Effects of Radiation on the Bone Strength of Spinal Vertebrae in Rats

Study Design. A controlled laboratory study. Objective. The aim of this study was to examine bone damage caused by irradiation to spinal vertebrae in rats. Summary of Background Data. Radiotherapy is widely used in the treatment of malignant spine tumors. However, a few studies have reported vertebral fractures following radiotherapy as an adverse reaction. There are no reports on irradiation- induced changes in bone fragility, mechanical and structural changes focusing on the spine, and the mechanism of irradiation-induced bone osteoporosis. Methods. Eighty-four female Wistar rats were randomly allocated to the 20 Gy irradiated or the nonirradiated (control) group. The lumbar vertebrae were irradiated with an external focal radiation dose of 20 Gy. Biomechanical, structural, and histological analyses were performed at 0, 2, 4, 6, 8, 12, and 24 weeks after irradiation. Structural analysis and bone density measurement of vertebral trabecular bone were performed by mu CT. Histopathological evaluation was performed by hematoxylin and eosin staining and immunostaining. Results. The bone strength at 2 weeks after irradiation (311 +/- 23 N) was 22% lower than that before irradiation (398 +/- 34 N) (P < 0.05). The trabecular spacing increased, and trabecular connectivity and width decreased significantly in the irradiated group compared with those in the non-irradiated group. The three-dimensional structure model became coarse, and the trabecular structure continued to thin and disrupt after irradiation. There was no significant change in the bone mineral density in both groups. Conclusion. A decrease in bone strength was observed 2 weeks after irradiation. Bone mineral density remained unaltered, whereas the microstructure of trabecular bone changed, suggesting bone damage by irradiation.