The pelvis is a ring-like structure of bones. The two sides of the pelvis are in fact three bones (ilium, ischium, and pubis) that grow together as people age. Strong connective tissues (ligaments) join the pelvis to the sacrum at the base of the spine. This creates a bowl-like cavity below the rib cage. On each side, there is a hollow cup (acetabulum) that serves as the socket for the hip joint.
Many digestive and reproductive organs are located within the pelvic ring. Large nerves and blood vessels that go to the legs pass through it. The pelvis serves as an attachment point for muscles that reach down into the legs and up into the trunk of the body. With all of these vital structures running through the pelvis, a pelvic fracture can be associated with substantial bleeding, nerve injury, and internal organ damage.