Histologic patterns of capital femoral growth plate fracture in the rabbit: the effect of shear direction.

Growth plate fractures were produced in vitro in the rabbit capital femoral physis by applying shear loading parallel to the physeal complex in four different directions. Load-displacement curves were recorded and histologic sections were prepared from each specimen. Different histologic patterns were observed with different directions of shear loading. The histologic level within the growth plate through which the fracture propagated varied with each specimen and with the different directions of shear loading. The "classical" pattern of failure through the hypertropic cellular zone of the physis was not uniformly seen. The mechanical patterns of failure also varied with the direction of shear loading. The shear strength of the physeal complex was significantly greater with anterior to posterior loading than with posterior to anterior loading. The possible factors contributing to this mechanical anisotropy are discussed, and the literature on related studies is reviewed.