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.