Experimental Investigation of Thermal Necrosis in Conventional and High Speed Drilling of Bone

Internal immobilization of fractured parts of bone depends on the drilling of fracture site and screw fixation of implanted devices to the bone. During drilling، the temperature may rise allowable temperature of 47°C and causes irreversible thermal necrosis. This study is concerned with methods of drilling to determine the best processing condition to minimize the osteonecrosis. Drilling tests were performed with two drilling techniques: conventional، and high speed drilling on the bovine femur and increase of temperature in drilling site، duration of temperature raise and thrust force were measured. The result for conventional drilling shows that in all processing conditions، the generated heat is over the allowable limit، which makes thermal necrosis inevitable. On other hand، it was found that increase of cutting speed of drill bit to 7000 rpm، leads to considerable decrease of thrust force and increase of heat dissipation with chips، simultaneously and leads to decrease of local temperature raise in drilling site. But with more increase of rotational speed of drill bit، because of not sensible change in drilling force and considerable increase of friction between chips، drill bit body and drilled hole، amount of temperature elevation is increased.