The bony structures of the pelvic ring play an extremely important role in all functions. These include the sacrum, hip bones and sacroiliac joint.
Sacrum, hip bones, and sacroiliac joint.
Sacrum (Os sacrum): this is a part of the lower spine, forms the back wall of the pelvis and connects it upward to the lumbar spine.
Hip bones (ossa coxae): these two structures join the sides of the sacrum and are again each composed of three bones fused together:
- Above, the ilium (Os ilium), with its large iliac crest and outer boundary, the iliac crest and several projections, the iliac spines. From the iliac crest can be taken bone marrow, the bony projections serve therapists for orientation, for example, when an injection must be administered into the pomus muscle.
- Down behind joins the ischium (Os ischii), whose projections down obliquely are called ischial tuberosities. After prolonged cycling on a hard saddle, these are often clearly felt.
- Downward in front lies the pubic bone (Os pubis), whose respective arcuate extensions meet in front in the middle as pubic symphysis and thus close the ring of the pelvic girdle.
Where the ilium, ischium and pubis meet, they form the left and right cup-like acetabulum, in which the head of the femur lies respectively. The acetabulum and condyle, together with fixed ligaments, form the strong hip joint. The hip joint and pelvis together are called the hip, which from the outside corresponds to the area between the upper edge of the pelvis and the base of the thigh.
Sacroiliac Joint: This joint between the ilium and sacrum on the left and right sides of the spine is virtually immobile due to fixed ligaments, but can cause discomfort due to minimal displacement. Such blockages are often addressed by orthopedists or osteopaths.
Large and small pelvis
A distinction is made between the greater and lesser pelvis, which are separated by an imaginary line (linea terminalis). This runs in an arc on the inner side of the pelvic ring from a projection of the sacrum obliquely forward downward to the upper edge of the pubic symphysis. Thus, the superior large pelvis (pelvis major) is bounded by the iliac blades and pubis and is open anteriorly; the small pelvis (pelvis minor) is encompassed posteriorly by the sacrum and coccyx, and laterally and anteriorly by the pubis and ischium.
Too narrow a pelvis?
In obstetrics, the linea terminalis and the lesser pelvis play a major role – after all, its diameter plays a major role in determining whether the baby’s head will fit through the so-called birth canal (which is actually not a canal, but a bone girdle that moves in itself). By nature, women not only have an outwardly different hip shape than their male counterparts, but are also well equipped internally for the task of childbearing – the bones are shaped and arranged somewhat differently than in men, so that the female small pelvis has a larger diameter.
By the way, a pelvis that is really too narrow (i.e. a mismatch between the diameter of the pelvis and the child’s head) is quite rare – usually the two are just not optimally positioned in relation to each other. Normally, the head, as the largest part of the baby’s body, has enough room – after all, the female pelvis can fit a volume of about 1000 ml.
