Finite Element Model of the Human Lower Cervical Spine: Parametric Analysis of the C4-C6 Unit

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Abstract
In this study, a three-dimensional finite element model of the human lower cervical spine (C4-C6) was constructed. The mathematical model was based on close-up CT scans from a young human cadaver. Cortical shell, cancellous core, endplates, and posterior elements including the lateral masses, pedicle, lamina, and transverse and spinous processes, and the intervertebral disks, were simulated. Using the material properties from literature, the 10,371-element model was exercised under an axial compressive mode of loading. The finite element model response agreed with literature. As a logical step, a parametric study was conducted by evaluating the biomechanical response secondary to changes in the elastic moduli of the intervertebral disk and the endplates. In the stress analysis, the minimum principal compressive stress was used for the cancellous core of the vertebral body and von Mises stress was used for the endplate component. The model output indicated that an increase in the elastic modulii of the disk resulted in an increase in the endplate stresses at all the three spinal levels. In addition, the inferior endplate of the middle vertebral body responded with the highest mean compressive stress followed by its superior counterpart. Furthermore, the middle vertebral body produced the highest compressive stresses compared to its counterparts. These findings appear to correlate with experimental results as well as common clinical experience wherein cervical fractures are induced due to external compressive forces. As a first step, this model will lead to more advanced simulations as additional data become available.