Conditioned Pain Modulation in Patients with Hemophilic Arthropathy: A Cross-Sectional Cohort Study

Background/Objectives: Hemophilic arthropathy causes functional impairment, disability, and chronic pain. Conditioned pain modulation describes the effect of endogenous pathways that potentiate or diminish the effects of noxious afferent stimuli. The objective was to identify conditioned pain modulation in patients with bilateral hemophilic ankle and knee arthropathy, and the best predictive model thereof. Methods: Cross-sectional cohort study. Forty-nine adult patients with hemophilic arthropathy were recruited. The dependent variable was the Conditioned Pain Modulation Index (CPMI). Age was the predictor variable. Secondary variables, estimated as modifying or confounding variables, were kinesiophobia (Tampa Scale for Kinesiophobia), catastrophizing (Pain Catastrophizing Scale), anxiety (State-Trait Anxiety Inventory), and clinical, anthropometric, and sociodemographic variables. Results: Conditioned pain modulation in patients with hemophilic arthropathy presents values close to zero (mean = 0.004: 95%CI: -0.05; 0.06). Anxiety, pain intensity, and pressure pain threshold explained the variability in the conditioned modulation of ankle pain (R²_adj = 0.24). Variables explaining 23.05% of variability of conditioned modulation of knee pain were age, inhibitor development, anxiety, and pressure pain threshold (R²_adj = 0.23). Conclusions: Patients with hemophilia presented a modulation close to zero, representing a balance between the ability to inhibit and facilitate painful stimuli. The predictive model of conditioned modulation of ankle pain includes anxiety, and pain intensity and threshold. Age, inhibitory development, anxiety, and pain threshold predict knee pain modulation.