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 are covered by smooth cartilage. If your cartilage is damaged by injury or worn away by arthritis, it can make your joint painful and stiff.
A new knee joint will usually reduce your pain, improve your mobility and help you become more active. However, your new knee won’t be able to bend quite as far as a normal knee joint.
Artificial knee parts are almost always made of metal and plastic. A knee replacement can last for up to 20 years. See our FAQs for more information.
Knee replacement surgery is also known as knee arthroplasty.
There are two main types of knee replacement surgery.
- Total knee replacement, also known as TKR, is the most common type of surgery. 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 under surface of your kneecap (patella) with a plastic button. However, this is often not needed.
- Partial knee replacement, also known as unicompartmental knee replacement. In this procedure, your surgeon will replace the ends of the bones on one side of your knee only. They may recommend this if the damage to your knee is only on one side (usually the inside of the knee). It may be possible for your surgeon to do a partial knee replacement through a smaller cut than is needed for a total knee replacement.
If you have a total knee replacement, you’re probably less likely to need a further knee operation than if you have a partial knee replacement. However, you’re more likely to have medical complications after a total knee replacement. Your surgeon will discuss with you which type of surgery is best in your circumstances. This will depend on a number of factors including the condition of your knee and your general health.
Before you go into hospital, think about how you’ll cope when you get home. You may need to arrange for family or friends to be with you for a while to help with everyday tasks like cooking, shopping and cleaning. If you can, it’s a good idea to stock the freezer with some pre-prepared meals. Have a look around your home. Make sure there’s nothing you might trip over while you’re less mobile. And think about where you’re going to sit. Arrange important items such as the telephone, your medicines and the TV remote control so that they are easily to hand.
You’ll probably be invited to a pre-admission assessment clinic at the hospital a week or two before the date of your operation. A nurse will check to see if you’re fit for your operation and arrange any tests that you might need. These might include blood tests to check for anaemia and to make sure your kidneys are working properly. They may also arrange an ECG (electrocardiogram) to check your heart.
If you smoke, it’s strongly recommended that you stop, as smoking increases your risk of getting a chest and wound infection, which can slow your recovery.
The operation usually requires a hospital stay of about two to five days.
If you’re having a general anaesthetic, you’ll be asked to follow fasting instructions. This means not eating or drinking, typically for about six hours beforehand. However, it’s important to follow your anaesthetist’s advice. See our section ‘What happens during a knee replacement’ for further information on anaesthesia.
Your surgeon will discuss with you what will happen before, during and after your procedure, and any pain you might have. This is your opportunity to ask questions so that you understand what will be happening. You don’t have to go ahead with the procedure if you decide you don’t want it. Once you understand the procedure and if you agree to have it, your doctor will ask you to sign a consent form.
You may be asked to wear a compression stocking on your unaffected leg to help prevent blood clots forming in the veins in your legs. This is called a deep vein thrombosis, or DVT. You may need to have an injection of an anticlotting medicine called heparin as well as, or instead of, wearing compression stockings.
Your surgeon will usually only recommend that you have surgery if non-surgical treatments no longer help to reduce your pain or improve your mobility. Non-surgical treatments might include physiotherapy and exercise, medicines or using physical aids like 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 is not a cure for arthritis.
Alternative surgical procedures include the following.
- Arthroscopy (if the arthritis isn’t too severe) – this is keyhole surgery where your surgeon clears out bits of debris inside your knee.
- Microfracture – using keyhole surgery, your surgeon makes 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 are younger, to allow your surgeon to delay your knee replacement surgery.
You may have already had these procedures before your knee replacement. Your surgeon will explain your options to you.
A knee replacement usually takes one to two hours.
Most people have knee replacement surgery under local anaesthesia. This means an anaesthetic is injected into your spine or the fluid around your spine. This completely blocks feeling from your waist down and you’ll stay awake during the operation. The procedure can also be done under general anaesthesia. This means you’ll be asleep during the operation.
