What can be examined?

The joint fluid obtained can first be examined purely visually for the presence of turbidity or coloration. This can provide indications of an inflammatory or traumatic process. In addition, the fluid can be analyzed to differentiate between an inflammatory and a non-inflammatory process with regard to protein content and cell number or cell types present.

For the diagnosis of rheumatic diseases, an immunological examination can also be performed to detect existing antibodies. A yellow liquid indicates that no ligaments have been injured. If the spot is yellow and cloudy, it is probably an inflammatory process.

However, if the fluid is clear and rather amber, this indicates a non-inflammatory cause, such as arthrosis. Arthrosis is a non-inflammatory wear and tear of the joint. A cloudy joint fluid indicates an inflammatory process.

This leads to an increase in inflammatory cells. The high cell density in the fluid leads to a cloudy appearance. An inflammatory change in the knee joint can occur as part of a rheumatic disease (especially psoriatic arthritis) or due to a bacterial infection, e.g. after surgery or knee arthroscopy.

An attack of gout also clouds the synovial fluid. A bloody synovial fluid suggests that ligaments in the knee joint have been injured. If the puncture is not only bloody but also covered with fat, this suggests that not only ligaments but also cartilage and bones have been injured. A bloody puncture can also be an indication of a capsule rupture or a blood clotting disorder. Even after an operation, the puncture is often bloody.

Risks

The risks of a knee puncture include infections. Bacteria enter the knee joint through the puncture. These are usually bacteria that are naturally found on the surface of the skin.

The most common bacteria are staphylococci (Staphylococcus aureus). They belong to our so-called physiological skin flora. If the skin is not sufficiently disinfected before a knee puncture, the bacteria can adhere to the syringe.

Thus, during the puncture they reach the knee joint where they cause a local inflammation. However, if the puncture site is disinfected sufficiently hygienically, the probability of such an infection can be greatly reduced, so that knee joint infections due to punctures occur only rarely. The term Hemarthros is composed of the two components Hem (Greek for blood) and Arthros (Greek for joint) and thus generally refers to a bleeding into a joint.

Hemarthros can be detected in knee punctures. In this case, blood cells can be found in the joint fluid. The cause is often traumatic (e.g. a torn meniscus or cruciate ligament).

Chronic hemorthrosis can be caused by a coagulation disorder. However, bleeding into the knee joint can also occur as a complication of knee puncture.If a small blood vessel is hit during the puncture, it can bleed into the joint space. In most cases, the body breaks down the blood quickly so that no serious symptoms occur.