Definition
By Mayo Clinic staffWater on the knee is a general term for excess fluid accumulation in or around your knee joint. Your doctor may refer to this condition as a knee "effusion."
Water on the knee may be the result of trauma, overuse injuries, or an underlying disease or condition. To determine the cause of water on the knee, your doctor may need to obtain a sample of the fluid for testing. If the fluid contains crystals, you might have gout or pseudogout. Bacteria indicates an infection, and blood suggests traumatic injury.
Removing some of the fluid also helps reduce the pain and stiffness associated with water on the knee. Once your doctor determines the underlying cause of your water on the knee, appropriate treatment can begin.
- Frequently asked questions about osteoarthritis of the knee. American Academy of Orthopaedic Surgeons. http://orthoinfo.aaos.org/topic.cfm?topic=A00228. Accessed Jan. 18, 2010.
- Johnson MW. Acute knee effusions: A systematic approach to diagnosis. American Family Physician. 2000;61:2391.
- Mathison DJ, et al. Approach to knee effusions. Pediatric Emergency Care. 2009;25:773.
- Knee problems. National Institute of Arthritis and Musculoskeletal and Skin Diseases. http://www.niams.gov/Health_Info/Knee_Problems/default.asp. Accessed Jan. 18, 2010.

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