Ebook Dynamic reconstruction of the spine: Part 1

(BQ) Part 1 book “Dynamic reconstruction of the spine” has contents: Dynamic stabilization of the lumbar spine, cervical and lumbar disc replacement, center of rotation, biomechanical testing of the lumbar spine, kinematics of the cervical spine motion, finite element analysis,… and other contents.

Daniel H Kim, MD, FAANS, FACS

Professor

Director of Spinal Neurosurgery

Reconstructive Peripheral Nerve Surgery

Department of Neurosurgery

Memorial Hermann

The University of Texas Health Science Center at Houston

Houston, Texas

Dilip K Sengupta, MD, DrMed

Director, Clinical Research

Attending Spine Surgeon

Texas Back Institute

Spine Care Institute

Hospital for Special Surgery

Professor of Orthopedic Surgery

Weill Medical College of Cornell University

New York, New York

Do Heum Yoon, MD, PhD

Professor

Department of Neurosurgery

Yonsei University College of Medicine

Seoul, Republic of Korea

Richard G Fessler, MD, PhD

Professor

Department of Neurological Surgery

Rush University College of Medicine

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Library of Congress Cataloging-in-Publication Data

Dynamic reconstruction of the spine

/ [edited by] Daniel H Kim, Dilip K Sengupta, Frank P Cammisa Jr.,

Do Heum Yoon, Richard G Fessler 2nd edition

p ; cm

Includes bibliographical references and index

ISBN 978-1-60406-873-3 (hardback) ISBN 978-1-60406-874-0

(eISBN)

I Kim, Daniel H., editor II Sengupta, Dilip K., editor III Cammisa,

Frank P., Jr., editor IV Yoon, Do Heum, editor V Fessler, Richard G.,

editor

[DNLM: 1 Spine surgery 2 Arthroplasty,

Replacement methods 3 Prostheses and Implants WE 725]

RD768

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by the publisher that it is in the public domain

This book, including all parts thereof, is legally protected by right Any use, exploitation, or commercialization outside the narrowlimits set by copyright legislation without the publisher's consent isillegal and liable to prosecution This applies in particular to photo-stat reproduction, copying, mimeographing or duplication of anykind, translating, preparation of microfilms, and electronic dataprocessing and storage

copy-I dedicate this volume to my wife Gail and our children Annie, Trey, and Jack copy-I will always

appreciate their support throughout this endeavor

Frank P Cammisa Jr

To my wife, Young-ran, and my sons, Dong-whan and Dong-min, for their encouragement, tolerance,

and unending love I will always appreciate their support throughout this endeavor

Do-Heum Yoon

To my teachers and mentors, Sean Mullan, Al Rhoton, Fred Brown, and Javad Hekmatpanah,

for giving me the opportunity to utilize the knowledge, skills, and advice that they so generously gave to me

for the benefit of the many patients for whom I have had the privilege to care

Richard G Fessler

Preface xi

Acknowledgments xiii

Contributors xv

Part 1 Motion Preservation of the Spine in Context

1 Dynamic Stabilization of the Lumbar Spine 2

Dilip K Sengupta

2 Cervical and Lumbar Disc Replacement 7

Do Heum Yoon, Karen M Shibata, Daniel H Kim, and Dilip K Sengupta

3 The Rationale behind Dynamic Posterior Spinal Instrumentation 20

Paul C McAfee, Bryan W Cunningham, and Dilip K Sengupta

Part 2 Clinical Biomechanics of the Spine

4 Basic Principles in Biomechanics: Force and E ffects 32

Paul C Ivancic

5 Basic Principles in Biomechanics: Loads and Motion (Kinematics) 38

Vikas Kaul, Ata M Kiapour, Constantine K Demetropoulos, Anand K Agarwal, and Vijay K Goel

6 Center of Rotation 46

Dilip K Sengupta

7 Biomechanical Testing of the Lumbar Spine 54

Avinash G Patwardhan, Robert M Havey, and Leonard I Voronov

8 Kinematics of the Cervical Spine Motion 61

Ata M Kiapour and Constantine K Demetropoulos

9 Biomechanical Testing Protocol for Evaluating Cervical Disc Arthroplasty 70

Dilip K Sengupta

10 Finite Element Analysis 75

Ali Kiapour, Vivek Palepu, Ata M Kiapour, Constantine K Demetropoulos, and Vijay K Goel

11 Biomaterials and Design Engineering 85

Michael B Mayor

Part 3 Restoration of the Cervical Movement Segment

12 Biomechanical Aspects Associated with Cervical Disc Arthroplasty 90

Dilip K Sengupta

13 Rationale and Indications for Cervical Disc Arthroplasty 98

Jesse L Even, Joon Y Lee, Moe R Lim, and Alexander R Vaccaro

14 Metal-on-Metal Cervical Disc Prostheses 104

Darren R Lebl, Federico P Girardi, and Frank P Cammisa Jr

15 Design Rationale and Surgical Technique of Metal-on-Poly Cervical Disc Prostheses 112

Darren R Lebl, Federico P Girardi, and Frank P Cammisa Jr

16 Bryan Cervical Disc Device 118

Dilip K Sengupta

17 M6-C Artificial Cervical Disc 125

Carl Lauryssen and Domagoj Coric

18 PEEK and Ceramic Cervical Disc Prostheses 135

Matthew N Songer

19 Complexities of Single- versus Multilevel Cervical Disc Arthroplasty 145

William E Neway III, Lisa Ferreara, and James Joseph Yue

20 Update on FDA IDE Trials on Cervical Disc Arthroplasty 152

Uday Pawar, Abhay Nene, and Dilip K Sengupta

21 Complications of Cervical Disc Replacement 157

Troy Morrison, Richard D Guyer, and Donna D Ohnmeiss

22 Retrieval Analysis of Cervical Total Disc Replacement 162

JayDeep Ghosh, Peng Huang, and Dilip K Sengupta

Part 4 Restoration of the Lumbar Motion Segment

23 Kinematics of the Lumbar Spine 172

Haibo Fan

24 Kinetics of the Lumbar Spine 177

Ata M Kiapour, Haibo Fan, and Constantine K Demetropoulos

25 Rationale and Principles of Dynamic Stabilization in the Lumbar Spine 184

Dilip K Sengupta

26 Design Rationale, Indications, and Classification for Pedicle

Screw –Based Posterior Dynamic Stabilization Devices 189

Dilip K Sengupta

27 Dynamic Stabilization with Graf Ligamentoplasty 196

Young-Soo Kim, Dong-Kyu Chin, and Dilip K Sengupta

28 Clinical Application of Dynesys Dynamic Stabilization 202

Gilles G DuBois and Dilip K Sengupta

29 Dynamic Stabilization for Revision of Lumbar Spinal Pseudarthrosis with Transition 207

Paul C McAfee, Liana Chotikul, Erin M Shucosky, and Jordan McAfee

30 Nonfusion Stabilization of the Degenerated Lumbar Spine with Cosmic 213

Archibald von Strempel

31 Minimally Invasive Posterior Dynamic Stabilization System 222

Luiz Pimenta, Roberto Diaz, and Dilip K Sengupta

32 Clinical Results of IDE Trial of Dynesys for Dynamic Stabilization 228

Alex Ha and Dilip K Sengupta

33 Classification, Design Rationale, and Mechanism of Action of Interspinous Process

Distraction Systems 234

Chadi Tannoury and Frank M Phillips

34 Clinical Results of Interspinous Process Spacers and Complications 240

Kern Singh, Alejandro Marquez-Lara, Sreeharsha V Nandyala, and Miguel Pelton

35 Clinical Results of IDE Trial of X-Stop Interspinous Systems 247

Elizabeth Yu and James F Zucherman

36 Clinical Biomechanics of Lumbar Facet Joints 253

Conor Regan, Moe R Lim, Joon Y Lee, and Todd J Albert

37 The Current Status of Facet Replacement Devices 258

Kern Singh, Sreeharsha V Nandyala, Alejandro Marquez-Lara, Steven J Fineberg, Matthew Oglesby,Larry T Khoo, Luiz Pimenta, Roberto Diaz, and Scott Webb

38 Biomechanics and Rationale of Prosthetic Nucleus Replacement 266

Naresh Kumar, Barry W L Tan, and Hee-Kit Wong

39 The Raymedica Prosthetic Disc Nucleus (PDN) 272

Naresh Kumar, Barry W L Tan, and Hee-Kit Wong

40 Classification of Lumbar Nucleus Replacement Systems, Mechanism of Action, and

Surgical Technique 281

Tim Brown, Qi-Bin Bao, William F Lavelle, Domagoj Coric, and Hansen A Yuan

41 Biomechanical Consideration for Total Lumbar Disc Replacement 287

Jean-Charles Le Huec, Antonio Faundez, and Stephane Aunoble

42 Indications for Total Lumbar Disc Replacement 292

Dilip K Sengupta and Rudolf Bertagnoli

43 Anterior Exposure to the Lumbar Spine 298

Jonathan D Krystal and Alok D Sharan

44 Classification of Total Lumbar Disc Replacement 304

Karin Büttner-Janz

45 Charité Artificial Disc 313

Fred H Geisler

46 ProDisc-L Artificial Disc 334

Jack E Zigler and Rob D Dickerman

47 Polymer-on-Metal Lumbar TDR Design Rationale and Classification 339

Christoph R Schätz

48 M6-L Artificial Lumbar Disc 343

Christoph R Schätz

49 The Mobidisc Prosthesis 350

Jean-Paul Steib, Joël Delécrin, Jacques Beaurain, Jean Huppert, Hervé Chataigner, Marc Ameil, Thierry Dufour,and Jérơme Allain

