The influence of the diameter of the pilot hole compared to the inner diameter of the screw on the pull-out resistance of a pedicular screw was studied. 5-, 6-, and 7-mm USS system screws for vertebral fixation were inserted into wood, polyurethane and bone test bodies. The pilot hole for screw insertion was drilled with burrs of smaller, equal or wider diameter than the inner diameter of the screw. Mechanical pull-out assays were performed using a universal testing machine. In the wood, polyurethane and bone test bodies, a pilot hole drilled with burrs of a wider diameter than the inner diameter of the screw produced reduced maximum pull-out strength on the implants, with statistical significance. The drilling diameter of the pilot hole compared to the inner diameter of the screw influences implant pull-out strength, with an increased pull-out resistance being observed with the use of smaller diameter burrs as compared to the inner diameter, and a reduction of pull-out resistance being observed with the use of burrs of a wider diameter than the inner diameter of the screw.
Spine; Bone screws; Biomechanics
