The effect of humeral component retroversion on external rotation and shoulder function outcomes in patients undergoing reverse total shoulder arthroplasty with a lateralized glenoid component

Deficits in shoulder external rotation create significant limitations in activities of daily living, including eating and reaching the top of the head. Reverse total shoulder arthroplasty (rTSA) changes the mechanics of the shoulder and improves forward elevation reliably, but external rotation deficits frequently persist. There is currently a wealth of information regarding the impact of glenoid component lateralization, neck shaft angle, and angulation of the glenoid component on external rotation. However, the impact of humeral component retroversion is less understood. The purpose of this study was to compare strength and range of motion in external rotation of patients undergoing rTSA at different degrees of humeral retroversion. We hypothesized that humeral retroversion at 30 degrees would result in superior external rotation and strength postoperatively than 0 degrees of retroversion. This is a retrospective study of prospectively collected data on patients who underwent rTSA with either 0 or 30 degrees of humeral component retroversion between November 2016 and 2018. A 36-mm-sized glenosphere with a system that lateralizes off the glenoid was utilized in all patients. Patient demographic information and postoperative outcomes at 3 months, 6 months, and latest follow-up including degree of external rotation, strength in external rotation, visual analog scale for pain, Simple Shoulder Test score, and American Shoulder and Elbow Surgeons score were recorded. Outcomes for 38 patients were included (N = 18 at 0-degree; N = 20 at 30-degree). No preoperative difference was observed between the two cohorts. There was no significant interaction between time and retroversion for any variable (P ≥ .16). Time had a significant effect on all outcomes (P ≤ .002) except for internal rotation (P = .17). Retroversion did not have a significant effect on outcomes at any time point (P ≥ .07), though external rotation strength nearly reached significance (P = .07). External rotation at the side increased from 25.0 to 35.3 degrees and external rotation in abduction increased from 39.2 degrees to 63.4 degrees from 3 months to final follow-up. External rotation at the side strength increased from 1.6 kg to 1.8 kg and external rotation in abduction strength increased from 1.2 kg to 1.7 kg from 3 months to final follow-up. No differences in outcomes were observed between 0° and 30° of humeral component retroversion. Strength in external rotation may be impacted by humeral component retroversion. Further clinical studies with larger sample sizes are needed to study the impact of humeral component retroversion on external rotation strength.