: Pathological fracture of long bones in the dog. J Am Anim Hosp Assoc 23:207, 1997. 42. Parker RB, Spencer CP, Shields RP: Radiographic diagnosis. Vet Rad 26:208, 1985. 43. Huss BT, Helmick KE: What is your diagnosis? J Am Vet Med Assoc 205:982, 1994. 44. Zontine WJ: Bilateral stress pattern in the distal ulna metaphyses of a Great Dane. J Am Vet Rad Soc 13:53, 1972. 45. McCartney WT, Carmichael S: Talar neck fractures in 5 cats. J Small Anim Pract 41:204, 2000. 46. Miller CW, Sumner-Smith G: Using the Unger System to classify 386 long bone fractures in dogs. J Small Anim Pract 39:390, 1998.

47. Johnson AJ, Smith CW, Schaeffer DJ: Fragment reconstruction and bone plate fixation versus bridging plate fixation for treating highly comminuted femoral fractures in dogs: 35 cases (1987-1997). J Am Vet Med Assoc 213:1157, 1998. 48. Marchiori DM: Trauma. In Marchiori DM, ed: Clinical Imaging, St. Louis, 1999, Mosby. 49. Anderson MA, Mann FA, Branson KR, et al: Use of an ultrasonic Doppler flow detector for determining tissue viability in a dog. J Am Vet Med Assoc 205:319, 1994. 50. Punto L, Puranen J, Mokka REM: Osteomedullography in tibial shaft fractures of the dog and pig. J Am Vet Rad Soc 18:102, 1977. 51. Anderson MA, Muhlbauer MC: Aberrant bone growth following phalangeal fracture. Vet Radiol Ultrasound 38:48, 1997. 52. Riser WH, Shirer JF: Normal and abnormal growth of the distal foreleg in large and giant dogs. J Am Vet Rad Soc 6:50, 1965. 53. Carrig CB, Morgan JP: Asynchronous growth of the canine radius and ulna—early radiographic changes following experimental retardation of longitudinal growth of the ulna. J Am Vet Rad Soc 16:121, 1975. 54. Carrig CB, Morgan JP, Pool RR: Effects of x-irradiation on the distal ulnar growth plate of the dog: gross radiographic changes. J Am Vet Rad Soc 16:211, 1975. 55. Carrig CB, Merkley DF, Mostosky UV: Asynchronous growth of the canine radius and ulna: effects of different amounts of ulnar growth retardation. J Am Vet Rad Soc 19:16, 1978.

C h a p t e r

3

Osteoarthritis

❚❚❚ THE LANGUAGE OF ARTHRITIS Osteoarthritis or Osteoarthrosis? The terms osteoarthrosis and osteoarthritis are synonymous. The suffixes osis and itis are for the most part cultural preferences, with the European medical community preferring osteoarthrosis, whereas North Americans generally favor osteoarthritis.

Generative or Degenerative Joint Disease A persuasive argument has been advanced in favor of the term generative joint disease over the currently favored expression, degenerative joint disease. Briefly, the line of reasoning supporting generative joint disease is that most of the radiographic signs of osteoarthritis, spurring (osteophytes), sclerosis, eburnation, and joint bodies, are additions to the joint—indications of a generative process, not a degenerative one. The only change that qualifies as degenerative is the gradual disappearance of the articular cartilage, as inferred by narrowing of the cartilage space. Moreover, angiographic studies on dogs with experimental and naturally occurring osteoarthritis consistently show localized and regional hyperemia, further attesting to the generative nature of osteoarthritis.1

Radiographic Appearance of Osteoarthritis First and foremost, osteoarthritis is characterized by periarticular osteophytes. As the disease progresses, the existing osteophytes enlarge, and new deposits form. Depending on which joint is affected, the cartilage space may narrow or even collapse. Although subchondral sclerosis is often mentioned as being a consistent and reliable indicator of osteoarthritis—presumably developing due to boneto-bone contact—I have found it to be inconsistently present. Another problem relates to the reliability of

this observation because periarticular osteophytes can mimic an increase in subchondral bone density (Figure 3-1, A, B).

MRI Appearance of Osteoarthritis Articular Cartilage. Baird and coworkers determined, based on experimentation with gelatin phantoms, that magnetic resonance imaging (MRI) can potentially be used to detect excessive hydration in articular cartilage, one of the pathologic precursors of osteoarthritis. Using a low-field strength magnet, T2, and inversion recovery with short inversion time provided the best images among the various sequences tried.2 Using experimental dogs whose cranial cruciate ligament had been cut, the authors were able to show a relative increase in signal intensity of the articular cartilage of the weight-bearing portion of the lateral femoral condyle and the caudal portion of the medial tibial condyle, presumably related to increased proteoglycan synthesis.

Synovitis: A Consequence of Osteoarthritis Osteoarthritis often leads to secondary synovitis, which if severe can cause extensive joint swelling. Cantwell described the use of arthrography to delineate the full extent of the resultant capsular distension.3

Categorizing Osteoarthritis Developmental Osteoarthritis. Hip dysplasia and osteochondritis are examples of common developmental diseases that cause osteoarthritis in part by decreasing or eliminating joint congruity (Figure 3-2, A, B). Posttraumatic Osteoarthritis. Dislocations, articular fractures, severe sprains, and arthroplasties are all capable of causing osteoarthritis, as shown in Figures 3-3, A, B, and 3-4. 93

94

SECTION I ❚❚❚ The Extremities

A A

B Figure 3-1 • Close-up lateral (A) and frontal (B) views of an

B Figure 3-2 • Two examples of developmental osteoarthritis in

arthritic stifle in a small dog, the result of an old injury, show a classic array of periarticular osteophytes.

the dog: hip dysplasia (A) and osteochondritis (B) of the coronoid process.

Specific Diseases Causing Osteoarthritis

replacement of the femoral head and neck was advocated (derotational osteotomy) but appeared to garner only limited interest.7 Another “corrective” surgery, acetabular relocation (triple pelvic osteotomy), often results in trading one problem for another. The hip is made more congruent, potentially decreasing the probability of osteoarthritis, but at the cost of narrowing the pelvic canal, which may then lead to chronic constipation. Additionally, the unstabilized ischial fragment often heals with a pronounced downward deflection, which can lead to an undesirable squatting posture.

Hip Dysplasia Background. Certain breeds of dogs are more susceptible to hip dysplasia than others, whereas others rarely develop it.4 Programs established to eradicate dysplasia in susceptible breeds have only been partially successful.5 As repeatedly shown in both people and animals with osteoarthritis, maintenance of body weight at or below the norm (for the individual) usually results in reduced pain and disability. My own observation is that daily nonforced exercise is even more beneficial.6 In the seemingly endless quest for a surgical solution to the problem of hip dysplasia, removal and

Imaging Findings Radiology. Morgan has drawn attention to a narrow, crescent-shaped ridge of bone located on the proximal

CHAPTER 3 ❚❚❚ Osteoarthritis

A

95

Figure 3-4 • Close-up lateral view of the stifle of a dog with a Steinmann pin protruding into the genual joint causing extensive dystrophic calcification. The tibia was fractured and subsequently pinned some months earlier. Also, note the focal bone loss at the base of the femoral trochlea, the result of repeated pin trauma, and the markedly swollen joint.

B arthritic stifle, the result of long-standing instability caused by a ruptured cranial cruciate, and second-degree sprain of the caudal cruciate ligament.

Figure 3-5 • Severe bilateral hip dysplasia with advanced osteoarthritis. Opinion differs as to whether the large cranial acetabular bone deposits are fractured osteophytes or merely atypical periarticular osteophytes.

aspect of the base of the femoral neck (as seen in the extended ventrodorsal projection). He terms this finding a “spur” and contends that it may be a very early indicator of canine hip dysplasia.8 However, most radiologic reports of osteoarthritis secondary to hip dysplasia have focused on new bone deposition, which initially develops at the edges of the joint capsule, and later, along the articular margins of the femoral head and acetabulum (Figure 3-5). As the hip becomes more arthritic, a large lip of new bone begins to form along the dorsal rim of the acetabulum; extending it laterally, in some cases by as much as 50 percent. This portion of the arthritic acetabulum is often mistakenly described as representing a line of

closely approximated osteophytes, or even more simplistically as subchondral sclerosis. In fact, this is a purposeful and predictable form of remodeling—an effort by the dysplastic acetabulum to accommodate the new dynamic of an excessively mobile femur. For its part, the contour of the femoral head begins to change from its normal spherical shape to a broader and shallower configuration. Concurrently, twin collars of new bone begin to form along the articular and capsular margins, which radiographically have often incorrectly been described as “filling in” or “thickening” of the femoral neck. Another misconception is that the bones of the coxal joint become incongruent. This is not the case. What

Figure 3-3 • Close-up frontal (A) and lateral (B) views of severely

96

SECTION I ❚❚❚ The Extremities

A

Figure 3-7 • Close-up lateral view of arthritic elbow (opposite side also affected, but not shown).

B Figure 3-6 • A, Defleshed elbow of a 2-year-old dog with osteochondritis (medial perspective) shows a myriad of bone deposits that characterize the arthritic pattern resulting from a detached medial coronoid process (emphasis zone). B, Closeup view of the articular surface of the detached medial coronoid process, photographed on the surface of a penny to enable the reader to better appreciate its actual size.

actually happens is that the area of congruency is reduced, with a commensurate loss of motion range. Ultrasound. Ultrasound as a means of early hip dysplasia detection in puppies is typically time-consuming, often ambiguous, and thus of little practical use.

Osteochondritis Osteochondritis, especially the fragmenting form (osteochondritis dissicans), causes opposing joint surfaces to become dissimilar, an incongruency that typically leads to osteoarthritis. If the affected part of the bone is weight bearing, for example, the medial coronoid process, the resultant osteoarthritis will be even greater due to partial dislocation and abnormal movement of the overlying bone (Figure 3-6). Detachment or relocation of the anconeal process also results in abnormal joint motion leading to severe osteoarthritis.

Figure 3-8 • Close-up frontal views of arthritic elbows of a dog afflicted by bilateral osteochondritis of the coronoid show the large bony beaks characteristic of the advanced form of the disease.

Figures 3-7 to 3-9 exemplify the characteristic arthritic pattern caused by osteochondritis of the elbow.

Avascular Necrosis, Legg-CalvéPerthes Disease Background. Lee was one of the first veterinary radiologists to graphically describe the radiographic disintegration of the femoral head in avascular necrosis (AVN).9 A unique, noninfectious form of bone necrosis, this disease initially causes core destruction, weakening the bone to the extent that portions of the perimeter fragment and collapse. The badly damaged femoral head then heals spontaneously, but not before becoming severely deformed. The resultant mismatch of the remodeled femoral head and normal acetabulum causes the hip to become gradually arthritic.

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97

A

Figure 3-10 • A ventrodorsal close-up view of the left hip of a dog with advanced Legg-Calvé-Perthes disease. In this final stage, the partially disintegrated femoral head has healed, but in a new shape that does not match the acetabulum (the cause of subsequent osteoarthritis).

Radiology (Human). Arlet and Ficat have proposed the following staging for human AVN, based on the following radiographic criteria10:

B Figure 3-9 • Close-up lateral (A) and frontal (B) views of a severely arthritic elbow caused by an ununited anconeal process in a 10-year-old Springer Spaniel mistakenly diagnosed as an osteosarcoma.

Imaging Findings Radiology (Veterinary). The first radiographic indication of AVN in dogs is a subtle widening of the hip joint—widening that often cannot be appreciated without an opposite side comparison. Next, the affected femoral head begins to take on a distinctive pockmarked appearance as the interior of the bone starts to become necrotic. As the damage becomes more extensive, so do the visible areas of bone loss. When there is sufficient trabecular destruction, the cortex begins to crack and then collapse. At this point, the femoral head may appear overtly fragmented. Healing is characterized by a reversal of the previously described events; however, the femoral head fails to regain its original spherical shape, instead, assuming a distinctive conical configuration. It is this deformity that provokes the structurally normal acetabulum to follow suit and become arthritic (Figure 3-10).

Stage 1: Normal radiographic appearance of the hip but abnormal bone scans; patient has pain and decreased range of motion. Stage 2: Radiographs show osteoporosis and multiple cystic or sclerotic lesions. Stage 3: Radiographs show marginal fissures, fragmentation, and collapse. Stage 4: Radiographs show overt disintegration of the femoral head. Stage 5: Severe deformation of the femoral head causes reciprocal acetabular remodeling and osteoarthritis of the hip. MRI. Little information appears in the veterinary literature on the magnetic resonance (MR) appearance on AVN in dogs, in part due to the fact that no satisfactory treatment currently exists. However, if core decompression (a treatment currently being tried in people with the disease) proves effective, MR could prove indispensable in the early identification of the AVN when decompressive surgery is believed to be most effective. In humans, AVN is characterized by variably sized and shaped areas of decreased signal intensity on T1weighted images. Intermediate-to-advanced lesions often appear as crescentic objects lying just beneath the articular surface of the femoral head.11 In an attempt to clinically stage the disease, Mitchell and co-workers devised the following classification (the lower the number, the better the prognosis).12

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SECTION I ❚❚❚ The Extremities

Class A: High-strength signal on short TR/TE images; medium strength signal on T2 (resembles fat). Class B: High-strength signal on both short and long TR/TE images (resembles blood). Class C: Low-strength signal on short TR/TE images (resembles fluid). Class D: Low-strength signal on all images (resembles fibrous tissue).

Intraarticular Calcification, Ossification, and Fragmentation (Table 3-1) Polyarthritis. Acute polyarthritis can sometimes be inferred radiographically because of bilateral swelling identified in the carpi, stifles, or hocks. In the case of the stifles, the observed swelling may be mistakenly attributed to cruciate trauma, especially if the animal is thought to have a unilateral lameness (Figure 3-11, A, B). Chronic polyostotic immunoarthritis often leads to multiple partial dislocations, especially in the carpal and tarsal joints. When the stifles are affected, these dislocations, combined with associated joint swelling, can be mistaken for a chronic cruciate injury resulting in posttraumatic osteoarthritis.13 So-called erosive polyarthritis (a term used almost exclusively by physician rheumatologists), which primarily affects the cubital, genual, and tarsocrural joints, has been described in a pair of 11-month-old Greyhounds. Radiographically, the elbows, stifles, and hocks were mildly swollen, whereas the distal radius and radial carpal bone appeared bilaterally osteopenic

with a narrowed cartilage space. Focal lesions in the articular cartilage (termed erosions by the authors) and synovial discoloration and plaque formation suggested immunoarthritis; however, the diagnosis could not be confirmed.14 Immunoarthritis (Immune-mediated Osteoarthritis) Background. Immunoarthritis is the simplest term for describing the various forms of immune-mediated polyarthritis found in dogs and cats. Laboratory testing is usually required to be more specific, for example, rheumatoid arthritis, rheumatoid-like arthritis, or systemic lupus. To describe arthritis as “deforming” or “nondeforming” does little to refine the diagnosis because deformity is more an indication of duration than of etiology. Imaging Findings. Among the radiographic features that potentially characterize immunoarthritis in dogs, multiple, variably shaped and sized areas of decreased bone density, especially in the carpal or tarsal bones, are the most reliable. In this latter regard a carpal fibrosarcoma has been reported, which radiographically appeared as numerous punctate lucencies resembling immunoarthritis. But unlike immune-mediated osteoarthritis, there were also large, poorly marginated lucencies with overlying soft tissue swelling in the distal radius and ulna.15 Animals that have had immunoarthritis for an extended period of time (months or years) are also likely to show varying degrees of osteopenia and joint laxity (Figure 3-12). Related postural abnormalities—

Table 3-1 • DIFFERENTIAL DIAGNOSIS FOR INTRAARTICULAR BONE OR BONELIKE DENSITIES Cause

Comment

Capsular dystrophic calcification Meniscal ossification

Capsular or pericapsular calcification suggests gout or pseudogout. Primary and secondary meniscal ossification/calcification have been reported but are extremely rare. Secondary meniscal calcification is believed to result from injury, including meniscal surgery. The cause of primary meniscal ossification is not known.20 Most often the result of serious knee injuries. Most common in the shoulder and hock. This disease is common in older cats, but rare in dogs. Usually very small, immobile fragments, positioned in the cranial aspect of the joint near the tibial tubercles. Rare, and when present, difficult to see.

Mineralized cartilage fragment Osteochondritis Osteochondromatosis Sprain-avulsion fracture of the caudal cruciate ligament Sprain-avulsion fracture of the cranial cruciate ligament Sprain-avulsion fracture of the medial or lateral collateral ligaments Strain-avulsion fracture of the long digital extensor tendon Torn medial or lateral meniscus

Typically best seen in frontal projection midway between the physeal growth scar and the joint cavity. Avulsion of the long extensor often produces a vary large fragment, which is readily identified in the lateral projection near an enlarged extensor fossa. Typically appears as a streaky form of mineralization in one of the miniscal fields, usually medially.

CHAPTER 3 ❚❚❚ Osteoarthritis

99

A

Figure 3-12 • Frontal view of the carpi of a dog with immunoarthritis shows characteristic swelling, focal areas of bone loss, and osteopenia in the surrounding bone.

B Figure 3-11 • A, Lateral close-up view of the genual joint of a dog referred for cruciate surgery (based on pain, swelling, and instability of the knee) shows severe swelling, but no dislocation or arthritis. B, Examination revealed similar signs in the opposite stifle, which was also radiographed, and found to have similar abnormalities. These findings are consistent with polyarthritis, probably of an autoimmune nature.

particularly evident in weight-bearing views—are typically most pronounced in the carpus (Figure 3-13), tarsus, and stifle, and in the case of the latter, may be mistaken for a ruptured cruciate ligament. Joint swelling and cartilage space narrowing are usually present in chronic cases but do little to distinguish immunoarthritis from other forms of osteoarthritis, except for the fact that they are found bilaterally. Some dogs with longstanding immunoarthritis have large extraarticular osteophytes, as well as numerous islands of periarticular bone. Joint surveys often reveal bilateral or quadrilateral limb involvement in such instances (Figure 3-14).

Figure 3-13 • Frontal, weight-bearing view of the carpi of a dog with immunoarthritis show bilateral: (1) valgus deformity, (2) joint swelling, (3) dislocation of numerous carpal bones, (4) cartilage space narrowing, and (4) focal areas of bone loss typical of immunoarthritis.

Postsurgical Osteoarthritis Most surgically repaired fractures in dogs and cats heal to the extent that the animal regains full and relatively pain-free use of the injured limb. When this does not happen, the surgery is deemed a failure or a partial success, depending on one’s level of optimism. Causes of failed orthopedic surgery include operatively

100

SECTION I ❚❚❚ The Extremities

A

B

C Figure 3-14 • Close-up frontal and lateral views of the elbows (A, B) and tarsi (C, D) of a dog initially diagnosed as having osteochondritis but later found to have immunoarthritis.

CHAPTER 3 ❚❚❚ Osteoarthritis

101

D Figure 3-14, cont’d For legend see opposite page.

Figure 3-15 • Lateral close-up view of the genual joint of a dog operated on for a cruciate injury 2 years earlier shows moderate osteoarthritis, especially of the femoropatella joint. Note the enlarged extensor fossa craniodistal aspect of femur, which some contend becomes larger with instability. The abnormally flattened femoral trochlea, which perfectly matches the deformed patella, is a true example of adaptive remodeling.

introduced infection; misapplied, dislocated, loosened or broken implants; malunion or non-union; and postoperative osteoarthritis (Figures 3-15 and 3-16). Reconstructive hip and knee surgery aimed at halting the progress of osteoarthritis has not always proven beneficial, in some instances creating problems more debilitating than those for which the animal was originally operated. Examples of such potentially hazardous procedures include the following: relocating the acetabulum of a dysplastic hip (acetabular reloca-

tion, triple pelvic osteotomy) and relocating the articular portion of the proximal tibial epiphysis (Figures 3-17 to 3-20).

Gout and Pseudogout False gout or pseudogout, also called calcium pyrophosphate dihydrate crystal deposition disease, has been reported in a 13-year-old dog with acute multiple limb lameness. Radiographs of the carpi

102

SECTION I ❚❚❚ The Extremities

A

B

C Figure 3-16 • A, Lateral close-up view of the elbow of a dog hit by a car shows a fracture–dislocation (Monteggia’s fracture). B, An immediate postoperative view shows near anatomic reduction. C, Three months later, after removal of all but one of the implants, the elbow appears severely arthritic.

CHAPTER 3 ❚❚❚ Osteoarthritis

A

103

B

Figure 3-17 • A, Ventrodorsal view of the pelvis and hips shows severe bilateral hip dysplasia with osteoarthritis on the right. B, After surgery to relocate the left acetabulum, the pelvic canal is severely narrowed, resulting in periodic constipation and a pronounced nonpainful mechanical lameness. Note the badly displaced left ischial tuberosity (emphasis zone, bottom right).

A

B

Figure 3-18 • Preoperative (A) and postoperative (B) ventrodorsal views of the pelvis and hips show bilateral acetabular relocations, which, although providing greater femoral head “coverage,” have severely narrowed the pelvic canal, causing chronic constipation.

104

SECTION I ❚❚❚ The Extremities

A

B

Figure 3-19 • A, Lateral close-up view of canine stifle operated on in an effort to restabilize the joint after acute cranial cruciate rupture. The joint is now painfully arthritic, and the stabilizing wire has predictably broken. B, In a second surgery, the cranial part of the proximal tibial epiphysis was relocated, but as seen in this lateral close-up, this only seems to have increased the degree of dislocation and amount of arthritis.

A B Figure 3-20 • A, Immediate postoperative film of a tibial relocation; B, subsequent progress check reveals a fracture proximally.

CHAPTER 3 ❚❚❚ Osteoarthritis

A

105

B

Figure 3-21 • Close-up lateral oblique view of proximal ulna (A) and rear view of distal humerus (B) show massive cavitation—the result of synovial storage disease. The shadow in the lateral oblique view, like a radiographic projection, shows the extent to which the articular contour has been altered.

showed faint mineralization on the perimeter of the antibrachial joints.16 Two other reports of false gout in dogs described capsular masses in the carpal and metacarpophalangeal joints.17,18

Storage Disease Doige and I have described a storagelike disease in a dog that featured marked subchondral cavitation of major limb joints caused by ingrowth of a hyperplastic synovium (Figures 3-21).19

References 1. Tirgari M: Blood pattern changes in primary and secondary osteoarthritis of the dog: an experimental study using intraosseous venography. J Am Vet Rad Soc 19:83, 1978. 2. Baird DK, Kinkaid SA, et al: Effect of hydration on signal intensity of gelatin phantoms using low-field magnetic resonance imaging: possible application in osteoarthritis. Vet Radiol & Ultrasound 40:27, 1999. 3. Cantwell DH: Radiographic diagnosis. Vet Rad 27:151, 1986. 4. Ackerman N: Hip dysplasia in the Afgan Hound. Vet Rad 23:88, 1982. 5. Leppanen M, Maki K, et al: Factors affecting hip dysplasia in German Shepherd dogs in Finland: efficacy of the current improvement program. J Small Anim Pract 41:19, 2000. 6. Impellzeri JA, Tetrick MA, Muir P: Effect of weight reduction on clinical signs of lameness in dogs with hip osteoarthritis. J Am Vet Med Assoc 216:1089, 2000.

7. Nunamaker DM, Biery DN, Newton CD: Femoral neck antiversion in the dog: its radiographic measurement. J Am Vet Rad Soc 14:45, 1973. 8. Morgan JP: Canine hip dysplasia. Vet Rad 28:2, 1987. 9. Lee R: Legg-Perthes disease in the dog: the histological and associated radiological changes. J Am Vet Rad Soc 15(1):24, 1974. 10. Arlet J, Ficat RP: Diagnostic de l’osteo-necrose femoro capitale primitive au stade. Rev Chir Orthop 54:637, 1965. 11. Murphy MD: The hip. In Haaga JR, ed: Computed Tomography & Magnetic Resonance Imaging of the Whole Body, ed 3, vol 2. St Louis, 1994, Mosby. 12. Mitchell DG, et al: Femoral head avascular necrosis: correlation with MR imaging, radiographic staging, radionuclide imaging, and clinical findings. Radiology 162:709, 1987. 13. Roberts R: Radiographs presented as part of the 1992 A.C.V.R. oral certification examination: musculoskeletal section. Vet Radiol & Ultrasound 34:185, 1993. 14. Woodard JC, Riser WH, et al: Erosive polyarthritis in two Greyhounds. J Am Vet Med Assoc 198:873, 1991. 15. Applewhite AA, Page RL: What is your diagnosis? J Am Vet Med Assoc 214:29, 1999. 16. DeHaan JJ, Anderson CB: Calcium crystal-associated arthropathy (pseudogout) in a dog. J Am Vet Med Assoc 200:943, 1992. 17. Gibson JP, Roenigk WJ: Pseudogout in a dog. J Am Vet Med Assoc 161:912, 1972. 18. Heimann M, Carpenter JL, Halverson PB: Calcium pyrophosphate deposition (chondrocalcinosis) in a dog. Vet Pathol 27:122, 1990. 19. Doige CE, Farrow CS, Gee BR: Astorage-like disease with skeletal involvement in a dog. Vet Rad 21:98, 1980.

C h a p t e r

3

Osteoarthritis

❚❚❚ THE LANGUAGE OF ARTHRITIS Osteoarthritis or Osteoarthrosis? The terms osteoarthrosis and osteoarthritis are synonymous. The suffixes osis and itis are for the most part cultural preferences, with the European medical community preferring osteoarthrosis, whereas North Americans generally favor osteoarthritis.

Generative or Degenerative Joint Disease A persuasive argument has been advanced in favor of the term generative joint disease over the currently favored expression, degenerative joint disease. Briefly, the line of reasoning supporting generative joint disease is that most of the radiographic signs of osteoarthritis, spurring (osteophytes), sclerosis, eburnation, and joint bodies, are additions to the joint—indications of a generative process, not a degenerative one. The only change that qualifies as degenerative is the gradual disappearance of the articular cartilage, as inferred by narrowing of the cartilage space. Moreover, angiographic studies on dogs with experimental and naturally occurring osteoarthritis consistently show localized and regional hyperemia, further attesting to the generative nature of osteoarthritis.1

Radiographic Appearance of Osteoarthritis First and foremost, osteoarthritis is characterized by periarticular osteophytes. As the disease progresses, the existing osteophytes enlarge, and new deposits form. Depending on which joint is affected, the cartilage space may narrow or even collapse. Although subchondral sclerosis is often mentioned as being a consistent and reliable indicator of osteoarthritis—presumably developing due to boneto-bone contact—I have found it to be inconsistently present. Another problem relates to the reliability of

this observation because periarticular osteophytes can mimic an increase in subchondral bone density (Figure 3-1, A, B).

MRI Appearance of Osteoarthritis Articular Cartilage. Baird and coworkers determined, based on experimentation with gelatin phantoms, that magnetic resonance imaging (MRI) can potentially be used to detect excessive hydration in articular cartilage, one of the pathologic precursors of osteoarthritis. Using a low-field strength magnet, T2, and inversion recovery with short inversion time provided the best images among the various sequences tried.2 Using experimental dogs whose cranial cruciate ligament had been cut, the authors were able to show a relative increase in signal intensity of the articular cartilage of the weight-bearing portion of the lateral femoral condyle and the caudal portion of the medial tibial condyle, presumably related to increased proteoglycan synthesis.

Synovitis: A Consequence of Osteoarthritis Osteoarthritis often leads to secondary synovitis, which if severe can cause extensive joint swelling. Cantwell described the use of arthrography to delineate the full extent of the resultant capsular distension.3

Categorizing Osteoarthritis Developmental Osteoarthritis. Hip dysplasia and osteochondritis are examples of common developmental diseases that cause osteoarthritis in part by decreasing or eliminating joint congruity (Figure 3-2, A, B). Posttraumatic Osteoarthritis. Dislocations, articular fractures, severe sprains, and arthroplasties are all capable of causing osteoarthritis, as shown in Figures 3-3, A, B, and 3-4. 93

94

SECTION I ❚❚❚ The Extremities

A A

B Figure 3-1 • Close-up lateral (A) and frontal (B) views of an

B Figure 3-2 • Two examples of developmental osteoarthritis in

arthritic stifle in a small dog, the result of an old injury, show a classic array of periarticular osteophytes.

the dog: hip dysplasia (A) and osteochondritis (B) of the coronoid process.

Specific Diseases Causing Osteoarthritis

replacement of the femoral head and neck was advocated (derotational osteotomy) but appeared to garner only limited interest.7 Another “corrective” surgery, acetabular relocation (triple pelvic osteotomy), often results in trading one problem for another. The hip is made more congruent, potentially decreasing the probability of osteoarthritis, but at the cost of narrowing the pelvic canal, which may then lead to chronic constipation. Additionally, the unstabilized ischial fragment often heals with a pronounced downward deflection, which can lead to an undesirable squatting posture.

Hip Dysplasia Background. Certain breeds of dogs are more susceptible to hip dysplasia than others, whereas others rarely develop it.4 Programs established to eradicate dysplasia in susceptible breeds have only been partially successful.5 As repeatedly shown in both people and animals with osteoarthritis, maintenance of body weight at or below the norm (for the individual) usually results in reduced pain and disability. My own observation is that daily nonforced exercise is even more beneficial.6 In the seemingly endless quest for a surgical solution to the problem of hip dysplasia, removal and

Imaging Findings Radiology. Morgan has drawn attention to a narrow, crescent-shaped ridge of bone located on the proximal

CHAPTER 3 ❚❚❚ Osteoarthritis

A

95

Figure 3-4 • Close-up lateral view of the stifle of a dog with a Steinmann pin protruding into the genual joint causing extensive dystrophic calcification. The tibia was fractured and subsequently pinned some months earlier. Also, note the focal bone loss at the base of the femoral trochlea, the result of repeated pin trauma, and the markedly swollen joint.

B arthritic stifle, the result of long-standing instability caused by a ruptured cranial cruciate, and second-degree sprain of the caudal cruciate ligament.

