19 Bony Pelvis – Male and Female

The Pelvis:

Like a foundation of a building, the pelvis is the weight bearing structure of the body which keeps humans upright. The hip or pelvis is composed of 3 bones that form a ring-like structure supporting the weight of the upper body and provide attachment points for the lower limbs. The pelvis also helps protect the reproductive organs and other visceral peritoneum.

The bones of the hip is made of 3 other bones fused together:

• Pubis: The anterior and inferior part of the pelvis, which fuses with each other to form the pubic symphysis.
• Ilium: The largest bone which forms the acetabulum, the socket head for the head of the femur. The superior part of the ilium forms the iliac crest which ends anteriorly forming the anterior superior iliac spine
• Ischium: The ischium is the inferior and posterior part of the pelvic which connects with the pubis to form the obturator foramen which is a common area for vasculature and nerves to flow through

The sacrum is a fusion of 5 sacral vertebrae (S1-S5) which position within the posterior section of the pelvis, specifically the two ilium. View the diagram below to get a visual representation of the hip bone and pelvic structure:

Pelvic Foramina:

The pelvic bones can come together to form several openings known as foramen:

• The Greater Sciatic Foramen (red arrow) is situated between the ilium and ischium formed by the sacrospinous ligament allowing the sciatic nerve – the largest nerve in the body – to pass from the pelvis to the gluteal region and down the leg.
• The Lesser Sciatic Foramen (green arrow) located just below the greater sciatic foramen allows the passage of the pudendal nerve, internal pudendal vessel and the obturator internus muscle
• The Obturator Foramen (blue arrow) is the largest foramen in the body located between the pubis and ischium covered by the obturator membrane allowing the obturator nerve, artery and vein to pass through into the thigh.

Pelvic Brim (Pelvic inlet):

Before delving into the true or false pelvises the pelvic brim must be discussed as it forms the barrier between the two pelvises. The pelvic brim is the circular shaped ring surrounding the sacral promontory (top end of the sacrum), the ilium, pectineal lines of the pubis and the pubic symphysis. The pelvic brim forms the upper opening into the pelvic cavity and divides the true pelvis (above the brim) from the false pelvis (below the brim).

The false pelvis located above the pelvic brim supports the abdominal organs and acts as a supportive structure.

The true pelvis below the pelvic brim encloses the pelvic cavity and contains the pelvic organs. The true pelvis also aids in childbirth and forms the bony passage from which the baby descends during delivery.

Below represents the pelvic brim and the true and false pelvises:

Pelvic Sexual Dimorphism:

While both male and female pelvises share the same bones and basic structure there are some distinct differences to point out.

Female pelvis:

The female pelvis is much shallower and wider providing a more circular or oval shaped pelvic inlet. A lower and wider pelvic outlet helps aid in childbirth. Further the angle formed beneath the pubic symphysis (subpubic angle) is wider, typically greater than 80-90 degrees. The female pelvic bones are usually lighter and thinner compared to the male pelvis.

Below is a diagram of the female pelvis:

Male pelvis:

The male pelvis has a more heart shaped or funnel like offering a smaller, narrower giving a more compact appearance. The male pelvic inlet is also smaller and more heart shaped with a subpubic angle around 50-60 degrees. Also, the male pelvis is usually thicker and heavier to support greater mass.

Below is a diagram of the male pelvis: