How to Reduce Fluid on the Knee

Treatments to Reduce Abnormal Joint Swelling

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 is 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 will explore the common causes and treatments of fluid on the knee and when to seek medical care.

fluid on the knee

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Causes

The knee joint is a synovial joint. This means that the joint is lined with a type of tissue that produces fluid. This helps provide nutrition to the cartilage lining the joint. It lubricates it, reduces friction, and supports joint rotation.

Cartilage is flexible tissue on the end of bones that allows them to glide over each other.

When there is excess fluid around the joint, it can cause swelling, pain, and stiffness.

Common causes of fluid on the knee are:

  • Injuries
  • Underlying medical conditions that cause joint inflammation, such as arthritis
  • Cysts, or fluid-filled sacs under the skin
  • Infections

Injuries

If you are active and healthy, the most common cause of knee swelling results from injuries such as:

  • Anterior cruciate ligament (ACL) tear, a common type of sprain located at the center of the knee. The ACL helps connect your thigh and shin bones and stabilizes your knee.
  • Meniscus tear, which is a tear of the C-shaped cartilage within your knee joint between the thigh and shin bones. If cartilage becomes damaged, it doesn't offer the same cushion and can cause inflammation.
  • Contusion, a tissue injury such a knee bruise

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

Underlying Conditions

Underlying diseases can lead to an abnormal inflammatory response causing excess fluid buildup as your body tries to protect your joint.

These conditions include:

  • Osteoarthritis, a common type of arthritis that happens when cartilage breaks down
  • Gout, also called gouty arthritis, where there is a buildup of uric acid that causes sudden, intense pain
  • Rheumatoid arthritis, an autoimmune disease in which the body attacks its own tissues, including joints

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 damaged due to an inflammatory condition or injury. Fluid flows toward the back of the knee and forms the cyst, and the cyst may contribute to additional swelling.

Infection

Infections can also cause fluid and pain. They can happen due to complications 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 Should You See a Healthcare Provider About Fluid in the Knee?

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

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 a tear or other injury is expected.

Recap

Damage to any part of the knee can lead to excess fluid. Your doctor will check your symptoms and may take a sample of the fluid to diagnose the cause of the swelling.

Treatment

Treatment to get rid of fluid in the knee will depend on the cause.

For mild cases, you can try these at-home treatments:

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

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, antibiotics will be prescribed to kill the bacteria. Typically, oral antibiotics, or those taken by mouth, over 14 days will be sufficient. But if the infection is due to resistant bacteria, intravenous (IV) antibiotics given though a vein may be necessary over two or four weeks.

For underlying conditions such as inflammatory arthritis, medications that suppress the overactive immune system response can be used.

If at-home methods of treatment are not working, or any prescribed medications are not improving symptoms, tell your healthcare provider right away.

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

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 experienced an injury or suspect an infection, make sure you tell your healthcare provider right away.

Frequently Asked Questions

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

    Choosing between heat or ice depends on the type of injury. Apply ice if you’re trying to reduce inflammation, which is necessary for recent injuries such as a sprain or meniscus tear.

    Apply heat if you want to relieve pain and improve flexibility, which is the goal for treating arthritis and chronic muscle or joint pain.

  • What kind of exercise reduces water on the knee?

    The type of exercises you can do to reduce water on the knee depend on the cause of the fluid buildup. Consider seeing your healthcare provider for a diagnosis, and a physical therapist who can give you specific exercises. Stretches that improve range of motion and strength-building exercises may be recommended.

  • Can fluid on the knee get worse?

    Yes, fluid on the knee can get worse if you don't address the issue. A bacterial infection could spread and lead to permanent damage. A meniscus tear can lead to long-term, debilitating pain and loss of mobility if it isn't treated. This is why it's important to get an immediate diagnosis from a healthcare provider.

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11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Tamer TM. Hyaluronan and synovial joint: function, distribution and healing. Interdiscip Toxicol. 2013;6(3):111-125. doi:10.2478/intox-2013-0019

  2. Pathria MN, Chung CB, Resnick DL. Acute and stress-related injuries of bone and cartilage: Pertinent anatomy, basic biomechanics, and imaging perspective. Radiology. 2016;280(1):21-38. doi:10.1148/radiol.16142305

  3. Frush TJ, Noyes FR. Baker’s cyst: Diagnostic and surgical considerations. Sports Health. 2015;7(4):359-365. doi:10.1177/1941738113520130

  4. Gupte C, St Mart JP. The acute swollen knee: diagnosis and management. J R Soc Med. 2013;106(7):259-268. doi:10.1177/0141076813482831

  5. Harvard Health Publishing. Persistent knee swelling in the adult.

  6. Patel DR, Villalobos A. Evaluation and management of knee pain in young athletes: overuse injuries of the knee. Transl Pediatr. 2017;6(3):190–198. doi:10.21037/tp.2017.04.05

  7. Martin CL, Browne JA. Intra-articular corticosteroid injections for symptomatic knee osteoarthritis: What the orthopaedic provider needs to know. J Am Acad Orthop Surg. 2019 Sep 1;27(17):e758-e766. doi:10.5435/JAAOS-D-18-00106

  8. Choi YJ, Ra HJ. Patient satisfaction after total knee arthroplasty. Knee Surg Relat Res. 2016;28(1):1–15. doi:10.5792/ksrr.2016.28.1.1

  9. Cleveland Clinic. Here’s how to choose between using ice or heat for pain.

  10. Bunt CW, Jonas CE, Chang JG. Knee pain in adults and adolescents: The initial evaluation. Am Fam Physician. 2018;98(9):576-585.

  11. Horowitz DL, Katzap E, Horowitz S, Barilla-LaBarca M-L. Approach to septic arthritis. Am Fam Physician. 2011;84(6):653-660.