The shoulder girdle is an extremely mobile joint. Rotator cuff tears alter the existing equilibrium between bony structures and muscles. The “subacromial impingement syndrome” resulting from this unbalance leads to an extension of the rotator cuff lesion.

Many authors have postulated a “mechanism of compensation”, but its existence still requires evidence. According to this model, the longitudinal muscles of the shoulder and the undamaged muscles of the rotator cuff would be able to functionally compensate, supersede the function of rotator cuff, and reduce symptoms.

The aim of this study was to evaluate muscular activation of the medium fibers of deltoid, the superior fibers of pectoralis major, the latissimus dorsi and the infraspinatus by a superficial electromyographic study (EMG) and the analysis of kinematics in patients with a massive rotator cuff tear.

We evaluated 30 subjects: 15 had pauci-symptomatic massive rotator cuff tear (modest pain and preserved movement), and 15 were healthy controls.

Paired t-test showed significant different activations (p< 0.05) of these 4 muscles between the pathological joint and the healthy one in the same patient.

The unpaired t-test, after comparing the mean EMG values of the 4 muscles, produced a significant difference (p< 0.05) between the experimental group and control group.

This study showed that a mechanism of muscular compensation is activated in patients suffering from rotator cuff tear, involving the deltoid and the infra-spinatus muscle, as already presented in literature, but also demonstrated the activation of 2 other muscles: the latissimus dorsi and the pectoralis major. It is, therefore, probable that, in these patients, these muscles, which would not normally pull the head of the humerus downwards, adapt in order to compensate for the pathological situation. We believe that these data are valuable in the surgical and rehabilitation planning in patients with a massive rotator cuff tear.