The full clinical name for the sacroiliac is sacroiliac joint, which is positioned below the waist and is the part of the body that connects the sacrum to the ilium. The ilium is made up of three bones, the ilium, the sciatica and the pubis, and there is a hip bone on the left and right side of the body, with symmetry on each side, tilted to form the sides of the pelvis. The sacrum consists of the base of the sacrum, the lateral portion, the sacral aponeurosis, the pelvic and dorsal facets fused together, and is the posterior upper wall of the pelvis, with the sacral aponeurosis being the base, and forming a joint with the coccyx. The sacrum consists of the sacral base, lateral portion, sacral apices, pelvic and dorsal facets, which are inverted triangles and form the posterior upper wall of the pelvic cavity. Based on the anatomical relationship of the ilium and sacrum, the ilium is positioned next to the sacrum, resulting in a sacroiliac joint that resembles a bony gap on both sides and projects to the body surface equivalent to the lower back.