Pain at the junction of the shoulder, back and armpit: First, it is usually caused by local muscle strain, or local chronic sterile inflammation, which is easily caused by frequent exertion of the shoulder or carrying things with the shoulder. Second, it may be cervical degeneration caused by cervical spondylosis, such as herniated discs or osteophytes, small joint misalignment compressing the nerve root on one side, which may lead to nerve pulling pain in the back of the shoulder. Thirdly, if the pain is on the left side, it must be ruled out that there is no heart problem. If there is pain in this area, and it is accompanied by chest tightness, palpitations, or even a feeling of chest pain, it must be considered whether angina pectoris or myocardial infarction, and this situation should be immediately diagnosed by going to the hospital for an electrocardiogram and serum troponin.