Footwear fit in schoolchildren of southern Spain: a population study

The literature about the association between footwear and children’s foot health is confusing and full of contradictory findings. Some recent studies strongly support the theory that ill-fitting shoes are an important cause of foot pain and the consequent emergence of malformations related to this [1]. Existing meta-analyses show that the impact of footwear on gait should be considered when assessing the paediatric patient and evaluating the effect of shoe or in-shoe interventions [2]. Observational studies carried out in this field have shown a high growth rate in the foot length of schoolchildren. A recent study conducted in German schoolchildren between 6 and 14 years of age, determined an average foot growth in length of 6.2 mm/ year in boys and 4.2 mm/year in girls [3]. In the same way, the current evidence shows that during the child’s development and until the age of 8 years, the foot predominantly grows in length and after this age, the width/length proportion in older children is similar to observed in adults [4].

These rapid changes may be conditioned by extrinsic factors, such as footwear, or intrinsic factors, such as foot morphology or body mass index, and which in combination, can influence the morphological and functional development of the adult foot. With these growth rates, it seems only logical that the footwear of schoolchildren may become small quickly. Current reviews on the topic emphasize the importance of taking into account the changing morphology of children’s feet, which, along with their high functional demand, must be considered when designing ergonomic footwear [5, 6]. In the same way, some studies have shown that foot shapes differ between populations and genders, and for proper footwear fit, footwear should have enough size varieties to imitate different foot shapes of all humanity [7, 8].

There are very few studies focused on analysing the ideal toe allowance in length and width of children’s footwear. Some authors consider that, for a shoe to fit properly in length, there should be a minimum toe allowance (TA) of 5–12 mm between the tip of the shoe and the longest toe in the footwear of schoolchildren until the age of 16 years [3]. This allowance takes into account the dynamic increases that occur in the size of schoolchildren’s feet, which may range between 2.1 and 4.4 mm in length and reach around 2 mm in width, according to previous studies [9, 10]. Müller et al. found that most static and dynamic foot characteristics change continuously during growth and maturation, and these changes should be taken into account when development of suitable children’s shoes [4]. Even though footwear width allowances have not been established in a precise manner, the authors recommend a sufficient allowance, since the forefoot is especially sensitive to external influence [3, 11, 12]. The main purpose of this study was to verify the outdoor footwear fit in a schoolchildren population of southern Spain, taking as reference the ideal toe allowance considered in the literature.

The left foot was longer than the right foot in 72.6% of the schoolchildren. The FL average in the age range of 5 to 12 years was 9.22 ± 3.68 mm in boys and 9.62 ± 8.17 mm in girls (P > 0.05). Highest FL average increase in girls occurred between 7 and 8 years. The FW average in the age range of 5 to 12 years was 0.22 ± 0.09 mm in boys and 0.18 ± 0.006 mm in girls (P > 0.05). The boys had wider feet than the girls with significant differences from 9 years old.

Considering the ideal allowances, it was observed that 72.5% of the schoolchildren used short footwear and 66.7% used narrow footwear. The Wilcoxon test for related samples showed that, in the age range between 7 and 11 years, the footwear was shorter than the foot, with significant differences. Likewise, in the age range between 4 and 9 years, the footwear was narrower than the foot, with significant differences. The Mann-Whitney U test did not show significant differences with respect to length and width according to gender.

Most authors agree in pointing out that children are more vulnerable to the effects of ill-fitting shoes. However, since there are numerous factors that influence foot morphology, it is difficult to ensure a correct fit between footwear and feet, unless footwear manufacturers pay special attention to this when designing shoes for schoolchildren. Considering the ideal TA, the results of the present study show that 72.5% of the children and preadolescents wore ill-fitting shoes when looking at the length of school shoes compared to the length of the feet. A cross-sectional study carried out in 858 Austrian preschool children of 3–6.5 years showed similar results, and observed that the outdoor footwear was shorter than the feet in 69.4% of the sample; they also reported a significant relationship between this occurrence and the risk of suffering from hallux valgus [11]. Similar results have been reported in a recent study conducted in South African children who found that 67% of the children and adolescents wore ill-fitting shoes shorter than the feet [16].

The results of our study are especially striking given that the ideal TA in length considered by other authors for the 90th percentile was less than 15 mm. Mean TA values obtained by Barisch-Fritz et al. were 5.0 ± 3.7 mm for girls and 6.9 ± 3.8 mm for boys participants. The 90th percentile of TA was 9.8 mm for female and 11.5 mm for male participants aged 6–14 [3].

We believe that TA is especially relevant considering that there are studies that associated too-short footwear and forefoot malformations [11]. It was not possible to compare the results of the present study in terms of footwear fit width and length, since no studies were found in the literature to analyse these parameters in schoolchildren. Even though there are no data regarding the necessary allowance in height for schoolchildren’s footwear, the results of some similar studies show the need to carry out periodic changes that favour such fit [3, 11, 12].

