Responsiveness of the Oswestry Disability Index and Zurich Claudication Questionnaire in patients with lumbar spinal stenosis: evaluation of surgically treated patients from the NORDSTEN study.

Abstract

To evaluate the responsiveness of the original low back pain specific Oswestry Disability Index (ODI) and the spinal stenosis specific Zürich Claudication Questionnaire (ZCQ), and to investigate cut-off values for clinical "success" for ODI and ZCQ in surgically treated patients with lumbar spinal stenosis (LSS). We included 601 LSS patients (218 with, 383 without degenerative spondylolisthesis) from the NORDSTEN trials. Outcome measures included ODI and ZCQ (symptom severity and physical function scales) with three alternative response parameters: scores at follow-up, absolute and relative changes from baseline to two-year follow-up. Effect size and standardised response mean evaluated internal responsiveness. External responsiveness was assessed by the Spearman rank correlation between patient-reported global perceived effect scale (GPE) and ODI and ZCQ, and receiver operating characteristics (ROC). We evaluated which cut-off values could maximise the percentage of correctly classified patients according to the GPE-anchor "completely recovered" / "much improved" for each parameter. Internal and external responsiveness were high for all three indices with effect sizes, standardized response means, ROC and corresponding area under the curve > 0.8. Correlations with GPE responses were moderate (> 0.50) for absolute change and strong (> 0.67) for relative change and follow-up scores. The 30% ODI relative change cut-off correctly classified 81% of patients to "success", within a range of accurate cut-offs according to the GPE-anchor. ODI and ZCQ demonstrate comparable responsiveness in evaluating outcomes for surgically treated LSS patients. The 30% ODI threshold was consistent with treatment "success" in NORDSTEN trials. ClinicalTrials.gov; NCT02007083 10/12/2013, NCT02051374 31/01/2014 and NCT03562936 20/06/2018.