Left shoulder pain may be an early sign of rotator cuff injury, frozen shoulder, cervical spondylosis and other diseases. 1. Rotator cuff injury: after rotator cuff injury, the tearing of shoulder cartilage, muscle and fascia may lead to left shoulder pain. 2. Frozen shoulder: some patients have frozen shoulder due to aseptic inflammation of the shoulder, which may lead to aggravation of inflammation and tissue damage in the process of activity, and thus left shoulder pain symptoms may appear. 3. Cervical spondylosis: usually keep a posture for a long time, such as looking down at the computer for a long time, which may lead to chronic strain of the neck muscles and tissues, the cervical nerves are compressed, affecting the blood circulation, and therefore may produce symptoms of left shoulder pain. If the pain symptoms have been more obvious, need to actively consult a doctor to check the symptomatic treatment.