Treatment guidelines recommend targeting both physical and psychological factors in interventions for degenerative lumbar spine disorders. Studying treatment mechanisms gives information on key factors explaining outcome improvement which can refine treatments for future research. This study explores treatment mediators in a physiotherapy treatment on disability, pain intensity and health related quality of life (HRQoL) in surgical candidates with degenerative lumbar spine disorders compared to waiting-list controls. An additional aim was to evaluate patients´ expectation as a moderator of treatment outcome.
Data collected from 197 patients in a single blinded randomized controlled trial comparing 9 weeks of multifaceted physiotherapy to waiting-list were used in this conditional process analysis. Analysis was carried out on group differences for change in Oswestry Disability Index (ODI), Pain Visual Analog Scale (VAS) back pain, EuroQol-5D (EQ-5D) and EQ-VAS. The putative moderation role of expectations and mediation role of change in physical variables and psychosocial variables were tested.
Change in self-efficacy mediated improvement in all outcomes. Improvement in ODI was also mediated by change in depression, VAS was mediated by change in fear avoidance beliefs and EQ-VAS was mediated by change in activity level and fear avoidance beliefs. Improvements were moderated by patients´ treatment expectations.
Self-efficacy, fear avoidance beliefs, physical activity level and patients´ treatment expectations were found to be important factors explaining treatment effects. Self-efficacy was the consistent mediator for effects of the pre-surgical physiotherapy on disability, back pain intensity and HRQoL.

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