50 Metal-on-Metal Lumbar Total Disc Replacements (Maverick, FlexiCore, Kineflex) 359

Brian J C Freeman and Julia S Kuliwaba

51 Clinical Results of Total Lumbar Disc Replacement 367

Kirill F Ilalov, Richard D Guyer, Jack E Zigler, and Donna D Ohnmeiss

52 Long-Term Outcomes of Lumbar Total Disc Arthroplasty 374

Steven J Fineberg, Sreeharsha V Nandyala, Alejandro Marquez-Lara, Matthew Oglesby, and Kern Singh

53 Complications of Lumbar Disc Arthroplasty 380

Sang-Ho Lee and Chan-Shik Shim

54 Complications of Investigational Device Exemption Trial after Total Disc Replacement 386

Adewale O Adeniran and Adam M Pearson

55 Complications of Total Lumbar Disc Replacement and Salvage

Procedures 390

Andre Van Ooij and Ilona M Punt

56 Multilevel Total Lumbar Disc Replacement 399

James Joseph Yue, Lisa Ferrara, and Jason O Toy

Part 5 Advancements in Lumbar Motion Preservation

57 Advancements in the Design of Lumbar Prosthetic Discs —Theken Disc and

Elastomeric Disc Physio-L 408

Vijay K Goel, Aakash Agarwal, Constantine K Demetropoulos, Anand K Agarwal, and Casey K Lee

58 Concept of Total Joint Replacement in the Lumbar Spine (Flexuspine —Total Disc with

Posterior Approach) 415

Jonathan A Gimbel, Charley Gordon, and Eric Wagner

59 Assessment of Lumbar Motion Kinematics In Vivo 423

Shaobai Wang, Guoan Li, and Kirkham Wood

60 Annulus Repair 432

Michael Y Wang and Faiz U Ahmad

61 Minimally Invasive Technology for Lumbar Motion Preservation 437

Paul D Kim and Choll W Kim

62 Molecular and Genetic Therapy in Repair of the Degenerative Disc 441

Michael P McClincy, Gwendolyn Sowa, Nam Vo, Bing Wang, and James D Kang

Index 448

this is no better thanfixing a car door that does not open or

close properly by welding it to the frame permanently! This is

far from what is commonly understood as a "fix." Nonfusion

alternatives to spinal fusion have emerged from the

limita-tions of fusion as experienced during the later part of the last

century During the last decade, dynamic reconstruction of

the spine, either by disc replacement or dynamic

stabiliza-tion, has gained attention in the surgical community A large

number of new technologies have been introduced, many of

which have died prematurely, although a few survived the

test of time while our knowledge was being consolidated

Dynamic reconstruction has to face many more challenges

for long-term survival than spinal fusion A thorough

knowl-edge of the biomechanics of normal and abnormal spine is

essential in the understanding of dynamic reconstruction

techniques Therefore, in the second edition of this book, a

new section on clinical biomechanics was added following

the section on historical perspective The two other sections

provide a thorough but critical discussion of cervical and

lumbar motion preservation techniques In thefirst edition of

this book, as well as in most other similar publications, the

major emphasis was on comprehensive presentation of all

the new techniques, including inventor or surgeon views,

allowing specific insight into each system But such

presen-tation can't be free from bias In the second edition, emphasis

was put on presentation of the scientific basis by

indepen-presented separately The discussions of the cervical andlumbar disc prosthesis have been grouped to some extent,according to the material structure of the prosthesis, forexample, metal-on-metal, or metal-on-plastic, etc The direc-tions of further development in thefield of disc replacementhave been presented by the original inventors of disc replace-ments and biomechanics engineers This section alsoincludes minimally invasive techniques, annulus repair, andadvances in genetic and molecular technologies for discrepair

The second edition of this book will prove useful to thecommunity practicing spinal surgery, including orthopedicand neurosurgeons, residents and fellows, radiologists, med-ical students, nurses, and physician assistants In addition,researchers and biomedical engineers, inventors, and others

in the spine industry willfind plenty of interest

The dynamic reconstruction of the spine is an changing subject, and the speed of publication competeswith advancing knowledge and experience on this subject.This book will bring the reader up to speed with information

ever-on the biomechanical background, as well as an outline of thecurrent status and future directions for the treatment ofspinal pain

Daniel H KimDilip K Sengupta

contributed their time, talents, and resources We would

like to acknowledge the valuable input of coeditors

Frank P Cammisa Jr., MD, Richard G Fessler, MD, and

Daniel H KimDilip K Sengupta

Lebanon, New Hampshire

Aakash Agarwal, BTech

Orthopedic Spine Surgeon

Departments of Bioengineering and Orthopaedic Surgery

Colleges of Engineering and Medicine

Department of Orthopedic surgery

Henri Mondor Hospital

Département Orthopédie Pr Chauveaux

Spine Unit Pr Le Huec, CHU Pellegrin

Université Bordeaux

Bordeaux, France

Minneapolis, Minnesota

Jacques Beaurain, MDDepartment of NeurosurgeryUniversity Hospital Bocage CentralDijon, France

Rudolf Bertagnoli, Prof, DrChief Executive OfficerPro Spine

Bogen, Germany

Tim Brown, MSClinical and Scientific Research Associates, LLCMarquette, Michigan

Karin Büttner-Janz, MD, PhDExtraordinary Professor at CharitéUniversitätsmedizin Berlin, GermanyBerlin, Germany

Frank P Cammisa Jr., MD, FACSChief

Spinal Surgical ServiceAttending SurgeonSpine Care InstituteHospital for Special SurgeryProfessor of Orthopedic SurgeryWeill Medical College of Cornell UniversityNew York, New York

Hervé Chataigner, MDService de Chirurgie des Scolioses et Orthopedie InfantileDepartment of Surgery and Orthopedics of Infantile ScoliosisHôpital St Jacques

Cedex, France

Dong-Kyu Chin, MDDepartment of NeurosurgeryThe Spine and Spinal Cord InstituteGangnam Severance HospitalSeoul, Republic of Korea

Liana Chotikul, RN, MSN, NP-C, CNOR, ONCOrthopedic Surgery of Spine

Towson Orthopedics AssociatesTowson, Maryland

Carolinas Medical Center

Carolina Neurosurgery and Spine Associates

Charlotte, North Carolina

Bryan W Cunningham, PhD

Director of Spinal Research

Orthopaedic Spinal Research Institute

University of Maryland St Joseph Medical Center

Towson, Maryland

Joël Delécrin, MD

Associate Professor

Department of Orthopedics Surgery

CHU de Nantes Hospital–Saint Jacques

Cedex, France

Constantine K Demetropoulos, PhD

Lead Researcher, Experimental Biomechanics

Biomechanics and Injury Mitigation Systems

Research and Exploratory Development Department

The Johns Hopkins University Applied Physics Laboratory

Laurel, Maryland

Roberto Diaz, MD

Assistant Professor, Chief of Neurosurgery

Neurosurgery Unit

Hospital Universitario San Ignacio

Pontificia Universidad Javeriana

Birmingham, Alabama

Antonio Faundez, MDOrthopaedic Spine Surgeon

La Tour Hospital and Geneva University HospitalsGeneva, Switzerland

Lisa Ferreara, PhDPresident

OrthoKinetic Technologies, LLCSouthport, North Carolina

Richard G Fessler, MD, PhDProfessor

Department of Neurological SurgeryRush University College of MedicineChicago, Illinois

Steven J Fineberg, MDResearch CoordinatorDepartment of Orthopaedic SurgeryRush University Medical CenterChicago, Illinois

Brian J C Freeman, MB, BCh, BAO, DM, FRCS (TR & Orth),FRACS (Ortho)

Professor of Spinal SurgeryDiscipline of Orthopaedics and TraumaUniversity of Adelaide

Head of Spinal ServicesDepartment of Spinal SurgeryRoyal Adelaide HospitalAdelaide, Australia

Fred H Geisler, MD, PhDChief Medical OfficerDepartment of NeurosurgeryRhausler, Inc

Chicago, Illinois

JayDeep Ghosh, MDSpine SurgeonSir Ganga Ram HospitalNew Delhi, India

Pittsburgh, Pennsylvania

Federico P Girardi, MD

Associate Orthopedic Surgeon

Associate Professor of Orthopedic Surgery

Department of Spinal Surgery, Orthopedics

Hospital for Special Surgery

Weill Medical College of Cornell University

New York, New York

Vijay K Goel, PhD

Distinguished University Professor

Endowed Chair and McMaster–Gardner Professor

of Orthopaedic Bioengineering

Co-Director, Engineering Center for Orthopaedic

Research Excellence

Departments of Bioengineering and Orthopaedic Surgery

Colleges of Engineering and Medicine

Spine Surgeon and President

Texas Back Institute

Department of Orthopaedic Surgery

The General Hospital of People's Liberation Army

University Orthopaedics, Hand and ReconstructiveMicrosurgery Cluster

HeadUniversity Spine CentreNational University Health SystemSingapore

Kirill F Ilalov, MDOrthopaedic Spine SurgeonThe Center for Bone and Joint DiseaseHudson, Florida

Paul C Ivancic, PhDAssistant ProfessorBiomechanics Research LaboratoryDepartment of Orthopaedics and RehabilitationYale University School of Medicine:

New Haven, Connecticutt

James D Kang, MDUPMC Endowed Chair in Orthopaedic Spine SurgeryProfessor of Orthopaedic and Neurological SurgeryUniversity of Pittsburgh School of MedicineVice Chairman, Department of Orthopaedic SurgeryDirector, Ferguson Laboratory for Spine ResearchPittsburgh, Pennsylvania

