Influence of Compressive Preloading on Range of Motion and Endplate Stresses in the Cervical Spine During Flexion/Extension

The natural weight of the head, any head supported mass and various muscle forces result in eccentric compressive loads that should be effectively supported by the human cervical spine to protect the spinal cord and maintain interrelationships among vertebrae. Different experimental studies have used various testing protocols to study the effect of a compressive preload on the biomechanics of the cervical spine. The objective of this study is to investigate the effect of such an in-vivo compressive load on the range of motion (ROM) of the sub-axial column using a novel computational method. An anatomically accurate and validated finite element model (FEM) of a human sub-axial spinal column (C2-T1) was used in this study. Material properties for all spine components were taken from literature. Cortical bone, cancellous core and intervertebral disks were modelled using linear isotropic elements. Ligaments were modelled using shell elements with non-linear material properties. An algorithm programmed using Python was interfaced with ABAQUS to calculate ROMs with nodal data extracted from its workspace. The code used nodal co-ordinates at the endplates to define physiological planes, and this process helped to calculate the angle between the deformed and undeformed model. The ROMs was successfully computed using these definitions, and EPS was measured across all the segmental units.