Anatomy of Pelvis: Sex Differences

Pelvis Structure and Function

• The pelvis is the region of the trunk below the abdomen, with main functions: transmitting weight from the vertebral column to the femur, containing and supporting pelvic viscera, and providing attachment for trunk and lower limb muscles.
• The bony pelvis is composed of four bones: two hip bones (lateral and anterior wall) and sacrum and coccyx (posterior wall).

Pelvis Divisions

• The pelvis is divided into two parts by the pelvic brim: above the brim is the false pelvis, and below the brim is the true pelvis.
• The pelvic brim is formed by: sacral promontory (posterior), upper surface of symphysis pubis (anterior), and ileopectineal line (lateral).

False Pelvis

• The false pelvis is part of the abdominal cavity, supporting the abdominal contents.
• It is bounded by: lumbar vertebrae (posterior), lower part of the anterior abdominal wall (anterior), and iliac fossa and iliacus (lateral).

True Pelvis

• The true pelvis has an inlet, an outlet, and a cavity.
• The pelvic inlet is the pelvic brim.
• The pelvic outlet is bounded by: pubic arch (anterior), ischial tuberosities (lateral), and coccyx (posterior).
• The pelvic cavity is a short, curved canal with a shallow anterior wall and deep posterior wall.

Pelvic Walls

• The anterior wall is formed by posterior surfaces of the bodies of the pubic bones, pubic rami, and symphysis pubis.
• The posterior wall is a long, curved wall formed by sacrum, coccyx, and piriformis muscle with their covering of parietal pelvic fascia.

Pelvic Diaphragm

• The pelvic diaphragm is formed by the levator ani muscles and small coccygeus muscles and their coverings fascia.
• It is incomplete anteriorly to allow passage of the urethra in males and the urethra and vagina in females.
• The levator ani muscle has a linear origin from: back of the body of the pubis, tendinous arch formed by a thickening of the fascia covering the obturator internus, and spine of the ischium.

Pelvic Inlet and Outlet

• The pelvic inlet is oval in females and heart-shaped in males.
• The pelvic outlet is larger in females than in males.

Pelvic Cavity

• The pelvic cavity is roomier in females than in males, and the distance between the inlet and outlet is much shorter.

Sacrum

• The sacrum is shorter, wider, and flatter in females than in males.

Pubic Arch

• The pubic arch is more rounded and wider in females than in males.

Pelvic Deformities

• Pelvic deformities are more common in women who have grown up in a poor environment and are undernourished.
• Pelvis types: gynecoid, android, anthropoid, and platypelloid.

Injury to the Pelvic Floor

• Injury to the pelvic floor during a difficult childbirth can result in the loss of support for the pelvic viscera leading to uterine and vaginal prolapse, herniation of the bladder, and alteration in the position of the bladder neck and urethra, leading to stress incontinence.