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

Abstract

Early-stage osteochondrosis (OC) lesions are focal failures of endochondral ossification in the 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, anatomical location to study early-stage development. Non-invasive CT and MRI techniques for distinguishing early-stage lesions were compared in images collected from Cross-sectional and Longitudinal Studies. Osteochondrosis lesion traits in the 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 wk of age. A longitudinal cohort was repeatedly imaged at 6, 12, and 18 wk of age. Subsets of femurs from each age group were selected for histological analysis. Ossification variants defined as abnormal physeal widths without defined OC lesions, were observed at 7 wk. At 12 wk, 2.7 ± 1.8 physeal lesions per pig with an average volume = 9.8 ± 10.0 mm³ were quantified but no epiphyseal lesions were detected. At 24 wk, 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 wk, atypical ossification variants not previously characterized, were unexpectedly observed in over 40% of the femurs. These large, undefined regions characterized by extreme undulations and irregular mineralization without physeal widening were labeled irregular physeal lesions. Although the quantitative outputs differed, both CT and MRI methods yielded consistent inferences regarding the developmental age and location (primary vs secondary centers of ossification) of OC lesion progression across Cross-sectional and Longitudinal Studies. These outcomes support future research efforts to identify pivotal molecular signals controlling the initiation, progression, and regression of early-stage lesion development.