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

Abstract

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. 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. 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). 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.