Nonfusion Technologies in Spine Surgery

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Front of Book > Editors

Editors Marek Szpalski MD Chairman and Associate Professor Department of Orthopedics, IRIS South Teaching Hospitals, Free University of Brussels, Brussels, Belgium Robert Gunzburg MD, PhD Senior Consultant Department of Orthopaedics, Edith Cavell Clinic, Brussels, Belgium Jean-Charles Le Huec MD, PhD Professor Spine Unit, Bordeaux University, Bordeaux, France; Chief, Orthopaedic Department, CHU Pellegrin, Bordeaux, France Marco Brayda-Bruno MD Chief Division of Spine Surgery III, Galeazzi Orthopaedic Institute-I.R.C.S.S., Milano, Italy

Secondary Editors Robert Hurley Acquisitions Editor Jenny Koleth Managing Editor

Bridgett Dougherty Production Manager Kathleen Brown Manufacturing Manager Sharon Zinner Director Of Marketing Risa Clow Design Coordinator Nesbitt Graphics, Inc. Production Services Edwards Brothers Printer

Contributing Authors Max Aebi MD, FRCSC Director Institute for Evaluative Research in Orthopaedic Surgery, University of Bern, Switzerland; Chief, Department of Orthopaedic & Spinal Surgery, Salem Hospital, Bern, Switzerland Michael Ahrens MD Mauro Alini PhD Head Biomaterials & Tissue Engineering Program, AO Research Institute, Davos Platz, Switzerland S. Aunoble MD

Département Orthopédie Pr Chauveaux, Pr Le Huec, Spine Unit, CHU Pellegrin Tripode, Bordeaux cedex, France Pavel Barsa MD Department of Neurosurgery, Regional Hospital, Liberec, Czech Republic Y. Basso MD Département Orthopédie Pr Chauveaux, Pr Le Huec, Spine Unit, CHU Pellegrin Tripode, Bordeaux cedex, France Jacques Beaurain MD Michel Benoist MD Department of Orthopaedic Surgery Rheumatology Section, University of Paris VII, Paris, France, Hopital Beaujon, Clichy, France Pierre Bernard MD Centre Aquitain du Dos. Clinique Saint-Martin, Pessac, France Philippe Boulu MD Department of Orthopaedic Surgery Rheumatology Section, University of Paris VII, Paris, France, Hopital Beaujon, Clichy, France Bruce Bowman MD Marco Brayda-Bruno MD Chief Division of Spine Surgery III, Galeazzi Orthopaedic Institute-I.R.C.S.S., Milano, Italy P. Buchvald MD Department of Neurosurgery, Regional Hospital, Liberec, Czech Republic Peter Donkersloot MD

Neurosurgeon Department of Neurosurgery, Virga Jesseziekenhuis, Hasselt, Belgium Peter Donceel MD, PhD Department of Occupational, Environmental and Insurance Medicine, Katholieke Universiteit Leuven, Leuven, Belgium Marc Du Bois MD Medical Adviser Alliance of Christian Sickness Funds, Brussels, Belgium, Department of Occupational, Environmental and Insurance Medicine, Katholieke Universiteit Leuven, Leuven, Belgium Thierry Dufour MD Jeremy Fairbank MD Professor of Spinal Surgery Nuffield Department of Orthopaedic, Nuffield Orthopaedic Centre, Oxford, United Kingdom; Consultant Orthopaedic and Spine Surgeon, Department of Spinal Surgery, Nuffield Orthopaedic Centre, Oxford, United Kingdom Brian J. C. Freeman MB, BCh, BAO, DM, FRCS (Tr & Orth) Consultant Spinal Surgeon Department of Spinal Surgery, University Hospital, Queen's Medical Centre, Nottingham, United Kingdom T. Friesem MD University Hospital of North Tees, Nardwick, Stokton on Tees, United Kingdom R. Froehlich MD Department of Neurosurgery, Regional Hospital, Liberec, Czech Republic Jean-Marc Fuentes MD

Franco Gobetti Spine Care Group, Galeazzi Orthopeadic Institute, Milano, Italy Sibylle Grad PhD Research Leader Biomaterials and Tissue Engineering Program, AO Reasearch Institute, Davos Platz, Switzerland Thijs Grünhagen MSc D.Phil Student Department of Physiology, Anatome and Genetics, Oxford University, Oxford, United Kingdom Pierre Guigui Department of Orthopaedic Surgery, Rheumatology Section, University of Paris VII, Paris, France, Hopital Beaujon, Clichy, France Robert Gunzburg MD, PhD Senior Consultant Department of Orthopaedics, Edith Cavell Clinic, Brussels, Belgium Richard D. Guyer MD Spine Surgeon and Co-Director of Spine Surgery Fellowship Program Texas Back Institute, Plano, Texas Ludo MFGB Haazen MD Clinical R&D Consultant Envision bvba, Lier, Belgium Henry Halm MD Bernard Luc Léonard Hanson MD, PhD

Université de Mons-Hainaut, Chargé d'exercices, Sociologie de la santé, Université de Mons-Hainaut, Mons, Belgique; Position Head of Internal Medicine, Hôpitaux Iris Sud, site Molière, Internal Medicine, Hôpitaux Iris Sud, site Molière, Brussels, Belgique Alejandro Hernandez MD Spine Unit, Hospital Universitari de Traumatologia i Rehabilitaci Vall d Hebron, Barcelona, Spain Scott Hook MD Istvan Hovorka MD J. Hradil MD Department of Neurosurgery, Regional Hospital, Liberec, Czech Republic Jean Huppert MD Philippe Lauweryns MD, PhD Professor Department of Orthopaedic Surgery, Catholic University Leuven, Leuven, Belgium; Head of Adult Spine Surgery, Department of Orthopaedic Surgery, University Hospital Catholic University Leuven, Leuven, Belgium Cyndi Lee Senior Scientist DePuy Biologics, Raynham, Massachusetts Joon Yung Lee MD Assistant Professor of Orthopedic Surgery Spinal Surgery Division University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania

Jean-Charles Le Huec MD, PhD Professor Spine Unit, Bordeaux University, Bordeaux, France; Chief, Orthopaedic Department, CHU Pellegrin, Bordeaux, France Ulf Liljenqvist MD John Louis-Ugbo MD Resident, Department of Orthopedics, Emory University School of Medicine, Atlanta, Georgia Alessio Lovi MD Spine Care Group, Galeazzi Orthopeadic Institute, Milano, Italy Arno Martin MD Donal McNally BSc, PhD Senior Lecturer in Biomechanics School of Mechanical, Materials, Manufacturing Engineering and Management, University of Nottingham, Nottingham, United Kingdom Dieter Moosmann MD Z. Patrick Moulin MD Chief Department of Orthopaedic and Spinal Surgery, Swiss Paraplegic Centre, Nottwil, Switzerland E. Munting MD, PhD Clinique Saint Pierrs, Ottignies Louvain-al-Neuve, Belgium Michael A. Pahl MD Resident, Department of Orthopaedic Surgery, Thomas Jefferson University

Hospital, Philadelphia, Pennsylvania Ferran Pellisé MD Spine Unit, Hospital Universitari de Traumatologia i Rehabilitaci Vall d Hebron, Barcelona, Spain B. Poffyn MD Department of Orthopaedic Surgery and Traumatology, Spine Section, Ghent University Hospital Sally Roberts PhD Reader Institute for Science and Technology in Medicine, Keele University, Keele, Staffordshire, United Kingdom; Director of Spinal Research, Centre for Spinal Studies, Robert Jones and Agnes Hunt Orthopaedic Hospital, Oswestry, Shropshire, United Kingdom Christoph P. Röder MD Senior Researcher Institute for Evaluative Research in Orthopaedic Surgery, University of Bern, Switzerland M. Ronai MD Département Orthopédie Pr Chauveaux, Pr Le Huec, Spine Unit, CHU Pellegrin Tripode, Bordeaux cedex, France J. Sénégas MD Bordeaux, France John E. Sherman MD Patrick Simons MD Department of Neurosurgery, MediaPark Klinik, Cologne, Germany

Francis W. Smith MD, FRCR, FRCSE Clinical Professor of Radiology Department of Radiology, University of Aberdeen, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, Scotland, United Kingdom; Consultant Radiologist, Department of Radiology, Woodend General Hospital NHS Grampian, Aberdeen, Scotland, United Kingdom P. Sourkova MD Department of Neurosurgery, Regional Hospital, Liberec, Czech Republic Jean-Paul Steib MD Professor University Louis Pasteur, Facult de medecine, Strasbourg, France; Orthopaedic Surgeon, Orthopaedic Department of Spine Surgery, Hopitaux Universitaures de Strasbourg, Strasbourg, France Christoph Stoos MD Petr Suchomel MD, PhD Head of Neurocenter and Department of Neurosurgery Regional Hospital, Liberec, Czech Republic; Assistant Professor, Department of Neurosurgery, 1st Medical Faculty, Charles' University, Prague, Czech Republic G. Sys MD Department of Orthopaedic Surgery and Traumatology, Spine Section, Ghent University Hospital Marek Szpalski MD Chairman and Associate Professor Department of Orthopedics, IRIS South Teaching Hospitals, Free University of Brussels, Brussels, Belgium

Marco Teli Spine Care Group, Galeazzi Orthopeadic Institute, Milano, Italy Jake Timothy MD Department of Neurosurgery, Leeds General Infirmary, Leeds, United Kingdom C. Tournier MD Atlantic Spine Center, CHU Pellegrin, 6 étage Orthopedie, Bordeaux, France Jill PG Urban PhD Senior ARC Research Fellow Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, United Kingdom D. Uyttendaele MD, PhD Department of Orthopaedic Surgery and Traumatology, Spine Section, Ghent University Hospital Cornelia Neidlinger-Wilke PhD Institute of Orthopaedic Research and Biomechanics, University of Ulm, Ulm, Germany Alexander R. Vaccaro MD Professor Spine Surgery, Department of Orthopaedic Surgery, Thomas Jefferson University and the Rothman Institute, Philadelphia, Pennsylvania Jan Van Lommel Département Orthopédie Pr Chauveaux, Pr Le Huec, Spine Unit, CHU Pellegrin Tripode, Bordeaux cedex, France Jean-Marc Vital MD

Unité de Pathologie Rachidienne, Centre Hospitalier Pellegrin-Tripode, Bordeaux, France Archibald von Strempel MD, Deng Professor Department of Orthopedic Surgery, Medizinische Hochschule Hannover, Hannover, Germany; Chief, Department of Orthopedic Surgery, Landeskrankenhaus Feldkirch, Feldkirch, Austria S. Tim Yoon MD, PhD Emory University, Department of Orthopaedic Surgery, Atlanta, Georgia Jing Yu PhD Research Scientist Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, United Kingdom Hansen Yuan MD James Zucherman MD Co-Director Stanford/San Francisco Combined Spine Surgery Fellowship, St. Mary's Spine Center, San Francisco Combined Residency Program; Medical Director, St. Mary's Spine Center, St. Mary's Medical Center, San Francisco, California

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Front of Book > Preface

Preface Surgery for spinal degenerative conditions has changed drastically in the last decade. Whereas, fusion was the standard surgical treatment for degenerative disorders, even without much evidence, new techniques to treat the condition while preserving motion have been introduced in recent years. Again, the efficacy of those methods was more often assessed based on biomechanical studies or even theoretical reasoning. With time, some devices where evaluated in methodologically acceptable trials, and some limited evidence is now available. Nevertheless, those technologies are gaining momentum, and preservation of motion in spinal pathologies appears to be here to stay. Therefore, it was time to edit a book which covers that subject in a thorough matter. The first section deals with basics. Biomechanical and physiological bases of spinal degeneration are covered as well as the radiological data on fused spines. The natural evolution of degenerative spinal disorders is also explained. The diagnosis and nonsurgical treatment sections treat the use of dynamic MRI as well as gene therapy, disc regeneration, and other non-invasive (or very minimally invasive) techniques. The sections on surgical nonfusion techniques are numerous. They deal with the different techniques and devices of nuclear replacement, total disc arthroplasty (lumbar and cervical), and other stabilization techniques. The important principles of indications and contraindications as well as surgical approaches are also covered. Finally, the last section deals with economic and ethical issues related to the use of new technologies, such as the ethics of novelty, use of registries, and regulatory

and cost issues. This book will be useful to many spine specialists who will find discussions and answers to many questions related to nonfusion technologies in spine surgery. Orthopedic surgeons, neurosurgeons, rheumatologists, rehabilitation specialists, neurologists, bioengineers, and specialists in regulatory affairs or social security issues will find this book useful in their practice. Marek Szpalski Robert Gunzburg Jean-Charles Le Huec Marco Brayda-Bruno

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Basics > 1 - Adjacent Level Disc Biomechanics

1 Adjacent Level Disc Biomechanics Brian J. C. Freeman Donal S. McNally Adjacent segment degeneration either above or below a previously fused lumbar motion segment has a reported incidence of between 25% to 45% (3,12,16,17). Not all such patients are symptomatic. Lehmann et al. (12) reported a 45% incidence of segmental instability above a previous fusion after a median follow-up of 33 years. Penta et al. (16) performed magnetic resonance imaging on 52 patients 10 years following anterior lumbar interbody fusion. All patients had had preoperative lumbar discography demonstrating a normal disc in the adjacent level. The incidence of a normal adjacent intervertebral disc 10 years following a solid fusion to the sacrum was 68%. This was not influenced by the length of the fusion. The findings suggest that degeneration after an anterior lumbar interbody fusion is determined more by individual characteristics than by the fusion itself. Aota et al. (3) suggested that age is the most significant predictor for developing adjacent segment degeneration above an instrumented fusion. Patients older than 55 years had an incidence of 37%, whereas the incidence for patients younger than 55 years was only 12%. Older patients appeared to be more susceptible with less ability to correct sagittal and coronal balance, leading to acceleration of the process. Rahm and Hall (17) studied 49 patients who had undergone an instrumented lumbar fusion. Thirty-five percent of patients showed degenerative changes above the fused segment after radiographic evaluation. For patients undergoing anterior cervical discectomy and instrumented fusion, approximately 25% will suffer from further degenerative disease at levels

adjacent to the fusion within 10 years of the initial surgery (10). Increased mechanical demands are known to affect the disc adversely and may interfere with the normal nutritional supply of the disc. However, there is dispute over whether the elimination of motion through fusion leads to higher forces on the remaining discs or whether the degenerative changes are merely a part of the inevitable natural history process (11). In two clinical studies, the levels adjacent to the adjacent segment were nearly as likely to have long-term degenerative change as the level immediately adjacent to the fusion (9,19). Battié et al. (5) showed that genetic inheritance accounts for approximately 70% of intervertebral disc degeneration with environmental factors such as heavy work and cigarette smoking having only a modest effect. Biomechanical testing of cadaveric specimens remains the gold standard for testing spinal implants. It is important to ensure that the spinal device is tested under conditions that simulate the loading conditions that are likely to occur in life. Compressive forces and bending moments can be applied using one or two rollers (13). Recommendations for the standardization of in vitro stability testing of spinal implants have been made by Wilke et al. (24). In particular, the magnitude of the applied loads and moments are P.2 important. Wilke et al. suggested a bending moment of 7.5 Nm for the lumbar spine to simulate everyday loading (24). Corresponding axial compressive loads for the lumbar spine might be of the order 1 to 2 kN for moderate activities. The key to understanding the effects of a fixation device on disc biomechanics is the measurement of the internal distribution of load within the disc. This information can be used to give further information about the relative load sharing of the disc and the fixation device. If measured correctly, it can give much information about the behavior of the disc tissues themselves. Load going through the disc may be measured as an intervertebral disc pressure in the center of the nucleus pulposus (15) or across the whole diameter of the disc using stress profilometry (14). In this technique, a needle-mounted solid-state transducer is withdrawn at a steady state across the disc while a static compressive load of 2 kN is applied to the motion segment for a period of 20 seconds. A standard apparatus for measuring stress distributions inside cadaveric intervertebral discs is shown in Fig. 1.1. Typical “stress profiles― for lumbar

intervertebral discs of varying degrees of degeneration have been described (2). One limitation of in vitro biomechanical studies is the fact that they take no account of functional muscle mass, bone density, or load transfers to other adjacent segments of the spine, particularly in the case of a spinal fusion model. In addition simply removing the disc and inserting an interbody cage device into the cadaveric specimen prior to testing will not make any allowance for the biologic changes in stiffness that would normally occur over time as the motion segment fuses. Despite these limitations, much can be gained from this type of research (13).

FIGURE 1.1 Standard apparatus for measuring stress profiles in cadaveric intervertebral discs. (Adapted from Adams MA. Mechanical function of the lumbosacral spine. Chapter 8, page 124. In: Adams MA (Ed). The Biomechanics of Back Pain. 1st edition, 2002, Elsevier Science Limited, with permission).

P.3

Adjacent Level Disc Biomechanics above a Simulated Fusion Model Weinhoffer et al. (23) carried out an in vitro study to determine the intradiscal pressure changes during flexion in levels above a simulated fusion. The authors used six fresh frozen cadaver spines and investigated two levels (L3-4 and L4-5) in each specimen. Pressure measurements were taken with the spine uninstrumented, with bilateral pedicle screw-rod instrumentation between L5 and S1, and with bilateral pedicle screw-rod instrumentation between L4 and S1. Pressure measurements were made using a Millar-mikro tip pressure transducer placed respectively within the nucleus pulposus of L3-4 and L4-5. Pressure data were recorded by computer data acquisition. The pressure data were compared by intervertebral level and by the effects of added instrumentation. The intradiscal pressure increased as the number of levels involved in the simulated fusion increased. The intradiscal pressure increased as flexion motion increased. A greater increase was seen at the L4-5 level compared with the L3-4 level. When the L5-S1 fixation was added, the intradiscal pressure increased. When the L4 to S1 fixation was added, the intradiscal pressure increased still further. Cunningham et al. (6) measured intradiscal pressure at three levels in 11 cadaveric lumbar spines under four conditions of spinal stability (intact, destabilized, laminar hook instrumentation, pedicle screw reconstruction). In response to destabilization and instrumentation, proximal disc pressures increased by as much as 45%, whereas in the bridged disc the pressure decreased by 41% to 55%, depending on the instrumentation used. The authors conclude that the changes in segmental intradiscal pressure levels occur in response to spinal destabilization and instrumentation. Intradiscal cyclic pressure differentials drive the metabolic production and exchange of disc substances. Conditions of high or low disc pressure secondary to spinal instrumentation may serve as the impetus for altered metabolic exchange and predispose operative and adjacent levels to disc pathology. Rohlmann et al. (18) studied the effect of an internal fixator and bone graft simulation on intersegmental spinal motion and intradiscal pressure in the adjacent regions. The authors used seven fresh frozen lumbar cadaver spines (mean age 28 years, range

16–69). Intradiscal pressures were measured in the nucleus pulposus of four levels of each specimen. Intersegmental motion was measured using a three-dimensional motion analysis system. Four situations were studied: Intact spine Intact spine with internal fixation device Post-corpectomy spines with a “wooden graft― and internal fixation Post-corpectomy spines and internal fixation but without graft The study showed a reduction in the intradiscal pressure and a reduction in the intersegmental motion for the bridged region in an intact spine. However, in the region adjacent to the fixator, the changes in intradiscal pressure and intersegmental motion due to mounting an internal fixator were “small.― The most critical point of this study was the load case used. It has been a matter of debate for some years whether spine specimens should be tested under “load― or “deformation― control. If one assumes that patients with a fused spine accept the limited motion, thereby exercising “load control,― the higher intradiscal pressures and intersegmental motion described by other authors P.4 would not be realized. In the case of Rohlmann's (18) study, load control was utilized, and therefore the higher intradiscal pressures and intersegmental motion did not occur in the adjacent levels. The authors suggest that adjacent level disc degeneration is not in their opinion caused by mechanical factors (18). Clearly, further studies are needed to clarify whether testing spine specimens under load or deformation control delivers more realistic results. Shono et al. (21) looked at the stability of posterior spinal instrumentation and its effects on adjacent motion segments in the lumbosacral spine. The authors used 18 calf lumbosacral spine specimens with three anterior instability patterns (one-level, two-level, three-level disc dissection). For each specimen, three situations were examined: The intact spine

The destabilized spine The instrumented spine (one compression hook system and three pedicle screw systems were compared) The stiffness of the various constructs was compared and segmental motion analyses were performed. The authors demonstrated as spinal instrumentation progresses from one level to three levels, the overall torsional and flexural rigidity of the construct increases. Application of segmental instrumentation changed the motion pattern of the residual intact motion segments. The change in motion pattern became more distinct as the fixation range extended and as the rigidity of the construct increased. This increased rigidity across the instrumented segment and the abnormal motion pattern within the adjacent level may accelerate degeneration of the adjacent motion segments. Eck et al. (8) investigated the effects of anterior cervical spinal fusion on the intradiscal pressure and segmental motion at adjacent levels. The authors subjected six cadaveric cervical spine specimens to biomechanical testing. Specimens were stabilized at T1 and loaded at C3. “Displacement-controlled― loading to 20 degrees of flexion and 15 degrees of extension was performed at a rate of 1 degree per second using an Instron materials testing machine. The intradiscal pressure was measured during load within the C4-5 and the C6-7 disc. Segmental motion from C4 to C7 was recorded using a motion analysis system. Measurements were made on the intact specimens and after anterior cervical plating at C5-C6. During flexion the intradiscal pressures at both adjacent levels were significantly increased after application of the plate at C5-C6. At C4-5 the intradiscal pressure increased by 73.2% and at C6-7 the intradiscal pressure increased by 45.3%. During extension, the intradiscal pressures were increased at both adjacent levels but these were not statistically significant. Segmental motion increased at both adjacent levels during flexion. C4-5 motion increased by 32.5% and C6-7 motion increased by 22.3% after anterior cervical plating at C5-6. The motion at C4-5 increased from 3.39 to 4.32 degrees after application of the C5-C6 plate. At C6-7 the motion increased from 4.35 to 4.91 degrees after application of the C5-C6 plate. These changes failed to reach statistical significance. The authors concluded that anterior cervical fusion causes a significant increase in intradiscal pressures in the adjacent levels during normal

flexion motion. The increased pressures appear directly related to increased segmental motion at the adjacent levels and it is possible that these increased pressures and hypermobility may accelerate the normal degenerative changes in levels adjacent to anterior cervical fusion. P.5

Adjacent Level Disc Biomechanics above Total Disc Replacement Adams et al. (1) used 10 cadaveric lumbar spines to compare the adjacent level disc biomechanics above a total disc replacement and above a fusion model. Each specimen was mounted on servo-hydraulic materials testing machine that allowed the application of both compressive and bending loads. After preconditioning, test loads of 100 N were applied for 10 seconds in three postures (flexion, neutral, and extension). Intervertebral disc stress profiles were measured in the superior intact disc in three situations (Figs. 1.2,1.3,1.4):

FIGURE 1.2 A: Lateral radiograph of cadaveric specimen (intact inferior disc). B: Typical stress profile obtained from disc adjacent to intact inferior disc. Heavy line, vertical stress; lighter line, horizontal stress. Highest stress peaks noted in the posterior annulus (to the left of stress profile).

P.6 Intact inferior disc Following total disc replacement (Maverick, Medtronic Sofamor Danek) Following anteroposterior spinal fusion using pedicle screws and a carbon fiber cage The mean intradiscal pressures for the adjacent disc were 0.43 MPa in the nucleus, 0.39 MPa in the posterior annulus, and 0.25 MPa in the anterior annulus for the intact spine. Following total disc replacement there was a universal reduction in stress P.7 in all regions of the adjacent disc, the intradiscal pressures reduced by between 5% and 21%. Following fusion there was a reduction in the nuclear and posterior annular regions but an increase in the anterior annular region. The pressure peaks and range of change in the fusion model was double that of the total disc replacement in the posterior and anterior annulus. The authors concluded that stress profiles in the adjacent level to a total disc replacement more closely resembled those observed in the adjacent level to an intact disc when compared with a fusion model.

FIGURE 1.3 A: Lateral radiograph of cadaveric specimen (with total disc replacement of inferior disc). B: Typical stress profile obtained from disc adjacent to total disc replacement. Heavy line, vertical stress; lighter line, horizontal stress. There was a universal reduction in stress in all regions of the adjacent disc.

FIGURE 1.4 A: Lateral radiograph of cadaveric specimen (inferior disc removed and anteroposterior fusion in situ). B: Typical stress profile obtained from disc

adjacent to anteroposterior fusion. Heavy line, vertical stress; lighter line, horizontal stress. Note increase in stress peaks in anterior annulus (to the right of stress profile).

Dooris et al. (7) used a previously validated finite element model of the osteoligamentous L3-4 motion segment to predict changes in posterior element loads as a function of P.8 disc implantation and associated surgical procedures. The finite element model was implanted with a ball and cup type artificial disc replacement via an anterior approach. The model was subjected to either 800 N of axial compression force alone or to a combination of 10 Nm flexion-extension moment and 400 N of axial preload. Implanted model predictions were then compared with those of the intact model. Facet loads were more sensitive to the anteroposterior location of the artificial disc than to the amount of the annulus removed. Under 800 N of axial compression, implanted models with an anteriorly placed artificial disc exhibited facet loads 2.5 times greater than loads observed with the intact model. In contrast, posteriorly implanted models predicted no facet loads in compression. Implanted models with a posteriorly placed disc replacement exhibited greater flexibility than the intact specimen and implanted models with anteriorly placed disc replacements. Restoration of the anterior longitudinal ligament reduced pedicle stresses, facet loads, and extension rotation to nearly intact levels. The finite element models suggest that by altering placement of the artificial disc in the anteroposterior direction a surgeon can modulate motion-segment flexural stiffness and posterior load-sharing. The more posteriorly implanted modes predicted reduced facet loads and less motion-segment flexural stiffness.

Adjacent Level Disc Biomechanics above a Dynamic Stabilization Model For patients with chronic low back pain presenting with some form of lumbar instability the Dynesys spinal system maybe used to provide spinal alignment and dynamic restabilization while preserving the disc and facet joint (20). The system consists of pedicle screws, polyethylene-terephthalate (PET) cords, and polycarbonate

urethane (PCU) spaces. The spacers are placed bilaterally between the pedicle screw heads to withstand compressive loads. Cords are run through the hollow core of the space and stabilize the construct by tensile preload. Schmoelz et al. (20) compared intersegmental motions of an intact spine with those of the dynamic stabilization system and the internal fixator. The authors also investigated the effects of both stabilization methods on the adjacent segment. Six fresh frozen cadaveric lumbar spines were used. These were embedded in polymethyl-methacrylate cement and placed in a materials testing machine. Each specimen was loaded with pure moments of + or - 10 Nm continuously with a constant rate of 1.0 degree per second. During load, the motion in each segment was recorded simultaneously by a three-dimensional ultrasound based motion analysis system. Four situations were studied: Intact spine Destabilized spine at L3-4 Stabilized spine at L3-4 with the Dynesys Stabilized spine at L3-4 with internal fixation With regard to the bridged segment, the instability model showed an increased range of motion and neutral zone compared with the intact specimen. Dynesys and the internal P.9 fixator both reduced the range of motion and neutral zone below the magnitude of the intact spine. However, in all three motion planes the stabilization with Dynesys showed greater intersegmental motion in the bridged segment compared with the internal fixator. With regard to the adjacent segment, in general the range of motion and neutral zone were not affected by the instrumentation. In this study it would appear that the adjacent segment does not seem to be influenced by the stiffness of the fixation procedure under the described loading conditions. The results suggest that the Dynesys system is capable of stabilizing an unstable segment sufficiently but allowing more motion in the segment than the internal fixator. The adjacent segment does not seem to be influenced by the stiffness of a fixation procedure under the described

loading conditions. Aylott et al. (4) investigated the effects of Dynesys on the human cadaveric lumbar spine. The biomechanical response of both the instrumented and adjacent intervertebral disc to compressive load in flexion and extension was evaluated. Twelve L3-5 cadaveric lumbar segments were compressed to 1 kN in 6 degrees of flexion, neutral, and 4 degrees of extension. The stress distribution in the midsagittal and posterolateral diameters of both the bridged and adjacent discs were measured by withdrawing a miniature pressure transducer across the disc (Fig. 1.5). In the absence of instrumentation, stress peaks in the anterior annulus increased with a greater degree of specimen flexion. In 0 and 6 degrees of flexion, Dynesys eliminated the anterior stress peaks observed in the instrumented disc in 80% of specimens. Little effect was seen with the application of Dynesys to a nondegenerated disc. Stress distribution through the adjacent disc remained relatively normal with instrumentation of the inferior motion segment. Dynesys has the potential to relieve stress peaks in the P.10 anterior annulus of the bridged segment particularly in positions of flexion. The intervertebral disc of the adjacent segment is not biomechanically prejudiced following the application of Dynesys.

FIGURE 1.5 Cadaveric specimen mounted in materials testing machine. Note Dynesys instrumentation across inferior motion segment (left) and pressure transducer in superior adjacent disc (right).

Adjacent Level Disc Biomechanics above the X-Stop Implant The X-stop spinal implant has been designed to treat symptomatic lumbar stenosis, especially in patients with neurogenic claudication who obtain near complete relief in sitting or flexing. The intent is to position the stenotic segment in slight flexion and by preventing extension to relieve symptoms of lumbar spinal stenosis. One possible concern is how the implant affects disc pressures both at the level of insertion and the adjacent level. Swanson et al. (22) performed an in vitro biomechanical analysis of eight cadaveric lumbar spines. The specimens were mounted and loaded onto a computer-controlled hydraulic materials testing machine capable of applying independent axial loads and

bending moments. Intradiscal stress profiles were measured while subjecting the specimen to an axial load of 700 N for 30 seconds (under load control). The specimens were tested in neutral, flexion, and extension. Flexion and extension were achieved by applying a 7.5-Nm bending moment in the respective direction with 700 N of superimposed compressive load. Measurements were made in the intact specimen and following insertion of the implant between the L3 and L4 spinous processes. In extension and in the neutral position, the mean pressures in the posterior annulus and nucleus were significantly reduced by the implant. There were no significant differences between the mean pressures of the intact and implanted specimens at the adjacent level of L2-3. The results suggest that the interspinous implant will not cause pressure-induced accelerated disc degeneration at levels adjacent to the implant.

Conclusion The phenomenon of adjacent level disc degeneration above or below a spinal fusion is very common. There is controversy whether fusion leads to higher forces in adjacent discs potentially accelerating degenerative changes or whether these degenerative changes are simply part of the inevitable process of natural history in genetically susceptible individuals. Spinal fusion appears to alter the biomechanics of the adjacent segment to a significant degree. Cunningham et al. (6) showed that the adjacent-level disc pressures increase substantially during flexion and extension, whereas the pressures at the instrumented levels decrease. On the other hand, Rohlmann et al. (18) showed that an internal fixator increased the pressures above and below the fused segments only “slightly.― A likely reason for the differences in these biomechanical studies lies in the testing mode. Some studies were performed under load control (18), whereas others used displacement control (6). There is no conclusive evidence that one testing mode is preferential over another but convincing arguments can be made for both modes. Rohlmann et al. (18) would argue that, during most daily activities, patients tend to accept the limited motion and that load control is probably therefore the adequate loading condition. Most authors agree that hypermobility above a stiffened segment occurs. This often leads to facet joint hypertrophy, which in turn may produce symptoms of spinal stenosis. P.11

Total disc replacement and dynamic stabilization appear to alter the adjacent level disc biomechanics to a lesser degree with authors showing “more normal stress profiles― in the adjacent segment. It remains to be seen, however, if this “more normal biomechanical environment― contributes to a lower rate of adjacent level disc degeneration with motion-preserving technology.

REFERENCES 1. Adams CI, McKinlay KJ, Freeman BJC et al. Does total disc replacement reduce stress in the adjacent level disc when compared to fusion? A biomechanical study on the human cadaver lumbar spine. Eur Spine J 2005; 14 (1): S12. 2. Adams MA. Mechanical function the lumbosacral spine. In: Adams MA (Ed). The Biomechanics of Back Pain. 1st edition. 2002 Elsevier Science Limited, Chapter 8. Mechanical function of the lumbosacral spine, 107–130. 3. Aota Y, Kumano K, Hirabayashi S. Post-fusion instability at the adjacent segments after rigid pedicle screw fixation for degenerative lumbar spinal disorders. J Spinal Disord 1995; 8 (6): 464–473. 4. Aylott CEW, McKinlay KG, Freeman BJC et al. Dynesys (Dynamic Neutralisation System for the spine): Acute biomechanical effects on the human cadaveric lumbar spine. J Bone Joint Surg 2005; 87-B Orthopaedic Proceedings Supplement III: 234. 5. Battié MC, Videman T, Gibbons LE, et al. 1995 Volvo award in clinical sciences. Determinants of lumbar disc degeneration: A study relating lifetime exposures and magnetic resonance imaging findings in identical twins. Spine 1995; 20 (24): 2601–2612. 6. Cunningham BW, Yoshihisa K, McNulty PS et al. The effect of spinal destabilisation and instrumentation on lumbar intradiscal pressure: An in-vitro biomechanical analysis. Spine 1997; 22 (22): 2655–2663.

7. Dooris AP, Goel VK, Grosland NM et al. Load-sharing between anterior and posterior elements in a lumbar motion segment implanted with an artificial disc. Spine 2001; 26 (6): E122–E129. 8. Eck JC, Humphreys C, Lim TH et al. Biomechanical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine 2002; 27 (22): 2431–2434. 9. Hambly MF, Wiltse LL, Raghavan N, et al. The transition zone above a lumbar sacral fusion. Spine 1998; 23: 1785–1792. 10. Hilibrand AS, Carlson JD, Palumbo MA et al. Radiculopathy and myelopathy at segments adjacent to the site of previous anterior cervical arthrodesis. J Bone Joint Surg Am 1999; 81: 519–528. 11. Hunter LY, Braunstein EM, Bailey RW. Radiographic changes following anterior cervical fusion. Spine 1980; 5: 399–401. 12. Lehmann TR, Spratt KF, Tozzi JE et al. Long-term follow-up of lower lumbar fusion patients. Spine 1987; 12 (2): 97–104. 13. McNally DS. The objectives for mechanical evaluation of spinal instrumentation have changed. Eur Spine J 2002; 11: S179–S185. 14. McNally DS, Adams MA. Internal intervertebral disc mechanics as revealed by stress profilometry. Spine 1992; 17: 66–73. 15. Nachemson AL. Disc pressure measurements. Spine 1981; 6: 93–97. 16. Penta M, Sandhu A, Fraser RD. Magnetic resonance imaging assessment of disc degeneration 10 years after anterior lumbar interbody fusion. Spine 1995; 20 (6):

743–747. 17. Rahm MD, Hall BB. Adjacent-segment degeneration after lumbar fusion with instrumentation: A retrospective study. J Spinal Disord 1996; 9 (5): 392–400. 18. Rohlmann A, Neller S, Bergmann G et al. The effect of an internal fixator and a bone graft on intersegmental spinal motion and intradiscal pressure in the adjacent regions. Eur Spine J 2001; 10: 301–308. 19. Schlegel JD, Smith JA, Schleusener RL. Lumbar motion segment pathology adjacent to thoracolumbar, lumbar and lumbosacral fusions. Spine 1996; 21: 970–981. P.12 20. Schmoelz W, Huber JF, Nydegger T et al. Dynamic stabilisation of the lumbar spine and its effects on adjacent segments: An in-vitro experiment. J Spinal Disord Tech 2003; 16 (4): 418–423. 21. Shono Y, Kaneda K, Abumi K et al. Stability of posterior spinal instrumentation and its effects on adjacent motion segments in the lumbosacral spine. Spine 1998; 23 (14): 1550–1558. 22. Swanson KE, Lindsey DP, Hsu KY et al. The effects of an interspinous implant on intervertebral disc pressures. Spine 2003; 28 (1): 26–32. 23. Weinhoffer SL, Guyer RD, Herbert M et al. Intradiscal pressure measurements above an instrumented fusion: A cadaveric study. Spine 1995; 20 (5): 526–531. 24. Wilke HJ, Wenger K, Klaes L. Testing criteria for spinal implants: Recommendation for the standardisation of in-vitro stability testing of spinal implants. Eur Spine J 1998; 7: 148–154.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Basics > 2 - Radiologic Assessment of All Unfused Lumbar Segments After Instrumented Posterior Spinal Fusion

2 Radiologic Assessment of All Unfused Lumbar Segments After Instrumented Posterior Spinal Fusion Ferran Pellisé Alejandro Hernández Accelerated segment degeneration (ASD) adjacent to a lumbar fusion (LF) has been reported in several papers (1,1,3). However, most of the evidence is derived from series that have not accounted for the natural history of degenerative changes developing at the unfused levels (4). Several experimental studies have suggested an important role for biomechanical changes as the origin or cause of ASD (4,5,6,7). Fusion, especially posterior instrumented, produces increased stress at the adjacent segment, which might be the cause of this syndrome; the stress would be affected by the length, location, and stiffness of the fusion mass (4,5,6,8,9,10). However, one should be cautious when considering the value of much in vitro data because the in vivo situation might be much more complex than is reproduced in vitro (11). Some investigators believe that degenerative changes appearing in the nonoperated segments after fusion may be predetermined by factors other than the presence of fusion (12,13). ASD could be nothing more than the normal degenerative process, largely determined by individual characteristics, rather than a consequence of biomechanical stress (14).

The great majority of studies analyzing ASD focus mainly on the motion segments immediately above and below the fusion. Little or no attention has been paid to the effects of lumbosacral fusion on nonadjacent mobile segments. Hence, the reported rate of ASD may include patients with true breakdown syndrome and isolated adjacent disc degeneration and patients with widespread degeneration.

Clinical Study (15, 16 and 17) To analyze the long-term effects of posterolateral instrumented LF on all the unfused lumbar segments, we evaluated 212 unfused lumbar segments in 62 patients, in whom LF had been performed using pedicular instrumentation (15,16,17). Thirty-one segments were located below the fusion, 62 at the first level above, 59 at the second level above, 45 at the third level above, and 15 at the fourth level above the fusion area. The mean number of fused segments per patient was 1.53 (range 1 to 4). P.14

Two independent observers, using the validated distortion-compensated method(18) measured lordosis, disc height (DAX), and dorso-ventral displacement (D) of all the unfused segments on digitized standing lateral radiographs taken immediately before surgery and after a mean follow-up of 7.51 years (range 4 to

FIGURE 2.1 Digitized radiograph with DCRA landmarks and measurements given by AutoCad 2000 software (Autodesk, Inc., San Rafael, CA).

Two independent observers, using the validated distortion-compensated method(18) measured lordosis, disc height (DAX), and dorso-ventral displacement (D) of all the unfused segments on digitized standing lateral radiographs taken immediately before surgery and after a mean follow-up of 7.51 years (range 4 to 11.5 years) (Fig. 2.1). The collected data were analyzed along with spinopelvic balance and sagittal angular parameters at follow-up.

Results DAX and D of the 31 segments below the fusion did not show significant differences between preop and follow-up. At the first, second, and third segments above the LF the same significant (p <0.05) loss of DAX was observed between preop and follow-up (Fig. 2.2). At the second cephalad segment, retrolisthesis increased significantly (p <0.01) between preop and follow-up (Fig. 2.3) and was weakly related to length of follow-up (p = 0.08) and loss of lordosis at the instrumented area (p = 0.09). Loss of DAX at the levels above the fusion did not depend (p >0.05) on lordosis of the LF, spinopelvic parameters at follow-up, number of fused segments, fusion level, or distance from fusion. The parameters predicting DAX at follow-up of a particular segment were the age of the patient (p <0.00), the length of follow-up (p <0.02), and loss of DAX at the other unfused segments (p <0.01). P.15

FIGURE 2.2 Same loss of disc height (DAX) was observed at all the levels located above the fusion area.

Discussion Our data suggest that after an instrumented LF, radiographic changes suggesting disc degeneration (loss of DAX) appear homogeneously at several levels cephalad to the fusion area and seem to be determined more by individual characteristics than by fusion itself. Isolated breakdown of the immediately adjacent segment would be more easily interpreted as the result of mechanical overload than a homogeneous loss of disc height, which is better explained by individual, nonmechanical, fusionunrelated parameters. Relatively few studies have determined to what degree mechanical changes contribute to adjacent segment degeneration after LF, and some would not endorse

the overload theory (4,11). Ghiselli et al. (19) evaluated 215 patients 6.7 years after posterior LF. The authors assessed cephalad and caudad levels, both those immediately adjacent to the fusion and those adjacent to the adjacent segment. The amount of disc degeneration was classified according to a numerical scale. Contrary to the hypothesis P.16 that fusion length would increase ASD, the authors found that patients with a multilevel fusion were significantly less likely to have ASD than those with a singlelevel fusion. Axelsson et al. (20) analyzed the motion pattern of the juxtafused L4L5 level in six patients with lumbosacral fusion by roentgen stereophotogrammetric study and showed that transformation of preoperative mobility in the lumbosacral segment to the adjacent segment was not a general phenomenon. Rohlmann et al. (11) mounted seven cadaveric lumbar spine specimens in a spine tester and loaded with pure moments of flexion-extension, lateral bending, and axial rotation. Mounting fixators to the intact spine strongly decreased intradiscal pressure in the bridged discs and reduced intersegmental motion. In most cases the effect was small in the regions above and below the fixators. Interspecimen differences in the regions adjacent to the instrumentation were much greater than changes due to the fixators (11).

FIGURE 2.3 A significant increase in retrolisthesis (D) was observed at the second level above the fusion area.

Traditionally, disc degeneration has been attributed to an accumulation of environmental effects, primarily mechanical injuries and insults, imposed on normal aging changes. Results of exposure-discordant monozygotic and classic twin studies suggest P.17 that mechanical factors play a very limited role and that heredity has a dominant role in disc degeneration, explaining 74% of the variance in adult populations studied to date (10). Radiographic findings may suggest that the fused patients have a greater prevalence of degenerative changes than the nonfused population (21). Unfortunately, the prevalence of degenerative changes in patients who have had fusion prescribed, but not performed, is not known. Some studies have

attempted to evaluate ASD in populations with a similar genetic predisposition to disc degeneration. In a long-term study with more than 10 years of follow-up after disc excision with and without fusion, Frymoyer et al. (22) reported no differences between the two groups with regard to adjacent segment degeneration. Wiltse et al. (13) compared 52 patients with instrumented fusion to 31 with a nearly identical operation without fixation and found that the addition of pedicle screws did not increase the incidence or severity of transitional syndrome in the first 7 years after surgery. Most studies pay particular attention only to the motion segments immediately above and below the fusion, ignoring what might have happened in the other unfused segments. Because disc degeneration can be explained to a large extent by genetic and constitutional factors (14), comparisons between adjacent and nonadjacent unfused segments in the same patient would be a better way to analyze whether juxtafusion overload accelerates degeneration. At least two studies (3,23) have shown that the segment next to the adjacent segment is almost as likely to break down as the adjacent segment. Penta et al. (8) prospectively evaluated 81 patients 10 years after anterior lumbar interbody fusion with magnetic resonance imaging (MRI). At final follow-up, a degenerated disc was present at the adjacent level in 12 of the 38 (31.6%) solid fusions to the sacrum. Among the patients with a degenerated adjacent disc, 50% of the remaining nonoperated levels also showed degeneration as compared with only 8.6% of the remaining levels in the 26 solid fusions in which a normal adjacent disc was noted. Recent data from the same group (24) and ours (15,16,17) parallel these findings. Genetically determined “natural progression of disc degeneration― is modified to some degree by environmental factors (14). The fact that disc height narrowing appears homogeneously in almost all the unfused lumbar segments suggests that disc degen-eration is more closely related to individual parameters than to the fusion itself. However, the finding that radiographic changes do not appear in all the unfused lumbar segments may suggest that mechanical factors have a subtle secondary role in segmental degeneration after instrumented posterior LF. The previously reported low risk of subsequent degeneration in the segment below the fusion area (19) and the (weak) relationship found between dorsoventral displacement and loss of lordosis at the instrumented area might be explained by mechanical factors (14,21,25). Hypolordosis may increase the posterior shear force

at the proximal segments (25). All our patients were instrumented with VSP plates, which may block the facet joints at the adjacent level; therefore, as we found, the posterior shear force originating retrolisthesis would be more relevant at the second level cephalad to fusion (25).

Conclusion When analyzing long-term radiographic changes in all unfused lumbar segments after posterior lumbar instrumented fusion, disc degeneration appears homogeneously at several levels cephalad to fusion and seem to be determined more by individual characteristics than by fusion itself. P.18

REFERENCES 1. Lee CK. Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine 1988; 13:375–377. 2. Whitecloud III TS, Davis JM, Olive PM. Operative treatment of the degenerated segment adjacent to a lumbar fusion. Spine 1994; 19: 531–536. 3. Schlegel JD, Smith JA, Schleusener RL. Lumbar motion segment pathology adjacent to thoracolumbar, lumbar, and lumbosacral fusions. Spine 1996; 21: 970–981. 4. Park P, Garton HJ, Gala VC, et al. Adjacent segment disease after lumbar or lumbosacral fusion: Review of literature. Spine 2004; 29: 1938–1944. 5. Ha KY, Schendel MJ, Lewis JL, et al. Effect of immobilization and configuration on lumbar adjacent-segment biomechanics. J Spinal Disord 1993; 6: 99–105. 6. Cunningham BW, Kotani Y, McNulty PS, et al. The effect of spinal destabilization and instrumentation on lumbar intradiscal pressure. An in vitro

biomechanical analysis. Spine 1997; 22: 2655–2663. 7. Shono Y, Kaneda K, Abumi K, et al. Stability of posterior spinal instrumentation and its effects on adjacent motion segments in the lumbosacral spine. Spine 1998; 23: 1550–1558. 8. Lee CK, Langrana NA. Lumbosacral spinal fusion. A biomechanical study. Spine 1984; 9:574–581. 9. Yang SW, Langrana NA, Lee CK. Biomechanics of lumbosacral spinal fusion in combined compression-torsion loads. Spine 1986; 11: 937–941. 10. Stokes IA, Iatridis JC. Mechanical conditions that accelerate intervertebral disc degeneration: Overload versus immobilization. Spine 2004; 29:2724–2732. 11. Rohlmann A, Neller S, Bergmann G, et al. Effect of an internal fixator and bone graft on intersegmental spinal motion and intradiscal pressure in the adjacent regions. Eur Spine J 2001; 10: 301–308. 12. Penta M, Sandhu A, Fraser RD. Magnetic resonance imaging assessment of disc degeneration 10 years after anterior lumbar interbody fusion. Spine 1995; 20: 743–747. 13. Wiltse LL, Radecki SE, Biel HM, et al. Comparative study of the incidence and severity of degenerative change in the transition zones after instrumented versus noninstrumented fusions of the lumbar spine. J Spinal Disord 1999; 12: 27–33. 14. Battié MC, Videman T, Parent E. Lumbar disc degeneration. Epidemiology and genetics influences. Spine 2004; 29: 2679–2690.

15. Pellisé F, Hernández A, MartÃnez C, Bagó J, Villanueva C. Radiologic assessment of all the unfused lumbar segments after an instrumented posterolateral lumbar fusion. Eur Spine J 2002;11(S1): 24. 16. Pellisé F, Hernández A, Vidal X, MartÃnez C, Bagó J, Villanueva C. Radiologic assessment of all the unfused lumbar segments 7.5 years after an instrumented posterolateral lumbar fusion. Presented at the 30th annual meeting, International Society for the Study of the Lumbar Spine, Vancouver, BC, Canada. 17. Pellisé F, Hernández A, Vidal X, MartÃnez C, Minguell J, Villanueva C. Radiologic assessment of all the unfused lumbar segments 7.5 years after an instrumented posterolateral lumbar fusion. Spine (in press). 18. Leivseth G, Brinckmann P, Frobin W, et al. Assessment of sagittal plane segmental motion in the lumbar spine. A comparison between distorsioncompensated and stereophotogrammetric roentgen analysis. Spine 1998; 23: 2648–2655. 19. Ghiselli G, Wang JC, Bhatia NN, et al. Adjacent segment degeneration in the lumbar spine. J Bone Joint Surg Am 2004; 86: 1497–1503. 20. Axelsson P, Johnsson R, Stromqvist B. The spondylolytic vertebra and its adjacent segment. Mobility measured before and after posterolateral fusion. Spine 1997; 22: 414–417. 21. Lehmann TR, Spratt KF, Tozzi JE, et al. Long-term follow-up of lower lumbar fusion patients. Spine 1987; 12: 97–104. 22. Frymoyer JW, Haley E, Howe J, et al. Disc excision and spine fusion in the management of lumbar disc disease: A minimum ten-year follow up. Spine 1978; 3: 1–6.

23. Hambly MF, Wiltse LL, Raghavan N, et al. The transition zone above a lumbosacral fusion. Spine 1998; 23: 1785–1792. 24. Wai E, Santos E, Fraser R, et al. Presented at the 2004 annual meeting of the International Society for the Study of the Lumbar Spine, Porto. 25. Umehara S, Zindrick MR, Patwardhan AG, et al. The biomechanical effect of postoperative hypolordosis in instrumented lumbar fusion on instrumented and adjacent spinal segments. Spine 2000; 25: 1617–1624.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Basics > 3 - Physiology of the Intervertebral Disc

3 Physiology of the Intervertebral Disc Jing Yu Thijs Grünhagen Cornelia Neidlinger-Wilke Sally Roberts Jill Urban The intervertebral disc has only a small number of cells embedded throughout a dense extracellular matrix (ECM), which the cells synthesize and maintain. As the mechanical functioning of the disc is governed by the composition and organization of this matrix, the continuing health and activity of these cells is vital for sustaining disc health and its biomechanical role. Here we review recent information on disc cell function and viability, particularly in relation to the response of the cells to extracellular signals such as mechanical stress and nutrient supply. New cell-based therapies proposed for treating disc degeneration are also discussed briefly.

Disc Composition The ability of intervertebral discs to fulfill their main mechanical tasks (viz. to support compressive loads and act as joints of the spinal column, allowing flexion, torsion, and extension) depends primarily on the organization and composition of the major macromolecules that make up this tissue, these being collagen and the large aggregating proteoglycan, aggrecan (51). The fibrillar collagens form an elaborate network that provides the structural framework of the disc, and aggrecan

has a high swelling pressure, imbibes water, and inflates the collagenous network; together these components form a load-bearing structure, allowing the disc to carry compressive load and to deform reversibly (36). Other macromolecules, although present in only low concentrations, also appear to have essential roles in regulating matrix organization. For instance, elastin, although present in only minor amounts, appears to have an important mechanical function in restoring disc organization after load-induced deformation. The role of other minor components is also important in tissue function and organization; small proteoglycans such as fibromodulin and decorin control the diameter of the fibrillar collagens (19), whereas the minor collagen, collagen IX, appears to play a vital part in linking network structures together (15). It is thus not surprising that polymorphisms in these molecules are associated with disc degeneration (1,15). This information shows that the biomechanical role of the disc is governed by a complex macromolecular network, comprised not only of the major fibrillar collagens and of aggrecan but also of a large number of other proteins and glycoproteins. P.20

Disc Composition Varies With Region The proportion, composition, and organization of these molecules varies considerably from one region of the disc to the other. The outer region of the disc, the annulus fibrosus, is highly organized (Fig. 3.1). It has a high concentration of fibrillar collagens, organized into concentric lamellae encircling the disc. These lamellae consist of bundles of collagen fibers running obliquely from one vertebral body to the next, firmly anchoring the disc to the bone. The angle of the collagen bundles alternates between successive lamella, thus forming a cross-woven and reinforced structure. Elastic fibers (Fig. 3.1) are concentrated between the annulus lamellae and may play a mechanical role in maintaining annulus organization. The annulus encloses the softer, more hydrated nucleus pulposus, which by contrast has only a loose random collagen network but has a high concentration of aggrecan compared to the annulus or to most other cartilages (51). The disc is separated from the vertebral body by a thin (1 mm) layer of hyaline cartilage, the cartilaginous endplate, which is less hydrated than the adjacent disc regions.

Changes With Age and Pathology There are large visible changes in appearance of the disc with age and degeneration. With increasing age, the nucleus becomes less hydrated and more collagenous; it discolors, changing from white and translucent in youth to becoming yellow-brown P.21 and opaque, and the boundary between nucleus and annulus becomes blurred (53). The annular rings thicken and appear to lose organization (Fig. 3.1). Eventually cracks and fissure appear in the endplate, nucleus, and annulus and the disc thins and distorts. These age- or degeneration-linked changes parallel (or follow) changes in disc composition. One of the most evident age- and/or degeneration-related changes is loss of aggrecan (Fig. 3.2). Because aggrecan, on account of its high swelling pressure, is responsible for maintaining disc hydration, loss of hydration follows from loss of aggrecan. Changes in the minor macromolecules have been less well studied, but recent work has shown that small proteoglycan concentrations in the nucleus also fall with increase in degeneration (13).

FIGURE 3.1 The organized lamellar structure of normal discs is lost in degenerated discs. The figure shows sections from normal adult annulus (A, B) and degenerate (grade 2–3) adult annulus from the same region (C, D). The sections are shown under polarized light to visualize collagen organization (A,

C) and under fluorescent light to visualize elastin (B, D).

FIGURE 3.2 Loss of proteoglycan with degeneration grade. Changes in proteoglycan content, measured in relation to concentration of negatively charged groups/dry weight, variation with spinal level, and disc degeneration grade (adapted from reference 51).

Matrix Degrading Enzymes As well as the macromolecular components discussed previously, the disc also contains several different classes of proteases, that is enzymes that can degrade matrix proteins (30,34,41,42,53). Inhibitors, which block activity of these enzymes, are also present in the disc. In their active form, that is, when the inhibitors are nonfunctional, these proteases can break down and disaggregate most of the macromolecular components of the disc. With age and pathology the level of active proteases present in the disc increases, supporting their suggested role in disc matrix turnover and degradation (11,41).

Disc Cells

The matrix is maintained and turned over by a small population of resident cells whose main function is to synthesize and maintain an appropriate macromolecular composition. The disc cells produce matrix macromolecules throughout life. They also produce P.22 proteases and their inhibitors. The disc remains healthy while the rate of macromolecular synthesis and breakdown is in balance; however, if the rate of breakdown increases over synthesis, ultimately the disc matrix begins to disintegrate. Disc degeneration thus results from failure of the disc's cells to produce, maintain, and repair the matrix.

Cell Types in the Disc Relatively little is known of the cells of the disc. Cell density is low, being around 0.25% to 0.5% of tissue volume and varies inversely with disc thickness in a manner that suggests it is under nutritional control (47). The cells of each region of the disc appear phenotypically distinct, possibly reflecting different embryologic origins (Fig. 3.3). The nucleus is derived from the notochord. Notochordal cells remain in the center of the disc for only a short time span in humans, but in other mammals (e.g., rodents) they are retained into old age (8). The nucleus pulposus of the adult disc is populated by what appear to be round/oval cells, resembling chondrocytes of cartilage (Fig. 3.3), often lying within a microfibrillar capsule. With aging or degeneration, nucleus cells can proliferate to form clusters (28). The annulus derives from the mesenchyme. Its highly organized ECM is dependent on the initial orientation of the cells directed by their stress fiber and cytoskeletal organization (18). The cells of the annulus are often P.23 elongated, especially in the outer region, and orientated along the lamellae (7); they can be described as fibroblastlike. The annulus and nucleus cells have extended cell processes, forming a network of cell-cell and cell-matrix contacts whose role is unknown but is thought to be related to mechanotransduction (7,14,27,37).

FIGURE 3.3 Cells of the intervertebral disc. Figure showing differences in cell phenotype and matrix produced (adapted from references 14 and 22). Rounded cells from the nucleus produce a high concentration of GAGs (immunostained brown with antibody to keratan sulphate, 5D4) and a loose collagen network. Extended fibroblastlike cells from the outer annulus produce low concentrations of GAG and highly organized collagen lamellae.

Matrix Production Depends on Cell Type Each of the disc cell types synthesizes a large number of different matrix components, as well as proteases and their inhibitors. However, the rate at which the different matrix components are produced varies significantly between cell types (22). The nucleus cells produce sulfated aggrecan molecules at a high rate compared to cells from the annulus. By contrast the annulus cells synthesize molecules that are more akin to those produced by fibroblasts such as type I collagen and versican, which are not normally produced by nucleus cells; annulus cells, however, also synthesize aggrecan and collagen II. It thus appears that the differences in composition across the disc arise from the regional differences in cell populations.

Factors Influencing Cell Activity Nutrient Supply Like all cells, those of the disc require nutrients to remain alive and function. The disc produces its energy mainly through glycolysis and thus the cells use glucose and produce lactic acid at high rates; they also use oxygen, although the pathways are unclear (20). Supply of nutrients and removal of wastes is precarious because the healthy adult disc is the largest avascular tissue in the body. Cells in the center of an adult lumbar disc may be as much as 6 to 8 mm from the nearest blood supply. Cells of the outer annulus are supplied with nutrients mainly by the blood vessels in the soft tissues at the annulus periphery (20,49). Nucleus and inner annulus cells, however, are supplied by capillaries that terminate in loops at the disc-bone interface; nutrients diffuse from these capillaries through the cartilaginous endplate and dense disc matrix to the cells (12). This pathway is thought to be at risk as calcification of the cartilaginous endplate occurs with age and pathology; changes in blood vessel architecture or supply all have adverse effects on transport of nutrients to nucleus cells (50).

Measurement of Nutrient Supply Recent advances in technology have enabled measurements of nutrient supply to discs directly. Magnetic resonance imaging (MRI) has been used to follow the diffusion of injected paramagnetic contrast medium into the disc in recent human studies; the diffusion pattern over 24 hours following contrast medium injection was studied in a large number of normal and degenerate discs. Transport was measured at regions of interest in the vertebral body, the subchondral bone, and the endplate zone as well as in the disc. It was found that, in degenerate discs (grades 2–4), nutrient transport was inhibited and that the status of the endplate zone was the principal factor influencing diffusion to the center of the disc (38); in severely degenerate discs, however, transport increased, possibly because of vascular ingrowth. P.24 Loss of nutrient supply with degeneration has also been shown using electrodes.

Oxygen electrodes have been used to monitor changes in oxygenation of dog discs following an increase in blood oxygen (21) and on human patients with scoliosis and back pain (4). Both these studies confirmed that oxygen levels in the center of the disc are very low. More recently, electrode studies were carried out monitoring both oxygen and nitrous oxide. The latter is administered as an anesthetic gas during surgery. It is small, freely soluble, and not metabolized and, unlike MRI contrast media, it is not excluded from any area of the disc. A study on scoliotic discs has shown that transport is severely reduced particularly at the apex of the curve, possibly because calcification of the endplate hindered nutrient transport into the disc (52).

Consequences of Loss of Nutrient Supply Loss of nutrient supply leads to a fall in concentrations of oxygen and glucose in the disc center and also to acidification of the matrix due to lactic acid accumulation (46). These conditions lead to a fall in production of matrix components (26), with no loss of protease activity (40), and even to cell death (6,23). Such in vitro studies are in agreement with findings that associate loss of nutrient supply with disc degeneration (50).

Mechanical Forces Exposure to heavy mechanical stress over long periods was thought to lead to disc degeneration, so effects of mechanical forces on the disc have been studied for many decades. Animal studies indeed show that overload can lead to cell death and adverse matrix changes (31). However, over the last decade, twin studies indicate that mechanical forces have only a minor effect on disc degeneration compared to genetics (5). Nevertheless, mechanical forces are now known to have a considerable influence on cellular activity. During daily activities the intervertebral disc tissue is exposed to complex and multiple physical loads including tensile strain, compression, hydrostatic pressure, and fluid flow. Disc cells have been shown to respond to such mechanical signals; matrix and protease production in vitro are influenced by changes in hydrostatic pressure, compression, or cyclic stretch (10,25,29,33,39). However, there is at present only little knowledge on how responses of

intervertebral disc cells to such mechanical signals are influenced by the different magnitudes, durations, and frequencies of the applied loads and by other extracellular factors such as pH or osmolarity. Also, little is known of how cellular origins (nucleus or annulus cells) influence responses to mechanical signals. Recent work has set out to investigate these interactions. For instance, cell loading devices that allow the application of cyclic strain or hydrostatic pressure on disc cells cultured in three-dimensional collagen type I scaffolds have been used to investigate the interactions among mechanical stresses, environmental factors, and cell origin and their influence on expression of matrix proteins or proteinases by human disc cells. The results demonstrate the complex nature of the responses of the cells to mechanical stresses. The effects of mechanical signals were influenced by the location of the cells in the disc (nucleus or annulus), by the magnitude of the applied load (for hydrostatic pressure), and by the osmolarity of the cell culture medium. Mechanical signals could both stimulate or inhibit gene expression, depending on signal magnitude, cell origin, and the cell's environment. In addition, high individual variations in disc cell responses to P.25 mechanical forces were seen, with some donors appearing to be more responsive than others for distinct target genes. Preliminary findings also indicate that mechanical loading, as well as affecting matrix turnover, can also stimulate cells to produce cell signaling molecules and angiogenic factors. Thus, in vitro studies at least show that mechanical signals have a substantial effect on production and turnover of the ECM. However, there is a long way to go before these results on isolated cells and explants can be translated into understanding effects of exercise or mechanical lifting on the disc in vivo.

Cellular Repair Therapies Over the last few years interest has increased in the possibility of treating degenerate discs using cell-based therapies. One proposed approach is the use of growth factors or gene therapy to stimulate the resident cells in degenerate discs to repair and regenerate the degraded matrix (9,32). Most interest, however, following the apparent success of autologous chondrocyte implantation (ACI) for repairing small cartilage defects (44), has been focused on introducing new cells

into the disc to replace those lost in the degenerative process.

Potential Problems Even though cell-based therapies are now in clinical use (16), many problems remain before these therapies can be used with confidence (2). Some of these are discussed in detail in the chapter by Alini et al. in this volume. One major problem is disc nutrition; as is now increasingly evident, many degenerate discs have lost a major fraction of their nutrient supply and the nutritional environment in the center of the disc inhibits cell matrix production and even survival (6,23). Is there any point in implanting new cells into this hostile environment or even stimulating the resident cells, possibly disturbing a fine balance between survival and death? Some means of identifying degenerate discs with an inadequate nutrient supply seems essential or patients will be offered useless and expensive therapies. Another problem is the source of cells. In the disc, there is no equivalent of the lesser loaded but healthy region of cartilage used as a cell source in ACI. As outlined later, the matrix produced varies with cell phenotype; thus, nucleus cells should be used to repair nucleus tissue and annulus cells to produce annulus. The only available source of autologous disc cells are from disc fragments removed at surgery; these are of mixed phenotype and cannot be readily separated as no specific markers yet exist. Moreover they are not healthy (43); they show signs of senescence. Then there is the speed and quality of the repair. Even in previously healthy animal discs, restoration of disc matrix and disc height takes several years (17,35,48). Because of nutritional constraints, the disc can only support a low cell density so it is likely that disc repair will take even longer in humans. The clinical consequences of such a slow repair have not been discussed. Moreover, the quality and durability of any repair tissue are not known to date. Can repair tissue restore the complex composition and organization of the disc matrix (Fig. 3.4), and what are the functional consequences if repair is incomplete? In studies on cartilage, repair tissue often fails after 18–24 months (24). Will such failures also occur in the disc?

P.26

FIGURE 3.4 Nutrient pathways to the disc nucleus. (Adapted from references 3, 12, and 45.) A: A schematic view of blood vessels supplying the disc (12). B: Details of the capillaries that penetrate the subchondral bone and terminate at the cartilaginous-bone interface (12). C: Drawn from a histologic section, showing the bone, disc, and cartilaginous endplate in a normal disc (45). The region of calcified cartilage is blacked in; it can be seen that it cuts off the pathway for nutrient transport from some blood vessels to the disc. D: The bony endplate with the disc and cartilaginous endplate digested away (3). Calcified cartilage blocking some of the spaces through which blood vessels penetrate can be seen.

It seems that many important aspects need further investigation before biologic disc repair becomes a useful therapy for treatment of back pain and other discdegeneration linked disorders.

Conclusions An intact and well organized ECM is vital for disc function. Appropriate cellular function is necessary to maintain this matrix throughout life. Very little is yet

known about disc cells and the factors that regulate them. However, it is clear that ultimately disc degeneration arises from a failure of cellular activity. If we are to understand why the disc degenerates so early with possibly distressing consequences, we need to know how to protect these vital cells and how to influence them to produce and repair the disc matrix.

Acknowledgments This work was supported by the Arthritis Research Campaign and the European Union (Eurodisc; QLK6-CT-2002-02582). P.27

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Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Basics > 4 - Natural Evolution and Resolution of Chronic Low Back Pain

4 Natural Evolution and Resolution of Chronic Low Back Pain Michel Benoist Philippe Boulu Pierre Guigui Low back pain (LBP) is a frequent problem in adults from western societies. Crosssectional surveys indicate a point prevalence of approximately 20% (1). The prognosis of acute LBP episodes is usually excellent, but a small proportion of sufferers experience persistent or relapsing episodes. According to insurance and industrial data, approximately 10% of sick-listed patients are still off work after 6 months (13). Epidemiology of chronic patients without compensation or work disability is less well known. This small proportion of chronic patients is responsible for most of the compensation and medical expenses linked to LBP. To modify this unfavorable evolution, prevention measures have been developed, including exercise programs, ergonomic education, weight loss, and cessation of smoking. However, despite appropriate prevention, the prognosis remains less favorable in a subset of patients who develop a chronic problem, with intermittent exacerbations well beyond the expected period of healing, often extending months or even years after the initial visit. When dealing with this category of patients, the treating physician must determine the cause of the pain and disability and subsequently define an appropriate

therapeutic program. The purpose of this chapter is to discuss the neurophysiologic mechanisms involved in the chronicity of LBP and accordingly have an overview of the therapeutic strategies capable of hastening resolution of pain and disability in this category of chronic, often sick-listed patients.

Neurophysiologic Mechanisms of Chronic Low Back Pain It is now admitted that pain transmission involves four main levels: the nociceptive input coming from peripheral tissues, the cord, the brain, and the descending inhibitory pathways (Fig. 4.1).

Peripheral Sensitization Peripheral sensitization is defined by reduction of the nociceptive response threshold. In the case of LBP, the first level of the pain system is located in the spinal unit. Discogenic origin is generally assumed to be the major cause of nonspecific LBP. However, sources of nociception are also found in other structures of the motion segment including facets, ligaments, and muscles. Yet, it is generally admitted that degenerative changes in the P.32 facets and ligaments follow degeneration of the intervertebral disc (4). In the case of pure LBP without radiculopathy, which is the topic of this chapter, the nerve fibers responsible for transmitting the pain message are located in the degenerated disc. Studies have shown the presence of nociceptive nerve fibers in the annulus and also in the inner nucleus of the intervertebral disc (5,19). The presence of innervation expressing substance P in the inner part of the annulus and in the nucleus has been demonstrated in the study by Freemont et al. (8) in degenerate discs painful at discography. Taken together these observations strongly suggest a role for these nerve terminals in the pathogenesis of LBP. An innervated disc can be a source of nociception. The nerve terminals can be sensitized in three different ways. Figure 4.2 presents a hypothetical and rough sketch of the biologic events leading to the sensitization of nerve terminals and the generation of LBP. First, neuropeptides, such as substance P and calcitonin P.33 gene-related peptide, expressed by nerve fibers directly excite the nociceptors and

induce a neurogenic inflammation by releasing inflammatory substances. Second, proinflammatory mediators, including prostaglandin E2 (PGE2) and cytokines [interleukin (IL)-6, IL-7, and IL-8] have been found at high levels in tissue cultures of patients undergoing lumbar interbody fusion for discogenic LBP (3). IL-1 and tumor necrosis factor (TNF) alpha have been detected in homogenates of contained subligamentous disc herniations inside the intervertebral space (22). These cytokines are potent stimulators of prostaglandins, which in turn sensitize the afferent pain fibers. In addition, neurotoxic properties have been demonstrated in the various cytokines present in the disc, particularly TNF alpha (21).

FIGURE 4.1 Pain is a complex phenomenon involving not only peripheral nociception but also the central nervous system.

FIGURE 4.2 Hypothetical sketch of peripheral sensitization of nerve terminal found in degenerate discs.

