Freedom Lumbar Disc Clinical Outcomes Benchmarked Against All TDRs in the SWISSspine Registry

Transcription

1 Freedom Lumbar Disc Clinical Outcomes Benchmarked Against All TDRs in the SWISSspine Registry CAUTION: Investigational device. Limited by Federal law to investigational use. 1

2 White Paper Freedom Lumbar Disc Clinical Outcomes Benchmarked Against All TDRs in the SWISSspine Registry Abstract This analysis was conducted to compare outcomes for patients treated with a viscoelastic lumbar total disc replacement (VTDR) to those treated with all other lumbar total disc replacements (TDR) in the SWISSspine Registry. The SWISSspine Registry is the first mandatory registry of Swiss orthopaedics. Its goal is to generate evidence for use in decision making by the Swiss Federal Office of Health regarding reimbursement for technologies and treatments by the basic health insurance of Switzerland. Since 2009, a viscoelastic total disc replacement (VTDR), the Freedom Lumbar Disc, has been included in the registry. To benchmark the initial data from a viscoelastic technology, clinical outcome data was evaluated and compared to that for the other total disc replacement (TDR) technologies in the registry. This analysis was conducted to compare outcomes for patients treated with a lumbar VTDR to those treated with all other lumbar TDRs in the SWISSspine Registry. Prospective, multi-center data from two surgeons for VTDR patients was collected pre-operatively and at 3 to 6 months, 1 year and 2 years postoperatively. The outcome data assessed were EQ-5D health status index and VAS low back and leg pain scores. This data was compared to data in the SWISSspine Registry for all other TDRs. A Wilcoxon Rank sum test was used for comparisons of continuous variables between the VTDR and pooled data for all other TDRs in the database. Proportions were compared using a chi-square test. The VTDR population included 30 patients (18 males, 12 females) with an average age of 52 (range 26-71). The SWISSspine TDR population included 800 patients (334 males, 466 females) with an average age of 42 (range 19-65). The prevalence of single-level and two-level cases was 34%/66% for VTDR and 85%/15% for TDR. EQ-5D health status indices and VAS low back and leg pain scores improved significantly more (p < 0.05) for the VTDR patients compared to the other TDR patients in the registry. Health status scores improved from preoperatively to at two years for VTDR patients and from preoperatively to at two years for other TDRs (Figure 1). VAS low back scores improved from 76.0 mm to 5.0 mm for the VTDR group and from 69.1 mm to 26.5 mm for the TDR group from pre-op to two years follow up (Figure 2). VAS leg pain scores improved from 68.8 mm preoperatively to 0.0 mm at two years follow up for the VTDR group and from 53.5 mm preoperatively to 19.3 mm at two years for the TDR group. In this early analysis, clinical outcomes improved significantly more for VTDR patients than for the pooled group of other TDR patients in the SWISSspine Registry. 2

