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Study Design: Secondary analysis of data from a double-blind randomized controlled trial., Objective: To identify mediators of the effect of lumbar epidural injections of corticosteroid plus lidocaine on patient satisfaction at 6 weeks postinjection in patients with lumbar spinal stenosis. We hypothesized that short-term (≤3 wk) change in leg pain would be a significant mediator of satisfaction., Summary of Background Data: No prior studies have identified mediators of effects of epidural injections on patient satisfaction with treatment of lumbar spinal stenosis., Methods: We used mediation analysis methods to examine selected intermediate variables (adverse events and change in leg pain, back pain, disability, depression, and fatigue at 3 wk) as potential mediators of the effect of lumbar epidural injections of corticosteroid plus lidocaine on patient satisfaction with treatment. We used the overall satisfaction item from the Swiss Spinal Stenosis Questionnaire as our primary outcome to measure patient satisfaction with the injection procedure at 6 weeks., Results: Among 400 patients randomized to receive epidural injections with corticosteroid plus lidocaine or with lidocaine alone, 369 had complete data for the satisfaction outcome and potential mediators and served as the analysis sample. Contrary to our expectations, 3-week change in leg pain intensity did not have significant mediation effects on patient satisfaction. Three-week change in disability as measured by the Roland-Morris Disability Questionnaire was a significant mediator of the effects of lumbar epidural corticosteroid injections on patient satisfaction at 6 weeks, explaining 48% to 60% of the treatment effect on satisfaction. Changes in pain intensity in the leg and back together explained very little of the treatment effect on satisfaction beyond the information contributed by disability change alone. We did not find other intermediate variables to be mediators of patient satisfaction., Conclusion: These findings support the current approach of examining disability as a primary patient-reported outcome in comparative effectiveness studies of lumbar spinal stenosis., Level of Evidence: 2.