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.
How Is a Total Joint Replacement Performed?
You will be given an anesthetic 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.
In an arthritic hip, the damaged ball (the upper end of the femur) is replaced by a metal ball attached to a metal stem fitted into the femur and a plastic socket is implanted into the pelvis, 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 materials used in a total joint replacement are designed to enable the joint to move just like a normal joint.
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. Joint replacements also can be implanted without cement when the prosthesis and the bone are designed to fit and lock together directly.
In general, your orthopaedic surgeon will encourage you to use your "new" joint shortly after your operation. After total hip or knee replacement, you will often stand and begin walking the day after surgery. Initially, you will walk with a walker, crutches, or a cane. Most patients have some temporary pain in the replaced joint because the surrounding muscles are weak from inactivity and the tissues are healing. This will end in a few weeks or months. Exercise is an important part of the recovery process. Your orthopaedic surgeon or the staff will discuss an exercise program for you after surgery. This varies for different joint replacements and for differing needs of each patient. After your surgery, you may be permitted to play golf, walk, and dance. More strenuous sports, such as tennis or running, may be discouraged. The motion of your joint will generally improve after surgery. The extent of improvement will depend on how stiff your joint was before the surgery.