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Sacrum
Last reviewed: 19.11.2021
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The sacrum (os sacrum) consists of five sacral vertebrae (vertebrae sacrales), which grow together into one bone in adolescence. The sacrum is triangular in shape. He is a massive bone, because he takes on the weight of almost the entire body. Allocate the base of the sacrum, the tip of the sacrum and two surfaces - pelvic and dorsal.
The base of the sacrum (basis ossis sacri) is connected to the lower articular processes of the V lumbar vertebra with the help of articular processes. In the area of the base connection with the V lumbar vertebrae, a rounded corner - promontorium - is protruded forward . On the concave pelvic surface (facies pelvica) facing forward, four transverse lines (lineae transversae) are clearly visible , traces of fusion of the bodies of the sacral vertebrae with each other. On each side at the level of these lines there are pelvic sacral orifices (foramina sacralia anteriora, S. Pelvica).
On the convex dorsal surface of the sacrum (facies dorsalis), dorsal sacral orifices (foramina sacralia posteriora, s.dorsalia) are visible on each side . Five longitudinal ridges were formed at the fusion of the processes of the sacral vertebrae. The unpaired median sacral crest (crista sacralis mediana) is a fused spinous process. The paired intermediate crista (crista sacralis intermedia) is the result of the fusion of the articular processes, and the paired lateral sacralis crest (crista sacralis lateralis) was formed when the transverse processes mesh.
On the lateral sections of the sacrum there are the ears (facies auriculares) for articulation with the same-named surfaces of the iliac bones. On each side between the ear surface and the lateral crest there is a sacral tuberosity (tuberositas sacralis), to which ligaments and muscles are attached. The vertebral openings of the fused sacral vertebrae form the sacral canal (canalis sacralis). This channel ends below the sacral slit (hiatus sacralis). On each side the slit is limited by sacral horns - rudiment of articular processes.
In addition to joints and strengthening ligaments, pelvic bones are connected to the sacrum with the help of two powerful extra-capsular ligaments. The sacro-ligamentous ligament (lig. Sacrotuberal) goes from the ischial to the lateral margin of the sacrum and coccyx. Continuation of the sacro-ligamentous ligament downward and anterior to the branch of the ischium is the crescent processus (processus falciformis) of this ligament. The sacro-nasal ligament (lig. Sacrospinal) connects the sciatic head with the lateral surface of the sacrum and coccyx.
The sacrum, located between the two pelvic bones, is the "key" of the pelvic ring. The gravity of the trunk can not displace the base of the sacrum forward and downward in the sacroiliac joints, since these joints are firmly strengthened by intercostal sacroiliac, as well as sacro-tubercular and sacro-ovate ligaments.
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