Acromial Fractures Following Reverse Total Shoulder Arthroplasty: A Cohort Controlled Analysis

Fractures of the acromion can develop after reverse total shoulder arthroplasty (RTSA). This study sought to identify risk factors for acromial fracturesin patients with RTSA. A total of 1146 RTSAs were performed at theauthors' institution between 1999 and 2016. In 21 patients ( 1.8%), the authors identified an acromial fracture during the postoperative course. These patients were compared with a matched cohort of 84 patients who had not developed an acromial fracture postoperatively. As an indicator of changes in pre- to postoperative deltoid loading, the authors created an angle called the "delta angle." There was an elevated risk for acromial fractures with lower lateralization of the humerus from pre- to postoperatively (4.1 +/- 7.1 mm vs 8.4 +/- 6.1 mm; P=.006), lower preoperative anteroposterior acromial slope (117.3 degrees +/- 11.2 degrees vs 121.7 degrees +/- 17.0 degrees; P=.044), and higher glenoid inclination (beta angle, 72.0 degrees +/- 5.5 degrees vs 76.5 degrees +/- 6.8 degrees; P=.005). Pre- topostoperative changes in the beta angle (9.2 degrees +/- 8.0 degrees vs 4.4 degrees +/- 9.4 degrees; P=.022) and the delta angle (29.4 degrees +/- 8.1 degrees vs 19.5 degrees +/- 9.7 degrees; P<.001) were larger in the fracture group. In addition, diagnosed and treated osteoporosis appeared to be a risk factor for acromial fractures (33% vs 13%; P=.047). The delta angle after RTSA seems to correlate with the risk of developing an acromial fracture. Patients with a high glenoid inclination and/or osteoporosis should be informed that they are at risk. Further, surgeons should be aware that lower distalization together with greater medialization of the center of rotation was associated with more acromial fractures in this study.