Do I need a knee replacement?

You’ll only need a knee replacement if your knee gives you pain, stiffness, instability or loss of function that affects your daily life and activities.

In a healthy knee, the ends of your thigh and shin bones are covered with hard cartilage which allows the bones to move easily against each other. Arthritis damages the hard cartilage so that it becomes thin. In places the cartilage may wear away so that your bones rub against each other and become worn.

In a knee replacement operation, the worn ends of the bones and any remaining hard cartilage are removed and replaced with metal and plastic parts. The plastic acts like hard cartilage, helping your joint to move freely. The interlocking parts of the artificial joint allow your knee to bend while also making it more stable.

You won’t necessarily need a knee replacement if you have arthritis of the knee. But it may be worth considering if your knee is damaged by arthritis and the pain, disability or stiffness are having serious effects on your daily activities.

Even then, your healthcare team will always try other measures before suggesting a knee replacement, including drug treatmentsphysiotherapy and weight loss. If your symptoms are still manageable and your medication is effective then you may prefer to wait.

Your orthopaedic surgeon will be able to advise you on the surgical options and the potential pros and cons of having or delaying surgery, taking into account your age, health and level of activity.

Most people who have a knee replacement are over 60. The earlier you have a knee replacement, the greater the chances that you’ll eventually need further surgery. However, there’s evidence that the surgical outcome may be better if you don’t wait until your knee becomes very stiff or deformed.

Are there any reasons why I can’t have a knee replacement?

Unfortunately, some people may not be able to have a knee replacement even though their arthritis is very bad. This may be because:

  • your thigh muscles (quadriceps) are very weak and may not be able to support your new knee joint
  • there are deep or long-lasting open sores (ulcers) in the skin below your knee, increasing your risk of infection.

What are the different types of knee replacement surgery?

The four main types of knee replacement surgery are:

  1. total knee replacement
  2. unicompartmental (partial) knee replacement
  3. kneecap replacement (patellofemoral arthroplasty)
  4. complex or revision knee replacement.

There are several kinds of replacement knee joint as well as different surgical methods. Your doctor and orthopaedic surgeon should help you to choose the best option for you, taking into account the condition of your knee and your general health.

Read more about the four main types of knee replacement surgery:

Total knee replacement

Most total knee replacement operations involve replacing the joint surface at the end of your thigh bone (femur) and the joint surface at the top of your shin bone (tibia).

A total knee replacement may also involve replacing the under-surface of your kneecap (patella) with a smooth plastic dome. Some surgeons prefer to preserve the natural patella if possible, but sometimes the decision will need to be made during the operation.

If you’ve had a previous operation to remove the patella altogether (patellectomy), this won’t stop you having a knee replacement, but it may affect the type of replacement part (prosthesis) your surgeon uses.

The new parts are normally cemented in place. If cement is not used then the surface of the component facing the bone is textured or coated to encourage bone to grow onto it, forming a natural bond.

Another common technique is to use a mobile plastic bearing which isn’t firmly fixed to the metal parts. This may help to reduce wear on your new joint, though it isn’t hasn't been shown to provide better long-term results.

An illustration of an artificial knee joint in place.

What are the possible advantages of knee replacement surgery?

There are several possible advantages of knee replacement surgery. These include:

  • freedom from pain
  • improved mobility
  • improved quality of life because everyday activities and exercise are easier.

Research has shown that four out of five people who've had knee replacement surgery are happy with their new knees. For those people who aren't happy, the main cause for dissatisfaction is continuing pain which may not be due to a problem with the operation. This is more of a risk if you have relatively minor joint damage (which may still cause severe symptoms) before surgery. If your joint damage isn't very severe it may be better to carry on with non-surgical treatments rather than risk a poor outcome from surgery.

What are the possible disadvantages of knee replacement surgery?

Possible disadvantages of knee replacement surgery can include replacement joints wearing out over time, difficulties with some movements and numbness.

We now know that knee replacements aren't so likely to be effective in the early stages of arthritis. We can be much more confident of a good outcome where the arthritis is more advanced.

