Orientador: José Elias Tomazini / Banca: Mauro Hugo Mathias / Banca: Luiz Carlos de Queiroz / Resumo: Para melhor entender os mecanismos degenerativos da coluna vertebral e avaliar o melhor método para seu tratamento é necessário que se conheça o comportamento dos diversos componentes das articulações intervertebrais. Com isso, torna-se essencial o desenvolvimento de dispositivos capazes de simular as condições fisiológicas de movimentos e cargas a fim de realizar testes in vitro que fornecerão dados para posteriormente serem testados in vivo. O objetivo deste trabalho é o desenvolvimento de dispositivos para a realização de testes in vitro com coluna vertebral. Estes dispositivos constam de uma máquina capaz de simular o movimento de flexão-extensão, pré-cargas axiais e a angulação pélvica, e uma lâmina de extensometria para captar as deformações dos tecidos testados. Foram realizados experimentos com discos invertebrais suínos a fim de avaliar a eficiência dos dispositivos. Realizaram-se dois experimentos usando os dispositivos desenvolvidos e um experimento na máquina universal de ensaios. Como resultado obteve-se valores de propriedades mecânicas coerentes com a literatura e o disco intervertebral comportando-se como um material viscoelástico. Outro ponto importante foi a obtenção da pressão intradiscal aproximada relacionando-a com o deslocamento angular da coluna. Conclui-se que os dispositivos apresentaram funcionamento satisfatório, abrindo perspectivas para outros estudos. / Abstract: The best way to understand the degenerative mechanisms of the vertebral column and to evaluate appropriated methods for its treatment it is necessary to know the behavior of the diverse components of the intervertebral joints. So, it becomes essential to simulate the physiological conditions of movements and loads in order to carry through test in vitro that they will supply datas to be tested in vivo. The objective of this study is the development of devices of low cont for the accomplishment of tests in vitro with spine. These devices consist of a machine capable to simulate the movement of flexion-extension, daily pay-loads and the pelvic inclination, and an extensometry blade to catch the deformations of tested structures. POrcine had been carried through experiments with intervertebral discs in order to evaluate the efficiency od the devices. Two experiments had been become fullfilled using the developed devices and an experiment in the universal test machine. As result we got values of coherent mechanical properties with literature and the intervertebral disc behaving as a viscoelastic material. Another important point was the attainment of the intradiscal pressure approached relating it with the angular displacement of the spine. It is concluded that the devices had presented satisfactory functioning, opening perspective for other studies. / Mestre

Introduction. To test the effects of torsion torques on intradiscal pressure and disc height in human lumbar specimens. Methods. Six human lumbar cadaveric functional spine units (FSU) were loaded in the neutral position with 600 N compression. Nucleus pressure measurements were obtained at 0 Nm, 0.5 Nm, 1.0 Nm and 2 Nm torsion torque. Posterior elements were removed and pressure measurements were repeated at the same torsion torques for the disc body unit (DBU). The pressure in the nucleus was measured by pulling a pressure probe through the disc along a straight path in the midsagittal plane. Results. There was no statistically significant difference of nucleus pressure or intervertebral disc height with different torsion torques among or between the FSU's and DBU's. However, a disc height increase ranging from 0.13 mm to 0.16 mm occurred with the insertion of a 1.85 mm diameter cannula. Conclusions. Small torsion torques showed no significant difference in intradiscal pressures or disc heights. Disc height increases were seen with the insertion of the cannula that could lead to methods of disc height restoration.

