Hip replacement. Artwork of the fitting of a prosthetic hip socket during hip replacement surgery. The hip joint is separated and the head of the femur (thigh bone, right) is removed. It will be replaced with a prosthetic head during the surgery. The majority of hip replacements are a result of osteoarthritis, a degenerative joint disease that results in the loss of cartilage between the joint and the growth of bone in place of the cartilage. This causes pain, stiffness and loss of mobility.