The role of acromial morphometry in the development of acromial stress fracture following reverse total shoulder arthroplasty

Background Indications for reverse total shoulder arthroplasty are expanding, and postoperative acromial stress fractures are a troubling postoperative complication. The purpose of this study was to determine if differences in acromial morphometry were present between cohorts with and without this complication. Methods A retrospective review of 101 reverse total shoulder arthroplasty procedures met criteria for the study. A total of eight acromial measurements on preoperative computed tomography scans were performed in axial, coronal, and sagittal views. Postoperative acromial stress fractures were confirmed by computed tomography scan on six patients and classified by fracture type. Statistical analysis was performed using a Mann–Whitney U test. Results The median acromial thickness at the posterior and lateral half was significantly thinner in the fracture cohort compared to the non-fracture cohort. Fracture and non-fracture cohort measurements demonstrated a median lateral thickness of 6.8 and 8.7 mm (p = 0.010), respectively, and median posterior thickness of 7.6 and 9.5 mm (p = 0.008), respectively. There were no demographic differences between cohorts. Discussion Two acromial measurements (lateral and posterior thickness) were associated with the development of postoperative acromial stress fracture following reverse total shoulder arthroplasty. These findings suggest that a thinner acromion in the lateral and posterior half is a risk factor for an acromial stress fracture following reverse total shoulder arthroplasty.