Electromyographic Analysis of Shoulder Muscle Activity after Reverse Shoulder Arthroplasty

A Comparison with Healthy Shoulders

Abstract

Purpose: To analyze shoulder muscle activity after reverse shoulder arthroplasty (RSA) using electromyography to identify any differences from the muscle activity of healthy shoulders.

Methods: The subjects included 12 RSA-treated shoulders and 17 healthy (control) shoulders. Shoulder muscle activity was evaluated using surface electromyography at 45° and 90° of shoulder elevation. The subjects held their arms aloft in three directions during recording at flexion, scaption, and abduction. Ratios of integrated electromyographic activity for different muscles at 45° and 90° were calculated and compared between the two groups.

Results: Muscle activity ratios in the posterior deltoid during flexion, the upper trapezius and posterior deltoid during scaption, and the clavicular pectoralis major during abduction were significantly higher in the RSA group (p<0.05).

Conclusions: Our results suggest that RSA-treated shoulder muscles behave differently from healthy shoulders during sustained elevation between 45° and 90°.