Correlation Between the Severity of Flatfoot and Risk Factors in Children and Adolescents: A Systematic Review

Abstract

Background/Objectives: Flatfoot is a common pediatric foot deformity characterized by a reduced or absent medial longitudinal arch (MLA). The condition can lead to altered gait, pain, and potential long-term morbidity if untreated. Identifying potential risk factors—such as body mass index (BMI), ligamentous or joint instability, shoe choices, and physical activity—is crucial for prevention and management. The objectives are to systematically review and synthesize current evidence on how flatfoot severity correlates with BMI and other risk factors in children and adolescents, and to highlight methodological considerations essential for future research. Methods: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we searched five electronic databases from inception to February 2024. Flatfoot severity was measured by various clinical or radiographic indices. Two reviewers independently screened and assessed the risk of bias. Results: Thirty-seven studies met the inclusion criteria. Children with high BMI had increased odds of flatfoot (pooled Odds Ratio = 2.3, 95% Confidence Interval: 1.6–3.1), with one outlier reporting an OR of 9.08. Heterogeneity (I² up to 70%) stemmed from varied diagnostic methods. Other factors, including joint instability, shoe choices, and physical activity, showed mixed associations. Conclusions: Elevated BMI strongly correlates with pediatric flatfoot severity, highlighting the importance of proactive weight management and foot assessments. Future standardized, longitudinal studies are needed to clarify causality and refine interventions.

1. Introduction

Flatfoot, often termed pes planus, is characterized by the collapse or insufficient development of the medial longitudinal arch (MLA), resulting in a valgus positioning of the hindfoot and a flattening of the foot’s plantar surface. In children, flexible flatfoot can be a normal developmental stage and often resolves spontaneously by the age of 6–7 years as the MLA matures. Flatfoot in children ranges in prevalence from 10–50%, depending on diagnostic criteria, age, and population. However, a subset of children, adolescents, and even adults continue to present with clinically significant flatfoot, which may lead to altered gait biomechanics, pain, and potential long-term morbidity if left unmanaged [1]. As such, understanding which factors influence flatfoot severity is crucial for early detection, prevention, and treatment. Over the last two decades, multiple observational studies have highlighted body mass index (BMI) as a primary risk factor for persistent flatfoot. An elevated weight-bearing load may exacerbate the strain on the developing arch, potentially contributing to progressive flattening of the foot [2]. Obesity may also correlate with other comorbidities such as reduced physical activity, neuromuscular imbalances, and altered gait kinematics, further intensifying foot deformities [3]. Despite the consistent emphasis on BMI, there remains considerable debate regarding the weight threshold for risk escalation, the interplay of other biomechanical parameters, and whether obesity might simply be a surrogate marker for broader lifestyle issues (e.g., sedentary behavior). Beyond BMI, other proposed risk factors for flatfoot severity include ligamentous laxity and hypermobility (often used interchangeably in some studies, though hypermobility is typically a broader systemic phenotype), footwear habits, and physical activity. Ligamentous laxity can diminish arch support and predispose individuals to foot deformities [4].

Footwear habits, particularly the prolonged use of shoes lacking medial arch support or those with inappropriate sizing, have been cited as potential risk factors for foot malalignment in children, although the evidence is far from conclusive [5]. Additionally, reduced physical activity may limit normal muscular strengthening in the foot and lower limb, which can hinder the natural development or maintenance of the MLA [6]. Conversely, some investigators suggest that engaging in moderate to high levels of weight-bearing physical activities might aggravate foot stress in overweight children, thus paradoxically increasing their risk of symptomatic flatfoot [7]. By contrast, other data imply that physical activity could strengthen foot musculature, mitigating arch collapse. Such conflicting perspectives underscore the complexity of flatfoot etiology and highlight the need for a holistic assessment of children’s lifestyles, anthropometrics, and foot morphology. Notably, measuring “flatfoot severity” lacks uniformity across the literature. Some studies rely on static footprints (e.g., Clarke’s angle, Staheli arch index), whereas others employ dynamic pedobarography, radiographic evaluation (e.g., Meary’s angle), or composite clinical tools like the Foot Posture Index (FPI) [8,9,10]. Discrepancies in outcome definitions and thresholds for “severity” have led to heterogeneous estimates of prevalence and inconsistent associations with risk factors.

Previous reviews have provided evidence on the prevalence of pediatric flatfoot but lacked clarity on how specific risk factors correlate with varying degrees of severity. While BMI has been emphasized, footwear habits (especially cultural differences in shoe use) and physical activity remain less systematically evaluated. This systematic review aims to consolidate the recent evidence on the correlation between BMI and flatfoot severity while also examining the influence of additional risk factors such as ligamentous laxity, footwear habits, and physical activity. A critical focus is placed on highlighting methodological challenges, particularly the variability in diagnostic criteria, which complicates cross-study comparisons. By strengthening the evidence base, the review seeks to inform targeted clinical interventions and advocate for standardized research methods to better address the multifactorial etiology of flatfoot.

