Objective: To investigate whether indirect effects via psychological mechanisms explain the effects of physical therapy (PT) or yoga versus education on back-related outcomes.
Design: Mediation analyses using data from a randomized controlled trial of PT, yoga, and education interventions for chronic low back pain.
Methods: Primary outcomes were changes in back-related pain on the 11-point numeric rating scale and disability on the modified 23-point Roland-Morris Disability Questionnaire, measured at 52 weeks after randomization. Hypothesized mediators were 12-week changes in pain self-efficacy, fear-avoidance beliefs, depression, anxiety, perceived stress, and sleep quality. We used causal mediation analysis to estimate the total effect, direct effect, indirect effect, and proportion mediated.
Results: We analyzed data from 230 adults (mean age = 46.2 years, 69.6% female, 79.6% non-White). In the PT-versus-education model, when the mediator was perceived stress, the total effect on disability was 2.6 points (95% confidence interval [CI]: 0.3, 4.9) and decomposed into a direct effect of 1.7 points (95% CI: -0.4, 3.8) and an indirect effect 0.9 points (95% CI: 0.1, 2.0; proportion mediated, 34%). No other psychological construct was a significant mediator.
Conclusion: Improvements in perceived stress mediated improvements in disability after PT treatment compared to education. Other psychological outcomes did not mediate the effect of yoga or PT on pain or disability outcomes compared to education. J Orthop Sports Phys Ther 2022;52(7):470-483. Epub: 18 May 2022. doi:10.2519/jospt.2022.10813.
Trial registration: ClinicalTrials.gov NCT01343927.
Keywords: biopsychosocial; chronic pain; mechanism; mediation; physical therapy; yoga.