[Electromyographic study associated with rotator cuff tears]

To determine the pathophysiological condition of rotator cuff tear, 23 cases were observed using electromyogram of the shoulder girdle muscles during elevation of the arm. The correlation between the action potential of these muscles and the angle of the arm was analyzed using computer in order to identify the pattern of that. The pattern of the electromyogram of the affected side with the ability to elevate the arm above 90 degrees was similar to that of the sound side. Differences were seen between the affected side with the inability and the sound side in the electromyogram of trapezius, deltoideus and supraspinatus. However, these differences were disappeared in patients who became able to elevate their arms above 90 degrees after surgery. It seemed that the restriction of joint motion due to rotator cuff tear caused impairment of coordination of muscular activities, and this phenomenon helped us to clarify the scapulohumeral rhythm.