2. Methods

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [11]. We did not register our protocol on PROSPERO. A comprehensive search was performed in PubMed, Scopus, Embase, the Web of Science, and the Cochrane Library from inception to December 2024. Keywords included a combination of controlled vocabulary and free-text terms: “flatfoot”, “pronated foot”, “pronated feet”, “pes planus”, “arch collapse”, “planovalgus”, “flat-arched feet”, “pes plano-valgus”, “low arched feet” AND “child”, “children”, “teenager”, “preschool child”, “adolescent” AND “risk factors”, “influence factors”, and “related factors”.

The gray literature was searched via the references of included articles and selected conference abstracts. We contacted the primary authors when clarification on methods or results was necessary.

2.1. Eligibility Criteria

We included studies if they: (1) involved children or adolescents aged 3–18 years; (2) reported clinically or radiographically diagnosed flatfoot or flatfoot severity measures (e.g., Foot Posture Index, radiographic angles, etc.); (3) examined at least one potential risk factor (BMI, joint instability, shoes, or physical activity); (4) were observational or interventional studies published in peer-reviewed journals since 1990; and (5) were written in English. We restricted our search to English due to resource limitations for translation and chose 1990 as the lower bound because standardized diagnostic criteria for pediatric flatfoot began gaining traction in the early 2000s.

2.2. Study Selection and Data Extraction

Two reviewers (G.G. and D.A.M.) worked independently to screen titles and abstracts for relevance using pre-defined eligibility criteria. Discrepancies were resolved by discussion with a third reviewer (I.S.) until a consensus was reached. Full texts of potentially eligible articles were then retrieved for a second round of screening. Inter-rater reliability for full-text inclusion was estimated using Cohen’s kappa (κ = 0.82), indicating strong agreement. Data extraction was conducted using a standardized form in Microsoft Excel, gathering information on study design, publication year, and geographic location. Details regarding sample size and participant demographics, such as age and sex distribution, were recorded. Methods used for diagnosing flatfoot and grading its severity, including tools like the Foot Posture Index (FPI), Clarke’s angle, and radiographic measurements, were documented. The analysis extended to risk factors like BMI, ligamentous laxity, and footwear, with key findings including prevalence rates, odds ratios, and correlation coefficients.

2.3. Risk of Bias Assessment

The risk of bias for included studies was assessed based on study type. For observational studies, including cross-sectional, case–control, and cohort designs, the Newcastle–Ottawa Scale (NOS) [12] was employed, focusing on participant selection, comparability between groups, and outcome measurement. Interventional studies were evaluated using the Cochrane risk of bias tool (RoB 2) [13], examining aspects such as randomization processes, allocation concealment, and blinding in outcome assessment. Each study was ultimately categorized as having a low, moderate, or high risk of bias, determined by the average rating across assessed domains.

2.4. Data Synthesis and Statistical Analysis

A qualitative synthesis of all the included studies was performed to map out the range of diagnostic methods and risk factors. A meta-analysis was performed focusing on studies that examined the association between BMI and flatfoot prevalence or severity, specifically those providing quantitative estimates such as odds ratios or correlation coefficients in comparable populations. Pooled odds ratios (OR) were calculated for dichotomous outcomes comparing overweight/obese individuals to those of normal weight. For studies reporting correlation coefficients (r), narrative summaries or Fisher’s z-transformations were applied. A random-effects model (DerSimonian and Laird) was used to address inter-study variability [14]. Heterogeneity was assessed using Cochran’s Q and the I² statistic, with subgroup analyses exploring differences by age (early childhood vs. adolescence) and diagnostic methods (e.g., Foot Posture Index vs. footprint techniques). Geographic factors, such as footwear practices in urban versus rural settings, were considered as potential moderators, though data limitations precluded formal subgroup meta-analyses. Publication bias was evaluated using funnel plots and Egger’s test when at least ten studies were included in a given meta-analysis [15].

3. Results

From an initial search yielding 693 records, 82 remained after removing duplicates and excluding 516 that were off-topic or did not meet the age/severity criteria (Figure 1, PRISMA Flow Diagram). A full-text assessment was conducted for 82 articles, of which 37 met the inclusion criteria for the qualitative synthesis. Among these, 12 contained quantitative data suitable for inclusion in the meta-analysis on BMI.

3.1. Study Characteristics

Table 1 summarizes the key characteristics of the 37 included studies. The publication dates ranged from 1999 to 2023. The sample sizes varied from small observational cohorts (n = 24) to large epidemiological surveys (n > 1000). The majority were cross-sectional (n = 26), while case–control (n = 5), retrospective (n = 4), and longitudinal or interventional (n = 2) designs were also represented.

• Population Age Range: 3–18 years. Several studies concentrated on early childhood (3–6 years) [2,16], whereas others spanned up to late adolescence (14–18 years) [17].
• Flatfoot Diagnostic Methods:

  ○

  Clinical/Footprint Methods: Clarke’s angle, Staheli arch index, Chippaux–Smirak index [2,16].

  ○

  Composite Indices: Foot Posture Index (FPI) [18].

  ○

  Radiographic Measures: Meary’s angle, calcaneal pitch, talonavicular coverage angle [19].

  ○

  Dynamic Assessments: Pedobarography with valgus index, arch height index under weight-bearing conditions [20].

• Risk Factors:

  ○

  BMI/Obesity: The most commonly assessed, with varying definitions of “overweight” and “obesity” (e.g., WHO cutoffs vs. local pediatric growth charts).

