Sesamoiditis is a general description for any irritation of the sesamoid bones, which are tiny bones within the tendons that run to the big toe. Like the kneecap, the sesamoids function as a pulley, increasing the leverage of the tendons controlling the toe. Every time you push off against the toe the sesamoids are involved, and eventually they can become irritated, even fractured. Because the bones are actually within the tendons, sesamoiditis is really a kind of tendinitis – the tendons around the bones become inflamed as well.