Analysis of Reverse Total Shoulder Arthroplasty Biomechanics Using a Dynamic Shoulder Simulator

Abstract

Despite the increasing use of reverse total shoulder arthroplasty (rTSA), questions remain regarding optimal implantation techniques to maximize range of motion while minimizing instability and scapular notching. Utilizing a dynamic shoulder simulator, the effects of altering joint tension, humeral version, and glenosphere offset were investigated in cadavers. In addition, common configurations of different implant designs were compared. Increased tension in a Grammont-style rTSA improved implant stability at the cost of reduced range of motion, while humeral version only affected range of motion. Glenosphere lateralization in a Grammont-style rTSA increased implant stability at the cost of greater deltoid force required to elevate the arm. The most commonly implanted configuration of a lateral glenosphere system improved adduction versus a medial glenosphere system, which could result in the reduced scapular notching seen with lateral glenosphere systems in clinical populations. Similarly, a more lateral glenosphere system resulting in a more lateralized humerus might improve posterior rotator cuff efficiency by maintaining a more anatomic muscle length/tension relationship. Translation of these results to the clinical setting provides guidance regarding implant selection and placement that can be used to improve functional outcomes and limit complications after rTSA