Female pelvic structure

People's body structure itself is very complex, but considering that everyone's body structure is different, especially the body structure of men and women, it can be said that the difference is very large. Women's skeletons are much smaller than men's. This is also the reason why girls' waist circumference is always inappropriate when buying clothes. The structural design of the female pelvis should start with these characteristics to understand.

(a) The pubic symphysis of the pelvic walls is short and wide, the pubic arch has a large angle, the sacral promontory is small, the ischial spines are flat, and the pelvic cavity is cylindrical, shallow and wide.

(ii) The pelvic inlet is nearly circular or oval.

(iii) The pelvic outlet is wide and the distance between the ischial tuberosities is wide.

Pelvic cavity

The pelvic cavity is a curved cylindrical tube that is short in front and long in the back. In order to facilitate understanding of the passage of the fetus in the birth canal during delivery, the shape of the pelvis is described in the following three planes: the entrance plane, the middle plane, and the exit plane.

Entrance Plan

It is the interface between the greater and lesser pelvis (i.e. the entrance to the pelvic cavity), and is in the shape of a horizontal oval with the following diameters:

(a) The anterior-posterior diameter is the distance from the upper edge of the pubic symphysis to the midpoint of the anterior edge of the sacral promontory, also known as the sacropubic internal diameter, with an average length of about 11 cm.

(ii) The transverse diameter is the maximum diameter of the entrance plane, which is the widest distance between the two iliopectineal lines and has an average of about 13 cm.

(iii) There is one oblique diameter on each side, which is the distance from the sacroiliac joint on one side to the iliopectine process on the other side, and is about 12.5 cm long. The left oblique diameter is from the left sacroiliac joint to the right iliopectine process, and the opposite is the right oblique diameter.

Clinically, the anteroposterior diameter is the most important. A flat pelvis has a smaller anteroposterior diameter, which will affect the insertion of the baby's head into the pelvis.

Mid-pelvis

The middle and upper section is the widest part of the pelvic cavity and is approximately circular. Its front is the midpoint of the back of the pubic symphysis, and its two sides are equivalent to the center of the acetabulum. The posterior edge is located between the second and third sacral vertebrae. The lower section is the smallest plane of the pelvis (the so-called midplane), which is the plane from the lower edge of the pubic symphysis, the ischial spine to the lower end of the sacrum, and is an ellipse with a long anterior-posterior diameter. The anterior-posterior diameter is about 11.5 cm, and the transverse diameter (inter-ischial spine diameter) is about 10 cm.