The impact of coracoid morphometry on internal rotation outcome in patients with cuff tear arthropathy treated with reverse shoulder arthroplasty

Abstract

Background: Functional internal rotation (fIR) motion remains a concern after reverse shoulder arthroplasty (RSA). The extreme variability of the coracoid morphometry together with the gain in tension of the conjoint tendon could impact internal rotation (IR) after RSA. Our aim was to evaluate the relationship between postoperative IR outcome and coracoid morphometry, evaluated as anteroposterior (AP) and mediolateral (ML) glenocoracoid distances in a 3-dimensional preoperative computed tomography scans, in a consecutive series of patients undergoing the same RSA implant. Materials and methods: A retrospective analysis of a prospectively collected series of 40 patients (18 male, 22 female; mean age (standard deviation [SD]), 73.4 years [4.1]) submitted to RSA for cuff tear arthropathy was performed. fIR function was measured as the highest midline segment of the back that can be reached and converted into 5 range segments of motion. Participants were divided into 2 groups according to the fIR (group A, ≤6; group B, >6). Passive IR was also measured. The AP and ML glenocoracoid distances were measured, in millimeters, on the preoperative 3-dimensional computed tomography scans. Statistics were performed. Results: The mean follow-up was 29 months (range, 24-39). The mean score for fIR was 6.45 (SD: 1.81) while the mean score for passive IR was 6.84 (SD: 1.75). No difference was found between fIR and passive IR (P = .328). No statistical difference was found between fIR and glenosphere size (P = .562) and fIR and size of the liner (P = .429). Significant statistical correlations have been found between AP and ML coracoid distances and the two groups (AP in group A: 28.50 and B: 31.265, P = .034; ML in group A: 23.053 and B: 14.27, P < .001). Conclusions: Our study demonstrated that coracoid morphometry, evaluated as glenocoracoid distance, significantly impact IR outcomes in a 145° neck shaft angle RSA; in particular, a high ML glenocoracoid distance (>23 mm) was found to be determinant. This anatomical parameter should be considered in the preoperative planning of RSA and additional surgical strategies addressed in order to gain satisfactory fIR.