Sesamoid bone

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Sesamoid bone
Sesamoid bones at the distal end of the first metatarsal bone of the foot.
Latin ossa sesamoidea
TA A02.0.00.016
FMA 32672
Anatomical terms of bone

In anatomy, a sesamoid bone (/ˈsɛsəmɔɪd/[1][2]) is a bone embedded within a tendon or a muscle.[3] It is derived from the Latin word "sesamum" (sesame seed), due to the small size of most sesamoids. Often, these bones form in response to strain.[4] Sesamoids act like pulleys, providing a smooth surface for tendons to slide over, increasing the tendon's ability to transmit muscular forces.[3]


Sesamoid bones can be found on joints throughout the body, including:

Sesamoid bones under the metatarsophalangeal joint of the great toe of the left foot of an adult woman
  • In the neck - Although the hyoid bone is free floating, it is not technically a sesamoid bone. All sesamoid bones form directly from the connective tissue found in tendons and ligaments. By contrast, the hyoid bone forms from a cartilaginous precursor like most other bones in the body.
  • In the ear - the lenticular process of the incus is a sesamoid bone and therefore is considered the fourth ossicle of the middle ear.

Clinical significance[edit]

  • A common foot ailment in dancers is sesamoiditis. This is a form of tendinitis which results from the tendons surrounding the sesamoid becoming inflamed or irritated.[3]
  • A bi-partite sesamoid bone is when the sesamoids are in 2 separate entities — usually congenital, but may be related to a history of trauma.
  • Sesamoid bones have a very limited blood supply. They are very difficult to heal when not treated early and often lead to avascular necrosis (bone death from lack of blood supply).[8]

Other animals[edit]

In equine anatomy, the term sesamoid bone usually refers to the two sesamoid bones found at the back of the fetlock or metacarpophalangeal/metatarsophalangeal joints in both hindlimbs and forelimbs. Strictly these should be termed the proximal sesamoid bones whereas the navicular bone should be referred to as the distal sesamoid bone. The patella is also a form of sesamoid bone in the horse.

In both the giant panda[9] and the red panda,[10] the radial sesamoid is larger than the same bone in counterparts such as bears. It is primarily a bony support for the pad above it, allowing the panda's other digits to grasp bamboo while eating it. The panda's thumb is often cited as a classical example of exaptation, where a trait evolved for one purpose is commandeered for another.[11]

See also[edit]


  1. ^ OED 2nd edition, 1989 as /sεsəmɔɪd/.
  2. ^ Entry "sesamoid" in Merriam-Webster Online Dictionary.
  3. ^ a b c "Sesamoid Injuries". 
  4. ^ a b Kenneth S. Saladin, Anatomy and Physiology, 6th edition (New York:McGraw Hill, 2012), 234.
  5. ^ Tim D. White, Human Osteology, 2nd edition (San Diego: Academic Press, 2000), 199, 205.
  6. ^ Kenneth S. Saladin, Anatomy and Physiology, 6th edition (New York:McGraw Hill, 2012), 263.
  7. ^ White, Human Osteology, 2nd edition, 257-261.
  8. ^ "bunion, hammer toe, nail fungus, hallux rigidus". 
  9. ^ "Evolution: The Panda's Thumb [Athro, Limited: Biology]". 
  10. ^ Evidence of a false thumb in a fossil carnivore clarifies the evolution of pandas PNAS December 30, 2005
  11. ^ Stephen J. Gould (November 1978). "The Panda's Peculiar Thumb". Nature Magazine Vol. LXXXVII No. 9.