Abstract
The goal of non-fusion stabilization is to reduce the mobility of the spine segment to less than that of the intact spine specimen, while retaining some residual motion. Several in vitro studies have been conducted on a dynamic system currently available for clinical use (Dynesys®). Under pure moment loading, a dependency of the biomechanical performance on spacer length has been demonstrated; this variability in implant properties is removed with a modular concept incorporating a discrete flexible element. An in vitro study was performed to compare the kinematic and stabilizing properties of a modular dynamic lumbar stabilization system with those of Dynesys, under the influence of an axial preload. Six human cadaver spine specimens (L1–S1) were tested in a spine loading apparatus. Flexibility measurements were performed by applying pure bending moments of 8 Nm, about each of the three principal anatomical axes, with a simultaneously applied axial preload of 400 N. Specimens were tested intact, and following creation of a defect at L3–L4, with the Dynesys implant, with the modular implant and, after removal of the hardware, the injury state. Segmental range of motion (ROM) was reduced for flexion–extension and lateral bending with both implants. Motion in flexion was reduced to less than 20% of the intact level, in extension to approximately 40% and in lateral bending a motion reduction to less than 40% was measured. In torsion, the total ROM was not significantly different from that of the intact level. The expectations for a flexible posterior stabilizing implant are not fulfilled. The assumption that a device which is particularly compliant in bending allows substantial intersegmental motion cannot be fully supported when one considers that such devices are placed at a location far removed from the natural rotation center of the intervertebral joint.
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References
Andersson GB (1999) Epidemiological features of chronic low-back pain. Lancet 354:581–585
Beastall J, Karadimas E, Siddiqui M et al (2007) The Dynesys lumbar spinal stabilization system: a preliminary report on positional magnetic resonance imaging findings. Spine 32(6):685–690
Cripton PA, Bruehlmann SB, Orr TE et al (2000) In vitro axial preload application during spine flexibility testing: towards reduced apparatus-related artefacts. J Biomech 33(12):1559–1568
Cripton PA, Jain GM, Wittenberg RH et al (2000) Load-sharing characteristics of stabilized lumbar spine segments. Spine 25(2):170–179
Dhillon N, Bass E, Lotz J (2001) Effect of frozen storage on the creep behaviour of human intervertebral discs. Spine 26(8):883–888
Eck JC, Humphreys SC, Hodges SD (1999) Adjacent-segment degeneration after lumbar fusion: a review of clinical, biomechanical, and radiologic studies. Am J Orthop 28:336–340
Freudiger S, Dubois G, Lorrain M (1999) Dynamic neutralization of the lumbar spine confirmed on a new lumbar spine simulator in vitro. Arch Orthop Trauma Surg 119:127–132
Fritzell P, Hagg O, Wessberg P et al (2001) Volvo award winner in clinical studies: lumbar fusion versus nonsurgical treatment for chronic low back pain: a multicenter randomized controlled trial for the Swedish Lumbar Spine Study Group. Spine 26:2521–2532 (discussion 32–34)
Gédet P, Thistlethwaite PA, Ferguson SJ (2007) Minimizing errors during in vitro testing of multisegmental spine specimens: considerations for apparatus design and experimental protocol. J Biomech 40(8):1881–1885
Jensen LM, Dawson JM, Springer S et al (2004) Kinematic evaluation of non-rigid posterior stabilization. Proceedings of the 50th annual meeting of the Orthopaedic Research Society, San Francisco
Lee CK (1988) Accelerated degeneration of the segment adjacent to a lumbar fusion. Spine 13:375–377
Lehmann TR, Spratt KF, Tozzi JE et al (1987) Long-term follow-up of lower lumbar fusion patients. Spine 12(2):97–104
Link HD (2002) History, design and biomechanics of the LINK SB Charite artificial disc. Eur Spine J 11(Suppl 2):98–105
Mayer HM, Wiechert K, Korge A et al (2002) Minimally invasive total disc replacement: surgical technique and preliminary clinical results. Eur Spine J 11(Suppl 2):124–130
McKinnon ME, Vickers MR, Ruddock VM et al (1997) Community studies of the health service implications of low back pain. Spine 22:2161–2166
Niosi CA, Zhu QA, Wilson DC et al (2006) Biomechanical characterization of the three-dimensional kinematic behaviour of the Dynesys dynamic stabilization system: an in vitro study. Eur Spine J 15:913–922
Panjabi MM (1988) Biomechanical evaluation of spinal fixation devices: I. A conceptual framework. Spine 13(10):1129–1134
Panjabi MM, Krag M, Summers D et al (1988) Biomechanical time-tolerance of fresh cadaveric human spine specimens. J Orthop Res 3(3):292–300
Patwardhan AG, Havey RM, Meade KP et al (1999) A follower load increases the load-carrying capacity of the lumbar spine in compression. Spine 24:1003–1009
Schlegel JD, Smith JA, Schleusener RL (1996) Lumbar motion segment pathology adjacent to thoracolumbar, lumbar, and lumbrosacral fusion. Spine 21:970–981
Schmoelz W, Huber JF, Nydegger T et al (2003) Dynamic stabilization of the lumbar spine and its effects on adjacent segments: an in vitro experiment. J Spinal Disord Tech 16(4):418–423
Schmoelz W, Huber JF, Nydegger T et al (2006) Influence of a dynamic stabilization system on load bearing of a bridged disc: an in vitro study of intradiscal pressure. Eur Spine J 15(8):1276–1285
Seitsalo S, Schlenzka D, Poussa M et al (1997) Disc degeneration in young patients with isthmic spondylolisthesis treated operatively or conservatively: a long-term follow-up. Eur Spine J 6(6):393–397
Stoll TM, Dubois G, Schwarzenbach O (2002) The dynamic neutralization system for the spine: a multi-center study of a novel non fusion system. Eur Spine J 11(Suppl 2):170–178
Tawackoli A, Marco R, Liebschner MA (2004) The effect of compressive axial preload on the flexibility of the thoracolumbar spine. Spine 29(9):988–993
Wilke H-J, Jungkunz B, Wenger K et al (1998) Spinal segment range of motion as a function of in vitro test conditions. Effects of exposure period, accumulated cycles, angular deformation rate and moisture condition. Anat Rec 251(1):15–19
Wilke HJ, Wenger K, Claes L (1998) Testing criteria for spinal implants: recommendations for the standardization of in vitro stability testing of spinal implants. Eur Spine J 7:148–154
Acknowledgments
This study was partially supported by Synthes GmbH, Oberdorf and the National Research Program NRP 53 “Muskuloskeletal Health—Chronic Pain” of the Swiss National Science Foundation (Project 405340-104681).
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Gédet, P., Haschtmann, D., Thistlethwaite, P.A. et al. Comparative biomechanical investigation of a modular dynamic lumbar stabilization system and the Dynesys system. Eur Spine J 18, 1504–1511 (2009). https://doi.org/10.1007/s00586-009-1077-7
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DOI: https://doi.org/10.1007/s00586-009-1077-7