What Is Joint Effusion?

Causes and Treatment of Abnormal Joint Swelling

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Joint effusion is a condition in which excess fluid accumulates in or around a joint, usually the knee. It is commonly referred to as water on the knee or fluid on the knee.

The condition is most often caused by infection, injury, or arthritis. In addition to swelling, the excess fluid can also result in pain and stiffness.

Effusion tends to affect the larger joints such as the knee, shoulder, elbow, or ankle. It is not the same as edema, a different type of swelling caused by inflammation, allergy, heart failure, and other conditions.

Read on to learn more about joint effusion, its causes and symptoms, and what treatments are available.

common joint effusion symptoms

Verywell / Emily Roberts

Joint Effusion Symptoms

Regardless of what is causing fluid in your joint, the symptoms are similar, though their severity can vary. Classic symptoms of joint effusion include:

  • Swelling: Ranging from a mild puffiness to severe swelling
  • Pain: Ranging from a dull throb to sharp pain that interferes with movement
  • Stiffness: Limiting a joint's range of motion or restricting movement entirely
  • Redness and warmth: Associated with inflammation

Depending on what is causing your joint effusion, you could have other symptoms such as:

  • Bruising and bleeding in the joint space (caused by an injury)
  • Fever, chills, malaise, and weakness (if infection is present)
  • Progressive muscle loss (from long-term arthritis, also called arthrogenic muscle inhibition)

A common complication of a joint effusion is the formation of the fluid-filled nodule, known as a Baker's cyst, in the joint space. It is caused when the amount of joint fluid is so excessive that it cannot be reabsorbed by the body. While a smaller Baker's cyst may not cause symptoms, larger ones can sometimes be felt and cause pain with movement.


Effusion is a sign of joint inflammation, and can be broadly classified as either infectious (septic) or non-infectious (aseptic). Joint effusion caused by infection is called "septic arthritis." Aseptic joint effusion can be the result of an injury or arthritis.


Septic arthritis is most commonly caused by an infection in the joint. Infection can come from from a wound, like a deep injury or medical procedure. An infection in the bloodstream—also called a systemic infection—can take hold in a joint and cause swelling and excess fluid.

When caused by an infection, the symptoms usually are intense and come on quickly. The effusion is usually extremely painful, particularly with movement.

Certain conditions can increase your risk of developing septic arthritis, including:

  • Older age
  • Diabetes
  • Intravenous (IV) drug use
  • Joint replacement
  • Recent joint surgery
  • Arthritis
  • A weakened immune system (such as those with advanced HIV infection, organ transplant recipients, or patients undergoing chemotherapy)

Fungal, viral, and parasitic causes are most commonly associated with a weakened or suppressed immune system.


A sports injury is a common cause of joint effusion, especially of the knee. Injuries—such as those from a car accident, serious fall, or blunt force impact—can also lead to an effusion. The injury may involve bone, connective tissues (such as tendons and ligaments), or joint cartilage (like the meniscus).

Repeated stress on a joint can also cause effusion. This type of injury happens after repeating a movement over and over, and is usually related to an occupation or a sports activity.

In people with joint effusion from repetitive stress injuries, bursitis (the inflammation of the fluid-filled sac that cushions a joint) and tenosynovitis (inflammation of the tendon sheath where a muscle attaches to a bone) are also common.

Pain, swelling, stiffness, and difficulty extending or rotating the joint are common symptoms of injury-related effusion.


In patients with arthritis, fluid buildup and joint swelling are common. Arthritis can be ongoing (chronic) or cause sudden (acute) episodes of inflammation, which can lead to edema.

Generally speaking, there are two types of arthritis:

With osteoarthritis, joint effusion primarily affects the knee and is most commonly associated with extensive joint damage. With autoimmune arthritis, joint effusion may be associated with either chronic inflammation or acute flare-ups (known as attacks or exacerbation).

Attacks are especially common with gout, an autoimmune disorder characterized by the accumulation of uric acid crystals in the joint space (mostly the big toe). Gout symptoms can be severe and appear rapidly, and can result in extra fluid around the joint.


Joint effusion can be caused by arthritis, injury, or even an infection. Symptoms are similar no matter what the cause.


Diagnosing a joint effusion may involve a physical exam, imaging tests, and a lab evaluation of the fluid in your joint. In addition, the healthcare provider will also review your medical history, current health, and other symptoms.

Physical Examination

Your healthcare provider will examine your joint thoroughly. They will touch (palpate) and bend (manipulate) the joint, which can reveal a lot about what is causing the effusion. For example:

  • With arthritis, the lubricating tissue between the joints, called the synovium, will feel "boggy" or "mushy." With the exception of gout, the swelling from most types of arthritis will be gradual rather than swift.
  • Joint infections tend to develop rapidly and cause excessive pain and redness.
  • Acute swelling accompanied by the inability to bear weight may suggest a torn ligament or fracture of the knee.

The healthcare provider will also determine whether a Baker's cyst has developed.