Figure 3-5 • Severe bilateral hip dysplasia with advanced osteoarthritis. Opinion differs as to whether the large cranial acetabular bone deposits are fractured osteophytes or merely atypical periarticular osteophytes.

aspect of the base of the femoral neck (as seen in the extended ventrodorsal projection). He terms this finding a “spur” and contends that it may be a very early indicator of canine hip dysplasia.8 However, most radiologic reports of osteoarthritis secondary to hip dysplasia have focused on new bone deposition, which initially develops at the edges of the joint capsule, and later, along the articular margins of the femoral head and acetabulum (Figure 3-5). As the hip becomes more arthritic, a large lip of new bone begins to form along the dorsal rim of the acetabulum; extending it laterally, in some cases by as much as 50 percent. This portion of the arthritic acetabulum is often mistakenly described as representing a line of

closely approximated osteophytes, or even more simplistically as subchondral sclerosis. In fact, this is a purposeful and predictable form of remodeling—an effort by the dysplastic acetabulum to accommodate the new dynamic of an excessively mobile femur. For its part, the contour of the femoral head begins to change from its normal spherical shape to a broader and shallower configuration. Concurrently, twin collars of new bone begin to form along the articular and capsular margins, which radiographically have often incorrectly been described as “filling in” or “thickening” of the femoral neck. Another misconception is that the bones of the coxal joint become incongruent. This is not the case. What

Figure 3-3 • Close-up frontal (A) and lateral (B) views of severely

96

SECTION I ❚❚❚ The Extremities

A

Figure 3-7 • Close-up lateral view of arthritic elbow (opposite side also affected, but not shown).

B Figure 3-6 • A, Defleshed elbow of a 2-year-old dog with osteochondritis (medial perspective) shows a myriad of bone deposits that characterize the arthritic pattern resulting from a detached medial coronoid process (emphasis zone). B, Closeup view of the articular surface of the detached medial coronoid process, photographed on the surface of a penny to enable the reader to better appreciate its actual size.

actually happens is that the area of congruency is reduced, with a commensurate loss of motion range. Ultrasound. Ultrasound as a means of early hip dysplasia detection in puppies is typically time-consuming, often ambiguous, and thus of little practical use.

Osteochondritis Osteochondritis, especially the fragmenting form (osteochondritis dissicans), causes opposing joint surfaces to become dissimilar, an incongruency that typically leads to osteoarthritis. If the affected part of the bone is weight bearing, for example, the medial coronoid process, the resultant osteoarthritis will be even greater due to partial dislocation and abnormal movement of the overlying bone (Figure 3-6). Detachment or relocation of the anconeal process also results in abnormal joint motion leading to severe osteoarthritis.

Figure 3-8 • Close-up frontal views of arthritic elbows of a dog afflicted by bilateral osteochondritis of the coronoid show the large bony beaks characteristic of the advanced form of the disease.

Figures 3-7 to 3-9 exemplify the characteristic arthritic pattern caused by osteochondritis of the elbow.

Avascular Necrosis, Legg-CalvéPerthes Disease Background. Lee was one of the first veterinary radiologists to graphically describe the radiographic disintegration of the femoral head in avascular necrosis (AVN).9 A unique, noninfectious form of bone necrosis, this disease initially causes core destruction, weakening the bone to the extent that portions of the perimeter fragment and collapse. The badly damaged femoral head then heals spontaneously, but not before becoming severely deformed. The resultant mismatch of the remodeled femoral head and normal acetabulum causes the hip to become gradually arthritic.

CHAPTER 3 ❚❚❚ Osteoarthritis

97

A

Figure 3-10 • A ventrodorsal close-up view of the left hip of a dog with advanced Legg-Calvé-Perthes disease. In this final stage, the partially disintegrated femoral head has healed, but in a new shape that does not match the acetabulum (the cause of subsequent osteoarthritis).

Radiology (Human). Arlet and Ficat have proposed the following staging for human AVN, based on the following radiographic criteria10:

B Figure 3-9 • Close-up lateral (A) and frontal (B) views of a severely arthritic elbow caused by an ununited anconeal process in a 10-year-old Springer Spaniel mistakenly diagnosed as an osteosarcoma.

Imaging Findings Radiology (Veterinary). The first radiographic indication of AVN in dogs is a subtle widening of the hip joint—widening that often cannot be appreciated without an opposite side comparison. Next, the affected femoral head begins to take on a distinctive pockmarked appearance as the interior of the bone starts to become necrotic. As the damage becomes more extensive, so do the visible areas of bone loss. When there is sufficient trabecular destruction, the cortex begins to crack and then collapse. At this point, the femoral head may appear overtly fragmented. Healing is characterized by a reversal of the previously described events; however, the femoral head fails to regain its original spherical shape, instead, assuming a distinctive conical configuration. It is this deformity that provokes the structurally normal acetabulum to follow suit and become arthritic (Figure 3-10).

Stage 1: Normal radiographic appearance of the hip but abnormal bone scans; patient has pain and decreased range of motion. Stage 2: Radiographs show osteoporosis and multiple cystic or sclerotic lesions. Stage 3: Radiographs show marginal fissures, fragmentation, and collapse. Stage 4: Radiographs show overt disintegration of the femoral head. Stage 5: Severe deformation of the femoral head causes reciprocal acetabular remodeling and osteoarthritis of the hip. MRI. Little information appears in the veterinary literature on the magnetic resonance (MR) appearance on AVN in dogs, in part due to the fact that no satisfactory treatment currently exists. However, if core decompression (a treatment currently being tried in people with the disease) proves effective, MR could prove indispensable in the early identification of the AVN when decompressive surgery is believed to be most effective. In humans, AVN is characterized by variably sized and shaped areas of decreased signal intensity on T1weighted images. Intermediate-to-advanced lesions often appear as crescentic objects lying just beneath the articular surface of the femoral head.11 In an attempt to clinically stage the disease, Mitchell and co-workers devised the following classification (the lower the number, the better the prognosis).12

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Class A: High-strength signal on short TR/TE images; medium strength signal on T2 (resembles fat). Class B: High-strength signal on both short and long TR/TE images (resembles blood). Class C: Low-strength signal on short TR/TE images (resembles fluid). Class D: Low-strength signal on all images (resembles fibrous tissue).

Intraarticular Calcification, Ossification, and Fragmentation (Table 3-1) Polyarthritis. Acute polyarthritis can sometimes be inferred radiographically because of bilateral swelling identified in the carpi, stifles, or hocks. In the case of the stifles, the observed swelling may be mistakenly attributed to cruciate trauma, especially if the animal is thought to have a unilateral lameness (Figure 3-11, A, B). Chronic polyostotic immunoarthritis often leads to multiple partial dislocations, especially in the carpal and tarsal joints. When the stifles are affected, these dislocations, combined with associated joint swelling, can be mistaken for a chronic cruciate injury resulting in posttraumatic osteoarthritis.13 So-called erosive polyarthritis (a term used almost exclusively by physician rheumatologists), which primarily affects the cubital, genual, and tarsocrural joints, has been described in a pair of 11-month-old Greyhounds. Radiographically, the elbows, stifles, and hocks were mildly swollen, whereas the distal radius and radial carpal bone appeared bilaterally osteopenic

with a narrowed cartilage space. Focal lesions in the articular cartilage (termed erosions by the authors) and synovial discoloration and plaque formation suggested immunoarthritis; however, the diagnosis could not be confirmed.14 Immunoarthritis (Immune-mediated Osteoarthritis) Background. Immunoarthritis is the simplest term for describing the various forms of immune-mediated polyarthritis found in dogs and cats. Laboratory testing is usually required to be more specific, for example, rheumatoid arthritis, rheumatoid-like arthritis, or systemic lupus. To describe arthritis as “deforming” or “nondeforming” does little to refine the diagnosis because deformity is more an indication of duration than of etiology. Imaging Findings. Among the radiographic features that potentially characterize immunoarthritis in dogs, multiple, variably shaped and sized areas of decreased bone density, especially in the carpal or tarsal bones, are the most reliable. In this latter regard a carpal fibrosarcoma has been reported, which radiographically appeared as numerous punctate lucencies resembling immunoarthritis. But unlike immune-mediated osteoarthritis, there were also large, poorly marginated lucencies with overlying soft tissue swelling in the distal radius and ulna.15 Animals that have had immunoarthritis for an extended period of time (months or years) are also likely to show varying degrees of osteopenia and joint laxity (Figure 3-12). Related postural abnormalities—

Table 3-1 • DIFFERENTIAL DIAGNOSIS FOR INTRAARTICULAR BONE OR BONELIKE DENSITIES Cause

Comment

Capsular dystrophic calcification Meniscal ossification

Capsular or pericapsular calcification suggests gout or pseudogout. Primary and secondary meniscal ossification/calcification have been reported but are extremely rare. Secondary meniscal calcification is believed to result from injury, including meniscal surgery. The cause of primary meniscal ossification is not known.20 Most often the result of serious knee injuries. Most common in the shoulder and hock. This disease is common in older cats, but rare in dogs. Usually very small, immobile fragments, positioned in the cranial aspect of the joint near the tibial tubercles. Rare, and when present, difficult to see.

Mineralized cartilage fragment Osteochondritis Osteochondromatosis Sprain-avulsion fracture of the caudal cruciate ligament Sprain-avulsion fracture of the cranial cruciate ligament Sprain-avulsion fracture of the medial or lateral collateral ligaments Strain-avulsion fracture of the long digital extensor tendon Torn medial or lateral meniscus

Typically best seen in frontal projection midway between the physeal growth scar and the joint cavity. Avulsion of the long extensor often produces a vary large fragment, which is readily identified in the lateral projection near an enlarged extensor fossa. Typically appears as a streaky form of mineralization in one of the miniscal fields, usually medially.

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A

Figure 3-12 • Frontal view of the carpi of a dog with immunoarthritis shows characteristic swelling, focal areas of bone loss, and osteopenia in the surrounding bone.

B Figure 3-11 • A, Lateral close-up view of the genual joint of a dog referred for cruciate surgery (based on pain, swelling, and instability of the knee) shows severe swelling, but no dislocation or arthritis. B, Examination revealed similar signs in the opposite stifle, which was also radiographed, and found to have similar abnormalities. These findings are consistent with polyarthritis, probably of an autoimmune nature.

particularly evident in weight-bearing views—are typically most pronounced in the carpus (Figure 3-13), tarsus, and stifle, and in the case of the latter, may be mistaken for a ruptured cruciate ligament. Joint swelling and cartilage space narrowing are usually present in chronic cases but do little to distinguish immunoarthritis from other forms of osteoarthritis, except for the fact that they are found bilaterally. Some dogs with longstanding immunoarthritis have large extraarticular osteophytes, as well as numerous islands of periarticular bone. Joint surveys often reveal bilateral or quadrilateral limb involvement in such instances (Figure 3-14).

Figure 3-13 • Frontal, weight-bearing view of the carpi of a dog with immunoarthritis show bilateral: (1) valgus deformity, (2) joint swelling, (3) dislocation of numerous carpal bones, (4) cartilage space narrowing, and (4) focal areas of bone loss typical of immunoarthritis.

Postsurgical Osteoarthritis Most surgically repaired fractures in dogs and cats heal to the extent that the animal regains full and relatively pain-free use of the injured limb. When this does not happen, the surgery is deemed a failure or a partial success, depending on one’s level of optimism. Causes of failed orthopedic surgery include operatively

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A

B

C Figure 3-14 • Close-up frontal and lateral views of the elbows (A, B) and tarsi (C, D) of a dog initially diagnosed as having osteochondritis but later found to have immunoarthritis.

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D Figure 3-14, cont’d For legend see opposite page.

Figure 3-15 • Lateral close-up view of the genual joint of a dog operated on for a cruciate injury 2 years earlier shows moderate osteoarthritis, especially of the femoropatella joint. Note the enlarged extensor fossa craniodistal aspect of femur, which some contend becomes larger with instability. The abnormally flattened femoral trochlea, which perfectly matches the deformed patella, is a true example of adaptive remodeling.

introduced infection; misapplied, dislocated, loosened or broken implants; malunion or non-union; and postoperative osteoarthritis (Figures 3-15 and 3-16). Reconstructive hip and knee surgery aimed at halting the progress of osteoarthritis has not always proven beneficial, in some instances creating problems more debilitating than those for which the animal was originally operated. Examples of such potentially hazardous procedures include the following: relocating the acetabulum of a dysplastic hip (acetabular reloca-

tion, triple pelvic osteotomy) and relocating the articular portion of the proximal tibial epiphysis (Figures 3-17 to 3-20).

Gout and Pseudogout False gout or pseudogout, also called calcium pyrophosphate dihydrate crystal deposition disease, has been reported in a 13-year-old dog with acute multiple limb lameness. Radiographs of the carpi

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A

B

C Figure 3-16 • A, Lateral close-up view of the elbow of a dog hit by a car shows a fracture–dislocation (Monteggia’s fracture). B, An immediate postoperative view shows near anatomic reduction. C, Three months later, after removal of all but one of the implants, the elbow appears severely arthritic.

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A

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B

Figure 3-17 • A, Ventrodorsal view of the pelvis and hips shows severe bilateral hip dysplasia with osteoarthritis on the right. B, After surgery to relocate the left acetabulum, the pelvic canal is severely narrowed, resulting in periodic constipation and a pronounced nonpainful mechanical lameness. Note the badly displaced left ischial tuberosity (emphasis zone, bottom right).

A

B

Figure 3-18 • Preoperative (A) and postoperative (B) ventrodorsal views of the pelvis and hips show bilateral acetabular relocations, which, although providing greater femoral head “coverage,” have severely narrowed the pelvic canal, causing chronic constipation.

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A

B

Figure 3-19 • A, Lateral close-up view of canine stifle operated on in an effort to restabilize the joint after acute cranial cruciate rupture. The joint is now painfully arthritic, and the stabilizing wire has predictably broken. B, In a second surgery, the cranial part of the proximal tibial epiphysis was relocated, but as seen in this lateral close-up, this only seems to have increased the degree of dislocation and amount of arthritis.

A B Figure 3-20 • A, Immediate postoperative film of a tibial relocation; B, subsequent progress check reveals a fracture proximally.

CHAPTER 3 ❚❚❚ Osteoarthritis

A

105

B

Figure 3-21 • Close-up lateral oblique view of proximal ulna (A) and rear view of distal humerus (B) show massive cavitation—the result of synovial storage disease. The shadow in the lateral oblique view, like a radiographic projection, shows the extent to which the articular contour has been altered.

showed faint mineralization on the perimeter of the antibrachial joints.16 Two other reports of false gout in dogs described capsular masses in the carpal and metacarpophalangeal joints.17,18

Storage Disease Doige and I have described a storagelike disease in a dog that featured marked subchondral cavitation of major limb joints caused by ingrowth of a hyperplastic synovium (Figures 3-21).19

References 1. Tirgari M: Blood pattern changes in primary and secondary osteoarthritis of the dog: an experimental study using intraosseous venography. J Am Vet Rad Soc 19:83, 1978. 2. Baird DK, Kinkaid SA, et al: Effect of hydration on signal intensity of gelatin phantoms using low-field magnetic resonance imaging: possible application in osteoarthritis. Vet Radiol & Ultrasound 40:27, 1999. 3. Cantwell DH: Radiographic diagnosis. Vet Rad 27:151, 1986. 4. Ackerman N: Hip dysplasia in the Afgan Hound. Vet Rad 23:88, 1982. 5. Leppanen M, Maki K, et al: Factors affecting hip dysplasia in German Shepherd dogs in Finland: efficacy of the current improvement program. J Small Anim Pract 41:19, 2000. 6. Impellzeri JA, Tetrick MA, Muir P: Effect of weight reduction on clinical signs of lameness in dogs with hip osteoarthritis. J Am Vet Med Assoc 216:1089, 2000.

7. Nunamaker DM, Biery DN, Newton CD: Femoral neck antiversion in the dog: its radiographic measurement. J Am Vet Rad Soc 14:45, 1973. 8. Morgan JP: Canine hip dysplasia. Vet Rad 28:2, 1987. 9. Lee R: Legg-Perthes disease in the dog: the histological and associated radiological changes. J Am Vet Rad Soc 15(1):24, 1974. 10. Arlet J, Ficat RP: Diagnostic de l’osteo-necrose femoro capitale primitive au stade. Rev Chir Orthop 54:637, 1965. 11. Murphy MD: The hip. In Haaga JR, ed: Computed Tomography & Magnetic Resonance Imaging of the Whole Body, ed 3, vol 2. St Louis, 1994, Mosby. 12. Mitchell DG, et al: Femoral head avascular necrosis: correlation with MR imaging, radiographic staging, radionuclide imaging, and clinical findings. Radiology 162:709, 1987. 13. Roberts R: Radiographs presented as part of the 1992 A.C.V.R. oral certification examination: musculoskeletal section. Vet Radiol & Ultrasound 34:185, 1993. 14. Woodard JC, Riser WH, et al: Erosive polyarthritis in two Greyhounds. J Am Vet Med Assoc 198:873, 1991. 15. Applewhite AA, Page RL: What is your diagnosis? J Am Vet Med Assoc 214:29, 1999. 16. DeHaan JJ, Anderson CB: Calcium crystal-associated arthropathy (pseudogout) in a dog. J Am Vet Med Assoc 200:943, 1992. 17. Gibson JP, Roenigk WJ: Pseudogout in a dog. J Am Vet Med Assoc 161:912, 1972. 18. Heimann M, Carpenter JL, Halverson PB: Calcium pyrophosphate deposition (chondrocalcinosis) in a dog. Vet Pathol 27:122, 1990. 19. Doige CE, Farrow CS, Gee BR: Astorage-like disease with skeletal involvement in a dog. Vet Rad 21:98, 1980.

C h a p t e r

4

Extremital Infection

❚❚❚ TERMINOLOGY Periostitis In the context of sepsis, periostitis refers to a primary or secondary surface infection, as indicated radiographically by the presence of periosteal new bone. Obviously, if there is an infection of the bone surface, it will necessarily come into contact with both the periosteum and the underlying cortical surface.

Osteitis Strictly speaking, osteitis involves the cortex of the bone but not the medulla. These infections are almost certain to involve the associated periosteum as well. Unchecked, osteitis may extend into the adjacent medullary cavity, erupt into a nearby joint or surrounding muscle, or kill and detach portions of the infected cortex—creating sequestra.

Osteomyelitis An infection that extends from the exterior to the interior surfaces of a bone is termed osteomyelitis. These infections are the result of one or more bacterial populations actively replicating within the substance of the bone.

Routes of Infection Local. Localized bone infections are usually the result of penetrating wounds, which carry to the bone surface, depositing one or more kinds of bacteria. In most cases, one bacterium outgrows the rest, eventually eradicating its competitors. Bite wounds are the most common form of localized bone infection. Somewhat surprisingly, there are relatively few true bone infections (bacteria replicating within the bone) caused by K-E pins, although there may be drainage and symmetric bone loss immediately surrounding one or more of the pins. 106

Less often, localized bone infections begin in the epiphyses or metaphyses of puppies, the result of a septicemia. In some instances, only a single lesion is present, whereas in others, two or more bones are affected. Because many of these lesions are intraarticular, they may cause a secondary septic arthritis. Regional. Regional infections are often initiated deep in the soft tissues, and like localized infections, are usually the result of penetrating wounds and deep lacerations. But unlike most localized infections, this form of sepsis rarely results in direct bacterial colonization of the bone. Rather, the nearby bone is stimulated by a combination of metabolic byproducts from the bacteria and the resultant host response. An exception to this is the surgical infection, which usually begins in the bones that are being manipulated. Disseminated. Disseminated infections may extend along either the exterior or interior surfaces of the bone, with the former being most common. Under the influence of gravity, most of these infections are inclined to spread gradually into the distal portion of the affected limb. If severe enough, some of these infections may resemble bone tumors, to include the development of an insufficiency fracture.

❚❚❚ METHODS AND SENSITIVITY OF IMAGING BONE INFECTIONS Radiology Most bone infections are associated with a known or suspected injury. They generally begin small and gradually enlarge if untreated. Drainage is common, but sequestration is rare compared with horses and cattle. Nonscreen film, owing to the greater detail it provides, will often reveal subtle lesions that are not apparent using screen film. Diagnostically, infections require differentiation from bone tumors, especially

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those unassociated with a known injury. This distinction can be more difficult than generally appreciated, especially in the case of small lesions. The speed at which a lesion enlarges and the rate at which bone is produced or destroyed are generally believed to be reliable means of distinguishing benign from malignant lesions. Tumor development outpaces that of infection; however, exceptions are regularly encountered.

Nuclear Imaging Bone scans are performed with either 99mTc-labeled polyphosphate or diphosphonate, compounds referred to as radiopharmaceuticals. Once injected into the body, these gamma-ray emitters congregate in the vasculature of bones, where they can be detected using a gamma camera and displayed as differences in gray scale: black representing hyperemia (typifying infection-inflammation), white indicative of avascularity, (in a sequestrum for example), and gray indicating a normal blood supply. In the case of osteomyelitis, bone scans are useful in determining the presence and extent of an infection at a known site, the existence of a sequestrum, and whether other bones are also infected.1 However, the entire radioactive tracer does not go to its intended destination; instead, it is divided between both the normal and abnormal soft tissues.2 Table 4-1 classifies soft tissue uptake as identified in delayed bone scans after administration of 99m Tc-labeled polyphosphate or diphosphonate.

Figure 4-1 • Frontal view of cat’s forepaw shows a cuff of new bone surrounding the proximal shaft of the fourth metacarpal bone, the result of osteomyelitis caused by a deep bite wound from another cat.

❚❚❚ RADIOGRAPHIC DISEASE INDICATORS OF BONE INFECTION

❚❚❚ SURGICAL INFECTIONS

The appearance of a bone infection is contingent on its duration; early on there is typically swelling of the overlying soft tissues but little perceptible change in the infected bone. However, as time passes, structural changes gradually become evident, largely in the form of surface new bone deposition and interior destruction. It is these three essential “ingredients”: bone loss, bone addition, and soft tissue swelling—often in different measures—that constitute the radiographic recipe for infection.

❚❚❚ NONSPECIFIC BACTERIAL BONE INFECTIONS Nonspecific bacterial bone infections are the most common form of osteomyelitis encountered in most veterinary clinics and hospitals. Of these, the majority occurs in cats, the result of bite wounds sustained in cat fights (Figures 4-1 to 4-3). Dogs also develop bone infections secondary to bite wounds but tend to develop these types of infections higher in their limbs.

The overall incidence of surgical infection in either private veterinary clinics or university teaching hospitals is unknown as far as I am aware. That said, I do encounter surgical osteomyelitis regularly (although infrequently) in both our own practice and in our referral material. A variety of surgical infections are exemplified in Figures 4-4 to 4-8.

❚❚❚ SOME SPECIFIC TYPES OF BONE INFECTIONS Hepatozoonosis Background. Systemic disease may lead to disseminated bone infection as exemplified by hepatozoonosis. In this tick-borne, protozoal infection, both long and flat bone may be affected. Associated signs of illness include fever, anorexia, lethargy, weight loss, myalgia, stiffness, lymphadenopathy, ocular discharge, and a waxing and waning course. Cases have also been reported from Oklahoma, Louisiana, Alabama, and Georgia.3

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Table 4-1 • TYPES OF RADIOPHARMACEUTICAL SOFT TISSUE UPTAKE Type of Soft Tissue Uptake

Examples

Physiologic Renal/bladder Mammary gland Uterus (during pregnancy) Normal calcification of cartilage Pathologic Heterotopic bone formation

Myositis ossificans Fibrodysplasia ossificans

Soft Tissue Calcification Metastatic Dystrophic

Idiopathic

Hyperparathyroidism Myocardial, pulmonary, vascular, or gastric mucosal calcification secondary to uremia Hypercalcemia (e.g., secondary to lymphosarcoma) Chronic inflammation Hyperadrenocorticism Parasitic calcification Primary tumor (not bony, e.g., chondrosarcoma, carcinoma) Primary soft tissue osteosarcoma Metastatic soft tissue osteosarcoma Calcified hematoma Infarct (e.g., myocardial) Fat necrosis Tumoral calcinosis Alveolar microlithiasis Nodular fat necrosis14

Urinary Tract Abnormalities Space-occupying renal lesions (e.g., cyst, infarct) Hydronephrosis, hydroureter Ruptured ureter or bladder Other Noncalcified Soft Tissue Lesions Dehydration Edema Various noncalcified soft tissue tumors (e.g., renal carcinoma) Therapeutically irradiated tissues Liver, spleen, or kidney uptake after chemotherapy Acute muscle injuries Myositis Muscle infarction or necrosis Strain, sprain Amyloidosis Artifacts Urine contamination Perivascular injection of radiopharmaceutical Lymph node uptake after perivascular injection Accidental intraarterial injection of radiopharmaceutical Thyroid, salivary, and gastric uptake due to free pertechnetate Diffuse whole body “activity” due to free pertechnetate Recent intravenous or intraarterial injection site (unrelated to radiopharmaceutical injection) Intramuscular injection site Diffuse liver or spleen uptake due to recent injection of sulfur colloid Modified from Lamb CR: Non-skeletal distribution of bone-seeking radiopharmaceuticals. Vet Rad 31:246, 1990.

A

B

Figure 4-2 • Lateral (A) and ultra close-up (B) views of the proximal radial diaphysis of a cat show a layer of recently formed new bone along the face of the radius, overlain by a large area of swollen soft tissue. In the context of multiple infected bite wounds, this finding indicates a secondary periostitis.

Figure 4-3 • Lateral view of the antibrachium of a cat shows an acute periosteal reaction extending the length of the radius (see emphasis zone for best view).

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B A

C

D

Figure 4-4 • A, Close-up lateral view of a freshly avulsed tibial tuberosity, in which associated hemorrhage has erased most of the normal facial planes. B, In the frontal view the displaced accessory growth center is seen superimposed on the lateral side of the proximal tibia growth plate. Postoperative films (C, D) reveal indications of infection including: (1) multiple areas of lysis in the tibial tuberosity, (2) new bone deposition unrelated to callus formation, and (3) localized extraarticular swelling.

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B

A

Figure 4-5 • A, Immediate postoperative frontal oblique view of badly fractured humerus. B, Three-week progress film shows abnormal lysis and nonpurposeful bone deposition indicative of infection, most likely surgical in origin.

Imaging Findings. Based for the most part on cases reported from Texas, Hepatozoon canis produces large, broad-based mounds of new bone on the exterior surfaces the pelvis, spine, femur, tibia, fibula, humerus, radius, and ulna.

Coccidioidomycosis Background. One in six dogs with pulmonary coccidioidomycosis subsequently develops osteomyelitis, usually in one or more limb bones. Most dogs with skeletal lesions appear lame. Imaging Findings. Characteristic bone lesions are mostly productive, in some instances, so productive that underlying cortical destruction is not recognizable. The presence of multiple, small spherical lucencies in the bone has been reported useful in differentiating coccidioidomycosis from tumors and other forms of osteomyelitis.4 In some instances (presumably chronic), the organism colonizes most of a long bone, causing it to assume a bizarre, bloated appearance, featuring a latticelike medulla5 (Figure 4-9).

Occasionally, mycotic osteomyelitis (particularly coccidioidomycosis and blastomycosis) closely resembles a primary bone tumor when initially diagnosed because it is in the metaphysis and features mixed production and destruction, in addition to cortical penetration (Figure 4-10, A). But when observed later, fungal bone infections often produce characteristic cortical bridges over the surface of the lesion, a feature rarely found in bone tumors (Figure 4-10, B).

Blastomycosis Background. Blastomycosis, like coccidioidomycosis, begins as a primary lung infection and may spread to other parts of the body, including the skeleton. In one report, two thirds of the dogs with the bony form of the disease had only a single lesion, whereas the minority had multiple bone infections—some as many as eight or nine. Imaging Findings. Roberts has reported that osteomyelitis caused by blastomycosis typically produces regional or locally destructive lesions in the ends of lung bones. Most are highly destructive and in some

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A

B

Figure 4-6 • A, Full-length lateral view of a dog’s femur fractured 6 days earlier. B, Six-week progress film after open surgical reduction shows severe, widespread bone destruction consistent with osteomyelitis.

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A

B D C Figure 4-7 • Lateral (A) and frontal (B) views of a displaced, short oblique, proximal femoral shaft fracture in an immature dog recently hit by a car. A 3-week progress film shows fragment and implant dislocation (C), whereas an 8-week close-up view (D) shows a nonunion, which appears infected based on the presence of a thick layer of new bone covering all visible bone surfaces.

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Figure 4-8 • Lateral sinogram shows contrast solution within the cubital joint, around the circlage wires, and at both ends of the pin, indicating infection.

A

B

Figure 4-9 • Close-up frontal (A) and lateral oblique (B) views of the proximal tibia/fibula show a mixed productive-destructive, partially expansile lesion involving the proximal thirds of the tibia and fibula. Also note the gradual, almost imperceptible change from abnormal to normal bone density. Although a long zone of transition is usually an indicator of malignancy, it wasn’t in this instance (coccidioidomycosis).

A

B

Figure 4-10 • A, Close-up lateral view of the proximal humeral metaphysis of a dog shows a large mixed productive-destructive lesion caudally. B, Similar projection made 1 month later shows cortical destruction and a distinctive cortical bridge, the result of coccidioidomycosis.

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A

Figure 4-12 • Close-up view of the distal half of the radius shows a mixed productive-destructive lesion occupying much of the distal shaft (but not the epiphysis or metaphysis) resembling a secondary bone tumor. Cortical bridging, however, suggests fungal infection, which turned out to be the case (blastomycosis).

B Figure 4-11 • Close-up (A) and ultra close (B) views of the proximal femur of a dog infected with blastomycosis show freshly deposited new bone (emphasis zone).

cases resemble primary bone tumors with respect to their aggressiveness. Flat bones such as the ischium are similarly affected, as are irregular bones like the talus and dorsal processes of the spine.6 Some reports of skeletal blastomycosis describe rather subtle changes, which in some ways resemble

previous injury: periarticular swelling, smoothsurfaced, extraarticular bone deposition, and faint bone loss.7 In contrast to the foregoing descriptions, many of the animals with skeletal blastomycosis imaged at our hospital initially show faint, somewhat ragged, layers of diaphyseal new bone without evidence of underlying cortical destruction (Figure 4-11, A, B). Some lesions are entirely diaphyseal and feature cortical bridging (Figure 4-12). Usually within 1 to 2 weeks, the appearance of the infected bone changes, showing multiple areas of cortical and medullary destruction, and a further build up of surface new bone (Figure 4-13).

Histoplasmosis Background. Typical of systemic fungal infections, the Histoplasma spores are initially inhaled, phagocytized

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Figure 4-13 • Dog shown in Figure 4-11, now worse. Progress film made only 8 days later shows a substantial increase in bone deposition, which is now accompanied by bone destruction.

by alveolar macrophages where they change into yeast, and then borne to other parts of the body (but rarely to the skeleton) by the blood and lymph. Imaging Findings. Aronson and co-workers have reported destructive, bilateral metaphyseal lesions in the radius and ulna of a cat with systemic histoplasmosis (as well as feline lymphosarcoma). The lesions resembled a severe case of metaphyseal osteopathy.8

Figure 4-14 • Close-up lateral view of the elbow and upper halves of the radius and ulna exhibits a uniformly moth-eaten appearance with fractures of both the anconeal and medial coronoid processes. Although the aggressive appearance of the lesions suggested cancer, this proved to be a fungal osteomyelitis.

