Onset of mandible and tibia osteoradionecrosis: a comparative pilot study in the rat.

Objectives: Osteoradionecrosis (ORN) is common in the jaws after radiotherapy. We hypothesized that the mandible is more susceptible to ORN than the tibia, based on site disparity in hypoxic, hypocellular, and hypovascular tissue breakdown.

Study Design: Twelve rats received 50 Gy irradiation to mandible or tibia; 4 of the rats further received minor surgical trauma to the irradiated sites. Structural and cellular skeletal changes were assessed with computerized tomography, histology, and immunostaining.

Results: Mandible developed ORN with 70% mean bone loss 10 weeks after irradiation (P < .05), whereas tibia was structurally and radiologically intact 20 weeks after irradiation. Hypocellularity, hypoxia, and oxidative stress were higher in irradiated mandible (P < .001) than tibia (P < .01) but vascular damage was similar at both skeletal sites. Combined effects of radiation and minor trauma promoted mandibular alveolar bone loss and tibial fracture.

Conclusions: ORN has a more rapid onset in mandible than in tibia in the rat.