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Home >> Patients >> Knee >> Knee replacement

Knee replacement

What is a knee replacement?

This is an operation to replace the knee joint with metal and plastic components. The very bottom of the thigh bone (femur) and top of the shin bone (tibia) are removed via a cut on the front of the knee and the bone ends are replaced with a metal piece on the bottom of the thigh bone and a plastic/metal component on the top of the shin bone.


In addition the back of the kneecap may also be replaced or resurfaced.

The operation is done to relieve pain which is usually caused by wear and tear of the knee joint called arthritis. The operation should also increase the mobility of the knee. Your surgeon will offer you this operation if he feels that you are not controlling your symptoms with non-operative means such as pain killers

The operation lasts about an hour and the patient usually stays in hospital for 5-10 days. The operation is performed through an incision down the front of the knee about 9 inches (20-25 cm) long. Stitches or clips may be dissolvable, but non-dissolvable types need to be removed at about 2 weeks after surgery.

The time it takes to get home largely depends on social circumstances; people in bungalows/flats or houses with bathrooms and bedrooms downstairs get home quicker than people with lots of stairs. People having a responsible carer or family member obviously will do better than those who live alone.

Return to work is usually at the 3-month stage, but many people, especially those in sedentary jobs, return quicker than this. Driving is usually allowed by the eighth week. Most people can manage stairs within a week or two of surgery.

Physiotherapists will help to mobilise you and get the knee moving after the operation. They may need to help you for many weeks afterwards in the outpatients if the knee is very stiff.

All surgery carries risks and the Knee replacement is no different. These risks have to be fully understood by patients and relatives before surgery takes place. Complications specific to knee replacement surgery include:

  • Urinary problems and the need for urinary catheters.
  • Chest infections
  • Ileus (intestines cease to function for a few days)
  • Constipation
  • Stomach/duodenal ulcers
  • Confusion and even psychosis
  • Nausea and vomiting
  • Inadequate pain relief
  • Delayed wound healing

Major but rare complications of Joint Replacement Surgery:

  • Deep venous thrombosis and Pulmonary embolus (blood clots on the leg and lung).
  • Heart Attacks/strokes
  • Infection in the joint following surgery
  • Nerve damage and blood vessel damage.
  • Fracture (break) of bones
  • Failure to cure symptoms or even worsening of knee pain.

Who needs a Knee Replacement?

In 2000, joint replacement procedures numbered more than 1.6 million worldwide, most performed as a result of arthritis. An estimated 500 million people (one in six ) throughout the world suffer from arthritis. (Dorland’s Biomedical, The Worldwide Orthopaedic Market, 2001)

The surgeon will want to know whether you can be helped by surgery. Key questions for the surgeon will be;

  • How severe is the pain?
  • Does it keep you awake at night?
  • How far can you walk?
  • What are you expecting to gain from the surgery?
  • Are you fit enough to survive the anaesthetic or conversely are you too young to have a knee replacement?
  • Have you tried simpler forms of treatment to help with your symptoms?

If your knee pain is mild, you live a full and active life unimpeded by your knee or you have had not tried simpler measures such as pain killers, braces, injections or even an arthroscopy (key-hole surgery to wash out the knee) then you should not be considered for surgery.

What other Treatments are available for Arthritis of the knee?

Physiotherapy certainly can help symptoms and the effect has been shown to last for up to 1 year. Taping and strapping has not been shown to be of any benefit.


Braces range from elastic bandaging to several hundred pounds worth of high-tech knee braces. No brace has been shown to alter the actual mechanics or disease progress in arthritis . However some  patients  have been helped by braces.

Anti-inflammatories and pain killers

  • These medications can be taken as tablets, gels, suppositories and even injections but all have side effects such as stomach ulcers.
  • Analgesia or pain killers tablets help with the symptoms. Chondroitin sulphate (shark cartilage tablets) are widely available from chemists and newspaper adverts and are safe and probably as effective as anti-inflammatory tablets.

Knee Injections

  • Joint Injections. Injections of steroids into joints can alleviate symptoms of arthritis. There are risks associated with this treatment, such as the risk of introducing infection into joints with the needle (1 in 50,000) and there are theoretical risks of causing cataracts, bone death and bone loss with these injections.
  • Newer materials can now be injected into joints and it is claimed alleviate symptoms of arthritis. Drugs such as Hyaluronic Acid (Hyalgan or Synvisc) have all been around for years but are relatively new to the UK. The jury is still out as to whether they are any better than anti-inflammatory tablets but they have huge sales in other parts of Europe. Reportedly only marginally better than injecting a placebo (e.g. a water injection).

Operations for Arthritis of the Knee

Arthroscopy, Lavage and debridement.

