The body has a number of mechanisms that help cushion and lubricate joints and bones. One of these is called the bursa, a fluid-filled sac that separates, cushions and lubricates in order to reduce the friction between two surfaces that move in opposing directions. These surfaces are mostly muscles and tendons that glide over bony structures or glide between bones, especially in the joint areas. In the process of protecting these structures from becoming inflamed, the bursa itself can become inflamed--a condition called “bursitis.”
In the foot, there is only one naturally-occurring bursa. It is located between the Achilles tendon and the heel bone (calcaneus). This bursa protects the Achilles tendon from the pressure of the heel bone pressing against it during walking and running. This is the most common area of bursitis in the feet, also known as retrocalcaneal bursitis.
The body also creates bursal sacs in response to damage. In the feet, these areas include the following:
- the first metatarsal phalangeal joint (the base of the big toe, often associated with a bunion)
- the base of the second metatarsal phalangeal joint (the base of the second toe)
- the base of the fifth toe (often associated with a bunionette)
- the bottom of the heel and the bottom of the forefoot
- the ankle area