536 research outputs found

    Towards Functional Preoperative Planning in Orthopaedic Surgery

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    Las cirugíıas del aparato locomotor suponen más de 20 millones de intervencionesanuales para la corrección de lesiones que afectan a músculos, articulaciones,ligamentos, tendones, huesos o nervios; elementos que conforman el sistema musculoesquelético. Este tipo de afecciones de la biomecánica pueden tener diversos orígenes; siendo los principales los traumatismos, las lesiones degenerativas en huesos y tejidos blandos, los malos hábitos posturales o motores, y los de origen congénito.El uso de las tecnologías actuales en los procesos de corrección de estas afecciones forma parte del día a día en los quirófanos y en la monitorización de los pacientes.Sin embargo, el uso de técnicas computacionales que permitan la preparación de las intervenciones quirúrgicas antes de proceder con la cirugía están todavía lejos de formar parte del proceso de evaluación preoperatoria en este tipo de lesiones. Por este motivo, el objetivo principal de esta tesis consiste en demostrar la viabilidad del uso de herramientas computacionales en la planificación preoperatoria de diferentes cirugías ortopédicas.Entre los tipos de cirugías más comunes, la mayor parte de ellas se centran en las articulaciones del tren inferior de la anatomía humana. Por este motivo, este trabajo se centraría en el análisis de diferentes cirugías cuya finalidad es solucionar lesiones en las principales articulaciones del tren inferior: región sacrolumbar, cadera, rodilla y tobillo.Para poder realizar el análisis de estas cirugías se hizo uso de algunas de lasherramientas computacionales más usadas habitualmente y cuya capacidad en diversos ámbitos ha sido comprobada. Se ha utilizado la reconstrucción 3D para la obtención de modelos anatómicos sobre los que comprobar la viabilidad de las cirugías. Estas reconstrucciones se basan en las imágenes médicas obtenidas mediante Tomografia Axial Computerizada (TAC) o Resonancia Magnética (RM). Las imágenes procedentes de RM permiten diferenciar todos los tejidos de la anatomía, incluyendo los blandos tales como tendones o cartílagos; mientras que los TAC facilitan la diferenciación de los huesos. Esta última es la prueba más habitual en los diagnósticos.Para su análisis y reconstrucción se hizo uso de los software Mimics v 20.0 y3-matic 11.0 (Materialise NV, Leuven, Belgium). Como alternativa para la generación de los modelos cuando no se dispone de las imágenes necesarias para realizar la reconstrucción o cuando se requiere dotar de flexibilidad a estos modelos, se recurrió al modelado en el software de análisis por elementos finitos Abaqus/CAE v.6.14 (Dassault Syst`emes, Suresnes, France). Dicho software fue además utilizado para la simulación del efecto de las diferentes cirugías sobre la región de interés. Para resalizar las simulaciones, se incluyeron en los modelos aquellos parámetros, elementos y condiciones necesarios para poder representar las caraterísticas propias de cada cirugía. Finalmente, para aquellas situaciones que requerían del análisis de datos se hizo uso de tecnologías de machine learning. La solución seleccionada para estos casos fueron las redes neuronales artificiales (ANN). Dichas redes se desarrollaronhaciendo uso del software MATLAB R2018b (MathWorks, Massachusetts, USA).El estudio de la rodilla se centra en uno de los ligamentos clave en la estabilidad de la rótula y que, sin embargo, es uno de los menos analizados hasta ahora, el ligamento medial patelofemoral. La reconstrucción de este ligamento es la principal solución clínica para solventar esta inestabilidad y diferentes cirugías utilizadas para dicho fin han sido analizadas mediante el desarrollo de un modelo paramétrico en elementos finitos que permita su simulación. En este modelo es posible adaptar la geometría de la rodilla de forma que se puedan simular diferentes condiciones que pueden afectar a la estabilidad de la rótula, tales como la displasia troclear y la patella alta.El estudio de la región sacrolumbar se centra en el análisis de diferentes posibles configuraciones para las cirugías de fusión vertebral. El análisis se centró en la fijación con tornillos y la influencia del Polimetimetacrilato (PMMA) como elemento de fijación en las vértebras. Para ello, se reconstruyó el modelo óseo de diferentes pacientes que necesitaron este tipo de intervención. Sobre estos modelos se simularon mediante elementos finitos las diferentes configuraciones consideradas de forma que se pudiera comparar su comportamiento en diferentes casos.En el caso de la cadera, el estudio se centra en el análisis de la artroplastia total de cadera, que implica el reemplazo de la articulación anatómica por una prótesis habitualmente de titanio. Cuando este tipo de cirugías es