This experimental study describes the mechanism of epiphyseal growth inhibition and eventual epiphyseodesis under staples in rabbits. The effect of stapling is a direct pressure inhibition of the proliferating stage of epiphyseal growth. The cartilage cells of the epiphyseal plate, however, continue their maturation so that the hypertrophic cells degenerate, the palisading cells hypertrophy and eventually degenerate, and finally the proliferating and resting cells pass through a similar sequence. The metaphyseal vascular channels, with the accompanying osteoblasts, invade each successively degenerating group of cartilage cells, thus gradually thinning the epiphyseal plate until eventual epiphyseodesis occurs.

Three histological changes are visible roentgenographically: (1) disappearance of the fine metaphyseal trabeculae, (2) the formation of a dense layer of subepiphyseal bone, and eventually, (3) thining of the epiphyseal plate. It is suggested that roentgenograms of stapled epiphyses in which growth has not resumed after the staple was removed be restudied to determine their value clinically as warning signs of premature closure of the epiphyseal plate under a staple.

In the transepiphyseal wire experiments it was noted that when a wire traversed the epiphyseal plate there was no interference with longitudinal growth. As the epiphysis grew beyond the wire, the transepiphyseal defect made by the wire was replaced by bone; the epiphyseal defect showed no signs of being replaced by epiphyseal cartilage cells. The degree of the deformity depended upon the location of the epiphyseodesis and its extent. This is demonstrated by the production of eccentric epiphyseodesis and deformity by eccentirc curetting of the plate through the intramedullary canal of the tibia. It is suggested, therefore, that when transepiphyseal wires are used clinically they be of small caliber and be placed centrally.

Crossed wires were not an effective means of epiphyseodesis

It should be emphasized that the results discussed are experimental, and that the studies were performed on rabbits. Since there is great similarity between these experimental observations and many clinical experiences, some of the observations many be of value in throwing light on the problem of epiphyseal growth arrest and deformities due to abnormal epiphyseal plate growth.