French translation and validation of 3 functional disability scales for neck pain

Objective: To translate and assess the reliability and the construct validity of 3 functional disability scales for neck pain. Design: Reliability and validity study. Setting: Tertiary care teaching hospital and outpatient clinic. Participants: One hundred one patients (mean age, 49y). Intervention: French translations were obtained by using the "translation-backward translation" method. Adaptations were made after a pilot study. Main Outcome Measures: Impairment outcome measures (visual analog scale [VAS] pain, neck range of motion, morning stiffness, score of neck sensitivity, radiologic score of Kellgren) and patients' perceived handicap (VAS) were recorded at the baseline visit. Three functional disability scales (Neck Disability Index [NDI], Neck Pain and Disability Scale [NPDS], Northwick Park Neck Pain Questionnaire [NPQ]) were recorded twice, at baseline visit and 24- hours later. Reliability was assessed by using the intraclass correlation coefficient (ICC) and the Bland and Altman method. Construct (convergent and divergent) validity was investigated by using the Spearman rank correlation coefficient and a factor analysis was performed. Results: Test-retest was excellent for the NPDS and NDI (ICC = .91, .93, respectively) and good for the NPQ (ICC = .84). The Bland and Altman method showed no systematic trend. Expected convergent and divergent validity were observed only for the NPDS; 3 main factors were extracted by factor analysis and explained 78% of the cumulative variance. Conclusion: The 3 translated scales are valid, but the NPDS seems to have the best construct validity.