The biology of sesamoid tissues in vertebrates - a PeerJ Collection

An x-ray of an ostrich knee joint, displaying the unusual “double-patella” in these birds; an example of mysterious sesamoids. From: Chadwick, K.P., Regnault, S., Allen, V., Hutchinson, J.R. 2014. Three-dimensional anatomy of the ostrich (Struthio camelus) knee joint. PeerJ 2:e706.

Sesamoid tissues in vertebrate animals are found in tendons or ligaments near joints, and can be mineralized or formed of softer connective tissues. Key examples of these include the patella (“kneecap”), sesamoids in digital flexor tendons of many vertebrates, and sesamoids in jaw joints or vertebral tendons/ligaments of varying species. Sesamoids tend to exhibit traits that are somewhat unusual for connective tissues, such as higher than expected variability and extreme responsiveness to mechanical environment (e.g. ossification during ontogeny dependent on loading regime). These leads to the speculation that they can become “genetically assimilated” during evolution; i.e. begin as phenotypically plastic tissues and then become fixed as their function becomes more selectively advantageous in a given environment. However, there is far more to sesamoids than just this evolutionary scenario. The vast diversity of forms, locations, development, presumptive functions and more that sesamoids take in vertebrate species prompt many exciting questions about what sesamoids do for organisms.

Here we gather a collection of original research papers from many modern, international experts in the study of sesamoids; from anatomy to function to development/genetics and evolution. We seek to use this collection to stimulate further interest in sesamoid biology, to advertise current topics in the field, to disseminate levels of understanding vs. ignorance about sesamoid biology, and to move toward an improved synthesis of sesamoids. We encourage all authors to emphasize the latter point, in particular—how do their focused studies relate to the bigger picture of what sesamoids do? We have also sought broadly to be inclusive of any career levels, countries and topics of sesamoid biology, to maximize the diversity of contributions; and we encouraged all authors to use preprints to improve dissemination and early feedback.

Associate Editors/proposers of this collection are Professors John R. Hutchinson and Virginia Abdala.

Example references:

- Alexander RM, Dimery NJ. 1985. The significance of sesamoids and retro-articular processes for the mechanics of joints. Journal of Zoology 205(3): 357–371.

- Eyal S, Rubin S, Krief S, Levin L, Zelzer E. 2019. Common cellular origin and diverging developmental programs for different sesamoid bones. Development 146(4): dev167452.

- Ponssa ML, Goldberg J, & Abdala V. 2010. Sesamoids in anurans: new data, old issues. Anatomical Record 293(10): 1646-1668.

- Samuels ME, Regnault S, Hutchinson JR. 2017. Evolution of the patellar sesamoid bone in mammals. PeerJ, 5, e3103.

- Sarin VK, Carter DR. 2000. Mechanobiology and joint conformity regulate endochondral ossification of sesamoids. Journal of Orthopaedic Research 18(5): 706-712.

- Tsai HP, Holliday CM. 2011. Ontogeny of the Alligator cartilago transiliens and its significance for sauropsid jaw muscle evolution. PLoS ONE 6(9):e24935.

- Vickaryous MK, Olson WM. 2007. Sesamoids and ossicles in the appendicular skeleton. In: Hall BK, ed. Fins into Limbs. Chicago: University of Chicago.

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