A burse is a fluid filled sac that decreases friction between two tissues. Burse are commonly found near a joint, and act as lubricating structures between tendon and bone. There are several bursa in the foot and ankle region. The most common are the retrocalcaneal bursa, subcutaneous calcaneal bursa, and subcutaneous bursa of the medial malleolus.
The retrocalcaneal bursa is located between the Achilles tendon and calcaneus (heel) bone. Direct or repetitive trauma such as consistent rubbing or friction can produce bursitis in this area. The subcutaneous calcaneal bursa, also called the Achilles bursa, is lower down near the heel. The subcutaneous bursa of the medial malleolus is located below the edge of the medial malleolus. Tight athletic footwear can produce rubbing and bursitis in this area.