Preoperative sacroiliac joint degeneration predicts dynamic changes in pelvic incidence and clinical outcomes following degenerative lumbar scoliosis correction.

PURPOSE: To investigate longitudinal changes in pelvic incidence (PI) and its association with preoperative sacroiliac joint (SIJ) degeneration, and to evaluate the subsequent effect on surgical outcomes following degenerative lumbar scoliosis (DLS) corrective surgery.

METHODS

A total of 138 patients with DLS who underwent long‑segment fusion (≥ 4 levels) were retrospectively analyzed. Patients were categorized into three groups according to PI change at the last follow‑up: Group A: stable PI (- 5° to 5°), Group B: decreased PI (> 5° decrease), and Group C: increased PI (> 5° increase). Preoperative SIJ degeneration was evaluated on CT scans. Radiographic parameters and patient‑reported outcome measures (PROMs) were analyzed at baseline and the last follow-up. Multivariable regression analysis was performed to identify factors associated with significant PI change.

RESULTS

Significant PI change was observed in 39.1% of patients. Among patients undergoing sacropelvic fixation, PI tended to decrease postoperatively, whereas PI increased in patients fused to L5 or the sacrum. Patients in group C demonstrated greater PI-LL mismatch and worse sagittal vertical axis at the final follow‑up. Moreover, group C exhibited inferior PROMs and lower rates of achieving minimal clinically important difference in VAS‑back pain, ODI, and SRS‑22r pain and activity domains. Preoperative SIJ degeneration was identified as an independent predictor of significant PI change.

CONCLUSION

PI changed in nearly half of patients undergoing DLS correction surgery, which is associated with preoperative SIJ degeneration. Patients who demonstrated significant PI increases after fusion to L5 or the sacrum tended to have greater postoperative PI-LL mismatch and global sagittal imbalance, as well as inferior pain- and activity-related outcomes. These findings highlight the importance of considering SIJ degeneration when planning sagittal alignment targets and distal fusion strategies in DLS surgery.