Assessing self-reported fear of movement in chronic low back pain: how specific should we be?

Fear of movement is a key contributor to chronic low back pain (CLBP). Because patients with CLBP often fear specific activities only, self-reported fear of movement assessment should be context-specific. The Photograph Series of Daily Activities (PHODA) contains photos of activities that are rated on perceived harmfulness, yet potentially essential contextual information impacting item-interpretation is missing (eg, frequency of activity performance). Therefore, considerable variability in fear of movement in patients with CLBP with similar scores on a PHODA-item may be present. To investigate this, we first performed a hierarchical cluster analysis in patients with CLBP (n = 254) and high scores (≥70/100) on the PHODA-item showing a person lifting with a bent back (=PHODA-Lift). Cluster analysis was performed using scores on context-specific fear of movement measures, ie, how afraid participants would be if they had to perform the PHODA-Lift 1x, 10x, or 20x. We showed large variability in self-reported fear of movement when the task was specified by frequency, resulting in 5 different clusters with increasing levels of context-specific fear of movement. Further support for these clusters was provided, as higher fear clusters reported increased task-related disability and avoidance behaviour. Second, we performed exploratory path analyses to investigate reasons for variability in context-specific fear of movement. Strong relationships between context-specific pain intensity and context-specific fear of movement were present, which were partially mediated by context-specific pain self-efficacy. In conclusion, using more context-specific self-report measures revealed clinically relevant variability in fear of movement that would remain undetected by currently available self-report measures.