INFLUENCE OF THE CONSTITUTIVE MATERIAL BEHAVIOR MODEL ASSIGNED TO THE ANNULUS FIBROSUS AND THE NUCLEUS PULPOSUS ON THE BIOMECHANICAL PERFORMANCE OF A MODEL OF THE CERVICAL SPINE: A FINITE ELEMENT ANALYSIS STUDY

摘要

One feature of the literature on finite element analysis of models of cervical spine segment(s) is that an assortment of constitutive models has been used for the elastic behavior of the annulus fibrosus (AF) and the nucleus pulposus (NF). The extent to which the model assigned to each of these tissues affects the values of the biomechanical parameters of interest of the model is lacking. This issue was the subject of the present study. We used a three-dimensional solid model of the C4-C6 motion segment units (which comprised the vertebral bodies, the bony posterior elements (transverse processes, pedicles, laminae, spinous processes, and facet joints), the intervertebral discs (IVDs), the endplates, and the five major ligaments) and eight combinations of constitutive models. It was found that (1) the influence of the constitutive material models used depended on the tissue considered, with some, such as the posterior endplate of C5 and the cancellous bone of C6, showing marked sensitivity, while others, such as the cancellous bone of C4 and the cortical bone of C5, were moderately affected; and (2) the biomechanical performance of the spine model is more sensitive to the material behavior model used for the AF than it is to that used for the NF. These results suggest that experimental and computational efforts expended in obtaining the most appropriate constitutive model for the elastic behavior of the two parts of the IVD, in particular the AF, are justified.