Parametric study on the interface pullout strength of the vertebral body replacement cage using FEM-based Taguchi methods.

Improper design of vertebral body cages may seriously affect the interface strength and cause the lose of fixation for a vertebral body replacement. This research used a FEM-based Taguchi method to investigate the effects of various factors to find the robust design of the body cage. Three-dimensional finite element models with a nonlinear contact analysis have been developed to simulate the pullout strength of the body cage. Then, the Taguchi robust design method was used to evaluate the spike design. In a situation without bone fusion, the spike row, the spike oblique, and the spike height were especially important factors. The optimum combination has been found to be the pyramidal spike type, a spike height of 2mm, a spike diameter of 2.2mm, an oblique geometry, 11 rows per 28 mm, and an inner diameter of 10mm. In a situation with bone fusion, the spike row, the spike height, and the inner diameter were the most significant factors. Here, the optimum combination has been found to be the conical spike type, a spike height of 2mm, a spike diameter of 2.2mm, an oblique geometry, 11 rows per 28 mm, and an inner diameter of 20mm. The finite element analyses could be used to predict the interface stiffness of the body cages. The FEM-based Taguchi methods have effectively decreased the time and effort required for evaluating the design variables of implants and have fairly assessed the contribution of each design variable.