Vikas Kaul, MSConsultant–TechnologyDassault SystèmesProvidence, Rhode Island

Larry T Khoo, MDThe Spine Clinic of Los AngelesLos Angeles, California

Ali Kiapour, PhDDepartment of BioengineeringUniversity of Toledo

Toledo, Ohio

Ata M Kiapour, PhDDepartment of Orthopaedic SurgeryBoston Children's Hospital

Harvard Medical SchoolBoston, Massachusetts

Minimally Invasive Spine Program

Spine Institute of San Diego

San Diego, California

Daniel H Kim, MD, FAANS, FACS

Professor

Director of Spinal Neurosurgery

Reconstructive Peripheral Nerve Surgery

Spine Institute of San Diego

San Diego, California

Kim Young Soo Hospital

Seoul, Republic of Korea

Jonathan D Krystal, MD

Department of Orthopaedic Surgery

Albert Einstein College of Medicine

Montefiore Medical Center

Bronx, New York

Department of Orthopaedic Surgery

Senior Consultant Orthopaedics

National University Health System

National University of Singapore

Singapore

Carl Lauryssen, MD

Co-Director of Spine Research and Development

Olympia Medical Center

Tower Orthopaedics

Beverly Hills, California

SUNY Upstate Medical UniversitySyracuse, New York

Darren R Lebl, MDDirector

Complex Cervical Spine SymposiumHospital for Special Surgery

The Spine Care InstituteSpine and Scoliosis SurgeryNew York, New York

Casey K Lee, MDClinical ProfessorDepartment of Orthopedic SurgeryCollege of Medicine

New Jersey Medical SchoolSpine Care and Rehabilitation Inc.Roseland, New Jersey

Joon Y Lee, MDAssociate ProfessorDepartment of OrthopaedicsUniversity of Pittsburgh Medical CenterPittsburgh, Pennsylvania

Sang-Ho Lee, MD, PhDChairman

Department of NeurosurgeryWooridul Spine HospitalSeoul, Republic of Korea

Jean-Charles Le Huec, MD, PhDProfessor

Orthospine UnitBordeaux University HospitalBordeaux, France

Guoan Li, PhDDirector, Bioengineering LaboratoryAssociate Professor

Harvard Medical SchoolDepartment of Orthopaedic SurgeryMassachusetts General HospitalHarvard Medical SchoolBoston, Massachusetts

Moe R Lim, MDAssociate ProfessorDepartment of OrthopaedicsUniversity of North Carolina–Chapel HillChapel Hill, North Carolina

Rush University Medical Center

Chicago, Illinois

Michael B Mayor, BEE, MD

William and Bessie Allyn Professor Emeritus

Geisel School of Medicine at Dartmouth

Dartmouth-Hitchcock Medical Center

Lebanon, New Hampshire

Paul C McAfee, MD, MBA

Chief of Spinal Surgery

University of Maryland St Joseph Medical Center

Towson, Maryland

Jordan McAfee, BSc

New York, New York

Michael P McClincy, MD

Department of Orthopaedic Surgery

University of Pittsburgh Medical Center

Department of Orthopaedic Surgery

Rush University Medical Center

Department of Orthopaedic Surgery

University of Alabama at Birmingham

Vivek Palepu, PhDORISE FellowFDA, Center for Devices and Radiological HealthOffice of Science and Engineering LaboratoriesDivision of Solid and Fluid Mechanics

Silver Spring, Maryland

Avinash G Patwardhan, PhDProfessor

Department of Orthopaedic Surgery and RehabilitationLoyola University Chicago

Maywood, Illinois

Uday Pawar, MDJunior Consultant Spine SurgeonP.D Hinduja National Hospital and Medical Research CentreMumbai, India

Adam M Pearson, MD, MSAssistant Professor of OrthopedicsDepartment of OrthopaedicsDartmouth-Hitchcock Medical CenterLebanon, New Hampshire

Miguel Pelton, BSResearch CoordinatorDepartment of Orthopaedic SurgeryRush University Medical CenterChicago, Illinois

Huang Peng, MD, PhDDepartment of OrthopaedicsChinese PLA General HospitalBeijing, China

Frank M Phillips, MDProfessor

Head, Section of Minimally Invasive Spine SurgeryDepartment of Orthopaedic Surgery

Spine Fellowship Co-DirectorRush University Medical CenterChicago, Illinois

University of California–San Diego

San Diego, California

Medical Director

Instituo de Patologia de Coluna

Sao Paulo, Brazil

Ilona M Punt, PhD

Clinical Researcher

Department of Orthopaedic Surgery

Maastricht University Medical Center

Maastricht, Netherlands

Department of Physical Therapy

University of Applied Sciences of Western Switzerland

Department of Spine Center

Orthopädische Klinik Markgroningen

Markgroningen, Germany

Dilip K Sengupta, MD, DrMed

Director, Clinical Research

Attending Spine Surgeon

Texas Back Institute

Plano, Texas

Alok D Sharan, MD

Chief

Orthopedic Spine Service

Montefiore Medical Center

Albert Einstein College of Medicine

Bronx, New York

Wooridul Spine Center Dubai

Dubai, United Arab Emirates

Erin M Shucosky, RN

Case Manager/Clinical Research Coordinator

Scoliosis and Spine Center

Towson Orthopaedics Associates

Michigan Technological UniversityAdjunct Professor

Northern Michigan UniversityMarquette, Michigan

Gwendolyn Sowa, MD, PhDAssociate Professor

Departments of Physical Medicine and Rehabilitation andOrthopaedic Surgery

University of PittsburghPittsburgh, Pennsylvania

Jean-Paul Steib, MDProfessor

Service de Chirurgie du RachisPavillon Chirurgical B

Hôpitaux Universitaires de StrasbourgStrasbourg, France

Archibald von Strempel, MD, DEng, Prof

Landeskrankenhaus FeldkirchOrthopadische AbteilungFeldkirch, Austria

Barry W L Tan, MBBS (Singapore), MRCS (Edinburgh)University Orthopaedics, Hand and ReconstructiveMicrosurgery Cluster

National University HospitalNational University Health SystemSingapore

Chadi Tannoury, MDAssistant ProfessorDepartment of Orthopedic SurgeryBoston University

Boston, Massachusetts

Jason O Toy, MDDepartment of Orthopaedics and RehabilitationYale University School of Medicine

New Haven, Connecticut

Professor of Neurosurgery

Co-Director of the Delaware Valley Spinal Cord Injury Center

Co-Chief Spine Surgery

Co-Director Spine Surgery

Thomas Jefferson University and the Rothman Institute

Philadelphia, Pennsylvania

Andre Van Ooij, MD

Department of Orthopaedic Surgery

University Hospital Maastricht

University Hospital

Maastricht, The Netherlands

Nam Vo, PhD

Assistant Professor

Ferguson Laboratory for Spine Research

Department of Orthopaedic Surgery

University of Pittsburgh Medical Center

Pittsburgh, Pennsylvania

Leonard I Voronov, MD, PhD

Adjunct Instructor

Department of Orthopaedic Surgery and Rehabilitation

Loyola University Chicago

Department of Orthopaedic Surgery and Neurology

University of Pittsburgh School of Medicine

Pittsburgh, Pennsylvania

Michael Y Wang, MD, FACS

Professor

Departments of Neurosurgery and Rehab Medicine

University of Miami Miller School of Medicine

Miami, Florida

Shaobai Wang, PhD

Instructor

Department of Orthopaedic Surgery

Massachusetts General Hospital

Harvard Medical School

National University Health SystemSingapore

Kirkham Wood, MDChief, Spine ServiceAssociate ProfessorDepartment of Orthopaedic SurgeryMassachusetts General HospitalHarvard Medical SchoolBoston, Massachusetts

Do Heum Yoon, MD, PhDProfessor

Department of NeurosurgeryYonsei University College of MedicineSeoul, Republic of Korea

Elizabeth Yu, MDAssistant Professor, Division of Spine SurgeryDepartment of Orthopaedics

The Ohio State University Wexner Medical CenterColumbus, Ohio

Hansen A Yuan, MDProfessor EmeritusDepartment of Orthopedic and NeurosurgerySUNY Upstate Medical Center

Syracuse, New York

James Joseph Yue, MDAssociate ProfessorDepartment of Orthopaedic Surgery and RehabilitationYale School of Medicine

New Haven, Connecticutt

Jack E Zigler, MD, FACS, FAAOSMedical Director

Texas Back InstitutePlano, Texas

James F Zucherman, MDSpine Surgeon

Senior Spine PartnerSan Francisco Orthopaedic Surgeons Medical GroupSan Francisco, California

