Temperature threshold levels for heat-induced bone tissue injury: A vital-microscopic study in the rabbit

Healing following bone surgery may be delayed or even prevented if the bone cells are severely injured by the frictional heat generated during the surgical preparation.lT4 However, little is known about the critical temperature that causes a reversible or irreversible bone injury. This critical temperature is popularly believed to be around 56” C because alkaline phosphatase is denatured at this temperature level.5-s Studies in which bone reactions to temperatures lower than 56” C have been investigated indicate that bone necrosis may result even if the denaturation point of alkaline phosphatase is not exceeded. Rouiller and Majno’ described hard tissue injury after heating the rabbit metatarsal or radial bone to 55” C for 3 minutes. In a rabbit experimental model, Lundskog’O found some histochemical evidence of bone death adjacent to an implanted scald that was heated to 50” C for 30 seconds. In both these investigations and others, indirect methods (histology and histochemistry) have been used for evaluating hard tissue viability. Other studies have shown that conventional histologic evaluations tend to underestimate the true extension of tissue death.“-13 One reason for the lack of knowledge of the critical temperature of bone tissue is the methodologic shortcoming of defining bone necrosis. Furthermore, the important question is not whether the bone will die, but whether it will survive as a differentiated tissue. Reliable studies on the short- and long-term hard tissue reactions after heating demand a direct method that allows for repeated in situ studies of the same bone compartment at varying times of follow-up. The thermal chamber for intravital microscopy of heated bone tissue was constructed to meet these demands.14 In this investigation the thermal chamber was applied in an investigation that sought to analyze the hard tissue changes after heating in the range of 470 to 500 C.