Abstract
Interventions developed to improve disability outcomes for low back pain (LBP) often show only small effects. Mediation analysis was used to investigate what led to the effectiveness of the Stratified Targeted Treatment (STarT) Back trial, a large primary care-based trial that treated patients consulting with LBP according to their risk of a poor outcome. The high-risk subgroup, randomized to receive either psychologically-informed physiotherapy (n = 93) or current best care (n = 45), was investigated to explore pain-related distress and pain intensity as potential mediators of the relationship between treatment allocation and change in disability. Structural equation modeling was used to generate latent variables of pain-related distress and pain intensity from measures used to identify patients at high risk (fear-avoidance beliefs, depression, anxiety, and catastrophizing thoughts). Outcome was measured using the Roland–Morris Disability Questionnaire. Change in pain-related distress and pain intensity were found to have a significant mediating effect of .25 (standardized estimate, bootstrapped 95% confidence interval, .09–.39) on the relationship between treatment group allocation and change in disability outcome. This study adds to the evidence base of treatment mediation studies in pain research and the role of distress in influencing disability outcome in those with complex LBP.PerspectiveMediation analysis using structural equation modeling found that change in pain-related distress and pain intensity mediated treatment effect in the STarT Back trial. This type of analysis can be used to gain further insight into how interventions work, and lead to the design of more effective interventions in future.
Highlights
Perspective: Mediation analysis using structural equation modeling found that change in painrelated distress and pain intensity mediated treatment effect in the STarT Back trial
There was a difference between the amounts of change in potential mediators observed in the treatment groups at 4-month follow-up compared with the control group, including a 4.4-point difference in change for catastrophizing thoughts and a 5.8-point difference in change for fear-avoidance beliefs, representing the largest changes
In the control group, residualized change in all potential mediators accounted for a large amount of variance of residualized change in Roland-Morris Disability Questionnaire (RMDQ)
Summary
Perspective: Mediation analysis using structural equation modeling found that change in painrelated distress and pain intensity mediated treatment effect in the STarT Back trial. This type of analysis can be used to gain further insight into how interventions work, and lead to the design of more effective interventions in future. A key example of this, the STarT Back approach,[20] was reported to be effective at reducing disability when patients consulting primary care for LBP were assessed for their risk of a poor outcome and matched to an intervention on the basis of their risk profile. The factors chosen to help stratify patients were known prognostic factors, this does not necessarily mean that these same factors were strong targets for treatment in this group (ie, were mediating factors)
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