PERONEUS QUARTUS MUSCLE: ITS INCIDENCE AND CLINICAL IMPORTANCE

Address for Correspondence: Dr. Amal Yousif Ahmed Elhag Mustafa, Department of Human Anatomy, Faculty of Medicine, Umm al Qura University, Makkaha, Saudi Arabia. E-Mail: amaalahmed50@yahoo.com Introduction and objectives: Muscular variations in the lower limb are very common. They have been described by many authors when performing cadaveric dissections and when using the different imaging techniques. Materials and Methods: Twenty lower limbs of adult cadavers, were dissected. Lower limbs deformed by trauma, malformations and scars were excluded. The compartment was examined for the presence of an accessory muscle. If this is present, the dissection was extended and the site of its origin and insertion and passage in the retromalleolar groove was noted. Result: A peroneus quartus was present in 4(20%) of the 20 legs. Two different area of origins and insertions. Two of them arose from the peroneus brevis muscle,and the other two from the distal fibula .three of the muscles were inserted into the retrotrochlear eminence of the calcaneum , the remaining one was inserted into the base of the first metatarsal bone. Conclusions: This study will supplement our knowledge on the possible variations of the muscles in this region, which would be useful for lower limbs surgeons.


INTRODUCTION
The peroneus quartus muscle is one of the accessory muscles present in the lateral compartment of the leg. It is said to have been first described by Ottoin 1816 and was studied in depth in 1923 by Hecker [1] who estimated its incidence to be 13% in the general population. There are only a few studies concerning this muscle. surgeons should be aware of the possible presence of the peroneus quartus muscle, not only because of possible associated pathology, but also for use in surgical reconstruction. Various anatomists have described it and Muscular variations in the lower limb are very common. They have been described by many authors when performing cadaveric dissections and when using the different imaging techniques. The presence of these muscles is frequently asymptomatic, but sometimes it can cause symptoms due to overcrowding and mechanical compression of adjacent structures. The lateral compartment of the leg contains the peroneus longus and peroneus brevis muscles.
given it different names according to its various origins and insertions. Sobel, W Levy and Bohne [2] described the anatomical variations of the muscle in a cadaver study on 124 legs with particular reference to the origins and insertions of the different anomalous muscles in the lateral compartment and suggested that these should all be referred to as variants of the same muscle, the peroneus quartus. They showed that it was present in 21.7% of cadavers. The peroneus quartus muscle, arises from the lower third of the fibula, peroneus brevis muscle, and/or peroneus longus muscle. However, its distal insertion has shown great variability, most often inserting onto the lateral surface of the calcaneus on the retrotrochlear eminence [3]. Believed to be an evolutionary acquisition for bipedal gait, the peroneus quartus muscle is unique to humans, assisting with eversion of the lateral border of the foot, pronation of the foot against the walking surface, and lateral stabilization of the ankle [1-6]. The peroneus quartus muscle was first described by Otto in 1816 [3] and has since been termed the peroneus sextus, peroneus calcaneus externus, peroneocuboidian, peroneus accessorius, peroneus medius [7], and peroneus muscle of the tarsus [1]. Anatomists, surgeons, and radiologists have discovered slight variations in the distal insertion of the peroneus quartus, resulting in both increased and ambiguous nomenclature [8][9][10][11]. The reported points of insertion include (from proximally to distally): retrotrochlear eminence of the calcaneus, the fibular (peroneal) trochlea of the calcaneus, tendons of the fibularis longus and brevis muscles, the cuboid, and the fifth metatarsal [10,[12][13][14]. In 1923, Hecker [1] classified the peroneus quartus variants into 3 categories according to the insertion onto the calcaneus (peroneocalcaneus externum), cuboid (peroneocuboideus), or tendon of peroneus longus (peroneoperoneolongus). However, the peroneoperoneolongus muscle is now referred to as the peroneus accessorius [10,15,16]. Other peroneus quartus variants include the peroneus digiti minimi, which inserts onto the fifth metatarsal [10] and the peroneotalocalcaneus muscle [17]. With so many variations of the peroneus quartus muscle, 2 studies attempted to resolve the nomenclature issues by suggesting that the peroneus quartus muscle inserts onto the lateral aspect of the calcaneus and the variants of the muscle have other distal attachments [10,14,12,18]. This study aims at investigating the incidence, anatomical variations and possible pathology relating to the peroneus quartus muscle.
This study was conducted at the Faculty of Medicine, Umm AL_qura University, Makka, Saudi Arabia between March 2016 and September 2017. Twenty lower limbs of adult cadavers, were dissected to perform this study. Their ages range between 45 and 77 years old. Lower limbs deformed by trauma, malformations and scars will be excluded. Each limb was dissected by an incision which was start about 10 cm proximal to the lateral malleolus and end 5 cm distal to it. The compartment was examined for the presence of an accessory muscle. If this is present, the dissection was extended and the site of its origin and insertion and passage in the retromalleolar groove was noted. All anatomical variations was registered, recorded and photographed.

MATERIALS AND METHODS
A peroneus quartus was present in 4(20%) of the 20 legs which were dissected (Figure 1). The muscles which were identified two different area of origins and insertions. Two of them arose from the peroneus brevis muscle,and the other two from the distal fibula .three of the muscles were inserted into the retrotrochlear eminence of the calcaneum(figure 1) , the remaining one was inserted into the base of the first metatarsal bone. The peroneus quartus muscle shown in Figure 3 arose from peroneus brevis. It passed as a separate tendon posterior to peroneus brevis and inserted into the eminence of the calcaneum. Figure 2 show it arising from the distal part of the fibula. The muscle belly was short and its tendon lay between peroneus longus and brevis in the retromalleolar groove and also inserted into the eminence of the calcaneum. One cadaver had peroneus quartus muscles with origin from peroneus brevis and the insertion into the base of the fifth metatarsal bone.

DISCUSSION
Knowledge of the anatomy of the peroneal muscles and its variations is important to surgeons dealing with pathologies in this region.
There are no precise data on the incidence of the peroneus quadrus muscle in the literature, and the studies are mainly based on the findings of many years ago [19]. In this study we found the incidence of peroneus qurtus was 20% in our specimens. Bhargava et al [20] gave the incidence of peroneus quadrus as 15.5%. Reimen [21] reported the presence of peroneus quadrus as 79.5%. Based on these data, Yammine [22] stated that there were differences regarding incidence of the muscle and declared that ethnicity was important in considering the incidence of peroneus quadrus in each community. In our specimen we noticed two different area of origins and insertions. Two of them arose from the peroneus brevis muscle, and the other two from the distal fibula .three of the muscles were inserted into the retrotrochlear eminence of the calcaneum, the remaining one was inserted into the base of the first metatarsal bone. As in previous reports, The most frequent origin was from the muscle fibres of peroneus brevis and its most frequent insertion was into the retrotrochlear eminence of the calcaneum (12,23).
Surgeons should be aware of the existence of this muscle, not only because of possible associated pathology, but also because of its potential use in reconstructive surgery. peroneal muscles which would be important for reconstructive foot surgeons attempting to repair this area. This study will supplement our knowledge on the possible variations of the muscles in this region, which would be useful for lower limbs surgeons.