The evaluation of pullout tests of an expandable newly designed screw

Biomechanical evaluation of pullout forces of newly designed cortical screws with openable tips was done in the tibia bone of the young bulls. Newly designed expandable titanium 14 cortical screws with openable tips were inserted in fresh tibia bone. Of these screws, 7 were used as controls. The bones were fixed with polymethylmethacrylate after the insertion of the screws. Screw heads were attached to a custom device and prepared for pullout tests. The elastic modulus values (Newton/mm²), yield forces (Newton) and maximum forces (Newton) of expandable and control groups were assessed. The median of yield forces (Newton) of expandable cortical screw group was found to be statistically higher than that of normal group (P=0.025). The median of maximum forces of expandable cortical screw group was found to be significantly higher than that of normal group (P=0.003). In the comparison of paired groups, it was found that the pullout forces of expandable cortical screws were significantly superior to that of normal control group. In the light of these results, it was concluded that such kind of newly designed screws are able to contribute to fracture fixation in the future, allowing more bone contact without enlarging the diameter of the screw.