Third, disc degeneration can contribute to the production of nonspecific LBP through mechanical mechanisms. Tears and clefts of the disc and a diminution of disc height, which are the macroscopic hallmarks of disc degeneration, lead to mechanical instability of the motion segment. Even micromovements may cause pain when sensitized nerve terminals are stimulated.

Central Sensitization in the Spinal Cord Central sensitization is defined by an increase of the nociceptive spinal neurons' excitability. There is now evidence that sensitization of the central nervous system (CNS) can enable persistent pain states. Animal models of chronic pain have demonstrated that the spinal cord is a major contributor in the maintenance of chronic pain after peripheral nerve damage (6). Long-lasting stimulation of the neurons of the dorsal horn of the cord by neurotransmitters (substance P, glutamate) and neuromodulators induces plasticity and reorganization of the whole dorsal horn synapse. Studies have also shown that activated glial cells produce proinflammatory cytokines inducing in turn algesic mediators enhancing the nociceptive activity. Neuroimmune activation and neuroinflammation of the cord following nerve injury have been demonstrated in a rodent model (29). This permits development and amplification of painful perception independent of a primary

afferent drive. It could explain the mismatch between chronic LBP and the poor physical and imaging findings.

The Brain There is also increasing evidence that in addition to the spinal cord the higher cortical centers play a role in CNS central sensitization and the perception of pain. A functional imaging study using functional magnetic resonance imaging (MRI) has compared a group of chronic LBP patients without major psychosocial factors or any anatomic abnormalities on plain radiographs or spinal MRI that could explain the symptoms with a group of healthy controls (11). Experimental pain testing was performed at a neutral site by increased pressures on the thumbnail to assess the pressure pain threshold. The pressure required to produce intense pain was significantly higher in the controls, demonstrating hyperalgesia in the chronic LBP group. At pressure pain threshold, an increase in cerebral blood flow was observed in multiple pain-related regions of the brain compared with a single activation in controls. Interestingly, when stimuli generated equally painful responses in the two groups, the neuronal activated areas were similar. These findings indicate an augmentation of central nociceptive activity in a certain group of chronic LBP patients in whom all the known anatomic or psychosocial P.34 factors did not explain the symptoms. The same investigation was applied to a group of fibromyalgia patients who experienced hyperalgia and altered brain processing similar to the chronic LBP group. The cortical nociceptive hyperactivity may also excite the nociceptive spinal neurons by putative glutamatergic descending excitatory pathways originating from the activated brain areas.

The Descending Pain Inhibitory System The descending inhibitory pathways constitute the fourth level of the pain system. The neurons of this system are located in the brainstem and higher in the hypothalamus. Via the dorsolateral funiculus they inhibit the nociceptive neurons of the dorsal horn of the cord by releasing neuropeptides, mainly serotonin. Noradrenergic neurons are also involved. The system is supposed to modulate the nociceptive input coming from the spinal unit. Impairment of this system will enhance the excitability and activity of the nociceptive neurons of the dorsal horn.

Drugs that affect central modulation, such as the tricyclics, act on enhancing this inhibitory system. In summary, dysfunctions in mechanisms of chronic pain may result from the following: Increase and persistence of the nociceptive input from the spinal unit (peripheral sensitization) Plasticity and synaptic alterations of the dorsal horn neurons of the spinal cord Activation by cytokines of spinothalamic tracts Activation at the brain level of higher cortical centers Inhibition of the descending inhibitory pathways It can be speculated that, in patients with chronic LPB, these various mechanisms act simultaneously. This concept of a simultaneous interaction of the four sites of the pain system is in harmony with the biopsychosocial model developed by G. Waddel (24): Pain and disability are not only influenced by an organic pathology but also by psychological and social factors. This model implies dysfunction of the pain system mechanisms not only at the periphery but at the CNS central level. This conceptual model, in keeping with the neurophysiologic mechanisms discussed previously, has obvious therapeutic implications. To better select the group of patients who require surgery and alternatively the patients who need continuation of conservative therapy, it is essential to clarify the source of the pain: peripheral, central, or both?

Resolution of Chronic Low Back Pain: Therapeutic Strategies In the second part of this chapter the various treatment methods for chronic LBP are briefly overviewed. Well-conducted RCTs have provided evidence-based facts, which can now be applied to treatment strategies. Existing scientific evidence of efficacy or inefficacy has been obtained for various treatments, medical or

surgical. This is taken into account in this discussion. P.35

Conservative Treatment: Evidence-Based Facts Various treatment methods can be applied in chronic LBP. They include medications; injections (epidural or facets); corsets; and physical therapy consisting of manual therapy, traction manipulation, and back exercises. Regarding their level of efficacy, there is evidence that most of these common interventions have no effect in these chronic sick-listed patients. Levels of evidence concerning treatment methods have been recently summarized according to recommendations of the Cochrane collaboration back review group (18). Moreover, the effects of common medical interventions on pain, back function, and work resumption in patients with chronic LBP have been studied prospectively in six countries in a 2year period (13). No positive effects on appropriate outcome measures were noted for any of the interventions. Efficacy of back schools for nonspecific LBP has been recently assessed in a systematic review within the Cochrane collaboration back review group (15). Nineteen RCTs were identified. Results of the review indicate that there is moderate evidence suggesting that back schools have better effect on pain and functional status than other treatments for patients with recurrent and chronic LBP. Authors of this review also point out a need for future high-quality RCTs to determine which type of back school is the most effective and to evaluate their cost-effectiveness. However, high-quality RCTs demonstrating that intensive biopsychosocial rehabilitation with cognitive behavior therapy improves pain and function in chronic LBP are now available. A systematic review of RCTs of multidisciplinary treatment compared with a control condition has provided strong evidence of efficacy of intensive rehabilitation (12). This review also indicates that less intensive interventions did not show improvements in clinically relevant outcomes. Two high-quality RCTs (2,7) have demonstrated that such programs focusing on physical, psychological, social, and occupational factors are a reasonable alternative to spinal fusion, which is in keeping with the Waddel model and with the neurophysiologic mechanisms of chronic pain discussed previously.

Surgical Treatment: Evidence-Based Facts

The aim of the surgical treatment is to suppress the nociceptive input coming from the peripheral tissues (spinal unit). For example, the role of fusion, the gold standard of surgical therapy, is to immobilize the motion segment to eliminate the physical stimulation of the nerve terminals. Results of surgical treatment are controversial and at the present time no clear guidelines exist to evaluate who should be operated on and with which technique. However, in a multicenter, randomized, controlled trial comparing surgical fusion of the lower lumbar spine with nonsurgical treatment (usual care) in a group of severely disabled chronic LBP patients, Fritzell et al. (10) have shown that lumbar fusion was significantly superior to nonsurgical treatment. In the study conducted by Brox et al. (2) in a group of patients similar to those assessed by the Swedish group an equal improvement was disclosed in patients treated by fusion and those treated by cognitive intervention and exercises. Fairbank et al. (7) have also compared surgical stabilization with an intensive rehabilitation program. No clear evidence emerged from that study that primary spinal fusion was any more beneficial than intensive rehabilitation. P.36

Where Do We Stand? The chronic LBP patients studied and treated in the three multicenter trials comparing fusion with conservative therapy are identical. In Fritzell's (10) study, fusion compared with usual care and not with a more comprehensive rehabilitation program appeared to be clearly superior to conservative therapy. Contradictory results were obtained in the two subsequent trials comparing fusion with an intensive multidisciplinary rehabilitation program. This is in keeping with the conclusions of the systematic review by Guzman et al. (12) showing that an intensive biopsychosocial rehabilitation program was superior to less intensive interventions. However, even though evidence exists to support rehabilitation programs as an alternative to fusion, a subset of patients randomized to rehabilitation were not satisfied by the results and had additional surgery. For example, 28% of these patients treated by rehabilitation in the Fairbank study had a subsequent fusion within 2 years. Results of surgery in this subset of patients are not known. Moreover, imaging description of the lower lumbar spine of these patients is not

available. Similarly, in Brox's study selection of patients was based on plain radiographs showing degeneration at L4-L5 and/or L5-S1 levels. Neither MRI nor provocative discography were obtained. Conversely, in a multicenter trial comparing disc replacement with conservative therapy, all patients had a Modic I discopathy and a positive pain response at discography (16). Results of surgery were clearly superior to conservative care, which unfortunately was not an intensive rehabilitation program. Further high-quality RCTs comparing, for example, surgery in patients with Modic I changes and positive discography with intensive rehabilitation are needed to demonstrate that this particular subset of patients with a predominant peripheral nociceptive input requires surgical treatment. Unlike osteoarthritis of the hip or knee, discal degeneration does not mean pain. Development of sensitive, specific imaging signs or other methods to ascertain the discogenic source of the pain is necessary. Prevalence and clinical relevance of endplate abnormalities in patients with discogenic pain have been reported and discussed (23). Weishaupt et al. (25) found that all discs with Modic I changes caused concordant pain with provocative discography. An acceptable specificity and positive predictive value of Modic I changes for LBP was shown in another study (17). Further identification of the indications of spinal stabilization or disc replacement is clearly needed. It is also imperative to develop methods to evaluate central sensitization as a possible cause of chronicity. Although no biologic mechanisms have been found to relate the psychosocial factors to the development and maintenance of chronic LBP, the role of psychosocial issues has been demonstrated by numerous studies. Whether psychological or social, political or cultural, these factors can play a major role in the chronicity of the pain (24). Until now, evaluation of central sensitization is mainly based on appreciation of these factors by interviews, validated questionnaires, or detection of nonorganic signs. Evaluation of central cause of the pain is still in infancy. Numerous chronic LBP patients have no major psychological or social abnormalities and no imaging features of hyperstimulation of the peripheral nerve terminals. Central sensitization begins at the spinal cord level. Attempts have been made to develop biologic methods to evaluate the neuronal activity in the cord. Levels of substance P and nerve growth factor have been found significantly increased in the

cerebrospinal fluid (CSF) of chronic LBP patients when compared with those of normal controls (18). New imaging strategies are being developed. Current status of medical imaging of intervertebral disc degeneration has P.37 been recently reviewed by Haughton (14). Application of magnetic resonance spectroscopy (MRS) in the study of spinal cord in back pain patients has been proposed, as the improvement of MRS seems to overcome the technical obstacles, due for example to the motion of CSF. Functional MRI of the cord might also be used in evaluation of chronic back pain syndromes. As discussed earlier, an augmented cerebral pain processing after peripheral stimulation has been shown in a group of chronic pain patients. The same abnormalities were found in fibromyalgia patients. More studies are required to support the hypothesis of augmented central pain processing as a pathomechanism in a subgroup of chronic LBP patients potentially different from those with depressive symptomatology.

Conclusion Chronic LBP is a common cause of long-term disability and is remarkably resistant to treatment. To reduce the disastrous personal and public financial consequences, it is imperative to provide an adequate management capable of hastening resolution of pain and disability. Recently, high-quality RCTs have compared surgical treatment with conservative therapy. These studies have shown that some chronic LBP patients can be successfully treated by surgery. It was also demonstrated that others obtain satisfactory results with an appropriate conservative therapy. In a recent letter to the editors of European Spine Journal, Fritzell (9) stated that the frontier now is “when and how should we use fusion procedures and when and how should we use rehabilitation.― One can agree with that statement. However, more studies are still needed to differentiate more clearly the patients who require surgery from those who should be directed to intensive rehabilitation.

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19. Roberts S, Eisenstein SM, Menage Y et al. Mechanoreceptors in intervertebral discs. Morphology, distribution and neuropeptides. Spine 1995, 20, 2645–2651. 20. Rutkowski MD, Winkelstein B, Hickey et al. Lumbar root injury induces central nervous system neuro immune activation and neuro inflammation in the rat. Spine 2002, 27, 1604–1613. 21. Sorkin LS, Xiao WH, Wagner R et al. Tumor necrosis factor alpha induces ectopic activity in nociceptive primary afferent fibers. Neuroscience 1997, 81, 255–262. 22. Takahashi H, Suguro T, Okazima Y et al. Inflammatory cytokines, in the herniated disc of the lumbar spine. Spine 1996, 21, 218–224. 23. Videman T, Battie M, Gibbon LE et al. Associations between back pain history and lumbar MRI findings. Spine 2003, 28, 582–588. 24. Waddel G. A new clinical model for the treatment of low-back pain. Spine 1987, 12, 632–644. 25. Weishaupt D, Zanetti M, Hodler J. Painful lumbar disc derangement: relevance of endplate abnormalities at MR imaging. Radiology 2001, 218, 420–427.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Diagnosis > 5 - Dynamic MRI in the Seated Position Increases Insight into Diseases of the Lumbar Spine

5 Dynamic MRI in the Seated Position Increases Insight into Diseases of the Lumbar Spine Francis W. Smith For the past 25 years, the lumbar spine has been studied using magnetic resonance imaging (MRI) in the supine position. This position is often the most comfortable for the patient, when in fact their symptoms are often worse when either standing or sitting. With the availability of an upright MRI scanner in which images can be made in the erect position, a number of studies have been performed to examine the changes in the appearances of both healthy and symptomatic patients in different postures. The effect of gravity on the body and the resultant differences in the appearances of the lumbar spine, abdomen, and pelvic contents are very obvious, as seen in Figure 5.1.

FIGURE 5.1 Supine/sitting erect.

P.40

P.41

FIGURE 5.2 Upright MRI scanner.

P.41

MRI Scanner The MRI system used for these studies has been designed specifically to image patients in both the erect and supine positions. The system operates at 0.6 Tesla utilizing a resistive magnet with a horizontal field, transverse to the axis of the patient's body (FONAR, Melville, NY). This provides a nonclaustrophobic open view from the magnet, allowing for unimpeded patient movement studies. A unique MRI-compatible, motorized patient handling system has been developed for the scanner, which allows for vertical (load bearing) to horizontal (supine) positioning of patients. Our system takes advantage of a 5-degree tilt in vertical studies to stabilize the patient and was used in all studies. The custom-built patient-handling system allows for patients to be imaged standing, sitting, lying supine, prone, or on their side, at any angle between vertical and 20 degrees in the Trendelenburg position. Because of its “open― design, patients are able to move within the scanner enabling images to be made in flexion and extension, in addition to the normal neutral position. A seat attachment has been developed to allow imaging in the sitting position. Data are acquired using a flexible, solenoidal radiofrequency (RF) receiver coil (Fig. 5.2).

Studies The initial work with upright scanner concentrated on measuring the variations in the dimensions of the normal spinal canal, nerve root canals, and intervertebral discs. In one study, 29 male volunteers with no symptoms of low back pain, age 21 to 61 years (mean 32 years), were studied. The following observations were made, confirming the accepted knowledge as measured in cadaver studies: We have shown a significant posture-dependent difference of the crosssectional dural sac area at the intervertebral disc level in asymptomatic volunteers. When changing posture from a supine to a standing position, the cross-

sectional area of the dural sac increases (Fig. 5.3). The smallest cross-sectional dural sac area was found in the supine position. The dural sac contour took the appearance of a longitudinal ellipse in flexion and a transverse ellipse in extension and that cross-sectional dural sac area did not change significantly at the L3-4 and L4-5 disc level (Fig. 5.4) (1). There are posture-dependent changes in the size and shape of the nerve root exit foramina (Figs. 5.5 5.6 5.7). In a further study, 32 male volunteers (age 21–61 years, mean 32 years) were studied. The subjects were scanned in the vertical posture within 2 hours of arising and again in the evening. The disc heights were measured using the Dabbs method: First ever MRI disc height study to investigate the spine in a true standing posture. There is a diurnal reduction in height at all lumbar disc levels. The time of day that the MRI scan was obtained influenced the height of the lumbar disc. In the erect posture, diurnal height loss is more pronounced at the lower disc levels. There is a detectable diurnal and postural variation in disc height (2). P.42

FIGURE 5.3 Axial T2-weighted sections showing the increase in size of the dural sac in the erect section when compared with that made in the supine position.

FIGURE 5.4 Axial T2-weighted MRI images showing alteration in dural sac shape between the two postures.

FIGURE 5.5 Supine versus standing. In the standing position, disc height and the distance between neighboring pedicles decreases because of vertical load.

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FIGURE 5.6 Flexion versus extension. During extension, posterior disc height decreases due to compression of the posterior disc and the distance between neighboring pedicles decreases due to increased lordosis.

FIGURE 5.7 Offset sagittal T2-weighted MRI images showing the alterations in size and shape of the exit foramina in the five different postures.

A number of studies have been performed to examine the differences in the appearances of the abnormal spine, in an effort to ascertain the potential for being able to scan in more than one position. Three hundred twenty patients (163 males and 157 females) aged between 24 and 78 years (mean 57 years), suffering from low back pain and sciatica, have been scanned using the 0.6 T “upright― scanner. Each patient was imaged supine, standing erect, sitting, and also seated in flexion and extension. Sagittal T2 and axial T2 weighted images were made through the lower three intervertebral discs in all five different postures. Of 960 discs examined, 522 were considered to be normal. These “normal discs― showed no significant change in disc height between supine and sitting, that is, a reduction in height anteriorly on forward flexion of 1 to 2 mm and a similar reduction in height posteriorly on extension. Four hundred thirty-eight showed degenerative change in their nuclei, half of which behaved like normal discs and are considered to be normal and classified as

degenerative P.44 P.45 change. The other half were classified as “degenerate discs,― showing 2 to 5 mm change in disc height between supine and sitting and also a reduction of greater than 3 mm in disc height on flexion and extension with varying degrees of disc prolapse. Thus, by being able to image the spine in both supine and erect positions we are able to differentiate between the “normal― aging disc that has a reduced signal from its nucleus and degenerate discs that show the same degenerative appearance but reduce in height when in the weight-bearing position.

FIGURE 5.8 Fluctuating spondylolisthesis.

One hundred eight prolapsed discs showed reduction of posterior prolapse on forward

flexion and increase in extension. Interestingly, 23 patients showed the reverse. Thirty-one had grade I spondylolisthesis not recognized on supine images. Twenty-five of them showed varying degrees of movement on flexion and extension (Figs. 5.8 and 5.9). A further 25 patients referred for MRI of the lumbar spine following at least one prior normal MRI examination within 6 months of referral have been reviewed. Fourteen men and 12 women aged between 38 and 67 years were examined. Each patient was scanned supine, standing erect, and in the seated position as described previously. In 12 cases, no significant abnormality was seen in any of the five postures. In 13, abnormalities were demonstrated in one or more of the seated postures that were not evident in the conventional supine examination. In three cases, lateral disc herniation was only seen in the seated position. In six cases, the presence of a hypermobile disc at one or more level was demonstrated. In two cases, previously unsuspected grade 1 spondylolisthesis was shown, and in two cases significant spinal canal stenosis was seen in the seated extended position. Thus, in 50% of these cases that had previously been unsuccessfully investigated for sciatica, a surgically remediable lesion was found. Each of the 13 patients has undergone appropriate surgery and 6 months after surgery remain symptom free. The investigation of postoperative pain is one that supine MRI does not often show a cause. To ascertain whether or not imaging in flexion and extension would be of value in assessing patients who returned with back pain following either spinal fusion or ligament stabilization, a series of 12 patients referred for MRI of the lumbar spine for the investigation of postspinal operative pain have been reviewed. Seven men and 5 women aged between 40 and 72 years were scanned supine, standing erect, and in the seated position. In four cases, no significant abnormality was seen in any of the five postures. In eight, abnormalities were demonstrated in one or more of the seated postures that were not evident in the conventional supine examination. One patient following unilateral laminectomy and discectomy was found to have spinal instability secondary to damage to the interspinous ligament (Fig. 5.10). Three patients had undergone ligament stabilization and four had had posterolateral

instrumented fusion of the lower lumbar spine. All seven showed varying degrees of hypermobility at the transitional intervertebral disc above the stabilization/fusion level (Fig. 5.11). In one case, this was so severe as to cause almost complete occlusion of the spinal canal in the flexed and extended positions. These studies show that MRI in the upright position, together with the ability to image with the body flexed and extended, aids diagnosis in more than 50% of difficult to diagnose cases of spinal instability and demonstrates fluctuating degenerate discs that would otherwise go unrecognized. P.46

FIGURE 5.9 Hypermobile discs. Note the change in appearances of the L4-5 and L5-S1 intervertebral discs between the five different postures. This patient had had three “normal― MRI scans prior to this examination.

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FIGURE 5.10 Postoperative, L4-5 laminectomy, instability at the L4-5 level seen in association with a tear of the L4-5 interspinous ligament.

FIGURE 5.11 Four years after posterolateral instrumented fusion of L4 to the sacrum, there is disc degeneration and spondylolisthesis at the L3-4 level, which is not evident in the supine position but is clearly seen in the three seated positions.

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REFERENCES 1. Hirasawa Y, Bashir W, Pope MH, Smith FW. Postural variation in dural sac cross sectional area measured in normal individual's supine, standing and sitting, using pMRI. RSNA 2003. Radiology (P) 1316 pg 641.

2. Bashir W, Hirasawa Y, Pope MH, Smith FW. Measurement of diurnal variation in intervertebral disc height in normal individuals: A study comparing supine with erect MRI. RSNA 2003. Radiology (P) 1315 pg 64.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Non-Surgical Treatment > 6 - Molecular Therapy of the Intervertebral Disc

6 Molecular Therapy of the Intervertebral Disc S. Tim Yoon John Louis-Ugbo The normal intervertebral disc is a complex avascular fibrocartilaginous structure consisting of a combination chondrocytelike and fibroblastlike cells that support a rich extracellular matrix (3). The cells within the disc synthesize and maintain the matrix. The extracellular matrix provides the mechanical characteristics of the disc. Disc degeneration is characterized by loss of the disc matrix and change in the composition of the matrix of the nucleus to a more fibrotic and less cartilaginous matrix. Disc degeneration is associated with low back pain and other important disease conditions of the spine (1,2). Current treatment options range from pain management to invasive procedures such as spinal fusion and spinal arthroplasty; however, there is no clinically proven biologic therapy of the disc. Although there is much research ongoing on disc therapy, none of the current treatment methods actually treat the disc in a biologic manner. However, there are many different approaches under intense investigation that use biologically active molecules to treat or prevent disc degeneration. This chapter reviews the current status in molecular therapy of the intervertebral disc.

Biology of Intervertebral Disc Degeneration The disc matrix consists of an elaborate framework of macromolecules that attract and hold water. Collagens and proteoglycans are the primary structural components of

the intervertebral disc macromolecular framework. Collagens give the disc tissues their form and strength. The proteoglycans, through their interactions with water, give the tissues stiffness, resistance to compression, and viscoelasticity (4). Table 6.1 shows the profile of the types of collagen and noncollagenous proteins found in the disk. Collagenous proteins are most abundant in the outer annulus, where they comprise 70% of the dry weight, whereas they make up only 20% of the central nucleus pulposus (4). The proteoglycans are present in the greatest concentrations in the central nucleus pulposus, where they comprise 50% of the dry weight of the nucleus in a child (4). The proteoglycan molecule is made up of a core protein to which a variable number of glycosaminoglycan units are covalently attached (5). The most common glycosaminoglycan side chains in the disc are chondroitin sulfate and keratan sulfate, with the former predominating in the normal disc and the latter in the degenerated disc (4,5,6). To better understand the molecular therapy strategies being investigated for the treatment of the disc, it is important to understand the hallmarks of disc degeneration. P.50 Degenerative processes associated with aging result in morphologic and molecular changes to the disc. Morphologic changes to the aging disc include dehydration, fissuring, and tearing of the nucleus, annulus, and endplates. On the molecular level, degenerative changes may include decreased diffusion of nutrient and waste products, decreased cell viability, accumulation of apoptosis debris, degradative enzyme activity, accumulation of degraded matrix macromolecules, fatigue failure of the matrix, decreased proteoglycan synthesis, and alteration in collagen distribution (4,7).

TABLE 6.1 Intervertebral Disc Components

Collagen

Proteoglycans

Disc Matrix

Disc Proteinases

Proteins Fibrilforming

Aggrecan (most abundant)

Fibronectin

Metalloproteinases (MMPs)

Versican

Elastin

-Collagenases MMP

collagens

I 0–80%

1, 8, 13

II 0–80%

Decorin

-Gelatinases MMP 2, 9

III <5%

Biglycan

-Stromelysin MMP 3

V 1–2%

Fibromodulin

ADAMS

XI 1–2%

Lumican

Short helix collagens

Perlecan

VI 5–20%

IX 1–2%

XII <1%

Disc degeneration begins when catabolism and/or the failure to retain matrix proteins consistently exceeds synthesis and/or retention. Decrease in disc nutrition may be an

important contributor to disc degeneration. This decrease nutrition may be the result of increased disc size and endplate changes, which when combined with cell density lead to decreased nutrition in the center of the nucleus, low pH, and possibly cell death (4,8). The most prominent change observed includes the progressive loss of proteoglycan, water, and collagen II in the disc matrix of the nucleus pulposus. There are qualitative changes in the matrix that are less well defined including the breakdown of the higher molecular weight proteoglycans and other changes that are more difficult to quantify (e.g., collagen cross-linking, organization of the proteoglycan). One other significant change seems to be the loss of the differentiated chondrocyte phenotype from the nucleus pulposus into a more fibrotic phenotype. Changes in the annulus fibrosus include disorganization of the annular lamella layers and physical defects in the collagenous matrix. Typically, these matrix changes take many years to become apparent and are a result of an imbalance between synthesis and degradation (Fig. 6.1). Inflammatory mediators have also been identified in the degenerated disc specimens including nitric oxide (NO), interleukin-6 (IL-6), prostaglandin E2 (PGE2), tumor necrosis factor-alpha (TNF-alpha), fibronectin, and matrix metalloproteinases (MMPs) (Table 6.2) (7,9,57,58). However, the pathologic role played by each of these mediators in the disc is not well understood. Insight into the roles played by these mediators is currently being investigated. NO, IL-6, and PGE2 appear to be factors in the inhibition of proteoglycan synthesis, and they are recruited into action by interleukin-1 (IL-1). The proteoglycan matrix also is vulnerable to breakdown in response to IL-1, and this process is thought to be mediated by the MMPs. It seems likely that IL-1 plays a central role in the elaboration of inflammatory mediators, but the nature of that role is not well P.51 defined (12). Seguin et al. (57) recently demonstrated that TNF-alpha, a proinflammatory cytokine present in herniated nucleus pulposus tissues, at doses of 1 to 5 ng/mL, induced multiple cellular responses including decreased expression of both aggre-can and type II collagen genes; decreases in the accumulation and overall synthesis of P.52 aggrecan and collagen; increased expression of MMP-1, MMP-3, MMP-13, ADAM-TS4, and ADAM-TS5; and induction of ADAM-TS dependent proteoglycan degradation. Within

48 hours, these cellular responses resulted in nucleus pulposus tissue with only 25% of its original proteoglycan content. Based on this result they suggested that TNF-alpha may contribute to the degenerative changes that occur in disc disease.

FIGURE 6.1 Disc matrix metabolism: balance of synthesis and degradation. A: In the homeostatic state, the disc undergoes matrix synthesis and degradation in balanced manner. B: As the disc matrix undergoes turnover over the course of an individual's lifetime, any small imbalance between synthesis and degradation can lead to significant changes in overall disc matrix content. C: One of the major goals of molecular therapy of the disc involves modulating this metabolic balance to the more favorable anabolic state. This can be accomplished by increasing synthesis or by decreasing catabolism.

TABLE 6.2 Inflammatory Mediators Implicated in Disc Degeneration a. Nitric oxide (NO) b. Interleukin-6 (IL-6) c. d. e. f.

Prostaglandin E2 (PGE2) TNF-alpha Fibronectin Matrix metalloproteinases (MMPs)

The goal of molecular therapy is to prevent or reverse these changes in the disc extracellular matrix by altering the balance of degradation to synthesis in favor of synthesis.

Molecular Therapy Strategies for Disc Disease Therapeutic strategies currently under investigation for the biologic treatment of disc degeneration include the use of cellular components (mesenchymal stem cells, chondrocytes, culture expanded disc cells, disc allograft, etc.), matrix-derivatives [extracellular matrix (ECM)], or molecules that influence disc cell metabolism and phenotype (Table 6.3) (14,15,16,17,18,19,20,21,22,23). This chapter is restricted to the discussion of the molecular intervention in disc degeneration repair. There are at least four different classes of molecules that are currently being investigated for disc therapy. These include anticatabolics, mitogens, morphogens, and intracellular regulators. Although all of these molecules have some in vitro data, few have been tested in vivo with an animal model of disc degeneration (Table 6.4). Each of these categories is defined and the key literature reviewed in this chapter.

Anticatabolics Anticatabolics block the activity of degradative enzymes within the disc. Because

matrix loss is a balance between matrix synthesis and degradation, it is possible to increase the disc matrix by increasing synthesis or by decreasing degradation. One approach is to prevent matrix loss by inhibiting the degradative enzymes. There are many different catabolic enzymes present in normal disc matrix, but the MMPs make up a particularly important group of catabolic enzymes (9,13). MMPs play an important role in the normal turnover of matrix molecules and are thought to be important in disc degeneration. Their P.53 actions may account for much of the degradation of collagen, aggrecan, versican, and link protein found in the degenerated disc (13). The main members of the MMP family are stromelysin (MMP3), collagenase (MMP1, 8, and 13), and gelatinase (MMP2 and 9). Stromelysin is found mainly in the nucleus pulposus, and it is active in degrading the core protein of proteoglycans. It is the only agent capable of gaining access to the proteolytic cleavage sites, leaving isolated hyaluronate binding regions, degraded proteoglycan aggregates, and glycosaminoglycan fragments as breakdown products (9,10,11,13). Collagenase and gelatinase are more prevalent in the annulus, and they cooperate in the breakdown of collagen. Aggrecan and versican degradation may also result from members of a second family of metalloproteinases, ADAMs. Two members of this family (ADAM-TS4 and 5) show a particular avidity for aggrecan and have been termed aggrecanases (7).

TABLE 6.3 Molecular Therapy Strategies for Disc Disease

Type of Intervention Cell-based

Examples Whole disc transplantation Transplantation of cultured disc cells Chondrocyte transplantation Mesenchymal stem cells transplantation Disc cell/scaffold constructs

Extracellular matrix component-

ECM–extracellular matrix protein

based

Molecule-based

Anticatabolic Mitogens Morphogen Intracellular regulators

TABLE 6.4 Molecules Investigated for Disc Therapy Category

Molecule

Anticatabolic

TIMP-1, -2, -3 Anti-TNF-alpha Anti-MMPs (CPA-926)

Mitogens

IGF-1 PDGF EGF FGF

Morphogen

TGF-beta BMP-2 BMP-7 (OP-1) BMP-13 (GDF-6, aka CDMP-2) GDF-5 (CDMP-1) Link N

Intracellular regulators

SMADs Sox9 LMP-1

TIMP, tissue inhibitor of matrix metalloproteinase; TNF-alpha, tumor necrosis factor-alpha; MMPs, matrix metalloproteinases; IGF-1, insulin-like growth factor-1; PDGF, platelet-derived growth factor; EGF, epidermal growth factor; FGF, fibroblast growth factor; TGF-beta, transforming growth factorbeta; BMP, bone morphogenetic protein; CDMP, cartilage derived morphogenetic protein; GDF, growth and differentiation factor; SMADs; Sox9; LMP-1.

Within the matrix, MMP activity is normally inhibited by tissue inhibitors of MMPs (TIMPs) (24,25). Wallach et al. (25) successfully delivered an anticatabolic gene, TIMPI, into cells from degenerated intervertebral discs using an adenoviral vector. They showed an increased expression of TIMP-1 in disc cells and also an increase in the “measured synthesis rate― of proteoglycans. This finding supports catabolic inhibition as a promising avenue of research for the treatment of degenerative disc disease via gene therapy. Another molecule, CPA-926 an esculetin prodrug, that has a better pharmacokinetic profile than esculetin itself has been shown to be antiinflammatory and antitumorogenic and to prevent degeneration in an osteoarthritic model of cartilage destruction (26). Okuma et al. (26) showed that oral administration of CPA-926 can prevent or delay the onset of disc height loss and demonstrated histologic evidence of disc degeneration in an annulotomy model of disc degeneration in the rabbit.

P.54 Along with the balance of synthesis and degradation, the rate of disc matrix metabolism may also be important. For example, the overall rate of disc metabolism in young may be much higher than in old discs. This may lead to qualitative changes in disc matrix such as the composition of degraded aggrecan versus newly synthesized aggrecan molecules. The overall metabolic rate may also dictate the nutritional requirements of the intradiscal cells. Cytokines such as IL-1 and TNF-alpha may have critical roles in disc metabolism. Therefore, molecules such as IL-1Ra and infliximab, which can block IL-1 and TNF-alpha, respectively, may be useful (27,28,29). Further research into anticatabolic molecules may yield important results.

Mitogens Disc cells modulate their metabolic activities by a variety of substances including cytokines, enzymes, enzyme inhibitors, and growth factors in a paracrine and/or autocrine fashion. The degeneration of a disc has been postulated to result from an imbalance between the anabolic and catabolic processes or the loss of steady state metabolism that is maintained in the normal disc. Alterations in both anabolic and catabolic processes are thought to play key roles in the onset and progression of disc degeneration. Growth factors tend to act as anabolic regulators of disc cell metabolism (31). Mitogens are defined by their ability to increase the rate of mitosis. These molecules constitute the true “growth factors,― and for purposes of this review chapter, we differentiate mitogenic growth factors from the set of molecules that are highly chondrogenic (morphogens) (Fig. 6.2). Growth factors are typically cytokines. Cytokines are defined by their ability to bind to specific transmembrane receptors resulting in the activation of an intracellular signaling cascade and exerting biologic effects, such as stimulation of cell proliferation, differentiation, migration, and apoptosis. They also regulate matrix production and repair by various types of cells (e.g., chondrocytes, skin fibroblasts, endothelial cells).

FIGURE 6.2 Mitogenic molecules. Mitogenic molecules are the truly growth factors. They increase cell number without necessarily enhancing cell differentiation. The increase in cell number leads to increase in matrix synthesis. However, this may also increase the nutritional requirement in the disc due to higher overhead of keeping the cell alive and perhaps increase the overall catabolism as well as synthesis. Furthermore, very high cell density can lead to cell death with decreases in disc nutrition. Finally, mitogens may have a higher likelihood of causing tumors as opposed to morphogens, which increase cell differentiation.

These mitogenic molecules include insulin-like growth factor-1 (IGF-1), epidermal growth factor (EGF), and fibroblast growth factor (FGF) (30). Thompson et al. (30) demonstrated in vitro experiments with mature canine disc cells that mitogenic molecules can increase the rate of mitosis and proteoglycan synthesis rates to various degrees, depending on which region of the disc the cells were obtained from. In

general, EGF performed better than the other mitogens. Okuda et al. (32) demonstrated an age-related decline in proteoglycan synthesis to IGF-1 in rat discs. Based on this information, researchers have speculated that by restoring the IGF-1 in aging discs perhaps matrix synthesis may be increased. In vivo experiments with growth factors using a mouse tail disc P.55 compression model for degeneration by Walsh et al. (33) produced results that were consistent with in vitro experiments by Thompson et al. (30). IGF-1 had mild effects (especially in the inner annulus) and FGF had no effect. In a related but different potential mechanism of therapy, some growth factors may protect disc cells from death by apoptosis. Gruber et al. (34) demonstrated a significant reduction in the percentage of apoptotic disc cells after exposure to 50 to 500 ng/mL IGF-1 or exposure to 100 ng/mL platelet-derived growth factor (PDGF). These findings expand the understanding of the cell biology of the disc cell and show that selected cytokines can retard or prevent programmed cell death in vitro. Although IGF-1 has some anabolic effects, it may also have an effect on catabolism, as IGF-1 was shown to decrease the levels of active TIMP-2 in tissue culture experiments, indicating a complex effect on disc matrix metabolism by IGF-1.

Morphogens Chondrogenic morphogens are cytokines that may have mitogenic capability but are really characterized by their ability to increase the chondrocyte specific phenotype of the cell (Fig. 6.3). Chondrogenic specific properties include the production of collagen II, Sox9, aggrecan, and sulfated-glycosaminoglycans. Examples of chondrogenic morphogens include transforming growth factor-beta (TGF-beta), bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs). These growth factors tend to act as anabolic regulators of disc cell metabolism (30). Chondrogenic morphogens are particularly attractive because they may reverse the fibrotic phenotype of disc cells to the more favorable chondrocytic phenotype of disc nucleus cells in younger and more “normal― disc. Disc cells have been shown to express TGF and BMP molecules and receptors, and the expression level and spatial distribution seems to change with the aging process (35,36). Okuda et al. (32) demonstrated that the responsiveness of intervertebral cells to IGF-1 and TGF-beta decreases with advancing age in rabbit disc cells.

FIGURE 6.3 Morphogenic molecules. Morphogens change the phenotype of the cell as their major mechanism of action without necessarily increasing the cell number. In the disc, morphogens may be used to increase the chondrocytelike phenotype of the cells and enhance chondrocytic matrix synthesis.

TGF-beta was one of the first disc morphogenic molecules studied. Thompson et al. (30) reported that TGF-beta was a mitogen, but they also showed that it was a highly anabolic molecule leading to significantly increased proteoglycan synthesis per cell. They also showed that TGF-beta was superior to growth factors such as EGF, IGF-1, PDGF, and FGF in increasing proteoglycan synthesis rate per cell (30). Subsequently, Nishida et al. (37) demonstrated that an adenoviral vector containing the TGF-β1 gene can be directly injected into immunocompetent rabbit (normal) discs in vivo and lead to expression of TGF-β1 and increased rate of proteoglycan synthesis. Another subsequent report showed that cells from degenerated human discs when exposed to TGF-β1 in in vitro experiments can increase proteoglycan and collagen synthesis rates, thus suggesting that cells from even degenerated disc are capable of responding to TGF-β1 (38,39). In vivo experiments in mouse tail discs

P.56 indicated that TGF-β1 had some effect on cell proliferation in the inner annulus but did not have a measurable effect on the disc height (33). Although TGF-β1 has potential, its efficacy in in vivo degeneration models has not yet been established. BMP-2 is another classic example of a chondrogenic morphogen. Yoon et al. demonstrated that recombinant human BMP-2 increased rat disc cell proteoglycan production and significantly increased the chondrocytic phenotype of the disc cells, as demonstrated by increased aggrecan and collagen II gene expression, while there was no change in collagen I gene expression (40,44). Kim et al. (41) reported that BMP-2 can partially reverse the inhibitory effect of nicotine on disc cell proteoglycan synthesis. Because BMP-2 is well known to promote the terminal differentiation of osteoblasts during bone formation, there was an initial concern that BMP-2 may also lead disc cell differentiation along an osteoblastic lineage. However, in vitro experiments with human disc cells demonstrated that BMP-2 enhanced the expression of chondrocytic genes but not osteogenic genes (42). Further evidence of BMP-2 anabolic effects on disc cells reported with the use of a gene therapy approach with in vitro human disc cells obtained during elective spinal surgery (25). As of yet, there are no published reports on the BMP-2 efficacy of treating disc degeneration in in vivo models; however, this is currently a highly active area of research. It remains to be determined whether cells in a degenerated disc, perhaps metabolically impaired cells, can respond to growth factors and regenerate a damaged intervertebral disc. Ahn et al. (43) recently reported that BMP-2 and BMP-12 stimulated proteoglycan and collagen synthesis by human nucleus pulposus cells from degenerated discs cultured in monolayer in the absence of serum. They found that a significant and optimal stimulation of proteoglycan synthesis by these cells was achieved at 50 ng/mL of BMP2 (560%) and BMP-12 (460%). Further studies using aging intervertebral disc cells are anticipated to prove the therapeutic concept that growth factors will be useful to treat degenerated disc disease in the aging population (31). BMP-7, also known as OP-1, is another potent disc cell morphogen (45,46). Masuda et al. (45) reported a dose-dependent increase in proteoglycan synthesis and expression of chondrocytic genes, aggrecan and collagen II, from both annulus fibrosus and nucleus pulposus of rabbit disc cells grown in vitro under the influence of BMP-7. Takegami et al. (14) demonstrated that rabbit disc cells grown in alginate in the presence of the inflammatory cytokine IL-1 leads to loss of proteoglycan and collagen

in the alginate as compared to control. However, adding BMP-7 at 200 ng/mL to the IL1 culture led to increased synthesis of proteoglycan and collagen even compared to the controls without IL-1. Zhang et al. (46) reported that in vitro cultured bovine disc cells from three distinct spatial zones (outer annulus, inner annulus, and nucleus) all increased cellular proliferation in the presence of BMP-7. However, only cells from outer annulus and nucleus increased the rate of proteoglycan synthesis in the presence of BMP-7. Preliminary in vivo experiments with BMP-7 in rabbit models of disc degeneration have been presented and seem quite promising. These experiments show that direct intradiscal injection of BMP-7 increases disc height and proteoglycan content in vivo in rabbits (47). Preliminary data also indicate that intradiscal injection of BMP-7 may be effective in treating an experimental rabbit disc degeneration model using a small annulotomy (46,48). BMP-13 is also known as GDF-6 or cartilage derived morphogenetic protein-2 (CDMP-2) (49). Although BMP-13 is in the BMP family, BMP-13 has only 50% homology to BMP-2 in amino acid sequence (50). Experiments with a cartilage cell line indicated that BMP-13 does increase proteoglycan synthesis rate and chondrocytic phenotype, but BMP-13 was much less potent than BMP-2. The effect of adding both BMP-2 and BMP-13 were additive, although there was no synergism between the two P.57 morphogens in proteoglycan production or chondrocytic gene expression (50). BMP-13 is not a recombinant protein that is manufactured in large quantities such as BMP-2 or BMP-7, and therefore research that requires larger quantities of recombinant BMP-13 has been difficult to accomplish. GDF-5 is also known as CDMP-1 (49). During embryogenesis, GDF-5 is predominantly found at the stage of precartilaginous mesenchymal condensation and throughout the cartilaginous cores of the developing long bones (49). Walsh et al. (33) compared in vivo effects of a single injection and multiple injections of growth factors, such as bFGF (8 ng/disc), GDF-5, IGF-1, or TGF-β1, in the mouse caudal disc with degeneration induced by static compression. Although the effects of a single growth factor injection were not apparent within 1 week, the appearance of clusters of inner anular fibrochondrocytes was observed in the GDF-5 group, although this did not reach a significant level quantitatively. Of the four molecules tested, GDF-5 was the only molecule that increased the disc height as compared to saline controls. Furthermore, there seemed to be some increase in cellular proliferation in the middle and inner

annulus and transitional zone as seen on histologic sections. However, repeated injection induced an inflammatory response that was thought to be secondary damage induced by the needles used and not necessarily the GDF-5 because even the saline group had similar inflammatory changes. A gene therapy approach was used by Wang et al. (51) to demonstrate that GDF-5 delivered by an adenovirus promoted the growth of disc cells cultured in vitro. GDF-5 is being developed commercially for spinal fusion application; therefore, larger quantities of recombinant protein are available, making it easier to perform in vivo experiments. Link protein is a glycoprotein that stabilizes the noncovalent binding between aggrecan and hyaluronan. Link N is an amino-terminal fragment of link protein that was shown by Mwale et al. (52) to have stimulatory activity on disc cells. Mwale et al. reported that Link N, at concentrations of 10 and 100 ng/mL, stimulated matrix assembly in pellet culture of nucleus pulposus and annulus fibrosus cells by increasing the production and/or accumulation of proteoglycans and collagen but did not increase cell number in a statistically significant fashion. This suggests that a certain level of degradation products of link protein, which can be generated by MMPs, acts as a “growth factor― in a feedback mechanism. Collagen type II production was found to be increased by 113% in cells derived from the nucleus pulposus and 25% in cells derived from the annulus fibrosus. The mechanism by which Link N induces the specific upregulation of an important chondrocyte marker (collagen II) without much effect on cell number is not yet clear. However, these findings allow categorization of Link N as a chondrogenic morphogen.

Intracellular Regulators Intracellular regulators are a class of molecules that are distinct because they are not secreted molecules and do not work through transmembrane receptors (Fig. 6.4). These molecules are neither cytokines nor growth factors in the classical sense, and yet they can have effects that are quite similar to the secreted molecules discussed previously. This group of molecules typically controls one or more aspects of cellular differentiation. Examples of these include SMADs, Sox 9, and LMP-1. LMP-1 is an intracellular molecule that was initially discovered by its positive effect on bone formation and osteoblast differentiation. Yoon et al. (53) found that in disc cells, LMP-1 upregulates the production of BMP-2, BMP-7, and proteoglycans both in

P.58 short-term monolayer cultures and in longer (3-week) experiments in alginate cultures. By showing that the upregulation of proteoglycan can be blocked with a specific inhibitor of BMPs (Noggin), Yoon et al. demonstrated that the effect of LMP-1 involved a BMP-dependent mechanism. Subsequent in vivo work with rabbit discs showed that gene therapy with low doses of adenovirus-LMP-1 increased disc tissue mRNA levels of BMP-2, BMP-7, and aggrecan. Because LMP-1 stimulates both BMP-2 and BMP-7, this was hypothesized to potentiate the formation of the BMP-2:BMP-7 heterodimers, which have been shown to be up to 20 times more effective than homodimers of BMP-2 and BMP-7 (54). It can be speculated that by inducing a more potent set of BMPs, it may be possible to reduce the dose of adenovirus that is necessary, minimizing any potential risks of adenovirus gene therapy.

FIGURE 6.4 Intracellular regulators. Intracellular regulatory molecules are differentiated from cytokines because intracellular molecules are not secreted molecules that act through a transmembrane receptor. Intracellular regulators, however, can induce the secretion of cytokines to act in autocrine or paracrine fashion or directly upregulate matrix production.

SMADs are intracellular molecules that mediate BMP-receptor signaling (55,56). Although there are no specific published papers on the effect of SMADs on disc cells, SMADs such as SMAD-1 and SMAD-5 are predicted to induce similar effects on disc cells as BMP-2, such as increasing proteoglycan and collagen II synthesis. Sox9 is a chondrocyte marker that is a positive regulator of collagen II mRNA transcription (59,60). Paul et al. (61) demonstrated that Sox9 delivered by adenovirus can increase Sox9 expression and disc cell collagen II production in in vitro experiments. When injected in vivo, the adenovirus-Sox9 construct prevented histologic evidence of degenerative changes in the disc in a rabbit annulus puncture model. Of note, the disc degeneration model used consisted of a 27-gauge needle puncture, which is a very small injury to the disc and therefore may lead to mild or no disc degeneration. The main in vivo finding was that Sox9 treated discs had a more chondrocytelike phenotype as compared with control virus injected discs (61); however, this paper did not present quantitative data on the effect on disc matrix quantity or composition from the in vivo experiment.

Summary Intervertebral disc degeneration is a complex process that starts with cellular and biochemical changes that can eventually progress to a disease state. One hallmark of intervertebral disc degeneration is the loss of proteoglycan and water. Because of the central role of proteoglycans in the function of the intervertebral disc, restoration of normal proteoglycan production of the intervertebral disc may be critically important in any biologic treatment of intervertebral disc degeneration. Of the many different biologic treatment strategies for intervertebral disc degeneration, the strategy of stimulating intervertebral disc cells with cytokines has received the most attention. The molecules used to treat disc degeneration have expanded beyond the classical “growth factor.― There are at least four different classes of molecules that may be effective in disc repair. P.59 These include anticatabolics, mitogens, morphogens, and intracellular regulators. Although all of these molecules have some in vitro data, few have been tested in vivo with an animal model of disc degeneration. The next wave of experiments in progress use more realistic animal models of disc degeneration. This will be necessary prior to

attempting human studies. Finally, better delivery methods to provide long-term molecular therapy without the need for repeat dosing are being developed. This includes gene therapy methods and slow-release formulations of therapeutic molecules. Progress continues rapidly in this field and the potential remains bright.

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Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Non-Surgical Treatment > 7 - Nucleus Pulposus Regeneration: Present Limitations and Future Opportunities

7 Nucleus Pulposus Regeneration: Present Limitations and Future Opportunities Cyndi Lee Mauro Alini Sibylle Grad

Clinical Problem Low back pain is a major public health problem in our society and the cause of significant morbidity. The prevalence is high: It has been documented that 80% to 90% of the population has suffered from low back pain once in their lives (1). Back disorders occupy the highest rank of musculoskeletal disability pension among the Swiss male population (2), and data from a survey of the Swiss population reported that 10% of those interviewed had suffered severe low back pain in the previous 4 weeks (3). It not only accounts for much suffering and distress to patients and their families but also puts an enormous economic burden on society. The societal costs, including direct medical costs, insurance, lost production and disability benefits, are estimated at £12 billion per year in the United Kingdom, and more than $50 billion in annual health costs in the United States can be related directly or indirectly to this disease (4). Although the etiologies are many, intervertebral disc degeneration appears to be the leading cause for chronic axial low back pain (5,6). The incidence of disc

degeneration is rising exponentially with current demographic changes and an increased aged population. Around 10% of 50-year-old discs and 60% of 70-year-old discs are severely degenerate (7).

Disc Degeneration The intervertebral discs transmit loads arising from body weight and muscle activity through the spinal column, while also maintaining flexibility and allowing bending, flexion, and torsion of the spinal column. The intervertebral discs are complex structures consisting of an outer ring of fibrous cartilage termed annulus fibrosus, which surrounds a more gelatinous core known as nucleus pulposus. The central nucleus pulposus contains randomly organized collagen fibers and radially oriented elastin fibers (8,9) embedded in a highly hydrated aggrecan-containing gel-like matrix (10,11). The annulus fibrosus consists of a series of concentric rings, or lamellae with collagen fibers lying parallel within each lamella (12,13). P.64 Throughout growth and skeletal maturation, the boundary between annulus and nucleus becomes less obvious, and with increasing age the nucleus generally becomes more fibrotic and less gel-like (7,14,15). The disc changes in morphology, becoming more and more disorganized. The degenerative changes, whose incidence increase with age, also include cell death, changes in cell proliferation, mucous degeneration, granular changes, and concentric tears. Apoptosis appears to play a prominent role in age-related degeneration, with higher rates of apoptosis present in older individuals (16). In addition, degenerative discs produce a multitude of inflammatory, degradative, and catabolic molecules, including proteolytic enzymes, oxygen-free radicals, nitric oxide, interleukins, and prostaglandins (17,18,19). In particular, cathepsin, lysozyme, aggrecanases and several matrix metalloproteinases (MMPs) are thought to play a role in disc degeneration. Compared to normal discs, elevated levels of MMP-1, MMP-2, MMP-3, MMP-9, and lysozyme have been observed in degenerate discs (20,21,22,23,24). The most significant biochemical change to occur in disc degeneration is loss of proteoglycan (11,14). The aggrecan molecules become degraded, with smaller fragments being able to leach from the tissue more readily than larger fractions

(23). This results in loss of glycosaminoglycans, which has a major effect on the load-bearing behavior of the disc. With loss of proteoglycan, the osmotic pressure of the disc falls and the disc is less able to maintain hydration under load (11). Loading may thus lead to inappropriate stress concentrations along the vertebral endplate or in the annulus, which has been associated with disc-related pain (25). Findings from epidemiologic and genetic studies point to the multifactorial nature of disc degeneration (26). One of the primary causes of disc degeneration is thought to be failure of the nutrient supply to the disc cells (27,28). The diffusion capacity of even the healthy disc is relatively poor, and it is further limited by aging and degenerative changes of the endplate tissue (29,30). Abnormal mechanical loads are also believed to cause damage to the disc and finally clinical symptoms and back pain (31). It is also evident that mutations in several different classes of genes may cause the changes in matrix morphology, disc biochemistry, and disc function associated with disc degeneration (32,33,34).

Present Clinical Treatment Current treatments attempt to reduce pain rather than repair the degenerated disc. They range from analgesia, the use of muscle relaxants, and injection of corticosteroids or local anesthetics to manipulation therapies. The degenerative disorders of the lumbar spine that require surgical intervention include herniated discs, spinal stenosis, degenerative spondylolisthesis, degenerative scoliosis, and degenerative disc disease. The most controversial among them is the treatment of idiopathic low back pain associated with lumbar degenerative disc disease, which remains a challenge for the orthopaedic surgeon. Surgical procedures involving vertebral fusion produce a relatively good short-term clinical result in relieving pain, but they alter the biomechanics of the spine and can lead to further degeneration of the discs at adjacent levels. In fact, the failure rate for lumbar fusions is estimated to be in the 20% to 40% range (35), and there is clinical and radiologic evidence that spinal fusion leads to accelerated degeneration of the adjacent motion segment (36,37). More recently, there has been an increasing interest in disc arthroplasty that can maintain motion of the intervertebral segment. The efficacy of arthroplasty, however, remains controversial, and none of the current artificial disc replacement designs fully replicate normal disc biomechanics.

P.65 In general, surgical procedures try to remove rather than repair the problems associated with the degenerate intervertebral disc. Repair is, however, the ideal therapeutic approach as it restores the normal structure and function of the intervertebral disc. We believe that future treatments will be able to effect biologic repair of the damaged tissue by restoring it to a tissue of similar functional competence to the healthy native one.

Intervertebral Disc Tissue Engineering Realistically, only two biologic approaches to the treatment of disc degeneration are likely to become clinically available within the next 10 years. At the earlier stage of disc degeneration, injection of inhibitors of proteolytic enzymes or cytokines or biologic factors that stimulate cell metabolic activity (i.e., growth factors) can be foreseen, to slow down the degenerative process (38,39,40). Alternatively, when disc degeneration is confined to the nucleus, it is not unreasonable to propose that implantation or injection of a biomatrix embedded with cells will have the potential to restore functionality and to retard further disc degeneration. In both cases, several questions need to be addressed before the two potential treatment modalities can be turned into clinical realities. Some studies have also attempted to apply tissue engineering approaches with the aim to generate constructs with molecular composition similar to native nucleus pulposus. One study evaluated the ability of scaffolds of type I collagen and hyaluronan to support the viability of intervertebral disc cells and to accumulate the extracellular matrix they produce (41). Scaffolds were seeded with bovine nucleus pulposus or annulus fibrosus cells and maintained in culture for up to 60 days in the presence of fetal calf serum or a variety of growth factors. During the culture period, different proteoglycans (aggrecan, decorin, biglycan, fibromodulin, and lumican) and collagen types I and II accumulated in the constructs. The proteoglycan deposition was highest under conditions in which transforming growth factor-beta was present, but under all conditions, more proteoglycan was lost in the medium than retained in the scaffold. Interestingly, both nucleus and annulus cells behaved in a similar manner with respect to their ability to synthesize matrix molecules and retain them in the scaffold. It was concluded from this study that,

although the collagen/hyaluronan scaffold was able to maintain functional disc cells, conditions would need to be modified to optimize proteoglycan synthesis and retention in the constructs. Similar observations were also made when we cultured bovine articular chondrocytes in macroporous poly(L/DL)-lactide (42) or polyurethane (43) carriers, suggesting that the problem of matrix molecule retention occurs independent of the carrier material. Nevertheless, in the experiment using nucleus and annulus cells, the ability of annulus cells to replicate the matrix production of nucleus cells suggests that disc repair might not be limited to the availability of authentic nucleus cells. A more recent study evaluated the potential of chitosan-based hydrogels as scaffolds for the encapsulation of intervertebral disc cells and the accumulation of a functional extracellular matrix (44). The specific hypothesis of this study was that the cationic chitosan would provide an ideal environment for the deposition of large quantities of newly synthesized anionic proteoglycan. In fact, all the formulations of cell-seeded chitosan hydrogels tested retained most of the proteoglycan produced by encapsulated nucleus pulposus cells rather than releasing them into the culture medium. In contrast, annulus cells often did not survive when cultured in chitosan formulations. It was concluded from this study that chitosan may be a suitable scaffold for cell-based P.66 supplementation to help restore the function of nucleus pulposus tissue (Fig. 7.1).

FIGURE 7.1 Calcein AM and ethidium homodimer-1 staining of nucleus pulposus cells embedded into chitosan after 20 days of culture. Almost all the cells show a green fluorescence color, indicating excellent cell viability.

Autologous disc cell transfer has already been used in a canine model and also in small groups of patients, with initial results reported to be promising (45,46). Nevertheless, an important issue still requires to be addressed: The source of clinically useful cells. It is difficult to imagine that healthy nucleus cells could be obtained from the degenerated tissue that needs to be replaced. Two possible alternatives are conceivable: allogenic donor disc cells and/or autologous stem cells. Although one can envisage the use of cells harvested from a donor, because of the immunologically privileged status of the nucleus pulposus, ethical considerations and the potential for spreading infectious diseases make the allogenic option less attractive. The use of stem cells as a source for generating nucleus pulposus cells would be the ideal choice. Indeed, in a recent study, Sakai et al. (47) demonstrated regenerative effects of transplanting mesenchymal stem cells (MSCs) embedded in atelocollagen in a rabbit model of disc degeneration. However, at present there are no defined cell culture conditions in which this differentiation process occurs. In addition, there are no well-defined cellular

markers that can be used to identify disc cells and clearly distinguish them from other chondrocytelike cells.

Intervertebral Disc Cell Populations Although knowledge of the basic molecular structure and cellular biology of cartilage tissue has expanded rapidly in recent years, the basic information on the intervertebral disc and the cells within the intervertebral disc remain poorly understood. The intervertebral disc is often compared to articular cartilage and definitely resembles it in many ways, especially in the biochemical components that constitute the disc. However, there are significant differences between these two tissues, particularly in the composition and structure of matrix molecules. For example, it has been found that the proteoglycan to collagen ratio is distinctly higher in nucleus pulposus compared to cartilage of the same-aged individuals (48). Such differences result in tissues with distinctly different mechanical properties. Whereas cartilage behaves largely like a viscoelastic solid, nucleus pulposus can behave both as a fluid and as a viscoelastic solid under different loading conditions (49). Likewise, the cells of the intervertebral disc are commonly referred to as “chondrocytelike― cells. There is, however, a heterogeneous cell population in normal human intervertebral discs that differ in morphology and in the production of chondroitin sulfate, keratan sulfate, and collagens (50,51). Rounded (chondrocytelike morphology) cells are interspersed at low density (approximately 5,000/mm3) throughout the nucleus pulposus (52), whereas the cells of the annulus, particularly in the outer region, appear fibroblastlike, with an elongated and thin morphology aligned parallel to the collagen fibers (53). Nevertheless, cells of the annulus fibrosus and cartilage endplates have been shown to express macromolecular profiles similar to nucleus pulposus cells (23,54,55,56). A study characterizing rabbit intervertebral disc cells demonstrated metabolic differences between disc cells and articular and growth plate cartilage, and P.67 the authors suggested that annulus cells could be chondrocytic at a different stage of differentiation than cartilage cells, whereas the phenotype of nucleus cells still remains to be determined (57). In a more recent study investigating the expression of chondrocyte markers by cells of the intervertebral disc, normal nucleus cells showed strong signals for Sox9 and type II collagen mRNA and staining for aggrecan

protein, indicating a chondrocytelike phenotype, whereas annulus cells showed lesser evidences of a chondrocytic phenotype (58). In young individuals and in adults of certain species, a second population of large cells with granular cytoplasmic inclusions is present in nucleus pulposus tissue. These are the so-called notochordal cells, presumed remnants of the embryonic tissue that guided formation of the spine and the nucleus pulposus (59,60). It is presently unclear whether the disappearance of the notochordal cells is due to a further differentiation into cells with a chondrocytic phenotype, to programmed cell death, or to some other process. A possible connection between loss of notochordal cells and disc degeneration has been discussed (61). As stated previously, MSCs would be an ideal cell population for the generation of autologous tissue-engineered grafts, provided that they can successfully be differentiated into nucleus pulposus cells. Recent in vivo and in vitro studies (62,63,64) indicate that MSCs have the potential to adopt the disclike phenotype. Nevertheless, the definition of the native phenotype of nucleus pulposus cells remains relatively vague. Most commonly, the cells of the nucleus pulposus are referred to as chondrocytelike. However, if stem cells are to be used in a tissue engineering approach, it is crucial to know if stem cell derived chondrocytelike cells are more similar to articular cartilage or nucleus pulposus cells. Therefore, with the ultimate aim to identify specific markers for nucleus pulposus cells, we used microarray analysis and real-time reverse transcriptase polymerase chain reaction (RT-PCR) to compare the gene expression profiles of nucleus pulposus, annulus fibrosus, and articular cartilage cells.

Preliminary Data from the Rat Microarray Analysis Microarray analysis of young rat cells revealed that, compared to articular cartilage cells, there were 19 genes with at least 5-fold higher expression in nucleus pulposus, including 3 genes that were at least 10-fold higher. In addition, expression of 22 genes was at least 5-fold lower in nucleus pulposus versus articular cartilage cells. Compared to annulus fibrosus cells, there were 27 genes with at least 5-fold higher, including 3 with at least 10-fold higher, and 36 genes with 5fold lower expression in nucleus pulposus cells. These data obtained from the microarray analysis could largely be confirmed by real-time RT-PCR, and

interestingly, no significant differences were seen between RNA extracted directly from the tissue of young rats versus RNA from isolated cells for the genes selected for analysis by RT-PCR. In this rat model, glypican-3 and keratin-19 mRNA expression levels were found to be more than 10 times higher in nucleus pulposus compared to both annulus fibrosus and articular cartilage cells. Although rats are skeletally mature by 2 months, their nucleus pulposus retains a relatively large percentage of notochordal cells up to 1 year of age (65). It was therefore important to confirm the results with RNA from aged rats (2–3 years old). Although there were changes between the young and aged expression levels, and nucleus P.68 pulposus and annulus fibrosus expression profiles converged, the large differences between nucleus pulposus and articular cartilage expression of glypican-3 and keratin-19 were obvious even in the aged animals. We concluded that glypican-3 and keratin-19 appear to be promising candidates as marker genes to distinguish nucleus pulposus from articular cartilage cells, essentially because the large differences in gene expression were obvious even in the aged animals (Fig. 7.2).

FIGURE 7.2 Relative glypican-3 (GPC-3) and keratin-19 (K-19) mRNA expression of nucleus pulposus (NP), annulus fibrosus (AF), and articular cartilage (AC) cells and tissue of young rats and of nucleus pulposus and annulus fibrosus tissue of aged rats.

In this initial work, we chose rat tissue because of (a) the commercial availability of a microarray (human, rat, or mouse), (b) the wide availability of normal tissue at different ages (rat or mouse), and (c) the ability to separate nucleus pulposus and annulus fibrosus tissue (rat or human). However, it is important to note that there are substantial differences between rat and human discs, both with regard to mechanical function and postnatal development of the disc, and additional studies are underway to determine if our selected cellular markers may be used as markers across species, in particular in human. Further to the previous gene expression investigations, the next challenge will be to define appropriate stimuli to direct MSCs toward the phenotype of intervertebral disc cells, which will be a significant step toward the development of new cellbased treatment strategies for degenerative disc disease.

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Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Non-Surgical Treatment > 8 - What is the Evidence Base for IDET?

8 What is the Evidence Base for IDET? Brian J. C. Freeman In 2000 Saal and Saal (25 ) introduced a new method for the treatment of chronic discogenic low back pain using intradiscal electrothermal therapy (IDET). The technique involved placement of a 17-gauge introducer needle under fluoroscopic guidance into the center of the disc. A navigable intradiscal catheter with a temperature controlled thermal resistive heating coil was then deployed through the needle and positioned under two-plane fluoroscopy to a final position at the inner posterior annulus (Fig. 8.1 ). The standard heating protocol raises the temperature of the catheter tip from 65° to 90°C over 12.5 minutes. The temperature is then maintained at 90°C for 4 minutes. According to Saal and Saal (23 ), this creates annular temperatures of 60° to 65°C. After heating, the catheter is removed and 10 mg of cephazolin is injected intradiscally. The authors propose the mechanism of action of IDET to be a combination of thermocoagulation of native nociceptors and ingrown unmyelinated nerve fibers plus annular collagen shrinkage stabilizing annular fissures (25 ). The postprocedural care allowed patients P.74 o walk and perform low-intensity leg stretches for the first month, to resume stabilization floor exercises by the end of the second month, and to increase the intensity of exercise at the end of the third month.

FIGURE 8.1 Anteroposterior and lateral radiograph showing final position of intradiscal catheter at L4-5. (From Freeman BJC, Fraser RD, Cain CMJ, et al. A randomised double blind controlled trial: intra-discal electrothermal therapy versus placebo for the treatment of chronic discogenic low back pain. Spine . 2005; 30: 2369–2377, with permission.)

Prospective Cohort Studies (Level of Evidence 2b) (22) Early studies were promising, with 80% of patients reporting a reduction of at least two points on the visual analogue scale (VAS) for low back pain and 72% reported improvement in sitting tolerance and reduction in analgesic requirement (25 ). Improvements in physical function and bodily pain subsets of the Short Form-36 (SF36) were also noted. Patients working prior to the procedure returned to work within 5 days of the procedure. The authors demonstrated statistically significant improvements in function as measured by VAS, sitting tolerance, and SF-36 following IDET. Saal and Saal (26 ) subsequently reported the 1-year outcome of an expanded cohort of 62 patients undergoing IDET. Between November 1997 and October 1998, 62 from 1,116 patients treated by the authors did not improve adequately after a minimum of 6 months of conservative care. All 62 patients were offered long-term pain management, fusion surgery, or IDET. All 62 chose to undergo IDET. From 62 patients, 33 were men and 29 were women. The mean age was 41 (range 21–58). Thirty-nine patients were private payers and 23 were receiving workers'

compensation. The mean duration of preoperative symptoms was 60 months (range 10 months to 17 years). Twenty of 39 private-paying patients were working; none of the 23 workers' compensation patients were working. Thirty patients were treated at one disc level and 32 patients at two or more disc levels. The VAS improved a mean of 3.0 points for the whole group. For the single-level patients the mean improvement in VAS was 3.4 points, but for the multilevel patients the mean improvement was only 2.6 points. Twelve of 62 patients did not show any improvement in VAS. For the whole group, the physical function score of the SF-36 improved 20 points (23.6 points for the single-level group and 17 points for the multilevel group). For the bodily pain score of the SF-36, the mean improvement for the whole group was 17.4 points (16.8 points for the single level group and 18.0 points for the multilevel group). Six of 62 patients did not improve in either physical function or bodily pain subscales of the SF-36. Three of 62 patients underwent an epidural injection during the first 8 weeks following the procedure. Two of 62 patients underwent fusion surgery 1 year following the IDET procedure. Ninety-seven percent of private-paying patients and 83% of the workers' compensation patients returned to work. The time to return to work varied between 14 days for those with sedentary jobs and 4 to 6 months for those with heavy jobs. There was no significant difference in clinical outcome between private-paying and workers' compensation patients. For patients with decreased disc height (more than 30% loss of disc height) who had treatment at multiple levels, the outcome was less favorable than those with multilevel treatment who had preserved disc height. Saal and Saal (27 ) reported on the 24-month outcome in the same cohort. The mean VAS dropped from 6.57 to 3.41, an improvement of 3.16 points. The sitting time increased on average by 52.7 minutes. The mean physical function score of the SF-36 improved 31.33 points and the mean bodily pain score improved 21.87 points (Fig. 8.2 ). Eighty-one percent of patients showed at least a 7.0-point improvement in physical function and 78% improved at least 7.0-point improvement in bodily pain. Seventy-two P.75 percent of patients improved their VAS by at least 2.0 points. Also striking was that the improvement continued over 2 years and seemed to be comparable in one-, two-, or three-level treated disease.

FIGURE 8.2 Global SF-36 scores pretreatment and 24 months following intradiscal electrothermal therapy (IDET). (From Saal JA, Saal JS. Intradiscal electrothermal treatment for chronic discogenic low back pain. A prospective outcome study with a minimum 2-year follow-up. Spine . 2002; 27: 966–973, with permission.)

