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A new insight into the fabella at knee: the foetal development and evolution
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Abstract
Using longitudinal semiserial sections of 12 lower extremities from 8 human foetuses at 15–18 weeks, we compared foetal morphologies of the knee in specimens with and without fabellae. We also compared the fabella, if present, with the hallucal sesamoid in the same foetus. Cartilaginous fabella, positive for versican and tenascin by immunohistochemistry, was found in 5 of the 8 foetuses. This structure was embedded in a thick and tight lateral fibrous band, providing a common origin of the plantaris muscle and the lateral head of the gastrocnemius muscle. The plantaris was covered by the lateral head of the gastrocnemius, but these 2 muscles were separated by a distinct fascia or space. Notably, the foetal fabella did not attach to the joint capsule. In the 3 specimens without fabellae, the lateral fibrous band was thin, containing a fibrous mass, negative for versican and tenascin, in place of the fabella. The “medial” head of the gastrocnemius faced or covered the plantaris, while the lateral head was continuous with the plantaris. A hallucal cartilaginous sesamoid, positive for versican and tenascin, was present in all 8 specimens. It carried a flat surface facing the joint cavity and was covered by tendons of the short muscles of the foot. Because of the difference in topographical relation of muscles between specimens with or without fabella, rather than mechanical stress to the tendon, fabella development may require a distinct plantaris muscle independent of the gastrocnemius. We discussed about an evolutionary aspect of the fabella and plantaris muscle.
Abstract
Using longitudinal semiserial sections of 12 lower extremities from 8 human foetuses at 15–18 weeks, we compared foetal morphologies of the knee in specimens with and without fabellae. We also compared the fabella, if present, with the hallucal sesamoid in the same foetus. Cartilaginous fabella, positive for versican and tenascin by immunohistochemistry, was found in 5 of the 8 foetuses. This structure was embedded in a thick and tight lateral fibrous band, providing a common origin of the plantaris muscle and the lateral head of the gastrocnemius muscle. The plantaris was covered by the lateral head of the gastrocnemius, but these 2 muscles were separated by a distinct fascia or space. Notably, the foetal fabella did not attach to the joint capsule. In the 3 specimens without fabellae, the lateral fibrous band was thin, containing a fibrous mass, negative for versican and tenascin, in place of the fabella. The “medial” head of the gastrocnemius faced or covered the plantaris, while the lateral head was continuous with the plantaris. A hallucal cartilaginous sesamoid, positive for versican and tenascin, was present in all 8 specimens. It carried a flat surface facing the joint cavity and was covered by tendons of the short muscles of the foot. Because of the difference in topographical relation of muscles between specimens with or without fabella, rather than mechanical stress to the tendon, fabella development may require a distinct plantaris muscle independent of the gastrocnemius. We discussed about an evolutionary aspect of the fabella and plantaris muscle.
Keywords
fabella, knee, hallucal sesamoid, metatarsophalangeal joint, gastrocnemius muscle, human foetus
About this articleTitle
A new insight into the fabella at knee: the foetal development and evolution
Journal
Issue
Article type
Original article
Pages
87-93
Published online
2016-08-29
Page views
2017
Article views/downloads
1667
DOI
Pubmed
Bibliographic record
Folia Morphol 2017;76(1):87-93.
Keywords
fabella
knee
hallucal sesamoid
metatarsophalangeal joint
gastrocnemius muscle
human foetus
Authors
Z. W. Jin
S. Shibata
H. Abe
Y. Jin
X. W. Li
G. Murakami
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