The infracalcaneal os peroneum.

There is some confusion in the literature regarding the nature of the os peroneum. It has been claimed to be either a supranumerary os or a sesamoid in the tendon of the peroneus longus muscle. Its position in the foot is also a subject of dispute. Most authors state that it is related to the cuboid bone, and it has in the past been termed the 'cuboidum secundarius.' Occasionally an ossicle is seen inferior to the distal calcaneus distal to the calcaneocuboid articulation. This may represent a developmental anomaly of position of the os peroneum or be the sequel of a rupture of the peroneus longus muscle.