The purpose of this study was to analyze the compensatory movement of the scapula on shoulder abduction by using surface electromyography(EMG). We evaluated the upper trapezius muscle, middle deltoid muscle, and infraspinatus activity using surface EMG during shoulder abduction of 10 cases 20 shoulders who had undergone rotator cuff repairment. We used Telemyo System 2400(Noraxon USA Inc) and analyzed it by MyoVideo and MyoResearch. The relative activity of the upper tarapezius muscle was significantly increased after an operation and gradually lowered while rehabilitation program proceeded. Relative activity of the middle deltoid and infraspinatus muscle approached normal EMG pattern. Upper trapezius muscle activity contributed to scapular substitution movement in compensation for impaired glenohumeral motion in patients with rotator cuff insufficiency. Sufficient rotator cuff functions stabilized the glenohumeral joint and increased the output power of the deltoid muscle, and decreased the trapezius muscle activity. EMG analysis of scapula substitution movement can be one of the indicators for rehabilitation program.
