Reverse total shoulder arthroplasty and resting radiographic scapular rotation

Background: It remains unclear whether changes in scapular rotation influence the surgeon's ability to achieve resting radiographic neutral or inferior baseplate tilt at final follow-up. The purposes of this study were (1) to determine whether reverse total shoulder arthroplasty (RTSA) changes the resting scapular rotation, (2) to determine the association between glenoid inclination with respect to the scapula (beta angle) and resting scapular rotation, and (3) to determine the beta angle threshold that will most likely lead to resting radiographic neutral or inferior baseplate tilt relative to the thorax. Methods: This was a retrospective radiographic study. Patients with adequate-quality standing anteroposterior and Grashey radiographs obtained preoperatively and after primary RTSA at a minimum of 1 year were included. Glenoid inclination (beta angle) was measured between the supraspinatus fossa and the glenoid. Resting scapular rotation was measured between the supraspinatus fossa and a vertical line. Baseplate tilt was then calculated as the angle between the glenoid and a vertical line. Results: The study included 74 patients with a mean follow-up period of 3 years (range, 1-9 years). Scapular rotation changed 2 degrees +/- 12 degrees (mean +/- standard deviation) into upward rotation (P = .048). No association was found between the beta angle and scapular rotation. In 71% of patients with a neutral or inferior baseplate tilt, a postoperative beta angle greater than 85 degrees was found. Conclusions: Resting radiographic scapular rotation changed 2 degrees into upward rotation with RTSA and was not associated with the beta angle. If the beta angle is greater than 85 degrees, resting radiographic baseplate tilt will most likely be inferior or neutral. (C) 2019 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.