In order for the human upper body to have a firm foundation, five sacral vertebrae provide appropriate support. They are located between the lumbar vertebra and the coccyx. The sacral vertebrae are firmly fused to each other as well as to the pelvis.
What is a sacrum?
The sacrum is a wedge-shaped bone. It is made up of five vertebrae that have grown together. They are also called sacral vertebrae or sacral vertebrae. The sacrum is a part of the human spine. It forms the posterior part of the bony pelvis. The sacrum encloses the posterior portion of the spinal canal. With the ilium it forms a unit, the pelvic girdle. The individual vertebrae, which are fused together, can still be recognized by lines of adhesion. The spinal nerves emerge from the sacrum. Together with the nerves emerging from the lower lumbar vertebrae, they form a plexus. This nerve plexus supplies the pelvis and legs. Medically, the sacrum is also called the os sacrum.
Anatomy and structure
Despite the fusion of vertebrae, the sacrum anatomically still provides all the characteristic features of vertebrae. The sacrum is appropriately curved laterally in a crescent shape, and the spinous processes form a distinct crest, also referred to as the christa sacralis mediana. An articular surface lies on a small process upward on both sides. It represents a connection to the last lumbar vertebra. The remaining articular processes form the already described, strip-like elevation. The transverse processes, on the other hand, form the lateral part, the broad plate (pars lateralis). The lateral parts of this plate are called the Christa sacralis lateralis. In the lower back, a lot of weight rests on the sacrum. That is why it is pronounced particularly stable. It is located below the lumbar vertebrae and above the coccyx. It is connected to the pelvis via the sacroiliac joint. With the hip bones, it forms the bony pelvis or pelvic girdle. The sacrum gives the upper body a firm base. On its back side are the openings from which the spinal nerves emerge. In some people, the uppermost sacral vertebra has not grown together with the other vertebrae. They have six cruciate vertebrae instead of the usual five. As a result, the spine has more mobility in these people. In return, however, they can only put less weight on their spine. This vertebral peculiarity is also called lumbarization.
Function and tasks
The sacrum allows movement, also called nutation or, appropriately, counter-nutation. The area between the 5th lumbar vertebra and the sacrum can be shifted forward or backward. This causes the tip of the sacrum to move upward or backward. The function of the sacrum is to provide appropriate support for the body. Without the sacrum, the upper body would not have enough stability to move upright. By fusing the sacral vertebrae and fusing them to the pelvis, the sacrum provides sufficient stability. Through the sacroiliac joint, the spine and pelvis are hinged together. It is a bony connection to the ilium of the pelvis. The sacrum thus belongs to both the spine and the human pelvis. It provides appropriate opportunities for the nerves through its openings to form the nerve plexus that supplies the pelvis and legs. Without the sacrum, the human body would lack its natural support. It would collapse in on itself. In every movement, the sacrum provides the appropriate stability, whether standing, walking or sitting. It keeps the body upright and cushions the weight created by movement. The sacroiliac joint is also called the ilio-sacral joint (ISG). Because it is fixed with very tight ligaments, it has little room to move. This joint is especially stressed when sitting. This position stretches the ligaments a lot and puts pressure on the joint.
Diseases and pain
Pain in the sacrum can be caused by sitting for a long time, sitting incorrectly or sitting too slouched. Because the vertebrae in the sacrum are fused together, they also cannot be easily loosened. In case of severe pain in the area of the sacrum, a doctor should be consulted in any case in order to locally narrow down the cause of the pain. Acute pain is treated by medication or physiotherapy. There are certain exercises that counteract the pain in the sacrum. This loosens the pelvis and eliminates tension.Severe pain can also occur when the sacroiliac joint is blocked. These blockages are deviations from normal joint function. In this case, the joint surface may be functionally or structurally altered. Furthermore, the soft tissue mantle may also show corresponding changes. With blockages, there is still a free direction of movement. Causally, a blockage of this ISG can result from a lifting trauma or a step into the void, for example, when overlooking a stair step. However, a blockage can also be an accompanying symptom. For example, in an orthopedic condition, after pain surgery, or as part of a spinal condition. Syndromic blockage can result in severe back pain, most of which is unilateral. Exercise and heat applications can lessen the pain, but prolonged sitting can increase it. The pain has a radiating effect and can be felt as far as the buttock area and the lumbar spine. Sensory disturbances such as persistent tingling may also occur. The ISG joint can be reset using various mobilization techniques. However, the ISG joint can also be inflamed. Inflammation in this area often occurs in ankylosing spondylitis or other rheumatic conditions. Inflammatory pain in the sacrum includes spondyloarthropathy or spondyloarthritis.
