Background Pain in osteoarthritis (OA) is very common and often involves multiple joints. It is multifactorial and individualised with multiple factors involved in the genesis and pain experience, such as structural pathology, psychological factors and pain coping strategies. Thus it may be possible to group people together based on specific factors which are linked to experiencing pain.
Objectives To identify and validate the phenotype of knee pain over 10.7 years.
Methods 1099 participants (mean age 63 years; range 51–81 years) from the population-based Tasmanian Older Adult Cohort study were recruited at baseline. 875, 768 and 563 participants attended years 2.6, 5.1 and 10.7 follow-up, respectively. Demographic, psychological, lifestyle and comorbidities data were obtained at baseline. T1-weighted or T2-weighted fat saturated MRI of the right knee was performed to measure knee structural pathology–cartilage defects, bone marrow lesions (BMLs) and effusion-synovitis at baseline. Knee pain was assessed using Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) at each time-point. Presence of pain (yes/no) at the neck, back, hands, shoulders, hips, knees and feet was also assessed by questionnaire at each time-point. Latent class analysis, which can identify unmeasured class membership among participants using observed variables, was used to differentiate “pain phenotypes” considering sex, body mass index (BMI), emotional problems, comorbidities, number of painful sites and knee structural damage on MRI.
Results Three pain phenotypes were identified: Class 1: high levels of emotional problems and low levels of structural damage (24%); Class 2: high levels of structural damage and low levels of emotional problems (20%); Class 3: relatively low levels of emotional problems and low levels of structural damage (56%). People within Class 1 were more likely to be female, had greater BMI, lower education level, more comorbidities, more severe knee pain and more painful sites as compared to Class 2 and Class 3. Furthermore, WOMAC pain scores and number of painful sites were consistently greater at baseline, 2.6, 5.1 and 10.7 years in Class 1 than Class 2 and Class 3 (all P<0.05).
Conclusions Psychological and structural factors interact with each other to influence pain perception.
Disclosure of Interest None declared