The pelvic ligaments are strong, thick bands of fibrous tissue that connect the pelvic bones. These ligaments are categorized into four groups: those that connect the ilium to the sacrum; the ligaments that pass between the sacrum and the ischium, which is the lower rear part of the pelvis; the ligaments that connect the sacrum to the coccyx, or tail-bone; and those located between the pubic bones.
The joint between the sacrum, the triangle-shaped bone between the hip bones, and the ilium bones, the upper part of the hip bones, is called the sacroiliac articulation. It is connected by two pelvic ligaments, the anterior and posterior sacroiliac ligaments. The anterior sacroiliac ligament connects the front part of the side of the sacrum to the ear-shaped, or auricular, part of the ilium. In a deep ridge between the sacrum and the ilium lies the posterior sacroiliac ligament, which creates the primary bond between the two bones.
The posterior sacroiliac ligament is divided into two parts. The short posterior sacroiliac ligament is the upper part, and the long posterior sacroiliac ligament the lower. Located far below the posterior sacroiliac ligament is the interosseous sacroiliac ligament, which connects the tuberosities of the sacrum and ilium, which are bony protrusions that permit muscle or ligament attachment.
In the second group of pelvic ligaments are the two that connect the sacrum to the ischium, the lower part of the hip bone; these are the sacrotuberous and the sacrospinous ligaments. The third group of pelvic ligaments start at the joint, also called the sacrococcygeal symphysis, between the top of the sacrum and the base of the coccyx, or tail bone. It is joined by the anterior sacrococcygeal, the posterior sacrococcygeal, the lateral sacrococcygeal, the interposed fibrocartilage, and the interarticular ligaments.
The pubic symphysis, the joint between the two oval-shaped surfaces of the sacrum and ischium, is joined together by the anterior pubic ligament, the posterior pubic ligament, the superior pubic ligament, the arcuate pubic ligament, and the interpubic fibrocartilaginous lamina. The anterior longitudinal ligament runs down the forward-facing surface of the spine. The iliolumbar ligament connects the fifth lumbar, or lower back, vertebra to the crest of ilium, which is the upper outside border of the ilium. The supraspinal ligament, also called the supraspinous ligament, connects the top of the seventh cervical, or neck, vertebra to the sacrum.