Mechanisms in psychosocial treatments of chronic pain: What does the evidence tell us?

The study of mechanisms is vital for validating theories on which psychosocial chronic pain treatments are founded, can help distinguish active ingredients from inert or redundant ones, and can justify people devoting time, energy and resources needed to participate in treatment procedures. Evidence for links between putative mechanisms and outcomes is reviewed following criteria of association, temporal precedence and specificity. Although changes in mechanism factors during treatment appear related to outcome changes and such changes may precede and predict outcome change, evidence for specificity - does a treatment work primarily via theoretically-specified mechanisms - has little support. Instead, most evidence suggests that psychosocial pain treatments engage a discrete set of shared but essential mechanisms. The continuing search for mechanisms (and new treatments) may need to come to terms with evidence indicating that common features are more important than distinct ones and that conceptual models embracing these shared mechanisms are critical to advance the field.