The possible disadvantages of knee replacement surgery include:

  • A replacement knee can never be quite as good as a natural knee – most people rate the artificial joint about three-quarters normal.
  • Most knee replacements aren’t designed to bend as far as your natural knee. Although it’s usually possible to kneel, some people find it uncomfortable to put weight on the scar at the front of the knee.
  • You may also be aware of some clicking or clunking in the knee replacement.
  • You may have some numbness at the outer edge of the scar to begin with. This usually improves over about two years but it’s unlikely that the feeling will completely return to normal.
  • A replacement knee joint may wear out after a time or may become loose.

Most knee replacements will last for 20 years or more, so younger patients are more likely to need a repeat knee operation at some point in later life. The chances of needing repeat surgery are increased if:

  • you’re overweight
  • you do heavy manual work.
  • you run or play vigorous sports.

Although your knee can be replaced again if necessary, revision surgery is more complicated and the benefits tend to lessen with each revision.

What are the alternatives to knee replacement surgery?

Most doctors recommend non-surgical (conservative) treatments before considering a knee replacement. These include:

  • Diet
    losing weight will reduce the strain on your knee.
  • Exercise
    Even though this may be difficult because of the pain, there's usually some form of non-impact exercise (for example swimming or cycling) that you can start gently and which will improve the strength and flexibility of your knee.
  • Drugs
    Painkillers can reduce the pain in your joint, while non-steroidal anti-inflammatory drugs (NSAIDs) may help if your knee is swollen.

Generally these don’t provide such good results as a new knee joint but they may allow you to delay having a knee replacement operation for some years.

If you’ve tried these options, you may want to think about the surgical alternatives to knee replacement:

Arthroscopic washout and debridement

Keyhole surgery techniques (arthroscopy) to smooth damaged cartilage and remove debris from the knee joint can only be used in very specific circumstances. If there are mechanical symptoms such as 'locking' of the knee then removing loose fragments of bone and cartilage may avoid having to have a knee replacement at that stage. There's no evidence that it's of benefit for arthritis generally.

How should I prepare for knee replacement surgery?

It's a good idea to make sure your general health is as good as it can be before your operation, for example if you have other health problems such as diabetes or high blood pressure. It’s also advisable to have a dental check-up and get any problems dealt with well before your knee operation. There’s a possible risk of infection if bacteria from dental problems get into the bloodstream.

Your orthopaedic surgeon will probably suggest exercises to strengthen the muscles at the front of your thigh (quadriceps), which often become weak with arthritis. The stronger these muscles are before surgery, the quicker your recovery is likely to be. Exercises that involve raising your foot against gravity are best.

Pre-admission clinic

You'll probably be invited to a pre-admission clinic a few weeks before surgery. You’ll be examined to make sure you’re generally well enough for the anaesthetic and the operation. This may include the following tests:

  • blood tests to check for anaemia and to make sure your kidneys are working properly
  • an MRSA swab to check that you’re not carrying resistant bacteria  
  • a urine sample to rule out infection
  • an electrocardiograph (ECG) tracing to make sure your heart is healthy.

You should also discuss with your surgeon, anaesthetist or nurse whether you should stop taking any of your medications or make any changes to the dosage or timings before you have your surgery. Different units may have different views.

You’ll have the opportunity to ask questions about your operation and discuss anything you’re concerned about. Start planning for your return home and recovery arrangements.

You may also meet a physiotherapist or occupational therapist, who’ll talk about the exercises you’ll need to do after your surgery, your arrangements for going home, and special equipment to help you manage at home. If you’re not invited to see an occupational therapist and you’re worried about coping at home after the operation, you should ask about home help and aids when you go for your pre-admission clinic.

What will my recovery from knee replacement surgery involve?

Most people can leave hospital between one and four days after having knee replacement surgery. You'll need to make arrangements for wound care and you'll usually have follow-up appointments from six weeks after your operation.

After the operation

Before going back to the ward you’ll spend some time in the recovery room, where you may be given fluids and painkillers through a tube in your arm. This may include:

  • patient-controlled analgesia (PCA) – a system where you can control your own supply of painkiller going into a vein by pressing a button
  • painkilling injections or tablets.

Oxygen therapy is likely to be given through a mask or through tubes into your nose. 

