What is Knee Replacement?

Knee ReplacementKnee Arthroplasty, or Knee Replacement Surgery is a surgical procedure in which a worn, damaged, or diseased knee is replaced with an artificial joint made of metal and plastic. The surgeon removes either part of the knee or all of it during the procedure.

The aim is to help the patient return to normal everyday activities and alleviate pain. It can take a long time – several months or even longer – to fully recover after the operation.

Why undergo knee replacement?

The human knee is vital for walking, running, jumping, and standing. However, sometimes the knee becomes damaged beyond repair.

The most common causes of extensive knee damage are:

  • Osteoarthritis – occurs when the protective cartilage that cushions the bones, including the knee, has worn down.
  • Rheumatoid arthritis – an autoimmune disease where the body’s own immune system mistakenly attacks healthy cells as if they were harmful bacteria, viruses, or fungi.
  • Injuries – professional sports people who play rugby, American football, soccer, and basketball are at a higher risk of knee injuries than the rest of the population. The same applies to competitive skiers, skateboarders, wrestlers, and martial artists.
  • Gout – a type of arthritis caused by an accumulation of uric acid crystals in the joint.

If you have knee damage, you may suffer from pain, stiffness, and walking difficulties. Knee replacement offers a new lease of life by providing a new knee part or whole knee that can alleviate pain and help you do everyday things that you once took for granted.

According to the UK’s National Health Service (NHS):

“The knee usually moves smoothly because the ends of the bones are covered with a layer of tough tissue called cartilage. If the cartilage is worn away by osteoarthritis or damaged by an injury, the bones rub against each other, making your joint painful and stiff. During a knee replacement, the damaged parts of your knee are replaced with metal and plastic parts.”

Alternative options

Before suggesting knee replacement surgery, your doctor will most likely recommend less invasive alternatives, such as:

  • Weight loss

If you are overweight or obese, losing weight will reduce stress on the knee.

  • Physical therapy (UK: physiotherapy)

Physical therapy helps strengthen the muscles around the knee.

  • Medications

Hyaluronic acid or corticosteroid injections can help manage pain and inflammation.

  • Aids

Wearing special shoes or insoles, as well as walking aids may help.

  • Cartilage regeneration

If you have moderate arthritis and a good alignment of bones, you should consider replacing cartilage rather than the whole joint. Several cartilage-regeneration procedures exist today.

In the following quote, Hopkins Medicine mentions one type of cartilage-regeneration technique:

“Autologous chondrocyte implantation (ACI) involves taking a sample of your cartilage cells, growing them in a lab and then surgically replanting them in your knee. It’s not for everyone, but young people and athletes affected by cartilage loss may be candidates.”

If none of these treatment options work, or the condition gets worse, your doctor will probably recommend surgery, i.e., knee replacement.

Knee Replacement - several images depicting the procedure

Created by MedicalVocab.com using material from Wikimedia Commons.

What happens during knee replacement surgery?

During the procedure, the surgeon removes the damaged parts of the knee and replaces them with a prosthesis, which is made of metal, high-grade plastics, or polymers. Polymers are very large molecules made up of several small parts (monomers), in the same way a very long train is made up of many small carriages.

The procedure is as follows (in order):

  1. You are anesthetized.
  2. The surgeon makes an incision in the skin to expose the joint.
  3. They carefully remove the damaged bone and cartilage and prepare the area to receive the new knee prosthesis.
  4. The artificial knee joint is correctly placed and secured.
  5. The surgeon closes the incision with staples or stitches.


How long it takes to fully recover from the operation varies considerably from person to person.

Initially, you may need crutches or a walker (UK: Zimmer frame). Part of the recovery process involves physical therapy to help you regain strength and mobility in your knee.

Within a few weeks, you should be able to walk unaided, until eventually you will resume your regular activities. However, high-impact activities may still be restricted.

Regarding recovery after the operation, Nuffield Health offers the following information:

“Following your operation you’ll be able to go home when your pain is under control, you can get about safely, and any care you may need has been arranged. Your wound is likely to take 10-14 days to heal. It may take up to 6 weeks to recover from the operation. It can take up to 12 months ​before you are back to normal activities.”

Complications of knee replacement

The vast majority of procedures are successful, and patients make a full recovery. However, in rare cases, there may be complications, including:

  • Nerve damage.
  • Infection
  • The prosthesis wears out over time.
  • Blood clots.

The world of surgery and prostheses have advanced dramatically over the past few decades, while the risk of complications has been greatly reduced.

If you suffer from knee pain, which has continued for more than a couple of weeks, or if it is getting worse, see your doctor.

Interesting related article: “Older knee replacements as good as newer models, study shows.” University of East Anglia, Norwich, UK.