APPLICATIONS OF FINITE ELEMENT ANALYSES-BASED TAGUCHI METHODS FOR SUBSIDENCE PROBLEM OF VERTEBRAL BODY CAGES USED IN CERVICAL SPINE

Abstract

The vertebral body cage has been widely used in anterior cervical discectomy and fusion to provide better stability and fusion rate. However, subsidence of a body cage into the vertebral body may cause severe problems. In this study, three-dimensional finite element models of C4-C6 were constructed and developed to simulate the situations of pre-subsidence and post-subsidence. The Taguchi method was used to obtain the optimal design parameters of the vertebral body cage to increase the subsidence resistance. The results showed that the optimum combination for a situation of pre-subsidence was gear ring, inner diameter of 4 mm, spike's height of 0.5 mm, twelve spikes, spike's oblique of 00, spike's upper width of 0.3 mm, spike's upper length of 0.85 mm, and spike's lower area of 1.2 × 0.85 mm2. For a situation of post-subsidence, the optimum combination was circular ring, inner diameter of 4 mm, spike's height of 2 mm, twelve spikes, spike's oblique of 00, spike's upper width of 0.3 mm, spike's upper length of 0.85 mm and spike's lower area of 1.2 × 0.85 mm2. Besides, subsidence is also affected by other variables including bone graft, bone mineral density, endplate preparation and implant material. Those variables were investigated and the results showed that the higher BMD, larger endplate preparation and less stiffness of implant material could reduce the risk of subsidence. The Taguchi method has an efficient reduction of time and cost of experiment and could determine the optimum combinations to enhance the ability to resist the subsidence.