Bones in the Human Hand

9. Sesamoid Bones

Sesamoid bones form within tendons to provide a smooth surface for tendons to guide muscle movement. They are small, round bones and often develop naturally, but can also form as a response to a strain or injury. The hand contains several sesamoid bones -- the number varies between individuals. The tendons of the metacarpophalangeal joints of the thumb almost always include a pair of sesamoid bones. They can develop at almost every metacarpophalangeal and distal interphalangeal joint, but this is uncommon.