FIBULARIS TERTIUS MUSCLE AMONG PRE-CLINICAL STUDENTS OF A MEDICAL COLLEGE: A DESCRIPTIVE CROSS-SECTIONAL STUDY

Background : The fibularis tertius muscle (FTM) is a variant muscle of the crural compartment of the leg that is thought to have evolved in human as a result of the development of the bipedal gait. The Fibularis tertius muscle, as an ankle dorsiflexor and foot evertor, plays an important physiological role in effective terrestrial locomotion related to midfoot biomechanical stabilization. The objective of this study is to determine the occurrence of the fibularis tertius muscle using a surface anatomical examination of the foot in medical and dental students of a medical college. Methods: This was a descriptive cross-sectional study comprising 294 pre-clinical medical and dental students of College of Medical Sciences, Chitwan, Nepal. In each student, the fibularis tertius muscle was palpated on both lower limbs for their presence or absence. The data was collected in terms of age and gender and was analyzed using the Statistical Package for Social Science version 20. Results: The prevalence of fibularis tertius muscle was 50.68%, with females accounting for 23.13% and males accounting for 27.55%. Fibularis tertius muscle was more common bilaterally (37.07%) than unilaterally (13.61%). Among unilateral fibularis tertius muscle, 24 (8.16%) were found only on the right foot and 16 (5.44%) on the left foot only. The bilateral prevalence of the fibularis tertius muscle was 17.01 % in females and 20.07 % in males, while its unilateral prevalence in females and males was 6.12 % and 7.48 %, respectively. Conclusions: The involvement of the fibularis tertius muscle in affecting midfoot stabilization and its potential role in delaying the healing process of John’s fracture cannot be ignored. Hence, understanding the theory behind foot biomechanics requires awareness of the existence of the fibularis tertius muscle.


INTRODUCTION
It is debatable whether the fibularis tertius muscles (FTM), the muscle of the crural compartment of the leg is a separate entity or not, but Colombio and Fallopio claimed that it is a part of or 5th digit of the extensor digitorum muscle that is inserted on the fifth toe. 1 The FTM is an ankle dorsiflexor and foot everter 2,3 and plays a significant part in efficient terrestrial locomotion linked to biomechanical roles in midfoot stabilization. 4,5 FTM is considered a secondary gait muscle; hence, there hasn't been much research into its sole role in human gait. However, FTM has recently acquired therapeutic interest as a result of the advent of ankle arthroscopy. Its tendon has also been used to treat ligamentous ankle injuries, 6 correct pes cavus 7 and repair ruptured tibialis anterior tendon. 8 Stress fractures of the base of the 5th metatarsal bone have been traced to the FTM insertion site in a few cases. [9][10][11] Furthermore, FTM contraction may be a key factor in the delayed healing of a fracture in the 5th metatarsal bone's shaft.
Despite the clinical importance of FTM, its incidence in the Nepalese population has not been studied. Hence, this study is undertaken with an aim of ascertaining the prevalence of FTM and its relationship to gender using a surface anatomical examination of the foot in students of medical college.

METHODS
The cross-sectional observational study was conducted in the Department of Anatomy of College of Medical Sciences, Bharatpur, Chitwan, Nepal. After obtaining ethical clearance from Institutional Review Committee (Ref. No-COMSTH-IRC/2021-59), the data was collected from preclinical medical and dental students from February to April 2021. The students with the age between 17 to 21 years were included in this study, while the students with the history of injury, fracture or congenital anomalies of foot were excluded. Sample size was calculated as below: The sample size was adjusted for finite population by using the formula, n o = (nN) / (N + (n-1)) = (601 x 300) / (300 + (601-1)) = 201 Where, n= minimum required sample size for infinite population Z= 1.96 at 95% Confidence Interval (CI) p= past prevalence taken as 50% for maximum sample size e= margin of error, 4% n o = adjusted sample size for finite population N= total number of Preclinical medical and dental students (300) Taking a 10% non-response rate, the optimal sample size was 221. However, 294 students were enrolled in the study. After taking verbal and written consent data was collected from the students by using non probability (convenient) sampling technique. The gender and the age of the students were noted.
In each student, the FTM was palpated on both lower limbs for their presence or absence. Palpation of FT was carried out based on the following criteria: 13,14 Criteria 1: The FT tendon was palpated without any muscle strain on the way to the fifth metatarsal. We labeled any tendon that met these conditions as F1 ( Figure 1). If no tendon was palpated, we proceeded to the second criterion. Criteria 2: The subjects' feet were asked to dorsiflex and evert. If the FT tendon was defined using the same criterion as criteria 1, we designated it as F2 ( Figure 2). We went on to third criterion if nothing was noticed here. Criteria 3: The same procedure as Criteria 2 was followed, but manual resistance was applied to the lateral side of the foot at the fifth metatarsals; if the tendon was visualized or palpated, it was designated as F3 ( Figure 3).
During the procedures, Position of student: The student sat with their knees flexed to about 110° Position of evaluator: The evaluator kneels on the floor in front of the patient's limb, which was fixed at the ankle joint and palpates the FTM insertion.
The collected data was entered and analyzed by using Statistical Package for Social Science version (SPSS) 20. Then data was analyzed using descriptive statistical tools. For the continuous variable mean and standard deviation was calculated, while categorical variables were expressed in term of frequency and percentage.

