Biomechanical comparison of 3 types of transdiscal fixation implants for fixing high-grade L5/S1 spine spondylolisthesis.

Abstract

There are several options for the stabilization of high-grade lumbosacral spondylolisthesis including transdiscal screws, the Bohlman technique (transdiscal fibular strut) and the modified Bohlman technique (transdiscal titanium mesh cage). The choice of an optimum construct remains controversial; therefore, we endeavoured to study and compare the biomechanical performance of these 3 techniques. The aim of this study was to compare 3 types of transdiscal fixation biomechanically in an in vitro porcine lumbar-sacral spine model. Porcine cadaveric biomechanical study. 18 complete lumbar-sacral porcine spines were split into 3 repair groups, transdiscal screws (TS), Bohlman technique, and a modified Bohlman technique (MBT). Range of motion (L3 - S1) was measured in an intact and repaired state for flexion, extension, left/right lateral bending, and left/right torsion. To recreate a high-grade lumbosacral spondylolisthesis a bilateral L5/S1 facetectomy, removing the intervertebral disc completely, and the L5 body was displaced 50%-60% over the sacral promontory. Results were analyzed and compared to intact baseline measurements. Standard quasi-static moments (5 Nm) were applied in all modes. All range of motion (ROM) were in reference to intact baseline values. TS had the lowest ROM in all modes (p=.006-.495). Statistical difference was found only in extension for TS vs. BT (p=.011) and TS vs. MBT (p=.014). No bone or implant failures occurred. TS provided the lowest ROM in all modes of loading compared to Bohlman technique and MBT. Our study indicates that TS results in the most biomechanically stable construct. Knowledge of the biomechanical attributes of various constructs could aid physicians in choosing a surgical construct for their patients.