An evaluation of the relationships between reverse shoulder design parameters and range of motion, impingement, and stability

Background: The purpose of this study was to evaluate the role of reverse shoulder design parameters on performance. Methods: A computer analysis was conducted on the Grammont reverse shoulder to quantify the effect of varying design parameters on functional measurements during humeral abduction/adduction. To demonstrate the application of these relationships, a novel prosthesis was designed. Results: The Grammont reverse shoulder impinged inferiorly and superiorly on the glenoid at 31° and 95° of humeral abduction with an average jump distance of 10 mm. Several linear relationships were identified. The proposed 38 mm, 42 mm, and 46 mm reverse shoulder designs impinged inferiorly and superiorly on the glenoid at 7.3°/87.5°, 1°/87.5°, and 0°/89.3° of humeral abduction with an average jump distance of 11.7 mm, 13.5 mm, and 14.1 mm, respectively. Conclusions: The results of this study demonstrate that subtle changes in design parameters can minimize inferior glenoid impingement and offer potential for dramatic functional improvements in ROM (39%) and jump distance (36%). Level of evidence: Basic Science Study, Computer Analysis.