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Knee replacement

Read about knee replacement surgery (arthroplasty), a procedure to replace a damaged, worn or diseased knee with an artificial joint.

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.

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Knee replacement

Read about how knee replacement surgery is performed. You'll usually be admitted to hospital on the day of your operation. The surgeon and anaesthetist will usually come and see you to discuss what will happen

You'll usually be admitted to hospital on the day of your operation. The surgeon and anaesthetist will usually come and see you to discuss what will happen and answer any questions you have.

Most people would have seen their surgeon at a pre-assessment clinic and had the chance to discuss any relevant details of the operation.

A senior-level surgeon, consultant or registrar will perform surgery. They may be helped by junior doctors. You should be told at your pre-operative assessment who will be doing the operation. If you're not told, don't be afraid to ask.

How the operation is carried out

Knee replacement surgery is usually performed either under general anaesthetic (you're asleep throughout the procedure) or under spinal or epidural anaesthetic (you're awake but have no feeling from the waist down).

The worn ends of the bones in your knee joint are removed and replaced with metal and plastic parts (a prosthesis) which have been measured to fit.

You may have either a total or a half-knee replacement (see below). This will depend on how damaged your knee is. Total knee replacements are the most common.

Read more information about what happens on the day of your operation.

Total knee replacement

In a total knee replacement (TKR), both sides of your knee joint are replaced. The procedure takes one to three hours:

  • Your surgeon makes a cut down the front of your knee to expose your kneecap. This is then moved to the side so the surgeon can get to the knee joint behind it.
  • The damaged ends of your thigh bone (femur) and shin bone (tibia) are carefully cut away. The ends are precisely measured and shaped to fit the appropriately sized prosthetic replacement. A dummy joint is positioned to test that the joint is working properly. Adjustments are made, the bone ends are cleaned, and the final prosthesis is fitted.
  • The end of your femur is replaced by a curved piece of metal, and the end of your tibia is replaced by a flat metal plate. These are fixed using special bone 'cement', or are treated to encourage your bone to fuse with the replacement parts. A plastic spacer is placed between the pieces of metal. This acts like cartilage, reducing friction as your joint moves.
  • The back of the knee cap may also be replaced, depending on the reasons for replacement.
  • The wound is closed with either stitches or clips and a dressing is applied to the wound. In rare cases a splint is used to keep your leg immobile, but you're usually encouraged to move your knee as early as possible.

Total knee replacement is a common procedure and the replacement should last around 15-20 years.

However, you're still likely to have some difficulty moving, especially bending your knee, and kneeling may be difficult because of the scar.

Read more information about recovering from knee replacement surgery.

Partial (half) knee replacement

If only one side of your knee is damaged, you may be able to have a partial (half) knee replacement (PKR). PKR is a smaller operation, which uses a smaller incision, and involves less bone being removed. It's suitable for around one in four people with osteoarthritis.

There are advantages to PKR including a shorter hospital stay and recovery period. Blood transfusions are also rarely needed. PKR often results in more natural movement in the knee and you may be able to be more active than after a total knee replacement.

Talk to your surgeon about the type of surgery they intend to use and why they think it's the best choice for you.

Other procedures

In some cases, there may be other types of procedure used. These are described below.

Kneecap replacement

If only your kneecap is damaged, an operation called a patellofemoral replacement or patellofemoral joint arthroplasty can be performed. This involves a smaller surgery with a faster recovery time. However, the long-term results are still unclear and it's not suitable for most people with osteoarthritis.

Mini-incision surgery (MIS)

This new technique has been recommended by the National Institute for Health and Care Excellence (NICE). It can be used for either total or half knee replacements, but is currently more commonly used for half knee replacements.

The surgeon makes a smaller cut than in standard knee replacement surgery. Specialised instruments are then used to manoeuvre around the tissue, rather than cutting through it. This should lead to a quicker recovery.

Read the NICE guidance on mini-incision surgery for total knee replacement.

Image-guided surgery

The surgeon performs this operation using computerised images, which are generated by attaching infrared beacons to parts of your leg and to the operating tools. These are tracked on infrared cameras in the operating theatre. Results so far suggest that this may enable the new knee joint to be positioned more accurately.

Most hospitals don't yet have the equipment to do this and only around 1% of knee replacements are performed in this way.

Patient-specific knee replacement

This is a more recent advance in knee replacement surgery. A guide is created using magnetic resonance imaging (MRI) scans. This helps to create the best fitting implant for each patient.

The potential advantage of this procedure is that the implant may last longer, as the most accurate fitting is used. However, as this is a new technique, the results and long-term effects aren't fully known yet.


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Knee replacement

Read about the risks of knee replacement surgery. As with any operation, knee replacement surgery has risks as well as benefits

As with any operation, knee replacement surgery has risks as well as benefits. Most people who have a knee replacement don't 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's very rare, you could have a clot on your lung (pulmonary embolism) which needs urgent treatment

Anaesthesia

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're 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 is usually 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 won't 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's no set limit to the number of times you can have revision surgery, but it's widely accepted the artificial knee joint becomes less effective each time it's replaced.


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Knee replacement

Read about recovering from knee replacement surgery. Recovery times can vary depending on individual and the type of surgery performed.

Recovery times can vary depending on the individual and type of surgery carried out. It's important to follow the 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'll be given a blood transfusion.

You'll 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's 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've 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'll 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's important to follow the physiotherapist's advice to avoid complications or dislocation of your new joint.

It's 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.

Going home

You'll 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're 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.

Recovering at home

Don't be surprised if you feel extremely tired at first. You've 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's essential you continue with them once you're 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's best to avoid extreme movements or sports where there's 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's 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're 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'll be given an outpatient appointment to check on your progress, usually six to 12 weeks after your knee replacement.

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've 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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