The hip joint is one of the body's most reliable structures, providing movement and support without pain or problem in most people for a lifetime. The hip's simple ball and socket arrangement, with the ball shaped femoral head rotating inside a cup shaped socket, the acetabulum, usually works well for many decades of a lifetime with amazingly little friction and little or no wear.
The well fitting surfaces of the femoral head and acetabulum which face each other, are lined with a layer of cartilage, lubricated by a thin film of synovial fluid. Friction inside a normal hip is less than 1/10 that of ice gliding on ice.
There are two types of cartilage that are found in the hip joint:
- Articular cartilage is found on the head of the femur and also lines the inner surface of the acetabulum. This cartilage provides a smooth contact surface which allows the femoral head to move smoothly within the acetabulum.
- The labrum is a rim of fibrous cartilage which lines the outer edge of the acetabulum. This cartilage serves to stabilize and cushion the hip joint.