Pain in the back and left shoulder is commonly caused by the following: First, periarthritis of the shoulder joint. The occurrence of periarthritis of the shoulder joint in middle-aged patients can lead to severe pain symptoms in the left shoulder joint, which can radiate to the back and deltoid area, and the patient will have limited movement of the shoulder joint and scapula. Secondly, cervical spondylosis, neurogenic cervical spondylosis and mixed cervical spondylosis can cause painful symptoms in the left shoulder joint and back, and the patient will have numbness and grip strength loss in the hands, and the cervical spine activity will be impaired. Third, coronary heart disease, some patients with angina can induce localized involvement pain, manifested as pain and discomfort in the back and left shoulder.