The effect of glenoid version on internal and external rotation in reverse total shoulder arthroplasty

Background: There is currently limited understanding of the contribution of glenoid version to postoperative internal (IR) and external rotation (ER) after reverse total shoulder arthroplasty (RTSA). The purpose of this study was to determine the impact of glenoid version on postoperative rotation after RTSA. Methods: Forty-five 3-dimensional (3D) computer models of human scapulae were created from de-identified computed tomography (CT) scans. The scapulae were divided into 3 separate groups based on glenoid version: normal (10° to -10°), moderate (-10 to -25°), and severe (< -25°). The scapulae then underwent virtual implantation with a Grammont-style RTSA prosthesis at either 0°, -20°, or -30° of retroversion based on the severity of the native glenoid version (normal, moderate, severe). Internal, external, and total rotation (TR) were determined for each construct at both 30° and 60° of humeral abduction. Results: Glenoids with a narrow width (< 25 mm) were noted to have minimal bony impingement on rotational testing and were excluded. In the remaining scapulae (n = 34), the achievable TR and IR for the humeral component decreased as glenoid retroversion increased. Changes in rotation for all categories were in general more pronounced at 60° of humeral abduction. Overall, ER generally increased as glenoid retroversion increased, with the largest increase occurring when going from 0° to -20° of retroversion, and minimal increase from -20° to -30° of retroversion regardless of humeral abduction. Conclusion: Placement of the glenoid component in increasing retroversion during RTSA results in a loss of IR and a corresponding increase in ER.