Keywords
anatomy - anatomic variation - skeletal muscular fiber - lower limb - fibularis tertius
Introduction
The peroneus tertius, also known as fibularis tertius, is a flat muscle located laterally
to the extensor digitorum longus muscle, originating along the medial face of the
fibula. Its fibers are sometimes mistaken for those of the extensor digitorum longus
muscle. Actually, peroneus tertius is detached from the extensor digitorum longus
muscle through a tendon that goes through the frondiform ligament of the extensor
retinaculum and is inserted into the base of the fifth metatarsal bone.[1]
The muscle evaluated here acts during the swing phase of gait and is a powerful synergist
for the extensor digitorum longus in dorsiflexion, abduction and lateral rotation
of the feet.[2]
[3] It is suggested, however, the insertion of the tendon in the fifth metatarsal could
put more stress and, therefore, make it more easy for a avulsion fracture of the head
of the fifth metatarsal to happen.[4]
The peroneus tertius is supplied by the anterior tibial nerve and anterior tibial
artery. Its prevalence is 86% in African American, 90% in Jewish, and 93% in European
as well as studies showing the muscle in constant development in bipedal animals.
There may be a unique or double tendon and the insertion occurs in the fifth metatarsal,
fourth metatarsal or in the interosseous space.[3]
[5]
The aim of the present study was to evaluate the prevalence and topography of the
peroneus tertius muscle in cadaver parts to help clarify conflicting literature reports
regarding this anterolateral structure of the leg.
Materials and Methods
This cross-sectional observational study was conducted in compliance with Brazilian
federal law number 8.501 of November 30, 1992, which authorizes the use of non-reclaimed
cadavers for research purposes. Lower limbs were obtained from two different anatomy
laboratories at two separate institutes. The samples were dissected on a stainless
steel bench without the use of optics, using a number 4 scalpel handle (ABC Stainless
Ltd.), a number 24 scalpel blade (Embramac) and a grasping forceps with teeth (Erwin
Guth). An incision was made from the anterolateral surface of the leg to the dorsal
region of the foot exposing the muscles and tendons.
Photographs were then taken to enable data analysis to be conducted, and data were
assembled to describe the frequency, origin and insertion of the peroneus tertius
muscle. Finally, the point of division between the tendons of the peroneus tertius
muscle and the extensor digitorum longus muscle was noted.
Results
Thirty-two lower limbs were analyzed. [Table 1] describes the prevalence of the peroneus tertius muscle according to sex.
Table 1
Prevalence and distribution of the peroneus tertius muscle according to sex
|
Sex
|
n
|
Frequency (%)
|
Prevalence (%)
|
|
Female
|
6
|
18.75
|
100
|
|
Male
|
26
|
81.25
|
66.66
|
|
Total
|
32
|
100.00
|
93.75
|
For the purposes of analysis, the fibula was divided into proximal, middle and distal
thirds, and the origin of the muscle was described accordingly ([Fig. 1]).
Fig. 1 Different origin sites of the peroneus tertius muscle marked with * in proximal third,
middle third and distal third of the fibula.
Fibers originating in the middle and distal thirds were equally common, being found
in 46.66% of the specimens ([Table 2]). Insertion of the tendon was either at the base of the fifth metatarsal or in the
space between the fifth and the fourth metatarsal ([Fig. 2]).
Fig. 2 Insertion sites of the peroneus tertius muscle marked with * in fifth metatarsal
and between the fourth and fifth metatarsal.
Table 2
Point of origin of the peroneus tertius muscle
|
Location
|
n
|
Percentage (%)
|
|
Proximal third of the fibula
|
2
|
6.68
|
|
Middle third of the fibula
|
14
|
46.66
|
|
Distal third of the fibula
|
14
|
46.66
|
However, the tendency was toward the fifth metatarsal, a finding recorded for 70%
of the specimens examined ([Table 3]). The fibers of the peroneus tertius muscle that mark the division site from the
fibers of the extensor digitorum longus muscle were found in the proximal, middle
or distal thirds of the fibula. Nevertheless, the distal third was the predominant
location, being the division site in 46.66% of the cases ([Table 4]).
Table 3
Insertion point of the peroneus tertius muscle
|
Location
|
n
|
Percentage (%)
|
|
Fifth metatarsal
|
24
|
70
|
|
Between the fourth and fifth metatarsal
|
6
|
30
|
Table 4
Division point between the peroneus tertius muscle and the extensor digitorum longus
muscle
|
Location
|
n
|
Percentage (%)
|
|
Proximal third of the muscle belly
|
5
|
16.66
|
|
Middle third of the muscle belly
|
11
|
36.66
|
|
Distal third of the muscle belly
|
14
|
46.66
|
Discussion
In the present study, the peroneus tertius muscle was found to be present in 93.75%
of the samples analyzed, a finding that contradicts the results of other previous
studies in which its presence was considered inconstant[2]
[6]
[7]
[8]
[9]
[10]
[11] or largely absent,[3]
[12] who determined that it was present in around 7 to 14% of cases.
To describe the origin of the peroneus tertius muscle fibers, the fibula was divided
into the proximal, middle and distal thirds. In 6.68% of cases, the fibers originated
in the proximal third, in 46.66% of cases in the middle third and in 46.66% of cases
they originated in the distal third. These findings are in agreement with the results
reported in another Brazilian study;[12] however, other studies have suggested that the distal third of the fibula would
be the only possible site of origin of the peroneus tertius muscle fibers.[1]
[2]
[3]
[7]
The peroneus tertius muscle was most commonly found to be inserted into the base of
the fifth metatarsal (70%), with the space between the fourth and the fifth metatarsal
bases being a less common insertion site (30%). Although these findings are confirmed
in the literature,[2]
[3]
[6]
[11]
[12] some studies have proposed the base of the fifth metatarsal as being the only possible
insertion site of the peroneus tertius tendon.[1]
[8]
[9]
[10]
There is a general consensus that the peroneus tertius muscle fibers can be mistaken
for those of the extensor digitorum longus muscle.[3] Notwithstanding, the fact that the peroneus tertius fibers separate themselves through
their own tendon, which is inserted into the base of the fifth metatarsal, leads us
to believe that the muscle belly and the tendon of the peroneus tertius muscle are
both distinct from those of the extensor digitorum longus muscle[11] and in contradiction with classic authors.[7]
The peroneus tertius muscle is considered a feature of anthropoids, particularly bipeds
such as humans, in whom, it represents an advantage from an evolutionary perspective.[13]
Some studies have suggested that during activation of the dorsiflexion and eversion
movements of the foot, the peroneus tertius muscle may play a role in protecting the
ligamentum talofibulare anterius against the risk of rupture induced by proprioception
and neuromuscular control.[14]
[15]
Due to the easy access of the peroneus tertius muscle through a longitudinal incision
in the anterolateral surface of the leg, its lack of primary function and its minimal
importance from an aesthetic point of view, it is an ideal muscle for use as a myocutaneous
flap in plastic surgery involving the distal part of the lower limb.[11]
[16]
The peroneus tertius muscle may also be detrimental to the healing process of a Jones
fracture, since it produces a positive torque at the base of the fifth metatarsal,
delaying the healing process.[17]
Conclusion
The presence of the peroneus tertius muscle is extremely common; however, its origin
and insertion sites may differ. The sample size of cadaver parts used here was small
and no data were available on ethnicity; therefore, further studies need to be conducted
to shed further light on such issues. Nevertheless, the data and the methodology used
here should serve as inspiration for investigators to design new studies to evaluate
the overall prevalence and topography of this anatomic structure.
