Abstract
Aiming to evaluate cortical bone microarchitecture and osteonal morphology after irradiation, twelve male New Zealand rabbits were used. The animals were divided: control group (no radiation-NIr); and 3 irradiated groups, sacrificed after: 7 (Ir7d); 14 (Ir14d) and 21 (Ir21d) days. A single radiation dose of 30 Gy was used. Computed microtomography analyzed the cortical microarchitecture: cortical thickness (CtTh), bone volume (BV), total porosity (Ct.Po), intracortical porosity (CtPo-cl), channel/pore number (Po.N), fractal dimension (FD) and degree of anisotropy (Ct.DA). After scan, osteonal morphology was histologically assessed by means: area and perimeter of the osteons (O.Ar; O.p) and of the Haversian canals (C.Ar; C.p). Microtomographic analysis were performed by ANOVA, followed by Tukey and Dunnet tests. Osteon morphology analyses were performed by Kruskal-Wallis, and test Dunn's. Cortical thickness was significant difference (p<0.010) between the NIr and irradiated groups, with thicker cortex at Ir7d (1.15±0.09). The intracortical porosity revealed significant difference (p<0.001) between irradiated groups and NIr, with lower value for Ir7d (0.29±0.09). Bone volume was lower in Ir14d compared to control. Area and perimeter of the osteons were statistically different (p<0.0001) between NIr and Ir7d. Haversian canals also revealed lower values (p<0.0001) in Ir7d (80.57±9.3; 31.63±6.5) compared to NIr and irradiated groups. Cortical microarchitecture was affected by radiation, and the effects appear to be time-dependent, mostly regarding the osteons morphology at the initial days. Cortex structure in Ir21d revealed similarities to control suggesting that microarchitecture resembles normal condition after a period.
Highlights
Ionizing radiation therapy used in radiotherapy (RT) in combination with surgical procedures are the main treatment modalities for malignant tumors [1]
High-dose irradiation causes irreversible side-effects on the tumor surrounding healthy tissues. These injuries lead to impairment in bone repair properties that could progress to complications, such as infections, healing delay and osterradionecrosis [3]
Previous publicatios from our group showed the effects of RT on cortical bone that revealed modification on the morphology of bone channels network [4], decreased anisotropy and increased bone fragility [5], with deficity in bone quality, with decrease of stiffness, more evident in later time points after radiation [6]
Summary
Ionizing radiation therapy used in radiotherapy (RT) in combination with surgical procedures are the main treatment modalities for malignant tumors [1]. High-dose irradiation causes irreversible side-effects on the tumor surrounding healthy tissues. These injuries lead to impairment in bone repair properties that could progress to complications, such as infections, healing delay and osterradionecrosis [3]. Cortical bone is considered not fully compact, once the structure is traversed by many Haversian (at the center of the osteons) and Volkmann canals. All of these canals have in their surfaces the lining that provide a surface area for remodelling [9]. About half of cortical bone loss at peripheral sites was the result of remodelling within the cortex adjacent to the marrow [9]
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