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Knee surgeryFrom Arthritis Research UK

Over 70,000 knee replacement operations are carried out each year, and the number is increasing.

Knee replacements are most commonly recommended for osteoarthritis, but sometimes for rheumatoid arthritis or other inflammatory joint disease.

Most people who have a knee replacement are over 65, and slightly over half the patients who have knee replacement surgery are women.

When is knee replacement surgery recommended?

Knee replacement surgery is normally only considered if you have severe pain and serious mobility difficulties and if your arthritis isn’t responding to other measures including drug treatments, physiotherapy and weight loss.

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

The earlier you have a knee replacement the greater the chances that you will eventually need further surgery. However, there’s some evidence that not waiting until the knee becomes very stiff leads to a better surgical outcome.

Some people may not be able to have a knee replacement even though their arthritis is very bad:

  • If the thigh muscles (quadriceps) are very weak they may not be able to support the new knee joint.
  • If there are deep or long-lasting open sores (ulcers) in the skin below the knee the risk of infection may be too great to consider surgery.

If you need a hip replacement as well as a knee replacement it’s best to have the hip surgery first, as you’ll need a flexible hip to exercise your new knee.

What are the benefits and disadvantages of knee replacement surgery?

Freedom from pain is the main benefit of a knee replacement and you should find you are more mobile too. However, a replacement knee can never be quite as good as a natural knee joint.

Although some people are disappointed with the outcome of their surgery, or are unsure whether there has been an improvement, about 9 out of 10 people who’ve had the operation say they are happy with their new knees.

Everyday activities should become much easier, and exercise such as swimming, cycling, tennis or golf should also be possible. However, you are still likely to have some difficulties with movement, as most knee replacements are not designed to bend completely. You may also be aware of some clicking or ‘clunking’ in the knee replacement. However, most people rate the artificial joint about ‘three-quarters normal’.

Although it’s usually possible to kneel, some people find it uncomfortable to put weight on the scar at the front of the knee. Initially there will be some numbness on the outer edge of the scar. It’s unlikely that the feeling will return completely to normal but it usually improves over about two years.

A replacement knee joint will wear out after a time and may become loose. For most people an artificial knee will last for over 20 years, so younger patients are likely to need a repeat knee operation at some point in later life. The likelihood of needing another operation is increased if you are overweight or involved in heavy manual work. Running or playing vigorous sport can also increase the risk of wear and loosening of the knee replacement.

Although artificial joints can be replaced again if necessary, ‘revision’ surgery is more complex and the benefits tend to diminish with each revision.

What is knee replacement surgery and how does it work?

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

In a knee replacement operation, the surgeon removes the worn ends of the bones and any remaining hard cartilage and replaces them with metal and plastic parts. The plastic acts like hard cartilage, helping the joint to move freely.

There are several kinds of artificial knee joint as well as differing surgical techniques.

Total knee replacement

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

Most surgeons prefer to leave the surface of the kneecap (patella) in its natural state because the natural patella is stronger than a resurfaced one and less likely to fracture. The pain should be less because the worn kneecap will be moving against a smooth metal surface. However, where the kneecap itself is causing a lot of pain it may be necessary to replace this surface too. This involves removing the rough underside of the kneecap and replacing it with a smooth plastic dome. Where a patient has already had the kneecap removed (patellectomy) the scar tissue, where the original patella lay, is carefully preserved.

The new parts are normally cemented in place. There is a trend, however, towards using uncemented joints. The components are textured to encourage new bone to grow onto the component, forming a strong natural bond.

Another increasingly common technique is to use a mobile plastic bearing, which isn’t firmly fixed to the metal parts. This should help to reduce wear on the new joint, though it isn’t yet clear whether it provides better long-term results.


Unicompartmental (partial) knee replacement

If arthritis affects only one side of your knee – usually the inner side – it may be possible to have a half-knee replacement (sometimes called ‘unicompartmental’ or partial replacement). This is only suitable for about 1 in 4 people with osteoarthritis, but is a less extensive operation and should therefore mean a quicker recovery.

Partial knee replacements can often be carried out through a smaller incision than a total knee replacement. Pain relief is just as good but with less bruising and scarring than results from a full knee replacement. The range of flexion is often as good as before the operation.

Partial knee replacement isn’t suitable for everyone because it depends on having strong, healthy ligaments within the knee. Sometimes this won’t be known until the time of surgery. If a partial knee replacement isn’t successful a second operation may be needed to convert it to a total knee replacement.

