Transforaminal lumbar interbody fusion (TLIF) with unilateral vs. bilateral pedicle screw fixation in iatrogenic spondylolysis: an in-vitro human cadaveric model.

Abstract

PURPOSE: Transforaminal lumbar interbody fusion (TLIF) utilizes an interbody cage augmented with pedicle screw fixation in the surgical treatment of lumbar spondylolisthesis. The current study compared the multidirectional flexibility of the lumbar spine following TLIF with unilateral (UPS) versus bilateral pedicle screw (BPS) fixation in a cadaveric pars defect model. METHODS: Eleven lumbosacral specimens underwent multidirectional testing (flexion-extension, FE; lateral bending, LB; axial rotation, AR) using a custom six-degree-of-freedom simulator providing unconstrained, angular displacement of 3° per second. Optoelectronic tracking at the operative (L4-L5) and adjacent levels (L3-L4, L5-S1). Seven sequential treatment conditions at the operative level were compared: intact pars, intact pars with UPS or BPS, pars defect with UPS or BPS, pars defect with TLIF and UPS or BPS. A Repeated-measures ANOVA with post hoc Bonferroni was utilized for group-to-group comparisons. RESULTS: BPS resulted in a significant decrease in FE, LB, and AR motion compared to UPS for the intact (FE: 3.1°, LB: 2.9°, AR: 1.7°) and pars defect conditions (FE: 3.5°, LB: 2.9°; AR: 2.5°). With the addition of TLIF, there was significant decrease in AR with BPS versus UPS (1.7°, 95% CI: 0.6–2.9). CONCLUSION: The biomechanical data suggest that TLIF with BPS improves axial rotational stability and should be a biomechanical consideration in the surgical management of bilateral pars defects. Clinically, this may be accomplished via traditional unilateral TLIF through a minimally invasive (MIS) approach with addition of percutaneous fixation contralaterally to preserve the characteristics of the MIS procedure while improving segmental stability of the surgical reconstruction.