The pelvis “a basin-like cavity”

The pelvis protects the reproductive organs, and is the bony passage through which the baby must pass in order to be born.

Consists of four bones:

ONE sacrum (triangular bone with five vertabrae fused together)
ONE coccyx (small bone at the tip of the sacrum) AKA “tailbone”
TWO innominate bones (hip bones on each side)
– Each innominate bone is formed by the fusion of three bones around the acetabulum:
A. Ilium AKA “the hips” is the uppermost pelvic bone.
B. Ischium
C. Pubis
– Both innominate bones are joined in the back to the sacrum at the sacroiliac synchondroses and in front to one another at the symphysis pubis.

Four joints of the pelvis:

  • Lumbosacral
  • Sacrococcygeal
  • Sacro-iliac
  • Pubic symphysis

Flexibility of the Pelvis during Pregnancy and Labor

Progesterone and relaxin make the pelvis joints flexible, letting the pelvis accomodate for the baby to pass through.

  1. The sacroiliac joints
    Increase its diameter during labor.
  2. The coccyx
    Is pushed back while the head descends down to the perineum.
  3. The symphysis pubis
    Increase in width and mobility during pregnancy which returns to normal following delivery.

Print and color here: Pelvis bones & joints

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