ProDisc Artificial Total Lumbar Disc Replacement: Introduction and Early Results From the United States Clinical Trial

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1 ProDisc Artificial Total Lumbar Disc Replacement: Introduction and Early Results From the United States Clinical Trial SPINE Volume 28, Number 20S, pp S167 S , Lippincott Williams & Wilkins, Inc. Rick B. Delamarter, MD, David M. Fribourg, MD, Linda E. A. Kanim, MA, and Hyun Bae, MD Study Design. Multicenter prospective randomized study of artificial disc replacement (ProDisc) versus circumferential fusion (standard of care) for one- and twolevel degenerative disc disease. This is an interim analysis on patients seen at the Spine Institute Saint John s Health Center, Santa Monica, California. Objectives. To evaluate early pain and functional outcomes of patients treated with disc replacement or fusion and to assess the capacity of this intervertebral disc replacement for preserving motion in the lumbar spine. Summary of Background Data. Disc replacement is intended to reduce pain via removal of the diseased disc while restoring physiologic motion and height at the affected level. The long-term physiologic advantage of disc replacement to fusion is that preservation of motion may prevent additional degeneration at adjacent levels. Methods. Patients meeting inclusion criteria were consented for study. Randomization was performed using a 2 to 1 ratio of disc replacement procedure to a fusion procedure. Patients rated their pain on the Visual Analogue Scale and completed the Oswestry Disability Index questionnaire. Radiographs were taken. Assessments were made before surgery and after surgery at 6 weeks, 3 months, 6 months, and 1 year (ongoing). Changes from preoperative pain, disability, or motion were separately evaluated as a function of treatment using repeated measures mixed design analysis of variance. Results. This analysis includes data up to 6 months from the first 53 randomized patients. There were 35 patients who underwent disc replacements, and 18 patients had fusion procedures. Disc replacement patients had a significant reduction in pain and disability at earlier evaluations. By 6 months, the relative improvement on both the Visual Analogue Scale and Oswestry (both, P 0.05) were similar for disc replacement and fusion patients. Greater motion was found at L4 L5 for disc replacement patients (P 0.05) than fusion patients. A similar trend was noted at L5 S1 (P was not significant). Conclusions. Disc replacement patients reported significantly less pain (Visual Analogue Scale) and disability From The Spine Institute at Saint John s Health Center, Santa Monica, California. The device(s)/drug(s) that is/are the subject of this manuscript is/are being evaluated as part of an ongoing FDA-approved investigational protocol (IDE) or corresponding national protocol. Benefits in some form have been or will be received from a commercial party related directly or indirectly to the subject of the manuscript. Although one or more of the author(s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript, benefits will be directly solely to a research fund, foundation, educational institution, or other nonprofit organization with which the author(s) has/have been associated. Address correspondence and reprint requests to Rick Delamarter, MD, Medical Director, The Spine Institute at Saint John s Health Center, th Street, Suite 400, Santa Monica, CA 90404, USA; rdelamarter@espineinstitue.com (Oswestry) in the early period following surgery compared to fusion patients. This difference disappeared by 6 months. When compared to fusion, the disc replacement allowed preservation of motion at L4 L5 with a similar trend at L5 S1. [Key words: outcomes, disc replacement, preservation of motion, randomized] Spine 2003;28: S167 S175 Inspired by the excellent results of total hip and knee replacements, Dr. Thierry Marnay invented a prosthesis for the lumbar disc with similar materials and design. He began implantation of the ProDisc in 1990 at the Clinique du Parc in Montpellier, France. Given the prevailing skepticism about lumbar disc replacement, Dr. Marnay felt that it was prudent to limit the initial use of the product until appropriate follow-up could be obtained. Sixty-four patients were initially implanted with the Pro- Disc from 1990 to The implantation was then halted until a minimum 5-year follow-up could be obtained on this cohort of patients. The development of the ProDisc resumed in Minor modifications were made to the original ProDisc to allow for modularity. This second generation prosthesis is the ProDisc II and is currently being used for the United States trial. It was initially released in Europe in December 1999 as part of a prospective clinical trial to a limited number of surgeons, whereas a retrospective review was performed for initial cohort of patients implanted with the original ProDisc (ProDisc I). Fifty-eight of the initial 64 patients returned for a follow-up visit 7 to 11 years after the original implantation. Promising results from these patients with 7- to 11-year follow-up with no mechanical implant failures paved the way for the pivotal clinical trial currently underway in the United States. 