What Causes Water on Your Knee?

What does it mean if you have water on your knee? You may have heard this expression tossed around and wondered what it means – or you may have been unfortunate enough to be told by your doctor you have water on your own knee. Find out what this commonly used expression means.

Water on the knee is a term used to describe fluid accumulation around the knee joint from any cause. It’s not a specific medical condition in and of itself. Fluid or water on the knee can come from a variety of causes – some of which are serious. Here are some of the most common reasons you can have water on your knee.

Causes of Water on Your Knee: It Can Come From a Knee Injury

If you tear the ligaments or cartilage in your knee while playing sports, especially when changing directions suddenly, you may get sudden knee swelling and the accumulation of fluid in the knee joint. If you tear a ligament, the swelling usually appears within six hours of the injury, and you may hear an audible “pop” when the ligament tears – followed by substantial pain and difficulty bearing weight on the knee. In this case, water on the knee comes from fluid leaking from damaged blood vessels.

When a cartilage or meniscus tears, you can also hear a “pop”, especially if it occurs due to injury, but, in other cases, the symptoms are more gradual with progressively worsening knee pain and swelling. The knee may “lock up”, making it difficult to straighten out the leg completely. It may be difficult to squat or kneel with a torn meniscus.

Water on Your Knee Not Due to Injury

There are other knee problems can cause water on your knee in the absence of an injury. The most frequent cause of fluid on the knee unrelated to injury is osteoarthritis. With this very common cause of knee pain and swelling, the knee feels stiff and painful, especially in the morning. Other forms of arthritis like rheumatoid arthritis can cause painful swollen knees too.

Another frequent cause of water on the knee is bursitis, which often affects carpenters and people who spend time on their knees. Bursa are thin sacs filled with a lubricating fluid that are nestled between a bone and a tendon. The bursa helps to cushion the space between bone and tendon and reduce friction as the two structures glide past one another. Unfortunately, a bursal space can also become inflamed. When they do, fluid accumulates around the knee, which is usually worse when kneeling. If bursitis of the knee doesn’t resolve, a doctor can remove the fluid using a needle and a syringe in their office.

Other less common causes of water on your knee include gout, tumors, cysts and a condition called pseudogout.

The Bottom Line?

If you have water on your knee, see a doctor, especially if the swelling came on while playing sports or after an injury. If you suspect a torn meniscus or ligament in the knee, keep the knee elevated, apply ice and see your doctor right away.

References:

EMedicine. “Knee Injury – Soft Tissue”

Merck Manual. Eighteenth edition. 2006.