BronxCare Health System 1 article published in JoVE Medicine Knee Arthrocentesis in Adults Arlene Tieng1, Giovanni Franchin1 1Department of Medicine, BronxCare Health System Here the protocol describes arthrocentesis of the knee, a procedure in which a needle is inserted into the knee joint, and synovial fluid is aspirated. Synovial fluid may be removed for testing to determine the nature of the knee effusion. Arthrocentesis of the knee is typically performed with the patient supine.