Anatomy, Bony Pelvis and Lower Limb, Pelvic Joints

The joints of the pelvis include the sacrococcygeal, lumbosacral, pubic symphysis, and the sacroiliac. The pelvic joints are also held together by various ligaments which include the sacrotuberous, sacrospinous, and iliolumbar. The lumbosacral joint forms from the fifth lumbar vertebrae and the sacrum. In between the articular processes, this joint has an intervertebral disc. The sacrococcygeal joint is a fusion of the bone between the sacrum and coccyx. It also consists of an intervertebral disc between the two vertebrae and several accessory ligaments. The sacroiliac joint is a synovial articulation between the surfaces of the ilium and sacrum on either side. Because of the articulation, the surface of the joint is smooth and flat. The sacroiliac joint has posterior strengthening by dorsal sacroiliac and inter-osseous ligaments. When a person is upright, the body weight usually transmits to the sacrum and ilia. While sitting or supine, the person's weight transmits to the ischial tuberosity. The pubic symphysis is a cartilaginous joint located between the main body of the pubic bone in the midline. The symphysis of the pubic bone is covered with hyaline cartilage and may have a cleft. The ligaments around the pubic symphysis are flexible and relax during pregnancy.