1 U.S. Pivotal Clinical Trial Currently, 18 U.S. sites are participating in a large scale prospective randomized study comparing clinical outcomes between patients receiving circumferential fusions and the ProDisc II total disc replacement for one- and two-level degenerative disc disease in the lumbosacral spine L3 S1 vertebral segments. This study is a Food and Drug Administration (FDA) Investigational Device Exemption multicenter, prospective randomized study to investigate the safety and efficacy of this ProDisc II implant. The current enrollment goal is 500 hundred patients. Approximately 300 patients in the U.S. have re- S167

2 S168 Spine Volume 28 Number 20S 2003 ceived the ProDisc implant at the time of this writing (January 2003). Rationale Low back pain often results from alterations in the normal mechanics of the lumbar spine associated with degeneration of the intervertebral disc. Disc degeneration is not so much a disease as a process in the normal aging of the lumbar spine. The vast majority of patients can be successfully treated without surgery. Ultimately, however, patients with severe pain refractory to conservative care have been treated with spinal fusion by a variety of techniques. 2,3 Spine fusion itself has been shown to lead to other problems including donor-site morbidity, pseudarthrosis, and, most notably, degeneration at an adjacent intervertebral disc. 4 9 An operation that eliminates pain by restoring motion not only makes more physiologic sense but may prevent adjacent level degeneration. The goal to restore normal painless motion to a joint is not a new concept in orthopaedics. Total joint arthroplasty for the hip and knee has been shown to provide excellent pain relief while maintaining motion in scores of clinical studies. Recently, this concept of treatment has been applied to degenerative disc disease of the lumbar spine in two large scale U.S. FDA clinical trials comparing total disc replacement to spinal fusion (SB Charitè and ProDisc II). The ProDisc has been available in the United States since early This is a preliminary comparative analysis and description of the first 53 randomized patients at minimum 6 months after ProDisc total disc replacement or anterior/posterior fusion from one site participating in the FDA-regulated IDE study (PRO- DISC investigational device exemption #G010133, Spine Solutions, Inc., NY). Materials and Methods Design. Approval to conduct the study was given by the FDA and by our participating center s Institutional Review Board (IRB). Patients with one or two levels of lumbar degenerative disc disease with predominately back pain were considered for the study. Patients were evaluated with magnetic resonance imaging (MRI), plain radiographs, and occasional discogram/ computed tomography (CT) scans. Inclusion criteria included age between 18 and 60, failed conservative treatment for at least 6 months, minimum Oswestry score of 40 out of 100, and no more than one- or two-level degenerative disc disease from L3 to S1. Patients with metal allergies, previous lumbar fusions, compromised vertebral bodies, and severe facet degeneration were excluded from the study. After all inclusion criteria were met, the patient was randomized to either anterior fusion with femoral allograft followed by a posterior fusion with instrumentation and iliac crest autograft or a total disc replacement through an anterior retroperitoneal approach. The randomization was weighted 1:2 ratio to receive either circumferential fusion or the artificial disc. All patients were blinded to the treatment until after the surgical procedure was performed. Device Description. PRODISC is manufactured by Spine Solutions. The investigational device is composed of three modular components: the inferior cobalt-chrome-molybdenum (CoCrMo) plate with a large central keel, the ultra high molecular weight polyethylene (UHMWPE) insert, and a superior CoCrMo plate with a central keel, for anchorage to the vertebral bodies. The UHMWPE insert snap-locks into the inferior plate and provides an inferior convex-bearing surface. The plate attached to the superior vertebral body maintains a highly polished surface that