Proceedings of the NASS 20th Annual Meeting / The Spine Journal 5 (2005) 1S–189S 75S

their only contraindication. Facet arthrosis was documented on imagingreports and/or OR notes in 94/100. Reduced extension was present in 82/85 charts that documented ROM. Facet blocks were performed in 12/100.CONCLUSIONS: Our findings mount a significant challenge to the ex-isting widespread belief that TDA represents an alternative procedure forthe average patient presently undergoing spinal fusion. Both our study andCammisa’s indicate that all lumbar fusion patients in our two institutionshave at least one contraindication to TDA. The average fusion patientdoes not appear to have isolated discogenic pain. Our 12 patients combining1) facet arthrosis, 2) clinically limited painful extension and 3) facet blocksconstitute a group clearly unsuited for TDA. Patients having limited ROMplus facet arthrosis seems controversial. The appropriateness of TDAin patients with arthrosis incidentally noted on imaging or OR reportsis very unclear. The point where facet arthrosis definitely constitutes acontradiction to TDA will require analysis during long-term arthroplastyfollow-up studies. Suitable patients for TDA may not represent a significantcohort presently undergoing lumbar fusion.DISCLOSURES: FDA device/drug: OP-1 Bone Morphogenic Protein.Status: Investigational/not approved. FDA device/drug: Trios Pedicle ScrewInstrumentation. Status: Approved for this indication. FDA device/drug:Stryker OPUS implant system. Status: Approved for this indication.CONFLICT OF INTEREST: Authors (DW, AK) Consultant: Stryker;Author (DW) Speaker’s Bureau Member: Stryker; Author (DW) GrantResearch Support: Stryker, Zimmer, DePuy, Archus; Authors (BA, TB, SDJ)Grant Research Support: Stryker Biotech, Zimmer; Author (TB) Stockholder:Stryker, Zimmer; Authors (AK, SJ) Grant Research Support: Zimmer.

doi: 10.1016/j.spinee.2005.05.146

9:43145. The fate of the facet joints after lumbar total disc replacement:a clinical and MRI studyFrank Phillips, MD1, Roberto Diaz, MD2, Luiz Pimenta, MD2; 1RushUniversity Medical Center, Chicago, IL, USA; 2Santa Rita Hospital,Sao Paulo, Brazil

BACKGROUND CONTEXT: With aging, both the intervertebral discand facet joint undergo progressive degeneration, which may become pain-ful. Total disc replacement (TDR) is proposed for treatment of discogenicpain in patients with relatively preserved facet joints. To our knowledgeno study has correlated facet degenerative changes with results of TDRand monitored the fate of the facet joints after TDR.PURPOSE: To assess the influence of the facet joints on outcome afterCharite TDR. Changes in facet joints over time after TDR were assessed.A scale for grading facet degeneration in the context of TDR is proposed.STUDY DESIGN/SETTING: Prospective clinical and MRI study.PATIENT SAMPLE: 16 consecutive patients undergoing Charite lumbartotal disc replacement had preoperative and 2-year postoperative lumbarMRI studies.OUTCOME MEASURES: Clinical outcome was measured using VASand Oswestry disability scale. Facet joint degenerative changes were graded(Table 1).

Table 1Facet joint grading

Grade Description

Grade I (normal) Normal facet jointGrade II (Early degeneration) Subtle facet joint narrowing with

widening articular surfaceGrade III (Moderate degeneration) Facet joint narrowing,

osteophytes with increased axialdimension of the facet joint

Grade IV (Ankylosis) Loss of joint space, facethypertrophy, degenerativechanges of the spine posterior arc

METHODS: 16 patients underwent Charite TDR between L3-4 and L5-S1 and were followed clinically and with MRIs at 2 years post surgery.Facet joint degenerative changes were graded on MRI preoperatively andat 2 years postoperatively.RESULTS: 16 patients (5 female, 11 male) had Charite TDR for symptom-atic DDD (8), failed discectomy (4), transition syndrome (2) and failedPDN procedures (2). Mean patient age was 44 yrs (range: 33–56). Atbaseline 2 patients had Grade I facet changes, 10 had Grade II, and 4 hadGrade III changes. No correlation between age, preoperative pain scores,anatomic level or clinical outcome and preoperative facet Grade was noted.Both patients with Grade I (normal) facets preoperatively, progressed toGrade II at 2 yrs. Of the 10 patients with Grade II facet changes preopera-tively, 6 remained at Grade II and 4 progressed to Grade III over 2 yrs.Of the 4 patients with Grade III preoperative facet changes, 3 did notprogress and 1 progressed to Grade IV. Overall 7/16 (44%) patients hadprogression of facet degeneration by one Grade in the 2 yrs. after TDR.Those patients who progressed from Grade II to Grade III facet degenerationhad mean 2 yr. pain VAS of 3.8 compared with a VAS of 1.3 in thosepatients without progression of facet degeneration.CONCLUSIONS: As TDR becomes more widely adopted; the significanceof the facet joints in terms of both patient selection and clinical outcome willrequire further study. Our data suggests that almost half of the patientstreated with Charite TDR had progressive facet changes as documentedon MRI over 2 yrs. In addition, the data suggests that patients with progres-sion of facet degeneration may have a less-satisfactory clinical outcome.As the facet joints undergo progressive degeneration in the presence of anartificially replaced disc, it is likely the resulting loads and biomechanicsof the disc prosthesis will change over time.DISCLOSURES: FDA device/drug: Charite lumbar TDR. Status: Ap-proved for this indication.CONFLICT OF INTEREST: Author (LP) Consultant: Johnson andJohnson; Author (LP) Speaker’s Bureau Member: Johnson and Johnson.

