Early detection of knee osteoarthritis – The role of a composite disease activity metric: Data from the Osteoarthritis Initiative

Objective: To evaluate whether dynamic disease processes in the knee (effusion-synovitis volume and bone marrow lesions; BML), summarized by a validated efficient continuous composite metric, are prognostic of incident symptomatic knee OA (sxKOA) over the subsequent three years. Methods: We analyzed knee magnetic resonance (MR) images from a sample of Osteoarthritis Initiative participants without sxKOA using a previously validated osteoarthritis disease activity metric that provides a normalized continuous score reflecting effusion-synovitis and BML volumes throughout the knee. The outcome was incident sxKOA during the subsequent three years, defined by the report of frequent knee pain and presence of radiographic OA (Kellgren-Lawrence grade ≥2). We used a modified Poisson model to assess the association between disease activity (continuous measures; relative risk [RR] per 1 unit of measure) and incident sxKOA, adjusting for gender, age, and body mass index. Results: Among 913 knees (572 participants; 56% female; mean (SD): 61 (9) years of age), disease activity ranged from -3.83 to 24.79 (higher values = greater pathology). Knees with greater disease activity (RR = 1.08 per 1 unit of disease activity [95% confidence interval: 1.04-1.11]) had a greater risk of incident sxKOA. Conclusion: Effusion-synovitis and BML volumes - represented by a validated composite score - predict the future incidence of sxKOA. This finding indicates that dynamic pathophysiologic processes are operative in knees before sxKOA becomes overt. This scenario could represent early knee OA. Moreover, the pathophysiological processes represented by effusion-synovitis and BMLs on MR images, much of which are probably inflammatory, could suggest therapeutic targets for preventive intervention.