ABSTRACT
Objective:To investigate the effect in lumbar mobility and stress of the facet joint and end plate after implantation of the movable artificial lumbar spine so as to lay a biomechanical foundation for its clinical application.Methods:Total lumbar CT data of a healthy adult male were selected to construct a finite element analysis model and its effectiveness was validated (physiological group). Two groups were replicated after removing the L 3 vertebral body and adjacent discs of the model in physiological group. One group was placed with each component of the movable artificial lumbar spine to construct the non-fusion model (non-fusion group). The other group was placed with titanium cage, titanium plate and other to construct the fusion model (fusion group). The models in the three groups were loaded with 500 N axial load and 10 Nm axial load, and the torque load was used to simulate the movement in six directions: forward flexion, backward extension, left and right lateral bending, and left and right torsion. The lumbar mobility and stress peak and distribution of the proximal facet joints (J 1-2, J 4-5), L 2 inferior endplate and L4 superior endplate at the three model operating sites (L 2-3, L 3-4) and adjacent segments (L 1-2, L 4-5) under the same conditions were compared. Results:The range of motions of the surgical site in flexion, extension, left bending, right bending, left torsion and right torsion were L 2-3of 3.9°-8.7° and L 3-4 of 3.6°-8.4° in non-fusion group, significantly increased compared with fusion group (L 2-3 0.1°-0.2°, L 3-4 0.1°-0.1°) and slightly increased compared with physiological group (L 2-3 2.3°-6.0°, L 3-4 2.3°-7.1°). The range of motions of the adjacent segments in the above six directions were L 1-2 of 1.4°-4.3° and L 4-5 of 1.4°-6.0° in non-fusion group, smaller than those in fusion group (L 1-2 2.1°-6.1°, L 4-5 3.3°-8.6°) and similar to those in physiological group (L 2-3 2.3°-6.0°, L 3-4 2.3°-7.1°). The peak values of von Mises stress in the proximal facet joints were J 1-2 of 7.07-19.21 MPa and J 4-5of 6.12-12.99 MPa in non-fusion group, similar to those in physiological group (J 1-2 8.42-18.53 MPa, J 4-5 7.49-11.70 MPa) and smaller than those in fusion group (J 1-2 10.54-21.16 MPa, J 4-5 10.63-16.13 MPa). The maximum von Mises stress of the L 2 inferior endplate and L 4 superior endplate in the above six directions was 29.39-54.72 MPa and 32.31-47.87 MPa in non-fusion group, significantly increased compared with the L 2 inferior endplate (21.20-42.07 MPa), L 4 superior endplate (22.50-36.76 MPa) and L 2 inferior endplate (11.04-29.55 MPa) in fusion group and the L 4 superior endplate (13.12-21.32 MPa) in physiological group. Conclusion:Compared with the traditional fusion prostheses, the placement of the movable artificial lumbar spine can reconstruct the range of motion of the surgical site in the direction of flexion, extension, lateral bending and torsion, greatly reduce the impact on the stress of adjacent facet joints and the range of motion of adjacent segments, and theoretically reduce the incidence of prosthesis subsidence.
ABSTRACT
Objective:To compare the effect of the new anterior cervical spine memory compression fixation device (GYZ memory alloy plate) and traditional titanium plate on the range of motion (ROM) and stress of the adjacent segment after anterior cervical discectomy and fusion.Methods:An adult male volunteer was recruited for a fee. After excluding cervical malformations, fractures, infections and other diseases, C 3-C 7 thin-layer CT scans were performed. Import the scanned data into the finite element modeling software to establish the finite element model of the physiological group and verify itseffectiveness. After C 5,6 discectomy, the intervertebral fusion device was inserted, and the anterior fixation was assisted by a conventional titanium plate or a new type of fixator. Thus, the finite element model of the traditional titanium plate group and the new fixer group was established. The three models were imported into the finite element analysis software ANSYS 16.0, and a vertical downward axial load of 73.6 N was loaded to simulate the head weight and the torque of 1.0 N·m to simulate the cervical spine flexion, extension, left lateral bending, right lateral bending, left rotation and right rotation.Compare the changes of intervertebral disc ROM and stress in adjacent segments of physiological group, traditional titanium plate group and new type fixator group. Results:The intervertebral disc ROM under six conditions was basically similar to the results of previous studies, and the model was effective. In the adjacent segment C 4,5, the three groups of activities in the flexion, extension, left lateral bending, right lateral bending, left rotation and right rotation conditions were: physiological group 3.9°, 4.2°, 3.7°, 3.7°, 2.2° and 2.2°, traditional titanium plate group 4.6°, 4.7°, 4.3°, 4.4°, 3.3° and 3.1°, and new fixture group 4.4°, 4.3°, 4.0°, 4.2°, 2.8° and 2.7°. The maximum stresses of the intervertebral discs under three different working conditions were: physiological group 1.81, 1.60, 3.99, 2.06, 3.63 and 3.41 MPa, traditional titanium plate group 1.86, 1.67, 4.21, 2.16, 3.82 and 3.63 MPa, and new fixture group 1.84, 1.64, 4.17, 2.14, 3.78 and 3.58 MPa. In the adjacent segment C 6,7, the activities of the three groups in six working conditions were: physiological group 3.1°, 3.2°, 2.5°, 2.5°, 1.2° and 1.3°, traditional titanium plate group 4.2°, 3.7°, 3.4°, 3.0°, 2.1° and 2.2°, and new fixture group 3.5°, 3.3°, 2.5°, 2.7°, 1.8° and 1.9°.The maximum stress of the intervertebral disc under three different working conditions was: physiological group 0.45, 0.66, 1.12, 0.85, 0.84 and 0.82 MPa, traditional titanium plate group 0.62, 0.93, 1.55, 1.24, 1.44 and 1.27 MPa, and new fixture group 0.61, 0.92, 1.54, 1.22, 1.07 and 1.24 MPa. The ROM and disc pressure of adjacent segments in the conventional titanium plate group were higher than those of the new fixator group. Conclusion:Compared with the traditional titanium plate, the new type of anterior cervical memory compression fixator has less effect on the ROM and stress of adjacent segments, which may slow down the process of adjacent segments degeneration to a certain extent.