The effects of plane and arc of elevation on electromyography of shoulder musculature in patients with rotator cuff tears

Abstract

Background: Arm elevations in different planes are commonly assessed in clinics and are included in rehabilitation protocols for patients with rotator cuff pathology. The aim of this study was to quantify the effect of plane and angle of elevation on shoulder muscles activity in patients with symptomatic rotator cuff tear to be used for rehabilitation purposes.

Methods: Eight symptomatic patients with rotator cuff tears were assessed by using EMG (11 surface and 2 fine wire electrodes) synchronized with a motion analysis. The subjects completed five elevations in full can position (arm externally rotated and thumb up) in frontal, scapular and sagittal planes. Muscle activity in three elevation arcs of 20° (from 0° to 60°) was presented as the percentage of mean activity. Data were analyzed by mixed linear models (α=0.003), and Tuckey Post-hoc comparisons for significant effects (α=0.05).

Findings: The effect of plane was significant for supraspinatus, middle trapezius, anterior, middle, and posterior deltoid, triceps, and pectoralis major (P<0.001). Supraspinatus was more active during abduction than scaption and flexion (P<0.05), and its activity did not increase significantly after 40° of elevation (P>0.05). Infraspinatus had similar activity pattern in the three planes of elevation (P>0.003) with increasing trend in accordance with the elevation angle.

Interpretation: In any rehabilitation protocol, if less activity of supraspinatus is desired, active arm elevation should be directed toward flexion and scaption and postponed abduction to prevent high level of activity in this muscle.

Keywords: 3D glenohumeral kinematics; Active arm elevation; Full can exercise; Indwelling EMG; Shoulder rehabilitation; Supraspinatus.