Ein junger Mann ist an einem Sandstrand und führt eine Yogaübung durch. Er trägt eine GenuTrain, eine Kniegelenksbandage von Bauerfeind, am linken Knie. Diese wirkt stabilisierend und aktivierend.

Is your knee swollen and unusually immobile? Does your knee hurt during bending and stretching? Then it is likely that fluid has pooled in the knee joint capsule. The reason for this may be knee joint effusion. It is often caused by an injury in the knee joint, such as a torn ligament or a dislocated kneecap. However, there may be other causes for your swollen knee. If appropriate treatment and relief of the knee are started early, acute knee joint effusion will fully heal.

What is knee joint effusion and what are the causes?

Illustration der Anatomie des Knies bei einem Kniegelenkerguss. Bei einem Kniegelenkserguss sammelt sich auffällig viel Flüssigkeit in der Gelenkkapsel an. Dabei handelt es sich um überschüssige Gelenkflüssigkeit, Blut oder Eiter.

Knee joint effusion predominantly affects the knee’s joint capsule. It is made up of two layers and surrounds all the knee joint surfaces. While the outer layer is responsible for the transmission of stimuli from the knee joint and brain, for example, the inner layer creates synovial fluid which supplies the knee joint with nutrients and acts like a shock absorber.


In the event of knee joint effusion, noticeably increased amounts of fluid pool in the knee joint capsule. This will be excessive synovial fluid, blood or pus. Physicians distinguish between acute and chronic knee joint effusion:

  • an acute infection is caused by bacteria or viruses, for example following surgery or an open injury.
  • In the event of chronic inflammation, injuries or damage to structures near or in the joint caused by excessive strain can be responsible.
  • If chronic inflammation occurs without a traumatic cause, autoimmune diseases may be the underlying reason. This is where the synovial membrane that lines the cavity of synovial joints is irritated and subsequently generates more synovial fluid.


In older patients, rheumatic diseases or osteoarthritis are often responsible for knee joint effusion. This is because degenerative joint wear impairs the knee joint function, resulting in recurring inflammation.

Symptoms of knee joint effusion

The first sign of joint effusion is severe swelling of the knee. At the same time, mobility is significantly restricted. The fluid in the knee causes significant pressure, which leads to pain that is often felt behind the kneecap. If the knee also turns red and feels hot, inflammation of the knee is likely.

We recommend consulting a physician if the swelling does not subside within a few days. It is important to act quickly, especially if the effusion has been caused by a bacterial infection. If left untreated, the joint may be permanently damaged.

Diagnosing joint effusion

A typical method for diagnosing knee joint effusion is with the patella tap test, otherwise known as “dancing patella” sign. During this test, the physician applies downward pressure on the kneecap. If the kneecap springs back afterwards, it means that the kneecap is swimming on the joint effusion. This provides a secure diagnosis of knee joint effusion.


During a different examination method, the fluid in the bursa above the kneecap is displaced, then the filled joint capsule is swiped or stroked. If there is joint effusion, a slight bulge will be visible on the outside of the knee joint.


Other diagnostics include imaging technology, such as ultrasound, X-ray, computed tomography (CT) or magnetic resonance imaging (MRI).

Joint effusion: how you can effectively support its reduction

If your knee is swollen because of joint effusion, elevating it will have a limited effect. Those affected should avoid excessive strain, but it is crucial to get moving again as quickly as possible. A GenuTrain support can help you with that. You can even wear it when your knee is swollen.


The GenuTrain reduces pain and stimulates metabolic processes and can therefore relieve your knee and accelerate the healing of the joint effusion. The support features a pad that distributes pressure from the joint to the surrounding tissue. During movement, the Train knitted fabric also exerts an intermittent compression massage. This reduces swelling, improves proprioception and stimulates the body’s own stabilization processes.

Ein junger Mann ist an einem Sandstrand und führt eine Yogaübung durch. Er trägt eine GenuTrain, eine Kniegelenksbandage von Bauerfeind, am linken Knie. Diese wirkt stabilisierend und aktivierend.


Would you like to know more about our Train supports and their effectiveness? Find out here how the GenuTrain can help you with your knee pain.


Discover our Train line now

You must be careful if the knee joint effusion was caused by excessive strain or a traumatic injury. In these cases, you should not subject your knee to strain and take a break from exercise. If the swelling is coupled with pain, cooling and pain-relieving creams can help. Make sure you ask your physician for advice.

Training for your knee

You can also do something beneficial for your knee at home: the Bauerfeind Treatment App will provide you with a personalized training program that is specifically adapted to your condition. Simple exercises will help you to strengthen your knee muscles with targeted movements, thus stabilizing and mobilizing your knee. This will reduce your pain in the long term. 

Download the app now

Darstellung der von Bauerfeind entwickelten Therapie-App mit Übungen für das Knie. Im Hintergrund ist die GenuTrain Kniebandage von Bauerfeind erkennbar.