RESUMEN
PURPOSE: To transculturally adapt the Neck Disability Index to Mexican Spanish (NDI-Mx) and to evaluate its psychometric properties. METHODS: Translation and transcultural adaptation of the NDI were conducted according to published guidelines. The test-retest reliability of the NDI-Mx was assessed with intraclass correlation coefficient (ICC3,1), the student t-test, standard error of measurement, minimal detectable change and Bland-Altman plot. Cronbach's α coefficient was used to evaluate internal consistency. Floor and ceiling effects were also evaluated. Convergent validity was assessed by comparison of the NDI-Mx with the Northwick Park Neck Pain Questionnaire (NPQ) through the Spearman correlation coefficient. Finally, a confirmatory factor analysis (CFA) was conducted. RESULTS: The sample was composed of 113 subjects (38 men and 75 women) with a mean age of 30 (SD, 12.19) years. All items of the NDI-Mx showed good test-retest reliability (ICC3,1 = 0.86) and good internal consistency (Cronbach's α = 0.85). Floor and ceiling effects were not observed. There was good convergent validity with a high correlation between NDI-Mx and NPQ (ρ = 0.83). The CFA revealed that a one-factor solution fitted adequately the data (χ2(32) = 41.18, p = .13). CONCLUSION: The NDI-Mx seems to be a valid and reliable tool that can be used in clinical practice and research on Mexican populations with neck pain.