Bursitisis the inflammation of the small fluid-filled pads, or bursae, that act as cushions among your bones and the tendons and muscles near your joints. Bursitis occurs when the bursa become inflamed, and often occurs in joints that perform frequent and repetitive motion.
The foot only contains one naturally occurring bursal sac between the Achilles tendon and the heel bone, which protects the Achilles from the pressure against the heel bone during ambulation. However, shoes may put pressure on this bursa. The bursa might also incur trauma from walking on hard ground. And, though they are not naturally occurring, bursa sacs can also form, and become inflamed, in other parts of the foot, including the bottom of the heel, and the metatarsal plate, the outside of the foot below the fifth toe, and so on.