Evaluation of the Relation Between Preload Values and Pull-Out Force of the Cortical Screw Used in Bone Fracture

This study aims to examine the relation between pull-out strength and preload values of the cortical screw used in bone fracture fixation. The research question is that "Does the pull-out strength of the cortical screw used in the bone fracture fixation change with the preload values of the screw change?". To perform this purpose, the finite element method was selected due to its ease to evaluate and calculate the stresses on the whole model. Models of a cortical screw, partial plate, and bone were created using the SolidWorks program. The material properties of the bone were selected orthotropic material type. The bone fixed on the distal and proximal ends. The pull-out forces were applied at the bottom of the plate. The screw that has been loaded ranges from 100 N-700 N as preload. The pull-out forces were determined 200-400-600 N as in the literature. The results show that the pull-out strength of the screw was changed when the preloaded values higher than 400 N. However, it was seen that the pull-out strength does not substantially change when the preload values were lower than 400 N. When the preload values were applied ≥500 N, the maximum von Mises stresses on the screw exceeded the critical strength of the screw material. In conclusion, the critical preload value was determined as 500 N for the optimum pull-out strength.