Danish version of the Oswestry Disability Index for patients with low back pain. Part 1: Cross-cultural adaptation, reliability and validity in two different populations

Over the past 10 years, a plethora of back-specific patient-orientated outcome measures have appeared in the literature. Standardisation has been advocated by an expert panel of researchers proposing a core set of instruments. Of the condition-specific questionnaires the Oswestry Disability Index (ODI) is recommended for use with low back pain (LBP) patients. To date, no Danish version of the ODI exists which has been cross-culturally adapted, validated and published in the peer-reviewed literature. A cross-cultural adaptation and validation of the ODI for the Danish language was carried out according to established guidelines: 233 patients [half of the patients were seen in the primary sector (PrS) and half in the secondary sector (SeS) of the Danish health care system] with LBP and/or leg pain completed a questionnaire booklet at baseline, 1 day or 1 week and 8 weeks follow-up. The booklet contained the Danish version of the ODI, along with the Roland Morris Disability Questionnaire, the LBP Rating Scale, the SF36 (physical function and bodily pain scales) and a global pain rating. For the ODI test–retest analysis (93 stable patients) resulted in an intraclass correlation coefficient of 0.91, a mean difference of 0.8 and 95% limits of agreements of − 11.5 to + 13. Thus, a worsening greater than 12 points and improvement greater than 13 points can be considered a “real” change above the measurement error. A substantial floor effect was found in PrS patients (14.1%). The ODI showed satisfactory cross-sectional discriminant validity when compared to the external measures. Concurrent validity of the ODI revealed: (a) a 10% and 21% lower ODI score compared to the disability and pain measures, respectively, (b) a poorer differentiation of patient disabilities and (c) an acceptable individual ODI score level compared to the external measures. Longitudinal external construct validity showed moderate correlations (range 0.56–0.78). We conclude that the Danish version of the ODI is both a valid and reliable outcome instrument in two LBP patient populations. The ODI is probably most appropriate for use in SeS patients.