Comparison of Clinical and Radiological Results according to Glenosphere Position in Reverse Total Shoulder Arthroplasty: A Short-term Follow-up Study

BACKGROUND In a previous biomechanical study, eccentric glenospheres with more inferior position of the center of rotation were shown to improve range of motion and reduce the incidence of scapular notching after reverse total shoulder arthroplasty (RSA). The purpose of this study was to compare the clinical and radiological results of RSA using an eccentric glenosphere to those using a concentric glenosphere and to determine the usefulness of the eccentric glenosphere. METHODS From 2009 to 2015, we performed a retrospective review of 20 consecutive patients who underwent RSA using a deltopectoral approach. Nine patients underwent RSA using a concentric glenosphere (group A) while 11 had an eccentric glenosphere (group B). The average follow-up period was 13.9 months (range, 12 to 18 months). All glenoid components were placed with 15° of inferior tilt. Clinical results were assessed using the visual analog pain scale score (VAS), the American Shoulder and Elbow Surgeon (ASES) score, the Korean shoulder scoring system (KSS), and the Constant score. On radiological evaluation, prosthesisscapular neck angle (PSNA), peg-glenoid rim distance (PGRD), scapular neck-inferior glenoshere rim distance (inferior glenoshpere overhang), acromion-greater tuberosity (AT) distance, glenoid-greater tuberosity (GT) distance, and severity of notching according to the Nerot-Sirveaux classification were assessed. RESULTS The clinical results improved significantly in both groups, but there was no statistically significant difference between the two groups. A significant intergroup difference was observed with regard to PGRD (24.8 ± 1.6 mm for group A vs. 22.2 ± 1.9 mm for group B; p = 0.002) and inferior glenosphere overhang (2.0 ± 1.7 mm for group A vs. 5.8 ± 1.6 mm for group B; p = 0.000). Seven of 9 patients in group A developed notching compared with 2 of 11 patients in group B (p = 0.022). The other radiological parameters such as inferior tilt and AT and GT distances were not significantly different between two groups. Complications such as loosening and scapular fractures did not occur. CONCLUSIONS The eccentric glenosphere in RSA was more effective in reducing the rate of notching than the concentric glenosphere although clinical outcomes were not significantly different in the short-term follow-up.