Long-Term Persistence of Sagittal Imbalance Following Single-Level Lumbar Fusion

STUDY DESIGN: Retrospective Cohort Study. OBJECTIVE: To assess long-term changes in spinopelvic alignment following single-level lumbar fusion. SUMMARY OF BACKGROUND DATA: Restoration of sagittal balance is known to influence outcomes in adult deformity surgery, but its relevance after short-segment fusion for degenerative disease remains uncertain. The durability of spinopelvic parameters after single-level fusion is not well defined. METHODS: Adult patients who underwent primary single-level fusion between L4-S1 (2010-2019) were retrospectively identified. Standing lateral radiographs were analyzed at baseline, immediately postoperatively, and at 6 months, 1 year, and 2-3 years. Parameters included lumbar lordosis (LL), segmental lordosis (SL), disc height (DH), sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), and PI-LL mismatch. Sagittal imbalance was defined as PT >20° or PI-LL >10°. Data were analyzed with t-tests or Mann-Whitney U tests as appropriate, and stepwise regression modeling identified predictors of imbalance. RESULTS: A total of 413 patients (mean age 62 y, 53% female) met inclusion criteria. SL decreased progressively, with a greater decline at 2-3 years than at 6 months (-1.48° versus -0.64°, P=0.028). Changes in LL, DH, SS, and PT were minimal across follow-up intervals. The proportion of patients with PI-LL mismatch >10° declined from 40.9% immediately postoperatively to 31.0% at 2-3 years (P 20° decreased from 67.6% to 56.9% (P