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.

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: https://osf.io/q8wf6/ ). 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.