Knee joint effusion - how dangerous is it?


A knee joint effusion is the pathological accumulation of fluid within the joint capsule. This fluid can be either synovial fluid (Synovial fluid), Blood (Hemarthrosis) or pus (Pyarthrosis) act.
The knee joint effusion is actually not an independent disease, but only a symptom. The effusion can occur after accidents or often in the context of osteoarthritis. Depending on the cause of the effusion, it should be treated with anti-inflammatory medication or with a small procedure in which the fluid is tapped off.

Causes of a knee joint effusion

In principle you can choose between one acute and one chronic Distinguish knee joint effusion. The acute knee joint effusion occurs quite suddenly as a result of a directly preceding event. Various traumas are possible triggers here, for example, frequent Cruciate ligament tears or Patellar luxation (Kneecap dislocation) the cause. But also Meniscus damage can explain an acute knee joint effusion. Bony injuries such as Damage to the kneecap can cause an effusion in the knee joint.

Recurrent, chronic knee effusion often occurs in the context of Infections and the associated inflammatory reactions of the body. The Synovial membrane (Synovium) is irritated here and reactively forms more synovial fluid. But also various rheumatic diseases or the arthrosisEspecially in the elderly, knee effusion can result. With younger people there are always excessive ones sporting loads considered as a reason. Also immediately after surgery on the knee a physiological swelling can occur as part of an effusion.

Knee joint effusion with no apparent cause

It happens again and again that a knee joint effusion occurs without an initially obvious cause. In this case, the development can be attributed to other diseases present, such as the presence of arthritis, arthrosis, gout or Infections. Especially in children, infections in the upper respiratory tract can lead to a so-called Reactive arthritis come, so an inflammation of the joint that is associated with an effusion. As a rare cause in children, especially with recurring joint effusions that hemophilia be excluded.
Most of these diseases result in an effusion of the knee. The acute effusion should also be treated therapeutically, but also the underlying disease in particular, as otherwise fluid accumulation can occur again and again.

Sometimes it is also possible that it is during pregnancy there is an effusion in the knee joint. This is within the general context of the Water retention possible. However, if the joint effusion does not recede after pregnancy or does not get better by putting the legs up, it is important to rule out other reasons.

An important distinction should be the presence of an effusion outside the joint cavity be considered. A swelling in the knee cannot only be due to a knee joint effusion, but also, for example, to a Bursitis or one bruise after accidents.

Appointment with a knee specialist?

I would be happy to advise you!

Who am I?
My name is dr. Nicolas Gumpert. I am a specialist in orthopedics and the founder of .
Various television programs and print media report regularly about my work. On HR television you can see me every 6 weeks live on "Hallo Hessen".
But now enough is indicated ;-)

The knee joint is one of the joints with the greatest stress.

Therefore, the treatment of the knee joint (e.g. meniscus tear, cartilage damage, cruciate ligament damage, runner's knee, etc.) requires a lot of experience.
I treat a wide variety of knee diseases in a conservative way.
The aim of any treatment is treatment without surgery.

Which therapy achieves the best results in the long term can only be determined after looking at all of the information (Examination, X-ray, ultrasound, MRI, etc.) be assessed.

You can find me in:

  • Lumedis - your orthopedic surgeon
    Kaiserstrasse 14
    60311 Frankfurt am Main

Directly to the online appointment arrangement
Unfortunately, it is currently only possible to make an appointment with private health insurers. I hope for your understanding!
Further information about myself can be found at Dr. Nicolas Gumpert

Knee joint effusion after a fall

If the knee swells after a fall on the knee, an effusion of the knee joint must be excluded using ultrasound or MRI. If the knee joint effusion is confirmed, however, a differentiation must be made as to whether it is a bloody effusion or whether it is only to be assessed as a normal swelling in the form of increased synovial fluid production. In the latter case, effective therapy can be initiated by applying the PECH rule.
This provides for: pausing with the load (P = break), cooling the swollen joint (E = ice), applying a bandage for compression (C = compression) and raising the affected leg (H = elevation).
A bloody effusion can indicate that vessels were injured by the fall. Then it is important to clarify the extent of the vascular injury and whether it may need surgical treatment. A knee puncture can be performed to relieve the swollen knee. However, in the case of moderate damage, it is usually sufficient to follow the PECH rule.

