The joint above the hip is the sacroiliac joint, which is a planar joint made up of the auricular surfaces of the sacrum and ilium together. The sacroiliac joint has a flattened articular surface, a narrow joint cavity, a tight and tightly packed joint capsule, and many surrounding ligaments. The joint supports weight and transmits gravity, but the joint is less mobile, so it is susceptible to incorrect posture or excessive activity and external pulling, resulting in sacroiliac arthritis and varying degrees of pain and swelling. On imaging, the sacroiliac joints in adults have cartilage and synovial tissues in the anterior part, the width of the joint space is consistent and regular, and the articular surfaces are clear and sharp, while the ligamentous tissues are in the posterior part of the joints, the joint space is wide and irregular, and the articular surfaces are thin and unsharp. In children, however, there is no significant difference between the anterior and posterior sacroiliac joints. If sacroiliac joint discomfort occurs, it is recommended to consult a doctor in time to make a clear diagnosis and follow the doctor’s instructions for treatment.