Pain above the buttocks and below the waist is mainly due to lesions near the sacroiliac joints, and there are three common causes: 1, there are a lot of muscles and soft tissue attachment points on the sacroiliac joints and the surrounding bony structures, and if there are muscle strains or strain and cold, local aseptic inflammatory foci will be formed, and inflammatory metabolites will stimulate the peripheral nerves around the area, and there will be pain. This is also the most common reason. 2, due to sacroiliitis, the sacroiliac joint parts of the degeneration of cartilage or bony hyperplasia, calcification, there will be obvious pain. 3, ankylosing spondylitis, this is an autoimmune disease, the autoimmune system on their own tissues to produce an immune response, the sacroiliac joints will be the location of the worm-eaten-like changes in the position, become very uneven, and the pain is relatively Obviously, this pain will gradually extend upward.