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.

Background and objective This study was designed to investigate heat accumulation and bone thermal necrosis for various distances between holes and time delays between drillings. Methods The tests were performed at three distances (6, 12, 16 mm) and three time delays: 0, 5 and 10 s. To examine the efficiency of coolants, CO 2 coolant was also tested in addition to two common cooling modes in bone drilling. Results The main results were the trend of temperature–time graph, maximum temperature at drilling site, temperature distribution on the surface of drilling site, temperature durability and returning time. The effect of lateral drillings on the initial hole was notable in drilling at a distance of 6 mm without cooling. This effect did not disappear even by increasing the time delay up to 10 s. The results obtained for drilling with normal saline coolant were not sufficiently acceptable due to the manual and non-uniform cooling process as well as the relative obstruction of the chips exit path. Generally, drillings with two common cooling modes, even when the distances between holes and time delays between drillings were controlled, did not yield all favorable conditions for preventing bone thermal necrosis. Conclusion Bone drilling using CO 2 coolant eliminates the risk of bone thermal necrosis completely even in cases that the distances between holes in plates or implants are 6 mm and there is no time delay between drillings. These results can be especially useful in emergency orthopedic surgeries and for designing the location of screw holes in implants and plates.