Validation of the Bulgarian Version of Oxford Foot and Ankle Questionnaire for Children with Flat Foot Deformity

Background Pediatric flexible flatfoot, defined by a diminished or absent medial longitudinal arch, is a common anatomical variant with potential biomechanical consequences. While many cases are asymptomatic, symptomatic flatfoot can impair gait mechanics and postural stability, leading to long-term functional limitations. Health-related quality of life (HRQoL) in children with flatfoot remains underexplored, necessitating validated, patient-reported outcome measures (PROMs). The Oxford Ankle Foot Questionnaire for Children (OxAFQ-C) is the only validated PROM designed for pediatric foot and ankle disorders, yet its psychometric properties have not been evaluated in Bulgarian-speaking populations. Objective This study aimed to adapt and validate the Bulgarian version of the OxAFQ-C, assessing its reliability, internal consistency, construct validity, and feasibility in pediatric patients diagnosed with flexible flatfoot. Methods The translation and cultural adaptation followed international guidelines, including forward-backward translations, expert panel reviews, and pre-testing with children and guardians. The final Bulgarian OxAFQ-C was administered to 995 children (aged 6-16) across three Bulgarian regions. Psychometric analyses included internal consistency (Cronbach’s alpha, α), test-retest reliability (lntraclass Correlation Coefficient, lCC), and construct validity through correlation with the Visual-Analogue-Scale Foot and Ankle (VAS FA). Exploratory Factor Analysis (EFA) assessed structural validity. Results The Bulgarian OxAFQ-C demonstrated excellent internal consistency (Cronbach’s α > 0.90). Parent-child agreement was highest in the Physical Function domain (lCC ≥ 0.75) and moderate for other domains. Construct validity was confirmed, with moderate correlations between the Physical Function domain and VAS FA scores (r ≈ −0.43). EFA confirmed the three-factor structure. Conclusion The Bulgarian adaptation of the OxAFQ-C is a reliable and valid instrument for assessing HRQoL in children with flexible flatfoot. lts strong psychometric properties support its clinical and research utility in orthopedic and epidemiological studies.