Kinematics and EMG activity in Reverse Total Shoulder Arthroplasty

Patients undergoing a Reverse Total Shoulder Arthroplasty (RTSA) often have functional limitations that affect the range of motion of the shoulder. These limitations are not mechanical in nature, but instead linked to a reduced ability to generate muscle force. The specific aims of this study was to offer a comparison between the muscle activity generated by a post-operative RTSA shoulder in a patient to that of their contralateral shoulder during a series of functional activities.

A convenience sample of 10 subjects between the ages of 50-75 years of age were recruited. EMG and kinematic data were concomitantly collected while subjects completed tasks that included common activities of daily living.

The main findings of this study were that all sub regions of the deltoid functioned as abductors, versus the native shoulder where the middle deltoid primarily works in abduction. For the scapular elevation activity there was a significant difference in flexion between the surgical and contralateral shoulder (p < .001), with the surgical shoulder having nearly 30° less range of motion.

Anticipating limitations in functional outcomes and range of motion for patients after RTSA may inform patient decision-making and improve clinical evaluations. The finding of increased mid deltoid function during lifting activity has implications for rehabilitation and encouraging protocols that strengthen the deltoid in concentric motions. Additionally, the decreased scapular elevation found in this study may guide rehabilitation focusing on regaining range of motion post-operatively.