Abstract:

BACKGROUND: The human tissue exhibits nonlinear property, and the cervical biomechanical characteristics are closely related with the changes of soft tissue material properties. So it is important to establish the nonlinear finite element model that close to the actual property of the human body.
OBJECTIVE: To establish cervical three-dimensional nonlinear finite element model and to verify the effectivity of the model.             
METHODS: The C₀-C₃ spine was scanned by MarConi MX8000 multislice spiral CT machine to obtain the two-dimensional image. The images were read with Dicom format, and then the accurate C₀-C₃ cervical three-dimensional model was established after image segmentation, data fairing and three-dimensional reconstruction. The model was imported to the ScanFE mode for meshing. Then the model was imported into the ANSYS 10.0 software directly to construct the C₀-C₃ cervical ligament elements and simulate the force-displacement curve, and thus the cervical three-dimensional nonlinear finite element model was established. After model establishment, 40 N preload was loaded on the vertically downward direction, and the flexion, extension, lateral bending and rotational motions were simulated with 1.5 N•m torque. The experimental results were compared to examine the stress distribution and clinical consistent degree.
RESULTS AND CONCLUSION: The three-dimensional nonlinear finite element model included 663 551 elements and 178 247 nodes. After loaded with preload and 1.5 N•m torque, the range of motion for occipitoatlantal joint was flexion 13.3°, extension 11.9°, lateral bending 4.3° and rotation 8.7°, the range of motion of atlantoaxial joint was flexion 15.5°, extension 12.6°, lateral bending 6.4° and rotation 30.8°, which consistent with the experimental results of cadaver specimens. Observed from the longitudinal stress distribution of the model, the stress on the backside odontoid process of axis was higher in any condition, and when extension, the region for stress increasing was increased. The upper cervical spine stress distribution mainly located around the vertebral tunnel, while the stress distribution on both end of the lateral mass and the axial transverse process was lower. Comparative study showed that the stresses on C₂-C₃ joint in flexion, extension, lateral bending and rotation conditions were greater than those on the uncovertebral joint, and the stress distribution of three-dimensional nonlinear finite element model was consistent with the clinical condition. The cervical three-dimensional nonlinear finite element model established with the two-dimensional images, the simple ware and Ansys10.0 software that obtained through multislice spiral CT scan are consistent with the motion law of the human body.

Key words: bone and joint implants, spinal implants, cervical vertebrae, biomechanics, finite element method, occipitoatlantal joint, atlantoaxial joint, provincial grants-supported paper