Pitting Edema Explained . In this photo, I’m pressing my thumb into the lower leg of a patient recovering from knee surgery. Notice how the indentation stays for a few seconds before slowly filling back in — that’s called pitting edema. . Pitting edema is swelling caused by fluid buildup under the skin, often seen after surgery or when circulation is reduced. It’s common after a total knee replacement, especially if you’ve been sitting or standing for long periods. . The good news — movement, el