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Knee replacement


Expert reviewer, Mr Damian McClelland, Trauma and Orthopaedic Consultant, and Clinical Director for Musculoskeletal Services at Bupa
Next review June 2023

Knee replacement surgery is an operation to remove damaged parts of your knee joint and replace them with artificial ones. You may need to have a knee replacement if your knee is painful and has been damaged or worn away. This is usually because of osteoarthritis.

About knee replacement

Your knee joint is made up of the lower end of your thigh bone (femur) and the upper end of your shin bone (tibia). These normally glide over each other easily because they’re covered by smooth cartilage. But if your cartilage is damaged by an injury or worn away by arthritis, this can make your joint painful and stiff.

Artificial knee parts are usually made from metal and plastic, and sometimes ceramic. A new knee joint should ease your pain and help you move around more easily, so you can be more active. But it won’t be able to bend as much as a normal knee joint.

A knee replacement can last for up to 20 years. Around 100,000 people have a knee replacement operation, which is also known as knee arthroplasty, each year in the UK. Most people who have knee replacement surgery are in their 70s.

An image showing the different parts of the knee

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About knee replacement

Your knee joint is made up of the lower end of your thigh bone (femur) and the upper end of your shin bone (tibia). These normally glide over each other easily because they’re covered by smooth cartilage. But if your cartilage is damaged by an injury or worn away by arthritis, this can make your joint painful and stiff.

Artificial knee parts are usually made from metal and plastic, and sometimes ceramic. A new knee joint should ease your pain and help you move around more easily, so you can be more active. But it won’t be able to bend as much as a normal knee joint.

A knee replacement can last for up to 20 years. Around 100,000 people have a knee replacement operation, which is also known as knee arthroplasty, each year in the UK. Most people who have knee replacement surgery are in their 70s.

An image showing the different parts of the knee

Types of knee replacement surgery

There are two main types of knee replacement surgery.

  • Total knee replacement (TKR) is the most common. Your surgeon will replace the lower end of your thigh bone and the upper end of your shin bone with artificial parts. They may also replace the surface under your kneecap (patella) with a plastic button if this is damaged too.
  • Partial knee replacement is called unicompartmental knee replacement (UKR). Your surgeon will replace the ends of the bones on one side of your knee only, usually the inside of your knee. They may make a smaller cut than with a TKR.

Your surgeon will discuss which type of surgery is right for you. It will depend on a number of things, such as the condition of your knee, your age and your general health.

Preparation for a knee replacement

Home preparations

Before you have a knee replacement, make some preparations in advance for when you get home. For example, arrange for family or friends to help with things like cooking and shopping. And stock your freezer with some cooked meals. Make sure there’s nothing you could trip over while you’re less able to move around. Move things you’ll need to hand, such as your medicines and TV remote control, so you can reach these easily.

Pre-admission assessment

Your hospital may invite you to a pre-admission assessment clinic a few weeks before your operation to check you’re fit for surgery. Let the team know if you’re taking any medicines. If you smoke, it’s best to stop as this will help you recover quicker. If you haven’t managed to give up, don’t smoke – or vape – on the day of your operation. You may also need to lose some weight before your surgery if you’re overweight.

Advice for a general anaesthetic

If you’re having a general anaesthetic, it can make you sick, so it's important that you don't eat or drink anything before your procedure. Your hospital will advise you when you need to stop. Follow your anaesthetist/doctor's advice. If you have any questions, just ask.

Compression stockings

You may need to wear compression stockings to help prevent blood clots forming in the veins in your legs (deep vein thrombosis). You may also need to have an injection of an anti-clotting medicine as well as wearing compression stockings.

Your surgeon will tell you what will happen before, during and after your surgery. If you’re unsure about anything, don’t be afraid to ask. No question is too small. It’s important that you feel fully informed so you feel happy to give your consent for the operation to go ahead. Your surgical team will ask you to sign a consent form.

Knee replacement surgery

A knee replacement usually takes up to two hours.

Most people have knee replacement surgery under spinal anaesthesia. Your surgeon will inject the anaesthetic into your back (between the bones of your spine). This will completely block any feeling from your waist down and you’ll stay awake during the operation. Another option is general anaesthesia, which means you’ll be asleep during the operation.

After your anaesthetic takes effect, your surgeon will make a cut down the front of your knee. They’ll then trim the worn or damaged surfaces from the end of your thigh bone and the top of your shin bone. They’ll shape the surfaces of your thigh and shin bones to fit the artificial knee joint and then fit the new joint over both bones.

