Sacroiliac refers to the sacrum and iliac bone intersection position, also called sacroiliac joint, the iliac bone is part of the hip bone, the whole hip bone is composed of the iliac bone, sit bone, pubic bone three parts constitute the left and right hip bone, the left and right two pieces of hip bone is symmetrical, inclined to form the pelvis on both sides, each piece of the hip bone as a whole is like a relatively wide electric fan blade, the iliac bone is a part of this electric fan blade, hip bone, tail bone, sacrum Together, they form the entire pelvis. The iliac bones are located next to the sacrum, and the iliac bones on both sides sandwich the sacrum and coccyx in the middle, thus forming the sacroiliac joints on both sides. The sacroiliac joint is different from other joints, as this joint is more like a skeletal gap, where the iliac bones and sacrum are connected are uneven, thus inserted together to form the sacroiliac joint, with fibrocartilage and ligaments covering the top to fix and protect the joint.