Introduction

Qualitative analysis of sexual dimorphism of foot dimensions is important to the study of ergonomics, forensic science and anthropometry hence, the relevance of this work to the development of these fields of study in Nigeria.

Anthropometry is a series of systematized measuring techniques that express quantitatively the dimensions of the human body and skeleton. Anthropometry is often viewed as a traditional and perhaps the basic tool of biological anthropology, but it has a long tradition of use in forensic sciences and it is finding increased use in medical sciences especially in the discipline of forensic medicine. It is highly objective and reliable in the hands of trained anthropometrists. The significance and importance of somatometry, cephalometry, craniometry and osteometry in the identification of human remains have been described and a new term of 'forensic anthropometry' is coined[₁].

The human foot, the foundation of bipedal locomotion, is a highly complex multibone structure with 26 bones and numerous articulation[₂₃]. It is required to be stable for supporting body weight in standing, resilient for walking and accommodating to variations of surface on which it is placed. The normal human foot shows great individual variation in length, breadth and general in males and females[₄₅].

Literature on sexual dimorphism in shape differences among human feet have focused on osteological difference between men and women. Linear measurement in size and shape differences between males and females foot bones showed that male bones were larger than female bones. Also measurement of articular surface suggested that females bones have the potential for more movement to occur in the direction of adduction, possibly resulting in the female first metatarsal being more adducted than it the male skeleton. Such differences may underline the predisposition of the female foot to develop hallus valgus deformity[₆].

A few studies have also compared population who habitually use different types of foot wear, but these studies have been limited in the variables examined and rarely considered ethnic differences unrelated to footwear[₇]. They documented that among Urban Japanese, proportionate to stature, women have smaller feet than men.

Appreciation to the sexual dimorphism of foot shape is essential to proper design of shoe shape as correct shoes is commonly recognised to be attained by matching shoe shape to foot shape. Hence, understanding the morphological and functional response to variation in foot pattern among ethnically different population necessitates a basic understanding of racial variation among population using similar foot wear. Information in gender and racial differences in foot pattern becomes very useful[₈].

Wunderlich and Cavanagh analyzed gender differences in foot shape in large samples of young individuals using data from the U.S. army foot and leg anthropometric data. In their study they found out that men have long and broader feet than women for a given stature after normalization of the measurements by foot length, males and females were found to differ significantly in four foot shape variables. Classification by gender using absolute value was correct at least 93% of the time. Using the variables standardized to foot length gender, was correct classified 85% of time from this, they demonstrated that female feet and legs are not simply scaled down versions of male feet but rather differ in number of shape characteristics, particularly at the arch, the lateral side of the foot, the first toe and ball of the foot. These differences should be taken into account in the design and manufacture of women’s shoes for better fit and more comfort[₈].

Didia et al in their study, the use of foot print contact index II for classification of flat feet in the Nigeria population, observed that contact indices values were lower in females than in males, a proof that the arches are better developed in males. Also, they mentioned that other factors such as type of foot wear, physical activities and weight bearing habits may also played a role[₉].

Obikili and Didia found that the mean values of the right foot length of young adult Nigeria males and females population were 27.1 ± 1.3cm and 25.1 ± 1.1cm, respectively. The values for the right foot were 9.9 ± 0.6cm and 9.2 ± 0.5cm respectively. Males had significantly higher values of foot length and breadth than females, p<0.001 comparing with other populations. They concluded that males and females in our populations had higher mean foot length than the Caucasian which probably is an adaptation to tropical climate[₁₀].

Although, several studies have been conducted on foot and footprints for stature estimation having bearing on personal identification, prediction and forensic medicine/science, and foot biomechanics[_{11121314151617}]; others have used foot and shoeprint[₁₈], foot and boot dimensions[₁₉] in determining stature. Recent study has correlated foot length and body weight[₂₀].

This present study is aimed at providing anthropometric values for foot length and width and comparing them to existing data needed for the establishment of reference standard for the Nigerian population on the basis of which populations can be compared with one another, and sexual differences established.

It is also aimed at providing standard needed for objective clinical assessment of individuals as well as body modelling. Also, to provide baseline data for design and manufacture of shoes for correct shoe fit.

Materials And Method

Materials

Method

For this study direct measurement techniques was employed. The foot dimensions were measured with sliding calliper, with foot placed on a horizontally flat surface, while the subject was standing. The maximum foot length was measured from acropodian (It is the most forwardly projecting point on the head of the 1st or 2nd toe whichever is larger when the subject stands erect) to pternion (It is the most backwardly projecting point on the heel when the subject is standing upright with equal pressure on both the feet). The foot breadth was measured as the distance between the medial margin of the head of the first metatarsal and the lateral margin of the head of the fifth metatarsal.

The foot index was calculated as shown in the formula below.

