The socket area, which is inside the pelvis, is called the acetabulum . The ball part of this joint is the top of the leg bone. It joins with the acetabulum to form the hip joint. The hip is one of the most stable joints in the body. But, its function, bearing the body's weight, makes it susceptible to arthritis due to excessive pressure.
Arthritis is the most common cause of the breakdown of hip tissue.
Rheumatoid arthritis , a disease in which, for unknown reasons, the synovial membrane becomes irritated and produces too much fluid. It damages the cartilage, leading to pain and stiffness. Traumatic arthritis , the result of an injury or fracture. There are more than 280,000 hip fractures in the United States every year. Bursitis , in which the the bursa, a closed fluid-filled sac that functions as a gliding surface to reduce friction between tissues of the body, becomes inflamed.