What is the Pelvic Girdle?
The pelvic girdle is an anatomical structure which connects the spine to the legs. It is often referred to as the “pelvis” or “pelvic bone,” although in fact several bones are part of this structure, not just one. Notably, the pelvic girdle in men and women looks very different, because the female pelvis is designed to accommodate pregnancy and delivery of a baby. The human pelvis in general is quite distinctive, because it supports upright walking, and this requires special adaptations which are not seen in other animals.
The key bones in the pelvis are the two hip bones, which connect to the sacrum in the back of the pelvis and the pubic symphysis in the front. In childhood, the hip bones are comprised of several sections which gradually fuse together, creating solid bones in late adolescence. The male pelvis tends to be narrower, allowing the femurs to fall straight down from the pelvic girdle, while women have a larger pelvis, which causes the femurs to splay slightly to the sides.
A network of ligaments connects the various components of the pelvic girdle to anchor it in place and provide support to the spine and legs, in addition to creating articulation for the hips so that people can bend and flex them. The space inside the pelvis creates a hollow which protects the reproductive organs and some of the lower abdominal organs. In fact, when viewed from above, this structure strongly resembles a bowl in shape.
In pregnancy, some of the hormones produced by the body soften the joints in the pelvic girdle. This is designed to make it easier for it to expand slightly to accommodate a pregnancy, and to ease the labor and delivery process. As a result of the softened joints, the bones in the pelvis can shift and move during pregnancy, instead of remaining firmly anchored in place, and as a result some women feel unsteady on their feet or experience strange sensations in the pelvis during pregnancy.
After pregnancy, the joints will gradually firm up again, but while a woman is pregnant, she may experience what is known as pelvic girdle pain, and her gait also changes as a result of the moving pelvic bones. The change in gait is also caused by the redistribution of weight across the woman's body, and the weight gain which typically occurs during pregnancy.
Wow! I was just thinking how much the pelvic girdle had to change by evolution before species could stand up and walk. And there must have been a lot of failed births until the female body evolved to the point where everything worked right for the pregnancy and the birth was successful.
I can't imagine how much trial and error went on in the evolution of hormones. Hormones produced during pregnancy signal the joints in the pelvic girdle to loosen up.
@ceilingcat - Weird pains is right! Of all the changes that go on in the body during pregnancy I had no idea the pelvic joints actually softened. I didn't think the human skeleton went through that many changes after adulthood but I guess I was wrong.
One of my friends is pregnant and she's been complaining of weird pains "in her bones" and feeling a little unsteady. I guess the softening of the pelvic girdle bones explains why. Her bones are probably moving and shifting all over the place!
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