Cause

The most common cause of chronic knee pain and disability is arthritis. Although there are many types of arthritis, most knee pain is caused by just three types: osteoarthritis, rheumatoid arthritis, and post-traumatic arthritis.

Osteoarthritis. This is an age-related "wear and tear" type of arthritis. It usually occurs in people 50 years of age and older, but may occur in younger people, too. The cartilage that cushions the bones of the knee softens and wears away. The bones then rub against one another, causing knee pain and stiffness.

Rheumatoid arthritis. This is a disease in which the synovial membrane that surrounds the joint becomes inflamed and thickened. This chronic inflammation can damage the cartilage and eventually cause cartilage loss, pain, and stiffness. Rheumatoid arthritis is the most common form of a group of disorders termed "inflammatory arthritis."

Post-traumatic arthritis. This can follow a serious knee injury. Fractures of the bones surrounding the knee or tears of the knee ligaments may damage the articular cartilage over time, causing knee pain and limiting knee function.

When Surgery Is Recommended

There are several reasons why your doctor may recommend knee replacement surgery. People who benefit from total knee replacement often have:

• Severe knee pain or stiffness that limits everyday activities, including walking, climbing stairs, and getting in and out of chairs. It may be hard to walk more than a few blocks without significant pain and it may be necessary to use a cane or walker.
• Moderate or severe knee pain while resting, either day or night
• Chronic knee inflammation and swelling that does not improve with rest or medications
• Knee deformity — a bowing in or out of the knee
• Failure to substantially improve with other treatments such as anti-inflammatory medications, cortisone injections, lubricating injections, physical therapy, or other surgeries

Total Knee Replacement

A total knee replacement is a surgical procedure whereby the diseased knee joint is replaced with artificial material. The knee is a hinge joint that provides motion at the point where the thigh meets the lower leg. The thighbone (or femur) abuts the large bone of the lower leg (tibia) at the knee joint.

During a total knee replacement, the end of the femur bone is removed and replaced with a metal shell. The end of the lower leg bone (tibia) is also removed and replaced with a channeled plastic piece with a metal stem. Depending on the condition of the kneecap portion of the knee joint, a plastic "button" may also be added under the kneecap surface. The artificial components of a total knee replacement are referred to as the prosthesis.

The posterior cruciate ligament is a tissue that normally stabilizes each side of the knee joint so that the lower leg cannot slide backward in relation to the thighbone. In total knee replacement surgery, this ligament is either retained, sacrificed, or substituted by a polyethylene post. Each of these various designs of total knee replacement has its own particular benefits and risks.

Partial knee replacement

A partial knee replacement is surgery to replace only one part of a damaged knee. It can replace either the inside (medial) part, the outside (lateral) part, or the kneecap part of the knee.

A partial knee replacement is an alternative to total knee replacement for some patients with osteoarthritis of the knee. This surgery can be done when the damage is confined to a particular compartment of the knee.
In the past, partial knee replacement was reserved for older patients who were involved in few activities. Now, partial knee replacement is often preferred in the younger population as their recovery is quicker and often with much less pain. About 5% to 6% of patients with arthritic knees are estimated to be eligible for partial knee replacement.