Derby et al. (9 ) reported 32 consecutive cases of IDET. All patients were initially assessed by an orthopaedic surgeon and told either they were not suitable for spine surgery or they were offered surgery and declined. Outcome measures included the Roland-Morris disability questionnaire, the VAS, a patient satisfaction index, and a questionnaire related to activities of daily living. The mean age of participants was 42 years, with only four workers' compensation cases. Seven patients had previous surgery. Derby treated both discrete annular fissures and global disc degeneration. The mean improvement in VAS was 1.84 (SD 6 2.38). The mean improvement in Roland-Morris was 4.03 (SD ± 4.82). There was no significant change in outcome measures at 6 months and at 12 months. Overall, 62.5% had a favorable outcome, 25% had no change, and 12.5% had a nonfavorable outcome. One patient underwent a spine fusion due to persistent discogenic back pain. Karasek and Bogduk (17 ) reported 12-month follow-up of a controlled trial of IDET

for back pain due to internal disc disruption. From 110 patients undergoing computed tomography (CT) discography, 53 satisfied the criteria for internal disc disruption at one or two levels. Authority to undergo IDET was sought from the insurance carriers of these patients. Authority was granted in 36 and denied in 17. The 36 patients constituted the index treatment group and underwent IDET followed by rehabilitation. The 17 patients constituted a “convenience sample control group― and underwent rehabilitation. Outcome measures included the VAS, return to work, use of opioid analgesics, and Oswestry Disability Index (ODI) in some patients. The control group were followed for 3 months: the median VAS was 8 (range 5–8) before rehabilitation and 8 (range 7 to 8) at 3 months. The IDET group had a median VAS of 8 (range 7–9) before treatment reducing to 3 (range 1–7) at 12 months. Some patients returned to work and reduced their opioid intake. Bogduk and Karasek (4 ) subsequently reported on the 24-month follow-up in the IDET group. Fifty-four percent of patients reduced their pain by half, with P.76 one in five patients achieving complete relief of pain. The authors concluded that IDET relieved discogenic pain, had a success rate of between 20% to 60%, and was superior to physical rehabilitation. The use of patients who had been denied treatment as a “control group― raises serious methodologic flaws in this paper. Gerszten et al.(15 ) studied 27 patients following IDET. Eight had private insurance and nine had received workers' compensation. Sixteen patients underwent IDET at one level and 11 patients underwent IDET at two or more levels. The mean duration of symptoms was 38 months and the follow-up was 12 months. Outcome measures included quality of life as assessed by the SF-36 and disability as measured by the ODI. The physical function score of the SF-36 improved from a baseline of 32 to 47 points at final follow-up. The bodily pain score of the SF-36 improved from 27 to 38 at final follow-up. The ODI improved from 34 at baseline to 30 points at final follow-up. The authors noted that at 1 year 45% of patients reported a significant improvement on the SF-36 survey and that 75% of patients had improvement of their symptoms following IDET. Pain was not measured in this study. The authors found no relationship between outcome and the number of levels treated, the duration of symptoms, or workers' compensation status. Spruit and Jacobs (31 ) reported on pain and function after IDET for symptomatic

lumbar disc degeneration in a cohort of 20 patients. The mean VAS improved by 1.4 points (p = 0.046), but the individual scores showed great variation. The ODI did not improve significantly. The SF-36 showed improvement, but only for the subscales vitality (p = 0.023) and bodily pain (p = 0.047). The authors concluded that IDET was not effective in reducing pain and improving functional performance. Lutz et al. (19 ) treated 33 patients with chronic constant lumbar discogenic pain of more than 6 months with IDET. The mean age was 40 years and the mean duration of symptoms was 46 months. The mean follow-up period was 15 months. The mean VAS improved from 7.5 to 3.9 (p , 0.001) and a mean improvement in the RolandMorris disability questionnaire of 7.3 points was noted (p 0.001). With regard to patient satisfaction, 75.7% reported that they would undergo the same procedure for the same outcome. Complete pain relief was achieved in 24% of the patients and partial pain relief in 46% of the patients. A summary of the clinical outcome following IDET for these prospective cohort studies is presented in Table 8.1 . From a total of 191 patients the mean improvement in VAS was 3.02 (range 1.48–5.0) at a mean of 15 months (range 12–28 months).

Retrospective Cohort Studies (Level of Evidence 3b) (22) Freedman et al. (13 ) reported on his experience with IDET for the management of chronic discogenic low back pain in active-duty soldiers. Forty-one active-duty soldiers (34 men, 7 women) underwent IDET for chronic discogenic low back pain unresponsive to nonoperative therapy. During the study period, 36 of 41 patients underwent a single trial of IDET and the remaining 5 underwent two trials of IDET. Only the results of the first 36 patients were analyzed. All 36 patients had follow-up data at 6 months but only 31 patients had reached final follow-up (mean 29.7 months, range 24–46). Success was defined as a 50% decrease in pain from baseline. The success rate was 47% (17 out of 36) at 6 months and 16% (5 of 31 patients) at latest follow-up. Fifty-two percent of patients had a two-point or greater decrease in the VAS for pain. P.77 Nineteen of 31 soldiers (61%) remained on active-duty at a minimum of 24 months

after IDET. Seven of 31 soldiers (23%) went onto spinal surgery within 24 months of failed IDET. The authors conclude that IDET is not a substitute for spinal fusion in the treatment of chronic discogenic pain. They consider it at best an antecedent rather than an alternative to spinal fusion. 1. Saal and Saal, 2000 (25 ) Prospective cohort 25 7 months VAS score SF-36 (PF) SF-36 (BP) 7.3 → 3.6 (3.7) 40.1 → 55.2 (15.1) 28.5 → 42.2 (13.7) 2. Saal and Saal, 2000 (26 ) Prospective cohort 62 16 months VAS score SF-36 (PF) SF-36 (BP) 6.6 → 3.7 (2.9) 39 → 59 (10) 29 → 46.2 (17.2) 3. Saal and Saal, 2002 (27 ) Prospective cohort 62 (4) 28 months (24 –35 ) VAS score SF-36 (PF) SF-36 (BP) 6.57 → 3.41 (3.2) 40.5 → 71.8 (31.3) 29.8 → 51.7 (21.9)

4. Derby etal., 2000 (9 ) Prospective cohort 32 12 months VAS score Roland-Morris (—1.84, SD 2.38) (—4.03, SD 4.82) 5. Karasek and Bogduk, 2000 (17 ) Prospective Quasi-controlled N=53 n=36 IDET 12 months VAS (median) IDET: 8 → 3 (5) Control:8 → 8 (0)

n=17 controls Success rate IDET: 20%–60% 6. Bogduk and Karasek, 2002 (4 ) Prospective N=53 (5) 24 months VAS (median) IDET: 8 → 3 (5) Quasi-controlled n=36 IDET

Control: 8 → 7.5 (0.5)

n=17 controls Success rate IDET: 54% reduce pain by half 7. Gerszten etal., 2002 (15 ) Prospective cohort 27 12 months ODI SF-36 (PF) 34 → 30 (4.0) 32 → 47 (15)

SF-36 (BP) 27 → 38 (11) 8. Spruit and Jacobs, 2002 (31 ) Prospective cohort 20 (1) 12 months VAS ODI 6.54 → 5.06 (1.48) 43.1 → 36.7 (6.4) 9. Lutz etal., 2003 (19 ) Prospective cohort 33 15 months VAS

7.5 → 3.9 (3.6) IDET, intradiscal electrothermal therapy; FU, follow-up; VAS, visual analogue scale; SF-36, Short Form-36; PF, Physical Function subset of SF-36; BP, Bodily Pain subset of SF-36. Authors

Study

Subjects

Follow-Up

Outcomes

Results

(Year)

Design

(Loss to FU)

(Range)

Measured

(Δ)

TABLE 8.1 Summary of Clinical Outcome Following IDET: Prospective Cohort Studies (Level of Evidence 2b) Cohen et al. (7 ) carried out a retrospective clinical data analysis on 79 patients undergoing IDET for discogenic low back pain. Forty-eight percent of patients reported more than 50% pain relief at 6 months. The authors divided the cohort into those in whom a positive outcome occurred (n = 38, 48%) and those in whom a negative outcome occurred (n = 41, 52%). For those with a positive outcome the VAS dropped from 5.9 to 2.1, a mean change of 3.8 points and for those patients with a negative outcome the VAS dropped from 6.2 to 5.1, an improvement of only 1.1 points. The complication rate was 10%, including transient radicular pain and one case of ipsilateral foot drop. Only one of P.78 ten obese patients had successful IDET. The authors suggest that obesity should be considered a relative contraindication to IDET. Lee et al. (18 ) studied 62 patients recruited from an academic-affiliated private physiatric practice. Fifty-one patients were available for a minimum follow-up of 24 months. The mean age was 41.4 years (18–60 years), the average duration of symptoms was 46 months (range 6–180 months), and the average follow-up was 34 months (range 6–47 months). Clinical improvement was defined as a change of more than two points on the pain scale and Roland-Morris scale. There was a statistically significant improvement in lower back pain scores, Roland-Morris scores, and lower extremity pain scores. On the North American Spine Society (NASS) patient satisfaction index, 63% (32/51) responded positively and would undergo the procedure again. Seven patients (14%) underwent additional

therapeutic procedures during the follow-up period. Two from 51 patients underwent a spinal fusion. Davis et al. (8 ) carried out a retrospective study with independent evaluation of patient outcomes 1 year following IDET. The outcome assessment consisted of a telephone interview and completion of a self-administered questionnaire. The mean age was 40 years (range 25–64 years). Responses were received from 44 of 60 patients. Six patients had undergone lumbar surgery within 1 year of the IDET procedure. Their outcomes were excluded from analysis. Ninety-seven percent of patients continued to have back pain, 29% reported more pain post-IDET, 39% had less pain, and 29% reported no change. Fifty percent were dissatisfied with IDET, 37% were satisfied, and 13% were undecided. The authors concluded that at 1-year post-IDET, half the patients remained dissatisfied with their outcome and the estimated proportion of patients undergoing fusion was predicted to be 15% at 1 year and 30% at 2 years. Webster et al. (32 ) investigated the outcome of workers' compensation claimants post-IDET. The authors identified 142 cases from 23 states treated by 97 different health care providers. The mean follow-up was 22 months. Ninety-six (68%) of the cases did not meet one or more of the published inclusion criteria. Fifty-three of 142 cases (37%) had at least one lumbar injection and 32 of 142 cases (23%) had lumbar surgery after IDET. The authors concluded that the procedure may be less effective when performed by a variety of providers compared with the initial case series performed by single providers or practices in work-related low back pain causes. A total of 379 patients were reported in these five retrospective studies (Level of Evidence 3b) (22 ) between 2003 and 2004 (Table 8.2 ). The mean follow-up was 20.7 months (range 6–29.7). Not all studies reported standard outcome measures. Between 13% to 23% of patients subsequently underwent surgery for low back pain within the study period.

Randomized Controlled Trials (Level of Evidence 1b) (22) Three randomized controlled trials of percutaneous intradiscal thermocoagulation for chronic discogenic low back pain have been published. The first reports on

percutaneous intradiscal radiofrequency thermocoagulation (PIRFT) (Radionics, Burlington, MA) and heats the disc up to 70°C for 90 seconds (3 ). The remaining two studies use IDET (Oratec Menlo Park, CA) (14 ,21 ). IDET uses a thermal resistive coil to deliver P.79 heat to the disc, raising the temperature of the catheter tip to 90°C over 12.5 minutes and maintaining for 4 minutes. In that respect the two techniques are different and it is not appropriate to compare the Barendse et al. (3 ) study with that of Freeman et al. (14 ) and Pauza et al (21 ). 1. Freedman etal., 2003 (13 ) Retrospective cohort 36 (5) 29.7 months (24–46) VAS 52% had >2.0 improvement

Success 5/31 (16%)

Surgery 23% underwent surgery within the FU period 2. Cohen etal., 2003 (7 ) Retrospective cohort 79 6 months VAS +ve outcome 5.9 → 2.1 (3.8) ve outcome 6.2 → 5.1 (1.1)

Success 48% reduce pain by half 3. Lee at al., 2003 (18 ) Retrospective cohort 62 (11) 34 months (6–47) VAS Satisfaction >2.0 points 63% satisfied and would have procedure again 4. Davis etal., 2004 (8 ) Retrospective cohort 60 (16) 12 months Satisfaction 50% dissatisfied 37% satisfied 13% undecided

Employment status Surgery 16 employed pre-IDET 11 employed post-IDET 6/44 (13.6%) underwent surgery within the FU period 5. Webster etal., 2004 (32 ) Retrospective cohort 142 22 months

Narcotic usage Surgery Unchanged following IDET 32/142 (22.5%) underwent surgery within FU period IDET, intradiscal electrothermal therapy; FU, follow-up; VAS, visual analogue scale. Authors

Study

Subjects

Follow-Up

Outcomes

Results

(Year)

Design

(Loss to FU)

(Range)

Measured

(δ)

TABLE 8.2 Summary of Clinical Outcome Following IDET: Retrospective Cohort Studies (Level of Evidence 3b) Barendse et al. (3 ) conducted a randomized controlled trial of PIRFT for chronic discogenic back pain. Outcome measures included VAS, the global perceived effect by the patient, ODI, the Dartmouth COOP functional health assessment chart, and a Quality of Life questionnaire. Questionnaires were completed before treatment and 8 weeks following treatment. The radiofrequency lesion of the disc was performed using a radiofrequency probe (Radionics, Burlington, MA). Patients were randomized to P.80 receive a 90-second 70°C lesion if allocated to the “lesion― group or no lesion if allocated to the “sham― group. From a total of 287 patients with chronic nonspecific low back pain, 28 were recruited according to the inclusion and exclusion criteria. Success was defined as a reduction of at least two points on the VAS and a 50% improvement on the global perceived effect. Fifteen patients were allocated to the sham group, and 13 were allocated to the lesion group. Eight weeks following treatment there were two treatment successes in the sham group and one in the lesion group. There were no statistically significant differences in the secondary outcome measures between both groups. Eight weeks after treatment VAS, global perceived effect, and ODI showed no significant differences between the two groups. The authors concluded that PIRFT was not effective in reducing chronic discogenic low back pain. Pauza et al. (21 ) reported a randomized placebo-controlled trial of IDET for the treatment of chronic discogenic low back pain. Inclusion criteria listed age between

18 and 65 years, low back pain more than leg pain for at least 6 months, failure to improve after 6 weeks of nonoperative care (including anti-inflammatory and analgesic medication and physical therapy and/or a home directed exercise program), low back pain exacerbated by sitting or standing, Beck depression index of less than 20 points, less than 20% loss of disc height on plain radiographs, and the presence of a posterior tear of the annulus fibrosus on CT discography. Exclusion criteria listed previous lumbar fusion, spondylolisthesis, spinal stenosis, scoliosis, disc herniation of more than 4 mm, workers' compensation, injury litigation, and disability remuneration. Also excluded were those with diffuse changes on CT discography. All patients received conscious light sedation and placement of the 17-gauge introducer needle down to the outer aspect of the annulus fibrosus. At this point, the randomization schedule was revealed to the principle investigator. Randomization employed a 3:2 ratio (3 IDET: 2 sham). For those randomized to active treatment the intradiscal catheter was positioned to provide complete coverage of the posterior annulus and the standard heating protocol was followed. After treatment was completed the electrode was withdrawn and 1 mL of 0.75% bupivacaine was injected into the disc. For those undergoing sham treatment, the introducer needle remained in position and the patient was exposed to a fluoroscope monitor showing passage of an intradiscal catheter and manufactured generator noises for the full 16.5 minutes to mimic an active treatment. Both groups underwent a monitored postoperative rehabilitation involving a lumbar corset for 6 weeks followed by a lumbar stabilization program for a further 6 weeks. Outcomes assessed included VAS, SF-36, and ODI, prior to treatment and 6 months after treatment. Publicizing the study attracted inquiries from 4,253 people. From 1,360 individuals who were prepared to submit to randomization, 260 (19.1%) were found potentially eligible after clinical examination and 64 became eligible after discography (4.7%). Thirty-seven were allocated to IDET and 27 to sham treatment. After treatment eight patients (12.5%) violated the prescribed protocol mandating their rejection from the analysis leaving a total of 56 patients: 32 from the IDET group and 24 from the sham group. Both groups exhibited significant improvement in the VAS, but improvements in the

IDET group were significantly greater than the sham group (p = 0.045). For patients in the IDET group, the mean VAS dropped from 6.6 to 4.2 (mean improvement 2.4, SD 2.3) and the ODI dropped 31 to 20 (mean 11 points, SD 11). For patients in the sham group, the mean VAS dropped from 6.5 to 5.4 (mean improvement 1.1, SD 2.6) and the mean ODI dropped from 33 to 28 (mean 4 points, SD 12). P.81 Taking this into context, the advantage for IDET patients over sham patients was 1.3 points on the VAS (p = 0.045) and 7 points on the ODI (p = 0.05). There were no significant differences in the SF-36 subsets bodily pain or physical function between the two groups. However, mean scores can hide individual scores. IDET was not a universally successful treatment in this study; some 50% of patients did not benefit appreciably or at all. Only 40% of patients treated with IDET achieved greater than 50% relief of pain. Freeman et al. conducted a prospective, randomized, double-blind, placebocontrolled trial with crossover offered to the placebo subjects when unblinding occurred at 6 months. A total of 57 subjects were enrolled without inducement according to the inclusion and exclusion criteria listed here. Subjects were selected from consecutive patients from the routine practices of three consultant spinal surgeons in a large city. All subjects had chronic discogenic low back pain, marked functional disability, evidence of degenerative disc disease on magnetic resonance scan, and subsequently failed conservative management. To successfully enroll, all subjects had one- or two-level symptomatic disc degeneration as determined by provocative lumbar discography followed by postdiscography CT to delineate the internal disc disruption. The study adopted a 2:1 (IDET: placebo) randomization schedule. From the total of 57 subjects, 38 were randomized to IDET and 19 to placebo (sham treatment). All procedures were carried out under light neuroleptic anesthesia and local anesthesia. A 17-gauge introducer needle was used employing a standard posterolateral approach to the symptomatic disc under multiplane fluoroscopic guidance. The intradiscal catheter was navigated to cover at least 75% of the posterior (interpedicular) annulus or at least 75% of the annular tear as defined by the postdiscography CT scan. Once a satisfactory position was obtained in the anteroposterior, lateral, and Ferguson views the catheter was connected to a lead and passed to an independent technician. The technician then opened a sealed envelope to ascertain the randomization schedule and covertly either

connected the catheter to the generator (active IDET group) or did not (sham placebo group). Critically both surgeon and subject were blinded to this step. The generator was switched on and the standard heating protocol commenced at 65°C, rising over 12.5 minutes to 90°C and held for 4 minutes. All subjects followed a common rehabilitation program including Pilates-based exercises. Subjects were reviewed at 6 weeks and 6 months by an independent third party to minimize investigator bias. Outcome measures recorded at baseline and 6 months included the VAS for back pain, the Low Back Pain Outcome Score (LBOS), the ODI, the Short Form-36 General Health questionnaire (Australian version) (SF-36), the Zung Depression Index (ZDI), the Modified Somatic Perception Questionnaire (MSPQ), sitting tolerance, work tolerance, medication, and the presence of any neurologic deficit. Successful outcome was defined as one demonstrating the following: no neurologic deficit resulting from the procedure, an improvement in the LBOS of seven or more points, and an improvement in the SF-36 subscales of bodily pain and physical functioning of greater than one standard deviation from the mean. The mean clinically important difference in secondary outcome measures was set at 2.0 points for the VAS (back pain), 10 points for the ODI, and 8.0 points for the ZDI. Using the 2:1 allocation for active and control treatment to have 80% power, the study required 50 patients to be treated with IDET and 25 with the sham treatment. Enrollment of subjects was slower than anticipated, with only 57 patients enrolled after 25 months. Following advice from the ethics committee, the study was halted and an independent statistical analysis carried out. The 2:1 (IDET: placebo) randomization produced two groups (38 IDET: 19 placebo) with well-matched LBOS, ODI, SF-36, ZDI, and MSPQ scores. After treatment, two P.82 subjects (both from the IDET group) from 57 (3.5%) violated the prescribed protocol mandating their rejection from analysis. One was considered a technical failure and was withdrawn from the study at the 6-week follow-up. The second subject experienced increased low back pain, withdrew from the study at 3 months, and subsequently underwent a spinal fusion. No subject in either treatment arm met the joint criteria for “success.― Hence, the specified primary analysis showed no difference between the

treatments. Secondary outcomes were compared at baseline and 6 months. These included comparisons of change at 6 months in LBOS, ODI, ZDI, MSPQ, and SF-36 scores. The mean LBOS for the IDET group was 39.51 at baseline and 38.31 at 6 months. The mean LBOS for the placebo group was 36.71 at baseline and 37.45 at 6 months. The mean ODI for the IDET group was 41.42 at baseline and 39.77 at 6 months. The mean ODI for the placebo group was 40.74 at baseline and 41.58 at 6 months. The following subgroups were analyzed: males only (the placebo group showed a preponderance of males), those with “adequate treatment of the tear― as assessed by Dr. Saal, those with psychological impairment, those not taking narcotic medication at baseline, those not taking 8 or more Panadeine Forte tabs per day at baseline, those with single level treatment for an annulus tear without global degeneration, and those with single-level treatment for an annulus tear without global degeneration, taking no analgesics at baseline and with “adequate treatment of tear― as assessed by Dr Saal. These detailed secondary analyses showed no statistically significant or clinically important differences in the measured study outcomes for either treatment. This was true irrespective of whether the comparison was further adjusted for the baseline measure. A further stratified analysis by surgeons conducting the IDET procedure showed no significant difference in secondary endpoints between treatment arms for any surgeon. There were no serious adverse events in either arm of the study. Transient radiculopathy (<6 weeks) was reported in four subjects who underwent IDET and in one subject who underwent the sham procedure. The Pauza et al. (21 ) study concluded that IDET is “an effective treatment for discogenic low back pain.― However, there was modest overall benefit and some patients did not benefit at all. The study by Freeman et al. (14 ) showed no significant benefit from IDET over placebo. How can two similarly sized randomized controlled trials show such different results? There are important differences between the two studies such as the inclusion criteria, severity of patient disease, how the sham procedures were performed, the blinding procedure, and how success and the mean clinically important differences were defined. These are highlighted in Table 8.3 . Pauza et al. (21 ) may well have shown statistical significance between their two groups, but Freeman et al. (14 ) would argue that

these differences do not necessarily amount to clinical significance.

Safety Issues Eckel and Ortiz (12 ) reported on the complications following IDET in a retrospective multicenter registry of 1,675 treated patients. These included 19 catheter breakages, 5 transient nerve root injuries, 1 partially resolved nerve root injury, and 6 cases of post-IDET disc herniation. In 2002, Djurasovic et al. (11 ) reported a case of vertebral osteonecrosis associated with the use of IDET. The patient continued to have severe unrelenting symptoms and subsequently underwent an L5-S1 anterior interbody fusion. Scholl et al. (28 ) reported P.83 a second case of vertebral osteonecrosis in a 26-year-old man undergoing surgery at L2-L3. The procedure was performed by sequential placement of intradiscal catheters bilaterally . The bilateral approach was judged necessary at the time of the IDET because the catheter tip could not be manipulated through a unilateral approach to heat the entire posterior annulus. This technique is described in the instructional course manual (24 ). The patient continues to complain of severe disabling low back pain. Start date of trial November 1999 September 2000 Finish date of trial December 2001 April 2002 Study Total N 57 64 Withdrawn or loss to follow-up 2 (3.5%) 8 (12.5%) Mean age (years) IDET 37.5

IDET 42 Placebo 40.2 Placebo 40 Disc height Up to 50% loss Up to 20% loss Disc morphology Discrete annular tear or global degeneration Posterior annular tear only Excluded from study Workers' compensation IDET 55.3 Excluded from study % in each group Placebo 57.9 Duration of symptoms IDET 41 IDET 78% over 24 (months) Placebo 66 Placebo 74% over 24 ODI baseline IDET 41.4 IDET 32 Placebo 40.7 40.7 Placebo 33 SF-36 PF baseline IDET 41.8 IDET 54 Placebo 35.0

Placebo 48 SF-36 BP baseline IDET 33.1 IDET 35 Placebo 24.4 Placebo 35 Definition of success No neurologic deficit LBOS >7.0 SF-36 PF >1 SD SF-36 BP >1 SD Comparison of mean Categorical outcomes IDET, intradiscal electrothermal therapy; ODI, Oswestry Disability Index; SF-36, Short Form-36; LBOS, Low Back Pain Outcome Score; PF, Physical Function subset of SF-36; BP, Bodily Pain subset of SF-36. Adapted from Freeman BJC, Fraser RD, Cain CMJ, etal. A randomised double blind controlled trial: intra-discal electrothermal therapy versus placebo for the treatment of chronic discogenic low back pain. Spine . 2005; 30: 2369–2377, with permission. Characteristic

Freeman etal. (14 )

Pauza etal. (21 )

TABLE 8.3 Comparison of Freeman etal. (14 ) and the Pauza etal. (21 ) Studies There have been three reports of caudal equina syndrome following IDET(1 ,16 ,33 ) and one report of a giant herniated disc following IDET (6 ). It would appear that IDET weakens the posterior annular wall, predisposing to disc prolapse. Orr and Thomas (20 ) presented a case whereby a broken IDET catheter tip migrated from the disc space into the thecal sac leading to radiculopathy. The symptoms improved after surgical removal of the catheter. Davis et al. (8 ) reported a case of discitis at L4-5 commencing within 4 weeks of her L4-L5 IDET procedure. Conservative treatment failed to resolve the infection

and the patient underwent an L4-5 lumbar interbody fusion 10 months later. P.84 The incidence of complications following IDET in one series was reported at 15% (7 ). Complications included radicular pain, paraesthesia, and numbness in the thighs, foot drop, cerebrospinal fluid leaks, and severe headaches.

Conclusions Initial reports from the originators of IDET were impressive with regard to improvements in subjective outcome measures for highly selected cases. Further prospective and retrospective studies carried out at beta sites appear much less impressive. There are two randomized controlled trials addressing the effectiveness of IDET (14 ,21 ). The Pauza et al. (21 ) study showed modest overall benefit, although many patients did not seem to improve at all. The study by Freeman et al.(14 ) showed no substantial benefit from the procedure. One must exercise caution in recommending this treatment for patients (5 ). The current published evidence does not provide clear evidence of benefit.

Postscript Oratec Interventions Incorporated (Menlo Park, CA) developed the SpineCath IDET system for low back pain. Oratec went public to a receptive market on April 4, 2000 and earned $56 million by offering 4 million shares at $14 each. By the end of the day, shares were trading at $25.63 and within 1 month they had reached $36.75. However, providers were unable to gain reimbursement for IDET therapy and the price fell to $5.13 at the year's end (10 ). Smith and Nephew acquired Oratec in February 2002 after an offer of $12.50 per share was accepted by Oratec. The cost to Smith and Nephew acquiring the equity of Oratec was $310 million. The net cost after deducting Oratec's cash and shortterm investments ($52 million as of December 31, 2001) was approximately $258 million. The IDET procedure had sales of $21 million in 2001 (29 ). Since FDA clearance in March 1998, more than 40,000 IDET procedures have been performed on patients throughout the world up to 2003 (30 ). As of June 2005, Smith and Nephew (Endoscopy division, Andover, MA) has estimated that 60,000 IDET procedures have been performed worldwide to date.

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10. DeviceLink: www.devicelink.com/mx/archive/01/03/0103 mx042.html. 11. Djurasovic M, Glassman SD, Dimar JR, et al. Vertebral osteonecrosis associated with the use of intradiscal electrothermal therapy. A case report. Spine 2002; 27: E325–E328. 12. Eckel TS, Ortiz AO. Intradiscal electrothermal therapy in the treatment of discogenic low back pain. Tech Vasc Itervent Radiol 2002; 5: 217–222. 13. Freedman BA, Cohen SP, Kuklo TR, et al. Intradiscal electrothermal therapy (IDET) for chronic low back pain in active-duty soldiers: 2-year follow-up. Spine J 2003; 3: 502–509. 14. Freeman BJC, Fraser RD, Cain CMJ, et al. A randomised double blind controlled trial: intra-discal electrothermal therapy versus placebo for the treatment of chronic discogenic low back pain. Spine 2005; 30: 2369–2377. 15. Gerszten PC, Welch WC, McGrath PM, et al. A prospective outcomes study of patients undergoing intradiscal electrothermy (IDET) for chronic low back pain. Pain Physician 2002; 5: 360–364. 16. Hsia AW, Isaac K, Katz JS. Cauda equina syndrome from intradiscal electrothermal therapy. Neurology 2000; 55: 320. 17. Karasek M, Bogduk N. Twelve-month follow-up of a controlled trial of intradiscal thermal anuloplasty for back pain due to internal disruption. Spine 2000; 25: 2601–2607. 18. Lee MS, Cooper G, Lutz GE, et al. Intradiscal electrothermal therapy (IDET) for treatment of chronic lumbar discogenic pain: a minimum 2-year clinical outcome study. Pain Physician 2003; 6: 443–448.

19. Lutz C, Lutz GE, Cooke PM. Treatment of chronic lumbar diskogenic pain with intradiskal electrothermal therapy: a prospective outcome study. Arch Phys Med Rehabil 2003; 84: 23–28. 20. Orr RD, Thomas S. Intradural migration of broken IDET catheter causing a radiculopathy. J Spinal Disord Tech 2005; 18: 185–187. 21. Pauza KJ, Howell S, Dreyfuss P, et al. A randomised, placebo-controlled trial of intradiscal electrothermal therapy for the treatment of discogenic low back pain. Spine J 2004; 4: 27–35. 22. Philips B, Ball, C, Sackett D, et al. The Oxford Centre for Evidence-Based Levels of Evidence. May 2001 www.cebm.net. 23. Saal JS, Saal JA. A novel approach to painful disc derangement: Collagen modulation with a thermal percutaneous navigable catheter. A prospective trial. Presented at NASS 13th Meeting 1998; October, San Francisco. 24. Saal JA, Saal JS. IntraDiscal Electrothermal Therapy (IDET) Training Course Syllabus. Oratec Interventions Inc, Menlo Park, CA, 1999. 25. Saal JS, Saal JA. Management of chronic discogenic low back pain with a thermal intradiscal catheter: a preliminary report. Spine 2000; 25: 382–388. 26. Saal JA, Saal JS. Intradiscal electrothermal treatment for chronic discogenic low back pain. A prospective outcome study with a minimum 1-year follow-up. Spine 2000; 25: 2622–2627. 27. Saal JA, Saal JS. Intradiscal electrothermal treatment for chronic discogenic low back pain. A prospective outcome study with a minimum 2-year follow-up. Spine 2002; 27: 966–973.

28. Scholl BM, Theiss SM, Lopez-Ben R, et al. Vertebral osteonecrosis related to intradiscal electrothermal therapy: a case report. Spine 2003; 28: E161–E164. 29. Smith and Nephew Press Release. Smith and Nephew reaches agreement to acquire Oratec. February 14, 2002 (www.smith-nephew.com/). 30. Smith and Nephew Sustainability report published April 28, 2003 (www.smith-nephew.com/). 31. Spruit M, Jacobs WCH. Pain and function after intradiscal electrothermal treatment (IDET) for symptomatic lumbar disc degeneration. Eur Spine J 2002; 11: 589–593. 32. Webster BS, Verma S, Pransky GS. Outcomes of workers' compensation claimants with low back pain undergoing intradiscal electrothermal therapy. Spine 2004; 29: 435–441. 33. Wetzel FT. Cauda equina syndrome from intradiscal electrothermal therapy. Neurology 2001; 56: 1607.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Non-Surgical Treatment > 9 - Lumbar Spinal Stenosis with Low Back Pain: Is Fusion Necessary?

9 Lumbar Spinal Stenosis with Low Back Pain: Is Fusion Necessary? E. Munting The symptoms provoked by lumbar spinal stenosis (LSS) range from none in up to 21% of the cases (1) to one or several of the following: neurogenic claudication, radicular pain, motor deficit, sensory alterations or deficit, and low back pain (LBP). Although often considered as a satellite or independent symptom not referred to, the latter is significant in up to 75% of the symptomatic cases of LSS. It is generally agreed that the surgical decompression of the compromised neural structures is the adequate treatment if conservative methods have failed. Surgical decompression will cure or relieve peripheral symptoms and improve walking capacity in 60% to 90% of the cases (9). The therapeutical attitude regarding LBP remains a subject of controversy. Indications for fusion, with or without instrumentation, or stabilization by some nonrigid means, are still not well defined. Major instability demonstrated on dynamic radiographs, iatrogenic instability induced by facetectomy or discectomy, as well as degenerative spondylolisthesis are admitted indications for fusion. The presence of LBP, disc degeneration, stable spondylolisthesis, and degenerative scoliosis are further situations that may lead the surgeon to consider arthrodesis or some type of stabilization method. The incidence of fixation associated with decompression is variable in the literature, but this is probably related in part to the variety of decom-pressive procedures that

may induce more or less instability. Several studies have shown that only 70% of the patients with aspecific LBP are improved after fusion and even that a few percent are aggravated by this procedure. Whether aspecific LBP is the same pathologic entity as the LBP associated with LSS remains to be demonstrated, but the clinical presentation is quite similar. Moreover, these inconstant results of fusion must be discussed in view of the demonstrated increase of morbidity associated with spinal instrumentation (2) as well as the advent of a series of contraindications for stabilization often arising in the older patients presenting with LSS: poor general health, osteo-porosis, obesity, multilevel hypermobility, and risk factors for infection (diabetes and cortisone therapy) (2,3). For each patient with spinal stenosis, several questions must be answered when surgical treatment is chosen: What type and extent of decompression? Is some type of fixation needed or not? Is back pain as a symptom an argument for fixation? Finally, we still do not know, when there is no demonstrated major and focal instability or progressive deformity, whether stabilization increases the frequency of favorable outcome and improves the quality of outcome, versus selective decompression alone. Also, it is not clearly demonstrated whether the type of decompression procedure—partial laminotomy sparing the spinous processes and the supraspinous ligament with reinsertion of the P.88 spinous ligament versus laminectomy—has an influence on pre-existing LBP or prevents postoperative instability and LBP (5,7,8). Our interrogations can be summarized as follows: Is partial laminotomy as efficient as laminectomy for decompression in LSS? Does it reduce the need for stabilization and thus the costs and complications related to fixation? Is selective decompression alone capable to cure or significantly improve LBP with a similar frequency as fusion? In an effort to bring an answer to these questions, we assessed the outcome of LBP in patients with LSS after decompression by minimal laminotomy, sparing the facet

joints, the spinous processes, and the supraspinous ligaments. In this group of patients, stabilization was only carried out when major instability was demonstrated intraoperatively.

Methods One hundred thirty-six patients operated for LSS with a minimum 1-year follow-up were reviewed. Patients were assessed pre- and postoperatively either by Dallas questionnaire or by grading their LBP as severe, significant, minor, or absent. The same was asked for leg/buttock pain and walking capacity. The decompression procedure is carried out by partial and selective laminotomy, also called “calibration.― It involves flavoligamentectomy, resection of the cranial third of the lamina, undercutting of the caudal part of the lamina, the facet joints, and the neuroforamina as needed, according to the preoperative magnetic resonance imaging (MRI) and/or computed tomography (CT) scan. This is carried out with a high-speed drill, oblique and curved Kerisson-like rongeurs, and little chisels. Discectomy and/or disc osteophytes resections is carried out in case of protrusion, if the canal calibration is not sufficient to decompress the neural structures. The caudal half of the lamina, the spinous processes, and the supraspinous ligament are preserved. Fixation is decided intraoperatively, only if major instability is demonstrated by means of an opening about the facet joints or anteroposterior translation superior to 5 mm between two adjacent vertebra manipulated through the spinous processes with two strong forceps. After decompression, the lumbar fascia is carefully reattached to the spinous process and the supraspinous ligament. The patient is encouraged to walk the day after surgery. No brace is prescribed.

Results A grade 1 degenerative spondylolisthesis was observed in 40 of these patients. This observation did not lead per se to fixation: This was done only if abnormal mobility was demonstrated between the two vertebral segments. No abnormal mobility was demonstrated during surgery in 30 of these patients, so only 10 had an instrumented arthrodesis. In the whole group, laminotomy was associated with some type of stabi-lization in 18 of the 136 cases (13%): instrumented arthrodesis

(11 cases: 8%) or Dynesis (7 cases: 5%). P.89 Five laminotomy cases were lost to follow-up. Overall results were good or excellent in 84 (74%) of isolated laminotomies, in 11 of 11 laminotomies with arthrodesis, and in 2 of 7 laminotomies with Dynesis. Out of 113 patients presenting with severe or significant LBP preoperatively and undergoing only laminotomy, 74% were significantly improved regarding LBP. Seven patients had to be reoperated for some reason, one because of symptomatic instability requiring instrumented fusion and one because of loosening of a Dynesis system. Radicular symptoms resolved or were significantly improved in 87% and walking distance was increased in 90% of the patients. Incidental durotomy had no adverse effect except in one case in which a revision was needed for dural tear repair.

Discussion Our results show that in patients with LSS, severe LBP can be significantly improved by decompression alone in 74% of the cases, as long as severe instability is not demonstrated at the time of surgery. The latter must be addressed by some type of stabi-lization. In our study, instrumented arthrodesis seems to be more efficient than semirigid fixation by means of a Dynesis system without arthrodesis. Obviously, LBP can be cured or significantly improved by decompression without fusion or stabilization in patients with LSS. Given these results, we think that LBP associated with LSS should be considered as a distinct pathologic entity in which, a priori, the treatment should be selective decompression and not arthrodesis when no instability is demonstrated preoperatively. The decision making during surgery regarding the performance of an arthrodesis is important: Although there are cases in which the instability is clearly demonstrated before surgery, instability, either iatrogenic or intrinsic to the patient, is sometimes discovered during surgery. In the same way, some patients with grade one or even grade two degenerative spondylolisthesis have almost no mobility about the considered level. In these cases we do not fuse that level, except if the level above, without spondylolisthesis, is unstable. The testing for stability during surgery is an objective observation that allows making the right decision on a mechanical standpoint. Our results clearly show that fixation and

fusion in the presence of obvious and intraoperatively demonstrated instability is very effective for curing LBP (11 out of 11 cases in this study). So-called dynamic stabilization without fusion seems far less effective, with one case of screw loosening within 7 months needing revision (only hardware removal and no fusion: good results at 2 years), four poor results, and only two good outcomes. However, the numbers are too small to allow for statistically valid conclusions. According to the results published in the literature about the outcome of LBP after fusion, it is not very likely that our results regarding LBP after decompression alone would have been significantly improved by associating a fusion. By avoiding fusion and instrumentation in this high-risk group of patients, we have certainly prevented the complications related to it as well as the high costs that are involved with instrumentation. In LSS, Grob at al. (5) found no difference in outcome of decompression with or without arthrodesis in the absence of obvious instability. They did not, however, refer specifically to the outcome of LBP in their study. The need for fusion in case of spondylolisthesis is advocated by several authors (4,6), but it seems that for most authors spondylolisthesis is synonymous with instability. This is not our impression according to intraoperative assessment of instability. P.90 The reasons for the favorable effect on LBP in LSS of decompression alone, in a percentage of cases quite similar to the frequency of satisfactory outcome of fusion for LBP, are probably multiple. Minimal laminotomy sparing the spinous processes and the supraspinous ligament obviously allows fixation of the paraspinal muscles and lumbar fascia to the vertebrae. The healing process and the unavoidable fibrosis associated with it provides a very strong and “dynamic― stabilization means that may partially explain the high frequency of significant improvement of LBP in patients undergoing only laminotomy without stabilization. The avoidance of direct adhesion of the muscles to the dural sac—as observed in classic laminectomy—is also theoretically favorable. The decompression of the nerve roots can also contribute to cure the LBP. Finally, the denervation of the facet joints and the release of interspinous conflicts may also contribute to pain relief.

Conclusions

Partial and selective laminotomies are an effective means of decompression in LSS. In the absence of obvious, intraoperatively demonstrated instability, this procedure alone allows significant improvement of the LBP that 75% of the patients presented before surgery. In case of significant instability, instrumented fusion limited to the involved levels, independent of further degenerative modifications seen on imaging, is very effective in curing LBP.

REFERENCES 1. Boden S, Davies DO, Dina TS et al. (1990) Abnormal magnetic resonance imaging of the lumbar spine in asymptomatic subjects. A positive investigation. J Bone Joint Surg Am 72: 404–408. 2. Ciol MA, Deyo RA, Howell E et al. (1996) An assessment of surgery for spinal stenosis: time trends, geographic variations, compli-cations and re-operations. J Am Geriatr Soc 44: 285–290. 3. Deyo RA, Cherkin DC, Loeser JD et al. (1992) Morbidity and mortality in association with operations on the lumbar spine: the influence of age, diagnosis and procedure. J Bone Joint Surg Am 74: 536–543. 4. Frazier DD, Lipson SJ, Fossel AH, Katz JN. (1997) Associations between spinal deformity and outcomes after decompression for spinal stenosis. Spine 22: 2025–2029. 5. Grob D, Humke T, Dvorak J. (1995) Degen-erative lumbar spinal stenosis. Decompression with and without arthrodesis. J Bone Joint Surg Am 77: 1036–1041. 6. Katz JN, Lipson SJ, Lew RA. (1997) Lumbar laminectomy alone or with instrumented or non-instrumented arthrodesis in degenerative lumbar spinal stenosis: patient selection, cost and surgical outcomes. Spine 22: 1123–1131.

7. Postacchini F, Cinotti G, Perugia D, Gumina S. (1993) Multiple laminotomy compared with total laminectomy. J Bone Joint Surg Br 75: 386–392. 8. Spivak JM. (1998) Current concept review. Degenerative lumbar spinal stenosis. J Bone Joint Surg Am 80: 1053–1066. 9. Turner JA, Ersek M, Herron L, Deyo RA. (1992) Surgery for lumbar stenosis: attempted meta-analysis of the literature. Spine 17: 1–8.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Surgical Non-Fusion Techniques Lumbar: Basics > 10 - Indication and Contraindication for Lumbar Surgical Nonfusion Techniques

10 Indication and Contraindication for Lumbar Surgical Nonfusion Techniques Jeremy Fairbank Treatment by spinal fusion is based on a concept of pain generated from a single site or segment of the lumbar spine. Indications for nonfusion techniques seem similar. There are four groups of patients with chronic low back pain (LBP) who may be considered for surgical treatment: Young people with spondylolysis/spondylolisthesis Middle-aged people with spondylolysis/spondylolisthesis Middle-aged people with chronic LBP Older people with degenerative spondylolisthesis (usually L4-5) This chapter considers the third group. Until recently spinal fusion by various means has been the standard surgical therapy. The evidence for efficacy has been largely observational. These studies have been the subject of various reviews.

Results of Spinal Fusion Spinal fusion has been shown to be effective in patients with lytic spondylolisthesis (16

,17 ) and in trauma, scoliosis, infection, or tumor (24 ). Instability is difficult to demonstrate in a condition in which similar changes are seen in asymptomatic individuals. The cause or causes of LBP remain unknown, involving interrelating physical, psychological, social, and occupational factors (11 ). A Cochrane review has reported little evidence of efficacy for spinal fusion, with a complete absence of randomized controlled trials (10 ), but four randomized trials of spinal fusion versus nonoperative care have been reported subsequently (1 ,5 ,8 ,16 ,17 ). Möller and Hedlund (16 ,17 ) reported a trial in isthmic spondylolisthesis, with 77 patients randomized to different forms of surgery and 34 patients randomized to an exercise program. The patients allocated to surgery appeared to do better than those allocated to exercise, but instrumentation and bone grafting was not found to produce an advantage over bone grafting alone. The Swedish trial compared three different surgical regimes with “physiotherapy,― which was essentially “usual medical care― (8 ). They randomized 222 patients to surgery and 72 to “physiotherapy― (8 ), with the surgery group randomized between three operative groups of equal size. Disability and other measures were significantly better in the surgical P.92 compared with the nonsurgical group, but no difference in these outcomes was seen between the different surgical techniques. These authors have later claimed that at least some of the patients were in an intensive physiotherapy program, although this was not in the protocol. Meantime in Norway another trial compared posterolateral fusion with instru-mentation with intensive rehabilitation. Sixty-four patients were compared with instrumented posterior fusion and a rehabilitation program followed to 12 months. They found a similar treatment effect in both groups. One surgery technique was used (posterolateral fusion with instrumentation), and all the rehabilitation patients attended the same program. The numbers were small, but the circumstances were well controlled (1 ). No advantage to surgery was demonstrated. Another trial in the United Kingdom, with the type of operation open to surgeons' choice of optimal method, again showed no advantage to surgery over an intensive rehabilitation program. The UK study was a multicenter randomized trial of 349 patients aged 18 to 55 years with chronic LBP of at least 1-year duration considered candidates for spinal fusion. They were randomized to a surgical group for spinal fusion of the lumbar spine (of the surgeons' choice, 98% instrumented) or a 3-week intensive rehabilitation program based

on cognitive behavioral principles. The surgical group was statistically better (by only 4.5 Oswestry points) than the rehabilitation group at 2 years (28% of the rehab group later had surgery, when the authors expected at least 50% to do this). The economic analysis showed the surgical arm to be twice as expensive as the rehabilitation arm (5 ,21 ). There are many ramifications to this issue including choice of patient and the skills and experience of the surgeon, but the bottom line is that intensive rehabilitation is a powerful method for treating back pain, with few complications, and surgery has little better results with more complications. Other investigators have shown that instrumentation increased the fusion rate (7 ,8 ,24 ); it is more expensive because of implant costs, duration of operation, and, in some studies, complications (24 ). Lumbar fusions have higher complication rates than other forms of spine surgery (13 ). Observational data may suggest that pseudoarthrosis (failure of fusion) may have a bad effect on outcome, but this was not confirmed in a randomized controlled trial (RCT) of two fusion techniques (22 ). All these trials have been criticized for poor patient selection, but there is little basis for this criticism. The treatment effect in the surgery arm was similar in all three trials (about 12–15 Oswestry points).

Indications for Nonfusion Surgery Nonfusion surgery covers various types of flexible fixation and disc replacement. These are covered in detail elsewhere in this book. The published indications for surgery are not totally consistent. The following are quotations from four sources concerning disc replacement: “Intervertebral disc replacement may be indicated for patients with degenerative disc disease at one or two levels of the spine. Patients may be candidates for one or both of the Investigational Trials on Intervertebral Disc Replacement in the United States if they have the following conditions: P.93 1. Degenerative disc disease in one or two adjacent vertebral levels between L3 and S1

2. Age between 18 and 60 3. Failed at least 6 months of conservative therapy― --(Bradford) http://www.spineuniverse.com/displayarticle.php/article1682.html “The indications for disc replacement may vary for each type of implant. Some general indications are pain arising from the disc that has not been adequately reduced with non-operative care such as medication, injections, chiropractic care and/or physical therapy. Typically, you will have had an MRI that shows disc degeneration. Often discography is performed to verify which disc(s), if any, is related to your pain. (Discography is a procedure in which dye is injected into the disc and X-rays and a CT scan are taken. See the NASS Patient Education brochure on Discography for more information.) The surgeon will correlate the results of these tests with findings from your history and physical examination to help determine the source of your pain. There are several conditions that may prevent you from receiving a disc replacement. These include spondylolisthesis (the slipping of one vertebral body across a lower one), osteoporosis, vertebral body fracture, allergy to the materials in the device, spinal tumor, spinal infection, morbid obesity, significant changes of the facet joints (joints in the back portion of the spine), pregnancy, chronic steroid use or autoimmune problems. Also, total disc replacements are designed to be implanted from an anterior approach (through the abdomen). You may be excluded from receiving an artificial disc if you previously had abdominal surgery or if the condition of the blood vessels in front of your spine increases the risk of significant injury during this type of spinal surgery.― --North American Spine Society “The overall indications for a CHARITÉ Artificial Disc are similar to that for an anterior lumbar interbody fusion (ALIF) using

BAK interbody cages. Currently, the CHARITÉ Artificial Disc is only available for use for one-level disc replacement, so it is not indicated for patients with symptomatic multi-level disc disease.― --(Spine health.com) “Potential candidates for artificial disc replacement have chronic low back pain attributed to degenerative disc disease, lack of improvement with non-operative treatment, and none of the contraindications for the procedure, which include multilevel disease, spinal stenosis or spondylolisthesis, scoliosis, previous major spine surgery, neurologic symptoms and other minor contraindications. These contraindications make artificial disc replacement suitable for a subset of patients in which fusion is indicated. Patients who require procedures in addition to fusion, such as laminectomy and/or decompression are not candidates for the Charité disc.― --(www.regence.com) It seems to me that these are close to the indications given for spinal fusion. Proponents of disc replacement believe changes in the posterior joints are contraindications for this procedure. It is unclear how these are detected in early stages, especially as these are probable accompaniments of disc degeneration in the majority of cases. So far only the Federal Drug Administration randomized controlled trial (FDA RCT) of the Charité disc replacement have been published. The Prodisc trial has yet to be reported in full although some centers have published their results (in my view, P.94 quite inappropriately). The FDA uses a 2:1 randomization model for which there seems no justification statistically. The trial is against anterior interbody fusion, which is the technique with the highest complication rate according to the Swedish study, all of which gives disc replacement the highest chance of showing up well. I believe spine surgeons should expect nonfusion surgery to show an important advantage over intensive rehabilitation in a randomized trial before it is adopted. Such a trial is

being conducted in Norway by Brox's group.

Cartesian Pain: Is the Disc a Pain Generator? The recommended indication for fusion and disc replacement is “discogenic pain.― It is worth questioning this concept, as it is not easy to establish that disc degeneration (or degenerative disc disease, as some prefer) is actually a cause of back pain.

Epidemiology Epidemiologic methods have had difficulty establishing this. van Tulder et al. reviewed the evidence in 1997. They found that disc degeneration was associated with nonspecific LBP, but odds ratios were low, ranging from 1.2 to 3.3.

Cadeveric Material In a cadaveric study, Videman and Nurminen (2004) found a relationship between lifetime back pain history and the occurrence of annular tears using barium sulphate discography. Annular degeneration occurred earlier than previously thought. They found the frequency of back pain had a highly significant relation to the occurrence of tears (model-based p = 0.0009).

Occupational The effect of occupational loading was of borderline significance (p = 0.045) (25 ).

MRI Studies Kjaer et al. (14 ) studied 412, 40-year-old individuals with magnetic resonance (MR) and found that hypointense disc signals reduced disc height, and Modic changes were significantly positively associated with LBP. The strongest association was with Modic changes and anterolisthesis (odds ratio 4.0). It is important not to forget that all these MR changes can be seen in asymptomatic individuals as well. Rajasekaran (personal communication) has extended his MR diffusion studies (20 ) to adolescent and young adult scoliotics. These show dramatic changes of disc degeneration in the intervertebral discs, although it is well known that back pain in this population is unusual.

Plain X-Rays

Flexion-extension films have been advocated by Frymoyer and Selby (9 ) as a method of defining levels for fusion, but it is hard to find any evidence for this method beyond anecdote. P.95

Discography and Dr. Carragee Discography has always been controversial, and I do not propose to examine this issue in detail. Disc replacers have usually advocated its use. I quote a study by Eugene Carragee looking at the predictive power of discography in “best bet― patients. His study is important and not published at the time of this writing, so I present his material in some detail. Dr. Carragee's argument runs as follows: If you believe the disc is a pain generator, then this means excising the disc and then either fusing it or replacing it. He notes that most fusion studies show low rates of “really good― (or “excellent―) results. For example: 10% of 360-degree fusion patients meet expectations (23 )! 7% of workmans' compensation patients having fusion meet “good― criteria of Stauffer Coventry (4 ). 14% of the surgical group in RCT have high grade outcomes (little better than cognitive behavioral therapy (1 ,5 ). 12% of discography patients have high grade outcome with fusion (personal communication to Dr. Carragee). Dr. Carragee goes on to present the “alibis― given by various parties when discography patients are not much better after solid fusion: The surgeon's alibi—Diagnosis is right, but then next level is bad Discographer's alibi—Diagnosis is right, but the surgery is too morbid The pain doctor's alibi—Diagnosis is right, but patient selection was bad

He argues that a “gold standard― of excellent clinical outcome is the one we should use and that the discography issue can never be addressed without a gold standard and that only a gold standard can stop the alibis and address best-case specificity. This accounts for failure related to patient selection (the pain doctor's alibi), failure related to operative morbidity (the discographer's alibi), and failure related to new structural pain (the surgeon's alibi). Carragee designed a study to explore the specificity of discography by looking at a series of ideal patients (Carragee, personal communication). His hypothesis was that if both a discogram positive group and a spondylolisthesis group are correctly diagnosed as having a single-segment “pain generator― and that both groups have equal patient selection and surgical risks and no adjacent segment disease, then the surgical outcomes should be the same. If the outcomes are different, then the difference will equal the false-positive rate. His inclusions were as follows: Single-level positive discography with full reproduction of symptoms No detectable adjacent level disease, confirmed by discography No evidence of comorbidities His exclusions were as follows: 24-months' duration of current episode Not working prior to the latest episode of back pain P.96 Abnormal DRAM (26 ) More than one abnormal segment No workmans' compensation/no litigation No other history of chronic pain history His control group was a group of ideal patients with single-segment pain generator, and

he chose unstable spondylolisthesis with >4 mm displacement and/or >22-degree kyphosis. He did an identical operation on all the patients, which was a 360-degree fusion via a minilaparotomy approach. He believed that this would exclude any alibis by excising the pain generator, having a precise diagnosis, and excluding risk factors for a poor result. It took him 5 years to find patients for his study, reflecting how unusual it is to find these subjects, even in a busy practice. There were 30 single-level “discography― + DDD patients and 32 unstable isthmic spondylolisthesis patients. His outcome measures were visual analogue scale (VAS; for back pain), Oswestry Disability Index (ODI), and medication usage. These were equivalent at baseline. Work loss, smoking, and duration of symptoms were also recorded. The outcome criteria were set at the start of study for an “excellent result.― These included VAS•2, ODI•15, no daily treatment needed, no consumption of narcotics, and a full return to work. He also defined criteria for “minimally acceptable― improvement. He suggests that difference in outcomes between the groups would be attributable to a diagnostic failure to identify a true “single segment― pain generator as cause of the patient's chronic LBP illness. The results show that 70% of the spondylolisthesis patients had an excellent result (he says “cured―), compared with only 25% of the back pain patients, a “falsepositive rate― for discography of 45%. Eighty-nine percent of the spondylolisthesis patients met the minimum standard compared with only 42% of the back pain patients, interpreted as a 47% false-positive rate for discography. The take-home message from this study is that surgeons are not good at selecting patients for back pain, even though some patients will do well with this procedure. It is up to the promoters of nonfusion techniques to show that they can do better than these results.

Non-Cartesian Pain The Cartesian model of pain goes back to Descartes. The famous drawing of a boy with his foot in the fire illustrates a simple pain pathway up the brain (actually it is the pineal gland that Descartes believed was the seat of the soul). Modern research on pain has shown that chronic pain can be influenced on all stages on the way to the brain,

particularly in the dorsal horn of the spinal cord. However, this concept is still based on a Cartesian model. An alternative model for chronic pain is hypothesized by Harris (12 ). He suggests that “distress― occurs in the central nervous system when there is a perceptual mismatch of expected and actual feedback to the brain. Distress means unpleasant sensations. In this context, the brain may be considered a “control freak― wanting everything to be “just so.― The brain does not like it when, through P.97 damage or environment, there are perceptual mismatches. There are a number of examples of this: Phantom limb pain. This is a well-known phenomenon that is difficult to explain using any Cartesian model. This explanation suggests it is due to a visual/sensory mismatch. Motion sickness. This is well-known to all of us. Harris's hypothesis suggests it is due to a vestibular/visual mismatch. Unilateral sensory neural deafness leads to a mismatch of auditory input from each ear. This leads to tinnitus often related to noise level. The tinnitus experience by those with poor hearing may be explicable in the same way, although many of these individuals suffer at rest even in a silent environment. Complex visual hallucinations occur in the visually impaired. This was first recognized more than 200 years ago by Charles Bonnet. So what does this have to do with back pain? The suggestion is that back pain is due to proprioceptive mismatches. There is abundant evidence of muscle dysfunction in back pain patients (2 ,3 ,6 ,15 ,18 ,19 ). One of these examples comes from Yale where Radebold et al. used a “wobbly― chair to test the capacity of subjects to keep it stable. Back pain patients were less good than controls at doing this. Harris uses the term cortical pain to explain this phenomenon. He suggests that chronic LBP can occur when proprioceptive input and expected activity do not match. I suggest that this can occur when there is:

Segmental dysfunction (disc degeneration, instability) Poor muscle control Disturbance of normal proprioception It is likely that psychological factors can influence the perception of this pain, and this hypothesis does not exclude any existing concept of chronic pain (e.g., bio-psychosocial, biomechanical, muscular). It also allows for discogenic pain and segmental “instability.― This concept fits clinical experience, particularly unexplained daily variations of symptoms. The thinking “outside the box― makes it attractive. So far I have not found any convincing evidence to refute the cortical pain hypothesis, and it provides an explanation for non-Cartesian pain. I have found it convenient to explain chronic pain to patients, particularly those of a mechanistic turn of mind. It provides an argument against the concept of excising a pain generator and why fusions do not always work. I believe this idea opens research into methods for restoring normal proprioception and may clarify when motion segment restoration may help symptoms.

Conclusions To my understanding, clear indications for disc replacement have not been agreed on. I suggest that they are not so different from those for spinal fusion (which are also not so well agreed on). P.98 Disc replacement is a major operation with potential immediate serious acute complications (major hemorrhage, sexual problems, acute infection and chronic infection, implant failure, and revision procedures among others). Surgical treatment of back pain depends on a Cartesian concept of a pain generator in the disc. This is not always demonstrated. Discography gives confusing results. Disc degeneration is largely genetically driven and its association with back pain is assumed but by no means proven. Investigators should consider alternative hypotheses of back pain, particularly

cortical pain as proposed by Harris. It is possible that when disc replacement works it does so by normalizing proprioception rather than by removing a pain source. It is clear that surgeons are not very good at identifying the best patients for surgery. Alternatively disc replacement should have a much lower morbidity than it currently has. If open disc replacement is going to be the way to go, then many surgeons are poorly equipped for this type of surgery. There is a serious risk that disc replacement may, because of a high complication rate, go the same way as chymopapain for disc prolapse (especially in young people), for which there was a much more solid body of evidence in favor of the technique.

REFERENCES 1. Brox J, Sørensen R, Friis A, et al. Randomized clinical trial of lumbar instrumented fusion and cognitive intervention and exercises in patients with chronic low back pain and disc degeneration. Spine 2003; 28: 1913–1921. 2. Brumagne P, Cordo P, Lysens R, et al. The role of paraspinal muscle spindles in lumbosacral position sense in individuals with and without low back pain. Spine 2000; 25: 989–994. 3. Brumagne S, Cordo P, Verschueren S. Proprioceptive weighting changes in persons with low back pain and elderly persons during upright standing. Neurosci Lett 2004; 366: 63–66. 4. DeBerard M, Masters K, Colledge A, et al. Outcomes of posterolateral lumbar fusion in Utah patients receiving workers' compensation: a retrospective cohort study. Spine 2001; 26: 738–746.

5. Fairbank J, Frost H, Wilson-MacDonald J, et al. Randomised controlled trial to compare surgical stabilisation of the lumbar spine with an intensive rehabilitation programme for patients with chronic low back pain: the MRC spine stabilisation trial. BMJ 2005; 330: 1233–1239. 6. Fairbank J, O'Brien J, Davis P. Intra-abdominal pressure rise during lifting as an objective measure of chronic low back pain. Spine 1980; 5: 179–184. 7. Fischgrund J, Mackay M, Herkowitz H, et al. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective randomized study comparing decompressive laminectomy and arthrodesis with or without spinal instrumentation. Spine 1997; 22: 2807–2812. 8. Fritzell P, Hagg O, Wessburg P, et al. Chronic back pain and fusion: a comparison of three surgical techniques: a prospective multicentre randomized study from the Swedish Lumbar Spine Study Group. Spine 2002; 27: 1131–1141. 9. Frymoyer J, Selby D. Segmental instability. Rationale for treatment. Spine 1985; 10: 280–286. 10. Gibson J, Grant I, Waddell G. The Cochrane review of surgery for lumbar disc prolapse and degenerative lumbar spondylosis. Spine 1999; 24: 1820–1832. 11. Guzman J, Esmail R, Karjalainen K, et al. Multidisciplinary rehabilitation for chronic low back pain: systematic review. BMJ 2001; 322: 1511–1516. 12. Harris A. Hypothesis: cortical origin of patho-logical pain. Lancet 1999; 354: 1464–1466. 13. Hu R, Jaglal S, Axcell T, et al. A population-based study of reoperations after back surgery. Spine 1997; 22:2265–2270.

P.99 14. Kjaer P, Leboeuf-Yde C, Korsholm L, et al. Magnetic resonance imaging and low back pain in adults: diagnostic imaging study of 40-year-Ood men and women. Spine 2005; 30: 1173–1180. 15. Mientjes M, Frank J. Balance in chronic low back pain patients compared to healthy people under various conditions in upright standing. Clin Biomech 1999; 14: 710–716. 16. Möller H, Hedlund R. Instrumented and non-instrumented posterolateral fusion in adult isthmic spondylolisthesis. A prospective randomized study Part II. Spine 2000; 25: 1716–1721. 17. Möller H, Hedlund R. Surgery versus conservative treatment in adult isthmic spondylolisthesis. A prospective randomized study Part 1. Spine 2000; 25: 1171–1177. 18. Radebold A, Cholewicki J, Panjabi M, et al. Muscle response pattern to sudden trunk loading in healthy individuals and in patients with chronic low back pain. Spine 2000; 25: 947–954. 19. Radebold A, Cholewicki J, Polzhofer G, et al. Impaired postural control of the lumbar spine is associated with delayed muscle response times in patients with chronic idiopathic low back pain. Spine 2001; 26: 724–730. 20. Rajasekaran S, Babu J, Arun R, et al. ISSLS Prize Winner: a study of diffusion in human lumbar discs: a serial magnetic resonance imaging study documenting the influence of the endplate on diffusion in normal and degenerate discs. Spine 2004; 29: 2654–2667. 21. Riviero-Arias O, Campbell H, Gray A, et al. Surgical stabilisation of the lumbar spine compared with a programme of intensive rehabilitation for the management of

patients with chronic low back pain: cost utility analysis based on a randomised controlled trial. BMJ 2005; 330: 1239–1243. 22. Sasso R, Kitchel S, Dawson E. A prospective, randomized controlled clinical trial of anterior lumbar interbody fusion using a titanium cylin-drical threaded fusion device. Spine 2004; 29: 113–122. 23. Slosar P. Indications and outcomes of reconstructive surgery in chronic pain of spinal origin. Spine 2002; 27: 2555–2562. 24. Thomsen K, Christensen F, Eiskjaer S, et al. The effect of pedicle screw instrumentation on functional outcome and fusion rates in posterolateral lumbar spinal fusion: a prospective, randomized clinical study. Spine 1997; 22: 2813–2822. 25. Videman T, Nurminen M. The occurrence of anular tears and their relation to lifetime back pain history: a cadaveric study using barium sulfate discography. Spine 2004; 29: 2668–2676. 26. Main CJ, Wood PLR, Hollis S, et al. The distress and risk assessment method: a simple patient classification to identify distress and evaluate the risk of poor outcome. Spine 1992; 17: 42–52.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Surgical Non-Fusion Techniques Lumbar: Basics > 11 - Lumbar Surgical Approaches for Nonfusion Techniques

11 Lumbar Surgical Approaches for Nonfusion Techniques Marco Brayda-Bruno Franco Gobetti Alessio Lovi Marco Teli A nonfusion option in low back pain (LBP) surgery has become more and more popular as an alternative strategy to fusion in the treatment of patients with disc-related pain unresponsive to nonoperative care. Although still in the early phases of development after some pioneer devices, the future in this field is promising and the motionpreservation techniques will become part of the spine surgeon's armamen-tarium, especially with the introduction of new materials and new implants designs. Lumbar disc or nucleus prosthesis and posterior lumbar “dynamic― instrumentations were introduced in the last 10 to 15 years, showing promising results in short- and midterm outcomes, which must be confirmed in long-term follow-up studies. One of the most important aspects in this “functional― surgery is to preserve as much of the anatomic structures as possible (muscles, fascia, ligaments, and joints) during the surgical exposure. Using less invasive surgical approaches to the spine, it is possible to adequately expose the desired anatomic structures while minimizing the disadvantages of excessive soft

tissue stripping, dissection, and prolonged retraction. Several studies have demonstrated that prolonged soft tissue retraction generates a greater force per unit area on the retracted tissues, resulting in an increased regional ischemia, leading to paraspinal electromyogram abnormalities and decreased muscle density. Muscle weakness and denervation could be critical consequences resulting in potentially long-term adverse side effects, such as chronic pain and muscular dysfunction. This can then be prevented by minimizing the traditional approaches (anterior or posterior) to the lumbar spine using new retractors, video-assisted techniques, and/or navigation. On the other side, one of the most important drawbacks to minimally invasive surgery entails the long learning curve necessary to master the various techniques (1 ).

Posterior Approaches Posterior approaches to the lumbar spine for nonfusion techniques are used for interspinous devices (2 ) and for dynamic pedicular screws implants (3 ). Interspinous systems are designed to provide dynamic stabilization to the lumbar spine, creating a tension-bend in the posterior column. These implants control the P.102 extension of the spine, reduce the stress on the facet joint, and maintain foraminal height. This kind of dynamic stabilization is totally reversible without compromising any other future option for revision/salvage surgery (Fig. 11.1 ). Different types of interspinous devices are available (i.e., peek, titanium, silicone).

FIGURE 11.1 Biomechanical behavior of an interspinous device (i.e., DIAM).

For the implantation of an interspinous device, the patient is placed in prone position, generally with some hip flexion. But it is crucial to choose the proper individual patient

position, according to the preoperative lordosis, to allow an easy approach to lumbar canal (when necessary) and the insertion of the correct size of implant, and to prevent any postoperative misalignment of the final segmental lordosis. A midline approach is used: The skin incision is centered over the target lumbar segment(s) to stabilize, using fluoroscopy (generally for a single-level implantation a 4cm skin incision is enough to address the two spinous processes). The multifidus muscle is detached from spinous processes bilaterally, the supraspinous ligament is cut, and the interspinous ligaments are deeply removed unto the ligamentum flavum, avoiding any damage to the bony structure of the spinous processes. For onelevel stabilization, soft tissues retraction can be obtained with a traditional Caspar retractor used in a specific way (Fig. 11.2 ). This technique is common for all interspinous devices (with a longer or shorter skin incision due to the specific characteristics and the ancillary instruments of each different implant). An appropriate size of implant is then inserted into the interspinous space, and if still possible, the supraspinous ligament is sutured.

FIGURE 11.2 Caspar retractor used across the spinous processes.

A soft interspinous device (DIAM Spinal Stabilization System, Medtronic) allows a lateral placement, too, by removing only the interspinous ligament and inserting the implant beneath the preserved supraspinous ligament (Figs. 11.3 , 11.4 , 11.5 ). In case a decompression of neural canal and/or a herniectomy-discectomy are necessary at the same level, they must be of course performed before the insertion of the interspinous device. A dynamic pedicular screws instrumentation (i.e., Dynesys) is designed to stabilize the spine, preserving painless intersegmental kinematics and avoiding fusion in degenerative disease associated with instability (Fig. 11.6 ). These implants can be placed throughout the classical midline approach or the Wiltse paraspinal approach (4 ); the P.103 actual trend in spinal surgery is favorable to the latter, whenever possible, because it is less traumatic than the former in muscular detachment and in blood loss. The Wiltse paraspinal approach allows to expose the posterolateral part of the lumbar pedicles through an intermuscular splitting between the multifidus and the longissimus muscles (Fig. 11.7 ).

FIGURE 11.3 Interspinous retractor for DIAM implantation.

FIGURE 11.4 Insertion of DIAM.

FIGURE 11.5 DIAM fixed between spinal processes.

FIGURE 11.6 Dynamic pedicular screws implants (Dynesys).

Wiltse et al. proposed to make the skin incision approximately 2 cm lateral from the midline and just medial to the posterior-superior iliac spine bilaterally. Similar incisions are made in the fascia at the same distance from the spinal processes. The index finger can then be used as a dissector inside the sacrospinalis above the L4-5 level to reach the lumbar spine. Although Wiltse et al. described the technical details of this approach in 1968, the exact location of trans-sacrospinalis splitting is still unclear. Only recently, Vialle et al. (5 ) described the natural fibrous cleavage between the multifidus and the longissimus muscles (Fig. 11.8 ), which can be located by the perforating P.104 vessels that leave this intermuscular space and are visible at the surface of sacrospinalis muscle. The mean distance between the perforating vessels and the midline is 4.04 cm (2.4–7 cm).

