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Swollen knee

Medically reviewed by Last updated on Jun 16, 2022.


A swollen knee occurs when excess fluid collects in or around your knee joint. Health care providers might refer to this condition as an effusion (uh-FU-zhun) in your knee joint.

A swollen knee may be the result of trauma, overuse injuries, or an underlying disease or condition. To find the cause of the swelling, your provider might need to test a sample of the fluid for infection, disease or blood from an injury.

Removing some of the fluid may help reduce the pain and stiffness associated with the swelling. Once the underlying cause is known, treatment can begin.


Signs and symptoms typically include:

When to see a doctor

See your health care provider if self-care measures, such as ice and rest, don't improve symptoms. Seek immediate medical attention if one knee becomes red and feels warm to the touch compared with your other knee. This can be a sign of infection within the joint.


Many types of problems, ranging from traumatic injuries to diseases and other conditions, can cause a swollen knee.


Damage to any part of your knee can cause excess joint fluid to accumulate. Injuries that can cause fluid buildup in and around the knee joint include:

Diseases and conditions

Underlying diseases and conditions that can produce fluid buildup in and around the knee joint include:

ACL injury

The anterior cruciate ligament (ACL) is one of the key ligaments that help stabilize the knee joint. The connects the thighbone (femur) to the shinbone (tibia). It's most commonly torn during sports that involve sudden stops and changes in direction — such as basketball, soccer, tennis and volleyball.

Torn meniscus

The meniscus is a C-shaped piece of tough, rubbery cartilage that acts as a shock absorber between the shinbone and the thighbone. It can be torn if you suddenly twist your knee while bearing weight on it.

Risk factors

Factors that may increase your risk of a swollen knee include:


Complications of a swollen knee can include:


A swollen knee is typically the result of an injury or chronic health condition. To manage your overall health and prevent injuries:


Your health care provider is likely to start with a detailed history and physical examination. After that you likely will need tests to find out what's causing your swollen knee.

Imaging tests

Imaging tests can help show where the problem is located. Options include:

Joint aspiration (arthrocentesis)

A needle is used to remove fluid from inside your knee. This fluid is then checked for the presence of:


Treatment varies depending on the cause of the swollen knee, its severity and your medical history.


Physical therapy exercises can improve your knee's function and strength. In some situations, a knee brace may be helpful.

Surgical and other procedures

Treating the underlying cause of a swollen knee might require:

Self care

Taking care of yourself when you have a swollen knee includes:

Preparing for your appointment

You may be referred to a health care provider who specializes in musculoskeletal and joint problems.

What you can do

Questions to ask your doctor

What to expect from your doctor

Your health care provider is likely to ask you a number of questions. Being ready to answer them may leave time to go over points you want to discuss in depth. You may be asked:

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