The course of treatment a person with fluid on the knee should follow depends on the underlying cause of the swollen knee, its severity and the person's medical history, explains Mayo Clinic. Pain medication and removal of the fluid from around the knee joint are the usual forms of treatment.
If over-the-counter pain relief is insufficient to ease the discomfort of a swollen knee, a doctor may prescribe an oral pain medication, states Mayo Clinic. To treat inflammation, the physician may suggest an oral corticosteroid such as prednisone. Alternatively, a doctor may administer other steroids by injecting them directly into the knee joint. In order to treat the underlying cause of a swollen knee, a procedure such as arthrocentesis, arthroscopy or even joint replacement may be necessary.