Your surgeon will make a cut down the front of your knee. They’ll then remove 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 part. This is called patellar resurfacing.
After your surgeon has fitted the new joint, they will close your wound with stitches or clips and cover it with a dressing. Your surgeon will tightly bandage your knee to help minimise swelling.
You’ll need to rest until the effects of the anaesthetic have passed. You may not be able to feel or move your legs for several hours after a spinal or epidural anaesthetic.
Your nurse will give you painkillers to help with any discomfort as the anaesthetic wears off. Always let your nurse know if you’re in pain at any time while you’re in hospital.
You’ll have a large dressing on your knee to protect your wound. There may be one or more tubes coming out from your wound through your dressing. These help to drain any fluid that collects around your wound. The tubes will usually be removed after a couple of days.
You’ll probably be moving your knee again from the day after surgery. Starting to move your knee within 24 hours after surgery may help you become mobile more quickly and may even help you get home sooner. A physiotherapist (a specialist in movement and mobility) will guide you daily through exercises to help your recovery.
You may also use a continuous passive motion exercise machine that will slowly bend and straighten your knee while you’re in bed. The aim is to restore movement and reduce swelling in your knee.
You’ll stay in hospital until you can walk safely with the aid of sticks, crutches or a walking frame. Your surgeon will also want to be sure that your wound is healing well. When you’re ready to go home, you’ll need to arrange for someone to drive you.
Your nurse will give you some advice about caring for your knee and a date for a follow-up appointment before you go home.
The stitches or staples that close your wound will need to be removed after about 10 to 12 days, unless you have dissolvable stitches. Before you go home, your nurse will explain the arrangements for having your stitches or staples removed.
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.
It usually takes around six to 12 weeks to make a full recovery from knee replacement surgery. However, this varies between individuals, so it's important to follow your surgeon's advice. Your knee will continue to improve for two years after your operation as scar tissue heals and your muscles get stronger through exercise.
You may find that you need some kind of pain relief for up to 12 weeks after your operation. Some people have discomfort for up to six months. If you feel that you need pain relief, you should speak to your GP about this.
You may be asked to wear compression stockings for several weeks at home.
You may have swelling which can last for three to six months. Keeping your foot raised, for example on a footstool, can help. But remember to get up and have a walk around for five minutes every hour to reduce the chance of a blood clot. You can also try applying ice, but don’t allow the ice to come into contact with your skin.
Build up your daily activities gradually. You should be able to move around your home and manage stairs carefully. However, some routine daily activities, such as shopping, may be difficult for a few weeks. You may need to use a walking stick or crutches for up to six weeks.
Physiotherapy exercises are a crucial part of your recovery, so it's essential that you continue to do them for at least two months. After three months, you can try kneeling using a soft cushion. Kneeling isn’t harmful. However, some people find that kneeling never becomes comfortable after knee replacement surgery.
If you work, you should be able to return after about eight weeks but this will depend on the type of work you do. If you have a physically demanding job, it may take up to 12 weeks before you’re ready. It may help to have a phased return, where you gradually build up to your usual work activities. Ask your surgeon what they would recommend in your circumstances.
Most people can drive after about six weeks following a total knee replacement, and about three weeks after a partial knee replacement. However, you have to be sure that you can control your vehicle and make an emergency stop. Follow your surgeon's advice, and check with your motor insurer to see what your policy allows.
As with every procedure, there are some risks associated with knee replacement surgery. Side-effects are the unwanted but mostly temporary effects you may get after having the procedure.
- Pain – you’ll probably have some pain or discomfort in your knee after your surgery. It’s quite normal in the first two months. Pain can last for around 12 weeks, or in some cases up to six months. If you’re finding it hard to control with painkillers or if it gets worse, see your GP.
- Swelling – it’s normal to get mild to moderate swelling of your leg for the first three to six months after surgery. This can particularly affect your ankle and foot. If you notice new swelling, or swelling that is severe, tell your GP because this might mean that you’re developing a blood clot.
