The word pelvis is generally used to refer to that part of the body just below the abdomen, which is the area where the trunk joins the legs. More specifically, the term refers to the part of the skeleton, also known as the bony pelvis or pelvic girdle, which encloses and supports that area of the body. The word means "basin" in Latin, which is what the shape of the bony structure resembles. Another use of the term refers to structures found in the kidneys, which have funnel-shaped renal pelvises formed from the top of the urine collecting tubes, or ureters, that carry urine to the bladder.
Four bones make up the bony pelvis, with two hip bones, called the inominate bones, forming the front and sides, while two bones at the bottom of the spine, known as the sacrum and coccyx, complete the rear wall. Around the inside of the pelvic bones is a ridge called the iliopectineal line which runs around the central opening to meet a joint at the front, known as the symphysis pubis. This ridge represents the pelvic brim, also called the inlet. While the area above the inlet is known as the false pelvis, the region below is referred to as the true pelvis.
The false pelvis flares out and supports the contents of the abdomen, and is continuous with the abdominal cavity. By contrast, the true one has more of a bowl shape and it encloses the reproductive organs, the lower gut and parts of the urinary tract. It has an inlet formed by the pelvic brim, and an outlet made from the structures at the bottom of the pelvic bone, which include the end of the spine, the arched lower edge of the symphysis pubis, and the lower parts of the hip bones. What is known as the pelvic cavity lies between the inlet and the outlet.
In women, the inlet, the pelvic cavity and the outlet form the canal through which a baby passes. Pelvises vary in shape between men and women, with female ones being adapted to cope with giving birth. For this reason, pelvises are shallower in women, with smoother bony surfaces and the pelvic cavity and outlet are roomier than in men.
Fractures of the pelvic region can occur, usually due to a severe, direct blow or crushing injury, or occasionally the thighbone may be pushed right through the hip socket as the result of a fall. Motor vehicle or motorcycle accidents are common causes of fractures. If the true pelvis is fractured there is usually also damage to the organs contained inside. Treatment of pelvic fractures involves fixing the fragments together with metal screws, wires and plates to allow the bones to heal.