Relation between preoperative electromyographic activity of the deltoid and upper trapezius muscle and clinical results in patients treated with reverse shoulder arthroplasty

Abstract

If patients susceptible to poor clinical outcomes could be predicted before reverse shoulder arthroplasty (RSA), it would help to set reasonable postsurgical patient expectations in the preoperative setting. Our hypothesis was that the preoperative electromyographic (EMG) activity of the deltoid and upper trapezius muscles would be correlated with clinical outcomes of patients undergoing RSA. EMG activity of the deltoid and upper trapezius muscles was measured in 25 patients scheduled to undergo RSA during 3 motions: shrugging, forward flexion, and abduction. Their postoperative clinical results were assessed prospectively during regular outpatient visits, including strength, active range of motion (ROM), pain, and functional scores. The correlations between the preoperative EMG activities and clinical results were analyzed. Postoperative shoulder strength after RSA was increased in patients with greater preoperative EMG activity of the middle deltoid and upper trapezius. Preoperative EMG activity of the anterior or middle deltoid muscle was associated with active ROM in flexion or abduction, whereas EMG activity of the posterior deltoid was associated with active ROM in external rotation. Shoulder strength after RSA was positively correlated with preoperative EMG activity of the deltoid and upper trapezius. Active ROM after RSA was positively correlated with preoperative EMG activity of the deltoid. Therefore, preoperative EMG measurements of the deltoid and upper trapezius may predict clinical outcomes after RSA.