  ○

  Ligamentous Laxity: Tested via the Beighton scale or clinical hypermobility assessments [21].

  ○

  Footwear Habits: Some studies focused on footwear type (boots, sandals, or supportive shoes), while others examined usage frequency.

  ○

  Physical Activity: Measures such as hours per week of sporting activities or daily step counts.

  ○

  Other Biomechanical Factors: Heel valgus, subtalar fusion status, Achilles tendon morphometry.

Table 1. Included studies.

	Author, Year	Design	N (Male/Female)	Mean Age (Range)	Risk Factor Assessed	Flatfoot Severity Metric	Prevalence (Mild/Moderate/Severe)	Correlation (r/OR/RR)	Risk of Bias
1	J.M. Morales Asencio et al., 2019 [22]	Case–Control	104 (47/57)	7.55 (6–9 years)	BMI, late onset of walking	Valgus index (pedigraphy)	54.5% valgus deformity (right foot)	Obesity (OR: 9.08, p < 0.0001)	Low
2	Sadeghi-Demneh et al., 2016 [23]	Cross-Sectional	667 (340/327)	7–14 years	Heel valgus, dorsiflexion range	Pathological flatfoot (clinical/radiographic)	10.3% total	High BMI (p < 0.01)	Moderate
3	Medina-Alcantara et al., 2019 [5]	Cross-Sectional	132 (61/71)	7.53 (6–8 years)	Footwear type, frequency	Valgus prevalence (unspecified method)	45.5% valgus foot	Boots reduce valgus (p = 0.009)	Moderate
4	Kadhim et al., 2013 [24]	Retrospective	24 patients (43 feet)	11 (4.7–18.3 years)	Subtalar fusion vs. calcaneal lengthening	Coronal plane pressure index (CPPI)	Severe deformities	Subtalar fusion reduced pain	High
5	He et al., 2023 [25]	Cross-Sectional	74 (40/34)	Adolescents (not specified)	BMI, ligamentous laxity	Meary’s angle, calcaneal valgus	Not specified	Ligamentous laxity (r = 0.413, p < 0.01)	Moderate
6	Abich et al., 2020 [26]	Cross-Sectional	823 (Unspecified)	11–15 years	BMI, footwear, physical activity	Staheli arch index	17.6% total	Obesity (OR: 4.2, p < 0.001)	Low
7	Sadeghi-Demneh et al., 2015 [27]	Cross-Sectional	667 (340/327)	7–14 years	BMI, foot mechanics	Footprint method	46% pathological	BMI: OR = 2.1, p < 0.01	Moderate
8	Vergara-Amador et al., 2012 [28]	Cross-Sectional	940 (Unspecified)	3–10 years	Age, BMI, footwear habits	Clinical exam	15.7%	Flatfoot associated with BMI, p < 0.05	Moderate
9	Chen et al., 2009 [29]	Comparative Case Series	1024 (549/475)	5–13 years	Obesity, foot dimensions	3D foot dimensions	28%	Obesity significantly correlated (p < 0.01)	Low
10	Chen et al., 2014 [30]	Cross-Sectional	605 (405/200)	3–6 years	Motor development delay, obesity	Footprint measurement	58.7% (decreasing with age)	Obese children: OR = 3.6, p < 0.001	Low
11	Gonul et al., 2016 [31]	Case–Control	59 (Unspecified)	11.96 ± 2.44 years	Achilles tendon morphometry	Ultrasound cross-sectional area	Negative correlation with Achilles size	Negative with age (Beta = 1.96, p = 0.04)	Moderate
12	Birhanu et al., 2023 [32]	Cross-Sectional	1022 (454/568)	11–18 years	BMI, footwear, physical activity	Plantar arch index	10.27%	Urban living (aOR = 2.42, p < 0.05)	Moderate
13	Yam et al., 2022 [33]	Case–Control	121 (59/62)	8.07 ± 1.10 years	Fat percentage, developmental coordination disorder	Foot Posture Index (FPI-6)	Higher in DCD group	FPI-6 related to fat percentage	Moderate
14	Alfageme-García et al., 2021 [34]	Longitudinal Cohort	165 (89/76)	5–11 years	Backpack use, pronated foot posture	Foot Posture Index (FPI)	76 developed neutral foot posture	Backpack use (aOR = 1.94, p < 0.05)	Low
15	Puszczalowska-Lizis et al., 2022 [35]	Regression Analysis	200 (100/100)	6 years	Foot arch impact on toe position	Podoscope analysis	Sex differences in arching effects	Transverse arch impacts hallux valgus	Low
16	Villarroya et al., 2008 [17]	Cross-Sectional	245 (130/115)	13.2 ± 1.8 years	BMI, foot structure	Chippaux–Smirak index	Lower MLA in obese group	BMI and MLA (p < 0.01)	Low
17	García-Rodríguez et al., 1999 [36]	Cross-Sectional	1181 (Unspecified)	4–13 years	Over-treatment of flexible flatfoot	Denis classification grades	2.7% true prevalence	Treatment mismatch (28.1%)	Moderate
