The human foot provides the structural foundation for upright posture and locomotion. It transmits forces between the body and the ground through 26 bones, 33 joints, and more than 100 muscles, ligaments, and tendons (1). The longitudinal and transverse arches of the foot play an important role in balance creation and efficient movement. The medial longitudinal arch (MLA) is particularly important for distributing the weight and absorbing the shock (2). Pediatric flatfoot or pes planus is defined by the collapse or absence of the MLA, which produces partial or complete sole-to-ground contact. The two clinical patterns are recognized: flexible flatfoot, in which the arch reappears when non-weight bearing, and rigid flatfoot, in which the arch remains absent regardless of position and is more often associated with the underlying pathology (3). Flatfoot is common in children whose skeletal structures are still developing. However, the MLA continues to mature through the first decade of life (4). Most cases of flexible flatfoot in children are physiologic and typically resolve spontaneously with growth. These cases are generally painless and do not impair function. However, a subset of children exhibit persistent, symptomatic, or rigid flatfoot, which can be associated with discomfort, altered gait, postural imbalance, and long-term complications such as ankle or knee pain, plantar fasciitis, and reduced quality of life (5, 6). Without intervention, persistent cases rarely resolve spontaneously and may progressively worsen, highlighting the importance of early recognition and management (7). The Prevalence estimates vary by the age and assessment method; ∼21%–57% in children aged 2–6 years, ∼13.4%–27.6% in primary-school children, and ∼5%–14% in adults (8). Consistent risk factors include male sex, younger age, and elevated body mass index (BMI) (9, 10). Urban environments are often associated with lower physical activity levels and more structured footwear use, factors that have been identified as contributors to weaker foot musculature and an increased risk of pediatric flatfoot (11). Within this context, Kunming represents an urbanized setting included in the present study. Conversely, in resource-limited areas such as Kandahar, limited access to appropriate footwear and preventive care presents distinct developmental challenges. This contrast highlights the importance of shoe practices; empirical evidence indicates that children who spend a greater proportion of time barefoot have a lower prevalence of flatfoot compared with those who begin wearing shoes at an earlier age (12). Despite a growing body of literature, no comparative study has used standardized school-based screening across the two countries to examine the associated factors and similarities. The current study aims to address this gap by evaluating schoolchildren who are between 7 and 14 years old in Kunming, China, and Kandahar, Afghanistan. These two groups differ in several aspects such as urbanization, socioeconomic status, footwear habits, and access to medical facilities. Using an optical podoscope with a line-based footprint classification, we estimate the prevalence of flatfoot and assess associations with demographic, anthropometric, and lifestyle factors (age, gender, residence, BMI, footwear, physical activity, and foot pain). We aim to provide comparable evidence across the urbanized and resource-limited environments.

A total of 4,205 schoolchildren were examined, including 2,050 from Kunming, China, and 2,155 from Kandahar, Afghanistan. The overall participation rate was 95.6%. The baseline demographic and lifestyle characteristics are summarized in Table 1. The distribution of sex differed between the sites with a higher proportion of boys in Kandahar than in Kunming (p < 0.05). The older children group (11–14 years) was more represented in Kandahar (51.9%) than in Kunming (47.4%; p < 0.05). BMI categories also varied significantly (p < 0.05): underweight was more common in Kandahar, whereas overweight and obesity were slightly more frequent in Kunming. Urban residence predominated in Kunming at 75.2% compared with Kandahar at 62.7%. Moreover, footwear patterns showed striking differences between the two groups (p < 0.05). Most children in Kunming wore closed-toe shoes (70.6%), whereas sandals were predominant in Kandahar with 61.9%. No significant differences were observed between the two sites in physical activity (≥180 min/week) or reported foot pain in the preceding 6 months (both p > 0.05).

The overall prevalence of the flatfoot was 12.8%, 540/4,205 with a higher prevalence in Kandahar compared with Kunming (14.6% vs. 11.0%). Flatfoot prevalence was greater among boys than girls in Kandahar with 18.2%, while the sex difference was less pronounced in Kunming with 12.3% (overall p < 0.05). Prevalence was also higher in the older children group (11–14 years), compared with the younger children group in both sites (p < 0.05). Urban children were more frequently affected than rural children in both Kunming (11.9% vs. 8.3%) and Kandahar (17.0% vs. 10.7%; p < 0.05).

BMI showed a clear dose–response relationship: the obese children had the highest prevalence at 26.5% in Kunming and 27.1% in Kandahar, overweight children had an intermediate prevalence, whereas underweight children had the lowest (p < 0.05). Children with foot pain in the past 6 months were substantially more likely to have the flatfoot (Kunming, 27.7% vs. 7.7%; Kandahar, 33.8% vs. 11.1%; p < 0.05). Insufficient physical activity was also associated with the higher prevalence (Kunming, 19.7% vs. 8.8%; Kandahar, 25.2% vs. 11.7%; p < 0.05). Closed-toe footwear was significantly associated with a higher prevalence compared with sandals in both sites (Kunming, 12.6% vs. 7.1%; Kandahar, 16.9% vs. 13.2%; p < 0.05; Table 2).

