BACKGROUND:
Increased use of reverse total shoulder arthroplasty (RTSA) has led to an understanding of unique complications such as acromial stress fractures (ASFs). The factors associated with ASFs are not fully known. This study investigates the incidence and predictors of ASFs following RTSA.

METHODS:
All RTSAs performed at a single tertiary referral hospital were retrospectively reviewed. ASF findings were classified as a definitive acromial or scapular spine stress fracture based on radiographic findings or stress reaction based on clinical findings (pain and tenderness at the acromion or acromial spine) without radiographic changes. Preoperative and postoperative radiographs were reviewed for radiographic predictors of postoperative acromial stress pathology. Clinical factors and implant characteristics were also investigated.

RESULTS:
Between September 2010 and January 2017, a total of 1170 RTSAs were performed, with 958 cases (81.9%) having at least 3 months' clinical follow-up (mean, 407 days; range, 90-1698 days). There were 40 ASFs (4.2%) and 61 acromial stress reactions (6.4%). For fractures and reactions, symptom onset averaged 8.8 and 7.3 months (P = .37), respectively, with durations of 4.5 and 2.9 months (P = .02), respectively, following RTSA. Independent predictors of acromial stress pathology were female sex, decreased change in deltoid length, and increased preoperative glenohumeral center-of-rotation medialization.

CONCLUSION:
Acromion-related symptoms are common following RTSA. Female patients with increased preoperative center-of-rotation medialization had an increased incidence of ASFs. Although this study establishes which patients are at risk of ASFs, methods for prevention of ASFs in these patients remain unclear.