For this experimental study we removed with a trephine in small (rabbit) and larger (pigs) animals cylinders of 2 mm respectively 8 mm diameter from the central growth plate area of proximal tibia. The direction of burring is in the axial line of the femur proximo-distally; the insertion point of the trephine is chosen on the cheek of the medial femoral condyle. As common reaction to that kind of trauma the defects in growth plates of rabbits become filled with a bone bridge that joins the epiphyseal core to the metaphyseal trabeculae, leading to gross growth disturbances. In pigs a similar solid bridging as first reaction develops, interrupted later by a zone of longitudinal collagen fibre bundles within a non-mineralized matrix. The distending pressure of surrounding intact growth cartilage continuously brakes fracture callus formation and its calcification. Such so-called internal callus distraction leads to unaltered longitudinal bone growth.
