Diagnostic performance of ultrasound in identifying early knee osteoarthritis features in a 33-year-old birth cohort.

Objective: To evaluate the diagnostic accuracy of ultrasound in detecting early patellofemoral and tibiofemoral joint osteoarthritis changes in a young population using magnetic resonance imaging (MRI) as the reference. Method: This cross-sectional study included 288 participants (aged 33 years) from the Northern Finland 1986 Birth Cohort. All underwent unilateral knee imaging with ultrasound, MRI, and conventional radiography. Osteophytes, joint space narrowing, and cartilage lesions were evaluated using standardized methods. Diagnostic performance was compared against MRI using contingency tables and McNemar's test. Results: Radiographic osteoarthritis prevalence was low in the study population. For cartilage lesions, ultrasound showed low sensitivity (0.33-0.41) but high specificity (0.86-0.90), achieving high overall accuracy (0.85-0.87). For osteophytes, ultrasound significantly outperformed radiography in the femoral tibiofemoral joint (sensitivity 0.68-0.83 vs. 0.03-0.28). Both modalities struggled with trochlear osteophytes. Conclusion: In a young population, ultrasound is a promising tool for tibiofemoral osteophyte detection. Although ultrasound's low sensitivity limits its ability to rule out cartilage pathology, its high specificity indicates that detected lesions likely represent true pathology. Patellofemoral joint assessment is challenging. Our findings support ultrasound as a complementary method alongside radiography in early osteoarthritis detection.