Distraction osteogenesis after irradiation in rabbit mandibles

The aim of this study was to investigate the influence of irradiation on the formation of bone after distraction osteogenesis in rabbit mandibles. Sixteen rabbits were randomly divided into 3 groups: one was given 50Gy (n=6), one was given 60Gy (n=6), and one acted as a control group (n=4). One month after irradiation, the distractors were inserted. The control group was not irradiated. After a latency period of 8 days, distraction was activated at a rate of 0.4mm twice a day. The mandibles were harvested 6 weeks after consolidation. The specimens and histological examination showed good formation of bone. Histological slides stained with haematoxylin and eosin confirmed that the regeneration was bone. The bony trabeculae of the control group were much better than those of the irradiated groups. However, the nuclei of osteocytes were round and the osteoblasts around the trabeculae were columnar or cubic in shape in the irradiated groups. Osteoid was present in the dense fibrous connective tissue. There were significant differences in the surface:volume ratio of areas of bony trabeculae between the control and both experimental groups (p=0.010 and p=0.001), but there was no significant difference between the 50Gy and 60Gy groups. The results suggested that preoperative radiation prevented optimal regeneration of bone. However, the microscopic appearance of osteocytes and osteoblasts and the osteoid in the dense fibrous connective tissue in both irradiated groups showed that osteogenesis was still active and in progress. These findings may indicate that bone formation had only been delayed. The evidence was similar for both 50Gy and 60Gy.