Above the hip and below the waist, this position is the human sacroiliac joint. It is composed of the outer side of the sacral vertebrae, and the inner face of the iliac bone, the two bones joint face to face, jagged bone structure, embedded in each other, resulting in a very narrow joint space, but the joint is also very stable, and the whole joint, relying on the outer cartilage and ligament connection. Sacroiliac joint is a micro-movement joint, long time overwork strain, posterior lumbosacral sprains, contusions, bruises and other traumatic conditions, can lead to injury to the sacroiliac joint. There are also many maternal, because of hormone ratio, and endocrine changes, will lead to laxity of the ligaments around the pelvis, which includes the ligaments around the sacroiliac joint. Once it is relaxed, it will cause the sacroiliac joint to be more prone to injury, and local pain will occur. There are also nerves in the vicinity of the sacroiliac joint, so if there is an injury or lesion, the nerves will be stimulated, resulting in radiating leg pain.