There's often no need to have a blood transfusion because your body can replace any blood lost during or after surgery. If the operation is more extensive you may need blood from a donor. An alternative is to recycle the blood which drains from your knee – returning it into your body through a tube in a vein (auto-transfusion).

After the first day or so, the tubes giving you painkillers, fluids or oxygen therapy will be removed. You may have a tube (catheter) inserted for a few days to drain urine from your bladder, especially if both knees have been replaced at the same time.

Pain will usually be worse on the second or third day after surgery when the anaesthetic and strong medication wears off, and you’ll probably need painkillers to control this. Without them it’ll be difficult to do the exercises needed to strengthen your muscles and restore mobility.

How quickly you get back to normal depends on many factors, including:

  • your age
  • your general health
  • the strength of your muscles
  • the condition of your other joints.

Enhanced Recovery Programme

Most people are able to start moving about soon after surgery, which is good for lung function and the circulation.

The hospital team encourage most people to follow the enhanced recovery programme (ERP). This aims to get you walking and moving within 12–18 hours and home within four days. If you're suitable, the ERP will start when you go for your pre-admission clinic to make sure you’re fully prepared for the surgery and understand the programme.

After the operation the programme aims to get you moving and eating normally as soon as possible, and when you’re discharged from hospital you’ll be given supporting therapy and follow-up checks. The programme focuses on making sure that you take an active role in your own recovery process.

Looking after your knee replacement

Your new knee will continue to improve for as much as two years after your operation as the scar tissue heals and you exercise your muscles. You'll need to look after yourself and pay attention to any of the following problems:

Stiffness – Sometimes the knee can become very stiff in the weeks after the operation for no obvious reason. Try placing your foot on the first or second step of the stairs, hold on to the banister and lean into your knee. This should help to improve movement and flexibility in your knee. It’s very important to continue with the exercises you were working on in the hospital.If the stiffness doesn’t improve after about six weeks your surgeon may need to move or manipulate your knee. This will be done under anaesthetic.

Pain – Pain caused by bruising from the operation is normal in the first two months, and you'll probably still need to take painkillers at six weeks to help you sleep through the night. You may still have some pain for as long as six months. If you still have pain after this, speak to your physiotherapist or GP.

Swelling – Swelling is a very common problem after a knee replacement, particularly affecting the ankle and foot, and may last for up to three months or so after the operation. The ankle swelling usually settles as your walking ability improves. Swelling of the knee itself is also common over the first few months after surgery. Applying ice can be very helpful for a swollen joint, but make sure you protect your skin from direct contact with the ice pack. Ice can be applied for up to 20 minutes at a time. Raising your foot above hip height (on a footstool or similar) is another good way of reducing swelling, but make sure you get up and walk around for at least five minutes every hour to help reduce the risk of a blood clot.

Infection – You should speak to your GP or hospital if you notice any signs of infection, for example:

  • breakdown of the wound with oozing/pus or sores
  • increased pain
  • redness and the affected area feeling warmer than usual or smelling unpleasant.

You should also look after your feet – see a doctor or podiatrist if you notice any problems such as ingrown toenails that could become infected.

Getting back to normal

It will be some weeks before you recover from your operation and start to feel the benefits of your new knee joint. Make sure you have no major commitments – including long-haul air travel – for the first six weeks after the operation.

Keeping up your exercises will make a big difference to your recovery time. You’ll probably need painkillers as the exercise can be painful at first. Gradually you’ll be able to build up the exercises to strengthen your muscles so that you can move more easily.

Walking

It's important to use crutches or walking sticks at first because the thigh muscles (quadriceps) will be weak after the operation, and falling could damage your new joint. Don't twist your knee as you turn around. Take several small steps instead. 

After two weeks, or sooner if you’re confident, you can go down to one crutch and then a walking stick. After about six weeks, if your muscles feel strong and supportive, you can try walking without aids. This process may take less time if you’ve had a partial knee replacement or longer if you’ve had a more complex operation.

You should be able to walk outside within three weeks of having surgery but make sure you wear good supportive outdoor shoes. After three weeks, try to take longer strides so you can fully straighten (extend) your leg.

