Bursae are small, fluid-filled sacs that lubricate and cushion pressure points between your bones and the tendons and muscles near your joints Bursitis occurs when a bursa becomes inflamed. When inflammation occurs, movement or pressure is painful. Bursitis often affects the joints in your shoulders, elbows or hips as well as your knee, heel and the base of your big toe. Bursitis pain usually goes away within a few weeks or so with proper treatment, but recurrent flare-ups of bursitis are common.