doi: 10.1016/j.spinee.2005.05.147

Friday. September 30, 200510:02–10:20 AM

2005 Outstanding Paper Award

10:02OPA1. Response of Charite total disc replacement underphysiologic loads: prosthesis component motion patternsPatrick O’Leary, MD*†; Michael Nicolakis, MD§; Mark A. Lorenz,MD*†; Leonard I. Voronov, MD*†; Michael R. Zindrick, MD*†;Alexander Ghanayem, MD*†; Robert M. Havey, BS*†;Gerard Carandang, MS*; Mark Sartori, BS*†; Ioannis N. Gaitanis,MD*†, Stanley Fronczak, MD*; and Avinash G. Patwardhan, PhD*†;*Musculoskeletal Biomechanics Laboratory, Department of VeteransAffairs, Edward Hines Jr. VA Hospital, Hines, Illinois; †Department ofOrthopaedic Surgery and Rehabilitation, Loyola University MedicalCenter, Maywood, Illinois; §Evangelisches Krankenhaus Wien, Vienna,Austria

BACKGROUND CONTEXT: Total disc replacement (TDR) has beenrecommended to reduce pain of presumed discogenic origin while preserv-ing spinal motion. The floating core of Charite TDR is professed to allowthe replication of the kinematics of a healthy disc under physiologic loads.While segmental motion after Charite TDR has been measured, littleis known about the effects of a physiologic compressive preload on vertebralmotion and the motion of prosthesis components after TDR.PURPOSE: (1) Does Charite TDR allow restoration of normal load-displacement behavior of a lumbar motion segment under physiologic loads?(2) How do the prosthesis components move relative to each other underphysiologic loads when implanted in a lumbar motion segment?

Proceedings of the NASS 20th Annual Meeting / The Spine Journal 5 (2005) 1S–189S76S

(Bryan Cervical Disc–MedtronicSofamorDanek, Memphis, TN) with anunconstrained (over normal range of motion) biconvex nucleus can beassociated with postoperative segmental kyphosis.PURPOSE: To quantitate the degree of postoperative kyphosis/segmentalimbalance in a substantial series of patients undergoing cervical disc re-placement with the Bryan Disc prosthesis and examine possible contributingfactors to segmental alignment, in order to further our knowledge of theindications and limitations in the use of this prosthesis.STUDY DESIGN/SETTING: Demographic and X-ray study of caseseries. Surgery performed by three surgeons in two countries.PATIENT SAMPLE: 62 patients who underwent anterior decompressionand Bryan Cervical Disc replacement surgery for degenerative spine disease.Median age was 47 years (range: 27–62). 16, 25 and 21 patients, were oper-ated by the three surgeons, respectively. 43 patients underwent single, 18double and 1 triple level disc replacement.OUTCOME MEASURES: Focal lordosis, spondylolisthesis and prosthe-sis shell angulation at operated level as well as overall cervical alignment.METHODS: Neutral pre- and postoperative erect and intra-operativeX-rays were examined using digital image analysis software (Medical Met-rics, Inc. Houston, TX). Additional manual X-ray measurements were madeby two observers of outcome measures and possible factors contributing tosegmental alignment including: preoperative alignment, angle of prosthesisinsertion, vertebral morphology and disc space degeneration. Factors suchas operating surgeon, level of implantation and number of levels operatedwere also examined. Inter-observer agreement was assessed. Non-paramet-ric tests were used for assessment of categorical and skewed continuousvariables. Multivariate linear regression was used to adjust significant corre-lation coefficients. Significance was set at p�.05.RESULTS: Inter-observer agreement ranged from fair for observations ofdisc-space degeneration to excellent for measures of shell angulation.Median preoperative focal lordosis of �0.5� (range: 21 to �14�, �ve�

kyphotic) changed by �1� (�14 to �17�), to postoperative: 0� (�11.5 to�16�). Postoperative shell angulation was �2� (�11.5 to �15�). Correlationco-efficients adjusted using multiple linear regression suggested that preop-erative focal lordosis (p�.001) and postoperative shell angle (p�.001), butnot angle of prosthesis insertion (p�.201), are significantly associated withfinal focal lordosis. There was a significant difference in the median changein focal lordosis for surgeon 1 (�3�) vs. surgeons 2 and 3 (�1�) (p�.005).The number of levels operated vs. change in lordosis may be significant(�1� vs. �1.5�, p�.03).CONCLUSIONS: The median change (loss) in focal lordosis was �1.5� butthere was considerable range: from �14 to �17�. Attempts to identifycontributing factors to postoperative kyphosis suggest that a number may beinvolved. No single factor has emerged as dominant in this series but at thisstage the disc prosthesis is not recommended for patients with significantpreoperative deformity. While the difference in outcomes between Surgeon1 and Surgeons 2 and 3 is probably not clinically significant, it is suggestive

