Infant, Children, and Adolescent Health
Age, Sex, Body Mass Index, and Laterality in the Foot Posture of Adolescents: A Cross Sectional Study

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Abstract

Objective

To investigate the relationship between the right and left foot posture in terms of body mass index (BMI), sex, and age in adolescents aged 10 to 14.

Methods

A total of 1400 adolescents were included. For assessment, the Foot Posture Index (FPI-6) was used. Each foot was assessed and ranked as supinated, normal, or pronated by the sum of the FPI-6 criteria. Each criterion was scored on a scale of –2 to +2, with negative for supinated and positive for pronated posture. A linear mixed model with repeated measures was used for statistical analysis.

Results

Sex, BMI, and right and left foot are associated with FPI-6. The total score attributed for male sex (β = 0.29, P = .04) and the left foot (β = 0.73, P < .001) was higher (male right foot: mean ± standard deviation [SD], 3.09 ± 2.84, male left foot: 3.76 ± 2.80; female right foot: mean ± SD, 2.28 ± 2.61, female left foot: 3.45 ± 2.66; laterality for left foot: mean ± SD, 3.55 ± 2.71, laterality for right foot: mean ± SD, 2.82 ± 2.7). On the other hand, the correlation coefficient for the BMI was negative (β = -0.08, P = < .001), which means that the higher the BMI the lower the score attributed to the FPI-6.

Conclusions

The FPI-6 is positively related to the male sex and the left foot—that is, the predicted score is higher, so the feet tend to present with a tendency to pronation. Although BMI is associated with FPI-6, it was not possible to establish a relationship between high BMI and pronation of the feet.

Introduction

The human foot reaches its full development in adolescence. Specifically, it can be said that it grows rapidly up to 3 years of age and, after this phase, maintains a pattern of continuous growth in both sexes. Around 12, the feet of girls stop growing, but boys exhibit a pattern of development to 15 years of age.1

The evaluation of foot posture can be affected by extrinsic and intrinsic factors. Extrinsic factors correspond to the place of residence (urban or rural), level of physical activity, types of footwear, and age at which the use of footwear begins. Intrinsic factors are categorized as biological (sex, age, ligamentous laxity, family history) or anthropometric (body composition).2, 3, 4, 5

Among the intrinsic factors, the most controversial in the literature is still the body mass index (BMI). Some studies in children and adolescents have shown that overweight and obese subjects have distinct morphology6 and more pronated feet,7 that is, with larger feet and greater circumference. However, other studies in adolescents and adults do not establish this relationship.8, 9, 10 One of the hypotheses for the discrepancy in results is the methodology and target population characteristics being studied, for example, age.11

The shape of the foot is influenced by age and the most frequent postural change is the pronated or flat foot, which corresponds to a reduction in the height of the medial longitudinal arch (MLA) and calcaneal valgus.2 Studies have shown that the prevalence of pronated feet in children under 3 years of age is quite high, and its prevalence decreases with advancing age because the arch develops in the first decade of life, more specifically from 2 to 6 years of age.1,12 In this sense, it has been observed that young people (3-17 years) and elderly people (60 and over) have more pronated feet than adults (18-59 years).9

In addition to age, it is important to emphasize the influence of sex on foot posture because it has been observed that boys present more cases of pronated feet than girls.3,13,14 Mickle et al14 corroborated this finding by comparing children from 3 to 5 years of age. The authors found that boys showed a thicker fat pad along the MLA, which suggests a later development because, in girls, the fat pad has been resorbed by this age. Other studies have also shown that boys more often have pronated feet and that considerable changes occur from childhood to adolescence.3

There are several methodologies for assessment and postural foot classification. Among them, we highlight the Foot Posture Index (FPI-6)15 for being valid and reliable16 and for allowing a multidimensional assessment in all planes of movement, opposite the footprints, which has as its focus the analysis of the midfoot region.17,18 The advantages of FPI-6 include the low cost, the reproducibility of the data, and the clinical access of the anatomical measurements to be palpated. Unlike an X-ray examination, this does not require expensive technology involving radiation.15

Although some studies have already investigated the anthropometric and biological determinants of foot posture, this study differs as to the research methodology used and the target population (adolescents), providing greater clarity regarding these variables in this period of life marked by intense body modifications.19 Despite the growing number of studies in this line of reasoning, it seems there is still no consensus on the influence of sex, BMI, age, and laterality (right and left side) in foot posture in adolescents, so it is important to better elucidate the effect of these factors.

