Temperature effects in the drilling of human and bovine bone

Bone is an anistropic material, the drilling of which is an essential part of internal fixation in orthopaedic and trauma surgery. Some research has been carried out into the drilling of bone, but there are no definitive recommendations available on the most suitable drill shape or on the optimum drilling speed that should be used in surgical practice. The heat generated during the drilling of bone is proportional to the drilling speed and may be partially dissipated by the presence of blood and tissue fluids and also partially carried away by the chips formed. However, some heat may be conducted into the bone which, if exposed to a temperature higher than 55°C, may sustain serious damage. This is important in orthopaedics, since most holes drilled are subsequently tapped for retaining screws. If the drill burns the bone to any great depth, the thread will not anchor properly and the fixation could work itself loose. This paper describes the drill design for accurate temperature measurement at the drill point and further shows that whilst the temperature may go to much higher than 55°C because of the poor conductivity of the bone the depth of damage is not critical insofar as screw fixation is concerned.