Analysis of Vertebral Stress Distributions and Ejection-Related Injury Mechanisms

Abstract

Abstract : Stress analyses of lumbar vertebrae were performed by a three dimensional finite element method for the purposes of (i) evaluating simplified models of the vertebrae which are suitable as injury post processors, and (ii) gaining a better understanding of injury mechanisms. The finite element analyses were linear and elastic. Axial and moment loads were applied over the end plates to simulate G sub z impact and on the facets to simulate load transmission between the articular facets and the vertebral bodies. The finite element model predicts that the maximum stresses under axial load are perpendicular to the axis of the vertebral body, which are called axial stresses; this is consistent with the predominance of compressive and wedge fractures. However, the maximum stresses predicted by the finite element model are only about a third of those predicted by the simplified injury model. This discrepancy is due to the fact that a substantial portion of the total load is transmitted through the vertebral centrum which is neglected in the simplified model. Furthermore, the finite element model exhibits a rather complex pattern of deformation even under axial load, which cannot be incorporated easily in a simplified model. The stresses predicted by the finite element model for bending also differ substantially from those given by the simplified model for the same reasons. Good agreement between the finite element model and simplified model is only achieved for torsion loads.