Your surgeon may also replace the back of your kneecap with a plastic button-shaped part. This is called patella resurfacing.

After your surgeon has fitted the new joint, they’ll close your wound with stitches and cover it with a dressing. Your surgeon will bandage your knee to protect it.

Aftercare for knee replacement surgery

You’ll need to rest until the effects of the anaesthetic have worn off. You might not be able to feel or move your legs for up to four hours after a spinal anaesthetic.

Your nurse will give you painkillers to help with any discomfort as the anaesthetic wears off.

You’ll have a large dressing on your knee to protect your wound, and there may be one or more tubes coming out of it. These will help to drain any fluid that builds up around your wound. One of your hospital team will usually take the tubes out after a day or two.

You’ll probably be able to move your knee again a day after your surgery. If you start to move your knee within 24 hours, it may help you recover more quickly and get home sooner. A physiotherapist will give you some exercises to do. You may also use a continuous passive motion exercise machine. This will slowly bend and straighten your knee while you’re in bed to get your knee moving again and reduce any swelling.

You’ll stay in hospital for three to five days after your surgery. Your nurses will encourage you to walk as soon as possible, with the help of crutches or a walking frame.

Your nurse will give you advice about caring for your knee and a follow-up appointment date before you go home. And your physiotherapist or an occupational therapist will give you tips on how to carry out daily activities, such as using the stairs or washing yourself. When you’re ready to go home, ask family or a friend to drive you.

You’ll need to have your stitches or staples out about 10 to 12 days after your operation, unless you have dissolvable stitches. A nurse at your local GP surgery can do this for you.

Recovering from knee replacement surgery

It usually takes around six to 12 weeks to recover from knee replacement surgery but follow your surgeon's advice. Your new knee will keep getting better and stronger for up to two years afterwards. This is because it takes time for the scar tissue to heal and for your muscles to get stronger through exercise.

You may need to wear compression stockings for several weeks at home or until you’re able to walk around regularly again.

Try to build up your daily activities gradually. You should be able to move around your home but you may find some things difficult for a few weeks, such as vacuuming. You may need to use a walking stick or crutches for up to six weeks. By six to eight weeks, you may be able to go for a walk, cycle and swim, but check with your physiotherapist first.

You can drive when you can safely control your car. This is usually between six and eight weeks after total knee replacement surgery, or around three weeks after a partial knee replacement. But follow your surgeon's advice. Check your motor insurance too, to see what your policy allows. Before you drive again, you need to stop taking any painkillers that can cause drowsiness.

If you work, you should be able to go back after about six weeks, but this will depend on the type of work you do. If you have a physically demanding job, it may be up to 12 weeks before you’re ready. Ask your surgeon what they recommend.

You may notice that your knee, ankle and/or foot is swollen after surgery. This can last for three months or more but should gradually get better over time as the healing continues. To help to reduce the swelling, keep your foot raised. But remember to get up and have a walk around for five minutes every hour to prevent blood clots. You can also put an ice pack on your knee, but wrap it on a towel so it doesn’t harm your skin.

You may need some kind of pain relief for up to 12 weeks after your operation. Speak to your GP if you need support.

Physiotherapy is an essential part of your recovery. If you don’t exercise your knee gently and regularly, it may feel stiff. Keep doing the exercises your physiotherapist has recommended. After around six weeks, you may be able to walk without crutches or a frame.

During the first six weeks, it’s best to not sit with your legs crossed. After three months, you can try kneeling, but put a soft cushion down first. Kneeling shouldn’t damage your knee but you need to wait until the scar tissue has healed. But it may never be entirely comfortable.

Don’t worry if you feel tired and a bit emotional for a while after your surgery – this is normal. You’ve had a major operation and your body needs time to heal and recover.

Side-effects of knee replacement surgery

After knee replacement surgery, you may have some temporary side-effects.

  • Pain – you’ll probably have some pain or discomfort in your knee. The pain may last for around 12 weeks, but can sometimes last longer. If you find it hard to ease your pain with painkillers or if it gets worse, see your GP.
  • Swelling – it’s normal to get some swelling of your leg, ankle and foot for the first three months or so after surgery. But if the swelling gets worse or your calf becomes painful it can be a sign of a blood clot and you’ll need urgent medical help.
  • Scarring – you’ll have a scar down the front of your knee, about 10 to 18 cm (4 to 7 inches) long. You may not have any feeling in the skin around your scar for a while. This should get better over two years but it might not ever feel completely normal.
  • Weakness – your leg may feel weak at first. But it will get stronger as you start exercising your muscles.

