Discordant radiologic and histological dimensions of the zone of provisional calcification in fetal piglets

Abstract

Studies have shown that the fracture plane of the classic metaphyseal lesion (CML) of infant abuse occurs in the region of the primary spongiosa, encompassing a radiodense fracture fragment customarily referred to as the "zone of provisional calcification" or ZPC. However, the zone of provisional calcification is defined differently in the pathology and the imaging literature, potentially impeding efforts to understand the fundamental morphological features of the classic metaphyseal lesion. We systematically correlated micro-CT data with histology in piglets to explore the differing definitions of the zone of provisional calcification and to elucidate the anatomical basis for divergent definitions. The distal tibias of five normal fetal piglets were studied postmortem. The specimens were resected and imaged with digital radiography (50μm resolution) and micro-CT (45μm(3) isotropic resolution). Image processing techniques were applied to the micro-CT data for visualization and data analysis. The resected tissue specimens were then processed routinely and the light microscopic features were correlated with the imaging findings. The longitudinal dimension of the radiologic zone of provisional calcification is greater than the histological ZPC, and these dimensions are statistically distinct (P < 0.0002). The radiologic zone of provisional calcification consists of two adjoining mineralized discoid regions that span the chondro-osseous junction-a thick discoid region that encompasses the densest region of the primary spongiosa, and a thin discoid region (corresponding to the histological ZPC) that is situated in the base of the physis adjacent to the metaphysis. The correlation of the normal histology and micro-CT appearance of this dynamic and complex region provides an anatomical foundation upon which a deeper appreciation of the morphology of the classic metaphyseal lesion can be built.