3 Introduction In March 2005, the Swiss Federal Office of Health initiated the SWISSspine Registry, intended as a nationwide observational study according to the principle of coverage with evidence development before taking the final decision about reimbursement of TDR by the basic health insurance. 2 The goal of the SWISSspine Registry is to gather data on the safety and efficacy of total disc replacement (TDR) for use in reimbursement decisions. The Swiss Federal Office of Public Health (SFOPH) uses acquired national and international results to decide whether the Swiss basic health insurance should reimburse a particular technology. 1 The methodology and implementation of the SWISSspine registry is based on specifications regarding health technology assessments (HTA) developed by the SFOPH. Swiss medical profession policy makers formed the Swiss Spinal Society (SSS), an expert group that certifies spine surgeons for TDR procedures. All Swiss spine surgeons who intend to perform TDR surgery must formally apply to the SSS with proof of qualification and adequate infrastructure. 1 The Institute for Evaluative Research in Orthopedic Surgery at the University of Bern (IEFO) provides the technology for the SWISSspine Registry and manages the data. The registry work group consists of stakeholders in industry, the SSS and the IEFO. Each participant in the registry can make use of its own data, but the data pool is owned by the SGS, and SGS can delegate data analysis to individual surgeons or to a neutral academic data clearing center like the IEFO. Data for VTDR patients has been included in SWISSspine Registry since There are five other lumbar TDRs currently available in Switzerland and included in the SWISSspine Registry. Materials & Methods The Viscoelastic Total Disc Replacement (VTDR) The VTDR (Freedom Lumbar Disc, AxioMed Spine Corp, Garfield Heights, OH) is a one-piece viscoelastic artificial disc consisting of an elastomeric core bonded to titanium alloy retaining plates with end caps. The VTDR is intended to re-establish the function of the lumbar spinal segment, augmenting the existing anatomical structures. The VTDR was designed to: re-establish flexibility and natural resistance while creating stability within the functional spinal unit (FSU); provide viscoelasticity to mimic the dynamic stiffness and load sharing in the natural disc; preserve physiological range of motion (ROM) in flexion, extension, lateral bending, rotation, and compression; and, provide the correct spine alignment and lordosis. The VTDR is intended to work in conjunction with the surrounding anatomy and mimic the biomechanics of the human disc. This is achieved through the combination of the viscoelastic polymer core and the overall design of the VTDR. The polymer core is able to expand both radially and axially. This axial feature, along with the mechanical characteristics of the polymer, allows the VTDR stiffness to approximate the stiffness of natural human disc. As the VTDR compresses, the polymer expands into the chamber formed by the end cap and retaining plate and expands radially along the polymer annulus (Figure 1). Both of these features are limited by the metal interface to control the stiffness of the VTDR. Data for VTDR patients has been included in SWISSspine Registry since There are five other lumbar TDRs currently available in Switzerland and included in the SWISSspine Registry. FIGURE 3: CROSS-SECTION OF FLD UNLOADED (LEFT) AND UNDER AXIAL COMPRESSION (RIGHT) 3

4 White Paper Freedom Lumbar Disc Clinical Outcomes Benchmarked Against All TDRs in the SWISSspine Registry TDR Data Pool Clinical outcome data for the VTDR has been included in the SWISSspine Registry since There are five other lumbar TDRs available in Switzerland and included in the SWISSspine Registry: ActiveL from Braun/Aesculap (Tuttlingen, Germany); Dynardi Dynamic Artificial Disc System from Zimmer (Warsaw, IN); Maverick from Medtronic Sofamor Danek (Memphis, TN); ProDisc II from Spine Solutions/Synthes (Paoli, PA); and SB Charite from DePuy Spine (Raynham, MA). 3 Data Assessment The documentation forms and outcome instruments that are required for the SWISSspine Registry include primary intervention forms for TDR administered by the surgeon, implant forms for TDR barcode stickers, follow-up forms administered by the surgeon, Euroqol-5D (EQ-5D) patient health status index forms, NASS patient assessments, co-morbidity questionnaires, patient consent forms, and forms explaining the registry and its purpose. Clinical outcome data for the VTDR was analyzed and compared to other TDR technologies in the registry by the IEFO to benchmark the initial data from the viscoelastic technology. The prospective, multi-center data included all TDR surgeons and devices in the registry, as well as data from two VTDR surgeons. The data provided by the IEFO includes the number of patients, gender, number of 1- vs. 2-level surgeries in each population, mean EQ-5D health index scores, mean VAS low back and leg pain scores and statistical power. Outcome data is provided pre-operatively and at each of 3 to 6 months, 1 year and 2 years follow-up. The SWISSspine Registry defined the desired outcomes for the 1-year follow-up to be achievement of both low back pain relief and leg pain relief greater than or equal to 18 mm on VAS, as well as an improvement of greater than or equal to 0.25 points for EQ-5D. The Wilcoxon Rank sum test was used for comparisons of continuous variables between the VTDR and pooled data for all other TDRs in the database. Proportions were compared using a chi-square test. Results and Discussion The patient populations for the TDR and VTDR groups are shown in Table 1. The number of patients for which data was available at each follow-up interval is summarized in Table 2. TABLE 1: TDR AND VTDR PATIENT POPULATION SUMMARY PARAMETER TDR VTDR Total Number of Patients Male : Female Patients 334 : : 12 Average Age (years) Age Range (years) Percentage of Patients with 1-Level vs. Multi-Level Implantation 85% : 15% 34% : 66% 4

