Predicting postoperative imbalance in adult spinal deformity staged surgery using predictive thresholds

Two-stage surgeries are increasingly used to minimize complications in adult spinal deformity (ASD) correction, yet the specific contributions of lateral lumbar interbody fusion (LLIF) and posterior column osteotomy/posterior spinal fusion (PCO/PSF) remain underexplored. This study evaluates their roles in deformity correction and establishes predictive thresholds for optimizing surgical planning. A total of 151 ASD patients (mean age 69.5 years) underwent staged LLIF and PCO/PSF surgeries one week apart. Radiographic parameters were analyzed preoperatively (Pre-), post- 1st LLIF (M-), post- 2nd PCO/PSF (Post-), and at two-year follow-up (F-). Correction rates were 80.9% for PI-LL mismatch (35.5% LLIF, 64.5% PCO/PSF), 40.5% for pelvic tilt (39.4% LLIF, 60.6% PCO/PSF), and 69.1% for C7 SVA (45.7% LLIF, 54.3% PCO/PSF). Coronal correction of the Cobb angle reached 76.7% (33.1% LLIF, 66.9% PCO/PSF). Significant ODI and SRS-22 score improvements were noted at two years. Predictive thresholds for imbalance were M-SVA 75.3 mm, M-PI-LL 32.5°, and M-PT 35.5°. The 2nd PCO/PSF contributes more to correction, and predictive thresholds aid surgical planning, reducing postoperative imbalance for better outcomes.