Fluid on the knee, also called water on the knee, may result from excessive repetitive use of the knee or develop from an underlying health condition. If water on the knee becomes severe, swelling and pain can develop as symptoms. For most cases of fluid on the knee, treatment involves managing pain and removing excess liquid on a regular basis.
Biology
Water on the knee may occur in two places. Sometimes, the joint where the bones of the upper and lower legs connect may become filled with excess fluids. Alternatively, small fluid filled structures called bursae that cushion the area where tendons attach muscles to bone may become inflamed and overfull. This condition is often referred to as bursitis.
Causes
Fluid on the knee often stems from a problem with drainage of the lymphatic system or an overproduction of fluid, according to Dr. Andrew Weil, M.D. The lymph that cushions the knee may be blocked from draining properly by scarring or swelling of the tissues inside the knee. In people with osteoarthritis, the knee often overproduces synovial fluid. Repetitive use of the knee, such as from scrubbing floors, may also lead to swelling that allows excess fluid to collect in the bursae of the knee. Acute injury to the knee may also cause fluid to accumulate there, as often happens in the case of ACL injuries.
Symptoms
A knee that contains excess fluid may or may not be painful. Often, the knee feels tense and stiff. The afflicted individual may discover that he can no longer bend or straighten his knee properly. Swelling that results from water in the knee may cause one knee to look larger than the other. If an infection takes hold within the fluid, the knee may begin to feel warm and turn red.
Risk Factors
Advanced age is a risk factor for developing water on the knee, according to the Mayo Clinic. People older than 55 years old tend to develop the condition more often than younger individuals. Because knee injuries also can cause fluid buildup in the joint, sports that have a high rate of injury or involve rapid changes in direction that may affect the knee can put someone at risk. Obesity is another risk factor, especially since it not only puts extra wear and tear on the knee joint, but also because it ups the risk of developing osteoarthritis, which can lead to fluid on the knee.
Treatment
A common treatment for water on the knee is fluid aspiration, the removal of fluid through a long needle. According to the American Academy of Family Physicians, after aspiration, the fluid often returns, especially when the buildup is large, and the procedure must be repeated on a regular basis to maintain the normal functioning of the knee. Pain medications, including over-the-counter remedies and oral or injected corticosteroids, may be used to manage the pain involved with fluid on the knee. In extreme cases, doctors may perform surgical repair of damaged tissue or a replacement of the knee joint.
