Water on the knee

Water 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 an effusion (uh-FU-zhun) in your knee joint.

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 to test for infection, disease or 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.

Symptoms Causes Risk factors Complications Prevention

Signs and symptoms of water on the knee typically include:

  • Swelling. The flesh around your kneecap may puff up noticeably. This swelling is most apparent when you compare the affected knee to the normal one.
  • Stiffness. When your knee joint contains excess fluid, you may not be able to bend or straighten your leg completely.
  • Pain. Depending on the cause of the fluid buildup, the knee may be very painful — to the point that it's impossible to bear weight on it.

When to see a doctor

Seek prompt medical attention if:

  • Self-care measures or prescribed medications don't relieve the pain and swelling
  • One knee becomes red and feels warm to the touch as compared to your other knee

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