Your knee joint normally contains a small amount of water-like liquid called synovial fluid. When an excessive amount of fluid accumulates in the joint — producing an effusion — your knee will appear swollen and may be stiff and sore.
Knee effusions are usually caused by an injury to the knee or a type of arthritis. The injury may be the result of sudden trauma to the knee or more prolonged overuse of the joint. Osteoarthritis, gout and rheumatoid arthritis are some of the most common types of arthritis that cause fluid in the knee. Septic arthritis, due to infection in the joint, can also produce a knee effusion.
There are various ways to reduce fluid in your knee, ranging from simple rest to medications to removing the fluid with a needle.
Rest and Elevate
One of the main ways to reduce fluid in your knee joint is to rest the knee. This is especially important when the effusion is caused by trauma or overuse of the knee. Stop any activity that increases your knee swelling or pain. A knee brace or crutches may be useful to reduce knee movement during everyday activities.
Apply Cold and Compression
Applying cold to your knee may reduce pain and fluid buildup. There are several options, such as a washcloth soaked in cold water, ice cubes in a plastic bag or a commercial cold pack stored in the freezer.
When using ice or freezer packs, do not place them directly on the skin — instead, wrap them in a towel before placing them on your knee. Whichever method you choose, apply the cold for 15 to 20 minutes every 2 to 4 hours.
Wrapping your knee with an elastic bandage to compress the joint may also reduce fluid accumulation. Be careful to avoid wrapping your knee too tightly, as this may decrease blood flow to your knee and lower leg. Remove the bandage immediately if you notice numbness, tingling or warmth in these areas.
Consider Over-the-Counter Medications
Over-the-counter nonsteroidal anti-inflammatory drugs, such as ibuprofen (Advil, Motrin) or naproxen (Aleve), may also help reduce fluid in your knee. Acetaminophen (Tylenol) can be used to relieve pain, but it will not affect the amount of fluid in your knee.
If over-the-counter medications are ineffective, ask your doctor about prescription medications. A short course of corticosteroid pills, such as prednisone or methylprednisolone (Medrol), may be useful.
If your knee effusion is due to rheumatoid arthritis or gout, your doctor may prescribe medications specific for these conditions. An effusion caused by septic arthritis will require antibiotics — usually by mouth but sometimes through a vein.
Ask About Knee Aspiration and Injections
When a knee effusion is severe or persists for a prolonged time, your doctor may recommend removing the excess fluid through a needle inserted into the joint. This procedure, called arthrocentesis, will reduce the swelling. It may also help determine the cause of the effusion, as your doctor will likely send a sample of the fluid to the lab for analysis.
Your doctor may also inject corticosteroid medication into your knee joint, which usually produces quick symptom improvement. This type of injection is generally performed immediately after fluid is removed during arthrocentesis.
When to See a Doctor
See your doctor if you have a swollen knee that lasts more than a few days. Obtain prompt medical attention if you have severe pain or swelling, if your symptoms are the result of significant trauma to your knee, if you are unable to bend or bear weight on your knee, or if you have signs of septic arthritis, such as a fever or redness and warmth of the knee.
Reviewed by Mary D. Daley, M.D.