An arthritic or damaged joint is removed and replaced with an artificial joint called a prosthesis. A joint is formed by the ends of two or more bones which are connected by thick tissues. For example, your knee joint is formed by the lower leg bone, called the tibia or shin bone, and your thighbone, called the femur. Your hip is a ball and socket joint, formed by the upper end of the femur, the ball, and a part of the pelvis called the acetabulum, the socket. The bone ends of a joint are covered with a smooth layer called cartilage.
Normal cartilage allows nearly frictionless and pain-free movement.
However, when the cartilage is damaged or diseased by arthritis, joints become stiff and painful. Every joint is enclosed by a fibrous tissue envelope or a capsule with a smooth tissue lining called the synovium. The synovium produces fluid that reduced friction and wear in a joint. The goal is to relieve the pain in the joint caused by the damage done to the cartilage. The pain may be so severe, a person will avoid using the joint, weakening the muscles around the joint and making it even more difficult to move the joint.