Figure 1

To ensure accurate result all measurements were done by one person while sitting on low chair to avoid errors that could be caused by discomfort or individual differences. All subject who did not know their age and those who had recognized foot deformities were exempted or excluded from this study. The measurements were repeated to avoid errors.

Results

A total of four hundred and seventy-seven (477) subjects 18yrs and above were used for the study. The parameters measured from each right and left foot are the foot length and foot breadth. This was measured directly from each foot with the subject placing the foot on a horizontally placed flat surface.

The age group and number of individuals in each group for both male and female are represented in table 1.

Figure 2

Table 1: Sample Size

Table 2 shows the range of the foot length and foot breadth for males and females in centimetres.

Figure 3

Table 2: Range of Foot Dimension for Males and Females

Table 3 and 4 show the mean foot length of males and females by age while table 5 and 6 shows the mean foot breadth of males and females by age. Also, tables 9 and 10 show the mean foot length and mean foot breadth of males and females population respectively and their coefficient of variation and confidence interval at 95% accuracy. Males had significantly higher foot length than females, and significantly broader foot breadth then females, p<0.001.

Table 7 and 8 shows the foot indices of males and females with the right foot index larger than that of the left, in both sexes. Table 11 is a comparative data in foot length.

Figure 4

Table 3: Foot Length of Males by Age in CM

Figure 5

Table 4: Foot Length of Females by Age in CM

Figure 6

Table 5: Foot Breadth of Males by Age in CM

Figure 7

Table 6: Foot Breadth of Females by Age in CM

Figure 8

Table 7: Foot Index of Males by Age

Figure 9

Table 8: Foot Index of Females by Age

Figure 10

Table 9: Mean Foot Length and Breadth of Male Sample Population

Figure 11

Table 10: Mean Foot Length and Breadth of Females Sample Population

Figure 12

Table 11: Comparative Data of Foot Length of Males and Females

Discussion

This study was carried out to determine the sexual dimorphism in the foot dimension among adult Nigerians and also provide anthropometrics data for foot length and foot breadth of adult Nigerians to add to existing data.

The small value for the standard deviation of foot dimensions for both sexes implies that the foot length and foot breadth are clustered around the mean values for both right and left foot in both sexes. The small percentages of coefficient of variation also observed in males and females in the right and left foot length and breadth, implies that small variation occurs between the mean values of foot length and foot breadth for sample population and mean values of foot length and foot breadth by age.

From this observation, we found that the males had significantly higher foot breadth than females p< 0.001 for the foot length, the right foot length was found to the higher than left foot length by 0.21cm and 0.25 for males and females respectively. This value is greater than the finding of bonnie et al, on Caucasian[₂₅].

The foot dimension in males and females in this study is comparatively larger than Caucasian values. This finding is in accord with theoretical expectation that populations living in warm climates would have longer arms and legs than populations living in cold environments[₂₆]. Schreider reported that tropical climate dwellers have longer limbs than temperate climate dwellers. Large foot dimensions are adaptation to tropical environment as they increase the surface area available for heat loss[₂₆].

Ashizawa et al and Wunderlich and Cavanagh reported in their respective study showed that males have longer and broader feet than females for a given stature[₇₈]. The larger foot dimension of males in this study in comparison with females is in agreement with this postulation. Besides, Saxena, and Obikli and Didia in their various study on the Nigeria population also found that males, have broader and longer foot dimensions than fermales[₂₄₁₀].

On the clinical application of foot dimension, Gorman et al in their study on the relationship between shoe size in women and mode of delivery noted that a woman with a small shoe size did not have a higher chance of being delivered by Caesarean section[₂₇]. Schultz et al reported that many girls with Rett Syndrome had small feet for height[₂₈]. Besides, Rodier et al noted that children with autism had smaller feet compared with the control group[₂₉]. This study like that of Obikili and Didia[₁₀] provides added reference standard of foot dimension for the Nigerian population and form a basis for further studies on clinical application of foot dimension.

Conclusion And Recommendation

This study is able to establish that the mean value of right foot length in males and females were 26.92 ± 1.02 and 25.00 ± 1.33 and the mean values for right foot breadth for males and females were 9.87 ± 0.53 and 9.14 ± 0.58. The males have longer and broader foot dimensions than females (p< 0.001). Besides, the right foot is longer and broader than the left foot. Females foot are not scaled–down versions of males as they differ in length and breadth.

This finding may be useful for both shoe design and selection of shoe size. As the right foot was significantly wider than the left foot, we suggest that the shape of the left and right shoes might not need to be symmetrical during design. The width of the shoe could be 2 to 3mm wider on the right foot for a better fit. This study suggests that one try the shoe on the right foot first and consider how it will fit. Besides, this study can be successfully utilized in forensic examination of the foot for personal identification. Because the subjects measured for this study were mostly right hand dominant, the question of whether side dominance has significant effects on the tested results needs further study.

Corrspondence