Optimization of Pedicle Screw Parameters for Enhancing Implant Stability Based on Finite Element Analysis

Abstract

ObjectiveTo improve the implant stability, the parameters including outer diameter, thread depth and pitch of pedicle screw were optimized by finite element analysis. MethodsThe insertion and pullout of pedicle screw were simulated by finite element analysis, and the precision of simulation was evaluated by comparing with mechanical tests. The influences of the parameters on the maximum insertion torque and maximum pullout force were analyzed by computational simulations including single-factor analysis and orthogonal experiment. ResultsThe simulation results agree with the mechanical tests. The influencing orders of the parameters on insertion torque and pullout force are both: outer diameter > pitch > thread depth. When the pilot hole diameter is 0.1 mm larger than the inner diameter of pedicle screw, the calculated Pearson correlation coefficient between the maximum insertion torque and maximum pullout force is r = 0.99. The optimized pedicle screw shows a maximum insertion torque of 485.16 N·mm and a maximum pullout force of 1726.33 N, which are 23.9% and 9.1% higher than those of standard screw, respectively. ConclusionsThe presently used models are feasible to evaluate the implant stability of pedicle screw. The maximum insertion torque and maximum pullout force of pedicle screw are highly correlated. The insertion torque and pullout force can be improved by increasing outer diameter and decreasing pitch. Beside the parameters of pedicle screw, the size of pedicle and bone mineral density are two considerable factors for a better implant stability.