Reliability and validity of the Infoot 3D foot digitizer for normal healthy adults

High Rate of Change of the Foot in Ecuadorian Children: The Need for Proper Shoe Design

BACKGROUND

Physiological changes in the foot may be influenced by external factors such as shoe types or demographic parameters, leading to podiatric conditions in adulthood. The aim of this study was to assess the changes in morphological measurements of the feet of boys and girls during childhood and adolescence.

METHODS

A total of 1678 Ecuadorian children aged 8 to 17 years participated in the study. The length, width, and height of the foot were analyzed using a 3D scanner to obtain the arch height ratio for the diagnosis of pediatric flat foot.

RESULTS

Statistical differences were observed for lengths, widths, and perimeters of the foot in boys aged 5 to 15-16 years and girls aged 5 to 12-13 years. Differences in the height of the navicular bone were found in all age groups, with changes from 2.8 to 4.1% in boys and from 1.3 to 1.5% in girls. The greatest differences between boys and girls of the same age were found at 14 years old onwards. The highest prevalence of flat foot was found in 8-year-old girls (64.9%) and in 12-year-old boys (82.5%).

CONCLUSIONS

The feet of Ecuadorian children develop progressively during childhood and adolescence. Boys presented with longer and wider feet than girls of the same age. The highest prevalence of flat foot was found in 12-year-old boys and 8-year-old girls.

The Features of Foot Morphology and Intrinsic Foot Muscle Property in Adolescent Swimmers: An Ultrasound-Based Study

This cross-sectional study aimed to investigate the relationship between foot shape and intrinsic foot muscles (IFMs) in adolescent swimmers compared with other athletes. Foot morphology of swimmers was compared with other athletes of comparable age and a competition level (n = 32 [64 feet]; a total of 64 feet; 128 feet in two groups). Foot morphology and variables of IFMs were measured using a three-dimensional foot scanner and an ultrasound imaging system, respectively. Multiple linear regression analysis with forced entry was performed to clarify the association of the thickness and the cross-sectional area (CSA) of IMFs with the navicular height in both sitting and standing positions. Navicular height in a standing position, the thickness of the abductor hallucis (AbH) and the flexor digitorum brevis (FDB), as well as the CSA were significantly lower in swimmers compared with other athletes (p < 0.05). A larger CSA for the flexor hallucis brevis (FHB) was observed in swimmers than in other athletes (p < 0.01). The navicular height of swimmers in sitting and standing positions was positively correlated with the thickness and the CSA of the FHB and the FDB (p < 0.05). Multiple regression analysis showed that navicular height was associated with the CSA of the FDB in both sitting and standing positions (β = 0.395; p < 0.002, β = 0.201; p < 0.018). This study showed that the navicular height of elite adolescent swimmers was lower than that of other athletes. Furthermore, the swimmers' high navicular height was associated with the CSA of the FDB, suggesting that the FDB might be more involved in the formation of the medial longitudinal arch than the AbH.

Methodological and statistical approaches for the assessment of foot shape using three-dimensional foot scanning: a scoping review

OBJECTIVE

The objectives of this study were to: (i) review and provide a narrative synthesis of three-dimensional (3D) foot surface scanning methodological and statistical analysis protocols, and (ii) develop a set of recommendations for standardising the reporting of 3D foot scanning approaches.

METHODS

A systematic search of the SCOPUS, ProQuest, and Web of Science databases were conducted to identify papers reporting 3D foot scanning protocols and analysis techniques. To be included, studies were required to be published in English, have more than ten participants, and involve the use of static 3D surface scans of the foot. Papers were excluded if they reported two-dimensional footprints only, 3D scans that did not include the medial arch, dynamic scans, or derived foot data from a full body scan.

RESULTS

The search yielded 78 relevant studies from 17 different countries. The available evidence showed a large variation in scanning protocols. The subcategories displaying the most variation included scanner specifications (model, type, accuracy, resolution, capture duration), scanning conditions (markers, weightbearing, number of scans), foot measurements and definitions used, and statistical analysis approaches. A 16-item checklist was developed to improve the consistency of reporting of future 3D scanning studies.

