Modeling Of Degenerative Cervical Spine And Its Application

Cervical spine, with its complicated geometry and kinematics, remains one of the most fragile parts of human musculoskeletal system. Cervical spine disorders are often related to osteophyte and disc degeneration in the elder people. The normal geometric details of cervical spine are usually used in biomechanical studies on cervical spine. However, to date, no models have been established based on degenerative cervical spine. Therefore, the purpose of this study was to establish and validate a three-dimensional finite element model for degenerative cervical spine. The validated model can be used to simulate the mechanical behaver of cervical spine. The following researches were conducted.Biomechanical effects on cervical spine due to unilateral laminectomy were analized. A C5 unilateral laminectomy FE(finite element) model was established. The inferior surface of C6 vertebra was constrained in all directions as boundary condition. Pure moment of 1.8 Nm was applied over the top surface of C4 vertebra to simulate the movements of C4-C6 spinal units under flexion, extension, lateral bending and axial rotation respectively. Results showed that there were apparent increases in facets stresses under unilateral laminectomy. Most increases were observed in the intact side of facets. No significant effects on stability due to unilateral laminectomy were observed.Biomechanical effects on cervical spine due to multilevel laminectomy were analized too. C5, C4-C5 and C3-C4-C5 laminectomy FE models were established. The inferior surface of C7 vertebra was constrained in all directions. Pure moment of 1.8 Nm was applied over the top surface of C2 vertebra to simulate the movements of cervical spine under flexion, extension, lateral bending and axial rotation respectively. Results showed that there were apparent effects on intersegmental stability due to multilevel laminectomy. The stiffness declined with the increasing of laminectomied level. The regions of high vertebral and intervertebral disc stresses were observed in or near the surgical altered vertebral.Biomechanical effects on cervical spine due to variable head-neck sleeping posture were analized also. The validated head-neck model was set up. The inferior surface of C7 vertebra was constrained in all directions. Head and vertebral weight were added. The stresses in vertebral, intervertebral disc, pedicle of vertebral arch and uncus of vertebral body were analyzed with different head-neck position. Results showed that the stresses increased with the increasing of head displacement. Low stresses were detected on atlas and axis. On the contrary, high stresses appeared in the lower cervical spine.