A knee joint effusion is the pathological accumulation of fluid within the joint capsule. This fluid can be either synovial fluid, blood (haemarthros) or pus (pyarthros). The knee joint effusion is not actually an independent disease, but only a symptom. The effusion can occur after accidents or often as part of arthrosis. Depending on the cause of the effusion, it should be treated with anti-inflammatory medication or a minor procedure in which the fluid is punctured.
Causes of knee joint effusion
In principle, one can distinguish between an acute and a chronic knee joint effusion. An acute knee joint effusion occurs quite suddenly as a consequence of a directly preceding event. This can be triggered by various traumas, such as torn cruciate ligaments or patella dislocation (dislocation of the kneecap).
But also meniscus damage can explain an acute knee joint effusion. Bony injuries, such as damage to the patella, can also cause an effusion in the knee joint. A recurrent, chronic knee joint effusion is often caused by infections and the associated inflammatory reactions of the body.
The joint mucosa (synovialis) is irritated and reactively produces more synovial fluid. But also various rheumatic diseases or arthrosis, especially in older people, can lead to knee joint effusion. In younger people, excessive physical exertion is always a possible cause.
Even immediately after knee surgery, physiological swelling can occur as part of the effusion. Again and again, it happens that a knee joint effusion occurs without an initially obvious cause. In this case, the development can be due to other existing diseases, such as arthritis, arthrosis, gout or infections.
Especially in children, infections in the upper respiratory tract can lead to so-called reactive arthritis, i.e. an inflammation of the joint that is accompanied by a joint effusion. As a rare cause, haemophilia should be excluded in children, especially in the case of recurrent joint effusions. In most cases, these diseases cause a knee joint effusion as a consequence.
Therapeutically, the acute effusion should also be treated, but especially the underlying disease, since otherwise fluid accumulation can occur again and again. In some cases, it is also possible that an effusion may occur in the knee joint during pregnancy. This is possible within the general context of water retention.
However, if the joint effusion does not recede after pregnancy or does not improve by putting the legs up, it is important to rule out other reasons. As an important distinction, the presence of an effusion outside the joint cavity should be considered. A swelling in the knee can not only be caused by an effusion of the knee joint, but also by an inflammation of the bursa or a bruise after an accident.
If the knee is swollen after a fall on the knee, an ultrasound or MRI must be used to rule out a knee joint effusion. If the knee joint effusion is confirmed, however, it must be differentiated whether it is a bloody effusion or merely a normal swelling in the form of increased synovial fluid production. In the latter case, an effective therapy can be initiated by applying the PECH rule alone.
The therapy consists of: pausing the load (P=Pause), cooling the swollen joint (E=Ice), applying a compression bandage (C=Compression) and elevating the affected leg (H=High support). A bloody effusion can be an indication that vessels were injured by the fall. It is then important to clarify the extent of the vascular injury and whether it may require surgical treatment.
To relieve the swollen knee, a knee puncture can be performed. However, if the damage is moderate, it is usually sufficient to follow the PECH rule. Since the knee joint is a frequent surgical area, especially in orthopedics, the medical intervention may cause an effusion.
As a complication of knee joint surgery, blood vessels may be injured, resulting in a bloody effusion.Depending on its size, it should be drained by puncture (i.e., by piercing the joint with a hollow needle) in order to avoid delaying the healing of the wound. In addition to this undesirable effusion, fluid accumulation after surgery can be evaluated in the course of normal wound healing. The production of synovial fluid can be increased in the first few days after surgery as part of normal wound healing and can be accepted without hesitation as long as a reduction in joint effusion is seen after a few days.
If there is no decongestant and receding swelling, purulent knee joint effusion should be ruled out, which is caused by an infection with bacteria during the operation or due to a lack of wound hygiene shortly after the operation. This is considered an extremely serious complication that must be treated immediately. To diagnose a possible infection, the knee joint effusion can be punctured and microbiologically examined. In most cases, however, blood tests also give an indication of an infection.
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