Relation between preoperative electromyographic activity of the deltoid and trapezius and clinical results after reverse shoulder arthroplasty

Abstract

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