5 TABLE 2: NUMBER OF TDR AND VTDR PATIENTS AT EACH FOLLOW-UP INTERVAL INTERVAL TDR VTDR Pre-operative to 6 Months Year Years EQ-5D health status index scores and VAS low back and leg pain scores improved for both the TDR and VTDR patient populations from pre-operative values to 2 years follow-up. Clinical outcome data is summarized in Table 3 and Figures 2, 3 and 4. Statistical analysis demonstrated significant differences between the TDR and VTDR patient scores at all intervals with the single exception of pre-operative EQ-5D health scores. In all cases, clinical outcome scores improved statistically significantly more for the VTDR group than for the TDR group. Radiographs for representative VTDR patients with one, two and three level disc replacement are shown in Appendix I. In all cases, clinical outcome scores improved statistically significantly more for the VTDR group than for the TDR group. TABLE 3: MEAN CLINICAL OUTCOME SCORES FOR TDR AND VTDR POPULATIONS INTERVAL EQ-5D HEALTH STATUS INDEX VAS LOW BACK PAIN (MM) VAS LEG PAIN (MM) TDR VTDR TDR VTDR TDR VTDR Pre-op Months Year Years

6 White Paper Freedom Lumbar Disc Clinical Outcomes Benchmarked Against All TDRs in the SWISSspine Registry FIGURE 2: MEAN EQ-5D HEALTH STATUS INDICES FOR TDR AND VTDR PATIENT POPULATIONS FIGURE 3: MEAN VAS LOW BACK PAIN SCORES FOR TDR AND VTDR PATIENT POPULATIONS 6

7 FIGURE 4: MEAN VAS LEG PAIN SCORES FOR TDR AND VTDR PATIENT POPULATIONS Observation: The VTDR population had statistically significantly better outcomes despite being older, having more levels of involvement and having more pain pre-operatively (Table 4). TABLE 4: TDR AND VTDR PATIENT POPULATION COMPARISON PARAMETER TDR VTDR Mean Patient Age Percent of Multi-Level Cases (compared to 1-level cases) 15% 66% The VTDR population had statistically significantly better outcomes despite being older, having more levels of involvement and having more pain pre-operatively Pre-Op Low Back Pain Score Pre-Op Leg Pain Score

8 White Paper Freedom Lumbar Disc Clinical Outcomes Benchmarked Against All TDRs in the SWISSspine Registry Conclusions In this early analysis, clinical outcomes improved significantly more for VTDR patients than for the pooled group of other TDR patients in the SWISSspine Registry. References 8 1. Aghayev E, Roder C, Zweig T, Etter C, Schwarzenbach O. Benchmarking in the SWISSspine Registry: Results of 52 Dynardi Lumbar Total Disc Replacements Compared with the Data Pool of 431 Other Lumbar Disc Prostheses. Eur Spine J 19; pp , Schluessmann E, Diel P, Aghayev E, Zweig T, Moulin P, Roder C. and On behalf of the SWISSspine Registry Group. SWISSspine: A Nationwide Registry for Health Technology Assessment of Lumbar Disc Prostheses. Eur Spine J 18 (6); p862, Zweig T, Aghayev E, Melloh M, Dietrich D, Roder C, SWISSspine Registry Group. Influence of preoperative leg pain and radiculopathy on outcomes in mono-segmental lumbar Total Disc Replacement: Results from a Nationwide Registry. Eur Spine J published online, 2011.

9 Appendix I: Representative VTDR Cases in the SWISSspine Registry One-level case: a 48 year old male who presented with a 20 year history of chronic low back pain and degenerative disc disease. PRE-OP 8 MONTHS POST-OP 2.5 YEARS FOLLOW UP 9

10 White Paper Freedom Lumbar Disc Clinical Outcomes Benchmarked Against All TDRs in the SWISSspine Registry Two-level case: a 38 year old male who presented with a disc herniation at L5/S1, persistent plegia during flexion and extension of the foot. PRE-OP POST-OP 1.5 YEARS FOLLOW UP 10

11 Three-level case: a 25 year old male who presented with a 10 year history of low back pain and persistent left foot plegia. PRE-OP IMMEDIATE POST-OP X-RAYS 2.5 YEARS FOLLOW UP 11

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