CONCLUSION

3D foot scanning methodological and statistical analysis protocol consistency and reporting has been lacking in the literature to date. Improved reporting of the included subcategories could assist in data pooling and facilitate collaboration between researchers. As a result, larger sample sizes and diversification of population groups could be obtained to vastly improve the quantification of foot shape and inform the development of orthotic and footwear interventions and products.

Analysis of hallux valgus angles automatically extracted from 3D foot scans taken in North America, Europe, and Asia

The forefoot is the foot part most affected by ill-fitting shoes. Footwear fitting considers the measurements of length, width, and arch length. Toe shape has not yet been used in sizing feet and fitting shoes. This study aims to investigate the variation in toe shape, as measured by the hallux valgus angle. An automatic and reproducible hallux valgus angle measuring method using 3D foot scans with no palpation markers is proposed and applied to about half a million samples collected across North America, Europe, and Asia. The measuring method is robust and can detect the medial contour along the proximal phalanx even in extreme cases. The hallux valgus angle has a normal distribution with long tails on both sides in the general population. Large dispersions of HVA values were observed for both genders and in all three geographical regions. Practitioner summary: The hallux valgus angle has a broad distribution in the general population. Females have larger hallux valgus angles than males, and people from Asia have larger hallux valgus angles than people from North America and Europe. Shoe toe boxes should be designed to fit the actual shapes of shoppers' toes. The proposed method for measuring HVA opens a new opportunity to study the causal relationship between shoe wearing habits and HVA on a large scale.

Evaluation of the Usability of the Tiger Full-Foot Three-Dimensional Scanner for the Measurements of Basic Foot Dimensions in Clinical Practice

BACKGROUND

Foot dimension information is important both for footwear design and clinical applications. In recent years, noncontact three-dimensional (3-D) foot digitizers/scanners have become popular because they are noninvasive and are valid and reliable for most of the measures. Some of them also offer automated calculations of basic foot dimensions. We aimed to determine test-retest reliability, objectivity, and concurrent validity of the Tiger full-foot 3-D scanner and the relationship between manual measures of the medial longitudinal arch of the foot and alternative parameters obtained automatically by the scanner.

METHODS

Intraclass correlation coefficients and minimal detectable change values were used to assess the reliability and objectivity of the scanner. Concurrent validity and the relationships between the arch height measures were determined by the Pearson correlation coefficient and the limits of agreement between the scanner and the caliper method.

RESULTS

The relative and absolute agreement between the repeated measurements obtained by the scanner show excellent reliability and objectivity of linear measures and only good to nearly good test-retest reliability and objectivity of arch height. Correlations between the values obtained by the scanner and the caliper were generally higher in linear measures (rp ≥ 0.929). The representativeness of state of bony architecture by the soft-tissue margin of the medial foot arch demonstrates the lowest correlation among the measurements (rp ≤ 0.526).

CONCLUSIONS

The Tiger full-foot 3-D scanner offers excellent reliability and objectivity in linear measures, which correspond to those obtained by the caliper method. However, values obtained by both methods should not be used interchangeably. The arch height measure is less accurate, which could limit its use in some clinical applications. Orthotists and related professions probably appreciate the scanner more than other specialists.

Stature estimation using foot dimensions via 3D scanning in Taiwanese male adults

In forensic identification, the use of foot dimensions to predict stature is a requisite. For Taiwanese male stature prediction, available information about stature estimation using foot dimensions is still lacking. Therefore, the primary purpose of this study was to establish Taiwanese adult male stature prediction models for various foot dimensions. A total of 2,072 male 3D foot models were collected and the subjects' ages ranged from 18 to 59 years old. Thirteen foot dimensions for each foot were utilized in this study. Bilateral differences were tested using pairedt-tests. Stature predictions based on different foot dimensions were conducted using simple linear and stepwise regression methods. The results showed significant bilateral differences in the majority of the selected foot dimensions (p < 0.001). Foot length had the highest positive correlation with stature in the right and left foot. Using length-related dimensions generated better prediction accuracy (0.356 < R² < 0.533, 4.193 < SEE < 4.928), whereas the worst accuracy was observed with angle-related dimensions (0.001 < R² < 0.023; 6.072 < SEE < 6.137) when employing a single foot dimension to estimate Taiwanese male stature. Stepwise regression analysis results indicated that the coefficient of determination was improved to 0.590 and 0.593 by applying five and six foot parameters to predict stature, respectively. The findings of the present study suggest that these stature estimation equations can be applied to predict Taiwanese male stature in the forensic science field.

