Knee bursitis is inflammation of a small fluid-filled sac (bursa) situated near your knee joint. Bursae reduce friction and cushion pressure points between your bones and the tendons, muscles and skin near your joints. Any of the bursa in your knee can become inflamed, but knee bursitis most commonly occurs over the kneecap or on the inner side of your knee below the joint. Knee bursitis causes pain and can limit your mobility. Treatment for knee bursitis often includes a combination of self-care practices and doctor-administered treatments to alleviate pain and inflammation.