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 <0.001). Similarly, PT >20° decreased from 67.6% to 56.9% ( P <0.001). Despite these modest improvements, over half of patients remained imbalanced at final follow-up. Regression analysis showed that older age and greater number of decompressed levels were associated with persistent imbalance. Conclusions. After single-level lumbar fusion, sagittal parameters stabilize by 6 months, with slight compensatory improvement thereafter. Most patients, however, continue to demonstrate imbalance, and the clinical significance of correcting spinopelvic parameters in focal degenerative disease remains uncertain.