Joint replacement in osteoarthritis of the knee

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Joint replacement may be an option if exercise therapy, painkillers and weight loss don't help enough in osteoarthritis of the knee. Ten years after surgery, more than 90% of artificial knee joints (prostheses) are still intact.

Joint replacement surgery can relieve the symptoms of advanced osteoarthritis of the knee very effectively in most people. But it is major surgery that carries various risks. Also, the younger you are at the time of surgery, the more likely the artificial joint (prosthesis) will have to be replaced at some point later on.

Some experts criticize that knee surgery is performed too often in Germany. Before making a decision about the procedure, it's a good idea to carefully consider the pros and cons and to learn about the possible alternatives. Our decision aid may help here.

It can also be a good idea to get a second opinion from another doctor. Various treatments can often help delay the need for surgery for a long time.

When is joint replacement surgery considered?

A German research group made up of scientists, doctors, and physical therapists worked together with patient advocates to develop recommendations on the right timing of joint replacement surgery. According to the recommendations, this treatment may be considered if

  • intense knee pain has been felt for months, either on several days a week or permanently,
  • other effective treatments, including painkillers and exercise therapy, haven’t provided enough pain relief for several months,
  • quality of life is greatly reduced, and
  • changes in the knee joint that are typical of osteoarthritis are clearly visible in an x-ray.

Other factors that play a role in the decision about whether to have knee replacement surgery include

  • difficulty walking and climbing stairs,
  • a misalignment in the legs,
  • an unstable knee joint or weak muscles,
  • problems when kneeling or sitting down,
  • limitations at work, at home or during your free time, and
  • being dependent on other people's help.

Sometimes there are medical reasons not to have surgery – such as serious medical conditions that increase surgery-related risks.

How much does an artificial knee help?

Conservative (non-surgical) treatment can still relieve symptoms effectively even if osteoarthritis of the knee has reached an advanced stage. In one study, Danish researchers looked into what people with advanced osteoarthritis of the knee can expect from knee replacement surgery. They compared two groups of people with an average age of about 66 years: One group had twelve weeks of conservative treatment. The other group had conservative treatment plus joint replacement surgery.

The conservative treatment consisted of exercise therapy, slight weight loss of about 3 kilos, painkillers, insoles, and patient education about coping with osteoarthritis.

After one year, the study showed the following:

  • The symptoms improved noticeably in 67% of the people who had conservative treatment only. They managed without surgery for the next two years.
  • The symptoms improved noticeably in 85% of people who had knee replacement surgery as well as conservative treatment.

The study also showed that knee replacement surgery reduces symptoms more than conservative treatment does alone.

The following table shows the severity of the symptoms before and after treatment. "100" is the maximum severity of symptoms, and "0" is no symptoms.

Illustration: How well does joint replacement surgery reduce pain when compared to conservative treatment?

The results of this study are averages – which means that joint replacement reduces symptoms more in some people and less in others. This depends, for example, on how bad the osteoarthritis was before surgery.

In summary, it’s fair to say that

  • conservative treatment is effective, even in most people with advanced osteoarthritis. It can help delay knee surgery for several years or even avoid the need for it altogether.
  • If the joint is replaced later, surgery can typically relieve the symptoms a lot.

What risks are associated with surgery?

Implanting a knee joint is a major operation that carries various risks. But most of the complications can be prevented or they can be treated effectively. Serious complications are rare.

The knee becomes stiff after about 5% of these procedures. This complication is most common in total knee replacements. Further treatment may then be needed in order to make the stiffness go away. This involves carefully bending and straightening the knee while using an anesthetic. Arthroscopy (keyhole surgery) might also be considered.

After about 1% of the procedures, develops around the new knee joint within the first year. If the can’t be treated effectively or is discovered too late, the prosthesis may need to be replaced.

The risk of a or stroke increases slightly in the first few weeks after the procedure, especially in older people or people who already have certain other medical problems. The overall risk of this happening is then 0.5%.

Deep vein thrombosis or pulmonary embolism (very rare) may occur after surgery. To prevent these complications, anticoagulant treatment (tablets or heparin injections) is usually given for at least two weeks.

There are also the general risks associated with surgery and anesthesia, such as severe loss of blood during the procedure or poor wound healing after the operation. These kinds of complications can make it necessary to stay in the hospital longer for more treatment.

What can I expect from an artificial knee joint in the long term?

Studies show that about 80% of people are satisfied with their artificial knee joint in the long term. It usually takes several months to get used to the new knee after surgery, with the help of follow-up treatment. The pain typically improves quite a bit. Many people can start doing activities again that were difficult or impossible to do before. Misalignment of the knee joint can often be corrected by surgery too.

About 20% of people who have had the surgery continue to have severe pain or other problems, such as not being able to easily bend their knee. Kneeling down can be difficult and painful too.

What determines how long an artificial knee lasts?

Many factors influence how long a knee prosthesis will last – for instance, the kind of strain put on it. The prosthesis may need to be exchanged if some of its parts loosen or wear out, if there's an , if ligaments become unstable, or sometimes because the prosthesis doesn’t fit properly.

The type of prosthesis matters too: In partial knee replacement, only one side of the knee joint is replaced. This type of prosthesis is considered if osteoarthritis has only damaged one side of the knee, for example, and all ligaments are still intact and stable. In total knee replacement, both the medial side (facing the other knee) and the lateral side (away from the other knee) are replaced – as shown in the illustration.

Illustration: Front view of the right knee; Left: Partial knee replacement; Right: Total knee replacement – as described in the article

Front view of right knee; Left: Partial knee replacement; Right: Total knee replacement

Partial knee replacements need to be exchanged slightly more often than total knee replacements do. Current data shows that the prosthesis has to be exchanged within five years in

  • an estimated 5 to 10% of all partial knee replacements, and
  • about 3 to 4% of all total knee replacements.

Aside from that, partial knee replacements are less complicated and the rehabilitation time after the procedure is shorter. Also, less bone is lost when exchanging partial knee prostheses, and the surgery is often technically easier than exchanging total knee prostheses. Ultimately, the choice of knee prosthesis will also depend on the reason why the prosthesis is exchanged and on the individual situation.

If the surgeon has a lot of experience with partial knee replacements, it's not very likely that the prosthesis will need to be exchanged. In Germany, hospitals are only allowed to offer full knee replacements if they can prove that they perform at least 50 of these operations per year. There is no such minimum number of procedures for partial knee replacements. So it's a good idea to carefully choose the hospital you go to for a partial knee replacement.

Will my prosthesis need to be exchanged at some point?

Over the long term, a knee prosthesis may need to be exchanged because of wear and tear. The amount of wear on a prosthesis can vary greatly. Whether it has to be exchanged within your lifetime also depends a lot on your age: The younger you are at the time of surgery, the more likely it will have to be exchanged at some point.

The following table provides an overview.

Table: How often do artificial knee joints need to be exchanged?
Age when implanted Likelihood of having to exchange prosthesis
  Men Women
50 years old 35% 20%
60 years old 18% 16%
70 years old 6% 5%
80 years old 2% 2%

If you're young when you first develop osteoarthritis and you manage to delay joint replacement surgery by using other effective treatments, you may be able to avoid having a second operation.

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Skou ST, Roos EM, Laursen MB et al. A Randomized, Controlled Trial of Total Knee Replacement. N Engl J Med 2015; 373(17): 1597-1606.

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IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on August 24, 2021
Next planned update: 2024

Authors/Publishers:

Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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