A Comparative Study of Bone Age Assessment of the Knee: MRI Versus Radiography in Living Individuals

Background Bone age assessment (BAA) plays a significant role in forensic practice, and magnetic resonance imaging (MRI) is a promising modality for this application. This study aimed to comprehensively compare knee radiography and multi-sequence MRI for bone age assessment. Materials and Methods Knee MRI and radiograph data from individuals aged 5–30 years were retrospectively obtained from two general hospitals in Southwest China (February 2012 to July 2025). Epiphyseal maturation of the distal femur and proximal tibia was assessed on T1-weighted (T1WI), T2-weighted (T2WI), proton density-weighted (PDWI) MRI and on anteroposterior/lateral (AP/LAT) radiographs using three grading systems (Schmeling & Kellinghaus, Vieth, Dedouit). Following statistical analysis, age prediction and age-threshold classification models were developed and evaluated using mean absolute error (MAE) and area under the curve (AUC). Results A total of 1,607 individuals (874 males and 733 females) were evaluated. Paired analysis revealed significant systematic differences between MRI and radiography using the Schmeling & Kellinghaus system (mean difference: −0.483 to − 0.631 stages; all p  < 0.001), with MRI showing slightly better performance. MRI achieved lower MAEs than radiography on the test set (1.486 vs. 1.755 years in males; 1.555 vs. 1.747 years in females). For 18-year classification, MRI achieved higher AUCs than radiography (0.943 vs. 0.913 in males; 0.963 vs. 0.894 in females). Conclusion Under the same grading system, MRI and radiography showed systematic differences in epiphyseal fusion stages, with comparable overall performance but a slight edge for MRI. Additionally, the Dedouit method performed best for males, whereas the combined Schmeling and Kellinghaus method may be more suitable for females.