Examples of sesamoid bone include the knee, the first metatarsal bone that connects to the big toe in the foot, and the hand, which contains four of these bones . Sesamoid bones are those small bones embedded within a tendon.
Sesamoid bones are most often found in parts of the body in which a tendon passes on a joint. This type of bone protects the tendon and increases its range of motion. Sesamoid bones attached to tendons holds the tendon far enough away from the center of the joint that it allows for an increase in movement.
Sesamoid bones may also be embedded within a muscle. In bone or muscle, the sesamoid bone forms a type of pulley, allowing the tendon to slide over its smooth surface, reducing strain.
Despite being there to help tendons and muscles avoid stress and injury, the sesamoid bones themselves are prone to injury. Dancers, for example, can suffer from a condition called sesamoiditis. This condition causes the sesamoid bone to become inflamed and painful. Due to the low blood supply in the sesamoid bones, treating an injury to one of these small bones is difficult and treatment should be started as soon as possible to avoid bone death.