New Interspinous Implant Evaluation Using an In Vitro Biomechanical Study Combined With a Finite-Element Analysis

Study Design. A combined in vitro and finite-element analysis was completed to assess the biomechanical effect of a new interspinous implant on the lumbar spine. Objective. The aim was to investigate the effect of an interspinous implant on the biomechanical behavior of a vertebral segment. Methods. An in vitro study on L3–L5 segments from fresh human cadavers was conducted combined with a 3-dimensional finite-element analysis. Intact, injured, and instrumented states of L4–L5 were compared loaded in flexion-extension, lateral-bending, and torsion. The evaluated implant is an interspinous spacer fixed to the spine by 2 polyester braids looped around the proximal and distal spinous. Results. The effect of the implant appeared mainly in flexion-extension: experimental results showed reduced range of motion of the instrumented spine regarding the injured and intact one; and finite-element analysis indicated a decrease of disc stresses and increase of loads transmitted to the spinous processes. Conclusion. In this in vitro and finite-element analysis, the role of the new interspinous implant appeared to reduce motion without suppressing it and to lower stress in the disc fibers and anulus matrix. Further in vivo investigations are necessary to draw definitive conclusions.

[1]  M M Panjabi,et al.  Biomechanical Evaluation of Spinal Fixation Devices: I. A Conceptual Framework , 1988, Spine.

[2]  P. Roughley.  Biology of Intervertebral Disc Aging and Degeneration: Involvement of the Extracellular Matrix , 2004, Spine.

[3]  S. Holm,et al.  Pathophysiology of disc degeneration. , 1993, Acta orthopaedica Scandinavica. Supplementum.

[4]  S. Yerby,et al.  The Effects of an Interspinous Implant on Intervertebral Disc Pressures , 2003, Spine.

[5]  Y. Morimoto,et al.  Intraoperative Measurement of Lumbar Spinal Instability , 1992, Spine.

[6]  D. R. Sumner,et al.  Biomechanics introduction. 1995 Focus Issue Meeting on Fusion. , 1995, Spine.

[7]  T. Hansson,et al.  1997 Volvo Award Winner in Biomechanical Studies: Kinematic Behavior of the Porcine Lumbar Spine: A Chronic Lesion Model , 1997, Spine.

[8]  J C Leahy,et al.  Slippage of a spinous process hook during flexion in a flexible fixation system for the lumbar spine. , 2001, Medical engineering & physics.

[9]  Minns Rj,et al.  Preliminary design and experimental studies of a novel soft implant for correcting sagittal plane instability in the lumbar spine. , 1997 .

[10]  J. Sénégas,et al.  Mechanical supplementation by non-rigid fixation in degenerative intervertebral lumbar segments: the Wallis system , 2002, European Spine Journal.

[11]  R. Baskerville,et al.  The Graf stabilisation system: early results in 50 patients , 2004, European Spine Journal.

[12]  A. Nachemson.  Recent advances in the treatment of low back pain , 2004, International Orthopaedics.

[13]  L. Claes,et al.  Testing criteria for spinal implants: recommendations for the standardization of in vitro stability testing of spinal implants , 1998, European Spine Journal.

[14]  Paul Park,et al.  Adjacent Segment Disease after Lumbar or Lumbosacral Fusion: Review of the Literature , 2004, Spine.

[15]  W. F. Deans,et al.  Mechanical testing of a flexible fixation device for the lumbar spine , 2000, Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine.

[16]  S Etebar,et al.  Risk factors for adjacent-segment failure following lumbar fixation with rigid instrumentation for degenerative instability. , 1999, Journal of neurosurgery.

[17]  Hansen A. Yuan,et al.  Prosthetic disc replacement: the future? , 2002, Clinical orthopaedics and related research.

[18]  G. Dubois,et al.  Dynamic neutralisation of the lumbar spine confirmed on a new lumbar spine simulator in vitro , 1999, Archives of Orthopaedic and Trauma Surgery.

[19]  V. C. Mow,et al.  Regional Variation in Tensile Properties and Biochemical Composition of the Human Lumbar Anulus Fibrosus , 1994, Spine.

[20]  F. Unglaub,et al.  Stimulierung degenerativer Veränderungen der Bandscheibe durch axiale Belastung , 2003 .

[21]  M M Panjabi,et al.  Disc Degeneration Affects the Multidirectional Flexibility of the Lumbar Spine , 1994, Spine.

[22]  J. Kleiner,et al.  The Effect of Instrumentation on Human Spinal Fusion Mass , 1995, Spine.

[23]  W. Skalli,et al.  Variability of the spine and pelvis location with respect to the gravity line: a three-dimensional stereoradiographic study using a force platform , 2003, Surgical and Radiologic Anatomy.

[24]  R. Aspden,et al.  An In Vitro Study of the Biomechanical Effects of Flexible Stabilization on the Lumbar Spine , 1997, Spine.

[25]  Manohar M. Panjabi,et al.  Clinical Biomechanics of the Spine , 1978 .

[26]  Astrid Junge,et al.  Clinical Experience With the Dynesys Semirigid Fixation System for the Lumbar Spine: Surgical and Patient-Oriented Outcome in 50 Cases After an Average of 2 Years , 2005, Spine.

[27]  J. Lotz,et al.  Effects of Controlled Dynamic Disc Distraction on Degenerated Intervertebral Discs: An in Vivo Study on the Rabbit Lumbar Spine Model , 2005, Spine.

[28]  F Lavaste,et al.  Three-dimensional geometrical and mechanical modelling of the lumbar spine. , 1992, Journal of biomechanics.

[29]  M. Moon.  Preliminary design and experimental studies of a novel soft implant for correcting sagittal plane instability in the lumbar spine. , 1999, Spine.

[30]  F Lavaste,et al.  [Quantitative 3D anatomy of the lumbar spine]. , 2001, Revue de chirurgie orthopedique et reparatrice de l'appareil moteur.

[31]  Rigby Mc,et al.  Graf ligament stabilisation: mid- to long-term follow-up. , 2001 .

[32]  C. Laudet,et al.  Comportement bio-mécanique d'un ressort inter-apophysaire vertébral postérieur analyse expérimentale du comportement discal en compression et en flexion/extension , 1993 .

[33]  W. F. Deans,et al.  Design of spinous process hooks for flexible fixation of the lumbar spine , 2000, Proceedings of the Institution of mechanical engineers. Part H, journal of engineering in medicine.