RESULTS
Of the total 294 students from first and second years of MBBS and BDS, 144 were females (48.98%) and 150 were males (51.02%). The mean age of overall students was 19.52±1.191 years. FTM was found in 149 students, resulting in a prevalence of 50.68%, with females accounting for 23.13 % and males accounting for 27.55 %. FTM was observed bilaterally in 37.07% and unilaterally in 13.61%. Among unilateral FTM, in 8.16% of the students it was present on the right side and in 5.44% on the left side. The bilateral prevalence of FTM was 17.01 % in females and 20.07 % in males, while the unilateral prevalence of FTM was 6.12% in females and 7.48% in males (Table 1). FTM were palpated by applying manual resistance to the lateral border of the foot which was dorsiflexed and everted at the fifth metatarsal (F3) in 176 feet. In 79 feet, FTM was identified by simply asking them to dorsiflex and evert their foot (F2) while, in three feet, the tendon was visualized on its way to the fifth metatarsal without any muscular tension (F1) ( Table 2). In the current study, 37.07% of the 294 students studied had bilateral FTM, while 13.61% had unilateral FTM, with no gender differences. In a study performed in 195 medical students at Sapthagiri Institute of Medical Sciences and Research Centre in Bengaluru, Karnataka State, India, bilateral FTM (41%) was found to be more frequent than unilateral FTM (22.05%) as in our study. 19 Similar findings were observed in the Nigerian population; bilateral FTM-52%, unilateral FTM-21%. 15 Amongst unilateral FTM, occurrence on the right foot (8.16%) was higher than that on the left foot (5.44%) in the present study. Similar findings were observed in previous study in which 15% were present on the right and 6% on the left foot. 20 Conversely, the prevalence of FsTM on the left foot (11.79%) was slightly higher than on the right foot (10.25%) in a study by Potu et al. 19 The occurrence of FTM in our study was slightly higher in males than in females on both the right and left foot in overall sample. The findings are consistent with those of previous studies conducted in Belgian, 10  Clinical studies on the use of vascularised muscle, such as the FTM flap, to treat osteomyelitis by filling soft tissue gaps in the lower limb have been reported, which significantly improves the flow of sufficient oxygen, nutrients, and immune cells to the healing tissue by filling a dead space. 21 The FTM is an auxiliary muscle for eversion and dorsiflexion of the foot, according to Witvrouw et al, so its absence does not significantly affect the force of eversion and dorsiflexion. Clinicians however, should regard its absence in young or elderly patients as a possible etiologic explanation for a number of talocrural zone stabilization problems. 10 Understanding the surface evaluation of FTM may indubitably help orthopaedic surgeons consider arthroscopic treatment or rehabilitation of lateral ankle instability, thereby minimizing the risk of injury to FTM that may be entrapped the beneath suture during the procedure. 22,23 This research was carried out only in single center among preclinical medical and dental students so the finding of this research cannot be generalized to the whole population (students) of Nepal. As the study sample consisted of lower limbs with no apparent pathologies, this research would not illuminate the association between FTM and foot deformities.

CONCLUSION
In the present study, we observed that the FTM was absent unilaterally or bilaterally in some students. As the agenesis of FTM has its major effect on the biomechanics of the foot, this research may be of interest to anatomists, physiotherapists, and orthopedic surgeons. Furthermore, it is essential to conduct detailed studies of this muscle in various populations of normal and abnormal feet and gaits to determine its effect on foot shape and biomechanics.