Abstract
Being considered an exclusive human structure for a long time, fibularis tertius (FT) is believed to have a secondary function of foot dorsiflexion and eversion. This study is an attempt to approach the issue from an anatomical perspective. A systematic literature search identified 35 studies (7601 legs) which met the inclusion criteria. The weighted results of FT presence were as follows: an “adult cadaveric” frequency of 93.2% and a clinical frequency of 80%. The most common FT origin and insertion sites were the distal half of fibula and the base of the 5th metatarsal, respectively. In 95% of cases, an accessory fibular muscle was detected when FT was lacking. We demonstrated that the discrepancy found between the adult cadaveric and clinical frequency values would point out a probable bias in interpreting previous kinesiological results. On an evolutionary level, comparative anatomy demonstrated a very low FT prevalence among monkeys while reaching a frequency of 30% in gorillas, the only non-human apes having an almost exclusive terrestrial locomotion. The consistent prevalence among humans and the presence of similar functional muscles when it is missing would support an essential role of FT during the phylogenetic development of the erect bipedal posture and probably during gait.
Highlights
Two issues have been debated over the “fibularis tertius” muscle (FT) or “peroneus tertius” or “anterior fibularis”: whether the FT is a separate entity and whether it is exclusively human
It is most likely that the first description of the PT muscle has been reported by Vesalius [1]. This ninth muscle “employed in the motion of the foot” has been rejected by some anatomists who were contemporaries of Vesalius, such as Colombio and Fallopio [2]. They stated that this “nonus proprius per se musculus” of Vesalius is part of the extensor digitorum muscle that it is inserted on the fifth toe and has no separate entity
In spite of later accurate and precise descriptions of FT reported by Albinus [3] and Winslow [4], the FT has been repeatedly negated its separate identity and associated with the extensor digitorum longus (EDL) [5]
Summary
Two issues have been debated over the “fibularis tertius” muscle (FT) or “peroneus tertius” or “anterior fibularis”: whether the FT is a separate entity and whether it is exclusively human. In spite of later accurate and precise descriptions of FT reported by Albinus [3] and Winslow [4], the FT has been repeatedly negated its separate identity and associated with the extensor digitorum longus (EDL) [5]. It was not until the nineteenth century that the original description of this muscle as a separate entity has been revalidated by some renowned anatomists such as Henle [6] and Hyrtl [7]. A comparative anatomical analysis is reported in the discussion; the interpretation of its results along with those of this meta-analysis will try to appraise the functional importance of this muscle
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