Kneecap (prepatellar) bursitis–Swelling in the front of the knee caused by constant friction that irritates the bursa, the small lubricating sac located just in front of the kneecap (patella), and causes it to become inflamed. Affects people who kneel to work, such as plumbers, roofers, carpet layers, coal miners, and gardeners; athletes who receive blows to the knee or commonly fall on the knees; and people with rheumatoid arthritis or gout; can also result from a motor vehicle collision. Symptoms include pain with activity, rapid swelling on the front of the kneecap, and a feeling of being tender and warm to the touch.

 

Source: American Association of Orthopaedic Surgeons