Clavicle chest cage angle difference (CCAD): A novel predictor of postoperative shoulder imbalance in patients with adolescent idiopathic scoliosis

Objective. To establish a new radiographical measurement method to determine the best preoperative predictor of postoperative shoulder balance. Summary of Background Data. Shoulder balance is an important aspect of the overall cosmetic balance in patients with adolescent idiopathic scoliosis. Despite recent reports, it is still difficult to estimate the postoperative shoulder balance accurately. Methods. A retrospective review of 89 consecutive patients who had thoracic fusion with a minimum 2-year follow-up (mean, 3.1 yr) was conducted to investigate the radiographical measurements and patient demographics. The shoulder height difference (SHD) was measured as the graded height difference of the soft tissue shadows. SHD more than 2 cm indicated an unbalanced shoulder. The clavicle chest cage angle difference (CCAD) was established and evaluated. The CCAD was graded as grade A: no imbalance (< 0° ), grade B: mild imbalance (0° -10° ), and grade C: significant imbalance (> 10° ). Results. Of the 89 patients, 22 patients had a moderate or significant SHD at 2 years postoperatively and were categorized as the unbalanced shoulder group (unbalanced SD). A significant difference was observed in preoperative CCAD between the balanced and unbalanced SD groups (P = 0.01). The intraclass correlation coefficient for CCAD was 0.94 among the observers. CCAD was consistent from the preoperative to the final postoperative followups in both groups. The classification of the CCAD preoperatively indicated that 12 of 22 (54.4%) patients who were classified into the postoperative unbalanced SD group showed grade 3 CCAD preoperatively, whereas only 9 of 67 (13.4%) patients who were classified in the postoperative balanced SD group had grade 3 CCAD preoperatively. Conclusion. The developed method to predict postoperative shoulder balance was demonstrated to be easy to perform, reliable, and practical. Additionally, we classified the estimation of postoperative shoulder imbalance by preoperation CCAD. The results of this comprehensive review will guide spinal surgeons in their preoperative planning and in the surgical management of adolescent idiopathic scoliosis to reduce postoperative shoulder imbalance.