Rotator cuff injuries have been overlooked by most physicians in the past. It is characterized by intractable pain, weakness and limited movement, and is more common in middle-aged and elderly people, and its symptoms are often more severe than the general sense of “frozen shoulder”. The bones of the shoulder joint, consisting of the humerus and the scapula, are the only bones in the shoulder joint that are neither stable nor mobile. The stability and power of the shoulder joint depends on the surrounding muscles. Etiology: 1. As we age, muscle strain, degeneration, and bone wear are the most common causes of rotator cuff injury, in other words, rotator cuff injuries tend to occur in middle-aged and elderly people; 2. If they occur in young people, they are usually accompanied by a history of severe trauma. Symptoms: pain, weakness and limitation of movement; especially pain at night. Diagnosis: Physical examination + MRI can confirm the diagnosis. Treatment: The treatment of the acute and chronic phase can still follow the principles of “subacromial bursitis” and “acromioclavicular impingement” previously described in this platform. Acute stage: rest, anti-inflammatory and analgesic drugs, physical therapy, and closure. In the acute stage, ice can be applied. Chronic phase: In addition to the above treatments, strengthen the rehabilitation therapy to restore the motor function of the shoulder joint without increasing the pain. Hot compresses can be applied in the chronic phase. Surgical treatment: If you still have persistent pain and weakness in shoulder joint movement after regular treatment, arthroscopic surgery is required. The surgery is performed to decompress the joint and repair and suture the rotator cuff. However, overly severe tears and those with a long history of disease make suturing difficult. This is why early diagnosis of rotator cuff injury is important.