Arthrocentesis involves the use of a puncture needle to enter the joint cavity to extract joint fluid for testing or to inject medication after the fluid has been extracted. Septic arthritis often requires a drainage and irrigation tube to be placed in the joint cavity by arthrocentesis, followed by continuous irrigation and drainage with an antibiotic solution to control the infection in the joint and eliminate the germs. The surgeon will inject local anaesthetic as appropriate before the procedure and it will not be particularly painful.