Longitudinal correlation between X-ray and MRI findings in medial compartment knee osteoarthritis: Insights into early cartilage loss and structural changes

Purpose: Knee osteoarthritis (OA) is a common joint disorder assessed using radiographic (X-ray) and magnetic resonance imaging (MRI). While X-rays are accessible, MRI provides detailed insights into meniscus and cartilage. Few studies have evaluated the correlation between X-ray and MRI findings in knee OA longitudinally. This study addresses this gap by investigating their relationship over time. Methods: The Multicenter Osteoarthritis Study (MOST) dataset, a public, longitudinal cohort study focusing on knee OA in older adults, was used. The analysis included 3710 knees with medial compartment OA from different follow-ups over the course of 7 years. X-ray findings were compared with MRI findings, encompassing cartilage, meniscal and bone pathologies. Results: In the central compartment, knee OA progression began with cartilage loss, followed by meniscal and bone pathology, while in the posterior compartment, meniscal changes preceded cartilage and bone lesions. Cartilage loss in the central femur was the earliest event, even in Kellgren–Lawrence grade 0 knees, preceding X-ray changes. Tibial osteophytes developed first on X-ray, followed by joint space narrowing and femoral osteophytes. Longitudinal regression identified meniscal extrusion, cartilage loss and meniscal tear as significant predictors of OA progression (p < 0.001), with meniscal extrusion being the strongest. Conclusion: Knee OA progression differs by compartment, with cartilage loss initiating changes centrally and meniscal pathology leading posteriorly. Tibial osteophytes appear early on X-ray. Meniscal extrusion is the strongest predictor of OA progression, highlighting the importance of MRI in identifying early changes and guiding personalised management. Level of Evidence: Level II.