articulates with the convex polyethylene surface to allow motion of 13 of flexion, 7 of extension 10 of lateral bending, and 3 of axial rotation. The bony contact surfaces of the two CoCrMo plates are coated with a titanium plasma spray for better bony ongrowth. Additional stability is obtained by a large central keel that interdigitates with the vertebral body above and below (Figure 1). Surgical Technique for the ProDisc. The ProDisc is implanted by an anterior approach to the lumbar spine. In our institution, we use the anterior retroperitoneal approach with a mini incision averaging 6 cm for the one-level cases and 8 cm for two levels. Intraoperative fluoroscopy is used throughout the case to verify the placement of the prosthesis. Once exposure is obtained, an anteroposterior (AP) view confirms the level and identifies the exact midline, which is marked with the cautery. A complete discectomy is then performed. Cartilage is removed from the vertebral endplates. If herniated disc material is identified on the preoperative MRI, this may be removed through the anterior approach. In some cases, the posterior longitudinal ligament has contracted and prevents reexpansion of the disc space, so this must be released from the posterior vertebral body with a forward-angled curette. Once the normal anatomic height has been restored with distraction under fluoroscopy, a trial is placed to help select the proper disc size, angle, and height. A sagittal groove is then cut in the vertebral endplates in the exact midline using a chisel placed over the trial. This groove will accept the central keel of the implant. The trial is removed, and the final implant is then gently impacted into place on an insertion tool. The insertion tool allows distraction of the disc space for placement of the UHMWPE liner, which is snap-fit into position. After the insertion instrument is removed, gross inspection is made to ensure the UHMWPE liner is properly flush against the inferior endplate (Figure 2A), and final fluoroscopic views are taken to confirm correct position of the prosthesis (Figure 2B). Surgical Technique for Circumferential Fusion. The same anterior approach is used for the anterior discectomy and fusion. The endplates are also prepared in the same manner except a femoral ring is placed instead of the prosthesis. A standard technique is used for the posterior pedicle screw instrumentation and fusion. The iliac crest autograft is taken through a separate incision. Outcome Instruments. Patients completed the standardized Oswestry Disability Index, 10,11 and rated their pain on the Visual Analogue Scale (VAS) before surgery and at each follow-up clinic visit (6 weeks, 3 months, 6 months, and 1 year). On the follow-up assessments, a patient was requested to remember the pain felt before surgery and asked, Remembering the pain you felt before surgery, would you have this surgery again? Additionally, a 10 cm line visual scale (similar to the VAS) was presented to the patient with the instruction to indicate the amount of satisfaction you feel with your treatment. Investigator-initiated structured queries were on types

3 Total Lumbar Disc Replacement Motion and Outcomes Delamarter et al S169 Figure 1. A, Three components of the ProDisc II disc replacement. Superior endplate, ultra high molecular weight polyethylene insert, and inferior endplate. Endplates are coated with a plasma spray finish for bony ongrowth. B, Anterior view of the implant demonstrating the bearing surface and the large central keel. of recreational activity, ambulatory status, and medications taken for pain. Fusion patients were asked to rate their pain at graft harvest site as none, mild, moderate, or severe. Radiographs. Flexion, extension, AP, lateral, and lateral sideto-side bending radiographs (6 views total) were taken before surgery and after surgery at 6 weeks and 3, 6, and 12 months for the artificial disc replacement patients (Figures 2C 2H). For fusion patients, only AP and lateral films were taken at 6 weeks and 3 months after surgery. At the 6-month and all subsequent postoperative visits, all 6 radiographs were taken. Statistical Analysis. Means and standard deviations for numerical data or frequencies for categorical data were calculated by treatment modality for outcomes, motion parameters, and patient characteristics. Outcome measures and motion data were analyzed using mixed designs analysis of variance (ANOVA) with repeated measures for assessment interval and a grouping effect for treatment modality (SAS, GLM procedures). Student t tests and 2 were employed for simple comparisons across treatments. To determine specific effects, post hoc pairwise statistical comparisons were