Negative affect, catastrophizing, and self-efficacy during transition from acute episode of low back pain to future disability: a causal mediation analysis of the Understanding persistent pain where it ResiDes longitudinal cohort study

Abstract – This study examined whether psychological factors mediate the relationship between acute low back pain and future disability. We conducted a secondary causal mediation analysis of the UPWaRD longitudinal cohort (N = 120 adults with acute low back pain of < 6 weeks' duration; ACTRN12619000002189; protocol:). Baseline pain intensity (11-point numerical rating scale) was the exposure, psychological factors measured at 3 months were the mediators (depression, anxiety, stress, pain catastrophizing, pain self-efficacy), and low back pain–related disability (Roland Morris Disability Questionnaire) assessed at 6 months was the outcome. Directed acyclic graphs informed confounder adjustment. Natural effect models estimated total, direct, and indirect effects with corresponding 95% confidence intervals. Missing data were addressed using multiple imputation and mediational E-values assessed sensitivity to unmeasured confounding. Higher baseline pain intensity was associated with greater disability at 6 months (B = 0.68, 95% CI 0.23-1.14). Pain self-efficacy was the only individual psychological factor showing evidence consistent with mediation, with an indirect effect of 0.16 (95% CI 0.04-0.35), accounting for 22% of the total effect (95% CI 7%-42%). The mediational E-value for the total natural indirect effect of pain self-efficacy on the risk ratio scale was 1.21, indicating that this finding may be sensitive to unmeasured confounding. Psychological factors, particularly self-efficacy, partly explain the transition from acute low back pain to future disability. Enhancing pain self-efficacy may represent an important early intervention target, although most variance remains unexplained.