Phialemonium obvatum Fungal osteomyelitis is often characterized as permeative in nature, creating deep corticomedullary lesions. However, there are exceptions. Phialemonium obvatum lesions have been shown to initially affect the exterior of the bone, causing smooth, broad-based, predominantly transparent lesions, closely resembling a severe subperiosteal hematoma.9

❚❚❚ CONSEQUENCES OF BONE INFECTIONS Pathologic Fracture The vast majority of pathologic limb fractures in dogs are caused by primary osteosarcomas (93 percent). Occasionally, bone infections become so destructive that the bone fractures. Because osteomyelitis is usually caused by the extension of soft tissue infection or open fracture reduction, when pathologic fractures occur, there appears to be little doubt about their cause. However, cancer is incorrectly assumed when the incit-

ing infection is blood-borne, an etiology that is rarely considered under such circumstances, particularly when there are obvious radiographic abnormalities in the fractured bone (Figure 4-14).10 Interlocking intramedullary pins (pins held in position by multiple screws) have been reported as an effective means of stabilizing a surgically infected femoral fracture.11

Chronicity Some bone infections, especially those caused by socalled super bugs that are often found in large hospitals, staunchly resist both medical and surgical treatment. Lingering infections of this sort, especially those whose progress has been somewhat impeded by ineffective treatment, often produce a distinctive form of new bone that resembles ocean coral (Figure 4-15). Unfortunately, coralization is not unique to chronic osteomyelitis. It has also been found in some slow-

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A

Figure 4-15 • Defleshed bone specimen (tibia, with attached surgical implants) taken from a dog with a chronic surgical osteomyelitis exhibiting marked coralization proximally.

growing primary and secondary bone tumors, as well as in fungal infections such as coccidioidomycosis. Figures 4-16 to 4-19 exemplify these types of infections.

❚❚❚ SEPTIC ARTHRITIS LEADING TO INTRAARTICULAR BONE INFECTIONS Bite wounds that puncture the joint capsule have the potential to infect the bones within, but because carpal and tarsal bones lack an inner layer of osteogenic periosteum, the development of characteristic radiographic indicators of bone infection is delayed, often for as much as 3 to 4 weeks. When signs do develop, they are usually first seen away from articular surfaces. Because of their avascular cartilage coverings, articular surfaces are capable of resisting bacterial encroachment longer than the adjacent unprotected bone. Porcupine quills imbedded in the carpus or other joints may break when being extracted, leaving intraarticular fragments behind that often cause an abscess. Occasional plant awns find their way into joints with similar consequences.

B Figure 4-16 • Frontal (A) and lateral (B) views of the proximal femur of a cat show signs consistent with either tumor or infection, which in this instance proved to be a malignancy.

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A

Figure 4-17 • Lateral view of the humerus shows full-length cloak of mature new bone indicative of chronic infection.

Intraarticular surgery, such as reconstruction of the genual joint, may also result in chronic septic arthritis and osteomyelitis (Figure 4-20).

❚❚❚ DIFFERENTIATING INFECTION FROM CANCER Generally, it is not difficult to distinguish osteomyelitis from bone cancer, especially in advanced stages. Subacute or chronic infection is usually more localized in nature and tends to be walled off (or at least relatively delimited) by surrounding new bone. Mature bone tumors, on the other hand, are more wide-ranging and usually quite destructive. Recent tumor growth and acute infection may share a number of characteristics such as subtle medullary bone loss, cortical bone formation, and soft tissue swelling. Occasionally, chronic osteomyelitis and longstanding bone tumors may resemble one another, with bone biopsy doing little or nothing to resolve the etiologic issue. Even the formation of sequestra, long

B Figure 4-18 • A, Close-up lateral stifle immediately before surgery for a third-degree sprain of the cranial cruciate ligament. B, Progress check of the same joint shows massive subchondral destruction as a result of a surgical infection.

believed to be the hallmark of chronic infection, can sometimes occur with bone cancer.12 Occasionally, a primary bone tumor may be mistaken for osteomyelitis, especially if it is atypically situated and grows slowly. For example, Rendano and co-workers described an osteosarcoma in the radial midshaft of a dog that initially resembled osteomyelitis, being characterized by a small area of localized bone loss surrounded by a thick cuff of mature-appearing new bone. It was not until 6

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Figure 4-19 • Close-up frontal (A) and lateral (B) views of the distal halves of the radius and ulna show multiple blocks of chronic appearing new bone arrayed along the edges of a coarsely thickened cortex. The distorted medulla contains numerous variably sized cavities interspersed among mounds of disorganized bone deposits. Chronic osteomyelitis.

Figure 4-20 • Close-up lateral view of the humeral midshaft shows a medium-sized defect in the cranial cortex associated with a pair of overgrown wire loops. A sterile abscess was found at surgery.

months later that the lesion began to reveal its true malignant nature as indicated by extensive cortical destruction.13 Some forms of osteoarthritis can also be mistaken for primary bone tumors. This is particularly true of long-standing osteochondritis of the elbow, in which associated new bone may extend well up into the humerus. The presence of a similar-appearing lesion in the opposite elbow is compatible with most forms of osteochondritis but inconsistent with a malignant bone tumor.

❚❚❚ ABSCESSES Bone abscesses are rare in animals, with most being sterile and often associated with surgical implants (see Figure 4-20). Many such lesions closely resemble localized bone loss caused by repetitive implant movement (RIM). Deep muscle abscesses may consist of a single cavity or multiple communicating cavities. Sinography is the optimal means of visualizing complex lesions, especially for surgical planning (Figures 4-21 and 4-22).

Figure 4-21 • Deep paraischial abscess: sinogram shows a mediumsized, rectangle-shaped abscess with multiple communicating cavities dorsally. The spherical lucency is the air-filled catheter cuff.

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Figure 4-22 • Sonogram of the lateral thigh region of a dog shows an abscess (oval-shaped area of decreased echogenicity in the far central field) resulting from a recent bite wound.

References 1. Gibson KL, van Ee RT, Watters J: Radiographic diagnosis. J Am Vet Med Assoc 28:231, 1987. 2. Lamb CR: Non-skeletal distribution of bone-seeking radiopharmaceuticals. Vet Rad 31:246, 1990.

3. Macintire DK, Vincent-Johnson N, et al: Hepatozoonosis in dogs: 22 cases (1989-1994). J Am Vet Med Assoc 210:916, 1997. 4. Millman TM, O’Brien TR, Suter PF, et al: Coccidioidomycosis in the dog: its radiographic diagnosis. J Am Vet Rad Soc 20:50, 1979. 5. Ackerman N, Owens J, Ticer J: Polyostotic Coccidioidomycosis in a dog. Vet Rad 22:83, 1981. 6. Roberts RE: Osteomyelitis associated with disseminated Blastomycosis in nine dogs. Vet Rad 20:124, 1979. 7. Widmer WR, Downing S: Radiographs presented as part of the 1995 ACVR oral certification examination, musculoskeletal section. Vet Radiol & Ultrasound 37:110, 1996. 8. Aronson E, Bendickson JC, et al: Desseminated Histoplasmosis with osseous lesions in a cat with feline lymphosarcoma. Vet Rad 27:50, 1986. 9. Smith AN, Spencer JA, et al: Disseminated infection with Phialemonium obovatum in a German Shepherd. J Am Vet Med Assoc 216:708, 2000. 10. Emmerson TD, Pead MJ: Pathological fracture of the femur secondary to hematogenous osteomyelitis in a Weimaraner. J Small Anim Pract 40:233, 1999. 11. Muir P, Johnson KA: Interlocking intramedullary nail stabilization of a femoral fracture in a dog with osteomyelitis. J Am Vet Med Assoc 209:1262, 1996. 12. Ackerman N, Halliwell WH, et al: Bone infection and sequestrum formation in a canine osteosarcoma. J Am Vet Rad Soc 16:3, 1975. 13. Rendano VT, Car B, Gilman M: Osteosarcoma in the middiaphysis of the radius in the dog. Vet Rad 28:127, 1987.

C h a p t e r

5

Extremital Bone Tumors

Metastatic bone tumors are relatively uncommon in dogs and cats compared with primary bone cancer— a frequency that is just the opposite in people. Soft tissue limb tumors are also comparatively rare. Radiology is, and in all likelihood will remain for the foreseeable future, the principal means of imaging bone tumors in pet animals. Obviously, there are far more sophisticated imaging methods available, such as computed tomography (CT), magnetic resonance imaging (MRI), and nuclear imaging, but these technologies are comparatively expensive, and as a consequence, tend to be used more sparingly. Although not employed routinely, ultrasound can be helpful in evaluating bone tumors, which have a juxtacortical soft tissue component. This is especially true of deeply situated tumors, such as those of the hip.1 Samii described using ultrasonography to assist in obtaining fine-needle aspirates of bone lesions in dogs and cats, primarily tumors.2

❚❚❚ BENIGN BONE TUMORS Background Excluding solitary and multiple hereditary exostoses (bone growths more accurately termed tumor-like lesions), benign bone tumors rarely occur in dogs and cats. Of these, the osteochondroma and enchondroma are most common.

Osteochondroma Osteochondroma in dogs is a benign, relatively rare tumor. Although it often closely resembles the lesions seen in multiple exostoses, it is an acquired, not a hereditary neoplasm. Radiographically, solitary osteochondromas are characterized by (1) expansion, (2) smooth margination, (3) lack of a discrete cortex in the region of primary tumor growth, and (4) interior trabeculation—often of a disorganized nature.3

Enchondroma Enchondroma is most often found in the feet of dogs, usually the metacarpals and metatarsals. These tumors typically expand the bone, thinning the cortex in the process. Although a pathologic fracture is certainly possible under such circumstances (as it is with any expansile lesion), I have yet to encounter one.

❚❚❚ MALIGNANT BONE TUMORS Primary Bone Tumors Background. Primary bone tumors almost always begin in the metaphyses of long bones. In the intermediate and advanced stages of their development, these tumors, for the most part osteosarcomas (estimated 85 percent of all canine primary bone tumors), begin by destroying a portion of the medulla and then attack the adjacent cortex. Once the cortex is breached, the tumor is then able to gain access to the surrounding soft tissues. Combined tumor and host bone often produce a dense calcific cloud surrounding the lesion, tending to underplay its severity. The more destructive the tumor becomes, the more likely the bone is to fracture. Occasionally, primary bone tumors originate in the shafts of long bones, rather than in the metaphyses, thus resembling secondary or metastatic bone tumors, or to a lesser extent, parosteal sarcomas.4 Most primary bone tumors occur in middle-aged and old dogs, but they occasionally develop in skeletally immature dogs.5 A majority of veterinarians believe that negative chest films of dogs with proven or suspected osteosarcoma do not eliminate the possibility of metastases. This belief stems from authoritative statements by experts that micrometastases (very small lung nodules, which are not detectable radiographically) almost always exist by the time a skeletal osteosarcoma is diagnosed, a viewpoint for which there is some support.6 121

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Table 5-1 • CLASSIFICATION OF PRIMARY BONE TUMORS Type of Bone Tumor

Classification

Cartilaginous Bone Tumors Benign

Malignant

Osteochondroma (hereditary exostosis: single and multiple) Chondroma (enchondroma) Parosteal chondroma (juxtacortical chondroma) Chondroblastoma Chondromyxoid fibroma Chondrosarcoma—primary or secondary

Osseous Bone Tumors Benign Malignant

Osteoma Osteoid osteoma Osteoblastoma Osteosarcoma Parosteal osteosarcoma (juxtacortical osteosarcoma) Periosteal osteosarcoma

Fibrous Bone Tumors Benign Malignant

Nonossifying fibroma Ossifying fibroma Fibrosarcoma Malignant fibrous histiocytoma

Fatty Bone Tumors Benign Malignant

Lipoma Liposarcoma

Modified from Juhl JH: Paul & Juhl’s essentials of roentgen interpretation, ed 4. Philadelphia, 1981, Haper & Row, p. 198.

Turrel and Pool reported on a small group of cats with primary bone tumors and concurrently reviewed the relevant literature.7 Juhl classified primary bone tumors as shown in Table 5-1.

Figure 5-1 • Close-up frontal view of a defleshed radius largely replaced by an osteosarcoma shows extensive coralization and large cortical breach—pathologic features shared with chronic osteomyelitis.

Osteosarcoma Background. Osteosarcoma is by far the most common type of primary bone tumor, typically developing in large and giant breed dogs at both ends of the age spectrum (1 to 2 years, and 7 years or older). The most common sites in the forelimb are the proximal humerus, distal radius, and distal ulna, and in the hindlimb, the distal femur and proximal tibia. Metastasis can be by either the blood or lymph systems, usually spreading first to the lung; although only about 10 percent of dogs show radiographic indications of pulmonary disease at the time the primary tumor is diagnosed. If the affected limb is amputated, and there is no chemotherapy, radiographically demonstrable pulmonary metastasis is likely to develop within 18 weeks. Occasionally, pulmonary metastasis causes hypertrophic pulmonary osteoarthropathy (HPOA), which is also known as hypertrophic osteopathy. The resultant metaphyseal inflammation typically produces severe quadrilateral lameness.8

Occasionally, osteosarcomas spread to unusual locations, as described by Daniel, who reported the scintigraphic detection of widespread subcutaneous metastases (from a distal radial osteosarcoma) that were not noted on either physical or radiographic evaluations conducted at the time of admission.9 Imaging Findings. Not all primary bone tumors look the same. Some are entirely destructive, others primarily productive. Most, however, exhibit some of both qualities, although usually not in equal measure. The following tendencies are shared by a majority of primary canine bone tumors, and thus are diagnostically useful: • • • •

Primarily destructive (“aggressiveness”) Appears to originate in the medulla Reduces and/or penetrates cortex Permeative (tumor penetrates the cortex and grows into surrounding soft tissue) • Exhibits coralization in advanced stages (Figure 5-1)

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B

A

Figure 5-2 • A, Close-up lateral view of the proximal humerus shows diffuse destruction characteristic of a primary bone tumor (osteosarcoma). B, Close-up lateral view of the proximal humerus shows a vague area of destruction in the greater tubercle. Broken strands of tumor bone can be seen extending deep into the adjacent muscle.

• Hard to distinguish precisely where tumor ends and normal bone begins (long zone of transition) • Rapid progression

A variety of primary bone tumors are exemplified in Figures 5-2 to 5-12.

Although most primary bone tumors begin in the central metaphysis, some do not, particularly in the proximal humerus where many osteosarcomas are eccentrically positioned (at least initially). In this respect, Carrig described an unusually well-circumscribed, half-moon–shaped osteosarcoma invading the lateral aspect of the proximal tibial metaphysis.10

Secondary (Metastatic) Bone Tumors

Chondrosarcoma Background. Although chondrosarcoma is the second most common skeletal tumor in dogs, it remains rare compared to osteosarcoma. Only one in four osteochondromas affect the limbs and even fewer involve long bones (14 percent). Chondrosarcomas show a clear preference for the flat bones: pelvis, scapulae, and ribs. Metastasis occurs about 20 percent of the time, initially to regional lymph nodes and then the lung.11 Imaging Findings. No single characteristic appearance exists. However, there is a tendency to large, billowy, centrally destructive lesions. Alternatively, the affected bone may simply disappear, seemingly amputated, leaving behind only a few small wispy densities.

Background. Secondary bone tumors exhibit a decided preference for the shafts (rather than the ends) of long bones, and in this way can often be distinguished from primary tumors. Unlike primary tumors, secondary bone tumors often develop in two or more bones simultaneously (polyostotic development), a trait that provides an additional distinguishing factor between primary and secondary bone cancers.12 The primary metastatic sites for canine osteosarcomas are the lung and skeleton. Less frequent sites of spreading include the liver, spleen, regional lymph nodes, kidney, heart, and amputation area. Bone scans are reported to be more sensitive than radiographic surveys in detecting skeletal metastasis.13 Walker and co-workers reported widespread skeletal metastasis from a plasma cell tumor, with ischial and femoral lesions appearing as small- to mediumsized lucencies. Atypically, one of the femoral lesions involved the distal metaphysis as well as the proximal diaphysis.14

Imaging Findings Fibrosarcoma. Fibrosarcomas are often intensely destructive, although like osteosarcomas and chondrosarcomas, they are capable of producing tumor bone in the surrounding soft tissues.

Radiology. Metastatic bone tumors share most of the radiographic features of primary bone tumors: centralized location, extensive medullary and cortical

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Figure 5-4 • Lateral view of the scapula shows a mixed productive-destructive lesion in the proximal blade (osteosarcoma) superimposed on the dorsal spinous processes.

destruction, and rapid progression. Occasionally, an undiagnosed secondary bone tumor will fracture, be conventionally repaired, and then be treated as a surgical infection as the tumor continues to grow. Figures 5-13 to 5-17 exemplify the radiographic features of a variety of secondary bone tumors.

A

Radionuclide Imaging. Radionuclide imaging is the best method of searching for skeletal metastases. Positive bone scans typically appear as variably shaped, dark areas, superimposed on a relatively light background. The dark areas clinically referred to as “hot spots” represent above average accumulations of an intravenously administered radiopharmaceutical (also termed areas of increased or intense uptake). Forrest and Thrall showed that radionuclide imaging is capable of detecting subclinical skeletal metastasis in dogs with osteosarcoma. Based on their findings, the authors advocate the use of nuclear medicine in such cases, claiming that it will potentially improve the effectiveness of treatment.15 Lamb and co-workers described the uptake of 99m Tc-MDP by regional lymph nodes during bone scans. They contend that if no perivascular loss of radiopharmaceutical has occurred, and if the identified lymph node drains a region containing a tumor, metastasis should be considered as a possible cause.16 B Figure 5-3 • Close-up lateral (A) and frontal (B) views of the shoulder joint show a subtle mixed lesion in the caudodistal aspect of the scapula, which turned out to be a chondrosarcoma. Caution: this part of the scapula, proximal to the infraglenoid tubercle and adjacent to the attachment of the teres minor, normally appears roughened and relatively decreased in density compared with the surrounding scapula.

Joint Tumors Synovial Sarcoma Background. Synovial sarcoma (also termed malignant synovioma) is the most commonly reported articular tumor in small animals. These tumors typically affect the larger joints in middle-aged and older dogs, only occasionally occurring in younger dogs. Thus acknowledged, it is important to realize that joint tumors, of this or any other cell type, are rarities, with many small animal veterinarians never having encountered one. Imaging Findings. Reported radiographic features are variable and include bone destruction-production and Text continued on p. 130

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A

B

C

D

125

Figure 5-5 • Close-up lateral (A) and frontal (B) views of the distal humerus show extensive bone destruction compatible with a primary bone tumor. The normal opposite elbow is included for comparison (C,D).

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A

B

Figure 5-6 • Lateral (A) and frontal (B) close-ups of distal tibia of a young adult Irish Wolfhound with an osteosarcoma.

A

B

Figure 5-7 • Close-up lateral oblique (A) and frontal (B) views of the distal aspect of the third metacarpal bone show a marked elevation of the periosteum in the lateral view and expansion in the frontal plane, the result of an osteosarcoma.

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B

Figure 5-8 • Lateral (A) and close-up lateral (B) views of the shoulder show destruction of a large part of the cranial aspect of the proximal humerus strongly suggesting a primary bone tumor (fibrosarcoma).

A

B Figure 5-9 • Ventrodorsal orientation view (A) of the pelvis and close-up view (B) of the right ischium show partial destruction strongly suggesting a bone tumor (chondrosarcoma).

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Figure 5-10 • Lateral close-up view of distal femur and stifle, previously fractured and surgically repaired, now appears infected. Biopsy showed osteosarcoma.

A Figure 5-11 • A, Close-up lateral view of the distal femur shows a relatively well-circumscribed area of metaphyseal bone destruction. Biopsy diagnosis was osteosarcoma, illustrating that not all primary bone tumors have long transition zones. B, The normal opposite distal femur is provided for comparison.

B

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B

Figure 5-12 • Lateral orientation (A) and close-up (B) views of cancerous ulna in a dog that is so destructive it appears at first glance that the distal part of the bone has been amputated.

Figure 5-13 • Close-up lateral view of the distal humeral shaft shows both interior and exterior bone deposition consistent with a secondary bone tumor (thyroid carcinoma).

Figure 5-14 • Close-up view of the stifle shows a mixed productive-destructive lesion centered on the distal femoral epiphysis, but also extending into the contiguous metaphysis. Faint areas of bone loss are also visible in the proximal tibial diaphysis. Biopsy showed metastatic fibrosarcoma in both sites.

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A

B

Figure 5-15 • Long lateral (A) and frontal (B) views of an undifferentiated metastatic sarcoma show near total envelopment of the tibia and fibula by the tumor, featuring a spectacular sunburst pattern.

joint swelling (Figure 5-18). Lameness is usually more pronounced than with posttraumatic osteoarthritis, but not as severe as with infection. Most synovial tumors develop slowly, and thus progress films should be spaced at longer intervals than in faster growing cancers such as osteosarcoma; (e.g., every 2 or 3 months rather than monthly). A recently reported case in the carpus of a cat was associated with new bone on the ulnar and accessory carpal bones and carpal swelling. In reviewing the literature, the author found only four other feline cases.17 The radiographic features of a primary synovial osteosarcoma18 and a synovial myxoma19 have been described in individual dogs, with the latter report also including sonographic and magnetographic images.

Metastatic Melanoma. A metastatic melanoma has been reported in the central tarsal bone of a dog, causing massive destruction. Metastatic melanoma has also been described in the elbow joint of a dog, destroying portions of the distal humerus and adjacent ulna.20

Other Tumors Parosteal Sarcoma Background. Parosteal sarcoma (also termed parosteal osteosarcoma and juxtacortical osteosarcoma) is a malignant bone-producing tumor of the periosteum. Parosteal sarcomas are uncommon malignancies that differ from other types of primary bone tumor by

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Figure 5-16 • Close-up of a proximal humerus shows a fresh pathologic fracture, as evidenced by a large but subtle area of bone loss and a patch of new bone. This was a metastatic carcinoma.

beginning on the exterior surface of the bone rather than in the interior. Typically, the underlying cortex is spared. However, there sometimes may be superficial involvement late in the course in the disease. Long bones, skull, and ribs are the usual sites of development, whereas spinal involvement is quite rare.21 Imaging Findings. The appearance of this uncommon tumor is quite variable, ranging from spectacular cortical cloaking, which all but obscures the underlying bone, to destructive-productive lesions involving much of the diaphysis. Occasionally, parosteal sarcomas may be eccentrically positioned at the end of the bone.22 Some parosteal osteosarcomas show seemingly normal bone surrounded by wispy strands of soft tissue calcification.23 Primary Hemangiosarcoma. Primary bone hemangiosarcomas are described as being rare. In one report of such a lesion, the authors asserted that arteriography was necessary for them to differentiate the described tumor from osteomyelitis. The included arteriograms showed extreme vascular distortion, said to be characteristic of malignancy.24

Figure 5-17 • Lateral view of the proximal two thirds of a barely recognizable humeral shaft shows massive bone destruction with a shaggy overlay of new bone, the result of multiple metastases (so-called skip metastases).

❚❚❚ CHARACTERIZATION AND DIFFERENTIATION OF DIGITAL TUMORS AND INFECTIONS The following facts regarding tumors and inflammation of the canine paw come from the work of Voges and co-workers25: • The incidence of tumors or inflammation is about the same in all feet. • The digits are more likely to be affected than either the metacarpus or the metatarsus. • As a generality, multiple lesions involving the toes are more apt to be inflammatory than neoplastic, but multiple tumors can occur. • Fore and hind paw tumors occur with about the same frequency as inflammatory lesions. • Tumors of the paw and toes are more likely to be malignant than benign.

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A

B

C

D Figure 5-18 • Close-up lateral (A) and frontal (B) views of the carpus of a dog with synovial sarcoma show destruction of the articular surface of the accessory carpal bone, swelling, and regional osteopenia. The normal opposite carpus is provided for comparison (C, D).

• Squamous cell carcinomas are the most common malignant tumor found in the feet of dogs. • Mast cell tumors and melanomas follow carcinomas in frequency of occurrence. • Soft tissue swelling is a feature of both tumors and inflammation, and thus does not distinguish one from the other. • Some tumors and tumorlike lesions are characteristically unassociated with bone involvement: mast cell tumor, hemangiopericytoma, plasmacytoma, fibrosarcoma, sebaceous gland adenocarci-

noma, histiocytoma, papilloma, and tumoral calcinosis. • The odds of a digital tumor or inflammation being associated with bone loss or addition (destruction or proliferation) are about even (52 percent). • There is a tendency for inflammatory lesions to be productive and cancers to be destructive. • Squamous cell carcinomas exhibit two distinct patterns: (1) distal phalangeal destruction, and (2) new bone deposition combined with overlying soft tissue swelling.

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Table 5-2 • BONE CYSTS Bone Cyst Type

Physical Features

Geographic Features

Etiology

Aneurysmal bone cyst

Large, lytic, expansive lesion, which can resemble a primary bone tumor

Located in the metaphysis or proximal part of the epiphysis of long bones

Theorized to develop secondary to a variety of vascular injuries induced by (1) trauma, (2) benign and malignant bone tumors, (3) tumorlike lesions such as fibrous dysplasia, and (4) unicameral or multicameral bone cysts34

Multicameral (complex, multilocular) bone cyst

Lytic, expansive (expansile) lesions, featuring internal compartmentalization May contain fluid and fibrous tissue Small, spherical, and often multiple Lytic, expansive (expansile) lesions that are often fluid-filled

Located in the metaphysis of long bones

Subchondral bone cyst Unicameral (simple, unilocular) bone cyst

Located within subchondral bone Located in the metaphysis, and less commonly, the shaft of long bones; in dogs, the distal radius is most commonly involved36

• Although it is not possible to predictably distinguish between benign and malignant lesions of the foot and toes, malignancy should be strongly considered in the face of a primarily destructive lesion.

❚❚❚ TUMORLIKE BONE LESIONS Bone Cysts Background. The cause (or causes) of bone cysts is uncertain. Many theorists focus on trauma, with subsequent hematoma formation within the developing metaphysis. Bone cysts are inconsistently classified according to a combination of etiologic, physical, and geographic features. Various types of bone cysts are described in the Table 5-2. Although most bone cysts are solitary findings, multiple bone cysts have been reported.26 Imaging Findings. Biery and co-workers provided an excellent pictorial account of solitary bone cysts in dogs.27 Solitary bone cysts are expansive, cystic lesions that are typically found in the metaphysis of long bones. Because they substantially thin the surrounding cortex, and thus greatly weaken the affected bone, cysts are susceptible to fracture—often the first and only indication of their presence. Shortly after fracture, repair begins, which may be mistaken for a malignant or infectious lesion. But with the passage of a few weeks’ time, most fractures heal spontaneously. Alternative explanations for these lesions include: (1) primary bone tumor, (2) enchondroma, (3) bone abscess, (4) fibrous dysplasia, and (5) nonossifying fibroma.

Theorized to form as a result of synovial invagination35

Multiple Exostosis in Cats (Feline Osteochondromatosis) In cats, multiple exostoses can appear malignant, featuring large, billowy, extraarticular lesions with irregular margins, and indistinct underlying cortex suggesting destruction. Unlike dogs, such lesions occur in skeletally mature individuals, and are theorized to be caused by feline leukemia virus (FeLV) infection of the periosteum—thus the resemblance to parosteal sarcoma. Multiple exostoses may occur in a wide variety of locations including long bones near joints, surface of the osseous bullae, hyoid bones, clavicle, spine, and ribs.28

Extraskeletal Chondroma Extraskeletal chondromas are rare in dogs and cats. Similar to parosteal sarcomas, these tumors develop outside the bone with most exhibiting the characteristic features of chondromas: a defined cortex and medulla (Figure 5-19).

Intraosseous Arteriovenous Fistulas Occasionally, puppies are born with skeletal arteriovenous fistulas (AV fistulas), which may locally or regionally cavitate and expand the affected bone. In one published report, the author described an external swelling on the cranial surface of the radius that vibrated synchronously with the heartbeat. Subsequently, angiography showed the swelling to be an AV fistula.29

Intraosseous Epidermoid Cyst Epidermoid cysts (epidermal cysts) are tumorlike lesions that are commonly found in the skin of dogs and occasionally in the skeleton. Although there are few reports of these cysts, what information that is

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A

A

B Figure 5-19 • Close-up lateral (A) and frontal (B) views of the carpus show a large extraskeletal chondroma resembling the patella, which exhibits a dense bony perimeter and a relatively lucent interior, radiographic features common to many chondromas.

B Figure 5-20 • Frontal (A) and lateral (B) close-up views of a

available indicates that most epidermal cysts are primarily lytic and may be mistaken for tumors like nailbed carcinoma.30

❚❚❚ SOFT TISSUE TUMORS THAT INVADE ADJACENT BONE Nailbed Carcinoma (Subungual Carcinoma) Squamous cell carcinoma and malignant melanoma are the most common cancers affecting the nailbed

severely swollen fourth digit show: (1) uneven bone deposition on the exterior surface of the middle phalanx, (2) expansive destruction of the third phalanx, and (3) dislocation of the distal interphalangeal joint. This was a squamous cell carcinoma.

of dogs, accounting for about 35 percent and 25 percent, respectively, of all tumors of the distal phalanx and nail. Dogs with nailbed cancer are most likely to be large (about 75 percent) and black (about 65 percent). Radiographically, extensive bone loss and relatively little new bone characterize these tumors. Skele-

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A

A

B Figure 5-21 • Lateral (A) and frontal (B) close-up views of a massively swollen tarsus in which the bones possess a distinctive moth-eaten appearance, characteristic of ingrowth from an adjacent soft tissue sarcoma.

B Figure 5-22 • A, Lateral close-up view of the distal half of a femur

tal metastasis may occur in the affected leg or in the other limbs, and usually has a combined productivedestructive appearance (Figure 5-20).31 Paronychia and osteomyelitis may also share some of these radiographic features, and thus deserve differential consideration.32

Soft Tissue Sarcoma In their advanced stages, soft tissue sarcomas, which extend into nearby bone, can be difficult to distinguish from primary bone tumors that grow into surround-

shows a gently arching periosteal elevation on the cranial aspect of the diaphysis proximally, and a shaggy periosteal reaction immediately below; soft tissue swelling is extensive. B, Frontal view of a proximal tibia shows a grapefruit-sized mass laterally and the ventral portion of a second mass on the lateral side of the femur. The lesion was an invasive lobulated soft tissue sarcoma.

ing muscle.33 However, in their early period of development, soft tissue tumors are more readily recognized because of their relatively large size and the subtle way they begin to erode the adjacent bony cortex. Figures 5-21 to 5-23 exemplify these tumors.

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Figure 5-23 • Close-up ventrodorsal view of the right hip shows a large, relatively organized bony mass overlying the proximal femur and paralleling the exterior surface of the adjacent ilium.

