Association of Pain Sensitization and Conditioned Pain Modulation to Pain Patterns in Knee Osteoarthritis

To examine the cross-sectional association of ascending pain mechanisms, implicated in pain sensitization, and descending pain modulation with pain patterns and unpredictability of pain.

The Multicenter Osteoarthritis Study is a longitudinal cohort of older adults with or at risk of knee osteoarthritis. Peripheral and central ascending pain mechanisms were assessed using quantitative sensory tests, pressure pain thresholds using a handheld pressure algometer (knee/peripheral and wrist/central), and temporal summation using weighted probes (wrist/central). Descending modulation was assessed by conditioned pain modulation using pressure pain thresholds and a forearm ischemia test. Pain patterns were characterized based on responses to the Intermittent and Constant Osteoarthritis Pain questionnaire: 1) no intermittent or constant pain, 2) intermittent pain only, 3) constant pain only, and 4) combined constant and intermittent pain. A question regarding frequency assessed unpredictable pain. We assessed the association of quantitative sensory test measures to pain patterns using regression models with generalized estimating equations.

There were 2,794 participants (mean age 63.9 years, body mass index 29.5 kg/m² , and 57% female). Lower pain sensitization by wrist pressure pain threshold (odds ratio [OR] 0.80 [95% confidence interval (95% CI) 0.68, 0.93]) and adequate conditioned pain modulation (OR 1.45 [95% CI 1.10, 1.92]) were associated with having constant ± intermittent pain compared with intermittent pain only. Higher pain sensitization (by pressure pain thresholds and temporal summation) was associated with a higher likelihood of unpredictable pain.

Knee pain patterns appear to be related to peripheral ± central facilitated ascending pain mechanisms and descending modulatory mechanisms. These findings highlight the need for a broader approach to understanding pain mechanisms by symptomatic disease progression.