Finite element modeling of multi-level cervical spinal segments (C3-C6) and biomechanical analysis of an elastomer-type prosthetic disc.

A three-dimensional finite element (FE) model for the multi-level lower cervical spinal segment C3-C6 has been developed using computed tomography (CT) data, and applied to study of the effects of the fusion and the artificial disc prosthesis on the biomechanical behavior of the lower cervical spine. The NURBS computer adided dedsig (CAD) data used in this study for modeling the vertebrae facilitate adding surface patch layouts for seamless attachment of the soft tissues, such as intervertebral discs onto the vertebrae. A FE model was completed by generating mesh out of this geometry. Its accuracy was validated by comparing with previously published experimental and numerical results for the flexion-extension, axial rotation, and lateral bending moments. An implantation of an elastomer-type disc prosthesis or fused graft between C4-C5 vertebrae was considered in the FE model by modifying the intact disc. It is shown that the fusion reduced the mobility at its level by about 50-70% for the considered loading cases. It is numerically demonstrated that an elastomer with Young's modulus of 5.9 MPa for the artificial disc prosthesis well restores the biomechanical behavior of the intact spine.