Thermal injury to bone. A vital-microscopic description of heat effects.

A titanium implant, the thermal chamber, allowing vital microscopic observations of bone tissue during heating and bone temperature measurements to be made simultaneously is described. The tissue reactions to a defined heat trauma may be followed and registered on slides and ciné film. The thermal chamber technique allows repeated observations of the same bone tissue compartment for indefinite follow-up period. In the present experiment, the chamber was inserted in the rabbit tibia and heating to 53 degrees C was applied for 1 min. During heating to the assigned temperature, the blood-flow velocity initially increased. At 53 degrees C the blood flow stopped in some vessels and became sluggish in others. 2 days after heating the blood flow in the pre-existing vessels had stopped. Gradually thereafter, all original vessels became replaced with ingrowing newly-developed vascular pathways. Fat cells seen before burning became resorbed and bone remodelling started 3-5 weeks after the heat injury. A temperature of 53 degrees C, i.e. below the denaturation point of alkaline phosphatase, caused an irreversible bone injury, after which healing occurred from the surrounding tissues.