What Causes Swelling In The Knees?

My husband's knee is swollen and painful on the front of the knee below the kneecap. More on the upper shin. I have been trying to research it online and I think it may be Bursitis. But everything I have found indicates that bursitis is on the kneecap itself. He is a roofer and is always on his knees, and refuses to go to a doctor. Do you have any suggestions? :)