EFFECTS OF VERTEBRAL BODY CHANGES ON CERVICAL SPINE LOAD SHARING

摘要

The objective of the study was to determine the effects of changes in the Young's modulus of elasticity of the cancellous bone that occur due to the ageing process on the biomechanical behavior of the cervical spine. An anatomically accurate three-dimensional (3-D) nonlinear finite element model of the C4-C5-C6 cervical spinal unit was used. The inferior surface of the C6 vertebrae was fixed in all degrees of freedom, and external loads were applied to the top surface of the C4 vertebra. The model was exercised under an axial compressive force of 754 N. In addition, flexion and extension bending moments of 3.44 Nm were applied individually to the model. The effects of ageing on bone strength were simulated by decreasing the Young's modulus of elasticity from 100 MPa in the healthy spine to 40 MPa in the degenerated spine. The degenerated spine was found to be more flexible than the healthy spine. In addition, the degenerated spine responded with increased forces in the outer anterior and posterior regions of the vertebral body. Furthermore, forces in the facet joints increased in the degenerated spine. In contrast, the middle region of the disc showed decreased forces. These increases in the forces leading to stress risers may explain the occurrence of osteophytes in the spine with age.