Preventive strategy of flatfoot deformity using fully automated procedure

A non-invasive, no radiation, out-of-hospital automated system is proposed to identify low arch integrated in the design and manufacturing of personalized orthoses using parametric modelling. The aim of the design process is to integrate assistive technology with assessment and prevent low arch progressing to a more serious case - flatfoot. In the automated procedure, we developed an assessment method including reliable thresholds of foot type classification and test protocol to reduce interferences due to preceding activities, an automation to translate scanned data into parametric design for orthotic customization, finite element model evaluating effectiveness of the personalized design, and a personalized comparative test to evaluate the long-term improvement of foot arch shape. Our low arch threshold established by subject-specific 3D models reduced the misclassification rate from 55%, as previously reported to 6.9%. Individuals who engaged in sedentary activity (i.e. sitting) had the greater change in arch height compared to active activity (i.e. standing and walking), which is more likely to affect the obtained measure. Therefore, a test protocol now states that participants are not allowed to sit over 100 min prior the measurement to reduce such interference. We have proposed and tested an automated algorithm to translate scanned data including seven foot's parameters into customised parametric design of the insert. The method decreases the required time of orthotic computer-aided design from over 3 h to less than 2 min. A finite element analysis procedure was additionally developed to assess the performance of geometries and material of designed orthotic based on the distribution of plantar pressure and internal stress. The personalized comparative assessment based on midfoot contact area was carried out periodically for follow-up and the orthotic could be re-designed if necessary. The proposed automated procedure develops a pre-screening system to distinguish low arch and provide preventatives before it becomes symptomatic. Furthermore, non-symptom flatfoot can be detected at early stages and referred to medics for further diagnosis or treatment.

Reliability and quality of statistical shape and deformation models constructed from optical foot scans

The unique shape of modern human feet, and how they change shape when loaded are thought to be integral to effective upright gait. This unique shape, and the natural variations therein, have previously been analysed using a range of methods; from visual assessments, anthropometric measurements, and footprints, to x-ray, ultrasound and magnetic resonance images. However, these methods are often limited by their use of linear two-dimensional measures. Only recently have advances in three-dimensional (3D) scanning technology and statistical shape analysis been applied to studying 3D foot shape variations. Given their novelty, information regarding the reliability and repeatability of 3D foot scanning and shape modelling is lacking. To investigate whether repeated foot scans captured by two examiners give the same 3D shape and produce consistent statistical shape models, 17 healthy adults' left feet were scanned while bearing half and full bodyweight, as well as minimal weight. Surface to surface distances between corresponding foot meshes and differences between shape model quality criteria were both found to be small and insignificant. The only exception being the specificity criterion for minimally loaded foot scans. Furthermore, Euclidean vectors were used to model the magnitude and direction of deformation that feet undergo as a consequence of increased loading. The deformation models showed that loading a minimally loaded foot results in greater, but less consistent, shape changes than when increasing the load on an already loaded foot. These results show that the utilized methods offer a valuable, reliable and repeatable approach to analysing foot shape and deformation.

Reproducibility of foot dimensions measured from 3-dimensional foot scans in children and adolescents with Down syndrome

BACKGROUND

Children and adolescents with Down syndrome have a distinctive foot shape (such as wide and flat feet) that often leads to difficulty with footwear fitting. 3-dimensional (3D) scanning can accurately measure the foot dimensions of individuals with Down syndrome, which may assist shoe fit. However, the reproducibility of measuring foot dimensions using 3D scans in children and adolescents with Down syndrome is unknown. The aim of this study was to determine the intra- and inter-rater reproducibility of measuring foot dimensions of children and adolescents with Down syndrome using 3D scanning.

