What is a knee replacement?

Dr. Vonda Wright, MD
Orthopedic Surgeon

I call total knee replacement, "healing with steel." Total knee replacement is one of Orthopaedic Surgery's most successful procedures. We have been replacing knees for more than 30 years and have a huge body of literature documenting the best ways to diagnose, implant as well as the outcomes of total knee surgery.

The purpose of any joint replacement is to remove the arthritic ends of the long bones, which cause patients so much pain and dysfunction, and realign the biomechanical axis of the joint. When the cartilage of a knee wears down the patient's leg often becomes profoundly bow legged or knock kneed. Replacement makes the leg straight again.

In addition to x-ray evidence of cartilage loss and joint deformity, a patient is ready for knee replacement when they can't take the pain another day and when they want to get their life back.
Knee replacement is major surgery requiring 2 to 4 days of hospitalization post-op and about 3 months of out-patient rehab afterwards. Following replacement we encourage patients to return to as much activity as possible. I let my patients with total knees do anything except long distance running, and there are many athletes in the senior olympic games with total joints.

It's the largest joint in the body, it's more intricate than it first seems and it's fun to rebound soccer balls off of—it's the knee. Your knee permits your lower leg to be moved outward or brought back toward your body. It's a critical part of our mobility (keep your legs straight for 60 minutes if you have any doubts). But as with everything else, most good things must come to an end, and so it is with this connection between the femur (thighbone), the tibia (shin) and the patella (kneecap).

More often than not, arthritis (an inflammation of a joint) is the basis for why a knee joint must be restored. However, sports injuries, extensive wear-and-tear and genetics also seriously deteriorate knees. A condition called avascular necrosis that impedes blood flow to the knee can also kill bone tissue. Progress in science and medicine now allow us to replace this necessary joint, improving not only mobility but also quality of life for individuals with impaired knees.

Early implant devices were essentially simple hinges, but modern artificial knees almost mimic the knee's unique sliding and rotating motions while affording strength and stability. Hundreds of thousands of people have total knee replacement surgery, also known as total knee arthroplasty, throughout the world each year—over 400,000 knee replacements are performed every year in the United States alone. With the population getting bigger and techniques advancing, that number will only increase.

Typically, people over 65 constitute the largest candidate pool for total knee replacement. The procedure can also provide relief for younger patients experiencing knee joint pain and loss of mobility, but it's prudent to put off this surgery for as long as possible. An artificial knee is functional for about 10 years. Middle-aged patients will probably need a second replacement in later years, and the second procedure is often not as successful as the initial one.

Dr. Howard J. Luks, MD
Sports Medicine Specialist

Many patients mistakenly believe that during a total knee replacement your actual knee is removed and a new knee is put back in. Some patients believe we actually utilize bone and cartilage from a cadaver. Other patients who have done some research realize that we are replacing your old knee with metal and plastic components.

A better term for a total knee replacement would be a total knee resurfacing. This is simply because we do not actually cut a major portion of the thigh bone or your shinbone out to perform a knee replacement. A typical total knee prosthesis or the piece that we use to resurface the knee is 9 mm thick. Therefore, in most situations we are only removing 9 mm of bone from the bottom of your femur and 9 mm of bone from the top of your tibia. Therefore, we are implanting a metal object that simply replaces the portion of the bone that we removed. Most implants are 9 mm thick based on many engineering experiments that have shown that that is the thickness of the metal that is necessary to withstand the forces and activities that you will be performing on these replacements.

During a total knee replacement both the end of the femur and the top of the tibia are resurfaced with metal components. A plastic or polyethylene spacer is placed between the two components and this acts as a gliding mechanism. Sometimes the under surface of your knee cap or patella is also resurfaced. Sometimes it is not. The decision to resurface the patella is based on your surgeons preference and whether or not the arthritis is affecting your patella.

A knee replacement is a very *big* procedure and a very *big* undertaking on your part. The type of prosthesis used is not nearly as important as having the prosthesis properly placed and performing your rehabilitation appropriately. You need to understand that you are making a big commitment that will be ongoing for a number of months to increase the odds of a successful procedure. As with any procedure,  there are potentially minor and major complications which can occur and you should have an in-depth discussion with your orthopedist about these potential complications before considering surgery.

Continue Learning about Knee Replacement

Home Is Where the Healing Happens
Home Is Where the Healing Happens
Dorothy spends her entireThe Wizard of Oz journey searching for a way home to Kansas, only to find the solution was as simple as clicking her ruby hee...
Read More
What can cause a total knee replacement to fail?
Presbyterian/St. Luke's Medical CenterPresbyterian/St. Luke's Medical Center
The most common cause of total knee replacement failure is loosening or de-bonding of the implant fr...
More Answers
Why should I discuss my expectations with my doctor before TKR surgery?
William A. Leone, MDWilliam A. Leone, MD
Defining success for total knee replacement (TKR) surgery begins prior to surgery, during a frank di...
More Answers
What Is a Total Knee Replacement?
What Is a Total Knee Replacement?

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.