Left back pain may be related to trauma, ankylosing spondylitis, frozen shoulder, lumbar muscle strain, kidney stone and other reasons, and the specific location of pain is different, which should be analyzed according to the actual situation. 1. Trauma: If the left back is hit, friction, collision and other factors lead to trauma, it can cause damage to the local muscle tissues or nerve tissues, which will cause pain sensation in the back. 2. ankylosing spondylitis: ankylosing spondylitis can occur in the spine, peripheral joints, sacroiliac joints and other parts of the spine, which is mainly manifested as pain in the lower back or buttocks, as well as muscle stiffness. 3. Frozen shoulder: Frozen shoulder belongs to the aseptic inflammation in the local tissues of shoulder joint, and the activity of shoulder joint is restricted, which can affect the toughness of back muscles, manifesting as pain around shoulder joint, muscle stiffness, and reduced range of motion. 4. lumbar muscle strain: if the local tissues of lumbar muscles or ligaments are damaged, the pain in the lumbar region or back will occur repeatedly. 5. Kidney stones: Since the kidneys are located in the lower part of the back, if there is a stone in the left kidney, it can also lead to pain in the back. If the location of the pain in the left back cannot be effectively determined, you should go to the hospital in time for examination and symptomatic treatment, so as to avoid other adverse effects on the body.