I have fluid in my knee and it is swollen and painful, but I have heard that the pain will stop after the fluid is removed.

There are generally strict indications for arthrocentesis, as there is a risk of joint infection following puncture, and joint infection can be devastating to the joint. The decision to aspirate joint fluid should be made in person at a local hospital after assessment by a specialist orthopaedic or rheumatologist. Small amounts of joint fluid from low-energy injuries are usually self-absorbing and do not need to be aspirated.