Ossification variants of the distal femoral condyle: longitudinal 3 T MRI evidence of progression to juvenile osteochondritis dissecans in asymptomatic siblings of patients with JOCD

OBJECTIVE: Ossification variants (OVs) of the femoral condyles are traditionally regarded as benign developmental findings distinct from juvenile osteochondritis dissecans (JOCD). We aimed to characterize the longitudinal MRI behavior of OVs and JOCD lesions in asymptomatic siblings of JOCD patients. MATERIALS AND METHODS: In this HIPAA-compliant longitudinal pilot study, seven asymptomatic siblings of JOCD patients underwent serial 3 T bilateral knee MRI. Two fellowship-trained musculoskeletal radiologists independently assessed 56 studies for bone marrow edema, lesion location, and MRI-defined category (OV or JOCD). RESULTS: OV and MRI-defined JOCD lesions were identified in 21 of 28 condyles (75%, 95% CI: 56.6-87.3%), while 7 condyles (25%, 95% CI: 12.7-43.4%) remained normal throughout follow-up. Six condyles demonstrated MRI-defined JOCD lesions at one or more timepoints. Three OV lesions evolved over time: two progressed to MRI-defined JOCD but remained clinically silent, and one progressed from OV to MRI-defined JOCD and subsequently to clinically manifest JOCD requiring surgery. Using Generalized Linear Mixed model, a statistically significant association was found between bone marrow edema and MRI-defined category (F = 31.73, p < 0.001). OV lesions showed absent or trace edema, whereas JOCD showed definite edema. Inter-reader agreement using Cohen's Kappa was moderate to substantial between the radiologists (κ = 0.479-0.739, 95% CI: 0.314-0.633, 0.644-0.845, p < 0.001). CONCLUSIONS: In siblings of patients with JOCD, OV lesions are common and may represent dynamic MRI phenotypes along a continuum of epiphyseal ossification abnormalities, with occasional progression to MRI-defined JOCD and rare progression to clinically manifest JOCD.