BIOMECHANICS OF BISEGMENTAL LUMBOSACRAL S TABILIZATION WITH FIXATEUR INTERNE OR WITH PMMA SIMULATED FUSIONS

The implantation of fixation devices increases the primary stability a fter surgery significantly. Little is known about the comparison of fl exibility of instrumented and posterolateral fusions or the lumbosacra l distractions spondylodesis (LSDS). The purpose of the study was to c ompare the flexibility of instrumented and posterolateral fusions or L SDS after simulation with polymethylmethacrylat (PMMA). Dynamic testin g from 0-16 Nm in flexion/ compression and 0-900 N in compression was performed on 14 lumbosacral spines. The spines were tested intact, aft er laminectomy, instrumentation with an internal fixateur L5-S1, and s imulation of posterolateral fusion L4-S1 or LSDS and thereafter a pseu doarthrosis was simulated. The laminectomy resulted in a significant i ncrease of flexibility and posterior distraction in flexion and compre ssion. The stabilization with an internal fixateur or PMMA simulation for posterolateral fusion or LSDS resulted in a significant decrease o f the flexibility. Creation of a unilateral pseudoarthrosis did not ef fect the flexibility. The instrumented fusion as well as the PMMA simu lated 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.