Fluid-filled, saclike cavities are known as bursae. These are located where muscles and tendons move over bony joint areas. Their function is to reduce friction caused by muscles and tendons moving against skin and bones, as well as to facilitate movement.

A knee bursa, also known as a subcutaneous prepatellar bursa, aids with movement when we walk, run, stretch, or even cross our legs. A knee bursa basically functions as a cushion; when one becomes inflamed, increased tension and pain can occur in a temporary condition known as bursitis. You will know when a knee bursa is inflamed by having an X-ray done to check for increased fluid and redness in the area. Bursitis of the knee bursa, also known as pes anserine bursitis or goosefoot bursitis, causes individuals, especially runners, to restrain motion; its most common causes are overuse and injury.

The knee bursa is located on the inside of each knee, between the three hamstring muscle tendons and the shinbone. Thus, knee bursitis may be caused by being overweight, tight hamstring muscles, a lack of stretching, improper turnout of the lower leg or knee, arthritis, or infection.