2 Cervical and Lumbar Disc Replacement 7

3 The Rationale behind Dynamic Posterior

1 Dynamic Stabilization of the Lumbar Spine

Dilip K Sengupta

1.1 Introduction

Stabilization of the spine by way of spontaneous fusion was

observed and recorded by Hippocrates as early as 380 BC

Per-haps motivated by this observation, surgical attempts were

made to achieve fusion of the spine by bone grafting at the

beginning of the last century In 1911 Drs Fred Albee and

Russell A Hibbs, both of whom were in New York City,

indepen-dently provided the first records of spinal fusion in the

litera-ture.1,2 Albee used tibial grafts between spinal processes to

stabilize the spine Hibbs, on the other hand, decorticated the

facet joints and then added morselized bone derived from the

local spinous processes and created a “feathered fusion” (his

own description) He reported three cases of fusion for

progres-sive spinal deformity.1

Although spinal fusion was originally introduced in the

treat-ment of progressive deformity, or infection/tuberculosis, it

became the standard surgical treatment for degenerative back

pain in the mid-20th century and gradually came to be

consid-ered the gold standard of surgical treatment for spine

stabiliza-tion Since the introduction of rigid spinal instrumentation,

suc-cessful fusion has been achieved in more than 90% of cases, but

clinically successful pain relief has never been achieved in more

than 70% of cases This raised questions as to the role of fusion

surgery in the treatment of back pain More importantly,

long-term problems and disadvantages began to emerge after fusion

surgery regardless of the initial success in pain relief One of the

most prevalent concerns following fusion at one or more levels

is the transfer of stress to the adjacent levels, which often

results in accelerated degeneration, other complications, and

more pain.3,4

Nonfusion technology developed as a result of fusion’s failure

to deliver the expected clinical results Dynamic reconstruction

of the spine, synonymous with motion preservation

stabiliza-tion technologies, includes spinal arthroplasty and dynamic

stabilization Arthroplasty devices, by definition, are prosthetic

devices that replace an anatomical segment of the spine, which

can be the disc (total disc replacement [TDR]), the facet joints,

or both Dynamic stabilization devices work in conjunction with

the existing degenerated anatomical segments by load sharing

while preserving motion to the degree possible, with the goal

of pain relief Spinal arthroplasty in the form of TDR was

intro-duced in clinical practice in the mid-20th century, much earlier

than dynamic stabilization The development of this technology

is described in Chapter 2 This chapter reviews the historical

development of dynamic stabilization to provide some

under-standing of its evolution The technology is so rapidly evolving

that by the time of publication it is expected to progress beyond

the description provided here

1.2 Dynamic Stabilization

Dynamic stabilization devices can be divided into to two broad

categories: pedicle screw–based posterior dynamic stabilization

(PDS) systems and interspinous process distraction (IPD)

systems Facet replacement systems are frequently describedunder dynamic stabilization, but they are actually prostheticdevices

One of the earliest dynamic stabilization devices wasdescribed by Henry Graf (▶Fig 1.1) in 19925and was popularlyknown as the Graf ligament (Neoligaments, Leeds, UK) Thismay be considered the first-generation PDS device and formsthe basis of many other devices subsequently introduced Itconsists of braided polypropylene bands that span betweenflanges at the titanium pedicle screw heads, applying a com-pressing force that locks the facet joints The design rationale orthe mechanism of action is found only in Graf’s monograph (inFrench) (▶Fig 1.2), which indicates that his intention was tostop an abnormal vertical translation of the facet joints byapplying compression between the pedicles

The clinical outcome in the short-term follow-up was reported

to be comparable with conventional fusion,6but the long-termoutcome with Graf ligament stabilization has conflicting reports

in the literature The most frequent disadvantage with the Grafligament is narrowing of the exit foramen of the nerve roots,

Fig 1.1 (a) Henry Graf and (b) Graf ligament applied to two segments

in a spine model

Fig 1.2 The French language monograph by Henry Graf describing themechanism of action of the device (Image courtesy of Dr Henry Graf.)

which is reported to cause new-onset radicular symptoms in 25%

of cases.6The Graf ligament is only infrequently used now, and

only in certain parts of the world

A fulcrum-assisted soft stabilization (FASS) system(▶Fig 1.3) was described by Sengupta and Mulholland7as an

improvement over the Graf system to prevent narrowing of the

exit foramen, as well as to unload the corresponding disc The

devices had never been used clinically in any patient

The second generation of PDS device is the Dynesys DynamicStabilization System (▶Fig 1.4a) (Zimmer Spine, Minneapolis,

MN), developed by Gill Dubois (▶Fig 1.4b) The device was first

implanted in Europe in 1994 The design rationale is based on

improvement over the Graf ligament system, preventing

com-pression between the screws by introduction of a plastic

cylin-der placed around the cord to apply a distraction force between

the pedicle screws and thereby preventing the narrowing of the

nerve root exit foramen This is currently the most extensively

used PDS device worldwide.8 The clinical efficacy has been

reported by many authors, but hardware failure, in the form ofscrew loosening or breakage, remains the most frequent dis-advantage of this device.9,10

The third-generation PDS system is the Transition StabilizationSystem (Globus Medical, Inc Audubon, PA) The design is verysimilar to that of the Dynesys but incorporates some changes toaddress the limitations experienced with the Dynesys system

This system uses a regular top-loading pedicle screw, actively ates lordosis, and permits increased pedicle-to-pedicle distanceexcursion by adding a soft bumper at the end The system comespreassembled or can be assembled on the back table and does notrequire in situ tensioning The capability of creating an active lor-dosis is built into the metal spools that connect the soft section ofthe device to the pedicle screws Lordosis ensures unloading ofthe disc The biggest advantage of this system is that it can be used

cre-in a segment adjacent to rigid cre-instrumentation with a regular rod,using the same top-loading screws (▶Fig 1.5)

The three foregoing systems represent nonmetallic PDS tems Many other systems have been developed consisting ofeither all metallic components, in the form of a spring, or hybriddevices with metallic rods and plastic components to allowdevice flexibility A more detailed description of the devicesthat are currently in clinical use is presented in the section ondynamic stabilization

sys-A simple nitinol coil spring design was developed by J Y Park(▶Fig 1.6) in Seoul, South Korea, which has been used as afusion device when used with interbody cages, or stand-alone

as a dynamic stabilization device.11A uniplanar C-shaped nium spring was described as DSS-C (▶Fig 1.7), which has notbeen used clinically, but a further modification of the systemusing an alpha-shaped titanium spring DSS-α has beendescribed by Sengupta and Pimenta, with limited clinical use inSão Paulo.12More recently, a combination of two metallic coilspring devices Stabilimax NZ (Applied Spine Technologies Inc.,New Haven, CT) was described by Panjabi, which is undergoingFood and Drug Administration investigational device exemption(FDA-IDE) clinical trial as a stand-alone dynamic stabilizationdevice.13The design rationale of this device is to specificallylimit the abnormal motion in the neutral zone while preservingthe normal motion in the elastic zone of the range of motion

tita-Fig 1.3 The concept of the fulcrum-assisted soft stabilization (FASS)

system (a) Application of a ligament to the pedicle screws across the

motion segment increases the load at the posterior aspect of the disc

(b) Introduction of a fulcrum in front of the ligaments in the FASS

system may unload the disc

Fig 1.4 (a) The Dynesys system (Zimmer Spine) (b) invented by GillDubois

Fig 1.5 The Transition system (Globus Medical)

The hybrid devices incorporate a metallic rod connected to a

flexible, nonmetallic plastic bumper to allow shock absorption as

well as some degree of movement These devices are simple, can

be used with conventional top-loading pedicle screws, and are

suitable for use in segments adjacent to rigid-rod fixation One

such device, the CD Horizon Agile Dynamic Stabilization Device

(Medtronic Sofamor Danek, Memphis, TN) system, has been

dis-continued for clinical use following early failure during an

FDA-IDE trial A similar hybrid device currently in clinical use is the

NFlex (Synthes, Inc., West Chester, PA, a J&J Company), which

consists of a 6 mm titanium fusion rod connected to a flexible

plastic over a cable The device has been used clinically since late

2006, but no clinical experience has been published.14

The concept of IPD for stabilization of the spine was initially

described in the literature by Minns and Walsh in 1997.15The

inventors never designed any clinically applicable device

Sev-eral IPD devices have been described for clinical application, but

the chronology of their development is difficult to ascertain

because their use has been reported in the literature at a muchlater period The primary goal of IPD devices is to address clau-dication pain from spinal stenosis by holding the motion seg-ment in a flexed position Their use to control spinal motion toaddress axial back pain is debatable

In 1986, one of the first interspinous process implants for bar stabilization was developed It consisted of a titanium inter-spinous spacer and an artificial ligament to prevent dislodgment

lum-of the device.16This was followed by additional design ments that resulted in a second-generation device—the WallisPosterior Dynamic Stabilization System (Zimmer Spine, Minne-apolis, MN) This device consists of a polyether ether ketone(PEEK) spacer, retained between the spinous processes by Dacrontape, which prevents its accidental dislodgment, and at the sametime limits further flexion of the segment.17

improve-Currently, the most frequently used IPD device is the X-StopSpacer (Medtronic, Minneapolis, MN) This is a metallic device(▶Fig 1.8) that distracts the spinous process and holds thesegment into flexion but does not limit further flexion.18TheDevice for Intervertebral Assisted Motion (DIAM) Spinal Stabili-zation System (Medtronic Sofamor Danek, Memphis, TN)consists of an H-shaped polyester-covered, silicone bumper todistract between the spinous processes (▶Fig 1.9) to addresscentral as well as foraminal stenosis and, at the same time,dynamically support the vertebrae by the sutures around thespinous processes, similar to the Wallis device.19A very differ-ent type of IPD device is the Coflex Interlaminar StabilizationDevice (▶Fig 1.10) (Paradigm Spine, LLC, New York, NY), whichconsists of a U-shaped titanium spring device, retained in place

by clamping its wings around the adjacent spinous processes

In contrast to other IPD devices it allows both flexion andextension and does not act as an extension stop.20

The Leeds-Keio artificial ligament (Neoligaments, a division

of Xiros, Leeds, UK) (▶Fig 1.11) was designed as a nonrigidimplant to stop movement in degenerative spondylolisthesis.Mochida et al21 reported that this innovative method usedfabric ligament, originally developed for reconstruction of theanterior cruciate ligament Subsequent studies using thismethod indicated that nonrigid stabilization can produceequally good results as compared with fusion in patients withdegenerative spondylolisthesis

1.3 Summary

Over the last half-century, understanding of the complexitiesand origins of spinal disorders and back pain has advancedremarkably Alongside the influx of new knowledge, surgicalapproaches and devices have also continued to advance to nowinclude spinal arthroplasty and dynamic stabilization, whichrepresent a new era of treatment options The continuing pro-gression of new treatment approaches will depend upon theclinical outcomes of the continuing research studies and efforts

by a multitude of researchers worldwide Because the ment of this new area of technology is still in its infancy, it may

develop-be a considerable amount of time develop-before spinal fusion will nolonger be considered the standard treatment method In theinterim, current research efforts to assess the efficacy of nonfu-sion approaches continue to gain momentum and generateinterest as new technology unfolds in motion preservation

Fig 1.7 (a) DSS-C and (b) DSS-α

Fig 1.6 Dr J Y Park and BioFlex BioFlex Spring Rod System invented

by Kyungwoo Park

Fig 1.10 Coflex interspinous process distraction device (ParadigmSpine) (a) Implant migration is prevented by the clamping of thelateral wings (b) The sagittal view of the Coflex This device isdesigned to be placed between two adjacent spinous processes.