You may feel or hear some clicking in your new implant in your knee when you bend your knee or walk. This is normal and you’ll probably get used to it over time.

Complications of knee replacement surgery

Most people don’t get serious complications after knee replacement surgery. But complications may include the following.

  • Blood clots – you could get a blood clot in the veins in your legs (deep vein thrombosis, DVT). You can help to prevent them by wearing compression stockings, staying active and taking blood thinning medicines.
  • Infection of your wound or joint – your surgeon will give you antibiotics during and after surgery to help prevent this.
  • An unstable joint – your knee joint may become loose or your kneecap may become dislocated. You need to have surgery to fix this.
  • Damage to nerves or blood vessels – this isn’t usually serious and is treated during the operation, especially if blood vessels are involved.
  • Stiffening due to scar tissue – the stiffness may carry on or get worse after surgery, as scar tissue builds up and restricts your movement. This can usually be treated with physiotherapy but it’s possible you may need more surgery.

Alternatives to knee replacement

Your surgeon will usually only recommend you have a knee replacement if other treatments are no longer helping to ease your symptoms. This includes things like physiotherapy and exercise, medicines or using physical aids, such as a walking stick. If you’re overweight, your doctor will encourage you to lose weight as this will reduce the strain on your knee. Corticosteroid injections can ease your symptoms for a few months, but this isn’t a cure for arthritis.

Alternative operations include the following.

  • Arthroscopy (if your arthritis isn’t too bad and your knee keeps locking into place) – this is keyhole surgery where your surgeon clears out bits of debris or trims torn cartilage inside your knee.
  • Microfracture – using keyhole surgery, your surgeon will make small holes in the surface layer of your bone to encourage new cartilage to grow.
  • Osteotomy (where your leg bones are cut and re-set) – this is sometimes used if you’re younger, to delay your knee replacement surgery.

Your surgeon will explain your options to you.

Frequently asked questions



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Related information


  • Discover other helpful health information websites.

    • Preparing for a knee replacement operation. Royal College of Anaesthetists. www.rcoa.ac.uk, published 2018
    • Total knee arthroplasty (TKA). Medscape. emedicine.medscape.com, updated 13 May 2020
    • Joint replacement (primary): hip, knee and shoulder. National Institute for Health and Care Excellence (NICE). www.nice.org.uk, published 4 June 2020
    • Knee joint anatomy. Medscape. emedicine.medscape.com, updated 2017
    • Osteoarthritis. BMJ Best Practice. bestpractice.bmj.com, last reviewed 25 April 2021
    • Knee replacement surgery. Versus Arthritis. www.versusarthritis.org, accessed 25 May 2021
    • Types of primary knee replacements undertaken. National Joint Registry. njrcentre.org.uk, accessed 25 May 2021
    • Age of patients undergoing primary knee replacement. National Joint Registry. njrcentre.org.uk, accessed 25 May 2021
    • Unicompartmental knee arthroplasty. Medscape. emedicine.medscape.com, updated 29 June 2020
    • Anaesthetic choices for hip or knee replacement. Royal College of Anaesthetists. www.rcoa.ac.uk, published February 2020
    • Knee surgery – total knee replacement. Royal College of Surgeons of England. www.rcseng.ac.uk, accessed 25 May 2021
    • Your spinal anaesthetic. Royal College of Anaesthetists. rcoa.ac.uk, published February 2020
    • Personal communication, Mr Damian McClelland, Trauma and Orthopaedic Consultant and Clinical Director for Musculoskeletal Services at Bupa, 2 June 2021
    • Osteoarthritis: Scenario: Management. NICE Clinical Knowledge Summaries. cks.nice.org.uk, last revised June 2018
    • Knee replacement implants. American Academy of Orthopaedic Surgeons. orthoinfo.aaos.org, last reviewed April 2016
  • Reviewed by Rachael Mayfield-Blake, Freelance Editor, June 2021
    Expert Reviewer, Mr Damian McClelland, Trauma and Orthopaedic Consultant, and Clinical Director for Musculoskeletal Services at Bupa
    Next review due June 2023

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