Among children, the flatfoot severity distributions were comparable between both sites. In Kunming, 35.6% were mild, 44.4% moderate, and 20.0% severe; in Kandahar, 34.9% were mild, 46.0% moderate, and 19.0% severe. Bilateral involvement was predominant at 85.3% in Kunming and 88.3% in Kandahar, with unilateral involvement less frequent (14.7% and 11.7%, respectively). No significant inter-site differences were found in severity or in laterality.

Multivariable logistic regression analyses (Table 3) identified several independent risk factors. Older age (11–14 years) was associated with increased odds of flatfoot in Kunming [adjusted odds ratio (AOR) 1.33, 95% CI: 1.01–1.75, p < 0.05], but not in Kandahar (AOR 1.11, 95% CI: 0.88–1.39, p > 0.05). Male sex was also a risk factor in Kunming (AOR 1.36, 95% CI: 1.03–1.79, p < 0.05), whereas no sex difference was observed in Kandahar (AOR 1.20, 95% CI: 0.94–1.54, p > 0.05). Urban residence was associated with higher odds in both sites (Kunming: AOR 1.45, 95% CI: 1.00–2.10; Kandahar: AOR 1.60, 95% CI: 1.20–2.13; pooled p < 0.05). BMI demonstrated a strong dose–response effect: overweight and obese children had 1.7–3.2 times higher odds compared with normal-weight peers (p < 0.05). Foot pain was one of the strongest predictors, associated with approximately threefold higher odds (Kunming AOR 3.00, Kandahar AOR 2.80; p < 0.05). Insufficient physical activity was also strongly associated (AOR ∼2.0 in both sites; p < 0.05). Finally, closed-toe footwear was consistently associated with a greater risk compared with sandals (Kunming AOR 1.80; Kandahar AOR 1.84; p < 0.05).

Pediatric flatfoot is common in school-aged children although reported prevalence varies depending on age structure, case definitions, and measurement methods. In this school-based comparison from Kunming (China) and Kandahar (Afghanistan), the overall prevalence was 12.8% with higher rates in Kandahar (14.6%) than in Kunming (11.0%). Kunming, the capital of Yunnan Province, is a high-altitude urban center with relatively structured school systems, greater access to healthcare, and widespread use of closed-toe footwear. In contrast, Kandahar is a southern Afghan city with a hotter and drier climate, where sandals and periods of barefoot walking are common, and preventive health infrastructure is more limited. To our knowledge, this is the first study to directly compare pediatric flatfoot between China and Afghanistan. No prior research has provided such a cross-country analysis. This approach provides unique benefits by distinguishing globally relevant determinants of the flatfoot from context-specific influences shaped by the environment, culture, and resources. Importantly, our experience also demonstrates that podoscope-assisted plantar image acquisition is feasible in Kandahar real-world school settings, providing standardized images that enable accurate line-based flatfoot classification, which in turn can directly inform school-based prevention efforts. This small difference shows that factors such as environment, lifestyle, and culture can still influence how common flatfoot is even when the same diagnostic method is used. Across both sites, urban residence, higher BMI, lower physical activity, closed-toe footwear, and foot pain in the previous 6 months were consistently associated with the flatfoot. These findings highlight the importance of the preventive strategies. In both locations, especially in Kandahar, access to preventive care is limited, and school-based programs that promote healthy body weight, encourage regular physical activity, teach safe footwear practices, and address foot pain early could have a significant public health impact. These modifiable correlates are directly relevant to the school health services in diverse cultural settings.

Age and sex-related patterns were not the same across the two study sites. Although many earlier studies have shown that the flatfoot tends to decrease as children get older, our results suggest that this pattern may depend on local conditions. In Kunming, the older children group (11–14 years) was more likely to have flatfoot, while in Kandahar, there was no clear difference between age groups. This difference suggests that the local factors, such as footwear choices, daily activity levels, growth rate, and even the type of flooring, may influence how age affects the development of flatfoot (16). Similarly, although the boys generally show a higher prevalence of flatfoot than girls, our findings also indicate that this pattern varies by location. After adjustment, sex differences were apparent in Kunming but not in Kandahar. This suggests that the gender related variations in flatfoot are not universal and may be shaped by cultural differences in physical activity, growth patterns, or footwear habits. In both populations, BMI showed a clear trend: overweight and obese children were increasingly more likely to have the flatfoot. This finding aligns with the existing biomechanical and epidemiological evidence that excess body weight increases pressure on the feet and contributes to the flattening of the arch (17). The consistent link between the BMI and the flatfoot across two culturally different populations supports BMI as a universal risk factor for pediatric flatfoot. Footwear also appeared to play an important role; those children who wore closed-toe shoes had a higher likelihood of developing flatfoot compared with those who wore sandals. This finding agrees with the previous research suggesting that the rigid or less flexible footwear may restrict arch development and the foot muscle function, while softer or minimal footwear may encourage the stronger arch formation (18).

