sesamoid bones

Two small bones (medial and lateral sesamoids) located above and at the back of the fetlock joint. Four common fractures of the sesamoids are apical (along the top of the bone), abaxial (the side of the sesamoid away from the ankle joint), mid-body (sesamoid broken in half) and basilar (through the bottom) fractures. See "Fractures" subsection of "Musculoskeletal System" in veterinary supplement for a more detailed explanation.