Study of the healing process after transplantation of pasteurized bone grafts in rabbits.

Different bone allografts (pasteurized, autoclaved, and frozen) were compared based on their osteoinductive properties. Our primary purpose was to examine the biologic qualities of pasteurized allografts, as pasteurization inactivates most viruses transmitted by transplantation. Frozen, pasteurized, and autoclaved allografts were packed into a standard defect of rabbit ulna. The animals were sacrificed at 2 and 4 weeks after surgery. The parts of bones with experimental defects were explored en bloc, and a roentgenogram was carried out. Ulna bone samples were then embedded in methyl-methacrylate. Roentgenograms showed that after 2 weeks, calluses were well-formed, but irregular in shape in all 3 types of allografts. After 4 weeks, the calluses were regular in shape in all but the autoclaved grafts. After 2 weeks, the healing processes had begun in the frozen and pasteurized grafts, with the reaching approximately the same stage, while in the autoclaved grafts these processes were not seen and the bone particles were surrounded by connective tissue without any changes. After 4 weeks, osteoinductive processes were very strong, with the first signs of complete bone remodeling at the bone edges of the defect in pasteurized and frozen allografts. The osteoinductive values of these 2 types were very high and similar. Autoclaved allografts, on the other hand, had very low osteoinductive values, as they were still at the very beginning of the healing process. Histomorphometric analysis revealed a significant difference in both newly formed osteoid thickness and osteoblast number per microm of bone surface in all experimental groups (P < 0.005). Values of osteoid thickness and osteoblast number were significantly higher in both frozen and pasteurized grafts when compared with the autoclaved ones (P < 0.005). Osteogenic properties of pasteurized bone allografts were preserved, and the allografts have been gradually replaced with newly formed bone. As such, pasteurized bone grafts from a bone bank have approximately the same biologic validity as frozen grafts, while autoclaved grafts impair bone healing.