There are 11 bursae surrounding each knee. Each bursa is a thin, fluid-filled sac that works to reduce friction and cushion the connection between tendons, muscles, and bones in the body. When a bursa becomes inflamed, its usually thin lining becomes thick causing pain and swelling in the knee. Usually knee bursitis is caused by the inflammation of two bursae located above the patella. BioSkin Knee braces are designed to reduce swelling with medical-grade compression and use supportive straps to relieve pressure on the joint while the bursae heal.