1 Freedom ® Lumbar Disc — Clinical Outcomes Benchmarked Against All TDRs in the SWISSspine Registry CAUTION: Investigational device. Limited by Federal law to investigational use.
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Freedom® Lumbar Disc —Clinical Outcomes BenchmarkedAgainst All TDRs in theSWISSspine Registry
CAUTION: Investigational device.Limited by Federal law to investigational use.
White PaperFreedom® Lumbar Disc —Clinical OutcomesBenchmarked Against All TDRs in theSWISSspine Registry
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Abstract
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 ofHealth regarding reimbursement for technologies and treatments by the basic healthinsurance of Switzerland. Since 2009, a viscoelastic total disc replacement (VTDR), theFreedom Lumbar Disc, has been included in the registry. To benchmark the initial datafrom a viscoelastic technology, clinical outcome data was evaluated and compared tothat 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 collectedpre-operatively and at 3 to 6 months, 1 year and 2 years postoperatively. Theoutcome data assessed were EQ-5D health status index and VAS low back and legpain scores. This data was compared to data in the SWISSspine Registry for all otherTDRs. A Wilcoxon Rank sum test was used for comparisons of continuous variablesbetween the VTDR and pooled data for all other TDRs in the database. Proportionswere compared using a chi-square test.
The VTDR population included 30 patients (18 males, 12 females) with an averageage of 52 (range 26-71). The SWISSspine TDR population included 800 patients (334males, 466 females) with an average age of 42 (range 19-65). The prevalence ofsingle-level and two-level cases was 34%/66% for VTDR and 85%/15% for TDR. EQ-5Dhealth status indices and VAS low back and leg pain scores improved significantlymore (p < 0.05) for the VTDR patients compared to the other TDR patients in theregistry. Health status scores improved from 0.274 preoperatively to 1.000 at twoyears for VTDR patients and from 0.349 preoperatively to 0.800 at two years for otherTDRs (Figure 1). VAS low back scores improved from 76.0 mm to 5.0 mm for the VTDRgroup and from 69.1 mm to 26.5 mm for the TDR group from pre-op to two yearsfollow up (Figure 2). VAS leg pain scores improved from 68.8 mm preoperatively to0.0 mm at two years follow up for the VTDR group and from 53.5 mm preoperativelyto 19.3 mm at two years for the TDR group.
In this early analysis, clinical outcomes improved significantly more for VTDR patientsthan for the pooled group of other TDR patients in the SWISSspine Registry.
This analysis wasconducted to compareoutcomes for patients
treated with a viscoelasticlumbar total disc
replacement (VTDR) tothose treated with all
other lumbar total discreplacements (TDR) in
the SWISSspine Registry.
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Introduction
In March 2005, the Swiss Federal Office of Health initiated the SWISSspine Registry, intended as anationwide 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 goalof 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 acquirednational and international results to decide whether the Swiss basic health insurance shouldreimburse a particular technology.1 The methodology and implementation of the SWISSspine registryis 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 thatcertifies spine surgeons for TDR procedures. All Swiss spine surgeons who intend to perform TDRsurgery must formally apply to the SSS with proof of qualification and adequate infrastructure.1 TheInstitute for Evaluative Research in Orthopedic Surgery at the University of Bern (IEFO) provides thetechnology for the SWISSspine Registry and manages the data. The registry work group consists ofstakeholders in industry, the SSS and the IEFO. Each participant in the registry can make use of itsown data, but the data pool is owned by the SGS, and SGS can delegate data analysis to individualsurgeons or to a neutral academic data clearing center like the IEFO.
Data for VTDR patients has been included in SWISSspine Registry since 2009. There are five otherlumbar 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-pieceviscoelastic artificial disc consisting of an elastomeric core bonded to titanium alloy retaining plateswith 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 andnatural resistance while creating stability within the functional spinal unit (FSU); provideviscoelasticity to mimic the dynamic stiffness and load sharing in the natural disc; preservephysiological range of motion (ROM) in flexion, extension, lateral bending, rotation, andcompression; and, provide the correct spine alignment and lordosis.
The VTDR is intended to work in conjunction with the surrounding anatomy and mimic thebiomechanics of the human disc. This is achieved through the combination of the viscoelastic polymercore 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 toapproximate the stiffness of natural human disc. As the VTDR compresses, the polymer expands into thechamber 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.
FIGURE 3: CROSS-SECTION OF FLD UNLOADED (LEFT) AND UNDER AXIAL COMPRESSION (RIGHT)
Data for VTDR patientshas been included in
SWISSspine Registry since2009. There are five other
lumbar TDRs currentlyavailable in Switzerland
and included in theSWISSspine Registry.
