Knee replacement surgery (arthroplasty) is a routine operation that involves replacing a damaged, worn or diseased knee with an artificial joint.

Adults of any age can be considered for a knee replacement, although most are carried out on people between the ages of 60 and 80. More people are now receiving this operation at a younger age.

A replacement knee usually lasts over 20 years, especially if the new knee is cared for properly and not put under too much strain.

When a knee replacement is needed

Knee replacement surgery is usually necessary when the knee joint is worn or damaged to the extent that your mobility is reduced and you experience pain even while resting.

The most common reason for knee replacement surgery is osteoarthritis. Other conditions that cause knee damage include:

  • rheumatoid arthritis
  • haemophilia
  • gout
  • disorders that cause unusual bone growth (bone dysplasias)
  • death of bone in the knee joint following blood supply problems (avascular necrosis)
  • knee injury
  • knee deformity with pain and loss of cartilage

Who is offered knee replacement surgery

A knee replacement is major surgery, so is normally only recommended if other treatments, such as physiotherapy or steroid injections, haven't helped reduce pain or improve mobility.

You may be offered knee replacement surgery if:

  • you have severe pain, swelling and stiffness in your knee joint and your mobility is reduced
  • your knee pain is so severe that it interferes with your quality of life and sleep
  • everyday tasks, such as shopping or getting out of the bath, are difficult or impossible
  • you're feeling depressed because of the pain and lack of mobility
  • you can't work or have a normal social life

You'll also need to be well enough to cope with both a major operation and the rehabilitation afterwards.

Types of knee replacement surgery

There are two main types of surgery, depending on the condition of the knee:

  • total knee replacement (TKR) – both sides of your knee joint are replaced
  • partial (half) knee replacement (PKR) – only one side of your joint is replaced in a smaller operation with a shorter hospital stay and recovery period

Read more about how knee replacement surgery is performed.

Alternative surgery

There are alternative surgeries to knee replacement, but results are often not as good in the long term. Your doctor will discuss the best treatment option with you. Alternatives may include:

  • arthroscopic washout and debridement – an arthroscope (tiny telescope) is inserted into the knee, which is then washed out with saline to clear out any bits of bone or cartilage
  • osteotomy – during an open operation, the surgeon cuts the shin bone and realigns it so that weight is no longer focused on the damaged part of the knee
  • mosaicplasty – a keyhole operation that involves transferring plugs of hard cartilage, together with some underlying bone from another part of your knee, to repair the damaged surface

Choosing a specialist

Choose a specialist who performs knee replacement regularly and can discuss their results with you.

This is even more important if you're having a second or subsequent knee replacement (revision knee replacement), which is more difficult to perform.

Your local hospital trust website will show which specialists in your area do knee replacement. Your GP may also have a recommendation, or arrange for you to follow an enhanced recovery programme.

You can also read a guide to NHS waiting times.

Preparing for knee replacement surgery

Before you go into hospital, find out as much as you can about what's involved in your operation. Your hospital should provide written information or videos.

Stay as active as you can. Strengthening the muscles around your knee will aid your recovery. If you can, continue to take gentle exercise, such as walking and swimming, in the weeks and months before your operation. You can be referred to a physiotherapist, who will give you helpful exercises.

Read about preparing for surgery, including information on travel arrangements, what to bring with you and attending a pre-operative assessment.

Recovering from knee replacement surgery

You'll usually be in hospital for three to five days, but recovery times can vary depending on the individual and type of surgery being carried out. 

Once you're able to be discharged, your hospital will give you advice about looking after your knee at home. You'll need to use a frame or crutches at first and a physiotherapist will teach you exercises to help strengthen your knee.

Most people can stop using walking aids around six weeks after surgery, and start driving after about eight to 12 weeks. 

Full recovery can take up to two years as scar tissue heals and your muscles are restored by exercise. A very small amount of people will continue to experience some pain after two years.

Read about recovering from knee replacement surgery.

Risks of knee replacement surgery

Knee replacement surgery is a common operation and most people don't experience complications. However, as with any operation, there are risks as well as benefits.

Complications are rare but can include:

  • stiffness of the knee
  • infection of the wound
  • deep infection of the joint replacement, needing further surgery 
  • unexpected bleeding into the knee joint
  • ligament, artery or nerve damage in the area around the knee joint
  • blood clots or deep vein thrombosis (DVT)
  • persistent pain the in the knee
  • fracture – a break in the bone around the knee replacement during or after the operation

In some cases, the new knee joint may not be completely stable and further surgery may be needed to correct it.

Read more about the risks of knee replacement surgery.

The National Joint Registry

The National Joint Registry (NJR) collects details of knee replacements carried out in England and Wales. Although it's voluntary, it's worth registering. This enables the NJR to monitor knee replacements, so you can be identified if any problems emerge in the future.

The registry also gives you the chance to participate in a patient feedback survey.

It's confidential and you have a right under the Freedom of Information Act to see what details are kept about you.

Knee replacement illustration

1. Upper prosthesis
2. Lower prosthesis
3. Tibia
4. Femur

Page last reviewed: 25/07/2016

Next review due: 25/07/2019