OP0179 DO DISTINCT PAIN PHENOTYPES HAVE DIFFERENT RISK OF KNEE REPLACEMENT: A 13.7-YEAR FOLLOW-UP STUDY?
Authors: Feng Pan, Jing Tian, Ishanka Munugoda, Stephen Graves, Michelle Lorimer, Flavia Cicuttini, Graeme Jones
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Pain is the main impetus for osteoarthritis (OA) patients to seek healthcare including joint replacement. The pain experience is very heterogeneous and affected by factors across multiple domains–peripheral, psychological, and neurological, which suggests the existence of homogenous subgroups/phenotypes within OA patients with pain. We recently identified three pain phenotypes using a wide spectrum of factors including main pain dimensions (structural damage on MRI, body mass index (BMI), comorbidities, psychological and multi-site pain (a surrogate of neurological factor)). <h3>Objectives</h3> To examine whether the risk of knee replacement (KR) varied when these three pain subgroups were compared. <h3>Methods</h3> 1099 participants (mean age 63 years; range 51-81 years) from a population-based 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 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 the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain questionnaire at each time-point. Presence of pain (yes/no) in the neck, back, hands, shoulders, hips, knees and feet was also assessed by questionnaire at each time-point. KR up to 13.7 years after recruitment was identified by linking to the Australian Orthopaedic Association National Joint Replacement Registry. Latent class analysis was used to differentiate pain phenotypes by considering sex, BMI, emotional problems, education level, comorbidities, number of painful sites and knee structural damage on MRI. Log-binomial regression was used to evaluate the association between three pain phenotypes and risk of KR. <h3>Results</h3> 963 participants were included in the analysis (BMI 27.7 kg/m<sup>2</sup>, 50% female). Three distinct phenotypes were identified: Class 1: high prevalence of emotional problems and low revalence of structural damage (25%); Class 2: high prevalence of structural damage and low prevalence of emotional problems (20%); Class 3: low prevalence of emotional problems and low prevalence of structural damage (55%). Participants in Class 1 had greater pain severity than those in Class 2 and 3. During a follow-up of 13.7 years, There were 46 right and 51 left TKR's in 79 participants In multivariable analyses, participants in Class 1 and 2 had higher risk of requiring KR on the right [Class 1 vs. Class 3: relative risk (RR) 6.66, 95%confidence interval (CI) 2.17-20.49; Class 2 vs. Class 3: RR 14.14, 95CI% 4.85-41.22], left (Class 1 vs. Class 3: RR 2.75, 95%CI 1.22-6.19; Class 2 vs. Class 3: RR 5.46, 95CI% 2.64-11.32), and any knee joints (Class 1 vs. Class 3: RR 3.65, 95%CI 1.88-7.09; Class 2 vs. Class 3: RR 6.81, 95CI% 3.68, 12.60) compared to Class 3, but the associations were stronger with Class 2 than Class 1. <h3>Conclusion</h3> Participants with distinct pain phenotype groups have different risks of KR. This suggests that the identified phenotypes reflect distinct clinical subgroups with different prognoses. As expected the highest risk of KR was found in those with the most structural damage (Class 2). However, those participants with low structural damage have an increased risk of KR when they have high compared to low emotional problems, indicating that selection of subjects for KR could be improved by screening out those in Class 1. <h3>Disclosure of Interests</h3> None declared