A comparison of the influence of three different lumbar interbody fusion approaches on stress in the pedicle screw fixation system: Finite element static and vibration analyses

This study aimed to examine breakage risk of the bilateral pedicle screw (BPS) fixation system under static and vibration loadings after three different types of lumbar interbody fusion surgery. A previously validated intact L1-sacrum finite element model was modified to simulate anterior, posterior, and transforaminal lumbar interbody fusion (ALIF, PLIF, and TLIF, respectively) with BPS fixation system (consisting of pedicle screws and rigid connecting rods) at L4-L5. As a risk parameter for breakage, the von Mises stresses in the pedicle screws and the rods for the ALIF, PLIF, and TLIF models under static loading (flexion, extension, lateral bending, and axial torsion moments) and vibration loading (sinusoidal vertical load) were calculated and compared. The calculated von Mises stresses were different in the ALIF, PLIF, and TLIF models, but these stresses for all the fusion models were found to be concentrated in neck of the pedicle screw and middle of the rod under both the static and vibration loadings. The results from static analyses showed that the maximum stress in the BPS fixation system was greater in the TLIF model than in the ALIF and PLIF models under all the applied static loadings. The results from transient dynamic analyses also showed that the TLIF generated greater dynamic responses of the stress in the BPS fixation system to the vertical vibration compared with the ALIF and PLIF. It implies that the TLIF procedure might incur a higher risk of breakage for the BPS fixation system than the ALIF and PLIF procedures.