| BackgroundLow lumbar vertebra(L3-5) and lumbosacral spine locate in the bottom of lumbar vertebra, it bears the larger pressure, rotating and shearing forces, has the lager range of motion(ROM). It is suffered the degeneration disease which is the most common clinical and frequently-occurring disease(such as herniated disk, lumbar spinal stenosis, lumbar instability and lumbar spondylolisthesis) from easy invasions and motor function damage in middle age and old age people. The golden standard of treating lumbar degenerative diseases is intervertebral fusions including anterior lumbar interbody fusion(ALIF), posterior lumbar interbody fusion(PLIF) and transforaminal lumbar imerbody fusion(TLIF); and their curative effects, indications, contraindications and complications have the obvious differences. Many studies show that initial low back pain and(or) lower limb radiation pain will also reappear to result in failed back surgery syndrom(FBSS) after a certain time of symptom continuation or remission in postoperation. In order to better prevent the occurrences of adjacent segment degeneration and FBSS, non-fusion systems based on intervertebral disc(such as artificial intervertebral disc replacement) and vertebral pedicle screw(posterior dynamic internal fixation system, such as X-STOP, Wallis, Coflex, Dynesys, Isobar and TFAS) are innovated, their some early clinical outcomes are satisfied and but long-term therapeutic effects have yet to verify. During multilevel degenerations of lumbar intervertebral discs, the degeneration and instability of each degenerative segment is different. Therefore, some scholars propose that their single-stage surgical treatment need include the fusion, non-fusion and the hybrid fixation of both. From May of 2009 to June of 2011, 58 patients with the degenerative disease of double adjacent segments in intervertebral disk of low lumbar vertebras operated with Isobar Posterior Dynamic Stabilization(IPDS) in Spine surgery, Department of orthopaedics, Changhai Hospital, Second Military Medical University. In order to make clear the clinical effects of IPDS, the clinical follow-up visit and assessment for more 4 years of patients with the operation of IPDS and PLIF(control) were carried out. The effects of lumbosacral disc degeneration on lumbar vertebra biomechanics were analyzed by means of establishing the reliable simulation three-dimensional finite element model of lumbosacral portion to provide the large amounts of data and theoretical foundations for the improvements and perfections of dynamic stabilization devices on keeping intervertebral disc in anterior lumbosacral spine and their clinical practices.Part one: The Clinical Assessment of Hybrid Fixation on Double Adjacent Segments Degeneration in Lower Lumbar VertebraObjectives: The clinical effects and motion characteristics of hybrid fixation with the combination of Isobar TLL(IPDS) and lumbar interbody fusion to treat degenerative disease of double adjacent segments in lower lumbar vertebra were investigated to make clear merits and demerits of the surgical method.Methods: In May of 2009 to June of 2011, 58 and 52 patients with the degenerative disease of double adjacent segments in intervertebral disk of low lumbar vertebras operated respectively with IPDS and PLIF in Spine surgery, Department of orthopaedics, Changhai Hospital, Second Military Medical University; the retrospective analyses of clinical follow-up visits and iconographic data for more 4 years of all patients were conducted.Results: Compared to pre-operation, IPDS and PLIF could extremely significantly improve the symptoms of low back pain and lower limb radiation pain and enhance life quality. They could significantly decrease the lordosis and full range of motion(ROM) during lumbar extension and increase the lordosis and ROM during adjacent segments extension, but didn’t significantly influenced on the lumbar lordosis and ROM of segments with dynamic fixation and had fewer complications. All indexes of both operations had no significant statistical differences.Conclusions: The clinical effects of IPDS and PLIF on treating degenerative disease of double adjacent segments in lower lumbar vertebra were similar; the better proofs of avoiding adjacent segment degeneration in IPDS and PLIF were not found. So IPDS was a better operation selection and its biomechanical characteristics need further research.Part Two: The Establishment and Validation Verification of Three Dimensional Finite Element Simulation Model on Lumbosacral PortionsObjectives: Three dimensional finite element simulation models on healthy person and lumbosacral degeneration patient were established and validly verified to provide the effective methods and approaches for studying the effects of lumbosacral intervertebral disc degeneration on lumbar vertebra biomechanics.Methods: First, the lumbosacral vertebrae images of healthy person were acquired with thinner CT scan, three dimensional cloud points model of spine was reversely reestablished with the acquisition CT images in Mimics17 software. Next, three dimensional cloud points model was fitted editable geometrical solid model(NURBS surface model) with running Geomagic Studio2012 software. Then, The fitting geometrical solid model was imported to Hypermesh 12 and conducted the operations of generating mesh, applying boundary conditions, giving material properties and defining contact with C3D8 I element(C3D expressed three-dimensional