Shoulder geometry after reverse total shoulder arthroplasty with a medialized glenoid and a lateralized humerus predicts subacromial notching and acromial or scapular spine fractures.

Abstract

The primary purpose of this study was to assess whether the difference between the distance from the acromion to the glenosphere center of rotation (DA) and the distance from the greater tuberosity to the glenosphere center (DGT) influences the incidence of subacromial notching (SaN) in shoulders following reverse total shoulder arthroplasty (rTSA) with a medialized glenoid and a lateralized humerus. The secondary purpose was to evaluate whether this relationship also impacts the incidence of acromion or scapular spine fractures. We conducted a retrospective cohort study of patients who underwent rTSA with a medialized glenoid and a lateralized humerus between 2007 and 2021. A total of 526 shoulders were included. Preoperative and postoperative functional outcome scores were evaluated. The Grashey view on plain radiographs preoperatively, within 3 months postoperatively, and at the final follow-up were evaluated. Shoulders were classified into 2 groups: DA ≥ DGT or DA < DGT. Propensity score matching was used to ensure comparability between groups. Clinical outcomes, SaN, and acromion or scapular spine fractures were assessed. After propensity score matching, 360 shoulders were analyzed (240 in the DA ≥ DGT group and 120 in the DA < DGT group). The DA ≥ DGT group exhibited a significantly lower incidence of SaN (0%) compared to the DA < DGT group (10.8%, P < .001). Additionally, the DA ≥ DGT group had a lower rate of acromion or scapular spine fractures (0.4%) compared to the DA < DGT group (5.0%, P = .006). Both groups showed significant and similar improvements in clinical outcomes postoperatively. Implanting components such that DA is greater than DGT in rTSA with a medialized glenoid and a lateralized humerus is associated with a lower incidence of SaN and acromion or scapular spine fractures. These findings suggest that adjusting humeral lateralization or glenosphere distalization to achieve DA ≥ DGT may reduce postoperative complications.