This protocol describes arthrocentesis of the knee, a procedure in which a needle is inserted into the knee joint and synovial fluid is aspirated. An arthrocentesis can be diagnostic or therapeutic. Synovial fluid may be removed for testing to determine the nature of the effusion.
Removing fluid from a knee can decrease pain. With the patient in a supine position carefully palpate the knee to locate the patella and use a skin marker to make marks at the four corners of the patella. Place an X using a skin marker at the site that is one finger breath, superolateral to the patella and avoid infected skin and visible veins.
If a large effusion is detected on examination and the patella appears to be sitting on fluid, consider a medial approach just posterior to the patella. Clean the selected needle entry site with three iodine soaked, two by two inch gauze sponges. Allow the antiseptic to dry.
Place the nondominant hand over the area superomedial to the patella and gently, manually compress the fluid laterally. Insert a 1.5 inch 18 to 22 gauge needle attached to the syringe along the anesthetized pathway. Advance the needle slowly and pull the plunger back gently until the visualization of synovial fluid.
If the first syringe fills up and further aspirated fluid is desired, switch to another syringe. Remove the needle and syringe in one smooth withdrawal motion, then place a sterile dressing over the site and apply pressure until any bleeding stops. Once hemostasis is achieved, apply a bandage after wiping the skin marker and iodine off with an alcohol pad.
A comparative study of complete aspiration of synovial fluid from the knee and intraarticular injection with corticosteroid alone demonstrated that aspirating as much synovial fluid as possible can reduce the risk for recurrence of arthritic symptoms when treating rheumatoid arthritis patients with intraarticular corticosteroids. A retrospective chart review of arthrocentesis and joint injections comparing the incidence of clinically significant bleeding in patients receiving Warfarin and those whose anticoagulation was adjusted to an international normalized ratio, less than 2.0, did not show a statistically significant difference in bleeding. The most important thing to remember is to advance the needle slowly while pulling the plunger back until synovial fluid is visualized.
The hand should be steady. Following this procedure, the synovial fluid can be sent for cell count, crystal, Gram stain and culture. This can help to diagnose the etiology of the knee effusion.
This technique enables viewing cells, crystals, or bacteria in the synovial fluid under microscopy to evaluate for inflammation and for infection. By aspirating synovial fluid from the knee, I can alleviate the patient's pain and diagnose the etiology of the swelling. This can help prevent recurrence of the arthritis.