Knee joint effusion after knee surgery

Since the knee joint is a frequent surgical area in orthopedics, an effusion can be caused by the medical intervention.
As Complication of knee surgery can it to Injury to blood vessels come, whereupon a bloody effusion forms. Depending on the size, this should be drained through a puncture (i.e. piercing the joint with a hollow needle) in order not to provoke any delay in wound healing.
In addition to this undesirable effusion, an accumulation of fluid after an operation can be assessed as part of normal wound healing. The production of synovial fluid can be reduced after surgery as part of normal wound healing be increased in the first few days and can be accepted without hesitation as long as the joint effusion recedes after a few days.
If there is no decongestion and regression, a purulent knee joint effusion excluded by a Infection with bacteria during the operation or due to poor wound hygiene shortly after the operation arises. This is considered an extremely serious complication that needs to be treated immediately. In order to diagnose a possible infection, the knee joint effusion can be punctured and examined microbiologically. Usually blood tests also give an indication of an infection.

How dangerous is a knee joint effusion?

A knee joint effusion can usually be treated conservatively and should be reduced with cooling, immobilization and anti-inflammatory ointments. If the effusion does not go away despite this treatment, a doctor should be consulted to decide on further treatment.


A joint effusion manifests itself as a swelling of the knee, which also severely restricts the mobility in the knee joint.The pressure that the fluid builds up in the joint also causes pain, which is usually described as dull and indicated behind the kneecap.
If the knee joint is not only swollen but also overheated and reddened, this is a sign of inflammation. This can mainly speak for an infection of the joint after surgery, but without surgery it is an indication of a rheumatological disease or a metabolic disease (such as gout or pseudogout). Most often behind it is, above all, in older people, activated osteoarthritis (osteoarthritis attack). Depending on the underlying cause, other symptoms may also be present. You can find more information on this on our respective pages:

  • Acute knee pain - that may be behind it
  • Pain behind the kneecap
  • Inflammation in the knee
  • Meniscal tear
  • Symptoms of a torn cruciate ligament
  • Osteoarthritis attack
  • gout


Diagnosis of knee joint effusion

The diagnosis of a knee joint effusion is generally based on the physical exam. A particularly important sign here is the so-called "dancing patella (Kneecap) ". Since the effusion fluid is located directly under the kneecap, the examiner can snap back if he presses the kneecap vertically downwards ("rebound“) Perceive.
So that's the Joint effusion practically secured, whereby one must note that the sign only becomes positive when the liquid already has an amount of at least 10ml has reached.

In addition, there are of course other options for a Knee joint effusion to prove.
These include above all the classic imaging methods such as:

  • Ultrasonic
  • Roentgen,
  • computed tomography (CT of the knee)
  • magnetic resonance therapy (MRI of the knee).

If infection is suspected to be the cause of the knee joint effusion, a Microbiological examination the liquid from a Puncture and thus provide an indication of the exact cause.

The knee joint effusion can be seen in the X-ray not so good or not so obvious like in an MRI scan. Nevertheless, the accumulation of fluid can be seen in the X-ray as a shadow in the area of ​​the soft tissue around the bone.

In principle, if a knee joint effusion is suspected, it is more likely to occur Ultrasound examination indicated, since the suspicion can be confirmed or ruled out quickly and without radiation.
Since the X-ray is more for the Representation of bony structures is suitable, one can use the X-ray to assess bony injuries as the cause of a knee joint effusion. On the other hand, soft tissue, such as muscles and ligaments, and fluid accumulations can be better assessed in an MRI.

