The relationship between postoperative shoulder balance and coronal sacral slanting in adolescent idiopathic scoliosis patients with double structural curves

BACKGROUND: Adolescent Idiopathic Scoliosis (AIS) is a complex spinal deformity where surgical correction aims to restore both spinal and shoulder balance. Postoperative shoulder imbalance (PSI) is a common complication, leading to patient dissatisfaction. While numerous factors contribute to PSI, the role of coronal sacral slanting, particularly in Lenke type 3 and 6 patients, is not well understood. This study investigated the relationship between postoperative shoulder balance and coronal sacral slanting in these patients. METHODS: A retrospective cohort study was conducted on 231 AIS patients (102 males, 129 females) with Lenke type 3 and 6 curves who underwent posterior fusion and had a minimum of 24 months of follow-up. Patients were divided into a postoperative shoulder imbalance (PSI) group (n = 61) and a postoperative shoulder balance (PSB) group (n = 170). They were also subdivided into three groups according to coronal sacral slanting: left-sided (> 3°), non-slanting (0°-3°), and right-sided (> 3°). Radiographic parameters, including clavicle angle (CA), coracoid height difference (CHD), T1 tilt, radiographic shoulder height (RSH), and distal vertebral wedge angle (DWA), were measured at various follow-up intervals. RESULTS: At final follow-up, the PSI group showed significantly worse outcomes in all shoulder parameters (RSH, CA, T1 Tilt, and CHD) and a larger sacral slanting angle compared to the PSB group (P < 0.05). No significant differences were found in main curve correction rates between the two groups. In the sacral slanting subgroups, while preoperative shoulder parameters and main curve correction rates were similar, the postoperative DWA was significantly different among the groups (P < 0.001). The right-side slanting group demonstrated a significant increase in DWA and the largest improvement in RSH, with a mean change of -7.26 mm, suggesting adaptive changes. CONCLUSION: Due to the observational nature of this study, a direct causal relationship cannot be definitively established; however, our findings indicate that right-side sacral slanting is significantly associated with a better long-term recovery of postoperative shoulder balance. This process may be mediated by an adaptive increase in the distal wedge angle. These insights may help surgeons better predict and manage postoperative shoulder imbalance in Lenke type 3 and 6 AIS patients.