The sacrum is a large bone located between the hip bones, at the base of the spine. The bottom part of the bone is located on top of the coccyx, or tailbone, and the top touches the lower part of the spine.

The posterior sacroiliac ligament is located behind the pelvis and connects the sacrum with the ilium, which is the upper part of the pelvis. The ligament consists of connective tissue and the upper part moves across the ilium and back of the sacrum bone. The lower part of the ligament connects the back of the ilium to sacrum. The anterior (front-most) ligament consists of thin bands of connective tissue that attach to the front of the region.

The anterior sacroiliac ligament connects the front of the ilium to the front of the sacrum and the preauricular sulcus. The preauricular sulcus is a grooved area on the hip bone that exists in both men and women. The ligaments connect the two separate bones, thus, creating joints in the pelvic area.