FIGURE 11.7 The natural cleavage plane between the multifidus and the longissimus muscles (arrows ).

Vialle et al. proposed then to open the superficial muscular fascia near the midline and to retract it later-ally to expose the posterior aspect of the sacrospinalis muscle as much as necessary to locate this vascular landmark. The intermuscular dissection through the fibrous cleavage (after vessels cauterization) permits the surgeon to easily reach the posterolateral aspect of the pedicles from L3 to the sacrum (a more careful dissection must be done at the cranial level to avoid damage of the posterior ramus of the L3 root). Foraminotomy or discectomy can be performed through this approach; if a central decompression with laminectomy or laminotomy is necessary, then a midline traditional approach is preferable.

Complications of Posterior Approaches The minimally invasive spinal access for posterior lumbar procedures is becoming more

and more common, but long-term follow-up is required to determine the relative risks and benefits of this approach compared with more traditional open procedures. Complications specifically related to the surgical exposure are rare, because these minimal approaches need much less soft tissue dissection and then morbidity. The major difficulty is the lack of visualization for safe neural decompression and implant placement: This could risk potential stretch neurapraxia or dural violation, which are much more difficult to repair through a minimal access.

Anterior Approaches These approaches are used for total disc replacement. The new generation of implants has been developed to be implanted through minimally invasive anterior retroperitoneal approaches to the lumbar levels L2-3, L3-4, L4-5, and L5-S1.

FIGURE 11.8 The natural fibrous cleavage between the multifidus and the longissimus muscles (dotted line ).

The patient is positioned supine with abducted and semiflexed hips. With the assistance of the C-arm, an accurate identification of the midline is made (it is P.105 crucial to carefully control the patient's position in a true neutral supine position without any lateral tilt). Once the centerline has been found, it is usually helpful to mark the

centerline on the skin, as well as to mark the skin for the lateral projection of the target vertebral bodies by lateral fluoroscopic check (6 ). Anterior minimally invasive retroperitoneal approach to L5-S1 (Fig. 11.9A ): 5 to 6 cm horizontal skin incision, fascia, and rectus abdominis sheath opened (Fig. 11.10 ). Retroperitoneum, approached through Douglas' space (Fig. 11.11 ).

FIGURE 11.9 Anterior retroperitoneal approach to L5-S1 (A) and L4-L5 (B) relative to the bifurcation of the great vessels.

FIGURE 11.10 Opening of the rectus sheath.

FIGURE 11.11 Douglas' space opening.

P.106 Left common iliac/aortic bifurcation mobilized (69% located at L4-5). Middle sacral artery and vein mobilized and ligated (they are below the bifurcation) (Fig. 11.12 ).

FIGURE 11.12 Middle sacral artery and vein ligated.

Blunt dissection and mobilization to the right of the left common iliac artery, also sweeping from left to right the prevertebral tissue (including the superior hypogastric plexus) off the lumbosacral disc (Fig. 11.13 ). Disc approached in the midline (Fig. 11.14 ). Anterior minimally invasive retroperitoneal approach to L4-L5 (Fig. 11.9B ): 5 to 6 cm vertical skin incision, fascia, and rectus abdominis sheath opened (Fig. 11.10 ). Retroperitoneum, approached through Douglas' space (Fig. 11.11 ). Left ileo-lumbar ascending vein ligated (at L4-L5), because this vein is a

horizontal tether, which crosses the body of L5 from right to left and ascends in the left paravertebral space. It acts as a direct tether to prevent retraction of the iliac vein off the spine and is very vulnerable to avulsion. Left common iliac vein mobilization from left to right (Fig. 11.12 ) and selfretractors in place. Disc approached in the midline (Fig. 11.14 ). Currently some TDA implants (i.e., O-MAV, Medtronic) may be correctly placed at L4-5 level by an oblique direction, thus reducing the retraction stress on the vessels because their complete dislocation to the right is no longer necessary.

FIGURE 11.13 Mobilization of left common iliac vein.

FIGURE 11.14 Midline disc approach, discectomy completed.

P.107

Complications of Anterior Approaches Most of the data available from the literature about the complication rate of anterior approaches to the lumbar spine refer to ALIF techniques, but because this access is the same as that used for total disc replacement, the data can be similarly considered in anterior lumbar spine nonfusion surgery. The most common approach-related intraoperative complications are vascular injuries, ureteral tears, and peritoneum violation, whereas the postoperative complications are sympathetic dysfunctions (especially retrograde ejaculation in males), urinary retention, and prolonged ileus. To expose the anterior lumbar spine, a transperitoneal approach can also be used, either open or laparoscopic. However, many comparative papers were published in the last few years, showing a clear superiority of the mini-open retroperitoneal anterior approach. Some homogeneous consecutive series of patients with an open traditional

retroperitoneal access can present a 22% to 38% total rate of intra- and postoperative complications, according to Gumbs et al. (7 ) and Rajaraman et al. (8 ), whereas with a minimally invasive retroperitoneal exposure in a large cohort of patients (684), Kleeman et al. (9 ) showed a very low complication rate of 2.5%. Among the comparative studies, Zdeblick et al. (10 ) evidenced significant lower complications in mini-open ALIF (4%) versus laparoscopic ALIF (20%) without any technical difference. Escobar et al. (11 ) compared four different approaches (two video-assisted and two open) in 135 patients: Their conclusion is that endoscopic approaches are not convenient when compared to open and that the best access is the mini-open retroperitoneal with a lower complication rate: retrograde ejaculation (RE) was present in 8% of males in total, whereas in the mini-open cohort it was 2%. The latter complication is one of the most dangerous postoperative unpredictable problems connected to the anterior access to lumbosacral junction: Sasso et al. (12 ) showed in a prospective study on 146 male patients that the incidence of RE, due to the superior hypogastric sympathetic plexus damage, was 10 times greater in the transperitoneal laparoscopic approach than in the mini-open retroperitoneal one. The advantage of mini-open versus laparoscopic technique is again confirmed by other papers (13 ,14 ,15 ), especially if we consider the difficulty of endoscopic biplanar surgery with a long learning curve and the possibility of at least 10% of open conversion from true endoscopic surgery also in very experienced operative teams.

Conclusion The minimal-access exposure of posterior and anterior lumbar spine has become more popular as newer access tools have been developed and refined, minimizing the morbidity and shortening the learning curve of previous endoscopic surgery. This minimally invasive technique requires adjustable blade retractor systems for anterior and posterior approach and is proving to be a valuable alternative to traditional open procedures. However, its acceptance will be slower in spinal surgery than in other surgical specialties, due to the risks of neural or vascular injury. Gradual conversion to minimal-access procedures is proceeding, and then more outcomes data will become available to determine the value of these mini approaches. P.108

REFERENCES 1. Lehman RA Jr, Vaccaro AR, Bertagnoli R, Kuklo TR. Standard and minimally invasive approaches to the spine. Orthop Clin North Am 2005; 36: 281–292. 2. Christie SD, Song JK, Fessler RG. Dynamic interspinous process technology. Spine 2005; 30: S73–78. 3. Grob D, Benini A, Junge A. Clinical experience with the Dynesys semirigid fixation system for the lumbar spine: surgical and patient-oriented outcome in 50 cases after an average of 2 years. Spine 2005; 30: 324–331. 4. Wiltse LL, Bateman JB, Hutchinson RH, et al. The paraspinal sacrospinalis-splitting approach to the lumbar spine. J Bone Joint Surg 1968; 50-A: 919–926. 5. Vialle R, Wicart P, Drain O, et al. The Wiltse paraspinal approach to the lumbar spine revisited. Clin Orthop Relat Res 2006; 445: 175–180. 6. Le Huec J, Basso Y, Mathews H, et al. The effect of single-level, total disc arthroplasty on sagittal balance parameters: a prospective study. Eur Spine J 2005; 14: 480–486. 7. Gumbs AA, Shah RV, Yue JJ, et al. The open anterior paramedian retroperitoneal approach for spine procedures. Arch Surg 2005; 140: 339–343. 8. Rajaraman V, Vingan R, Roth P, et al. Visceral and vascular complications resulting from anterior lumbar interbody fusion. J Neurosurg 1999; 91: 60–64. 9. Kleeman TJ, Michael Ahn U, Clutterbuck WB, et al. Laparoscopic anterior lumbar interbody fusion at L4-L5: an anatomic evaluation and approach classification. Spine 2002; 27: 1390–1395.

10. Zdeblick TA, David SM. A prospective com-parison of surgical approach for anterior L4-L5 fusion: laparoscopic versus mini anterior lumbar interbody fusion. Spine 2000; 25: 2682–2687. 11. Escobar E, Transfeldt E, Garvey T, et al. Video-assisted versus open anterior lumbar spine fusion surgery: a comparison of four techniques and complications in 135 patients. Spine 2003; 28: 729–732. 12. Sasso RC, Kenneth Burnus J, LeHuec JC. Retrograde ejaculation after anterior lumbar interbody fusion: transperitoneal versus retroperitoneal exposure. Spine 2003; 28: 1023–1026. 13. Dewald CJ, Millikan KW, Hammerberg KW, Doolas A, Dewald RL. An open, minimally invasive approach to the lumbar spine. Am Surg 1999; 65(1): 61–68. 14. Chung SK, Lee SH, Lim SR, et al. Comparative study of laparoscopic L5-S1 fusion versus open mini-ALIF, with a minimum 2-year follow-up. Eur Spine J 2003; 12: 613–617. 15. Regan JJ, Yuan H, McAfee PC. Laparoscopic fusion of the lumbar spine: minimally invasive spine surgery. A prospective multicenter study evaluating open and laparoscopic lumbar fusion. Spine 1999; 24: 402–411.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Lumbar: Nuclear Replacement > 12 - Nucleus Pulposus Replacement: Basic Science and Indications for Clinical Use

12 Nucleus Pulposus Replacement: Basic Science and Indications for Clinical Use Michael A. Pahl Joon Yung Lee Alexander R. Vaccaro Degenerative disc disease affects millions of people within the United States each year. When patients are not responsive to conservative management, surgery rarely may be an option. However, traditional surgical treatment such as an arthrodesis creates a nonphysiologic motion within the spinal axis that may produce greater stresses across the remaining discs as they compensate for the nonmobile motion segment. As a result, the risk for adjacent segment degeneration may increase in up to 35% to 41% of patients who undergo a discectomy and fusion (1,2,3). One solution to this problem may be to treat degenerative disc disease with a more physiologic surgery. An artificial disc prosthesis, such as Charité by DePuy-Acromed (Raynham, MA), attempts to recreate stable intervertebral spinal segment motion by replacing the excised disc with an articulating implant. Several artificial disc prostheses have been used clinically in Europe for many years, and the Charité device has been recently approved by the Food and Drug Administration (FDA) for general use in the United States for single-level degenerative disc disease as of this writing. The designs of the current total disc replacements,

however, mandate similar surgical dissection as the traditional anterior lumbar interbody arthrodesis with complete removal of the intervertebral disc anulus. As minimally invasive procedures become more sophisticated, there have been some technologic advances that may allow less invasive replacement of the diseased disc. This alternative is the nucleus pulposus replacement procedure. The theory behind nucleus pulposus replacement is that the native anulus is left intact, and the diseased nucleus is replaced via more minimally invasive approaches. The technology of delivery of these implants and mechanisms to ensure their stability and positioning are currently in the infant stages, and further testing to validate their theoretical advantages are presently ongoing.

Nucleus Pulposus Anatomy and Biomechanics The nucleus pulposus is a jellylike structure located within the core of the intervertebral disc and is surrounded by the lining of the disc or the anulus fibrosus. The nucleus pulposus consists of a matrix of collagen, proteoglycans, and water. The anulus fibrosus also consists of collagen, proteoglycans, and water; however, the type of collagen is different and the relative proportion of collagen is higher than in the nucleus pulposus. The nucleus pulposus, in turn, has a higher relative proportion of proteo-glycans and water. P.110 The proteoglycans are large extracellular molecules consisting of glycosamino-glycans linked to proteins. The glycosaminoglycans found within the nucleus pulposus include chondroitin 6-sulfate, chondroitin 4-sulfate, keratin sulfate, and hyaluronate (4). Proteoglycans are negatively charged and have the ability to attract and link with water molecules, primarily due to their content of chondroitin 4-sulfate. As the relative proportion of chondroitin 4-sulfate increases, so does the ability to attract and retain water. A disc with high proteoglycan content has the ability to maintain a higher fluid capacity than a disc with lower proteoglycan content. A newborn disc contains high proteoglycan content and has a fluid content that comprises up to 88% of the disc's weight. With aging, the proteoglycan content decreases and the net charge of the extracellular matrix of the nucleus pulposus becomes less negative (5). This leads to a reduction in disc hydration with the fluid content of the disc only accounting for approximately 65% of the disc weight in a 77-year-old (6).

Disc collagen is composed primarily of type I and type II collagen. In the outer anulus fibrosus, collagen accounts for about 70% of the dry weight of the disc, decreasing to around 6% to 25% in the center of the nucleus pulposus (7). The nucleus pulposus is comprised primarily of type II collagen, which is designed to resist compression. The anulus fibrosus is made primarily of type I collagen and is designed to resist tensile forces. However, due to the tensile and compressive forces to which the anulus fibrosus is subjected, it contains a substantial amount of type II collagen as well (8). The proportion of type I collagen decreases from its highest concentration in the periphery of the anulus fibrosus to its lowest concentration next to the nucleus pulposus. Type II collagen concentration is inverse to this with its highest concentration in the center of the nucleus pulposus and decreasing outward toward the periphery of the anulus fibrosus. The collagen in the anulus fibrosus is arranged in sheets, called lamellae, with the fibers arranged in opposite directions to each other at an angle of 120 degrees (9). The blood supply to the disc is limited, as is its ability for regeneration (10). A healthy nucleus pulposus maintains the joint space between adjacent vertebrae and places tension on the anular fibers of the disc, which increases the stability across the disc space. This allows for proper shear force transmission across the disc and compressive force disbursement. Adjacent vertebrae are connected together by the “triple joint complex.― This consists of the intervertebral disc anteriorly and each of the facet joints posteriorly. In the presence of a diseased nucleus pulposus, water content is lost and the disc decreases in size, primarily in height. This causes slackening of the anular fibers as they relax and allows greater shear forces to be transmitted across the disc space, in turn placing greater loads on the facet joints. This can cause changes in the facet articular cartilage biology. The fluidlike nature of the nucleus pulposus also gives it a floating center of rotation and allows for it to shift within the disc in response to forces placed on it (11). During forward flexion, the nucleus pulposus translates dorsally, and during extension, translates ventrally. This allows for great spinal motion segment flexibility while decreasing the loads across the facet joints.

Indications for Nucleus Pulposus Replacements The trend in spinal surgery is to minimize soft tissue dissection and restore physiologic

motion. Replacement of the nucleus pulposus may fulfill these two goals. Nucleus pulposus replacement is primarily indicated for symptomatic lumbar discogenic back pain. As with any surgical intervention, nucleus pulposus replacement is only considered if the patient's complaint of back pain, preferably isolated to a single symptomatic disc P.111 level, is not responsive to conservative treatment for at least 6 months. Consideration for primary replacement of the nucleus of a disc following disc herniation excision in the presence or absence of low back pain is presently under debate. Nucleus pulposus replacement should not be technically performed if disc height loss is greater than 50% of an adjacent normal disc or if there are Schmorl nodes present within the disc's respective endplates (12,13). Nucleus pulposus replacement is best indicated for discs with early degenerative changes on magnetic resonance imaging (MRI), with no more than grade I spondylolisthesis, in the setting of a positive discogram.

Nucleus Pulposus Replacement Design As the disc degenerates, the nucleus pulposus loses its ability to attract and maintain water. This causes the nucleus pulposus to lose its height and allows for loss of tension within the fibers of the anulus fibrosus. Mechanically this may lead to multidirectional increased motion of the spinal interspaces. By replacing the nucleus pulposus, the surgeon hopes to restore tension to the fibers of the anulus fibrosus in tension. Key in the development of a nucleus pulposus replacement is to design a device that can handle repetitive stresses over an extended period of time. A total disc replacement, for example, is designed with materials such as cobalt chromium and high molecular weight plastics, which have a proven track record in other motion preserving procedures such as total joint replacement devices in hips and knee surgery. Kostuik (14) determined that the average implant would experience approximately 100 million loads as a result of strides over the course of 40 years. The implant must also have low wear characteristics and generate minimal particulate matter with use. The particulate matter formed must also have no associated toxicity or carcinogenicity.

Finally, the nucleus pulposus implant should have stiffness similar to that of the native disc. This is to prevent stress shielding, atrophy, and resorption of the underlying vertebral endplate. This can all lead to subsidence of the vertebral endplate with extrusion of the implant into the vertebral body if the implant is too stiff and the loads carried by the implant are greater then the underlying bone (15). There are currently numerous nucleus pulposus replacement designs that are under clinical investigation. Several of these devices use a variety of three-dimensional expanding polymers including hydrogels and elastomers, and others are mechanical and built from pyrocarbons and metallic springs. Several of the polymers are implanted in a semihydrated state through minimally invasive methods and then hydrated once inside the disc to restore the disc space height, whereas others are injected in a liquid state and cure in situ. The mechanical devices are implanted much like a disc replacement, except that they are designed to be anulus fibrosus sparing as they function as a nucleus pulposus replacement.

Nucleus Pulposus Implant Devices Polymer Based Implants Aquarelle (Stryker Spine, Allendale, NJ) This device is a hydrogel pellet. It is composed of a semihydrated polyvinyl alcohol hydrogel. When implanted, it contains approximately 80% water, but its final volume P.112 depends on the water content at equilibrium (Fig. 12.1A). Its swelling pressure is similar to that of the nucleus pulposus in vivo. In biomechanical testing, it has demonstrated durability up to 40 million cycles. It is implanted in a minimally invasive fashion by a pressurized trocar into the disc through a small annulotomy (Fig. 12.1B, C). It can be implanted using either a posterior or lateral approach. Cadaveric studies have demonstrated a high extrusion rate of up to 20% to 33% with devices implanted in a posterolateral and anterior approach, respectively (5). However, further testing has revealed that when fully hydrated, extrusion only occurred when the disc space was placed under loads well beyond what is expected in vivo (16).

FIGURE 12.1 The Aquerelle hydrogel has an in vivo swelling pressure that approximates that of a native disc. Its final volume depends on the water content at equilibrium, but tends to contain approximately 80% water (A). Lateral (B) and anteroposterior (AP) (C) plain radiographs demonstrate the insertion and postoperative positioning in a cadaveric model. (Reprinted with permission from Stryker Spine, Allendale, NJ.)

P.113 The device had been involved in clinical trials in Europe, but at present the manufacturer has placed further development of this product on hold until results of these trials are analyzed.

NeuDisk (Replication Medical Inc., New Brunswick, NJ)

This device is composed of a modified hydrolyzed poly-acrylonitrile polymer called Aquacryl. The polymer is reinforced by a Dacron mesh. It is inserted in a dehydrated state using minimally invasive methods and hydrolyzed in vivo where it absorbs up to 90% of its weight in water (Fig. 12.2A). It is designed to expand primarily in a vertical direction to restore disc height and absorb compressive axial load forces (Fig. 12.2B, C). In vitro biomechanical testing in normal healthy lumbar spines has shown a mean disc space height increase of 1.8 mm (17). It has undergone testing in New Zealand rabbits, which has demonstrated no toxic reactions.

Memory Coiling Spiral (SulzerMedica, Winterthur, Switzerland) This device is composed of a polycarbonate urethane elastomere (Sulene PCU). It is curled in a preformed shape termed a memory-coiling spiral (Fig. 12.3A). It is placed via minimally invasive methods using an instrument that inserts the implant unrolled into the disc following removal of the nucleus pulposus (Fig. 12.3B). As it is being introduced into the disc, it coils automatically to its preformed shape to fill the cavity left by the removal of the nucleus pulposus (Fig. 12.3C). Once the void is filled, a special blade cuts the implant in situ to the correct size (18). This allows the same implant to be used regardless of the void to be filled, fills a greater area within the disc, and requires only a small opening in the anulus fibrosus (19). The device absorbs up to 35% of its weight in water once inside the disc, further filling the cavity and obtaining its stiffness. Once the device is in place, its position can be adjusted using fluoroscopy prior to repairing the anular defect. The unique feature of this device is that it does not function on a fixed axis. This allows it to be implanted without precision, yet still resist compressive forces and allow motion. Its lack of a fixed axis means that it replicates the normal kinematics of a native nucleus pulposus and does not alter the motion segments as much as a fixed device. It has undergone testing that has demonstrated durability up to 50 million cycles without significant wear or microscopic cracks (19). Sheep studies followed by histologic examination have revealed no significant adverse host response to its implantation (20). Cadaver studies were performed comparing motion segments in

intact, post-nucleotomy, and post-nucleus replacement discs (21,22). These showed increased motion and loss of disc height following nucleus pulposus removal with restoration of normal disc biomechanics and disc space height following replacement of the nucleus pulposus using the memory-coiling spiral implant. A human clinical study involving five patients has demonstrated decreased radicular and low back pain complaints following placement, improved Oswestry scores, as well as improved patient satisfaction in all cases (19). Currently, the device is being studied by an international multicenter study looking at long-term performance. P.114

FIGURE 12.2 NeuDisk is an Aquacryl hydrogel reinforced by a Dacron mesh. It is inserted in a dehydrated state and hydrolyzed in vivo where it absorbs up to 90% of its weight in water (A). It is designed to expand primarily in a vertical direction to restore disc height (B). Postoperative anteroposterior (AP) and lateral fluoroscopy (C) demonstrate restoration of disc height following implantation. (Reprinted with permission from Replication Medical, Inc., New Brunswick, NJ.)

P.115

FIGURE 12.3 The Memory Coiling Spiral is composed of a polycarbonate urethane elastomere (Sulene PCU) (A). It is inserted unrolled into the disc (B) where it coils automatically to its preformed shape (C). (Reprinted with permission from SulzerMedica, Winterthur, Switzerland.)

PDN-SOLO (Raymedica, Inc., Bloomington, MN) This device, developed by Dr. Charles Ray, is a hydrogel pellet that is enclosed in a polyethylene jacket (Fig. 12.4A) (23,24). It is currently the most extensively studied nucleus pulposus replacement device. Its hydrogel core is composed of polyacrylamide and polyacrylonitrile. These copolymers have hydrophilic and nonhydrophilic properties. This allows the hydrogel to absorb and release water depending on the load applied, mimicking the native nucleus pulposus. The hydrogel can absorb up to 80% of its weight in water. This allows it to swell and potentially restore the disc space height (Fig. 12.4B, C). The polyethylene jacket is inelastic and restrains the degree of implant expansion and therefore disc space height. The jacket serves to prevent implant overexpansion, which prevents fractures of the vertebral body endplates. Initially, implantation of the PDN device was performed in pairs, allowing for the devices to be placed through a smaller annulotomy. A suture placed in vivo connected the two devices. Due to the occurrence of implant migration and the technical

complexities of placing dual implants, a single large implant was felt to be more optimal. In biomechanical endurance tests, the PDN has maintained disc space height, implant form, and viscoelasticity for up to 50 million cycles. In 11 cadaveric intervertebral disc segments, physiologic testing was performed to evaluate the biomechanical integrity of an intact lumbar segment, segments with the nucleus pulposus removed, and segments with two PDN devices implanted (25,26). It was shown that, by removing just 5 to 6 g of nucleus pulposus, there was an increase in spinal segment motion of between 38% to 100%. The device has been implanted clinically in Europe for approximately 10 years. Results from European studies have led to changes in the formulation of the hydrogel, making the implant softer and more expansive. Klana and Ray (13), in 2002, reported on 480 completed procedures and showed that with implanting two PDN devices, disc height was increased by approximately 2 mm, with overall reduction in patient complaints of pain and symptoms associated with degenerative disc disease. The current design is a single larger device with greater capacity to expand then the dual prosthesis and is called the PDN-SOLO. This device is implanted using either an anterolateral approach through the psoas muscle or a standard posterior approach. The anterolateral transpsoatic approach has been devised to avoid disrupting the posterior structures of the spine (27). P.116

FIGURE 12.4 The PDN device is a hydrogel pellet that is enclosed in a polyethylene jacket (A). Its hydrophilic core absorbs up to 80% of its weight in water causing the device to swell and restore disc height (B). Lateral plain radiographs demonstrate the restoration of disc height following implantation of the PDN device (C). (Reprinted with permission from Raymedica, Inc., Bloomington, MN.)

Studies looking at the biocompatibility of the device have also demonstrated no systemic toxicity or carcinogenicity (28). These studies were performed according to the guidelines of the International Standards Organization.

DASCOR Disk Arthroplasty Device (Disk Dynamics, Inc., Eden Prairie, MN) This device is an in situ curable polymer injected under pressure into an expandable polyurethane balloon catheter (Fig. 12.5A). The polymer cures to a firm but pliable implant in minutes, at which point the remaining balloon catheter stem is removed.

The injection pressure in the balloon is high enough to allow for maintaining or increasing disc height without compromising endplate integrity (Fig. 12.5B). The advantages of the DASCOR device is its ability to create an implant with a large cross-sectional area through a small anular opening, thus minimizing the potential for implant migration. Additionally, the filling of the entire nucleus cavity created by the nuclectomy can deliver a patient-specific implant. Replacing the entire diseased nucleus with this device may more optimally restore the physiologic load distribution of the spinal motion segment (Fig. 12.5C, D). It can be delivered via any approach that provides access to the outer anulus, which includes percutaneous and minimally invasive approaches. Extensive preclinical testing including biomechanical studies have been conducted to fully characterize the device. Clinical trials are currently underway in Europe and patient outcomes after 1.5 years have successfully demonstrated safety and efficacy of the DASCOR device. P.117

FIGURE 12.5 The DASCOR Disk Arthroplasty Device is injected as a liquid under pressure through the catheter (A), filling the balloon and the disc space and allowing for disc height restoration (B). Sagittal (C) and axial (D) magnetic resonance imaging (MRI) at 6-weeks postimplantation show restoration of disc height and no signs of extrusion.

NuCore Injectable Nucleus (Spine Wave, Inc., Shelton, CT) This device is an in situ curable polymer. It is composed of a synthetic silk-elastin copolymer that is created through DNA bacterial synthesis fermentation. It is placed using minimally invasive methods by injecting it through a needle into the disc space following mixing with a diisocyanate-based cross-linking agent. It begins to cure when the cross-linking agent is added, and the surgeon has approximately 90 seconds to inject the material before gelation occurs. Final mechanical strength is attained in approximately 30 minutes (Fig. 12.6). This occurs without a measurable exothermic reaction. P.118

FIGURE 12.6 Axial (A) and lateral (B) photographs of cadaver vertebrae following the injection of the NuCore injectable nucleus into the nuclear cavity. The injectate has gelled and restored the disc height. Note that pigment is used in cadaver studies to enhance visualization; the clinical product is nonpigmented.

(Reprinted with permission from Spine Wave, Inc., Shelton, CT.)

The protein and water content and pH of the protein polymer closely mimics the native nucleus pulposus. Acute and long-term animal studies have demonstrated that this device is noncytotoxic, nonirritating, and nontoxic. Cadaveric biomechanical testing has demonstrated that it can resist extrusion and restores disc space height under load (29,30). This device has also withstood cyclic loading up to 10 million cycles without failure in dynamic testing. Human clinical trials are currently underway (unpublished data from Spine Wave, Shelton, CT).

Biodisk (Cryolife, Kennesaw, GA) This device is an in situ curable polymer. The Biodisk is a protein hydrogel that begins to polymerize within 30 seconds of being injected into the disc space and occurs without a significant exothermic reaction. It polymerizes to a pliable solid state within 2 minutes. This device is based on Cryolife's Bioglue surgical adhesive, which is marketed for cardiovascular repair.

Mechanical Implants Regain (EBI, Parsippany, NJ) This device is built with a pyrocarbon material that is used in cardiac valve prostheses. It is biocompatible and hemocompatible and has a high level of strength and resistance to wear and causes minimal articular cartilage degeneration when compared with other biomaterials. It is a one-piece design that was developed using electromagnetic motion sensors that simultaneously analyzed motion above and below the nucleus replacement site by tracking changes in position, rotation, and translation (Fig. 12.7). This allowed the device design to closely mimic the normal biomechanics of a healthy intact disc space. The one-piece design also prevents wear debris between multiple implant pieces. It is currently undergoing a clinical study in Europe and is expected to begin a clinical trial in the United States within the year. P.119

FIGURE 12.7 The Regain artificial disc is composed of pyrocarbon (A). Lateral fluoroscopy (B) demonstrates its position within the disc. (Reprinted with permission from EBI, Parsippany, NJ.)

IPD (Dynamic Spine, Mahtomedi, MN) The intervertebral prosthetic disc (IPD) is an anulus-sparing device that consists of metallic springs connected to fixation components. It is fixed to the vertebral bodies following the removal of the nucleus pulposus and vertebral endplates. Studies thus far have been limited to animal models.

Conclusions What does the future hold? Implant extrusion has been an issue with many of the nucleus pulposus replacement devices. Studies are in the works to develop technologies to prevent this complication (31). DePuy Spine (Raynham, MA) is studying a patch made of small intestine submucosa that will cover the annular defect that is necessary for the nucleotomy and implantation of a nucleus pulposus replacement. Intrinsic Therapeutics (Woburn, MA) is developing and testing a stent made from an internal fabric and memory metal. This stent will be placed at the junction of the nucleus pulposus and annulus fibrosus and act as a barrier to extrusion. Anulex Technologies, Inc. (Plymouth, MN) is also developing a device to seal anular defects secondary to the annulotomy, nucleotomy, and implant insertion. New surgical

methods are also being developed to limit damage to the posterior structure of the spine, which should decrease the extrusion rate of implants (27). Attention must also be focused on proper implant size, surface area, apposition, and mechanical compatibility of the device, which can all have an effect on the vertebral body endplate response to a nucleus replacement. Also, the storage and distribution techniques still need to be perfected, especially for the hydrogel replacement devices. It was shown that increased dehydration can result in changes to the compressive properties of the implant following rehydration (32). Although synthetic nucleus pulposus replacements are being developed, other researchers are focusing on stem cell regeneration of the nucleus pulposus (10,33). Nucleus pulposus tissue formed in vitro can mimic appropriate nuclear proteoglycan P.120 content and has demonstrated compressive properties similar to that of a native nucleus pulposus (34). Research into stem cell regeneration of disc material is promising; however, its applicability in humans is still many years off. Although there are only limited human trials investigating nucleus pulposus replacements, some results have been promising thus far. Further basic science and animal and clinical trials will better elucidate the utility of these devices in our armamentarium to manage symptomatic degenerative disc disease.

REFERENCES 1. Gillet P: The fate of the adjacent motion segments after lumbar fusion. J Spinal Disord Tech 2003; 16: 338–345. 2. Kumar MN, Baklanov A, Chopin D: Correlation between sagittal plane changes and adjacent segment degeneration following lumbar spine fusion. Eur Spine J 2001; 10: 314–319. 3. Rahm MD, Hall BB: Adjacent segment degen-eration after lumbar fusion with instrumentation: a retrospective study. J Spinal Disord 1996; 9: 392–400.

4. Norkin CC, Levange PK: Joint Structure and Function, A Comprehensive Analysis, 2nd edition. F.A. Davis Company, Philadelphia, 1992. 5. Allen MJ, Schoonmaker JE, Bauer TW, et al: Preclinical evaluation of a poly (vinyl alcohol) hydrogel implant as a replacement for the nucleus pulposus. Spine 2004; 29: 515–523. 6. Urban JP, McMullin JF: Swelling pressure of the lumbar intervertebral disks: Influence of age, spinal level, composition, and degeneration. Spine 1988; 13: 179–186. 7. Ghosh P: The Biology of the Intervertebral Disk, Vol 1. CRC Press, Boca Raton, FL, 1988. 8. Bogduk N, Twomey LF: Clinical Anatomy of the Lumbar Spine. ChurchillLivingstone, Edinburgh, 1987. 9. White AA, Panjabi MM: Clinical Biomechanics of the Spine, 2nd edition. JB Lippincott, Philadelphia, 1990. 10. Risbud MV, Shapiro IM, Vaccaro AR, et al: Stem cell regeneration of the nucleus pulposus. Spine J 2004; 4(6S): S348–353. 11. Panjabi MM: Centers and angles of rotation of body joints: a study of errors and optimization. J Biomech 1979; 12: 911–920. 12. Bao QB, Yuan HA: New technologies in spine: nucleus pulposus replacement. Spine 2002; 27: 1245–1247. 13. Klana PM, Ray CD: Artificial nucleus replacement: clinical experience. Spine 2002; 27: 1374–1377.

14. Kostuik JP: Intervertebral disk replacement, experimental study. Clin Orthop 1997; 337: 27–41. 15. Meakin JR: Replacing the nucleus pulposus of the intervertebral disk: prediction of suitable properties of a replacement material using finite analysis. J Mater Sci Mater Med 2001; 12: 207–213. 16. Ordway NR, Vamvani V, Zhao J, et al: Failure properties of the intervertebral disk with a hydrogel nucleus. Paper presented at the 44th Meeting of the Orthopaedic Research Society; New Orleans, LA; March 16–19, 1998; 6: 85. 17. Ledet EH, Carl AL, Tymeson MP, et al: Preliminary biomechanical evaluation of a synthetically engineered hydrogel for nucleus replacement. Presented at the 52nd Annual Meeting of the Congress of Neurologic Surgery; Scottsdale, AZ; September 19–26, 2002; 314. 18. Korge A, Nydegger T, Polard JL, et al: A spiral implant as nucleus prosthesis in the lumbar spine. Eur Spine J 2002; 11(S2): S149–153. 19. Husson JL, Korge A, Polard JL, et al: A memory coiling spiral as nucleus pulposus prosthesis: concept, specifications, bench testing, and first clinical results. J Spinal Disord Tech 2003; 16: 405–411. 20. Husson JL, Scharer N, Le Nihouannen JC, et al: Nucleoplasty during discectomy: concept and experimental study. Rachis 1997; 9: 145–152. 21. Frei HP, Rathonyi G, Orr TE, et al: Effect of a nucleus prosthetic device on the biomechanical behavior of the functional spine unit. Eur Spine J 1999; 8: S36–37. 22. Scharer N, Husson JL, Froehlich M: Translation of the endplate during flexion and extension on intact human spines: an in-vitro study. Eur Spine J 1999; 8:

S52–53. P.121 23. Ray CD. The PDN prosthetic disk-nucleus device. Eur Spine J 2002; 11(2): S137–142. 24. Ray CD: Lumbar interbody threaded prosthesis. Flexible for an artificial disk and rigid for a fusion. In: Brock M, Mayer HM, Weigel K, eds. The Artificial Disk. Springer-Verlag, Berlin, Germany, 1991. 25. Eysel P, Rompe J, Schoenmayer R, et al: Biomechanical behavior of a prosthetic lumbar nucleus. Acta Neurochir 1999; 141: 1083–1087. 26. Wilke HJ, Kavanagh S, Neller S, et al: Effect of a prosthetic disk nucleus on the mobility and disk height of the L4–5 intervertebral disk postnucleotomy. J Neurosurg Spine 2001; 95: 208–214. 27. Bertagnoli R, Vasquez RJ: The anterolateral transpsoatic approach (ALPA): a new technique for implanting prosthetic disk-nucleus devices. J Spinal Disord Tech 2003; 16: 398–404. 28. Ray CD, Sachs BL, Norton BK, et al: Prosthetic disk nucleus implants; an update. In Gunzburg R, Szpalski M, eds. Lumbar Disk Herniation. Lippincott Williams & Wilkins, Philadelphia, 2002. 29. Viscogliosi AG, Viscogliosi MR, Viscogliosi JJ: Spine arthroplasty. Spine Industry Analysis Series, November 2001. 30. Walkenhorst J, Kitchel S, Spenciner D: Effect of injectable disk nucleus on function of the human cadaveric spine. Presented at the International Society for the Study of the Lumbar Spine, Scotland, UK; March 21–24, 2004.

31. Carl AL, Ledet EH, Yuan HA, et al: New developments in nucleus pulposus replacement technology. Spine J 2004; 4: S325–329. 32. Thomas J, Gomes K, Lowman A, et al: The effect of dehydration history on PVA/PVP hydrogels for nucleus pulposus replacement. J Biomed Mater Res Part B Appl Biomater 2004; 69(2): 135–140. 33. Sakai D, Mochida J, Yamamoto Y, et al: Transplantation of mesenchymal stem cells embedded in Atelocollagen gel to the intervertebral disk: a potential therapeutic model for disk degener-ation. Biomaterials 2003; 24: 3531–3541. 34. Seguin CA, Grynpas MD, Pilliar RM, et al: Tissue engineered nucleus pulposus formed on a porous calcium polyphosphate substrate. Spine 2004; 29: 1299–1306.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Lumbar: Nuclear Replacement > 13 - Prosthetic Disc Nucleus: Treatment with the Anterior Approach

13 Prosthetic Disc Nucleus: Treatment with the Anterior Approach Peter Donkersloot Chronic low back pain is a common problem in our society. Where does conservative treatment end and surgical therapy begin? The idea of treating patients with pain caused by the initial stage of degenerative disc disease (DDD) is attractive, because it is surgically possible to stabilize the affected motion segment with a nucleus prosthesis only. Contrary to treatment with a total disc replacement, the surgical procedure could be less extensive as only a minimally invasive nucleotomy is required. The selection of proper candidates for surgical treatment is still controversial, especially because the correlation between the morphologic and radiologic changes in the initial degenerated disc with the patient's complaints has until now not been fully clear. The optimal indication for treatment with a prosthetic disc nucleus (PDN) is a patient with a more than 6-month history of low back pain with or without leg pain, not responding to conservative treatment, due to the initial degree of disc degeneration. It is possible to treat more than one level (1,2).

The Prosthetic Disc Nucleus

The PDN is a hydrogel core that can absorb up to 80% of its weight in water and so it expands when it is implanted in a surgically prepared disc nucleus cavity. Water absorption allows the device to swell and to maintain the disc height, resulting in stabilization of the motion segment. The hydrated core mimics the biomechanical features including cushioning of a healthy disc nucleus. The polymer core is encased in a polyethylene jacket that helps to preserve the device shape during heavy loading in the motion segment (2). The PDN device passed biomechanical tests, showing that the device is able to maintain disc height, structural integrity, and burst strength up to 50 million cycles, with loads ranging from 200 to 800 N with no significant wear debris (3). The biocompatibility, systemic toxicity, genotoxicity, and carcinogenicity have also been successfully tested (4,5). Eysel et al. (6) published the results of the biomechanical behavior of the PDN device on 11 cadaveric lumbar spinal motion segments. Physiologic testing of intact lumbar segments, nucleotomized segments, and segments with two implanted PDN prostheses were performed to analyze changes in segmental mobility. Removal of the major part of the disc nucleus led to an increase in mobility ranging from 38% to 100%. The insertion of two PDN implants restored disc height and reconstituted the mobility of the implanted segment similar to the prenucleotomized level (6,7). Note that these studies P.124 report on the first generation of PDN (duo) implants, which were smaller than the present ones. Nowadays two types of single-unit devices are available: the PDN-solo for discs with an anteroposterior (AP) diameter of less than 35 mm and the PDNsolo XL for those with an AP diameter more than 35 mm (Fig. 13.1).

FIGURE 13.1 Prosthetic disc nucleus (PDN)-solo and PDN-solo XL. (Published by permission of Raymedica Inc.)

Disc Degeneration—Magnetic Resonance Imaging Discography The very initial stage of disc degeneration was described by Crock (8) as internal disc disruption (IDD). At about 30 years of age the nucleus begins to dehydrate and shrink, resulting in a loss of function and therefore more mechanical stress on the annulus fibrosus (9). The nucleus itself is not innervated; nerve structures are found in the outer part of the annulus fibrosus. These have their origin in the disc surrounding plexus of interlacing nerve fibers localized around the anterior and posterior longitudinal ligament (10). The dorsal part of this plexus is supplied by the recurrent sinuvertebral nerve, which consists of branches of the sympathetic trunk, the rami communicantes, and the dorsal root ganglion. The innervation is not monosegmental, but one or more segments above and below can contribute to the innervation of one single disc level (11,12,13). The clinical implication is that more load leads to a small disruption of the annulus fibrosus, which causes pain. Because of the multisegmental innervation of the interver-tebral disc, the determination of the source of the pain could be difficult if there is more than one affected level. The magnetic resonance imaging (MRI) examination is the gold standard for the

detection of DDD. It is widely available and noninvasive and has been shown to be very sensitive in detecting abnormalities in disc morphology. T1 and T2 weighted sequences in the sagittal and axial direction are clinically used. More sophisticated use of MRI, such as magnetic resonance spectroscopy, functional and dynamic imaging, is so far not available in daily routines (14). In the initial stage of DDD, the MRI shows a “black disc,― sometimes in combination with a slight loss of disc space height and a small rupture of the posterior part of the annulus. Although there is significant controversy as to whether discography adds any diagnostic data greater than those provided by the noninvasive MRI (15), others P.125 think that because discogenic pain is caused by internal disruption of the normal structural integrity of the symptomatic disc, discography is necessary to establish and confirm this diagnosis. This means that the primary indication for lumbar discog-raphy is chronic low back pain with or without radicular pain in the absence of MRI-documented neural compression (16). It is believed that the pain generated by discography occurs when annular fissures or nuclear herniations extend into the outer third of the annulus fibrosis (17). In 1990, Walsh et al. (18) performed a controlled prospective study to establish the specificity of lumbar discography by comparing the results of 10 asymptomatic volunteers with those of 7 patients with chronic low back pain. In this study, the discogram only was defined as “positive― when, with an accurately placed injection in the center of the nucleus, the typical pain could be induced (positive pain provocation). Based on this criterion, there were no positive discograms demonstrated in the asymptomatic individuals (a false-positive rate of 0% and a specificity of 100%). So although both asymptomatic and symptomatic “black discs― might show morphologically pathologic findings, additional information is given by the functional part of the discography if the needle is positioned in the center of the disc. Malposi-tioning or annular injection is known to be painful and can give falsepositive results (19). Some patients show, despite analgesic and sedative medication, an extremely low tolerance for the nociceptive stimuli caused by the discographical examination. These are less suitable candidates for surgical

treatment (16).

Materials and Methods During the period of January 2003 and March 2005, 44 patients (20 women, 24 men) mean age 42 (22–64) years were treated with the implantation of 52 PDN devices. The data are listed in Table 13.1. Indication for treatment was a more than 6-month history and clinical findings suggestive of DDD with no response to conservative treatment, a “black disc― leading to a moderate loss of disc space height in the MRI (minimal disc height more than 5 mm), and a positive discogram. Contraindications were prior surgery at the affected level, a stenosis of the spinal canal and/or the lateral recessus, facet degeneration, a body mass index (BMI) greater than 30, osteoporosis, and age older than 65 years.

TABLE 13.1 Overview of 52 Treated Intervertebral Discs N L1-2 + L2-3

1

L2-3

2

L2-3 + L3-4

1

L3-4

3

L3-4 + L4-5

5

L4-5

27

L4-5 + L5-S1

1

L5-S1

4

P.126

FIGURE 13.2 The results of the Oswestry questionnaire of 44 patients.

The first five patients (total six levels) were treated with the PDN duo, all the other with the PDN solo or PDN solo XL depending on the AP diameter of the disc, that is, less or more than 35 mm. Umehara et al. (20) reported that the annulus in degenerated discs is abnormal and that its elastic modulus is lowest in the posterolateral section of the disc. To avoid damage to this vulnerable posterior part of the annulus fibrosus, all patients were operated by an anterior route. A left anterolateral transpsoatic approach (ALPA) as described by Bertagnoli and Vazquez (21) was used for all discs above L5-S1; for the L5-S1 level an anterior minimally invasive left retroperitoneal exposure was used. The nucleus was removed through a small annulotomy. After determining the implant size (5, 7, 9 mm) with a trial, the PDN was inserted with x-ray control. The patients were mobilized with a brace 24 to 48 hours after the operation.

FIGURE 13.3 The results of the visual analogue scale (VAS) back pain and leg pain of 44 patients.

P.127

Results The clinical results were evaluated with the Oswestry and visual analogue scale (VAS) scores. An improvement from 62% preoperatively to 18% 24 months postoperatively, 7.2 to 2.1 for the VAS back pain and 4.9 to 1.6 for the VAS leg pain was noted (Figs. 13.2 and 13.3). There were no complications during the surgical procedures or during the hospital stay. Two infections occurred, one L5-S1 device with Staphylococcus aureus and one L4-5 PDN with Corynebacterium spec. Treatment followed with removal of the implant and high-dose antibiotics. Five (9.6%) of the implants were expelled within 4 to 12 months of the operation. Two L5-S1 PDNs in the anterior direction, one L4-5 device through the annulotomy to the left side, and, bizarrely, one L4-5 into the right iliopsoas muscle. Only one L4-5 nucleus prosthesis migrated into the spinal canal causing radicular leg pain; a posterior lumbar interbody fusion (PLIF) was performed after the PDN removal. The postoperative MRI evaluation showed normal endplates in 33 levels; 9

endplates were intact but with signs of deformation (adaptation) by the PDN (Fig. 13.4). Subsidence was seen in four cases, subsidence and rotation of the device in the sagittal plane also in four. Fusion and subsidence occurred in one patient and fusion and subsidence with sagittal rotation of the PDN in one (Table 13.2). Modic changes in the MRI due to the ingrowth of implantate were seen, 16% Modic I (II) after 6 months and 33% Modic I/II after 2 years (Table 13.3).

FIGURE 13.4 Left prosthetic disc nucleus (PDN) L4-5 and right PDN L4-5 with subsidence and fusion, both 12 months postoperatively.

TABLE 13.2 Magnetic Resonance Imaging (MRI) Findings of the Endplates Endplates Postoperatively

N

Normal

33

Deformity but intact

9

Subsidence

4

Subsidence + sagittal rotation

4

Subsidence + fusion

1

Subsidence + fusion + sagittal rotation

1

Total

52

TABLE 13.3 Postoperative Magnetic Resonance Imaging (MRI) Modic Changes Modic Changes

None

I

I/II

II

Preoperative n = 52

48

4

0

0

6-mo postoperative n = 52

45

6

1

0

12-mo postoperative n = 47

34

5

7

1

24-mo postoperative n = 22

14

0

3

5

P.128

Discussion The clinical outcome of the 44 patients was similar to those described in the literature: An Oswestry score improvement from 62% preoperatively to 18% 24 months postoperatively and 7.2 to 2.1 for the VAS back pain was noted. Jin et al. (22) reported 45 patients treated for chronic low back pain with the PDN device at 6-month follow-up. Patients improved their Oswestry scores from 52% to 16.5%. Shim et al. (23) followed 45 patients for 12 months. The Oswestry scales were comparable to Jin, the VAS improved from 8.5 to 3.1. The world results of the PDN prosthesis as reported by Bertagnoli and Schönmayr (24) are difficult to interpret because of changing both the device and the surgical technique during the study. Despite the anterior surgical approach expulsion of the PDN was seen with the same frequency (9.6%) as reported by the other authors (22,23,24), but there was a significant difference in migration into the spinal canal, only 1 of 52 (1.9%). This suggests that the anterior implantation technique is of benefit to avoid posterior ruptures of the annulus fibrosus, which also leads to a reduction of the risk of

neurologic complications. Although Eysel et al. (6) published the results of the lifting capacities of the PDN in the cadaveric nucleotomized disc, we tried not to implant an oversized device during the procedures, to avoid too much load on the endplates in the center of the disc, which is localized in the most vulnerable part of the vertebral body. Deformed but intact endplates were observed in 17.3% of the implanted levels, subsidence eventually combined with rotation of the PDN in the sagittal plane in 15.4% and fusion in 3.8%. Shim et al. (23) made similar observations. MRI confirmed that the swelling PDN leads to endplate irritation during the first months after the operation; Modic I changes (edema) are frequent. This might be the reason for prolonged pain after the implantation (23). After 2 years Modic II changes are observed. An explanation could be the quadrangular shape and the stiffness of the PDN device, which forces the endplates to remodel with a rather high risk of endplate damage. This implies that, although the clinical outcome is acceptable, improvement of the shape of the PDN is desirable.

REFERENCES 1. Bao QB, Yuan HA. New technologies in spine: nucleus replacement. Spine 2002; 27: 1245–1247. 2. Klara P, Ray CD. Artificial nucleus replacement. Spine 2002; 27: 1374–1377. 3. Ray CD. The PDN prosthetic disc-nucleus device. Eur Spine J 2002; 11(Suppl 2): 137–142. 4. Ray CD, Sachs BL, Norton BK, et al. Prosthetic disc nucleus implants: an update. In: Gunzburg R, Szpalski M, eds. Lumbar Disc Herniation. Philadelphia: Lippincott Williams & Wilkins, 2002. 5. Bushell GR, Ghosh P, Taylor TF, et al. Proteo-glycan chemistry of the intervertebral disks. Clin Orthop 1977; 129: 115–123.

6. Eysel P, Rompe J, Schönmayr R, et al. Biomechanical behaviour of a prosthetic lumbar nucleus. Acta Neurochir (Wien) 1999; 141: 1083–1087. 7. Wilke HJ, Kavanagh S, Neller S, et al. Effect of a prosthetic disc nucleus on the mobility and disc height of the L4–5 intervertebral disc postnucleotomy. J Neurosurg Spine 2001; 95: 208–214. 8. Crock HV. Internal disc disruption: a challenge to disc prolapse fifty years on. Spine 1986; 11: 650–653. 9. Bao QB, McCullen GM, Higham PA, et al. The artificial disc: theory, design and materials. Biomaterials 1996; 17: 1157–1167. P.129 10. Yoshizawa H, et al. The neuropathology of intervertebral discs removed for low-back pain. J Pathol 1980; 132: 95–104. 11. Oh WS, Shim JC. A randomized controlled trial of radiofrequency denervation of the ramus communicans nerve for chronic discogenic low back pain. Clin J Pain 2004; 20: 55–60. 12. O'Niell CW, et al. Disc stimulation and patterns of referred pain. Spine 2002; 27: 2776–2781. 13. Groen GJ, Baljet B, Drukker J. Nerves and nerve plexuses of the human vertebral column. Am J Anat 1990; 188: 282–296. 14. Haughton V. Medical imaging of intervertebral disc degeneration. Spine 2004; 29: 2751–2756.

15. Resnick DK, Malone DG, Ryken TC. Guidelines for the use of discography for the diagnosis of painful degenerative lumbar disc disease. Neurosurg Focus 2002; 13: (12). 16. Tomecek FJ, Anthony CS, Boxell C, Warren J. Discography interpretation and techniques in the lumbar spine. Neurosurg Focus 2002; 13: (2). 17. Moneta GB, Videman T, Kaivanto K, et al. Reported pain during lumbar discography as a function of anular ruptures and disc degeneration. A reanalysis of 833 discograms. Spine 1994; 19: 1968–1974. 18. Walsh TR, Weinstein JN, Spratt KF, et al. Lumbar discography in normal subjects. A controlled, prospective study. J Bone Joint Surg Am 1990; 72: 1081–1088. 19. Aprill C, Bogduk N. High-intensity zone: a diagnostic sign of painful lumbar disc on magnetic resonance imaging. Br J Radiol 1992; 65: 361–369. 20. Umehara S, Tadano S, Abumi K, et al. Effects of degeneration on the elastic modulus distribution in the lumbar intervertebral disc. Spine 1996; 21: 811–820. 21. Bertagnoli R, Vasquez RJ. The anterolateral transpsoatic approach (ALPA): a new technique for implanting prosthetic disc-nucleus devices. J Spinal Disord Tech (United States) 2003; 16: 398–404. 22. Jin DD, Qu DB, Zhao L, et al. Prosthetic disc nucleus (PDN) replacement for lumbar disc herniation: preliminary report with six months' follow-up. J Spinal Disord Tech 2003; 16: 331–337. 23. Shim CS, Lee SH, Park CW, et al. Partial disc replacement with the PDN prosthetic disc nucleus device: early clinical results. J Spinal Disord Tech 2003;

16: 324–330. 24. Bertagnoli R, Schönmayr R. Surgical and clinical results with the PDN prosthetic disc-nucleus device. Eur Spine J 2002; 11(suppl): 8.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Lumbar: Nuclear Replacement > 14 - Functional Lumbar Artificial Nucleus Replacement—DASCOR

14 Functional Lumbar Artificial Nucleus Replacement—DASCOR John E. Sherman Bruce Bowman Michael Ahrens Henry Halm J.-C. Le Huec Ulf Liljenqvist Peter Donkersloot Scott Hook Hansen Yuan The human intervertebral disc consists of two primary structures: the annulus fibrosus and the nucleus pulposus. Annular tearing and disruption is associated with decreased proteoglycan synthesis with dehydration of the nucleus leading to degeneration of the disc. This may be symptomatic, at which time traditional surgical treatment, consisting of discectomy or arthrodesis can be performed. Arthrodesis, with many surgical variations, has resulted in satisfactory clinical outcomes (1,2). Successful arthrodesis is clearly a nonphysiologic approach to the symptomatic spinal motion segment, eliminating motion of the functional spinal motion segment. Total disc arthroplasty, such as the Charité, Prodisc, Maverick, Flexicore (3,4,5), and others has

received much focus as an alternative to arthrodesis. Implantation of total disc replacement requires an extensive surgical exposure with mobilization of the great vessels, near complete resection of the nucleus and annulus, and bony fixation to the endplates. If revision of TDA is necessary, access will be extremely challenging. Potentially, to address the clinical situation of degenerative disc disease, replacement of only the dehydrated nucleus in a less surgically invasive approach is appealing (6,7,8,9). Nucleus replacement arthroplasty presents different biomechanical, biochemical, and anatomic challenges than total disc arthroplasty. The goal of either treatment is to relieve pain, restore disc biomechanics, restore and maintain disc height, limit progression of adjacent level disease, and improve long-term outcomes.

Goals of Nucleus Replacements Normal disc structure biomechanically allows both stability and flexibility within each individual spinal motion segment. As the disc degenerates the normal load carried by the nucleus diminishes with increasing load on the annulus, accelerating annular incompetence with diminished disc height. Discogenic low back pain might become a clinical manifestation of this process. Increased stimulation of nociceptors within the outer aspect of the annulus and vertebral endplates secondary to the increased loads likely contributes to the underlying pain syndrome of discogenic back pain (10,11). A microdiscectomy performed for herniated nucleus pulposus can further disrupt the load sharing function of the nucleus resulting in increased compressive loads on the annulus and facet joints accelerating the degenerative cascade (12). P.132 Whereas a biologic replacement of the nucleus is appealing, a more practical biomechanical solution could achieve these goals. Replacement of the disc nucleus would be done to re-establish the normal load on the nucleus and annulus and restore disc height. This would help to restore the overall normal disc function of stability as well as allowing motion (13,14). The ideal artificial nucleus has a number of basic requirements (13). Multiple surgical approaches could be used for any given nucleus replacement procedure based on specific patient indications. Ideally, the procedure would involve a small annular incision, minimizing the biomechanical impact and decreasing the risk of migration of the implant. The implant would have good conformity to the superior and inferior

endplates, improving the loading characteristics. The procedure would allow for a minimally invasive or percutaneous type technique and be technically practical. If a postoperative clinical failure occurs, the revision strategy should be safe allowing for different surgical solutions, for example, explanation, arthrodesis in situ, or total disc arthroplasty. The technique of prosthetic implantation should be adaptable to address the patient's pathology and symptoms. If the patient has a typical posterolateral extruded herniation requiring excision, the prosthetic nucleus would ideally be implanted by a posterior laminotomy approach, yet this requires limited further disruption of the annulus. This limitation makes the nuclectomy as well as implantation more difficult. Implantation of a preformed nucleus replacement device with a fixed geometry is unlikely to be successful as a stand-alone device as placement requires an equivalent annular opening. If this were inserted without bony fixation, it is quite likely that the preformed device would extrude out through the annular defect. The annular defect created for placement of such a device or an existing large annular defect may be associated with extrusion. This could lead to the additional requirement of repair of the annular defect for them to be safely applied. Revision surgery of a nucleus replacement prosthesis will be driven by the surgical approach of the index procedure. Repeated anterior surgery may require mobilization of the great vessels. However, if the initial retroperitoneal approach did not require mobilization of the great vessels, such as would occur with a small annulotomy, the revision could be accomplished with less risk than after a total disc arthroplasty. The potential for catastrophic bleeding in this approach needs to be considered (15,16). As clinical failure might occur, it also remains to be seen whether a disc prosthesis could be left in situ as an anterior spacer and pain relief would be achieved by adding a posterior fusion or other posterior stabilization. Restoration of the nuclear load is a basic principle of nucleoplasty (8,13). This load is created by the interface of the nucleus implant with the vertebral endplates and annulus. A device with greater conformity to the endplates with large surface area coverage and appropriate modulus of elasticity should result in more balanced, even loading. This likely will result in less bony reaction and postoperative Modic changes. This is best accomplished by forming the implant in situ or allowing a preformed device to deform in situ under the influence of load, as with certain hydrogel

prostheses. The ideal nucleus replacement should have a similar modulus of elasticity of the intact nucleus. A prosthesis with a modulus that is too low will have a high incidence of extrusion and will not re-establish normal biomechanical loading. Nucleus replacement with a relatively high modulus of elasticity would be associated with increased load on the endplates and possibly lead to subsidence or other untoward effects as reported by Fernstrom (18) with the use of the stainless steel ball endoprosthesis. The goal of minimal endplate wear would occur if the ideal prosthesis distributes the forces evenly over the endplates with a large surface area. Likewise, a lower coefficient of friction P.133 between the implant and the endplates would be expected to lead to less endplate or prosthetic wear. An additional benefit of improved implant endplate conformity is likely a diminished risk of implant extrusion.

The Dascor Disc Arthroplasty System Disc Dynamics Inc. (Eden Prairie, MN) has developed an injectable in situ curable polyurethane nucleus replacement device called the DASCOR Disc Arthroplasty Device (32) (Fig. 14.1). The DASCOR device is made by mixing two parts of liquid polymer while delivering it through a catheter to an expandable polyurethane balloon that is placed in the disc space (Fig. 14.2). The polymer cures in a few minutes, changing state from a liquid to a firm but pliable solid device. After 15 minutes, the delivery catheter is detached, leaving the final implant device.

FIGURE 14.1 The DASCOR Disc Arthroplasty nucleus replacement device shown in a spine model. The in situ curable polymer is injected into a polyurethane balloon placed in the disc space. The balloon expands to fill whatever void that has been created during the discectomy. The polymer cures in a matter of minutes from a liquid to a firm but pliable state. (From Disc Dynamics, Inc. reprinted with permission.)

There are several features to this system. The balloon catheter has a low profile and requires only a 5.5-mm annulotomy for introduction. The mixed liquid polymer is delivered to the balloon under controlled pressure, allowing the balloon to expand contouring and filling the entire disc space left by the nuclectomy procedure. This creates a large prosthetic footprint and a large volume device through a small annulotomy, thus making migration unlikely. In addition, the system creates an implant of variable size that conforms to the nuclectomy. The deployment of a large, pliable, endplate-contouring prosthesis maximizes the load transfer between the annulus and the artificial nucleus while minimizing endplate disruption. The DASCOR device also has the ability to distract the disc space. Therefore, the implantation of the device offers not only the ability to fill any given space established by nuclectomy

but also the potential to re-establish normal disc height.

FIGURE 14.2 The DASCOR Disc Arthroplasty System. The two-part liquid polymer is packaged in a dual barrel syringe cartridge. A custom injection device drives the liquid polymer through an inline mixer and into the delivery catheter. The mixed, pressurized polymer then enters the containment balloon, which has been placed in the disc space, expanding the balloon to fill the entire space. (From Disc Dynamics, Inc. reprinted with permission.)

P.134 The DASCOR prosthesis can be implanted using multiple surgical approaches, that is, posterior laminotomy, extraforaminal, anterior, and lateral, with minimal variation in surgical technique. Key to any approach, however, is achieving total nucleus removal (TNR) and minimizing annular disruption. The implantation of a nucleus prosthesis should not be perceived to be a simple adjunct to a standard discectomy for herniated nucleus pulposus. To create a prosthesis with maximal size, endplate conformity, and optimal biomechanical loading, complete removal of the nucleus must be conducted while preserving the annulus and endplates. This has resulted in the principle of TNR (33,38). Human cadaveric studies identified that standard discectomy instruments did not allow TNR to be adequately performed through a 5.5-mm annulotomy. A set of

standard pituitary rongeurs was chosen and customized pituitary rongeurs were developed according to each instrument's ability to reach a particular mapped region of the nucleus (Fig. 14.3). When specific instruments are utilized and coupled with detailed intraoperative fluoroscopic imaging, TNR can be reliably accomplished. Evaluation with an imaging balloon further characterizes the geometric location of the prosthesis as well as the anticipated volume of the final implant (Fig. 14.4) prior to implanting the final device.

FIGURE 14.3 5-Zone anterolateral total nucleus removal approach. Instruments are specifically chosen according to their ability to reach and remove nucleus material from each of the five zones shown. The step-by-step approach to nucleus removal one zone at a time results in total nucleus removal. (From Disc Dynamics, Inc. reprinted with permission.)

FIGURE 14.4 Radiograph of the imaging step prior to DASCOR implantation. An imaging balloon is placed through the annulotomy and into the disc space. Contrast solution is injected and images are taken from multiple directions to assess the completeness of total nucleus removal (TNR). (From Disc Dynamics, Inc. reprinted with permission.)

P.135 The initial annulotomy is created by using a 5.5-mm trephine. Particular care is taken to avoid damage to the remaining annulus and the cartilaginous endplates (Fig. 14.5A). Following TNR, an imaging balloon is inserted into the disc space and contrast media is injected under pressure, filling the balloon and disc cavity created by TNR. Fluoroscopic images are then taken in multiple planes, and an assessment is made as

to the completeness and symmetry of the nuclectomy. If the cavity is not symmetrical and centrally located, additional steps of nucleus removal and fluoroscopic imaging are conducted. Posterior annular integrity can also be assessed at this time. The contrast media and imaging balloon are then removed, and the implant balloon is inserted (Fig. 14.5B). The liquid polymer is then injected under controlled pressure into the balloon, filling the cavity (Fig. 14.5C). After 15 minutes, the delivery catheter is cut off and removed (Fig. 14.5D). The patients are gradually mobilized postoperatively, allowing for soft tissue healing.

FIGURE 14.5 Technique for the Implantation of DASCOR Disc Arthroplasty Device. A: A series of rongeurs are used to perform total nucleus removal (TNR). Confirmation of TNR is made by injecting contrast solution into an expandable balloon placed in the disc space and taking multiple fluoroscopic images. B: Following TNR, the implant balloon is inserted into the disc space. C: The two-

part liquid polymer is mixed as it is being injected under pressure through the catheter, filling the balloon and the disc space and allowing for disc height restoration. The device cures to form a firm but pliable implant that conforms to the individual's anatomy. D: The delivery catheter is then cut off at the edge of the implant using a special tool, and the catheter is removed. (From Disc Dynamics, Inc. reprinted with permission.)

P.136

FIGURE 14.6 Contact stress evaluation in human cadaver using Tekscan 121 element array sensor. A: Tekscan sensor is shown in position over implant device following transection of the functional spine unit. The sensor was placed between the implant and the endplate and monitored during axial, flexion, and extension loadings. Each element color is related to stress, with darker colors representing

low stress and light colors (orange, red) representing high stress (uncalibrated). B: Array showing color distribution related to stress distribution during 1,200-N axial loading. C: Array showing color distribution related to stress distribution during 500-N flexion. D: Array showing color distribution related to stress during 500-N extension. The relative even distribution in color demonstrates a relatively even distribution in contact stress. (From Disc Dynamics, Inc. reprinted with permission.)

P.137 Extensive preclinical testing of the DASCOR device has been conducted including component and device characterization, biodurability bench testing, biomechanical testing (34), and biocompatibility confirmation. The biodurability of the device was investigated in a custom-made six-station mechanical testing apparatus using unconstrained device conditions to create a worst-case test construct. Cyclic axial compression was combined with cyclic ±5.5-degree flexion-extension to represent high-end daily activity loads of 1.8 MPa peak stresses. None of the six samples tested for 25 million cycles showed signs of device degradation. Wear rate was measured for devices tested during the first 10 million cycles. Average wear rate was only 0.26 mg/million cycles, and no significant permanent set was observed (34). Segmental flexibility using a human cadaveric model was studied by comparing intact, nuclectomy, and instrumented constructs. It was demonstrated that the device was able to restore the segmental flexibility lost after a nuclectomy while still preserving segmental level biomechanics to within ±5% of the intact motion-segment behavior (35). In a similar study, human cadaveric specimens were instrumented with a 121element Tekscan sensor placed between the implant and endplates (Fig. 14.6A). Contact stress was evaluated during segmental flexibility testing. A typical stress distribution at 1,200-N axial compressive load is shown in Fig. 14.6B. Similarly, Figs. 14.6C and D show stress distribution during 500-N flexion and extension loads, respectively. A relatively uniform contact stress distribution was observed during all segmental flexibility loads applied (34,39). The initial clinical experience of the DASCOR system evaluating safety and effectiveness is being investigated in a multicenter prospective nonrandomized European study (36,37). Inclusion criteria include patients with symptomatic single-

level lumbar degenerative disc disease diagnosed by magnetic resonance imaging (MRI) and a positive discogram with a minimum disc height of 5.5 mm. They must have failed 6-month nonoperative care and have had no prior fusion. A standardized retroperitoneal midline or lateral approach was used to perform a TNR and implant the DASCOR device in this study. As of early 2005, seventeen patients (8 female, 9 male) with an average age of 38.1 years were implanted at the L5-S1 (n = 10) or L4-5 (n = 7) levels. Eleven patients have been followed up to 1 year. The mean operating time was 78.1 minutes with an average blood loss of 59.1 mL. A 6-week postoperative MRI of the DASCOR device in a patient is shown in Fig. 14.7. The implant is centrally located and fills the former nucleus space. Outcome measures have been tracked from preoperative measures through 12 months. Average Oswestry results showed a 64% reduction from a preoperative average of 52.2 (Fig. 14.8). Average visual analogue scale (VAS) back pain scores showed a 60% reduction from a preoperative average of 7.3 (Fig. 14.9), whereas VAS leg pain scores showed a 68% reduction from a preoperative average of 5.3. Analgesic use based on a three-point scale decreased 89% from a preoperative average of 1.8. In addition, MRI evaluations showed that the DASCOR device had not led to any significant Modic changes, bone edema, subsidence, or migration. Anteroposterior (AP) and lateral radiographic films showed that disc height and range of motion were maintained (36,37). Although clinical experience has been limited at this time, early results were very encouraging. Study subjects demonstrated pain reduction and functional improvement allowing a considerable early clinical success with the DASCOR Disc Arthroplasty System. DASCOR has received CE mark and further studies are being initiated, with long-term data to be accumulated. P.138

FIGURE 14.7 Magnetic resonance imaging (MRI) of DASCOR device 6-weeks postimplantation. Images show the implant device centrally located without and signs of Modic changes or inflammatory reaction. (From Disc Dynamics, Inc. reprinted with permission.)

FIGURE 14.8 Oswestry low back pain score results. Seventeen patients had an average Oswestry preoperative pain score of 52.2. Eleven patients have been followed to 12 months and showed a 64% drop in pain score to 18.6.

P.139

FIGURE 14.9 Visual analogue scale (VAS) low back pain score results. Seventeen patients had an average VAS preoperative back pain score of 7.3. Eleven patients have been followed to 12 months and showed a 60% drop in pain score to 2.9.

