A swollen knee occurs when excess fluid accumulates in or around your knee joint. Some people call this condition “water on the knee.”
A swollen knee may be the result of trauma, overuse injuries, or an underlying disease or condition. To determine the cause of the swelling, your doctor might need to obtain a sample of the fluid to test for infection, disease or injury.
Signs and symptoms typically include:
Swelling: The skin around your kneecap can puff up noticeably, especially when you compare the affected knee to the normal one.
Stiffness: When your knee joint contains excess fluid, you might not be able to bend or straighten your leg completely.
Pain: Depending on the cause of the fluid buildup, the knee might be very painful to the point that it’s difficult or impossible to bear weight on it.