What is the definition or description of: arthrocentesis?

Removing fluid: Arthrocentesis usually involves inserting a needle into the joint to remove fluid. This may be done to remove a hematoma or to investigate the fluid to see if it is infected or contains chemical markers that may be indicative of joint diseases (like rheumatoid arthritis). It's not uncommon for medicine, like corticosteroid (the proverbial "cortisone shot") to be inserted through the needle.

Draining joint: Draining fluid from a joint.

Arthrocentesis: Arthrocentesis is the medical term for putting a needle into a joint. This is done to either draw fluid off of the joint or to put medication into the joint.