Triangulated pedicle screw construct technique and pull-out strength of conical and cylindrical screws

To compare the mechanical effectiveness of a new conical screw design with a conventional cylindrical screw design, the screw insertion time, torque, and pull-out strength of single-pedicle screw and triangulated-pedicle scre w constructs of each type of screw were compared in human cadaveric vertebr al bodies. The time required to insert the conical screws was less than tha t required for cylindrical screws. Regression analysis revealed a positive correlation between insertion torque and pull-out strength of single and tr iangulated constructs of each type of screw. The conical screw had a greate r increase than the cylindrical screw in the pull-out strength of triangula ted pedicle screw constructs. Application of the new conical screw design w as significantly faster, and the new screw had better mechanical fixation t o the vertebral body than did the conventional cylindrical screw tested.