Conclusions The concept of nucleus replacement is exciting, yet unproved. The ideal implant will allow for re-establishment of disc height as well as re-establishing the normal biomechanics of the motion segment. The potential for significant clinical improvement with diminished morbidity over current techniques remains the ultimate goal. However, many questions still need to be addressed with respect to nucleus replacement devices and technologies. Although, no “perfect― material has been identified for the nucleus replacement, the DASCOR design currently under study does address many of the perceived needs of nucleus replacement. There are significant differences in design features between DASCOR and other nucleus devices, which likely influence clinical results. The injectable, contained DASCOR device results in a large cross-sectional area that contours to the endplates, combined with a favorable modulus of elasticity. This creates a more uniform distri-bution of

load on the vertebral endplates and potentially may contribute to the lack of endplate reaction seen in early studies, in contrast to other nucleus replacement devices reported. Enhanced load sharing between the annulus and implant is consistent with the biomechanical results of returned motion-segment stability and functional performance following DASCOR implantation. Even though the DASCOR is implanted through a small annulotomy, a prosthesis with a large volume and geometry is created making migration unlikely, which has not been the case for preformed devices that require large annulotomies. Nucleus arthroplasty does require rigorous clinical studies to be performed with appropriate control groups to access this emerging technology. However, as with any technology, selecting the appropriate patient and applying precise surgical technique will optimize the possibility for successful long-term clinical outcome. Given the early state of this technology, it will be some time before data are available to identify the P.140 ideal patient for DASCOR and potentially the value of selected surgical approach and multilevel application. This does not diminish the potential enthusiasm for successful clinical introduction of nucleus replacement arthroplasty in general and the DASCOR technology, specifically.

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39. Ahrens M, Ordway N, Tsantrizios A, Yuan H, Bowman B. Nucleus replacement with an in situ curable balloon contained polymer and restoration of segmental kinematics. Eur Cells Mater Suppl 2005; 10:46.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Total Disc Arthroplasty > 15 - Total Lumbar Disc Arthroplasty: Overview of Clinical Results for Existing Implants

15 Total Lumbar Disc Arthroplasty: Overview of Clinical Results for Existing Implants S. Aunoble J.-C. Le Huec Y. Basso C. Tournier Lumbar spine arthroplasty started 20 years ago and was in a lull for 15 years (1). In the past 5 years the interest has grown dramatically, and under the pressure of health systems and insurance companies more information is requested to support reimbursement of this new treatment. To treat low back pain (LBP) it is important to differentiate the pain generator. Discogenic pain is usually admitted as the main diagnosis for disc replacement. Interbody fusion is the gold standard to treat discogenic pain, and, at a minimum, to support a new therapeutic a noninferiority study is requested. Many retrospective studies were published during the 1990s, but their methodologies were poor and patients were lost at follow-up (2,3,4). Very few prospective studies are published. Recently to get Food and Drug Administration (FDA) approval, many prospective randomized trials started in the United States, and the results of three of them are now available. Analysis of published data is very enriching.

Retrospective Data Retrospective series reported excellent and good results based on patients' clinical satisfaction with a success rate higher than 90% (3). Unfortunately there was no relevant clinical evaluation using the common scores such as Oswestry or SF-36 for functional activities. Even visual analogue scoring was not available. Griffith's (4) series reporting Charité experience in 1994 showed only 66% clinical success. Two retrospective series are very interesting. The first one is reported by Putzier et al. (1) and is the original experience of Charité with 17-year follow-up. Seventy-one patients were treated with 84 Charité TDRs types I to III. Indication for TDR was moderate to severe DDD. Fifty-three patients (63 TDRs) were available for longterm follow-up of 17 years. Evaluation at revision only included Oswestry Disability Index (ODI), visual analogue scale (VAS), overall outcome score, and plain and extension-flexion radiographs. Implantation of Charité TDR resulted in a 60% rate of spontaneous ankylosis after 17 years. No significant difference between the three types of prostheses was found concerning clinical outcome. Reoperation was necessary in 11% of patients. Although no adjacent segment degeneration was observed in the functional implants (17%), these patients were significantly less satisfied than those with spontaneous ankylosis. The second paper reported Lemaire's (2) experience using Charité III in 107 patients with 11-year follow-up. Of these 107, one hundred were followed for a minimum of 10 years (range 10–13.4 P.144 years). One hundred forty-seven prostheses were implanted with 54 one-level and 45 two-level procedures and 1 three-level procedure. Clinically, 62% had an excellent outcome, 28% had a good outcome, and 10% had a poor outcome, but this evaluation was not performed with Oswestry and SF-36 scores but only on patient satisfaction. Of the 95 eligible to return to work, 88 (91.5%) either returned to the same job as prior to surgery or to a different job. These included 63.2% (12) of those working in heavy labor employment returning to the same job. Mean flexionextension motion was 10.3 degrees for all levels (12.0 degrees at L3–L4, 9.6 degrees at L4-L5, 9.2 degrees at L5-S1). Mean lateral motion was 5.4 degrees. Slight subsidence was observed in two patients, but they did not require further surgery. No subluxation of the prostheses and no cases of spontaneous arthrodesis were identified. There was one case of disc height loss of 1 mm. Five patients

required a secondary posterior arthrodesis. The difference in between those two retro-spective series is amazing. Spontaneous fusion moves from 0% at 10 years in one series to 60% at 17 years. The difference needs to be analyzed. Patient selection is probably different but no data are available on this point in both series.

Prospective Series Some prospective series report experience with Prodisc and Maverick. Tropiano et al. (5) recently reported Marnay initial experience. Sixty-four patients had singleor multiple-level implantation between 1990 and 1993. The mean duration of follow-up was 8.7 years. Clinical results were evaluated by assessing preoperative and postoperative lumbar pain, radiculopathy, disability, and modified StaufferCoventry scores. At an average of 8.7 years postoperatively, there were significant improvements in the back pain, radiculopathy, disability, and modified StaufferCoventry scores. Thirty-three of the 55 patients with sufficient follow-up had an excellent result, 8 had a good result, and 14 had a poor result. Neither gender nor multilevel surgery affected outcome. An age of younger than 45 years and prior lumbar surgery had small but significant negative effects on outcome. Radiographs did not demonstrate loosening, migration, or mechanical failure in any patient. Using Prodisc II, Bertagnoli et al. (6,7,8) recently reported their experience. This prospective analysis was performed on 118 patients treated with single-level lumbar disc arthroplasty (6). A total of 104 patients (88%) fulfilled all follow-up criteria. The median age of all patients was 47 years (range, 36–60 years). Statistical improvements in VAS, Oswestry, and patient satisfaction scores occurred 3 months postoperatively. These improvements were maintained at the 24-month follow-up. Radicular pain also decreased significantly. Full-time and part-time work rates increased from 10% to 35% and 3% to 24%, respectively. No additional fusion surgeries were necessary either at the affected or at the unaffected levels. Radiographic analysis revealed an affected disc height increase from 4 to 13 mm (p < 0.001) and an affected disc motion from 3 to 7 degrees (p < 0.004). The same author (7) also reported his experience regarding the safety and efficacy of singlelevel lumbar disc (ProDisc prosthesis) replacement in patients 60 years of age or older. Twenty-two patients presented with disabling discogenic LBP with or without radicular pain. The involved segments ranged from L2 to S1. Patients in whom there was no evidence of radiographic circumferential spinal stenosis and with minimal or

no facet joint degeneration were included. Outcome was evaluated postoperatively at 3, 6, 12, and 24 months by administration of standardized tests (VAS, ODI, and patient satisfaction). The median age of all patients was 63 years (range 61–71 years). There P.145 were 17 single-level cases, 4 two-level cases, and 1 three-level case. Statistical improvements in VAS, ODI, and patient satisfaction scores were observed at 3 months postoperatively and were maintained at 24-month follow-up. Patient satisfaction rates were 94% at 24 months. Radicular pain also decreased significantly. Patients in whom bone mineral density was decreased underwent same-session vertebroplasty following implantation of the ProDisc device(s). There were two cases involving neurologic deterioration: unilateral foot drop and loss of proprioception and vibration in one patient and unilateral foot drop in another patient. Both deficits occurred in patients in whom there was evidence preoperatively of circumferential spinal stenosis. There were two cases of implant subsidence and no thromboembolic phenomena. Although the authors' early results indicate that the use of ProDisc lumbar total disc arthroplasty in patients older than 60 years reduces chronic LBP and improves clinical functional outcomes, they recommend the judicious use of artificial disc replacement in this age group in whom bone quality is adequate in the absence of circumferential spinal stenosis. The use of cement bone augmentation to avoid subsidence as proposed in this series is probably the limit to avoid and at the moment we definitively advise against this kind of indication as our experience is definitively different. Even if this author never reported complications related to the implant, Aunoble et al. (9) experienced two cases of polyethylene inlay dislocation after 30 cases operated. This was mainly related to some technical errors during implantation, but it is still a problem particularly at the level L5-S1 where the disc height is sometimes less than 9 mm and the sacral slope is important. In those cases this author recommends a fusion. Le Huec et al. (10) reported in a prospective study the outcome of the Maverick device and demonstrated that the degree of improvement was equivalent to that obtained with anterior fusion cages using the mini-invasive technique. Radiographic follow-up in this series showed a degree of mobility close to normal at L5-S1 (5.9 degrees, SD: 2.2) and L4-5 (9.6 degrees, SD: 3.1). The Oswestry score (at least 25%

improvement) combined with the VAS (at least 2 points improvement) as requested by the FDA as a criteria for success was improved for 75% of patients. Patient satisfaction was 87%. This improvement is significantly correlated with facet arthrosis and muscle fatty degeneration. There has been little analysis assessing the correlation between the clinical functional result of total disc replacement and the arthrosis of the posterior facets or the fatty degeneration of the spinal muscles. However, such knowledge is essential for understanding the long-term outcome of devices in functional terms. Le Huec et al. (11) reported a prospective study on 64 patients in which a Maverick (Medtronic) was implanted. Oswestry score preoperatively and at 2-year follow-up was 43.8 and 23.1, respectively (p < 0.05). LBP improved from a mean VAS score of 7.6 ± 1.7 preoperatively to 3.2 ± 1.8 at 2 years. Mean VAS leg pain score decreased from 3.9 to 2.1 at 2 years (p < 0.05). Facet osteoarthritis grade 1 or 2 did not influence outcome (p = 0.82). On the other hand, muscle degeneration of grades 1 and 2 led to a better outcome than grades 3 and 4 (p = 0.006). This is the first study showing that a semiconstrained implant with a fixed posterior center of rotation can be implanted with grade 1 and 2 facet arthrosis with a good clinical outcome. This seems to confirm previous work showing that a posterior center of rotation lightens the load on the facets. This is also the first study to show a relationship between muscle fatty degeneration and clinical results because the greater the amount of fat, the less satisfactory the result. These promising midterm results must be confirmed by further studies. The effect of single-level, total disc arthroplasty on sagittal balance parameters could be a main reason to support the benefit of disc arthroplasty in the lumbar spine. The influence on the sagittal balance of the spine, especially on sacral tilt (ST), pelvic tilt (PT), P.146 and lumbar lordosis were the selected criteria analyzed by Le Huec et al. (12) It has been shown that lumbar fusion may deleteriously alter the sagittal balance of the spine, including a decrease in the ST and lumbar lordosis. Clinically, postfusion pain has been shown to be significantly related to a decreased ST, increased PT, and decreased lumbar lordosis, independent of other factors such as pseudoarthrosis. In this prospective study, 35 patients received a single-level disc replacement using the Maverick Total Disc Arthroplasty system (Medtronic Sofamor Danek, Memphis, TN). The parameters studied were ST, PT, global and segmental lordosis, and global

kyphosis. The disc arthroplasty was performed at the L4-5 level in 19 patients and at the L5-S1 level in 16 patients. The average follow-up was 14 months (range 6–22 months). The preoperative values of global lordosis, ST, and PT were 51.5, 37.8, and 16.9 degrees and, at last follow-up, they were 51.4, 37.4, and 17.5 degrees, respectively. These changes were not significantly different. When the groups were separated according to the level operated, there was still no statistical difference with regard to the overall lordosis, ST, PT, or kyphosis from pre- to postoperative period or when the two groups were compared with each other. The level above the prosthesis always has significantly less lordosis. In the present study with use of a motion-preserving Maverick prosthesis, it appears that the patient is able to maintain the preoperative sagittal balance. The prosthesis has enough freedom of motion to allow the patient to maintain the natural sagittal and spinopelvic balance needed to prevent potential undue stress on the muscles and the sacroiliac joint.

Prospective Randomized Trial Data of the first prospective randomized series requested by the FDA for approval are now available (13,14). Blumenthal et al. (14) reported this investigational device exemption clinical trial for Charité disc prosthesis (DEPUY). They compared the safety and effectiveness of lumbar total disc replacement to anterior lumbar interbody fusion using cages for the treatment of single-level degenerative disc disease from L4-S1 unresponsive to nonoperative treatment. A total of 304 subjects were randomized in a 2:1 ratio, with 205 in the investigational group (TDR with the Charité artificial disc) and 99 in the control group (anterior lumbar interbody fusion with BAK cages and iliac crest bone graft). A 24-month follow-up was performed and 14 centers participated. Data were collected pre- and perioperatively at 6 weeks and at 3, 6, 12, and 24 months following surgery. The key clinical outcome measures were a VAS assessing back pain, the ODI questionnaire, and the SF-36 Health Survey. Patients in both groups improved significantly following surgery. Patients in the Charité artificial disc group recovered faster than patients in the control group. Patients in the Charité artificial disc group had lower levels of disability at every time interval from 6 weeks to 24 months, compared with the control group, with statistically lower pain and disability scores at all but the 24-month follow-up (p < 0.05). The Oswestry

score (at least 25% improvement) combined with the VAS (at least 2 points improvement) as requested by FDA as a criteria for success was improved for 63% of patients in the Charité group and 49% in the control group. This is the worst result ever reported with a disc replacement. The Charité artificial disc group demonstrated statistically significant superiority in two economic areas, a 1-day shorter hospitalization, and a lower rate of reoperations (5.4% compared with 9.1%). At 24 months, the investigational group had a significantly higher rate of satisfaction (73.7%) than the 53.1% rate of satisfaction in the control group (p = 0.0011). McAfee et al. (13) wanted to determine in the same series if a correlation exists between clinical outcomes and surgical accuracy of TDR placement within the disc P.147 space. Prosthesis placement in the coronal and midsagittal planes was analyzed for the 276 patients with TDR. Correlations were performed between prosthesis placement and clinical outcomes. Patients in the investigational group had a 13.6% mean increase, and those in the control group an 82.5% decrease in mean flexionextension range of motion (ROM) at 24 months postoperatively compared with baseline. Patients in the investigational group had significantly better restoration of disc height than the control group (p < 0.05). There was significantly less subsidence in the investigational group compared with the control group (p < 0.05). The surgical technical accuracy of Charité artificial disc placement was divided into three groups: I, ideal (83%); II, suboptimal (11%); and III, poor (6%) and correlated with clinical outcomes. The flexion-extension ROM and prosthesis function improved with the surgical technical accuracy of radiographic placement (p = 0.003). Geisler et al. (15) demonstrated the neurologic complications of Charité III artificial disc replacement in relation to the necessity of overdistraction during insertion but also core migration. On the other hand Van Oiij et al. (16) reported on 27 patients reoperated for complications after Charité implan-tation. The objective of this work was to describe the possible short- and long-term unsatisfactory results of disc prosthesis surgery. Twenty-seven patients were seen in a tertiary university referral center with persisting back and leg complaints after having received a Charité disc prosthesis. All patients were operated on in a neighboring hospital. Most patients were operated on at the L4-L5 and/or the L5-S1 vertebral levels. The patients were evaluated with plain

radiography, some with flexion-extensionx-rays, and most of them with computed tomography scans. The group consisted of 15 women and 12 men. Their mean age was 40 years (range 30–67 years) at the time of operation. The patients presented to us at a mean of 53 months (range 11–127 months) following disc replacement surgery. In two patients, an early removal of a prosthesis was required and in two patients a late removal. In 11 patients, a second spinal reconstructive salvage procedure was performed. Mean follow-up for 26 patients with mid- and long-term evaluation was 91 months (range 15–157 months). Early complications were the following: In one patient, an anterior luxation of the prosthesis after 1 week necessitated removal and cage insertion, which failed to unite. In another patient with prostheses at L4-L5 and L5-S1, the prosthesis at L5-S1 dislocated anteriorly after 3 months and was removed after 12 months. Abdominal wall hematoma occurred in four cases. Retrograde ejaculation with loss of libido was seen in one case and erection weakness in another case. A temporary benefit was experienced by 12 patients, whereas 14 patients reported no benefit at all. Main causes of persistent complaints were degeneration at another level in 14, subsidence of the prosthesis in 16, and facet joint arthrosis in 11. A combination of pathologies was often present. Slow anterior migration was present in two cases, with compression on the iliac vessels in one case. Polyethylene wear was obvious in one patient 12 years after operation. In eight cases, posterior fusion with pedicle screws was required. In two cases, the prosthesis was removed and the segment was circumferentially fused. These procedures resulted in suboptimal long-term results. In this relatively small group of patients operated on with a Charité disc prosthesis, most problems arose from degeneration of other lumbar discs, facet joint arthrosis at the same or other levels, and subsidence of the prosthesis. Philipps (17) showed on 16 patients with Charité inserted in between levels L3 to S1 that 7 of these 16 had progression of facet degeneration by at least one grade in 2 years after tda; patients with grade 2 to 3 progression had a VAS mean of 3.8 compared with 1.3 in those without progression. Dickerman (18) is the first author to report stretch P.148 neuropraxia after Charité tda; 67 of 250 patients undergoing sb Charité were investigated to look at pre- and postoperative disc heights and lateralization of implants. Those 67 patients with neurapraxia had anterior and posterior disc

heights elevated. The author suggests that this is probably in direct relation with the necessity of overdistraction of the annulus to insert the polyethylene core. Zigler et al. (19) reported the FDA IDE prospective randomized two-centers controlled study, which is a 2:1 randomization of the investigational group receiving the Prodisc II total disc replacement (Synthes) and the control group receiving an anterior interbody fusion with cage and a posterior stabilization with pedicular screws and posterolateral fusion. One hundred eighty patients were randomized 2:1 total disc arthroplasty to fusion (127/53). Patient satisfaction rate was 87% for the prosthesis versus 62% for fusion at 6 months. The prosthesis group had significant reduced pain and disability at final follow-up. Prosthesis and fusion patients had similar VAS and Oswestry improvements: disc replacement (7.3 to 3.3 and 33 to 15), fusion (7.1 to 4.1 and 31 to 19). Patient satisfaction was 87% and compared favorably to Charité, which was 73%. Gornet (20) reported the FDA IDE prospective randomized five-centers controlled study, which is a 2:1 randomization of the investigational group receiving the Maverick total disc replacement (Medtronic, Memphis, TN) and the control group receiving the LT cage device with the INFUSE bone graft replacement. All patients received an open anterior transperitoneal or retroperitoneal approach. The clinical outcomes of 151 patients who had completed 24 months of follow-up are studied. Male-to-female ratio was 70 male to 81 female (N = 151). The mean age was 40.0 years. The mean weight was 176 pounds. Those seeking workmans' compensation were 24.5%. Patients were assessed and evaluated clinically before surgery and at 6 weeks and 3, 6, and 12 months postoperatively. Clinical assessment included an Oswestry LBP disability questionnaire, neurologic status, SF-36, and back and leg pain questionnaires. The treatment levels were 73.5% L5-S1 and 25.8% L4-5. At 24 months, there was significant improvement in the mean Oswestry score. The mean Oswestry score was 20.2 with an improvement of 34.9 points or 63.9% (p < 0.001) versus preoperative scores. Oswestry scores showed significant improvement and sequentially better outcomes in all measured time intervals starting at 6 weeks. The mean SF-36 (PCS) score at 12 months was 43.3, an improvement of 16.1 points versus preoperatively (p < 0.001), and this result was stable at 24 months. Back and leg pain scores also showed significant improvement (p < 0.001) and successively better results versus preoperatively at all time intervals.

German and Foley (21) performed a review of the published literature regarding lumbar arthroplasty. Their conclusion is that, in appropriately chosen patients, lumbar disc arthroplasty provided clinical results similar to those obtained with interbody fusion at 2 years. The long-term results with respect to the effect of these devices on adjacent segment degeneration are not known, as the incidence of adjacent segment degeneration is not an endpoint of the current trials. In summary at 2-year follow-up in prospective randomized trials there is no evidence of superiority of the nonfusion group versus lumbar fusion. The implant-related complications reported with the Charité prosthesis are significantly higher than with Prodisc II or Maverick. Polyethylene wear seems to become a problem with time. There are arguments for nonfusion if the indications are limited to one-level DDD on young patients between 30 and 50 years old without additional problems (facets and muscles in good conditions and no balance problems). The advantages of disc arthroplasty could appear at 5-year follow-up with a decrease of adjacent level disc disease due to less junctional stress and better balance. Follow-up is mandatory and inscription on registrar is recommended to have a long-term database. P.149

REFERENCES 1. Putzier M, Funk JF, Schneider SV, Gross C, Tohtz SW, KhodadadyanKlostermann C, Perka C, Kandziora F. Charite total disc replacement-clinical and radiographical results after an average follow-up of 17 years. Eur Spine J. 2006; 15(2): 183–195. 2. Lemaire JP, Carrier H, Sari ali, Hel-adi, Skalli W, Lavaste F. Clinical and radiological outcomes with the Charite artificial disc: a 10-year mini-mum follow-up. J Spinal Disord Tech. 2005; 18(4): 353–359. 3. Lemaire JP, Skalli W, Lavaste F, Templier A, Mendes F, Diop A, Sauty V, Laloux E. Intervertebral disc prosthesis. Results and prospects for the year 2000. Clin Orthop Relat Res. 1997; (337): 64–76.

4. Griffith SL, Shelokov AP, Buttner-Janz K, LeMaire JP, Zeegers WS. A multicenter retrospective study of the clinical results of the LINK SB Charite intervertebral prosthesis. The initial European experience. Spine. 1994; 19(16): 1842–1849. 5. Tropiano P, Huang RC, Girardi FP, Cammisa FP Jr, Marnay T. Lumbar total disc replacement. J Bone Joint Surg Am. 2006; 88(1 Suppl 1): 50–64. 6. Bertagnoli R, Yue JJ, Nanieva R, Fenk-Mayer A, Husted DS, Shah RV, Emerson JW. Lumbar total disc arthroplasty in patients older than 60 years of age: a prospective study of the ProDisc prosthesis with 2-year minimum follow-up period. J Neurosurg Spine. 2006; 4(2): 85–90. 7. Bertagnoli R, Yue JJ, Shah RV, Nanieva R, Pfeiffer F, Fenk-Mayer A, Kershaw T, Husted DS. The treatment of disabling single-level lumbar discogenic low back pain with total disc arthroplasty utilizing the Prodisc prosthesis: a prospective study with 2-year minimum follow-up. Spine. 2005; 30(19): 2230–2236. 8. Bertagnoli R, Yue JJ, Shah RV, Nanieva R, Pfeiffer F, Fenk-Mayer A, Kershaw T, Husted DS. The treatment of disabling multilevel lumbar discogenic low back pain with total disc arthroplasty utilizing the ProDisc prosthesis: a prospective study with 2-year minimum follow-up. Spine. 2005; 30(19): 2192–2199. 9. Aunoble S, Donkersloot P, Le Huec JC. Dislocations with intervertebral disc prosthesis: two cases report. Eur Spine J. 2004; 13(5): 464–467. 10. Le Huec JC, Mathews H, Basso Y, Aunoble S, Hoste D, Bley B, Friesem T. Clinical results of Maverick lumbar total disc replacement: two-year prospective follow-up. Orthop Clin North Am. 2005; 36(3): 315–322. 11. Le Huec JC, Basso Y, Aunoble S, Friesem T, Bruno MB. Influence of facet

and posterior muscle degeneration on clinical results of lumbar total disc replacement: two-year follow-up. J Spinal Disord Tech. 2005; 18(3): 219–223. 12. Le Huec J, Basso Y, Mathews H, Mehbod A, Aunoble S, Friesem T, Zdeblick T. The effect of single-level, total disc arthroplasty on sagittal balance parameters: a prospective study. Eur Spine J. 2005; 14(5): 480–486. 13. McAfee PC, Cunningham B, Holsapple G, Adams K, Blumenthal S, Guyer RD, Dmietriev A, Maxwell JH, Regan JJ, Isaza J. Abstract A prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: part II: evaluation of radiographic outcomes and correlation of surgical technique accuracy with clinical outcomes. Spine. 2005; 30(14): 1576–1583. 14. Blumenthal S, McAfee PC, Guyer RD, Hochschuler SH, Geisler FH, Holt RT, Garcia R Jr, Regan JJ, Ohnmeiss DD. A prospective, randomized, multicenter Food and Drug Administration investigational device exemptions study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: part I: evaluation of clinical outcomes. Spine. 2005; 30(14): 1565–1575. 15. Geisler FH, Blumenthal SL, Guyer RD, McAfee PC, Regan JJ, Johnson JP, Mullin B. Neurological complications of lumbar artificial disc replacement and comparison of clinical results with those related to lumbar arthrodesis in the literature: results of a multicenter, prospective, randomized investigational device exemption study of Charite intervertebral disc. J Neurosurg Spine. 2004; 1(2): 143–154. 16. Van Ooij A, Oner FC, Verbout AJ. Complications of artificial disc replacement: a report of 27 patients with the SB Charite disc. J Spinal Disord Tech. 2003; 16(4): 369–383.

17. Philipps F. The fate of facets after lumbar total disc arthroplasty, 2 years clinical and radiographic study, SAS, May 2005, New York. P.150 18. Dickerman R. Stretch neuropraxia after anterior interbody fusion or tda, incidence and prevention SAS, May 2005, New York. 19. Zigler JE, Burd TA, Vialle EN, Sachs BL, Rashbaum RF, Ohnmeiss DD. Lumbar spine arthroplasty: early results using the ProDisc II: a prospective randomized trial of arthroplasty versus fusion. J Spinal Disord Tech. 2003; 16(4): 352–361. 20. Gornet M. Maverick. Total Disc Replacement: a review of 12-month data from 5 investigational centers, NASS, October 2005, Philadelphia. 21. German JW, Foley KT. Disc arthroplasty in the management of the painful lumbar motion segment. Spine. 2005; 30(16 Suppl): S60–67.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Total Disc Arthroplasty > 16 - U.S. Update of CHARITÉ: One Year after FDA Approval

16 U.S. Update of CHARITÉ: One Year after FDA Approval Richard D. Guyer Lucius Craig The development of the CHARITÉ began in 1982. Karin Büttner-Janz and Kurt Shellnack are the pioneers who developed the device. The name for the artificial disc, “CHARITÉ,― was derived from the Berlin Hospital where the work was performed. The SB CHARITÉ prosthesis, which was introduced in 1987, is now in its third generation of design. Initially, the SB CHARITÉ was owned by the Link Company. Link sold the design to J & J DePuy who subsequently named the device the CHARITÉ Artificial Disc. The current prosthesis is available in multiple core heights, endplate sizes, and endplate angles, which allows for anatomic restoration of disc height and lordosis. The CHARITÉ Artificial Disc was introduced to the United States in March of 2000 through an Investigational Device Exemption study and was made commercially available in the United States following Food and Drug Administration (FDA) approval in October 2004. It has been used successfully in more than 11,000 patients worldwide.

Biomechanics In biomechanical kinematic studies, it has been shown that the sliding core of the CHARITÉ mimics the instantaneous axis of rotation of the normal intervertebral disc.

Simply, as one flexes, the center of the nucleus moves posteriorly. In extension, the center of the nucleus moves anteriorly. In comparison to normal intervertebral discs, the CHARITÉ's motions are nearly identical. Additionally, the wear characteristics of the CHARITÉ are favorable compared to metal and polyethylene prosthesis for the hip and knee. At 10 million cycles, the core showed 0.11 mm of wear per million cycles tested. Ten million cycles is the equivalent of lifting 20 kg 125,000 times per year for 80 years (1).

Clinical and Radiologic Outcomes Compared to fusion, total disc arthroplasty offers potential advantages including motion preservation, avoidance of the morbidity associated with a posterior exposure, and potential decrease in adjacent segment breakdown. Both short- and long-term clinical studies have addressed these issues and have yielded promising results. Lemaire et al. (2) reported on the initial patients who underwent the procedure in Europe. They implanted 147 CHARITÉ devices in 100 patients at a mean follow-up of 11.3 years (range 10 to 13.4 years). The mean range of motion was 10.3 degrees in flexion/extension and P.152 5.4 degrees in lateral bending. Ninety-two percent of the patients returned to work. No difference in clinical outcome was found between one- and two-level disc arthroplasty. Their failure rate was 3.3% and these patients were treated with posterior fusions. No migration or spontaneous fusions were noted. Yoon et al. (3) studied their results on a series of 800 patients with the majority at 5year follow-up. Their series consisted of 704 single-level, 92 two-level, and 4 threelevel disc arthroplasties for a total of 825 artificial discs. The mean age was 44.8 years (range 21–81 years). Disc height increased 52% on postoperative radiographs. Visual analogue scale (VAS) pain measurement decreased 5.4 points in leg pain and 4.7 points in back pain (on a 0 to 10 scale). The authors determined that poor prognosis was directly related to poor positioning, violation of the endplate, and obesity. Recently, in the United States, the results of the FDA IDE clinical trial have been published (4,5). These two studies are the landmark articles comparing artificial disc to stand-alone anterior fusion for the treatment of single-level discogenic degeneration in the lumbar spine. A prospective, randomized, controlled, FDA-

regulated trial was conducted at 15 centers across the United States. The study included 375 patients randomized in a 2:1 ratio of CHARITÉ to BAK cages (205:99) plus 71 nonrandomized “training cases.― In March 2000, the first artificial disc was implanted in the United States. An additional 635 disc implantations were performed under a continued access protocol from May 2002 to October 2004. Primary inclusion and exclusion criteria are described in Table 16.1. Two-year follow-up clinical and radiographic data were submitted to the FDA, leading to subsequent approval (October 26, 2004). The data from these studies demonstrate the CHARITÉ Artificial Disc is safe and effective for symptomatic degenerative disc disease at one level (L4-5 or L5-S1) compared with stand-alone ALIF with BAK cages. It provides superior early clinical improvement (p < 0.05) with a shorter hospitalization period and higher patient satisfaction. The authors concluded that results directly correlate to placement of the device. Ideal placement is within 3 mm of midline in both planes. Criticisms of the study include corporate sponsorship, the exclusion of the nonrandomized data in the statistical analysis, and the quoted clinical success rate of 64%. Notwithstanding, the authors' rebuttal with the fact that funding is arbitrary, the clinical success and complication rate of the nonrandomized cases were comparable to the randomized cases, and the success rate is understated secondary to FDA criterion of success.

TABLE 16.1 Overview of Primary Inclusion and Exclusion Criteria

Inclusion criteria • Age 18–60 years • Symptomatic disc degeneration confirmed by discography • Single-level symptomatic disc degeneration at L4-5 or L5-S1 • Oswestry score ≥30 • Visual analogue score (VAS) score ≥40 (of 100) • Failed 6 mo of appropriate nonoperative care

Exclusion criteria • Osteopenia (T-score <-1.0) • Spondylolisthesis >3mm • Scoliosis (>11 degrees sagittal deformity)

P.153 The Texas Back Institute has one of the largest series of CHARITÉ Artificial Disc patients in the United States. From March 2000 through June 2005, 303 discs have been implanted in 283 patients. In our population, the mean operative time was 68.5 minutes for a single-level TDR with an additional 20 minutes for an additional level. The mean blood loss was 134.3 mL. Patients were generally discharged on the first or second postoperative day with a soft corset. Return to normal activity was allowed after 2 weeks with extreme extension limited for 3 months. Normal activity was allowed after 3 months. At 2-year follow-up, VAS scores decreased from 69.1 to 29.5 and the Oswestry Disability Index (ODI) decreased from 49.5 to 24.0. Complications included major neurologic deficit in two patients (foot drops, one of which was transient), minor neuropraxia in five patients, and vascular injury in three patients. The reoperation rate was 3.1%. There were seven posterior fusions and two of the discs were revised. One patient had an intraoperative conversion to a fusion. Subsidence was not clinically significant. None of the devices failed.

Artificial Discs and Facet Joints Data from two separate FDA IDE trials were analyzed to determine the effect that

degenerated facets have on the outcome of total disc arthroplasty (6). The radiographic appearance of the facets of 80 patients (95 operated levels) from TBI who were enrolled in either the CHARITÉ or the ProDisc (Synthes) trial were graded (Grade 0–3) according to the system proposed by Pathria et al. (7). No significant difference was found between the grade 0 and grades 1 and 2 combined at 2-years' follow-up. There were no patients with grade 3 facet degeneration enrolled in either of the trials. These results are similar to Le Huec's study involving the Maverick artificial disc (8). Concerns have arisen about the fate of facet joints after lumbar total disc arthroplasty. Phillips et al. (9) reported on their results of 24 patients with 2-years' follow-up magnetic resonance imagings (MRIs). Fifty-seven percent of patients showed progressive changes in the facet joints after surgery. However, these changes did not correlate with clinical outcomes. Trouillier et al. (10) also studied the changes in facet loading using computed tomography (CT) osteoabsorptiometry preoperatively and at 12 months postoperatively. The rationale for this method of facet evaluation derived from the assumption that changes in load on the facets would result in changes in the subchondral bone density of the facets. No increase in density at the arthroplasty level was noted. Decreased density was seen in the operated level in 10 of 13 patients, the level above the arthroplasty level in 6 of 12 patients, and the level below in 3 of 5 patients. No changes in distribution were seen in the areas of maximal bone density. The authors concluded that arthroplasty is not associated with increased loading of facets at the operated or adjacent levels.

Charité Post-Approval Adverse Events in the United States Since the release of the CHARITÉ Artificial Disc, there have been more than 3,500 implanted in the United States. As required by the FDA, all reoperations, revisions, removals, and vascular approach-related events extending surgical time by at least P.154 30 minutes must be reported by the manufacturer, physicians, hospitals, distributors, and device representatives. Currently, there are approximately 70 known cases of early revision surgery (2.1%). Table 16.2 displays the etiology of these revisions. Keys to avoiding complications including proper patient selection, proper sizing, and proper implantation are reviewed in Table 16.3.

TABLE 16.2 Etiology of Early Revision Surgery • Approximately 70 known cases of early revision surgery (2.1%), similar to IDE • Etiology: - Anterior migration = 18 - Posterior migration = 1 -

Improper sizing/malpositioning = 15 Bone fragment/endplate fracture = 2 Posterior element fracture = 12 Subsidence = 2 Vascular injury = 5 Other = 20

Since release for marketing in October 2004, more than 3,500 CHARITÉ devices have been implanted in the United States.

TABLE 16.3 Keys to Avoiding Complications

• Patient selection - Bone density testing: • Females > yr of age • Males > yr of age • T score <-1.0 - Pars defects (MRIs are not sensitive enough) - Avoid “off label use― • Sizing - Hybrid endplates and porous coating will lessen previous problems (available 2006 of migration and malpositioning ~50% of problems) • Proper implantation technique • Other sources of complications to avoid - Not recognizing and/or not compensating for mismatch ofendplates and retrolisthesis, especially at L5-S1 (study standing lateral x-rays and sagittal MRI) - Oversizing prosthesis and not recessing satisfactorily or inadequate discectomy (hybrid and porous coated endplates will obviate) - Not making metal articular surfaces parallel so that there are not undue stresses on core rim

MRI, magnetic resonance imaging.

P.155

The Future of the CHARITÉ Titanium calcium phosphate coated endplates for the CHARITÉ have been available outside the United States since 1998. Porous coating for the CHARITÉ should be available in the United States in the near future. In a study by McAfee et al. (11), baboons underwent disc arthroplasty with the porous coated version. At 6 months,

mean bone ingrowth of the total endplate coverage area was found to be 47.9%. No evidence of implant loosening or histopathologic change was seen. The porous ingrowth was as favorable as any previously reported ingrowth on other coated total joint prosthesis. Benchtop testing demonstrated a 41% increase in resistance to migration compared to nonporous coated CHARITÉ implants. Hybrid sizing will also be available in the near future. A wider variety of sizes with the same anteroposterior (AP) depths but varying lateral widths will allow for greater coverage of the vertebral body.

Economic Impact As with most new technology, TDR cost effectiveness has been called into question. A cost analysis comparing lumbar TDR with the CHARITÉ Artificial Disc, stand-alone ALIF with iliac crest bone graft, stand alone ALIF with Infuse, and instrumented PLIF was performed from two different perspectives: the hospital and the payer (Figs. 16.1 and 16.2) (12). Single-level TDR procedures were essentially equivalent to the cost associated with the three comparison groups from both the hospital and payer P.156 perspectives. The analysis supports that the introduction of the lumbar TDR as a novel device for the treatment of symptomatic disc degeneration does not increase cost associated with the treatment of these patients.

FIGURE 16.1 Results: hospital perspective.

FIGURE 16.2 Results: payer perspective.

Summary The age of motion preservation in spine surgery has arrived. As with any new technology, there are some early problems. However, they are not at an unreasonable level. Long-term follow-up will determine if motion is maintained, transitional syndrome is avoided, and significant facet changes occur. With the CHARITÉ, there is initially less surgical trauma, faster rehabilitation, better overall early results, and a total economic savings. Porous coated and hybrid endplates may obviate approximately 50% of the early revisions. Overall, CHARITÉ Artificial Disc arthroplasty is one of the most satisfying operations that the senior author performs.

REFERENCES

1. Hedman TP, Kostuik JP, Fernie GR, et al. Design of an intervertebral disc prosthesis. Spine 1991; 16: S256–260. 2. Lemaire JP, Carrier H, Sari Ali E, et al. Clinical and radiological outcomes with the CHARITÉ™ artificial disc: a 10-year minimum follow-up. J Spinal Disord 2005; 18: 353–359. 3. Yoon. Artificial disc replacement with CHARITÉ III in lumbar disc disease: 5 years follow up on 653 patients. Spinal Arthroplasty Society, May, 2005, New York, NY. 4. Blumenthal SL, McAfee PC, Guyer RD, et al. A prospective, randomized, multicenter FDA IDE study of lumbar total disc replacement with the CHARITÉ™ Artificial Disc vs. lumbar fusion: Part I–Evaluation of clinical outcomes. Spine 2005; 30: 1565–1575. P.157 5. McAfee PC, Cunningham B, Holsapple G, et al. A prospective, randomized, multi-center FDA IDE study of the CHARITÉ™ Artificial Disc: a radiographic outcomes analysis, correlation of surgical technique accuracy with clinical outcomes, and evaluation of the learning curve. Spine 2005; 30: 1576–1583. 6. Elders GJ, Blumenthal SL, Guyer RD, et al. Effect of facet joint arthrosis on outcome after artificial disc replacement. Spinal Arthroplasty Society, May, 2005, New York, NY. 7. Pathria M, Sartoris DJ, Resnick D. Osteoarthritis of the facet joints: accuracy of oblique radiographic assessment. Radiology 1987; 164: 227–230. 8. Le Huec JC, Basso Y, Aunoble S, et al. Influence of facet and posterior muscle degeneration on clinical results of lumbar total disc replacement: two-year followup. J Spinal Disord Tech 2005; 18: 219–223.

9. Phillips F, Diaz R, Pimenta L. The fate of the facet joints after lumbar total disc replacement: a clinical and MRI study. Spine J 2005; 5(1S): 75S. 10. Trouillier H, Kern P, Refior HJ, et al. A prospective morphological study of facet joint integrity following intervertebral disc replacement with the CHARITÉ Artificial Disc. Eur Spine J 2006; in press. 11. McAfee PC, Cunningham BW, Orbegoso CM, et al. Analysis of porous ingrowth in intervertebral disc prostheses: a nonhuman primate model. Spine 2003; 28: 332–340. 12. Guyer RD, Tromanhauser SG, Regan JJ, et al. An economic analysis of lumbar total disc replacement vs. fusion. SA5: Global Symposium on Motion Preservation Technology. New York, NY, 2005.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Total Disc Arthroplasty > 17 - Charité III Artificial Disc Replacement: Indications, Preoperative Examinations, and Contraindications

17 Charité III Artificial Disc Replacement: Indications, Preoperative Examinations, and Contraindications B. Poffyn G. Sys D. Uyttendaele The Charité III intervertebral disc prosthesis is the most widely used artificial disc replacement (ADR) in the world for the treatment of lumbar degenerative disc disease (DDD). Artificial discs (ADs) are primarily designed to relieve pain and to preserve the range of motion, while providing segmental stabilization and restoring the natural function of the disc. The success depends on proper patient selection for this type of surgery. A systematic standard battery of technical investigations and a course of conservative treatment in the preoperative period are mandatory to achieve a good outcome.

Preoperative Examinations The preoperative examinations that are necessary for a correct diagnosis include xrays, dynamic x-rays, magnetic resonance imaging (MRI), facet blocks, and discography.

Plain x-rays demonstrate single- or multiple-level DDD, spondylolisthesis, and spondylolytic problems. Spondylodiscitis, infections, spinal tumors, translational instabilities and retrolisthesis/anterolisthesis are identified on anteroposterior and lateral views. Dynamic x-rays disclose ligamentous hypermobility and anteroposterior slip due to instability. MRI provides an appreciation of disc degeneration, with or without Modic changes and also detects disc fragment expulsion, disc herniation, discitis, tumors, and fractures. In cases of radiographic suspicion of osteoporosis and in female patients older than the age of 45 years preoperative dual-energy x-ray absorptiometry (DEXA) is mandatory. Facet blocks at the involved level can indicate whether the facet joints are the pain generators. If they are, complete pain relief will be obtained after injection of lidocaine. If the pain fails to disappear, it does not originate in the facet joints. Discography is one of the most important examinations. Through the injection of radio-opaque fluid the pressure in the affected disc is increased. If the disc is pathologic, the pain the patient experiences in daily life can be reproduced. Discography at the level above and below the “black disc― is very important to document that the affected disc actually is the pain source in that particular patient. P.160

FIGURE 17.1 Overdistraction of the disc space.

Indications Ideal candidates are patients younger than 50 years with single or double DDD and decompensated segment instability, primarily due to nucleotomies, chemonucleolysis, and physiologic degeneration of the disc. Conservative treatment during 6 months before surgery should have been unsuccessful. The back pain must be discogenic and confirmed by history and radiographic studies. Degenerative disc changes are usually combined with narrowing of the disc space. Narrowing to a height of 5 mm does not interfere with the distraction required during AD implantation. In previously operated patients, posterior scar tissue might elongate the nerve roots during distraction of the disc space (Fig. 17.1), with residual radicular pain after surgery. Patients with failed disc surgery syndrome without laminectomy nor severe facet

alterations can be treated with ADR (Fig. 17.2).

FIGURE 17.2 Disc degeneration after discectomy L4-5.

P.161 The median disc herniation at L4-5 and L5-S1 can be removed through an anterior approach before AD placement. Patients with persistent back pain after treatment of spondylolysis are also candidates for ADR. Soft tissue foraminal stenosis with nerve root irritation can be treated with distraction of the neuroforamen and the disc space, followed by ADR. Borderline indications for ADR are adjacent-level degeneration and instability after

fusion (Fig. 17.3). An option after failure of nucleus replacement at L5-S1 with symptomatic L4-5 discopathy is AD placement at the symptomatic level, combined with an anterior fusion at L5-S1 after removal of the artificial nucleus.

FIGURE 17.3 Adjacent-level degeneration after fusion.

P.162

FIGURE 17.4 L4-5 artificial disc replacement (ADR) after PDN disc at the L5-S1 level with positive discography at L4-5.

Contraindications Even more important are the contraindications to ADR: Patients with translational instability as in scoliosis for example are not good candidates. In the majority of cases, significant facet arthrosis and hypertrophic facet joints are responsible for facet pain not for discogenic pain.

Recessus stenosis might result in radicular pain after distraction of the disc space due to nerve root impingement by the osteophytes. Degenerative and isthmic spondylolisthesis might contribute to instability and failure of ADR. P.163 In patients with osteoporosis and metabolic bone diseases, subsidence of the endplates into the vertebral body might lead to a poor outcome. Patients with neuromuscular diseases, infections, and tumors are not eligible for ADR, nor are patients older than the age of 50 years because the quality of subchondral bone decreases with age. Facet joint degeneration increases, and during the operative procedure the large blood vessels must be manipulated with a higher risk of thrombosis, stenosis, and venous tears.

Conclusion Exclude patients older than 50 years, patients with facet degeneration and spinal instability, patients with spondylolisthesis and osteoporosis, and patients with infections and tumorous conditions. Try to indicate one or two discs as the principal source of pain with MRI and discography. Do not promise “heaven―! Many patients are doing better after ADR, only a minority are perfect!

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Total Disc Arthroplasty > 18 - Clinical Results of Lumbar Total Disc Replacement with the Maverick Prosthesis Prospective Study, 2 to 4 Years Follow-Up

18 Clinical Results of Lumbar Total Disc Replacement with the Maverick Prosthesis Prospective Study, 2 to 4 Years Follow-Up J.-C. Le Huec S. Aunoble M. Ronai Y. Basso Jan Van Lommel T. Friesem The development of total lumbar disc prostheses has been a logical step in the management of chronic back pain. Clinical results of studies on disc prostheses report patient satisfaction rates, Oswestry scores, and visual analogue assessments for back pain (1,2,3,4,5,6). However, there has been little analysis of visual analogue scores for associated root pain and SF36 score. For example, no study has yet assessed the correlation between the clinical functional result and the position of the implants, the arthrosis of the posterior facets, or the fatty degeneration of the spinal muscles. However, such knowledge is essential for understanding the long-term outcome of devices in functional terms (7). Disc degeneration around the device is also of prime importance because this conditions the final result in the mid and long term.(8) This prospective study therefore reports the outcome of 64

Maverick (Medtronic USA) devices implanted between January 2002 and November 2003. Minimum follow-up was 2 years postoperative with a mean of 31 months (range 24–48 months).

Material and Method Sixty-four patients were included in this prospective study and operated in one center by one surgeon. All patients had been suffering from chronic back pain resistant to conservative treatment for at least l year and had received medical and rheumatologic follow-up and rehabilitation physiotherapy. Contraindications for disc arthroplasty were the following: previous spinal surgery other than discectomy at the painful level, lumbar fracture, permanent symptomatic disc hernia, narrow lumbar canal or isthmic spondylolisthesis, scoliosis greater than 15-degrees Cobb angle, spinal tumor, general or local infection, evolving autoimmune disease, pregnancy, morbid obesity, psychiatric disturbances, and major bone disease. Inclusion criteria were as follows: age between 20 and 60 years irrespective of gender, symptomatic degenerative lumbar discopathy as evidenced by radiography and magnetic resonance imaging (MRI), failure of conservative treatment given for longer P.166 than 12 months, Oswestry score > 30%, predominant chronic back pain, and absence of permanent nerve root compression. There were 64 patients, mean age 44 years (SD 7), measuring a mean height of 1.68 m (SD 0.09) and weighing 68 kg (SD 12). There were 39 women and 25 men, all of Caucasian type. Thirty percent were smokers and 9% had back pain associated with a work accident. Professionally, 20 were attending work, 21 were absent on account of their back pain, and 23 were no longer able to work. Eighteen patients had had previous spinal treatment: 3 isolated rhizolysis of the posterior facets and disc annuloplasties by radiofrequency at the painful level, one of which was followed by discectomy. There were also 8 patients who had received disc nucleolysis with chymopapain, one of which was followed by discectomy. Twentyfour had a history of abdominal surgery as follows: 13 appendicectomies, 2 extrauterine pregnancies, 6 cesarean sections, 3 surgeries for groin hernia, 2

cholecystectomies, 4 tubal ligations under coelioscopy, and 2 hysterectomies. Levels to be operated were the following: disc prosthesis L5-S1 (35 cases), L4-5 (14 cases) and arthrodesis L5-S1 with disc prosthesis at L4-5 (13 cases), and prosthesis at L3-4 (2 cases). All had received radiologic, static, dynamic, and load-bearing evaluation, in addition to MRI. Preoperative MRI was used to assess the state of the disc. Disc degeneration was measured on T2-weighted sagittal slices and classified as described by Fujiwara (8): grade 1, normal disc; grade 2, normal height with median transversal dark band; grade 3, normal height but with hypointensity; grade 4, slightly decreased height accompanied by inhomogeneous hypointensity; and grade 5, clearly diminished hypointense heterogeneous disc with hyperintense transversal lines. High intensity zone (HIZ) was noted. For facet arthrosis, we used the MRI classification described by Fujiwara (9): grade 1, normal facets; grade 2, moderately compressed facets with small osteophytes; grade 3, facets with subchondral sclerosis and moderate osteophytes; and grade 4, facets lacking articular joint space and with large osteophytes. For muscle degeneration, Goutallier's scale was applied (10): grade 1, normal muscle; grade 2, muscle interspersed with some fat; grade 3, as much muscle as fat; and grade 4, more fat than muscle. Radiography was used to examine mobility during flexion-extension around the device and the two adjacent levels. Sagittal equilibrium was assessed by radiography in standing anteroposterior (AP) and lateral position. Measurements performed by an independent radiologist on AP and lateral radiographs were accurate to 3 degrees for angles and 3 mm for distances. The prosthesis is inserted by a mini-invasive anterior approach (11) with complete discectomy and release of the discal space. The patient is positioned supine in the so-called French position, with legs bent and open laterally (12,13). The surgeon stands between the legs facing the lumbar spine in the cephalad-caudal direction, which is ergonomic for checking the midline of the spine when approaching the L5S1 and L4-5 levels. The assistant stands on the right or left side of the patient. The incision is longitudinal or horizontal crossing the midline, 7 to 8 cm long. A Pfannenstiel incision is more cosmetic for one-level surgery. After vertical incision of the rectus abdominis sheath, the muscle is retracted laterally to reach the

common fascia of the external oblique muscle. The retroperitoneal space is reached and the peritoneal sac retracted. The peritoneal sac is pushed to the contralateral side with the ureter and the hypogastric plexus. The vessel bifurcation is now exposed and analyzed. To reach L5-S1, the left iliac vein must be carefully retracted and the medial sacral vessels ligated. An opening to the anterior part of the L5-S1 disc of least 32 mm must be exposed. At the L4-5 level, the left approach is commonly used. The surgeon must pay attention to the ascending lumbar vein, which is located at the corner of the psoas belly and the left iliac vein. This P.167 important collateral must be ligated. The segmental vessels at L4 and L5 must also be ligated to allow retraction of the aorta and vena cava. Traction on the left iliac vein must be controlled throughout the procedure. The anterior part of the disc is opened according to the size of the templates. The anterior annulus and nucleus are removed using disc rongeur, Kerrison, curettes, and a scraper. The posterior annulus must be opened to free the disc space and to allow good restoration of the disc height. It is not necessary to open the posterior longitudinal ligament, but it must be detached from the posterior border of the endplates using the specific instruments. The mobility of the disc space is tested with a spreader under C-arm control. The midline is checked with AP fluoroscopy. A dedicated instrument is introduced in the disc space and makes it possible to create a parallel distraction of the disc, thus restoring the disc height. The upper or the lower keel cutter is slid onto a guide and impacted into the vertebral body to prepare the bed for the fin of the prosthesis. The prosthesis is impacted into the prepared disc space under fluoroscopic control. The retractors are carefully removed and bleeding is controlled. The rectus abdominis fascia and subcutaneous fat are closed with drainage. The implant used is a metal on metal disc prosthesis Maverick (Medtronic, Memphis, TN) made of cobalt chrome, with a ball and socket design. The prosthesis has a fixed posterior center of rotation located below the lower endplate. The production of wear debris is very low without epidural reaction on animal studies (3,12,14). All patients were seen at 1, 3, and 6 months, then 1 and 2 years, and each year after this point with assessment of pain, according to a visual analogue scale (VAS),

neurologic function, Oswestry scores, and the SF36 (15). Clinical success was taken to be a 25% improvement on the Oswestry score, that is, the success rate defined by the U.S. Food and Drug Administration (FDA) in a randomized prospective study concerning the SB Charité prosthesis (16). Degree of patient satisfaction was noted, as were need of antalgics and duration of treatment with antalgics or antiinflammatory agents. All patients received postoperative physiotherapy from 1 week postoperative and wore a supple girdle for 6 weeks. Statistical analysis was with the t test and the chi-square test.

Results All the patients underwent follow-up examinations. Oswestry score preoperative and at 4-years' follow-up was 43.8 and 24.1, respectively. Low back pain improved from a mean VAS of 7.6 ± 1.7 preoperatively to 3.3 ± 1.7 at 4 years. Mean VAS leg pain score decreased from 3.9 to 2.2 at 4 years (p < 0.05). Mean daily duration of back pain decreased from 70% to 42% (p < 0.05). Daily duration of leg pain decreased from 36% to 23% (p < 0.05). According to the FDA criteria (>25% improvement of Oswestry score) (17), the success rate was 75.6% (p < 0.05). Improvement in back pain directly affected the improvement in Oswestry score (p = 0.008) (Table 18.1).

TABLE 18.1 Clinical Results of Lumbar Total Disc Replacement With the Maverick Prosthesis

Preoperative

1

3

6

month

months

months

1 year

4 years

Oswestry

43.8

34.8*

26.3*

24.2*

22.8*

24.1*

Leg pain

3.9

3

2.7

2*

2.4*

2.2*

Back

7.6

3.7*

3*

3*

3.5*

3.3*

pain

P.168 Evolution of SF score was weighted according to gender and age of the patient. An improvement >15% was taken as success (7,16). Thus, 85% of patients experienced physical improvement at 1 year, and improvement of mental health was noted in 43%. The mean hospital stay was 4.6 days (3 to 10 days).

Complications There were four cases of postoperative root pain and two sequelae from previous surgery for discectomies. Seventeen patients received posterior facet infiltration including 11 with a good result. Three patients had spinal pain other than in the lumbar region. One patient had a superficial infection treated by local debridement. There was one visceral lesion due to the surgical incision. This was damage to a ureter in a female patient operated on several times for gynecologic problems. The damage was successfully repaired and the orthopaedic result is excellent. Minor intraoperative complications were noted due to the surgical approach in 11 cases. There was never any breakage of the device. No implant had to be removed or surgically revised. Consumption of antalgics was reduced overall because no patient needed any morphine-based drugs postoperatively, whereas 62% were taking them preoperatively. With regard to resumption of professional activity, 63% returned to work, mean time to return to work being 5 months (range: 2 months to 1 year). When the Oswestry score was improved by ≥25%, there was a 44.4% chance of

returning to work. When the score was improved 75%, the chance was 73% (p = 0.004). Factors influencing the clinical result in terms of success were as follows: young age associated with a good result (p = 0.05) and female gender associated with better results (p = 0.003). On the other hand, previous spine surgery decreased the chance of having a good result (p = 0.005), whereas being off work before the intervention did not influence clinical outcome (p = 0.14).

Radiologic Results Mobility in flexion and extension was 7.9 degrees at L5-S1, 9.4 degrees at L4-5, and 7.4 degrees at L4-5 when there is an arthrodesis at L5-S1. Postoperatively the device migrated axially 3 to 5 mm in the region of the superior endplate in 5 patients. This subsidence was stable at l-year follow-up. The outcome was satisfactory in 3 patients with an Oswestry score averaging 14 and a VAS pain score of 2. For the other two patients, one had a very poor result (Oswestry improvement zero) and the other a poor one (Oswestry improvement 10). There was no case of anterior or posterior migration. Three patients had heterotopic ossification, including two type 1 and one type 3; according to McAfee classification (17), all were mobile on dynamic x-rays. Correlations between improvement in Oswestry score and radiologically diagnosed criteria were as follows: facet osteoarthritis grade 1 or 2 did not influence outcome (p = 0.82); the presence of an HIZ in the indication did not influence outcome (p = 0.66); the presence of an osteophyte did not influence outcome (p = 0.69); the presence of intradiscal gas did not influence outcome (p = 0.34); the presence of a change in Modic 1 or 2 type signal in the indication did not influence outcome (p = 0.33). On the other hand, certain criteria did influence functional outcome: muscle degeneration, grades 1 and 2 leading to a better outcome than grades 3 and 4 (p = 0.006); absence of McNab osteophytes on the spine other than at the operated region being associated with success (p = 0.003). P.169

Discussion Discectomy with insertion of total disc prosthesis has been widely reported to

improve the clinical symptoms of chronic back pain (5,6,16,18,19,20). The degree of improvement is equivalent to that obtained with anterior fusion cages using the mini-invasive technique (21). Radiographic follow-up in our series showed a degree of mobility close to normal (14,22) and confirms the results obtained with other devices such as the SB Charité, as reported by many authors (5,6,16,17,19,20), and with the Prodisc, as reported by Bertagnoli and Kumar (2) and Mayer et al. (11). The technique is safe because the intra- and postoperative complication rate is very low and equivalent to others series (2,3,16). The patients recover rapidly and the mean hospital stay of 3 to 5 days is close to Bertagnoli and Kumar (2) and Lemaire et al (5). This is to compare with 8 to 12 days for an arthrodesis reported by Katz (23). The Oswestry score improved for 75% and this improvement is significantly correlated with facet arthrosis and muscle fatty degeneration. It has been demonstrated that the disc degenerates before the facets (24), but facet arthrosis could be a limiting factor for total disc replacement, particularly in adjacent level disease after fusion (25,26). This is the first study showing that a semi-constrained implant with a fixed posterior center of rotation can be implanted with grade 1 and 2 facet arthrosis with a good clinical outcome. This seems to confirm the work of Doris et al. (27), showing that a posterior center of rotation lightens the load on the facets. This is also the first study to show a relationship between muscle fatty degeneration and clinical results because the greater the amount of fat, the less satisfactory the result. Contrary to the posterior approach, the anterior implantation technique does not damage the spinal muscles and shortens the delay until activity can be resumed. The SF36 is well improved for the physical score and less for the mental score. This is similar to the prospective randomized study of the FDA with SB Charité device (16). In total, a semiconstrained device with a fixed center of rotation is a biomechanical tradeoff for obtaining a very good clinical outcome, providing the device is implanted within the safety margins outlined previously. This is the first report of such an outcome. Other disc prosthesis designs were less successful in the past (18,28,29). Disc prostheses offer the prospect of earlier treatment of certain recalcitrant chronic back pain without having recourse to an arthrodesis. It is always possible to

revert to an arthrodesis if results are poor or if there is progressive degeneration of the posterior structures (25). A few cases of arthrodesis with posterior fixation and a posterolateral graft have been reported by Lemaire et al. (5) for treating patients whose pain is recalcitrant. The failure may be due to a technical error or to an erroneous indication, so patients should be selected according to very rigorous criteria. Le Huec et al. (12) have proposed guidelines that take into account the characteristics not only of the pathologic level (disc and posterior elements) but also of the adjacent levels. The spontaneous fusion of certain prostheses has been reported by Lemaire et al. (5), a problem always accompanied by intraprosthetic calcification. One solution is to prescribe postoperative nonsteroidal antiinflammatory drugs, as in hip prostheses. Another is to limit the bleeding of the vertebral endplates by applying a hemostatic agent on the bony tissue not covered by the prosthesis. Even heterotopic calcifications allowed the prosthesis to be mobile in our three cases. On the basis of the McAfee classification (17), it is not possible to know whether these patients will reach grade 4 calcification and therefore lose their mobility. The metal on metal couple of the implant used seems very safe as demonstrated by animal studies (14) and previous works in total hip by Jacobs et al. (30) and Haynes et al. (31). The quantity of wear debris produced by a metal on metal P.170 implant is very low compared to metal on polyethylene prosthesis (30). Le Huec et al. (32) showed that there was no shock absorption difference in between metal on metal and metal on polyethylene disc prosthesis in physiologic conditions. Prosthesis dislocation have been reported for Prodisc (33) and SB Charité prosthesis (34) but never with the Maverick implant. The design of the Maverick in respect to fundamental criteria proposed by Hedman et al. (35) and Dooris et al. (27) is probably very important regarding the biomechanics.

Conclusion The metal-metal Maverick device with a posterior center of rotation and controlled translation is a promising therapeutic technique. Its mechanical characteristics and resistance to wear make it an interesting option in terms of its life cycle. Only longterm follow-up exceeding 5 years will make it possible to confirm these very favorable preliminary results and to analyze the effects on the segments adjacent

to the levels operated. This series shows that, for one-level degenerative disc disease, the early results are equivalent to the best ALIF series (21) with a low complication rate. The total disc replacement could offer benefit by preventing adjacent level disease thanks to decreased stress on the adjacent disc once the sagittal balance is restored (36).

REFERENCES 1. Allen et al. The effects of particulate cobalt, chromium, and cobaltchromium alloy on human osteoblast-like cells in vitro. J Bone Joint Surg Br 1997; 79: 475–482. 2. Bertagnoli R, Kumar S. Indications for full prosthetic disc arthroplasty: a correlation of clinical out-come against a variety of indications. Eur Spine J 2002; 11: 131–136. 3. Cinotti G, David T, Postacchini F. Results of disc prosthesis after a minimum follow-up period of 2 years. Spine 1996; 21: 995–1000. 4. Enker P, Steffee A, McMillin C, et al. Artificial disc replacement: preliminary report with a 3 year minimum follow-up. Spine 1993; 18: 1061–1070. 5. Lemaire JP, Skalli W, Lavaste F, et al. Intervertebral disc prosthesis: results and prospects for the year 2000. Clin Orthop 1997; 337: 64–76. 6. Zeegers WS Bohnen LMU, Laaper M, et al. Artificial disc replacement with the modular type SB Charité III: 2-year results in 50 prospectively studied patients. Eur Spine J 1999; 8: 210–217. 7. Mayer HM, Korge A. Non fusion technology in degenerative lumbar spinal disorders: facts, questions, challenges. Eur Spine J 2002; 11: 85–91.

8. Fujiwara A, Tamai K, An HS, Kurihashi T, Lim TH, Yoshida H, Saotome K. The relationship between disc degeneration, facet joint osteoarthritis, and stability of the degenerative lumbar spine. J Spinal Disord 2000; 13: 444–450. 9. Fujiwara A, Tamai K, An HS, Lim TH, Yoshida H, Kurihashi A, Saotome K. Orientation and osteoarthritis of the lumbar facet joint. Clin Orthop 2001; (385): 88–94. 10. Goutallier D, Postel JM, Bernageau J, Lavau L, Voisin MC. Fatty muscle degeneration in cuff ruptures. Pre- and postoperative evaluation by CT scan. Clin Orthop 1994; 304: 78–83. 11. Mayer HM, Wiechert K, Korge A, Qose I. Minimally invasive total disc replacement: surgical technique and preliminary results. Eur Spine J 2002; 11: 124–130. 12. Le Huec JC, Aunoble S, Friesem T, Mathews H, Zdeblick T. Maverick total lumbar disk prosthesis: biomechanics and preliminary clinical results. In: Gunzburg R, Spalzski M, eds. Arthroplasty of the spine. Lippincott, 2004: 53–58. 13. Le Huec, Aunoble S, Magendie J, Hadidane R. Video-assisted anterior approach to the spine. In: Surgical techniques in orthopaedics and traumatology. Editions scientifiques et médicales Elsevier SAS, Paris; 2003. 55–060-D-I0. P.171 14. Mathews Hallett H, Le Huec JC, Friesem T, Zdeblick T, Eisermann L. Design rationale and biomechanics of Maverick Total Disc arthroplasty with early clinical results. Spine J 2004; 4: S268–S275. 15. Frymoyer JW. Indications for consideration of the artificial disc. In:

Weinstein JN, ed. Clinical efficacy and outcome in the diagnosis and treatment of low back pain. Raven Press, New York, 1992: 227–236. 16. Guyer RD, McAfee PC, Hochschuler SH, Blumenthal SL, Fedder IL, Ohnmeiss DD, Cunningham BW. Prospective randomized study of the Charite artificial disc: data from two investigational centers. Spine J 2004;4(6 Suppl): S252–259. 17. McAfee PC, Cunningham BW, Devine J, Williams E, Yu-Yahiro J. Classification of heterotopic ossification (HO) in artificial disk replacement. J Spinal Disord Tech 2003; 16: 384–389. 18. Cunningham BW, Lowery GL, Serhan HA, Dmitriev AE, Orbegoso CM, McAfee PC, Fraser RD, Ross RE, Kulkarni SS. Total disc replacement arthroplasty using the acroflex lumbar disc: a non human primate model. Eur Spine J 2002; 11: 115–123. 19. Griffith SL, Shelokov AP, Buttner-Janz K, et al. A multicenter retrospective study of the clinical results of the LINK SB Charité intervertebral prosthesis: the initial European experience. Spine 1994; 19: 1842–1849. 20. Hochschuler SR, Ohnmeiss DD, Guyer RD, Blumenthal SL. Artificial disc: preliminary results of a prospective study in the United States. Eur Spine J 2002; 11: 106–110. 21. Burkus JK, Gornet MF, Dickman CA, Zdeblick TA. Anterior lumbar interbody fusion using rhBMP-2 with tapered interbody cages. J Spinal Disord Tech 2002; 15: 337–349. 22. Buttner-Janz K, Schellnack K, Zippel H. Biomechanics of the SB Charité lumbar intervertebral disc endoprosthesis. Int Orthop 1989; 13: 173–176.

23. Katz JN. Lumbar spinal fusion: surgical rates, costs, and complications. Spine 1995; 20(Suppl):78–83. 24. Butler D, Trafimow JH, Andersson GB, et al. Discs degenerate before facets. Spine 1990; 15: 111–113. 25. Eck JC, Humphreys SC, Hodges SD. Adjacent-segment degeneration after lumbar fusion: a review of clinical, biomechanical, and radiologic studies. Am J Orthop 1999; 28: 336–340. 26. Lee CK. Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine 1988; 13: 375–377. 27. Dooris AP, Goel VK, Grosland NM, Gilbertson LG, Wilder DG. Load sharing between anterior and posterior elements in a lumbar motion segment implanted with an artificial disc. Spine 2001; 26: 122–129. 28. Ferstrom U. Arthroplasty with intercorporal endoprosthesis in herniated disc and painful disc. Acta Orthop Scand 1996; 10(IJ): 287–289. 29. Kostuik. JP Intervertebral disc replacement: experimental study. Clin Orthop 1997; 27–41. 30. Jacobs IL, Skipor AK, Doorn PF, et al. Cobalt and chromium concentrations in patients with metal on metal total hip replacements. Clin Orthop 1996; (Suppl): 256–263. 31. Haynes D, Rogers S, Hay S, Pearcy M, Howie D. The differences in toxicity and release of bone resorbing mediators induced by titanium and cobaltchromium alloy wear particles. J Bone Joint Surg Am 1993; 75: 825–834. 32. Le Huec JC, Kiaer T, Friesem T, Mathews H, Liu M, Eisermann L. Shock

absorption in lumbar disc prosthesis, a preliminary mechanical study. J Spinal Disord 2003; 16: 346–351. 33. Aunoble S, Donkersloot P, Le Huec JC. Dislocations with intervertebral disc prosthesis: two case reports. Eur Spine J 2004; 13: 464–467. 34. Van Ooij A. Analysis of 21 patients with clinically failed Charité disc prosthesis. Eur Spine J 2002; 1(Abstract 47). 35. Hedman TP, Kostuik JP, Fernie GR, et al. Design of an intervertebral disc prosthesis. Spine 1991; 16: 256–260. 36. Le Huec JC, Basso Y, Mathews H, Mehbod A, Aunoble S, Friesem T, Zdeblick T. The effect of single level total disc arthroplasty on sagittal balance parameters: a prospective study. Eur Spine J 2005; 14: 480–486.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Total Disc Arthroplasty > 19 - Influence of Frontal and Sagittal Position of Total Disc Arthroplasty on Clinical Outcomes at 3 Years Follow-Up

19 Influence of Frontal and Sagittal Position of Total Disc Arthroplasty on Clinical Outcomes at 3 Years Follow-Up S. Aunoble J.-C. Le Huec The development of total lumbar disc prostheses has been a logical step in the management of chronic back pain. Clinical results of studies on disc prostheses report patient satisfaction rates, Oswestry scores, and visual analogue assessments for back pain (1,2,3,4,5,6). This motion technology requires an optimal positioning of the implant as reported by Mayer (7). The correlation between the clinical functional result and the position of the implants has rarely been reported. However, such knowledge is essential for understanding the long-term outcome of devices in functional terms (7). This prospective study therefore reports the outcome of 64 Maverick (Medtronic USA) devices implanted between January 2002 and November 2003. Minimum follow-up was 2 years postoperative, with a mean of 24 months (range: 18–36 months).

