Subacromial impingement syndrome is a condition in which repeated impingement of the greater tuberosity of the humerus against the rostral shoulder arch during shoulder pronation, abduction or internal rotation causes inflammation of the subacromial bursa and degeneration or even tearing of the rotator cuff tissue resulting in shoulder pain and impaired motion. This impingement can be primary impingement related to anatomic factors or secondary impingement triggered by aging, decreased rotator cuff strength, or glenohumeral instability due to exercise. The concept of subacromial impingement syndrome was introduced by Neer in 1972, who divided the condition into 3 phases according to the damage to the rotator cuff tissue: a period of rotator cuff edema and hemorrhage, a period of aseptic inflammation of the rotator cuff tendon, and a period of rotator cuff tissue tear damage. Features: 1. History of excessive shoulder activity. Teachers, porters, swimmers and other occupations have a high probability of occurrence. 2. Most patients have a history of chronic development. 3.The main symptom is shoulder joint pain. The pain increases when the hand is raised, behind the back or when the shoulder is lifted. Nocturnal pain may occur later in the course of the disease, and the pain increases when the patient is lying on the affected side. 4. The range of motion is basically unaffected, and can be differentiated from frozen shoulder. 5. After rotator cuff injury, muscle strength may decrease and shoulder abduction may not occur. Treatment: 1. Non-surgical treatment: rest for the affected limb, non-steroidal anti-inflammatory and analgesic drugs, closure therapy, physical therapy, functional exercise. 2.Surgical treatment: conservative treatment for 3 months without improvement of symptoms can be done by shoulder arthroscopy or open surgery.