Accuracy of obtaining optimal base plate declination in reverse shoulder arthroplasty

Reverse total shoulder arthroplasty has shown promising early and midterm results; however, complication rates remain a concern. Glenoid loosening and notching, for example, can be deleterious to the long-term success. A 15° inferior inclination angle has been shown to offer the most uniform compressive forces across the base plate and the least micromotion at the base plate-glenoid interface. The inferior inclination angle may also avoid scapular notching. The purpose of this study was to determine the accuracy of obtaining 15° of inferior inclination of the base plate.

The radiographs of 138 reverse total shoulder patients were included. Overall, glenoid inclination and change in inclination from preoperative radiographs were measured using a previously described standardized method. Measurements were obtained by 2 orthopedic surgeons, who repeated all measurements 3 weeks apart. The final angle and change in inclination were averaged.

Seventy-two patients had pre- and postoperative radiographs of sufficient quality to accurately measure inclination. Average pre- and postoperative inclination measured -4.8° (-27.2° to 28.1°) and -13.3° (-22.8° to 43.6°), respectively. The average change in inclination was -8.5° (-53.7(o) to 34.6(o)). No scapular notching was observed, which may relate to the lateralized center of rotation of the implant used in this study.

Overall, the average decrease in inclination was very close to the intended target value using the standard guide. However, patients with preoperative superior glenoid erosion from advanced rotator cuff tear arthropathy appeared to be consistently tilted superiorly, suggesting the standard guide may be inadequate in these patients.