Fig 1.9 Device for Intervertebral Assisted Motion (DIAM) Spinal

Stabilization System (Medtronic) is a silicone “bumper” that is inserted

between the spinous processes

Fig 1.8 An image of the X-Stop depicting theadjustable universal wing, tissue expander, fixedwing, and spacer The universal and fixed wingslimit anterior and lateral migration of thespacer The spacer limits extension of thetreated spinous processes (Images provided byMedtronic, Inc X-Stop, device incorporatestechnology developed by Gary K Michelson,MD.)

Fig 1.11 The Leeds-Keio Tension Band System (Neoligaments) (a)Both upper and lower spinous processes are surrounded with anartificial ligament as a figure eight at the base of each spinous process

(b) The waist of the figure eight is sutured several times at just inferior

to the upper spinous process and just superior to the lower spinousprocess with traction of the artificial ligament This multiple-suturedwaist acts as an interspinous spacer

1.4 References

[1] The classic: the original paper appeared in the New York Medical Journal

93:1013, 1911 I An operation for progressive spinal deformities: a nary report of three cases from the service of the orthopaedic hospital.

prelimi-Clin Orthop Relat Res 1964; 35: 4 –8 [2] Hibbs RA A report of fifty-nine cases of scoliosis treated by the fusion opera-

tion By Russell A Hibbs, 1924 Clin Orthop Relat Res 1988: 4–19 [3] Bao QB, Yuan HA Artificial disc technology Neurosurg Focus 2000; 9: e14

[4] Traynelis VC Spinal arthroplasty Neurosurg Focus 2002; 13: E10

[5] Graf H Lumbar instability: surgical treatment without fusion Rachis 1992;

412: 123 –137 [6] Grevitt MP, Gardner AD, Spilsbury J et al The Graf stabilisation system: early

results in 50 patients Eur Spine J 1995; 4: 169–175, discussion 135 [7] Sengupta DK, Mulholland RC Fulcrum assisted soft stabilization system: a

new concept in the surgical treatment of degenerative low back pain Spine 2005; 30: 1019 –1029, discussion 1030

[8] Stoll TM, Dubois G, Schwarzenbach O The dynamic neutralization system for

the spine: a multi-center study of a novel non-fusion system Eur Spine J 2002; 11 Suppl 2: S170–S178

[9] Grob D, Benini A, Junge A, Mannion AF 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 [10] Schnake KJ, Schaeren S, Jeanneret B Dynamic stabilization in addition to

decompression for lumbar spinal stenosis with degenerative sis Spine 2006; 31: 442–449

spondylolisthe-[11] Park H, Zhang HY, Cho BY, Park JY Change of lumbar motion after

multi-level posterior dynamic stabilization with bioflex system : 1 year follow up.

J Korean Neurosurg Soc 2009; 46: 285 –291 [12] Pimenta L, Diaz R, S.D K., DSS—minimally invasive posterior dynamic stabili-

zation system In: Kim DH, Cammisa FP, Jr, Fessler RG, eds Dynamic Reconstruction of the Spine New York, NY: Thieme; 2006

[13] Yue JJ, Malcolmon G, Timm JP The Stabilimax NZ Posterior Lumbar Dynamic Stabilization System In: Yue JJ, McAfee PC, An, HS, eds Motion Preservation Surgery of the Spine—Advanced Techniques and Controversies Philadelphia, PA: Saunders Elsevier; 2008:476–482

[14] Wallach CJ, Teng AL, Wang JC NFlex In: Yue JJ, McAfee PC, An HS, eds Motion Preservation Surgery of the Spine —Advanced Techniques and Controversies Philadelphia, PA: Saunders Elsevier; 2008:505 –510

[15] Minns RJ, Walsh WK Preliminary design and experimental studies of a novel soft implant for correcting sagittal plane instability in the lumbar spine Spine 1997; 22: 1819–1825, discussion 1826–1827

[16] Senegas J, Etchevers JP, Vital JM, Baulny D, Grenier F Recalibration of the lumbar canal, an alternative to laminectomy in the treatment of lumbar canal stenosis [in French] Rev Chir Orthop Repar Appar Mot 1988; 74: 15–22

[17] Sénégas J Mechanical supplementation by non-rigid fixation in degenerative intervertebral lumbar segments: the Wallis system Eur Spine J 2002; 11 Suppl 2: S164 –S169

[18] Zucherman JF, Hsu KY, Hartjen CA et al A multicenter, prospective, ized trial evaluating the X STOP interspinous process decompression system for the treatment of neurogenic intermittent claudication: two-year follow-

random-up results Spine 2005; 30: 1351–1358 [19] Kim KA, McDonald M, Pik JH, Khoueir P, Wang MY Dynamic intraspinous spacer technology for posterior stabilization: case-control study on the safety, sagittal angulation, and pain outcome at 1-year follow-up evaluation Neurosurg Focus 2007; 22: E7

[20] Kong DS, Kim ES, Eoh W One-year outcome evaluation after interspinous implantation for degenerative spinal stenosis with segmental instability.

J Korean Med Sci 2007; 22: 330 –335 [21] Mochida J, Toh E, Suzuki K, Chiba M, Arima T An innovative method using the Leeds-Keio artificial ligament in the unstable spine Orthopedics 1997; 20: 17–23

2 Cervical and Lumbar Disc Replacement

Do Heum Yoon, Karen M Shibata, Daniel H Kim, and Dilip K Sengupta

2.1 Introduction

Spinal arthroplasty, or artificial disc replacement (ADR), has

increasingly been attracting the attention of spinal surgeons

Spinal arthroplasty is used to relieve pain, restore function of

the degenerated motion segment, and prevent adjacent

seg-ment degeneration.1Intervertebral discs fundamentally serve

to transmit load, preserve motion, and maintain height

Con-ventional surgical treatment for degenerative disc disease is

discectomy or fusion or both Arthrodesis allows load

transmis-sion and restoration of disc height, but it can not provide shock

absorption and segmental motion The long-term problems

associated with spinal arthrodesis include adjacent segment

degeneration (ASD) and donor site morbidity.2,3 Therefore, a

desire to preserve the intervertebral disc itself or its functions

with artificial discs has arisen This chapter explores the history

of spinal arthroplasty and reviews the attributes of momentous

artificial discs

2.2 Spinal Arthroplasty

Spine arthroplasty was first introduced around the advent of

knee and hip arthroplasties Although knee and hip

arthroplas-ties have become the standard treatment of degenerative knee

and hip diseases, replacing knee and hip arthrodesis, spinal

arthroplasty has not been accepted with equivalent status over

fusion The main reason may be in the difference in loss of

func-tion between arthrodesis of the knee/hip versus spinal mofunc-tion

segment Arthrodesis of the knee/hip causes significant loss of

function, and arthroplasty restores it to a nearly normal level

Conversely, spinal motion segments are stacked in the midline

of the skeleton, and loss of function from fusion of one or even

multiple motion segments may largely be compensated by the

neighboring segments The difference in clinical outcome of

spine arthroplasty over fusion is subtle, compared with that in

knee/hip joints In addition, spine arthroplasty raises debate

about the complex anatomy and functions of spinal motion

seg-ments, and surgical difficulties.4–8Total disc replacement

repre-sents only a partial joint replacement in a spinal motion

seg-ment, which is a three joint complex consisting of a disc and a

pair of facet joints Although the intervertebral disc itself is of

utmost importance in providing load bearing and spinal

stabil-ity, the facet joints contribute an important biomechanical role

toward both of these functions Facet joints may be replaced

independently for predominant facet arthropathy A total joint

replacement in a spinal motion segment would require facet

replacement in conjunction with the disc replacement

In general, there are two types of spinal arthroplasty devicesfor intervertebral discs: nucleus replacement (replacing the

nucleus only) and total disc replacement (replacing the entire

disc)

In a nucleus replacement, only the inner portion of the disc(the nucleus) is removed and replaced with an implant

Ongoing research into various designs for replacements has

incorporated the use of metal, ceramic, hydrogel, elastic coils,

and other similar materials Another promising replacementdesign consists of injectable polymers that are cured in situ toform a nucleus prosthesis, which has the desirable element ofdelivery via a minimally invasive, outpatient procedure In com-parison with total disc replacement, the primary advantage tothis option is that it preserves the annulus and end plates whilereplacing only the defective portion of the nucleus.9

