A joint is formed by the ends of two or more bones that are connected by thick tissues. For example, the knee joint is formed by the lower leg bone (tibia and fibula) and the thighbone (femur). The 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. 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 reduces friction and wear in a joint.

Why is total joint replacement necessary?

The goal is to relieve the pain and improve function in the joint caused by damage to the cartilage by fracture or arthritis. The pain may be so severe that a person will avoid using the joint, weakening the muscles around the joint and making it even more difficult to move the joint. A physical examination, and possibly some laboratory tests and X-rays, will show the extent of damage to the joint. Total joint replacement will be considered if more conservative treatment options will not relieve the pain and disability.

How is a total joint replacement performed?

You will be given an anesthetic (either general or regional) and the surgeon will replace the damaged parts of the joint. For example, in an arthritic knee the damaged ends of the bones and cartilage are replaced with metal and plastic surfaces that are shaped to restore knee movement and function. If only one half of the knee joint is replaced, its called a Uni-Knee Replacement. If both sides require replacement, its called a Total Knee Replacement.

In an arthritic hip, the damaged ball or head  (the upper end of the femur) is replaced by a metal ball attached to a metal stem fitted into the femur and a plastic or metal socket is implanted into the pelvis (the acetabulum) , replacing the damaged socket.

Although hip and knee replacements are the most common joint replaced, this surgery can be performed on other joints, including the ankle, foot, shoulder, elbow, and fingers.

The prosthesis is generally composed of two parts: a metal piece that fits closely into a matching sturdy plastic piece. Several metals are used, including stainless steel, alloys of cobalt and chrome, and titanium. The plastic material is durable and wear resistant (polyethylene). A plastic bone cement may be used to anchor the prosthesis into the bone.