Sesamoid bone

Sesamoid bone is a type of bone that is embedded within a tendon or a muscle. It is named after the sesame seed, which it somewhat resembles in size and shape. The primary function of the sesamoid bone is to modify pressure, reduce friction, and change the direction of muscle pulls.

Anatomy

Sesamoid bones can be found in several parts of the body. The most recognized sesamoid bones are the patella (knee cap) and the two sesamoid bones in the foot, which are approximately the size of a corn kernel and are located in the underside of the forefoot near the big toe. Other sesamoid bones include the pisiform (smallest of the wrist bones) and the two small sesamoid bones of the hand.

Function

Sesamoid bones act like pulleys, providing a smooth surface for tendons to slide over increasing the tendon's ability to transmit muscular forces. The presence of sesamoid bones in a body part implies that that body part is subject to high stress. For example, the patella improves the mechanical advantage of the quadriceps muscle and protects the knee joint.

Clinical significance

Sesamoid bones can be involved in various medical conditions. Sesamoiditis is a common ailment that involves the sesamoid bones of the foot. It is an inflammation of the sesamoid bones and the surrounding tissues, usually caused by activities that put pressure on the balls of the feet. Other conditions include turf toe, which is a sprain of the soft tissue surrounding the big toe joint, and fractures of the sesamoid bones.

See also

• Ossicles
• Sesamoiditis
• Turf toe

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