Validity and Reliability of the European Foot and Ankle Society (EFAS) Score in Patients With Hallux Valgus in Singapore

The European Foot and Ankle Society score is a popular tool for monitoring treatment outcomes of foot or ankle conditions. However, few studies have assessed its psychometric properties in patients with hallux valgus. We aimed to validate the European Foot and Ankle Society score in patients with hallux valgus in Singapore. This is a cohort study of 121 patients with operatively managed hallux valgus from a tertiary referral hospital, evaluated preoperatively and at 6 months postoperatively with the primary endpoint of restoring patients to premorbid status. Internal consistency was assessed via Cronbach's alpha. Construct validity was assessed through 7 a priori hypotheses by correlating the European Foot and Ankle Society score with other patient-reported outcomes measures. Structural validity was assessed via Confirmatory Factor Analysis, whereby a good fit was indicated when Comparative Fit Index >0.95, Tucker-Lewis Index >0.95, Root Mean Square Error of Approximation <0.06, and Standardized Root Mean Residuals <0.08. Among our subjects, the European Foot and Ankle Society score demonstrated reliability, reflected by a good internal consistency (Cronbach's alpha = 0.773). Six out of the 7 a priori hypotheses were fulfilled, indicating both convergent and divergent construct validity. Structural validity was confirmed with our European Foot and Ankle Society score model which showed good fit for a 1-factor structure (Confirmatory Factor Analysis = 0.998, Tucker-Lewis Index = 0.996, Root Mean Square Error of Approximation = 0.025 [90% CI: 0-0.111], Standardized Root Mean Residuals = 0.027). In conclusion, the European Foot and Ankle Society score was validated for monitoring treatment outcomes of patients with hallux valgus in Singapore.