For partial knee replacements the likelihood of a repeat operation is about 1 person in 10 by 10 years. It is usually easier to convert a partial knee, than convert a total knee. Partial knee replacement is preferred for younger patients, but older patients who may be less fit may also benefit from this less stressful operation.

Minimally invasive surgery (reduced invasive surgery)

A half-knee replacement can be performed using a technique called minimally invasive surgery or reduced invasive surgery. This needs smaller incisions than conventional surgery, which should further reduce the recovery time.

Minimally invasive surgery isn’t currently used for total knee replacements because there is an increased risk of complications when implanting a full knee replacement through a small incision.

Kneecap replacement

It’s possible to replace just the kneecap (patella) and its groove (trochlea) if these are the only parts of your knee affected by arthritis. This is also called a patellofemoral replacement or patellofemoral joint arthroplasty. The operation has a slightly higher rate of failure than total knee replacement – usually caused by the arthritis progressing to other parts of the knee.

Many surgeons advise a total knee replacement as a more predictable option. The operation is only suitable for about 1 in 10 people with osteoarthritis. However, the outcome of kneecap replacement can be good if the arthritis doesn’t progress and is a less major operation offering speedier recovery times.

Complex or revision knee replacement

Some people may need a more complex type of knee replacement. The usual reasons for this are:

  • major erosion of bone
  • major deformity of the knee
  • weakness of the main knee ligaments.

These knee replacements usually feature a longer stem, which allows the component to be more securely fixed into the bone cavity. The components interlock in the centre of the knee to form a hinge that prevents the joint sliding apart and dislocating. Extra pieces of metal and/or plastic may be used to compensate for any deficiencies of bone.

One of these complex knee replacements could be preferable if you have very severe arthritis, and may be necessary if you are having revision surgery (a second or third joint replacement in the same knee).

Image-guided and robotic surgery

Image-guided surgery (sometimes called ‘computer-assisted surgery’) is a technique where surgery is performed with the aid of computerized images. Usually this is done by attaching infrared beacons to parts of the leg and to the operating tools. These are tracked on infrared cameras in the operating theatre. Only about 1 in 100 knee operations are currently performed in this way, but results so far suggest this offers greater accuracy in positioning the new knee joint.

There are also developments in the use of robotic appliances linking operating tools with computerized scans of the knee. These should provide more accurate surgery although these techniques are still under review.

Potential complications of knee surgery

Most knee joint operations are problem-free but complications can arise in about 1 in 20 cases. 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. Your surgeon will discuss the risks with you.

Thrombosis – Any operation on the lower limbs can lead to a small blood clot forming in the leg (deep vein thrombosis), which can cause pain and swelling. The problem is usually treated with blood-thinning medicines such as heparin or warfarin. These are sometimes given as a precaution. Blood-thinning drugs can increase the risk of bleeding, bruising or infection so your surgeon will need to balance these risks.

Pulmonary embolism – In a very small number of cases a blood clot can travel to the lungs, leading to breathlessness and chest pains. In extreme cases a pulmonary embolism can be fatal. However, it’s usually possible to treat pulmonary embolism with blood-thinning medicines and oxygen therapy.

Wound infection – On average this happens in about 1 in 50 cases. Usually the infection can be treated with antibiotics. About 1 in 150 patients develop a deep infection which may mean removing the new joint until the infection clears up. In extreme cases, where the infection cannot be cured, the knee replacement has to be removed permanently and the bones fused together so the leg no longer bends at the knee.

Nerve or tissue damage – There is a small risk that the ligaments, arteries or nerves will be damaged during surgery.

  • Less than 1 in 100 patients have nerve damage and this usually improves gradually in time.
  • About 1 in 100 have some ligament damage – this is either repaired during the operation or protected by a brace while it heals.
  • About 1 in 1,000 suffer damage to arteries that usually requires further surgery to repair the damage.
  • In about 1 in 5,000 cases blood flow in the muscles around the new joint is reduced (compartment syndrome). This usually also requires surgery to correct the problem.

Bone fracture – The bone around the artificial knee joint can sometimes break after a minor fall – usually after some months or years and in people with weak bones (osteoporosis). Further surgery is usually needed to fix the fracture and/or replace the joint components.

Dislocation – When a mobile plastic bearing is used there is a small risk of dislocation of the knee, and this would also require further surgery.

