Effect of drilling direction and depth on thermal necrosis during tibia drilling: An in vitro study.

Thermal necrosis is one of the main concerns in bone drillings. This study has been designed with the aim of improving the surgeons' knowledge on how to reduce thermal necrosis in tibia drilling with various depths and directions. A drilling machine was developed, which made the direct transfer of gas coolants into the drilling site during drilling possible. Results indicated that 2000 r/min is the most proper rotational speed for minimizing thermal necrosis. Changing the drilling direction from radial to longitudinal raised the temperature at drilling site. Increasing the drilling depth from 8 to 50 mm raised the temperature by at least 22.5%. Increasing the drilling depth up to 50 mm raised the drilling site temperature above the threshold temperature of tibia thermal necrosis as well as the temperature durability at the drilling site. However, in contrast to conventional cooling modes, using gas coolants, especially CO2, brought the temperature to a level less than the threshold temperature of tibia thermal necrosis and reduced the durability of temperature at the drilling site by at least 1 minute. Using the drilling machine developed in this study and CO2 coolant, orthopedic surgeons can perform tibia drilling in various directions up to the depth of 50 mm without the risk of thermal necrosis since the internal gas coolants, due to their direct contact with the drilling site and the rapid discharge of the chips, reduce the temperature increase in tibia caused by changing the drilling depth and the drilling direction from radial to longitudinal, greatly.