Moderators and Mediators of Activity Intolerance Related to Pain

There is wide variation in activity intolerance for a given musculoskeletal pathophysiology. In other words, people often experience illness beyond what one would expect given their level of pathophysiology. Mental health (i.e., cognitive bias regarding pain [e.g., worst-case thinking] and psychological distress [symptoms of anxiety and depression]) is an important and treatable correlate of pain intensity and activity intolerance that accounts for much of this variation. This study tested the degree to which psychological distress accentuates the role of cognitive bias in the relationship between pain intensity and activity intolerance.

We enrolled 125 adults with musculoskeletal illness in a cross-sectional study. Participants completed measures of activity intolerance related to pain (Patient-Reported Outcomes Measurement Information System [PROMIS] Pain Interference Computer Adaptive Test [CAT]) and in general (PROMIS Physical Function CAT]), measures of psychological distress (PROMIS Depression CAT and PROMIS Anxiety CAT), a numeric rating scale (NRS) for pain intensity, measures of pain-related cognitive bias (4-question versions of the Negative Pain Thoughts Questionnaire [NPTQ-4], Pain Catastrophizing Scale [PCS-4], and Tampa Scale for Kinesiophobia [TSK-4]), and a survey of demographic variables. We assessed the relationships of these measures through mediation and moderation analyses using structural equation modeling.

Mediation analysis confirmed the large indirect relationship between pain intensity (NRS) and activity intolerance (PROMIS Pain Interference CAT and Physical Function CAT) through cognitive bias. Symptoms of depression and anxiety had an unconditional (consistent) relationship with cognitive bias (NPTQ), but there was no significant conditional effect/moderation (i.e., no increase in the magnitude of the relationship with increasing symptoms of depression and anxiety).

Psychological distress accentuates the role of cognitive bias in the relationship between pain intensity and activity intolerance. In other words, misconceptions make humans ill, more so with greater symptoms of depression or anxiety. Orthopaedic surgeons can approach their daily work with the knowledge that addressing common misconceptions and identifying psychological distress as a health improvement opportunity are important aspects of musculoskeletal care.

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.