Clues in the Fluid

Practitioners have a variety of reasons for going into medicine, but most would probably admit to having a healthy enjoyment of exercising their "inner detective." Making a diagnosis is in many ways like solving a crime. What caused the symptoms, were there contributing factors (fall or co-existing illness), has it happened before, etc. One of the more satisfying procedures, from an orthopaedic perspective, is the removal or "aspiration" of fluid from a swollen joint – such as a knee. The patient generally presents with terrible pain and stiffness in the knee accompanied by significant swelling (known as an effusion). Sometimes there is trauma associated, but sometimes the patient will report going to bed feeling fine and waking up with an excruciatingly painful knee.

A careful history is taken from the patient by asking a series of questions, but the real treatment and diagnostic tool for this condition is to remove the fluid from the knee and send it to the lab for microscopic evaluation. This procedure is accomplished by using sterile technique to carefully clean the surface of the knee. The skin is numbed using a topical anesthetic, and a needle is inserted. Fluid is withdrawn into a syringe which is then sent to the lab for diagnostic evaluation.

If the needle is inserted correctly, the fluid pulses out of the knee into the syringe. Looking at the fluid is a key component of diagnosis. It is it the usual clear yellow color of joint fluid? Is blood present suggesting a traumatic tear of a ligament? Does the fluid appear cloudy or contain pus, consistent with an infection? Can small white particles be seen floating in the fluid that would tend to be present in an attack of gout? It's all in the fluid, and an astute practitioner will have a good idea what condition he is treating before the results come back from the lab – something that can't help but appeal to the Sherlock Holmes in us all.