Material and Method Sixty-four patients were included in this prospective study and operated in one center by one surgeon. All patients had been suffering from chronic back pain resistant to

conservative treatment for at least l year and had received medical and rheumatologic follow-up and rehabilitation physiotherapy. Contraindications for disc arthroplasty were the following: previous spinal surgery other than discectomy at the painful level, lumbar fracture, permanent symptomatic disc hernia, narrow lumbar canal or isthmic spondylolisthesis, scoliosis greater than 15degrees Cobb angle, spinal tumor, general or local infection, evolving autoimmune disease, pregnancy, morbid obesity, psychiatric disturbances, and major bone disease. Inclusion criteria were as follows: age between 20 and 60 years irrespective of gender, symptomatic degenerative lumbar discopathy as evidenced by radiography and magnetic resonance imaging (MRI), failure of conservative treatment given for longer than 12 months, Oswestry score >30%, predominant chronic back pain, and absence of permanent nerve root compression. There were 64 patients, mean age 44 years (SD 7.1), measuring a mean height of 1.68 m (SD 0.09) and weighing 68 kg (SD 12). There were 39 women and 25 men, all of the Caucasian race. Thirty percent were smokers and 9% had back pain associated P.174 with a work accident. Professionally, 20 were attending work, 21 were absent on account of their back pain, and 23 were no longer able to work. Eighteen patients had had previous spinal treatment: 3 isolated rhizolysis of the posterior facets and 4 disc annuloplasties by radiofrequency at the painful level, one of which was followed by discectomy. There were also 8 patients who had received disc nucleolysis with chymopapain, one of which was followed by discectomy. Twenty-four had a history of abdominal surgery as follows: 13 appendectomies, 2 extrauterine pregnancies, 6 cesarean sections, 3 surgeries for groin hernia, 2 cholecystectomies, 4 tubal ligations under coelioscopy, and 2 hysterectomies. Levels to be operated were the following: disc prosthesis L5-S1 (35 cases), L4-5 (14 cases), and arthrodesis L5-S1 with disc prosthesis at L4-L5 (13 cases), and prosthesis at L3-4 (2 cases). All had received radiologic, static, dynamic and load-bearing evaluation, in addition to MRI. Preoperative MRI was used to assess the state of the disc. Radiography was used to examine mobility during flexion-extension at the level of the device and the two adjacent levels. Measurements performed by an independent

radiologist on anteroposterior (AP) and lateral radiographs were accurate to 3 degrees for angles and 3 mm for distances. Implant position was defined according to coronal x-rays as shown in Fig. 19.1. In this way, the keel of the device serves as a landmark to establish its position. The symmetrical center of the vertebra corresponds coronally to the midpoint of its width. The distance between the midpoint of the vertebra and the keel of the device is related to the radius of the vertebra and expressed as a percentage. When the device is centered, its degree of lateralization is 0%. The more lateralized it is, the closer it is to a score of 100%. Our arbitrary rating system is as follows: 0 to 9%, well centered; 10 to 19%, moderately off center; and 20% and above, off center. Implant position was defined on lateral x-rays as shown in Fig. 19.2. The position of the device was defined according to the distance between its posterior edge and the posterior edge of the inferior vertebral body of the segment. To obtain a value independent from the radiographic enlargement factor, measurements were related to the size of the keel of the device, which was constant whatever the model. If the device was too posterior (in the vertebral canal), the distance was expressed as a negative value. A distance from P.175 the posterior edge of the vertebra between 4 and 7 mm was considered to represent a moderately correct position, whereas a distance <4 mm was taken to be satisfactory. Any distance >7 mm was considered inadequate.

FIGURE 19.1

FIGURE 19.2

The prosthesis is inserted by a mini-invasive anterior approach (11) with complete discectomy and release of the discal space. The patient is positioned supine in the socalled French position, with legs bent and open laterally (12,13). The incision is longitudinal or horizontal crossing the midline, 7 to 8 cm long. After vertical incision of the rectus abdominis sheath, the muscle is retracted laterally to reach the common fascia of the external oblique muscle. The peritoneal sac is pushed to the contralateral side with the ureter and the hypogastric plexus. To reach L5-S1, the left iliac vein must be carefully retracted and the medial sacral vessels ligated. At the L4-5 level, the surgeon must pay attention to the ascending lumbar vein, which is located at the corner of the psoas belly and the left iliac vein. This important collateral must be ligated. The segmental vessels at L4 and L5 must also be ligated to allow retraction of the aorta and vena cava. The anterior part of the disc is opened according to the

size of the templates, then the anterior annulus and nucleus are removed using disc rongeur, Kerrison, curettes, and a scraper. It is not necessary to open the posterior longitudinal ligament, but it must be detached from the posterior border of the endplates using the specific instruments. The mobility of the disc space is tested with a spreader under C arm control. The midline is checked with AP fluoroscopy. A dedicated instrument is introduced in the disc space and makes it possible to create a parallel distraction of the disc, thus restoring the disc height. The upper or the lower keel cutter is slid onto a guide and impacted into the vertebral body to prepare the bed for the fin of the prosthesis. The position of the implant on the lateral view is controlled on the fluoroscopic image and the correct position is a distance in between the posterior part of the inferior vertebral endplate and the posterior part of the implant inferior to 4 mm. The prosthesis is impacted into the prepared disc space under fluoroscopic control. The retractors are carefully removed and the rectus abdominis fascia and subcutaneous fat are closed with drainage. The implant used is a metal on metal disc prosthesis Maverick (Medtronic, Memphis, TN) made of cobalt chrome, with a ball and socket design. The prosthesis has a fixed posterior center of rotation located below the lower endplate. The production of wear debris is very low without epidural reaction on animal studies (3,12,14). All patients were seen at 1, 3, and 6 months, then 1 and 2 years, with assessment of pain, according to a visual analogue scale (VAS), neurologic function, Oswestry scores, and the SF36 (15). Clinical success was taken to be a 25% improvement on the Oswestry score, and 2 points improvement on the VAS back pain score, that is, the success rate defined by the U.S. Food and Drug Administration (FDA) in a randomized prospective study concerning the SB Charité prosthesis (16). Degree of patient satisfaction was noted, as were need of antalgics and duration of treatment with antalgics or anti-inflammatory agents. All patients received postoperative physiotherapy from 1 week postoperative and wore a supple girdle for 6 weeks. Statistical analysis was with the t test and the chi-square test. P.176

Results All the patients underwent follow-up examinations preoperatively, immediate postoperatively, and at 2-years' follow-up. Oswestry score preoperatively and at 2-

years' follow-up was 43.8 and 23.1, respectively (p < 0.05). Low back pain improved from a mean VAS of 7.6 ± 1.7 preoperatively to 3.2 ± 1.8 at 2 years (p < 0.05). Mean visual analogue leg pain score decreased from 3.9 to 2.1 at 2 years (p < 0.05). Mean daily duration of back pain decreased from 70% to 40% (p < 0.05). Daily duration of leg pain decreased from 36% to 20% (p < 0.05). According to the FDA criteria (>25% improvement of Oswestry score and >2 points of back pain on VAS) (17), the success rate was 75% (p < 0.05). Improvement in back pain directly affected the improvement in Oswestry score (p = 0.008) (Table 19.1). Evolution of SF score was weighted according to gender and age of the patient. An improvement >15% was taken as success.(7,16) Thus, 85% of patients experienced physical improvement at 1 year, and improvement of mental health was noted in 43%. The mean hospital stay was 4.6 days (3 to 10 days).

Complications Minor intraoperative complications were noted due to the surgical approach in 11 cases. There was never any breakage of the device. No implant had to be removed or surgically revised. Consumption of antalgics was reduced overall because no patient needed any morphine-based drugs postoperatively, whereas 62% were taking them preoperatively. With regard to resumption of professional activity, 63% returned to work, mean time to return to work being 5 months (range: 2 months to 1 year). When the Oswestry score was improved by ≥ 25%, there was a 44.4% chance of returning to work. When the score was improved 75%, the chance was 73% (p = 0.004). Factors influencing the clinical result in terms of success were as follows: young age associated with a good result (p = 0.05) and female gender associated with better results (p = 0.003). On the other hand, previous spine surgery decreased the chance of having a good result (p = 0.005), whereas being off work before the intervention did not influence clinical outcome (p = 0.14).

Radiologic Results Mobility in flexion and extension was 7.9 degrees at L5-S1, 9.4 degrees at L4-5, and 7.4 degrees at L4-5 when there is an arthrodesis at L5-S1. The coronal position of the device was considered excellent in 51 cases (79.6%) and satisfactory in 13 cases

P.177 (20.4%); there was no insertion with an offset superior to 19% (Table 19.2A). The average offset in the excellent group was 2.80%, and in the satisfactory group was 14.40%. The position of the implant on lateral was considered excellent in 57 cases (89%) and satisfactory in 7 cases (11%). No implant was inserted with a distance superior to 7 mm from the posterior wall of the inferior vertebra (Table 19.2B). The global lateral offset was 1.07 mm. No implant was inserted inside the canal. The position of the implant on AP x-rays did not influence outcome (Oswestry and VAS) if the implant was situated in between 0% and 19% (p < 0.05). The position of the implant on lateral view X rays did not influence outcome if the implant was situated in between 0 and 7 mm from the posterior wall of the inferior vertebra (p < 0.05). There was no correlation between functional outcome (Oswestry >25% and VAS >2 improvement) and the position of the device on the basis of the criteria applied in AP and lateral x-rays in this series.

TABLE 19.1 Pre-op

1 month

3 months

6 months

1 year

4 years

Oswestry

43.8

34.8*

26.3*

24.2*

22.8*

23.1*

Leg Pain

3.9

3

2.7

2*

2.4*

2.1*

Back Pain

7.6

3.7*

3*

3*

3.5*

3.2*

TABLE 19.2A Position on AP view

0% to 9%

10% to 19%

Superior to 19%

Number

51

13

0

Average

2.80%

14.40%

0%

TABLE 19.2B Position on lateral view

0 to 4mm

4 to 7mm

>7mm

Number

57

7

0

Average

1.07

5.1

0

There was no case of anterior or posterior migration. Three patients had heterotopic ossification, including two type 1 and one type 3 according to McAfee classification (17); all were mobile on dynamic x-rays.

Discussion Discectomy with insertion of total disc prosthesis has been widely reported to improve the clinical symptoms of chronic back pain (5,6,16,18,19,20). The degree of

improvement is equivalent to that obtained with anterior fusion cages using the miniinvasive technique (21). Radiographic follow-up in our series showed a degree of mobility close to normal (14,22) and confirms the results obtained with other devices such as the SB Charité, as reported by many authors (5,6,16,17,19,20), and with the Prodisc, as reported by Bertagnoli P.178 and Kumar (2) and Mayer et al. (11). The technique is safe because the intra- and postoperative complication rate is very low and equivalent to other series (2,3,16). The patients recover rapidly and the mean hospital stay of 3 to 5 days is close to Bertagnoli and Kumar (2) and Lemaire et al. (5). This is to compare with 8 to 12 days for an arthrodesis reported by Katz (23). The Oswestry score improved for 75% and this improvement is significantly correlated with facet arthrosis and muscle fatty degeneration as reported by Le Huec et al. (24). Adjacent level disease after fusion is also an important and controversial problem (25,26). Total disc replacement is an alternative to fusion in selected cases. The SF36 is well improved for the physical score and less for the mental score. This is similar to the prospective randomized study of the FDA with SB Charité device (16). The position of the implant on AP x-rays is very satisfactory with the instruments used; all were implanted in good or excellent position. The functional outcome (Oswestry and VAS scores) is not correlated with the position providing the device is implanted in a safety region demarcated on coronal views as defined in the protocol. Outside this safe area the results could be different but there were no data to access this point. This means that within the yellow line defined as less than 4.5 mm offset from the exact midline and using a prosthesis with a fixed posterior center of rotation the clinical results are not modified by the position of the implant. The position of the implant on lateral views is highly satisfactory with the instruments used. The functional outcome (Oswestry and VAS scores) is not correlated with the position providing the device is implanted in a safety region demarcated on lateral views as defined in the protocol. Outside this safe area the results could be different but there were no data to access this point. In this series the posterior center of rotation of the prosthesis was always located behind the midline on the lateral view as recommended by many authors (5,14,27). The design of the implant is very important to obtain this position. The ball and socket of the Maverick is posteriorly located

allowing this advantage that even in case of moderately inadequate positioning of the implant (due to anatomical problems or per operative difficulties) the biomechanics of the disc is respected as long as the offset is less than 7 mm on lateral view. In total, a semiconstrained device with a fixed center of rotation is a biomechanical tradeoff for obtaining a very good clinical outcome, providing the device is implanted within the safety margins outlined previously. This is the first report of such an outcome. Other disc prosthesis design were less successful in the past (3,6,18). Disc prostheses offer the prospect of earlier treatment of certain recalcitrant chronic back pain without having recourse to an arthrodesis. It is always possible to revert to an arthrodesis if results are poor or if there is progressive degeneration of the posterior structures (25). A few cases of arthrodesis with posterior fixation and a posterolateral graft have been reported by Lemaire et al. (5) for treating patients whose pain is recalcitrant. The failure may be due to a technical error or to an erroneous indication, so patients should be selected according to very rigorous criteria (12). Prosthesis dislocation have been reported for Prodisc (28) and SB Charité prosthesis (29) but never with the Maverick implant. For those complications the authors always mentioned that the bad positioning of the implant, mainly inserted too anteriorly, was the main reason for the dislocation of the polyethylene core. The design of the Maverick in respect to fundamental criteria proposed by Hedman et al. (30) and Dooris et al. (27) is probably very important regarding the biomechanics. Moderate AP and lateral offset during the insertion of the prosthesis can be compensated by the design of the Maverick implant. Van Ooij (29) also reported cases of scoliosis induced by frontal offset using the Charité prosthesis. The main difference between Maverick and Charité prosthesis is the center of rotation. This one is fixed in the Maverick implant (14), and this allows a capacity to maintain the spine alignment even if there is a moderate frontal offset as reported in our P.179 series. On the other hand when a Charité prosthesis is implanted with an offset, the core slides laterally and stays in this position due to the offset load transmission (29). There is no possibility to compensate even a moderate error of implantation.

Conclusion The metal-metal Maverick device with a posterior center of rotation is a promising

therapeutic technique. Its mechanical characteristics and resistance to wear make it an interesting option in terms of its life cycle. The position of the implant is a very important criterion but the biomechanics of this prosthesis allows a yellow line of positioning making the device safer. Only long-term follow-up exceeding 5 years will make it possible to confirm these very favorable preliminary results and to analyze the effects on the segments adjacent to the levels operated. This series shows that the early results are equivalent to the best ALIF series (21) with a low complication rate. The total disc replacement could offer benefit by preventing adjacent level disease thanks to decreased stress on the adjacent disc once the sagittal balance is restored (31).

REFERENCES 1. Allen, et al. The effects of particulate cobalt, chromium, and cobalt-chromium alloy on human osteoblast-like cells in vitro. J Bone Joint Surg Br 1997; 79: 475–482. 2. Bertagnoli R, Kumar S. Indications for full prosthetic disc arthroplasty: a correlation of clinical out-come against a variety of indications. Eur Spine J 2002; 11: 131–136. 3. Cinotti G, David T, Postacchini F. Results of disc prosthesis after a minimum follow-up period of 2 years. Spine 1996; 21: 995–1000. 4. Enker P, Steffee A, McMillin C, et al. Artificial disc replacement: preliminary report with a 3-year minimum follow-up. Spine 1993; 18: 1061–1070. 5. Lemaire JP, Skalli W, Lavaste F, et al. lntervertebral disc prosthesis: results and prospects for the year 2000. Clin Orthop 1997; 337: 64–76. 6. Zeegers WS, Bohnen LMU, Laaper M, et al. Artificial disc replacement with the modular type SB Charité III: 2-year results in 50 prospectively studied patients. Eur Spine J 1999; 8: 210–217.

7. Mayer HM, Korge A. Non fusion technology in degenerative lumbar spinal disorders: facts, questions, challenges. Eur Spine J 2002; 11: 85–91. 8. Fujiwara A, Tamai K, An HS, Kurihashi T, Lim TH, Yoshida H, Saotome K. The relationship between disc degeneration, facet joint osteoarthritis, and stability of the degenerative lumbar spine. J Spinal Disord 2000; 13: 444–450. 9. Fujiwara A, Tamai K, An HS, Lim TH, Yoshida H, Kurihashi A, Saotome K. Orientation and osteoarthritis of the lumbar facet joint. Clin Orthop 2001; (385): 88–94. 10. Goutallier D, Postel JM, Bernageau J, Lavau L, Voisin MC. Fatty muscle degeneration in cuff ruptures. Pre- and postoperative evaluation by CT scan. Clin Orthop 1994; 304: 78–83. 11. Mayer HM, Wiechert K, Korge A, Qose 1. Minimally invasive total disc replacement: surgical technique and preliminary results. Eur Spine J 2002; 11: 124–130. 12. Le Huec JC, Aunoble S, Friesem T, Mathews H, Zdeblick T. Maverick total lumbar disk prosthesis: biomechanics and preliminary clinical results. In: Gunzburg R, Szpalski M, eds. Arthroplasty of the spine. Lippincott, 2004, pp. 53–58. 13. Le Huec, Aunoble S, Magendie J, Hadidane R. Video-assisted anterior approach to the spine. In: Surgical techniques in orthopaedics and traumatology. Editions scientifiques et médicales Elsevier SAS, Paris; 2003, 55–060-D-I0. 14. Mathews Hallett H, Le Huec JC, Friesem T, Zdeblick T, Eisermann L. Design rationale and biomechanics of Maverick Total Disc arthroplasty with early clinical results. Spine J 2004; Issue 61001: S268–S275. P.180

15. Frymoyer JW. Indications for consideration of the artificial disc. In Weinstein JN, ed. Clinical efficacy and outcome in the diagnosis and treatment of low back pain. Raven Press, New York, 1992, pp. 227–236. 16. Guyer RD, McAfee PC, Hochschuler SH, Blumenthal SL, Fedder IL, Ohnmeiss DD, Cunningham BW. Prospective randomized study of the Charite artificial disc: data from two investigational centers. Spine J 2004; 4(6 Suppl): S252–259. 17. McAfee PC, Cunningham BW, Devine J, Williams E, Yu-Yahiro J. Classification of heterotopic ossification (HO) in artificial disk replacement. J Spinal Disord Tech 2003; 16: 384–389. 18. Cunningham BW, Lowery GL, Serhan HA, Dmitriev AE, Orbegoso CM, McAfee PC, Fraser RD, Ross RE, Kulkarni SS. Total disc replacement arthroplasty using the acroflex lumbar disc: a non human primate model. Eur Spine J 2002; 11: 115–123. 19. Griffith SL, Shelokov AP, Buttner-Janz K, et al. A multicenter retrospective study of the clinical results of the LINK SB Charité intervertebral prosthesis: the initial European experience. Spine 1994; 19: 1842–1849. 20. Hochschuler SR, Ohnmeiss DD, Guyer RD, Blumenthal SL. Artificial disc: preliminary results of a prospective study in the United States. Eur Spine J 2002; 11: 106–110. 21. Burkus JK, Gornet MF, Dickman CA, Zdeblick TA. Anterior lumbar interbody fusion using rhBMP-2 with tapered interbody cages. J Spinal Disord Tech 2002; 15: 337–349. 22. Buttner-Janz K, Schellnack K, Zippel H. Biomechanics of the SB Charité lumbar intervertebral disc endoprosthesis. Int Orthop 1989; 13: 173–176.

23. Katz JN. Lumbar spinal fusion: surgical rates, costs, and complications. Spine 1995; 20(Suppl):78–83. 24. Le Huec JC, Basso Y, Aunoble S, Friesem T, Brayda Bruno M. Influence of facet and posterior muscle degeneration on clinical results of lumbar total disc replacement. J Spinal Disord Tech 2005; Mar. 25. Eck JC, Humphreys SC, Hodges SD. Adjacent-segment degeneration after lumbar fusion: a review of clinical, biomechanical, and radiologic studies. Am J Orthop 1999; 28: 336–340. 26. Lee CK. Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine 1988; 13: 375–377. 27. Dooris AP, Goel VK, Grosland NM, Gilbertson LG, Wilder DG. Load sharing between anterior and posterior elements in a lumbar motion segment implanted with an artificial disc. Spine 2001; 26: 122–129. 28. Aunoble S, Donkersloot P, Le Huec JC. Dislocations with intervertebral disc prosthesis: two case reports. Eur Spine J 2004; 13: 464–467. 29. Van Ooij A. Analysis of 21 patients with clinically failed Charité disc prosthesis. Eur Spine J 2002; (1)Abstract 47. 30. Hedman TP, Kostuik JP, Fernie GR, et al. Design of an intervertebral disc prosthesis. Spine 1991; 16: 256–260. 31. Le Huec JC, Basso Y, Mathews H, Mehbod A, Aunoble S, Friesem T, Zdeblick T. The effect of single level total disc arthroplasty on sagittal balance parameters: a prospective study. Eur Spine J 2005, online.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Total Disc Arthroplasty > 20 - Motion Preservation—Disc Replacement for Lumbar Degenerative Disorders with the ProDisc®-L Prosthesis

20 Motion Preservation—Disc Replacement for Lumbar Degenerative Disorders with the ProDisc®-L Prosthesis R. Bertagnoli The development of innovative treatment options for the treatment of degenerative disc disease (DDD) is presently more important than ever. Worldwide, the number of patients who suffer from chronic low back pain and musculoskeletal diseases is increasing. Many of the patients who are affected by back ailments can be treated with conservative therapy. But more often this treatment option fails and a surgical intervention is necessary. Presently there are different surgical options available, but not every intervention shows satisfactory results. Because the existing treatment options cannot reach a “restitutio ad integrum,― we should apply not the maximum possible but the most adequate treatment for the specific condition of the patient. Based on a “treatment of little and increasingly invasive therapy steps,― the therapy should ideally consist of a series of small therapy steps. The goal is to achieve a better success rate and to minimize the number of patients who undergo a more extensive surgery, with higher risks and collateral damage, by using a “negative patient selection― process (i.e., using exclusion criteria to direct patients toward an alternative form of therapy, only focusing on “nonresponders― in each category)

(1,2). Along this “step algorithm― the risks and the collateral trauma caused by a surgical intervention can be kept to a minimum, and if one treatment option fails, the patient can be offered a further therapy step. Within this step algorithm, motionpreserving spine surgeries can fill the gap between decompression techniques and fusion techniques. Presently, DDD can be treated with a modern step algorithm in seven surgical steps (Fig. 20.1): (a) percutaneous decompression techniques, (b) open decompression techniques, (c) nucleus replacement (e.g., PDN, Neudisc, DASCOR), (d) interspinous implants (e.g., Wallis, Coflex, X-Stop, Diam), (e) total disc replacement (e.g., Charité, ProDisc, Maverick, Flexicore, Mobidisc, Centurion, activL), (f) posterior dynamic stabilization (e.g., Dynesys), and (g) fusion surgeries. Higher therapy steps mean a larger treatment size combined with higher risk factors and larger collateral damage to the surrounding structures (1,2). Total disc replacement became more and more important over the past years as an alternative solution for patients who were not candidates for a fusion surgery or nucleotomy. Nucleus replacement technologies are not indicated for multilevel DDD, and at this time of the investigation there is no standard definition of when the implantation will be successful (i.e., the degree of annulus degeneration and disc height loss) (3). The disadvantages of fusion surgeries include not achieving restoration of the natural disc P.182 function and additionally eliminating the motion of the affected segment. This results in rapid degeneration of the adjacent segments by developing a transitional zone syndrome (“fusion diseases―) including discopathy, facet hypertrophy, and spinal stenosis (1).

FIGURE 20.1 Step algorithm: modern surgery.

Total disc replacement is an innovative technique to restore stability without definitive destruction of the function of the motion segments, leading to pain relief with maintenance or restoration of motion. To find the most effective treatment for each patient, careful patient selection is still the most important step before every surgical intervention.

The ProDisc-L Inspired by the promising results of total hip and knee replacements (4), several authors designed artificial lumbar disc prostheses consisting of similar materials. In the early 1990s the first ProDisc was implanted in humans, and by 1993 it was implanted in 64 patients. The analysis of the long-term results of these patients and their success indicated that the prosthesis would have a good outcome. In 1999 the first ProDisc II

(4) was released. The ProDisc-L device has been completely redesigned into a second generation. A new application technique has been developed as well, leading to a higher precision of application and ability to perform the procedure in a minimally invasive way. The ProDisc II, a semiconstrained prosthesis, has a three-component design: two metal endplates made of cobalt-chromium-molybdenum alloy with a single central keel and a central convex weight-bearing surface made from ultrahigh molecular weight polyethylene (UHMWPE) (5,6). The prosthesis primary fixations are the central keel and two anterior lateral spikes (6). The secondary and long-term fixation are provided by a titanium plasma spray coating at the bone-implant interface. Since the late 1990s, 11,000 ProDisc-L prostheses have been implanted worldwide. P.183

Study Results The patients have been investigated in a prospective, nonrandomized study. The 2year follow-up assessment has been compared to the results of the 3- to 5-year followup periods.

Materials and Methods Patients were assessed by means of clinical and radiologic parameters before surgery and in predefined periods after surgery: 3, 6, 12, 24, 36, 48, and 60 months. Clinical parameters included Oswestry Disability Index (ODI), Visual Analogue Scale (VAS), the SF 36, back pain frequency, satisfaction, and use of medication. Radiologic assessment included measurements of range of motion (ROM) and disc height in the operated and adjacent levels. Complications and adverse events were also reported.

Demographics One hundred seventy-two female and 179 male patients with an average age of 45 years (range 23-70 years) have been operated on (Table 20.1). Two hundred nineteen

patients have been operated in L5-S1, 150 patients in L4-5, 56 patients in L3-4, 17 patients in L5-6, 15 patients in L2-3, 4 patients in L6-S1, and 3 in L1-2. Two hundred sixty-four patients were treated in one level, 71 in two levels, 15 in three levels, and 1 in four levels.

Clinical Outcomes The preoperative ODI decreased from 49% to 29% after 2 years and to 30% after the 3year, 4-year, and 5-year follow-up period (Fig. 20.2). The VAS declined from 7.2 to 3.8 at 2-year follow-up, to 4.0 after 3 years, to 3.8 after 4 years, and to 3.9 after 5 years (Fig. 20.3). The average SF 36 score preoperatively was 268 and improved to 435 after 2 years, to 429 after 3 years, to 416 after 4 years, and to 413 after 5 years (Fig. 20.4). Before surgery, 83% of the patients had extreme back pain and 17% severe back pain. After surgery there was a significant decrease in back pain frequency as shown in Table 20.2. The use of medication could be reduced as shown in Table 20.3. Eighty-nine percent of the patients reported that they were completely satisfied or at least satisfied with the surgery 2 years after the procedures, 88% after 3 years, 92% after 4 years, and 96% after 5 years.

TABLE 20.1 Demographics 2 Years

3 Years

4 Years

5 Years

Patients

351

197

75

29

Male

179

94

33

14

Female

172

103

42

15

Implants

455

230

86

32

Average age

45y

45y

48y

49y

Range of age

23–70y

24–67y

30–67y

30–67y

P.184

FIGURE 20.2 Oswestry Disability Index (ODI).

FIGURE 20.3 Visual analogue scale.

FIGURE 20.4 SF 36.

TABLE 20.2 Back Pain Frequency Preop

2 Years

3 Years

4 Years

5 Years

(%)

(%)

(%)

(%)

(%)

Extreme

83

0

0

0

0

Severe

17

0

0

0

0

Moderate

0

30

28

15

11

Occasional

0

44

43

43

44

Not at all

0

26

29

42

41

TABLE 20.3 Use of Medication Preop (%)

2 Years (%)

3 Years (%)

4 Years (%)

5 Years (%)

Steroids

7

0

0

0

0

Nonsteroids

74

34

19

34

10

Morphine and derivatives

47

28

28

9

0

P.185

Radiologic Outcomes The ROM showed an increase of 4 degrees after 2 and 3 years (from 4 degrees preoperatively to 8 degrees at 3 years). The average ROM after 4 and 5 years shows an average measurement of 7 degrees. The disc height of the operated level increased from 5 mm to 13 mm and could be maintained throughout the follow-up periods. The preoperative disc height of the adjacent levels was measured at 10 mm and has not changed in the follow-up periods. A complication rate of 13% has been reported for all 351 patients. Device-related complications occurred in six patients (one case of migration, one case of motor deficit, and four cases of partial subsidence) and approach-related complications in seven patients (one case of retrograde ejaculation, one case of retroperitoneal hematoma, one case of epidural hematoma, one case of bladder disturbance, and three cases of subcutaneous hematoma.). No life-threatening complications occurred.

Conclusion The clinical results in our series have demonstrated that total lumbar disc replacement with the ProDisc-L prostheses is a safe and efficacious treatment method for

debilitating lumbar DDD without severe facet arthropathy (grade III and grade IV) (7). The good or excellent results represented previously confirm the outcomes with the ProDisc-L listed in the literature (5). The most important factor to achieve good results is the patient selection process and the selection of the ideal indication for this procedure by an experienced surgeon (8). Precision of these surgeries is more demanding than any fusion devices. Longer follow-up periods are necessary to confirm the maintenance of the short- and midterm results.

REFERENCES 1. Bertagnoli R. Disc surgery in motion. Spine Line 2004; 11/12: 23–28. 2. Bertagnoli R. Review of modern treatment options for degenerative disc disease. In: Kaech DL, Jinkins JR, editors. Spinal restabilization procedures. Elsevier 2002: 365–375. 3. Bertagnoli R, Karg A, Voigt S. Lumbar partial disc replacement. Ortho Clin North Am 2005; 36: 341–347. 4. Delamarter RB, Fribourg DM, Kanim LEA, et al. ProDisc Artificial Total Lumbar Disc Replacement: Introduction and early results from the United States clinical trial. Spine 2003; 28(20S): S167–S175. 5. Delamarter RB, Bae HW, Pradhan BB. Clinical results of ProDisc-II Lumbar Total Disc Replacement: Report from the United States clinical trial. Ortho Clin North Am 2005; 36: 301–313. 6. Frelinghuysen P, Huang RC, Girardi FP, et al. Lumbar total disc replacement. Part I: Rationale, biomechanics, and implant types. Ortho Clin North Am 2005; 36: 293–299.

7. Thompson JP, Pearce RH, Schechter MT, et al. Preliminary evaluation of a scheme for grading the gross morphology of the human intervertebral disc. Spine 1990; 15: 411–415. 8. Bertagnoli R, Yue JJ, Shah R, et al. The treatment of disabling multilevel lumbar discogenic low back pain with total disc arthroplasty utilizing the ProDisc prosthesis: A prospective study with 2 year minimum follow-up. Spine 2005; 30: 2192–2199.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Total Disc Arthroplasty > 21 - A New Approach to Lumbar Disc Prosthesis

21 A New Approach to Lumbar Disc Prosthesis J. P. Steib Spine surgery is the little sister of orthopaedic surgery. In the last century, we saw limb surgery advance with arthrodeses then osteotomies of the hip and knee held by plaster and then by osteosynthesis. Prostheses were a natural progression, first for the hip and then the knee. After a few years of trial and error these prostheses became firmly established as the gold standard of surgery, causing indications for arthrodesis to disappear and indications for osteotomies to decrease dramatically. But there are only two hips and two knees, whereas there are five lumbar stages and at each level there are three joints providing six degrees of freedom: flexionextension, right and left tilt, and right and left rotation. Ontogenic evolution has made us leave behind the global kyphosis of the baby to achieve cervical and then lumbar lordosis (1). Lordoses are sectors of mobility, and areas in kyphosis are hypomobile. Lumbar lordosis makes walking possible and ensures the anteroposterior balance of the spine. The mobility of a lumbar segment (two vertebrae, a disc, and the soft parts) is achieved on three axes, permitting rotation (3): a horizontal frontal axis for flexion-extension, a horizontal but sagittal axis for right and left tilt, and finally a vertical axis for axial rotation. These movements are checked by the soft parts, which are opposed and guided by the joints that, through their shape, impose the axis of rotation. Modern tools (computer software, finite-element analyses) have shown that the centers of rotation are not single but are dispersed over an area [scatter of points =

instantaneous centers of rotation (ICR), the mean of which gives the mean center of rotation (MCR)]. For flexion-extension, the MCR is slightly below the upper vertebral end plate of the lower vertebra, on the posterior third of the vertebra. In flexion a more anterior MCR leads to posterior stretching, an excessively posterior MCR leads to bumping of the anterior corners of the vertebral bodies, and finally an excessively inferior MCR implies severe antelisthesis. Because of the truncated shape of the posterior joints (4), axial rotation is achieved around a posterior vertical axis situated on the spinous process. Each rotation is accompanied by translation of the intervertebral disc (Fig. 21.1), which permits but also checks this movement. The same posterior joints are P.188 responsible for changes in the ICR in the sectors of mobility and impose translation at each movement. These notions of mobile ICR and translation must be taken into account in prosthesis design.

FIGURE 21.1 Translation and rotation.

FIGURE 21.2 Mobile core.

Currently there are semiconstrained disc prostheses (5) with a single set center of rotation that is close to the MCR of flexion-extension. The first prosthesis to be implanted in the world, which has been used for 20 years, is the Charité (6), a nonconstrained prosthesis. This prosthesis with biconvex core has two axes of rotation (upper and lower) that permit an interesting combination of movements to try to adapt to the play of the rear joints. The Mobidisc is a new prosthesis that takes into account the biomechanical study of lumbar intervertebral movement. Like current traditional prostheses, it has a posterior and inferior MCR, but translation of the polyethylene core increases the ICR possibilities (Fig. 21.2). This prosthesis was developed by a group of surgeons: J. Allain, M. Ameil, J. Beaurains, H. Chataignier, J. Delecrin, J. Huppert, M. Gau, M. Onimus, J.-P. Steib, and W. Zeegers. The translation mobility of the polyethylene core on the horizontal plane enables it to adapt to the CRI, which reduces posterior articular stress, wear on the

implant, and constraints on the bone-prosthesis interface. The core can center itself on the inferior vertebral endplate by translation and rotation, which assists the relationship between the two vertebrae and forgives an imperfectly median implantation. The prosthesis consists of two endplates, an upper and a lower one, and a polyethylene core. The endplates (three dimensions: 29/24, 34/27, 39/29) are of a truncated elliptical shape. They are made of cobalt-chromium. The surface in contact with the bone is titanium plasma spray coated to facilitate bone integration. An angle-adjustable keel permits primary fixation. Its orientation permits conventional or oblique anteroposterior placement. The lower surface of the upper endplate is concave to fit the convex shape of the polyethylene core. The upper surface of the lower endplate is flat and has four pegs containing the polyethylene and limiting its mobility. There are three versions of the lower endplate: 0-, 5-, and 10-degrees lordosis. The polyethylene core (ultrahigh molecular weight polyethylene) has a flat base and dome-shaped peak 15 mm in diameter. This dome may be median or lateralized backward to bring the MCR further back. Two lateral feet or wings on the right and left fit between the pegs of the bottom endplate. Dislocation of the core is impossible. Its dimensions adapt widthwise to the size of the chosen prosthesis and heightwise to the intersomatic space. Different heights of the polyethylene (6 to 11 mm) determine the prosthesis height of 10, 12, or 14 mm. The endplates-polyethylene core assembly permits all the physiologic movements of a normal intervertebral disc. On the bottom endplate, the core has a mobility of 1.5 mm in all directions. In flexion-extension, the core moves forward and backward and its mobility is ±12 degrees. In lateral tilt, the core moves to the right and left and its mobility is ±10 degrees. In rotation, the core rotates ±6 degrees and shifts to the right and left to follow the translation. Various biomechanical tests were conducted before the prosthesis was made available for clinical placement. These tests were conducted at the CRIT laboratory in Charleville Mézières, and the LBM of ENSAM in Paris. First, repeated sliding movements of the polyethylene core on the bottom endplate with the wings homing against the pins on the bottom endplate: 5 million cycles with a load of 25 to 450 daN and a frequency of 2 Hz. No fracture or wear was observed. The prosthesis was tested for P.189

more than 15 million cycles under a load of 30 to 200 daN at a frequency of 1.1 Hz, in a physiologic environment of bovine serum at a temperature of 37.5°C ±0.5°C. The lubricant was changed every 0.5 million cycles and filtered at 1 µm before each test period. The movements tested in succession were flexionextension (10/-5 degrees, F = 1 Hz), lateral flexion (5/-5 degrees, F = 0.95 Hz), and axial rotation (3/-3 degrees, F = 1.05 Hz). Few or no changes were observed. Studies on anatomic parts were conducted on seven lumbar segments (L3-5: 5 M, 2 F; 62 years [50–67], storage at -20°C) with a prosthesis fitted at L4-5. L5 was immobilized and the loads applied on L3 in 1 Nm increments. The parts were tested in flexion-extension, lateral tilt, and axial rotation before and after placement. There were no significant variations in flexion-extension, but there was an increase in main rotations in lateral tilt (3 degrees) and axial rotation (3.9 degrees). Axial rotation was studied in coupled movements: coupled rotations (flexion-extension, lateral tilt), coupled translations (transversal, posteroanterior, and vertical). There were no significant variations for the coupled rotations, but there was an increase in lateral coupled translation in axial rotation (4 mm). The first prosthesis placement dates back to November 2003. Clinical experience is now considerable and of international scope (France, Belgium, Germany, Korea, South Africa, and Australia). The first 40 patients (45 prostheses) have been followed up. Thirty-five prostheses were single: 1 in L2-3, 11 in L4-5, and 23 in L5S1 (Fig. 21.3). Five prostheses were double: one in L2-3, L3-4, one in L3-4, L5-S1, and three in L4-5, L5-S1. The visual analogue scale (VAS) improved by 71% for back pain (from 7.46 to 2.18) and 72% for leg pain (from 5.73 to 1.59). The Owestry score improved by 66%, decreasing from 0.53 to 0.18. Posterior release is essential to encourage movement. Two prostheses were locked in extension without movement but with a very good clinical result. We deplore one subsidence in this series at the upper end plate, and despite vertebroplasty the patient had to be fused. One prosthesis was replaced because its position was too lateral and it was responsible for radicular pain. Unfortunately one vascular injury occurred, although with no consequences for the patient. There was no migration, osteolysis, loss of discal height, or heterotopic ossifications. The range of motion (ROM) mobility of the prosthetic segment was 8 degrees (5–16 degrees) in L4-5 and 7 degrees (0–17 degrees) in L5-S1. Lumbar lordosis was not significantly modified (45.4 degrees preoperative and 49.5 degrees postoperative). The pre- and postoperative MCR

P.190 was studied on the first prostheses using Spineview software. It was present for mobility of more than 6 degrees. Preoperatively, the MCR was abnormal or absent and generally became normal postoperatively. It remained abnormal when the prosthesis was too anterior or too tall. On the adjacent levels, the MCR remained normal or was restored. It is difficult to say whether the MCRs are correlated with the clinical results.

FIGURE 21.3 L5-S1 arthroplasty.

Disc prostheses are a new approach to spine surgery. Arthrodesis is no longer the only alternative and we must change our habits and tackle problems differently. The Mobidisc is an unconstrained prosthesis with a mobile core that enables it to follow the instantaneous center of rotation as well as possible. Its constant search for balance makes it suitable for every patient. Disc prostheses will become the new surgical standard over the next 10 years.

REFERENCES 1. Louis R. (1982): Chirurgie du rachis. Anatomie chirurgicale et voies d'abord. Springer-Verlag, Berlin, Heidelberg, New-York.

2. Kapandji L.: The physiology of the joints, part III. Churchill Livingstone, New York. 3. Templier A, Skalli W, Lemaire J-Ph. (1999): Three dimensional finiteelement modelling and improvement of abispherical disc prosthesis. Eur J Orthop Surg Traumatol 9: 51–58, 1999. 4. Fick R. (1904): Handbook der Anatomie and Mechanik der Gelenke. Jena, Verlag G. Fischer. 5. German JW, Foley KT. (2005): Disc arthroplasty on the management of the painful lumbar motion segment. Spine 30(16S): S60–S67, 2005. 6. Buttner-Janz K. (1992): The development of the artificial disc SB Charité. Hundley & Associates, Ann Arbor.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Total Disc Arthroplasty > 22 - Design and Surgical Technique of the FlexiCore Lumbar Artificial Disc

22 Design and Surgical Technique of the FlexiCore Lumbar Artificial Disc Philippe Lauweryns

Design The FlexiCore Intervertebral Disc is comprised of four components, which are assembled by the manufacturer and provided to the surgeon as a single unit (Fig. 22.1). The four components are as follows: A highly polished semi-spherical head A superior baseplate having a domed upper surface and a cylindrical stem extending from the lower surface and into the head An inferior baseplate having a domed lower surface and a semispherical recess formed in the upper surface to accommodate the head A shield seated around the head and press fit to the upper surface of the inferior baseplate The exterior surfaces of the superior and inferior baseplates each have a central dome that rises 2 mm at its peak to ensure proper seating of the device between the endplates of the adjacent vertebral bodies. Two sets of 1.5-mm spikes are provided on

each baseplate for additional bone fixation. The principal articulating components of the FlexiCore Intervertebral Disc are the semispherical head and the semispherical recess in the upper surface of the inferior baseplate. These components are located directly between the domes on the exterior surfaces of the baseplates, providing a center of rotation similar to that of a healthy natural disc. The FlexiCore Intervertebral Disc was designed to allow for repositioning in situ. Three holes pass through the edge of the shield and into the upper surface of the inferior baseplate and enable anterior, anterolateral right, or anterolateral left attachment of the inserter/impactor and repositioner/extractor instruments. Four holes in the superior baseplate can be engaged for implant repositioning or removal. The implant is comprised of cobalt chromium molybdenum alloy (ASTM F-1537). To promote fusion with the vertebral body endplates, the external surfaces of the superior and inferior baseplates are plasma sprayed with a layer of CP titanium. The FlexiCore Intervertebral Disc is available in two baseplate areas (28 ÷ 35 mm and 30 ÷ 40 mm) and seven heights (12, 13, 14, P.192 15, 16, 17, and 18 mm). The overall height of each implant is measured between the base of the spikes on the superior and inferior baseplates when the device is in the parallel (nonlordosed) position.

FIGURE 22.1 FlexiCore Intervertebral Disc.

The range of motion of the implant is designed to be 32 degrees (at least 30 degrees) in both flexion/extension and lateral bending when the device is in the neutral position. The neutral position is nonlordosed and at the midpoint of those articulations. Axial rotation between the baseplates is designed to be 14 degrees (at least 10 degrees) when the device is in the neutral position. Range of motion in situ is limited by soft tissue balance and the mechanical stops provided by the facet joints of the individual subject. The FlexiCore Intervertebral Disc incorporates a semispherical articulating surface that maintains a fixed rotation point centered between the peaks of the domes of the baseplates. Because the domes fit within the concavities of the vertebral body endplates, the device's center of rotation is biased toward a location that causes the modes of motion of the spinal segment to be similar to those of a healthy natural segment. The FlexiCore Intervertebral Disc is indicated for the treatment of lumbar discogenic pain unresponsive to conservative treatment associated with degenerative disc disease (DDD). The FlexiCore Intervertebral Disc is intended to replace a degenerated lumbar intervertebral disc (L1-S1), permit motion of the treated segment, improve function, and reduce back pain associated with DDD. The primary goal of the disc arthroplasty consists of, but is not limited to, restoring or preserving the segmental motion of the intervertebral joint(s) (1,3,11,16,19,22,38). The total disc replacement (TDR) is aimed as well at reducing stresses on the adjacent level in the hope of reducing adjacent level degeneration (1,11,16,19,38). The facet joints must be protected from further degeneration (22). Segmental stability, disc height and sagittal alignment are expected to be provided as well (16,22). The overall goal is to relieve pain and to get the patient back to normal activity and work (1,16,38). Ideally some designers looked at reproducing the native disc performances. But basically two different designs came out: some designs aimed to reproduce the viscoelastic properties of the disc, whereas others aimed at the reproduction of

“only― the motion characteristics of the disc. The latter design was mostly inspired from the peripheral joints prostheses (10,38). Due to the sensitive location of a disc prosthesis it is commonly agreed the device must be safe so that no catastrophic consequence and vessels injury may happen when it fails (17). It is expected that the disc replacement device must protect the posterior elements, that is the facet joints for long-term results (12,22). There is one more important feature of the design: Because the anterior stabilizing structures are disrupted during the implantation, the device must be self stable, with primary and secondary fixation characteristics (22). The design of an artificial disc may include some constraints in the design to limit the range of motion. No standard has been made yet but one can distinguish three concepts: unconstrained, semiconstrained, or a fully constrained design (1). It is expected an unconstrained device would more likely provide a physiologic center of rotation (22,35), to be less sensitive to error of placement (22), and to have the longest survival (32), but at the risk of transferring more rotational load on the facet joints (35). Constrained designs include a fixed center of rotation by means of a fixed polyethylene (PE) core (Prodisc) or a ball-in-socket design (Maverick-Flexicore). Constraints may aim in addition at protecting the posterior elements from increased loads (22,26). As the native disc has a function of creeping and relaxation (23) various materials have been suggested. With the exception of the rubber material included in some discs, it has been demonstrated that the most common materials do have the same very P.193 limited shock absorption capacity. It has been generally believed that softer material like PE will provide some cushioning, but tests showed that PE-based devices and metal on metal (MoM) devices both have a similar behavior and no significant shock absorption capacity (29). Considering the age of patients suffering from chronic low back pain it is usually expected a TDR to be viable for 40 years (17,26,40). The SB Charité prosthesis has been tested for 20 million cycles only at 8000 N without cracks (4), but cracks and wear have been reported in clinical use (39). Kostuik et al. (26) suggested a test for an implantable device to be up to 100 million cycles from which 85 million standard cycles would represent the claimed 40 years of life (17,26). To assess its durability, the MoM Maverick device has been successfully tested in a different model simulating

more than 31 years of activity (30). Due to the extended exposure and the extensive annulotomy necessary to insert a disc, the primary and secondary fixation are critical issues to consider. Various designs/techniques have been used with success so far, but the available follow-up is of a maximum of 17 years (36). The surgical technique differs from a standard anterior lumbar interbody fusion (ALIF): Stability cannot be provided by excessive disc distraction, which would limit the motion and painfully stretch the nerve roots (14). Some TDR designs rely on a keel inserted into the adjacent vertebral body to be stable in the short term, that is, Prodisc and Maverick (14,30). Other designs rely on small teeth on the device endplate to anchor the TDR device into the soft bone (SB Charité) (4). Both concepts showed in clinical use a fairly reliable fixation in the immediate postoperative period. Keels look intuitively very effective and safe but they mandate skilled hands and a very accurate preparation before insertion, because no per operative adjustment is possible (14). Long-term fixation is biologic and calls for a tight bone bonding onto the device endplate. Various surface coatings are used: titanium, hydroxy apatite, and plasma spray (7,14,30,37,41) of which the effectiveness has been demonstrated in the hip and knee prosthesis experience. A healthy adult disc moves about 13 degrees in flexion, 3 degrees in extension, 3 degrees in lateral bending, and ± 1 degrees in axial rotation (17). All current designs include this range of motion (4,14,28,30,41). The postoperative range of motion is affected by the location of the center of rotation, therefore, by the placement of the device: If placed anteriorly the flexion decreases by 19%, whereas a more posterior location increases the flexion by 44% (8,12). The range of motion of the operated disc not only depends on the design of the TDR device but also on the surgical insertion technique. An extensive excision of the annulus results in 40% more axial rotation than the intact segment as opposed to a limited excision with only 30% additional rotational mobility (12). As for every technique, TDR technique has specific indications. It is important to understand that a limited number of patients will benefit from it (21). Many surgeons, mostly U.S. surgeons with a slightly different experience from European surgeons, are considering TDR indications similar to the ALIF indications

(18,19). Claiming arthroplasty is an alternative for ALIF would consider the two techniques equivalent (19), which is not the case. Through the past 20 years, indications for the technique have been refined but yet not fully standardized. TDR is indicated in painful, symptomatic DDD (5,6,14,19,22,24,32,34,43,44). Often discogram and magnetic resonance imaging (MRI) are used to confirm the diagnosis and the level to operate. Root pain may be associated (25,43), but the facet joints P.194 should be preserved (12,20,22,25,27). Some patients with a previous surgical history may be included, for example, microdiscectomy, spinal fusion, laminectomy, or even a revision of a nucleus replacement (2,6,8,19,31,32,42,44). Finding an indication with a single disc disease is very rare (13), making the decision often difficult. The patient scope is usually from 18 to 60 years (9,14,19,32,39), but the average age at the operating time is quite young, about 40 to 45 years (14,15,32,42). Although lumbar disc degeneration is a multilevel disease, surgeons tend to operate more often on one level than on two levels (2,6,14,19,30,33,42), but both are common indications. Some indications remain to explore such as the use of a disc replacement on top of a previously fused segment (18,25) and painful discs involved in a scoliosis (25). Based on his extended experience, to help better patient selection, Bertagnoli (2) defined different grades of candidate appropriateness: (a) grade 1: prime indication: one level, more than 4-mm disc height, no change on facets, no degeneration of the adjacent disc, intact posterior elements; (b) grade 2: borderline indication: less than 4-mm disc height, osteoarthritis (OA) change of the posterior facets, minimal adjacent level changes, adjacent to a fusion, minimal posterior elements instability; and (c) grade 3: poor indication includes gross degeneration of the spine, secondary OA facet changes, less than 4-mm disc height associated with a posterior elements instability. Over time, disc prosthesis users came to a clearer set of contraindications: weak bone and osteoporosis due to the inability to transmit the load and prevent subsidence (2,14,25), and facet degenerative changes (12,20,25,27), especially in the case of a

totally unconstrained TDR device. An unstable spine with more than a few millimeters (4 mm) slip and misaligned lumbar segments are considered a standard contraindication (2,18) as well as other evidence of posterior element incompetence (25).

Surgical Technique The surgeon should review the computed tomography (CT) or MRI and choose a FlexiCore Intervertebral Disc having a footprint that does not exceed 90% of the anterior-to-posterior depth and 90% of the lateral width of the disc space. The appropriate height of the implant is determined intraoperatively, using distraction spacers to judge annular tension and restoration of disc height (compared to the adjacent disc level). The patient is positioned in the Trendelenburg position as required for an anterior or anterolateral surgical approach to the lumbar spine. Slight elevation of the lumbar spine using an inflatable pad may be appropriate. Exposure of the spinal segment is performed using an open or mini-open anterior or anterolateral retroperitoneal approach. First of all, the disc space should be prepared. A window is dissected in the annulus that approximates the width of the implant. The disc and the endplate cartilage are removed to expose the subchondral bone until punctate bleeding is produced. The posterior margin of the disc space should be cleared of any osteophytes or soft tissue material that may inhibit the full distraction of the posterior portion of the disc space and/or inhibit proper posterior positioning of the FlexiCore Intervertebral Disc. It is not required that the posterior longitudinal ligament or the remaining portion of the annulus be sacrificed. However, it is advised that the posterior part of the disc space be fully prepared to receive the FlexiCore Intervertebral Disc. P.195

FIGURE 22.2 Distraction Spacers.

The next step is the distraction of the disc space. The height of the disc space should be restored slowly, using any suitable technique generally utilized for distracting collapsed disc spaces after a discectomy. This technique may, for example, include the sequential insertion and removal of distraction spacers of incrementally larger sizes. The use of these distraction spacers gradually increases the height of the disc space without damaging the integrity of the endplates (Fig. 22.2). Once an intervertebral height of at least 11 mm had been achieved, the Static Distractors are employed to achieve the appropriate height (Fig. 22.3). The Static Distractors range in height from 11 mm (10.75 mm in the posterior) to 18 mm, in 1-mm increments. The appropriate height, and the corresponding final-sized Static Distractor that should be utilized, is one that restores disc height without overtensioning the remaining annulus and ligaments or damaging the vertebral endplates. One should verify disc height and insertion depth by lateral radiographic imaging of the Static Distractor in situ. After removal of the Static Distractor, which restores the desired annular tension, the Dynamic Distractor should be used to distract the disc space an additional 1.5 to 2.0 mm (Fig. 22.4). This temporarily-created additional height minimizes the risk of P.196

damage to the upper and lower vertebral endplates from the spikes. Remove the Dynamic Distractor just prior to insertion of the FlexiCore Intervertebral Disc. Use caution when distracting the disc space. As with any spinal procedure, excessive distraction may result in damage to endplates, facet joints, or soft tissue.

FIGURE 22.3 Static Distractors.

FIGURE 22.4 Dynamic Distractor.

If it is difficult to sufficiently distract or maintain the distraction of the posterior disc space using the previously described distraction tools, the Parallel Jaw Distractor includes a pair of opposing bifurcated jaws that are coupled to a parallel distracting mechanism. Once distracted, the jaws may be maintained in an open disposition by advancing a locking nut on the handle. The bifurcated jaws are provided in two sizes, which correspond to the 35-mm and 40-mm implant sizes. The Parallel Jaw Distractor may stay in place during initial insertion of the FlexiCore Intervertebral Disc. The surgeon should select an implant height that most closely matches the size of the Static Distractor, which restored the desired height of the disc space without overtensioning the annulus, prior to the use of the Dynamic Distractor and/or the Parallel Jaw Distractor. There are two different and distinct Inserter/Impactor instruments: the first Inserter/Impactor is used when implanting the FlexiCore Intervertebral Disc without the aid of a supplementary insertion tool or when using the Parallel Jaw Distractor to guide the FlexiCore Intervertebral Disc into the intervertebral space. This Inserter/Impactor's head has a ledge that comes into contact with the implant, holding both baseplates of the implant firmly in place. It also had two depth stops, on the top and bottom of the head, to prevent overinsertion of the implant. Do not use this Inserter/Impactor with the Wedge-Ramps. The second Inserter/Impactor is used only in combination with the Wedge-Ramps to guide the FlexiCore Intervertebral Disc into the intervertebral space. This Inserter/Impactor's head has a smooth mating surface that comes into contact with the implant, allowing the upper baseplate of the implant to flex and extend and accommodate changes in the angle of insertion. By allowing motion of the upper baseplate, the implant maintains steady contact with the ramps during insertion. This Inserter/Impactor has one depth stop on the bottom of the head to prevent overinsertion of the implant. Do not use this Inserter/Impactor without the WedgeRamps. P.197

To use either of the two Inserter/Impactor instruments, advance the j-hook of the Inserter/Impactor by applying pressure to the flange on the shaft of the instrument. In the advanced position, insert the tip of the j-hook into one of the holes on the anterior portion of the lower baseplate (either the anterior or an anterolateral hole). Release of the flange will retract the j-hook and bias the implant against the impaction plate of the instrument, holding it securely in the lordotic position, and prepared for insertion. Both Inserter/Impactors include a locking nut on the shaft of the handle. This nut may be tightened for more secure fastening of the FlexiCore Intervertebral Disc to the instrument during handling. To lock the nut, turn it counter-clockwise to the proximal ends of the threads. The nut should be loosened prior to impaction. To loosen the nut, turn it clockwise to the distal ends of the threads. Moderate force may now be used against the Inserter/Impactor handle to impact the FlexiCore Intervertebral Disc to the appropriate anteroposterior (AP) depth. The FlexiCore Intervertebral Disc is correctly positioned when its baseplate domes are seated within the concavities of the vertebral body endplates with the posterior of the implant within 2 to 3 mm of the posterior margin of the disc space. Verify the positioning with lateral radiography. AP imaging is also useful if available. To remove the Inserter/Impactor, confirm that the nut has been fully loosened to the distal end of the threads, push the flange on the shaft forward, and tilt the handle down to disengage the j-hook. If it is necessary to maintain the distraction of the disc space, use the Inserter/ Impactor with the ledge in combination with the Parallel Jaw Distractor to insert the FlexiCore Intervertebral Disc into the disc space. Insert the FlexiCore Intervertebral Disc into the disc space between the opened jaws of the Parallel Jaw Distractor such that the spikes of the implant ride just outside the jaws during insertion. Once the implant has been seated within 2 to 3 mm of the posterior margin of the disc space, release the locking nut of the Parallel Jaw Distractor and remove the distractor from the disc space while leaving the FlexiCore Intervertebral Disc in place. To detach the Inserter/Impactor from the implant, confirm that the nut on the handle has been fully loosened to the distal end of the threads, push the thumb flange forward, and then tilt the handle down to disengage the j-hook. To facilitate insertion of the FlexiCore Intervertebral Disc, the Wedge-Ramps may be

used. The Wedge-Ramps comprise a pair of ramps coupled at the proximal end by a C-lip. Insert the tow flat prongs at the distal ends of both ramps into the disc space. Place the FlexiCore Intervertebral Disc between the ramps and advance it into the disc space. The implant spikes ride in grooves on the inner surfaces of the ramps, guiding the implant into position. At the end of the ramp, the implant spikes ride just outside the distal prongs to the proper insertion depth. As with the Parallel Jaw Distractor, the ramps are provided in sizes that correspond to the 35-mm and 40-mm implant sizes. Under fluoroscopy, the posterior edge of the FlexiCore Intervertebral Disc should be within 2 to 3 mm of the posterior margin of the superior and inferior vertebral endplates. The implant should be recessed at least 2 to 3 mm from the anterior margin of the vertebral endplates. On the AP view, the implant should be contained symmetrically within the lateral margins of the vertebral endplates. After implantation, inspect the anterior faces of the upper and lower baseplates to ensure that the vertical positioning marks on the anterior faces of the baseplates are aligned. This indicates that the FlexiCore Intervertebral Disc is in the neutral axial P.198 rotation position. If needed, the baseplates can be repositioned, using the Repositioner/Extractor Tools to grasp pairs of the holes in the upper or lower implant baseplates. The Inserter/Impactor is not recommended for repositioning. The FlexiCore Intervertebral Disc is properly seated when the spikes on the upper and lower baseplate penetrate and engage the vertebral endplates. To ensure this, the Leveling Tool is gently wedged between the upper and lower baseplates. Full insertion of the Leveling Tool is possible only if the baseplates of the implant can reach a parallel position. If resistance is met, do not force the leveling tool beyond this point, as the spikes have been seated sufficiently. Impaction on, or forcing the Leveling Tool after resistance is met, may result in fracture of the prongs. Finally, a standard surgical closure procedure is performed as for anterior or anterolateral spinal surgery. The goal of the postoperative rehabilitation is to return the patient to normal activity

as soon as possible without jeopardizing soft and hard tissue healing. The patient should wear a corset for 2 to 3 weeks to support healing of the abdominal incision (depending on patient comfort). The patient's rehabilitation program should be based on the individual's needs, taking into account his or her age, stage of healing, general health, and physical condition.

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Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Stabilization Techniques I > 23 - X STOP Interspinous Implant for Lumbar Spinal Decompression

23 X STOP Interspinous Implant for Lumbar Spinal Decompression Jim F. Zucherman Patrick Simons Jake Timothy Neurogenic intermittent claudication (NIC) secondary to lumbar spinal stenosis (LSS) is a posture-dependent complaint and it typically affects patients at the age of 50 years or older. NIC is defined as pain or numbness in the buttocks, thighs, and/or lower legs caused by decrease of the spinal canal area and brought on by either prolonged standing or exercise in the erect posture. The symptom is typically relieved by various maneuvers that flex the lumbar spine, which increases the spinal canal area significantly(1,2,3,4,5,6,7,8,9). Decompressive surgery with or without fusion is the current gold standard treatment for moderate to severe symptomatic LSS.

Interspinous Process Decompression (IPD) A new minimally invasive, stand-alone alternative to conservative and standard surgical decompressive treatments has been developed (10,11,12,13). The interspinous implant (X STOP, St. Francis Medical Technologies Inc., Alameda CA) is placed between the spinous processes to prevent extension of the symptomatic

levels, yet allowing flexion, axial rotation, and lateral bending (Fig. 23.1)(14). Eliminating the symptomatic extension at the abnormal segment and keeping it in that position would maintain the asymptomatic state and allow the more normal spinal segments to function normally. The patient would no longer be forced to keep the entire lumbar spine in flexion just to maintain enough space at the localized stenotic areas. Because the load-bearing element is anterior to the retained supraspinous ligament a cantilever effect results, unloading the middle column of the spine while restoring height loss from degenerative changes. This is born out by biomechanical testing mentioned later. Also the retained posterior supraspinous ligament prevents kyphotic deformity as is verified by the radiographic studies mentioned later. The load that is taken up by the device is taken from the middle column of the spine, which has deteriorated from its inability to efficiently handle loads over the years. This then may allow slowing of the degenerative process or even some recovery of inflamed chronically overloaded tissues over time as is evidenced by the persistence of benefit from the device with a 78% success rate at 4-year follow-up based on P.202 Oswestry Disability Index (ODI) scores (15). Because sagittal balance effect is minimal, motion limitation is minimal, and adjacent disc and facet joint pressures are unaffected, there is no reason to believe the device will adversely affect the natural history of adjacent segments.

FIGURE 23.1 X STOP interspinous implant.

Biomechanical studies have shown that, in extension, the implant significantly increases the canal area by 18%, the subarticular diameter by 50%, the canal diameter by 10%, the foraminal area by 25%, and the foraminal width by 41%. These dimensions were not affected at adjacent levels. This is the primary mechanism of action (16). Wardlaw et al. reported equal results in their clinical study evaluating positional magnetic resonance imaging (MRI) changes after X STOP implantation (17,18). Further studies have also demonstrated that, at the implanted level, the implant significantly reduces the pressure on the facets, in the nucleus pulposus, and in the posterior annulus of the disc, without influence on adjacent levels (16,19,20).

Surgical Procedure Patients may be operated on under local anesthesia with light intravenous sedation, placed in either lateral decubitus or prone position. A 4- to 8-cm midline incision is made exposing the spinous processes at the appropriate disc level, which is confirmed radiographically. The supraspinous ligament and its attachments are

preserved, which is of paramount importance to prevent postoperative kyphosis and also to serve to stabilize the implant. The interspinous ligament is pierced, but retained, and the implant is placed between the spinous processes. The spinous processes are not modified to allow implantation, but in cases where hypertrophied facets protrude posteriorly, they should be trimmed without interfering its integrity in function (Fig. 23.2). The spinal canal is not violated, and neither laminotomy, nor laminectomy, nor foraminotomy is performed. Removal of any portion of the ligamentum flavum is unnecessary.

Clinical Results in Literature X STOP Prospective Randomized Multicenter Study Based on very promising results of a clinical pilot study of ten symptomatic LSS patients treated with the X STOP, a United States Food and Drug Administration (US FDA) prospective randomized clinical multicenter study was undertaken, comparing the interspinous implant with conservative (nonoperative) treatment for the management of NIC. Study results demonstrated a clinically and statistically significant difference favoring the interspinous implant. Two years after the surgery, 60% of the patients reported that their symptoms were significantly improved, compared to 18% of the control patients. Regarding physical function, 57% of X STOP patients reported significant improvement, compared to 15% of control patients. Among X STOP patients, 73% were satisfied or very satisfied with their treatment compared to 36% of the control group patients (Table 23.1)(21). Of interest, 39 patients with grade I degenerative spondylolisthesis were treated in the U.S. study with the X STOP and 22 patients were treated nonoperatively. Using 15-point improvement over baseline scores in the Zurich Claudication Questionnaire P.203 P.204 (ZCQ) as the criterion of clinical success, 69% of the X STOP patients had a successful outcome at 2-year follow-up, compared to 9% of the control patients. The mean improvement score for the 39 X STOP patients was 26 points. There were no significant differences in the mean percentage of slip between X STOP and control patients at baseline or at 2-year follow-up. The X STOP represents a significantly less invasive alternative therapy for these patients, resulting in very good clinical

outcomes, and most importantly, no evidence that the implant results in any instability of the motion segment. In this study, more than a third of the patients treated with the X STOP implant suffered from a degenerative spondylolisthesis up to grade 1 (out of 4). Spondylolisthesis patients are mostly treated with an instrumented spinal fusion. Analysis of this subgroup showed that the X STOP procedure is as effective as that applied on patients without spondylolisthesis (22).

FIGURE 23.2 The X STOP interspinous process decompression (IPD) implant procedure.

TABLE 23.1 Zurich Claudication Questionnaire (ZCQ) Success Rates 2 Years After Surgery Success Rates X STOP (N = 93)

Control (N = 81)

P value

Symptom severity

60%

19%

<0.001

Physical function

57%

15%

<0.001

Patient satisfaction

73%

36%

<0.001

Furthermore, Implicito et al. (23) reported on their subanalysis of the X STOP patients in this study, comparing 63 one-level and 33 double-level IPD patients. With the current surgical options, NIC patients treated surgically at multiple levels typically have worse outcomes than those treated at one level. This study showed that both X STOP groups had significant improvements postoperatively (p <0.0001). The success rate of the one-level IPD patients was 56% and for the two-level IPD patients it was 73%, with no significant difference between the success rates, showing the X STOP to be an effective way to surgically treat patients with NIC at more than one level.

Sagittal Balance The requirement to maintain proper sagittal alignment and balance in patients receiving spinal implants is well understood. Experience with lumbar fusion

procedures that cause a flat back has overwhelmingly resulted in unacceptable clinical outcomes. Three different radiologic studies were therefore undertaken to measure any possible effect of the X STOP on sagittal alignment. In the U.S. study, x-rays were taken at each follow-up visit for both X STOP and control patients and measurements were made of the lumbosacral angle (L1 to S1) and the treated intervertebral angle. At 2-year follow-up, there were no significant differences in the mean scores between the two groups of patients. Preoperative x-rays from a subset of X STOP patients were also compared to standing films taken at 2-year follow-up. In 23 patients with single-level implants, the change in the intervertebral angle was only 0.5 degree (±2.0 degrees), and the change in the P.205 lumbosacral angle was 0.1 degree (±3.8 degrees). Similar values were recorded for 18 patients with double-level implants. Interim data from an ongoing study being conducted at the University of Aberdeen by Wardlaw and Smith (24) have recently been presented, in which preoperative images were compared to postimplant images obtained in a positional MRI scanner. In addition to confirming in vivo the increases in the area of the foramen and canal that were measured in the preclinical in vitro cadaver study, results of this study confirm a change in angulation for both the lumbosacral angle and intervertebral angle of between 1 and 2 degrees. These three studies confirm that the X STOP results in only minimal changes to sagittal alignment. This due is to preserving the supraspinous ligament and its original insertions. This ligament is a very robust structure receiving the confluence of the lumbodorsal fascia and its preservation prevents overdistraction of the segment.

X STOP Versus Decompressive Laminectomy The success rate of decompressive surgery varies greatly due to a number of factors such as patient selection, surgical technique, and outcome measures. An attempted meta-analysis of 74 surgical LSS studies reported a mean rate of good to excellent outcomes of 64% in the first year (25). Compared to literature-reported outcomes of decompressive surgery there are significant differences in operative time, estimated blood loss, hospital stay, complication rate, and reoperation rates, favoring the X STOP IPD

(26,27,28,29,30,31,32,33,34,35,36,37,38) (Table 23.2). During the course of the U.S. study, 24 patients in the control group underwent decompressive laminectomy for the relief of their stenosis symptoms and outcomes are available for 22 patients. At a mean follow-up time of 12.8 months outcomes for these patients were very similar to outcomes of the X STOP patients at 2-year follow-up. Sixty-four percent had clinically significant improvement in Symptom Severity Domain of ZCQ, 68% had clinically significant improvement in Physical Function Domain of ZCQ, and 60% were satisfied with the outcome of their treatment. Furthermore, Katz et al. (39) published a large series of surgically treated spinal stenosis patients using the ZCQ outcomes tool. When the same success criteria that were used in the X STOP series are applied to Dr. Katz's series, the results in all three domains are equivalent for two surgical procedures (40).

TABLE 23.2 X STOP Decompression Versus Laminectomy Operative and Hospitalization Details

X STOP

Laminectomy

Average OR time (minutes)

27–54

104–224

Average blood loss (mL)

46

120–1,040

Average length of hospital stay

<24 hours–2

7–8 days

days

Operative or device-related complications

7%

20% (with arthrodesis) 14% (without arthrodesis)

Reoperation rate

6%

10%–23%

OR, operating room.

P.206 Both the multicenter randomized clinical trial (RCT) study in the United States and Strömqvist et al. (41), as part of the Swedish national register of lumbar surgery, used the SF-36 to evaluate general health outcomes after surgical treatment. A comparison between two matched subsets of patients, 90 each, showed that the postoperative scores were improved for both groups in all domains except for general health 1 year after surgery. Mean postoperative scores in the two physical and emotional domains improved more markedly for the X STOP group (42). Okumu and Hannibal (43) evaluated the cost and effectiveness of X STOP and laminectomy surgery during index hospitalization for the treatment of 33 patients with LSS in the United States. Patients were matched for age, number of levels treated, and preoperative disability. It was shown that X STOP is significantly more cost-effective than laminectomy for the treatment of single- and double-level LSS (Table 23.3). Turner et al. (25) reported on complications such as dural tears, neural injuries, deep wound infections, pulmonary embolism, myocardial infarction, and death in their meta-analysis of 74 LSS surgery studies. To date, with the exception of a death that occurred 3 days postoperatively and was determined to be unrelated to the X STOP implant, there were no complications of this nature reported during or after the X STOP procedure.

