Effect of High Pelvic Incidence on Fixation Failure in Single-Level Transforaminal Lumbar Interbody Fusion for Low-Grade Spondylolisthesis: A Retrospective Cohort Study

Objective: To investigate the association between pelvic incidence (PI) and fixation failure following single-level transforaminal lumbar interbody fusion (TLIF) for low-grade spondylolisthesis and to identify risk factors for pedicle screw loosening. Methods: This retrospective study included 80 patients who underwent single-level TLIF and were divided into a high PI group (n = 40) and a normal/low PI group (n = 40). Radiographic parameters including PI, lumbar lordosis (LL), pelvic tilt (PT), sacra l slope (SS), listhesis magnitude, and PI-LL mismatch were evaluated pre- and postoperatively. Screw loosening and fusion status were assessed at 6, 12, and 24 months. Multivariate logistic regression analysis was performed to identify independent risk factors for screw loosening. Results: The high PI group demonstrated significantly higher screw loosening rates than the normal/low PI group at all follow-up time points, with a rate of 57.5% versus 28.2% at 24 months (p = 0.012). Fusion rates were comparable between groups. Multivariate analysis identified high PI and residual listhesis were independent risk factors for screw loosening (Odds ratio 1.05 and 1.35). PI-LL mismatch > 10° showed higher odds but were not statistically significant. Conclusions: High PI is associated with an increased risk of pedicle screw loosening after single-level TLIF. Careful preoperative assessment and postoperative monitoring may help reduce fixation-related complications.