The main causes of left shoulder and back pain are as follows: 1. Frozen shoulder: the clinical manifestation is not only the shoulder and back pain, but also the limitation of the upper limb activities, the inability to reach the opposite shoulder or the inability to reach the normal part when probing the back, and the inability to lift up. 2. Neuritis of the back of the shoulder: it can lead to overcharge-like or radiating pain in the back of the shoulder, which is so intense that some patients cannot be relieved by taking painkillers. 3. Cervical spondylosis Some patients may experience pain in the left shoulder and back, such as acute attack of heart attack, and may show pain in the shoulder and back. Therefore, there are more factors affecting shoulder and back pain and more reasons for its onset, so patients need to go to the hospital for a comprehensive diagnosis to prevent misdiagnosis.