Inside the body, bursa are sacs filled with a lubricating fluid. They reduce friction between different tissues and provide a cushion against pressure. Bursa are found between bodily structures like bones, tendons, muscles or skin. In every human body, there are approximately 160 bursa.
If the fluid within a bursa becomes inflamed, a painful condition called bursitis may occur. Bursitis is more common in adults over the age of 40 and commonly affects areas with bones and rotating joints. Problematic areas include the shoulder, elbow and hip. The knees, which contain a collective total of 22 bursa, are also common sites of bursitis.