Two parts comprise the hip joint: a ball on the upper end of the thigh bone, called the head of the femur; and a socket in the pelvis known as the acetabulum.

The hip joint, like other joints, is made up of specialized structural elements that serve as precisely fitting, moving parts. The head of the femur rotates freely within the smooth, concentric surfaces of the acetabulum. An extremely low friction tissue, hyaline cartilage, lines this joint as well as others in the human body. The friction between two hyaline cartilage surfaces is much less than the best man-made bearing.

Acetabulum fractures often result from automobile or motorcycle accidents, falls from great heights and industrial accidents, when a accidental strong force drives the head of the femur through the acetabulum.

Fractures of the acetabulum disrupt the smooth surface and precise fit of the hip joint. If the bone is allowed to heal with large gaps and irregularities, severe abrasion to and the ultimate destruction of the cartilage will result. In some cases, the bone itself will show wear. The consequence: severe hip arthritis. Patients who develop arthritis have pain when walking, loss of hip motion, and limited functional capabilities.

Fractures of the acetabulum cause internal bleeding from the broken bone and the surrounding injured soft tissues. Major blood vessels may be torn, causing severe bleeding. There can be damage to internal organs, such as the bowel or bladder. The nerves that provide sensation and muscle function to the leg or that control bowel, bladder and sexual function may also be impaired.