What is the sacrum?
The sacrum (Os sacrum) is the penultimate segment of the spine. It consists of the five fused sacral vertebrae and their rib remnants, which together form a large, strong and rigid bone. This has a wedge shape: it is broad and thick at the top and becomes narrow and thin toward the bottom. The sacrum is curved backward (sacral kyphosis).
Anterior surface of the sacrum
Dorsal surface of the sacrum
The convex, rough, outwardly curved side of the os sacrum faces the back. It has five longitudinal ridges: The middle one is bumpy and represents the remains of the spinous processes of the sacral vertebrae. Parallel to this, one groin each runs on the right and left, which was formed by fusion of the articular processes.
The lower tip of the sacral wedge is connected to the coccyx, which is adjacent below, by an intervertebral disc.
Sacroiliac joint and pelvic ring
The os sacrum is articulated to the right and left sides of the respective ilium. These two joints are called the sacroiliac joints (ISG, sacroiliac joints). They are stabilized by tight ligaments and therefore have little movement. Actively, the ISG cannot be moved at all.
What is the function of the sacrum?
The sacrum connects the spine to the hip bones, transferring the load of the torso to the thighs.
Where is the sacrum?
The sacrum is located in the pelvic area, between the lumbar spine and the tailbone.
What problems can the sacrum cause?
In a sacrum acutum (S. arcuatum), the sacrum is bent in its lower third almost perpendicular to the lumbar spine.
The so-called spondylarthritides (spondyloarthropathies) are chronic rheumatic diseases that are primarily associated with inflammation of the spine and sacroiliac joints. They include, for example, Bekhterev’s disease (ankylosing spondylitis).