Normal shoulder internal rotation activities include two kinds, neutral internal rotation 45-70 degrees, and external rotation 7 degrees: first, neutral internal rotation, mainly related to the subscapularis muscle, when the subscapularis tendon is injured, the shoulder joint internal rotation strength is weakened, the affected arm is placed behind the waist and hangs in the air, and the forearm and the hand can not be stayed, and it will fall back to the back of the waist, when this situation occurs, it is usually necessary to perform arthroscopic surgical repair of the scapula The subacromial tendon is repaired to restore neutral internal rotation of the shoulder joint. Second, internal rotation in the external position is usually associated with subacromial impingement syndrome. When the acromion impinges with the greater tuberosity of the humerus, internal rotation of the shoulder joint in the external position will produce symptoms of shoulder impingement and pain, and arthroscopic acromioplasty is needed to resolve the impingement.