It begins to ossify in children ages 9–12. In the foot—the first metatarsal bone usually has two sesamoid bones at its connection to the big toe (both within the tendon of flexor hallucis brevis).

How does a sesamoid bone develop?

Sesamoid bones form within tendons in regions that wrap around bony prominences. They are common in humans but variable in number. Sesamoid development is mediated epigenetically by local mechanical forces associated with skeletal geometry, posture, and muscular activity.

Does everyone have sesamoid bones in their foot?

The foot is comprised of 28 bones. Two of them are what are called 'sesamoids. ' These bones are named for their shape, which resembles a sesame seed. Everyone has two of these bones in each foot and sometimes one or both can naturally occur in two pieces (called bipartite).