Many people with shoulder pain think that they have frozen shoulder, but in fact, it could be a rotator cuff injury. Most shoulder pain arises from the rotator cuff tendon and the subacromial bursa area. Although there is no obvious trauma, the pain arises after performing repeated supination activities of the shoulder joint. The shoulder joint is mainly formed by the bones of the upper arm and shoulder. The shoulder joint is not as stable as other joints and its stability is maintained by the four surrounding muscles that form the rotator cuff, which can be further damaged once the rotator cuff is injured. Why does the rotator cuff cause pain? The supraspinatus tendon is located at the very top of the shoulder joint and passes between the outermost bones of the shoulder joint (acromion) and the bones of the upper arm, which makes it easy to be crushed by the bones and cause pain. How is a rotator cuff injury determined? Rotator cuff injury pain is usually located on the front or outside of the shoulder, and it worsens when the upper arm is raised, seriously affecting daily activities. Sometimes the pain is so pronounced at night that it prevents you from sleeping. How can I reduce the pain? Pain can be reduced and normal function restored with proper and timely treatment. Avoiding strenuous exercise and heavy lifting of the shoulder, using ice on the affected area, and taking oral NSAIDs can partially relieve the pain. Local injections can be used to further relieve pain and identify the site of injury to guide the next step in treatment. After the pain is relieved, the patient should perform functional exercises, range of motion training of the shoulder joint under the guidance of a physical therapist to prevent secondary shoulder adhesions, followed by strength exercises against resistance. When is surgery necessary? Prolonged and persistent pain can cause a tear in the tendon. This injury cannot be relieved by rest and will require surgical treatment. Rotator cuff tears are often accompanied by loss of previous shoulder pain and loss of function.