Bone tissue status in early stages of recovery after thermal exposure

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Abstract
BACKGROUND: Thermal ablation is a promising method for the treatment of bone tumors. However, to maximize the potential of this method, it is important to select the optimal dose/time ratio of high temperature exposure. AIM: The aim of the study was to evaluate in vivo the response of rabbit bone tissue during early recovery (days 3 and 7) after local intraoperative hyperthermic ablation at 55–60°C in the medullary canal. MATERIALS AND METHODS: The study used 6 outbred rabbits aged 15 weeks and weighing 3–4 kg. Animals were removed from the experiment on days 3 and 7 after local thermal ablation of the femoral diaphysis. Microscopic visual examination of bone tissue sections was performed after standard hematoxylin and eosin staining. In addition, the morphometric measurements were performed to determine area of non-mineralized bone matrix (Mallory staining); absorbance and area of osteoblast cytoplasm; absorbance and area of osteocyte nuclei (Einarson staining for nucleic acid detection). The results obtained were compared with those of the femur of the contralateral limb, which was not subjected to direct hyperthermia and served as a control. R-Studio, a free development environment for R programming language, was used to statistically process the data. RESULTS: After high temperature exposure, histological sections of bone tissue stained with hematoxylin and eosin showed evidence of cellular abnormalities such as denucleated osteocytes and empty bone lacunae. Mallory staining showed no evidence of a negative effect of local thermal ablation on the intercellular bone matrix. Morphometry of Einarson stained sections showed an increase in osteoblast area on day 7 after exposure, with a decrease in their synthetic activity, signs of which were observed as early as day 3 of the experiment. There was also a decrease in the area and absorbance of osteocyte nuclei in the diaphysis of thermally ablated bones by day 3 after exposure. However, on day 7 after exposure, the area of nuclei in mature bone cells did not differ from the corresponding value in the contralateral limb. Considering the decrease in nuclei absorbance, the described changes may indicate colliquative necrosis of osteocytes. CONCLUSIONS: Local intraoperative thermal ablation of the femoral diaphysis in rabbits at a marrow canal temperature of 55–60℃ reduces the absorbance of osteoblast cytoplasm and osteocyte nuclei in the early recovery period, reflecting damage to the organelles of bone cells and disruption of metabolic processes in these cells. However, there was evidence of remodeling of the damaged area, presumably caused by migration of endosteal and periosteal cells from the metaphysis, which had not been exposed to direct hyperthermia. The results obtained may be useful for choosing the optimal regime (dose and duration) of high temperature exposure to bone tissue tumors, given the higher sensitivity of malignant cells to heating.

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