In a total disc replacement procedure, all or most of the disctissue is removed and an entirely new device is implanted intothe space between the vertebra The many designs being stud-ied for artificial discs incorporate metal, polyethylene, poly-urethane, and other biomaterials or combinations of materials

The most commonly used design incorporates two plates thatare anchored to the top and bottom surfaces of the vertebrae,above and below the disc being replaced, along with some type

of compressible, pliable piece between the plates A total discreplacement is used when all elements must be removed,including the nucleus and annulus, to remove the pain and treatthe defective area.10

2.3 Nucleus Replacement

In the late 1950s, initial attempts at replacing the nucleus posus space involved implanting polymethyl methacrylate(PMMA), silicone, or stainless steel ball bearings.11,12,13 Fern-ström attempted to preserve motion by inserting stainless steelball bearings into the intervertebral disc space areas of the cer-vical and lumbar spine in an effort to reproduce the “ball joint”

pul-mechanism of the disc.13 Unfortunately, the results were notvery promising McKenzie also published preliminary and long-term clinical study reports of this device reporting reasonablygood results; however, its use has been discontinued because ofconcerns regarding subsidence and migration.14,15During thissame period, Nachemson16performed biomechanical testing todemonstrate the relative restoration of some disc properties byinjecting self-hardening silicone rubber into cadaver discs Healso tried silicone testicular prostheses but found that theimplants rapidly dissolved after 20 to 30 thousand cycles ofwalking load.12,16,17Similarly, Hamby and Glaser tried injectingPMMA into the disc, which resulted in flow control problems.11

In 1973, Urbaniak et al used an injectable mixed silicone/

Dacron device in nonhuman primates and reported boneresorption along with aberrant bone formation.18 In 1974,Schneider and Oyen performed experimental work on siliconenucleus replacement that was similar to Nachemson’s work inthe 1960s.19In an effort to replicate the natural properties ofthe nucleus, in 1975 Froning developed a discoid device with acentral, collapsible bladder to be fixated to the vertebrae with aspike.20 In 1977, Roy-Camille et al tried to contain medical-grade silicone in a latex bag while injecting it into a humancadaveric disc.21

Fassio and Ginestié designed and patented an elastic disc thathad a Silastic central sphere and was bordered by a lateral pla-teau in an uncompressible synthetic resin.22They subsequentlyreported the first clinical study of the silicone nucleus using a

monkey model, followed by human implantation into three

patients in 1977 Follow-up reports showed a marked disc

nar-rowing and absence of motion in all patients because the device

had subsided and migrated into the vertebral body of all

patients.23 Later, Horst improved the design of the device,

which had better positive locking and more uniform stress

distribution.24

In the early 1980s, research efforts continued Hou conducted

biomechanical and animal studies in a monkey model and

sub-sequently implanted a silicone prosthesis in more than 30

patients.25The results from this study were not published In

1981, Edeland suggested that the principle of

hydrophilic-hydroelastic intervertebral interposium be used as a nucleus

replacement after discectomy surgery He described a disc

con-taining a hygroscopic agent, which would be used to expand

the disc after introduction.26 In 1982, a nucleus replacement

device was developed and patented by Kunze.27He designed a

fish-shaped device with a fin-type tail with transverse grooves

to provide a friction fit in concert with the broadened tail

Research into reproducing both the mechanical and the

phys-iological properties of the nucleus was accomplished by Bao

and Highman, who subsequently developed a hydrogel

inter-vertebral nucleus that contained ~70% water content under

physiological loading conditions Similar to natural nucleus

material, the hydrogel contained the required mechanical

prop-erties and the ability to absorb and release water with changes

in the applied load Biomechanical studies have confirmed the

restoration of disc anatomy after the implantation of this

device.28,29

In 1988, Ray developed a nucleus replacement composed of

dual-threaded cylinders with an ingrowth fiber capsule, an

injectable thixotropic gel that would swell from a collapsed

state.30 However, technical problems in manufacturing and

development led to concept changes Subsequently, in 1990,

Ray developed the Prosthetic Nucleus Device (PDN) (Raymedica,

Inc., Bloomington, MN), which consisted of a hydrogel core

enclosed in a woven polyethylene jacket resembling a pillow31,32

(▶Fig 2.1) The hydrogel contained hydrophilic properties to

imitate the behavior of the nucleus pulposus After several device

migrations, additional design modifications were made.33

2.3.1 Recent Developments

The PDN device marked a new era in the development of

nucleus replacement devices Since 1996, the device has

experi-enced widespread use in humans, with more than 4,000

patients implanted internationally to date (with the PDN or the

most recent PDN-SOLO device, Raymedica).34 Clinical results

from the beginning have been encouraging.35The first 10 PDN

devices implanted in Germany in 1996 reported only one

extru-sion By 2002, there were 480 procedures recorded with a

removal rate of 5%.36 The most recently updated version, the

single PDN-SOLO device, shows considerable improvement over

the initial paired PDN devices, and its methods of implantation

have had good to excellent results.34

Newcleus (Centerpulse Spine-Tech, Minneapolis, MN),

another nucleus replacement device implanted into humans, is

a stand-alone device made of polycarbonate urethane curled

into a preformed spiral and inserted via an open technique This

device was implanted in five patients in a pilot study.37The

fol-low-up reports indicated no failures, migration, or plications, and retained disc motion was documented on plainX-rays with facet function monitored using a computed tomo-graphic scan.38,39

com-The Aquarelle (Stryker Spine, Allendale, NJ) is another gel-based nuclear replacement that is composed of a polyvinylalcohol, which is hydrated to a physiological water content of ~80% prior to implantation.18,40 Once it reaches physiologicalequilibrium, the implant expands and contracts freely in situ.Testing indicated that extrusion occurred during in vitro testingonly under loads well in excess of those expected in vivo.41

hydro-The NeuDisc SNI Hydrogel Polymer (Replication Medical, Inc.,Cranbury, NJ) has recently been reported as a hydrogel thatimbibes water and expands preferentially in the axial direc-tion42(▶Fig 2.2)

The Prosthetic Intervertebral Nucleus (PIN) (Raymedica, Inc.,Bloomington, MN) is an in situ curable polyurethane that isinjected into a balloon catheter delivery system.43The curableprotein hydrogel cures within minutes in the disc space, afterwhich the catheter is removed

The BioDisc Nucleus Pulposus Replacement (CryoLife, Inc.,Kennesaw, GA) is an injectable protein hydrogel device based

on CryoLife’s surgical adhesive product Early bench workfatigue testing at 10 million cycles indicated a 10% loss of discheight, which later recovers.39

The Injectable Disc Nucleus (IDN) (Spine Wave, Inc., Shelton,CT), is a hydrogel composed of synthetic silk-elastic copolymerproduced through DNA bacterial synthesis fermentation, whichcures within a few minutes Early test results indicate that discheight is restored under load, and the material resisted extru-sion during cadaveric mechanical testing.39

The DASCOR Disc Arthroplasty System (Disc Dynamics, EdenPrairie, MN) is an injectable cool polyurethane polymer thatcures in situ within 12 to 15 minutes using a balloon that cre-ates space in the disc for the delivered material9(▶Fig 2.3)

Fig 2.1 Photograph of the PDN-SOLO implant (Raymedica) showingthe internal copolymeric pellet (lower figure) and the intact implantwith its woven jacket of high molecular weight polyethylene (HMWPE).The arrows at the ends of the pellet indicate the internal location of theX-ray visible Pt-Ir wire stubs

There are numerous other studies under way, with newresearch efforts that will undoubtedly continue into the future.

Among these are a one-piece ceramic or metal implant that

anchors to the inferior vertebral body as a hemiarthroplasty

(being developed by Interpore Cross International, Irvine, CA); a

hydrogel memory coiling material that imbibes fluid to restore

disc height (by Mathys Medical in Bettlach, Switzerland); and a

chemonucleolysis product to identify a formulation and dose to

initiate the regeneration process of the nucleus pulposus (by

NuVasive, Inc., San Diego, CA)

2.4 Total Disc Replacement

Total disc replacements can generally be categorized into two

types: lumbar and cervical

2.4.1 Lumbar Total Disc Replacement

Although initial efforts by Fernström in the late 1950s were not

promising, much has been learned since then During the

1980s, renewed interest in spinal arthroplasty brought about a

flood of studies and research efforts Steffee, who had been

involved in designing artificial discs since the mid-1970s, made

substantial advancements with the development of a

high-density polyethylene (PE)/CoCr prosthesis This led to the

devel-opment of the AcroFlex device (DePuy Spine, Raynham, MA) in

the mid-1980s, which was composed of a polyolefin-based

rub-ber core sandwiched between titanium end plates and was

subsequently used in six patients between 1988 and 1989.44

However, because of disintegration of the rubber core in the

preliminary clinical trials, further efforts were suspended

In the 1990s, Steffee developed the second-generation sion of the AcroFlex (DePuy Spine) that was similar to the first,

ver-except that now it consisted of silicone instead of rubber.45,46,47

A 3-year follow-up published in 1993 on six patients who wereimplanted with the device indicated average results.44,48 Animproved design using HP-100 silicone elastomer developed bySteffee et al resulted in the third-generation AcroFlex artificialdisc.49,50However, after the first 40 implantations, the elasto-mer developed minor defects in several cases, which were evi-dent in a computed tomographic scan after 1 to 2 years Simi-larly, later animal studies also indicated poor maintenance ofsagittal and lateral flexion ranges of motion.51

