Specific and shared mechanisms associated with treatment for chronic neck pain: the SS-MECH mechanistic clinical trial

INTRODUCTION: The effects of interventions such as manual therapy (MT) and exercise on chronic neck pain (CNP) are thought to work through different specific mechanisms. However, randomized clinical trials comparing MT and exercise frequently demonstrate similar outcomes, suggesting the possibility of shared mechanisms. Objectives: To compare specific and shared mechanisms (primary) and clinical outcomes (secondary) across patients randomized to an MT or an exercise treatment group for CNP. METHODS: A mechanistic clinical trial consented and randomized 124 participants with CNP. Mechanistic measures assessing mobility, pain modulation, endurance, self-efficacy, therapeutic alliance, clinical engagement, fear, and positive coping were captured at baseline, at 2-weeks and at 3-weeks. Clinical outcomes for pain interference, intensity and physical function were gathered at baseline, 4-weeks, and 6-months. Differences between treatment groups were analyzed using repeated-measures, linear mixed effects models. RESULTS: There were no significant differences between groups in any of the mechanistic measures, although significant changes occurred over time. Between-group differences were observed favoring MT at 4 weeks for physical function. DISCUSSION/CONCLUSION: MT and exercise produced comparable effects on both specific and shared mechanisms, as well as a majority of clinical outcomes. Collectively, the results support the notion that MT and exercise are influenced by common mechanisms. CLINICAL TRIAL REGISTRATION: The www.clinicaltrials.gov identifier is NCT05940012.