- Scarring – you’ll have a vertical scar over the front of your knee, probably about 10–18 cm (4–7 inches) long. You may not have any feeling in the skin around your scar for a while. This can be permanent, but should improve over two years.
Most people also feel or hear some clicking of the new implants in their knees when bending or walking. This is quite normal and you’ll probably get used to it over time.
Complications are when problems occur during or after the operation. We haven’t included the chance of these happening as they are specific to you and differ for every person. However, most people do not get serious complications following knee replacement surgery.
Complications of knee replacement may include the following.
- Blood clots – blood clots in the veins in the legs (deep vein thrombosis, DVT) can happen after knee replacement surgery. These clots can break off and go to your lung (pulmonary embolism) which can be very serious. Blood clots may be prevented by wearing compression stockings, staying active and taking blood thinning medicines.
- Infection of the wound or joint – your surgeon will give you antibiotics during and after surgery to help prevent this. Very occasionally, you may need further surgery to clear up an infection.
- An unstable joint – your knee joint may become loose, or your kneecap may become dislocated and you may require further surgery to correct this.
- Damage to nerves or blood vessels – this usually gets better on its own, but occasionally you may need surgery, especially if blood vessels are involved.
- Stiffening due to scar tissue – stiffness may continue or increase 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 further surgery.
If you want to know more about the complications of knee replacement surgery, and how they may apply to you, ask your surgeon.
Almost all knee replacements last at least 10 to 15 years, and many as long as 20 years. You’re more likely to need a repeat knee replacement in the future if you’re overweight or do heavy manual work.
Replacement joints are designed to last for a long time. The modern materials that are used are strong enough to stand up to the requirements of young and active people.
Currently, about eight or nine out of 10 artificial joints used for knee replacement last for 20 years or more. Total knee replacements tend to last a little longer than partial knee replacements. There is active research into improving the design and material of replacement knee joints to make them last longer.
It’s important to have regular X-rays on your knee to check how your knee replacement is faring. Your surgeon will let you know how often this should be – perhaps every five years. If your replacement joint is loosening or breaking, you may need another operation to correct this. This is called a revision operation.
FAQ: Sport and knee replacement Are there any sports or activities I shouldn't take part in after my knee replacement?
It’s good to be active after your knee replacement, but build up activities gradually. Once you’re fully recovered, you can exercise and participate in sport. However, this advice excludes high-impact exercises, such as running, jumping and heavy lifting. You should be able to do a short, light jog – for example to run for a bus. Ask your surgeon about sporting activities you want to do, and how these might affect your knee. Always follow your surgeon’s advice.
During your recovery, your physiotherapist will recommend exercises for you that will improve your strength and range of motion. It’s important to do these for at least two months after your operation.
As you recover, you can start swimming and do more walking to strengthen your muscles around the joint. You may find that using a stationary cycle helps to maintain your muscle tone and improve flexibility in your knee.
When you have made a full recovery, you can have a more active lifestyle. Ask your surgeon about which sports and activities are suitable for you. They’ll probably advise against high-impact activities or contact sports which can weaken your new knee joint. So don’t do sports such as football, rugby, basketball, squash, skiing or anything that involves squats, jumping or weightlifting. But you can do low-impact sports such as golf, bowls or gentle doubles tennis or dancing.
Regular exercise will help to improve and maintain your mobility. When returning to any sport, it's important to take your time to rebuild your strength and co-ordination. You may find that you can't return to your chosen sport at the same level that you were at before.
Your doctor, surgeon or physiotherapist will be able to give you more information about what activities are suitable, and which you should avoid.
Try to be as fit and healthy as possible before your operation and prepare your home for when you return.
If you’re having a knee replacement, it's a good idea to try to be as fit and healthy as possible before your operation. This will help to speed up your recovery.
