What is knee replacement surgery?

Knee Replacement Surgery
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Knee replacement surgery: Overview

Joint replacement involves surgery to replace the ends of bones in a damaged joint. This surgery creates new joint surfaces.

In total knee replacement surgery, the ends of the damaged thigh and lower leg (shin) bones and usually the kneecap are capped with artificial surfaces. These surfaces are lined with metal and plastic. Doctors usually secure parts of the knee joint components to the bones with cement.

Doctors are working on ways to replace just the damaged parts of the knee joint. This is sometimes called partial joint replacement. Unicompartmental replacement is one example of partial knee replacement. It replaces just the inner knee surfaces or the outer knee surfaces, depending on where the damage is. Another partial replacement is called a patellofemoral replacement. In this surgery, the end of the thigh bone is replaced. Then an artificial surface is used to line the back of the kneecap.

Your doctor may use regional anesthesia. This means you can't feel the area of the surgery. You'll have medicine that makes you unaware and lightly asleep. Or your doctor may use general anesthesia. This means you'll be asleep during surgery. Which type of anesthesia you get depends on your doctor and on your overall health. Your doctor might also ask what you prefer.

If you need any major dental work, your doctor may recommend that you have it done before the surgery. Infections can spread from other parts of the body, such as the mouth, to the artificial joint and cause a serious problem. But some experts don't agree that this is likely to happen.

Need for repeat knee replacement

Graph with 100 figures, showing 10 figures colored to represent how many need repeat knee replacement surgery within 20 years.

The information shown here is based on the best available evidence.

What are the risks of knee replacement surgery?

Risks from knee replacement surgery include blood clots, infection, problems with healing, and nerve injury (rare). In some cases, the knee may be unstable. Your range of motion may be limited after the surgery. As with any surgery, anesthesia also has some risks.

Knee Replacement: Recovery

Knee replacement surgery

Normal knee joint

Normal knee joint

Inside a normal knee joint, thick cushioning (cartilage) covers and protects the ends of your bones. This is called hyaline cartilage. Another type of cartilage, called meniscal cartilage or meniscus, acts like a shock absorber between the bones and keeps the knee joint stable by spreading out the load evenly across the joint. The two menisci (plural of meniscus) protect and cushion the surface of the joint and the ends of your bones.

Osteoarthritis of the knee

Knee joint with osteoarthritis

In osteoarthritis, the cartilage that protects and cushions the knee joint breaks down over time. As the cartilage wears down, the bone surfaces rub against each other. This damages the tissue and bone, causing pain. Osteoarthritis is common in the knee joints.

Femoral component is placed

Knee replacement surgery: Femoral component

Removal of damaged cartilage and bone from the lower end of the femur and placement of the femoral component

Tibial component is placed

Knee replacement surgery: Tibial component

Removal of damaged cartilage and bone from the upper end of the tibia and placement of the tibial component

Patellar component is placed

Knee replacement surgery: Patellar component

Removal of damaged cartilage and bone from the patella and placement of the patellar component

Knee replacement surgery is complete

Completed knee replacement surgery

Completed knee replacement

Why is knee replacement surgery done?

Doctors recommend joint replacement surgery when:

  • X-rays show bones and cartilage are damaged.
  • Knee pain and loss of function are severe.
  • Medicine and other treatments no longer help with pain.

Doctors may not recommend knee replacement for people who:

  • Have poor general health and may not tolerate anesthesia and surgery well.
  • Have an active infection or are at risk for infection.
  • Have osteoporosis (significant thinning of the bones).
  • Have severe weakness of the quadriceps muscles at the front of the thigh.
  • Have a knee that appears to bend backward when the knee is fully extended (genu recurvatum), if this condition is due to muscle weakness or paralysis.
  • Are severely overweight. Replacement joints may be more likely to fail in people who are very overweight.
  • Have very high expectations for how much they will be able to do after surgery. These include doing sports that stress the knee.

Some doctors will recommend other types of surgery if possible for younger people and especially for those who do strenuous work. A younger or more active person is more likely than an older or less active person to have an artificial knee joint wear out.

Knee Replacement Surgery: Pros and Cons

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