Three distinct knee pain phenotypes have been identified among older adults, lending support for the existence of homogeneous pain groups despite considerable variation in the perception of pain, according to the results of a population-based, longitudinal cohort study that was conducted as part of the Tasmanian Older Adult Cohort (TASOAC) study from Australia. Study findings were published in Rheumatology (Oxford).
Investigators sought to differentiate and validate knee pain phenotypes in an older population of adults across a variety of pain-related domains over a period of 10.7 years. A total of 963 participants (mean age 62.8 ± 7.4 years) from the TASOAC Study were examined at baseline and followed up at 2.6 years (n = 875), 5.1 years (n = 768), and 10.7 years (n = 563). Baseline demographic, psychological, comorbidity, and lifestyle data were gathered. Magnetic resonance imaging was performed to measure participants’ knee structural pathology. Questionnaires were used at each time point to evaluate Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain score and pain at multiple sites. Knee pain phenotypes were identified with the use of latent class analysis, taking into account gender, body mass index (BMI), educational level, comorbidities, and number of painful sites.
Overall, 3 distinct pain phenotypes were identified: class 1: high prevalence of emotional problems and low prevalence of structural damage (25% of participants); class 2: high prevalence of structural knee damage and high prevalence of emotional problems (20% of participants); and class 3: low prevalence of emotional problems and low prevalence of structural knee damage (55% of participants).
Patients in classes 1 and 2 had more comorbidities, higher BMI, and a higher prevalence of radiographic knee osteoarthritis and knee structural pathology compared with those in class 3. Additionally, WOMAC pain and number of painful sites among participants in class 1 were consistently greater at each time point assessed over 10.7 years compared with those in classes 2 and 3. When the analyses were restricted to patients with radiographic knee OA, the results were similar.
The investigators concluded that based on the fact that both psychological and structural factors interact with each other to exacerbate pain perception, tailored treatment approaches for older individuals with knee pain in clinical practice are warranted to optimize therapeutic outcomes.
Pan F, Tian J, Cicuttini F, Jones G, Aitken D. Differentiating knee pain phenotypes in older adults: a prospective cohort study [published online September 20, 2018]. Rheumatology (Oxford). doi: 10.1093/rheumatology/key299