This dissertation has two major parts; Analytical and Experimental. The analytical section contains a study using Finite Element Analysis of dynamic instrumentation to demonstrate stress reduction in adjacent level discs. The experimental section contains biomechanical testing of facet fusion allograft technique and finally a comparison between In Vivo and In Vitro intradiscal pressures to determine forces acting on Lumbar spine segment L4-L5. A comprehensive study of available data, technology and literature was done. Conventional fusion instrumentation is believed to accelerate the degeneration of adjacent discs due to the increased stresses caused by motion discontinuity. A three dimensional finite element model of the lumbar spine was obtained which simulated flexion and extension. Reduced stiffness and increased axial motion of dynamic posterior lumbar fusion instrumentation designs results in a ~10% cumulative stress reduction for each flexion cycle. The cumulative effect of this reduced amplitude and distribution of peak stresses in the adjacent disc may partially alleviate the problem of adjacent level disc degeneration. Traditionally a pedicle screw system has been used for fixation of the lumbar spine and this involves major surgery and recovery time. Facet fixation is a technique that has been used for stabilization of the lumbar spine. The cadaver segments were tested in axial rotation, combined flexion/extension and lateral bending. Implantation of the allograft dowel resulted in a significant increase in stiffness compared to control. Facet fusion allograft provides an effective minimally invasive method of treating debilitating pain caused by deteriorated facet joints by permanently fusing them. An In Vitro biomechanical study was conducted to determine the intradiscal pressure during spinal loading. The intradiscal pressures in flexion/extension, lateral bending and axial rotation was compared to In Vivo published data. There is no data that explains the actual forces acting on the spine during flexion, extension, lateral bending or axial rotation. The functional spinal units were tested in combined axial compression and flexion/extension, combined axial compression and lateral bending and combined axial compression and axial rotation using a nondestructive testing method. Overall, this study found a good correlation between In Vivo and In Vitro data. This can essentially be used to make physiological relation from experimental and analytical evaluations of the lumbar spine. It is important to know how much load needs to be controlled by an implant.

Pedicle screw-rod instrumentation is considered a standard treatment for spinal instability, and titanium is the most common material for this application. Cobalt-chromium has several advantages over titanium and is generating interest in orthopedic practice. The aim of this study was to compare titanium versus cobalt-chromium rods in posterior fusion, with and without transverse connectors, through in vitro biomechanical testing and determine the optimal configuration. Six cadaveric lumbar spines (L1-S1) were used. Posterior and middle column injuries were simulated at L3-L5 and different pedicle screw constructs were implanted. Specimens were subjected to flexibility tests and range of motion, intradiscal pressure and axial rotation energy loss were statistically compared among the following conditions: intact, titanium rods (without transverse connectors), titanium rods with transverse connectors, cobalt-chromium rods (without transverse connectors) and cobalt-chromium rods with transverse connectors. The novel measurement of energy loss was examined to determine its viability in fusion investigations. All fusion constructs significantly (p0.05) were observed in axial rotation among all conditions. Intradiscal pressure significantly increased (p≤0.01) after fusion, except for the cobalt-chrome conditions in extension (p≥0.06), and no significant differences (p>0.99) were found among fixation constructs. Energy loss, differences became significant between the cobalt-chrome with transverse connector condition with respect to the cobalt-chrome (p=0.05) and titanium (p There is not enough evidence to support that the cobalt-chrome rods performed biomechanically different than the titanium rods. The use of titanium rods may be more beneficial because there is a lower probability of corrosion. The inclusion of the transverse connector only increased stability for the cobalt-chromium construct in axial rotation, which suggests that it is beneficial in complete facetectomy procedures.

Background: Approximately 40% of low back pain cases are attributed to internal disc disruption. Since mechanical loading directly affects intradiscal pressure and the stresses that the inner annulus fibrosus experiences, the mechanism that leads to disruption of the inner annulus fibrosus may be linked to changes in intradiscal pressure. Hence, there is a need to examine how intradiscal pressure changes over time during a flexion extension cyclic (FEC) loading protocol known to induce internal disc disruption. Purpose: 1) To determine whether a bore-screw pressure sensor system could be used as an alternative sensor for measuring intradiscal pressure, and 2) to characterize changes in intradiscal pressure, moments, and axial deformation using a FEC loading protocol. Study 1 summary: Technical specifications of the bore-screw pressure sensor system were compared to the needle pressure sensor. The error projected at a static compressive load of 1500 N was approximately eight percent and the bore-screw pressure sensor had an excellent dynamic response compared to the needle pressure sensor. Study 2 methods: The bore-screw pressure sensor system was successfully instrumented in 14 porcine specimens. The FEC loading protocol consisted of 3600 cycles of 1 Hz flexion-extension movement while applying a 1500 N compressive load. The four dependent variables collected were intradiscal pressure, moment, axial deformation, and angular displacement. Study 2 results: Intradiscal pressure and specimen height decreased by 45 % and 62 %, respectively, and the peak moment increased by 102 % following the FEC loading protocol. There were strong correlations between average intradiscal pressure and both peak moment and average axial deformation. The angle where maximum pressure occurred demonstrated a significant difference after 2700 cycles. There were no sequential changes in pressure difference after 2100 cycles. Twelve out of 14 specimens showed partial herniation (85.7%); however, the injury type was not correlated to the pressure change. Conclusions: Changes in intradiscal pressure were successfully characterized over time using a new pressure sensor system. Although the change in pressure difference was not predictive of an injury type, its increasing trend over time suggested that the inner annulus fibrosus failure mechanism may be related to fatigue.

