Drainage of a joint is called arthrocentesis, and involves the use of a needle to draw out fluid contained within the joint space. Sometimes this fluid turns out to be blood; this may be the case in patients with bleeding disorders or traumatic injuries to the joint. However, in many other cases, it is regular non-bloody fluid that is drawn out of a joint; this fluid may be inflamed due to joint injury
, infection, auto-immune disease or crystal deposit disease.
In the case of the knee, your doctor
will have you lie or sit on the exam table. The knee will be prepped in a sterile fashion and then a local anesthetic such as lidocaine will be used to numb the skin where a larger needle will be inserted. Your doctor will insert the needle under the knee cap, and this can be done from either side. When the needle enters the joint space, a syringe can be used to pull off any excess fluid found in the joint space. This fluid can be analyzed under a microscope to help determine the cause of the fluid build-up. If the suspicion for infection is very low, then your doctor may choose to inject a combination of lidocaine and steroids into the joint at the time of this procedure, in order to help reduce pain and swelling.
For more information about your knee, I advise you to discuss this with your primary care physician
. Good luck!