This information is for people who have osteoarthritis. It tells you about knee replacement, a treatment used for osteoarthritis. It is based on the best and most up-to-date research.
Does it work?
Yes. Having the joint in your knee replaced with an artificial one should reduce the pain in your knee or get rid of it completely. You should also be able to move more easily after your operation. In one study, 9 in 10 people rated their new knee as good or excellent five years after surgery.
What is it?
In a knee replacement operation, a surgeon removes the damaged surfaces from bones in your knee, and replaces them with artificial surfaces.
There are a several different operations that surgeons can do on the knee joint. There are also lots of different kinds of artificial knee. Your surgeon will decide which operation is best for you depending on where you have osteoarthritis.
Replacing the knee joint is quite a serious operation. You'll usually be in hospital for between 7 and 10 days.
We've prepared some extra information for people thinking of having this operation. To read more, see Knee replacement.
How can it help?
If you have a knee replacement operation, there's a very good chance that the pain in your knee will get better or go away completely, whatever type of operation you have.    
You'll be able to bend your knee and move more easily.   This should help you get around more easily than you used to. For example, you should find it easier to walk and climb the stairs.
The benefits of your operation will last for at least five years. In one review of nearly 10,000 people who had a knee replacement operation, 9 in 10 of them rated their lack of pain and ease of movement as good or excellent five years after their operation. 
Knee replacement operations seem to work well whatever your age.  
How does it work?
Osteoarthritis causes pain in your knee because the joint doesn't move as smoothly as it should. Bone grows where it shouldn't, and the cartilage in the joint can become rough. Osteoarthritis also makes the joint swollen and puts stress on the muscles and ligaments around the joint. Replacing the knee joint allows it to move smoothly again.
Can it be harmful?
All surgery carries risk. Having your knee replaced is quite a serious operation, but the results are generally very good and side effects are rare.
Some problems can happen straight after surgery, while others happen some years after the operation. The biggest problem in the first few days after surgery is getting a blood clot in your veins. This is called deep vein thrombosis, or DVT for short. If the blood clot travels to your lungs it can lead to pulmonary embolism, which is very serious and can lead to death. DVT affects about one-quarter of people who have knee surgery.   But you should be given drugs after your operation to prevent it.
The main problem in the years after knee replacement surgery is that the artificial joint can become loose and you may need to have the operation repeated. Between 4 and 9 people out of 100 need to have their artificial knee joint replaced with a new one within about five years of surgery.