Made available in DSpace on 2014-06-11T19:28:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-01-13Bitstream added on 2014-06-13T19:37:19Z : No. of bitstreams: 1 lemos_ff_me_guara.pdf: 3167749 bytes, checksum: 900a2570260a39cccd178d8a2ecb5b4a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Para melhor entender os mecanismos degenerativos da coluna vertebral e avaliar o melhor método para seu tratamento é necessário que se conheça o comportamento dos diversos componentes das articulações intervertebrais. Com isso, torna-se essencial o desenvolvimento de dispositivos capazes de simular as condições fisiológicas de movimentos e cargas a fim de realizar testes in vitro que fornecerão dados para posteriormente serem testados in vivo. O objetivo deste trabalho é o desenvolvimento de dispositivos para a realização de testes in vitro com coluna vertebral. Estes dispositivos constam de uma máquina capaz de simular o movimento de flexão-extensão, pré-cargas axiais e a angulação pélvica, e uma lâmina de extensometria para captar as deformações dos tecidos testados. Foram realizados experimentos com discos invertebrais suínos a fim de avaliar a eficiência dos dispositivos. Realizaram-se dois experimentos usando os dispositivos desenvolvidos e um experimento na máquina universal de ensaios. Como resultado obteve-se valores de propriedades mecânicas coerentes com a literatura e o disco intervertebral comportando-se como um material viscoelástico. Outro ponto importante foi a obtenção da pressão intradiscal aproximada relacionando-a com o deslocamento angular da coluna. Conclui-se que os dispositivos apresentaram funcionamento satisfatório, abrindo perspectivas para outros estudos. / The best way to understand the degenerative mechanisms of the vertebral column and to evaluate appropriated methods for its treatment it is necessary to know the behavior of the diverse components of the intervertebral joints. So, it becomes essential to simulate the physiological conditions of movements and loads in order to carry through test in vitro that they will supply datas to be tested in vivo. The objective of this study is the development of devices of low cont for the accomplishment of tests in vitro with spine. These devices consist of a machine capable to simulate the movement of flexion-extension, daily pay-loads and the pelvic inclination, and an extensometry blade to catch the deformations of tested structures. POrcine had been carried through experiments with intervertebral discs in order to evaluate the efficiency od the devices. Two experiments had been become fullfilled using the developed devices and an experiment in the universal test machine. As result we got values of coherent mechanical properties with literature and the intervertebral disc behaving as a viscoelastic material. Another important point was the attainment of the intradiscal pressure approached relating it with the angular displacement of the spine. It is concluded that the devices had presented satisfactory functioning, opening perspective for other studies.

