Sesamoid bone - Definition

In anatomy, a sesamoid bone is a bone embedded within a tendon.

Sesamoid bones are typically found in locations where a tendon passes over a joint. Functionally, they act to protect the tendon and to increase its mechanical effect. The presence of the sesamoid bone holds the tendon slightly further away from the center of the joint and thus increases its moment arm. The sesamoid prevents the tendon from flattening into the joint as the tendon tension increases, and therefore also maintains a more consistent moment arm through a variety of possible tendon loads.

Examples in human anatomy include:

• The patella, a bone at the front of the knee.
• The sesamoid bones of the first metatarsal of the foot. This area is beneath the pad on the foot just proximal to the big toe. These two bones serve to protect the tendon that flexes the toe, by protecting it from the body's weight.
• The pisiform, a carpal bone of the hand.