Cross-cultural adaptation and psychometric properties of the Vietnamese version of the Lower Extremity Functional Scale (LEFS) in individuals with knee osteoarthritis

Abstract Objective To translate, cross-culturally adapt, and examine the psychometric properties of the Vietnamese version of the Lower Extremity Functional Scale (LEFS-V) in individuals with knee osteoarthritis (KOA). Design A cross-sectional study. Setting Two hospitals and two Catholic convents in Vietnam. Participants 174 Vietnamese individuals aged ≥ 45 years with KOA were diagnosed based on clinical examination using the National Institute for Health and Care Excellence (NICE) criteria. Main outcome measures Participants completed the baseline assessment and 5-7days retest, which included the LEFS-V, Numerical Pain Rating Scale (NPRS), and Knee Injury and Osteoarthritis Outcome Score (KOOS). Psychometric property testing included content validity (CVI), internal consistency (Cronbach’s α), test–retest reliability (ICC (3,1) , standard error of measurement (SEM), minimum detectable change (MDC95), and construct validity. Spearman correlations were used to examine associations with the KOOS subscales and NPRS. Results Strong content validity with item-CVI from 0.83 to 1.00. LEFS-V demonstrated high internal consistency (Cronbach’s α = 0.942) and excellent test–retest reliability (ICC (3,1)  = 0.985; 95% CI: 0.974–0.991), SEM = 1.4 and MDC 95  = 3.88. LEFS-V correlated positively with KOOS-Pain (r s = 0.59), KOOS-Symptoms (r s = 0.30), KOOS-ADL (r s = 0.71), KOOS-Sport/Rec (r s = 0.50), and KOOS-QoL (r s = 0.18), and negatively with NPRS (r s = -0.63). Conclusion The LEFS-V is a reliable and valid scale for assessing lower extremity functional status in Vietnamese individuals with KOA.