Postoperative Pelvic Tilt and Sagittal Alignment Outcomes Following Transforaminal Lumbar Interbody Fusion (TLIF)

Retrospective cohort study. To evaluate whether elevated 6-week postoperative pelvic tilt (PT) is associated with reduced 1-year age-adjusted sagittal alignment target achievement after TLIF, independent of baseline alignment and patient/surgical factors. Elevated postoperative PT has been associated with poor sagittal alignment, but prior analyses in degenerative TLIF cohorts have been criticized for reliance on simplified thresholds and limited adjustment for baseline alignment phenotype. The clinical importance of persistent or newly developed postoperative compensation remains incompletely defined. A retrospective analysis of 817 primary TLIF patients was performed. Patients were stratified by 6-week PT into high PT (≥ 25°) and low PT (< 25°) groups. The primary endpoint was 1-year age-adjusted PI–LL target achievement (Lafage age-specific thresholds). The primary multivariable logistic model adjusted for preoperative PT, preoperative PI–LL mismatch, age, sex, BMI, CCI, and number of fused levels; 6-week age-adjusted target status was not included, as it lies on the causal pathway between exposure and outcome, and the corresponding over-adjusted model is reported as a supplementary analysis. A prespecified sensitivity model used continuous 6-week PT. Supportive transition-phenotype analyses (Low→Low, Low→High, High→Low, High→High) were performed in patients with both preoperative and postoperative PT data. High PT was present in 306/817 patients (37.5