Sesamoid bones

In anatomy, a sesamoid bone is a bone embedded within a tendon or a muscle. It is derived from the Latin word sesamum ('sesame seed'), indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be present as a normal variant. The kneecap is the largest sesamoid bone in the body. Sesamoids act like pulleys, providing a smooth surface for tendons to slide over, increasing the tendon's ability to transmit muscular forces.

The sesamoid is a small nodular bone most often present embedded in tendons in the region of the thumb. Calcification of sesamoid bone is one of the important features of pubertal growth spurt, which is earlier in females than in males. Absence of sesamoid bone indicates delay in reaching puberty.