Reverse total shoulder arthroplasty (RTSA) is increasingly utilized in the aging population, with a growing list of surgical indications including rotator cuff tear arthropathy, proximal humerus fractures, and revision arthroplasty. Acromial insufficiency fractures following RTSA are poorly understood, difficult to diagnose, and associated with inferior clinical outcomes. There is limited knowledge in the literature regarding the etiology of post-operative acromial fractures. The purpose of this study is to evaluate the role of implant parameters on acromial strain following RTSA.

Using a cadaveric model, a custom designed modular RTSA system was implanted that allowed for evaluation of modifiable parameters including glenoid lateralization, humeral lateralization, and neck-shaft angle. Acromial strain was measured by 4 strain gauges placed along the acromion and scapular spine. Total deltoid force was measured as a secondary outcome. All specimens were tested in 4 planes of elevation including 0° and 90° abduction and 0° and 90° forward flexion.

Lateralization of the glenoid component was found to increase acromial strain with the arm in forward flexion. Lateralization of the humeral component was found to decrease acromial strain with the arm in abduction. Neck-shaft angle had no significant effect on acromial strain. Disruption of the coracoacromial (CA) ligament had no significant effect on acromial strain. The findings of this study have clinical importance in the future research and design of RTSA implants.A continued focus needs to be placed on the evaluation of additional implant parameters and their role on acromial fractures following RTSA.