Bursitis is the painful inflammation or irritation of the bursa. The bursa is a soft, fluid-filled sac that covers and cushions the movement between the bones, tendons and muscles near the joints.

Bursitis usually occurs under the shoulder muscles, at the elbows (called epitrochlear bursitis or "tennis elbow"), the hip sockets (called trochanteric bursitis), heel bones (called retrocalcaneal bursitis) or the kneecaps (called infrapatellar bursitis or "housemaid's knee"). It can also occur in the...