METHODS

3D foot scans of 30 participants with Down syndrome aged 5 to 17 years were obtained using the FotoScan 3D scanner. Foot dimensions assessed were foot length, ball of foot length, outside ball of foot length, diagonal foot width, horizontal foot width, heel width, ball girth, instep girth, first and fifth toe height, and instep height. Additionally, the Wesjflog Index and forefoot shape were determined. Measurements were completed by two raters independently on two separate occasions, 2 weeks apart. Intra- and inter-rater reliability were assessed using intra-class correlation coefficients (ICCs) and Gwet's AC1 statistics with 95% confidence intervals. Agreement was determined by calculating limits of agreement (LOA) and percentage agreement.

RESULTS

Eighteen participants were female and 12 were male (mean age 10.6 [3.9] years). Intra-rater reproducibility (ICCs ranged from 0.74 to 0.99, 95% LOA from - 13.7 mm to 16.3 mm) and inter-rater reproducibility (ICCs ranging from 0.73 to 0.99, 95% LOA from - 18.8 mm to 12.7 mm) was good to excellent, although some measurements (ball of foot length, outside ball of foot length, heel width and girth measurements) displayed wider LOAs indicating relatively poorer agreement. Forefoot shape displayed substantial to almost perfect reliability (Gwet's AC1 0.68 to 0.85) and percentage agreement ranged from 73 to 87%, indicating acceptable agreement.

CONCLUSIONS

The measurement of specific foot dimensions of children and adolescents with Down syndrome using 3D scans is reproducible. Findings of this study may be used to support future research measuring specific foot dimensions of children and adolescents with Down syndrome using 3D foot scans.

How do we fit underground coal mining work boots?

Acceptable footwear fit, particularly width, is subjective and vaguely quantified. Proper shoe fit is important because it affects both comfort and the potential to prevent injury. Although mismatches between the feet of underground coal miners and their internal boot dimensions are known, no research has been undertaken to determine the impact of these mismatches on worker perceptions of fit, comfort and pain. This study aimed to quantitatively assess mining work boot fit relative to underground coal miners' subjectively rated work boot fit and comfort, reported foot problems, lower limb pain and lower back pain in order to develop evidence-based work boot fit recommendations. Traditional footwear fitting methods based predominantly on foot length are insufficient for underground coal mining-specific footwear. Instead, fit at the heel, instep and forefoot must be considered when fitting underground coal mining work boots, in conjunction with the traditional length measurement.Practitioner summary: Underground coal miners report their work boots fit but are uncomfortable. This study assessed actual fit relative to perceived fit, comfort, foot problems, lower limb pain and lower back pain of 197 miners. Fit at the heel, instep and forefoot must be considered when fitting mining work boots.

Reliability and validity of the Zebris FDM-THQ instrumented treadmill during running trials

Little is known about the reliability, validity and smallest detectable differences of selected kinetic and temporal variables recorded by the Zebris FDM-THQ instrumented treadmill especially during running. Twenty male participants (age = 31.9 years (±5.6), height = 1.81 m (±0.08), mass = 80.2 kg (±9.5), body mass index = 24.53 kg/m² (±2.53)) walked (5 km/h) and ran (10 and 15 km/h) on an instrumented treadmill, wearing running shoes fitted with Pedar-X insoles. A test-double retest protocol was conducted over two consecutive days. Maximal vertical force (F_max), contact time (CT) and flight time (FT) data from 10 consecutive steps were collected. Within- and between-day reliability, smallest detectable differences (SDD) and validity (95% limits of agreement (LOA)) were calculated. ICC values for the Zebris for Fmax were acceptable (ICC ≥ 0.7) while CT and FT reliability indices were predominantly good (ICC ≥ 0.8) to excellent (ICC ≥ 0.9). The Zebris significantly underestimated Fmax when compared with the Pedar-X. The 95% LOA increased with speed. SDD ranged between 96 N and 169 N for Fmax, 0.017s and 0.055s for CT and 0.021s and 0.026s for FT. In conclusion, Zebris reliability was acceptable to excellent for the variables examined, but inferior in comparison with Pedar-X. With increased running speeds, a bias effect (underestimation) existed for the Zebris compared with Pedar-X.

