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Knee replacement

Knee replacement surgery (arthroplasty) is usually necessary if your mobility is severely reduced and you experience pain in the knee joint even while resting.

Knee replacement surgery (arthroplasty) 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.

How the knee works

The knee joint acts as a hinge between the bones of the leg and is effectively two joints. The major joint is between the thigh bone of the upper leg (femur) and the shin bone of the lower leg (tibia). The smaller joint is between the kneecap (patella) and the upper leg (femur).

A smooth, tough tissue called articular cartilage covers the ends of the bones, allowing them to slide smoothly over each other. The synovial membrane covering the other surfaces of the knee joint produces synovial fluid, which lubricates the joint, reducing friction.

If the articular cartilage becomes damaged or worn, the ends of the bones rub or grind together, causing pain and difficulty moving the knee joint.

Replacing the damaged knee joint with an artificial one can help reduce pain and increase mobility.

Causes of knee pain

The most common reason for knee replacement surgery is osteoarthritis.

Osteoarthritis in the knee occurs when the articular cartilage becomes damaged through natural wear and tear. The bones have little or no protection to prevent them rubbing against each other when the knee moves.

The bones may compensate by growing thicker and producing bony outgrowths to try to repair themselves, but this can cause more friction and pain.

Other conditions that may make knee replacement necessary 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

When is surgery necessary?

You may be offered knee replacement surgery if:

  • you have severe pain, swelling and stiffness in your knee joint and your ability to move the joint is significantly 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 are feeling depressed because of the pain and lack of mobility
  • you cannot work or have a normal social life

Read information about how knee replacement surgery is performed.

Surgical alternatives to knee replacement

There are alternative surgeries to knee replacement, but results are often not as good in the long term. These are described below.

Arthroscopic washout and debridement

An arthroscope (tiny telescope) is inserted through small incisions in the knee. The knee is washed out with saline and any bits of bone or cartilage are cleared away. It is not recommended if you have severe arthritis.


A keyhole operation in which small holes are made in the surface layer of bone with a small, sharp ‘pick’. This allows cells from the deeper, more blood-rich bone beneath to come to the surface and stimulate cartilage growth. It can be a good option if you have just a small area of damaged cartilage. However, the benefits are not well proven and the results are not as good as knee replacement for severe arthritis.


An open operation in which the surgeon cuts the shin bone and realigns it so that weight is no longer focused on the damaged part of the knee. It is sometimes used for younger people with limited arthritis, where it may enable a knee replacement to be postponed. However, you will usually need a knee replacement at a later date, and the operation may make knee replacement surgery more difficult if it is needed.

Autologous chondrocyte implantation (ACI)

New cartilage from your own cells is grown in a test tube and introduced into the damaged area. It is usually used for accidental injury to the knee rather than arthritis. As yet, ACI is only available as part of a clinical trial.

Mosaicplasty (cartilage replacement)

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.

Read the NICE guidance on mosaicplasty for knee cartilage defects.

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Knee replacement

Choose a specialist who performs knee replacement regularly and can discuss their results with you. Make sure to ask them any questions you have.

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

This is even more important if you are having a second or subsequent knee replacement, known as 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.

How can I prepare for going into hospital?

  • Get informed. Find out as much as you can about what is involved in your operation. Your hospital may provide written information or videos.
  • Arrange help. Arrange for a friend or relative to help at home for a week or two after you come out of hospital.
  • Sort out transport. Arrange for someone to take you to and from the hospital.
  • Prepare your home. Before you go for your operation, put your TV remote control, radio, telephone, medications, tissues, address book and a glass on a table next to where you will spend most of your time when you come out of hospital.
  • Stock up. Buy easy to prepare food, such as frozen ready meals, cans and staples like rice and pasta, or freeze meals and reheat them during your recovery.
  • Clean up. Before going into hospital, have a long bath or shower, cut your nails (take off any nail polish) and wash your hair. Put on freshly washed clothes. This helps prevent unwanted bacteria coming into hospital with you and complicating your care.

Things to take into hospital

  • a change of nightclothes
  • something comfortable and easy to wear
  • suitable footwear – shoes should be flat, supportive (with a back or heel strap) and with some room to allow for any swelling
  • toiletries
  • medication
  • antiseptic hand wipes and gel
  • a book, iPod and other things to help pass the time during recovery
  • important phone numbers

It is advisable not to take valuables, jewellery or large sums of money into hospital with you. Ask a friend to look after your valuables if you do not want to leave them at home.