18	El et al., 2006 [4]	Screening Study	579 (299/280)	9.23 ± 1.66 years	Hypermobility, hindfoot alignment	Dynamic weight-bearing arch assessment	Moderate–severe: 17.2%	Hypermobility increases risk (p < 0.05)	High
19	Chen et al., 2010 [37]	Cross-Sectional	1598 (833/765)	3–6 years	Age, sex, obesity, W-sitting	Weight-bearing medial arch assessment	54.5% at age 3, 21% at age 6	W-sitting increases risk (OR > 1)	Moderate
20	Halabchi et al., 2013 [21]	Cross-Sectional	120 (Unspecified)	6–10 years	Ligamentous laxity, footwear habits	Foot arch grading	50% flexible flatfoot	Ligamentous laxity (p<0.01)	Moderate
21	Yan et al., 2013 [19]	Retrospective	100 (54/46)	8–13 years	Radiographic talonavicular angle	Talonavicular coverage angle	10.3% symptomatic	Navicular angle OR = 1.89	Moderate
22	Troiano et al., 2017 [38]	Cross-Sectional	281 (139/142)	4–20 years)	Age and sex effects on prevalence	Baropodometric analysis	Flatfoot: 31.7%, Hollow foot: 68%	Flatfoot risk (OR = 2.23)	Low
23	Shapouri et al., 2019 [39]	Cross-Sectional	194 (112/82)	6–7 years	Obesity and lower extremity deformities	Clinical observation	13.38%	BMI linked to prevalence (OR = 1.89)	Moderate
24	Han et al., 2017 [40]	Cross-Sectional	72 (32/40)	15.4 ± 4.0 years	Heel valgus, arch index, Q-angle	Arch index, valgus measurement	Moderate–severe in adolescents	Heel valgus correlated with Q-angle (r = 0.81)	Moderate
25	Abolarin et al., 2011 [41]	Cross-Sectional	560 (Mixed)	6–12 years	Footwear habits and BMI	Footprint analysis	Significant in urban population	Urban living OR = 1.5	Moderate
26	Alsuhaymi et al., 2019 [42]	Cross-Sectional	403 (193/210)	7–14 years	Age, sex, BMI	Staheli’s plantar index	29.5%	BMI a significant predictor	Moderate
27	Chen et al., 2022 [43]	Retrospective Cohort	69 patients (107 feet)	7–14 years	Surgical success factors	Radiographic measures (Meary’s angle)	Significant improvement post-surgery	Meary’s angle improvement (p<0.001)	Moderate
28	Pfeiffer et al., 2006 [2]	Cross-Sectional	835 (424/411)	3–6 years	Age, sex, BMI (weight categories)	Rearfoot angle via laser scanner	44% flexible flatfoot, <1% pathological	Higher BMI strongly linked to flatfoot prevalence (OR > 2)	Low
29	Evans & Karimi, 2015 [18]	Retrospective Analysis	728 (Mixed)	3–15 years	BMI, sex, Foot Posture Index	Foot Posture Index (FPI)	FPI ≥ +6 in 40%, ≥ +8 in 20%	Weak correlation BMI and FPI (r = −0.077)	Moderate
30	Drefus et al., 2017 [44]	Reliability Study	30 (Mixed, 60 feet)	9.61 ± 1.96 years	AHI in sitting/standing postures	Arch height index (AHI)	Moderate to severe: 21–24%	AHI ICC ≥ 0.76	Low
31	Twomey et al., 2010 [45]	Comparative Study	50 (25/25 Normal/Low Arch)	11.1 ± 1.2 years	Kinematic differences during gait	Heidelberg foot measurement method	Low arch differences noted in gait	Forefoot supination significant (p < 0.03)	Low
32	Stavlas et al., 2005 [46]	Cross-Sectional	5866 (Mixed)	6–17 years	Foot morphology and growth	Dynamic footprints	Growth-related changes in prevalence	Significant growth-related differences (p < 0.05)	Moderate
33	Yin et al., 2018 [47]	Cross-Sectional	1059 (Mixed)	6–13 years	BMI, age, foot size	FootScan SAI ratio	FFF 39.5% at age 6 to 11.8% at age 12	BMI positively correlates (OR 2.43 obese)	Moderate
34	Boryczka-Trefler et al., 2021 [48]	Prospective Cohort	50 patients (100 feet)	5–9 years	Static vs. Dynamic Flatfoot	Static and dynamic pedobarography	Static 87%, Dynamic 56%	Static vs. Dynamic metrics inconsistent	Low
35	Chang et al., 2014 [49]	Cross-Sectional	1228 (Mixed)	6–12 years	Bimodal footprint index distribution	Staheli’s and Chippaux–Smirak indices	Bimodal arch distribution noted	Arch indices stable across groups	Low
36	Tashiro et al., 2015 [50]	Cross-Sectional	619 (311/308)	11.3 ± 0.7 years	Toe grip strength	Staheli’s arch index	17.8% flatfoot	Toe grip significantly lower in flatfoot	Moderate
37	Pauk et al., 2014 [51]	Cross-Sectional	93 (60/33)	9–16 years	Plantar pressure and Clarke’s angle	Clarke’s angle	Significant medial pressure in flatfoot	Clarke’s angle correlates with plantar pressure (r > 0.9)	Moderate

Table 1. Included studies.

