Effect of Pilot Hole Tapping on Pullout Strength and Insertion Torque of Dual Core Pedicle Screws.

OBJECTIVE To evaluate the influence of pilot hole tapping on pullout resistance and insertion torque of pedicle screws with a conical core. METHODS Mechanical tests using a universal testing machine were performed on pedicle screws with a conical core that were inserted into pedicles in the fifth lumbar vertebra of calves. The insertion torque was measured using a torque meter with a capacity of 10 Nm, which was considered to be the highest torque value. The pilot holes were prepared using a probe of external diameter 3.8 mm and tapping of the same dimensions and thread characteristics as the screw. RESULTS Decreased insertion torque and pullout resistance were observed in the group with prior tapping of the pilot hole. CONCLUSIONS Pilot hole tapping reduced the insertion torque and pullout resistance of pedicle screws with a conical core that had been inserted into the pedicle of the fifth lumbar vertebra of calves.