Sensitivity and sensitisation in relation to pain severity in knee osteoarthritis: trait or state?

Objectives: It is not clear whether heightened pain sensitivity in knee osteoarthritis (OA) is related to sensitisation induced by nociceptive input from OA pathology ('state') versus other confounding factors. Conversely, some individuals may be predisposed to sensitisation irrespective of OA ('trait').

Methods: The Multicenter Osteoarthritis Study is a longitudinal cohort of persons with or at risk of knee OA. We obtained knee X-rays, pain questionnaires and comprehensive assessment of factors that can influence pain sensitivity. We examined the relation of sensitisation and sensitivity assessed by mechanical temporal summation (TS) and pressure pain thresholds (PPTs) to knee OA and knee pain severity. To test whether sensitisation and sensitivity is a 'state' induced by OA pathology, we examined the relation of PPT and TS to knee OA duration and severity.

Results: In 2126 subjects (mean age 68, mean body mass index (BMI) 31, 61% female), PPT and TS were not associated with radiographic OA (ORs 0.9-1.0 for PPT and TS; p>0.05). However, PPT and TS were associated with pain severity (ORs: 1.7-2.0 for PPT; 1.3-1.6 for TS; p<0.05). Knee OA duration and radiographic severity were not associated with PPT or TS.

Conclusions: PPT and TS were associated with OA-related pain, but not radiographic OA after accounting for pertinent confounders in this large cohort. Lack of association with disease duration suggests at least some sensitisation and pain sensitivity may be a trait rather than state. Understanding the relationship between pathological pain and pain sensitivity/sensitisation offers insight into OA pain risk factors and pain management opportunities.