Quantitative traits of early-stage osteochondrosis lesions in porcine distal femurs are consistent with skeletal developmental age

Early-stage osteochondrosis (OC) lesions are focal failures of endochondral ossification in physeal and epiphyseal regions. Lesions are initially detected and quantified as ossification variants using non-invasive imaging methods. The etiology of OC lesions is not understood, as early-stage lesions are rarely imaged in children or animals until symptoms advance to stages that require intervention. The distal femur, a common site for OC lesions, provides an easily accessible, anatomic location to study early-stage development. Non-invasive computed tomography (CT) and magnetic resonance imaging (MRI) techniques to distinguish early-stage lesions were compared in images collected from Cross-sectional and Longitudinal Studies. OC lesion traits in physeal and epiphyseal regions of swine distal femurs were quantified. Cross-sectional subjects were randomly selected from asymptomatic, crossbred swine at 7, 12, and 24 weeks of age. A longitudinal cohort was repeatedly imaged at 6, 12, and 18 weeks of age. Subsets of femurs from each age were selected for histological analysis. Ossification variants defined as abnormal physeal widths without defined OC lesions, were observed at 7 weeks. At 12 weeks, 2.7+1.8 physeal lesions (volume = 9.8+10.0 mm3) per pig but no epiphyseal lesions were detected. At 24 weeks, similar numbers (2.1+1.4) of epiphyseal and physeal lesions were observed. Epiphyseal lesions had greater volumes (44.5+53.5 mm3). At 24 weeks, atypical ossification variants not previously characterized, were unexpectedly observed in over 40% of femurs. These large, undefined regions characterized by extreme undulations and irregular mineralization without physeal widening were labeled irregular physeal lesions. Although quantitative outputs of lesion traits differ, both clinical CT and MRI methods yielded consistent inferences regarding developmental age and location (primary vs. secondary centers of ossification) of OC lesion progression for Cross-sectional and Longitudinal Studies. Outcomes support future research efforts to identify pivotal molecular signals controlling initiation, progression, and regression of early-stage lesion development.