Interestingly, it was observed that the inner footwear length was greater than that indicated by the footwear manufacturers in all the sizes analysed. Although this occurrence may be considered an advantage, it is recommended to purchase footwear according to the size of the feet and not to the size of the shoe indicated by the footwear manufacturers.

Previous studies show that footwear manufacturers do not take into account the anthropometric differences related to the digital formula. Current shoe designs do not allow for the comprehensive 3-D foot shape, which means they are unable to reproduce the wide variability in foot morphology [8]. The general procedure used to design children’s footwear is on a linear scale, from lasts taken in adult feet with a square forefoot morphotype. These lasts constitute the model for the production of different sizes of children’s footwear. These same authors emphasize the fact that most footwear manufacturers companies do not change the size of the lasts to include feet with different digital formulae [7]. We have not found significant differences regarding footwear fit in length and width with respect to digital formula. It was observed that the square foot was the one that was best fitted to the tip of the shoe; however, we consider that when designing ergonomic footwear for schoolchildren, not only the different digital formulae must be taken into account, but also the position and orientation of the forefoot inside the shoe and its interaction with the shoe tip.

With respect to width, the results of the present study show that 66.7% of the children and preadolescents wore ill-fitting shoes too narrow. Most shoemaking systems do not consider this parameter when producing children’s footwear and the shoes available in the market do not always comprise different widths for the same length. On the other hand, the width considered when designing children’s footwear is that of the resting foot, even though the evidence shows that both length and width are greater in the weight-bearing foot, and even greater when moving. However, we consider that, although the existence of different widths for the same size would be ideal, it cannot be asserted categorically that it is necessary to produce different widths for the same length, since the differences observed in the present study were more homogenous for width than for length. It was not possible to compare the results of the present study in terms of footwear fit in height, since no studies were found in the literature to analyse this parameter in footwear of schoolchildren. Regarding gender, the variations in foot measurements underwent a gradual increase with age in both boys and girls. Although we have not found significant differences with respect to FL, as in similar studies carried out in our country, we have also found gender differences with regard to the FL average appeared at the age of 8–9 years with a greater FL of the girls [17]. Some studies have shown that the change foot size in length that occurs in North American girls ages 6 to 7 may represent an early marker for the transition to puberty [18]. Regarding the FW, and coinciding with recent studies, measurements showed that the boys had significantly wider feet than the girls in all of the age categories, although we have observed significant differences from 9 years old. Unlike this study, we have not found significant differences between boys and girls with regards to foot and shoe width [16]. The results of the present study demonstrate the need to adapt the sizes of footwear to the rapid increase in FL registered. Based on ours observations, and in coincidence with other authors, we propose changing footwear twice per year for children between 4 and 6 years of age, and three times per year for those between 6 and 12 years of age [3, 12]. This recommendation can suppose an impact on the family economy and to avoid these considerable financial implications, we agree with Barisch-Fritz et al. on the need to consider the use of 90th percentiles instead of mean values for the schoolchildren’s footwear manufacturing with adequate TA for both sexes [3]. We consider that footwear dynamic adjustments are applicable without customising to gender and age. However, it is important to account for the high variability and the different static and dynamic situations, with the purpose of improving footwear design and thus contribute to healthy foot development in children and adolescents.

As reinforcement for the study, the results regarding the quality of the anthropometric measurements made and especially the Inter-observer relative technical error of measurement (TEM %), have shown the reliability of the measurements made by the two operators who participated in the study. On the other hand, we highlight that we have considered the interior capacity of the footwear in the points where the foot presented the greatest dimensions, unlike other studies that measure the maximum interior capacity of the footwear without taking into account the different digital formulas. On the contrary, as a weakness, we point out the lack of a stop for the touch probe due to the non-resistance typical of the characteristics of the footwear’s material in the metatarsal area and of the upper. This circumstance may have generated some bias in the measurements results referring to height especially.

The scarce evidence available makes it necessary to conduct prospective longitudinal studies to analyse the relevance that ill-fitting footwear during childhood may have on the future development of malformations in the adult foot. Thus, children’s footwear manufacturers will understand the need to design lasts from 3D technology adapted to the different foot morphologies, with the necessary allowances in length, width and height. On the other hand, when designing and selecting schoolchildren’s footwear size, it is also necessary to consider the biomechanical requirements of the children’s feet in primary education. We believe that the public administrations and the general population should be aware of the problem in order to find a solution. Meanwhile, public health practitioners should consider widespread implementation of school health programs that raise awareness among parents and teachers about the advisability of replacing periodically the footwear of schoolchildren within the age range of 5 to 12 years.