Alternatives to knee replacement surgery

Most surgeons recommend non-surgical treatments before contemplating a knee replacement. However, there are also surgical alternatives to knee replacement. 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.

Arthroscopic washout and debridement – Keyhole surgery techniques (arthroscopy) can be used to smooth damaged cartilage and remove debris from the knee joint. It isn’t recommended for severe arthritis but there’s some evidence that it can be useful for younger patients with less advanced arthritis, especially if there are loose fragments of bone or cartilage in the knee which can cause it to lock.

Microfracture – This operation, which is performed by keyhole surgery, entails making holes in the bone surfaces with a drill or pick, which encourages new cartilage to grow. The technique isn’t recommended for advanced arthritis.

Osteotomy – This involves cutting the shin bone crosswise, creating a wedge to shift the load away from the area affected by arthritis. Osteotomy may be considered as a way of putting off a knee replacement operation  However, it can make it more difficult to carry out a successful total knee replacement later on – especially if at the osteotomy the surgeon had to cut through the medial collateral ligament on the inner surface of the knee.

Autologous chondrocyte therapy (ACT) – If only the hard cartilage is damaged, new cartilage can be grown in a test tube from your own cells. The new cartilage is then applied to the damaged area. The technique is primarily designed to repair small areas of cartilage damage resulting from injury. It isn’t yet proven for arthritis and would only be appropriate for younger patients whose cartilage cells are more active.

Preparing for knee replacement surgery

If you’re consdering knee replacement surgery it’s important to know what to expect before and after your operation, and to think about how you will manage during your recovery.

Your 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 you undergo surgery, the quicker your recovery will be. Exercises that involve raising the foot against gravity are best.

It’s also advisable to have a dental check-up and get any problems dealt with well before your knee operation. There is a risk of infection if bacteria from dental problems get into the bloodstream.

Pre-operative visit

You will usually be invited to a pre-operative assessment clinic. This will involve a number of tests to assess whether you are generally fit and healthy enough to undergo surgery. You’ll also have the opportunity to discuss anything you are concerned about.

You should also meet a physiotherapist or occupational therapist who will talk about the exercises you’ll need to do after your surgery and discuss your arrangements for going home.

Going into hospital

You will probably be admitted to hospital on the day of your operation or the evening before. You’ll be asked to sign a form consenting to surgery, and you may also be asked if you are willing for details of your operation to be entered into the National Joint Registry (NJR) database. The NJR collects data on hip and knee replacements in order to monitor the performance of joint implants. Your knee will then be marked for the operation.

If you are taking any tablets or medicines routinely then you should take these as usual on the day of the surgery unless your doctor or surgeon has advised you not to.

The operation

Most knee joint replacements are now performed under either a spinal anaesthetic or an epidural anaesthetic. These numb the body from the waist down, but you will remain awake throughout the operation. If you have a general anaesthetic instead, a nerve block may also be given – this will block pain in the leg for up to 36 hours after surgery.

The operation itself takes between 45 minutes and 2 hours depending on the complexity of the surgery.

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. You may be given a switch so that you can administer painkillers yourself (patient-controlled analgesia or PCA). Oxygen therapy is likely to be given through a mask or through tubes into your nose.

If necessary you will be given a blood transfusion. Increasingly there is a trend to recycle blood which drains from your knee – returning it into your body through a tube in a vein (auto-transfusion). Some surgeons do not feel the need to use a drain, especially for partial knee replacements.

Recovering from knee replacement surgery

This section covers: getting mobile again, going home, looking after knee, warning signs and getting back to normal.

Getting mobile again

After the first day or so, the various tubes giving 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 will probably need strong painkillers to control this. Without adequate painkillers it will be difficult to do the exercises needed to strengthen the muscles and restore mobility.

Nursing staff and physiotherapists will help you to start walking. If you’ve had minimally invasive surgery this may be on the same day as your operation. At first you’ll need crutches or a walking frame. If you have had a spinal anaesthetic or nerve block you will have very little feeling in your leg for the first day or two.

You may have a temporary brace or plaster on your leg if there is a risk of weak ligaments, deformity or poor wound healing. Your surgeon may recommend longer rest if your knee replacement is due to rheumatoid arthritis or if your tissues are particularly delicate.

Your physiotherapist will be able to advise you on getting about and will explain the exercises you need to do to keep improving your mobility.

