Send Orders for Reprints to reprints@benthamscience.net The Open Spine Journal, 2014, 6, 9-25 9 1876-5327/14 2014 Bentham Open Open Access In Vitro Testing of Lumbar Disc Arthroplasty Devices Denis J. DiAngelo a,b,* , Kevin T. Foley a,b , Brian P. Morrow a , Peter Wong a , Kelly Kiehm b , Anthony Sin b , Rudolf Bertagnoli c , Celeste Abjornson $ and Brian P. Kelly a a Department of Orthopedic Surgery and Biomedical Engineering, University of Tennessee Health Science Center, Memphis, TN, USA b Department of Neurosurgery, University of Tennessee Health Science Center, Memphis, TN, USA c Spine Center, St. Elizabeth Klinikum, Straubing, Germany $ Synthes Spine, West Chester, PA Research support from Synthes Spine, West Chester, PA and use of the surgical facilities at the Medical Education and Research Institute, Memphis, TN, USA Abstract: Background Context: Interest in lumbar disc arthroplasty as an alternative to fusion surgery continues to grow. The goal of disc arthroplasty is to replace the diseased disc while preserving and/or restoring motion at the operated spinal level. Different paradigms exist in the design of total disc arthroplasty devices. Purpose: The purpose of this study was to compare the in vitro biomechanics of a more constrained ball-and-socket design (Prodisc-L, Synthes Spine and Maverick, Medtronic) and a less constrained mobile-bearing design (Charité, DePuy). The biomechanical performance of the disc prostheses was compared to harvested and fused spine conditions. The fused model was simulated using single-level posterior pedicle screw fixation instrumentation. Study Design/Setting: In vitro test to compare the biomechanical properties of three different lumbar disc replacement devices in a human cadaveric model. Methods: Twenty human cadaveric lumbar spines (L1-sacrum) were tested in flexion, extension, lateral bending, and axial rotation under displacement control to a target bending moment of 8Nm. The spine conditions tested were: harvested spine (n=19); L5-S lumbar disc replacement using Prodisc-L (n=13); Maverick (n=7); Charité (n=6); and L5-S pedicle screw fixation (PSF) (n=19). The first 12 spines were split into 2 groups: 6 were instrumented with the Charité and 6 with the ProDisc-L. The next 7 spines tested were split into 2 groups: 4 instrumented with ProDisc-L and 3 with the Maverick. After completing all tests on the second group of 7, the Maverick and ProDisc-L discs were swapped between spines and retested. The Click’X pedicle screw system (Synthes Spine) was used to simulate the fusion model in all spines tested. For axial rotation tests, a 100N compressive load was applied. Measurements included vertebral motions, total spine rotation, and applied loads. The percent contribution of rotation at the instrumented (L5-S) level relative to total rotation (L1-S), as well as at the remaining adjacent levels relative to total rotation, was determined a common load limit (8Nm) and compared using a one-way ANOVA and SNK test (P<0.05). Results: A significant reduction in motion occurred at the operated level of PSF condition compared to the three disc arthroplasty conditions for all loading modes. No differences occurred between the 3 disc conditions for all modes tested, except at the instrumented level of the ProDiscL (93% of H) and Maverick (128% of H) spine conditions during combined flexion+extension. The reduced motion at the operative level of the PSF condition was transferred to the adjacent levels and caused a significant increase in motion during combined flexion+extension at all adjacent levels for the 3 disc arthroplasty conditions, during combined right+left lateral bending at L1-L2 for all disc conditions and at L3-L4 for the Charité, and during combined right+left axial rotation at L3-L4 for all three disc conditions. Conclusions: Issues pertaining to adjacent segment disease (ASD) with pedicle screw fixation were supported by increased motion contributions at multiple sub-adjacent segments. However, disc arthroplasty eliminated any significant increase and may prevent ASD. Compared to pedicle screw fixation, the three differently designed disc prostheses (Prodisc-L, Maverick, and Charité) remained stable and provided improved lumbar mobility. The only notable difference between the disc designs was the increased combined flexion+extension motion at the operative level of the Maverick disc compared to the ProDisc-L device. Keywords: Lumbar spine, biomechanical testing, spinal instrumentation, lumbar disc, arthroplasty, biomechanics. INTRODUCTION Back pain is one of the most common reasons to seek care and affects approximately one fourth of the adult *Address correspondence to this author at the Department of Orthopedic Surgery and Biomedical Engineering, The University of Tennessee Health Science Center, 956 Court Ave., Suite E226, Memphis, TN 38163, USA; Tel: 901-448-7744; Fax: 901-448-7387; E-mail: ddiangelo@uthsc.edu population in the United States [1]. When conservative treatments for this disease fail, surgery may be indicated. For lumbar spine structural pain, the gold standard surgical treatment has been vertebral body fusion. Reported drawbacks and complications associated with spinal fusion surgery have included the need for external orthosis, the development of pseudoarthrosis, which may be associated with continued symptoms of back pain, the degeneration of