3D scanning and children’s footwear
Dr Carina Price, University of Salford & Dr Stewart Morrison, University of Brighton
Foot shape and size are important factors in determining footwear shape and resultant fit. This is particularly so in childhood where shape and proportions of feet change rapidly. Feet grow very quickly, particularly before three years of age. Children, particularly when younger, may be less able to describe the fit of their shoes as appropriate or not. They are also less capable of making footwear related decisions and might well prioritise a design or a colour over fit.
A standard set of measures is commonly used to describe the dimensions of feet in relation to footwear. These include lengths (such as whole foot length), widths (such as foot width/breadth, heel width/breadth) and circumferences (such as the ball circumference). However, these measures only tell us about these specific dimensions of the foot at specific points and do not provide a thorough measure of the morphology of the foot. The arch shape and size, for example, is not routinely captured and described, and cannot truly be so with just a two-dimensional measure. Indeed, two feet with the same width and length can look very different.
Advantages of 3D scanning
The influx of affordable 3D scanning technology and improvements in mobile camera technology led us to better capture the dimensions and shape of the whole foot in clinical and home settings. The recent trend in online footwear fitting imposed by the restrictions due to covid-19 also provides an opportunity. Various technologies exist to capture foot shape using mobile technology by wearers at home, describing the shape of the plantar or whole foot and then using a ‘best-fit’ to match this to dimensions of a shoe. These mobile applications are being used to match wearers to a size, some incorporating the influence of materials and also utilising user feedback to improve the process.
However, if we do not consider more measures other than two-dimensional ones between set points such as width/breadth and length, we are not making the most of the opportunities this technology offers. Advances in processing software enable us to make a more detailed analysis of these 3D shapes which come from scanners. Researchers have considered measures such as cross-sections, volume, the location of each point on a surface and shape characteristics of the surface of the foot. These measures all make a more detailed interpretation of the shape of the foot.
Some have been used to compare between genders and other factors in order to describe feet belonging to specific populations. However, their translation to footwear or clinical outcomes has not always been finalised at this relatively early stage. This is the essential step to enable these measures to be ‘useful’ in a more applied setting.
Changing shape of children’s feet
Infant feet grow rapidly, with length growing by around 2mm per month up to the age of three years. Whilst later on in childhood this rapid growth becomes slower, foot length nevertheless still increases by around 1cm per year. In terms of proportions, the foot starts out relatively wide and round. Between the ages of two and seven, changes are predominately in length. Some research has found that this trend continues until 11 years of age when the proportions become more similar to the adult foot.
Variance in foot shape is multifactorial with genetic, ethnic, socio-economic, and environmental factors all thought to have an influence. Whilst this is a difficult topic to explore, there is some data that suggests ethnicity as an important variable in explaining differences in structural characteristics of children’s feet. These differences are thought to underpin associations between ethnicity and the predisposition to specific foot and ankle pathologies, but much more work is needed. Despite current opinion, most studies undertaken have considered characteristics relating to shape or proportions of the feet, or frequency of pathology, with little recognition of the functional demands on the feet. Linked with this, the debate about whether footwear impacts on the structure of children’s feet has been argued for decades with studies often comparing shod and non-shod populations.
Why is fit so important?
Appropriate design and fit of footwear in children are essential for supporting the healthy development of the foot and gait. A child’s foot is a soft structure which is still developing and maturing with numerous bones yet to ossify and gain their mature shape. The footwear provided for such children must enable the foot to be free to move and not restrict developing movements. It must also not be too big. Ill-fitting footwear can lead to acute issues such as blisters and affects the way children walk.
Shoes that are too big make children walk with a shorter step length and lift their foot higher when they swing it through to the next step. This occurs alongside a more flexed knee when the foot is in the air. More chronic influences of ill-fitting footwear are less easy to identify even though impacts on foot development and morphology are apparent. Research shows us that children who grow up habitually barefoot or with less time in closed shoes have different shaped toes and higher foot arches than those who are primarily shod. The impact of these differences to overall foot health in the short or long-term however remains unclear.
On a more holistic level, footwear enabling freedom of movement of the child and facilitating them interacting in their environment is also key. Like adulthood, in children we can recognise a requirement for footwear to be seen as facilitative. This translates as children being able to undertake activities relevant to their age group, such as running, jumping and playing football. Children, particularly those of school age, want to fit in with their peers and the expectations of their age group to not appear ‘old’ or ‘babyish’.
We also see an importance for parents to address social expectations in terms of footwear and to purchase shoes which they think are ‘beneficial’ for their children. This relies on the credibility of a brand and, quite frequently, family tradition and expectation. Despite this, parents highlight a lack of awareness about foot health alongside a lack of available foot health information, with their knowledge largely coming from their experiences or being shared by peers or family members. In a normal situation, where access and finance allows, parents seemed to prioritise having their children’s feet measured in a store and then purchasing recommended footwear.
Purchasing shoes online
A key factor during the past year has been the measurement of feet at home, so as to be able to purchase footwear online due to the large-scale closure of retail outlets caused by covid-19. A review of online information was undertaken in 2019, before these closures, to appraise what was available to parents in terms of fitting resources and information. This review identified that the majority of available information online was produced by footwear companies and that professional bodies, such as the College of Podiatry, made up very little of these resources.
These resources from commercial footwear companies were however highly accessible for parents, frequently appearing as the first result of an online search. Nevertheless, some of them were lacking in validity in terms of the measures they were asking parents to take and their recommendations in making footwear choices using such measures. High quality advice, measures and recommendations for fitting footwear in childhood are essential.
How can 3D scanning improve fit?
Scanning the feet and analysing the 3D shape enables us to understand specific structural and surface shapes. This can point to specific changes which relate to larger circumferences and volumes of a shoe last for a specific age or ethnicity of child. If we look at the 3D shape of the foot and how it changes with time we can also find valuable information concerning the grading of the last and how relative foot morphology and size changes across foot sizes (Figures 1-3).
Each point on the surface of the foot captured by the scanner can be described mathematically. Exploring these points on the surface of the scan and its specific shape can teach us about regional variations in shape of the foot surface and how these change as children grow or age. One example is measuring the curvedness of the foot shape at each point of the medial-lateral arch of the foot.
Examining this curvedness visually shows us the longitudinal arch developing with age in these average feet. The plantar sole of the foot is blue, which means it is flat as these scans were captured during standing. With increasing age, we can see an increase in green colours which represents an increase in curved shapes with orange/red being the most curved. These changes in curvedness on the plantar foot are localised to the medial midfoot area where the longitudinal arch is developing.
This change in surface shape of the foot means that the area of the foot in contact with the shoe changes with age and the overall shape of the midfoot area is altering. These measures show us that a universal children’s shoe or last simply being scaled up in size is not going to fit each age or foot the same. In the same way, looking at other areas of the foot can provide us with useful information for other footwear features such as considering the dorsal foot curvedness when designing uppers.
With the new trend in fitting and purchasing footwear online there exists a real opportunity for the integration of more complex measures from 3D scans into footwear fit. Some novel data analysis approaches might be able to provide detailed information to measure and interpret the childhood foot and be able to apply this directly to footwear design. At the same time, there is scope for the footwear industry to exploit its online messages and considerable reach. They have significant influence with parents and an opportunity to support well informed public foot health messages. Greater collaboration between health professionals and the footwear industry (both retailers and brands) is important for improving footwear fit in children.
Photo Credit: Pexel/Keira Burton
