The relationship between changes in pain intensity and functional disability in persistent disabling low back pain during a course of cognitive functional therapy

Objectives - Pain relief and reduced disability are both common treatment targets for persistent disabling low back pain (LBP). Cross-sectional studies show a moderate relationship between functional disability and pain intensity, but little is known about the relationship between changes in pain intensity and functional disability over multiple time points. The objective of this study was to investigate the associations between changes in functional disability and pain intensity and whether changes occurred simultaneously or differentially during a course of cognitive functional therapy for people with persistent disabling LBP. Methods - Self-reported measures of pain intensity and patient-specific functional disability were collected prior to each treatment session from 40 participants during a 12-week intervention period. Linear mixed modeling was used to assess simultaneous and lagged associations between pain intensity and functional disability over time. Sensitivity analysis using nonparametric subject-specific methods (simulation modeling analysis) was also performed. Results - Thirty-five participants had sufficient data for analysis. Using the linear mixed-model approach, there was evidence of a moderate and simultaneous association between pain intensity and functional disability over time (regression coefficient = 0.56, 95% confidence interval: 0.44-0.68, p < 0.001). Simulation modeling analysis supported weak to mostly strong associations and supported for simultaneous change in pain and disability for the majority of participants (22 of 35, 64%). Conclusion - Changes in pain intensity and functional disability were moderately related across the intervention. Visual inspection of graphs indicated a very close relationship in some individuals and a decoupling of pain intensity and functional disability in others. The changes in pain intensity and functional disability seem to occur simultaneously in most individuals.