Incidence and risk factors of acromial fracture following reverse total shoulder arthroplasty

Background: The occurrence and related predictors of acromial fracture following reverse total shoulder arthroplasty (RTSA) have not been fully elucidated. The aim of this study was to determine the incidence and risk factors of acromial fractures after RTSA. Methods: We conducted a multicenter, retrospective case-control study of 787 cases (29 in acromial fracture group and 758 in control group) that underwent RTSA performed by 6 surgeons. The mean duration of follow-up after RTSA was 31.6 ± 21.8 months (range, 12-136 months). Demographic variables (age, sex, arm dominance, body mass index, working status, bone mineral density [BMD]), clinical variables (preoperative diagnosis, previous operation, implant design, preoperative clinical scores, screw size in glenoid fixation, postoperative rehabilitation), and radiographic variables (acromial thickness, critical shoulder angle, deltoid length, humeral offset to lateral acromion) were investigated. To determine risk correlation, univariate analysis and multivariate logistic regression analysis with calculated odds ratios (ORs) were performed. Results: Postoperative acromial fractures occurred in 29 of the 787 shoulders with RTSA (3.7%). Acromial fractures were detected at a mean of 10.0 months (range, 1-66 months) postoperatively. Univariate analysis revealed that the occurrence of an acromial fracture was significantly associated with a previous operation (38% [11 of 29] vs. 21% [156 of 758], P =.025) and BMD (–2.33 vs. –1.74, P =.013). Multivariate logistic regression analysis found that the occurrence of a postoperative acromial fracture was significantly associated with a previous operation (P =.034; OR, 2.91; 95% confidence interval, 1.08-7.84) and deltoid length (P =.004; OR, 1.04; 95% confidence interval, 1.01-1.07). Conclusion: Acromial fracture following RTSA is not an uncommon complication, with an overall incidence of 3.7%. A previous operation, increased deltoid length, and low BMD were risk factors of acromial fracture following RTSA.