The accumulation of fluid within a joint, such as the knee joint. Joint effusion may be caused by trauma, infection, gout, or arthritis. The resulting swelling may cause pain and restricted movement in the affected area. The escaped fluid is usually reabsorbed by the body within 1 t o 2 weeks, after which the symptoms of joint effusion improve. Sometimes, withdrawing the fluid with a fine needle (aspiration) is necessary for analysis or to help relieve pressure.
Increased fluid within a joint cavity. There may be increased production of synovial fluid following trauma, with some arthritic disease processes, or blood accumulating in the joint following trauma or surgery or due to hemophilia. Excessive amounts of synovial fluid, pus, or blood accumulate in many arthritic diseases (such as gout or rheumatoid arthritis), after trauma, in joint infections, following joint surgery, or in hemophilia.