made with Student t tests (group) or paired t tests (interval within subjects). Difference in angular measurements between flexion and extension radiographs yielded a value of angular motion in the sagittal plane for each of the segments L3 L4, L4 L5, and L5 S1. Right-bending and left-bending radiographs were measured and yielded a value of degrees of motion in the coronal plane (data not presented herein). Analysis of variance (GLM, SAS) equations were computed on degrees of motion data including a grouping effect for treatment and within effect for assessment interval, separately for each treated segment (L3 L4, L4 L5, L5 S1). Results Data from the first 53 randomized patients (35 ProDisc and 18 fusion) with 6- to 15-month follow-up were available for an interim analysis. The average age, gender, narcotic use, smoking history, worker s compensation percentage, and duration of back pain before surgery was similar between patients treated with artificial disc replacement (DR) and those treated with a spinal fusion (F), presented in Table 1. The duration of back pain of greater than 12 months before surgery was reported by all the disc replacement-treated patients compared to most of the fusion patients (100% vs. 89%, P 0.04). Of the 27 patients that were treated for one-level disc disease, there were 19 patients who had disc replacement procedures and 8 patients who had fusion procedures. Of the 26 patients treated who had two-level disease, there were 16 patients who had disc replacement and 10 patients who had fusion procedures. There were no instances of implant migration, breakage, or mechanical failure, nor was any revision surgery required. Outcome Measures Preoperative values on the VAS and Oswestry Disability Index (ODI) were not significantly different among pa-

4 S170 Spine Volume 28 Number 20S 2003 Figure 2. A, Intraoperative picture of the ProDisc II placed in the L4 L5 disc space. B, Intraoperative fluoroscopy of the ProDisc II placed in the L4 L5, L5 S1 disc space. C and D, Anteroposterior and lateral radiographs of the ProDisc II at the L4 L5 level 6 months after surgery. Flexion and extension radiographs of a patient before surgery (E and F) and 6 months after surgery after the ProDisc II was implanted at the L4 L5 level (G and H). tients randomized to disc replacement or fusion. After treatment, the disc replacement patients had significantly better results at 6 weeks (VAS) and 3 months (VAS, ODI) compared to the fusion patients. By 6 months, although both treatment groups showed significant improvement compared to preoperative values, there was no longer a significant difference between the groups. These data are presented in Table 2 and Figures 3A and 3B. The patients that received a disc replacement had a significant decrease in pain as measured by the VAS as early as 6 weeks after surgery (DR: 2.88 [6 weeks] versus 7.48 [preop], P 0.05). At 3-month and 6-month intervals, this significant reduction in pain was maintained at about a 50% decrease than preoperative levels (3.789, P 0.05 [3 months]); 4.47, P 0.05 [6 months]). Fusion patients showed significant improvement relating to a lower VAS score at 6 months compared to their preoperative (3.96 [6 months] versus 6.8 [preop], P 0.05). A direct comparison between the groups of patients revealed disc replacement treated patients had significantly less pain than fusion treated patients at 3 months (2.88 [DR] versus 4.74 [F], P 0.05). The patients treated with the disc replacement also reported quicker increase in functional ability than those

5 Total Lumbar Disc Replacement Motion and Outcomes Delamarter et al S171 Figure 2. Continued. patients receiving fusions. Disability was significantly reduced from that reported before surgery (ODI) for disc replacement patients by 3 months (DR: [preop] versus [3 months], P 0.001). It took fusion patients 6 months before a significant improvement was observed (F: [preop] versus [6 months], P 0.01). Disc replacement patients had significantly more reduction in early pain and disability (Table 2). At 6 months, disc replacement patients and fusion patients had similar scores on both the VAS (4.47 vs. 4.65, 10 cm scale) and the Oswestry (13.45 vs ). Estimated Motion From Flexion Extension Radiographs Motion data are presented separately for treated vertebral segments L4 L5 in Figure 4A and for L5 S1 in Figure 4B. Flexion extension angle difference measured from radiographs yielded a measure of estimated motion. Motion between disc replacement and fusion treated segments are presented for preoperative and 6 months postoperative intervals. Flexion and extension films were not taken after surgery for fusion patients until the 6-month follow-up visit.

