Anatomy of the Pelvis

Pelvic Girdle

• The pelvis is formed by the fusion of four bones: ilium, ischium, and pubis.
• The ilium forms the upper two-fifths of the acetabulum and expands superiorly into a flattened plate, the ala.
• The gluteal surface of the ilium gives attachment to the glutei muscles.
• The medial surface of the ilium is divided into a posterior auricular surface and an anterior iliac fossa.
• The ischium forms the lower two-fifths of the acetabulum and expands inferiorly to form the ischial tuberosity.
• The ischial tuberosity gives attachment to the hamstring muscles and the sacrotuberous ligament.
• The pubis forms the anterior part of the pelvis and articulates with the femur.

Sacrum

• The sacrum is formed by the fusion of five sacral vertebrae.
• The sacrum is triangular in shape with a base superiorly, an apex inferiorly, and a dorsal, pelvic, and two lateral surfaces.
• The sacrum is divided into a median portion and a pair of lateral masses.
• The pelvic and dorsal sacral foramina communicate with the central sacral canal and convey the sacral segmental nerves.

Joints and Ligaments of the Pelvic Girdle

• The sacroiliac joint is a plane synovial joint between the irregular auricular surfaces of the sacrum and ilium.
• The sacroiliac ligaments are very strong and unite the auricular surfaces of the sacrum and ilium.
• The interosseous sacroiliac ligament is also very strong and unites the auricular surfaces of the sacrum and ilium.
• The sacrospinous and sacrotuberous ligaments resist the rotation of the sacrum forwards.

Symphysis Pubis

• The symphysis pubis is a secondary cartilaginous joint between the two pubic bones.
• The articular surfaces are united by a fibrocartilaginous disc.
• Little movement occurs except for a slight separation of the pubic bones in late pregnancy.

The Articulated Pelvis

• The pelvis lies obliquely in the erect posture with the anterior superior iliac spines and pubic symphysis in the same vertical plane.
• The pelvis is divided into greater and lesser parts by the pelvic brim.
• The greater (false) pelvis is above the brim and bounds the lower abdominal cavity.
• The lesser (true) pelvis lies below the brim and forms the birth canal.

Sex Differences

• The male pelvis is rougher, thicker, and heavier than the female pelvis.
• The male pelvis has a heart-shaped brim, whereas the female pelvis has a round or oval brim.
• The male pelvis has a longer and narrower cavity than the female pelvis.
• The male pelvis has a larger acetabulum and an everted ischiopubic ramus.

Pelvimetry

• Obstetricians require measurements of the pregnant woman's pelvis to assess whether problems may occur in childbirth.
• Pelvimetry is now achieved ultrasonically.

Fractures of the Pelvis

• Fractures of the pelvis are commonly caused by crush injuries and frequently result in injuries to related soft tissues.
• Bladder and urethral trauma are associated with fractures of the pubis and major vessel trauma with sacroiliac fractures and dislocation.