The association between age-related vertebral fractures (VFx) and disc degeneration (DD) is not clear, despite the high prevalence of both conditions. Load is transferred to the vertebra by the adjacent intervertebral discs, and degenerative changes within the disc alter how the net force is distributed over the interface between vertebra and disc, known as the vertebral endplate (EP). The ability of the vertebra to resist fracture depends not only on the magnitude of the net force, but also on the distribution. Multiple lines of evidence suggest that the ability of the vertebra to withstand the distribution of applied force depends on the spatial distribution of bone mineral density (BMD) within the vertebra. First, the strength and stiffness of a region of bone in the vertebra are highly correlated with the BMD of that region. Second, changes in the spatial distribution of regional BMD have been associated with aging and DD. Thirdly, some of these observed changes have been replicated in computer models bone adaption with in the presence of progressive DD, suggesting that bone adaption is occurring in response to the altered force distribution associated with DD, and that maladaptation could elevate the risk of fracture. Notably, the current clinical method of identifying patients at risk of fracture is to use an average measure of BMD for the entire vertebra. The lack of consideration of the spatial distribution of BMD may explain why the clinical method used at present does not adequately identify those at risk of fracture. The possible relationship among spatial distribution of BMD, DD, force distribution across the endplate, and vertebral strength suggests that characterizing the spatial distribution of BMD within a vertebra could add to the understanding of why some vertebra are more likely to fracture. This project sought to determine if an association exists between the spatial distribution of vertebral BMD and disc health in order to provide an improved perspective of the clinical sequelae of DD and to improve the ability of clinicians to identify those who would benefit most from intervention. This study found evidence that the distribution of bone in the vertebral body and EP depend on the health of the adjacent disc. The distribution of pressure in discs favors the anterior most portion of the disc in anteriorly flexed postures and the density in the anterior most portion of the EP appears to respond to this shift, suggesting that bone is adapting to loading patterns associated with certain postures more than others. This study also found association between reduced regional disc height and altered distribution of trabecular density which was positive in the nuclear region and negative in the annular region. In some cases there was a lack of association between disc height and density distribution that may indicate maladaptation and thus increased risk of fracture. This study, being cross-sectional could not identify whether the observed alterations in density and degeneration initiated in the vertebra or the disc. However, this study contributes to the understanding of the relationship between the distribution of vertebral density and the functional properties of the adjacent disc that may ultimately improve the clinician's ability to predict VFx. / 2017-06-21T00:00:00Z

Bien que les orthèses lombaires (OL) soient couramment employées depuis de nombreuses années dans le traitement conservateur des lombalgies, leurs effets mécaniques et posturaux restent, à notre connaissance, partiellement inexplorés. Des obstacles d'ordre méthodologique en sont la principale cause avec en premier lieu la difficulté d'évaluer les effets des OL à l'intérieur du tronc sans être invasif et sans nécessiter un équipement coûteux difficilement utilisable lors de la pratique médicale courante. La levée de ces verrous scientifiques a guidé l'ensemble de ce travail doctoral à travers le développement d'une méthodologie spécifique. L'effet mécanique a été étudié à partir d'une nouvelle méthode non-invasive de mesure de la pression intradiscale réalisée à partir d'une modélisation par éléments finis contrôlée par radiographie. Les premiers résultats ont démontré la possibilité de diminuer de 15 à 22% en moyenne la pression intradiscale lors du port d'une OL modifiant la statique rachidienne. Les différents travaux sur l'équilibre postural ont permis de définir une méthodologie d'analyse de la posture en station debout puis assise adaptée à l'évaluation des OL. Les premiers résultats chez des patients lombalgiques subaiguës ont mis en évidence un contrôle postural plus efficient (réduction de la raideur active du tronc) lors du port de l'OL la plus rigide. A terme, cette méthodologie facile à mettre en œuvre permettra d'adapter les caractéristiques du produit (raideur passive / forme) aux caractéristiques des patients (raideur active / courbure lombaire) dans le but d’optimiser l'efficacité clinique / Although lumbar orthoses (LO) are commonly used for many years in the conservative treatment of low back pain, postural and mechanical effects are, to our knowledge, partly unexplored. Methodological difficulties are the main cause with, in the first place, the difficulty to assess the LO effects inside the trunk with a non-invasive and not expensive method adapted for current medical practice. This Ph.D work attempts to address these difficulties through the development of a specific methodology. The mechanical effect was studied by a non-invasive estimation of the intradiscal pressure through a finite element modeling controlled by radiographs. The first results showed the possibility of a mean reduction from 15 to 22% of the intradiscal pressure while wearing an LO which is able to change the spinal posture. The different works on postural balance allowed us to define a methodology for a suitable LO assessment in standing and then sitting postures. The first results in patients with subacute low back pain showed a more efficient postural control (reduction of active stiffness of the trunk) while wearing the most stiffer LO. In the future, this easy-to-implement assessment could be helpful to more accurately target the appropriate LO for a given patient in order to improve his / her clinical status