What can I expect from knee replacement surgery?

Photo of a man working in the garden (PantherMedia / Monkeybusiness Images) Joint replacement may be an option if exercise therapy and painkillers don't provide enough pain relief in osteoarthritis of the knee. Ten years after surgery, more than 90% of knee implants (prostheses) are still intact.

In most people, joint replacement surgery can very effectively relieve osteoarthritis symptoms. But it is major surgery that carries various risks. Also, the younger you are at the time of surgery, the more likely the implant will have to be replaced at some point later on. And some experts criticize that knee surgery is performed too often in Germany. So it’s worth finding out about the procedure before making a decision. 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. Even after they receive a knee implant, some people still need painkillers.

When is joint replacement surgery considered?

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

  • intense knee pain has been felt on multiple days a week or permanently for several months,
  • 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 taken while standing up.

In addition to these main criteria, the group of researchers defined secondary criteria that can also be considered when deciding about joint replacement. These secondary criteria include difficulty walking and climbing stairs, leg deformities or worsening of deformities, an unstable knee joint, weak muscles, problems when kneeling or sitting down, problems in the household or when using means of transport, limitations affecting work and leisure, and dependence on the help of others.

Sometimes there are medical reasons not to have surgery – such as serious medical conditions that increase the risks associated with surgery.

How much do knee implants help?

Conservative (non-surgical) treatment can still relieve symptoms effectively even if osteoarthritis of the knee has reached an advanced stage. Danish researchers have 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 66 to 67 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 joint replacement surgery as well as conservative treatment.

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

The following diagram shows the severity of symptoms before and after treatment, where "100" is the most pain imaginable and "0" is no pain at all. 

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?

Complications arise in about 5% of joint replacement surgeries.

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

In their first year after surgery, about 1% of patients have an inflammation around the new knee joint. If the inflammation can’t be treated effectively or is discovered too late, the knee implant may need to be exchanged.

Other rare complications include severe blood loss during surgery, requiring a blood transfusion, and problems with wound healing after surgery. This can make it necessary to stay in the hospital longer and get more treatment. It’s very rare for nerves, tendons, or ligaments to be injured during surgery.

There are also the general risks associated with surgery and anesthesia.

What can I expect from a knee implant in the long term?

Studies show that about 80% of people are satisfied with their knee implant in the long term. After surgery, it usually takes several months to get used to the new knee, 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 is often difficult, and can be painful too. Also, the range of motion after surgery is sometimes not big enough to be able to kneel all the way down with your bottom against your heels.

What determines how long knee implants last?

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

The type of implant matters too: In partial knee replacement, only one side of the knee joint is replaced. This type of implant is considered if osteoarthritis has only damaged the inner side of the knee, for example, and all ligaments are still intact and stable. In total knee replacement, on the other hand, both the inner (medial) and the outer (lateral) sides of the 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 articleFront 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. For example, this may be necessary if other parts of the same knee develop osteoarthritis too.

So far, there is no data from Germany on the lifespan of partial and total knee replacements because an implant registry was only started a few years ago. But data from other countries can give us a general idea. The illustration below shows what percentage of knee implants need to be exchanged within ten years of having partial or total knee replacements:

Illustration: What percentage of artificial knee joints need to be exchanged within 10 years?

It's important to know that partial knee implants have to be exchanged a little more often. But the operation is smaller, and you recover more quickly. Also, less bone is lost when exchanging partial knee implants, and the surgery is often technically easier than exchanging total knee implants. Ultimately, the choice of knee implant will also depend on the reason why the implant is exchanged and on the individual situation.

Will my implant need to be exchanged at some point?

Over the long term, a knee implant may need to be exchanged because of wear and tear. The amount of wear on an implant 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: Probability of a knee implant having to be exchanged at some point
Age when implanted Probability in men Probability in 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.