Effect of feed rate and drill speed on temperatures in equine cortical bone

Objective-To examine the amount of heat generated in equine cortical bone b y a 6.2-mm drill, using low- and high-speed and controlled feed rate drilli ng. Sample Population-10 metacarpal bones harvested from five 2-year-old draft- type horses. Procedure-Drilling on metacarpal bones was done using a machine shop mill w ith which the feed rate and drill speed could be precisely controlled. Bone s were drilled, using 6 combinations of feed rate (1, 2, and 3 mm advance/s ) and drill speed (317 and 1,242 revolutions/min [rpm], with maximal temper atures recorded by thermocouples placed 1, 1.5, and 2 mm from the drill. Ma ximal temperatures were evaluated for the effect of feed rate, drill speed, cortical thickness, and distance from the drill, using linear regression a nalysis. Results-Increasing feed rate from 1 to 2 and from 2 to 3 mm/s significantly decreased mean maximal temperature. Increasing drill speed from 317 to 124 2 rpm significantly increased mean maximal temperature. Increasing cortical thickness significantly increased mean maximal temperature, and increasing the distance from the drill hole significantly decreased mean maximal temp eratures. Conclusions-On the basis of our results, we recommend using low drill speed s while applying sufficient axial force to advance the drill as rapidly as possible through the bone. Clinical Relevance-Results of using this in vitro model suggest that temper atures at the drill-bone interface may be sufficiently high to result in si gnificant thermal necrosis when drilling equine cortical bone.