Development of the Italian version of the neck pain and disability scale, NPDS-I: Cross-cultural adaptation, reliability, and validity

Study design.: Evaluation of the psychometric properties of the Neck Pain and Disability Scale (NPDS). Objective.: Translating, culturally adapting, and validating the Italian version of the NPDS-I. Summary of background data.: Great importance is devoted to validated and comprehensive outcome measures to improve interventions for neck pain. A translated form of a functional scale in patients with neck pain has never been studied within the Italian population. Methods.: The Italian version of the NPDS questionnaire was developed involving forward-backward translation and final review by an expert committee to establish multidimensional correspondence with the original English form. Psychometric testing included factor analysis with Varimax rotation, reliability by internal consistency (Cronbachs alpha) and test-retest repeatability (Spearmans rank test), validity by comparing the Italian version of SF-36 to NPDS-I (Pearsons correlation); further subscales comparisons to single SF-36 domains were also conducted. Results.: The authors required a 4-month period before achieving a shared version of the NPDS-I. The form was administered to 157 subjects, presenting good acceptability. Factor analyses demonstrated 3 subscales (63% of explained variance), defined as neck dysfunction related to general activities (subscale 1, 8 items), neck pain and cognitive-behavioral aspects (subscale 2, 8 items), neck dysfunction related to activities of the cervical spine (subscale 3, 4 items). The questionnaire showed high internal consistency (NPDS: 0.942, subscale 1: 0.919, subscale 2: 0.856, subscale 3: 0.889) and good test-retest reliability (P < 0.001). Validity was explained by high correlations with SF-36 total score (r = -0.47, P < 0.001) and with single SF-36 domains scores, highly significant (P < 0.001) with the exception of physical role domain (r = -0.17, P = 0.035). Finally, the 3 subscales demonstrated good correlations when compared with selected SF-36 domains. Conclusion.: The NPDS-I outcome questionnaire was successfully translated into Italian, showing good multidimensional and psychometric properties, supporting the results of the already existing versions of the scale. Its use is recommended in clinical and research practice.