German Registry In Germany, a registry is being maintained to gather prospective data on NIC patients, who are treated with the X STOP implant in general practice. Patients are assessed pre- and postoperatively using the validated, condition-specific ZCQ. The ZCQ is the only validated LSS-specific outcomes measure (46,47). The questionnaire consists of three domains: Symptom Severity (SS), Physical Function (PF), and

Patient Satisfaction (PS). To date 212 patients have been evaluated 1 year after surgery with very good results (Table 23.4). Two patients had a reoperation because of lack of efficacy and one because of dislocation of the implant.

TABLE 23.3 X STOP Versus Laminectomy: Average Hospital Costs for Single- and Double-Level Lumbar Spinal Stenosis (LSS) Laminectomy

Laminectomy

X STOP 1

X STOP 2

1 level

2 levels

level

levels

Hospital charges

$10,446

$9,797

$561

$412

Lab/ECG

$1,314

$1,531

$481

$673

OR/OR supplies

$23,605

$22,768

$6,588

$7,105

X-rays

$1,366

$847

$2,106

$3,347

Pharmaceuticals

$4,764

$4,935

$1,153

$1,254

Anesthesia

$2,184

$2,228

$356

$229

Other

$1,652

$3,632

$314

$332

Subtotal

$45,331

$45,739

$11,559

$13,353

$5,500

$11,000

Hardware (est)

Total

$45,302

$45,739

$17,059

$24,353

ECG, electrocardiogram; OR, operating room.

P.207

TABLE 23.4 Zurich Claudication Questionnaire (ZCQ) Success Rates 6 and 12 Months After Surgery Success Rate 6 Months

12 Months

Symptom severity

82%

82%

Physical function

81%

77%

Patient satisfaction

82%

82%

In addition to the German results presented here, Katz et al. (33) reported outcomes with 2-year follow-up on 197 NIC patients treated with a lumbar laminectomy using the same success criteria in a patient population similar to those enrolled in the registry. The German X STOP patients show higher ZCQ success rates compared to the scores of the laminectomy patients reported by Katz et al. (Fig. 23.3).

European Clinical Experience A prospective clinical evaluation of 15 patients with 3- and 6-month follow-up was carried out by Wardlaw (46) in conjunction with pre- and postoperative positional

MRI scan measurements. All cases demonstrated clinical improvement and the X STOP implant increased the cross-sectional area of the dural sac and exit foramina without affecting overall movement of the lumbar spine. Heijnen and Kramer (47) reported on the satisfaction of 14 patients with NIC, who were treated with the X STOP implant. One patient died of a non-back related disorder. Eleven of the other 13 patients expressed a great satisfaction. They are free of NIC symptoms and all but one would undergo the surgery again, if the choice had to be made again.

Scientific Evidence X STOP in Perspective to Worldwide Literature Surgery for Degenerative Lumbar Spondylosis Gibson and Waddell (48) evaluated the current scientific evidence on the effectiveness of surgical interventions for degenerative lumbar spondylosis, involving surgical procedures of spinal decompression, nerve root decompression, and fusion of adjacent vertebra. Thirty-one published RCTs of all forms of surgical treatment for degenerative lumbar spondylosis were identified. There is moderate evidence that instrumentation can increase the fusion rate, but strong evidence that it does not improve clinical outcomes. The trials varied a lot in quality: only in 16, more recent, trials there was some form of centralized P.208 randomization scheme or assignment system. Eighteen of the 31 trials had the recommended follow-up for surgical studies of at least 2 years. Only 6 trials reported on the surgical treatment for spinal stenosis and/or nerve root decompression. Just 1 of the 6 trials was an RCT with a large patient population, it concerns the prospective randomized clinical multicenter study, comparing the X STOP interspinous implant with conservative (nonoperative) treatment (21) (Table 23.5).

FIGURE 23.3 Zurich Claudication Questionnaire (ZCQ) success rates: X STOP versus laminectomy patients reported by Katz et al.

Turner et al. (25) also reported on the poor scientific quality of the published studies in their attempted meta-analysis of 74 surgical therapy studies for LSS. None of the 74 studies were randomized and just 3 studies were clearly prospective.

Conclusion The decompression of the lumbar spine with X STOP IPD implant offers a wellproven, safe, effective, and cost-effective treatment of patients suffering from NIC secondary to LSS. The X STOP can be implanted with local anesthetic, and many patients can return home within 24 hours after surgery. In brief, regarding X STOP decompression of the lumbar spine: It is clinically well proven as an effective treatment for symptoms of LSS with or without degenerative spondylolisthesis. It is safe.

It has a short surgery time and can be made under local anesthesia. It is minimally invasive. P.209 It can be implanted during a short stationary or ambulatory stay. There is an immediate and subsistent relief of pain. It is cost-effective.

TABLE 23.5 Scientific Review on Degenerative Spondylosis; The Cochrane Review 2005 No. Randomized Controlled Trials

16

No. Clinical Controlled Trials

15

TOTAL

31

Six trials on spinal and nerve root stenosis

Author

Year

No. Patients

Randomized

Subject

Herkowitz

1991

50

No

Decompression vs. decompression with fusion

Postacchini

1993

70

No

Different surgical decompression techniques

Bridwell

1993

44

No

Decompression vs. decompression with fusion

Grob

1995

45

No

Decompression vs. decompression with fusion

Amundsen

2000

31

No

Surgical decompression vs. conservative

Zucherman

2004

200

Yes

X STOP vs. conservative treatment incl. epidural injections

The X STOP implant offers the benefits of decompression, yet with a low-risk profile, for NIC patients. The comparative analyses suggest that the outcomes of the X STOP decompression may at least be comparable to outcomes reported in the literature for decompressive laminectomy. However, mainly due to flaws in studies on decompressive treatments, no definitive conclusions can be drawn.

Acknowledgment For participation in the German registry: Dr. D. Werner, Arkade Privatklinik, Niederschmalkalden; Dr. P. Simons, MediaPark Klinik, Cologne; Dr. P. Krause, Orthopädische Schmerztherapie, Munich; Dr. G. Godde, Gemeinschaftspraxis Konigsallee, Düsseldorf; and Dr. P. Mark, Westend Krankenhaus, Berlin.

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18. Siddiqui M, Karadimas E, Nicol M et al. The positional MRI changes in the lumbar spine following insertion of a novel interspinous process distraction device. In: Trans WorldSpine 2005, Rio de Janeiro, Brazil. 19. Swanson KE, Lindsey DP, Hsu KY, Zucherman JF, Yerby SA. The effects of an interspinous implant on intervertebral disc pressures. Spine 2003; 28: 26–32. 20. Wiseman CM, Lindsey DP, Fredrick AD, Yerby SA. The effect of an interspinous process implant on facet loading during extension. Spine 2005; 30: 903–907. 21. Zucherman JF, Hsu KY, Hartjen CA, Mehalic TF, Implicito DA, Martin MJ et al. A multicenter, prospective, randomized trial evaluating the X STOP interspinous process decompression system for the treatment of neurogenic intermittent claudication: two-year follow-up results. Spine 2005; 15; 30: 1351–1358. 22. Anderson PA. The effect of spondylolisthesis on the outcomes of lumbar neurogenic intermittent claudication patients treated with interspinous process decompression (IPD). In: Trans ISSLS 2005 New York. 23. Implicito D, Martin M, Ozuna R. Outcomes of neurogenic intermittent claudication patients treated with interspinous process decompression as a function of number of levels treated. Spine J 2005; 5: IS-90S. 24. Siddiqui M, Nicol M, Karadimas E, Smith F, Wardlaw D. The positional magnetic resonance imaging changes in the lumbar spine following insertion of a novel interspinous process decompression device. Spine (in press). 25. Turner JA, Ersek M, Herron L, Deyo R. Surgery for LSS. Attempted metaanalysis of the literature. Spine 1992; 17: 1–8.

26. Benz RJ, Ibrahim ZG, Afshar P, Garfin SR. Predicting complications in elderly patients undergoing lumbar decompression. Clin Orthop 2001; 384: 116–121. 27. Deyo RA, Cherkin DC, Loeser JD, Bigos SJ, Ciol MA. Morbidity and mortality in association with operations on the lumbar spine. J Bone Joint Surg Am 1992; 74: 536–543. 28. Iguchi T, Kurihara A, Nakayama J, Sato K, Kurosaka M, Yamasaki K. Minimum 10-year outcome of decompressive laminectomy for degenerative LSS. Spine 2000; 25: 1754–1759. 29. Postacchini F, Cinotti G, Perugia D, Gumina S. The surgical treatment of central lumbar stenosis. Multiple laminotomy compared with total laminectomy. J Bone Joint Surg Br 1993; 75: 386–392. 30. Hu RW, Jaglal S, Axcell T, Anderson G. A population-based study of reoperations after back surgery. Spine 1997; 22: 2265–2271. 31. Jonsson B, Annertz M, Sjoberg C, Strömqvist B. A prospective and consecutive study of surgically treated LSS. Part II: five-year follow-up by an independent observer. Spine 1997; 22: 2938–2944. 32. Katz JN, Lipson SJ, Larson MG, McInnes JM, Fossel AH, Liang MH. The outcome of decompressive laminectomy for degenerative lumbar stenosis. J Bone Joint Surg Am 1991; 73: 809–816. 33. Katz JN, Lipson SJ, Chang LC, Levine SA, Fossel AH, Liang MH. Seven- to 10year outcome of decompressive surgery for degenerative LSS. Spine 1996; 21: 92–98. 34. Hu RW, Jaglal S, Axcell T, Andersson G. A population-based study of reoperations after back surgery. Spine 1997; 22: 2265–2271.

35. Jonsson B, Annertz M, Sjoberg C, Stromqvist B. A prospective and consecutive study of surgically treated LSS. Part II: Five-year follow-up by an independent observer. Spine 1997; 22: 2938–2944. 36. Katz JN, Lipson SJ, Larson MG et al. The outcome of decompressive laminectomy for degenerative lumbar stenosis. J Bone Joint Surg Am 1991; 73: 809–816. 37. Katz JN, Lipson SJ, Larson MG, McInnes JM, Fossel AH, Liang MH. Seven- to 10-year outcome of decompressive surgery for degenerative LSS. Spine 1996; 21: 92–98. P.211 38. Timothy J, Pal D, Ross S, Marks P. Early experience with the X-STOP a lumbar spinous process distractor for the treatment of lumbar canal stenosis. Br J Neurosurg 2005 abstract, in press. 39. Katz JN, Stucki G, Lipson SJ, Fossel AH, Grobler LJ, Weinstein JN. Predictors of surgical outcome in degenerative lumbar spinal stenosis. Spine 1999; 24: 2229–2233. 40. Katz JN. Spinal stenosis data. Boston: Harvard Medical School, 2003: 1–33. 41. Strömqvist B, Jonsson B, Fritzell P, Hagg O, Larsson BE, Lind B. The Swedish National Register for lumbar spine surgery: Swedish Society for Spinal Surgery. Acta Orthop Scand 2001; 72: 99–106. 42. Strömqvist B, Zanoli G, Zucherman J, Hsu K. SF-36 profiles before and one year after spinal stenosis surgery: a prospective comparison of two techniques in two nations. In: Trans Eurospine 2004, Porto, Portugal.

43. Okuma K, Hannibal M. Cost analysis of interspinous process decompression versus laminectomy for the treatment of lumbar spinal stenosis. In Trans ISSLS 2005, New York. 44. Stucki G, Liang MH, Fossel AH, Katz JN. Relative responsiveness of condition specific and generic health status measures in degenerative lumbar spinal stenosis. J Clin Epidemiol 1995; 48: 1369–1378. 45. Stucki G, Daltroy L, Liang MH, Lipson SJ, Fossel AH, Katz JN. Measurement properties of a self-administered outcome measure in lumbar spinal stenosis. Spine 1996; 21: 796–803. 46. Wardlaw D. Change in spinal canal and nerve root foraminal measurements before and six months following insertion of the X STOP Interspinous Process Distraction Device in relation to early clinical outcome. In: Trans ISMISS 2004, Zurich, Switzerland. 47. Heijnen SAF, Kramer FJK. Spinale distractie als therapie bij lumbale wervelkanaalstenose—de eerste resultaten. Ned. Tijdschrift voor Orthopaedie 2004; 11(4): 199–203. 48. Gibson JNA, Waddell G. Surgery for degenerative lumbar spondylosis. The Cochrane Database of Systematic Reviews 2005; 2050, Issue 2.Art. No.: CD001352.pub2. DOI: 10.1002/14651858.CD001352.pub2.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Stabilization Techniques I > 24 - MRI Changes in the Lumbar Spine Following Treatment with the X STOP Interspinous Distraction Device

24 MRI Changes in the Lumbar Spine Following Treatment with the X STOP Interspinous Distraction Device F. W. Smith Intermittent neurogenic claudication as a result of lumbar spinal stenosis accounts for between 3% and 14% of patients complaining of low back pain who attend a specialist (1,2,3). Therefore, this is not an inconsiderable health care problem, causing significant disability to the patient and cost to society. The clinical symptoms, cause, and treatment of the problem are well documented and are generally attributed to lumbar spinal stenosis resulting in nerve root compression at one or more levels (4,5,6,7). Facet joint specific pain is exacerbated by extension and relived by flexion or lying in the recumbent position (8,9). During extension the load on the facet joints is increased, resulting in narrowing of the spinal canal and nerve root canals, and deformity of the joint capsule with or without resultant pressure on the adjacent nerve root (9,10). The stability of the spinal column is dependent on the individual motion segments acting together. The load-bearing structures of each segment are the vertebral body and the two facet joints. Loading between adjacent vertebral bodies is transmitted both by the intervertebral disc between the vertebrae and the facet joints between each pedicle. If any part of a motion segment is damaged,

abnormal, altered loading will result on the other structures. Degenerative disease of the intervertebral disc resulting in reduction in disc height is recognized as a cause of altered stress on the facet joints, which in turn may result in narrowing of the spinal canal at that level (11,12,13). Facet joint degeneration has been shown to accelerate disc degeneration, as a result of destabilization of the motion segment (14). Long-term intervertebral disc and facet joint degeneration is recognized as a precursor of spondylolisthesis (9,10,11). The treatment of patients with intermittent neurogenic claudication varies depending on the severity of the symptoms and will usually begin conservatively and include analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs), physiotherapy, spinal manipulative treatment, and epidural steroid injection. Those who fail to respond to conservative treatment may be offered decompressive surgery by way of laminectomy with or without a spinal fusion technique. The success of decompressive surgery is very variable, with risks of surgical complication and may be associated with the need for reoperation (15,16,17). Analysis of 74 published studies of surgery for spinal stenosis found the success rate for a good outcome varied from 26% to 100% (18). P.214

FIGURE 24.1 X-Stop implant.

With the knowledge that extension exacerbates spinal stenosis and exit foraminal narrowing, a simple minimally invasive implant for preventing this has been developed (X STOP Interspinous Process Decompression System, St. Francis Medical Technologies Inc., Almeda, CA). The implant prevents narrowing of the spinal canal and neural foramina in extension. It is placed between the spinous processes from a lateral approach through the interspinous ligament. It is held in place by the interspinous ligament posteriorly, the lamina anteriorly, and by two wings on the implant laterally (Fig. 24.1). Cadaveric studies have shown that the implant does increase the cross-sectional area of the spinal canal as well as widen the exit foramina (19) (Fig. 24.2). In another study, the implant significantly reduced the mean peak pressure, contact area, and force pressures at the implanted level (20). The 1- and 2-year follow-up studies of a prospective, randomized multicenter study conclude that the X STOP

provides an effective treatment for patients suffering from lumbar spinal stenosis, offering a minimally invasive alternative to both conservative treatment and decompressive surgery (21,22). The theory of how the implant works as borne out by the cadaveric studies is confirmed by the good early clinical results. In an effort to show in vivo that the implant works as it is supposed to, a prospective study using an “upright― magnetic resonance P.215 imaging (MRI) scanner in which the patient can be studied either supine or erect and also in different degrees of flexion and extension has been performed. Prior to this study, the upright MRI scanner (FONAR Corp., Melville, NY) has been used to demonstrate the alteration in dural sac dimensions between lying and standing and also between flexion and extension (23) and to measure the diurnal variation in disc height (24). In addition, preliminary clinical studies have shown the value of being able to examine patients with low back pain and sciatica in different postures (25). The X STOP implant is very MRI compatible showing no significant peri-implant artifact (Fig. 24.3) to distort the MRI image, enabling accurate measurement of the spinal canal and nerve root canal dimensions.

FIGURE 24.2 Axial MRI of cadaveric specimen in the extended position (A) without implant and (B) with implant showing the increase in canal dimensions after implant insertion.

FIGURE 24.3 MRI T2-weighted axial and sagittal sections showing the appearances of the X STOP implant.

Twenty-six patients, 13 men and 13 women aged between 57 and 93 years have been entered into a study. For inclusion into the study each patient had to be older than 50 years and suffer from radicular leg pain with or without back pain, which came on when standing and/or walking and was relieved by sitting. The symptoms did not respond to rest, physiotherapy, analgesic/NSAID, and caudal epidural injection with anesthetic and steroid. Each patient had had an MRI examination showing spinal canal/exit foramina stenosis at one or more levels. Each patient had to be able to sit comfortably for the duration of the positional scan, which normally takes 50 minutes. Patients were excluded from the study if they suffered unremitting pain in any posture or suffered from the cauda equina syndrome with bowel/bladder disturbance. Those with pathologic fractures of a vertebrae, severe osteoporosis of the spine,

active infection, Paget's disease or metastases at the involved segment, or ankylosing spondylitis or fusion at the affected level were excluded, as were those suffering from morbid obesity [body mass index (BMI) ≥40 Kg/m2]. In total, 37 levels were treated. There were 15 single-level procedures (L2-3 = 1, L3-4 = 3, L4-5 = 11) and 12 two-level procedures (L3-4 + L4-5 = 11; L4-5 + L5-S1 = 1). Positional MRI examination was performed prior to implantation and at 6 months and 1 year after operation. The positional MRI scanner is an open configuration magnet based on a 0.6 Tesla resistive magnet (FONAR “Upright―; FONAR Corp., Melville, NY) (Fig. 24.4). This configuration gives enough space to allow the scanning table to rotate from 15 degrees of Trendelenburg position to vertical (standing or sitting), and to move vertically up and down so as to be able to place any part of the body in the isocenter of the magnet with the patient in any position (i.e., with the spine P.216 P.217 in neutral, flexion, or extension). Using positional MRI, it is possible to compare the relative positions of the lumbar vertebrae throughout a full range of movement, both anterior/posterior flexion extension and lateral flexion. Furthermore, the patient may be imaged in the very position that causes the symptoms (e.g., standing) and then compared with the position that relieves the symptoms (e.g., lying supine).

FIGURE 24.4 Positional, “upright― MRI scanner showing the different imaging positions. A: Supine. B: Standing. C: Seated. D: Seated in flexion. E:

Seated in extension.

Each patient, once enrolled in the study, had a preoperative positional MRI scan in which T2-weighted sagittal scan of the entire lumbar spine and axial images through the lower five intervertebral discs in the erect standing position were made. This was followed by the same imaging protocol with the patient seated comfortably, seated flexed, and seated in extension (Fig. 24.4). Further scans following the same protocol are performed at 6 months and at 1 year following X STOP implantation. The following measurements were made using the Osiris 4.19 program (University of Geneva): The lumbosacral angle (L1-S1 angle) by measuring the angle between the superior endplate of L1 and the superior endplate of S1. This measurement was made in the erect position to determine the true extent of ant alteration in the lumbar curvature between the pre- and postoperative images. From midline sagittal images, the anterior and posterior disc heights, in the seated neutral, flexed, and extended positions (Fig. 24.3). From the parasagittal sections, the area of exit foramen at the treated levels was made using the region of interest cursor. From the axial images, the area of the dural sac was measured at the narrowest point (Fig. 24.5).

FIGURE 24.5 Axial sections (A) preoperative and (B) postoperative showing measurement of the area of the dural sac.

P.218

Results To reduce error, each measurement was made on five separate occasions by two separate observers. Dural Sac Area: The dural sac area increased after X STOP implantation by approximately 15% in the standing and seated positions and by 8% when seated flexed. In the seated extended position, there was a much larger increase in the area in the region of 27%. Postoperatively, in the single-level group, a significant increase was noted between neutral and standing (21% and 10%, respectively), whereas in the two-level group there was significant increase in the seated neutral and extended postures and the seated and standing postures (by 15% to 20%, respectively). The area of the dural sac measured before surgery decreased by 26.7% from flexion to standing, by 20.3% from flexion to extension, and by 16.5% from

neutral to standing. Six months after operation the amount of reduction in dural sac area decreased significantly, indicating the efficacy of the procedure at maintaining spinal canal dimensions. After surgery the area only reduced by 18.1% between flexion and standing, 5.9% between flexion and extension, and 13.8% from neutral to standing. Neural Foraminal Area: It was interesting that in this group of patients, the left nerve root foramina showed a larger change in area between the different postures than the right. Before surgery the left exit foramen at the treated level decreased by 31.2% between flexion and extension and the right by 18.3%. After surgery the degree of reduction in area was less but again the difference between right and left remained, the left reducing by only 14.1% and the right by 9.4%, between flexion P.219 and extension. In real terms this showed a relative increase in exit foramen area after X STOP implantation of 17.1% for the left foramina and 8.9% for the right side. Disc height: There was no significant difference in either anterior or posterior disc height. Total Lumbar Range of Movement (L1-S1): The overall posture of the lumbar spine and the range of movement were not significantly altered. Endplate angle changes: The changes above and below the level of instrumentation were statistically insignificant. The overall reduction in the range of movement at the instrumented level was statistically insignificant.

FIGURE 24.6 The same patient (A)the day before X STOP implantation and (B)the day after.

As we conclude in our recently published results of the first 12 patients entered into the study (26), this ongoing study shows that the posterior disc height at the treated level did not increase as may have been expected and that the X STOP device significantly increases the cross-sectional area of the spinal canal and exit foramina. The overall range of lumbar spine movement at the operated and adjacent segments are unaffected, and the patient's posture is immediately improved (Fig. 24.6).

REFERENCES 1. Hart LG, Deyo RA, Cherkin DC. Physician office visits for low back pain. Frequency, clinical evaluation and treatment patterns from a US national survey. Spine 20: 11–19, 1995. 2. Fanuele JC, Birkmeyer NJ, Abdu WA, et al. The impact of spinal problems on

the health status of patients: have we underestimated the effect? Spine 25: 1509–1514, 2000. 3. Long DM, BenDebba M, Torgerson WS, et al. Persistent back pain and sciatica in the United States: patient characteristics. J Spinal Disord 9: 40–58, 1996. 4. Arbit E, Pannullo S. Lumbar stenosis: a clinical review. Clin Orthop 384: 137–143, 2001. 5. Inufusa A, An HS, Lim TH, et al. Anatomic changes in the spinal canal and intervertebral foramen associated with flexion-extension movement. Spine 21: 2412–2420, 1996. 6. Jenis LG, An HS. Spine update. Lumbar foraminal stenosis. Spine 25: 398–394, 2000. 7. Schonstrom N, Willen JT. Imaging lumbar spinal stenosis (review). Radiol Clin North Am 39: 31–59, 2001. 8. Cavanaugh JM, Ozaktay AC, Yamashita HT, et al. Lumbar facet pain: biomechanics, neuroanatomy and neurophysiology. J Biomech 29: 1117–1129, 1996. 9. Dreyer SJ, Dreyfuss PH. Low back pain and the zygapophyseal (facet) joints. Arch Phys Med Rehabil 77: 290–300, 1996. 10. Berven S, Tay BB, Coleman W, et al. The lumbar zygapophyseal (facet) joints: a role in the parthenogenesis of spinal pain syndromes and degenerative spondylolisthesis. Semin Neurol 22: 187–196, 2002. 11. Sharma M, Langana NA, Rodriguez J. Role of ligaments and facets in lumbar spinal stability. Spine 20: 887–900, 1995.

12. Adams MAQ, Hutton WC. The effect of posture on the role of the apophyseal joints in resisting intervertebral compressive forces. J Bone Joint Surg Br 62: 358–362, 1980. 13. Dooris AP, Goel VK, Grosland NM, et al. Load sharing between anterior and posterior elements in a lumbar motion segment implanted with an artificial disc. Spine 26: E122–129, 2001. 14. Haher TR, O'Brien M, Dryer JW, et al. The role of the lumbar facet joints in spinal stability. Identification of alternative paths of loading. Spine 19: 2667–2670, 1994. 15. Ciol MA, Deyo RA, Howell E, et al. An assessment of surgery for spinal stenosis: time trends, geographic variations, complications and re-operations. J Am Geriatr Soc 44: 285–290, 1996. 16. Deyo RA, Cherkin DC, Loeser JD, et al. Morbidity and mortality in association with operations on the lumbar spine. The influence of age, diagnosis and procedure. J Bone Joint Surg Am 74: 536–543, 1992. P.220 17. Katz JN, Stucki G, Lipson SJ, et al. Predictors of surgical outcome in degenerative lumbar spinal stenosis. Spine 24: 2229–2233, 1994. 18. Turner JA, Ersek M, Herron L, et al. Surgery for lumbar spinal stenosis. Attempted meta-analysis of the literature. Spine 17: 1–8, 1992. 19. Richards JC, Majumdar S, Lindsey DP, et al. The treatment mechanism of an interspinous process implant for lumbar neurogenic claudication. Spine 30: 744–749, 2005.

20. Wiseman CM, Lindsey DP, Fredrick AD, Yerby SA. The effect of an interspinous process implant on facet loading during extension. Spine 30: 903–907, 2005. 21. Zuchermann JF, Hsu KY, Hartjen CA, et al. A prospective randomized multicenter study for the treatment of lumbar spinal stenosis with the X STOP interspinous implant: 1 year results. Eur Spine J 13: 22–31, 2004. 22. Zuchermann JF, Hsu KY, Hartjen CA, et al. Multicenter, prospective, randomized trial evaluating the X STOP interspinous process decompression system for the treatment of neurogenic intermittent claudication: Two year follow up results. Spine 30: 1351–1358, 2005. 23. Hirasawa Y, Bashir W, Pope MH, Smith FW. Postural variation in dural sac cross sectional area measured in normal individual's supine, standing and sitting, using pMRI RSNA 2003. Proceeding of the 89th Scientific Assembly and Annual Meeting of the Radiological Society of North America 641:1316. 2003. 24. Bashir W, Hirasawa Y, Pope MH, Smith FW. Measurement of diurnal variation in intervertebral disc height in normal individuals: a study comparing supine with erect MRI. RSNA 2003. Proceeding of the 89th Scientific Assembly and Annual Meeting of the Radiological Society of North America 641:1315. 2003. 25. Smith FW, Pope MH. Potential value for MR Imaging in the seated position: a study of 63 patients suffering from low back pain and sciatica. RSNA 2003. Radiology (P)1312: 640, 2003. 26. Siddiqui M, Nicol M, Karadimas E, Smith F, Wardlaw D. The positional magnetic resonance changes in the lumbar spine following insertion of a novel interspinous process distraction device. Proceeding of the 89th Scientific Assembly and Annual Meeting of the Radiological Society of North America 640:1312. 2003.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Stabilization Techniques I > 25 - Impliant TOPS: Total Posterior Arthroplasty System

25 Impliant TOPS: Total Posterior Arthroplasty System Richard D. Guyer

Introduction Pain arising from degenerative changes in the posterior elements has long been treated with decompression or decompression combined with fusion. While decompression alone may leave the spine at risk for instability, decompression with fusion leaves it incapable of allowing motion due to the rigid fixation. We have seen the expansion of total disc replacement to address disc-related pain without fusing the spine. Such treatment holds promise to reduce the patient's pain while allowing normal movement of the spine and minimizing the potential problem of adjacent segment deterioration. We are now witnessing the development of various treatments to address pain arising from the posterior elements. Just as with the emerging option of nucleus replacement versus total disc replacement, the development of posterior dynamic stabilization devices is taking place, such as the Dynesys System and now a step further to total posterior element replacement. One such device is the Impliant TOPSâ„¢ Total Posterior Arthroplasty System.

Device description The TOPSâ„¢ device is designed to completely replace the posterior elements and is comprised of a titanium construct with an interlocking polycarbonate urethane

(PcU) articulating core (Figs. 25.1, 25.2, 25.3). It is a unitary device that is anchored to the spine with pedicle screws using a familiar surgical technique. Specialized instrumentation has been developed to direct optimal screw placement to properly accept the device. Within the core, there are stops designed to control the degree of motion in the various planes. It allows for dynamic, multiaxial, 3column stabilization after complete neural decompression recreating near-normal spine biomechanics.

Indications The primary indication for total posterior replacement is moderate to severe lumbar spinal stenosis, with or without spondylolisthesis (up to grade 1) and with or without facet P.222 hypertrophy. The TOPSâ„¢ device can be viewed as a treatment option for latestage posterior degeneration that requires a destabilizing decompression.

FIGURES 25.1 (A) The TOPSâ„¢ device and (B) the device attached to pedicle screws.

FIGURE 25.2 The implant allows motion in three planes.

FIGURES 25.3 Schematics of the device implanted into the spine.

Materials and Biomechanical Testing Impliant has performed comprehensive and rigorous preclinical testing on the TOPSâ„¢ device. This includes biomechanical testing to assess the long-term fatigue resistance of the implant. After completing 10 million fatigue cycles in either flexion/extension, lateral bending, or axial rotation, a static load test to assess the implant's strength in unidirectional loading until failure was P.223 performed. In addition, the TOPSâ„¢ device was subjected to a 5-million cycle coupled motion simulator to further test the implant's fatigue resistance as well as calculate wear particulate production. The implant and all of its components passed both the fatigue testing and subsequent static load tests. The amount of wear that was produced was within the established acceptance criteria. The components of the TOPSâ„¢ device [titanium alloy, PcU, and polyetheretherketone (PEEK)] also underwent extensive biocompatibility testing to ensure its safety. This included testing for mutagenicity, chronic toxicity, hemolysis, humoral immunology, pyrogenicity, and carcinogenicity. The materials were found to meet safety standards on all of these parameters. Even with the original pedicle screw and rod constructs of the 1980s, the issue of stresses on the screw-bone interface was a concern. This is particularly relevant considering the required longevity of the implants. With the new generation of devices designed to allow motion, the stresses on the screws is of greater concern. Unlike fusion devices that theoretically have to carry significantly reduced demands as the operated segment becomes rigid from the bone incorporation, the motionsparing implants will be required to carry the same loads for the duration of use. As such, a biomechanical test has been conducted (Source: Professor Tim Wright, Hospital for Special Surgery, New York, NY, Biomechanical Laboratory, April, 2004) to investigate the stresses on the screws used to anchor the TOPSâ„¢ device compared to the Dynesys system. The results of that study found that the load transmission to the pedicle screws is significantly less on the four anchoring screws of the TOPSâ„¢ when compared to the Dynesys implant. Therefore, it is reasonable to expect that the TOPSâ„¢ screw loosening rate will meet if not exceed that established by the Dynesys system over time.

Clinical Experience Clinical data from a pilot study performed outside the United States is available on twenty-four patients (range 50 to 71 years) that have been implanted with the TOPSâ„¢ device to date. The majority of patients were being treated for stenosis and the others had spondylolisthesis as well. In the series, all of the patients were treated at the L4-5 level, and the mean operative time was 2.7 hours with a mean blood loss of less than 200 mL. There were no intra-operative complications or postoperative infections. Patients were discharged, on average, in 2.5 days. The length of follow-up available on the patients was six weeks (n = 19) to twelve months (n = 5). The VAS pain scores improved from 9.1 to 1.4 at twelve months. Oswestry scores improved 39 points over the same timeframe. The operated segment maintained 4 to 7 degrees of motion, with no evidence of screw loosening or pull-out.

Surgical Technique The surgical technique for implantation of the TOPSâ„¢ is similar to the technique used for decompression and placement of standard pedicle screws. The approach to the posterior lumbar spine is the same as used for any commonly performed decompression and fusion surgery. A total laminectomy and facetectomy should be performed at the level to be treated. The pedicle screws are implanted in such a way as to properly accept the TOPSâ„¢ device. The crossbars on the TOPSâ„¢ device are anchored to the polyaxial P.224 screw heads using standard set screws. A standard closure is undertaken following implantation of the device, and routine postoperative care is employed.

Summary The TOPSâ„¢ Total Posterior Arthroplasty System has been found to be safe from a materials standpoint and has biomechanical properties that are favorable with respect to motion, load bearing, and the stress distribution on the anchoring screws. This dynamic implant may help decrease the stresses on adjacent segments to reduce or prevent acceleration of adjacent segment deterioration, as may occur after fusion.

With the increasing array of treatment options for patients with painful posterior spine problems, there will likely be a greater need to have a thorough diagnostic evaluation to more specifically identify the patient's pathology, leading to the optimal matching of the problem to the implant. The preliminary TOPSâ„¢ results are promising, although based on a relatively small number of patients. The results of a large-scale clinical trial, such as the pending investigational device exemption study (IDE), will provide much more information on the clinical results and complications associated with this device. As with any of these newly developing treatment technologies, one must still employ well-defined selection criteria. Over the next several years, the outcomes of these devices will be determined and greater refinement of indications will be delineated.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Stabilization Techniques I > 26 - Mechanical Supplementation by Dynamic Fixation in Degenerative Intervertebral Lumbar Segments: The Wallis System

26 Mechanical Supplementation by Dynamic Fixation in Degenerative Intervertebral Lumbar Segments: The Wallis System J. Sénégas

Background Necessity being the mother of innovation, distal joint repair and replacement began much earlier than analogous work on spinal segments. Indeed, the unique organization of the intervertebral articulations in a kinetic chain provides the capacity to compensate relatively well for the loss of a single mobile segment caused by operative fusion. This explains the continued extensive use of spinal arthrodesis to date. Nonetheless, prompted by progress in the surgical management of distal joint disorders, we began studying and developing nonrigid stabilization of lumbar segments in 1984. After preliminary biomechanical cadaver studies between 1984 and 1986, we opted for a tension-band system with no bony fixation, because of the incompatibility of bony purchase (such as that provided by pedicle screws) with a dynamic stabilization device. The pioneer system that we developed and first implanted in 1986 included a titanium interspinous spacer and a cord of woven polyester. Following an observational study in 1988 (1,2), we carried out a prospective controlled study from 1988 to 1993 (3,4). We permitted only cautious, limited

diffusion of this device while waiting for assessment of long-term results. These studies and subsequent limited diffusion having shown promising results and an absence of serious complications, we then developed a second-generation device called the “Wallis― system, which was fundamentally updated and improved over the first-generation implant. The former, metallic interspinous spacer was replaced by a redesigned spacer made of polyetheretherketone (PEEK), a more resilient material, and the cord was replaced by flat bands of woven polyester.

Basic Concepts Three aspects are fundamental to understanding the Wallis implant and the mechanical normalization it provides: Until the confirmation of biologic techniques, mechanical interventions are our primary means of action against degenerative disc disease. P.226 Acute or progressive disc lesions create instability of the motion segment. This instability is best characterized by a loss of stiffness, which contributes to further deterioration leading to a vicious cycle exacerbated by a concentration of stress on the posterior portion of the disc. As in any mobile, dynamic system submitted to a force, intervertebral segments undergo acceleration inversely proportional to the moment of inertia. The stiffness of the segment dampens this movement. This braking action preserves a margin of security and contributes to protection of the disc and intervertebral ligaments. Stiffness is a mechanical parameter defined in terms of load for a given displacement. It corresponds to the derivative of the load/deformity curve. Ebara et al. (5) and Mimura et al. (6) demonstrated that segmental laxity or loss of stiffness is constant in degenerative disc disease. This is observed throughout the course of the degenerative process. Early on, before loss of disc height, bending studies reveal a wider range of motion corresponding to increased laxity (7). Even in advanced lesions in which intervertebral

mobility is reduced because of disc narrowing, the system still exhibits loss of stiffness. This decrease in rigidity corresponds to an increase in the neutral zone of disc loading over displacement. The stretching of the connective tissues uniting two vertebrae leads to a force resisting the displacement. The dissipation of kinetic energy in the form of heat is mediated by the visco-elastic properties of these connective tissues. This passive damping would, in fact, be quite insufficient to protect the disc if it were not constantly supplemented by the much more effective active damping provided by the reflex contraction of the powerful paravertebral muscles. Although the dynamic equilibrium of the intervertebral articular system is dependent on a combination of muscle activity and tension of the passive elements of union, the active system constantly protects the passive elements, which consequently remain within the limits of their elasticity under healthy physiologic conditions. The mechanically mediated changes we attempt to achieve in degenerative disc disease are influenced by the biologic environment. The disc and intervertebral ligaments can be overloaded and fail when loading is excessive or the active system of damping is deficient. Sustained excessive stresses on the connective tissues of the disc and ligaments prevent normal healing, because the cells can only persist and fulfill their functions under a restricted range of mechanical stresses. Under mechanical conditions outlined previously, the intervertebral disc cells that synthesize the extracellular matrix exhibit normal activity. Lotz and Chin (8) have shown that disc cells function normally only within a precise range of mechanical loading. Too much or too little loading leads to direct cell destruction and programmed cell death (apoptosis). Discs consist almost entirely of connective tissue, with a disappearance of notochord remnants by 20 years of age (9). As in all connective tissues, notably the annulus, cell activity can repair damage if lesions are limited or if the lesional process takes place over time in a manner analogous to stress fractures. In fact, an indisputable healing process can be observed in the intervertebral disc, with a fibroelastic reaction and neovascularization, at least during early degenerative change. However, just as in pseudarthrosis

of long bones and in meniscal lesions, when deleterious conditions persist, the healing process can be overwhelmed. Based on these mechanical and biologic aspects of degenerative disc disease, different working hypotheses were involved in the concept of nonrigid stabilization and development of the Wallis system. One was that, by increasing the stiffness of P.227 the damaged intervertebral segment and by limiting the amplitude of mobility, one provides mechanical normalization, which should slow the progression of degenerative lesions. Moreover, provided that disc height is sufficiently preserved, creation of the proper range of loading stresses on the disc by the interspinous process implant should foster the healing process of the disc tissue. Finally, although many years of follow-up will be necessary for confirmation, it is anticipated that dynamic stabilization will slow the domino effect of accelerated degenerative change in the segments adjacent to the treated level, especially in comparison to treatment by fusion. This brings us to the third aspect fundamental to the Wallis system. One should not propose radical surgical solutions for early degenerative changes. Surgery rarely affords definitive solutions. If the threshold of surgery is low and if a surgical procedure leaves other options open, it is beneficial to adopt a step-by-step strategy to treat low back pain without compromising future solutions. More and more patients are turning to the Internet health sites and may be aware of the advent of biologic methods of treating degenerative discs with the patients' own stem cells or fibroblasts (10). How many spinal surgeons would compromise their own access to such future techniques by accepting an arthrodesis, or even a disc prosthesis, as long as other viable solutions exist? This is no far distant perspective. Stem cell injection is already being used for tendon and ligament lesions (11). Conservative treatment, dynamic stabilization, disc prosthesis, and fusion are all good solutions depending on the stage of degenerative changes. The Wallis implant is designed for patients who have exhausted the possibilities of conservative treatment but for whom the prosthesis or fusion would be

an overly radical solution. The Wallis is completely and easily reversible, leaving all other options open. In reference to the theme of the present congress, one might add that many, if not most, failures in spinal surgery are related to a failure of the indication.

Materials and Methods The implant has been developed with the idea of creating a tension-binding system, including an interspinous spacer made of PEEK and bands of woven polyester. This obviates the need for a permanent fixation in the vertebral bone, avoiding the risk of loosening. We believe that it is not possible to stabilize all joint elements of the intervertebral segment with a simple system. In designing the present implant (Fig. 26.1), we focused on damping flexion by the bands and extension by an interspinous spacer, which absorbs posterior shocks. The titanium interspinous spacer of the first-generation implant has been replaced by one made of PEEK in the Wallis system. This spacer is 30 times less rigid than the titanium model. Minns and Walsh (12) have shown elsewhere that an interspinous spacer displaces mechanical stresses dorsally and reduces the load on the disc and facet joints. This load sharing reached 50% for spacers 12 mm in thickness. Wallis implants are currently available in a range from 8 to 16 mm in thickness for patients of different sizes. The patient should be in a position of normal lumbar lordosis when the implant procedure is performed to avoid focal kyphosis of the treated segment. The two woven polyester bands of the implant are wrapped around the spinous processes and fixed under tension to the spacer. This is facilitated by the design of the implant and dedicated instrumentation. P.228

FIGURE 26.1 The nonrigid fixation “Wallis― implant.

The Wallis procedure calls for removal of the interspinous process ligament of the segment involved. Small apertures next to the spinous process are made in both adjacent interspinous ligaments to permit passage of the bands and slight trimming of the bone around the spacer may be helpful in some cases for a better, deeper fit. Indeed, it is recommended to place the spacer snugly against the laminae to act as an interposterior arch spacer rather than simply an interspinous spacer. In summary, the spinal segment is left structurally and functionally intact.

Results First-Generation Nonrigid Stabilization As stated earlier, the results of the first-generation implant developed in 1986 were promising. An observational study was conducted in 1988 followed by a prospective controlled study from 1988 to 1993. The clinical trial results of the first-generation implant provided evidence that the interspinous system of nonrigid stabilization is efficacious against low back pain due to degenerative instability while remaining technically straightforward and free of serious complications. The first-generation devices achieved significant resolution of residual low back pain (3,4).

Wallis System

An in vitro study was commissioned in March 2002 in an independent biomechanics laboratory. They used L4-5 cadaver segments that were first intact, then subjected to partial discectomy. A Wallis implant was subsequently placed in each injured segment to test the extent of mechanical normalization. Finally, the segments were retested after removal of the implant. Under these four conditions, the L4-5 specimens were submitted to flexion-extension torques. These studies demonstrated that the implant limits the range of motion (ROM) by 35% and increases the stiffness by 150% and stability of the segment (reduces neutral zone and translation). Furthermore, the Wallis device was shown to relieve the disc by supporting part of the load on the segment. In this fashion, stresses in P.229 the disc were considerably reduced. After removal of the mechanical normalization system, the segment returned to the initial conditions induced by the disc damage. An intact finite element model applied to these lumbar segments found that the implant led to reduced load on discs, especially the posterior aspect of the disc. The Wallis system mediated a sharing of disc loads by the neural arch. The implant did not alter the mechanical behavior of the adjacent segment. In other words, stresses in the adjacent L3-4 disc remained unchanged by placement of the Wallis implant in the injured L4-5 segment. A single-arm prospective multicentric international study was begun in 2002. Two hundred sixty-two patients were recruited into the study. Preliminary results on more than 150 patients confirm the clinical efficacy of this treatment on low back pain and nerve root symptoms, especially in degenerative disc disease with low back pain and voluminous herniated disc. The learning curve is short and the complication rate is negligible. A prospective observational study of the second-generation, Wallis implant is being conducted in Argentina, France, South Africa, Switzerland, the United Kingdom, and Venezuela. At this writing 220 patients (37% female, 63% male; age range, 18 to 82 years; average age, 44 years) were enrolled. Thirty-six percent of the patients were operated for degenerative disc disease without disc herniation, 30% for voluminous disc herniation, 18% for canal stenosis, and 16% for recurrent disc herniation. Implant placement required an average of 19 minutes and the average time for the

entire surgical procedure was 79 minutes, with an average blood loss of 190 mL. The 12-mm Wallis implant was the most frequently used (48%) followed by the 10mm Wallis implant (38%). Ninety-two percent of patients were operated at L4-5. Six of the 220 patients (2.72%) had postoperative complications. There were three deep infections resulting in removal of the device. One patient had the implant removed by another surgeon 10 months after the intervention for psychological reasons. In two patients, the initial Wallis implant was replaced by another one, in one case after recurrence of disc herniation and in the other after the implant migrated posteriorly. In all six cases, the revision procedure was straightforward with no complications. At this writing preliminary, 12-month results have been obtained for 52 of the patients in the multicenter study. Preoperative evaluation of the functional and pain status of the patients was performed using the Japanese Orthopedic Association assessment of lumbar pain management (JOA score) (13); a visual analogue scale (VAS) for lumbar pain; and two quality-of-life questionnaires, the first version of the medical outcomes score short form 36 (SF-36) (14) and the Oswestry low back pain disability questionnaire (15). Preoperatively, 65% of the patients had VAS pain scores between 7 and 10, whereas 90% had VAS scores between 0 and 30 1-year postoperatively. Sensory symptoms were present preoperatively in 75% of the patients and in only 10% 1 year later. Motor deficits were observed preoperatively in 61.5% of the patients and in less than 4% after 1 year. The clinical results (Odom's criterion) at 1-year follow-up were judged by the treating surgeon to be excellent or good in 89.6% of the patients, satisfactory in 6.25%, and poor in 4.15%. At present, the Wallis system is recommended for lumbar disc disease in the following indications: Discectomy for massive herniated disc leading to substantial loss of disc material. A second discectomy for recurrence of herniated disc.

P.230 Discectomy for herniation of a transitional disc with sacralization of L5. Degenerative disc disease at a level adjacent to a fusion or prosthesis. Isolated disc resorption, notably with concomitant type 1 Modic changes, associated with low back pain. Symptomatic narrow canal treated using partial laminectomy consisting in resection of the superior aspect of the laminae (a technique that we refer to as the “recalibration― procedure). Furthermore, many surgeons have begun using the implant for patients with facet joint syndrome. The Wallis system should only be used in patients who do not have substantial loss of disc height, that is, only for discs corresponding to stages 2, 3, and 4 of the magnetic resonance imaging (MRI) disc classification proposed by Pfirrmann et al. (16) in which stage 1 is a healthy aspect and stage 5 corresponds to a black disc with severe loss of disc height. One should also note that the implant is not intended for the L5-S1 segment, because the spinous process of S1 is inadequate for this purpose.

Discussion It was evident from the outset that this new system of dynamic stabilization did not have the inherent drawbacks of fusion or disc replacement: With Wallis, there is less intraoperative bleeding because it is less invasive, operative duration is shorter because the system is simpler, and the procedure is completely reversible. To this should be added the anticipated difference regarding adjacent levels compared to fusion but theoretically not compared to disc replacement. This follow-up evidence has convinced us that, to date, the efficacy of Wallis is at least as good as that of fusion. We now have a validated operative alternative for many young patients with degenerative disc disease who suffer, but for whom fusion, or even disc prosthesis, might seem too radical. In view of the good long-term results of the first-generation device, there is no reason to believe that the good intermediate-term results of the Wallis will not persist. For patients and surgeons, however, it is a fail-safe solution, because even

if relief fails to persist, the procedure is completely reversible. The patient would be able to start over again with all the original options. Consequently, this method should rapidly assume a specific role along with total disc prostheses in the new step-wise surgical strategy for initial forms of degenerative intervertebral lumbar disc disease. Regarding the three previously mentioned working hypotheses behind the development of Wallis, the clinical evidence is in favor of the first two. Stabilizing the degenerative segments and limiting amplitudes of mobility with Wallis is associated with clinical findings consistent with a halt in the degenerative process. Levels of pain and functionality have significantly improved over preoperative values. Furthermore, many patients with Modic 1 changes exhibit either normal bone or Modic 2 changes on follow-up MRIs. It is still too early to determine whether the anticipated healing of this connective tissue is actually occurring. There is MRI evidence of disc rehydration at follow-up. Many initially black discs are coming back with normal, white signal. An example is shown in Fig. 26.2. P.231 As indicated previously, it will take years to ascertain whether Wallis has a protective effect on the adjacent discs (third working hypothesis). A fourth, accessory working hypothesis concerned the decision to use a tensionbinding system rather than screw fixation, to permit this dynamic stabilization to last by avoiding screw toggle and to make it less invasive, more reversible. The two types warrant a comparative study, but for ethical reasons, this would seem likely only in centers in which surgeons expect equivalent advantages and drawbacks from both.

FIGURE 26.2 Evidence of rehydration in a patient shown preoperatively and 6 months after placement of Wallis.

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Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Stabilization Techniques I > 27 - Posterior Nonfusion Stabilization of the Degenerated Lumbar Spine with Cosmic

27 Posterior Nonfusion Stabilization of the Degenerated Lumbar Spine with Cosmic Archibald von Strempel Dieter Moosmann Christoph Stoos Arno Martin

Introduction The degeneration of the lumbar motion segment starts with a height loss of the disc caused by a water loss of the nucleus pulposus. The facet joints lose their congruence, which may cause a consecutive spondylarthritis (1 ). The fibers of the annulus fibrosus and the vertebral column ligaments lose tension so that a structural loosening occurs, complete with increased rotation instability (2 ,3 ,4 ). To compensate for the instability, a hypertrophy of the yellow ligament as well as the facet joints occurs very frequently, which may lead to a reduction of the surface of the cross-section of the central as well as lateral spinal canal. At the same time the motion segment may lose its original position, and scolioses, flat backs, rotations, and rotation slidings may develop. During the further course of the degeneration, lateral and front spondylophytes up to and including syndesmophytes may form, which in turn may lead to a spontaneous stiffening of the segment. The complaints depend on the respective stage of the vertebral column degeneration.

In the first phase with a reduction of the height of the vertebral disc and loss of the congruence of the facet joints, chronically recurrent lumbalgies may occur that increase under load stress. When the stenosis of the spinal channel increases, additional symptoms may occur in one or both legs with the indications of a claudicatio spinalis. If a spontaneous ankylosis of the segment occurs before a symptomatic spinal channel stenosis occurs, the frequency and intensity of lumbalgies decrease.

Why Are Spondylodeses Carried Out in the Treatment of Degenerative Lumbar Vertebral Column Diseases? Until recently, there were few alternatives to a standard spondylodesis. One important reason is that the surgery of the degenerative lumbar vertebral column is a relatively young chapter in spine surgery. The techniques of correction and fusion, so successful in scoliosis surgery, were transferred to this new area of spine surgery, ever increasing since the early 1980s. An essential task of the spondylodesis consists of protecting the implants used against failure (dislocation, breakage). P.234

When Is a Correction Necessary? In contrast to the treatment of an adolescent scoliosis, in which the correction of the deformity is also the objective of the treatment, there are not very many indications for the correction of the degenerative lumbar vertebral column that actually serve the direct objective of the operation with pain release and restoration of neurologic functions. Positional deformities in the sagittal and frontal planes that in total do not lead to a loss of the body vertical plump line need not be corrected. This concerns most lateral deviations. Therefore, the correction of a degenerative lumbar scoliosis is only necessary in exceptional cases. The reduction of the vertebral disc always leads also to a flattening of the lumbar vertebral column, which also does not need to be corrected as long as the patient assumes an upright well-balanced posture. True and degenerative olistheses at an adult age are mostly not progressive. Stabilization and decompression without correction lead to the objective of the treatment. Therefore, it is not meaningful to transfer the principles of scoliosis surgery noncritically to the surgery of the degenerative lumbar

vertebral column.

When Is a Fusion Necessary? Fusion is necessary when corrections (mostly in the sagittal plane) are necessary to treat pain.

When Will It Be Possible to Do Without a Fusion? The precondition is a dynamic implant, which does not require the protection of a spondylodesis. It must be possible to achieve the treatment objective (pain release, restoration of the neurologic function) without correction. The stabilization does not need to include more than three segments.

The Cosmic Implant System A posterior nonfusion implant system, which can do without protection by a spondylodesis, should not have any rigid characteristics. However, to be able to control instabilities effectively, the system must also feature stable characteristics. The cosmic system is a stable nonrigid implant. Stability is assured by the 6.25-mm rod, and nonrigidity is ensured by the hinged screw head. The screw features a hinged joint between head and threaded part, which causes the load to be shared between the implant system and the anterior vertebral column (Fig. 27.1 ). It was possible to show by means of laboratory tests that cosmic allows the same rotation stability as a healthy motion segment (5 ). In a cyclic loading test with 0.3 to 3.0 KN/1 Hz, we did not find an implant breakage or any debris after 10 million cycles (6 ). Because cosmic is used like a stability endoprosthesis, the bone healing of the pedicle screws is of major importance here. For this reason, the threaded part of the screw is coated with bonit. Bonit is the second generation of P.235 bioactive calcium phosphate coatings on implants. In 1995, it was originally used for the first time in oral surgery for dental implants (7 ). In the area of vertebral column surgery, there exists a study on the use of a first-generation of bioactive calcium phosphate coating on Schanz screws. It was found that there was a significantly improved fixation of the coated screws in comparison to the uncoated screws (8 ). Thus, the screw is introduced transpedicularly into the vertebral body, similar to an orthopædic endoprosthesis. To achieve a sufficient press-fit behavior, the pedicle is widened by

drilling to 3.2 mm maximum but only along approximately 50% of the screw. The screw has a self-tapping thread so that the tapping instrument only needs to be used in cases of extremely hard spongiosa. To prevent any early loosening of the screw, the screw must not be manipulated in any major way. Before the rods are implanted, these must be prebent such that they can be connected without any problems to the screw heads.

FIGURE 27.1 Cosmic screws and rod.

After the screw heads have been connected to the longitudinal rods, there remains only a micromobility in the hinges, which are placed close to the facet joints (Fig. 27.2 ). This micromotion and the shock absorber function of the preserved disc protect the adjacent levels. Due to the good rotation stability, cosmic is not only used for purely discogenic pain conditions but also used together with a conventional laminectomy or even a facetectomy. A transverse stabilizer is only used for a monosegmental application in combination with a laminectomy. For two- or three-segmental applications, no transverse stabilizer is used.

FIGURE 27.2 Flexion-extension view after 1 year.

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FIGURE 27.3 Angle of screw direction in the horizontal plane 15 to 25 degrees.

The implantation of the screws is affected either by means of a conventional midline

approach with a point of entry lateral to the facet joint and an angle of approximately 15 degrees horizontal to the sagittal plane or by means of the more laterally situated Wiltse access with a somewhat ventrally located point of entry close to the base of the transverse continuations and an angle of 20 to 25 degrees horizontal to the sagittal plane (Fig. 27.3 ). A purely sagittal implantation direction is not recommended, as this will lead to a parallel positioning of the hinges and thus to an increased mobility in the sagittal plane. Before the rod is implanted, the correct positioning of the patient will be checked again by means of lordosis that is as physiologic as possible. To avoid any early loosening, correction forces must not be applied to the screw.

Indications for Dynamic Stabilization with Cosmic Symptomatic lumbar stenosis (claudicatio spinalis). A stand-alone decompression of the spinal channel carries the risk of a reoccurrence of spinal narrowness, as the instability that led to the hypertrophy of the yellow ligament and the facet joints is not taken into consideration. In addition, lumbalgies and deformities may increase as an expression of the increased clinical instability. For this reason, we always carry out an additional stabilization with cosmic (Fig. 27.4A–C ). Chronically recurring lumbalgy in the case of discogenic pain and facet syndrome. A degenerated disc disease is present if, in the magnetic resonance tomography (MRT), a vertebral disc dehydration with height loss and positive Modic signs is detected. If there are further changed vertebral discs (black disc), we carry out an additional discography. A positive memory pain confirms the suspicion of a symptomatic vertebral disc degeneration (9 ). In the case of a facet syndrome, we carry out a diagnostic local anesthesia under x-ray control, using 2-mL local anesthetic, respectively. If the pain subsides for some hours, the suspected diagnosis is confirmed. In such cases we carry out the cosmic stabilization using a paraspinous transmuscular approach according to Wiltse et al (10 ). (Figs. 27.5A–C and 27.6A–C ). Recurrent disc herniation.

In the case of a second recurrence of a disc herniation we carry out a stabilization with cosmic in addition to the nerve root decompression. In combination with a spondylodesis. Cosmic can also be used if, in addition to the nonfusion stabilization, there is an indication of a spondylodesis in one or two segments. For example, if there is a spondylolisthesis with a clear shift in the function x-rays and, in addition, in a further segment a symptomatic vertebral disc degeneration. In addition to the cosmic stabilization in situ, a posterolateral fusion is set up within the area of the spondylolisthesis. A laminectomy or facetectomy is carried out if there is an indication for this purpose. Extension of an existing spondylodesis in the case of a painful adjacent level degeneration. P.237

FIGURE 27.4 A–C: Spinal stenosis, pseudospondylolisthesis, decompression, and stabilization with cosmic.

FIGURE 27.5 A–C: Degenerated disc disease, positive Modic sign, contrast CT.

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FIGURE 27.6 A–C: Paraspinal approach L5-S1, single-level stabilization anteroposterior and lateral view 2-years follow-up.

Typically, in the case of a rigid 360-degree spondylodesis with cage and pedicle screw rod or pedicle screw plate fixation, there is the risk of developing a painful connection instability. In these cases, we remove the pedicle screw rod or plate system and stabilize the adjacent segment with cosmic together with a decompression, if indicated. We fill up the existing pedicle drilling holes with bone chips and use 7-mm revision screw for this purpose.

Contraindications

Cosmic should only be used for a maximum of three segments. If corrections are necessary, to influence the complaints of the patient (as stated previously, in almost all cases of a degenerative deformity this is not indicated), a spondylodesis must be provided in addition to the cosmic instrumentation. Such a case exists, for example, for a postfusion kyphosis in which a correction, for example, via a closing wedge, osteotomy is necessary to treat the pain. In adulthood, in the case of a spondylolisthesis vera, there is as a rule of no significant shift in the lateral function x-rays. If this should be the case, cosmic is used in combination with a posterolateral fusion in situ. In cases of greater instability, as typically found in younger adults or youths, we carry out a posterior partial repositioning with cosmic in combination with a posterolateral and interbody spondylodesis.

Stabilizations Extending Beyond Three Segments In the case of the degenerative lumbar vertebral column, it should in principle be avoided to carry out extended instrumentations. If this is unavoidable, cosmic may only be used beyond three segments in combination with a posterolateral spondylodesis. If, for example, there is a degenerative kyphoscoliosis with a loss of balance in the sagittal plane, where there is a necessity to correct the kyphotic part, longer extended instrumentations are required as a rule. Here, in the correction area, cosmic can be used with a posterolateral spondylodesis and in the further cranial segments in the nonfusion technology. P.239

Results From January 2002 to June 2005, 203 patients were operated on in Feldkirch (Austria). For 96 patients there is 12-month follow-up available, and for 38 patients out of these 96 there is 24-month follow-up available. Preoperatively, there was a conventional x-ray image for all patients anteroposteriorly (AP) and laterally, in a standing position, and additionally a MRT, and where this was not possible (agoraphobia) a CT. The complaints are documented by a 10-part analogue pain scale from 0 to 10 (0 = no pain, 10 = an unbearable pain) and by the Oswestry score. Three months, 12 months, and 24 months postoperatively conventional x-rays will be carried out again AP and laterally, in a standing position, and the clinical results

documented by the pain scale and the Oswestry score. The x-ray images are studied for implant fractures, screw loosening, or screw dislocations. A screw loosening is defined as a loosening seam around the screw without any dislocation having occurred. Of these 96 patients, 51 were female (53%) and 45 were male (47%). The age distribution was as follows: 30–40 years 3 patients 41–50 years 8 patients 51–60 years 30 patients 61–70 years 19 patients 71–80 years 31 patients 81–90 years 5 patients Four additional patients could not be examined for their 2-year check-up as they had died (3 patients without any connection to the operation) or, in one case, they had moved. Fifty-one patients were stabilized in one segment, 35 patients in two segments, and 10 patients in three segments. In total, 494 screws, 192 longitudinal rods, and 23 transverse stabilizers were implanted. We found a total of 2 broken screws in the case of 2 patients, and in the case of 5 patients a total of 10 screws with loosening edges (2.4 % out of 494 implanted screws). In total, 7 patients were affected; from these, 3 patients developed symptoms causing a revision to be carried out. All implant failures observed so far occurred within the first year. The clinical results were compared with those from 75 patients with a follow-up of at least 24 months that, for the same indications, had been treated with the Segmental Spinal Correction System (SSCS), which also contains a jointed head pedicle screw but without a coating and with a conventional posterolateral fusion. The SSCS has been used

since 1989. In both groups, the indications were comparable: symptomatic lumbar stenosis, painful olistheses, painful osteochondroses, painful spondylarthroses, recurring vertebral disc prolapses, and discogenic pains. The average age in the nonfusion group was 67.2 years, and in the fusion group was 55.9 years. The reason for the increased age of the group without fusion is that, during the first year, we predominantly used the nonfusion technique for the treat-ment of older patients to keep the surgery trauma as low as possible. With increasing experience we then used the nonfusion technique also in patients in the mid-range age of adult life. P.240 In the nonfusion group, the pain on the visual analogue scale (VAS) was 5.7 preoperatively, and 2.9 postoperatively, and in the fusion group the pain was 5.8 preoperatively and 3.4 postoperatively. The Oswestry activity score in the nonfusion group was 25.4 points or 50.8% preoperatively and 17.0 points or 34% postoperatively. In the fusion group, the Oswestry activity score was 23.7 points or 47.4% preoperatively and 14.7 points or 29.4% postoperatively. The hospital stay in the nonfusion group was 7.4 days (6–18 days), and in the fusion group 16.9 days (9–36 days). The surgery time (skin to skin) in the nonfusion group was 118.8 minutes (62–200 minutes), and in the fusion group 172.4 minutes (120–215 minutes). Perioperatively, a total of 0.60 units of eryconcentrate were transfused (0–4 units), and, in the fusion group, 2.96 units of eryconcentrate (0–6 eryconcentrates) were transfused on average. In the nonfusion group, revisions were carried out in 4 patients (4.2% out of 96 patients) and, in the fusion group, revisions were carried out in 6 patients (8.0% out of 75 patients). The revisions were caused by wound infections (once in the case of the nonfusion group as well as three times in the case of the fusion group), twice by symptomatic loosening of a screw in the nonfusion group, once by a screw breakoff in the nonfusion group, and a total of three times due to a pseudoarthrosis in connection with an implant fracture or implant loosening in the fusion group. In June 2005 a multicenter study was started in cooperation with six international spine

centers. So far, 215 patients have been documented; and for 100 out of these 215 there is a 3-month follow-up available, and for 58 there is a 12-month follow-up. After 3 months no implant failures were found by this study, and after 12 months a screw fracture was found that led to a revision, as well as six loosening seams around the screws that, however, remained without symptoms and so far did not cause any revision. A screw dislocation was not observed.

Discussion Degenerative diseases of the lumbar vertebral column represent their own nosologic entity. So far they have been treated primarily in accordance with the principles of deformities surgery and traumatology. It was endeavored to achieve a correction of existing deformities that was as complete as possible, and to ensure the result, rigid implants were used that were able to provide for three-dimensional correction if at all possible. The experience that the fusion of individual segments of the degenerative lumbar vertebral column may cause painful connection instabilities—and this applies obviously in particular to the rigid 360-degree fusions—increasingly puts a question mark over the use of such techniques for the treatment of degenerative diseases (11 ,12 ,13 ,14 ,15 ,16 ,17 ,18 ,19 ,20 ,21 ,22 ,23 ). The postoperative sagittal profile of the lumbar spine did not have any influence on the development of adjacent instabilities (24 ). In addition, there is the problem in the case of older patients that the quality of the bone frequently does not allow for any secure fixing of rigid implants or for any corrections. Some of the patients at an advanced age also show additional secondary diseases that cause the perioperative complication rate, in the case of more invasive operations on the vertebral column, to increase. Fusion as the gold standard for the treatment of chronic pain within the area of the degenerative lumbar vertebral column must also be questioned, as a 100% spondylodesis is not the equivalent of a 100% clinical success rate (25 ,26 ). P.241 The significance of patient selection is justifiably regarded as a decisive criterion for achieving a good clinical result (27 ). For this reason it is not astonishing that there is a search for different alternative operative techniques that prevent any fusion (28 ).

However, what may possibly be astonishing is that it took so long to place a question mark over fusion as the gold standard. However, for some time already, there have been individual efforts to develop alternative solutions in relation to the fusion concept. The Graf band is possibly the first pedicle screw supported nonfusion system for the treatment of painful degenerative instabilities of the lumbar vertebral column. Biomechanically, it is to increase the use of dorsal tension cords and to reduce painful movements in the facet joints and also in the disc. There are some reports about excellent clinical success (29 ,30 ,31 ,32 ,33 ). What remains disadvantageous is surely the missing rotational stability and the risk of an early failure of the cable. The DYNESYS system represents a further development of the Graf system. The band is provided with a plastic sleeve, and the band is tensioned against this sleeve. This causes the stability to be increased but also an increase in the load on the interface between vertebral bone and screw, which may cause a loosening to occur (34 ). In relation to the rotational forces, the DYNESYS system does not show any stability comparable to that of an intact vertebral column (35 ). The clinical reports that have so far been published on the DYNESYS system are mostly positive (36 ,37 ). In combination with decompressions, these two systems are used somewhat more rarely as even partial removal of the facet increase the rotational instability (38 ). Other nonfusion techniques, not based on pedicle screws, stabilize the motion segment by spreading the processus spinalis vertebraes and thereby also expanding the spinal channel. The indications are limited to light spinal narrowness and facet syndrome. Interspinous spreaders can be implanted minimally invasively. At this time, major clinical studies are not yet available. In contrast to the previously mentioned posterior nonfusion systems, cosmic is used for symptomatic spinal stenosis, in combination with decompressions, as well as in the case of purely discogenic or facet joint related pain. The hinged screw provides for a sufficient degree of dynamization and load sharing between the implant and the vertebral column and prevents at the same time any rotation and translatation instability. The rotation stability corresponds to that shown by an intact lumbar vertebral column (5 ).

As nonfusion implants act like stability prostheses and must last permanently without the protection of a fusion, the cosmic screw was additionally coated with Bonit to ensure a better anchoring in the vertebral bone (8 ). The clinical results found so far, when compared with conventional fusions, are equally good. The perioperative trauma was much lower. The careful transmuscular (between musculus multifidus and musculus longissimus) access to the pedicles may further decrease the operation trauma. Even when using cosmic, a careful selection of patients is the precondition for clinical success. The radiologic complex implant-related complications are in the lower range of those specified in the literature with regard to rigid implants in combination with a fusion. Here, between 2.5% and 15% screw fractures are specified (39 ,40 ). Radiologic loosening seams, as documented in the present study, are not really taken very much into account in the literature, unless they have noted screw dislocations. In fusion surgery as well as in nonfusion surgery, the meaning of implant-related complications cannot always be equated with a clinical failure. In those cases in which a patient P.242 again develops pain after experiencing a temporary relief from complaints and in which an implant-related complication can be radiologically detected, revision is recommended in all cases. In principle, when using a nonfusion implant system, there is the option to carry out a conventional fusion in addition to the replacement of implants. The three patients revised in the present study due to symptomatic implant problems again received cosmic revision screws without fusion. The results found so far with the cosmic system are very encouraging. However, additional long-term observations are necessary. For this reason we have started an international multicenter study in June 2004, which is on an Internet base.

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segment. Mobility measured before and after posterolateral fusion. Spine 1997; 22: 414–417. 20. Sudo H, Oda I, Abumi K et al. In vitro biomechanical effects of reconstruction on adjacent motion segment: comparison of aligned/kyphotic posterolateral fusion with aligned posterior lumbar interbody fusion/posterolateral fusion. J Neurosurg 2003; 99: 221–228. 21. Okuda S, Iwasaki M, Miyauchi A, Aono H, Morita M, Yamamoto T. Risk factors for adjacent segment degeneration after PLIF. Spine 2004; 29: 1535–1540. 22. Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J 2004; 4: 190S–194S. 23. Wenger M, Sapio N, Markwalder TM. Long-term outcome in 132 consecutive patients after posterior internal fixation and fusion for Grade I and II isthmic spondylolisthesis. J Neurosurg Spine 2005; 2: 289–297. 24. Lai PL, Chen LH, Niu CC, Chen WJ. Effect of postoperative lumbar sagittal alignment on the development of adjacent instability. J Spinal Disord Tech 2004; 17: 353–357. 25. Bohnen IM, Schaafsma J, Tonino AJ. Results and complications after posterior lumbar spondylodesis with the “Variable Screw Placement Spinal Fixation System―. Acta Orthop Belg 1997; 63: 67–73. 26. Tunturi T, Kataja M, Keski-Nisula L et al. Posterior fusion of the lumbosacral spine. Evaluation of the operative results and the factors influencing them. Acta Orthop Scand 1979; 50: 415–425. 27. Fritzell P. Fusion as treatment for chronic low back pain—existing evidence, the scientific frontier and research strategies. Eur Spine J 2005; 14: 519–520.

