How to Reduce Fluid on the Knee

Treatments to reduce abnormal joint swelling

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Fluid on the knee, also known as knee effusion or water on the knee, is a painful condition resulting from fluid accumulating around and inside the knee joint. If you have this condition, learning the causes and symptoms and ways to reduce fluid on the knee can help. The methods you use to reduce swelling will depend on the cause and may need a doctor’s diagnosis.

fluid on the knee

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Fluid on the knee can be caused by injuries, overuse, infections, cysts, or underlying diseases such as gout, rheumatoid arthritis, and osteoarthritis. 

The knee joint is a synovial joint that contains fluid. This helps provide nutrition to the cartilage lining the joint, lubricating, and reducing friction. When there is excess fluid around the joint, it can cause swelling, pain, and stiffness.

If you are active and healthy, the most common cause of knee swelling results from an ACL tear, meniscus tear, or a contusion. Repetitive movements from sports such as running or from squatting and lifting often cause knee pain, but not necessarily swelling.

Underlying disease conditions such as gout, rheumatoid arthritis, and osteoarthritis can lead to an abnormal inflammatory response causing excess fluid build-up as your body tries to protect your joint. Sometimes, osteoarthritis or tears can cause cysts, called Baker’s cysts, that can cause knee effusion.

Traumatic injuries and infections can also cause knee effusion. If you’ve experienced an injury or have a fever with unexplained knee swelling, see your doctor immediately.

When Should You See a Doctor About Fluid in the Knee?

Tell your doctor if you've experienced a traumatic injury, have a fever, redness, or warmth of the joint. If at-home methods of treatment are not working, or any prescribed medications are not improving symptoms, tell your doctor right away.


To diagnose fluid on the knee, your doctor will check for these symptoms:

  • Swelling
  • Stiffness
  • Decreased range of motion
  • Fever
  • Loss of sensation
  • Difficulty walking or bearing weight on the affected leg
  • Warmth and redness

To determine the underlying cause of fluid on the knee, your doctor may order a procedure called joint aspiration, where a sample of the fluid is taken with a needle. The fluid is then analyzed for white blood cells, which indicate inflammation, bacteria that reveals infection, or uric acid crystals from gout. Imaging techniques such as an X-ray or MRI may be ordered for diagnosis as well, especially if a tear or other injury is expected.


Treatment to get rid of fluid in the knee will depend on the cause and the doctor’s diagnosis. For mild cases, you can try these at-home treatments:

  • R.I.C.E.—which stands for rest, ice, compression, and elevation—is best for minor pain directly after an injury
  • Compression by gently wrapping the knee with elastic bandaids
  • Over the counter anti-inflammatory pain medication (NSAIDs) such as ibuprofen or naproxen
  • Physical therapy exercises
  • Wearing a knee brace

If medical treatments are necessary, your doctor may perform a joint aspiration to drain some of the fluid, providing temporary relief. Injections of corticosteroids into the joint are another form of treatment, which reduces pain and inflammation from injury or arthritic joint damage.

If fluid on the knee is caused by infection, antibiotics will be prescribed. Typically, broad-spectrum oral antibiotics over 14 days will be sufficient, but if the infection is due to resistant bacteria, intravenous antibiotics may be necessary over two or four weeks.

Signs of Infection

Infections in the joint can be extremely painful and come on rapidly. If your knee is tender, warm, red, and if you have a fever, chills, or feel ill, seek medical care immediately.

For underlying conditions such as inflammatory arthritis, medications that suppress the overactive immune system response can be used. For severe cases of fluid on the knee, you may require joint surgery called arthroplasty or even joint replacement. These methods are only used as a last resort if all other medical interventions fail.

A Word From Verywell

Fluid on the knee can be painful and interfere with your quality of life. Knowing the causes, symptoms, and methods to reduce swelling at home or with your doctor’s help can greatly improve your symptoms. If you’ve experienced an injury or suspect an infection, make sure you tell your doctor right away.

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