Read more information about preparing for surgery.

How can I prepare for the operation?

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.

What will happen before the operation?

A couple of weeks before the operation, you will usually be asked to attend a preoperative assessment clinic to meet your surgeon and other members of the surgical team. You may be offered an enhanced recovery programme.

They will take a medical history, examine you and organise any tests (such as blood tests and urine tests), ECGs (electrocardiograms) and X-rays needed to make sure you are healthy enough for an anaesthetic and surgery.

Take a list of any medication you are taking. Some rheumatoid arthritis medications suppress the immune system, which can affect healing. For this reason, you may be asked to stop taking your medication before surgery. If you take any anticoagulants (blood thinning medication), they may also need to be stopped before surgery. Your surgeon can advise on alternative medications.

There may be leaflets, booklets and videos to look at or take away that can give you more information about the operation.

Read more information about seeing a specialist before an operation.

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Knee replacement

As with any operation, knee replacement surgery has risks as well as benefits. Most people who have a knee replacement do not experience serious complications.

As with any operation, knee replacement surgery has risks as well as benefits. Most people who have a knee replacement do not experience serious complications.

After having a knee replacement, contact your doctor if:

  • you develop hot, reddened, hard or painful areas in your legs in the first few weeks after your operation although this may just be bruising from the surgery, it could mean a blood clot has developed
  • you experience chest pains or breathlessness although it is very rare, you could have a clot on your lung (pulmonary embolism) which needs urgent treatment


Anaesthetics are extremely safe, but carry a risk of minor side effects such as sickness and confusion (usually temporary). There is also a slight risk of serious complications.

The risk of death in a healthy person having routine surgery is very small. Death occurs in around one in every 100,000 general anaesthetics given.

The risk is higher if you are older or have other health conditions, such as heart or lung disease.

Your anaesthetist and surgeon can answer questions you may have about your personal risks from anaesthetic or the surgery itself.

Other complications

Complications occur in about one in 20 cases, but most are minor and can be successfully treated. Possible complications are described below.

  • Infection of the wound  this will usually be treated with antibiotics, but occasionally the wound can become deeply infected and require further surgery. In rare cases it may require replacement of the artificial knee joint  
  • 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) clots may form in the leg veins as a result of reduced movement in the leg during the first few weeks after surgery. They can be prevented by using special support stockings, starting to walk or exercise soon after surgery, and by using anticoagulant medicines
  • Fracture in the bone around the artificial joint during or after surgery  treatment will depend on the location and extent of the fracture
  • Excess bone forming around the artificial knee joint and restricting movement of the knee  further surgery may be able to remove this and restore movement
  • Excess scar tissue forming and restricting movement of the knee  further surgery may be able to remove this and restore movement
  • The kneecap becoming dislocated  surgery can usually repair this
  • Numbness in the area around the wound scar
  • Allergic reaction  you may have an allergic reaction to the bone cement if this is used in your procedure

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

How long will a replacement knee last?

Wear and tear through everyday use means your replacement knee will not last forever. However, for most people it will last at least 15-20 years, especially if cared for properly and not put under too much strain.

Revision knee replacement surgery (replacing the replacement knee) is usually more complicated and a longer procedure than the original surgery. There is no set limit to the number of times you can have revision surgery, but it is widely accepted the artificial knee joint becomes less effective each time it is replaced.

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Knee replacement

Recovery times can vary depending on individual and the type of surgery performed. It is important to follow the advice the hospital gives you.

Recovery times can vary depending on the individual and type of surgery carried out. It is important to follow advice the hospital gives you on looking after your knee.

After surgery

In the surgical ward, you may be given a switch that enables you to self-administer painkillers at a safe rate. You may also be given oxygen through a mask or tubes. If necessary, you will be given a blood transfusion.

You will have a large dressing on your knee to protect your wound. Various drains will syphon off blood from the operation site to prevent it collecting inside the wound.

Your wound dressing will be changed regularly until it has healed over.

Read more information about what happens after an operation.

How soon will I be up and about?

The staff will help you to get up and walk about as quickly as possible. If you have had minimally invasive surgery or are on an enhanced recovery programme, you may be able to walk on the same day as your operation. Generally, you will be helped to stand within 12-24 hours after your operation.

