[Biomechanical studies of bisegmental lumbosacral stabilization using the internal fixator or PMMA-simulated fusion]

The implantation of fixation devices increases the primary stability after surgery significantly. Little is known about the comparison of flexibility of instrumented and posterolateral fusions or the lumbosacral distractions spondylodesis (LSDS). The purpose of the study was to compare the flexibility of instrumented and posterolateral fusions or LSDS after simulation with polymethylmethacrylate (PMMA). Dynamic testing from 0-16 Nm in flexion/compression and 0-900 N in compression was performed on 14 lumbosacral spines. The spines were tested intact, after laminectomy, instrumentation with an internal fixateur L5-S1, and simulation of posterolateral fusion L4-S1 or LSDS and thereafter a pseudoarthrosis was simulated. The laminectomy resulted in a significant increase of flexibility and posterior distraction in flexion and compression. The stabilization with an internal fixateur or PMMA simulation for posterolateral fusion or LSDS resulted in a significant decrease of the flexibility. Creation of a unilateral pseudoarthrosis did not effect the flexibility. The instrumented fusion as well as the PMMA simulated bony posterolateral fusion and LSDS resulted in this model in a significant stabilization of the laminectomy. After unilateral fusion the flexibility was not significantly increased.