The weakest zone, or layer, of the physis is its third layer of cells and matrix (hypertrophic cell zone). It is particularly susceptible to shearing, bending, and tension stresses. It represents the layer of the physis that is most consistently fractured. Consequently, the reserve and proliferative cartilage cells in the first two zones of the injured physis usually remain with the epiphysis. This is relevant in that the predominant circulatory support of the cells in these two reproductive zones of the physis arises through the epiphyseal vasculature and thus is more likely to be spared in the event of physeal injury ( Fig 132-1).
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