Parsons, Bradford O.

Background The purpose was to evaluate the relationship of component size and position to postoperative range of motion following reverse shoulder arthroplasty. The hypothesis was that increased lateralization, larger glenospheres, and a decreased acromiohumeral distance would be associated with excellent postoperative range of motion. Methods A retrospective multicenter study was performed at a minimum of one year postoperatively on 160 patients who underwent primary reverse shoulder arthroplasty with a 135° humeral component. Outcomes were stratified based on postoperative forward flexion and external rotation into excellent ( n = 42), defined as forward flexion >140° and external rotation > 30°, or poor ( n = 36), defined as forward flexion <100° and external rotation < 15°. Radiographic measurements and component features were compared between the two groups. Results A larger glenosphere size was associated with an excellent outcome ( p = 0.009). A 2-mm posterior offset humeral cup ( p = 0.012) and an increased inferior glenosphere overhang (3.1 mm vs 1.4 mm; p = 0.002) were also associated with excellent outcomes. Humeral lateralization and distalization were not associated with an excellent outcome. Conclusion: Larger glenosphere size and inferior positioning as well as posterior humeral offset are associated with improved postoperative range of motion following reverse shoulder arthroplasty. Level of Evidence Level 3, retrospective comparative study.

Background Glenoid morphology, glenoid version and humeral head subluxation represent important parameters for the treating physician. The most common method of assessing glenoid morphology is the Walch classification which has only been validated with computed tomography (CT). Methods CT images and magnetic resonance imaging (MRI) images of 25 patients were de-identified and randomized. Three reviewers assessed the images for each parameter twice. The Walch classification was assessed with a weighted kappa value. Glenoid version and humeral head subluxation were comparted with a reproducibility coefficient. Results The Walch classification demonstrated almost perfect intraobserver agreement for MRI and CT images (k = 0.87). Weighted interobserver agreement values for the Walch classification were fair for CT and MRI (k = 0.34). The weighted reproducibility coefficient for glenoid version measured 9.13 (CI 7.16–12.60) degrees for CT and 13.44 (CI 10.54–18.55) degrees for MRI images. The weighted reproducibility coefficient for percentage of humeral head subluxation was 17.43% (CI 13.67–24.06) for CT and 18.49% (CI 14.5–25.52) for MRI images. Discussion CT and MRI images demonstrated similar efficacy in classifying glenoid morphology, measuring glenoid version and measuring posterior humeral head subluxation. MRI can be used as an alternative to CT for measuring these parameters.