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PeerJ2023; 11; e14352; doi: 10.7717/peerj.14352

The bony cap and its distinction from the distal phalanx in humans, cats, and horses.

Abstract: It has been recognized as early as the Victorian era that the apex of the distal phalanx has a distinct embryological development from the main shaft of the distal phalanx. Recent studies in regenerative medicine have placed an emphasis on the role of the apex of the distal phalanx in bone regrowth. Despite knowledge about the unique aspects of the distal phalanx, all phalanges are often treated as equivalent. Our morphological study reiterates and highlights the special anatomical and embryological properties of the apex of the distal phalanx, and names the apex "the bony cap" to distinguish it. We posit that the distal phalanx shaft is endochondral, while the bony cap is intramembranous and derived from the ectodermal wall. During development, the bony cap may be a separate structure that will fuse to the endochondral distal phalanx in the adult, as it ossifies well before the distal phalanges across taxa. Our study describes and revives the identity of the bony cap, and we identify it in three mammalian species: humans, cats, and horses (, and ). During the embryonic period, we show the bony cap has a thimble-like shape that surrounds the proximal endochondral distal phalanx. The bony cap may thus play an inductive role in the differentiation of the corresponding nail, claw, or hoof (keratin structures) of the digit. When it is not present or develops erroneously, the corresponding keratin structures are affected, and regeneration is inhibited. By terming the bony cap, we hope to inspire more attention to its distinct identity and role in regeneration.
© 2023 Smith et al.
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Publication Date: 2023-01-10 PubMed ID: 36643632PubMed Central: PMC9838202DOI: 10.7717/peerj.14352Google Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't
  • Research Support
  • U.S. Gov't
  • Non-P.H.S.

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article focuses on the special anatomical and embryological properties of the apex of the distal phalanx, commonly termed as the “bony cap”. This area, often considered equivalent to all phalanges, has been found to have a distinct role and identity in bone regrowth.

Morphological Study and Distinct Properties

  • The research revisits the unique aspects of the distal phalanx, particularly the “bony cap”, an area at the top of the phalanx.
  • The authors propose that while the shaft of the distal phalanx is endochondral, the bony cap has a different, intramembranous nature and is derived from the ectodermal wall.
  • This indicates that during development, the bony cap could have been a separate structure that fuses with the endochondral distal phalanx in adulthood. Interestingly, the ossification of the bony cap occurs prior to the distal phalanges across species.

The Bony Cap across Different Species

  • The study identifies and describes the presence and characteristics of the bony cap in three distinct mammalian species: humans, cats, and horses.
  • During embryonic stages, the bony cap has a thimble-like shape that encompasses the proximal endochondral distal phalanx.

Role in Differentiation and Regeneration

  • The research sheds light on the possible inductive role of the bony cap in differentiation, impacting the formation of nails, claws, or hoofs (keratin structures) of the digit across different species.
  • Any aberration in the presence or development of the bony cap affects the corresponding keratin structures and can inhibit the process of regeneration.

Framing the Relevance

  • By giving the term “bony cap”, the authors aim to emphasize its distinct identity as compared to the general phalanges and stress on its importance in terms of regenerative medicine.

Cite This Article

APA
Smith S, Yohe LR, Solounias N. (2023). The bony cap and its distinction from the distal phalanx in humans, cats, and horses. PeerJ, 11, e14352. https://doi.org/10.7717/peerj.14352

Publication

PeerJ
ISSN: 2167-8359
NlmUniqueID: 101603425
Country: United States
Language: English
Volume: 11
Pages: e14352
PII: e14352

Researcher Affiliations

Smith, Shannon
  • College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, New York, United States.
Yohe, Laurel R
  • Bioinformatics and Genomics, University of North Carolina at Charlotte, Charlotte, North Carolina, United States.
  • Earth and Planetary Sciences, Yale University, New Haven, Connecticut, United States.
  • North Carolina Research Center, Kannapolis, North Carolina, United States.
  • Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, New York, United States.
Solounias, Nikos
  • College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, New York, United States.
  • Department of Paleontology, American Museum of Natural History, New York, NY, United States.

MeSH Terms

  • Humans
  • Cats
  • Horses
  • Animals
  • Finger Phalanges / diagnostic imaging
  • Extremities
  • Hoof and Claw / diagnostic imaging
  • Mammals

Conflict of Interest Statement

The authors declare that they have no competing interests.

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Citations

This article has been cited 1 times.
  1. Vincelette AR, Renders E, Scott KM, Falkingham PL, Janis CM. Hipparion tracks and horses' toes: the evolution of the equid single hoof. R Soc Open Sci 2023 Jun;10(6):230358.
    doi: 10.1098/rsos.230358pubmed: 37351494google scholar: lookup
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