It is important to note that, in a study using the same methodology as this research in the adult population, no significant differences were found between the position of both feet (right and left)20; however, it is essential to perform this observation in adolescence, as a phase of life marked by development and physiological and anatomical adaptations,19 so that other findings can most likely be verified.

Identifying the parameters that affect the normal development of the foot during adolescence facilitates the development of an understanding of important risk factors related to any misalignment of the foot and of other dysfunctions (eg, musculoskeletal disorders such as sprains or patellofemoral pains) or foot injuries. The posture of the foot can be altered by anthropometric factors, among them excess body mass. A study by Smith et al21 identified evidence that obese children and adolescents presented greater prevalence of fractures, self-reported ankle and foot problems, valgus and hyperextension of the knees, and pain symptoms in particular segments of the lumbar spine, knees, ankles, and feet. This had a direct impact on the level of physical activity (exercises and sports) of the child or adolescent and quality of life in general. These changes affect body balance and performance for dynamic motor coordination.22 Understanding foot posture in adolescents according to FPI-6 criteria may yield reference values for assessing the anthropometric characteristics of the feet. Knowledge of these parameters will support more accurate therapeutic treatments for the rehabilitation of anthropometric foot changes, such as pronation and supination, and will help in health surveillance.

Thus, the primary objective of this study was to characterize foot posture in school children aged 10 to 14 years and the secondary was to verify that there is a relationship between foot posture classified by the FPI-6 with BMI, sex, age, and right and left laterality. Our main hypotheses are that there will be a positive relationship with the male sex, age, and high BMI; that is, in all conditions, the foot will present as more pronated. It is believed that there will be no postural differences between the feet, taking into consideration what has been presented in the literature in adults.

Section snippets

Location and Population Study

This is a cross-sectional study with a convenience sample. Data from this research were collected in conjunction with a doctoral project titled “Prevalence of idiopathic scoliosis in adolescents in cities in the state of São Paulo.”23,24 Data were collected between 2013 and 2014 in public schools, administered by the School Board of Mogi Mirim—Amparo and Pedreira—in São Paulo, Brazil. The study was approved by the Ethics Committee of the Medical School of the University of São Paulo (protocol

Results

In Table 2, it can be observed that the distribution of adolescents by age and sex is not homogeneous. The lowest percentage for adolescent age groups corresponds to 10-year-olds (8%) and the highest corresponds to 12-year-olds (26%). Moreover, the proportion of girls was greater than the boys, representing 66% of the total sample.

It can also be observed in Table 3 that, for all BMI ranges, the proportions of adolescents evaluated with pronated or highly pronated feet are larger for the left

Discussion

The hypotheses of this study have not been fully confirmed because the foot posture was shown to be related only to the male and, interestingly, to the left foot. As for BMI and age, it is not possible to say from our findings that these are crucial determinants in foot posture.

It can be seen through our data and other studies that adolescent males have more cases of pronated feet, as the predicted score in the evaluation of boys is higher than in girls.3,13,14 This finding is due to the fact

Conclusion

The FPI-6 in adolescents aged 10 to 14 years is related to the male sex and the left foot—that is, in both conditions, the predicted score is higher so the feet tend to present with a tendency to pronation. In relation to BMI, however, a negative relation is observed—that is, the score attributed to the FPI-6 in the adolescents who are classified as overweight and obese is lower. However, regardless of the sex and BMI of the adolescent and the foot on which the evaluation is performed, the foot

Acknowledgments

The authors are grateful to the CEA USP- Centro de Estatística Aplicada da Universidade de São Paulo for the statistical analysis.

Funding Sources and Potential Conflicts of Interest

No funding sources or conflicts of interest were reported for this study.

Contributorship Information

Concept development (provided idea for the research): B.K.G.C., P.J.P., S.M.A.J.

Design (planned the methods to generate the results): B.K.G.C., P.J.P., S.M.A.J.

Supervision (provided oversight, responsible for organization and implementation, writing of the manuscript): B.K.G.C., S.M.A.J.

Data collection/processing (responsible for experiments, patient management, organization, or reporting data): B.K.G.C., P.J.P., N.L.J.P.R., R.M.A.

Analysis/interpretation (responsible for statistical analysis,

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