The sacrum (os sacrum) consists of the five fused sacral vertebrae and is hardly mobile. Read more about the sacrum!


The sacrum (Os sacrum) is the area of ​​the spine that lies between the last lumbar vertebra and the first coccygeal vertebra. His vertebrae are - unlike those of the cervical, thoracic and lumbar spine - immobile. Read everything important about the structure and function of the sacrum and health problems in this area!

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  • What is the sacral bone?

  • What is the function of the sacrum?

  • Where is the sacrum?

  • What problems can the sacral bone cause?

What is the sacral bone?

The sacrum (os sacrum) is the penultimate part of the spine. It consists of the five fused sacral vertebrae and their remains of ribs, which together form a large, strong and rigid bone. This has a wedge shape: it is wide and thick at the top and is narrow and thin down. The sacrum is curved backwards (sacral kyphosis).

Anterior surface of the sacrum

The sacrum has a smooth, concave, hollow side that faces the body (towards the pelvis). On this surface you can see four transverse bars, which mark the boundaries of the (coalesced) sacral vertebrae. Next to these lines are four holes on each side, leading backwards to the spinal canal, through which the strong branches of the sacral nerves emerge.

Posterior surface of the sacrum

The convex, rough, outward-curved side of the sacrum points to the back. It has five longitudinally extending ridges on: The average is nodular and represents the radicals of the spinous processes of the sacral vertebrae parallel extending left and right each have a strip which is formed by fusion of the articular processes..

These ridges contribute to the upper end of an articulating surface that articulates with a disc with the fifth lumbar vertebra and at the lower end has a very variable in its mold opening - the lower opening of the sacral canal (of lying in the sacral portion of the spinal canal).

The lower tip of the sacral wedge is connected to an intervertebral disc with the tailbone adjacent below.

Sacroiliac joint and pelvic ring

The sacrum is articulated on the right and left with the respective ilium. These two joints are called sacroiliac joints (ISG, sacral iliac joints). They are stabilized by tight bands and are therefore not very flexible. Actively, the ISG can not be moved at all.

With the adjacent hipbones, the sacrum forms the pelvic ring, an essential part of the pelvic girdle.

What is the function of the sacrum?

The sacrum connects the spine to the hipbones, which transfers the weight of the trunk to the thighs.

Where is the sacrum?

The sacrum is located in the pelvic area, between the lumbar spine and the coccyx.

What problems can the sacral bone cause?

In a sacrum acutum (S. arcuatum), the sacrum in its lower third is bent almost perpendicular to the lumbar spine.

The so-called ISG syndrome refers to pain in the sacroiliac joint, which occur as an attack when bending or turning the trunk. Even when walking, after a long physical effort or longer sitting in a certain position, the symptoms occur.

The so-called Spondylarthrititiden (Spondylarthropathien) are chronic rheumatic diseases, especially with inflammation of the spine and the sacrumArm joint joints go along. It includes, for example, ankylosing spondylitis (ankylosing spondylitis).

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