Also known as Prepatellar Bursitis.
The points of contact between your bones, tendons and ligaments are cushioned by small fluid-filled sacs called bursae (singular: bursa). When a joint is overused or injured, these bursae can swell up with extra fluid. As a result, they may push against the inner tissues within the joint, causing pain, inflammation, tenderness, and swelling known as bursitis. Since it most often affects those who are on their feet and kneel often, the condition is often called "Housemaid's Knee". If bursitis is left untreated, it can lead to pain and inflammation in the soft tissues, which may restrict the motion in that knee and cause pain when it is moved, and bone spurs.