Responsiveness of Outcome Measures in Nonsurgical Patients with Lumbar Spinal Stenosis: A Secondary Analysis From a Randomized Controlled Trial

STUDY DESIGN. Secondary analysis from a randomized controlled trial on nonsurgical interventions for patients with lumbar spinal stenosis (LSS). OBJECTIVE. The aim of this study was to assess the responsiveness of the Self-Paced Walking Test (SPWT), Swiss Spinal Stenosis Questionnaire (SSS), and Oswestry Disability Index (ODI) and determine their minimal clinically important differences (MCID) in nonsurgical LSS patients. SUMMARY OF BACKGROUND DATA. Limited information is available about the responsiveness of these tests in nonsurgical LSS population. METHODS. A total of 180 participants completed the SPWT, SSS, and ODI at baseline, 2, and 6 months. Responsiveness was assessed by distribution-based method, including effect size and standardized response mean, and anchor-based method, using the patient global index of change (PGIC) as the external anchor to distinguish responders and non-responders. Areas under the curve (AUC) were calculated along with MCIDs for “minimal” and “moderate improvement” subgroups. RESULTS. The following values represent 2- and 6-month analyses of each outcome measure, respectively. Standard effect sizes: 0.48 and 0.50 for SPWT, −0.42 and −0.36 for SSS, and −0.29 and −0.25 for ODI. Spearman correlation coefficients between PGIC and outcomes were: 0.44 and 0.39 for SPWT, −0.53 and −0.55 for SSS, and −0.46 and −0.54 for ODI. MCIDs for the “minimal improvement” subgroup were: 375.9 and 319.3 ms for SPWT, −5.3 and −5.8 points for SSS, and −9.3 and −10.8 points for ODI. AUCs was 0.68 to 0.76. MCIDs for the “moderate improvement” subgroup were: 344.2 and 538.2 m for SPWT, −5.5 and −7.5 points for SSS, and −9.1 and −13.6 points for ODI. AUCs ranged from 0.68 to 0.76. CONCLUSION. The SPWT, SSS, and ODI are responsive outcome measures to assess nonsurgical patients with LSS. This finding, along with the reported MCIDs, can help clinicians to monitor changes in their patients’ walking and physical function over time and make clinical decisions. They also provide researchers with reference for future studies in LSS. Level of Evidence: 2