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Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Cervical DISC > 28 - ProdiscC™ Cervical Disc Prosthesisin the First 68 Patients: One-Year Evaluation of Results

28 ProdiscC™ Cervical Disc Prosthesisin the First 68 Patients: One-Year Evaluation of Results Petr Suchomel Pavel Barsa P. Sourkova P. Buchvald R. Fröehlich J. Hradil A promising experience with lumbar disc functional replacement led investigators to the development of mobile disc prostheses for the cervical spine. The search for dynamic devices was initiated following reports by Hilibrand and Carlson (8) and Goffin and van Loon (5), describing adjacent segment overload in the long term after cervical fusion procedures. Overall results of anterior cervical discectomy and fusion (ACDF) are very good (3,11,16,19); however, nowadays there is also a desire to preserve at least a part of a spine segment motion, simply to adapt our surgical efforts to the natural spine behavior. Initial clinical success of the first-generation (6,18), simplified introduction technique and advanced design of the second generation of cervical prostheses has changed the

indication philosophy in the treatment of cervical degenerative disc disease (cDDD), resulting in increased frequency of implantations (2,4,9,14). We present our experience with the first 68 patients treated with ProdiscCâ„¢ prosthesis and include a detailed analysis of 1-year follow-up data in 30 of them.

Material and Methods Between February 2004 and August 2005, we performed anterior cervical discectomy in 170 patients with cDDD. Seventy-nine ProdiscCâ„¢ mobile disc prostheses were used in 68 patients; single level in 58 patients, two levels in 9 patients, and three levels in 1 patient. Indication for surgery was based on harmony of clinical and radiologic findings. Most of our patients suffered from radiculopathy and/or myelopathy. Purely axial pain was an indication only in three cases. Soft disc herniation with or without spondylosis were the main reasons for total disc replacement in our series. Well-preserved motion in the target segment on dynamic radiographs and disc height greater than 3 mm preoperatively were the main indication criteria in the decision-making process. Conversely, mechanical segmental instability as well as patient's age younger than 20 years or older than 65 years were the contraindications to the procedure. Other contraindications were similar to those for cage implants (osteoporosis, allergy, etc.). At the time of this publication, 30 patients (39 implants) were available for 1-year follow-up. This group is further analyzed in detail. P.246

FIGURE 28.1 Operated segments—30 patients (39 implants).

Average age of these patients was 45 years (range 21–60 years). Male gender was slightly more prevalent—57%. Most of our patients (60%) were overweight or obese according to body mass index measurements. Preoperatively 60% of them were fully employed, 7% in part-time employment, and 33% out of work due to their cervical disc disease. All, except those with rapid progression of neurologic deficit, were treated conservatively for at least 8 weeks preoperatively. The most frequently involved segments were the C5-6 and C6-7 levels (Fig. 28.1). The majority of patients (22 patients) required only a single-level operation. A two-level procedure was performed in 7 and three-level in 1 patient in this group.

Surgery A standard, right-sided anterolateral approach was performed in all cases. After a total anterior discectomy, posterior osteophytes were removed when necessary. The posterior longitudinal ligament was resected in the majority of cases. Trial implant was used to determine the proper height and size of implant. Primary stability of ProdiscCâ„¢ implant is achieved by anchoring of central keels in bone of the endplates (Fig. 28.2). The keel grooves were cut with specialized chisel guided by the trial

implant. Finally, the implant was simply introduced attached to the implant holder similarly to cage application. All steps of the disc implantation were monitored with the aid of lateral fluoroscopy. External semirigid collar was used only for the duration of the recovery from general anesthesia. All patients were mobilized immediately thereafter.

FIGURE 28.2 Design of ProdiscCâ„¢ implant and radiograph of position in C5-6 space.

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Outcome Measures Clinical, Neck Disability Index (NDI), visual analogue scale (VAS), and radiologic followup data were collected immediately after surgery, at discharge, 6 weeks, 6 months, and 1 year after the operation. Neurologic status and VAS scoring was evaluated by an independent neurologist, and radiologic results were reviewed by two involved surgeons (S.P. and B.P.). NDI data were collected by an independent party over the phone. All patients included in this prospective long-term study signed an informed consent.

Results ProdiscC™ implants are available in three different heights (5–7 mm). However,

only 5- or 6-mm disc prostheses were used in our series. The mean operative time was 72 minutes (range 40–200 minutes) and the mean blood loss 74 mL (5–300 mL). Inadvertent sagittal split of the vertebral body occurred in 2 cases (out of 10 patients treated in more than one level). This complication was related to chiseling of grooves for central keels of the implant. Both patients were female with small vertebral bodies and were undergoing a two-level disc replacement. Other procedures were uneventful. Patients were discharged from hospital on postoperative day 4 on average (range P.248 1–7 days) and collars were not used. Neither infectious complications nor recurrent laryngeal nerve palsies occurred in the series.

When comparing motor and sensory functions preoperatively and at 1-year follow-up, there was an improvement from initial 63% to 83% and from 70% to 93%, respectively.

FIGURE 28.3 Evaluation of visual analogue scale (VAS) for neck and arm pain in 12-month follow-up.

When comparing motor and sensory functions preoperatively and at 1-year follow-up, there was an improvement from initial 63% to 83% and from 70% to 93%, respectively. The mean VAS value for neck pain intensity improved from 4.5 to 2.8 and the VAS for neck pain frequency from 6.1 to 3.2 on a scale of 10. VAS for arm pain intensity improved from 5.6 to 2.5 and VAS for arm pain frequency from 7.0 to 2.7 (Fig. 28.3). Mean preoperative value of NDI was 33 and improved to 22 at 3-months' follow-up. However, it was found to be 32 at 1 year (Fig. 28.4). The patient satisfaction VAS at 12 months was 8.1 and 83% of patients stated that, retrospectively, they would undergo the surgery again (Fig. 28.4). Heterotopic ossifications (HO) were evaluated on plain cervical lateral radiographs (Fig. 28.5). Modified McAffee (12) grading scale was implemented (Table 28.1). There was no evidence of HO in 12 of 39 operated disc spaces (31%). In two discs (5%), ossification was visible but did not reach the interspace (Grade I). Marked HO reaching the intervertebral space but not bridging (Grade II) was detected in 15 cases (38%). Bridging HO with limited motion (Grade III) was present in 5 levels (13%). Definite segmental ankylosis/fusion (Grade IV) was noted in 5 of 39 operated levels (13%). These findings had no clinical consequences. There were no cases of implant migration or subsidence.

FIGURE 28.4 Twelve-month trend evaluation of Neck Disability Index (NDI), visual analogue scale (VAS) for patient satisfaction, and answer to offer to be operated again.

P.249

FIGURE 28.5 Lateral radiographs showing Grades I–IV of heterotopic ossification (HO).

TABLE 28.1 Characterization of Different Grades of Heterotopic Ossification (HO) in Total Cervical Disc Replacement

Grade 0

HO is not present

Grade I

HO is detectable in front of the body but not in the anatomic interspace

Grade II

HO reaching interspace but not bridging

Grade

Bridging HO but still allowing movement (with restriction)

III

Grade IV

Completed fusion, no movement

Discussion Our clinical results are similar to those of ACDF series (16) and comparable with other published studies using cervical disc replacement devices. Using Odom criteria at 1year follow-up, Goffin et al. (7) reported good clinical results using Bryan cervical disc prosthesis in 86% of patients with single-level disease (89 patients) and 96% in twolevel procedures (25 patients). Pimenta et al. (14) used PCM prosthesis in 53 patients (81 disc spaces) and described 97% excellent or good clinical results at 1 year. Bertagnoli et al. (2) used ProdiscCâ„¢ in 27 patients and described similar clinical results to our series. Contrary to previously mentioned series, we did not find the same results with respect to the NDI. We observed an improvement in this parameter after 3 months, but the value was similar to the preoperative assessment at 1-year follow-up. This result needs P.250 to be further analyzed but may possibly be explained by the degree of pre-existing cervical comorbidity. This finding is in contrast to the patient satisfaction rate (VAS 8.1) and a positive answer with regards to repeating the surgery (83%). The ProdiscCâ„¢ was stable enough immediately after surgery and we did not see any

cases of implant migration as previously described for prostheses without keel stabilization (14). The frequency of heterotopic ossification was unexpectedly high. We observed this phenomenon in 69% of cases at 1-year follow-up. Ossification limiting segmental motion was present in 26%, with definite fusion occurring in 13% of operated segments. This is in contrary to the majority of published series. Pimenta et al. (14) reported only one case of Grade I HO in their series of 81 treated spaces. Wigfield et al. (18) using Frenchay type of prosthesis in 15 patients also did not see any limitations of segmental movement after one year. In Bertagnoli et al.'s series (2), there were also no cases of fusion reported. Some authors do indeed describe cases of motion limitation at operated segments but do not discuss fusion (7). Nevertheless, one can register an increasing number of publications with case reports or even larger series describing delayed fusion of total cervical disc replacement (TCDR) devices. Bartels and Donk (1) reported a case of Bryan prosthesis fused at 2 years, and similarly, Parkinson and Sekhon (13) found the same type of implant fused after 17 months. Sola et al. (15) presented a 28.5% fusion incidence and 47% of motionless segments in their study of 21 patients (26 levels) treated with the Bryan device with a 3-year follow-up. The last publication involving data from the original European multicenter Bryan study (10) presented 1-year followup results. HO was described in 17.8% of 90 involved patients with nearly 7% of them being Grade III or IV. Unfortunately, data with a longer follow-up from this study have not been published despite the study beginning in January 2000. The observed differences among studies describing the appearance of HO with mobile implants could be explained by variable methodology. It is still not clear whether the observed phenomenon represents ossification or calcification. The other issue is the method by which they are localized. Plain films can only demonstrate bony bridges or lack of segmental motion. Computed tomography would appear to be more accurate in evaluation of the phenomenon (17) but cannot be recommended for routine use because of irradiation and cost. As the main argument for TCDR is the preservation of motion and thus prevention of subsequent adjacent segment overload, the frequency of detected HO in our series does not support this theory and certainly suggests that further investigation of this phenomenon is necessary.

Conclusion

Despite the preliminary nature of our results, ProdiscCâ„¢ seems to be a suitable disc prosthesis with an easy implantation technique. The clinical results appear comparable with fusion techniques. Although advanced motion technology is used, the frequency of spontaneous fusions in cervical disc replacement surgery during the follow-up remains currently unpredictable. ProdiscCâ„¢ implant with keels should probably be avoided in cases with small vertebral dimensions. Longer follow-up is necessary to evaluate long-term maintenance of implant mobility as well as clinical outcome. P.251

REFERENCES 1. Bartels R, Donk R (2005) Fusion around cervical disc prosthesis: case report. Neurosurgery 57: E 194. 2. Bertagnoli R, Yue JJ, Pfeiffer F, Fenk-Mayer A, Lawrence JP, Kershaw T, Nanieva R (2005) Early results after ProDisc-C cervical disc replacement. J Neurosurg Spine 2: 403–410. 3. Bishop RC, Moore KA, Hadley MN (1996) Anterior cervical interbody fusion using autogenic and allogenic bone graft substrate: a prospective comparative analysis. J Neurosurg 85: 206–210. 4. DiAngelo DJ, Foley KT, Morrow BR, Schwab JS, Song J, German JW, Blair E (2004) In vitro biomechanics of cervical disc arthroplasty with the ProDisc-C total disc implant. Neurosurg Focus 17: 44–52. 5. Goffin J, van Loon J (1995) Long-term results after anterior cervical fusion and osteosynthetic stabilisation for fractures and/or dislocations of cervical spine. J Spine Disord 8: 499–508. 6. Goffin J, Casey A, Kehr P, Liebig K, Lind B, Logroscino C, Pointillart V, Van

Calenbergh F, Loon J (2002) Preliminary clinical experience with the Bryan cervical disc prosthesis. Neurosurgery 51: 840–847. 7. Goffin J, Van Calenbergh F, Loon J, Casey A, Kehr P, Liebig K, Lind B, Logroscino C, Sgrambiglia R, Pointillart V (2003) Intermediate follow-up after treatment of degenerative disc disease with the Bryan cervical disc prosthesis: single-level and bi-level. Spine 28: 2673–2678. 8. Hilibrand A, Carlson G (1999) Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 81: 519–520. 9. Lee CK, Goel VK (2004) Artificial disc prosthesis: design concepts and criteria. Spine J 4: 209–218. 10. Leung C, Casey A, Goffin J, Kehr P, Liebig K, Lind B, Logroscino C, Pointillart V (2005) Clinical significance of heterotopic ossification in cervical disc replacement: a prospective multicenter clinical trial. Neurosurgery 57: 759–763. 11. Matgé G, Leclercq TA (2000) Rationale for interbody fusion with threaded titanium cages at cervical and lumbar levels. Results of 357 cases. Acta Neurochir 142: 425–434. 12. McAfee PC, Cunningham BW, Devine J et al (2003) Classification of heterotopic ossification (HO) in artificial disk replacement. J Spinal Disord Tech (US) 16: 384–389. 13. Parkinson JF, Sekhon LHS (2005) Cervical arthroplasty complicated by delayed spontaneous fusion. J Neurosurg Spine 2: 377–380. 14. Pimenta L, McAfee PC, Cappuccino A, Bellera FP, Link HD (2004) Clinical experience with the new artificial cervical PCM (Cervitech) disc. Spine J 4:

315–321. 15. Sola S, Hebecker R, Knoop M, Mann S (2005) Bryan cervical disc prosthesis—three years follow-up. Eur Spine J 14(Suppl 1): 38. 16. Suchomel P, Barsa P, Buchvald P, Svobodnik A, Vanickova E (2004) Autologous versus allogenic bone grafts in instrumented anterior cervical discectomy and fusion: a prospective study with respect to bone union pattern. Eur Spine J 13: 510–515. 17. Tortolani PJ, Heller JG, Park AE, Tong F, Goffin J (2003) Computed tomography (CT) scan assessment of paravertebral bone after total cervical disc replacement: temporal relationships and the effect of NSAIDs. Proceedings of 31st Annual Meeting of the Cervical Spine Research Society, Scottsdale, Arizona, USA, 2003. Paper 32: 99–101. 18. Wigfield C, Gill SS, Nelson RJ, Metcalf NH, Robertson JT (2002) The new Frenchay artificial cervical joint. Spine 27: 2446–2452. 19. Zdeblick TA, Ducker TB (1991) The use of freeze-dried allograft bone for anterior cervical fusions. Spine 16: 726–727.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Cervical DISC > 29 - A New Cervical Disc Prosthesis: Mobi-C. Preliminary Results of a Prospective Study

29 A New Cervical Disc Prosthesis: Mobi-C. Preliminary Results of a Prospective Study Pierre Bernard Jean-Marc Vital Thierry Dufour Jacques Beaurain Jean-Marc Fuentes Jean Huppert Istvan Hovorka With most joints, for several decades now, arthrodesis has already been superseded by prosthesis implantation. In view of the good results of the decompression-arthrodesis process, the vertebral column was left out of this trend for a very long time, until modern and efficient prostheses became available in the 1980s for lumbar discs and 10 to 15 years later for cervical discs. At the same time, more and more studies have shown the harmful effect of cervical intervertebral fusion on the adjacent levels, which tend to degenerate more rapidly. This argument encouraged the development of several interbody implants allowing preservation of intervertebral mobility, thus avoiding overstressing neighboring segments. The Mobi-C prosthesis has been developed with this perspective, giving particular care to simplifying ancillary equipment and surgical technique.

Rationale for Cervical Disc Arthroplasty At the beginning of the 1950s, Cloward (6) and Smith and Robinson (24) described the anterolateral approach route to the cervical spine and its use in the treatment of compressive disc disease. The performance of an isolated discectomy without associated fusion is recognized as being generally deceptive, as this technique can lead to new cervicalgia caused by postdiscectomy instability and also secondary local kyphosis. Over the years, this anterior surgery has been complemented with plate osteosynthesis then interbody fusion cage, and, increasingly, the use of nonautologous intervertebral grafts: bone substitutes or even allografts replacing bone graft of iliac origin. On the whole, these operations give a highly satisfactory and durable result with regard to both cervical and brachial pain, while retaining generally satisfactory cervical function and mobility, often compensated by neighboring levels. Therefore, the decompression-arthrodesis combination is currently the technique of reference for most cervical pathologies requiring surgical intervention. However, in a large number of cases the initial symptom that gives rise to surgery is neurologic, and complementary arthrodesis is only carried out to prevent the possibility of iatrogenic instability of the total discectomy. This fusion can lead to restricted cervical mobility. Moreover, this operation is not without disadvantages: risk of pseudarthrosis, morbidity associated with harvesting an iliac graft if this is required, and so forth. At the same time more and more evidence has accumulated concerning the repercussions of arthrodesis on the adjacent cervical levels by acceleration of the degeneration P.254 phenomena. These arguments are at the same time biomechanical, clinical, and radiologic. Eck et al. (10), DiAngelo et al. (9), Wigfield et al. (26), and Matsunaga et al. (20) showed in biomechanical studies an increase in stresses and mobility of a disc segment situated beside a fused area. Many clinical studies have also shown the same. Hilibrand et al. (16) reviewed 409 cervical arthrodeses in 374 patients with a follow-up of up to 21 years. They reported an incidence of occurrence of symptomatic degeneration of an adjacent level of 2.9% per year in the first 10 years, projecting that about a quarter of the patients operated on would suffer another disc problem in the first decade. In their group of patients, more than two thirds underwent a further operation. Gore and Sepic (14) reported that 16% of the 50 patients operated on and

monitored with an average follow-up of more than 20 years had to undergo further operations on another level. In their group of patients, Goffin et al. (12) found discopathy on an adjacent level in 92% of cases with a follow-up of only 5 years. Finally, several radiologic studies (2,17,25) showed accelerated wear occurring in the subsequent years above or below a cervical arthrodesis. All these arguments have weighed against the development of cervical arthroplasty. In addition to sparing the adjacent levels, an artificial cervical disc must enable the physiologic local lordosis to be regained, intervertebral mobility to be retained, and the postoperative immobilization, which is usually the rule following arthrodesis, to be dispensed with. Finally, it eliminates the disadvantages associated with harvesting an iliac graft.

The Mobi-C Prosthesis The Mobi-C artificial disc (LDR médical, Troyes, France) is made up of two vertebral plates (one superior and one inferior) and a polyethylene mobile insert (Fig. 29.1). Different sizes are available (13 ÷ 15, 13 ÷ 17, 15 ÷ 17 and 15 ÷ 20, depth ÷ length). The plates are manufactured from cobalt-chrome, and the surface in contact with the vertebral body has a coating of plasma sprayed porous titanium to facilitate bone integration. Different insert heights are available to restore the physiologic height of the disc (5, 6, and 7 mm). The self-positioning of the superior plate versus the inferior plate, through the controlled mobility of the inlay permits a uniform and more physiologic load distribution on the discovertebral segment. The “nonconstraining― nature of this disc prosthesis limits the constraints on the boneimplant interface and favors the decrease of the constraints on the posterior facet joints. The self-centering of the mobile insert favors the respect of the instantaneous rotation centers and also gives back to the treated intervertebral segment its natural physiologic movements within the respect of the cervical lordosis.

FIGURE 29.1 The Mobi-C is an unconstrained prosthesis.

To implant this prosthesis, the surgical approach is identical to a classical anterior cervical arthrodesis. Patients will first undergo conventional anterior discectomy to remove the dam-aged disc. When the disc is largely exposed, the midline of the vertebra is located thanks to the width gauge, and a radio-opaque centering pin is placed on this midline at the inferior edge of the superior plate or at the upper edge of the inferior plate of the vertebrae of the operated level. It is used as a reference mark throughout the surgery to be certain of the accurate P.255 centering of the prosthesis. The intersomatic space is then distracted by distraction forceps and distraction is then maintained by a Caspar distractor. Total discectomy is then completed, up to the posterior ligament. The vertebral endplates are cleaned to remove the osteophytes and to make the flattest surface possible on the inferior plate. The aim is to be able to push the prosthesis to the posterior limit of the disc space. With the disc perfectly cleaned, one may proceed with the choice of the device. The depth gauge allows determination of the appropriate template size use. The distractor allows obtaining an intervertebral space of the desired height, and one

proceed then to introduction of the trial implant corresponding to the size and the height of the future prosthesis. This trial implant must be inserted to the maximum depth because its position will dictate the correct placement of the prosthesis. The prosthesis is introduced using the specific implant holder with reference of the centering pin on the midline. The stop on the implant holder allows control of the depth positioning during the insertion. The implant holder must be located in the disc axis and the positioning should be controlled by visual checking or using the level (option). The implant holder must maintain contact with the anterior face of the vertebra and the prosthesis is then slowly inserted with a mallet. The millimetric adjustment of the stop allows repositioning of the implant if necessary. An image intensifier should be used to confirm accurate positioning of the implant. The release of the Caspar distractor will put the implant in compression. The primary anchoring optimization is obtained through compression of the Caspar. Once compression is completed, the Caspar distractor is removed. Once the prosthesis in place, closure can be made as usual.

Material and Methods The Mobi-C prosthesis was first implanted in man in November 2004. At the same time, a prospective study began, combining the data of the seven French participating centers. The aim of this study was to evaluate the safety and the efficacy of the MobiC prosthesis in treating cervical degenerative spondylodiscal lesions. On October 1, 2005, 51 patients were included in the follow-up protocol, but we only present the preliminary results of the first 19 patients who were monitored with a follow-up of more than 6 months (6 to 10 months, average follow-up 8 months). At this time, more than 150 patients worldwide have received a Mobi-C prosthetic implant. The indications were degenerative lesions at one or two levels between C3 and C7, leading to radicular and/or medullar symptoms resistant to well-conducted conservative treatment. In the case of established myelopathies, only patients with a wide osseous canal (over 12 mm) were chosen. The exclusion criteria comprised age older than 65 years, severe osteoporosis, congenital or post-traumatic abnormality, current infection or neoplasia, established discoligamentary instability, and narrow osseous canal. These first 19 cases operated on comprised 10 men and 9 women. Two had already

undergone a first arthrodesis and were suffering a degenerative disease affecting an adjacent level. Three patients had two levels operated on. Oral nonsteroidal antiinflammatories were prescribed for 2 weeks following surgery. The average age of the patients in the group was 43 years (28 to 56 years). The evaluation was done using the visual analogue scale (VAS), the Neck Disability Index functional score, the Short Form 36 (SF-36) quality of life score, and the patient satisfaction subjective score. All the patients also underwent radiologic follow-up comprising standard anteroposterior (AP) and lateral x-rays and, at each postoperative check, dynamic checks in flexion and P.256 extension and left and right lateral bending, with measurement of the angle of mobility of the level operated on. The patients were reviewed and evaluated clinically and radiologically at 1, 3, and 6 months after the operation.

Results For the group of the first 19 patients who were monitored with a follow-up of more than 6 months, the average operating time was 75 minutes (44–95 minutes), fairly similar to the duration of a conventional decompression-arthrodesis. The average operative bleeding was around 100 mL (50–300 mL). No revisions were made. Usual postoperative complications were reported: temporary dysphagia and posterior and interscapular pain, which regressed spontaneously. Only one more unusual complication arose: sideration of the deltoid contralateral to the initial symptomatic radiculopathy. The mechanism at fault was excessive traction of the shoulder during the operation. Full recovery was achieved within 3 months, with rehabilitation. Concerning the prosthesis itself, there were no specific complications associated with the implant, either during the operation or in the longer term up until the most recent check-up: no migration, no subsidence. The average duration of hospitalization was 2.8 days (2 to 4 days). An examination of the evaluation scores shows the efficacy of surgery on the initial symptoms. On the VAS, the improvement was very significant for both cervicalgia and brachialgia, and the benefit was maintained at the most recent check-up (Fig. 29.2). Similarly, the Neck Disability Index improved rapidly after the operation, reducing from 48 to 22 postoperatively, and this functional improvement was maintained over time (Fig. 29.3). The study of the SF-36 questionnaire shows clear progress on the 8 scales, indicating a significant overall improvement in the patients' quality of life at

the latest check-up (Fig. 29.4). P.257 P.258 Finally, two thirds of the patients were “very satisfied― and one third were “satisfied― with the operation at the latest check-up, according to the subjective patient satisfaction questionnaire concerning the surgery.

FIGURE 29.2 Pain analysis.

FIGURE 29.3 Neck Disability Index.

FIGURE 29.4 Results of Short-Form 36.

FIGURE 29.5 Anteroposterior (AP) view of Mobi-C.

FIGURE 29.6 Lateral view of Mobi-C.

By examining the postoperative x-rays, we studied the behavior of each of the 22 prostheses implanted in these 19 patients. The angle measurements were carried out by an independent observer. No secondary migration was noted. All are mobile in both flexion-extension and right and left bending. Only two implants, initially incorrectly centered on the frontal plate, are mobile on only one of the x-rays in bending. The average amplitude of mobility is 10.2 degrees in flexion-extension and 8.3 degrees in right-left bending (Figs. 29.5 and 29.6). The preliminary clinical results with a follow-up of more than 6 months are therefore very satisfactory. They are nevertheless comparable to those that would normally be expected from decompression and arthrodesis surgery on a cervical degeneration problem. Concerning mobility, the prosthesis is efficacious as it works in both flexionextension and lateral bending in all the patients. In the two cases in which there was no mobility on one of the two plates in lateral bending, the cause could be attributed to a laterally slightly eccentric perioperative position; this means that meticulous implantation on the median line is required, although clinically the patients were

satisfied. The primary stability of the prosthesis is excellent, allowing immediate mobilization of the neck, and this good stability was confirmed up until the most recent check-up. No spontaneous fusion occurred.

Discussion Apart from the initial, discontinued experiment by Fernström (11), who used metal balls on a small group of patients in the middle of the 1960s, the development of effective cervical prostheses is recent. This is compared with the highly satisfactory nature of cervical decompression and arthrodesis surgery. However, the problem, as mentioned previously, of degeneration of adjacent levels has led to a recent revival in interest in cervical arthroplasty. In 1998, Cummins et al. (7) reported the results of the first 20 patients operated on with the “Bristol disc,― a metal-metal prosthesis that was clinically satisfactory but had sufficiently consistent morbidity to justify technical developments. On the basis of this experiment, a second generation called “Prestige― was produced and its results were reported by Wigfield et al. (27) in 2002. Fourteen of the 15 prostheses were radiologically mobile, but four patients reported persistent cervicalgia, and one of these required a revision because of instability of the artificial disc. Pointillart (21) developed a unipolar disc prosthesis and implanted it in 10 patients. P.259 Eight fused spontaneously, whereas the remaining two were mobile but cervicalgic. The experiment was suspended. At the same time a new prosthesis concept emerged, using an articulated polyurethane core between two convex titanium plates: the Bryan prosthesis. A prospective multicenter European study started in 2000. The results published by Goffin et al. (13) are highly satisfactory. Eighty-six percent of patients obtained a very satisfactory, satisfactory, or acceptable result after 6-month follow-up, and 90% at the 1-year check-up. All the prostheses were working and no mobilization of the implant was reported. Further studies confirmed these good results (15,22). However, secondary spontaneous fusions were reported in 12% of cases after 2 years (13). This could be associated with the necessarily aggressive reaming of the vertebral plates, which is an integral part of the technique. Moreover, the surgical technique is complicated and time-consuming, requiring the use of a stereotactical frame and complex ancillary equipment (18).

Two other prostheses based on the “ball-in-socket design― principle, with metal plates and a hemispherical polyethylene core, are currently being evaluated: the ProDisc-C and PCM. The results appear to be promising (1,4,19,23). The Mobi-C prosthesis belongs to this line of second-generation disc prostheses: efficacious, safe, and easy to implant.

Conclusion Naturally a follow-up of more than 5 or 10 years is required to be certain that the use of an artificial disc really does protect the disc levels adjacent to the level operated on. However, it can already be stated that according to this study, up until the most recent check-up the Mobi-C prosthesis is stable, safe, efficacious, and remains mobile. Moreover, all the investigating surgeons emphasized the great ease of implantation of this prosthesis, which is scarcely more difficult to place than an interbody cage.

Acknowledgment The other investigators in this study are Thierry Dufour, Jacques Beaurain, Jean-Marc Fuentes, Jean Huppert, and Istvan Hovorka.

REFERENCES 1. Anderson PA, Rouleau JP: Intervertebral disc arthroplasty. Spine 29: 2279–2786, 2004. 2. Baba H, Furusawa N, Imura S et al: Late radiographic findings after anterior cervical fusion for spondylolytic myelopathy. Spine 18: 2167–2173, 1993. 3. Bertagnoli R, Duggal N, Pickett GE, et al: Cervical total disc replacement, part II. Orthop Clin North Am 36: 355–362, 2005. 4. Bertagnoli R, Yue JJ, Pfeiffer F, et al: Early results after ProDisc-C cervical disc replacement. J Neurosurg Spine 2: 403–410, 2005. P.260

5. Bryan VE: Cervical motion segment replacement. Eur Spine J 11[suppl 2]: S92–S97, 2002. 6. Cloward R: The anterior approach for removal of disrupted discs. J Neurol 15: 602–616, 1958. 7. Cummins BH, Robertson JT, Gill SS: Surgical experience with an implanted artificial cervical joint. J Neurosurg 88: 943–948, 1998. 8. Durbhakula MM, Ghiselli G: Cervical total disc replacement, part I. Orthop Clin North Am 36: 349–354, 2005. 9. DiAngelo D, Foley K, Vossel K, et al: Anterior cervical plating reverses load transfer through multilevel strut-graft. Spine 25: 783–795, 2000. 10. Eck JC, Humphreys SC, Lim TH et al: Biomechanical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine 27: 2431–2434, 2002. 11. Fernström U: Arthroplasty with intercorporal endoprosthesis in herniated disc and in painful disc. Acta Chir Scand [suppl 57]: 154–159, 1966. 12. Goffin J, Geusens E, Vantomme N, et al: Long-term follow-up after interbody fusion at cervical spine. J Spinal Disord Tech 17: 79–85, 2004. 13. Goffin J, Casey A, Kehr P, et al: Preliminary clinical experience with the Bryan Cervical Disc Prosthesis. Neurosurgery 51: 840–847, 2002. 14. Gore DR, Sepic SB: Anterior discectomy and fusion for painful disc disease. A report of 50 patients with an average follow-up of 21 years. Spine 23: 2047–2051, 1998.

15. Guyer RD, Ohnmeiss DD: Intervertebral disc prostheses. Spine 28: S15–S23, 2003. 16. Hilibrand AS, Carlson GD, Palumbo MA, et al: Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 81: 519–528, 1999. 17. Katsuura A, Hukuda S, Saruhashi Y, et al: Kyphotic malalignment after anterior cervical fusion is one of the factors promoting the degenerative process in adjacent intervertebral levels. Eur Spine J 10: 320–324, 2001. 18. Le H, Thongtrangan I, Kim DH: Historical review of cervical disc arthroplasty. Neurosurg Focus 17: 1–9, 2004. 19. McAfee PC, Cunningham B, Dmitriev A, et al: Cervical disc replacement-Porous Coated Motion. Spine 28: S176–S185, 2003. 20. Matsunaga S, Kabayama S, Yamamoto T, et al: Strain on intervertebral discs after cervical decompression and fusion. Spine 24: 670–675, 1999. 21. Pointillart V: Cervical disc prosthesis in humans: first failure. Spine 26: E90–E92, 2001. 22. Pracyk JB, Traynelis VC: Treatment of the painful motion segment. Spine 30: S23–S32, 2005. 23. Pullitz CM, Rousseau MA, Xu Z, et al: Intervertebral disc replacement maintains cervical spine kinetics. Spine 29: 2809–2814, 2004. 24. Smith GW, Robinson RA: The treatment of certain cervical spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am 40: 607–624, 1958.

25. Shoda E, Sumi M, Kataoka O, et al: Developmental and dynamic canal stenosis as radiologic factors affecting surgical results of anterior cervical fusion for myelopathy. Spine 24: 1421–1424, 1999. 26. Wigfield C, Gill S, Nelson RJ, et al: Influence of an artificial cervical joint compared with fusion on adjacent-level motion in the treatment of degenerative cervical disease. J Neurosurg 96[suppl 1]: 17–21, 2002. 27. Wigfield C, Gill S, Nelson RJ, et al: The new Frenchay artificial cervical joint: results of a 2-year pilot study. Spine 27: 2446–2452, 2002.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Economy and Ethics > 30 - The Quest for the New

30 The Quest for the New B. Hanson This is a congress in which orthopedic surgeons meet to learn, to discuss new techniques, and to discard obsolete techniques. This is an act of faith. Our faith is that the future can be better than the past, this is a faith in Progress. Mankind has not always been searching for new things. The longest period of time in the history of man has been one of cyclic time. This means that man was doing what man had always been doing. A First Ancestor had done everything for the first time at the beginning of the world, in the “dreamtime,― as say the aboriginals of Australia. Of course, some peculiar men did invent new ways of feeding themselves, new techniques to cut stones, or better devices to hunt their prey. Modern anthropologists studying the societies that still rely on hunt and prick and still have no history have found that those of the same generation do know who has invented a peculiar technique. Their children think that this technique has always been around and the third generation has invented a myth that explains why and in which circumstances the First Ancestor has first used the technique (1). So, there was no progress at all in these times. Even if an external observer could have described the apparition of something new, society in these times did not have room for progress. Then, man wrote history. By itself, it meant a dramatic change in perspective. To

have history written was, for the king, to try to be remembered for his deeds. With history, his deeds were his, and not anybody else's. Society by itself did not value change. The place of all men was known before birth, and everybody was supposed to keep his place. The quest for the new may be traced back, in our civilization, to the Renaissance. This quest was associated with a quest of the past, with a quest of the old Greek and Roman thinkers. This quest for a forgotten past was, in itself, a quest for the new. The old texts were not read anymore, so the search for them was a quest for new ideas. New was stimulating, and the world began to change. For Hobbes, “felicity involves continual progress; it consists in prospering, not in having prospered; there is no such thing as a static happiness—excepting, of course, the joys of heaven, which surpass our comprehension.(2)― Happiness needs an evolving society; this does not mean that a society without progress cannot exist, but that man cannot live happily in such a society. Progress was man-made. Some men did not want to keep their places, nor did they accept living in a society that has forgotten its own values. Reformation occurred, and this process brought us the Declaration of Independence and the Déclaration des Droits de l'Homme et du Citoyen. P.262 Later, man began to “believe in progress as an universal law.(3)― Darwin, with his introduction of the theory of evolution, made progress the observed result of variation and selection of the fittest according to a specific environment. Political and philo-sophical liberalism quickly endorsed the new theory. “There is, however, [an] aspect of liberalism which was greatly strengthened by the doctrine of evolution, namely the belief in progress. So long as the state of the world allowed optimism, evolution was welcomed by liberals […](4)― Progress also became a central dogma of Marxism: Whatever was done, the perfect society shall come. Progress was not man-made anymore, it was the inevitable tide of history.

Unattainable Hopes It was in these times of belief in progress that modern medicine grew quickly. Soon, medical advances became an important part of this general belief. The deciphering of human DNA was a new quest for the Holy Grail: We would understand every disease and cure them. Human DNA has been read, and here we are, afraid of bird influenza that kills fewer men than motorcars. We are afraid of what might happen, of what will happen, but nobody knows when. Advocates of a reform always overstate their case, so that their converts expect the reform to bring the millennium. When it fails to do so there is disappointment, even if very solid advantages are secured(5). Modern medicine has brought much. But it has not brought the same progress everywhere or to everybody. Many promises have been fulfilled, this seems normal. There are expectations that medicine has not met, and perhaps never will. Death comes later (at least among the richest) and our treatments lessen suffering. But death and suffering are still around us. To allow oneself excessive hopes is to court disappointment(6). In spite of this disappointment, medical progress should continue. We must continue the fight on behalf of humankind. “The chief source of social cohesion in the past […] has been war: the passions that inspire a feeling of unity are hate and fear. These depend upon the existence of an enemy, actual or potential. (7)― The enemy of our time could be disease and suffering. Against such an enemy can the unity of humankind be dreamed of. Power brought to mankind by scientific knowledge has transformed the way man sees himself. Nothing should resist us. “We were told that faith could remove mountains, but no one believed it; we are now told that the atomic bomb can remove mountains, and everyone believes it. (8)― Man is able to destroy the very planet and knows it. This never-ending gain of power makes it more difficult for our patients to endure their sufferings. With such a power, we should be able to do more. How many times have I heard a patient say: “We are able to walk on the moon, but there is no cure for the common

cold.― The discrepancies between what the lay people want from us and what medicine has brought put us in a difficult position: People often think we should have done more. To forget that we are hemmed in by facts which are for the most part independent of our desires is a form of insane megalomania. This kind of insanity has grown up as a result of the triumph of scientific technique(9). P.263 We are, in some sense, victims of this megalomania. This has put us in a difficult situation: We have to explain that we are not almighty and that the work for progress needs more resources.

Is Science Good? But we are now living in a time when scientific progress is questioned. Since Hiroshima, the logical implication Science → Progress → More Happiness does not appear to be true anymore. Earth's natural disasters are not controlled, and the future of this warming planet is not without dangers. Progress is not ineluctable anymore. Changes can be two-sided. “Some of our activities will do good, some harm, but all alike will show our power. and so, in this godless universe, we shall become gods. (10)― Will the gods destroy themselves? The impact of the ecologic movement has been deep, and we cannot rely on the assumption that all scientific or medical research will bring a better future for patients. I do agree that every research cannot bring progress, but the taming of human suffering is not possible without any research. Our society is confronted with the urgent task to rethink the usefulness of our technologies, and we have to explain to the people that the resources we are asking will not be used in vain.

How to know Whether Newer is Better When new devices are tried, the first question is the ability of the new device to bring relief or to make possible what was not. Then, newer devices appear, and the question then is are they better than the first one, or are they better for a selected population?

This implies scientific protocols. The randomized protocol, double-blinded whenever possible, has been the Golden Rule. Surgery has not followed the rule for many decades (11). Such an investigation is not easily done in surgical research. When a physician can give saline intravenously or sugar orally, the patient is unable to know whether he or she has had the study medication or a placebo. Surgery implies wounds, even minimally invasive surgery. The patient will know whether he or she is in the intervention group or not, unless the researcher does a sham operation (12). Sham surgery may seem unethical because it is a kind of fraud: to make somebody falsely believe that he or she has been operated on. But we owe the best treatments to our patients. How can we learn what is best without comparison? Some studies showed that the new treatment that was hoped to be better killed more patients than the control treatment. So, to introduce a new treatment without solid grounds is to fail our patients. The ethics of clinical research calls for a complex balancing of commitments to rigorous science, improvement of medical care and protection of research subjects from undue risks of harm and exploitation(13). Surgical placebos should meet some requirements: The disease studied should not have an effective treatment (whether surgical or not), the risks to the patients must be weighed against the expected gain of knowledge, informed consent must state that a sham operation may be done, and in every other aspect of care, the treatment must be of the highest standard. P.264 We have seen that sham operations are not without problems and should not be the rule for every research. How would you do a sham amputation? But randomized protocols should become the rule to be able to prove that one technique is better than another, or better than nothing. This last point reminds us that medicine can be toxic and that our treatments should not shorten the lives of our patients. The survival of the fittest technique is a modern Darwinian creed. But this implies a free access to every bit of information. This is a problem because the industry that sponsors research often claims propriety rights on the results. Those are published if favorable to the industry. That is why the International Committee of Medical Journal Editors requested the registration of all studies (14). In addition, gifts are given to doctors, and participation in industry-sponsored research is sometimes at

odds with the patient's best interest (15). The main goal of some of poorly designed “studies― is to bring the doctor to use a new drug or a new material. We now know that spin doctors do work with industry and that important caveats have been hidden. The Vioxx story showed that industry sometimes uses misleading information and subliminal selling techniques to modify drug prescribing (16).

What Image of Modern Surgery is Given to Our Patients? The ways that patients are informed are manifold: doctors, books, general or health journals, and the World Wide Web. Because journals and books are commercial firms, their first goal is to make money. To make money, they have to sell what they print, and to sell, they have to offer some unheard-of news (17). The fact that new is bewitching is clear from the study of Hungerford (18) that introduced “minimally invasive hip replacement― in the Google search engine and got 5,170 matches, whereas Pubmed delivered only 17, none peer-reviewed. Internet medical information is known to be poor, especially when provided by sites with financial interest (19). We must be aware of all the previously mentioned facts: Science is not Progress for everybody. Some miss the good old times, some await progress that should already have been done. To be credible, we have to discuss the pros and cons of the treatment we suggest to the patient, without promising some miracle. We also have to be strongly dedicated to our ethics code to gain the patient's confidence. We can escape the fate of always being inferior to what has been awaited for by telling our patients that we are not gods; we are humans with our own limitations, but the goal we have set for ourselves is to lessen suffering and to help them, our fellow humans.

Summary The belief in never-ending progress has been one stage of the history of mankind. This is put in perspective. Unfulfilled promises have been made. Science is not what will bring eternal progress anymore. The modern surgeon is confronted with a changing paradigm: He or she has to convince patients that new techniques have been weighed and are confirmed to be better than the old ones. The surgeon is not

a god, he or she is a human that sincerely tries to help another. P.265

REFERENCES 1. Eliade M. Le Sacré et le profane, Paris, Gallimard, 1965. 2. Russel B. The History of Western Philosophy, Simon & Schuster, New York, London, Toronto, Sidney, Tokyo, Singapore, 1945, p. 550. 3. Russel B. The History of Western Philosophy, Simon & Schuster, New York, London, Toronto, Sidney, Tokyo, Singapore, 1945, p. 788. 4. Russel B. The History of Western Philosophy, Simon & Schuster, New York, London, Toronto, Sidney, Tokyo, Singapore, 1945, p. 727. 5. Russell B. Democracy and Scientific Technique. In “The Impact of Science on Society― (1st ed. 1952), London, Sidney, Wellington, Unwin Paperbacks, reprint 1990, p. 69. 6. Russell B. Democracy and Scientific Technique. In “The Impact of Science on Society― (1st ed. 1952), London, Sidney, Wellington, Unwin Paperbacks, reprint 1990, p. 996. 7. Russel B. The Impact of Science on Society, London, Unwin Hyman, 1990, p. 37. 8. Russel B. The Impact of Science on Society, London, Unwin Hyman, 1990, p. 25. 9. Russell B. Democracy and Scientific Technique. In “The Impact of Science on Society― (1st ed. 1952), London, Sidney, Wellington, Unwin Paperbacks,

reprint 1990, p. 94. 10. Russel B. The Impact of Science on Society, London, Unwin Hyman, 1990, pp. 25–26. 11. Brower V. The ethics of innovation. EMBO Rep 2003; 4: 338–340. 12. Moseley JB, O'Malley K, Petersen NJ, et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med 2002; 347: 81–88. 13. Miller FG, Kaptchuk TJ. Sham procedures and the ethics of clinical trials. J R Soc Med 2004; 97: 576–578. 14. De Angelis C, Drazen JM, Frizelle FA, Haug C, Hoey J, Horton R, Kotzin S, Laine C, Marusic A, Overbeke AJPM, Schroeder TV, Sox HC, Van Der Weyden MB. Clinical trial registration: a statement from the International Committee of Medical Journal Editors. N Engl J Med 2004; 351: 1250–1251. 15. Epps CH Jr. Ethical guidelines for orthopaedists and industry. Clin Orthop Relat Res 2003; (412): 14–20. 16. Waxman HA. The lessons of Vioxx—drug safety and sales. N Engl J Med 2005; 352: 2576–2578. 17. Bourdieu P. Sur la télévision, Paris, Liber, 1996. 18. Hungerford DS. Minimally invasive total hip arthroplasty: in opposition. J Arthroplasty 2004; 19(4 Suppl 1): 78–80. 19. Moshirfar A, Campbell JT, Khasraghi FA, Wenz JF Sr. Evaluating the quality of Internet-derived information on plantar fasciitis. Clin Orthop Relat Res 2004;

(421): 60–63.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Economy and Ethics > 31 - The SWISSspine Registry

31 The SWISSspine Registry C. Röder P. Moulin M. Aebi Cost containment is a pressing issue in all modern health care systems. Although medical innovations, demographic changes, and an ever-increasing entitlement mentality of patients have lead to severe financial problems, convincing and sustainable solutions to overcome this crisis are not at hand. The orthopaedic sector is always in the focus of debate; orthopaedic interventions, especially total joint arthroplasty, are expensive and do not directly save lives. However, their impact on patients' quality of life and regained mobility and independence are undisputed. In contrast, scientific evidence is lacking for many interventions and innovations of the fastest growing orthopaedic subspecialty, that is, spinal surgery. Accordingly, opinion leaders in spinal surgery recommend cautious approaches toward emerging new techniques and devices and closer scrutiny of spinal implants and their use for unapproved indications. They further suggest randomized controlled trials (RCTs) for new implants and indications and rigorous postmarket surveillance for adverse events (1).

Reimbursement for Total Disc Arthroplasty in Switzerland Although total disc arthroplasty (TDA) is nowadays reimbursed in many European

countries such as Germany and the United Kingdom, the Swiss federal office of health has chosen an approach similar to the previously mentioned expert proposals. Instead of conducting RCTs, it was preferred to conduct an observational study, thereby recognizing the value and practicability of such an endeavor (2). Until March 2005, TDA and balloon kyphoplasty (BKP) belonged to the so-called negative list of medical services. Interventions were not reimbursed and expenses for complications resulting from the treatments were directly charged to the respective patients. With increasing evidence about the success of TDA and BKP resulting from clinical studies and health technology assessment (HTA) projects, it was decided to temporarily reimburse the new technologies under the prerequisite that all implanted discs and used BKP sets are documented in a national registry. P.268

A Capacious Alliance—Industry, Politics, Medicine, Science Given the new restrictions for market release of medical innovations in Switzerland, the implant industry approached the decision-making political bodies and the Swiss Society for Spinal Surgery (SGS). A consensus was formed to implement a medical device registry for collecting data and providing the evidence of the safety and “efficiency― of the new treatments, that is, their performance in the clinical setting (3). The Institute for Evaluative Research in Orthopaedic Surgery at the University of Bern (IEFO), an international leader in the field of registry implementation (4,5,6), was mandated to serve as technology provider and organizer of the SWISSspine registry. In a working group consisting of stakeholders of industry, the SGS, and the IEFO, the different tasks and duties were assigned. An expert committee of the society worked up the medical content, the industry partners provided funding according to market share and support for device-related questions, and the IEFO implemented all questionnaires in an online and paper-based version for optical mark reader (OMR) scanning on its scientific documentation portal www.memdoc.org (Figs. 31.1, 31.2, and 31.3). Hereby, all content needed to be available in three of the four official Swiss languages: German, French, and Italian.

FIGURE 31.1 Organization of the SWISSspine Registry.

FIGURE 31.2 MEMdoc data input and retrieval possibilities.

P.269

FIGURE 31.3 SWISSspine scannable optical mark reader (OMR) questionnaire for primary intervention of total disc arthroplasty (TDA).

P.270 P.271

The SwissSPINE Registry—Concept and Implementation A unique maneuver in the Swiss medical profession policy making was the formation of an SGS expert group that decided about certification of spine surgeons. To obtain certification, a formal application with proof of qualification and infrastructure had to be submitted by all Swiss spine surgeons who intended to perform TDA or BKP. Along with the approval went the written consent to participate in the registry. The certification can be withdrawn if data analysis shows an unacceptably high number of complications or if the proportion of documented interventions is too low. For the latter, the industry partners deliver their sales figures to the SGS register group and the IEFO delivers the numbers of documented interventions.

Content and Follow-Up Schemes The following documentation forms and outcome instruments make up the mandatory SWISSspine registry dataset: One of the three primary intervention forms for cervical TDA, lumbar TDA, or BKP (surgeon administered). Implant form (for TDA barcode stickers). Follow-up form for cervical TDA, lumbar TDA, or BKP (surgeon administered). Euroqol-5D (patient assessment). Cervical outcome assessment instrument (COSS) for cervical and North American Spine Society (NASS) outcome instrument for lumbar TDA and BKP

(patient assessment). Comorbidity questionnaire (patient assessment). Two patient consent forms (one remains at the treatment center, one at IEFO). One annotation form about the registry and its purpose (also signed by the patient). The primary intervention and implant forms are completed by the surgeon at the time of surgery. The patient has to give informed consent about his or her participation in the registry and complete the Euroqol-5D, COSS/NASS, and comorbidity questionnaire. At the time of the mandatory TDA follow-ups, at 3 months, 1 year, and annually thereafter, the follow-up form is completed by the surgeon, and the patients fill in the Euroqol-5D and COSS or NASS questionnaires. For the BKP, there is an additional mandatory follow-up at 6 weeks after surgery. Validated translations of all patient-based instruments were available for all three needed languages. Without any exception, all surgeons outsourced their data entry to the technical staff at IEFO, thereby sending the paper questionnaires to the institute by mail where data were punched or questionnaires were scanned. Thanks to the MEMdoc technology, surgeons can autonomously view, print, or analyze their data via the online interface after the data have been entered.

Experiences of the First Year Although the surgeon-administered documentation forms were worked up as an expert consensus, several changes were still necessary during the first three quarters of year P.272 one; the main reason for this being the lack of any registry pilot phase due to time restrictions. This led to a multitude of versions of the surgeon-based questionnaires. The consequences were a necessary backward compatibility of the database with all previous form versions and hence more “open― validation rules at the expense of a sophisticated and stricter system ensuring data completeness and logic of entries. Despite distributed manuals about the organization of patient study numbers, hospital identification codes, completion of

forms, administration of consent forms, and so forth, some participating institutions were overcharged with the necessary changes in their processes and workflows. As a result, the quality and completeness of the delivered forms was poor and intensive telephone and email support for the hospitals and practices with explanation of typical mistakes and proposed solutions were necessary. Finally, the IEFO had to impose a common system for generating the study numbers and give out hospital codes because the solutions the hospitals had “invented― were inappropriate.

Discussion After clearing out the political and professional policy obstacles the way was paved for implementation of the SWISSspine registry. Given the time constraints for working up content, technology, and organization of the registry, professional medical consensus was quickly achieved. This is usually one of the most difficult and time-consuming processes in the planning phase. Nevertheless, even if content is provided by an expert panel, insufficiencies of the questionnaires only become clear if real cases are documented. This is usually done in a pilot phase, which was not conducted in this project. The price paid for a seemingly time-saving decision was a significant amount of needed extra support and compromises regarding data quality and completeness. The implementation of content as online and OMR questionnaires was quickly achieved thanks to an existing documentation system with a very generic structure. However, the process of translating all surgeonadministered documentation forms and all official correspondence into three languages took longer than expected. Finally, the industry partners did not free resources for a traveling employee for on-site support of participants. Thanks to the small geographic size of Switzerland, one full-time person would have sufficed for covering the needs of the registry community. The results were more compromises regarding data quality and completeness and a prolonged learning curve for most participants, which some of them, after 1 year of data collection, have still not overcome. Finally, giving participants freedom to organize key aspects of the registry themselves, even if they can be considered as concerning sovereign territory (e.g., patient study numbers, hospital code), is a likely source of errors. Instead, the registry framework should be clearly predefined and centrally administered by one organizing institution. An implicit and intuitive aspect of a

registry is its simplicity. The amount of information collected in the SWISSspine registry corresponds with a multicenter study. Availability of human support and study monitors is even more crucial in such a setting. The resulting workload and challenge for the management skills of the participants is all the more problematic as the SWISSspine registry is the first step in a period of a “cultural― change, that is, a new era in which paper forms not only have to be completed for billing and legal purposes but also for maintaining the certification to perform certain interventions. P.273

Lessons Learned A strong alliance between politics, industry, medical societies, and scientific institutions is a good background for a sustainable registry endeavor. Any new questionnaire, even if designed by experts in the respective field, that has not been in clinical use needs to go through a pilot phase to discover deficiencies and identify superfluous content that could be discarded. In case of several language versions of registry questionnaires and information material, the time for translation should be generously planned. Written instructions for hospitals, acquaintance with content, and training of users should all be available and organized BEFORE the registry is officially launched. In addition to telephone and email support, staff should be available for onsite support of participants for repeated training (fluctuation of hospital staff!), monitoring, and exchange of ideas and experiences made in other centers. The learning curve of hospitals and the cultural change that a very first national registry entail is a serious threat for project failure and needs to be counteracted with comprehensive preparation, information, and ongoing

human on-site support. Given the presence of an already well-functioning and debugged software, the time frame for setting-up a registry of the size of the SWISSspine registry is about 8 to 12 months.

Outlook Most centers have adapted their processes and integrated the documentation into their day-to-day workflow. The return rate of questionnaires is steadily increasing and the quality of form completion is improving. The next products that will become part of the registry are interspinous spacers and motion-preserving stabilization systems. Their integration will be easier because methodology and patient-based assessment remain the same, and solely the surgeon-administered content will have to be newly implemented.

REFERENCES 1. Deyo RA, Nachemson AN, Mirza SK. Spinal fusion surgery—the case for restraint. N Engl J Med 2004; 350: 722–726. 2. Röder C, Müller U, Aebi M. The rationale for a spine registry. Eur Spine J 2006; 15(Suppl 1): S52–56. 3. Cochrane A. Archie Cochrane in his own words. Controlled Clinical Trials 1989; 10: 428–433. 4. Röder C, EL-Kerdi A, Eggli S, Aebi M. A centralized total joint replacement registry using web-based technologies. J Bone Joint Surg Am 2004; 86: 2077–2080. 5. Röder C, EL-Kerdi A, Frigg A, Kolling C, Staub LP, Bach B, Müller U. The Swiss Orthopaedic Registry. Bull Hosp Jt Dis 2005; 63(1&2): 15–19.

6. Röder C, Chavanne A, Mannion AF, Grob D, Aebi M. Spine Tango: content, workflow, set-up. Eur Spine J 2005; 14: 920–924.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Economy and Ethics > 32 - An Introduction to the Medical Device Regulation in Europe

32 An Introduction to the Medical Device Regulation in Europe Ludo Haazen Medical devices are a huge and very heterogenous group of products, varying from wheel chairs and hospital beds, diagnostic devices, and basic surgical materials to the most sophisticated and technically demanding instruments and implants for debilitating and/or life-threatening conditions. Medical devices, as a group, are therefore intended for use by potentially also very different groups of end users, for example, from isolated, handicapped patients to highly qualified surgeons working in a highly secured environment. The acceptability of risks and hazards that are potentially associated with the use of medical devices may therefore vary extensively. Medical devices are regulated in the European Union by three directives: Directive 90/385/EEC on active implantable medical devices, Directive 93/42/EEC on medical devices, and Directive 98/79/EC on in vitro diagnostic medical devices. These regulations were needed to protect consumers and patients, including their health and their rights, to facilitate trade throughout the European Union, and to harmonize standards throughout the member states to allow mutual recognition of certifications. These well-defined and recognized standards pertaining to the investigation, design, manufacture, and quality assurance of devices essentially create a common understanding that facilitates communication between the major players, that is, the manufacturer, the Notified

Bodies that provide the required Conformity European (CE) certifications, and the regulating Competent Authorities of the member states but also ultimately result in facilitating the flow of trade within the European Union, which was a major force driving the creation of the Medical Device Directives. All EU member states are required to apply the provisions of these directives in their national law but are also still free to add additional items as well. Whereas the regulatory assessment of medicinal products or drugs is essentially based on demonstrating clinical efficacy, clinical safety, and the quality of the drug from a manufacturing point of view, the focus of the market authorization procedure of medical devices in Europe is mainly on an in-depth assessment of potential safety risks and hazards associated with their use and on the containment of these, while ensuring that the devices also perform as proposed and comply with essential quality standards. Based on the potential risks associated with their use, the duration of contact with the human body, and the degree of invasiveness, medical devices are classified into four different classes: Class I, Class IIa, Class IIb, and Class III. Detailed guidance as to the definition of what products should be considered as medical devices, and which products not, and to which class a specific medical device P.276 belongs to can be obtained from consulting the Medical Device Directives and/or Notified Bodies' Web pages. Central in the European medical device regulation is the requirement to hold a Technical File and the assessment that the medical device is in conformity with the Essential Requirements that are specified in the Medical Device Directive. A Technical File typically includes a general and technical description of the device, documentation of the quality system, design information, risk analysis data, stability analysis, testing results (and, where needed, clinical data), labels and instructions for use (IFU), and quality assurance of the manufacturing process. Complying with the Essential Requirements essentially consists of performing a comprehensive risk assessment of the device (including detailed characterization, impact assessment, and risk/benefit assessment), applying the “safety principle― in design and manufacture (including risk elimination/reduction and protection and/or warning against residual risks),

assessing the characteristics and performance of the device over time, and providing detailed information on labels and instructions for use. Additional requirements may exist according to the type of device, for example, sterility needs for implantable devices. The assessment whether the medical device conforms to the Essential Requirements differs according to the classification of the medical device. For class I devices, for example, conformity assessment is typically performed by the manufacturer (“self-declaration― of conformity). For Class IIa and IIb devices to be cleared for marketing, standard quality systems, [e.g., International Standards Organization (ISO) and European Norm (EN)] need to be obtained, as well as a successful audit by a Notified Body of the manufacturer's choice, and Class III devices require, in addition to the procedure for class II devices, a successful examination of the Product Dossier by a Notified Body. Being essentially private organizations, Notified Bodies add flexibility, dynamism, and expertise to the regulatory pathway of medical devices, as they have the required technical abilities (and are as such accredited or designated by the Competent Authority) to certify that products intended for marketing within the European Union conform to the Essential Requirements as specified in the Medical Device Directive. As the EU system for market authorization of a medical device relies primarily on the approval of quality systems and the continued compliance of established quality systems, clinical trial data are therefore not always required, especially when the device uses an accepted technology and there is no (new) risk or safety concern. For new technologies and/or new indications, clinical data are generally required, as for implantable and class III devices. Before starting a clinical trial with an investigational device, the manufacturer must notify the Competent Authority of the Member State and provide a statement that the investigational device complies with the Essential Requirements. Moreover, relevant documentation on the device and the clinical trial plan must be provided, including approval by an Independent Ethics Committee. The manufacturer is generally allowed to start the clinical trial 60 days after providing the required documents if no objection was made by the Competent Authority. Once assurance is provided that the medical device is safe and fit for its purpose, a CE mark may be carried by the device. The CE mark, however, is invalidated if the device is modified or used outside its intended purpose. New or modified devices require reassessment of compliance with the Essential Requirements (including adequate risk assessment), Ethics Committee (EC) approval, and Competent Authority (CA) notification before they can be used.

P.277 Finally, an important aspect of implantable medical devices regulation is the con-tinuous postmarket surveillance and safety after approval, because most permanent implants, for example, only reveal their weaknesses (and strengths) after having been in clinical use for a number of years. In this respect it is vital that clinicians report problems without delay to enable emerging hazards to be handled promptly.

Bibliography 1. Directive 90/385/EEC on active implantable medical devices: http://europa.eu.int/eurlex/lex/LexUriServ/site/en/consleg/1990/L/01990L0385–20031120-en.pdf 2. Directive 93/42/EEC on medical devices: http:// europa.eu.int/eurlex/lex/LexUriServ/site/en/consleg/1993/L/01993L0042–20031120-en.pdf 3. Directive 98/79/EC on in vitro diagnostic medical devices: http://europa.eu.int/comm/enterprise/newapproach/standardization/harmstds/reflist.html 4. Chai J, Law D (2000). Regulation of medical devices in the European Union. The Journal of Legal Medicine 21: 537–556. 5. Randall H, Croft RJ (2001). The CE mark for implantable medical devices. Hospital Medicine 62(6): 332–334. 6. Spencer SA, Nicklin SE, Wickramasinghe YA, Nevill A, Ellis SJ (2003). An essential ‘health check’ for all medical devices. Clinical Medicine 3(6): 543–545.

Editors: Szpalski, Marek; Gunzburg, Robert; Le Huec, Jean-Charles; BraydaBruno, Marco Title: Nonfusion Technologies in Spine Surgery, 1st Edition Copyright ©2007 Lippincott Williams & Wilkins > Table of Contents > Economy and Ethics > 33 - Outcome & Cost of Lumbar Disc Replacement Versus Lumbar Fusion

33 Outcome & Cost of Lumbar Disc Replacement Versus Lumbar Fusion Marc Du Bois Peter Donceel Painful lumbar disc degeneration is the leading cause of pain and disability in adults in the United States and in the rest of the world. This represents a large socioeconomic impact with estimates of more than $50 billion in direct and indirect health costs in the United States annually. In most cases, degenerative disc disease can be treated successfully nonoperatively (2 ,3 ). There are, however, substantial numbers of people who have failed exhaustive nonoperative treatments and who seek surgical solutions for their incapacitating back pain. Currently, fusion is a widely accepted treatment for degenerative disc disease. However, outcome measures of fusion surgery show mixed results, particularly in the long-term. The innovative properties that artificial discs bring to the treatment of spine disorders through spinal joint replacement, as opposed to fusion, include: (1 ) relief of pain by maintaining spinal motion; (2 ) prevention of adjacent segment disease by eliminating adjacent joint-segment rigidity, lessening the potential for future disease-related events and surgeries; and (3 ) the continuance of a lifestyle that more closely resembles a preillness state (2 ).

Objectives

We conducted a retrospective cohort study to establish whether disc replacement surgery can be performed with a better outcome comparable to combined discectomy and fusion. Our primary objective was to compare return to work rates after disc replacement surgery and combined discotomy and fusion. Determination of the costs associated with disc replacement surgery was our secondary objective.

Methods Medical and financial claims data were abstracted from the administrative database of the Alliance of Christian Sickness Funds. This database is nationally representative for the Belgian population and includes data from 4,500,000 enrollees. All records including the reimbursement codes for combined discectomy and fusion between January 1, 2003, and December 31, 2003 were identified. A total of 310 patients met these criteria (fusion group). Next, 174 cases with disc replacement surgery were identified for the final dataset (disc replacement group). Patient age, gender, sick leave before surgery, employment state, and surgeon's specialty were considered as covariates in the analysis. P.280 Detailed cost data incurred during the hospital stay were collected. The costs represent the cost of anesthesia, radiology tests, nursing, lodging, and implants. All reported costs are in 2004 Euros. A logistic regression model at the patient level was developed to determine the predictors of return to work Covariates significant at the 0.05 level in bivariate analyses were entered in the multivariate model in a stepwise manner. Statistical analyses were performed using SPSS 8.0.

Results Patient Characteristics Study patients consisted of 310 consecutive patients who underwent combined discectomy and fusion and 174 consecutive patients in whom a disc replacement surgery was performed. Baseline characteristics of the two treatment groups differed in several nonmedical factors shown to predict subsequent work outcomes (Table 33.1 ). Overall, the combined discectomy and fusion group encompassed significantly more female patients, and significantly less operations were

performed by neurosurgeons. Importantly, these differences were taken into account by adjusting for these covariates in the logistic regression.

Outcomes One year after surgery, the disc replacement group had a return to work rate of 43%. In the fusion group, 48% of the patients were able to resume work 1 year after intervention. Table 33.2 shows the logistic regression analysis in detail. After adjusting for patient gender, age, period of work incapacity before surgery, employment, and P.281 surgeon's specialty, type of intervention was not associated with a higher return to work rate 1 year after surgery. This means that disc replacement surgery was not significantly better in terms of return to work than combined discectomy and fusion. This analysis also clearly shows the expected detrimental effect of long work incapacity before surgery. Another finding was that orthopaedic surgeons had faster return to work rates. Self-employed patients had better outcomes. Median age (years) 43 (Range: 25–70) Male/female 118/56 68/32 Median sick leave before surg. (days) 1 (Range: 0–443) Neurosurgeon/orthopaedic surgeon 130/44 75/25 Blue/white collar/self-employed 105/36/13 60/32/8 Fusion group N = 310 (No. = number; % = percentage) Median age (years)

44 (Range: 22–72) Male/female 176/134 57/43 Median sick leave before surg. (days) 4 (Range: 0–723) Neurosurgeon/orthopaedic surgeon 182/128 59/41 Blue/white collar/self-employed 199/95/16 64/31/5 Disc replacement group N = 174 (No. = number; % = percentage) Characteristics

No.

%

Characteristics

No.

%

TABLE 33.1 Characteristics of patients Age -0,029 0,013 4,870 1 0,027 0,971 0,946 0,997 Male 0,454

0,231 3,850 1 0,05 1,574 1,001 2,477 Work incapacity before surgery -0,051 0,009 31,803 1 0,001 0,950 0.933 0.67 Orthopedic surgeon 0,653 0,221 8,704 1 0,003 1,922 0,933 0,967 Self-employed 1,180 0,395 8,920 1 0,282 3,254 1,245 2,967

Disk replacement 0,042 0,224 0,036 1 0,850 1,043 0,673 1,617 Constant 0,575 0,663 0,752 1 0,386 1,778

95% CI B

S.E.

Wald

df

P

Odds

Lower

Upper

TABLE 33.2 Logistic regression analysis The patients who had disc replacement surgery had a median hospital stay of 5 days (25th percentile to 75th percentile, 3 to 7 days) compared with 7 days (25th percentile to 75th percentile, 6 to 9 days) for those who had combined discectomy and fusion. The disc replacement group had lower costs for anesthesia, nursing, lodging, and imaging during the hospital stay but a 75% higher cost for implants (Table 33.3 ).

TABLE 33.3 Median in-hospital costs (EUR) P.282

Discussion We reported the return to work rates and costs of disc replacement surgery and combined discectomy and fusion. In the current study, we examined the costs during the hospital stay of these procedures. Because patients who have disc replacement surgery cannot return to work earlier than those who have combined discectomy and fusion, disc replacement has no additional economic advantage compared with standard surgery for degenerative disc disease. The relative economic effects of these two procedures for longer periods remain to be determined. This especially applies for lumbar fusion given the well-known incidence of adjacent segment complications in the long run. In a representative clinical follow-up study of the surgical disc replacement experience of Lemaire et al. (5 ), 82% returned to work of whom 72.7% continued the same level of activity. Nine percent did not return to work. These return to work rates are much higher than our findings owing to the type of compensation system in place.

Previous studies have shown that return to work rates are influenced more by nonmedical than by medical factors. After statistical adjustment for the effect of differences in baseline characteristics, patients who underwent combined discectomy and fusion or disc arthroplasty had indistinguishable rates of return to work. The major nonmedical factor associated with a poor return to work rate was the duration of work incapacity before intervention. This supports the general finding that few patients who are disabled for more than 6 months will return to work even if their physical health is fully restored. Because there is no single surgical standard for the treatment of chronic back pain attributed to degenerative disc disease, surgery may not be an option for these long-term disabled patients. A prospective randomized study of the Charité artificial disc revealed that total disc replacement appears to be a viable alternative to fusion for the treatment of single-level symptomatic disc degeneration unresponsive to nonoperative management (1 ). However, follow-up periods were no longer than 24 months. These follow-up periods are too short to advise arthroplasty as the procedure of choice in primary discectomy associated with long-standing back pain. Our study confirmed that there is no evidence that disc arthroplasty itself is superior in terms of return to work to combined discectomy and fusion in the short run (4 ). Our study has important shortcomings because of its retrospective design with a maximum follow-up of 1 year. Second, although conclusions were drawn after adjustment for some nonmedical differences, unregistered information about the medical condition before surgery and perioperative findings may be obscuring significant differences. The major strength lies in its multicenter and representative nature. In summary, we observed similar return to work rates following disc replacement surgery and combined discectomy and fusion. However, days of hospitalization and costs were significantly lower with disc replacement surgery even after adjustment for population characteristics. Longer follow-up of this retrospective cohort and additional randomized prospective clinical trials may help address the relative merits of different surgical approaches for degenerative disc disease. We strongly support attention to quality of life and costs in evaluating disc prostheses. Disc replacement surgery is too costly a procedure with unknown long-term health consequences to be performed without sufficient scientific backing.

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