Walking with a frame or crutches is encouraged. Most people are able to walk independently with sticks after about a week but this can vary depending on the individual.

During your stay in hospital, a physiotherapist will teach you exercises to help strengthen your knee. You can usually begin these the day after your operation. It is important to follow the physiotherapist's advice to avoid complications or dislocation of your new joint.

It is normal to experience initial discomfort while walking and exercising, and your legs and feet may be swollen.

You may be put on a passive motion machine to restore movement in your knee and leg. This support will slowly move your knee while you are in bed. It helps to decrease swelling by keeping your leg raised and helps improve your circulation.

When can I go home?

You will usually be in hospital for three to five days, depending on what progress you make and what type of knee replacement you have. Patients who have a half knee replacement usually have a shorter hospital stay.

If you are generally fit and well, the surgeon may suggest an enhanced recovery programme where you start walking on the day of the operation and are discharged within one to three days.

Read more information about getting back to normal after an operation.

How will I feel when I get home?

Do not be surprised if you feel extremely tired at first. You have had a major operation and muscles and tissues surrounding your new knee will take time to heal. Follow the advice of the surgical team and call your GP if you have any particular worries or queries.

You may be eligible for home help and there may be aids that can help you. You may also want to arrange for someone to help you out for a week or so.

The exercises your physiotherapist gives you are an important part of your recovery. It is essential you continue with them once you are at home. Your rehabilitation will be monitored by a physiotherapist.

How long will it be before I feel normal?

You should be able to stop using your crutches or walking frame and resume normal leisure activities six weeks after surgery. However, it may take up to three months for pain and swelling to settle down. It can take up to a year for any leg swelling to disappear.

Your new knee will continue to recover up to two years after your operation. During this time, scar tissue will heal and muscles will be restored by exercise.

Even after you have recovered, it is best to avoid extreme movements or sports where there is a risk of falling, such as skiing or mountain biking. Your doctor or a physiotherapist can advise you.

When can I drive again?

You can resume driving when you can bend your knee enough to get in and out of a car and control the car properly.

This is usually around four to six weeks after your surgery, but check with your physiotherapist or doctor whether it is safe for you to drive.

When can I go back to work?

This depends on your job, but you can usually return to work six to 12 weeks after your operation.

When can I do housework?

For the first three months, you should be able to manage light chores, such as dusting and washing up.

Avoid heavy household tasks such as vacuuming and changing the beds. Do not stand for long periods as this may cause ankle swelling and avoid stretching up or bending down for the first six weeks.

How will it affect my sex life?

You may find that having the operation gives your sex life a boost. Your surgeon can advise when you can have sex again. As long as you are careful, it should be fine after six to eight weeks. Avoid vigorous sex and kneeling positions.

Will I have to go back to the hospital?

You will be given an outpatient appointment to check on your progress, usually six to 12 weeks after your knee replacement.

The surgeon will want to see you again a year later, and every five years after that to X-ray your knee and make sure it is not beginning to loosen.

Will I need another new knee?

The knee can be replaced as often as necessary, although results tend to be slightly less effective each time. Recovery may take longer, but once you have recovered, results are usually good.

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Knee replacement

Janet Collins has had both her knees replaced and can walk much better than before.

Janet Collins has had both her knees replaced and can walk much better than before.

“I have severe arthritis and had been in a lot of pain with my knees for some time. They were very swollen too. I went to the hospital and had an X-ray and the doctor suggested a knee replacement.

"I had my left knee done in 2002 and my right in 2004. I was quite nervous before the first operation, but the consultant came down to greet me and held my hand. The operation went well and the next day the physiotherapist helped me to lift my leg up and bend it slightly. After that, I got up and had a walking frame. I was out of hospital within a week. The operation affected my sciatic nerve, which was very painful at first, but it gradually got better.

“When I had my right knee done, I was in hospital for three weeks because doctors thought I had a blood clot. Thankfully I didn’t. Since then I haven’t looked back. I'm disabled and use a wheelchair or scooter, but I am much more able to go about with just my sticks, whereas before I would have used a frame.

“I can’t kneel on the bed or the floor because it feels strange. They do click, but you get used to that. I exercise for five minutes every morning and evening. I would say my knees are 100% better than they were before. I would recommend the operation to anyone.”

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