References 1. Kramer M, Gerwing M, et al: Sonography of the musculoskeletal system in dogs and cats. Vet Radiol & Ultrasound 38:139, 1997. 2. Samii VF, Nyland TG, et al: Ultrasound-guided fineneedle aspiration biopsy of bone lesions: a preliminary report. Vet Radiol & Ultrasound 40:82, 1999. 3. Ackerman N, Halliwell WH, et al: Solitary osteochondroma in a dog. J Am Vet Rad Soc 14(2):13, 1973. 4. Brodey RS, Riser WH: Liposarcoma of bone in a dog. J Am Vet Rad Soc 7:27, 1966. 5. Phillips L, Hager D, et al: Osteosarcoma with a pathologic fracture in a six-month-old dog. Vet Rad 27:18, 1986. 6. Spodnick GJ, Berg J, et al: Prognosis for dogs with appendicular osteosarcoma treated by amputation alone: 162 cases (1978-1988). J Am Vet Med Assoc 200:995, 1992. 7. Turrel JM, Pool RR: Primary bone tumors in the cat. Vet Rad 23:152, 1982. 8. Love NE, Millis D, et al: Radiographic diagnosis. Vet Rad 31:29, 1990. 9. Daniel BD, Avenell JS, et al: Scintigraphic detection of subcutaneous metastasis in a dog with appendicular osteosarcoma. Vet Radiol & Ultrasound 37:146, 1996. 10. Carrig C: Radiographs presented as part of the 1993 A.C.V.R. oral certification examination. Vet Radiol & Ultrasound 35:100, 1993. 11. Boudrieau RJ, Schelling SH, Pisanelli SH: Chondrosarcoma of the radius with distant metastasis in a dog. J Am Vet Med Assoc 205:580, 1994.

12. Anderson MA, Reed AR: What is your diagnosis? J Am Vet Med Assoc 204:211, 1994. 13. Forrest LJ, Thrall DE: Bone scintigraphy for metastasis detection in canine osteosarcoma. Vet Radiol & Ultrasound 35:124, 1994. 14. Walker M, Green R, et al: Radiographs presented as part of the 1994 A.C.V.R. oral certification exam: musculoskeletal section. Vet Radiol & Ultrasound 36:113, 1995. 15. Forrest LJ, Thrall DE: Bone scintigraphy for metastasis detection in canine osteosarcoma. Vet Radiol & Ultrasound 35:124, 1994. 16. Lamb CR, Schelling SH, Berg J: Lymph node uptake of 99m Tc-MDP during bone scintigraphy in dogs. Vet Rad 30:268, 1989. 17. Borenstein N, Fayolle P, Moissonnier P: What is your diagnosis? J Small Anim Pract 40:205, 1999. 18. Thamm DH, Maudlin EA, et al: Primary osteosarcoma of the synovium in a dog. J Am Anim Hosp Assoc 36:326, 2000. 19. Hayes AM, Dennis R et al: Synovial myxoma: MRI in the assessment of an unusual canine soft tissue tumor. J Small Anim Pract 40:489, 1999. 20. Alexander JW, Dueland R, Appel GO: Malignant melanoma with skeletal metastasis in a dog. J Am Vet Rad Soc 17:7, 1976. 21. Thomas WB, Daniel GB, McGavin MD: Parosteal osteosarcoma of the cervical vertebra in a dog. Vet Radiol & Ultrasound 38:120, 1997. 22. Burk RL, Ackerman N: Small Animal Radiology & Ultrasonography. Philadelphia, 1996, WB Saunders Co. 23. Huber DJ, Allen DG, et al: What is your diagnosis? J Am Vet Med Assoc 211:1509, 1997. 24. Barber DL, Thrall DE, et al: Primary osseous hemangiosarcoma in a dog. J Am Vet Rad Soc 14:17, 1973. 25. Voges AK, Neuworth L, et al: Radiographic changes associated with digital, metacarpal and metatarsal tumors, and pododermatitis in the dog. Vet Radiol & Ultrasound 37:327, 1996. 26. Huff RW, Brody RS: Multiple bone cysts in a dog—a case report. J Vet Rad Soc 5:40, 1964. 27. Biery DN, Goldschmidt MH, Riser W, Rhodes WH: Bone cysts in the dog. J Am Vet Rad Soc 17:202, 1976. 28. Magnussen KL: What is your diagnosis? J Am Vet Med Assoc 210:1734, 1997. 29. Tanabe S, Nakama S, et al: What is your diagnosis? J Am Vet Med Assoc 206:314, 1995. 30. Homer BL, Ackerman N, et al: Intraosseous epidermoid cysts in the distal phalanx of two dogs. Vet Radiol & Ultrasound 33:133, 1992. 31. Ackerman N, Spencer CP: Radiographic diagnosis. Vet Rad 26:10, 1985. 32. Barrand KR: What is your diagnosis? J Small Anim Pract 39:107, 1998. 33. Geiger T, McEntee M: What is your diagnosis? J Am Vet Med Assoc 214:1156, 1999. 34. Pernell RT, Dunstan RW, DeCamp CE: Aneurysmal bone cyst in a six-month-old dog. J Am Vet Med Assoc 201:1897, 1992. 35. Basher AW, Doige CE, Presnell KR: Subchondral bone cysts in a dog with osteochondrosis. J Am Anim Hosp Assoc 24:321, 1988. 36. Stickle R, Flo G, Render J: Benign bone cyst. Vet Radiol & Ultrasound 40:365, 1999.

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6

Extremital Soft Tissue Tumors

With the exception of fatty tumors, few soft tissue neoplasms possess any distinguishing radiographic features. A soft tissue tumor should be suspected when a slowly growing mass is present, particularly in an older dog or cat.

❚❚❚ LIPOMA Lipoma and its malignant counterpart, liposarcoma, are unique among soft tissue tumors in terms of their radiographic visibility. Because they are composed of fat, these tumors appear relatively dark and well marginated compared with their lighter muscular surroundings.1

❚❚❚ LIPOSARCOMA Large liposarcomas, like lipomas, also can be visible on plain films. In cats, liposarcomas have been associated with type C virus particles, feline sarcoma virus, and feline leukemia infections. Although no causative infectious agent has been identified in dogs, a potential association with skeletal-muscle foreign bodies has been suggested, similar to what has been reported in people.2

Figure 6-1 • Close-up lateral angiogram of a muscle tumor located caudal to the stifle joint in a dog. Note how the major blood vessels encircle the mass, generating characteristically undulant branches, which then penetrate deep into the interior.

resonance imaging, except for embolization or other therapeutic purposes (Figure 6-1).3

References

❚❚❚ IMAGING FINDINGS Radiography continues to be a valid departure point in the medical imaging of extremital tumors, particularly for detecting the involvement of nearby bone. Angiography, on the other hand, has been largely replaced by computed tomography and magnetic

1. DeHaan J, Ackerman N: What is your diagnosis? J Am Vet Med Assoc 203:371, 1993. 2. McCarthy PE, Hedlund CS, et al: Liposarcoma associated with a glass foreign body in a dog. J Am Vet Med Assoc 209:612, 1996. 3. Sutton D: Arteriography and therapeutic angiography. In Sutton D, ed: A Textbook of Radiology & Imaging. New York, 1993, Churchill Livingstone.

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Osteochondritis

❚❚❚ OVERVIEW Osteochondritis, especially of the elbows, appears to be increasing in incidence in North America. At our hospital, we believe this is due in large part to the immense popularity of Labrador and Golden Retrievers, breeds that have high incidences of osteochondritis. Based on the findings of several puppies in the same litter being affected and affected dogs producing affected puppies, we assume the disease is heritable, much like hip dysplasia. In our opinion, detachment or deformity of the coronoid process is not a separate disease but simply a form of osteochondritis and, accordingly, does not require special designation (fragmented coronoid process [FCP]). Neither do we use the modifier dissecans (dissected) unless we are able to image a discrete fragment, as is often possible with computed tomography (CT) or magnetic resonance imaging (MRI) but rarely with radiography.1 We believe the term elbow dysplasia is too vague and, from a pathophysiologic perspective, invites confusion with hip dysplasia. Likewise, the term elbow arthrosis, as proposed by Swenson and colleagues, seems equally ambiguous and does little to inform an already bloated taxonomy.2 The distinction between osteochondrosis and osteochondritis seems more cultural than clinical; thus somewhat arbitrarily, I have chosen to call the disease osteochondritis in this book, although I generally think of these terms as synonymous.

❚❚❚ COMMONLY AFFECTED BREEDS In our practice, Retrievers, both Golden and Labrador, are affected more than any other breeds. 138

❚❚❚ CHARACTERISTIC LESIONS ACCORDING TO SITE Elbow Medial Coronoid Process Historical Perspective. Ljunggren and Olsson are generally credited with discovering what they termed at the time “a new type of elbow dysplasia (ununited coronoid process) and osteochondritis dissecans.”3 Although the primary lesion was often radiographically invisible, the osteoarthritic aftermath was not subchondral sclerosis of the trochlear notch and periarticular bone deposits on the distal humerus, proximal ulna, and proximal radius. In 1984 Henry pointed out the benefits of frontal oblique and flexed lateral projections in detecting the typically elusive coronoid lesion.4 Later, Voorhout and Hazewinkel reviewed the radiographs and surgical findings of 14 young large-breed dogs with osteochondritis of one or both elbows.5 Armed with surgical hindsight, the authors were able to identify a variety of subtle coronoid lesions as well as more obvious defects and areas of reduced density in the subchondral portion of the medial humeral condyle. Like those before them, the authors attempted to develop a standard film series that would identify both early and late lesions. Their recommended protocol was as follows: (1) frontal, (2) frontal oblique, (3) lateral, and (4) extended lateral oblique views. Using this protocol, the authors drew the following conclusions: • A mature “osteochondral lesion” (author’s quotes to remind the reader that cartilage is radiographically invisible) of the coronoid process has a highly distinctive appearance. • Immature lesions, on the other hand, especially those that have not yet become overtly arthritic, are less striking but nevertheless distinctive in their own right.

CHAPTER 7 ❚❚❚ Osteochondritis

• Very early lesions (present in 6- to 12-month-old dogs) may or may not reveal signs indicative of osteochondritis. Berry then drew attention to the characteristic way in which the medial coronoid became blunted as seen in a partially (but not extremely) flexed view of the elbow, asserting that this finding strongly suggested a coronoid lesion.6 Shortcomings Associated With Sole Reliance on Hyperflexed Lateral View of Elbow. In 1995 attention was drawn to the dangers of relying solely on a flexed lateral view of the cubital joint, as is the practice of the Orthopedic Foundation for Animals (OFA), pointing out the following limitations inherent in such a practice.7 • The hyperflexed view makes accurate assessment of the humeroulnar and humeroradial joints difficult or impossible. Because these areas are usually first to become altered with either anconeal or coronoid process lesions, it seems likely that sole reliance on a hyperflexed view will delay radiographic detection. • The highly characteristic deformity of the medial coronoid process, indicative of osteochondrosis, is appreciable only in the craniocaudal view. Once again, sole reliance on a flexed lateral projection surely will impede diagnosis. • If the principal reason for the hyperflexed lateral projection is to evaluate the outer margin of the anconeal process with a minimum of superimposition by the medial epicondyle of the humerus, there must be awareness of the radiographic variation between the flexed and extended lateral views of the elbow. This is yet another limitation of having only one view. • The proximal border of the anconeal process varies among different dog breeds, in some instances resembling what has erroneously been termed an osteophyte, said to be indicative of “elbow dysplasia.”

139

Even in the face of growing concern that there were serious limitations to relying solely on a flexed lateral view to screen the elbows of dogs for osteochondritis, the OFA continued to insist that the flexed lateral projection “appeared to be sufficient” (to do the job). An article by Keller (an employee of the OFA) and coworkers, published in Veterinary Radiology & Ultrasound in 1997, purported to establish the validity of the flexed lateral view as a screening instrument for “elbow dysplasia” by demonstrating a positive radiographic– pathologic correlation in eight German Shepherds but continued to refer to an “abnormal periosteal reaction” on the proximal border of the anconeal process as being the radiographic basis for reliably identifying affected individuals.8 Imaging Findings Radiology Normal Anatomic and Radiographic Variation. The size, shape, and curvature of the anconeal process vary from one dog to the next and are unreliable disease indicators (Figure 7-1). Likewise, individual differences in the length and width of the medial coronoid process and the size of the cranial radial lip are inaccurate predictors of osteochondritis (Figure 7-2, A-D). Even the overall appearance of the proximal ulna can vary from extremely upright to moderately arched, with neither conformation providing any diagnostic clues. The variation of greatest concern is that which occurs along the lateral margin of the anconeal process, specifically the extent to which the lateral articular margin curls proximally, forming a lateral ridge (Figure 7-3). The larger the lateral ridge and the greater the angle of the anconeal process (as viewed frontally in Figure 7-4), the greater the likelihood it will be projected on or over the proximal edge of the anconeal process in a lateral radiograph, resembling a bone deposit (osteophyte), a finding that some consider to be nearly certain

Figure 7-1 • Defleshed proximal radius and ulna (lateral perspective) from four normal dogs show variation in size, shape, curvature, and position of the anconeal process.

140

SECTION I ❚❚❚ The Extremities

Figure 7-2 • Defleshed proximal radius and ulna (proximal perspective) from four normal dogs show variation in size, shape, curvature, and position of the coronoid process and cranial radial margin. Normal anatomic differences in the overall shape of proximal ulna also are regularly encountered but play little or no role in the diagnosis of osteochondritis.

evidence of “elbow dysplasia.” I term this normal variant a false ridge sign (Figure 7-5). It is also possible to produce false ridge sign when making a lateral radiograph by tipping the elbow, a common radiographic error (Figure 7-6). An even longer bony ridge exists on the medial side of the ulna, extending distally from the medial edge of the anconeal process to the tip of the medial coronoid process. Like the lateral ridge, the medial ridge varies in prominence from dog to dog (Figure 7-7). Larger medial ridges absorb more radiation than smaller ridges, resulting in increased density, which may be mistaken for so-called sclerosis and in the past supported a diagnosis of “elbow dysplasia.” Like bias, the flexed lateral view of the elbow can be either an ally or an adversary. It may reveal an abnormal anconeal process otherwise obscured by the medial epicondyle of the humerus in the nonflexed projection, or it may result in a false ridge sign, the result of oblique positioning (Figure 7-8).

Additionally, flexed lateral views of the elbow are often underexposed, making it difficult or impossible to evaluate the critical interior surfaces of the joint and the cartilage spaces (Figure 7-9). This is due in large part to the bulging of nearby muscles when the elbow is hyperflexed. This problem can be overcome by measuring the elbow in the flexed rather than in the extended position before setting the radiographic technique. Lesion Development and Progression. Osteochondritis of the coronoid process may result in deformity (Figure 7-10) or detachment (Figure 7-11) of the coronoid process. Thus, the term fragmented coronoid process is not always appropriate. As with osteochondritis of the anconeal process, most affected dogs develop severe osteoarthritis involving all the bones of the elbow. Although not affected with the frequency of the ulna, the humerus is usually secondarily involved irrespective of the primary site (Figure 7-12). Text continued on p. 145

CHAPTER 7 ❚❚❚ Osteochondritis

Figure 7-3 • Defleshed proximal ulna of a normal dog (lateral perspective) shows the distinctive curl on the lateral articular margin of the anconeal process, the lateral ridge (emphasis zone).

141

Figure 7-4 • Defleshed proximal ulna of a normal dog (frontal perspective) shows laterally to medially angled anconeal process (emphasis zone).

Figure 7-5 • Defleshed proximal ulna of a normal dog (lateral perspective) shows how tipping the ulna during radiography can create a false ridge sign by superimposing the lateral ridge on the proximal edge of the anconeal process.

142

SECTION I ❚❚❚ The Extremities

A

B

Figure 7-6 • A, Lateral view of a normal elbow shows a false ridge sign (faint bone density superimposed on the proximal border of the anconeal process, partially overlain by the medial epicondyle of the humerus), the result of nonstandard positioning (lateral oblique rather than true lateral). B, The frontal view is included for completeness.

Figure 7-7 • Defleshed elbow joints (minus the humerii) of four normal dogs shown in lateral perspective show variations in the medial ulnar ridge—the thin arch of bone connecting the anconeal and coronoid processes that marks the medial most aspect of articular surface of the ulna.

CHAPTER 7 ❚❚❚ Osteochondritis

143

A

B Figure 7-8 • A, Close-up flexed lateral view of a normal elbow in a young dog shows a false ridge sign (emphasis zone) caused by oblique positioning. B, A second lateral with improved positioning appears normal.

B

A Figure 7-9 • Close-up, flexed lateral views of the elbow of a healthy dog show a false ridge sign in the initial image, the result of inadvertent oblique positioning (A) and a normal anconeal process in a subsequent film (B). In both images, the upper slope of the anconeal process is clearly visible; however, in the more flexed of the two films (B), the joint spaces are underexposed (and thus invisible) because of greater part thickness resulting from a greater degree of flexion. In general, the more the elbow is flexed, the greater the obliquity and the more likely the possibility of a false ridge sign.

SECTION I ❚❚❚ The Extremities

144

A A

B

B Figure 7-10 • A, Defleshed bone specimens of the elbow of a dog with osteochondritis of the medial coronoid (lateral perspective, viewer’s left) and comparably sized normal dog (lateral perspective, viewer’s right). In the arthritic elbow, the anconeal process is normally positioned but is elongated and lacks a normal slope. Large, bony ridges extend distally from the proximal tubercles to the base of the lateral coronoid process. B, The medial perspective shows a badly deformed coronoid but no detached or ridge sign. Comparison of the shadows cast by the normal and abnormal elbows shows the characteristic disfigurement caused by this form of osteochondritis.

Figure 7-11 • A, Defleshed bone specimens of the elbow of a dog with osteochondritis of the medial coronoid process (medial perspective) shows (1) triangular coronoid fragment (emphasis zone), (2) radial saddle horn, (3) deformed anconeal process, and (4) a large medial ridge. B, A second view of the same specimen but with the coronoid fragment displaced is also shown. C, A lateral perspective shows a lengthy lateral ridge superimposed on the anconeal process (emphasis zone), producing a false ridge sign.

C

CHAPTER 7 ❚❚❚ Osteochondritis

145

I have yet to encounter any form of elbow surgery that either halts or slows the development of related osteoarthritis. Nor have I seen any dogs crippled by the disease, with the provisos that they exercise regularly and do not become grossly overweight (contrary to some published claims).

A

B Figure 7-12 • Lateral (A) and medial (B) perspectives of the distal humerus, with normal comparisons, show osteoarthritis that typically accompanies osteochondritis of either the coronoid or anconeal processes.

Not all coronoid lesions appear to develop at the same rate. For example, many retrievers show radiographic abnormalities in the second half of their first year; German shepherds, on the other hand, may show no abnormalities until they have finished growing. Chows may appear normal in all respects until they reach 4 to 5 years of age, at which time they begin to exhibit subtle lameness associated with deformity of the coronoid process and radial head. Follow-up examinations of mature dogs with osteochondritis of the coronoid or anconeal process (made 1 or more years apart) usually show progression but not always at a predictable rate (Figure 7-13).

Early Disease. Ridge signs usually are configured in one of three ways: shallow, medium, or deeply arched (Figures 7-14 to 7-17). Occasionally, ridges are blocked or irregular in appearance rather than smoothly arched. A fairly strong correlation exists between the overall size of the ridge and the extent of the related osteoarthritis elsewhere in the elbow. In some animals with osteochondritis resulting in secondary proximal migration of the anconeal process, osteophytes originating atop the olecranon merge with the lateral ridge, producing varying degrees of proximal ulnar disfiguration. The distal humerus also becomes secondarily disfigured as a result of osteoarthritis, particularly the lateral aspects of the condyle and epicondyles. As the arthritis progresses, the cranial aspect of the radial head also begins to change, developing a distinctive saddle horn cranially, presumably an adaptation designed to help retain an increasingly mobile humerus (Figure 7-18). In some instances of early or mild osteochondritis, there is no visible ridge sign; instead, there may be new bone deposits on the medial side of the distal humeral condyle and on the outer edge of the medial coronoid (Figure 7-19). This appearance is often seen in Chows and in other medium-sized breeds with delayed-onset osteochondritis of the elbows. Late Disease. As the elbow loosens because either the coronoid or the anconeal process has detached, deformed, or migrated, the resultant arthritis worsens, often taking the form of a large rhino-horn osteophyte emanating from the cranial edge of the medial condyle, as seen in the lateral view. The radial saddle horn, as mentioned previously, becomes larger, matching or surpassing the overlying humeral spike. The anconeal process becomes difficult or impossible to identify because more and more bone is deposited on the exterior surfaces of the elbow. In some instances, large cyst-like areas are present in the olecranon. In the frontal projection, distinctive osteophytes form on the medial epicondyle, medial coronoid process, and outer corner of the radial head, which, along with the new bone on the lateral humeral condyle, give the elbow a “lumpy-bumpy” appearance (Figures 7-20 and 7-21). False Disease. Occasionally, an old injury results in the formation of osteophytes, and plaques of new bone in and around the elbow can be mistaken for osteochondritis. Unlike osteochondritis, these deposits are usually away from the joint and typically are found unilaterally (as opposed to the characteristic bilateral

B A

D

C

E

F

Figure 7-13 • Close-up lateral (A), frontal (B), and frontal oblique views (C) of a mildly arthritic elbow in an 18-month-old Labrador Retriever caused by osteochondritis of the medial coronoid process (emphasis zones show subtle new bone deposits in characteristic locations). D to F, show the same elbow 1 year later, having worsened as indicated by increased arthritis (emphasis zones).

CHAPTER 7 ❚❚❚ Osteochondritis

147

A

Figure 7-14 • Close-up flexed lateral view of the elbow of a young dog with a ridge sign (shallow arch type) supporting osteochondritis of the coronoid.

B o x

7 - 1

Abnormalities Found in Computed Tomographic Examinations of a Series of Dogs with Elbowrelated Forelimb Lameness Ulna

Cracking of coronoid process Fragmentation of coronoid process

Radius

Humerus

B Flattening of medial aspect of humeral condyle Increased lucency of humeral condyle

Increased density of medial coronoid process Increased density of trochlear notch Irregularity of radial notch Lucency of radial notch Misshapen medial Proximal Increased density coronoid process osteophytes of humeral condyle Separation of coronoid process Ununited anconeal process

Figure 7-15 • A and B, Close-up flexed lateral views of the elbows of a dog show bilateral ridge signs (medium arch type).

involvement of osteochondritis). Figure 7-22 shows such an injury. Computed Tomography. Reichle and co-workers published their CT findings in a medium-sized group of dogs imaged because of elbow lameness.9 One of the most interesting aspects of this article is the variety of reported lesions. Although it seems probable that most of these less publicized abnormalities (lesions?) probably are related to osteochondritis (at least indirectly), it is also possible that they are not related and that we are encountering a new disease. More likely, however, is the explanation that CT simply provides better anatomic detail and less structural superimposition, allowing previously obscure changes to become apparent. The CT abnormalities found in the elbows of the described dogs are tabulated in Box 7-1. Additionally, the authors reported articular malalignment in all three components of the elbow joint: humeroulnar (53%), humeroradial (32%), and radioulnar (20%). It appeared that most of these subluxations were of a secondary nature. Figure 7-23 shows a CT image (including a three-dimensional reconstruction) of the elbow of a dog with osteochondritis of the medial coronoid process. Radiographs showing the characText continued on p. 152

148

SECTION I ❚❚❚ The Extremities

A

B

Figure 7-16 • Close-up natural and flexed lateral views of the elbow of a young retriever with coronoid osteochondritis. In the nonflexed view (A), a ridge sign is present but faint, whereas in the flexed view (B), the ridge sign (deep arch type) is clearly visible.

B

A Figure 7-17 • Close-up natural and flexed lateral views of the elbow of a young German Shepherd with coronoid osteochondritis. A, In the nonflexed view a ridge sign is partially visible; B, in the flexed view the ridge sign is more completely visualized.

CHAPTER 7 ❚❚❚ Osteochondritis

A

149

B Figure 7-18 • Close-up natural (A) and flexed lateral (B) views of the elbows of a young Golden Retriever fail to show a definite ridge sign; however, bone deposits on the humeral condyle and radial head circumstantially suggest coronoid disease.

A

B

Figure 7-19 • Close-up flexed lateral (A) and frontal (B) views of the elbow of a dog with very early osteochondritis of the coronoid process. Although there is no ridge sign, the radial head has developed a small lip, and there is abnormal roughening of the medial border of the distal humerus.

150

SECTION I ❚❚❚ The Extremities

B A

C

D

Figure 7-20 • Close-up lateral (A) and frontal (B) views of an arthritic elbow in a 5-year-old Labrador Retriever, the result of osteochondritis of the medial coronoid process. The cause of the oval lucency in the ulna was not determined, but since this finding was present bilaterally (C, D) and found unchanged in earlier films, it was not diagnostically pursued.

CHAPTER 7 ❚❚❚ Osteochondritis

B

A

C

D

Figure 7-21 • Close-up lateral (A, C) and frontal (B, D) views of the elbows of a 5-year-old Sharpei. Many abnormalities are present, including (1) abnormal proximal positioning and deformity of the anconeal process, (2) abnormal distal positioning and deformity of the medial coronoid process, and (3) partial dislocation of both the humeroulnar and humeroradial joints. Although there are bone deposits on the radial head and medial aspect of the distal radius indicative of osteoarthritis, they are not so pronounced as might be predicted given the described structural and spatial abnormalities. These findings are characteristic of a delayed form of osteochondritis.

151

152

SECTION I ❚❚❚ The Extremities

A

B

Figure 7-22 • A, Close-up flexed lateral view of a dog’s elbow shows no evidence of osteochondritis, but multiple bone deposits arrayed over the surface of the proximal radial shaft suggest a previous injury. B, The opposite elbow is provided for comparison.

teristic arthritic pattern of this disease also provide diagnostic comparison. Magnetic Resonance Imaging. Snaps and co-workers compared the relative merits of three different types of magnetography for imaging the canine elbow: spin echo (T1, T2), gradient echo, and fat saturation.10 Using the normal elbows of four large-breed dogs, each about 18 months of age, gradient-echo imaging (fast imaging with steady-state precession) provided the best images. Specifically, the fast-imaging gradient-echo images provided thin, highly detailed contiguous slices of both the anconeal and coronoid processes. Multiplanar capabilities resulted in comparatively brief scan times.

Anconeal Process Generally, the radiographic diagnosis of anconeal osteochondritis (also termed ununited anconeal process) is perceived as being straightforward, the diagnosis being based on a single finding: the physical separation of the anconeal process from the adjacent ulna. The resultant osteoarthritic pattern is similar to that resulting from osteochondritis of the coronoid. Reliance on a single disease indicator has its shortcomings, however. First, in older dogs that have had the disease for 2 or 3 years, secondary osteoarthritis may be so severe that it obscures the anconeal process, making close scrutiny impossible. Second, not all diseased anconeal processes are clearly separated from the ulna, or at least there may be some doubt concerning the matter.

A solution to this problem is to use a second, equally reliable disease indicator: the proximal displacement of the anconeal process. Although not widely appreciated, osteochondritis of the anconeal process may not result in a loose fragment (Figure 7-24); instead, the anconeal process remains attached to the ulna by nonosseous tissue but moves to a new location near the upper edge of the olecranon as the bone matures. Proximal displacement of the anconeal process also can be used in severely arthritic elbows to distinguish between osteochondritis of the coronoid and anconeal processes (Figure 7-25). Even though osteochondritis of the anconeal process secondarily deforms the coronoid process, it does not cause upward displacement of the anconeal process. Thus, if displacement is present, the disease probably began in the anconeus (Figure 7-26); if not, the problem is more apt to reside with the coronoid or, less likely, the distal humerus. Figures 7-27 to 7-29 exemplify the characteristic features of osteochondritis of the anconeal process.

Distal Humeral Epiphysis Fragmenting lesions of the distal humerus often cause an arthritic pattern that closely resembles osteochondritis of the coronoid or anconeal processes. Most such lesions originate from the articular surface of the distal humerus medially, just above the coronoid process (Figures 7-30 and 7-31). In some instances, it is difficult or impossible to differentiate a primary from a secondary lesion, the latter typically stemming from an underlying coronoid lesion.

CHAPTER 7 ❚❚❚ Osteochondritis

153

A B

C

D Figure 7-23 • A, Close-up cross-sectional view of a dog’s elbow at the level of the medial coronoid process (small bone fragment) shows complete detachment. B, A flexed lateral, three-dimensional computed tomographic reconstruction of the same elbow shows the coronoid fragment just below the medial epicondyle. Frontal (C) and lateral (D) radiographs of the same animal are provided for comparison.

154

SECTION I ❚❚❚ The Extremities

Figure 7-24 • Defleshed bone specimen of the elbow of a dog with osteochondritis of the anconeal process (proximal perspective) shows proximally displaced, detached anconeal process (white triangular object at top of joint).

A

Figure 7-25 • Defleshed bone specimen of the elbow of a dog with osteochondritis of the anconeal process (proximal perspective) shows proximally displaced but attached anconeal process.

B

Figure 7-26 • A, Close-up frontal view of the elbow shows a large coronoid “hook,” which may be seen with either coronoid or anconeal osteochondritis. B, However, the proximal displacement and detachment of the anconeal process seen in the lateral projection are unequivocal indicators of anconeal osteochondritis.

CHAPTER 7 ❚❚❚ Osteochondritis

A

155

B

Figure 7-27 • Close-up natural (A) and flexed lateral (B) views of the elbow of a dog with osteochondritis of the anconeal process; both images clearly show the characteristic lesion: separation and proximal dislocation of the anconeal process.

Figure 7-28 • Close-up flexed lateral view of the elbow of an immature German Shepherd with osteochondritis of the anconeal process shows: (1) proximal displacement of the anconeal process, (2) a large bony lip on the cranial aspect of the radial head, (3) widening of the humeroradial joint, and (4) malalignment of the articular surfaces of the radius and ulna. In addition (and a more likely explanation for the dog’s acute, painful forelimb lameness), there is panosteitis in the distal humerus as indicated by interior bone deposition.

Figure 7-29 • A most unusual case of an acute proximal olecranon fracture sustained by this dog after being struck by a car. The fracture enters the arthritic humeroulnar joint just below the base of the anconeal process, which shows the characteristic proximal displacement and deformity of osteochondritis. The opposite elbow featured a similar pattern but no fracture.

156

SECTION I ❚❚❚ The Extremities

A

B

C Figure 7-30 • Frontal (A), frontal oblique (B), and close-up frontal oblique (C) views of the elbow joint in a dog with humeral osteochondritis shows: (1) abnormal widening of the medial aspect of the humeroradial joint, (2) subtle flattening and decreased density of the articular surface of the humerus medially, (3) roughening of the medial margin of the humeral epiphysis, and (4) blunting of the medial coronoid process.

