Sesamoiditis is inflammation of the sesamoid bones. Sesamoiditis occurs on the bottom of the foot, just behind the big toe. There are normally two sesamoid bones on each foot; sometimes sesamoids can be bipartite, which means they each comprise two separate pieces. The sesamoids are roughly the size of jelly beans. The sesamoid bones act as a fulcrum for the flexor tendons, the tendons which bend the big toe downward.