Female pelvic bones

The pelvis is the bony connection between the torso and lower limbs. It is an important structure that supports the torso and protects the pelvic organs. The female pelvis is also the bony birth canal through which the fetus must pass when it is delivered. Its size and shape are closely related to the delivery of pregnant women. Abnormalities in the shape of the pelvis and the diameters of its constituent bones can cause abnormal delivery. Generally, the female pelvis is wider and shallower than the male pelvis, which is beneficial for the delivery of the fetus.

1) Bones of the pelvis

The pelvis is composed of the sacrum (os sacrum), the coccyx (os coccyx), the upper and lower hip bones (os coxae) and tendons. Each hip bone is also an irregular bone composed of the ilium (os ilium), sciatic nerve (os ischium) and toe bones (os pubis). The sacrum is nearly triangular in shape, with the front indentation called the sacral fossa. The middle outer edge of the triangle base is prominent, forming the sacral promontory (equal to the level of the bifurcation of the common iliac artery). The sacral promontory is one of the key landmarks in gynecological laparoscopy and a key gathering point for accurate measurement of the apex angle diameter in the obstetric pelvis.

(ii) Pelvic joints

1. Ischial tuberosity: a fibrous cartilage connection between two toes.

2. Sacroiliac joint: located between the sacrum and ilium, connected by a thick sacroiliac tendon.

3. Sacro-coccygeal joint: It is very active and can move back 51080x during childbirth, thus expanding the anterior-posterior and lateral diameters of the pelvic entrance.

(III) Pelvic tendons

The pelvis has two pairs of important tendons, including the sacrotuberous ligament between the sacrum, coccyx and ischial tuberosity and the sacrospinalis tendon between the sacrum, coccyx and ischial spine. The width of the sacrospinalis tendon, that is, the width of the sciatic notch, is an important indicator for determining whether the posterior sagittal diameter of the mid-pelvis is narrow. During pregnancy, under the influence of growth hormone, tendons are more relaxed and the mobility of various joints is also improved, which is beneficial to the delivery of the fetus.

Features of the female pelvis

The female pelvis is the safe passage for the fetus to be delivered, so there are obvious differences between the pelvis of men and women. The specific characteristics of the female pelvis are: the entire pelvis is short and spacious, the upper opening is circular and relatively spacious, the diameters of the lower hole (sagittal diameter and thick diameter) are larger than those of men, and the coccyx is very active, the ischial tuberosity is also wider, and the ischial tuberosity is everted, which causes the diameters of the pelvis to increase to a certain extent when pregnant women give birth.

1. The ischial tuberosities on the four walls of the pelvis are short and wide, the pubic arch has a large angle, the sacral promontory is small, the ischial spines are flat, and the pelvis is cylindrical, shallow and wide.

2. The pelvic passage is almost circular or oval.

3. The pelvic entrance and exit are spacious and the ischial tuberosities are wide apart.