Assessment in the MRI

The MRI (Magnetic resonance tomograph) is suitable in addition to ultrasound as an imaging method for diagnosing knee joint effusion very good. The knee joint effusion can clearly be seen as an accumulation of fluid. It is located either behind the kneecap (patella), in the joint space or in the back of the hollow of the knee. If the volume of the knee joint effusion expands too much, the joint capsule in the hollow of the knee can expand, which is then referred to as Baker's cyst designated. With the MRI, you can usually already guess whether the problem is increased synovial fluid or serious accumulations of blood or pus in the knee joint.
In the MRI, however, not only the effusion itself can be determined, but also causes can be searched for. E.g. Capsule ruptures, Meniscus and cruciate ligament injuries or other injuries to the tissue around the knee joint.

You can find more information on this topic here: MRI of the knee


The therapy of a knee joint effusion is primarily carried out causalwhich means that the underlying disease is treated so that the effusion stays away in the long term.

Since the knee joint effusion is usually accompanied by pain due to swelling, the generally applicable one helps PECH rule: Break, ice, compression, elevation. Often an overload or a traumatic injury of the surrounding knee structures is the trigger for the effusion, so that the immobilization and protection in the form of Taking a break from exercise is a good approach to treatment. Using compression bandages in combination with cooling and pain relieving ointments the swelling can also be combated well. Elevation serves to ensure that the fluid escapes from the joint following gravity.

The knee joint effusion can be medicated anti-inflammatory ointments care that should be applied to the swelling. One is especially suitable for this Voltaren® ointment with the anti-inflammatory and pain reliever active ingredient Diclofenac.

The effusion should not be affected by these measures within a few days regress, a doctor should be consulted.

If the knee joint effusion is due to an infection with bacteria, antibiotic therapy must be given as soon as possible, otherwise the knee joint can be damaged forever.

Joint puncture and surgery

If those conservative approaches to treating knee joint effusion do not work, the fluid that has accumulated in the knee joint can be drained off as part of a joint puncture in order to alleviate the symptoms.
It is important to work in a sterile manner, as a needle is inserted directly into the joint and germs can be carried over into the joint when working in a non-sterile manner. This would be a fatal complication of the otherwise simple and safe procedure.
Before the effusion is punctured, the exact extent of the accumulation of fluid can be estimated with an ultrasound. The joint puncture ultimately offers 2 therapeutic approaches:

  • On the one hand, the effusion can flow away through the inserted needle
  • on the other hand, drugs such as the anti-inflammatory cortisone can be injected with the puncture needle. You can read more information about this here: Cortisone therapy for joint diseases

A surgical intervention is generally not necessary and is only necessary in rare, complicated cases to drain the effusion and to repair possible damage after bacterial infestation.

Read more about this at: Knee puncture

A physiotherapeutic follow-up treatment is useful for aftercare. In the case of minor injuries, a knee brace may also be useful to stabilize the joint after it has healed.
Depending on the severity of the cause of the knee joint effusion, healing after injuries, such as a cruciate ligament tear, can take between 6-12 weeks. During this time, the knee should be spared and not subjected to extreme loads.

You can read more information about this here: Knee school exercises

Home remedies for a knee joint effusion

In addition to the typical treatment approaches, experience has shown that many home remedies have also proven themselves. Since the knee joint effusion is often of inflammatory origin and is associated with swelling or redness, help Quark or clay wrap to relieve inflammation in the knee joint. To reduce overheating, a common symptom of knee effusion, a local cold application with ice packs respectively. They apply more and more frequently Schüssler® salts and as a homeopathic remedy the globules (e.g. Byronia alba, Rhus toxicodendron, Apis mellifica) as the home remedy of choice for the treatment of knee joint effusion.
Furthermore, it is a helpful one to reduce possible excess weight, as this significantly reduces the stress on the knee joint.