<P> When the knee joint contains excess fluid, it may become difficult or painful to bend or straighten . Fluid may also show under the knee when straightened . Icing may help to decrease swelling . Heat may help relax the muscles of the knee . </P> <P> If an individual has injured his or her knee, he or she may note bruising on the front, sides or rear of the knee . Bearing weight on the knee joint may be impossible and the pain unbearable. bruising may be seen as bluish lesion . </P> <P> Causes of the swelling can include arthritis, injury to the ligaments of the knee, or an accident after which the body's natural reaction is to surround the knee with a protective fluid . There could also be an underlying disease or condition . The type of fluid that accumulates around the knee depends on the underlying disease, condition or type of traumatic injury that caused the excess fluid . The swelling can, in most cases, be easily cured . </P> <P> Underlying diseases may include </P>

Where does fluid on the knee come from