realizado, es común que surjan posteriormente problemas derivados de la disposición de la prótesis y que pueden llevar al pinzamiento entre sus componentes y, en algunas ocasiones, su dislocación.Esto ocurre cuando el rango de movimiento de la articulación es reducido. Este tipo de sucesos son más comunes cuando se realizan los movimientos de extensión externa (EE) o de rotación interna (RI) de la extremidad. El estudio se desarrolló con el objetivo de elaborar una herramienta computacional capaz de predecir este choque y dislocación basándose en el diámetro de la cabeza del femur y de los ángulos de abducción y anteversión. Para ello, se recurrió al uso de redes neuronales artificales(ANN). Se configuró una red independiente para cada movimiento (EE y RI) y cada posible evento (pinzamiento y dislocación), de forma que se obtuvieron cuatro redes completamente independientes. Para el entrenamiento y primer testeo de las redes se recurrió a un modelo paramétrico en elementos finitos de la prótesis con el que se realizaron diferentes simulaciones determinando el rango de movimiento para cada caso. Finalmente, las redes fueron de nuevo validadas con el uso de datos procedentes de pacientes que sufrieron dislocación tras ser sometidos a este tipo de cirugías.Finalmente, el estudio de la región del tobillo se centró en la lesión de la sindesmosis del tobillo. Este tipo de lesiones implica la rotura de algunos de los ligamentos que unen los principales huesos de esta articulación (tibia, peroné y astrágalo) junto con parte de la membrana intraósea, que se extiende a lo largo de la tibia y el peroné ligando ambos huesos. Cuando se produce este tipo de lesiones, es necesario recurrir a la inclusión de elementos que fijen la articulación y prevengan la separación de los huesos. Los métodos más comunes y que centran este análisis comprenden la fijación con tornillos y la fijación mediante botón de sutura. Para poder realizar un análisis que permita comparar la efectividad y incidencia de este tipo de cirugías se recurrióa la reconstruccción 3D de la articulación de un paciente que sufrió este tipo de lesión. Con este modelo geométrico, se procedió al desarrollo de diferentes modelos en elementos finitos que incluyeran cada una de las alternativas consideradas. Las simulaciones de estos modelos junto a las situaciones anatómicas y lesionadas, permitió hacer una aproximación sobre la solución quirúrgica que mejor restablece el estado incial sano de la región afectada.Locomotor system surgeries represents more the 20 million interventions per year for the correction of injuries that affect muscles, joints, ligaments, tendons, bones or nerves; elements that form themusculoskeletal system. This kind of biomechanical affections may have several sources, being the main ones traumas, bones and soft tissues degenerative injuries, poor postural or motor habits and those of congenital source. The use of current technologies in the correction process for these injuries is part of the day-to-day in the operating rooms and the monitoring of patients. However, the use of computational tools that allow preoperative planning is still far from being part of the preoperative evaluation process in this kind of injuries. For this reason, the main goal of this thesis consists in demonstrating the viability of the use of computational tools in the preoperative planning of different orthopaedic surgeries. Among the most common surgeries, most of them focus in the lower body joints of the human anatomy. For this reason, this work will focus in the analysis of different surgeries whose purpose is to solve injuries in the main joints of the lower body: lumbosacral region, hip, knee and ankle. Some of the most commonly used computational tools, and whose capability in different fields has been widely proven, were used in order to be able of performing the analysis of these surgeries. 3D reconstruction has been used for obtaining anatomical models in which the viability of the surgeries could be verified. These reconstructions are based on the medical images obtained through Computerized Tomography (CT) or Magnetic Resonance Imaging (RMI). Images from RMI allow differentiating all the tissues of the anatomy, including soft ones such as tendons and cartilages; while CT scans make easier the bones differentiation. This last procedure is the most commonly used in diagnoses. For their analysis and reconstruction software Mimics v 20.0 and 3-Matic 11.0 (Materialise NV, Leuven, Belgium) were used. As alternative for the models generation when the necessary images for the reconstruction are not available or when flexibility is required for these models, modelling in the Finite Element Analysis software Abaqus/CAE v.6.14 (Dassault Syst‘emes, Suresnes, France) was used. This software was also used for the simulation of the effects of the different