Assessing the concordance between ultrasonography and MRI for evaluation of structural features in knee osteoarthritis: a prospective cross-sectional study

Abstract

Knee osteoarthritis (KOA) is a prevalent degenerative joint disease characterized by progressive structural and functional impairment. While magnetic resonance imaging (MRI) is regarded as the reference standard for assessing joint pathology, ultrasonography (US) offers a cost-effective, accessible, and dynamic alternative. This study aimed to evaluate the concordance between US and MRI findings in assessing key structural features of KOA. In this prospective cross-sectional study, 320 patients fulfilling the American College of Rheumatology (ACR) criteria for KOA underwent both standardized US and MRI of the affected knee. Imaging assessments included cartilage integrity, meniscal extrusion, marginal osteophytes, and joint effusion. MRI served as the reference imaging modality for calculating the diagnostic performance of US. Cohen’s kappa (κ), Spearman correlation, intraclass correlation coefficients (ICC), and Bland–Altman analyses were applied to evaluate agreement between modalities, while sensitivity, specificity, and diagnostic accuracy of US were calculated using MRI as the reference standard. Good agreement was observed between US and MRI for osteophytes (κ = 0.79), joint effusion (κ = 0.67), and meniscal extrusion (κ = 0.52–0.72), whereas cartilage grading showed moderate agreement (κ = 0.52). US demonstrated high diagnostic performance for joint effusion (sensitivity = 98.7%, specificity = 100%) and strong correlations for quantitative meniscal extrusion (ρ = 0.79–0.96; ICC = 0.84–0.93, 95% CI: 0.600–0.957). Bland–Altman analysis demonstrated minimal measurement bias and narrow limits of agreement between the two imaging modalities. US provides a reliable, noninvasive, and accurate assessment of structural alterations in KOA, demonstrating strong agreement with MRI in evaluating joint effusion, osteophytes, and meniscal extrusion. These findings support the use of US as a valuable complementary imaging modality in the comprehensive evaluation of knee osteoarthritis, particularly when standardized imaging protocols are applied.