Fulcrum flexibility of the main curve predicts postoperative shoulder imbalance in selective thoracic fusion of adolescent idiopathic scoliosis

Abstract

PURPOSE: To identify preoperative predictors for postoperative shoulder imbalance (PSI) after corrective surgery of adolescent idiopathic scoliosis (AIS) and using the fulcrum-bending radiograph to assess flexibility. METHODS: A consecutive surgical cohort of AIS patients undergoing selective thoracic fusion with alternate-level pedicle screw fixation was prospectively studied. Preoperative anteroposterior, lateral and fulcrum-bending radiographs were analysed. Postoperatively, a minimum of 2 years clinical and imaging follow-up was performed of all patients. PSI was defined as a radiographic shoulder height difference of more than 20 mm. RESULTS: A total of 80 patients were included, and 14 patients (18%) were confirmed with PSI at final follow-up. The flexibility of MT curve was an independent risk factor for PSI (odds ratio (OR) = 3.3 per 10% decrease, 95% confidence interval (CI) 1.6-8.2). Twenty-seven patients had a preoperative MT flexibility of < 55% (OR = 11.5, 95% CI 2.8-46.2). Postoperative T1 tilt was significantly higher in the PSI group (p < 0.001), and a T1 tilt of more than 9° resulted in 7.2 times higher odds of developing PSI (95% CI 2.0-26.0). Fulcrum-bending correction index (FBCI) was significantly higher in the PSI group at final follow-up, and 25 patients had a final postoperative MT FBCI above 120% (OR = 8.5 (95% CI 2.3-31.0). CONCLUSIONS: A low preoperative curve flexibility is a significant predictor for PSI. The surgical strategy should consider proximal fusion in presence of low-flexibility MT curves and consider less aggressive MT curve correction. Achieving a level T1 should be a main priority during intraoperative correction and may require fusion of the PT curve.