	Author, Year	Design	N (Male/Female)	Mean Age (Range)	Risk Factor Assessed	Flatfoot Severity Metric	Prevalence (Mild/Moderate/Severe)	Correlation (r/OR/RR)	Risk of Bias
1	J.M. Morales Asencio et al., 2019 [22]	Case–Control	104 (47/57)	7.55 (6–9 years)	BMI, late onset of walking	Valgus index (pedigraphy)	54.5% valgus deformity (right foot)	Obesity (OR: 9.08, p < 0.0001)	Low
2	Sadeghi-Demneh et al., 2016 [23]	Cross-Sectional	667 (340/327)	7–14 years	Heel valgus, dorsiflexion range	Pathological flatfoot (clinical/radiographic)	10.3% total	High BMI (p < 0.01)	Moderate
3	Medina-Alcantara et al., 2019 [5]	Cross-Sectional	132 (61/71)	7.53 (6–8 years)	Footwear type, frequency	Valgus prevalence (unspecified method)	45.5% valgus foot	Boots reduce valgus (p = 0.009)	Moderate
4	Kadhim et al., 2013 [24]	Retrospective	24 patients (43 feet)	11 (4.7–18.3 years)	Subtalar fusion vs. calcaneal lengthening	Coronal plane pressure index (CPPI)	Severe deformities	Subtalar fusion reduced pain	High
5	He et al., 2023 [25]	Cross-Sectional	74 (40/34)	Adolescents (not specified)	BMI, ligamentous laxity	Meary’s angle, calcaneal valgus	Not specified	Ligamentous laxity (r = 0.413, p < 0.01)	Moderate
6	Abich et al., 2020 [26]	Cross-Sectional	823 (Unspecified)	11–15 years	BMI, footwear, physical activity	Staheli arch index	17.6% total	Obesity (OR: 4.2, p < 0.001)	Low
7	Sadeghi-Demneh et al., 2015 [27]	Cross-Sectional	667 (340/327)	7–14 years	BMI, foot mechanics	Footprint method	46% pathological	BMI: OR = 2.1, p < 0.01	Moderate
8	Vergara-Amador et al., 2012 [28]	Cross-Sectional	940 (Unspecified)	3–10 years	Age, BMI, footwear habits	Clinical exam	15.7%	Flatfoot associated with BMI, p < 0.05	Moderate
9	Chen et al., 2009 [29]	Comparative Case Series	1024 (549/475)	5–13 years	Obesity, foot dimensions	3D foot dimensions	28%	Obesity significantly correlated (p < 0.01)	Low
10	Chen et al., 2014 [30]	Cross-Sectional	605 (405/200)	3–6 years	Motor development delay, obesity	Footprint measurement	58.7% (decreasing with age)	Obese children: OR = 3.6, p < 0.001	Low
11	Gonul et al., 2016 [31]	Case–Control	59 (Unspecified)	11.96 ± 2.44 years	Achilles tendon morphometry	Ultrasound cross-sectional area	Negative correlation with Achilles size	Negative with age (Beta = 1.96, p = 0.04)	Moderate
12	Birhanu et al., 2023 [32]	Cross-Sectional	1022 (454/568)	11–18 years	BMI, footwear, physical activity	Plantar arch index	10.27%	Urban living (aOR = 2.42, p < 0.05)	Moderate
13	Yam et al., 2022 [33]	Case–Control	121 (59/62)	8.07 ± 1.10 years	Fat percentage, developmental coordination disorder	Foot Posture Index (FPI-6)	Higher in DCD group	FPI-6 related to fat percentage	Moderate
14	Alfageme-García et al., 2021 [34]	Longitudinal Cohort	165 (89/76)	5–11 years	Backpack use, pronated foot posture	Foot Posture Index (FPI)	76 developed neutral foot posture	Backpack use (aOR = 1.94, p < 0.05)	Low
15	Puszczalowska-Lizis et al., 2022 [35]	Regression Analysis	200 (100/100)	6 years	Foot arch impact on toe position	Podoscope analysis	Sex differences in arching effects	Transverse arch impacts hallux valgus	Low
16	Villarroya et al., 2008 [17]	Cross-Sectional	245 (130/115)	13.2 ± 1.8 years	BMI, foot structure	Chippaux–Smirak index	Lower MLA in obese group	BMI and MLA (p < 0.01)	Low
17	García-Rodríguez et al., 1999 [36]	Cross-Sectional	1181 (Unspecified)	4–13 years	Over-treatment of flexible flatfoot	Denis classification grades	2.7% true prevalence	Treatment mismatch (28.1%)	Moderate
18	El et al., 2006 [4]	Screening Study	579 (299/280)	9.23 ± 1.66 years	Hypermobility, hindfoot alignment	Dynamic weight-bearing arch assessment	Moderate–severe: 17.2%	Hypermobility increases risk (p < 0.05)	High
