A bursa is a sac-like structure found over large joints. Ordinarily, these sacs are empty and you’d never know they’re there. However, they do serve a useful purpose. They allow the skin, muscles, tendons and other surrounding structures to move smoothly as the joint moves.

A bursa may become painful or inflamed (a condition called bursitis) for a number of reasons. The most common cause is overuse. But often bursitis develops for no apparent reason. It typically happens without swelling. When there is swelling, your doctor would consider other causes including trauma, infection (septic bursitis) or gout.

The knee actually has several bursae. The prepatellar bursa (which lies directly over the kneecap) and the anserine bursa (located just below the knee joint toward the inside) are the most common ones to cause pain. Bursal swelling over two years is unlikely to be related to infection or gout. Although bursal swelling from moderate exercise is unusual, it could be due to the trauma or overuse of the knee during exercise.

Reasonable first approaches include changing the way that you exercise, pain relievers or anti-inflammatory medicine.

It might be helpful to get a cortisone shot or other treatment. But your doctor would first want more information, including a detailed review of your symptoms, physical examination, X-rays and a sample of the fluid from the bursa.

Finally, it is unlikely that bursitis of the knee will lead to knee degeneration since bursae that most often cause problems do not communicate with the joint itself. Bursitis on its own does not lead to arthritis. However, there are conditions, such as rheumatoid arthritis, that may be associated with both arthritis and bursitis, But with your only problem being inflammation of a single bursa, this does not sound like it applies to you.