If you smoke, you should try to stop because smoking can increase your chances of getting a wound infection and slows your recovery. If you’re overweight, your doctor may recommend a weight-loss programme to reduce the strain on your new joint.
Think about preparing your body with some exercises. You can exercise to strengthen your upper body. This will help you to get around after the surgery when using walking aids such as crutches. If possible, try to strengthen your leg muscles. Strengthening the muscles around your knee will speed your recovery and will make it easier to perform the postoperative exercises. Your surgeon or physiotherapist will be able to recommend exercises for you.
It's a good idea to prepare your home for when you return from hospital. This may mean rearranging furniture to make it easier to move around. Also, place commonly used items at arm level so you don't have to reach for them. It's also a good idea to stock up on non-perishable food such as frozen or tinned items, and toiletries. This means you don't need to go shopping immediately after your surgery.
You may need someone to help during the first few weeks after surgery. It's a good idea to arrange to have a friend or family member stay with you for a couple of days after the operation.
It’s best not to fly long haul for at least 12 weeks after knee replacement surgery. This is to reduce your chance of getting a blood clot in your leg veins (deep vein thrombosis, DVT). You should also be aware that your artificial knee joint might set off airport security scanners.
If you’ve had knee replacement surgery, you have a risk of getting a blood clot in your legs. This can become serious if the blood clot breaks off and reaches your lungs (pulmonary embolism). If you sit in one position for a long time, for instance on a long flight, this increases your chance of getting a blood clot. Pressure changes in the air cabin and immobility may cause your knee to swell, especially if it’s still healing. For these reasons, your surgeon will probably recommend that you do not fly for about 12 weeks after your surgery. It may be helpful to wear compression stockings during your flight.
Talk to your surgeon if you’re planning air travel. They’ll be able to discuss what’s best in your particular circumstances. Always follow your surgeon’s advice.
When you’re going through airport security, be aware that your knee implants may affect the scanners. If the alarm goes off, the security officer will usually do a pat-down search. Tell the security officer about your knee replacement before entering the scanner. It may help to carry a letter from your doctor or a medical alert card confirming that you have an artificial joint.
There are many different designs of knee implant but the most common are made of metal (titanium or cobalt/chromium-based alloys) and plastic (ultra high-density polyethylene). Designs of knee implant differ in which parts are connected together, and how the implant is held in place within your bone. Ask your surgeon to explain which type of implant would be best for you.
When you have knee replacement surgery, your surgeon will replace the lower end of your thigh bone (femur) and the upper end of your shin bone (tibia) with artificial parts. Sometimes they will also replace the under surface of your kneecap (patella). Together, the artificial parts are called a knee implant.
There are over 150 designs of knee implant on the market – most are made of a combination of metal and plastic. Metal components replace the lower end of your thigh bone and the upper end of your tibia. The metal is typically either titanium or a cobalt/chromium-based alloy. Between the metal components lies a plastic tray, or cushion, made of ultra high-density polyethylene. Some designs of implants don’t have a metal component at the top of your tibia. With these, your surgeon attaches a plastic part directly to the bone. If your surgeon replaces the under surface of your patella, they will use another plastic component there.
Sometimes the plastic cushion is attached firmly to the metal part underneath – this is called a fixed bearing implant. The metal part at the end of your femur then rolls on this fixed cushion as you move. An alternative design is a mobile bearing implant where the plastic cushion can rotate a little against the metal part lying under it. This allows you a small amount of rotation in your new knee joint.
Your surgeon will usually fix your knee implant in place using a fast-setting bone cement (polymethylmethacrylate). However, some implants have special textured surfaces which allow new bone to grow into them to hold them in place without the need for cement. These are called cementless implants.
A complete artificial knee weighs about 500–600 grams (18–21 ounces).
The type of knee implant you have will depend on many factors including your age, your weight, your level of activity and your health. Ask your surgeon to explain your options and discuss with you what is best in your circumstances.
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Reviewed by Dylan Merkett, Health Information Team, March 2016
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