19	Chen et al., 2010 [37]	Cross-Sectional	1598 (833/765)	3–6 years	Age, sex, obesity, W-sitting	Weight-bearing medial arch assessment	54.5% at age 3, 21% at age 6	W-sitting increases risk (OR > 1)	Moderate
20	Halabchi et al., 2013 [21]	Cross-Sectional	120 (Unspecified)	6–10 years	Ligamentous laxity, footwear habits	Foot arch grading	50% flexible flatfoot	Ligamentous laxity (p<0.01)	Moderate
21	Yan et al., 2013 [19]	Retrospective	100 (54/46)	8–13 years	Radiographic talonavicular angle	Talonavicular coverage angle	10.3% symptomatic	Navicular angle OR = 1.89	Moderate
22	Troiano et al., 2017 [38]	Cross-Sectional	281 (139/142)	4–20 years)	Age and sex effects on prevalence	Baropodometric analysis	Flatfoot: 31.7%, Hollow foot: 68%	Flatfoot risk (OR = 2.23)	Low
23	Shapouri et al., 2019 [39]	Cross-Sectional	194 (112/82)	6–7 years	Obesity and lower extremity deformities	Clinical observation	13.38%	BMI linked to prevalence (OR = 1.89)	Moderate
24	Han et al., 2017 [40]	Cross-Sectional	72 (32/40)	15.4 ± 4.0 years	Heel valgus, arch index, Q-angle	Arch index, valgus measurement	Moderate–severe in adolescents	Heel valgus correlated with Q-angle (r = 0.81)	Moderate
25	Abolarin et al., 2011 [41]	Cross-Sectional	560 (Mixed)	6–12 years	Footwear habits and BMI	Footprint analysis	Significant in urban population	Urban living OR = 1.5	Moderate
26	Alsuhaymi et al., 2019 [42]	Cross-Sectional	403 (193/210)	7–14 years	Age, sex, BMI	Staheli’s plantar index	29.5%	BMI a significant predictor	Moderate
27	Chen et al., 2022 [43]	Retrospective Cohort	69 patients (107 feet)	7–14 years	Surgical success factors	Radiographic measures (Meary’s angle)	Significant improvement post-surgery	Meary’s angle improvement (p<0.001)	Moderate
28	Pfeiffer et al., 2006 [2]	Cross-Sectional	835 (424/411)	3–6 years	Age, sex, BMI (weight categories)	Rearfoot angle via laser scanner	44% flexible flatfoot, <1% pathological	Higher BMI strongly linked to flatfoot prevalence (OR > 2)	Low
29	Evans & Karimi, 2015 [18]	Retrospective Analysis	728 (Mixed)	3–15 years	BMI, sex, Foot Posture Index	Foot Posture Index (FPI)	FPI ≥ +6 in 40%, ≥ +8 in 20%	Weak correlation BMI and FPI (r = −0.077)	Moderate
30	Drefus et al., 2017 [44]	Reliability Study	30 (Mixed, 60 feet)	9.61 ± 1.96 years	AHI in sitting/standing postures	Arch height index (AHI)	Moderate to severe: 21–24%	AHI ICC ≥ 0.76	Low
31	Twomey et al., 2010 [45]	Comparative Study	50 (25/25 Normal/Low Arch)	11.1 ± 1.2 years	Kinematic differences during gait	Heidelberg foot measurement method	Low arch differences noted in gait	Forefoot supination significant (p < 0.03)	Low
32	Stavlas et al., 2005 [46]	Cross-Sectional	5866 (Mixed)	6–17 years	Foot morphology and growth	Dynamic footprints	Growth-related changes in prevalence	Significant growth-related differences (p < 0.05)	Moderate
33	Yin et al., 2018 [47]	Cross-Sectional	1059 (Mixed)	6–13 years	BMI, age, foot size	FootScan SAI ratio	FFF 39.5% at age 6 to 11.8% at age 12	BMI positively correlates (OR 2.43 obese)	Moderate
34	Boryczka-Trefler et al., 2021 [48]	Prospective Cohort	50 patients (100 feet)	5–9 years	Static vs. Dynamic Flatfoot	Static and dynamic pedobarography	Static 87%, Dynamic 56%	Static vs. Dynamic metrics inconsistent	Low
35	Chang et al., 2014 [49]	Cross-Sectional	1228 (Mixed)	6–12 years	Bimodal footprint index distribution	Staheli’s and Chippaux–Smirak indices	Bimodal arch distribution noted	Arch indices stable across groups	Low
36	Tashiro et al., 2015 [50]	Cross-Sectional	619 (311/308)	11.3 ± 0.7 years	Toe grip strength	Staheli’s arch index	17.8% flatfoot	Toe grip significantly lower in flatfoot	Moderate
37	Pauk et al., 2014 [51]	Cross-Sectional	93 (60/33)	9–16 years	Plantar pressure and Clarke’s angle	Clarke’s angle	Significant medial pressure in flatfoot	Clarke’s angle correlates with plantar pressure (r > 0.9)	Moderate

