A rabbit model modified from the one originally used by Osterman was used to test the effectiveness of interposition materials in the prevention of epiphyseal-metaphyseal bone bridge formation. Although fat was a moderately effective interposition material, cartilage was more effective in preventing growth retardation and angular deformity of the involved distal femur. None of the interposition materials, however, allowed for completely normal growth. It is theorized that the effectiveness of cartilage may be enhanced by the presence of a factor contained therein which inhibits bone formation.