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The Development of Ti2448 Pedicle Screw System with Lower Elastic and Higher Strength: A Finite Element Analysis and Biomechanical Research

Author: WangZheng
Tutor: LeiWei
School: Fourth Military Medical University
Course: Surgery
Keywords: Ti2448 lumbar vertebrae pedicle screw finite element analysis
CLC: R687.3
Type: PhD thesis
Year: 2011
Downloads: 53
Quote: 0
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Abstract


The spinal pedicle screw instrumentation system has been the most frequently-used, the most important and the core technology, and it has been the landmark of the spinal surgery. Nowadays, the material consisting of pedicle screws is mainly Titanium alloy. Although the Titanium alloy has a good biocompatibility, the modulus of it is much higher than the spinal bone. And thus it causes the stress-shielding of the spine which will affect the sinal bone fusion. To seek a new spinal instrument which may have a more similar modulus with even more mechanical strength and more biocompatibility, and to apply it into the spinal surgery has become the hotspot focused by the orthopaedic scholars all of the world and the problems to be solved.In the prior experiment, we apply the alloy with lower modulus and more strength into the research of spinal instrumentation. Firstly, we should establish the finite element model of the lumbosacral spine and to compare the spinal internal fixation system of different design and different material. According to the result of the finite element analysis, we optimize the spinal internal fixation system, and produce the spinal pedicle screws with lower notch, lower elastic modulus and higher strength. Then we compare the novel spinal fixation system with the ones most frequently used nowadays, and test the safety and reliability of it, and provide the evidence of its further clinical application.Experiment One: The comparison of biomechanical characteristics of different spinal pedicle fixation devices by finite element analysisObjective: to compare the immediate fixation effect of spinal pedicle devices of different materials and designs to the lower lumbar vertebrae. Methods: we use the computer-aided technology to establish the lumbosacral finite element model (L3-S1). The intervertebral disc between L4-5 and the lower lamina between the spaces were removed simulatively, the intervertebral cages was implanted and pedicle screws were inserted at the L4 and L5 vertebrae. The CD-M8, MOSS MIAMI and SINO-M10 pedicle screws was inserted respectively with the same gauge (6.5×45mm).400N load was preloaded axially and 7.5Nm bending moment was applied to the model, the fixed segment’s motion angles and displacement, the maximum stress at the adjacent intervertebare discs, the maximum stress the screw and cage bear at extension, flexion, and torsion condition was compared respectively. Result: The pedicle screws made of novel alloy could provide the similar immediate stability of the fixed segment of lumbar as the most-frequently used commercial screws available. And it can decrease the stress shielding and increase the stimulation on the cage between the fixed segments. Conclusion: The pedicle screws made of the same gauge can provide enough mechanical property to stable the fixed segments and decrease the stress shield as well.Experiment Two: The optimized design of novel alloy pedicle screw fixation device based on finite element analysisObjective: By finite element analysis, to optimize the appropriate gauge of the pedicle screw made of novel alloy, which will provide enough mechanical strength and has lower notch as well. Methods: The finite element model established priorly was used to simulate the same―operation‖procedure, and the SINO-M10 pedicle screws was adopted,the original length remained, and the diameter decreased from the original gauge 6.5mm to 5.2mm(80%), 4.875mm(75%), and 4.55mm(70%) gradually. The diameter of the connecting rod was 6mm, 4.8mm, 4.5mm, and 4.2mm respectively. The axial 400N load was preloaded and 7.5Nm moment was applied. The fixed segment motion and maximum stress of the adjacent intervertebral discs and pedicle screw and cage beared was measured and compared. Result: Compared with the 100% diameter pedicle screw, the 80% diameter pedicle screw can provide sufficient stability, 75% diameter can provide partially stability and in 70% diameter group, the angle loss proved more severe. Conclusion: The novel alloy decreased to 80% in diameter can provide enough stability and notably decrease the gauge of the implantation.Experiment Three: The comparison of biomechanical property of novel alloy pedicle screws in vitroObjective: To compare the biomechanical property of CD-M8, SINO-M10, novel SINO-M10, novel 80%SINO-M10 screws. Methods: biomechanical strength analysis: three point bending test. Pedicle screws of different types, inclusive of CD-M8, SINO-M10, novel SINO-M10 and novel 80%SINO-M10 screws, were divided into four groups. Each group was 8 screws. The pedicle screws were mounted on MTS 858 for test. SPSS 11.5 software was used for statistics. Result: 1.In three bending test, 80% diameter novel alloy pedicle screw has the similar strength compared with other groups. Conclusion: The 80% diameter novel alloy SINO-M10 pedicle screws can provide sufficient spine segmental stability having experienced posterior laminectomy and discectomy and anterior cage insertion plus posterior instrumentation, and what’s more it decreases the notch or the gauge of the common pedicle screw that may reduce the further stimulation on the soft tissue.ConclusionThe results of finite element analysis and biomenchanical study show that Ti2448 can be applied in instrument minimization of spinal fixation device. Compared with Ti6l4V, Ti2448 can reduce the volume, as well as height of pedicle screws. In addition, it can maintain the stiffness and stability of instrumented segments decrease the stress concerntration in adjacent segments. Ti2448 pedicle screw system might promote spinal fusion consequently.

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CLC: > Medicine, health > Surgery > Orthopaedic Surgery ( movement system diseases,orthopedic surgery ) > Orthopedic surgery and surgery > Bone surgery
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