The knee is the largest joint in the human body and is suspended in a complex network of ligaments, tendons, cartilage and muscle. It can pivot, bend, twist, flex, push, rotate and thrust. Because of the stresses it endures, the knee is prone to injury. One of the most common symptoms of a knee injury is "water on the knee," or swelling around the knee joint. Knowing how to tell if you have fluid on the knee can help you make decisions about treatment.
Begin by standing in front of a mirror with your knees clearly in view. Make sure both of your legs are locked in the exact same position.
Examine the reflection closely, and look for swelling or puffiness around the kneecap or around the knee joint.
Sit on a bed with your knees bent loosely and your feet flat on the floor. Make sure your knees are exposed to view. Have a partner look at the knees and compare them and note any puffiness or swelling.
Move the knee back and forth, then move your unhurt knee back and forth. If there is fluid in the affected knee, the movement will feel sluggish and there might be a sense of numbness or thickness in the joint.
Press your finger into the suspected area of swelling. If there is fluid on the knee, there will be a slight indention for a moment after you release the pressure, whereas on a normal joint the skin bounces back immediately.
Having a second person to help you with this examination is a huge plus.
If you experience sharp, shooting pains in the knee during movement, you need to seek medical help right away.