Weight-bearing and non-weight-bearing pain may reflect different pain mechanisms in knee osteoarthritis

Purpose: Knee osteoarthritis (OA) is predominantly characterized by pain with weight-bearing (WB) activities, which thought to be reflective of nociceptive pain. However, at rest, i.e., non-weight bearing (NWB), also common in individuals knee OA. Why NWB may occur a disease that largely biomechanically driven not clear, though altered neurobiological functioning pathways hypothesized play role, such as ascending facilitation (pain sensitization) and inefficient descending modulation. We, therefore, sought determine whether sensitization or conditioned modulation (CPM) have different associations WB Methods: We used data from The Multicenter Osteoarthritis Study (MOST), NIH-funded longitudinal cohort older adults risk To assess sensitivity CPM, we employed the following quantitative sensory testing (QST) measures: 1) pressure threshold (PPT) wrist patellae using handheld algometer, defined point first changed into slight pain, categorized sex-specific tertiles. Low PPT reflect greater central while low patella peripheral +/- sensitization; 2) mechanical temporal summation (TS) assessed weighted punctuated probe applied train 1Hz over 10 seconds. An increase rating end indicates 3) Efficiency CPM forearm ischemia conditioning stimulus. A ratio post-conditioning stimulus pre-conditioning being ≤1 CPM. was presence least moderate on each WOMAC subscale questions regarding stairs, standing, walking; similar approach define based upon sitting/lying, sleeping night. evaluated relation QST measure separate models, logistic regression generalized estimating equations account for correlations between two knees within an individual, adjusting potential confounders (age, sex, body mass index (BMI), catastrophizing, depressive symptoms, poor sleep quality, widespread pain). Results: 2749 subjects (5479 knees) were included (mean age 64±11, 57% female, mean BMI 29.5±5.7 kg/m2). Lower patellar associated odds both (Table). but facilitated TS only stairs. any outcomes. Conclusions: Greater sensitization, measured PPT, TS, measures only. surrogate modulation, either type Our findings challenge hypothesis than suggest other mechanisms responsible merit further examinations, inflammation psychological factors.