The rotator cuff, also known as the rotator cuff or tendon cuff, is a general term for the tendon tissue of the supraspinatus, infraspinatus, teres minor and subscapularis muscles. It is closely attached to the joint capsule and forms a sleeve-like tissue at the upper end of the humerus. In the front is the subscapularis tendon, above is the supraspinatus tendon, behind and below are the infraspinatus tendon and the lesser circularis tendon. The function of the rotator cuff is to tighten the humeral head toward the glenoid during upper arm abduction, maintaining a normal fulcrum joint between the humeral head and the glenoid. Rotator cuff injuries can cause shoulder joint pain and severely affect upper extremity abduction function. The supraspinatus and subscapularis muscles of the rotator cuff are susceptible to injury due to their anatomical characteristics. The tendons of the supraspinatus and subscapularis are located under the rostral dome of the shoulder in the second shoulder joint. During the activities of shoulder joint adduction, abduction, supination and posterior extension, the above two muscles move back and forth under the rostral dome of the shoulder and are susceptible to injury due to pinching and punching. The supraspinatus muscle within l cm of the terminating end proximal to the greater tuberosity stop is the ischemic canal zone, i.e. the danger zone, and is a good site for degeneration and and tendon rupture. Patients with rotator cuff injuries have some of the following presentations: History of trauma A history of acute injury or a history of repetitive injury and cumulative strain is informative for the diagnosis of this disease. Pain and pressure pain Shoulder joint pain is an early symptom of rotator cuff rupture: the pain is mostly located in the front of the shoulder joint, involving the anterior and lateral deltoid muscles, and the anterior shoulder pain is aggravated by bending the elbow 90 degrees to make the affected shoulder do passive external rotation and internal retraction. In the acute stage, the pain is severe and persistent, while in the chronic stage, it is spontaneous and dull, and the pain is aggravated after shoulder activities. The most typical pains are nocturnal pain in the neck and shoulder and “over-the-top” activity pain (when the affected limb is raised above the top of one’s head). In the presence of chronic subacromial bursitis, the pain is persistent and intractable. The pain is sometimes accompanied by radiating pain to the neck and upper extremities, and is aggravated by lying on the affected side, often worsening at night and seriously affecting sleep. Pain becomes the main reason for patients to visit the clinic and an important parameter to evaluate the effectiveness of treatment. Shoulder joint pressure pain is mostly located in the proximal aspect of the greater tuberosity of the humerus or in the subacromial space, and a popping sound can be felt when the arm is lifted or rotated, and the obvious popping sound is mostly seen in the late stage of impingement sign, especially in complete rotator cuff tears. Shoulder joint weakness Depending on the site of rotator cuff injury, shoulder joint weakness can be abduction weakness, supination weakness, or posterior extension weakness, respectively. Due to pain and weakness, active movement of the shoulder joint is limited, preventing supination and abduction and affecting the function of the shoulder joint, but the passive range of motion of the shoulder joint is usually not significantly limited. Muscle atrophy In those with a history of more than 3 weeks, there are different degrees of atrophy of the muscles around the shoulder, with the deltoid, supraspinatus and infraspinatus muscles being more common. Secondary contracture of the joint In cases with a history of more than 3 months, there are varying degrees of limitation in the range of motion of the shoulder joint, with abduction, external rotation and supination being the most obvious.