Introduction
In case of a joint effusion in the knee, fluid accumulates in the knee joint. This is often synovial fluid, which is produced in excessive quantities by the joint mucosa (synovia). However, blood (haemarthros) or pus (pyarthros) can also accumulate in the knee.
The patients affected often complain of pain and restricted mobility of the knee. Joint effusion is not a disease in itself, but a symptom that can occur in the context of injuries, infections or other diseases of the knee joint. For this reason, therapy is usually focused on the underlying disease, i.e. the cause of the effusion.
Cause
The causes of a joint effusion in the knee can be mechanical or inflammatory in nature. A mechanical cause, especially in young patients, is overloading of the knee joint due to sports. In older people, however, joint effusion is often caused by wear and tear of the joint (arthrosis).
In many cases, however, articular effusion in the knee is a symptom of an injury, for example after a fall or an accident. Articular effusion can occur in the following injuries to the knee: Other mechanical causes can be gout crystals or bone tumors in the area of the knee joint. While effusions caused by wear and tear or overloading usually contain synovial fluid, injuries often result in a bloody joint effusion.
Inflammation-related causes include rheumatic diseases and various other forms of arthritis. But bacterial infections can also cause joint effusion in the knee, in which case it is often a purulent effusion.
- Damage of the meniscus
- Cruciate ligament rupture
- Tear of inner or outer belts
- Fracture of the kneecap, tibial head or femur
- Contusion, sprain or twist (distortion)
- Even after an operation on the knee, effusion may continue to occur for a long time.
Symptoms
A joint effusion in the knee is externally manifested by a swelling of the knee joint, through which the contours of the joint appear to have elapsed. As a rule, the mobility of the joint is limited, so that some patients can hardly bend or stretch the knee. In addition, affected patients usually complain of pain in the joint.
If there is an inflammatory cause for the joint effusion, the typical symptoms of an inflammation can also occur: The knee is then reddened and overheated. The diagnosis is based on a detailed interview with the patient (anamnesis), which provides the doctor with information about possible causes of the symptoms. The subsequent physical examination plays an equally important role.
During this examination, the mobility of the joint is checked and various functional tests are performed to look for indications of an injury to the ligaments or menisci as a possible cause of the effusion. A larger joint effusion in the knee can be reliably diagnosed by the so-called “dancing patella phenomenon”: The doctor spreads the joint fluid above and below the knee joint and then presses the kneecap (patella) against the thigh with the index finger. If he feels a springy resistance, this indicates a joint effusion, since the patella “floats” on the excess joint fluid.
However, lower effusions of a few milliliters can only be detected by the so-called “bulge sign”: When lateral pressure is applied underneath the patella, a bulge becomes visible on the other side, which spreads out as a small wave when lightly tapped. In many cases it is useful to use additional imaging techniques. In ultrasound, X-ray and MRI of the knee, the fluid in the joint is clearly visible.
In addition, the MRI images often provide information about the cause of the joint effusion, such as an injury. If the cause of the joint effusion in the knee remains unclear, a knee puncture is usually performed. This relieves the joint by reducing the amount of fluid in the knee.
On the other hand, the biochemical examination of the fluid obtained can provide information about the cause. In the case of an inflammatory joint effusion, for example, a large number of white blood cells and protein are found in the synovial fluid, whereas bacteria can be detected in the case of an infection. Small crystals in the fluid, on the other hand, indicate a gouty arthritis as the cause.
To visualize the fluid in the knee, an ultrasound of the knee is usually sufficient. Imaging procedures such as MRI of the knee joint and X-rays also show the joint effusion well.However, they are more likely to be used when it is unclear where the joint effusion comes from. X-ray of the knee joint is particularly suitable for imaging the skeletal structure and thus the structure of the knee joint.
Bone fractures or splinters caused by accidents or trauma can be made visible. In addition, cartilage damage in the knee joint, e.g. destroyed or worn cartilage such as occurs in knee arthrosis, can be depicted. In addition, arthrosis (a joint disease caused by damaged cartilage) becomes noticeable by a narrowed joint space, which is also recorded in an X-ray.
The X-ray of the knee is usually taken in a standing position, so that the joint is shown under the greatest and also natural load. If ligament structures, soft tissue in the knee joint and surrounding soft tissue or damage to the menisci are the reason for the joint effusion in the knee, they can be easily visualized with the help of MRI. It allows a three-dimensional representation of the knee joint and is suitable for early detection of defects in the bone structure. The MRI therefore has an advantage over X-rays, but it is also more cost and time intensive. However, MRI is also a selective procedure that is used for specific problems.
