Total knee replacement (TKR), also referred to as total knee arthroplasty (TKA), is a surgical procedure where worn, diseased, or damaged surfaces of a knee joint are removed and replaced with artificial surfaces. Materials used for resurfacing of the joint are not only strong and durable but also optimal for joint function as they produce as little friction as possible.

The "artificial joint or prosthesis" generally has two components, one made of metal which is usually cobalt -chrome or titanium. The other component is a plastic material called polyethylene.

The procedure has been proven to help individuals return back to moderately challenging activities such as golf, bicycling, and swimming. Total knees are not designed for jogging, or sports like tennis and skiing (although there certainly are people with total knee replacements that participate in such sports).

The general goal of total knee replacement is designed to provide painless and unlimited standing, sitting, walking, and other normal activities of daily living.

• The head of the femur, which is situated within the pelvis socket, is replaced with a metal ball and stem. This stem fits into the shaft of the femur.
• The socket is replaced with a plastic or a metal and plastic cup.

For nearly a century, doctors have been putting various materials into diseased and painful hip joints to relieve pain. Up until the 1960s, outcomes had been unreliable. At that time, the metal ball and plastic socket for the replacement of the hip joint was introduced. Today, the artificial components used in THR are stronger and more designs are available.

There are many different shapes, sizes, and designs of artificial components of the hip joint. For the most part these are composed of chrome, cobalt, titanium, or ceramic materials. Some surgeons are also using custom-made components to improve the fit in the femur.

The knee joint performs similar to a hinge joint. It consists of three bones:

• Thigh bone (Femur)
• Leg bone (Tibia)
• Knee cap (Patella)
• The junction where the femur and tibia couple together is called the femorotibial joint.
• The region of the knee where the patella and femur form a junction is called the patellofemoral joint.
• These two joints are what allow the bending and straightening of the knee. It is these joints that are replaced in a total knee joint replacement.

For a knee to function normally, the quality of smoothness where each bone moves upon the other becomes important in the function of the knee joint.

The surfaces of all three bones coming into contact with each other are normally covered with a smooth gliding surface known as articular cartilage.

The condition of this cartilage lining the knee joint is a key aspect of normal knee function and is important to the physician when evaluating a potential need for a knee joint replacement.

In addition to the smooth cartilage lining on the joint surfaces, there are two smooth discs of cartilage that cushion the space between the bone ends. The inner disc is called the medial meniscus, while the disc on the outer side of the knee joint is called the lateral meniscus. The role of the menisci is to increase the conformity of the joint between the femur and the tibia. The menisci also play an important function as joint shock absorbers by distributing weight-bearing forces, and in reducing friction between the joint segments.

Generally speaking, there are four major ligaments that play an important part in stability of the knee joint. One on each side of the knee (but actually outside the joint) known as collateral ligaments and two more centrally located ligaments within the joint known as anterior and posterior cruciate ligaments.

Any condition affecting the knee that causes damage to the normally smooth lining cartilage of the knee may eventually end up with the same end result. The protective cartilage lining the joint becomes worn away, producing increasing damage to the bone surfaces inside the joint. This may cause pain, swelling and stiffness, as the exposed bone ends grind painfully against each other.

Osteoarthritis
Resulting from "wear and tear" is the most common reason individuals need to undergo knee replacement surgery. This condition may be due to an old injury or infection to the knee joint, but mostly there is no obvious cause as to why this happens. The major problem in osteoarthritis of the knee joint is that the smooth cartilage lining the inside of the joint wears away. This results in a narrowing of the joint space with the development of cysts and erosions in the bone ends. As a result, bone comes directly in contact with bone, which will be painful. Bone spurs (small bone growths) form around the joint. All of these changes ultimately lead to increasing pain and stiffness of the joint.
For further information about osteoarthritis, go to Osteoarthritis

Rheumatoid arthritis
An inflammation of the tissue surrounding the joints, can cause deterioration of cartilage and other parts of the joint and result in the need for knee joint replacement. It is one of the inflammatory types of arthritis that may affect other areas of the body such as skin, kidneys and spleen. Rheumatoid arthritiscan also affect other joints including hands, feet, elbows, hips etc.

Post-traumatic arthritis
A type of arthritis that can arise following an injury to the joint cartilage or through damage to the ligaments leading to an unstable knee. Generally speaking, any abnormalities causing excessive wear within the joint (from fractures of the knee, torn cartilage, and torn ligaments) can lead to degeneration long after the original injury and ultimately result in the need for a knee replacement.

Avascular necrosis
Results from an inadequate supply of blood to the bone end inside the joint. As a result articular cartilage wears away.

Malalignment of the knee joint
Knock-knees or bowlegs - results from an excessive angle where the upper and lower leg bones meet at the knee joint. The result is abnormally high stress on either the outer half or inner half of the joint.

Total knee replacements are usually performed on people suffering from painful arthritic conditions of the knee severe enough to limit one's normal day to day activities.

Most people who have artificial knees are over age 55, but the procedure is also offered to younger people with knee degeneration if their quality of life is severely affected.