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Why You Might Have Fluid on the Knee and How to Treat It

When your knees are healthy, they’ll have a small amount of fluid in them. That fluid helps lubricate your knee joint, so it moves smoothly and without pain. But sometimes, excess fluid collects in and around your knee joint. Your knee may look larger, puffier or swollen and may feel painful. You know something isn’t right.

Neal McKimpson, DO, a family and sports medicine specialist with Banner Health in Loveland, CO, explained more about the causes of fluid or water on the knee, how to treat it and what steps you can take to keep it from happening again.

What causes fluid on the knee?

When you have fluid buildup on the knee, also known as knee effusion, it’s a sign of some type of damage. That damage could come from an injury or an underlying condition.

Sprains, broken bones around the joint, meniscus tears or ligament injuries such as an anterior cruciate ligament (ACL) tear could cause fluid on the knee. “These injuries often occur when your knee is forcefully twisted or bent in an abnormal direction,” Dr. McKimpson said. Osteoarthritis and rheumatoid arthritis, infections, gout or pseudogout (a form of arthritis caused by calcium pyrophosphate crystals) can also cause fluid on the knee. The pain and knee swelling will probably get worse if you overuse the joint since that can cause a repetitive injury.

How can you treat it at home?

You can help reduce knee pain and alleviate the swelling by:

  • Resting your knee
  • Avoiding activities that make the pain worse
  • Compressing the knee with a sleeve or wrap
  • Taking over-the-counter anti-inflammatory medications, such as ibuprofen (Advil) or naproxen (Aleve)
  • Wearing a knee brace, which can decrease a swollen knee by offloading the knee joint
  • Maintaining a healthy weight, so you’re not placing unnecessary stress on your knee 

When should you see a doctor?

If you’re treating fluid on the knee at home and the swelling and pain are getting worse, you should seek medical care. You should get medical attention immediately if your knee is red or feels warmer than the other knee since that could be a sign of infection. And, if you think you might have a broken bone or torn ligament, have reduced range of motion or can’t move your knee or can’t put weight on your knee, you’ll want to see a health care professional immediately.

What treatments might a doctor recommend?

Your doctor might suggest you continue with the at-home treatments you’ve been using. Depending on what’s causing the fluid on your knee, they might also recommend:

  • Antibiotics if you have an infection
  • Other prescription medications
  • Physical therapy
  • Joint aspiration, which removes fluid from the joint to temporarily relieve pressure
  • A corticosteroid injection into the joint to reduce inflammation
  • Hyaluronic acid injections into the joint that provide nutrients and lubrication 
  • Joint replacement surgery for advanced arthritis
  • Arthroscopic surgery, which uses small incisions along with a camera to repair the damaged joint

“One area of cutting-edge research is regenerative medicine for excess fluid on the knee, particularly with arthritis,” Dr. McKimpson said. For example, some studies have found that platelet-rich plasma (PRP) injections into the knee improve symptoms related to arthritis. However, these techniques are still in development, continually evolving and rarely covered by insurance. They can cost several hundred dollars. Speak with your doctor about the pros and cons if you are interested in considering these new techniques.

How can you prevent fluid on the knee?

You can’t always prevent an injury, but you can help prevent excess fluid on the knee. 

  • Avoid sudden movements, such as quick changes in direction, that can harm your knee. 
  • Make sure all your underlying conditions are properly managed, and you’re seeing your doctor regularly.
  • Stay active with low-impact activities, such as walking, biking and swimming, to help maintain a healthy weight and reduce stress on your knees. 

The bottom line

If you injure your knee or have an underlying condition that affects it, you could develop fluid on the knee. Your doctor can evaluate your knee to identify the causes and recommend steps to reduce the swelling and alleviate the pain. And you can try to keep your knee strong and healthy, so the problem doesn’t happen again.

Need help treating fluid on your knee? 

Schedule an appointment with a primary care provider.
Schedule an appointment with an orthopedic sports medicine specialist.

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