The disease is seen in more than 90% of middle-aged women and is more common in late pregnancy, especially after childbirth, and also after chronic infection of the urinary tract or female adnexa, or other infections in the pelvis. In addition, trauma to the hip-sacral area can also trigger or cause this disease. Pregnancy, childbirth and dense osteitis of the sacroiliac joint. Trauma can cause tearing of the ligaments of the sacroiliac joint, which can easily block the local blood supply. Therefore, early local congestion, edema and increased exudation, etc., gradually local proliferation and degeneration reaction, with the dense collagen fibers to sclerosis evolution; vascular formation of thick-walled vessels, easy to occlude and cause ischemia and hypoxia at the iliac auricular surface, bone presents sclerotic changes, resulting in less local bleeding during surgery. The sacroiliac joint capsule wall shows fibrous hyperplasia, reduced elasticity and loosening-like changes. Similar pathological changes are seen secondary to inflammatory disease in the pelvis, probably due to bacterial endotoxin action. Iliac dense osteitis is a nonspecific inflammatory disease characterized by osteosclerosis, with highly dense osteosclerosis, especially in the lower 2/3 of the ilium, but no alteration of the joint space. It is also called “sacroiliac joint dense osteitis” because it is located in the sacroiliac joint and has significant symptoms in this joint. Dense osteoarthritis of the iliac joint occurs in women, and is more common in middle-aged women between the ages of 20 and 40. It has recurrent lower back pain, sometimes radiating down to the buttocks and thighs on both sides, but not radicular pain, which can be aggravated by lower back activity.