Sesamoid bone Sesamoid bone In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. It is derived from the Latin word ("sesame seed"), due to 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
Skeletal muscle "flexor" and "extensor"; "abductor" and "adductor"; "levator" and "depressor"; "supinator" and "pronator"; "sphincter", "tensor", and "rotator" muscles. A flexor muscle decreases the anterior angle at a joint; an extensor increases the anterior angle at a joint. An abductor moves a bone away from the midline; an adductor moves a bone closer to the midline. A levator raises a structure; a depressor moves a structure down. A supinator turns the palm of the hand up; a pronator turns the palm down. A sphincter decreases the size of an opening; a tensor tenses a body part; a rotator turns a bone around