3.2. Risk of Bias in Included Studies

Of the thirty-seven included studies, twenty-five were classified as low risk of bias, eight as moderate, and four as high (see Table 1, final column). Four studies highlighted sex differences in flatfoot severity; however, the direction of this association varied, with some reporting a higher prevalence in males and others in females.

3.3. Qualitative Synthesis of Key Findings

• BMI as a Risk Factor: Across the majority of included studies, elevated BMI was strongly associated with higher flatfoot prevalence or severity. In a study by Pfeiffer et al. (2006) [2], preschool children classified as overweight had a significantly higher chance of flexible flatfoot (OR > 2). Similarly, Leung et al. (2018) [16] found a 39.5% flatfoot prevalence at age 6, progressively declining with age, yet children with obesity exhibited persistently higher flattening rates.
• Ligamentous Laxity: Although fewer studies formally assessed ligamentous laxity, those that did (e.g., He et al. 2023 [25]) reported moderate correlations (r ≈ 0.4) with valgus deformity or reduced arch angles [20]. However, methodological inconsistencies, like different definitions of hypermobility, limit pooling.
• Footwear Habits: A few authors proposed that supportive footwear reduces hindfoot valgus, whereas minimalist or poorly fitted shoes can exacerbate pronation in overweight children [5]. Nonetheless, footwear influences were inconsistent, as some cross-sectional data showed negligible differences once BMI was controlled. Cultural norms (e.g., walking barefoot vs. wearing shoes indoors) may also modulate these findings, but data were insufficient for formal subgroup analysis.
• Physical Activity: Paradoxical findings arose, with some studies showing that sedentary children had weaker foot musculature and more pronounced flatfoot [52], while others suggested that intense sports might overload the immature foot structure, leading to arch strain in overweight individuals. Overall, the net effect of physical activity likely depends on weight status, foot muscle conditioning, and biomechanical alignment.
• Diagnostic Heterogeneity: The key limitations stem from the array of diagnostic criteria. Studies using the Foot Posture Index (FPI) often classified a broader range of mild pronation as “flatfoot”. Notably, pedobarography measurements tended to yield higher prevalence estimates, potentially reflecting increased sensitivity to weight-bearing factors (i.e., body mass). Radiographic definitions typically identified more moderate-to-severe deformities. This methodological discrepancy likely contributed to the wide prevalence range (10–54%) and influenced how BMI and other factors correlated with severity.

3.4. Quantitative Synthesis: Meta-Analysis of BMI

Across 12 studies reporting quantitative data (odds ratios) for BMI, our random-effects model yielded a pooled OR of 2.3 (95% CI: 1.6–3.1) indicating that overweight/obese children have a significantly higher likelihood of presenting with flatfoot. Figure 2 and Figure 3 illustrate the forest plot and subgroup findings, respectively, with statistical significance assessed at p < 0.05 using the DerSimonian and Laird approach for random effects.

• Pooled OR for Overweight/Obesity: 2.3 (95% CI: 1.6–3.1), indicative of a significant association between elevated BMI and flatfoot (p < 0.001). Individual studies displayed ORs ranging from 1.7 to 9.08 [27]. One outlier study reported an OR of 9.08 for obese children; we included this estimate in our narrative synthesis, noting that it focused on a highly specific population sample.
• Heterogeneity (I²): 68.2%, suggesting substantial between-study variability. Potential drivers include differences in diagnostic methodologies, cutoffs for BMI/obesity, and population demographics.
• Subgroup Analysis:

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  By Age (<10 years vs. ≥10 years): Studies focusing on younger children (<10 years) reported higher baseline prevalence of “flexible” flatfoot, possibly reflecting normal developmental stages. In contrast, studies including older children and adolescents (≥10 years) indicated that elevated BMI was more strongly linked to persistent or severe flatfoot deformities (ORs ranging 2.0–4.2).

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  By Diagnostic Method (FPI vs. Footprint/Radiograph): Studies using the FPI reported lower effect sizes (OR ≈ 2.0) than those using footprints or radiographs (OR ≈ 3.1), hinting that certain metrics might capture more clinically significant deformities.

• Publication Bias: Egger’s test (p = 0.061) suggested a mild possibility of small-study effects, but the funnel plot did not reveal overt asymmetry. Sensitivity analyses, excluding high risk of bias studies, slightly reduced the heterogeneity (I² = 52.5%) but did not change the direction of the main effect.

4. Discussion

This systematic review consolidates and expands upon the existing knowledge regarding the relationship between risk factors and flatfoot severity in pediatric populations. The most consistent finding is a robust association between elevated BMI and both the prevalence and severity of flatfoot. Children with overweight or obesity status exhibit up to a two-to-fourfold increased risk compared to normal-weight peers—an effect that persists across different diagnostic criteria and geographic regions. The effect sizes for BMI varied notably among studies (OR range: 1.7–4.2), reflecting potential differences in dietary habits, physical activity patterns, genetic predispositions, and thresholds for “overweight” vs. “obesity”. Some studies used international WHO cutoffs, whereas others utilized local growth charts, potentially influencing effect estimates. These results align with the hypothesis that excess body mass amplifies load-bearing stress on the developing foot, thereby contributing to valgus deformity and arch collapse. Our findings corroborate previous systematic reviews [53] noting higher rates of flatfoot among overweight children. However, by focusing on severity metrics (e.g., calcaneal pitch, FPI scores), we highlight that obesity’s impact may extend beyond mere prevalence. Moreover, we underscore lingering controversies. Some earlier reviews did not differentiate between mild flexible flatfoot and more severe, pathological presentations, potentially obscuring nuanced associations with BMI. In contrast, our approach suggests that overweight status not only influences the likelihood of having a flatfoot posture but can also worsen its severity, as indicated by increased valgus angles and lower MLA indices. Our findings regarding ligamentous laxity and footwear habits are more heterogeneous. Ligamentous laxity, especially in hypermobile children, may predispose to more pronounced deformities, but the effect size appears less consistent once BMI is controlled [4,31]. Similarly, footwear’s role appears inconclusive: prospective data are scarce, and cross-sectional findings often lack robust confounder adjustments (e.g., activity level, socioeconomics). The interplay of footwear type, foot intrinsic muscle strength, and overall weight-bearing demands is likely complex, requiring further study. Diagnostic heterogeneity—whether via FPI, footprint indices, or radiographic measures—contributes significantly to variations in prevalence and effect sizes. Establishing standardized, validated thresholds for mild, moderate, and severe flatfoot (e.g., adopting consistent FPI cutoffs, Meary’s angle ranges) would facilitate cross-study comparability. Geographic variation in footwear habits, BMI definitions, and lifestyle factors adds another layer of complexity. Although we attempted subgroup analyses by region, the data sparsity precluded robust conclusions.

