Patient information from BMJ

Knee injections

Last published:Aug 02, 2021

People usually have a knee injection to help with joint problems like arthritis, or to have fluid removed from around the knee, for testing.

This information tells you what happens when you have an injection in your knee, including whether it will hurt, how it might help, and what the risks are. You can use our information to talk with your doctor about this procedure.

Why might I need a knee injection?

Some people have injections in the knee to help with swelling or pain. For example, drugs called corticosteroids are sometimes injected into the knee to help with arthritis, or after an injury.

But knee injections are also used to take samples of fluid from around the knee for testing. Taking fluid with a needle in this way is called aspiration.

You might need this test if you have symptoms that suggest certain medical problems. For example, it can help to diagnose conditions including:

• septic arthritis. This is an infection of the knee joint, which needs urgent treatment with antibiotics. The symptoms are a red, swollen, stiff, and painful knee

• gout. This is a type of arthritis that can cause problems such as pain and swelling when tiny crystals build up around the joint

• osteoarthritis. This is the most common type of arthritis, which often happens as people get older and their joints suffer from wear and tear

• other types of arthritis. Arthritis can develop for many reasons: for example, after an infection elsewhere in the body.

What will happen?

Whether you are having an injection of medication or having fluid taken for testing, the procedure will feel the same.

The doctor will:

• clean your knee using an antiseptic wipe

• insert the needle into the soft tissue at the side of the knee

• either inject the medication you need, or take some fluid into the syringe. This might take a minute or so

• withdraw the needle, and

• apply a small dressing or plaster over the place where the needle went in.

What are the risks?

Although it’s a short procedure, a knee injection can be a bit painful at the time. And corticosteroid injections can cause dull pain for several hours afterwards.

Other complications from this procedure are rare, but they can happen. Your doctor should explain all the possible complications to you before you have the procedure. They include:

• bleeding

• infection

• damage to the joint if you have frequent injections of corticosteroids. You and your doctor should discuss the balance between the benefits and possible problems with these injections. Your doctor is likely to recommend that you have only a few injections in your knee each year.

Is there anyone who should not have an injection in the knee?

Your doctor should ask you some questions before you have the injection, to make sure that it is safe for you. For example, you might not be able to have this procedure if you:

• have a skin infection that could spread to the joint if you have an injection

• have a condition that means that your blood doesn't clot normally, such as haemophilia

• are taking medication to stop your blood from clotting too easily

• might have a fractured knee

• have diabetes that is poorly controlled, or

• have a weakened immune system. This is called being immunocompromised.

What can I expect afterwards?

If your injection has been to test the fluid in your knee, your doctor should arrange a follow-up appointment to discuss the results.

The follow-up appointment is also a chance for the doctor to check on any complications that might have been caused by the procedure.

If you have had a corticosteroid injection, your doctor should tell you how long the injection will take to work, and how long the pain-killing effects should last.

These injections usually take a few days to start working, and the effects last from a few weeks to a few months, depending on the medication used. Your doctor will be able to tell you more.

Your doctor should also caution you that corticosteroid injections can vary a lot in how well they work. They can sometimes make a big difference, while other times they don’t seem to work at all.