A significant advancement in total disc replacement deviceswas made with the development of the SB Charité (DePuySpine) prosthesis, which was designed by Schellnac and Bütt-ner-Janz in 1982 and first implanted by Zippel in 1984 (Formore details, see related chapter in this book.) The sliding core

of this device consisted of ultra-high-molecular weight ethylene (UHMWPE) interposed between metallic end plates

poly-However, there were problems with migration and metalfatigue, which led to a second-generation (SB Charité II) devicethat featured flat extensions on both sides of the end plates

Although this version was an improvement over the previousdevice, fatigue fractures still led to early failures Then a thirdand current version (SB Charité III; DePuy Spine) of the devicewas developed in 1987, which featured broader, flat end plates(▶Fig 2.4) Numerous studies worldwide since 1987 have indi-cated encouraging and promising results.52 Among these areGriffith et al in 1994,53Lemaire et al in 1997,54Cinotti et al in

1996,55 Zeegers et al in 1999,56 McAfee et al in 2003,57 andDavid in 2005.58The SB Charité III is currently the most widelyimplanted total disc replacement system, with more than 7,000implants worldwide.38,55,59,60

The ProDisc (Aesculap AG & Co., Tuttlingen, Germany), a totaldisc replacement device developed by Marnay61 in the late1980s, consisted of two cobalt-chromium-molybdenum(CoCrMo) alloy end plates coated with a titanium Plasma-poresurface to improve osteointegration (▶Fig 2.5) Unlike the free-

Fig 2.3 DASCOR Disc Arthroplasty Nucleus Replacement Device (DiscDynamics) shown in a spine model The in situ curable polymer isinjected into a polyurethane balloon placed in the disc space Theballoon expands to fill any void that has been created during thediscectomy The polymer cures in a matter of minutes from a liquid to

a firm but pliable state

Fig 2.2 Flexion and extension motions about the major axis of the

NeuDisc (Replication Medical) were performed to a simulated life of

10 years Three of the flexion-extension samples were removed from

endurance testing to be evaluated against controls The remaining

three samples proceeded to lateral bending testing The three

flexion-extension endurance samples removed for evaluation showed

no signs of delaminations, tears, cracks, or major surface defects

All three samples had small wear lines oriented radially from the

major axis

floating core of the SB Charité III, the ProDisc implant relied on

a single articulating interface between the core fixed to the

inferior end plate and the superior metallic end plate Initially,

Marnay implanted the device into 64 patients between 1990

and 1993 In 1999, a long-term follow-up study indicated

promising results.62After several design modifications, the

sec-ond-generation design, the ProDisc II (Aesculap AG & Co.) was

released in Europe in 1999 Favorable results were also reported

by Mayer et al and Bertagnoli and Kumar on this improved

device, which was implanted into 108 patients.63,64In 2001, the

FDA allowed the first ProDisc implantations under an

investiga-tional device exemption (IDE) In early 2003, Synthes-Stratec,

Inc (Oberdorf, Switzerland) acquired ProDisc Recent studies

continue to show positive results using this disc.65

The Maverick artificial disc (Medtronic Sofamor Danek,

Mem-phis, TN) is a two-piece metal-on-metal design utilizing a

pol-ished, CoCrMo ball and socket that incorporates a more

poste-rior center of rotation (▶Fig 2.6) It was first clinically used in

January 2002, and early clinical results are encouraging.66,67

Maverick FDA multicenter has completed its randomized

por-tion of the study and is now in the continued access mode of

the FDA approval process clinical trials, which began in the

United States in May 2003 and span a 2-year follow-up period

on the enrolled patients

The FlexiCore (Stryker Spine, Kalamazoo, MI) intervertebral

disc replacement device is another metal-on-metal design that

is inserted as a single unit (▶Fig 2.7) The dome-shaped endplates are shaped to approximate the concavities of the verte-bral body end plates and can be inserted via multiple angles.68

U.S clinical trials through an IDE granted by the FDA for thisdevice began in August 2003 with a 2-year follow-up period.The randomized study has been completed and is currently incontinued access mode

The Theken eDISC (Theken Disc, Akron, OH) is one of themost recently developed artificial discs (▶Fig 2.8) The eDISC isconstructed using proprietary Theken-developed polymer,which is an elastomeric polymer specifically tailored to with-stand the loads and motions of the lumbar spine It has a micro-electronics module and integral sensors that allow the disc tocollect data on the motions and loads experienced by theimplant The data are used to monitor patient rehabilitation,improve surgical placement, and assist in detecting autofusion.The microelectronics module monitors any dynamic high-loadevents that may take place; it immediately warns the patient ofthe high load by sending a wireless signal to a belt-worn audi-ble alarm.69However, there is as yet no paper reporting theclinical and radiological outcome with this innovative implant

Fig 2.4 Charité Artificial Disc (DePuy Spine)

Fig 2.5 ProDisc-C cervical prosthesis is a semiconstrained, socket design with fixed axis of rotation It consists of two forgedcobalt-chromium-molybdenum (CoCrMo) alloy end plates and an ultrahigh-molecular-weight polyethylene inlay element, which is fixed tothe inferior prosthetic end plate The metal end plates have twovertical fins for immediate fixation in the end plates and are plasmasprayed with titanium for long-term fixation through osseointegration.(Courtesy of DePuy Synthes Spine ProDisc-C is a trademark of DePuySynthes Spine.)

ball-and-Fig 2.6 (a) Maverick Total Disc Arthroplasty two-piece ball-and-joint

prosthesis and (b) Maverick metal-on-metal end plates

(cobalt-chromium-molybdenum alloy) (Images provided by Medtronic, Inc

Maverick device incorporates technology developed by Gary K

Michelson, MD.) Fig 2.7 FlexiCore Intervertebral Disc (Stryker) (anterior view lordosed)

2.4.2 Cervical Total Disc Replacement

Subsequent to the first cervical disc arthroplasty attempt using

Fernström’s ball implantations during the 1950s, similar

attempts were made by McKenzie beginning in 1969 (using

Fernström balls) and by Harmon in 1957 (using Vitallium

spheres).14,70Reitz and Joubert, from South Africa, also reported

use of the Fernström prostheses for the treatment of intractable

headaches and cervicobrachialgia, although no long-term

fol-low-up is available.71

The next major advancement in cervical disc devices wasmade in 1989 by Cummins in Bristol, England, at Frenchay Hos-

pital The device, known today as the Prestige Cervical Disc

(Medtronic, Minneapolis, MN), was initially constructed of

stainless steel and secured to the vertebral bodies with solid

screws It allowed unconstrained motion across the segments

(▶Fig 2.9)

Initial clinical trials implanted this new prosthesis in 20patients between 1991 and 1996, and the results were promis-

ing and encouraging.72The original Bristol/Cummins disc was

modified in 1998 into the second-generation design, the tige I (Medtronic Sofamor Danek, Memphis, TN), which wasdesigned to allow more physiological cervical motion thatwould otherwise be restrained by the facet joints and surround-ing tissues A 2-year follow-up study on 15 patients continues

Pres-to show promise because cervical motion across the implantedsite was preserved in all patients but one.73In 1999, the Pres-tige II (Medtronic Sofamor Danek, Memphis, TN) was devel-oped, which featured a more anatomical end plate design Sub-sequent clinical studies continued to show improved andencouraging results.74In 2002, further modifications led to thecurrent design, the Prestige ST disc (Medtronic Sofamor Danek,Memphis, TN)

In 1999, Pointillart developed and implanted a spacer-typeartificial disc However, 8 of the 10 patients who received theimplant had spontaneous fusions after 2 years, and efforts weresubsequently discontinued.75Similarly in 1999, Ramadan beganimplantation of the Cervidisc (Scient’x, Guyancourt, France),which consisted of titanium end plates bearing zirconia ceramicgliding surfaces (▶Fig 2.10) (For more details on the Cervidisc,see related chapter in this book.)

The Bryan Cervical Disc (Medtronic Sofamor Danek, phis, TN) is a one-piece composite-type metal-on-polymerdevice composed of a wear-resistant, elastic polymer nucleuswith a fully variable instantaneous axis of rotation that is not

Mem-Fig 2.8 The Theken eDisc

Fig 2.9 (a) Prestige II and (b) Prestige LP (Images provided byMedtronic, Inc Prestige device incorporates technology developed byGary K Michelson, MD.)

Fig 2.10 The Cervidisc (Alphatec) is made of aceramic mobile interface surrounded by titanium,zirconium, and a hydroxyapatite coating

dependent on supplemental fixation75(▶Fig 2.11) This device,

developed in the late 1990s, has undergone considerable

research and numerous studies worldwide with satisfactory to

promising results.76–82 In 2002, clinical trials began in the

United States under an IDE regulated by the U.S FDA (For more

details on the Bryan disc, see related chapter in this book.)

The Porous Coated Motion (PCM) cervical disc (Cervitech,

Inc., Rockaway, NJ), originally developed by Dr McAfee, features

a unique large layer radius UHMWPE bearing surface attached

to the lower end plate that allows translational motion in an arc

consistent with the natural motion of the cervical spine

seg-ment83(▶Fig 2.12) Human implantations were first performed

in December 2002 in São Paulo, Brazil.84The results from a pilot

study reported in 2004 indicated promising results.83Clinical

trials in the United States are expected to begin soon (For more

details, see related chapter in this book.)