STUDY DESIGN: A biomechanical study using human lumbar spines(L1-sacrum).METHODS: Five lumbar spines (age: 52�9.3) were used. Specimenswere tested under flexion (8 Nm) and extension (6 Nm) moments withcompressive follower preloads of 0 N and 400 N in the following sequence:(i) intact (ii) Charite TDR at L5-S1 (iii) simulated healed fusion at L5-S1with Charite TDR at L4-L5. Segmental motion was measured optoelectron-ically. Motions between prosthesis end plates and core were visually assessedusing sequential digital video-fluoroscopy over the full range of motion. Herewe report on kinematics of 10 Charite TDRs: 5 at L5-S1 and 5 at L4-L5.RESULTS: Charite TDR increased the flexion-extension range of motionof lumbar segments (p�.05). At 400 N preload, the range of motion increasedfrom intact values of 6.8�4.4 to 10.0�2.4 degrees at L5-S1 and from7.0�2.6 to 10.8�2.9 degrees at L4-L5. Charite TDR increased segmentallordosis by 8.1�6.9 degrees at L5-S1 (p�.05) and 5.4�3.5 degrees at L4-L5 (p�.05). Four patterns of prosthesis component motion were noted: (1)angular motion only between the upper end plate and core, with little orno visual evidence of core translation (9/10 TDRs at 0 N preload and5/10 TDRs at 400 N preload); (2) lift-off of upper prosthesis end platefrom core or of core from lower end plate (observed in extension in 9/10TDRs under 0 N preload only); (3) core entrapment, resulting in a lockedcore over a portion of the range of motion (observed in extension in 8/10TDRs under 400 N preload); (4) angular motion between both the upperand lower end plates and core, with visual evidence of core translation (1/10 TDRs at 0 N preload, 5/10 TDRs at 400 N preload). The pattern ofload-displacement curves was substantially changed under a physiologicpreload in 8/10 TDRs; instead of a relatively gradual change in angle withchanging moment application as seen for an intact segment, the TDRdisplayed regions of both relatively small and relatively large angularchanges with gradual moment application.CONCLUSIONS: Charite TDR restored near normal quantity of flexion-extension range of motion under a constant physiologic preload; however,the quality of prosthesis motion differed from the intact case over theflexion-extension range. While some TDRs showed visual evidence ofcore translation, the predominant angular motion within the prosthesisoccurred between the upper end plate and polyethylene core. Likelyfactors affecting the function of the Charite TDR include implant placementand orientation, intra-operative change in lordosis, and magnitude of physio-logic compressive preload. Further work is needed to assess the effects ofthe prosthesis motion patterns identified in the study on the load sharingat the implanted level and polyethylene core wear.Keywords: total disc replacement, lumbar spine, biomechanics, kinematicsDISCLOSURES: Approved for this indication: Charite’ artificial discCONFLICT OF INTEREST: No conflicts

doi: 10.1016/j.spinee.2005.05.148

Friday, September 30, 20054:22–5:05 PM

Concurrent Session: Cervical

4:22146. Postoperative kyphosis and segmental imbalance with anunconstrained, variable I.A.R. cervical disc prosthesisWilliam Sears1, Lali Sekhon, MD, PhD2, Neil Duggal, MD3,Owen Williamson4; 1Sydney NeuroSpine Clinic, Sydney, New SouthWales, Australia; 2University of Sydney, Sydney, New South Wales,Australia; 3London Health Sciences Centre, London, Ontario, Canada;4Monash University, Melbourne, Victoria, Australia

BACKGROUND CONTEXT: The early clinical results of cervical discreplacement surgery are encouraging. However, the in vivo kinematics ofprostheses and their role in patients with pre-existing deformity is poorlyunderstood. Two recent published reports suggest that use of a prosthesis

of intra-operative factor(s) being involved (other than angle of prosthesisinsertion).DISCLOSURES: FDA device/drug: Bryan Cervical Disc (MedtronicSofamor Danek, Memphis, TN). Status: Investigational/not approved.CONFLICT OF INTEREST: Author (WS) Consultant: MedtronicSofamor Danek, Memphis, TN; Author (WS) Grant Research Support:Medtronic Sofamor Danek paid for and provided access to the digitalimage software analysis.

doi: 10.1016/j.spinee.2005.05.149

4:28147. Reoperation rates for cervical arthroplasty vs. arthrodesisPaul Anderson, MD1, Rick Sasso, MD2, Newton Metcalf, Jr.3,K. Daniel Riew, MD4*; 1University of Wisconsin-Madison, Madison, WI,USA; 2Indiana Spine Group, Indianapolis, IN, USA; 3MedtronicSofamor Danek, Memphis, TN, USA; 4Washington University in St.Louis, St. Louis, MO, USA