Utility of ultrasound as a diagnostic tool for measuring knee cartilage thickness in patients with osteoarthritis: correlation with MRI

Background Knee osteoarthritis (OA) requires precise cartilage evaluation for disease monitoring; however, MRI is constrained by cost and limited availability. Ultrasound (USG) offers a pragmatic, economical alternative. This study aimed to evaluate the correlation and agreement between USG and MRI in measuring medial femoral condyle cartilage thickness in patients with knee OA. Results MRI recorded greater mean medial femoral cartilage thickness (anterior: 1.35 mm, middle: 1.66 mm, posterior: 2.05 mm) than USG (anterior: 0.91 mm, middle: 0.97 mm, posterior: 0.99 mm). Strong positive correlations were observed between modalities across all regions ( r = 0.767–0.904, p < 0.001). Intraclass correlation coefficient (ICC) analysis demonstrated only moderate-to-poor absolute agreement (anterior ICC = 0.541, middle ICC = 0.416, posterior ICC = 0.264). Age was significantly associated with cartilage thinning; gender and BMI were not. Conclusions USG demonstrates strong correlation with MRI in measuring medial femoral cartilage thickness but consistently underestimates absolute values. It serves as a useful, accessible adjunct for cartilage assessment, particularly in resource-limited settings, while MRI remains the gold standard for precise morphological evaluation.