The ultrastructure of osteochondrosis of the articular-epiphyseal cartilage complex in growing swine

Osteochondrosis of the articular-epiphyseal cartilage complex (A-E complex) is a significant clinical disease in swine. It has been suggested that osteochondrosis is the underlying cause of osteochondritis dissecans in humans. The purpose of this investigation was to characterize the ultrastructural changes in the earliest macroscopically visible lesion of the epiphyseal cartilage in osteochondrosis of the A-E complex in swine. Osteochondritic epiphyseal cartilage from the distal femora and humeri of growing crossbred boars was collected, embedded in plastic, and studied light and electron microscopically. The predominant lesion was chondronecrosis, characterized by chondrocyte death and loss of matrical proteoglycan. Transition from normal to abnormal cartilage was abrupt. Lipid accumulated in chondrocytes within and adjacent to lesions, but not in chondrocytes distant from lesions. Intracellular lipid accumulation was an important feature of the lesion and may play a role in its initiation. It is hypothesized that intracellular lipid accumulation results from hypoxia/anoxia and may precede matrix degeneration, which precedes cell death.