Because the footwear was grouped broadly as either closed-toe shoes or sandals, these findings reflect the general differences between categories rather than specific design, fit, or duration of wear and should therefore be interpreted with caution. It is worth noting that most children in Kunming wore closed shoes, while sandals were more common in Kandahar. Despite these cultural contrasts, the association between the footwear type and flatfoot was consistent across both sites. This consistency indicates that the footwear is likely to have a direct effect on how the arch develops rather than just reflecting the differences in lifestyle or climate.

Physical activity showed a protective effect, with those children who were less active having higher odds of flatfoot. This supports the idea that regular walking, play, and engagement of the foot intrinsic muscles also help maintain a healthy arch structure. Children who reported foot pain had a much higher prevalence of flatfoot, which is consistent with earlier studies showing that flatfoot can negatively affect quality of life and lead to other foot problems, even in children who were once thought to be “asymptomatic” (19).

The strong association between foot pain and flatfoot in both sites highlights the need to avoid dismissing pediatric flatfoot as purely physiological or harmless. Most of the identified cases were bilateral, and approximately 20% were classified as severe based on the line-based footprint method. The similarity in the severity and the laterality between the Kunming and Kandahar indicates that once the flatfoot develops, its clinical characteristics are largely consistent across the populations, even when environmental factors differ. Although evaluating treatment was beyond the scope of this study, existing evidence supports conservative approaches such as maintaining a healthy weight, modifying physical activity, strengthening the intrinsic foot muscles, and using orthotic devices judiciously and for limited periods to improve outcomes in the symptomatic children (20).

Placing our findings in an international context, our estimates sit within the global spread for school-age children. In Iran, school-based studies report a prevalence of approximately 17%, with flatter feet more common at younger ages, consistent with developmental consolidation of the MLA (16). In Colombia, a two-city sample (ages 3–10) found ∼15.7%, higher in younger strata and varying by city, underscoring how age structure and urban context shape absolute rates (21). In Saudi Arabia, several regional studies using footprint/posture indices report ∼25%–30% among schoolchildren, highlighting heterogeneity by instrument and sampling frame (22). In Taiwan, cohorts enriched with younger primary-school ages show higher detection, with one large study identifying elevated odds in 7–9-year-olds and strong associations with male sex and overweight/obesity, illustrating how age mix and BMI shift prevalence (23). A meta-analytic view also suggests a pooled detection rate of approximately 25%, with higher odds in boys and a declining prevalence with age (11).

Overall, these comparisons position Kunming (11.0%) toward the lower-middle range of the global estimates and Kandahar (14.6%) closer to the mid-range, which emphasizes that factors such as the study methods, age distribution, footwear habits, and levels of urbanization can strongly influence the prevalence rates. The slightly higher prevalence in Kandahar may reflect the nutritional transitions, a mix of the underweight and overweight patterns, differences in the footwear availability, and the limited access to preventive healthcare. In contrast, the lower prevalence in Kunming may be linked to the structured school-based activity programs and better access to the pediatric screening services.

This study has several strengths, including its large sample size n = 4,205, the high participation rate, pre-specified analysis plan, cluster-robust modeling by school, and standardized podoscope imaging conducted in two culturally diverse settings. The consistency of the key associations across both sites highlights the practicality of implementing school-based initiatives that combine the BMI monitoring and simple foot posture screening, promotion of regular physical activity, and context-appropriate footwear recommendations that focus on flexibility, comfort, and safety. Growing evidence that the flexible footwear and the targeted foot-core strengthening enhance muscle strength, balance, and arch development supports the value of such population-level preventive approaches (24).

Pediatric flatfoot was common in both Kunming and Kandahar, with prevalence slightly higher in Kandahar. Most cases were bilateral, and approximately one-fifth were severe. Consistent associations with BMI, physical activity, footwear, and foot pain across both sites suggest that these are globally relevant determinants of flatfoot and should be central to prevention efforts. In contrast, age- and sex-related associations varied between sites, showing that demographic influences are context-dependent rather than universal. Importantly, this study represents the first direct cross-country comparison of pediatric flatfoot between China and Afghanistan. By demonstrating that standardized measurement is feasible even in resource-limited settings such as Kandahar, it highlights both the research value and the practical benefit of such work.