Are illness perceptions and patient self-care enablement mediators of treatment effect in best practice physiotherapy low back pain care? Secondary mediation analyses in the BetterBack trial.

A best practice physiotherapy model of care (BetterBack MoC) for low back pain (LBP) aimed to improve patients' illness perceptions and self-care enablement, according to the Common-Sense Model of Self-Regulation (CSM). To confirm if illness perceptions and patient self-care enablement, in line with the CSM, are mediators of treatment effects on disability and pain of the BetterBack MoC for patients with LBP compared to routine primary care. A secondary aim was to explore if illness perceptions and patient self-care enablement are mediators of guideline adherent care. Pre-planned single mediation analyses tested whether hypothesized mediators at 3 months mediated the treatment effect of the MoC ( No indirect effects were identified. The BetterBack intervention did not have superior effects over routine care on the hypothesized mediators. Illness perceptions and self-care enablement were significantly associated with disability and pain at 6 months. Secondary analyses showed significant indirect effects of guideline adherent care through tested mediators. Despite no indirect effects, patients' illness perceptions and self-care enablement were associated with disability and back pain intensity outcomes and are potentially relevant treatment targets.