Much less frequently, the medial epicondyle is affected, usually bilaterally. A typical lesion consists of a long, relatively thick bone fragment lying just beyond the edge of what remains of the medial epicondyle (Figure 7-32). Moderate flexion of the elbow usually improves lesion visibility, provided the elbow is not rotated in the process, which could produce the opposite effect.

Shoulder Background. Osteochondritis of the proximal humerus often produces a highly characteristic

lesion requiring little or no differential diagnosis.11 Arthrography demonstrates a strong correlation between the size of a subchondral defect in the humeral head (as seen radiographically) and the amount of damage to the overlying articular cartilage. These observations correlate well with the presence and severity of pain and lameness experienced by most affected animals. Carrig and Morgan described the microvascular circulation of the normal canine humeral joint and determined that development of the medial aspect of the humeral head and its vasculature normally lags behind that of the lateral aspect. They hypothesize that this relative difference in intraepiphyseal maturation may

CHAPTER 7 ❚❚❚ Osteochondritis

A

157

B

Figure 7-31 • Close-up lateral (A) and frontal (B) views of an arthritic elbow in a young dog show a detached humeral fragment located just above the medial coronoid process consistent with osteochondritis. Progress films made a year later showed a classic coronoid hook and a portion of the humeral fragment.

Figure 7-32 • Close-up flexed lateral views of the right (left) and left (right) elbows of a dog show large, detached bone fragments from the margins of the medial epicondyles caused by osteochondritis.

render the medial side of the humeral head susceptible to injury, which in turn can lead to osteochondritis.12 Based on these findings, van Bree devised a radiographic measurement that he asserts will accurately predict the probable condition of the articular cartilage overlying an osteochondral defect and, by inference, the degree of probable associated morbidity. The measurements are made from a lateral projection of the humeral joint and include the lengths of the osteochondral defect and the humeral head. The length of the lesion then is expressed as a percentage of the sagittal diameter of the associated

humeral head. For dogs with clinical signs, the mean measured lesion percentage was 27.4, whereas dogs without clinical signs measured only 21.4%, a difference of about 20%.13 Imaging Findings Radiography and Radiology. Callahan and Ackerman described the diagnostic benefits of outward rotation when making a lateral projection of the shoulder joint to confirm osteochondritis of the humeral head.14 Not only can this supplementary view improve lesion

158

SECTION I ❚❚❚ The Extremities

detail, but it also may reveal otherwise undetectable bone flaps. A close-up conventional lateral view of the shoulder is provided for comparison with the following osteochondral lesions (Figure 7-33). The classic lesion is located along the caudal perimeter of the humeral head, as projected laterally, and consists of an elliptical defect and or closely approximated bone fragment. Lesions may range from a barely perceptible loss in bone density to a cavernous subchondral defect. In some instances, the entire subchondral margin may detach from the underlying bone (Figures 7-34 to 7-36). Following surgical removal of large marginal bone fragments and curettement of underlying subchondral defects, especially if they are long and deep, the femoral head often heals with a pronounced “scar” in the form of a marked flattening, plus or minus a ventral spur (Figure 7-37).

Figure 7-33 • Close-up lateral view of a normal shoulder joint.

A

B Figure 7-34 • A, Close-up lateral view of the right shoulder of a Newfoundland dog show a vague area of decreased density in the subchondral bone of the caudal aspect of the humeral head consistent with early mild osteochondritis. B, The opposite shoulder was similarly affected.

B

A Figure 7-35 • A, Close-up lateral view of the shoulder joint shows a concave defect in the caudal margin of the humeral head consistent with osteochondritis. B, Close-up lateral view of the shoulder joint shows a narrow but lengthy osteochondral fragment detached from the caudal third of the humeral head.

CHAPTER 7 ❚❚❚ Osteochondritis

159

A

B Figure 7-36 • A, Close-up lateral view of the shoulder joint of a dog with osteochondritis shows a large rectangular defect in the caudal third of the humeral head, littered with a number of small bone fragments. B, Close-up lateral view of the shoulder joint shows a large defect in the caudal part of the humeral head, the bottom of which contains a number of vague, nonstructured radiolucencies. The latter proved to be an elaborate network of necrotic channels that extended deeply into the underlying epiphysis, making the actual lesion approximately twice the size of that originally estimated from radiographs.

Arthrography. Story described the use of shoulder arthrography for both diagnostic and prognostic purposes (Figures 7-39 to 7-41).15 Van Bree and coworkers compared arthrographic with arthroscopic findings in 20 shoulder joints and concluded the following15:

Figure 7-37 • Close-up lateral view of the humeral joint shows a pronounced flattening of the caudal aspect of the humeral head consistent with healed osteochondritis (although there is no way to know the status of the overlying cartilage). Also note the decreased subchondral bone density in the cranial half of the humeral head.

Occasionally, gas is seen within the humeral joint appearing as bubbles or outlining one or both articular surfaces, an observation variably termed (1) the vacuum phenomenon (scientific) or (2) nature’s arthrogram (humorous). Although seen only occasionally, this is a normal finding, especially in the humeral joint (Figure 7-38).

• Arthroscopy confirmed the presence of 12 of 12 arthrographically identified cartilage flaps. • Only three of eight arthrographic studies showed a distinct crack in the articular cartilage of the humeral head, whereas arthroscopy revealed a fissure line in all eight shoulders. • Arthroscopy identified chondromalacia in two dogs; arthrography did not. • Arthroscopy identified a focal concave deformity in the articular cartilage in three dogs; arthrography did not. • Arthroscopy identified small joint mice in two dogs; arthrography did not. • Arthroscopy identified a kissing lesion in the glenoid, opposite a cartilage flap; arthrography did not. • Arthroscopy identified synovial inflammation; arthrography did not. The obvious conclusion from this study was that arthroscopy was capable of detecting smaller and subtler osteochondral and synovial lesions than was arthrography.16 The same investigators also determined that for shoulder arthrography, low osmolar, nonionic

160

SECTION I ❚❚❚ The Extremities

A

B

Figure 7-38 • A, Close-up lateral view of the humeral joint made during traction shows gas in the joint cavity indicating a vacuum effect; B, a comparable view of the opposite shoulder shows no intraarticular gas.

Figure 7-39 • Close-up lateral humeral arthrogram of a dog with osteochondritis shows disrupted articular cartilage over much of the caudal third of the humeral head. Additionally, contrast solution is faintly outlining a cartilage fragment.

Figure 7-40 • Close-up lateral humeral arthrogram of a dog with osteochondritis shows a short band of contrast dissecting beneath the articular cartilage of the caudal third of the humeral head.

contrast media are far superior to high osmolar, ionic agents.17 Osteochondritis also occasionally affects the greater tubercle, glenoid, and less often the supraglenoid and coracoid processes (Figure 7-42). As with most forms of osteochondritis, the lesions are usually present bilaterally. In some cases, associated lameness is minimal, although most lesions are uncovered in the course of a seeking a cause for an obvious abnormality.

Occasionally, dogs without known shoulder lameness have osteoarthritis in both humeral joints, which some attribute to previous osteochondritis. Although it is not my intention to generalize, especially based on a single individual, I have radiographed the shoulder region of a dog at 6 and later at 11 years of age for an unrelated problem. In the initial examination, the shoulder joints appeared normal, but in a subsequent examination performed 5 years later, both shoulders were arthritic (Figure 7-43).

CHAPTER 7 ❚❚❚ Osteochondritis

161

Figure 7-41 • Close-up lateral humeral arthrogram of a dog with osteochondritis shows intact articular cartilage above subchondral defect.

A

Tarsal Joint Disease Forms and Sites of Involvement. To date, there appear to be at least three forms of osteochondritis affecting the hocks of dogs: one involving the medial trochlear ridge of the talus; another, the medial malleolus of the tibia; and a third, the medial malleolus and the underlying talus. Alternatively, there may only be two primary forms of the disease, malleolar or talar, and any additional lesions, especially those on an adjacent joint surface, are of a purely secondary nature (a so-called kissing lesion). Talar Lesions. The most common type of tarsal osteochondritis in dogs occurs in the proximal aspect of the medial ridge of the talus, usually taking the form of a single small, semiattached bone fragment. In my experience, immature retrievers (often as young as 6 months of age) are most often affected, usually bilaterally. Clinically indicated by swelling and mild lameness, traction-stress radiography (under sedation) often is required to demonstrate the lesion. Unlike many other forms of osteoarthritis, the tarsocrural joints of dogs with advanced osteochondritis are often widened, especially medially. Figures 7-44 and 7-45 exemplify many of the radiographic disease indicators (RDIs) associated with osteochondritis of the canine tarsus. Figure 7-46 illustrates the strong resemblance between osteoarthritis caused by longstanding osteochondritis and that resulting from a severe tarsal sprain. Medial Malleolar Lesions. Newell and co-workers described the radiographic appearance of isolated osteochondral-like lesions of the medial malleolus

B Figure 7-42 • Close-up lateral views of the right (A) and left (B) shoulders of a dog show partial disintegration of the supraglenoid tubercles.

and combined malleolar–talar lesions in a small series of dogs in which all but one were Rottweilers.18 Radiographically, the isolated malleolar lesions often featured a detached bone fragment with variable degrees of associated lucency involving both the fragment and its bed. In the combined form of the disease, there was a fragment in the proximal part of the medial talar ridge in addition to the overlying

162

SECTION I ❚❚❚ The Extremities

A

A

B Figure 7-43 • A, Close-up lateral view of the humeral joint of a 6-year-dog, which at the time appeared normal. B, A second examination performed 5 years later showed severe osteoarthritis featuring large osteophytes extending from the caudal edges of the glenoid and humeral head (emphasis zone). The dog’s forelimb lameness was barely detectable and could not be definitely localized to the shoulder or any other bone or joint. The cause or causes of the arthritis were not determined, even after extensive diagnostic testing.

B Figure 7-44 • A, Close-up frontal view of the hock of a 5-month-

medial malleolus. Additionally, the tarsocrural joint was usually widened medially.

Stifle Osteochondritis of the stifle is uncommon in dogs, especially compared with the incidence of the disease in the elbow and shoulder. When it does occur, the lateral aspect of the femoral condyle is most often involved (Figures 7-47 and 7-48). As in other species, such as the horse, osteochondritic lesions range from distinct cysts to vague subchondral lucency. Marginal defects occur occasionally but only rarely in conjunction with fragments. Osteochondritis of the patella is rare, with diagnosis often being of a presumptive nature. Patella abnormalities asserted to be the result of osteochon-

old Golden Retriever shows joint swelling, which is characteristic of early osteochondritis involving the medial ridge of the talus. B, Opposite hock is provided for comparison.

dritis by one group of authors were (1) soft tissue swelling, (2) multiple small peripatellar fragments, and (3) marginal irregularity. A tangential projection (cranioproximal–craniodistal oblique) of the patella was necessary to establish the left lateral location of the lesion.19 I also have seen an 8-month-old dog with bilateral osteochondritis-like lesions of the tibial tuberosity, which resembled Osgood–Schlatter disease in humans. In addition to the tibial lesions, the animal also had bilateral osteoarthritis and subluxation of the stifles, presumed to be secondary to the tibial lesions (Figure 7-49).

CHAPTER 7 ❚❚❚ Osteochondritis

163

B

A

Figure 7-45 • A, Close-up frontal view of hock in a dog with osteochondritis shows: (1) marked widening of the medial aspect of the tarsocrural joint, (2) marginal irregularity of the apex of the medial talar ridge, and (3) regional subchondral demineralization. B, The opposite tarsocrural joint is included for comparison.

Table 7-1 • THE INTERNATIONAL ELBOW WORKING GROUP’S CLASSIFICATION AND GRADING SYSTEM OF “ELBOW DYSPLASIA” IN DOGS Grade

Grading Criteria

0

Normal. No signs of arthrosis or minimal increased radiographic density in the ulna, caudal to the trochlear notch and/or head of the radius. Mild arthrosis with one or more of the following findings: (a) Less than 2-mm-high osteophyte formation seen on the dorsal edge of the anconeal process (b) Minimal osteophyte formation (<2 mm in any direction) on the dorsal proximal ridge of the radius (c) Or the coronoid process (d) Or the lateral palmar part of the humeral trochlear (e) Obvious sclerosis in the area caudal to the distal end of the ulnar trochlear notch to the proximal radius Moderate arthrosis: One or more of the following findings: (a) Osteophyte 2- to 5-mm high on the anconeal process (b) Moderate osteophyte formation (2-5 mm in any direction on locations b, c, d [as described for grade 1]) Severe arthrosis: One or more of the following findings: (a) Osteophyte > 5-mm high on the anconeal process (b) Severe osteophyte formation (>5 mm in any direction on locations b, c, d [as described for grade 1])

1

2 3

Modified from International Elbow Working Group Protocol. Vet Radiol & Ultrasound 36:172, 1995.

❚❚❚ CLASSIFICATION SCHEMES The International Elbow Working Group (IEWG) proposed a classification for what they term elbow dysplasia. In the proposed scheme, dysplastic canine elbows are graded numerically 1 through 3, depending on which radiographic abnormalities are present. Judgment is rendered on the basis of a single flexed lateral projection of the cubital joint (elbow). The particulars of their evaluation system are shown in Table 7-1.20

Alternatively, Lang and colleagues proposed what they term the Elbow Dysplasia (ED) Score, asserting that it is more sensitive than the IEWG system (especially in large-breed dogs 1 to 2 years of age) because it screens for the presence of arthritis as well as for dislocation and the various forms of osteochondritis.21 Radiographic judgment is made on the basis of two projections: a flexed mediolateral and a 10-degree craniolateral–caudomedial oblique. The specifics of their method are shown in Tables 7-2 and 7-3.

164

SECTION I ❚❚❚ The Extremities

B

A

C

D

Figure 7-46 • Close-up lateral (A) and frontal (B) views of a dog’s hock that resemble osteochondritis but actually constitute an old sprain fracture that has caused instability and widening of the tarsocrural joint (especially well seen in lateral projection). An avulsion fracture of the medial malleolus is also evident in the frontal view. C and D, The opposite tarsocrural joint is provided for comparison.

CHAPTER 7 ❚❚❚ Osteochondritis

Figure 7-47 • Close-up frontal view of the stifle shows a centrally located dimple in the margin of the lateral femoral condyle associated with a diffuse loss of density in the surrounding bone, one of the variants of osteochondritis in the dog.

165

Figure 7-49 • Close-up lateral view of the stifle shows an enlarged, pockmarked tibial tuberosity, caudal inclination of the tibial articulation, caudal displacement of the femur, and a swollen joint. These abnormalities (present bilaterally) were hypothesized to be results of a congenital overgrowth of the tibial tuberosity.

Table 7-2 • THE ELBOW DYSPLASIA GRADING/SCORING SYSTEM Grade

Score

Normal Grade 1 Grade 2 Grade 3

0-1 point (criteria 3, 4) 1 point in criteria 1 + 2 or up to 4 points in total 5-8 points >8 points or 3 points in any of the criteria 5-7

Modified from Lang J, Busato A, Baumgartners D, et al: Comparison of two classification protocols in the evaluation of elbow dysplasia in the dog. J Small Anim Pract 39:169, 1998.

A Personal Perspective In my estimation, both the IEWG and ED scoring systems are too complex for routine clinical use. Additionally, by omitting a nonflexed projection of the elbow, valuable information concerning the width of the humeroulnar and humeroradial joints is not available for consideration, information that often is critical in deciding ambiguous cases. Accordingly, I propose the following simplified method of assessing the canine elbow:

Figure 7-48 • Arthrogram: Close-up frontal oblique view of the lateral femoral condyle in an immature dog with severe osteochondritis shows an absence of articular cartilage beneath multiple cystlike lesions.

• First, no grades or scores are given. Because the assessment is subjective, the descriptors should be qualitative. Stating that the disease is mild, moderate, or severe is sufficient. Numerical classification may sound scientific but usually serves to do little more than clutter already overtaxed memories.

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SECTION I ❚❚❚ The Extremities

Table 7-3 • CRITERIA FOR SCORING ELBOW DYSPLASIA GRADES Score

1

2

3

4

5

6

7

Osteophytes on anconeal process

Osteophytes on other locations

Density of trochlea notch, ulna head, and radius

Congruity of humerulnar joint, “step” radius/ulna

Medial coronoid process

Anconeal process

Medial aspect of the humerii

0 points 1 point 2 points 3 points Modified from Lang J, Busato A, Baumgartners D, et al: Comparison of two classification protocols in the evaluation of elbow dysplasia in the dog. J Small Anim Pract 39:169, 1998.

• Second, the term elbow dysplasia should be abandoned as imprecise and replaced with the term osteochondritis. • Third, where possible, the diagnosis of osteochondritis should be refined (for example, osteochondritis of the coronoid process) by using characteristic osteoarthritic patterns to determine the most probable disease site (coronoid process, anconeal process, humeral condyle). • Fourth, if the articular surfaces of the proximal radius and ulna are misaligned, and there are no other abnormalities, the diagnosis is radioulnar subluxation (mild, moderate, or severe), which may or may not eventually lead to osteoarthritis. Bear in mind, however, that osteochondritis of either the coronoid or anconeal processes produces characteristic dislocation of the humeroulnar joint. • Fifth, radiographic judgment should be based on at least three projections: (1) a nonflexed lateral view (neutral or natural limb position), (2) a flexed lateral projection, and (3) a standard frontal (craniocaudal) view. Additional oblique or penetrated views may be added where needed.

References 1. De Haan JJ, Goring RL, Beale BS: What is your diagnosis? J Am Vet Med Assoc 201:927, 1992. 2. Swenson L, Audell L, Hedhammar A: Prevalence and inheritance of and selection for elbow arthrosis in Bernese mountain dogs and rottweilers in Sweden and benefit:cost analysis of a screening and control program. J Am Vet Med Assoc 210:215, 1997. 3. Ljunggren G, Olsson S-E: Osteoarthrosis of the shoulder and elbow joints in dogs: a pathologic and radiologic study of necropsy material. J Am Vet Rad Soc 16:33, 1975. 4. Henry WB: Radiographic diagnosis and surgical management of fragmented medial coronoid process in dogs. J Am Vet Med Assoc 184:799, 1884. 5. Voorhout G, Hazewinkel HAW: Radiographic evaluation of the canine elbow joint with special reference to the medial humeral condyle and the medial coronoid process. Vet Rad 28:158, 1987.

6. Berry C: Evaluation of the canine elbow for fragmented medial coronoid process. Vet Radiol Ultrasound 33:273274, 1992. 7. Farrow CS: Radiographic assessment of the cubital joint for dysplasia: limitations of the hyperflexed lateral projection. Abstracts: 1995 Annual Meeting of the American College of Veterinary Radiology. Vet Radiol Ultrasound 36:351, 1995. 8. Keller GG, Kreeiger JM, et al: Correlation of radiographic, necropsy and histologic findings in 8 dogs with elbow dysplasia. Vet Radiol Ultrasound 38:272, 1997. 9. Reichle JK, Park RD, Bahr AM: Computed tomographic findings of dogs with cubital joint lameness. Vet Radiol Ultrasound 41:125, 2000. 10. Snaps FR, Saunders JH, et al: Comparison of spin echo, gradient echo and fat saturation magnetic resonance imaging for imaging the canine elbow. Vet Radiol Ultrasound 39:518, 1998. 11. Craig PH, Riser WH: Osteochondritis in the proximal humerus of the dog. J Am Vet Rad Soc 6:40, 1965. 12. Carrig CB, Morgan JP: Microcirculation of the humeral head in the immature dog. J Am Vet Rad Soc 15:28, 1974. 13. Bree H: Evaluation of subchrondral lesion size in osteochondrosis of the scapulohumeral joint in dogs. J Am Vet Med Assoc 204:1473, 1994. 14. Callahan TF, Ackerman N: The supinated mediolateral radiograph for detection of humeral osteochondrosis in the dog. Vet Rad 26:144, 1985. 15. Story EC: Prognostic value of arthrography in canine osteochondrosis. Vet Clin North Am 8:301, 1978. 16. Van Bree HV, Ryssen BV, Desmidt M: Osteochondrosis lesions of the canine shoulder: correlation of positive contrast arthrography and arthroscopy. Vet Radiol Ultrasound 33:342, 1992. 17. Van Bree H, Van Ryssen B: Positive contrast shoulder arthrography with iopromide and diatrizoate in dogs with osteochondritis. Vet Radiol Ultrasound 36:203, 1995. 18. Newell SM, Mahaffey MB, Aron DN: Fragmentation of the medial malleolus of dogs with and without tarsal osteochondrosis. Vet Radiol Ultrasound 35:5, 1994. 19. Brizzee-Buxton BL, Lewis DL, et al: What is your diagnosis? J Am Vet Med Assoc 205:1537, 1994. 20. International Elbow Working Group Protocol. Vet Radiol Ultrasound 36:172, 1995. 21. Lang J, Busato A, et al: Comparison of two classification protocols in the evaluation of elbow dysplasia in the dog. J Small Anim Pract 39:169, 1998.

C h a p t e r

8

Congenital and Developmental Bone Disease ❚❚❚ THE ROLE OF DIETARY CALCIUM IN THE DEVELOPMENT OF BONE DISEASE Voorhout and Hazewinkel determined that the development of secondary ossification centers and longitudinal radial growth are inversely related to calcium intake.1 They reached this conclusion by feeding high, normal, and below normal amounts of calcium to Great Dane puppies and then observing the radiographic effects on the radius and ulna over time. Their observations are tabulated in Box 8-1.

❚❚❚ PARTIAL ABSENCE OF DISTAL LIMB Carrig and co-workers, as part of a multiinstitution collaboration, described the various iterations of ectrodactyly, the partial absence of a paw.2 For those seeking more information on the subject, I suggest medical textbooks because comparatively little has been published about this condition in dogs and cats.

❚❚❚ PANOSTEITIS The cause or causes of panosteitis are unknown. The disease affects mostly immature German shepherds, 6 to 18 months of age, and causes varying degrees of bone pain and associated lameness. Because the disease affects different bones at different times, the pattern of lameness changes, a phenomenon often described as a shifting leg lameness. Most affected dogs recover in a few months irrespective of treatment (rest, steroids, antibiotics, reduction in dietary protein, supplementary bone meal, to name a few), but some do not recover. Occasionally, mature dogs develop the disease and, like young dogs, usually recover spontaneously.3

Patches of medullary new bone characterize panosteitis radiographically. These abnormal bone deposits are predictably located in the distal aspect of the humeral shaft, distal femoral shaft, proximal radius and ulna, and proximal tibia. Chronic lesions are often associated with a thin layer of periosteal new bone. Once the disease subsides, the described lesions gradually disappear over the next few months. Figures 81 to 8-3 illustrate the typical appearance of this disease.

❚❚❚ METAPHYSEAL OSTEOPATHY (HYPERTROPHIC OSTEODYSTROPHY) The cause or causes of metaphyseal osteopathy (MO) are not known. The incidence of this disease appears lower than in the past; however, I continue to see two or three cases a year characterized by the following clinical profile: skeletally immature dog; large to medium-sized breed; marked quadrilateral lameness; hot swollen “joints,” particularly the radiocarpal regions; and variable systemic signs of illness (fever, abnormal blood values). Radiographically, the lesions are symmetrically distributed throughout both forelimbs and hindlimbs, affecting the metaphyseal sides of the growth plates. Like most radiographically visible ailments, there is a spectrum of change, with most advanced lesions exhibiting the classic double growth plate sign as well as variable amounts of metaphyseal bony cuffing. In severe cases, the metaphyseal cuffs can become extremely large. Figures 8-4 and 8-5 show the salient radiographic features of MO. Riser and Shirer described two variations of what they preferred to call hypertrophic osteodystrophy (HOD). Large bony cuffs surrounding the metaphysis and adjacent diaphysis characterize the first form of the disease, which they refer to as type 1. The type 2 variant resembles type 1 with respect to abnormal bone deposition, 167

168

SECTION I ❚❚❚ The Extremities

B o x

8 - 1

Radiographic Observations in the Radius and Ulna of Great Dane Puppies Fed High, Low, and Normal Amounts of Calcium

Above Normal Dietary Calcium

• Retarded development of the ulnar styloid process • Retarded development of the humeral medial epicondyle • Retarded development of the olecranon apophysis • Retarded development of the anconeal process

Normal Dietary Calcium (Control)

Normal

Below Normal Dietary Calcium

• Faster than normal development of secondary ossification centers

but it also features a radiolucent band in the upper part of the metaphysis, which looks like a second growth plate.4 In radiographically screening for this disease, I recommend a long-bone survey consisting of a lateral view of one front and one hindlimb, centered on the elbow and stifle, respectively, using either two 7- by 17-inch films or a single (alternatively shielded) 14- by 17-inch film. In the face of characteristic lesions identified in lateral projection, frontal views are unnecessary to confirm the diagnosis. Further surveys usually are motivated by curiosity and rarely play any significant role in treatment planning or prognosis. Because the disease occasionally affects the mandible and distal ribs, these areas should be imaged as dictated by suggestive clinical signs or physical findings. Most dogs recover regardless of treatment, not surprisingly, given that MO is a disease of unknown cause. Eventually, the metaphyseal bone deposition subsides and the bones slowly resume their original shapes. Some affected puppies develop bilateral valgus deformities in their mid and distal forelimbs. Although corrective ostectomy or osteotomy has been performed in a few animals, I am not convinced that it is necessary because most of these animals recover fully without surgery.

❚❚❚ HYPERTROPHIC PULMONARY OSTEOARTHROPATHY Background Hypertrophic pulmonary osteoarthropathy (HPOA), also known as hypertrophic osteopathy, is a painful secondary bone disease of unknown cause. Usually (but not exclusively) triggered by a lung mass or lobar pneumonia, HPOA is characterized by a uniquely config-

A

B Figure 8-1 • Close-up flexed lateral views of the right (A) and left (B) elbows of a young Basset Hound show medullary opacification in the right humerus and left radius consistent with panosteitis.

ured bone deposition, which typically forms on the outside surfaces of the bones of the front or hind paws, and slowly progresses proximally. Occasionally, abdominal masses trigger the disease, but this is relatively rare. The cause (or causes) of HPOA is not known, but speculation continues to focus on a pair of possible explanations known as the humeral and neuronal theories, both of which attribute the characteristic new bone formation to peripheral hyperemia. Advocates of the humeral theory contend that HPOAdevelops as a result of peripheral vasodilatation secondary to the formation of arteriovenous shunts within the inciting lung lesion. Supporters of the neuronal theory also posit a peripheral hyperemia but instead ascribe it to a vagally mediated reflex initiated by the pulmonary mass.5

Imaging Findings The radiographic appearance of HPOA varies from relatively smooth, plaque-like bone deposit (Figure

CHAPTER 8 ❚❚❚ Congenital and Developmental Bone Disease

A

169

B

Figure 8-2 • Close-up lateral views of the proximal (A) and distal (B) aspects of the radius and ulna show medullary opacification consistent with panosteitis.

8-6) to coralization (Figure 8-7). Some animals exhibit a highly distinctive form of new bone deposition resembling a line of blocks stacked on the cortical surface.

❚❚❚ RETAINED CARTILAGE CORE (RETAINED HYPERTROPHIED ENCHONDRAL CARTILAGE IN THE ULNAR METAPHYSIS)

dislocate, eventually leading to osteoarthritis. In these respects, the retained cartilage core resembles premature closure of the distal ulnar growth plate following injury. Caution: Voorhout and co-workers showed that many normal Great Dane puppies have retained cartilage cores in their distal ulnar metaphyses between 15 and 21 weeks of age.6

Imaging Findings Background The so-called retained cartilage core has always been a rarity, but it is even more so now. Traditionally found in giant-breed dogs such as the Great Dane, and categorized as a metabolic bone disease (even though its cause was unknown), cartilage cores are now grouped with “pediatric” or developmental bone disorders. The retention of a core of hyaline cartilage within the distal ulnar metaphysis may adversely affect bone growth by retarding ulnar length, thus causing the radius to bow cranially and, more importantly, causing the humeroulnar joint to partially

Riser and Shirer published a brief but informative account of the radiographic features of this disease, which I have summarized as follows.7 • The disease is symmetric; that is, it affects both forelimbs: primarily the distal ulna and secondarily the radial shaft and elbow joint. • The lesion, located in the distal ulnar metaphysis and diaphysis, usually resembles the lateral profile of a cone, outlined by a radiodense band (Figure 8-8). Less often, the cartilage core appears solid and is shaped like a slim candle flame. Occasionally, the abnormal core appears to be composed of

170

SECTION I ❚❚❚ The Extremities

A

B

Figure 8-3 • Long (A) and close-up (B) views of the humerus of two dogs show medullary opacification consistent with panosteitis.

CHAPTER 8 ❚❚❚ Congenital and Developmental Bone Disease

171

B A

C

D Figure 8-4 • Close-up views of proximal (A) and distal (B) humerus, proximal and distal radius (B, C), and distal femur and proximal tibia (D). All show a dark band on the metaphyseal side of the growth plate, the hallmark of metaphyseal osteopathy.

172

SECTION I ❚❚❚ The Extremities

A

B

Figure 8-5 • Orientation (A) and close-up (B) views of the tibia of a dog with metaphyseal osteopathy show the characteristic bony blooms associated with chronicity.

CHAPTER 8 ❚❚❚ Congenital and Developmental Bone Disease

173

B

A

C Figure 8-6 • A, Close-up frontal view shows layers of new bone coating the profiled surfaces of the distal radial and ulnar bodies, the result of hypertrophic pulmonary osteoarthropathy secondary to a bronchogenic carcinoma (B, C).

high-density bone, outlined by a lucent band (or perhaps by a Mach band). • The radius may be bowed, depending on the influence (if any) of the cartilage core on ulnar growth. • The humeroulnar joint may be subluxated.

smaller by the time they reach 4 months of age. An abbreviated torso and short limbs, due to retarded axial and appendicular bone growth, also characterize affected puppies. This decreased stature, however, does not appear to be related to any disability.

