Shoulder muscle activation and coordination in patients with a massive rotator cuff tear: an electromyographic study

Adaptive muscle activation strategies following a massive rotator cuff tear (MRCT) are inadequately understood, and the relationship among muscles during everyday activities has not been considered. Thirteen healthy subjects comprised the control group, and 11 subjects with a MRCT the patient group. Upper limb function was assessed using the Functional Impairment test-hand, neck, shoulder, and arm (FIT-HaNSA). Electromyography (EMG) was recorded from 13 shoulder muscles, comprising five muscle groups, during a shelf-lifting task. Mean FIT-HaNSA scores were significantly lower in MRCT patients (p≤0.001), reflecting a severe functional deficit. In MRCT patients, EMG signal amplitude was significantly higher for the biceps brachii-brachioradialis (p < 0.001), upper trapezius-serratus anterior (p= 0.025), muscle groups and for the latissimus dorsi (p = 0.010), and teres major (p=0.007) muscles. No significant differences in the correlation among muscle groups were identified, pointing to an unchanged neuromuscular strategy following a tear. In MRCT patients, a reorganization of muscle activation strategy along the upper limb kinetic chain is aimed at reducing demand on the glenohumeral joint. Increased activation of the latissimus dorsi and teres major muscles is an attempt to compensate for the deficient rotator cuff. Re-education towards an alternate neuromuscular control strategy appears necessary to restore function.