6 S172 Spine Volume 28 Number 20S 2003 Table 1. Characteristics of Randomized Patients Treated With Artificial Disc Compared to Those Treated With a Fusion Procedure Treatment Subject Characteristics Disc Replacement (n 35) Fusion (n 18) P 0.05 Gender: % males Age (average yrs) (19 59) (26 59) (range) Body mass index (19 34) (range) Smoking history Current smokers 9% 22% (4/18) Former smokers 31% 28% (5/18) Never smokers 60% 50% (9/18) Narcotic use 74.95% 79% (15/19) Previous surgery 38.23% 44.44% (8/18) Worker s compensation 28.57% 38.89% (7/18) Duration of back pain % pain 1 yr 100% 89% (16/18) P 0.04 % pain 6 mos 11% (2/18) Vertebral levels treated 19/35 8/18 (1-level surgery) L3 L4 1 L4 L5 9 4 L5 S Vertebral levels treated 16/35 11/18 (2-level surgery) L3 L5 1 L4 S An analysis of sagittal angular motion revealed an increase in motion from preoperative to the 6-month postoperative value for the L4 L5 vertebral segment in patients treated at L4 L5 with the disc replacement. Conversely, patients who had a fusion at L4 L5 had a Table 2. Means for the Oswestry and Visual Analogue Scale of Randomized Patients Treated With Artificial Disc Compared to Those Treated With a Fusion Procedure Assessment Interval Preop 6 wks 3 mos 6 mos VAS (10 cm scale) Average Average Average Average Disc replacement * Fusion Comparison DR vs. F NS P 0.01* P NS Oswestry (50 pt. scale) Average Average Average Average Disc replacement Fusion Comparison DR vs. F NS NS P 0.05 NS Oswestry preop vs. 6 wks, F 19.77, P 0.001, main effect of follow-up after surgery (time). * Preop vs. 6 wks F 11.05, P 0.002, significant for the interaction for type of treatment *time after surgery. Preop vs. 3 mos, F 10.80, P ; significant for the interaction for type of treatment * time. Preop vs. 6 mos F 11.05, P 0.005, significant main effect for time after surgery. Preop vs. 3 mos, F 4.67, P 0.05, interaction between type of treatment * time; preop vs. 6 mos, F 44.78, P , main effect of follow-up after surgery. VAS Visual Analogue Scale; DR disc replacement; F fusion; NS not significant. Figure 3. A, Mean and standard deviations of disability as measured by the Oswestry Questionnaire for patients treated with artificial disc compared to those treated with a fusion procedure. B, Mean and standard deviations of pain as measured by the Visual Analogue Scale (10 cm line) for patients treated with artificial disc compared to those treated with a fusion procedure. significant decrease in motion from the preoperative to the 6-month postoperative value. The pretreatment sagittal motion was similar for both groups. A significant treatment effect was observed at L4 L5 from preoperative to 6 months. Significantly greater motion was found at L4 L5 for disc replacement patients compared to fusion patients (F 7.15, P 0.04; difference at 6 months) (Tables 3 and 4). The 6-month results for the L5 S1 treated segments have a similar trend, as there is increased motion at L5 S1 in disc replacement patients and less motion for fusion patients, although this difference is not statistically significant (F 8.02, not significant). For an evaluation of consistency in the methodology used to compute motion from radiographic angular measurements, data from the untreated L3 L4 intervertebral segments were evaluated separately in both groups. There was no significant difference in angular motion at the untreated L3 L4 level measured before surgery and after surgery at 6 months for either the patients treated with fusion or disc replacement procedures. Figure 4A presents L3 L4 data for patients treated at L4 L5 (not significant) and Figure 4B presents L3 L4 data for patients treated at L5 S1 (not significant).