Imaging Findings

❚❚❚ HYPOCHONDROPLASTIC DWARFISM Background Hypochondroplastic dwarfism, a heritable form of chondrodysplasia, has been reported in a number of dog breeds (Figure 8-9). Affected animals appear normal at birth but fail to keep pace with the growth of their littermates, usually appearing obviously

Sande and co-workers provided a detailed radiographic description of the skeletal abnormalities associated with dwarfism in Alaskan Malamutes from birth to maturity.8 These changes are shown chronologically in Table 8-1. Radiographic abnormalities associated with dwarfism have also been reported in Irish Setters, including shortening of long bones and variable degrees of forelimb curvature (bowing of the radius and ulna). Growth plates and flat bones appeared unaffected.9

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Table 8-1 • SKELETAL FORELIMB ABNORMALITIES IN ALASKAN MALAMUTE DWARFS Age

Radius

Ulna

Other Bones

7-10 days

Shorter than unaffected animals

Flattening of distal metaphysis (most consistent finding) Like the radius, the ulna is shorter than normal

Delayed ossification of accessory carpal bones

3 wk

Distal radial metaphysis is abnormally flattened and irregular, with a narrow, highdensity band situated along its margin Radius (and ulna) remains abnormally short

Distal ulnar metaphysis remains flattened and irregular instead of assuming its normal triangular shape

5 wk

Radial (and ulnar) length now noticeably shorter than normal

Distal ulna remains flattened or becomes concave Trabeculation appears haphazard rather than organized Ulnar body is the same length as that of the radius, where normally the ulnar shaft is decidedly longer Abnormal limb curvature is now physically and radiographically evident

Distal aspects of the ribs appear flared and concave

12 wk

Distal radial margin is concave and flared Dense band on the metaphyseal side of the growth plate has increased Difference in radial and ulnar length becomes more pronounced

Distal ulnar metaphysis is abnormally widened with course Trabeculation and a serrated margin Curvature increases, and is now accompanied by lateral deviation of the paw Width/length ratio of the ulna dramatically increases

The carpal bones appear immature

6 mo

Distal metaphysis remains wide and flat Gap between the radial and ulnar metaphyses continues to increase

Distal metaphysis increases in width and flares Overall length may be reduced by as much as a third (compared with normal) Trabeculae remain coarse and disorganized in appearance Curvature continues with adaptive thickening of the cortices along the lesser curvatures of the diaphysis Width of the ulna continues to be disproportionately wide compared with its length (approximately 1 : 10, compared with a normal ratio of 1 : 25)

11 mo

Radial (and ulnar) curvature persists Compensatory thickening of the caudal radius (and ulna) cortex remains

Distal ulnar metaphysis is now shaped normally as the associated growth plate closes Distance between radial and ulnar metaphyses is normal or near normal Disorganized trabeculation is present in the distal portions of both the radius and ulna, but metaphyseal trabeculation appears normal Increased width-to-length ratio persists

CHAPTER 8 ❚❚❚ Congenital and Developmental Bone Disease

Figure 8-7 • Defleshed distal radius and ulna of a dog with hypertrophic pulmonary osteoarthropathy shows bony coralization induced by a primary lung tumor.

175

Figure 8-9 • Radius and ulna from an Alaskan malamute puppy with hypochondroplastic dwarfism show the shortness and thickening characteristic of this disease.

❚❚❚ NUTRITIONAL SECONDARY HYPERPARATHYROIDISM Background

Figure 8-8 • Close-up frontal view of the distal radius and ulna show an inverted ‘V’ in the distal ulnar metaphysis (emphasis zone), signaling the presence of a retained cartilage core.

Nutritional secondary hyperparathyroidism is now a rarity among pet animals, although it is still regularly encountered in exotic animals, particularly pet iguanas. Hyperparathyroidism is caused by insufficient dietary calcium, a feature of all-meat diets, which are also low in phosphorus. The resultant mineral deficiencies are partially compensated for by (1) increased absorption of intestinal calcium, (2) decreased excretion of urinary calcium, and (3) resorption of skeletal calcium. Nevertheless, neither the body’s efforts to conserve calcium nor its aggressive removal of calcium from the bones can prevent an elevation in parathormone. The result is the further depletion of skeletal calcium, eventually causing a radiographically visible decrease in bone density (osteopenia).10

❚❚❚ SCOTTISH FOLD OSTEODYSTROPHY Scottish fold osteodystrophy is a heritable bone disease of kittens that initially is expressed as a short, thickened, rigid tail and later by thickened carpi and tarsi.

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Radiographically the metacarpal and metatarsal bones appear abnormally shortened, bowed, and have deformed, conical epiphyses. The vertebrae of the tail are abnormally short and disproportionately wide, with distinctively flared metaphyses and misshapen epiphyses.11

❚❚❚ SKELETAL AND OCULAR DYSPLASIA IN LABRADOR RETRIEVERS Carrig and co-workers described heritable, combined skeletal–ocular dysplasia in Labrador Retrievers.12 Skeletal abnormalities are confined to the limbs and include long-bone shortening and abnormal joint development, particularly of the cubital and coxal joints. The authors recommend using the abnormally shortened radius and ulna as a means of identifying affected pups. Associated ocular abnormalities, although not pathognomonic, include cataracts, vitreal strands, persistent hyaloid remnants, retinal folds, retinal dysplasia, peripapillary hyperreflectivity, and rhegmatogenous retinal detachment.

❚❚❚ CONGENITAL HYPOTHYROIDISM Saunders and Jezyk described the skeletal abnormalities associated with congenital hypothyroidism: (1) a short, broad skull; (2) shortened vertebral bodies, (3) epiphyseal dysgenesis, a condition in which epiphyseal centers may be irregularly formed or appear to be fragmented or stippled; (4) delayed epiphyseal appearance; and (5) delayed epiphyseal maturation.13

❚❚❚ DISSEMINATED IDIOPATHIC HYPEROSTOSIS Morgan and Stavenborn reported diffuse periarticular and extraarticular bone deposition in a 4-year-old Great Dane involving the spine, humeral, cubital, coxal, and genual joints.14 The authors termed the condition disseminated idiopathic skeletal hyperostosis, or “DISH,” noting that it resembled Forestier’s disease in people. Diagnostic criteria are extensive and include the following: • Flowing calcification and ossification along ventral and lateral aspects of three contiguous vertebral bodies leading to segmental bony ankylosis

• Relative preservation of the disc width within involved areas and absence of extensive radiographic changes of degenerative disc disease, such as endplate sclerosis, nuclear calcification, or localized spondylosis deformans • Periarticular osteophytes surrounding true vertebral joints • Formation of pseudoarthrosis between the bases of the dorsal spinous processes • Periarticular osteophytes and calcification or ossification of soft tissue attachments (enthesiophytes) in both axial and peripheral potions of the skeleton • Periarticular osteophytes, sclerosis, and ankylosis of sacroiliac joints • Bony ankylosis of the symphysis pubis

References 1. Voorhoot G, Hazewinkel HAW: A radiographic study on the development of the antebrachium in Great Dane pups on different calcium intakes. Vet Rad 28:152, 1987. 2. Carrig CB, Wortman JA, et al: Ectrodactyly (split-hand deformity) in the dog. Vet Rad 22:123, 1981. 3. Sebesstyen P: What is your diagnosis? J Am Vet Med Assoc 212:494, 1998. 4. Riser WH: Radiographic differential diagnosis of skeletal disease of young dogs. J Am Vet Rad Soc 5:15, 1964. 5. Wylie KB, Lewis DD, Pechman RD, et al: Hypertrophic osteopathy associated with Mycobacterium fortuitum pneumonia in a dog. J Am Vet Med Assoc 202:1986, 1993. 6. Voorhout G, Nap RC, Hazewinkel HAW: Aradiographic study on the development of the antibrachium in Great Dane pups, raised under standardized conditions. Vet Radiol Ultrasound 35:271, 1994. 7. Riser WH, Shirer JF: Normal and abnormal growth of the distal foreleg in large and giant dogs. J Am Vet Rad Soc 6:50, 1965. 8. Sande RD, Alexander JE, Padgett GA: Dwarfism in the Alaskan Malamute: its radiographic pathogenesis. J Am Vet Rad Soc 15:10, 1974. 9. Hanssen I, Falck G: Hypochondroplastic dwarfism in the Irish Setter. J Small Anim Pract 39:10, 1998. 10. Tomsa K, Glaus T: Nutritional secondary hyperparathyroidism in 6 cats. J Small Anim Pract 40:533, 1999. 11. Partington BP, Williams JF, Pechman RD: What is your diagnosis? J Am Vet Med Assoc 209:1235, 1996. 12. Carrig CB, Schmidt GM, et al: Growth of the radius and ulna in Labrador Retriever dogs with ocular and skeletal dysplasia. Vet Rad 31:165, 1990. 13. Saunders HM, Jezyk PK: The radiographic appearance of canine congenital hypothyroidism: skeletal changes with delayed treatment. Vet Rad 32:171, 1991. 14. Morgan JP, Stavenborn M: Disseminated idiopathic skeletal hyperostosis (DISH) in a dog. Vet Rad 32:65, 1991.

C h a p t e r

9

Miscellaneous Extremital Disorders ❚❚❚ DISLOCATION OF THE PATELLA (PATELLAR SUBLUXATION, PATELLAR LUXATION) Congenital Medial dislocation of the patella is most common in toy breeds. Typically, the major long bones of the knee, the femur, and the tibia appear S-shaped when viewed frontally. Arguments abound as to whether the displaced patella causes the change in bone shape or whether the deformed limb bones cause the dislocation of the patella. In general, small dogs dislocate their patellae medially (Figure 9-1, A), whereas large dogs do so laterally (Figure 9-1, B). Medium-sized dogs can go either way. An experimental study designed primarily to induce hip dysplasia in Greyhounds by administering estradiol coincidentally showed that the same drug also caused underdevelopment of the patellar groove and, subsequently, medial dislocation of the patella. This finding led the authors to challenge the then widely held belief that patellar luxation led to hypoplasia of the trochlear groove.1 In giant breeds (and some large breeds as well), congenital or developmental patellar dislocation is usually lateral (as mentioned previously). One theory to explain this difference between patellar dislocation in giant and toy breeds contends that lateral subluxation is induced by a preceding medial bowing of the hind limbs at the level of the stifles: a so-called genu valgum deformity. The authors hypothesize that this deformity is caused by a slowing of growth in the lateral aspects of the distal femoral and proximal tibial growth plates, which is prompted by a growth-related physeal ischemia.2

Traumatic Traumatic dislocation of the patella nearly always is associated with a sprain or sprain-avulsion fracture. The key to radiographic diagnosis is the position of the patella when the injured limb is viewed in the

neutral position. If the patella is displaced proximally, the distal patellar tendon is ruptured or the tibial tuberosity is avulsed. If the patella is displaced distally, the quadriceps is torn or the proximal patellar tendon is ruptured. If the patella is oriented horizontally, articular surface facing downward (when viewed in lateral projection), the proximal portion of the patella has torn free from the parapatellar fibrocartilages and femoropatellar ligaments and rotated backwards 90 degrees (rotary intraarticular dislocation).3

❚❚❚ MINERALIZATION OF THE SUPRASPINATUS TENDON Mineralization of soft tissue, particularly muscles and tendons, traditionally has been considered presumptive evidence of injury (dystrophic calcification). Precise radiographic localization is often impossible, however, to the extent that small chip fractures, detached osteochondral fragments, osteophytes, and vestigial sesamoid bones cannot always be distinguished from soft tissue mineralization. A case in point is the shoulder joint of large-breed dogs, where small, oval-shaped bony objects are regularly observed superimposed on or adjacent to the greater tubercle of the humerus and frequently are described as incidental findings (especially if present bilaterally in a sound dog). Flo and Middleton assert that abnormal bone densities in this location are potentially located within the supraspinatus tendon or on the surface of the underlying intertubercular groove. They advocate a skyline projection of the proximal humerus, which they contend optimizes the appearance of the lesion and differentiates supraspinatus from bicipital lesions.4 In a related article, Laitinen and Flo report that the mineralized tissue in the supraspinatus tendon, surgically removed from a series of dogs 5 years earlier, had re-formed, although all but one of the animals were 177

178

SECTION I ❚❚❚ The Extremities

A

A

B Figure 9-2 • Lateral (A) and tangential (B) views of the greater

B Figure 9-1 • A, Close-up frontal (viewer’s left) and lateral (viewer’s right) views of the stifle of a small dog show medial dislocation of the patella. B, Close-up lateral view of the stifle of a large-breed dog shows lateral dislocation of the patella.

now sound. These later findings cast further doubt on the merits of surgery compared with rest or medical treatment.5

❚❚❚ MINERALIZATION OF THE BICEPS BRACHII TENDON Muir and co-workers chronicle the case of a young Rottweiler in which they diagnosed mineralization of the biceps brachii tendon. Borrowing liberally from the literature on rotator cuff injuries in people, the authors term their finding calcifying tendinopathy and speculate that it was most likely the result of an earlier injury that had damaged the tendon’s blood supply, leading to metaplasia.6

❚❚❚ BICIPITAL TENOSYNOVITIS Barthez and Morgan reported using plain radiography and arthrography to diagnose bicipital tenosynovitis in the dog.7 The primary plain film radiographic

humeral tubercle show multiple bony densities on the lateral edge of the bicipital groove. Diagnosis is not clear-cut in this case, but tenosynovitis is a possibility.

disease indicator (RDI) for tenosynovitis is increased bone density in the intertubercular groove, as seen in lateral projection. Alternatively (and more frequently in my experience), the disease may appear as one or more discrete, fragment-like bone densities arrayed along the outer margin of the greater tubercle, as seen in lateral or frontal oblique projections (Figure 9-2, A, B). Arthrographic RDIs compatible with tenosynovitis include (1) diminished or incomplete filling capacity of the bicipital tendon sheath, (2) abnormal narrowing of the bicipital tendon sheath, and (3) marginal irregularity of the bicipital tendon sheath (Figure 9-3, A, B). Iohexol was used as a contrast medium at a concentration of 100 mg/ml and a dose of 0.4 ml/kg. The volume of contrast injected into an individual shoulder joint was determined by a combination of factors: (1) the completeness of bicipital tendon sheath filling (as observed fluoroscopically) and (2) increasing injection pressure.

❚❚❚ GASTROCNEMIUS AVULSION Both traumatic and atraumatic avulsion of the gastrocnemius muscle have been reported. In one especially unusual instance, bilateral atraumatic avulsion of the origin of the gastrocnemius muscle was

CHAPTER 9 ❚❚❚ Miscellaneous Extremital Disorders

179

A

Figure 9-4 • Close-up lateral radiograph of the proximal aspect of the calcaneus and distal part of the Achilles tendon shows marked swelling with islands of dystrophic calcification, the results of a third-degree strain.

B Figure 9-3 • A, Close-up tangential view of the greater humeral tubercle shows multiple bone-like densities on the proximolateral slope of the bicipital groove suggesting tenosynovitis. B, Closeup lateral arthrogram shows (1) synovial distension, (2) abnormal thinning, and (3) marginal irregularities of the bicipital tendon.

described. Associated radiographic abnormalities included (1) new bone on the caudal aspect of the distal femur, (2) bone spurs on the fabellae, and (3) displacement of a single fabella (inconsistent finding).8 Distal Achilles tears are more common, however, usually associated with calcaneal bone deposition, disfigurement, and dystrophic calcification (Figure 9-4).

❚❚❚ TUMORAL CALCINOSIS The term tumoral calcinosis refers to a comparatively rare, extensively mineralized soft tissue mass, which characteristically forms adjacent to the humeral, cubital, coxal, and genual joints of large breed dogs (Figure 9-5).9 Tumoral calcinosis also has been reported in the cervical musculature of German Shepherds, adjacent to the spine.10 Depending on the radiographic projection and the position of the mass relative to the adjacent vertebrae, tumoral calcinosis can be mistaken for a spinal tumor. It is difficult to distinguish tumoral calcinosis from other forms of soft tissue calcification, such as a calcified hematoma, other than on the basis of its preferred locations.

Figure 9-5 • Close-up frontal view of the elbow of a dog shows a calcified mass superimposed on the lateral aspect of the cubital joint (emphasis zone). The texture of the mass is distinctive, being composed of a number of closely approximated, roughly spherical bone-like densities, a feature strongly indicative (along with its periarticular location) of tumoral calcinosis.

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SECTION I ❚❚❚ The Extremities

❚❚❚ CALCANEAL DISLOCATION OF THE SUPERFICIAL DIGITAL FLEXOR TENDON

over the suspected lesion, constitutes strong presumptive evidence of an AV fistula.17

Imaging Findings The tendon of the superficial digital flexor muscle attaches to either side of the proximal part of the calcaneus. If one of these two insertions gives way, the tendon slips to the opposite side, where it is still attached, resulting in acute lameness and a characteristic eccentric swelling. Prevailing theory holds that dislocation of the Achilles is most likely the result of injury. Shetland Sheepdogs, especially if overweight, are thought to be at greatest risk, although there is no indication that this is a heritable trait.11

Plain films are useful in establishing the presence of bone involvement and also may be used to plot roughly the limits of the fistula (Figure 9-6). Whereas ultrasound can be used to identify the principal vascular components of an AV fistula, and to some extent the presence of accelerated venous blood flow, angiography is indispensable for accurate and effective presurgical planning (Figures 9-7 and 9-8).18

❚❚❚ BONE INFARCT

Lameness Secondary to Arterial Blockage by Heartworms

Bone infarction is a rarity in pet animals. Scattered reports by Riser and co-workers describe infarcts in the long bones of dogs caused by malignant bone tumors.12 Madewell and co-workers also reported finding long-bone infarcts in a dog with renal adenocarcinoma.13

Occasionally, heartworms obstruct a major peripheral artery, causing varying degrees of pain, lameness, and disability.19 In some instances, ischemic ulceration may develop on the paw surface.20 Again, angiography is required for diagnosis.

Radiation-induced Bone Lesions

❚❚❚ STRAINED ILIOPSOAS MUSCLE Breur and co-workers reported acute iliopsoas muscle strain in three dogs. They were able to diagnose the lesion by eliciting pain when the affected hip was simultaneously extended and internally rotated. Sonographically, the damaged muscle was described as hypoechoic and swollen.14 Seims and Breur published an account of a severe strain and subsequent contracture of the infraspinatus muscle of a Brittany Spaniel.15

❚❚❚ OSTEOPETROSIS SECONDARY TO MYELOPHTHISIC ANEMIA As described elsewhere in this section, osteopetrosis is most often a congenital disease, but occasionally it can be acquired, as exemplified by its development in a dog with severe myelophthisic anemia.16

❚❚❚ ARTERIOVENOUS FISTULA Background Most arteriovenous (AV) fistulas are caused by injuries, especially deeply penetrating wounds, such as gunshots. Other causes include severe bite wounds, lacerations, and amputations (both surgical and traumatic). Highly invasive tumors, necrotizing infections, and the inadvertent perivascular injection of thiobarbiturates and other highly injurious chemicals are also capable of creating direct AV communications. The presence of fremitus, a palpable vibration detectable

Morgan and Pool reported the appearance of bone lesions produced by experimental radium poisoning in dogs, some of which later became cancerous (malignant transformation).21 The precancerous lesions were, for the most part, destructive in appearance, initially appearing, in the words of the authors, as “linear cortical porosities.” Later, a futile attempt to restore the damaged cortex (a unique form of bone deposition) was observed; the authors termed it a neocortex. This resultant disturbance in the ability of the damaged bone to repair itself (as determined histologically) was termed radiation osteodystrophy. Eventually, the lesions began to assume the radiographic features of malignancy, such as poorly defined margins, long transition zones, and varying degrees of cortical disintegration.

❚❚❚ SKELETAL LEISHMANIASIS Background Turrel reported multiple bone lesions in a small group of dogs with visceral leishmaniasis, a protozoal disease transmitted by sand flies that is usually contracted in the Middle East and in countries bordering the Mediterranean Sea.22 The disease resembles Hepatozoon canis, which commonly affects the reticuloendothelial system (lymph nodes, spleen, liver, and bone marrow), kidneys, and skin.

Imaging Findings Lesions can develop nearly anywhere in the skeleton, including the shafts of long bones, bodies of irregular

CHAPTER 9 ❚❚❚ Miscellaneous Extremital Disorders

181

B

A

Figure 9-6 • Frontal (A) and lateral (B) close-ups of a hind paw show a large, full-length swelling over the lateral aspect that enlarged with exercise and shrank with rest. It later proved to be an arteriovenous fistula.

bones (e.g., carpus and tarsus), sesamoids (e.g., patella), flat bones (e.g., pelvis and scapula), and cranium. Longbone lesions resemble panosteitis, initially appearing as focal or regional areas of increased medullary density and later developing faint overlying periosteal cuffs. Lesions in other locations usually appear destructive. Joint swelling typically accompanies intraarticular lesions.22

❚❚❚ PERIPHERAL NERVE SHEATH TUMOR Platt and co-workers described a palpable malignant nerve sheath tumor (malignant schwannoma) in a dog. The tumor grew in the radial nerve adjacent to the proximal humeral body. The tumor imaged sonographically and with magnetic resonance caused chronic, progressive, unilateral forelimb lameness with associated

muscle atrophy. Electromyography showed denervation potentials in all muscles innervated by the radial nerve. T2 images revealed a medium-sized, welldefined hyperintense lobulated mass in the soft tissues of the proximal brachial region, which showed marked enhancement in T1, following administration of intravenous gadolinium.23

❚❚❚ NEUROMA Hudson and co-workers reported the sonographic identification of an 8-mm neuroma, which formed on the proximal stump of the tibial nerve following experimental transection 5 weeks earlier. The described neuroma appeared as a hypoechoic, tapered oval with a short blunted tail;24 however, the prospects of sonographically identifying naturally occurring neuromas appear remote.

182

SECTION I ❚❚❚ The Extremities

A

B

Figure 9-7 • Arteriovenous fistula: Lateral (A) and lateral close-up (B) arteriograms of a large posttraumatic arteriovenous fistula in the soft tissues of the mid lower forelimb of a dog show characteristic features, including (1) multiple large venous sinuses (patchy white areas), (2) an increased number of blood vessels, (3) vascular tortuosity, and (4) regional swelling (with a palpable vascular vibration).

❚❚❚ EXTREMITAL ISCHEMIA Goggin and co-workers reported the use of nuclear imaging to evaluate distal extremital perfusion in a variety of animals suffering from freeze injury, thromboembolism, vasculitis, electric shock, overly tight bandages, and devascularizing injuries. Limb scans were performed 5 and 10 minutes following injection of technetium-99 (99mTc)-MDP or 99mTc-DTPA. According to the authors, the results correlated closely with clinical outcome.25

❚❚❚ VILLONODULAR SYNOVITIS Background Villonodular synovitis occurs occasionally in horses (most often in the dorsal aspect of the fetlock) but

only rarely in dogs (carpus, stifle, hip). Most often, the lesion appears as a discrete mass and, as such, is amenable to surgical removal. At other times, the lesion is not so well defined, more closely resembling a diffuse synovial hypertrophy, which is not so readily extirpated. Some lesions are pigmented, but others are not, explaining use of the qualifier pigmented (as in pigmented villonodular synovitis). The precise cause of tumoral or diffuse villonodular synovitis is unknown; however, speculation continues to center on either repetitive injury or joint hemorrhage (hemarthrosis).

Imaging Findings Hanson described a case of villonodular synovitis in the carpus of an 8-year-old Shepherd cross.26 Radiographic abnormalities were confined to the craniome-

CHAPTER 9 ❚❚❚ Miscellaneous Extremital Disorders

A

183

B

Figure 9-8 • Close-up frontal views of proximal (A) and distal (B) radius and ulna of a dog with a proximal arteriovenous fistula caused by repeated surgeries to remove a suspected quill fragment. Close inspection of both images reveals many small intravascular filling defects, the result of blood clots caused by catheterization.

dial aspect of the distal radius and the underlying radiocarpal joint and included (1) multiple, vague areas of periarticular and extraarticular bone loss; (2) numerous small bone deposits; (3) decreased width of the cartilage space; and (4) eccentrically positioned joint swelling. As the author points out, these radiographic findings (or similar abnormalities) potentially may be shared by a wide variety of joint disorders, including posttraumatic osteoarthritis, immunoarthritis (immune-mediated osteoarthritis), infectious arthritis, parasitic osteoarthritis, tumors such as synovioma and synovial sarcoma, chronic hemarthrosis, amyloidosis, and osteochondromatosis.26 My preference in such cases is to begin with plain films to evaluate the nearby bone and joint

and then to follow with ultrasound (plus or minus an ultrasound-guided biopsy). Only rarely is singleor double-contrast arthrography necessary. In small dogs and cats, neither procedure tends to be informative.

❚❚❚ HINDQUARTER WEAKNESS AND PAIN DUE TO AORTOILIAC THROMBUS Drost and co-workers described the multimodality appearance of a caudal aortic–iliac thrombus in a dog with hindquarter weakness and pain.27 Radiographs showed calcification in the caudodorsal aspect of the abdomen thought to represent possible aortic calcifi-

184

SECTION I ❚❚❚ The Extremities

Figure 9-9 • Close-up lateral view of catheter fragment lodged in the cephalic vein of a dog (emphasis zone).

cation. Sonography showed narrowing and turbulent blood flow in the caudal aorta consistent with a thrombus, a diagnosis that was further supported by magnetic resonance angiography. Aortography revealed obstruction of the caudal aorta and the presence of sublumbar collaterals.

❚❚❚ INTRAVENOUS CATHETER FRAGMENTS Catheter fragments occasionally become lodged in receiving arteries or veins, leading to thrombosis and sometimes emboli. Small, superficially located catheter fragments are radiographically detectable if they contain a radiopaque marker; otherwise, they are invisible. In the latter instance, ultrasound can be used. Most catheter fragments lodge in the cephalic vein, simply because this is where most intravenous catheters are placed (Figure 9-9). Catheters do break off (or are cut off) elsewhere, for example, in the jugular vein. In some instances, these fragments eventually reach the heart or even the lung. Small fragments, lodged deep within the interior, can be extremely difficult to identify radiographically, even when they contain a safety marker. In human patients, radiologists, practicing one of the newer imaging subspecialties, interventional radiology, now often retrieve deep catheter fragments.

❚❚❚ DISLOCATED SURGICAL PINS Both the veterinary and medical radiographic literatures abound with descriptions of the unintended jour-

Figure 9-10 • Ventrodorsal view of the hips (right side slung) shows a dislocated intramedullary (IM) pin. The implant had been placed through the hip joint following dislocation to keep it in position while it healed but subsequently become dislodged, migrating deep inside the pelvic canal, doing considerable damage in the process.

neys of surgical implants, especially pins. Surprisingly, many of these stray implants seem to do little harm, but occasionally some do (Figure 9-10).

References 1. Gustafasson PO, Kasstrom H, Ljunggren G: Estradiol induced patellar luxation in the dog: an experimental study. J Am Vet Rad Soc 10:49, 1969. 2. Riser WH, Parkes LJ, et al: Genu valgum: a stifle deformity of giant dogs. J Am Vet Rad Soc 10:28, 1969. 3. Gee M, Lenehan TM, Tarvin GB: Rotary intra-articular dislocation of the patella in two dogs. J Am Vet Med Assoc 209:2082, 1996. 4. Flo GL, Middleton D: Mineralization of the supraspinatus tendon in dogs. J Am Vet Med Assoc 197:95, 1990. 5. Laitinen OM, Flo GL: Mineralization of the supraspinatus tendon in dogs: a long-term follow-up. J Am Anim Hosp Assoc 36:262, 2000. 6. Muir P, Goldsmid SE, et al: Calcifying tendinopathy of the biceps brachii in a dog. J Am Vet Med Assoc 201:1747, 1992. 7. Barthez PY, Morgan JP: Bicipital tenosynovitis in the dog—evaluation with positive contrast arthrography. Vet Radiol Ultrasound 34:325, 1993. 8. Robinson A: Atraumatic bilateral avulsion of the origins of the gastrocnemius muscle. J Small Anim Pract 40:498, 1999. 9. Mahoney PN, Lamb CR: Articular, periarticular and juxtaarticular calcified bodies in the dog and cat: a radiologic review. Vet Radiol Ultarsound 37:3, 1996. 10. Morgan PW, Cockshutt J: What is your diagnosis? J Am Vet Med Assoc 203:969, 1993. 11. Mauterer JV, Prata RG, et al: Displacement of the tendon of the superficial digital flexor muscle in dogs: 10 cases (1983-1991). J Am Vet Med Assoc 203:1162, 1993. 12. Riser WH, Brodey RS, Biery DN: Bone infarctions associated with malignant bone tumors in dogs. J Am Vet Med Assoc 160:411, 1972.

CHAPTER 9 ❚❚❚ Miscellaneous Extremital Disorders

13. Madewell BR, Wilson DW, et al: Leukemoid blood response and bone infarcts in a dog with renal tubular adenocarcinoma. J Am Vet Med Assoc 197:1623, 1990. 14. Breur GJ, Blevins WE: Traumatic injury of the iliopsoas muscle in three dogs. J Am Vet Med Assoc 210:1631, 1997. 15. Seims JJ, Breur GJ, et al: Use of two-dimensional realtime ultrasonography for diagnosing contracture and strain of the infraspinatus muscle in a dog. J Am Vet Med Assoc 212:77, 1998. 16. O’Brien SE, Riedesel EA, Miller ID: Osteopetrosis in an adult dog. J Am Anim Hosp Assoc 23:213, 1987. 17. Ackerman N, Ticer J: Phalangial arteriovenous fistula in a dog. Vet Rad 22:85, 1981. 18. Bouayard H, Feeney DA, et al: Peripheral acquired arteriovenous fistula: a report of four cases and literature review. J Am Anim Hosp Assoc 23:205, 1987. 19. Burt JK, Lipowitz AJ, Harris JH: Femoral artery occlusion by Dirofilaria immitis in a dog. J Am Vet Rad Soc 18:166, 1977.

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20. Berry CR: Answers for film reading session: 1995 A.C.V.R. annual meeting. Vet Radiol Ultrasound 36:449, 1995. 21. Morgan JP, Pool RR: Radium-236-induced bone lesions in beagles. Vet Rad 23:261, 1982. 22. Turrel JM, Pool RR: Bone lesions in four dogs with visceral leishmaniasis. Vet Rad 23:243, 1982. 23. Platt SR, Graham J, et al: Magnetic resonance imaging and ultrasonography in the diagnosis of a malignant peripheral nerve sheath tumor in a dog. Vet Radiol Ultrasound 40:367, 1999. 24. Hudson JA, Steiss JE, et al: Ultrasonography of peripheral nerves during Wallerian degeneration and regeneration following transection. Vet Radiol Ultrasound 37:302, 1996. 25. Goggins JM, Hoskinson JJ, et al: Scigraphic assessment of distal extremity perfusion in 17 patients. Vet Radiol Ultrasound 38:211, 1997. 26. Hansen JA: Canine carpal villonodular synovitis. Vet Radiol Ultrasound 39:15, 1998. 27. Drost WT, Bahr RJ, et al: Aortoiliac thrombus secondary to a mineralized arteriosclerotic lesion. Vet Radiol Ultrasound 40:262, 1999.