What about exercise following a knee replacement?

Exercise and sport are recommended after knee replacement, apart from contact sports, which may weaken the cement and lead to loosening of the joint components. Recreational sports – including golf, tennis and skiing – will gradually become possible depending on how fit and sporty you were before the operation. Cycling is a very good way of building up strength and mobility after knee surgery.

Exercising the main muscle groups around your knee is very important both before and after having a knee replacement. You can download a selection of exercises that are designed to stretch, strengthen and stabilise the structures that support your knee. Try to perform these exercises regularly, for instance for 10 minutes six to eight times a day. However, it’s important to find a balance between rest and exercise so you don’t overwork your knee. It’s a good idea to get advice from your doctor or physiotherapist about specific exercises before you begin.

What are the possible complications of a knee replacement?

Most knee joint operations are problem-free but about 1 person in every 20 may have complications. Most of these complications are minor and can be successfully treated.
The risk of complications developing will depend on a number of factors including your age and general health. In general, a younger patient with no other medical problems will be at a lower risk of complications.

It's important to remember that any drugs used throughout your stay in hospital, for example anaesthetic or painkillers, may also have side-effects. Your surgeon or anaesthetist will be able to discuss these with you.

Blood clots

Blood clots which form in the deep veins in the leg (deep vein thrombosis, or DVT) can cause pain and/or swelling. This is because of changes in the way blood flows and its ability to clot after surgery. There are various ways to reduce the risk of this happening, including special stockings, pumps to exercise the feet and drugs that are given by injection such as heparin.

Blood-thinning drugs can increase the risk of bleeding, bruising or infection so your surgeon will need to balance these risks. Rivaroxaban, dabigatran and apixaban are tablets to help prevent DVT which have recently become available as an alternative to injections. The tablets are more convenient than injections, which makes them easier to take at home. However, they still carry a risk of bleeding.

How long will the new knee joint last?

For 80–90% of people who have total knee replacement, the new joint should last about 20 years, and it may well last longer.

If you've had a partial knee replacement, you're more likely to need a repeat operation – about 1 person in 10 needs further surgery after 10 years.

The chances of needing another operation is greater if you're overweight and/or involved in heavy manual work.

Revision surgery

Some people need a repeat knee replacement operation on he same knee. This is called a revision. The repeat operation is more difficult than the first, but the techniques are becoming more routine and more successful all the time. If you’re having a second or third operation on the same leg, your surgeon may suggest using the more complex knee replacement components rather than the standard type.

Research and new developments for knee replacement surgery

Helping patients to make informed decisions 

We're funding research to improve patient experience before, during and after knee replacement surgery. This includes a project based at the University of Sheffield which aims to help patients make informed decisions about their surgery. The research team will use the UK National Joint Registry dataset to develop and validate a personalised, web-based decision aid to help patients considering knee joint replacement to make informed choices about their treatment.

Understanding why some joint replacements fail

We're also supporting research to improve the outcome of knee replacement surgeries, such as a project aimed at increasing the understanding of why joint replacements sometimes fail by investigating whether there are genetic risk factors that influence surgery outcome. This research has the potential to improve patient experience and increase the life of the joint replacement.

TRIO study

Our TRIO study is investigating the effect of targeting specific physiotherapy at patients who are functioning poorly after knee replacement surgery. The aim of this study is to find out whether this early treatment improves pain, satisfaction and function after a year. If successful, it could benefit more than 15,000 patients per year in the UK alone, who are not satisfied with their knee replacement one year after the operation.

Providing better after care for patients

We're funding research which aims to provide a standardised approach and assessment for virtual clinic follow-up of total joint replacement patients and subsequent management of patients identified as 'at risk' by this approach. This study would enable us to deliver better and more streamlined after care for patients.

Looking for alternatives to total knee replacements

We're also funding research which is investigating alternative approaches to total knee replacement. For example, total knee replacement is not recommended for many young people. This study aims to develop a new method called ToKa®, which uses images of the patient's joint and specially designed software to design a patient specific implant that will be made via 3D printing. If successful, this technique could prevent osteoarthritis patients from needing total joint replacement.