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Anat Cell Biol

Published online October 17, 2022


Copyright © Korean Association of ANATOMISTS.

Distally-extending muscle fibers across involved joints: study of long muscles and tendons of wrist and ankle in late-term fetuses and adult cadavers

Shaohe Wang1 , Shogo Hayashi2 , Zhe-Wu Jin1 , Ji Hyun Kim3 , Masahito Yamamoto4 , Gen Murakami4,5 , Shinichi Abe4

1Department of Anatomy, Wuxi School of Medicine, Jiangnan University, Wuxi, China, 2Department of Anatomy, Division of Basic Medicine, Tokai University School of Medicine, Isehara, Kanagawa, Japan, 3Department of Anatomy, Chonbuk National University Medical School, Jeonju, Korea, 4Department of Anatomy, Tokyo Dental College, Tokyo, 5Division of Internal Medicine, Cupid Clinic, Iwamizawa, Japan

Correspondence to:Zhe Wu Jin
Department of Anatomy,Wuxi School of Medicine, Jiangnan University, Wuxi, Jiangsu 214122, China
E-mail: zwjin@jiangnan.edu.cn

Received: July 12, 2022; Revised: August 18, 2022; Accepted: August 31, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


It is unclear whether forearm and crural muscle fibers extend distally across the wrist and ankle joints, respectively. We hypothesized, in late-term fetuses, an over-production of muscle bellies extending over the joint. Muscle fibers in histological sections from unilateral wrists and ankles of 16 late-term fetuses (30–40 weeks) were examined and compared with 15 adult cadavers. Muscle fibers of the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) in fetuses, especially muscle bellies to the third and fourth fingers, were found to extend far distally beyond the radiocarpal joint. The extensor digitorum and extensor pollicis longus on the extensor side of the wrist were found to carry distally-extending muscle fibers, but these fibers did not extend beyond the distal end of the radius. In the ankle, most muscle bundles in the flexor hallucis longus (FHL), fibularis brevis (FB) and extensor digitorum longus extended distally beyond the talocrural joint, with most FB muscle fibers reaching the level of the talocalcaneal joint. In adult cadavers, muscle fibers of the FDP and FHL did not reach the levels of the radiocarpal and talocrural joints, respectively, whereas the FB muscle belly always reached the talocalcaneal joint. Similarly, some of the FDS reached the level of the radiocarpal joint. Generally, infants’ movements at the wrist and ankle could result in friction injury to over-extended muscle. However, the calcaneal and FDP tendons might protect the FB and FDS tendons, respectively, from friction stress.

Keywords: Muscle fibers, Tendons, Wrist, Ankle, Fetus

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