Background/Purpose: Pain with weightbearing in knee OA is thought to be related to the activation of nociceptors; however, this is not considered the sole mechanism by which pain is experienced in OA as it would not explain the pain with non-weight-bearing that often occurs. Pain sensitization, reflecting altered pain processing, may contribute to pain at rest or while sleeping. The aim of this study was to determine the extent to which pain with different degrees of weight-bearing were associated with objective measures of pain sensitization.

Methods: Participants from the Multicenter Osteoarthritis (MOST) study, a longitudinal prospective cohort of older adults with or at risk of knee OA, were included in this cross-sectional analysis. Mechanical pressure pain threshold (PPT) at the wrist and patellae were assessed with a handheld algometer, and categorized into sex-specific tertiles. Lower PPTs indicate greater sensitization. Weighted mechanical punctate probes were used to assess temporal summation (TS) at the wrist, an indicator of central sensitization, with a train of 10 stimuli at 1 Hz; increase in pain by the end of the train indicates TS. Adequacy of conditioned pain modulation (CPM) was determined by assessing PPT at the wrist (test stimulus, PPT1) with forearm ischemia as the conditioning stimulus, followed by PPT reassessment (PPT2). Adequate CPM (pain inhibition) was operationalized as PPT2:PPT1 >1. Individual WOMAC pain questions were dichotomized as having at least moderate pain on each question, and categorized into weight-bearing pain (stairs, standing, walking) vs. non-weight-bearing pain (sitting, nocturnal), based on having moderate or greater pain on at least one question. We evaluated the relation of each QST measure to WOMAC pain questions or categories using logistic regression, adjusting for age, sex, body mass index (BMI), catastrophizing, depressive symptoms, and widespread pain.

Results: 2749 subjects were included (mean age 64±11, 57% female, mean BMI 29.5±5.7 kg/m²). Higher patellar PPT was significantly associated with lower odds of reporting at least moderate pain for each WOMAC pain question (Table 1), with similar magnitudes of association for weight-bearing and non-weight-bearing pain. Higher wrist PPT was significantly associated with weight-bearing activities, while TS was only significantly associated with stair climbing; neither were significant associated with non-weightbearing pain. Adequate CPM was not significantly associated with either weight-bearing or non-weight-bearing.

Conclusion: Greater peripheral sensitization, as assessed by patellar PPT, was associated with having moderate pain with both weight-bearing and non-weight-bearing activities. Wrist PPT and TS, reflecting central sensitization, were significantly associated with weight-bearing but not non-weight-bearing pain. CPM, a marker of descending pain modulation, was not significantly associated with either category of pain. Our findings may challenge the hypothesis that non-weight-bearing pain may reflect greater pain sensitization than pain while weight-bearing. The contribution of other pain mechanisms, including inflammation, should be further explored.

Table 1. Results for the multivariable analyses of the association between QST measures and individual or grouped WOMAC pain questions (n=5479 knees)

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/do-weight-bearing-versus-non-weight-bearing-pain-reflect-different-pain-mechanisms-in-knee-osteoarthritis-the-multicenter-osteoarthritis-study/