Coracoid bone block transfer procedure: Correlation between subscapularis volume below the bone graft and shoulder stability

Abstract Introduction Coracoid bone graft transfer has become the gold standard in patients with recurrent anterior shoulder instability associated with bony defect. Several studies have shown that the main stabilizing component of this procedure is the sling effect by the conjoint tendon and the lower portion of subscapularis (SS). The purpose of this study was to determine whether a larger SS volume below the bone block was correlated to greater postoperative shoulder stability. Materials and methods This prospective study included a cohort of patients who underwent open coracoid bone graft transfer for post-traumatic recurrent anterior shoulder instability. Forty patients were reviewed at 2 years with a clinical and CT scan evaluation. A correlation analysis assessed the relation between the SS volume index (ratio of SS volume below the bone block to volume over the bone block) and Rowe and Walch-Duplay instability scores. Results There exists a positive and significant correlation between SS volume index and postoperative Rowe score, r  = 0.37 ( P  = 0.03). The same trend was observed for Walch-Duplay score without statistical significance. A larger inferior SS volume did not result in a limitation of external rotation, greater fatty infiltration, or malposition of the coracoid graft. Conclusion A larger SS volume below the bone block is related to greater postoperative shoulder stability. We recommend performing the split in the middle of the SS or higher instead of the junction of the superior two-thirds and inferior one-third as usually reported. Level of evidence III, prospective study.