Objectives: To translate and to assess the reliability and the construct validity of the French translation of the Neck Pain and Disability Scale (NPDS), an American functional disability scale for neck pain.
Patients and methods: Non randomised prospective study, where patients with neck disorders were included. Impairment outcomes measures (VAS Pain, range of motion of neck, score of neck sensitivity, radiologic score of Kellgren) and patientsperceived handicap (VAS) were recorded at the baseline visit. Disability was assessed with the NPDS, that was recorded twice, at baseline visit and 24 hours later. Reliability was assessed using the intraclass correlation coefficient (ICC) and the Bland and Altman method. Construct (convergent and divergent) validity was investigated using the Spearman rank correlation coefficient and a factor analysis was performed.
Results: One hundred and one patients were included. French versions were obtained using the "translation/backward translation" method. Expected convergent (r = 0.51 with VAS Pain, 0.63 with VAS Functional Disability, 0.67 with VAS Handicap) and divergent (r = 0.39 and 0.49 respectively for the anxiety and depression scores of HAD, palpation sensitivity r = 0.31, neck mobility r = - 0.45 and 0.28, and Kellgrens radiologic score r = 0.04) validity were observed, suggested good construct validity. Test-retest was excellent for NPDS with ICC = 0.91. The Bland and Altman method showed distribution of differences homogenous and no systematic trend. Three mains factors were extracted by factors analysis of the NPDS, and explained 78% of the cumulative variance.
Conclusion: The French version of NPDS has good metrologic qualities. This scale can be used in clinical practice to assess disability in neck pain and to normalise disability assessment.