A Study of the Stress-Strain State of a Pedicle Screw

The article analyzes the effect of the torque moment in a pedicle screw on its stress-strain state using the finite element method. The research object is a polyaxial pedicle screw made of titanium alloy VT6. The article explores the methods used for strengthening the screw. The critical areas of the screw that are prone to destruction were identified. It was hypothesized that stresses arising in pedicle screws during screwing cause cracks and affect the nature of destruction. Various classes of meshes for finite element analysis were studied. The choice of a tetrahedral mesh was justified. The finite element analysis of the screw made it possible to determine stresses arising during screwing. It was established that maximum stresses arise in the screw neck and at the transition of the spherical head into the cylindrical part. The torque graph was constructed using the calculation results. It was revealed that with an increase in torque to 8 Nm, the graph inclination angle decreases significantly due to a significant distribution of stresses above the yield strength deep into the section. The study determined the maximum torque the exceedance of which can increase stress values inside the screw and cause the subsequent initiation of fatigue cracks in operation. Conclusions about the feasibility of using the finite element modeling method to optimize the design of pedicle screws were drawn. Avenues for further research using a more regular tetrahedral mesh and subsequent fatigue testing of samples on special equipment were provided.