continuum element, 8 represented 8 joints of this element, I showed non-coordinating element). Finally, all informations were submitted to ABAQUS 6.12 to perform finite element analysis.Results: Three-dimensional vertebral model with hexahedral mesh was established on the base of lumbar vertebra anatomical morphology and skeleton biomechanics. Reference to the intervertebral disc anatomical structures, the surface meshs of adjacent vertebrae were xtracted, the lines of corresponding joints were built in the space, and then the finite element models of intervertebral disc matrix and nucleus pulposus were formed. According to the descriptions of lumbar vertebra L3-S segments in their anatomical atlas and primal pictures 3D human anatomy medical software, one dimensional Springa element was established in the starting and ending points of corresponding ligament. The simulation values and their changing trends in the ranges of experimental standard deviation of the six dimensions ROM in established lumbosacral vertebrae models were consistent with the comparative literatures and met statistic rules.Conclusions: Through validation verification, established three-dimensional finite element model of spine could be used to ananlyze the effects of lumbosacral intervertebral disc degeneration on lumbar vertebra biomechanics because of more reliable simulations. Part Three: The Three Dimensional Finite Element Analysis on the Effects of Lumbosacral Intervertebral Disc Degeneration on Lumbar Vertebra BiomechanicsObjectives: The effects of lumbosacral intervertebral disc degeneration on lumbar vertebra biomechanics were analyzed to provide the large amounts of data and theoretical foundations for the improvements and perfections of dynamic stabilization devices on keeping intervertebral disc in anterior lumbosacral spine and their clinical practices.Methods: Based on the finite element model of healthy person, the finite element mathematical models on the different degeneration degrees of lumbosacral intervertebral disc(L4-5 and L5-S1) were established through changing materials and geometric characteristics. Coupling correlation of all element joints in the first sacral vertebrae(LS1) and L3 upper surface were established with the calculation of Abaqus 6.12 software under controlling the boundary conditions of all six freedom degrees in LS1. They were respectively simulated the four loading functions of posterior extension, anteflexion, lateral bending and torsion around axis to study their changes of ROM, the Von mises stress and displacement fringes of fibrous rings, the pressure of nucleus pulposus in the motions of anteflexion, posterior extension, left or right bending and torsion.Results: During the moderate or severe double segments degeneration of L4-5 and L5-S1, their ROMs of anteflexion, posterior extension, left or right bending and torsion obviously decrease with the 60% of L4-5. When the double segments of lumbosacral intervertebral disc simultaneously occurred in the different degrees of degenerations, the intervertebral disc of L5-S1 would burden enormous stress change in the anteflexion of the combination with severe degeneration of L4-5 and moderate degeneration of L5-S1. In the anteflexion of the combination with moderate degeneration of L4-5 and severe degeneration of L5-S1, the intervertebral disc stress of L4-5 changeg slightly, but the intervertebral disc of L5-S1 would burden more itself stress and suddenly increase 72.3%. In the left and right bending, the combination with severe degeneration of L4-5 and moderate or severe degeneration of L5-S1 led to increase the about 25% stress of fibrous ring in L5-S1 segment of intervertebral disk. However, the combination with moderate degeneration of L4-5 and severe degeneration of L5-S1 only led to increase the 13.3% stress of fibrous ring in L4-S5 segment of intervertebral disk. The severe degeneration of L4-5 had great effect on L5-S1 and increased the stress of fibrous rings in the all motions, especially the degeneration of L4-5 occurring; but the severe degeneration of L5-S had less effect on the stress distributions of L4-5 fibrous rings in the all motions. The double segments degeneration of L4-5 and L5-S1 would decrease twofold the pressure of nucleus pulposus in the all motions, the pressures decrease of L4-5 and L5-S1 in posterior extension and left or right bending had minor differences, but the pressures decrease of L4-5 in anteflexion and left or right torsion were further higher than those of L5-S1.Conclusions: The effects of L4-5 segment degeneration on the ROM, stress of fibrous rings, pressure of nucleus pulposus of L5-S1 in the all motions were greater than those of L5-S1 segment degeneration on L4-5; the effects order was pressure of nucleus pulposus > stress of fibrous rings > ROM, so the sudden pressure decrease of nucleus pulposus was taken as an measurable indicator of segment degeneration. The combination with severe degeneration of L4-5 and moderate degeneration of L5-S1 should be operated with the hybrid fixation of L4-5 fusion static stabilization and L5-S1 dynamic stabilization. The combination with severe degeneration of L5-S1 and moderate degeneration of L4-5 should be operated with the single segment fusion of L5-S1 to avoid decreasing the ROM of L4-5 fixation that would cause the biomechanics change of superior adjacent segment to occur adjacent segment disease. |
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