“Bursa” is taken from the same Greek word that gives us our word for “first,” which means “sac.” The body has numerous bursa, which can be thought of as flattened water balloons, positioned between two structures that move and would otherwise create friction and irritation between them. These bursa act as cushions and lubricants to allow free movement between adjacent structures. Normally, the amount of fluid in these bursa is minimal providing just a thin film. However, with irritation due to trauma or infection or other systemic illnesses (see gout, rheumatoid arthritis), the fluid volume will increase and painful inflammation can occur.