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Skeletal Deficiencies, Dysplasias, and Deformities ❚❚❚ DELAYED GROWTH PLATE CLOSURE IN CASTRATED AND SPAYED CATS Root and co-workers reported delayed growth plate closure in gonadectomized cats.1 Specifically, male kittens castrated at 7 weeks or 7 months had delayed distal radial closure compared with noncastrated animals. Females experienced similar delays, demonstrating the role of gonadal steroids in normal skeletal development.

❚❚❚ ECTRODACTYLY Background Ectrodactyly is the congenital absence of all, some, or parts of the digits. The malformation is also called splitpaw deformity, or lobster claw, and it can affect one or both front or hind limbs. Ectrodactyly may be associated with dislocation of the elbow, contracted tendons, limb curvature, and limb shortening.2 Importantly, most affected dogs limp to some degree, but few have pain, and most never develop arthritis. The merit of surgical treatment in affected cats and dogs appears dubious.

❚❚❚ RICKETS, SECONDARY TO CHOLESTASIS Extrahepatic biliary atresia leading to rickets was reported in a 17-week-old male Border Collie with painful lameness. A long-bone radiographic survey showed pronounced metaphyseal deformity (cupping), growth-plate widening, and poor bony mineralization, which were attributed to the dog’s inability to absorb fat-soluble vitamins, in particular, vitamin D.3 The precise cause of juvenile rickets is often unknown (Figures 10-1 and 10-2). In older dogs, advanced immunoarthritis bears some resemblance to rickets, but 186

it can be readily differentiated on the basis of related laboratory findings (Figure 10-3).

❚❚❚ CONGENITAL ELBOW DISLOCATION Congenital elbow dislocation (luxation or subluxation) is occasionally the cause of forelimb lameness in young dogs. This anomaly can assume a variety of forms, depending on the bones involved and their degree of displacement. A single cubital joint is most often involved, but occasionally both are affected. Displaced articular elements, particularly the radial head, characteristically appear small, dark, and misshapen, a consequence of their non–weight bearing.4 Typically, the proximal ulna appears abnormally arched when viewed from the side, a shape that reflects its abnormal alignment with the humerus (Figure 104, A). The latter is tipped medially as seen in the frontal plane, resulting in a pronounced varus deformity (Figure 10-4, B). The full extent of this malformation, including its effect on the carpus and foot, can be appreciated only by using stress radiography. In my experience, dogs with complete or near complete congenital dislocation of the radius do not become arthritic, although their bones undergo extensive remodeling, and they often have abnormal forelimb carriage and gait. Accommodative postural changes are usual in the opposite normal leg in cases of unilateral dislocation (Figure 10-5). Aside from revealing changes in size, shape, and volume of the involved joint cavities, arthrograms show what appears to be normal articular cartilage (Figure 10-6, A, B). On the other hand, mild or mild-to-moderate congenital subluxation of the elbow often leads to osteoarthritis (Figure 10-7), although there are exceptions (Figure 10-8). Once such deformities are discovered, rendering a sound, outcome-based prognosis is impossible because little other than anecdotal information is available on the subject.

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Figure 10-1 • Frontal postural view (standing) of the bilaterally deformed lower forelimbs in a puppy with rickets shows (1) medial bowing; (2) flared, scalloped, spiked metaphyses; and (3) increased physeal width.

Figure 10-2 • Lateral view of the forelimb of a young puppy with rickets shows characteristic enlargement and cupping of the distal radial and ulnar metaphyses.

Figure 10-3 • Close-up frontal view of the stifle joints of an old dog with chronic immunoarthritis shows severe subchondral bone destruction, which loosely resembles rickets in a puppy.

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A

B

Figure 10-4 • Congenital elbow dislocation: A, Close-up lateral view of the elbow shows (1) severely bowed proximal ulna; (2) shallow, elongated semilunar arch; and (3) subluxation of the humeroulnar joint. The proximal radius is clearly abnormal, but little more can be said with a frontal view. B, Close-up frontal view shows (1) lateral dislocation of a severely bowed radius with formation of a false joint, (2) compensatory centering and deformity of the proximal ulna, (3) compensatory remodeling of the distal humerus resulting in a downward medial angulation.

Figure 10-5 • Angular limb deformity: Frontal view of the lower forelimbs (postural film made with dog standing and a horizontally directed x-ray beam) shows valgus deformities at the level of the carpi and varus deformities at the elbows. This abnormal posture is due to a fracture dislocation of the left proximal radius (viewer’s top right), subsequent lateral bowing of the ulna, and postural compensation by the left limb.

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A

189

B

Figure 10-6 • Close-up lateral (A) and frontal (B) arthrograms in a young dog with a congenital dislocation of the elbow show how the soft tissues of the cubital joint can accommodate.

A

B Figure 10-7 • A, Close-up lateral view of a unilateral elbow dislocation in a small dog, presumed to have resulted from a congenitally deformed ulna (accounting for its deformity and downward displacement); B, a view of the opposite leg is provided for comparison.

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Figure 10-8 • Close-up lateral view of a nonpainful congenitally dislocated elbow in a small dog with no osteoarthritis.

❚❚❚ DIVIDED DISTAL RADIUS Although not as common as congenital deformities of the paw, additions, subtractions, and unnatural divisions of the middle and upper limb also occur. One such example is what I term miniatures (in lieu of more elaborate Latin descriptors), small replicas of bones or parts of bones. Displaced, longitudinally oriented articular fractures sometimes migrate proximally, giving rise to a miniature facsimile of the injured bone (Figure 10-9).

❚❚❚ INCOMPLETE OSSIFICATION OF THE HUMERAL CONDYLE Incomplete ossification of the humeral condyle is a developmental bone disease of spaniels in that the right and left halves of the humeral condyle are separated by a thin irregular gap. In the few published accounts of this rare disorder, the authors speculated that the described discontinuity structurally weakens the bone to the extent that it is predisposed to fracture. Alternatively, the underlying articular cartilage may give way beneath the subchondral crevice, resulting in the presence of interosseous joint fluid (with its attendant inflammatory properties). Radiographically, incomplete ossification of the humeral condyle is difficult to demonstrate because of the superimposition of the olecranon in both the frontal and frontal oblique projections. The lesion is invisible in lateral perspective. In one reported case involving a 10-year-old Cocker Spaniel, mature new bone deposition was noted on the lateral aspect of the distal shaft of the humerus; however, no mention was made of how this finding related to the primary articular lesion.5 Computed

Figure 10-9 • Close-up frontal view of the distal radius of a puppy with a lateral paw deflection shows a miniature “distal radius” emanating from the medial aspect of the metaphysis. Although the precise cause of this anomaly was not determined (congenital cause was the leading candidate), it did not appear to be traumatic because the opposite limb was similarly affected.

tomography is the superior method in revealing this type of lesion as demonstrated by Marcellin and co-workers.6

❚❚❚ OSTEOGENESIS IMPERFECTA Osteogenesis imperfecta is a heritable bone disease characterized by a loss of cortical and medullary bone density and the presence of numerous healed or healing fractures. In these respects, osteogenesis imperfecta resembles nutritional secondary hyperparathyroidism. Affected puppies appear stunted, often assume a crouched position when resting, have abnormal gaits, have pink teeth, and have marked muscle atrophy. Osteogenesis imperfecta is diagnosed by analyzing type 1 collagen from cultured skin fibroblasts.7

CHAPTER 10 ❚❚❚ Skeletal Deficiencies, Dysplasias, and Deformities

❚❚❚ ERYTHROCYTE PYRUVATE KINASE DEFICIENCY IN BASENJIS Severe chronic hemolytic anemia and osteopetrosis (osteosclerosis) clinically characterize pyruvate kinase deficiency in Basenjis. Radiographically, the marrow cavities, which normally look dark compared with the lighter cortices, instead appear completely opacified, making corticomedullary distinction difficult or impossible. Abdominal radiography often reveals hepatic and splenic enlargement; thoracic images may show cardiomegaly related to chronic anemia.8 The disease also was reported in three 2-month-old Dachshund puppies from the same litter. These puppies eventually were euthanized because they were unable to stand. Radiographically, their long bones and vertebrae appeared uniformly white. Microscopically, the medullae contained calcified cartilage, osteoid, and primitive bone, accounting for their abnormal opacity.9

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References 1. Root MV, Johnston SD, Olson PN: The effect of prepuberal and postpuberal gonadectomy on radial physeal closure in male and female cats. Vet Radiol Ultrasound 38:42, 1997. 2. Frey M, Williams J: What is your diagnosis? J Am Vet Med Assoc 206:619, 1995. 3. Extrahepatic biliary atresia in a border collie. J Small Anim Pract 41:27, 2000. 4. Farrow CS: Congenital elbow luxation. In Farrow CS, ed: Decision Making in Small Animal Radiology, Toronto, 1987, BC Decker. 5. Berry CR: Answers for film reading session: 1995 ACVR annual meeting. Vet Radiol Ultrasound 36:449, 1995. 6. Marcellin DJ, Roe SC, DeYoung DJ: What is your diagnosis? J Am Vet Med Assoc 209:727, 1996. 7. Campbell BG, Wootton JAM, et al: Clinical signs and diagnosis of osteogenesis imperfecta in three dogs. J Am Vet Med Assoc 211:183, 1997. 8. Giger U, Noble NA: Determination of erythrocyte pyruvate kinase deficiency in Basenjis with chronic hemolytic anemia. J Am Vet Med Assoc 198:1755, 1991. 9. Riser WH, Fankhauser R: Osteopetrosis in the dog: a report of three cases.

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The Skull, Brain, Eye, and Ear

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Radiographic Disease Indicators of the Skull The following are the principal radiographic disease indicators of skull disease in dogs and cats.

❚❚❚ NASAL MASS In older dogs and cats, nasal masses are nearly always malignant, although associated fluid often hides them from view.

❚❚❚ NASAL FLUID Nasal fluid may be the result of injury, infectious or noninfectious sinonasal disease, or cancer. In many instances, medium or large fluid volumes completely hide the conchae.

❚❚❚ DEVIATION AND DESTRUCTION OF THE VOMER Deviation or destruction of the vomer nearly always indicates cancer of the nasal cavity. Only rarely is infection associated with similar findings. Congenital defor-

mity or a serious facial injury conceivably could distort the vomer but in most cases would also distort the lateral facial bones and possibly the lower jaw.

❚❚❚ CONCHAL DISAPPEARANCE Inability to identify the conchae radiographically is usually due to one of two possible causes: (1) the conchae have been destroyed or (2) they are being hidden by fluid.

❚❚❚ LATERAL NASAL BONE DESTRUCTION Destruction of the lateral facial bones is nearly always the result of cancer and only occasionally the consequence of infection.

❚❚❚ INCREASED JAW DENSITY Widespread symmetric bone deposition in the lower jaw suggests metaphyseal osteopathy. New bone ori193

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ented about the temporomandibular joints, bullae, and vertical rami suggest mandibular osteopathy. Localized asymmetric sclerosis suggests possible callus, infection, or tumor, differentials that usually can be ranked and pursued according to clinical context (contextual diagnosis). It is particularly important to take radiographs of such lesions regularly where cancer is a contending diagnosis.

❚❚❚ DECREASED JAW DENSITY Marked loss of mandibular bone, to the extent that the teeth appear to be floating in space, usually heralds serious metabolic skeletal disease, such as renal osteodystrophy. When subtle osteopenia is observed, nutritional secondary hyperparathyroidism warrants consideration, especially if accompanied by extremital fracture. It is a good practice to perform long-bone surveys in such circumstances. Localized loss of jaw density is common with fractures, especially if they are not surgically reduced and immobilized. Focal, spherically shaped

areas of bone loss, particularly around tooth roots, are strong indicators of infection and abscess. Vaguely demarcated, marginal mandibular bone loss is often the earliest radiographic sign of squamous carcinoma.

❚❚❚ INCREASED CRANIAL DENSITY Increased cranial density usually is caused by new or old bone deposition. In the case of the latter, an old fracture is likely, especially if associated with deformity. A discrete object may be a benign or malignant bone tumor. Disorganized new bone may be the result of a recent injury, a response to localized infection, or the beginning of a tumor.

❚❚❚ DECREASED CRANIAL DENSITY A localized decrease in bone density often indicates the development of a tumor or, less frequently, an infection.

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Head Injury and Infection

❚❚❚ FACIAL INJURIES Facial depression fractures potentially can cause a variety of nasal cavity problems. Nasal or maxillary bone fragments can be driven into nearby turbinates or nasal passages, resulting in airflow obstruction. Because of the open nature of such fractures, infection is always a possibility, occasionally complicated by sequestration. With moderate or severe fragment displacement, there is usually accompanying devascularization, which encourages delayed healing and, in some instances, nonunion. Noninfectious sinusitis may develop after a serious sinus injury (Figure 12-1), although its precise cause often is not determined. Facial deformity, especially nonpainful asymmetry of the frontal sinuses, is often the result of an old injury.

❚❚❚ MANDIBULAR AND MAXILLARY INJURIES About 6% of all fractures in dogs and cats involve the mandible, usually the symphysis or body. Fractures of the vertical ramus and its bony extensions, the mandibular condyle and condyloid process, occur much less frequently. Although some of these injuries require surgery, many do not, for example, fractures of the condyloid process.1 Untreated hinge fractures— complete transverse breaks across the upper or lower jaws just behind the canine teeth—usually fail to heal and, depending on how they are treated, may have a higher incidence of postsurgical infection.

❚❚❚ TEMPOROMANDIBULAR JOINT INJURIES AND MOTION IMPAIRING DISORDERS Fractures or dislocations of the temporomandibular joint (TMJ), whether unilateral or bilateral, often are signaled by an inability to close the jaws fully or symmetrically (Figure 12-2). Ticer and Spencer published

a detailed description of the radiographic appearance of fractures and dislocations of the feline TMJ,2 and Schwarz and co-workers recently covered similar ground in a recent review article on the canine TMJ.3

❚❚❚ ANKYLOSIS AND IMPINGEMENT EXOSTOSIS Ankylosis or joint fusion may be of two types: primary ankylosis, in which the joint is actually fully or partially solidified and thus incapable of moving, and secondary ankylosis, in which the joint is structurally normal but unable to move (or move very little) because of an adjacent impinging callus. Such injuries are most common in cats that have been hit by cars4 and in dogs with severe depression fractures of the zygoma, which physically prevent opening of the mouth (Figures 12-3 and 12-4). The latter type of injury can require prolonged physiotherapy because the jaw muscles become severely atrophied under such conditions so that even after the zygoma is surgically removed, the tightened muscles still can prevent the mouth from opening. Occasionally, extraarticular callus, formed on or near the mandibular condyle, will behave like a fulcrum when the mouth is opened, causing complete or partial dislocation of the lower jaw, which in most cases is transient. In some instances, however, the jaw temporarily locks in the open position. Repeated dislocation can cause condylar remodeling, especially in a skeletally immature animal, which then can lead to chronic dislocation and the formation of a false joint.

❚❚❚ CONGENITAL TEMPOROMANDIBULAR DEFORMITY AND DISLOCATION Avariety of congenital condylar deformities, variously termed temporomandibular dysplasia, misplaced coronoid process, and jaw locking, have been reported in dogs, 195

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Figure 12-1 • Close-up lateral view of a healed depression fracture of the frontal sinus resulting in a shallow depression in its normally convex contour. The sinus is now abnormally clouded, the result of sinusitis, which was believed to have resulted from obstructed drainage.

Figure 12-2 • Mandibular fracture-dislocation: Close-up ventrodorsal oblique view of the temporomandibular joints shows bilateral dislocation; additionally, there are bilateral fractures of the condyloid processes and a comminuted fracture of the right vertical ramus (reader’s left).

Figure 12-3 • Frontal view of the face and jaw shows marked deformity of the right zygoma and mandible, the result of fractures. Currently, the dog can barely open its mouth because of secondary ankylosis.

most of which are associated with an inability to close the lower jaw fully and an absence of known injury.5–6 Radiographically, the key elements in these disorders are condylar displacement and deformity; however, it is usually impossible to know whether this is the result of (1) recent injury, (2) past injury, or (3) congenital disease. As a consequence, establishing dislocation does not necessarily establish cause. Flattening of the glenoid and hypoplasia of the retroglenoid process may accompany dysplasia but are also usually present in cases of trauma-induced dislocation of the TMJ, especially if the injury occurred before completion of skeletal development. With dislocation (subluxation), the articular surfaces of the glenoid and mandibular condyle overlap, producing a characteristic a thick white band (Figures 12-5 and 12-6). The best means of radiographically demonstrating a deformed or dislocated TMJ is with a traction–stress

maneuver. In this projection, the dog is positioned on its back, head flush against the table, with the closely collimated x-ray beam centered between the TMJ. The rostral aspect of the lower jaw is grasped by the canines and forcefully pulled forward, and the exposure made.7 There are few other projections of comparable value, although a conventional ventrodorsal projection can be somewhat useful, especially if made with a penetrated technique. Standard lateral and lateral oblique views usually contribute little to a diagnosis.

❚❚❚ CRANIAL INJURIES Subperiosteal Hematoma Background. Acute subperiosteal hematomas typically appear as nonspecific, localized soft tissue

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Figure 12-6 • The left temporomandibular joint is included for comparison.

Figure 12-4 • Ventrodorsal oblique view of the face and jaw shows marked deformity of the right zygoma and mandible, the result of fractures. Currently, the dog can barely open its mouth because of secondary ankylosis.

Imaging Findings. Radiographically, a cranial subperiosteal hematoma typically appears as a variably bordered, smoothly surfaced localized mound on the dorsal or dorsolateral aspect of the cranium. In some instances, the lesion may partially overlie the frontal sinuses. Its interior is usually semitransparent overall, but it may be partially calcified or ossified. Depending on the age of the lesion, interior fluid may be identified sonographically. In captive primates, especially adolescents, such lesions are common. Magnetic resonance imaging of such lesions clearly shows how the hematoma forms between the inner and outer layers of the frontal bone (the most common location), dramatically elevating the former.9

Cephalhematoma Following injury, young dogs or cats may develop an expansive bony swelling on the dorsal or dorsolateral aspect of the cranium, a common lesion in primate colonies.10

Cranial Fractures Figure 12-5 • Close-up lateral oblique views of the temporomandibular joints (TMJ) of a dog with a partially dislocated right TMJ.

swellings that gradually disappear over time. Some of these lesions, perhaps the most severe, leave a characteristic “fingerprint” that becomes discernable weeks or months later and can be used to infer the original injury. More importantly, awareness of this distinctive lesion can assist in helping to distinguish it from a bone tumor.8

Cranial fractures may result in protruding bone fragments (expression fracture) or intruding fragments (depression fracture), or they may be nondisplaced. Fractures in and around the basilar portion of the cranium are typically the most difficult to identify, often requiring multiple supplementary views (Figure 12-7).

Gunshot Wounds Gunshot wounds are usually fatal if the bullet (or bullet fragments) enters the brain (Figure 12-8). Nasal wounds may become secondarily infected because they are a form of open fracture, depending on the extent of the

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Figure 12-7 • Penetrated ventrodorsal view of the caudal basilar region of the skull shows a nondisplaced fracture through the lateral aspect of the left bulla (emphasis zone).

injury, and may lead to a chronic nasal discharge. Occasionally, lead fragments may lodge in one of the TMJs or the eyes or sever the facial nerve or nasolacrimal duct.

References 1. Salisbury SK, Cantwell HD: Conservative management of fractures of the mandibular condyloid process in three cats and one dog. J Am Vet Med Assoc 194:85, 1989. 2. Ticer JM, Spencer CP: Injury of the feline temporomandibular joint: radiographic signs. J Am Vet Rad Soc 19:146, 1978. 3. Schwarz T, et al: Imaging of the canine and feline temporomandibular joint: a review. Vet Radiol Ultrasound 43:85, 2002.

Figure 12-8 • A single high-powered bullet to the head killed this dog instantly as it lay on the front steps of a home. The fragment pattern supports a frontal entry wound.

4. Meomartino L, Fatone G: Temporomandibular ankylosis in the cat: a review of 7 cases. J Small Anim Pract 40:7, 1999. 5. Robins G, Grandage J: Temporomandibular joint dysplasia and open mouth jaw locking in the dog. J Am Vet Med Assoc 171:1072, 1977. 6. Widmer WR, Blevins WE: Radiographs presented as part of the 1995 ACVR oral certification examination: musculoskeletal section. Vet Radiol Ultrasound 37:108, 1996. 7. Farrow CS: Stress radiography. 8. Lutz SE, Williams J: What is your diagnosis? J Am Vet Med Assoc 206:1145, 1995. 9. Hill LR, Bernacky BJ, et al: What is your diagnosis? J Am Vet Med Assoc 216:1913, 2000. 10. Ardran GM, Kemp JR, et al: Cephalhematoma in squirrel monkeys. J Am Vet Rad Soc 18:70, 1977.

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Skull Tumors

Skull tumors vary in radiographic appearance according to both their cell type and location. For example, osteosarcomas of the cranial vault are typically productive with defined margins, whereas osteosarcomas in long bones are usually destructive and poorly marginated. Osteosarcomas of the face and jaw, on the other hand, typically feature creeping osteolysis, overt cortical destruction, and tumor bone extending into the surrounding soft tissue.1

❚❚❚ CRANIAL TUMORS Radiology and Computed Tomography Because of the pronounced curvature of the cranium, tangential views, made at right angles to suspicious surfaces, often produce a diagnostic image (Figure 13-1) where standard lateral and ventrodorsal projections of the same region fail to reveal any abnormalities (Figure 13-2). Some cranial osteosarcomas produce relatively little soft tissue swelling while extensively lysing underlying bone (Figures 13-3 and 13-4). Hathcock and Newton described the computed tomographic (CT) appearance of seven cranial and two facial bone tumors in dogs. These bones were optimally imaged using a bone window.2 The principal CT features of these tumors are shown in Box 13-1.

❚❚❚ FACIAL TUMORS

tinctive dished-out areas, reflecting areas of creeping substitution (Box 13-2).

❚❚❚ MANDIBULAR TUMORS Background Most mandibular tumors are actually squamous cell carcinomas (or other soft tissue tumors) of the gum or tongue, which become evident radiographically only once they invade the nearby jawbone. Primary bone tumors such as osteosarcoma, fibrosarcoma, and chondrosarcoma also may develop in the lower jaw but do so considerably less often (Figure 13-10). Thrall and co-workers reported the development of a mandibular osteosarcoma in a dog 77 months after orthovoltage radiotherapy for a fibromatous epulis (periodontal origin, acanthomatous type).3 To qualify as a radiation-induced bone tumor, a lesion must meet the following criteria (according to the authors): • Microscopic or radiographic evidence must exist that the original bone, whether normal or not, was nonmalignant. • The tumor must have developed within previously irradiated tissue. • The latent period between irradiation and tumor detection must be long. • The malignant nature of the tumor suspected to be radiation-induced must be proved.

Radiology and Computed Tomography

Imaging Findings

Radiographically, facial malignancies can be quite variable in appearance, ranging from intensely destructive (Figure 13-5) to moderately productive; alternatively, they may feature a combination of productive and destructive changes (Figures 13-6 to 138). Most, however, are primarily destructive (Figure 13-9). Tomographically, facial tumors often feature dis-

Most invasive gingival and glossal cancers cause local bony destruction; however, some do not. On the contrary, there are reports of invasive carcinomas causing intensely productive mandibular lesions resembling primary bone tumors.4 Mixed (destructive–productive) mandibular tumors occur as well (Figures 13-11 to 13-15). 199

Figure 13-1 • Osteosarcoma: A slightly oblique lateral view of the cranium of a dog shows a faint, smoothly surfaced mound of tumor bone, underlain by a ragged area of cortical destruction (emphasis zone).

Figure 13-2 • An earlier true lateral view of the same region predictably failed to show this eccentrically located bone tumor.

Figure 13-3 • Orientation view of the cranium of a dog shows a vaguely marginated area of uneven bone destruction (sometimes referred to as permeative), which in this instance is being caused by an osteosarcoma.

Figure 13-4 • Close-up view of the cranium of a dog shows a vaguely marginated area of uneven bone destruction (sometimes referred to as permeative), which in this instance is being caused by an osteosarcoma.

Figure 13-5 • Ventrodorsal open-mouth view of the skull of a cat with a highly destructive carcinoma that has destroyed much of the right side of the face (emphasis zone).

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Figure 13-6 • Lateral view of a cat with a squamous cell carcinoma of the rostral aspect of the right zygoma. Note how lesion visibility varies depending on projection, attesting to the fact that anatomically complex parts such as the skull often require customized imaging.

Figure 13-8 • Ventrodorsal open-mouth view of a cat with a squamous cell carcinoma of the rostral aspect of the right zygoma. Note how lesion visibility varies depending on projection, attesting to the fact that anatomically complex parts such as the skull often require customized imaging.

Figure 13-7 • Ventrodorsal view of a cat with a squamous cell carcinoma of the rostral aspect of the right zygoma. Note how lesion visibility varies depending on projection, attesting to the fact that anatomically complex parts such as the skull often require customized imaging.

Figure 13-9 • Intraoral projection of the upper jaw of a dog with a fibrosarcoma shows dissolution of much of the rostral aspect of the right maxilla and loss of most of the associated incisors.

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Figure 13-10 • Close-up lateral oblique view of the rostral mandible of a dog with an unusual osteosarcoma. The radiograph was deliberately underexposed to accentuate the frond-like cancer bone contained within the soft tissue bulk of the tumor.

Figure 13-11 • Ventrodorsal view of a dog with an unusually located squamous cell carcinoma on the medial side of its right mandible. The tumor features new bone production, combined with deep marginal bone loss (center middle of the close-up).

Figure 13-12 • Open-mouth view of a dog with an unusually

Figure 13-13 • Close-up open-mouth view of a dog with an

located squamous cell carcinoma on the medial side of its right mandible. The tumor features new bone production, combined with deep marginal bone loss (center middle of the close-up).

unusually located squamous cell carcinoma on the medial side of its right mandible. The tumor features new bone production combined with deep marginal bone loss (center middle of the close-up).

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Figure 13-14 • Squamous cell carcinoma. Lateral view of the facial region of a cat shows that the left zygoma has been destroyed and replaced with an amorphous calcified mass.

B o x

1 3 - 1

Computed Tomographic Features of Cranial Tumors in Dogs • Most tumors were located in or near the occipital region. • Tumors were characteristically large, protruding, spherical masses, which were sometimes lobulated. • Exterior tumor margins were for the most part smooth and of uniform thickness. • Interior tumor margins were relatively less well defined, often rough and irregular. • Tumor interiors typically appeared as granular bone densities arranged into multiple large, variably sized and shaped clumps. • Most tumors were associated with large defects in the cranium as a result of bone destruction.

References 1. Hardy WD, Brodey RS, Riser WH: Osteosarcoma of the canine skull. J Am Vet Rad Soc 8:5, 1967. 2. Hathcock JT, Newton JC: Computed tomographic characteristics of multilobular tumor of bone involving the cranium in 7 dogs and zygomatic arch in 2 dogs. Vet Radiol Ultrasound 41:214, 2000.

Figure 13-15 • The ventrodorsal view of the facial region of a cat shows that the left zygoma has been destroyed and replaced with an amorphous calcified mass.

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1 3 - 2

Computed Tomographic Features of Facial (Zygomatic) Tumors in Dogs • Most zygomatic tumors, like cranial tumors, appeared as large, well-defined convexities. • Unlike the described cranial tumors, tumors of the zygoma had a coarse, granular appearing interior.

3. Thrall DE, Goldschmidt MH, et al: Bone sarcoma following orthovoltage radiotherapy in two dogs. Vet Rad 24:169, 1983. 4. Madewell BR, Ackerman N, Sesline DH: Invasive carcinoma radiographically mimicking primary bone cancer in the mandibles of two cats. J Am Vet Rad Soc 17:213, 1976.

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Nasal Cavity Disease

Persistent nasal discharge characterizes most, but not all, chronic nasal disease, particularly malignant nasal tumors. Potential diagnoses and their probabilities have been reported and are tabulated later in this chapter.1 Although nasal passage tumors are diagnosed regularly, associated pulmonary metastasis is rare, making screening thoracic radiography a statistically debatable practice (Tables 14-1 and 14-2).2

❚❚❚ NASAL TUMOR (INTRANASAL TUMOR, NASAL CAVITY TUMOR) Background Nasal tumors usually occur in older dogs, particularly breeds with elongated faces (Figure 14-1). The most common cell types are squamous cell or adenocarcinoma, followed by osteosarcoma, fibrosarcoma, and chondrosarcoma.3 In cats, tumors of the nasal cavity account for about 3% of all neoplasms; like dogs, the most common cell types in cats are squamous cell and adenocarcinoma. Less common feline nasal tumors include fibrosarcoma, lymphohistiocytic sarcoma, chondrosarcoma, chondroma, and lymphoma.4

Imaging Findings Normal Radiology Nasal Cavity and Frontal Sinuses. The nasal conchae are visible in both the lateral and ventrodorsal views as somewhat vague, alternating light and dark gray lines. In the lateral projection, because of their natural curvature, the dorsal and ventral conchae give the impression of swirling objects (Figure 14-2). The openmouth view is the more valuable because of its lack of superimposition by the mandible; however, it must not be more than slightly oblique lest it falsely create the impression of unilateral disease (Figure 14-3). The same 204

restriction applies to the standard frontal sinus view, which although strictly speaking is not part of the nasal cavity, nevertheless is an integral part of most nasal series (Figure 14-4). Nasal Septum. In 1979, Harvey showed that the nasal septum of a normal dog was radiographically invisible, thereby overturning the long-held, prevailing belief of most of his contemporaries. According to Harvey, what was currently being called the nasal septum was actually the vomer bone. This discovery was extremely important because septal destruction was the principal, and thought by many to be the most reliable, diagnostic feature of nasal tumors.5 Cribriform Plate. Schwarz and co-workers described the radiographic appearance of the normal cribriform plate in canine cadavers, indicating that it may vary with both skull type and projection angle.6 Abnormal Radiology Fluid, Bone Destruction, and the Nasal Conchal Pattern. Destruction of one or more of the bony elements of the nasal cavity is believed by most authorities to be a strong and reliable indicator of malignancy and less often of mycotic or bacterial infection. Schmidt and Voorhout showed experimentally that surrounding fluid causes loss of the normal maxillary conchal pattern, which typically is characterized by a combination of fine and coarse, alternating light and dark parallel lines. When just the fine conchal striations disappear, leaving only the coarse trabeculation behind, bone destruction is probable. When extensive conchal destruction and fluid are combined, the nasal cavity becomes completely opacified.7 Although I have tried repeatedly to distinguish malignant from benign disease based on these criteria, I have generally been unsuccessful. In a conflicting report, however, Schwarz and colleagues found that nasal fluid appeared to have little or no effect on the normal turbinate pattern, support-

CHAPTER 14 ❚❚❚ Nasal Cavity Disease

205

ing the contention that despite the presence of diseaserelated nasal fluid or soft tissue, sizable defects in the nasal borders are still potentially detectable by radiographic means.8

Harvey and co-workers also reviewed canine nasal tumors, in addition to performing a metanalysis on previous radiographic reports on the subject. Their conclusions are discussed here, along with some examples (Figures 14-5 to 14-11; Box 14-1).9

Table 14-1 • POTENTIAL CAUSES OF CHRONIC

Differentiating Nasal Infection from Neoplasia. The presence or absence of lesion symmetry has been used to assess the relative probabilities of intranasal neoplasia and chronic rhinitis in cats.10 Predictors of nasal cancer include (1) unilateral involvement, (2) lysis of lateral bones, (3) turbinate destruction, and (4) loss of teeth. Alternatively, bilaterally symmetric nasal lesions suggest benignity in the form of chronic rhinitis. Russo and co-workers reported a significant lack of interobserver agreement in the interpretation of abnormal nasal radiographs in dogs. Additionally, they

NASAL DISEASE IN DOGS Diagnosis

Probability (%)

Comment

Aspergillosis Cancer

7 33

Extension of periodontal disease

10

Inflammatory rhinitis Nasal foreign body

24

Primary infection Adenocarcinoma is the most common cell type Usually secondary to apical abscess but also seen in conjunction with uncomplicated extractions and in cases where root fragments remain behind Probably underdiagnosed

Surgical injury, sequestrum, or bone fragments

?