White PaperFreedom® Lumbar Disc —Clinical OutcomesBenchmarked Against All TDRs in theSWISSspine Registry
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TDR Data Pool
Clinical outcome data for the VTDR has been included in the SWISSspine Registry since 2009. Thereare five other lumbar TDRs available in Switzerland and included in the SWISSspine Registry: ActiveLfrom Braun/Aesculap (Tuttlingen, Germany); Dynardi Dynamic Artificial Disc System from Zimmer(Warsaw, IN); Maverick from Medtronic Sofamor Danek (Memphis, TN); ProDisc II from SpineSolutions/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 Registryinclude primary intervention forms for TDR administered by the surgeon, implant forms for TDRbarcode stickers, follow-up forms administered by the surgeon, Euroqol-5D (EQ-5D) patient healthstatus 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 theregistry 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 twoVTDR 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 andleg pain scores and statistical power. Outcome data is provided pre-operatively and at each of 3 to 6months, 1 year and 2 years follow-up.
The SWISSspine Registry defined the desired outcomes for the 1-year follow-up to be achievement ofboth low back pain relief and leg pain relief greater than or equal to 18 mm on VAS, as well as animprovement 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 andpooled 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 patientsfor which data was available at each follow-up interval is summarized in Table 2.
TABLE 1: TDR AND VTDR PATIENT POPULATION SUMMARY
PARAMETER RDTVRDT
Total Number of Patients 800 30
Male : Female Patients 334 : 466 18 : 12
Average Age (years) 42 52
Age Range (years) 19 – 65 26 – 71
Percentage of Patients with 1-Level vs. Multi-Level Implantation
85% : 15% 34% : 66%
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TABLE 2: NUMBER OF TDR AND VTDR PATIENTS AT EACH FOLLOW-UP INTERVAL
EQ-5D health status index scores and VAS low back and leg pain scores improved for both the TDR andVTDR patient populations from pre-operative values to 2 years follow-up. Clinical outcome data issummarized in Table 3 and Figures 2, 3 and 4. Statistical analysis demonstrated significant differencesbetween the TDR and VTDR patient scores at all intervals with the single exception of pre-operativeEQ-5D health scores. In all cases, clinical outcome scores improved statistically significantly more for theVTDR group than for the TDR group. Radiographs for representative VTDR patients with one, two andthree level disc replacement are shown in Appendix I.
TABLE 3: MEAN CLINICAL OUTCOME SCORES FOR TDR AND VTDR POPULATIONS
INTERVAL TDR VTDR
Pre-operative 755 30
3 to 6 Months 647 14
1 Year 514 15
2 Years 151 4
In all cases, clinicaloutcome scores improvedstatistically significantly
more for the VTDR groupthan for the TDR group.
INTERVAL EQ-5D HEALTH STATUS INDEX VAS LOW BACK PAIN (MM) VAS LEG PAIN (MM)
TDR VTDR TDR VTDR TDR VTDR
Pre-op 0.349 0.274 69.1 76.0 53.5 68.8
3-6 Months 0.727 0.860 30.5 15.6 24.0 12.3
1 Year 0.749 0.928 29.6 4.2 21.3 8.5
2 Years 0.800 1.000 26.5 0.5 19.3 0.0
White PaperFreedom® Lumbar Disc —Clinical OutcomesBenchmarked Against All TDRs in theSWISSspine Registry
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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
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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
The VTDR populationhad statistically
significantly betteroutcomes despite being
older, having more levels of involvement and having more pain
pre-operatively
PARAMETER TDR VTDR
Mean Patient Age 42 52
Percent of Multi-Level Cases(compared to 1-level cases)
15% 66%
Pre-Op Low Back Pain Score 69.1 76.0
Pre-Op Leg Pain Score 53.5 68.8
White PaperFreedom® Lumbar Disc —Clinical OutcomesBenchmarked Against All TDRs in theSWISSspine Registry
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Conclusions
In this early analysis, clinical outcomes improved significantly more for VTDR patientsthan for the pooled group of other TDR patients in the SWISSspine Registry.
References1. 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 2190-2199, 2010.
2. 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, 2009.
3. Zweig T, Aghayev E, Melloh M, Dietrich D, Roder C, SWISSspine Registry Group. Influence of preoperative legpain and radiculopathy on outcomes in mono-segmental lumbar Total Disc Replacement: Results from aNationwide Registry. Eur Spine J published online, 2011.
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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 anddegenerative disc disease.
PRE-OP 8 MONTHS POST-OP
2.5 YEARS FOLLOW UP
White PaperFreedom® Lumbar Disc —Clinical OutcomesBenchmarked Against All TDRs in theSWISSspine Registry
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Two-level case: a 38 year old male who presented with a disc herniation at L5/S1, persistent plegiaduring flexion and extension of the foot.
PRE-OP POST-OP
1.5 YEARS FOLLOW UP
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Three-level case: a 25 year old male who presented with a 10 year history of low back pain andpersistent left foot plegia.
PRE-OP
IMMEDIATE POST-OP X-RAYS 2.5 YEARS FOLLOW UP
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