Many surgeons will advise an arthroscopy of the knee as a treatment for arthritis. This keyhole surgery also allows the surgeon to view the inside of the knee directly and so allows more accurate planning if a knee replacement is later needed. In some studies, simply squirting salt water into and out of the knee with needles has been shown to be as effective as a full blown arthroscopy and causes much less discomfort to the patient. However an arthroscopy also allows the surgeon to detect and treat torn cartilages, remove loose fragments from inside the knee and to trim loose pieces of joint surface away. This is often a good treatment for pain and the reason why many surgeons always arthroscope the knees of all their arthritic patients. It is a waste of time in patients with rheumatoid arthritis, those with badly aligned knees (e.g. knock-knees) and those with severe Osteoarthritis.

Rheumatoid arthritis is defined as a systemic disease characterised by inflammation of the soft tissues surrounding a joint.

Osteoarthritis is defined as a non-inflammatory degenerative disease of the joints, particularly weight-bearing joints.

Arthroscopy is usually performed as a day-case, in and out of hospital on the same day. Most people are back to light work in 2 weeks, with manual workers needing up to 4 to 6 weeks off.

However, arthroscopies are not without risk and not everyone will benefit from an arthroscopy.  Overall 50 to 80% of patients with osteoarthritis having an arthroscopy will benefit from the operation, with a decrease in pain, especially night-pain being reported. The pain relief seems to last about a year and may last much longer. Patients who are found to have damaged or torn cartilages that are treated at the operation usually do well. Some people who have severe pain who receive an arthroscopy, never need any further surgery.

Cartilage Transplantation

Cartilage transplantation means transferring undamaged pieces of cartilage from unaffected areas of the knee joint to where it is needed, or alternatively transplanting cartilage from donors (dead people). It offers possibilities for the treatment of arthritis but is still experimental and as yet unproven.

Osteotomy about the knee

Sometimes, if the knee is bow-legged (varus) or knock-kneed (valgus), this puts huge abnormal forces through the knee, resulting in arthritis. An operation called an Osteotomy to-reset the leg bones so that the knee is straight may be offered. Again, controversial, but hugely popular in Europe where results of 80% + success are claimed at up to 15 years even in young patients. Unpopular in the UK, partly because the complications of surgery such as nerve damage and failure of the bones to mend or mending in the wrong position. Arguably, subsequent Total Knee Replacement surgery is more difficult if the operation fails.

However, as is discussed below, this may be a very good operation for younger patients as it may at least buy some time before a TKR is needed.

Should the above measures fail to control the pain of an arthritic knee and the patient‘s quality of life is affected then they may be offered a knee replacement

Knee Replacements

With modern materials and improvements in techniques and antibiotic therapy, total knee replacement (TKR) is the best treatment  currently available  for end stage osteoarthritis and rheumatoid? and is an increasingly common operation. There is still reluctance to offer TKR to young patients (< 60 years) as the results of surgery beyond 10 to 15 years, are unknown with many patients complaining of pain and poor function.

Although there have been numerous survival studies of the better known implants, confirming the procedure does have successful long-term survivals in older age groups, pain and function is often not assessed.

Which Knee Replacement ?

There are large numbers of different designs of knee replacements from which your surgeon may choose.

The early designs of knee replacement were simple hinges. However the natural knee rotates as well as bends so these early designs tended to fail. The majority of current designs just replace the surface of the joint and are not hinged. They rely on your own existing knee ligaments to keep the knee stable. In situations where knee ligaments are damaged, there is the option with some designs to use stabilised components that reproduce some of the functions of the ligaments.

With knee replacements there is a worry that the plastic surface of the joint replacement may wear out; in order to minimise this risk and retain full movement, some knee replacements use mobile bearings(mobile bearing knee replacements)

Most of the designs introduced 10 years ago or more have been superseded by new and supposedly better knee replacements. There are therefore very few that have ten year results. We will therefore have to wait a few years to see how well they will do.


The components of the knee replacement can be either cemented to the bone ends or be attached to the bones without cement (uncemented); most surgeons prefer to use cement for both parts of the replacement as it does not appear to cause any problems and studies have shown that cementing the tibial component definitely gives better results. Some will use cement for one half and not the other while others will not use cement for either.


It is possible to replace the back of the kneecap. Some surgeons do this for virtually every case, some hardly ever do it and some do it if the kneecap is badly worn. It is generally believed that there is less likely to be pain if the surface of the kneecap is replaced. However there are risks with doing this. For example it increases the risk of your kneecap breaking after surgery and the plastic in your kneecap may fail. Again there are only a few studies to show whether or not your kneecap should be replaced or not and there is no obvious overall better outcome with either option. Having the kneecap resurfaced lowers the risk of knee pain after surgery but increases the need for revision (redo) surgery for failure; not having the kneecap resurfaced increases the need of redo surgery for knee pain that persists after surgery.

Ligament retaining/sacrificing

The normal knee is stabilised by muscles and tendons and ligaments. Some designs of knee replacement necessitate cutting some of these ligaments, whilst some are designed to allow continued function of the normal ligament; we still don’t know which is the best option.


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