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%). At 1 year, high PT patients achieved the age-adjusted target less often than low PT patients (21.5% vs. 56.5%, p < 0.001). In the baseline-adjusted primary model (N = 450, 193 events), high 6-week PT was independently associated with lower odds of 1-year age-adjusted target achievement (OR 0.41, 95% CI 0.21-0.79, p = 0.008). In the prespecified continuous sensitivity model, each 1° increase in 6-week PT was associated with lower odds of 1-year target achievement (OR 0.88, 95% CI 0.84-0.93, p < 0.001). Transition analysis showed that patients who shifted from low preoperative PT to high postoperative PT (Low→High, 12.1%) had worse 1-year PI-LL (10.0 vs. 1.4, p < 0.001) and lower 1-year target achievement (26.8% vs. 57.5%, p < 0.001) than patients remaining Low→Low.

Elevated 6-week postoperative PT identifies a persistent compensated sagittal phenotype after TLIF and independently predicts lower likelihood of 1-year age-adjusted alignment success. Monitoring postoperative PT may improve early risk stratification for residual sagittal malalignment in degenerative TLIF patients.