The ProDisc-C (Synthes, Inc., West Chester, PA), the cervicalversion designed based on the lumbar ProDisc (Aesculap), is anarticulating disc with a PE core and metal end plates sprayedwith titanium and two vertical fins for fixation in the end plate-

s Although research is still ongoing, initial investigative reportsare encouraging.85,86 The first implantation in a human tookplace in December 2002,87and clinical trials in the United Statesare in progress

The M6-C Artificial Cervical Disc (Spinal Kinetics, Inc., vale, CA) (▶Fig 2.13) is distinct from other joints like the knee

Sunny-or hip in terms of complex, coupled motions requiring sixdegrees of freedom.88The M6-C Artificial Cervical Disc closelymimics the anatomical, physiological, and biomechanical char-acteristics of the intervertebral disc of the human cervicalspine It consists of a compressible artificial nucleus manufac-tured with polycarbonate urethane and a woven fiber annulusmanufactured with PE The unique design closely replicatesthe motion characteristics of a native intervertebral disc It pro-vides compressive capabilities along with a controlled range ofnatural motion in all six degrees of freedom The M6-C has twotitanium outer plates coated with a titanium plasma spraywith keels for anchoring the disc into the bone of the vertebralbody Reyes-Sánchez et al89reported clinical and radiographicoutcomes for 25 patients implanted with the M6-C ArtificialCervical Disc The NDI, arm pain, neck pain, and Short Form(SF)-36 scores showed 46%, 43%, 51%, and 26% improvements at

24 months, respectively The ROM returned to pretreatmentlevel by 24 months.89

The Mobi-C Cervical Disc (LDR USA, Austin, TX) are composed

of two titanium shells with a PE(PE insert The implant is

a metal-on-polymer articulating device With lateral retaining teeth, the implant is designed for optimal anchorageand stability The inclined shape of the teeth favors the intro-duction of the implant and ensures a reliable anchorage on thesolid parts of the vertebral plates The self-centering mobileinsert favors the instantaneous rotation centers and allows nat-ural physiological movement back to the treated intervertebralsegment with respect to the cervical lordosis The mobility ofthe insert decreases the transmission of the constraints on thebone–implant interface and reduces the constraints of the pos-terior facet joints Kim et al reported successful clinical andradiological results in 23 patients with the Mobi-C ADR.90The

self-Fig 2.12 Porous Coated Motion (PCM) Artificial Disc (Courtesy of

NuVasive, Inc.)

Fig 2.13 The Spinal Kinetics Cervical Disc’s core construct is made of

an elastomeric material surrounded by a redundant polymer fiberconstruct

Fig 2.11 The Bryan disc device has porous titanium end plates that

promote bony ingrowth Device diameters range from 14 to 18 mm

with one height The metal tabs on the right side of the figure attach to

the insertion instrument and also eliminate the risk of device migration

into the central canal (Images provided by Medtronic, Inc Bryan

device incorporates technology developed by Gary K Michelson, MD.)

VAS for neck pain significantly decreased from 6.5 to 1.4 at

6-month follow-up, and the VAS for radiculopathy decreased

from 6.7 to 0 points at the last follow-up They also reported

radiological success, including preservation of motion from C2

to C7 (preoperatively 56.3 degrees, postoperatively 52.6

degrees), segmental range of motion (ROM) (preoperatively

10.6 degrees, postoperatively 14.6 degrees) and adjacent

seg-ment motion (97% at 6-month follow-up compared with the

preoperative value) Park et al reported intermediate follow-up

of 75 patients undergoing cervical total disc replacement (TDR)

(TDR.91According to Odom criteria, this represented an overall

success rate of 86.7%, although with a trend toward reduction

in alignment and motion at 24 months postoperatively The

superior outcome of hybrid surgery consisting of a cerviccal

artificial disc replacement (C-ADR) using the Mobi-C disc with

ACDF compared with two-level ACDF was demonstrated by

Shin et al.92

2.5 FDA Approval Status

Although lumbar ADR was introduced as early as the 1950s,only two devices (Charité and ProDisc-L) have been approved

by the FDA The Charité (DePuy Spine) and ProDisc-L (Synthes)discs are indicated for spinal arthroplasty in skeletally maturepatients with single-level degenerative disc disease (DDD),defined as discogenic back pain confirmed by clinical historyand radiographic studies The Charité is approved for use inlevels L4–S1, and the ProDisc-L is approved for use in levelsL3–S1 Other lumbar devices are currently under investigation

in the United States, including the FlexiCore (Stryker Spine,Allendale, NJ), Maverick (Medtronic Sofamor Danek, Memphis,TN), Theken eDisc (Theken Disc, Akron, OH), Mobidisc (LDRUSA, Austin, TX), Activ-L (Aesculap, Center Valley, PA), andKineflex (SpinalMotion, Inc., Mountain View, CA) devices(▶Table 2.1) The Prestige received the FDA PMA approval as a

Table 2.1 Summary of lumbar artificial discs

Device Manufacturer Classification Biomechanics FDA approval Biomaterials

MN Unconstrained Polymer Hydrogel pelletencased in a

polyethylene jacket

MA Unconstrained Metal on polymer Oct 26, 2004 CoCrMo end plateswith UHMWPE core

ProDisc-L Synthes, West Chester,

PA Courtesy of DePuySynthes Spine; ProDisc-L

is a trademark of DePuySynthes Spine

Semiconstrained Metal on polymer Aug 14, 2006 CoCrMo end plates

with UHMWPE core

MA Unconstrained Metal on polymer Titanium end plateswith a polyolefin

rubber core

(continued on page 14)

Table 2.1 Summary of lumbar artificial discs (continued)

Device Manufacturer Classification Biomechanics FDA approval Biomaterials

Maverick Medtronic, Memphis, TN Semiconstrained Metal on metal CoCrMo

Theken eDisc Theken Disc, Akron, OH Unconstrained Metal on polymer Titanium end plates

with developedelastomer

LDR USA, Austin, TX Unconstrained Metal on polymer CoCrMo end plateswith UHMWPE core

Aesculap, Inc., CenterValley, PA

Semiconstrained Metal on polymer CoCrMo end plates

with UHMWPE core

Mountain View, CA Unconstrained Metal on metal CoCrMo

Abbreviations: CCM, cobalt chrome molybdenum; UHMWPE, ultra-high-molecular weight polyethylene

Class III device on July 16, 2007 The Prestige is indicated in

skeletally mature patients for reconstruction of the disc from

C3 to C7 following single-level discectomy The device is

implanted via an open anterior approach Intractable

radicul-opathy and/or myelradicul-opathy should be present, with at least

one of the following items producing symptomatic nerve

root and/or spinal cord compression as documented by

patient history and radiographic studies: herniated disc and/

or osteophyte formation The FDA has required the Prestige

disc manufacturer (Medtronic) to conduct a 7-year

postap-proval clinical study and a 5-year enhanced surveillance study

The ProDisc-C received FDA PMA approval in December 2007

The FDA approval of ProDisc-C is contingent on 7-year

follow-up of the 209 subjects included in the noninferiority trial,

7-year follow-up on 99 continued access subjects, and a 5-year

enhanced surveillance study to more fully characterize

adverse events The Bryan disc was approved by the FDA in

May 2009 for treatment of single-level cervical DDD defined

as any combination of the following: disc herniation with iculopathy, spondylotic radiculopathy, disc herniation withmyelopathy, or spondylotic myelopathy resulting in impairedfunction and at least one clinical neurological sign associatedwith the cervical level to be treated, and necessitating surgery

rad-as demonstrated using radiographic studies The FDA requiredthe manufacturer (Medtronic) to extend its follow-up ofenrolled subjects to 10 years after surgery In addition, themanufacturer must perform a 5-year enhanced surveillancestudy to characterize adverse events more fully A number ofother cervical devices are under study in FDA IDE trials in theUnited States, including Activ-C (Aesculap, Center Valley, PA),Discocerv (Scient’x, Carlsbad, CA), Discover Cervical Arthro-plasty Disc Replacement System (DePuy Spine, Inc., Raynham,MA), Kineflex-C (SpinalMotion, Inc., Mountain View, CA),CerviCore (Stryker Spine, Allendale, NJ), NeoDisc (NuVasive,San Diego, CA), and Secure-C (Globus Medical, Audubon, PA)devices (▶Table 2.2)

Table 2.2 Summary of cervical artificial discs

Device Manufacturer Classification Biomechanics FDA approval Biomaterials

Prestige LP Medtronic, Memphis, TN Unconstrained Metal on metal July 16, 2007 Titanium ceramic

composites

Bryan Medtronic, Memphis, TN Unconstrained Metal on polymer May 12, 2009 Titanium alloy shells

with polyurethanenucleus withpolyurethane core

PCM NuVasive, San Diego, CA Semiconstrained Metal on polymer CoCrMo end plates

with UHMWPE core

Chester PA Courtesy ofDePuy Synthes Spine;

ProDisc-C is a trademark

of DePuy Synthes Spine

Semiconstrained Metal on polymer Dec 17, 2007 CoCrMo end plates

with UHMWPE core

Table 2.2 Summary of cervical artificial discs (continued)

Device Manufacturer Classification Biomechanics FDA approval Biomaterials

CA Unconstrained Metal on polymer Titanium alloy shellswith polycarbonate

urethane and awoven polyethyleneannulus

USA, Austin, TX Semiconstrained Metal on polymer Titanium alloy endplates with

UHMWPE core

Aescu-lap, Inc., Center Valley, PA Semiconstrained Metal on polymer CoCrMo end plateswith UHMWPE core

Discocerv Scient’x, Carlsbad, CA

Not FDA approved for sale

in the United States

Semiconstrained Ceramic on

ceramic Titanium alloy endplates with ceramic

bearings

MA Courtesy of DePuySynthes Spine; DiscoverDisc is a trademark ofDePuy Synthes Spine and

is not available in theUnited States

Semiconstrained Metal on polymer Titanium alloy end

plates withUHMWPE core