Do Existing Magnetic Resonance Imaging Definitions of Knee Osteoarthritis Identify Knees That Will Develop Clinically Significant Disease Over Up To 11 Years of Follow-Up?

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In individuals without radiographic knee osteoarthritis (OA), we investigated whether magnetic resonance imaging (MRI)-defined knee OA at baseline was associated with incident radiographic and symptomatic disease during up to 11 years of follow-up. Osteoarthritis Initiative participants without tibiofemoral radiographic knee OA at baseline were assessed for MRI-based tibiofemoral cartilage damage, osteophyte presence, bone marrow lesions, and meniscal damage/extrusion. We defined MRI knee OA using alternative, reported definitions (Def A and Def B). Kellgren-Lawrence (KL) grade, joint space narrowing (JSN), and frequent knee symptoms (Sx) were assessed at baseline, 1-, 2-, 3-, 4-, 6-, 8-, and 10/11-year follow-up visits. Incident tibiofemoral radiographic knee OA (outcome) was defined as (1) KL ≥2, (2) KL ≥2 and JSN, or (3) KL ≥2 and Sx. Adjusted Cox proportional hazards regression models examined associations of baseline MRI-defined knee OA (Def A and Def B) with incident outcomes during up to 11 years of follow-up. Among 1,621 participants (mean ± SD age 58.8 ± 9.0 years, mean ± SD body mass index 27.2 ± 4.5 kg/m2, 59.5% women), 17% had MRI-defined knee OA by Def A and 24% by Def B. Baseline MRI-defined knee OA was associated with incident KL ≥2 (odds ratio 2.94 [95% confidence interval (95% CI) 2.34-3.68] for Def A and 2.44 [95% CI 1.97-3.03] for Def B). However, a substantial proportion of individuals with baseline MRI-defined knee OA did not develop incident KL ≥2 during follow-up (59% for Def A and 64% for Def B). Findings were similar for the other two outcomes. Current MRI definitions of knee OA do not adequately identify knees that will develop radiographic and symptomatic disease.