Sacrum and coccyx (English)

The lumbosacral joint is formed between the vertebrae L5 and S1. It consists of two separate articulations: the anterior intervertebral joint formed by the L5/S1 intervertebral disc and the two posterior zygapophysial (facet) joints between their articular processes. The lumbosacral symphysis is strengthened and stabilised by the iliolumbar and lumbosacral ligaments. The transverse ridges located on the anterior or pelvic surface of the sacrum indicate the site of fusion of each sacral vertebra. The sacroiliac joint is formed by the synovial articulation between the sacrum and ilium anteriorly and by the syndesmoses between their tuberosities posteriorly. The sacroiliac joint is stabilised by the anterior, interosseous and posterior sacro-iliac ligaments. An intervertebral disc lies between the apex of the sacrum and base of the coccyx to form the secondary cartilaginous sacrococcygeal joint. Reinforcing this joint are the superficial posterior, deep posterior, anterior and lateral sacrococcygeal ligaments, as well as the sacrotuberous and sacrospinous ligaments. Stabilising the intercoccygeal joints, which are frequently fused inferiorly, are the sacral portions of the supraspinous and anterior longitudinal ligaments as well as the anterior and lateral sacrococcygeal ligaments.