Experimental study of the temperature distribution in long tubular bones with a periossal arrangement of heaters

Purpose to study the changes in the temperature outside and inside the long tubular bones of animals under the influence of different temperature regimes for a given time. Material and Methods. The experiments were conducted using fresh frozen pig long bones. The heating was carried out using surface heaters, the temperature of which was determined by the selected mode for 1 hour; fixation of temperature values was carried out every minute. Four heating modes were used: 3 modes of constant heating (60, 70, 80 °C) and the maximum heating mode, in which no special temperature limit was set, so heating was carried out up to 120 °C. Results. During the first 10 min of heating, a rapid rise in temperature occurred. The temperature increase rate on the outer surface outstripped the temperature increase rate on the inner surface of the bone, thus leading to a significant temperature difference. Further, there was a slowdown in the rate of temperature increase, which led to a gradual convergence of the temperature values inside and outside the bone, followed by temperature stabilization at a stable level (plateau), which was different for the studied areas. During this period, the temperature difference was 3.5-6 °C and it remained at this level until the end of the study. At a constant heating mode (60/70/80 °C), temperature stabilization occurred at the level of 55/61/70 °C in the center of the medullary canal and at the level of 58/67/75 °C under the heater, respectively. The period before reaching the stabilization temperature was 30-40 min. The stable temperature levels both inside and outside the bone were below the temperature stabilization level of the heater. Therefore, to achieve the planned temperature in the center of the bone to its outer surface, it is necessary to apply a high temperature, i.e., a downward temperature gradient is formed: the heater stabilization temperature - the temperature on the outer surface - the temperature inside the medullary canal. Increasing the exposure temperature can shorten the heating period, but increase the temperature difference during the heating period (up to 25 °C in the fifth minute of heating when using the maximum heating mode). Conclusion. To ensure reaching the required temperature (60°C) within a short time (15-20 min) while maintaining optimal temperature parameters, it was proposed to develop variable temperature modes that would combine the initial use of the maximum heating mode until reaching the desired temperature in medullary cavity, followed by switching to a constant temperature mode, which allowed maintaining the achieved temperature level during therapeutic exposure.