Specific and shared mechanisms mediating pain intensity and functional outcomes in chronic neck pain

BACKGROUND: To date, very few studies have used mediation analysis to explore the reasons why people with chronic neck pain improve after physical therapy intervention involving manual therapy or exercise. OBJECTIVES: To evaluate which specific mechanisms (mobility, pain modulation and endurance) and shared mechanisms (self-efficacy, working alliance, engagement, fear, and positive coping) mediated the effects of treatment on clinical outcomes at 4-weeks and 6-months in individuals with chronic neck pain. METHODS: The study incorporated planned indirect‑only mediation analyses to evaluate both specific and shared mechanisms as mediator using data from a mechanistic clinical trial comparing manual therapy and exercise interventions, which demonstrated no between‑group differences. Baseline pain intensity was modeled as the independent variable, and pain interference and physical function at four-weeks and six-months were specified as outcomes. Direct, indirect, and total effects were estimated across four mediation models. RESULTS: None of the mediation analyses found specific or shared mechanisms that mediated the relationship of baseline pain intensity to long-term pain interference and physical function. Discussion/Conclusion: Our findings suggest that the absence of significant mediation implies that commonly targeted mechanisms may not be the primary drivers of the relationship of pain intensity to longer-term pain interference or physical function. CLINICAL TRIAL REGISTRATION: www.clinicaltrials.gov identifier is NCT05940012.