Initial stability of two PLIF-techniques. A biomechanical comparison usinga finite element model

The purpose of this study was to compare the initial stiffness of two techn iques for posterior interbody lumbar fusion (PLIF) by a finite element appr oach. Thus a finite element model of a human L3/4 spinal segment was genera ted. Stiffness of the intact model was tested under compression (600 N), to rsion (25 Nm) and shearing forces (250 N) without preload. The results were compared to the stiffness following simulation of PLIF with two BAK-Cages and PLIF with two Harms-Cages and additional posterior screw-rod-osteosynth esis. PLIF with two BAK-Cages resulted in a loss of stiffness in compressio n, torsion and shearing. PLIF with two Harms-Cages and posterior osteosynth esis resulted in an increase of stiffness in compression, torsion and shear ing.