Cross-cultural adaptation and validation of the NASS outcomes instrument in Spanish patients with low back pain

Objectives: The aim of the study was to evaluate validity, reliability, responsiveness and practicality of the NASS-AAOS (North American Spine Society—American Academy of Orthopaedic Surgeons) questionnaire in patients with low back pain. Methods: The sample included 70 patients with herniated disk, stenosis, chronic low back pain of unknown etiology or acute low back pain. They were assessed twice before treatment (test–retest) and a third measure six months to one year afterwards. Results: The mean time of administration was 24 and 20 min for the test and post-treatment evaluation, respectively. Cronbach’s alpha coefficient was between 0.78 and 0.92 on the baseline test and 0.90 or higher on the post-treatment evaluation. The test–retest reproducibility was 0.95 (0.91–0.98) for ‘neurological symptoms’, 0.82 (0.63–0.91) for ‘pain/disability’ and 0.63 (0.25–0.82) for ‘expectations’. The associations with other measures and clinical criteria were generally moderate to high and in the expected direction. The effect size for ‘pain/disability’ in combination with ‘neurological symptoms’ was 2.02 for patients who improved versus an effect of −0.09 in patients who were stable between test and retest; the area under the curve on this joint scale was 0.81 (0.69–0.90). Conclusions: The instrument is valid, sensitive to clinical changes and reliable for comparisons between groups, but further study is needed for its application in monitoring individual patients.