As time goes by, normal wear and tear can add up. Cartilage may begin to rub together, they become rough and pitted. This wears down the socket.
A chronic disease, such as rheumatoid arthritis or gout, can cause swelling and heat (inflammation) in the joint lining. As the disease progresses, cartilage may be worn away and the joint may stiffen.
A bad fall or blow to the hip can break (fracture) bone. Of the broken bone does not heal properly, the joint may slowly wear down.
A bad injury or long-term use of alcohol or steroids can reduce blood supply to the bone. If the bone dies (necrosis), the joint will decay.