POS0108 WOMAC KNEE PAIN: DOES IT WALK THE WALK?

Background Due to its major public health impact, knee osteoarthritis (KOA) has been designated as a serious disease by the US Food and Drug Administration (FDA). Approval of a disease modifying osteoarthritis drug (DMOAD) to slow or prevent disease progression hinges on demonstrating both symptomatic (i.e., how a patient feels or functions) and structural improvement. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the questionnaire most commonly used to assess symptomatic improvement, may not adequately reflect pain reporting due to KOA. The lack of DMOAD approval to date has largely been attributed to the lack of clinical translation of structural benefits that also yield symptomatic improvements. Drugs targeting inflammation are an example of a therapeutic approach that has yielded evidence of structural benefit but not symptomatic improvement as assessed by the WOMAC. Objectives Evaluate potential heterogeneity of the effects of structural damage on knee pain reporting across activities assessed in the WOMAC pain subscale following recent development of radiographic knee osteoarthritis. Methods The Osteoarthritis Initiative is a longitudinal observational study of participants with or at risk of symptomatic knee OA. We identified incident cases of radiographic KOA, defined as Kellgren-Lawrence [KL] grade 2 or 3 based on centrally graded x-rays. Participants underwent bilateral posteroanterior fixed-flexion weight-bearing knee radiography at clinic visits annually or biannually through year 10. Non-contrast 3T MRI was also acquired at clinic visits up to year 8. Musculoskeletal radiologists graded structural damage, including effusion-synovitis (ES), Hoffa-synovitis (HS), bone marrow lesions (BMLs), cartilage and meniscal damage using the MRI Osteoarthritis Knee Score (MOAKS). The WOMAC knee pain subscale is calculated by adding reported pain scores from various activities, including walking on a flat surface, going up or down stairs, at night while in bed, sitting or lying down, and standing, during the last seven days, rated on a 5-point scale from none (0), mild (1), moderate (2), severe (3), or extreme [4]. Pain in each knee was reported separately. We fit a proportional odds logistic regression to model the ordinal pain scores reported for each activity on the WOMAC pain scale using penalized maximum likelihood estimation; predictors included each of the MRI structural damage scores, KL grade, age, and BMI at the same clinic visit, as well as sex and race. We estimated the predicted probability of pain rated moderate or worse (Pr[Y ≥ 2 | X]), and reported nonparametric bootstrap 95% confidence intervals (CI) with cluster sampling at the participant-level. Results We identified 690 knees contributed by 623 participants that developed radiographic KOA. The mean participant age was 65 years (SD 9), mean BMI was 29.3 (SD 4.8), 66% reported female sex and 83% self-identified as white. The predicted probability of knee pain rated moderate or worse (≥2) increased with greater ES during walking and stair climbing, but there was no evidence that ES affected knee pain while in bed, sitting or lying down, or standing (Figure 1). We did not find evidence that HS, BMLs, cartilage or meniscal damage affected the WOMAC knee pain items cross-sectionally in our fully adjusted models. Conclusion Our study suggests that ES seen on MRI produces heterogeneous effects on pain reporting, depending on the type of activity. Treatments that are developed to target inflammation may reduce pain during some activities, such as walking and stair climbing, but may have little benefit during other activities, such as sitting or lying down. If a treatment effectively reduces or limits structural damage that differentially impacts pain across the activities included in the WOMAC pain subscale, analysis that focuses only on the WOMAC pain subscale score may mask the clinical benefit of the treatment. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests C. Kent Kwoh Consultant of: Avalor Therapeutics, Express Scripts, Kolon Tissue Gene, LG Chem Regeneron, Grant/research support from: AbbVie, Cumberland, Lilly, Pfizer, Frank Roemer Shareholder of: BICL, LLC, Consultant of: Calibr, Grünenthal, Ali Guermazi Shareholder of: BICL, LLC., Consultant of: Pfizer, Kolon TissueGene, Novartis, Regeneron, TrialSpark, Medipost, ICM, Erin Ashbeck: None declared.

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