Chondrolysis associated with cartilage canals of the epiphyseal cartilage of the distal humerus of growing pigs.

The articular-epiphyseal (A-E) cartilage of the distal humeri of 7 pigs weighing 13.1 to 18.2 kg and of 3 pigs weighing 36.4 to 40.9 kg was studied. Frozen samples of A-E cartilage were stained for the presence of reduced nicotinamide adenine dinucleotide dehydrogenase, lactate dehydrogenase, isocitrate dehydrogenase, and uridine diphosphate galactose-4-epimerase. Additional frozen sections and paraffin-processed sections were stained using the Alcian blue-critical electrolyte concentration method, safranin O-fast green, and hematoxylin and eosin. An area of grossly visible, opaque A-E cartilage of the medial condyle corresponded to regions of chondrolysis of the epiphyseal cartilage. The chondrolytic regions contained chondrocytes that did not stain for enzymes, had reduced staining for proteoglycans in the matrix, and were located at the site where the A-E cartilage increased in thickness. Cartilage canals were associated with the chondrolytic areas. Cartilage canals in both groups of pigs were commonly in various stages of chondrification, some of which were associated with degenerative cartilage. The regions of chondrolysis may indicate sites of biomechanical weakness in the A-E cartilage during the transformation of the epiphyseal cartilage into bone.