Sesamoid bone

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Sesamoid bone
Sesamoid bones at the distal end of the first metatarsal bone of the foot.
Details
Identifiers
Latin
  • os sesamoideum
  • pl. ossa sesamoidea
MeSHD012716
TA98A02.0.00.016
TA2374
FMA32672
Anatomical terms of bone

In anatomy, a sesamoid bone (/ˈsɛsəmɔɪd/)[1][2] is a bone embedded within a tendon or a muscle.[3] Its name is derived from the Greek word for 'sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain,[4] or can be present as a normal variant. The patella 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.[3]

Structure

Prevalence, structure, and locations of sesamoid bones of the hand.[5][6]

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

Common variants

X-ray of the foot by dorsoplantar view, with most common accessory and sesamoid bones.[11]
  • One or both of the sesamoid bones under the first
    metatarsophalangeal joint (of the great toe) can be multipartite – in two or three parts (mostly bipartite – in two parts).[12]
  • The
    condyle of the femur. It is a variant of normal anatomy and present in humans in 10% to 30% of individuals. The fabella can also be mutipartite or bipartite.[13]
  • The cyamella is a small sesamoid bone embedded in the tendon of the popliteus muscle. It is a variant of normal anatomy. It is rarely seen in humans, but has been described more often in other primates and certain other animals.[14]

Clinical significance

  • A common foot ailment in dancers is sesamoiditis (an inflammation of the sesamoid bones under the first metatarsophalangeal joint of the big toe). This is a form of tendinitis which results from the tendons surrounding the sesamoid becoming inflamed or irritated.[3]
  • Sesamoid bones generally have a very limited blood supply, rendering them prone to avascular necrosis (bone death from lack of blood supply), which is very difficult to treat.[15]

Other animals

See also: The Panda's Thumb (book)

In

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.

Although many carnivores have radial sesamoid bones,

independently evolved to have an enlarged radial sesamoid bone.[16][17] This evolution has caused the two species to diverge from other carnivores.[16] The red panda likely originally evolved the "pseudo-thumb" in order to assist in arboreal locomotion.[17][16] When the red panda later evolved to consume a bamboo diet, the enlarged bone underwent exaptation to assist in grasping bamboo.[18][16][19][17] The giant panda, however, evolved the enlarged radial sesamoid bone around the same time as it evolved a bamboo diet.[17] In the giant panda, the bone allows for a pincer-like motion and is used in grasping the bamboo.[20][21] In these two panda species, DYNC2H1 gene and PCNT gene have been identified as possible causes for the pseudo-thumb development.[22]

Recently, the enlarged radial sesamoid bone of cotton rats has been studied.[23] Their enlarged radial sesamoid bone and that of the giant panda have a similar morphology and size relative to the rest of the hand.[23] The reason for this evolutionary change is still unknown; however, it may be to assist in grasping small objects and thin branches.[23]

Elephants have similarly enlarged sesamoid bones in both their forelimbs and hindlimbs, referred to as the prepollex and prehallux, respectively. These sesamoids function as "sixth toes", helping to distribute the animals' weight. In contrast to other sesamoids in elephants, which ossify at 3-7 years of age, the ossification of the prepollex and prehallux is delayed and is known to not have yet occurred in animals in excess of 20 years of age. The prehallux is further divided into two elements; the more proximal of these is fixed, whilst the more distal is mobile. Evidence of these "predigits" has also been found in certain fossil proboscideans.[24]

The forepaws of moles also possess a prepollex consisting of an enlarged, sickle-shaped sesamoid.

See also

Footnotes

  1. OED
    2nd edition, 1989 as /sεsəmɔɪd/
  2. ^ Entry "sesamoid" in Merriam-Webster Online Dictionary.
  3. ^ a b c "Sesamoid Injuries". aofas.org. Archived from the original on 2016-08-19. Retrieved 2014-12-06.
  4. ^
    ISBN 978-0-07-337825-1
    .
  5. ^ Erica Chu; Donald Resnick (June 2014). "Sesamoid Bones: Normal and Abnormal". MRI Web Clinic. Retrieved 2017-11-04.
  6. PMID 26380010
    .
  7. ^ Erica Chu; Donald Resnick (June 2014). "Sesamoid Bones: Normal and Abnormal". MRI Web Clinic. Retrieved 2017-11-04.
  8. ISBN 978-0-12-746612-5
    .
  9. ISBN 978-0-07-337825-1
    .
  10. ISBN 978-0-12-746612-5
    .
  11. ^ a b Reference list for image is located at Commons:Template:Accessory and sesamoid bones of the foot - references.
  12. ^ Knipe, Henry. "Multipartite hallux sesamoid | Radiology Reference Article | Radiopaedia.org". radiopaedia.org.
  13. ^ Luijkx, Tim; Knipe, Henry. "Fabella". Radiopaedia. Retrieved 2015-09-18.
  14. S2CID 13339926
    .
  15. ^ "bunion, hammer toe, nail fungus, hallux rigidus". footankleinstitute.com.
  16. ^
    PMID 17118063
    .
  17. ^
    PMID 16387860
    .
  18. S2CID 16846874
    .
  19. PMID 11325067
    .
  20. PMID 11273049
    .
  21. S2CID 4302142
    .
  22. PMID 28096377
    .
  23. ^
    S2CID 17239724
    .
  24. S2CID 206536505
    .

References

External links

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