Post-Spinal Mobilization Conditioned Pain Modulation Stratifies Recovery Trajectories in Chronic Neck Pain: Toward a Mechanism-Informed Biomarker for Precision Rehabilitation

Study DesignProspective exploratory mechanistic cohort study. ObjectiveTo examine whether subgrouping post-spinal mobilization (post-SM) conditioned pain modulation (CPM) using grouping based on a median threshold predicts 4-week recovery and discharge outcomes better than continuous post-SM CPM values in adults with chronic mild mechanical neck pain. BackgroundThe identification of early responders to spinal mobilization remains suboptimal. Baseline CPM subgrouping has been shown to possess predictive value in pharmacology research; however, the value of post-SM CPM as an active mechanism-based biomarker remains poorly explored. MethodsThirty-one participants (18 women) with chronic neck pain received 10 minutes of cervical spinal mobilization. The post-treatment CPM responses were categorized using a median threshold to form subgroups. Associations with pain, disability, and global recovery were assessed, as were discharge rates. Receiver operating characteristic (ROC) analyses were used to identify thresholds for discharge prediction. ResultsPost-SM CPM subgrouping accurately predicted 4-week perceived recovery ({beta}=0.66; 95% CI: 0.03-1.29; p=0.04), explaining >50% of the variance after adjustment for age, sex, and BMI. Likewise, the lower CPM subgroup demonstrated clinically relevant improvements in pain and function with moderate-to-large effect sizes. Discharge was also more common in this subgroup (56% vs. 13%). ROC-based thresholds optimized sensitivity for predicting discharge, but with decreasing specificity over time. However, continuous post-mobilization CPM values did not predict improvement in pain or disability scores and highlighted the exploratory nature of such results. ConclusionsPost-SM CPM subgrouping can identify responders to spinal mobilization interventions. Post-mobilization stratification based on a mechanism can guide earlier discharge planning and prevent overtreatment. The quantification of CPM immediately after spinal mobilization can help clinicians guide treatment and allocate appropriate care pathways. These results must be used with caution since the sample size was small and must be investigated in larger samples.