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| Finite Element Analysis of the Sagittal Axial Dynamic Pedicle Screw and Rod System for Unstable Lumbar |
| WEI Guo-qiang, LI Yao-chen, XU Wang-yang, et al |
| Nanhai Hospital, the Southern Medical University, Foshan, Guangdong 528244 |
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Abstract 【Objective】To analyse the biomechanical characteristics of the lumbar instability model with the sagittal axial dynamic pedicle screw and rod system by the finite element method, providing the biomechanical basis and theoretical for the clinical application of the dynamic internal fixation system.【Methods】The normal lumbar model and L4/L5 instability model was established on the base of by lumbar CT data of a healthy Chinese male adult volunteer, which was previously acquired. The finite element models were calculated and established on the basis of the material parameters of the sagittal axial dynamic pedicle screw and rod system and the strong pedicle screw and rod system, and were introduced into the verified L4 and L5 instability model to establish the single-segment dynamic fixation model and the single-segment strong fixation model. Under the constraints of L5 vertebral endplate and under axial 500N load and 10 N·m torque, five working conditions of normal physiological axial load, flexion, extension, lateral bending and rotation of the human lumbar were simulated respectively. Under the axial load conditions of the 4 models, the axial displacement of L4, 5 and the fixed segments of L4, 5 in the latter four conditions are recorded respectively; at the same time, the L3, 4 adjacent segment activity, the intervertebral disc stress, the stress of the adjacent facet joints and the stress of the instrument were analyzed and compared.【Results】The axial dynamic pedicle screw rod system fixation of unstable lumbar vertebrae can make the motion range of the fixed segment of intervertebral joint have a proper range of motion, which was larger than that of the strong fixation group, less than the complete spinal group. The effect of the model on the lumbar motion of the adjacent segments was also less than that of the rigid fixation group. At the same time, the stress of the fixed segment intervertebral disc was greater than that of the rigid fixation group, but the stress of the instrument was less than that of the strong pedicle screw rod system, while the stress of the adjacent segment of lumbar intervertebral disc and facet joint was smaller than that of the rigid fixation group.【Conclusion】The application of dynamic pedicle screw rod system in fixation of unstable lumbar spine not only retains the lumbar fixation segments appropriate activity, and but also provides immediate stability. At the same time, the system bears the load with the spinal column, which can effectively avoid the complications of internal fixation failure, caused by stress shielding and stress concentration of the instrument. It can also reduce the stress of intervertebral disc and intervertebral joint in the adjacent segment. Compared with the rigid fixation, its influence on adjacent segment lumbar activity is rather small, which theoretically, is beneficial to reduce and prevent adjacent segment degeneration.
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Received: 05 June 2017
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. [J]. JOURNAL OF CLINICAL RESEARCH, 2017, 34(9): 1771-1773. |
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2017, Vol. 34 