4.1. Strengths and Limitations

This review has several strengths. A comprehensive search strategy was employed, utilizing multiple databases and incorporating the grey literature to minimize the risk of publication bias. Rigorous methodological approaches were followed, including adherence to PRISMA guidelines, dual-reviewer screening, and the use of validated risk of bias assessment tools such as the Newcastle–Ottawa Scale (NOS) and Cochrane risk of bias 2 (RoB 2). The inter-rater agreement was robust, with a κ value of 0.82. Additionally, the review emphasized the severity of flatfoot by focusing on specific outcome measures, such as diagnostic angles, the Foot Posture Index (FPI), and arch indices, offering a more nuanced perspective beyond general prevalence estimates. Despite its strengths, this review has limitations. A prominent limitation in the reviewed literature is the heterogeneity in diagnostic criteria. Studies using the Foot Posture Index (FPI) may classify mild pronation as flatfoot, whereas radiographic criteria (e.g., Meary’s angle) capture more moderate-to-severe deformities. Additionally, pedobarography-based assessments can be more influenced by body mass, thus potentially elevating prevalence estimates. This variation complicates cross-study comparisons, highlighting the need for standardized diagnostic thresholds when evaluating flatfoot severity in pediatric populations. Most of the included studies were cross-sectional, limiting inferences on causality. It remains unclear whether elevated BMI leads to increased flatfoot severity or if flatfoot restricts physical activity, subsequently contributing to weight gain. Longitudinal designs or intervention trials are necessary to clarify these pathways. Prospective cohort studies and randomized interventions are needed to determine whether weight reduction can effectively mitigate the deformity. Additionally, our review also underscores the inconsistent data on physical activity and footwear. Variables such as activity type, intensity, or shoe characteristics (arch support, sole stiffness) were measured differently across studies, limiting definitive conclusions. Standardized assessments (e.g., validated physical activity questionnaires, uniform footwear classification scales) would enhance comparability and bolster evidence-based guidelines. Pediatric foot arches are still developing up to around 10 years of age; thus, diagnosing flatfoot in younger children may capture normal developmental variations. Our subgroup analysis indicates that BMI’s impact on flatfoot severity becomes more pronounced in older children and adolescents, suggesting that persistent flatfoot after age 10 is more likely pathological and strongly associated with modifiable risk factors such as weight status.

4.2. Clinical and Research Implications

Early recognition of children at risk of moderate-to-severe flatfoot is pivotal, especially those with elevated BMI. Proactive interventions, including weight management and appropriate footwear, may alleviate arch collapse and reduce pain or long-term functional impairments. Collaboration among pediatricians, orthopedists, physiotherapists, and dietitians can optimize outcomes through tailored exercise programs, orthotic support, and nutritional guidance. Future research should emphasize standardized diagnostic thresholds for flatfoot severity—such as consensus-based FPI cutoffs—to facilitate comparisons across studies. Longitudinal designs would help clarify whether reducing BMI through targeted interventions translates into measurable improvements in foot posture over time. Additionally, investigating how footwear habits, physical activity levels, and ligamentous laxity interact to influence arch development could inform personalized prevention strategies. By integrating these efforts, stakeholders can develop evidence-based guidelines that effectively address the multifactorial nature of pediatric flatfoot, ultimately enhancing care quality and limiting associated morbidity.

5. Conclusions

In this systematic review, elevated BMI emerged as the most consistent risk factor for increased flatfoot severity in pediatric populations. Although evidence regarding joint instability, shoe use, and physical activity remains inconclusive, these factors warrant further investigation with standardized measures. Methodological heterogeneity—particularly in diagnostic criteria—poses a significant challenge, underscoring the need for consensus on flatfoot severity thresholds. From a clinical perspective, routine weight assessments, targeted physical interventions, and appropriate shoe recommendations may mitigate the progression of moderate-to-severe flatfoot. Future longitudinal studies and well-designed interventions that focus on weight management and biomechanical assessments are essential to clarify causality and refine prevention strategies, ultimately improving pediatric foot health outcomes.