The three-dimensional shapes of underground coal miners' feet do not match the internal dimensions of their work boots

Mining work boots provide an interface between the foot and the ground, protecting and supporting miners' feet during lengthy coal mining shifts. Although underground coal miners report the fit of their work boots as reasonable to good, they frequently rate their boots as uncomfortable, suggesting that there is a mismatch between the shape of their feet and their boots. This study aimed to identify whether dimensions derived from the three-dimensional scans of 208 underground coal miners' feet (age 38.3 ± 9.8 years) differed from the internal dimensions of their work boots. The results revealed underground coal miners wore boots that were substantially longer than their feet, possibly because boots available in their correct length were too narrow. It is recommended boot manufacturers reassess the algorithms used to create boot lasts, focusing on adjusting boot circumference at the instep and heel relative to increases in foot length. Practitioner Summary: Fit and comfort ratings suggest a mismatch between the shape of underground coal miners' feet and their boots exists. This study examined whether three-dimensional scans of 208 miners' feet differed from their boot internal dimensions. Miners wore boots substantially longer than their feet, possibly due to inadequate width.

The relationship between arch height and foot length: Implications for size grading

OBJECTIVE

Medial longitudinal Arch Height is synonymous with classifying foot type and conversely foot function. Detailed knowledge of foot anthropometry is essential in the development of ergonomically sound footwear. Current Footwear design incorporates a direct proportionate scaling of instep dimensions with those of foot length. The objective of this paper is to investigate if a direct proportional relationship exists between human arch height parameters and foot length in subjects with normal foot posture.

METHOD

A healthy convenience sample of 62 volunteers was recruited to participate in this observational study. All subjects were screened for normal foot health and posture. Each subject's foot dimensions were scanned and measured using a 3D Foot Scanner. From this foot length and arch height parameters were obtained. Normalised ratios of arch height with respect to foot length were also calculated. The arch height parameters and the normalised arch ratios were used interchangeably as the dependent variables with the foot length parameters used as the independent variable for Simple Linear Regression and Correlation.

RESULTS

Analysis of foot length measures demonstrated poor correlation with all arch height parameters.

CONCLUSION

No significant relationships between arch height and foot length were found. The predictive value of the relationship was found to be poor. This holds significant implications for the current method of proportionate scaling of footwear in terms of fit and function to the midfoot region for a normative population.

Comparing 3D foot scanning with conventional measurement methods

BACKGROUND

Foot dimension information on different user groups is important for footwear design and clinical applications. Foot dimension data collected using different measurement methods presents accuracy problems. This study compared the precision and accuracy of the 3D foot scanning method with conventional foot dimension measurement methods including the digital caliper, ink footprint and digital footprint.

METHODS

Six commonly used foot dimensions, i.e. foot length, ball of foot length, outside ball of foot length, foot breadth diagonal, foot breadth horizontal and heel breadth were measured from 130 males and females using four foot measurement methods. Two-way ANOVA was performed to evaluate the sex and method effect on the measured foot dimensions. In addition, the mean absolute difference values and intra-class correlation coefficients (ICCs) were used for precision and accuracy evaluation. The results were also compared with the ISO 20685 criteria.

RESULTS

The participant's sex and the measurement method were found (p < 0.05) to exert significant effects on the measured six foot dimensions. The precision of the 3D scanning measurement method with mean absolute difference values between 0.73 to 1.50 mm showed the best performance among the four measurement methods. The 3D scanning measurements showed better measurement accuracy performance than the other methods (mean absolute difference was 0.6 to 4.3 mm), except for measuring outside ball of foot length and foot breadth horizontal. The ICCs for all six foot dimension measurements among the four measurement methods were within the 0.61 to 0.98 range.

CONCLUSIONS

Overall, the 3D foot scanner is recommended for collecting foot anthropometric data because it has relatively higher precision, accuracy and robustness. This finding suggests that when comparing foot anthropometric data among different references, it is important to consider the differences caused by the different measurement methods.