Since its discovery in 1826, the fibularis quartus muscle has been objective of researches with different results, but complementaries (Tables and ).
Quantitative research on the incidence of fibularis quartus muscle, XIX century, by the method of dissection in cadavers.
Quantitative research on the incidence of fibularis quartus muscle, XX and XXI centuries, by different methods.
The fibularis quartus muscle is described as a variation of the fibularis brevis muscle in the majority of the authors. Goss [10
] states that the most common incidence is as fibulocalcaneus externum, originating at the back of fibula between the fibularis brevis and flexor hallucis longus with insertion on the fibular trochlea, as a statistical citing Gruber's work of dissection [15
] with 3% of incidence, although both authors do not disclose the size of the sample. Standring [16
] only cited as one variation of the fibularis brevis muscle, assuming that its insertion can vary and may be in the calcaneus or in the cuboid.
Le Double [23
] however, states that the fibularis quartus muscle, when fully developed, has origins in the lateral distal quarter of fibula below the fibularis brevis muscle, followed by malleolar sulcus, inserting on the base, on the proximal phalanx, or middle phalanx of fifth toe. Also according to Le Double [23
] the presence of fully developed fibularis quartus muscle is quite rare and usually has its distal end withered, and this would be the reason why this muscle receives various names, according to the author who first described: Fibulocuboid muscle—Chudzinski; Fibularis accessorius muscle—Henle; Fibulocalcaneus externum muscle—Wood, Theile, and Macalister; Fibularis quartus muscle—Otto; Fibulofibularis accessorius sixth or lower—Macalister. However, Testut [24
] considers the muscles fibulocuboid and fibulocalcaneus externum as a variant of fibularis quartus, and this as an incomplete variable of the fifth finger fibularis muscle. Poirier and Charpy [25
] consider it as one of the many incomplete variants of the muscle known as fifth finger fibularis muscle, citing although this muscle is also present in chimpanzees and in a number of mammals.
Testut and Latarjet [26
] treat any supernumerary tendon of the fibularis brevis muscle, with or without muscle belly, which has no inferior insertion at the base of the fifth finger as a rudimentary and atrophied fifth finger fibularis muscle.
] explains that the absorption of this muscle by the others fibularis muscles—brevis and longus—would be something normal and expected due to its low incidence, investigated by Wood [17
] and Pozzi [19
] (). Le Double [23
] reinforces this theory by explaining that, unlike the upper limbs, where the muscle movements are more diverse and accurate, the muscular action of the lower limbs comes down to support body weight, balance, and gait, and therefore the lateral muscles of the lower limb, which have same function and action, are in the process of absorption by the fibularis brevis and longus muscles, larger and more constants.
Its incidence varies among studies conducted after the nineteenth century (), from 0% to 26% [3
The Testut [24
] and Le Double [23
] theory is based on the low incidence of fibularis quartus muscle, suggesting that this muscle would be absorbed by other fibularis muscles and disappear however, the incidence of fibularis quartus muscle remains, and the new analytical methods—ultrasound and MRI—showed its incidence to be increasing, although this can be explained by the increase of the studied sample and easy assessment of this muscle by the new imaging methods already mentioned.
It is useful to highlight that with the advancement of diagnostic imaging techniques, particularly magnetic resonance imaging, its study and evaluation are now simpler and more accurate, but not less intriguing. Its incidence varies according to the method used for research, with lower prevalence observed in studies using cadavers and higher incidence in studies using ultrasound exams [6
]. Our results fall within the limits of what has been demonstrated until now by several studies conducted on it which suggests that after more than 180 years of its first description, its incidence is still imprecise and inconsistent.
His presence, even in a few cases, is associated with some diseases that affect the ankle joint and may also be a differential diagnosis for the hypothesis of longitudinal rupture of the fibularis brevis. However, its presence has providential value in cases where surgical repair or reconstruction of the inferior fibularis retinaculum is necessary, as described by Mick and Lynch [27
] as “[
] an excellent source of tissue for reconstruction of the peroneal retinaculum to prevent recurrent dislocation of the peroneal tendons.”
The presence of this muscle together with the fibularis tertius muscle—already well established, with 83–95% of incidence [6
]—is contributing to the possibility of human adaptation at bipedal gait, composing a muscle tendon not only stabilizer of the ankle joint, but also contributing effectively to save energy during walking, working in eversion (fibularis quartus muscle), and dorsiflexion (fibularis tertius muscle) of the foot during the bipedal swing gait [16
]. The absence of the fibularis tertius muscle—considering an evolutionary muscle to be uniquely human and its importance in bipedal gait—is still discussed by some authors, about the lateral support to the foot during gait would be compromised [29
Other authors investigated [31
] did not mention the fibularis quartus muscle, whether as a variation or as incomplete or stunted form of another muscle. These authors cite only the presence of fibularis tertius muscle as a constant and not as an inconstant muscle.
Our results indicate that its incidence is independent of the individual's gender, being common to human beings as a whole, suggesting no relationship to gender.
Still according to the results obtained, the chance that a person who has the fibularis quartus muscle also has fibularis tertius muscle is three to one; in other words, one of three individuals that have the fibularis quartus muscle also has a fibularis tertius muscle, whether man or woman. Therefore, the presence of fibularis tertius muscle does not depend on the presence of the fibularis quartus muscle in contrast, the presence of fibularis quartus muscle increases the chances that there is a presence of fibularis tertius muscle too.