Fibularis tertius muscle in women & men: A surface anatomy cross-sectional study across countries.

Marta Elena Losa-Iglesias,Daniel López-López,Patricia Palomo-López,César Calvo-Lobo,Emmanuel Navarro-Flores,Ricardo Becerro-de-Bengoa-Vallejo,David Rodríguez-Sanz

doi:10.1371/journal.pone.0215118

Abstract

The fibularis tertius muscle (FTM) is a rare anatomic variation. The prevalence of this exclusively human structure, which is found in the anterior compartment of the leg, is often underestimated, and it is believed that foot and ankle conditions are more difficult to manage in patients with an FTM. The aim of this study was to assess the presence of the FTM palpation and determine whether its presence is associated with an individual’s sex, because the exact prevalence in males and females is unclear. An observational cross-sectional study was carried out. The study included 481 people (23.49% men and 76.51% women) with a mean age of 23.51±5.369 years, who were recruited from a Podiatric Medicine and Surgery Clinic (Spain). Data on routine demographic and clinical factors were recorded, and the presence or absence of the FTM was determined based on surface visual or palpated localization of the tendon (using a consistent protocol). The FTM was present in 38.25% (184/481) of the participants. Furthermore, FTM were present in 38.6% (142/481) of females and 37.2% (42/481) of males. The study revealed that the presence of the FTM varies between individuals and does not depend on an individual’s sex. Significant differences in the prevalence of the FTM between countries should be carefully evaluated rather than generalizing the results of this Spanish study to other non-Spanish populations. Larger numbers of participants should be enrolled in future studies in order to meet the statistical criteria.

Highlights

The fibularis tertius muscle (FTM) was first described by Vesalius in 1816 [1] and was subsequently studied in detail by Henle [2] and Hyrtl [3] in the nineteenth century
As prevalence of the FTM has not been described in Spain, the purpose of this study was firstly to determine the prevalence of the presence or absence of the FTM, and to identify whether it is associated with an individual’s sex and whether it is more likely to be present in a Spanish population compared with populations in other countries
Regarding the FTM in the right foot, there were no significant differences in the presence or absence between males and females (P>0.05)

Summary

Introduction

The fibularis tertius muscle (FTM) was first described by Vesalius in 1816 [1] and was subsequently studied in detail by Henle [2] and Hyrtl [3] in the nineteenth century. Fibularis tertius muscle & surface anatomy documented in anatomy textbooks that the muscle forms part of the anterior compartment of the leg and crosses anterior to the ankle joint to extend up to its insertion in the anterior part of the 5th and 4th metatarsal bases as well as in the 5th metatarsal shaft, explaining its main muscle function as an ankle evertor [4] It usually appears between the distal third and the half of the fibula from the intermuscular septum and is associated with a derivation of the extensor digitorum longus muscle, and extends into the nearby deep fascia [5–8]. The prevalence of FTM among humans as well as similar functional muscles if FTM is missing could support a key role of FTM regarding the erect bipedal posture and gait phylogenetic development [8,13]

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