Going home

At your pre-assessment you should be given some idea how long you are likely to be in hospital after the operation. It’s usually possible to go home as soon as your wound is healing well and you can safely manage to get about at home with the help of crutches or a frame. Most people are fit to go home between 2 and 5 days after surgery. The key is to plan in advance how you will manage the practicalities of daily living.

Before you leave hospital an occupational therapist or physiotherapist will explain the best ways to get dressed, take a bath, and move about and will assess what equipment you might need to help you. You should also make arrangements for wound care. If you have stitches or clips that need removing, this can be on a return visit to hospital, at home by a visiting nurse, or at your GP’s surgery.

You’ll usually have a follow-up hospital appointment about six weeks after your operation to check on your recovery. Further follow-up appointments are usually recommended – say at two, five and ten years – to check on any difficulties that may arise.

Looking after your new knee

Your new knee will continue to improve for as much as two years after your operation as the scar tissue heals and the muscles are restored by exercise. During this time you need to look after yourself and pay attention to any problems such as stiffness, pain or infection.

  • Stiffness – 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 in to your knee. This should help to improve flexibility. If it doesn’t improve after about six weeks your surgeon may need to move or manipulate your knee. This will be done under a general anaesthetic.
  • Pain – Pain caused by bruising during the operation should reduce after about four weeks although some pain is likely for as long as six months. If you still have pain after this, speak to your physiotherapist or GP who may recommend more painkillers or a rest from exercise.
  • Swelling – Applying ice can be very helpful for a swollen joint, but make sure you protect the skin from direct contact with the ice pack. Ice can be applied for up to 20 minutes at a time. Raising the foot off the floor (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 so as not to increase the risk of a blood clot.
  • Infection – If you notice any infection or sores on your leg you should seek early advice from your GP. You should also look after your feet – see a doctor or podiatrist (chiropodist) if you notice any problems such as ingrown toenails which could become infected.

Warning signs

Contact your GP, hospital doctor or nurse if you have any hot, reddened, hard or painful areas in your legs in the first few weeks after your operation. This may just be bruising from the surgery but it could mean a blood clot has developed which needs treatment.Contact your nearest hospital or GP immediately if you experience pains in your chest and/or breathlessness at any time after your operation. Although very rare, this could mean you have a clot on your lung which needs urgent treatment.

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 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 will be able to build up the exercises to strengthen your muscles so that you can move more easily.

It’s important to use crutches during the first few weeks after surgery as falling could damage your new joint. You’ll need to take care in the first few weeks when moving around and doing household jobs so that you don’t damage your new knee. Your physiotherapist or occupational therapist should advise you on these tasks but here are a few tips:

  • Walking – Don’t twist your knee as you turn around. Take several small steps instead. It should be possible to walk outside about three weeks after your knee surgery but make sure you wear good supportive outdoor shoes. After three weeks, try to take longer strides to regain full straightening (extension) of the leg.
  • Walking aids ­– Crutches are useful at first. After three weeks 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. Your surgeon or physiotherapist will be able to advise you on this.
  • Going up and down stairs – When going upstairs put your unoperated leg onto the step first, then move your operated leg up. When going downstairs, put your operated leg down first, followed by your unoperated leg.
  • Sitting – Don’t sit with your legs crossed for the first six weeks.
  • Kneeling – You can try kneeling on a soft surface after three months when the scar tissue has healed sufficiently. Kneeling may never be completely comfortable but should become easier as the scar tissue hardens up.
  • Sleeping – You don’t need to sleep in a special position after knee surgery. However, you should avoid lying with a pillow underneath your knee. Although this may feel comfortable it can affect the muscles resulting in a permanently bent knee.
  • Household jobs – You should be able to manage light household tasks, but avoid heavier jobs, or get help with them, for the first three months. Avoid standing for long periods as this could lead to your ankles swelling. Avoid reaching up or bending down for the first six weeks.
  • Driving – You should be able to drive again after about six weeks if your knee replacement was carried out by the conventional method, or about three weeks if you had  a partial knee replacement. If you’ve had surgery on your left knee and you drive an automatic you should be able to drive earlier – as long as you’re not taking strong painkillers.
  • Exercise and sport – High impact loading, such as in contact sports isn’t recommended as it may weaken the cement and lead to loosening of the joint components. Other recreational sports – including golf, tennis and skiing – gradually become possible depending on how fit and sporty you were before the operation. And cycling is a very good way of building up strength and mobility after knee surgery.