What is the coccyx?
The coccyx (Os coccygis) is the last section of the spine. It consists of four to five vertebrae, which in adults are usually fused into a single bone that is bent slightly forward. Movements in the coccyx are possible only forward and backward.
Some of the individual coccygeal vertebrae are only rudiments of the normal vertebral shape, i.e. they are strongly degenerated:
The first vertebra of the os coccygis still has a vertebral body, transverse processes and remnants of articular processes that point upward – toward the sacrum. The vertebral arch is missing from the first coccygeal vertebra as well as from all the vertebrae below it. The vertebral arches are replaced by ligaments. The remaining three to four vertebrae of the coccyx consist only of remnants of the vertebral bodies: they have degenerated into roundish pieces of bone.
Fusion of vertebrae
Similar to the border between the lumbar spine and the sacrum, where the last lumbar vertebra may be fused with the first sacral vertebra (upper sacralization), a so-called sacralization (lower sacralization) may also occur at the border between the sacrum and the coccyx. These assimilation or transitional vertebrae remain unnoticed and without symptoms in most cases.
The longitudinal ligaments of the spine
The anterior longitudinal ligament of the spine (ligamentum longitudinale anterius), which runs along the entire spine and is firmly attached to the vertebrae, stabilizes the spine and limits its backward movement. It is lost on the front of the sacrum and reappears only at the coccyx.
The posterior longitudinal ligament of the spine (ligamentum longitudinale posterius), which is firmly attached to the intervertebral discs and, together with the anterior longitudinal ligament, serves to stabilize the spine, connects the coccyx to the sacrum.
What is the function of the coccyx?
The coccyx serves as an attachment point for various ligaments and muscles of the pelvis, pelvic floor and hip joints. Since the pelvis is open at the bottom, the ligaments and muscles of this area are important in holding the organs in place.
The articulated connection between the sacrum and the first two vertebrae of the female coccyx is important during childbirth: when the baby’s head passes through the birth canal, the pressure causes the tip of the coccyx to move backward about two centimeters, widening the pelvic outlet and facilitating the baby’s passage.
Where is the coccyx located?
The coccyx (Os coccygis) forms the lowest section of the spine, i.e. it follows the sacrum.
As in all sections of the spine, congenital or acquired changes (malpositions, malformations, etc.) can also occur in the coccyx.
A fracture of the coccyx, which occurs mainly in the event of a fall on the buttocks, or the less common luxation, causes the end piece of the coccyx to bend forward. Pain resulting from a fracture or dislocation occurs especially when sitting or sneezing, when the pelvic muscles become tense (coccygodynia). Other causes of pain in this area may include a difficult delivery. Sometimes they are also psychogenic.
Osteoporosis, as in all bone areas, causes the coccyx to fracture more easily if the person falls.
If the connection of the coccyx to the sacrum is bony, this can be an obstacle to birth.
