A comparison of the thermal properties of 2- and 3-fluted drills and the effects on bone cell viability and screw pull-out strength in an ovine model.

BACKGROUND

Drilling of bone is associated with an increase in temperature of the surrounding bone which may result in osteonecrosis.

METHODS

In this study, cutting efficiency and thermal properties of one 2-fluted drill and two 3-fluted drills were determined in vitro using a porcine model. Drills were then used to create pilot holes in an in vivo ovine model to facilitate implantation of pedicle screws. The effect of the characteristic thermal profiles of each drill on cortical bone cell viability and screw pull-out strength was then assessed.

FINDINGS

Cutting efficiencies of both 3-fluted designs were found to be greater than that of the 2-fluted drill, but this did not translate into a decrease in the maximum temperatures during drilling for both drills. Histologically, no empty osteocyte lacunae were seen at 2 or 4 weeks, suggesting that temperatures were not sufficiently high enough to induce thermonecrosis in the ovine tibia. No differences were found in the pull-out strength of the screws.

INTERPRETATION

Both 2- and 3-fluted drills are currently in clinical use. Despite the theoretical advantage that 3-fluted drills possess over their 2-fluted counterparts, there is a lack of evidence in the literature in support of their use. In this study the observed increases in cutting efficiency of the 3-fluted drills tested did not translate into a reduction in heat generation or improvement in bone healing or screw fixation.