Acromial stress fractures and reactions after reverse total shoulder arthroplasty: a case-control study.

Background: Acromial stress fractures can occur after reverse total shoulder arthroplasty (RTSA). We performed this study to assess the incidence, risk factors, characteristics, and outcome of acromial stress fractures and reactions after RTSA.

Methods: We determined the incidence of acromial stress fractures and reactions in a cohort of patients who underwent RTSA, and assessed risk factors using a case-control design. Each patient who developed an acromial stress fracture or reaction after RTSA (case) was matched by date of RTSA with two patients who did not develop acromial stress fractures/reactions after RTSA (control subjects); univariate and multivariable analyses were performed to identify risk factors. Characteristics of acromial stress fractures/reactions are described. Outcomes were compared between cases and control subjects.

Results: The incidence of acromial stress fracture/reaction after RTSA was 11% (24/220 RTSAs). Acromial stress fractures/reactions occurred at a median time of 5.5 months after RTSA (range: 20 days to 118 months) and most were fractures (18/24, 75%). Using a multivariable analysis, we found two factors to be independently associated with the occurrence of an acromial stress fracture/reaction after RTSA: corticosteroids use (adjusted OR: 9.6, 95% confidence interval: 1.1 to 86.1, p = 0.04) and previous shoulder surgery (adjusted OR: 7.2, 95% confidence interval: 1.4 to 36.6, p = 0.02). In this cohort, in which the management was exclusively conservative, the occurrence of post-RTSA acromial stress fracture/reaction was associated with a significantly worse functional outcome at last follow-up visit, as compared with control subjects. This was illustrated by significantly lower ASES score, higher SPADI and DASH scores, and worse forward elevation and internal rotation as compared with control patients who did not develop acromial stress fracture/reaction after RTSA.

Conclusions: In our Australian cohort, acromial stress fractures/reactions were relatively common after RTSA, and independently associated with corticosteroids use and previous shoulder surgery. The occurrence of acromial stress fracture/reaction was associated with a significantly worse functional outcome, as compared with patients who do not develop this complication after RTSA.