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Abstract
Background: Global estimates show that back pain is the leading cause of disability among all documented health conditions. Despite this, there is no clear understanding about the causes and mechanisms of back pain. This compounds the clinical problem by leaving patients filled with uncertainty and apprehension. The lack of causal knowledge has also stifled the development and implementation of effective treatments. An important step towards addressing these issues would be to clarify our understanding of the causes and mechanisms in the onset, clinical course, and treatment of back pain.
Methods and Main Findings: This thesis is presented as a series of publications. The first study identified proximal causes of back pain by applying a case-crossover design to a worldwide social-media database (n=742,028). Psychological factors, compared to physical and general health factors, were estimated to be the most likely proximal cause. A systematic review of 12 mechanism studies (n=2961) found that distress, fear, and self-efficacy explain how pain leads to disability. Contrary to prevailing view, catastrophization did not explain this mechanism. These results were corroborated by a mechanism evaluation of a longitudinal cohort (n= 799) that refuted the role of catastrophization in explaining the link between pain knowledge acquisition and disability. Based on the findings and methodological lessons from these studies, a mechanism analysis plan was devised for a randomised trial (n=202) to understand how pain education could prevent chronic back pain, or why it might fail. The final study, an embedded recruitment trial (n=744), found that a recruitment strategy informed by marketing principles did not improve recruitment rates primary care.
Conclusions: Proximal causes of acute back pain are primarily driven by psychological factors. The clinical course of back pain can also be explained by selected psychological mechanisms, but evidence suggests that there are unknown causal pathways yet to be discovered. Robustly understanding these causal mechanisms will generate important treatment targets. Future evaluation of these treatment mechanisms will also be important in developing and refining interventions to reduce the global burden of back pain.