The possible causes of subacromial pain in the left side of the back include trauma, sports injury, fasciitis of the back of the shoulder, ankylosing spondylitis, and so on. 1. Trauma: Most of the time, there is a clear history of trauma, because the role of violence leads to soft tissue injuries around the scapula, or fractures such as thoracic vertebrae compression fracture, scapula fracture and so on, resulting in pain. 2. Sports injury: Lactic acid accumulation caused by excessive exercise, muscle strain caused by improper posture, muscle strain caused by long-term exertion can trigger pain, which can be relieved after proper rest. 3. Dorsal shoulder fasciitis: a specific inflammation of the fascia of the back of the shoulder, with common symptoms such as pain and discomfort in the back of the shoulder and pulling sensation in the neck. 4. Ankylosing spondylitis: a chronic inflammatory disease that occurs in our body, because of the inflammatory stimulus, can cause pain in the thoracic spine and surrounding tissue damage. Causes of back pain under the shoulder blade is more, may also be related to heart attack, cervical spondylosis, nerve entrapment syndrome and other diseases, if the symptoms continue to be unrelieved, it is recommended to consult a doctor in a timely manner, to clarify the cause of the disease, targeted treatment.