Changes in Pain Catastrophizing and Fear-Avoidance Beliefs as Mediators of Early Physical Therapy on Disability and Pain in Acute Low-Back Pain: A Secondary Analysis of a Clinical Trial.

Objective: The Fear-Avoidance Model (FAM) of chronic pain posits that pain catastrophizing and fear-avoidance beliefs are prognostic for disability and chronicity. In acute low-back pain, early physical therapy (PT) is effective in reducing disability in some patients. How early PT impacts short- and long-term changes in disability for patients with acute pain is unknown. Based on the FAM, we hypothesized that early reductions in pain catastrophizing and fear-avoidance beliefs would mediate early PT's effect on changes in disability (primary outcome) and pain intensity (secondary outcome) over 3 months and 1 year.

Subjects: Participants were 204 patients with low-back pain of <16 days duration, who enrolled in a clinical trial (NCT01726803) comparing early PT sessions or usual care provided over 4 weeks.

Methods: Patients completed the Pain Catastrophizing Scale (PCS), Fear-Avoidance Beliefs Questionnaire (FABQ work and physical activity scales), and outcomes (Oswestry Disability Index and Numeric Pain Rating Scale) at baseline, 4 weeks, 3 months, and 1 year. We applied longitudinal mediation analysis with single and multiple mediators.

Results: Early PT led to improvements in disability and pain over 3 months but not 1 year. In the single mediator model, 4-week reductions in pain catastrophizing mediated early PT's effects on 3-month disability and pain intensity improvements, explaining 16% and 22% of the association, respectively, but the effects were small. Pain catastrophizing and fear-avoidance beliefs did not jointly mediate these associations.

Conclusions: In acute low-back pain, early PT may improve disability and pain outcomes at least partly through reducing patients' catastrophizing.