Validity, reliability, responsiveness and interpretability of the EFAS-DK PROM: an observational cohort study of Danish speaking foot and ankle patients

Background: This study is an external evaluation of the Patient Reported Outcome Measure (PROM) EFAS-DK developed by the European Foot and Ankle Society (EFAS). The evaluation included a test of the psychometric properties. Methodology: From October 2019 to September 2022, 101 patients undergoing elective foot or ankle surgery completed questionnaires (EFAS-DK, SEFAS-DK, EQ-5D-5L) prior to surgery and 6 months post-surgery. A subgroup of patients completed a retest. A foot-healthy group control group was added. Testing covered construct validity with hypothesis testing, floor and ceiling effects, internal consistency (Cronbach’s Alpha), test-retest reliability (ICC 2.1), effect size (ES), Standardized Response Mean (SRM), Smallest Detectable Change (SDC) and Minimal Important Change (MIC). Results: Moderate construct validity with 59% confirmed hypothesis. High content validity, no floor ceiling effects. Cronbach’s alpha 0.88, ICC 0.93. ES and SRM were both 1.06. SDC 4 and MIC 6. Control group score changes was insignificant. Conclusion: EFAS-DK is a valid, reliable, and responsive foot and ankle PROM score. EFAS-DK can detect a clinically subjective relevant change score of 6 (25% of the total scale), which makes it useful for implementation in the clinic when evaluating patients undergoing foot and ankle surgery. Comparison with a control group showed results that significantly differ from the patients. Level of evidence: IIa prospective observational analytic cohort study.