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 collecting around and inside the knee joint.

Whenever there's damage to the knee, such as from injuries or underlying diseases, it can lead to excess fluid. The methods you use to reduce swelling will depend on the cause and may need a healthcare provider’s diagnosis.

This article explores the common causes and treatments of fluid on the knee and when you should get medical care.

Home Remedies to Get Rid of Fluid on the Knee - Illustration by Jessica Olah

Verywell / Jessica Olah

Causes of Fluid On the Knee

The knee joint is a synovial joint. This means that the joint is lined with a type of tissue that produces synovial fluid.

Synovial fluid provides nutrition to the cartilage lining the joint, lubricates it, reduces friction, and helps with joint movement. Excess fluid around the joint can cause swelling, pain, and stiffness.

Common causes of fluid on the knee are:

What Is Cartilage?

Cartilage is a flexible tissue on the ends of bones that allows bones to glide smoothly over each other.

Injuries

If you are active and healthy, the most common cause of fluid on the knee results from injuries. These can include:

  • Anterior cruciate ligament (ACL) tear: A common type of sprain at the center of the knee. The ACL helps connect your thigh and shin bones and stabilizes your knee.
  • Meniscus tear: A tear in the C-shaped cartilage within your knee joint between the thigh and shin bones, which impairs its ability to provide a cushion for bones.
  • Contusion: A tissue injury such as a bruise

Repetitive movements from sports such as running or from squatting and lifting often cause knee pain and sometimes contribute to swelling.

Underlying Conditions

Underlying diseases can lead to an abnormal inflammatory response that causes excess fluid on the knee as your body tries to protect your joint.

These conditions include:

  • Osteoarthritis: A common type of arthritis caused by cartilage breakdown
  • Gout: Also called gouty arthritis; A buildup of uric acid crystals in the joint causes sudden, intense pain
  • Rheumatoid arthritis: An autoimmune disease in which the body attacks the synovial lining of joints plus other tissues

Cysts

Sometimes, osteoarthritis or tears can cause cysts, called Baker’s cysts, that can cause fluid on the knee.

Baker's cysts are fluid-filled lumps that form behind the knee when the joint is inflammed from injury or disease. Fluid flows toward the back of the knee and forms the cyst, and the cyst may contribute to swelling.

Infection

Infections can also cause fluid and pain. They can happen as a complication from surgery or inflammation and can be due to dangerous bacteria.

Infections in the joint can be extremely painful and come on rapidly. They require prompt medical care.

When to See a Healthcare Provider About Fluid on the Knee

If your knee is tender, warm, red, and if you have a fever, chills, or feel ill, get immediate medical care.

Diagnosis

To diagnose fluid on the knee, your healthcare provider will do a physical exam and 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 healthcare provider may order a procedure called joint aspiration, where a sample of the fluid is removed with a needle.

The fluid is then analyzed for white blood cells that indicate inflammation, bacteria that reveal infection, or uric acid crystals that signal gout.

Imaging tests such as an X-ray or MRI may be ordered for diagnosis as well, especially if your healthcare provider suspects a tear or other injury.

Treatment

Treatment to get rid of fluid on the knee depends on the cause. For mild cases, you can try at-home treatments:

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

If medical treatments are necessary, your healthcare provider may perform a joint aspiration to drain some of the fluid, providing temporary relief.

Does Draining Fluid From Knee Hurt?

Local anesthetic (one applied directly to the knee) should keep joint aspiration from being very painful. You may have some discomfort for a few days afterward but it shouldn't be severe.

Injections of corticosteroids into the joint can help reduce pain and inflammation from injury or arthritic joint damage.

If fluid on the knee is caused by an infection, your provider will prescribe antibiotics to kill the bacteria. Taking oral (by mouth) antibiotics for 14 days usually takes care of it.

If the infection is due to drug-resistant bacteria, you may be given up to four weeks of intravenous (IV, through a vein) antibiotics.

For underlying conditions such as rheumatoid arthritis, typical treatment includes medications that suppress an overactive immune system.

For severe cases of fluid on the knee, you may require joint surgery (arthroplasty) that may include joint replacement. These methods are only used as a last resort if all other medical interventions fail.

If at-home treatment methods or any prescribed medications don't work, tell your healthcare provider right away.

Summary

Fluid on the knee can be due to injuries, infections, or medical conditions such as arthritis.

A healthcare provider can recommend treatments, such as medications and physical therapy, based on the cause of the fluid buildup.

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 healthcare provider’s help can greatly improve your symptoms.

If you’ve had an injury or suspect an infection, make sure you tell your healthcare provider right away.

Frequently Asked Questions

  • Is it common to have fluid on the knee after knee replacement?

    Yes, fluid on the knee is common after knee replacement surgery. Expect your healthcare provider to explore various causes, though, including rheumatoid arthritis and infection.

  • Which is better for knee pain, heat or ice?

    It depends on the injury. Ice reduces inflammation, which is helpful for a recent sprain or meniscus tear. Heat relieves chronic (long-lasting) joint or muscle pain and improves flexibility.

  • What kind of exercise reduces water on the knee?

    It depends on what's causing it. Once you have a diagnosis, ask about physical therapy so you can learn the right exercises. Common ones are stretches to improve range of motion and strength-building exercises.

  • Can fluid on the knee get worse?

    Yes, it can get worse without treatment. A bacterial infection can spread and cause permanent damage. An untreated meniscus tear can cause debilitating pain and loss of mobility. See a healthcare provider right away.

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By Rachel Macpherson
Rachel MacPherson is a health writer, certified personal trainer, and exercise nutrition coach based in Montreal.