7

Plant awns and miscellaneous plant fragments are the most common nasal foreign bodies seen in our hospital Intranasal bone fragments, presumably left over from an earlier rhinotomy, and identified with CT have been reported* The so-called nasal flush is likely more harmful than initially realized

Traumatic turbinate ? or vomer damage, diagnostic nasal irrigation

CT, Computed tomography. *Modified from Hawks DM, Daniel GB: Radiographic diagnosis. Vet Rad 32:307, 1991.

Figure 14-1 • Skulls of three dogs illustrating differences in facial length, from left to right: abbreviated, normal, and elongated.

Table 14-2 • DIFFERENTIAL RADIOGRAPHIC DIAGNOSIS OF NASAL CAVITY LESIONS IN DOGS RDI

Tumor

Trauma

Plant Awn

Infection

Sinusitis

Conchae fully or partially concealed by fluid

Often

Often

Often

Occasionally, depending on severity

Clouded frontal sinus or sinuses Destruction of one or more facial bones Exterior mass Fracture Missing teeth

Often

Occasionally

Occasionally, depending on duration of foreign body Rarely

Often

Occasionally

Occasionally

Often

Rarely

Occasionally

Never

Occasionally Very rarely Occasionally, depending on tumor type Often

Never Often Often

Never Never Never

Rarely Very rarely Rarely

Never Never Never

Occasionally

Occasionally

Occasionally

Rarely

Occasionally

N/A

N/A

N/A

N/A

Nasal septum invisible or partially destroyed Visible tumor bone

Modified from Morgan JP, Suter PF, et al: Tumors in the nasal cavity of the dog: a radiographic study. J Am Vet Rad Soc 13:18, 1972. RDI, Radiographic disease indicator; N/A, not applicable.

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further confirmed the ambiguity of the radiographic signs caused from nasal tumors and infections, which make diagnostic differentiation difficult.11 Like others before them, they sought to identify specific radiographic abnormalities that would strongly suggest either tumor or infection. Their findings are shown in Table 14-3. Evaluating Postoperative-Postradiation Nasal Radiographs. Progress studies of dogs that have had their nasal tumors partially removed (debulked) and then irradiated can be extremely difficult to evaluate. Even using earlier comparison films, it is often impos-

Table 14-3 • RADIOGRAPHIC DIFFERENTIATION

Figure 14-2 • Normal nasal cavity and frontal sinus. Lateral

OF NASAL INFECTION AND TUMOR

view of the nasal cavity of a healthy Labrador Retriever (“Sooner”). Tumor

Infection

Complete opacification, with concurrent loss or concealment of associated conchae Frontal sinus involvement: fluid, mass, or both Surrounding bone destruction, including the vomer

Focal or multifocal abnormalities

B o x

Localized lucency Localized densities Absence of frontal sinus involvement

1 4 - 1

Tendencies of Canine Nasal Tumors

Figure 14-3 • Open-mouth view of the nasal cavity of a healthy Labrador Retriever (“Sooner”).

• Dogs with nasal tumors show greater radiographic abnormalities of the nasal cavity and frontal sinuses than dogs with benign disease. • The combination of vomer bone destruction and an external mass strongly suggests cancer. Conversely, if both these features are lacking, tumor is highly unlikely. • Abnormal lucency of one or both sides of the nasal cavity suggests fungal infection, especially if the vomer appears normal. • About one third of the dogs with radiographically abnormal nasal cavities provide no indication as to the nature of their disease.

Figure 14-4 • Frontal sinus view of the nasal cavity of a healthy Labrador Retriever (“Sooner”).

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207

Figure 14-5 • Lateral view of the nasal cavity of a dog with a nasal adenocarcinoma, which features the following: (1) patchy areas of increased density; (2) reduced turbinate detail, especially on the left side; (3) abnormal thinning of the central vomer (implying destruction); and (4) clouding of the frontal sinuses (implying fluid). Typically, the ventrodorsal view is the more informative because of the lack of superimposition.

Figure 14-6 • Open-mouth view of the nasal cavity of a dog with a nasal adenocarcinoma, which features the following: (1) patchy areas of increased density; (2) reduced turbinate detail, especially on the left side; (3) abnormal thinning of the central vomer (implying destruction); and (4) clouding of the frontal sinuses (implying fluid). Typically, the ventrodorsal view is the more informative because of the lack of superimposition.

Figure 14-7 • Close-up intraoral view of the nasal cavity of a dog with a nasal tumor shows almost complete opacification of the right side.

Figure 14-8 • A skyline projection of the associated frontal sinus shows partial destruction of the right dorsolateral rim with tumor extruding through the defect.

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Figure 14-9 • Lateral view of the nasal cavity of a dog with a nasal osteosarcoma. The tumor has erupted from the right upper side of the face, opacifying much of the nasal cavity and disfiguring the face.

Figure 14-11 • Close-up intraoral view of a nasal adenocarcinoma in a dog shows extensive opacification of the left nasal cavity, combined with bowing, thinning, and partial destruction of the vomer.

Figure 14-10 • Intraoral view of the nasal cavity of a dog with a nasal osteosarcoma. The tumor has erupted from the right upper side of the face, opacifying much of the nasal cavity and disfiguring the face.

on a number of dogs with ambiguous radiographic findings, but generally we have found the technique unrewarding. Our few diagnostic successes have come when we have combined rhinography with postural radiography, specifically, supporting the head and neck of the unconscious dog on a large covered sponge, infusing a medium volume of high-viscosity diagnostic iodine solution into the nasal cavity, briefly letting the excess contrast drain away, and obtaining a lateral projection of the nasal cavity using a horizontal x-ray beam. One or two supplementary views then are made according to what was seen initially. Computed Tomography

sible to separate postoperative rhinitis from tumor regrowth or from radiation necrosis. All these diseases are inclined to cause intranasal fluid, and, as such, alterations in the conchae—assuming any remain—are difficult or impossible to appreciate (Figure 14-12).

Rhinography Goring and co-workers described the technique and clinical applications of positive-contrast rhinography in dogs.12,13 We also attempted contrast rhinography

Normal. Both Burk and George and Smallwood published articles illustrating the normal tomographic (computed) appearance of the nasal passages of the dog. The report by George and Smallwood went farther, including comparable xerograms and anatomic sections, additions that greatly enhance anatomic understanding of the CT scans.14,15 Losonsky and co-workers described the normal tomographic (computed) appearance of the nasal cavity and paranasal sinuses of the cat.16

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Table 14-4 • COMPARATIVE SENSITIVITIES OF COMPUTED TOMOGRAPHY AND RADIOGRAPHY IN THE DIAGNOSIS OF CANINE NASAL TUMORS AND MYCOTIC INFECTION Specificity Sensitivity

B o x

Radiography (%)

Computed Tomography (%)

76.5 54

98.8 100

1 4 - 3

Diagnostic Advantages of Computed Tomography Over Radiography in Identifying Nasal Disease

Figure 14-12 • Progress intraoral radiograph of a dog following removal of a nasal adenocarcinoma and radiation therapy. The tumor has regrown and displaced part of the vomer toward the right. No discrete conchae are apparent on the expanded left side, replaced in part by a smeared amorphous soft tissue density (tumor and fluid) and numerous variably sized lucent areas, believed to be caused by radiation necrosis.

B o x

1 4 - 2

Computed Tomographic Disease Indicators (CTDI’s) of Serious Nasal Cavity Disease in Dogs • Abnormal soft tissue located in the retrobulbar space • Areas of opacification containing patches of increased density • Destruction in one or both lateral maxillae • Destruction of the rostral portion of the dorsal maxilla • Ethmoidal destruction • Hyperostosis of the lateral maxilla • Nasal bone destruction

Indicators of Nasal Cancer. Burk was also one of the first to undertake a comprehensive review of a large number of computed tomograms made of dogs with nasal disease. This was done in an effort to establish reliable and predictive computed tomographic disease indicators (CTDIs).17 According to the author, seven CTDIs, or combinations of CTDIs, were regularly associated with serious nasal passage disease, especially tumors (Box 14-2).

• Abnormal opacification of the sphenoid sinus • Destruction of the cribriform plate, presphenoid bone, and horizontal portion of the palatine bone • Destruction of the frontal, nasal, maxillary, and vertical parts of the palatine bone • Destruction of the nasal septum or turbinates • Extranasal masses of the olfactory lobes of the brain, nasopharyngeal opening, nasopharynx, retrobulbar region, and oral cavity • Fluids, masses, or bone destruction in the frontal sinus

firmed nasal cavity cancer. CT proved more effective than radiology in identifying the following: (1) unilateral versus bilateral disease and (2) tumor spread to the cranial cavity, hard palate, and pterygopalatine fossa. They asserted that CT also may be superior to radiology for tumor staging, predicting possible treatment-related injury, and planning surgery and radiation therapy.18 Park and co-workers showed that CT is the superior method for evaluating nasal tumors in dogs and that it is far more sensitive than radiography in diagnosing the following pathology (Box 14-3). Schwarz also compared the relative specificities and sensitivities of radiography compared with CT in the diagnosis of canine nasal tumors and mycoses (Table 14-4).19 Equipped with three-dimensional reconstruction software, CT surpasses stereoradiography in its ability to convey a sense of anatomic depth, a feature that is indispensable for radiation therapy planning.20 Koblik and Berry reported the diagnostic advantage gained by dorsal-plane rather than transverse-plane imaging of the ethmoid region, particularly the cribriform plate of dogs with nasal tumors (squamous cell, transitional cell, and adenocarcinoma).21 In a followup project, the authors created cribriform lesions in previously healthy dogs and then compared images of these lesions using radiography, linear tomography, and CT.22

Plain Radiographs Versus Computed Tomography

Magnetic Resonance Imaging

Thrall and co-workers evaluated paired radiographic/tomographic examinations in dogs with con-

Moore and co-workers described the use of both magnetic resonance imaging (MRI) and CT in the diagno-

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adenocarcinoma, pointing out its value in presurgical or radiotherapy planning.24 Two case examples were included that showed tumor spread to the retrobulbar region in one instance and the intracranial area in another case.

❚❚❚ SINONASAL INFLAMMATORY DISEASE

Figure 14-13 • Transverse magnetic resonance images of portions the nasal cavity of a dog with chronic rhinitis and sinusitis show severe, predominantly right-sided mucosal thickening and frontal sinus fluid.

Diseases of the nasal cavity and frontal sinuses, also known as sinonasal inflammatory diseases, are best imaged by CT, even though MRI is more than capable of producing a diagnostic image (Figures 14-13 and 1414); sinonasal tumors are best seen with MRI. The latter is best performed with unenhanced routine sequences and postcontrast, fat-suppressed sequences.25 Sinusitis, in conjunction with bronchiectasis and situs inversus, has been reported in a dog; this condition is a rare combination of heritable disorders seen in humans, known as Kartagener syndrome.26

References

Figure 14-14 • Frontal sinus of a dog with chronic rhinitis and sinusitis shows severe, predominantly right-sided mucosal thickening and frontal sinus fluid.

sis of occult nasal tumors invading the rostral portion of the brain in four dogs. Although both types of imaging demonstrated the nasal and cerebral lesions, MRI provided superior anatomic detail. Even more importantly, MRI revealed peritumor edema and ventricular collapse, which were not appreciable in CT images made through comparable tissue planes.23 Voges and Ackerman used nuclear magnetic resonance imaging to assess the regional spread of nasal

1. Tasker S, Knottenbult, et al: Etiology and diagnosis of persistent nasal disease in the dog: a retrospective study of 42 cases. J Small Anim Pract 40:473, 1999. 2. MacEwen EG, Withrow SJ, et al: Nasal tumors in the dog: retrospective evaluation of diagnosis, prognosis and treatment. J Am Anim Heart Assoc 170:45, 1977. 3. Forrest LJ: The cranial and nasal cavities—canine and feline. In Thrall DE, ed: Textbook of Diagnostic Radiology. Philadelphia, 2002, WB Saunders. 4. Madewell BR, Priester WA, et al: Neoplasms of the nasal passages and paranasal sinuses in domesticated animals as reported by 13 veterinary colleges. Am J Vet Res 37:851, 1976. 5. Harvey CE: The nasal septum of the dog: is it visible radiographically? J Am Vet Rad Soc 20:88, 1979. 6. Schwarz T, Sullivan M, Hartung K: Radiographic anatomy of the cribriform plate. Vet Radiol Ultrasound 41:220, 2000. 7. Schmidt M, Voorhout G: Radiography of the canine nasal cavity: significance of the presence or absence of the trabecular pattern. Vet Radiol Ultrasound 33:83, 1992. 8. Schwarz T, Sullivan M, Hartung K: Radiographic detection of defects of the nasal boundaries. Vet Radiol Ultrasound 41:226, 2000. 9. Harvey CE, Biery DN, et al: Chronic nasal disease in the dog: its radiographic diagnosis. J Am Vet Rad Soc 20:91, 1979. 10. O’Brien RT, Evans SM, et al: Radiographic findings in cats with intranasal neoplasia or chronic rhinitis: 29 cases (1982–1988). J Am Vet Med Assoc 208:385, 1996. 11. Russo M, Lamb CR, Jakovljevic S: Accuracy of radiographic diagnosis of nasal lesions in fifty-five dogs. Vet Radiol Ultrasound 40:533, 1999. 12. Goring RL, Ticer JW, et al: Positive-contrast rhinography: a technique for radiographic evaluation of the nasal cavity, nasopharynx, and paranasal sinuses in the dog. Vet Rad 25:98, 1984.

CHAPTER 14 ❚❚❚ Nasal Cavity Disease

13. Goring RL, Ticer JW, et al: Contrast rhinography in the radiographic evaluation of disease affecting the nasal cavity, nasopharynx, and paranasal sinuses in the dog. Vet Rad 25:106, 1984. 14. Burk RL: Computed tomographic anatomy of the canine nasal passages. Vet Radiol Ultrasound 33:170, 1992. 15. George TF, Smallwood JE: Anatomic atlas for computed tomography in the mesaticephalic dog: head and neck. Vet Radiol Ultrasound 33:217, 1992. 16. Losonsky JM, Abbott LC, Kuriashin IV: Computed tomography of the normal feline nasal cavity and paranasal sinuses. Vet Radiol Ultrasound 38:251, 1997. 17. Burk RL: Computed tomographic imaging of nasal disease in 100 dogs. Vet Radiol Ultrasound 33:177, 1992. 18. Thrall DE, Robertson ID, et al: A comparison of radiographic and computed tomographic findings in 31 dogs with malignant nasal cavity tumors. Vet Rad 30:59, 1989. 19. Schwarz T: Comparison of sensitivity and specificity of conventional x-ray and computed tomography in nasal tumors and mycoses in dogs. Vet Radiol Ultrasound 36:428, 1995.

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20. Pechman RD: Stereoradiography of the dog and horse skull. J Am Vet Rad Soc 19:53, 1978. 21. Koblik PD, Berry CR: Dorsal plane computed tomographic imaging of the ethmoid region to evaluate chronic nasal disease in the dog. Vet Rad 31:92, 1990. 22. Berry CR, Koblik PD: Evaluation of survey radiography, linear tomography and computed tomography for detecting experimental lesions of the cribriform plate in dogs. Vet Rad 31:146, 1990. 23. Moore MP, Gavin PR, et al: MR, CT and clinical features from four dogs with nasal tumors involving the rostral cerebrum. Vet Rad 32:19, 1991. 24. Voges AK, Ackerman N: MR evaluation of intra and extracranial extension of nasal adenocarcinoma in a dog and cat. Vet Radiol Ultrasound 36:196, 1995. 25 Som PM, Curtin HD: Sinuses. In Stark DD, Bradley WG, eds: Magnetic Resonance Imaging, vol III, ed 3, St Louis, 1999, Mosby. 26. Stowater J: Kartagener’s syndrome in a dog. J Am Vet Rad Soc 17:174, 1976.

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Dental, Gum, and Tongue Diseases ❚❚❚ DENTAL DISEASE IN DOGS AND CATS Hamp (a dentist) and co-workers were among the first to provide a radiologic perspective on the problem of canine dental disease.1 From their extensive investigation of necropsy material, they reached the conclusions listed in Box 15-1. Zontine was one of the first North American veterinary radiologists to take more than a passing interest in dental radiography. First in Veterinary Clinics of North America and later in Veterinary Radiology, he described the imaging of a dog’s teeth, along with the appropriate anatomic descriptors.2,3 Subsequently, some veterinary radiologists and nonradiologists adopted purpose-built, human dental x-ray machines for use in dogs and cats. Most veterinarians, however, have continued to do their dental radiography with conventional x-ray machines, albeit with somewhat more sophisticated screen-film systems.4

❚❚❚ NORMAL TEETH The jaws of a puppy initially contain 28 temporary teeth, variably referred to as puppy, deciduous, milk, or baby teeth. Subsequently, these teeth are lost and are replaced by a permanent dentition (Figure 15-1) that includes 14 additional adult teeth, not preceded by temporaries. Thus, the final complement of permanent teeth in an adult dog is 42 (Figure 15-2).

❚❚❚ A SIMPLIFIED RADIOGRAPHIC APPROACH TO DENTAL DISEASE Veterinarians specializing in the dental diseases of pets by and large have adopted the terminology used in human dentistry. Adaptation of the existing human 212

dental lexicon has the advantage of a legacy literature, albeit a human one. The disadvantage of learning a new terminology, one that is unfamiliar to most pet owners, is that it would likely require some “translation.” For those desiring a simpler approach, as well as one with a radiographic emphasis, most dental disease can be conceptualized as consisting of two essential elements: the tooth and its socket. Obviously, the surrounding jawbone forms the backdrop for any dental assessment, particularly as concerns the focal bone destruction that often accompanies abscess. The following material illustrates the various types of structural changes that occur with a variety of dental diseases in dogs and cats. Tip: Placing both a right and a left marker along either side of the maxilla or mandible when making oblique dental projections, termed double-marking, provides additional assistance in identifying which side of the jaw contains the diseased tooth or teeth (Figure 15-3).

❚❚❚ PERIODONTITIS Like people, dogs and cats lose more teeth to periodontal disease than to any other cause; however, periodontitis must be well advanced before it can be appreciated radiographically. A better way to assess periodontal disease is to measure the depth of the natural pocket (sulcus) formed by the inside surface of the gum and the outer surface of the tooth. As periodontal disease worsens, the depth of the sulcus increases until the tooth loosens, becomes painful, and is eventually lost.

❚❚❚ DENTAL ABSCESS In my experience, the carnassial tooth of the dog (fourth premolar) becomes abscessed more often than any

CHAPTER 15 ❚❚❚ Dental, Gum, and Tongue Diseases

213

Figure 15-1 • Close-up right lateral oblique view of the maxilla of an older puppy shows a combination of temporary and permanent teeth, exemplified in the side-by-side adult and puppy canine teeth.

Figure 15-2 • Close-up right lateral view of the maxillary dentition of a young adult dog (excluding the incisors) shows the normal anatomy of healthy teeth and jaw.

B o x

1 5 - 1

Clinical Generalizations About Canine Dental Disease • Caries and root resorption were found less frequently than periapical destruction. • Missing teeth were common regardless of age. • Most dogs had dental calculus. • Periapical destruction was a common finding. • Periodontitis was the most common dental disease, becoming worse with advancing age. • Small dogs were more often affected with periodontitis than large dogs. • Within different breeds, periodontitis varied markedly. Figure 15-3 • Left lateral oblique view of the maxillary dentition of a normal dog featuring double marking.

other. Typically, these abscesses appear as relatively discrete circular areas of lucency surrounding the top of a single root, although occasionally multiple roots can be affected (Figures 15-4 and 15-5). In chronic disease, there also can be varying degrees of root destruction, in which case much or all the dental socket is destroyed and the adjacent jawbone is lysed (Figures 15-6 to 15-8).

Infected teeth usually do not involve the nasal cavity or frontal sinuses as they often do in horses, and only rarely are they associated with nasal discharge. Thus, when an infected tooth is detected in a nasal examination, it is in all likelihood an incidental finding (Figures 15-9 and 15-10).

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Figure 15-4 • Close-up lateral oblique view of an abscessed right maxillary carnassial tooth in a dog shows characteristic well-marginated, circular lucency surrounding the upper portion of the intact caudal root.

Figure 15-5 • A view of the normal left carnassial tooth is provided for comparison.

Figure 15-6 • Orientation view of the right maxillary carnassial tooth in a dog shows destruction of the dental socket and surrounding bone. The caudal tooth root is severely lysed, including the root canal. The visible rostral root contains a central teardrop-shaped cavity; the cranial cusp of the tooth is missing and shows evidence of associated decay (irregular marginal lucency).

Figure 15-7 • Close-up view of the right maxillary carnassial tooth in a dog shows destruction of the dental socket and surrounding bone. The caudal tooth root is severely lysed, including the root canal. The visible rostral root contains a central teardrop-shaped cavity; the cranial cusp of the tooth is missing and shows evidence of associated decay (irregular marginal lucency).

Figure 15-8 • The opposite healthy carnassial tooth is provided for comparison (left and right).

CHAPTER 15 ❚❚❚ Dental, Gum, and Tongue Diseases

Figure 15-9 • Open-mouth view of left maxillary carnassial tooth in a dog shows lateral alveolar expansion, the result of infection. Although it is not apparent, a small alveolar defect has allowed pus to leak into the adjacent soft tissues causing an abscess, which is suggested by adjacent swelling that is not present on the opposite side of the face.

215

Figure 15-11 • Intraoral view of a dog with combined cavitation and abscess of the left upper second and third incisors, teeth that were previously fractured. The associated canine tooth is absent.

❚❚❚ CAVITIES AND ROOT RESORPTION Cavities occur less often in dogs than in people, largely because of a combination of dental morphology and diet. Unlike humans, the benefits of canine dental hygiene, in particular brushing, are debatable. Except for the tops of broken teeth, cavities in dogs and cats are most likely to occur along the sides of teeth, often near the base. Basilar cavities are particularly common in older cats, giving rise to a variety of names, ranging from the straightforward to the pretentious: feline neck lesions, dental reabsorptive lesions, cervical line lesions, and odontoclastic reabsorptive lesions.5

❚❚❚ DENTAL FRACTURE AND DISLOCATION Figure 15-10 • Close-up view of left maxillary carnassial tooth in a dog shows lateral alveolar expansion, the result of infection. Although it is not apparent, a small alveolar defect has allowed pus to leak into the adjacent soft tissues causing an abscess, which is suggested by adjacent swelling that is not present on the opposite side of the face.

Dental fractures, particularly of the canine teeth, may or may not require treatment, depending largely on where they break off. When the nerve is exposed, a root canal is the only effective treatment, short of extraction. Left untreated, some such fractures may become infected (Figure 15-11). Occasionally, a canine tooth may be propelled upward into the rostral part of the nasal cavity and act as a foreign body.6

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Figure 15-12 • Close-up lateral oblique view of the first premolar of a dog with an infected retained root (emphasis zone) following a previous dental fracture.

Figure 15-13 • Close-up ventrodorsal openmouth view of the rostral maxilla shows extensive bone loss and dental displacement, primarily on the right side, the result of an undifferentiated dental tumor.

❚❚❚ RETAINED DENTAL ROOTS AND ROOT FRAGMENTS Occasionally, a root or root fragment is broken off during extraction of a diseased tooth. This is particularly a problem in older dogs and cats that have basilar reabsorption or ankylosis. In most instances, the remaining root is painful and must be removed. Atooth also may be sheared off just below the gum line as a result of injury, with the root remaining undetected until it eventually becomes diseased (Figure 15-12).

❚❚❚ DENTAL AND PERIODONTAL TUMORS In dogs, the oral cavity is the site of about 6% of all tumors, 60% of which originate in the dental or periodontal tissues.7 Occasionally, puppies develop dental

tumors, which are capable of radically deforming the nearby teeth and gums (Figure 15-13). In an adult dog, however, extreme dental displacement is more likely to be the result of a fibrosarcoma.

❚❚❚ GUM AND TONGUE As previously indicated, most mandibular and maxillary tumors are actually invasive soft tissue cancers such as squamous cell carcinomas. Most such tumors gradually erode away the margin of the adjacent bone, and others erase it completely. Some cause an uneven pattern of bone destruction that resembles a piece of lace. Solano and Penninck described the sonographic appearance of the normal tongue in dogs, cats, and horses. In addition, they also described a variety of tumors: squamous cell carcinoma, rhabdomyoma,

CHAPTER 15 ❚❚❚ Dental, Gum, and Tongue Diseases

melanoma, and adenocarcinoma, in addition to an abscessed foreign body.8 In my experience, most glossal tumors occur in older cats and are usually carcinomas. To date, medical imaging appears to be playing only a minor role in the diagnosis and treatment of such lesions, although I have used sonography to locate and remove abscessed porcupine quill fragments from the tongue of a large dog.

References 1. Hamp S-E, Olsson S-E, et al: A macroscopic and radiologic investigation of dental diseases of the dog. Vet Rad 25:86, 1984. 2. Zontine WJ: Dental radiographic technique and interpretation. Vet Clin North Am 4:741, 1974.

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3. Zontine WJ: Canine dental radiography: radiographic technic, development, and anatomy of the teeth. J Am Vet Rad Soc 16:75, 1975. 4. Roman FS, Llorens MP, et al: Dental radiography in the dog with a conventional x-ray devise. Vet Rad 31:235, 1990. 5. Lund EM, Bohacek LK, et al: Prevalence and risk factors for odontoclastic resorptive lesions in cats. J Am Vet Med Assoc 212:302, 1998. 6. Morris EL: Radiographic diagnosis. Vet Rad 30:119, 1989. 7. Theon AP, Rodriquez C, et al: Analysis of prognostic factors and patterns of failure in dogs with periodontal tumors treated with megavoltage irradiation. J Am Vet Med Assoc 210:785, 1997. 8. Solano M, Penninck DG: Ultrasonography of the canine and equine tongue: normal findings and case history reports. Vet Radiol Ultrasound 37:206, 1996.

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Brain Disease and Injury (Intracranial Lesions) ❚❚❚ METHODS OF IMAGING THE BRAIN: INTRODUCTION Radiography

on the basis of vascular displacement and deformity (Figure 16-3).3 The procedure was dangerous and often imprecise; as a result, it has become obsolete.

Other than in cases of head trauma where a fracture is suspected, plain radiography predictably does little to suggest, confirm, or exclude the presence of a brain lesion. Thus, there is little justification for plain radiography under most circumstances, even as an inexpensive preliminary screening technique. The task of imaging brain lesions is clearly now the purview of computed tomography (CT) and magnetic resonance imaging (MRI).

Ventriculography. Before the advent of ultrasound, CT, and MRI, hydrocephalus was diagnosed by ventriculography, a procedure in which a bone biopsy needle was first used to puncture the cranium, making way for a spinal needle that was then passed through the cerebral cortex into one of the underlying lateral ventricles. A diagnostic opaque then was injected to assess the size, shape, and patency of the ventricular system. The procedure was associated with a high incidence of seizures and protracted recovery periods.

Special Radiographic Procedures

Nuclear Medicine Imaging

Combined Linear Tomography and Cysternography. Voorhout described the use of linear tomography and cysternography to evaluate the pituitary gland in healthy dogs and how this imaging combination compared with CT.1 Although it may be perhaps of academic interest to some, this procedure is unlikely to garner any serious degree of acceptance, if only because most facilities have long since discarded their tomographic equipment.

Because of the far greater sensitivity of CT and MRI in localizing and characterizing brain disease, nuclear imaging is gradually fading from the diagnostic scene, with the exception of a few specialized indications, such as the evaluation of cerebral blood flow, cerebral metabolism, and cerebrospinal fluid (CSF) mechanics, investigative endeavors that are for the most part physiologically oriented.4 The occasional veterinary publication on the subject, however, does still appear.5

Venography. Cavernous sinus venography is currently used on a limited basis to investigate disorders of the cavernous venous sinus, in particular its influence on the eye (Figures 16-1 and 16-2). Among other things, cavernous sinus venography has been used to diagnose an adenocarcinoma of the olfactory lobe that was compressing the optic nerves and causing blindness2 and a retrobulbar arteriovenous fistula that caused a dog’s eye to protrude temporarily whenever the dog became excited.

Sonography

Cerebral Angiography. Before the advent of CT, and later MRI, cerebral arteriography (cerebral angiography) was the only means by which a medium-sized to large brain lesion could be imaged, albeit indirectly, 218

Ultrasound is a safe, effective, and rapid means of establishing the presence of moderate or severe hydrocephalus in puppies or kittens, but it is often useless once the cranial fontanels have closed. Sonography also can be used intraoperatively as a means to assess an exposed tumor or cyst.6 Hudson and colleagues reported the capabilities of color flow and spectral Doppler in evaluating the flow characteristics of selected cerebral vasculature (rostral cerebral, middle cerebral, and internal carotid arteries) in newborn puppies.7,8 Normal values (for the largest lateral ventricle featuring normal histology) appear in Table 16-1.

CHAPTER 16 ❚❚❚ Brain Disease and Injury (Intracranial Lesions)

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Figure 16-1 • Lateral view of a normal cavernous sinus venogram in a dog.

Figure 16-3 • Normal ventrodorsal cerebral angiogram showing a focused digital subtraction of the circle of Willis.

Table 16-1 • MAXIMUM SONOGRAPHIC DIMENSIONS OF THE CANINE LATERAL VENTRICLE

Figure 16