Pain in the lumbar and crotch region can be attributed to the following causes: 1. Ankylosing spondylitis. Ankylosing spondylitis belongs to the autoimmune system disease, which is due to the destruction of its own tissues by its own immune system, from the sacroiliac joint gradually upward, initially manifested as sacroiliac joint pain, inflexible activities. 2, sacroiliac arthritis. For example, frequent cold and strain on the sacroiliac joint will lead to the formation of local inflammation, and gradually degeneration and hyperplasia of the articular cartilage will form further stimulation, leading to increased pain. 3, the location around the sacroiliac joint, there are muscle attachment points on some bones, and these attachment points are prone to strain, strain and cold, which will form local aseptic inflammatory lesions, and the inflammatory metabolites will stimulate the The inflammatory metabolites will stimulate the peripheral nerves, and obvious pain will appear.