7 Total Lumbar Disc Replacement Motion and Outcomes Delamarter et al S173 Figure 4. A, Means for motion at the L4 L5 segment and the L3 L4 segment (comparison) for patients treated at the L4 L5 segment for those treated with artificial disc compared to those treated with a fusion procedure. Motion was determined from extension flexion angular measurements. B, Means for motion at the L5 S1 segment and the L3 L4 segment (comparison) for patients treated at the L5 S1 segment for those treated with artificial disc compared to those treated with a fusion procedure. Motion was determined from extension flexion angular measurements. Discussion New treatments for degenerative disc disease must show superiority over the natural history of the disease and at least equivalency with the current standard of care. Smith et al followed 25 patients with low back pain and positive discograms who declined surgical intervention. 12 After 5 years, 68% showed clinical improvement, and 24% had more severe back pain and disability. One of the best recent series of patients with fusion for chronic low back pain shows that 60% to 68% rated themselves better or much better at 2 years after surgery, and 12% to 16% were worse. 13 On average, back pain decreased from 6 to 4, and leg pain from 4 to 3 on a Visual Analogue 10 cm Scale. In another analysis, Fritzell et al showed that lumbar fusion reduced back pain by 33% compared with 7% in the nonsurgical group. 13 In this study, disability according to the ODI was reduced by 25% compared with 6% in the nonsurgical patients. Although lumbar fusion led to some improvement in symptoms compared to nonsurgical care, unfortunately, many patients continue to have pain and functional limitations. In comparison to these results from lumbar spinal fusion, the initial European study on the ProDisc showed promising results. A retrospective review of the original ProDisc, ProDisc I, with 7- to 11-year follow-up on 61 patients was conducted. One-third of patients had twolevel ProDisc implantation. There were no cases of subsidence or migration, and no implants were removed or revised. Overall, 92.7% of the patients reported that

8 S174 Spine Volume 28 Number 20S 2003 Table 3. Means and Standard Deviations for Motion at the L4 L5 Segment and the L3 L4 Segment (Comparison) for Patients Treated at the L4 L5 Segment for Those Treated With Artificial Disc Compared to Those Treated With a Fusion Procedure (Includes 1-Level and 2-Level Patients) Preop 6 wks 3 mos 6 mos L4 L5 Treated Average and SD Range Average and SD Range Average and SD Range Average and SD Range Disc replacement L3 L4 degrees of motion 5.48, , , , L4 L5 degrees of motion 7.04, , , , Fusion L3 L4 degrees of motion 5.00, , L4 L5 degrees of motion 11.46, , Motion was determined from extension flexion angular measurements. they were satisfied or entirely satisfied with the procedure. The average VAS for back pain went from 8.5 before surgery to 3 after surgery, and VAS for leg pain from 7 preop to 2 postop. The European experience with the second generation ProDisc, ProDisc II, shows similar excellent results. In one spine center in Germany, a total of 134 discs were replaced in 108 patients with 3-month to 2-year followup. 14 The study is ongoing, with prospective data collection for clinical examination, VAS, Oswestry, and SF-36 score. The preliminary data reveals 91% excellent and good results, 8% fair, and 1% poor results. The authors note that fair and poor clinical outcomes were found primarily in patients with more severe, multilevel degenerative disease including facet arthritis. There were no cases of implant migration or subsidence. The excellent results obtained with the ProDisc and the lack of any catastrophic failure with the ProDisc II in Europe paved the way for the FDA pivotal clinical trial currently underway in the United States. The interim results presented here are derived from the subset of all patients with minimum 6 months follow-up at a single institution. Although this analysis is limited to one site in the U.S. trial and has a relative short follow-up period, it does provide prospective information on how randomized patients recover after prosthetic disc replacement versus fusion procedures in the postoperative period up to 6 months. Disc replacement patients display less pain on the VAS at the 6-week and the 3-month assessments and have a significantly improved functional status (lower ODI) at 3 months compared to fusion patients. The early superiority of the disc replacement over fusion may be partially explained by decreased postsurgical morbidity in the disc replacement group. Disc replacement patients have only an anterior procedure performed and thus do not have to recover from the additional posterior approach and harvesting of iliac crest autograft necessary for spinal fusion. Fusion patients did not report a significant increase in functional status and decrease in pain until the 6-month follow-up assessment. At this 6-month assessment, the fusion patients had similar VAS and ODI scores to the disc replacement patients, showing a marked improvement from 3 to 6 months. It is noteworthy that the spinal fusion patients had a dramatic improvement in their VAS and ODI scores by 6 months compared to preop (possibly associated to consolidation of the fusion). However, this may partially be explained by a selection bias, be- Table 4. Means and Standard Deviations for Motion at the L5 S1 Segment and the L3 L4 Segment (Comparison) for Patients Treated at the L5 S1 Segment for Those Treated With Artificial Disc Compared to Those Treated With a Fusion Procedure (Includes 1-Level and 2-Level Patients) Preop 6 wks 3 mos 6 mos L5 S1 Average and SD Range Average and SD Range Average and SD Range Average and SD Range Disc replacement L3 L4 degrees of motion 5.75, , , , L5 S1 degrees of motion 6.17, , , , Fusion L3 L4 degrees of motion 4.75, , L5 S1 degrees of motion 3.33, , Motion was determined from extension flexion angular measurements.

