Date Published: April 9, 2019
Publisher: Public Library of Science
Author(s): Patricia Palomo-López, Marta Elena Losa-Iglesias, César Calvo-Lobo, David Rodríguez-Sanz, Emmanuel Navarro-Flores, Ricardo Becerro-de-Bengoa-Vallejo, Daniel López-López, Gabriel Costa Serrão de Araújo.
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.
The fibularis tertius muscle (FTM) was first described by Vesalius in 1816  and was subsequently studied in detail by Henle  and Hyrtl  in the nineteenth century. It is well-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 .
A total 481 people completed all the stages of the research process, 113 of whom were male (23.49%) and 368 of whom were female (76.51%). The demographic and clinical characteristics of the sample are shown in Table 1.
This research focused on identifying the prevalence of the FTM in a sample from Spain compared with samples from other countries, because this issue was not previously addressed in the literature.
The present study revealed that the presence of the FTM is variable and is not influenced by an individual’s sex. In light of our results regarding 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 including to populations with different proportions of people from various ethnic backgrounds. Larger numbers of participants should be enrolled in future studies in order to meet the statistical criteria used in the sample size calculation in this study.