Imaging Tests

After examining your knee, the healthcare provider may order imaging tests to determine the exact cause of the effusion. Each test has its benefits and limitations. Tests can include:

  • Ultrasonography uses sound waves to visualize bone and connective tissues. It can be used to confirm arthritis or the inflammation of tendons or ligaments. However, it is less able to visualize soft tissues than other forms of imaging.
  • X-rays and computed tomography (CT) scans, both of which use ionizing radiation, are best suited for diagnosing bone fractures and arthritis.
  • Magnetic resonance imaging (MRI), uses magnetic fields and radio waves. MRI is used to visualize soft tissue, cartilage, and joint structures that the other tests can't. It sometimes involves the use of an IV contrast agent to help see certain tissues better.

Joint Fluid Analysis

Your healthcare provider may want to drain (aspirate) fluid from your swollen joint. This will help reduce pressure and relieve some pain.

The fluid, known as synovial fluid, is removed during a procedure called an arthrocentesis. Your healthcare provider will look at the fluid, and may also choose to send a sample to a lab for analysis.

Synovial fluid will usually be clear and have the viscosity of an egg white. Any changes in its appearance, texture, and cellular composition can provide clues as to the underlying cause of joint effusion.

Synovial fluid can provide valuable information include:

  • Cloudy fluid may suggest rheumatoid arthritis due to an increase in white blood cells (generally over 10,000 per cubic millimeters).
  • Yellow-green fluid may suggest an infection, particularly if the white blood cell count is greater than 20,000 per cubic millimeter. Traces of pus may also be seen.
  • Golden fluid is commonly associated with gout. Microscopic examination may also reveal needle-like uric acid crystals.
  • Bloody or pink fluid can indicate blood, a classic sign of a joint injury.
  • Clear fluid is typically seen with osteoarthritis since it doesn't involve any inflammation. The WBC will usually be below 2,000.

If an infection is suspected, the lab may also perform a culture to grow and identify the responsible bacteria or fungus.

Diagnosing joint effusion often involves both a physical exam and imaging tests, like ultrasound, x-rays and even MRI scans. Your healthcare provider may drain fluid from your knee to examine and send to the lab for analysis.


The standard first-line treatment for fluid on a joint includes rest, ice application, immobilization, and a non-steroidal anti-inflammatory drug (NSAID) like Advil (ibuprofen) or Aleve (naproxen).

If your swelling is especially severe, your healthcare provider may drain fluid as part of your treatment. They may give you a cortisone injection after the procedure. This can quickly reduce pain and inflammation, particularly if there is a severe injury or joint damage from arthritis.

Infections can usually be treated with a 14-day course of a broad-spectrum oral antibiotic such as ciprofloxacin. Other more serious types, like those caused by systemic gonorrhea or methicillin-resistant Staphylococcus aureus (MRSA), may require between a two- and four-week course of IV antibiotics.

If you have rheumatoid arthritis or another form of autoimmune arthritis, steps can be taken to control your condition. This can involve the use of immune-suppressive drugs, like methotrexate and Humira (adalimumab), aimed at reducing the abnormal immune response.

Arthroplasty (joint surgery) is reserved for serious joint injuries or to repair joints immobilized by arthritis. Severe cases may require joint replacement.


While joint effusion can’t always be avoided, there are things you can do to significantly lower your risk:

  • Lose weight. This can reduce stress on the hips and lower extremities.
  • Start a low-impact exercise plan. If you're experiencing pain in the knee, hip, or ankle, avoid high-impact activities like heavy weightlifting or deep squats.
  • Use resistance training to strengthen muscles in and around your joint. This may include using a leg extension machine for the knees or resistance band training for the shoulder and rotator cuff.
  • Stretch. Perform gentle knee and shoulder stretches before exercise or throughout the day if you're sitting at a desk for a long period of time.
  • Support your joints. Use an elastic knee support or elbow brace during contact sports, hiking, or other activity.
  • Don't over-do it. Never exceed your physical capabilities, especially as you get older. This may involve changing the types of sports you engage in (such as switching from running to cycling), or even using a stool for hard-to-reach items.
  • Listen to your body. If you experience any sudden or persistent joint pain, get it checked by a healthcare provider sooner rather than later.


Excess fluid around a joint—called an effusion—affects larger joints, such as the knee. A joint effusion can occur as a result of injury, infection, or different types of arthritis.

In many cases, fluid can be drained, and steps taken to address the cause (such as antibiotics for an infection). Regardless of what is causing your joint effusion, there are steps you can take to avoid future episodes and improve your joint health.

A Word From Verywell

Joint pain can be frustrating, especially when it limits your regular activity. If you experience fluid buildup in a joint (like the knee, shoulder, elbow, or ankle), talk to your healthcare provider right away to determine the cause. Postponing treatment can result in long-term damage to your joints and tissues.

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13 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.
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Additional Reading
  • Gupta C, St. Mart J. The acute swollen knee: diagnosis and management. J Royal Soc Med. 2013; 106(7):259-68. doi:10.1177/0141076813482831

  • Marx J. Rosen's Emergency Medicine: Concepts and Clinical Practice (7th Edition). Philadelphia, Pennsylvania: Mosby/Elsevier; 2010. ISBN 978-0-323-05472-0.