Fulcrum Side-Bending Radiographs as Predictors of Postoperative Shoulder Imbalance in Lenke Type 5 Adolescent Idiopathic Scoliosis.

Introduction: Postoperative shoulder imbalance (PSI) is a cosmetically and psychologically significant complication following surgical correction of adolescent idiopathic scoliosis (AIS). While commonly studied in thoracic curve patterns, its occurrence in Lenke type 5 curves remains under-investigated. This study aimed to identify radiographic predictors of PSI in Lenke type 5 AIS, with particular emphasis on preoperative fulcrum side bending (FSB) flexibility assessment. Methods: A retrospective review was conducted on 21 patients with Lenke type 5C AIS (mean age 14.6±2.6 years) who underwent posterior spinal fusion using all-pedicle screw constructs. Preoperative and postoperative radiographic parameters were analyzed, including Cobb angles of proximal thoracic, main thoracic (MT), and thoracolumbar/lumbar (TL) curves. Flexibility was assessed with active side bending (ASB) and FSB radiographs. ΔASB and ΔFSB were calculated as the difference from the standing Cobb angles. PSI was defined as a coracoid height difference ≥9 mm or a clavicle angle ≥2°. Results: PSI occurred in 7 patients (33.3%). The PSI group showed significantly greater ΔFSB in the TL curve (41.7°±5.7 vs. 35.3°±2.2, p=0.01), smaller ΔFSB in the MT curve (p=0.04), and a higher TL correction rate (p=0.03). Logistic regression identified ΔFSB in TL (odds ratio [OR] 1.21, p=0.03) and TL correction rate (OR 1.15, p=0.04) as independent predictors of PSI. Conclusions: Preoperative FSB radiographs are valuable not only for estimating curve flexibility but also for identifying patients at risk of PSI in Lenke type 5 AIS. Surgeons should consider not only the absolute flexibility of each curve but also the relative flexibility between TL and MT segments when determining correction magnitude; intraoperative moderation of TL correction may be warranted when the MT segment demonstrates limited compensatory flexibility.