9 Total Lumbar Disc Replacement Motion and Outcomes Delamarter et al S175 cause all patients in this study have to meet strict selection criteria (age 60, body mass index 40, absence of facet disease and spondylolisthesis, etc.) before qualifying for the study. The issue of motion preservation was critically evaluated from preop to 6 months in both disc replacement and fusion group of patients. Two patients from the study were treated at the L3 L4 level and were excluded secondary to insufficient data for comparison. All patients in this motion analysis were treated either at the L4 L5 level or L5 S1 level, or both. At the L5 S1 level, an increase in sagittal motion in the disc replacement patients was observed compared to the fusion patients; however, this difference was not statistically significant. The L5 S1 level was the most difficult to measure radiographically secondary to the shadow of the sacral ala on the lateral projection. Also, it is the least mobile motion segment in the lumbar spine, and therefore differences in motion are hard to detect with a relatively small sample size. At the L4 L5 level, the sagittal motion data suggests that the disc replacement not only preserves motion but also can increase or restore motion, at least in this short follow-up period. Theoretically, by maintaining motion, there will be a protective effect on future degeneration at adjacent levels. In the future, it will be important not only to evaluate whether or not there is motion, but also to qualify the type of motion that occurs across the spinal segment, as this may play a role in facet displacement and loading. Each prosthetic design will have its own motion parameters, with differing constraints in flexion extension, rotation, and translation. All disc replacements may maintain motion and protect the adjacent level, but the local effect at the facets may be the differentiating factor. Only long-term follow-up will reveal whether a significant effect is observed at the adjacent level to a disc replacement and whether facet arthrosis will be prevented or even exacerbated depending on the prosthetic design. Other issues that may exist with disc arthroplasty such as infection, wear particles, subsidence, implant failure, and longevity have not been a factor at this early stage of the study. Conclusions Chronic low back pain from degenerative disc disease is endemic in our society. The surgical treatment of this problem can often be frustrating. Circumferential fusion is often associated with mediocre results, long recovery time, significant postoperative morbidity, and future degeneration at the adjacent levels. Disc replacement has been shown to be a promising alternative to the treatment of low back pain and may eliminate the stigmas associated with fusion. The U.S. IDE Pivotal Clinical Trial currently underway at selected clinical sites will provide valuable information comparing this new technology to the current mainstay treatment of spinal fusion. The preliminary results from our site demonstrate that the objective of decreasing postoperative morbidity and improving recovery has been met. Patients who received the disc replacement as opposed to fusion had a significant improvement in pain and functional status in the early postoperative period. Over the short-term, the disc replacement does act to preserve motion at the surgical level. The more important benefit of protection of adjacent levels can only be assessed with completion of the multicenter study and long-term follow-up. Key Points Disc replacement patients reported earlier improvement in pain (Visual Analogue Scale) and function (Oswestry) than did fusion patients; however, there was no difference at 6 months. Angular motion can be maintained or reestablished in the L4 L5 lumbar intervertebral segment after implantation of artificial disc devices. The procedure was safe for experienced spine surgeons to perform, with no device-related complications and no revision surgery. References 1. Marnay T. ProDisc. The 7 11 Year Clinical Experience. New York, NY: Spine Solutions, Inc; Christensen FB, Hansen ES, Eiskjaer SP, et al. Circumferential lumbar spinal fusion with Brantigan cage versus posterolateral fusion with titanium Cotrel- Dubousset instrumentation: a prospective, randomized clinical study of 146 patients. Spine 2002;27: Fritzell P, Hagg O, Wessberg P, et al. Chronic low back pain and fusion: a comparison of three surgical techniques: a prospective multicenter randomized study from the Swedish lumbar spine study group. Spine 2002;27: Deyo RA, Cherkin DC, Loeser JD, et al. Morbidity and mortality in association with operations on the lumbar spine. 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