Synonyms
Os sacrum (Latin), Sacrum (English)
Introduction
The sacrum is characterized by its sphenoid shape. It is formed by the merging (synostosis) of the five sacral vertebrae. In humans, this fusion does not end until the growth phase is completed. The sacrum is the last section of the spinal column and encloses the rear part of the spinal canal. Together with the hip bone, it forms the pelvic girdle.
Anatomy
The os sacrum has basically the same structural principle as the rest of the spine. Due to the fusion, certain anatomical structures are only distinguished differently. The spinous processes form a crest (lat.
Crista sacralis mediana), which runs along the midline from top to bottom on the back surface. The remaining articular processes form a crest that runs slightly to the side of the midline, the crista sacralis intermedia. On both sides of a small extension on the upper part of the sacrum there is a small articular surface which is connected to the last lumbar vertebra.
The transverse processes form a lateral plate in which the anterior part has increased in size to form the sacral wing (lat. Ala ossis sacri). On top of the sacral wings lies an auricular surface (lat.
Facies auricularis), which is in connection with the ilium of the same name and forms the sacro-iliac joint. It is also called sacroiliac joint. At its lateral edge, the lateral plate forms a crest, the crista sacralis lateralis, which runs down the side of the crista sacralis mediana.
At the back of the sacrum are the dorsal sacral foramina, the openings in which the dorsal (posterior) spinal nerves emerge. On the side facing the pelvis are the holes (lat. Foramina sacralia pelvina) from which the ventral (front) nerve branches emerge. Together with parts of the nerves of the lumbar vertebrae, the emerging spinal cord nerves form a network of nerves, the plexus lumbosacralis. They mainly supply the pelvis and legs.
