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

- Supraspinatus is significantly more active during abduction than scaption and flexion.
- The plane of elevation does not change the activity pattern of infraspinatus muscle.
- Infraspinatus activity increases significantly in accordance with the elevation arcs.
- Supraspinatus activity does not significantly increase after a certain angles.
- If less activity of supraspinatus is desired, the plane of arm elevation should be adjusted accordingly.

BackgroundArm 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.MethodsEight 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).FindingsThe 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.InterpretationIn 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.