Effect of Drill Speed in Thermal Necrosis of Bone (An Animal Study)

Internal immobilization of skeletal fractures is usually done by drilling of fracture site and screw fixation. During bone drilling، the temperature could increase above 47°C causing irreversible thermal necrosis. This study will try to determine the best drilling condition to minimize the chance of osteonecrosis. Drilling tests were performed with two different drilling techniques -conventional and high speed- on the femur of bovine measuring the temperature and thrust force in drilling site. The results demonstrated that in conventional drilling، in all of the processing conditions، the value of generated heat was higher than allowable limit and occurrence of thermal necrosis was unavoidable. On the other hand، the increase of cutting speed of drill bit in high speed range (6000-7000 rpm) lead to considerable decrease of thrust force and increase of heat dissipation with chips، leading to reduction of local temperature raise in drilling site. But with more rotational speed of drill bit، the amount of temperature elevation was increased due to very little change in drilling force but increased friction between body of drill bit with the chips. High speed bone drilling in 6000-7000 rpm، compared to conventional drilling، produces less heat and less thermal necrosis.