surgeries in the interest region. In order to perform the simulations, those parameters, elements and conditions necessary to represent the characteristics of each surgery were included. Finally, for those situations requiring data analysis, machine learning technologies were used. The selected solution for these cases were Artificial Neural Networks (ANN). These networks were developed using the software MATLAB R2018b (MathWorks, Massachusetts, USA). The study of the knee joint focuses in one of the key ligaments for the patellar stability and which, however, is one of the least analysed so far, the medial patellofemoral ligament. The reconstruction of this ligament is the main clinical solution for solving this instability and different surgeries used for that purpose have been analysed through the development of a finite element parametric model that allows their simulation. In this model adapting knee geometry is possible so that those conditions that can affect the stability of the patella, such as trochlear dysplasia or patella alta, can be simulated. The study of the lumbosacral region focuses in the analysis of different possible configurations for spine fusion surgeries. The analyses focused in the pedicle screws fixation and the influence of polymethyl methacrylate (PMMA) as fixation element in the vertebrae. To do this, osseous models for different patients that required this kind of intervention were reconstructed. The different configurations considered were simulated on these models through finite element analysis comparing their behaviour. In the case of the hip, the study focuses in the analysis of the total hip arthroplasty, which implies replacing the anatomical joint by a prosthesis, usually made of titanium. When this kind of surgery is performed, it is common for later issues arising from the arrangement of the prosthesis and which can lead to impingement between its components and, on some occasions, their dislocation. This happens when the range of movement of the joint is limited. This kind of events are more common when the external extension (EE) or internal rotation (IR) movements of the leg are performed. The study was developed with the goal of elaborating a computational tool able to predict the impingement and dislocation based on the diameter of the head of the femur and the anteversion and abduction angles. To do this, artificial neural networks (ANN) were used. An independent network was configured for each movement (EE and IR) and for each possible event (impingement and dislocation), so that four completely independent networks. For the training and the first testing of the networks, a parametric finite element model of the hip was used; with which different simulations were performed determining the range of movement for each case. Finally, the networks were validated again with the use of data proceeding from patients that suffered dislocation after going through this kind of surgery. Finally, the study of the ankle region focused in the ankle syndesmosis injury. This kind of injuries implies the tear of some ligaments that connect the main bones of the joint (tibia, fibula and talus) together with part of the intraosseous membrane, which extends along the tibia and fibula linking both bones. When this kind of injuries happens, it is necessary to resort to the inclusion of elements that fix the joint and prevent the bones distance. The most common methods, which focus this analysis, include the screws fixation and the suture button fixation. In order to carry out an analysis that allows comparing the effectiveness and incidence of this kind of surgeries, a 3D reconstruction of the joint from a patient that suffered this kind of injury was used. With this geometrical model, different finite element models including each of the considered alternatives were developed. The simulations of these models, together with the injured and anatomical situations, allowed an approximation of the surgical solution that better restores the initial healthy state of the affected region.<br /

    Biomechanical evaluation of predictive parameters of progression in adolescent isthmic spondylolisthesis: a computer modeling and simulation study

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    <p>Abstract</p> <p>Background</p> <p>Pelvic incidence, sacral slope and slip percentage have been shown to be important predicting factors for assessing the risk of progression of low- and high-grade spondylolisthesis. Biomechanical factors, which affect the stress distribution and the mechanisms involved in the vertebral slippage, may also influence the risk of progression, but they are still not well known. The objective was to biomechanically evaluate how geometric sacral parameters influence shear and normal stress at the lumbosacral junction in spondylolisthesis.</p> <p>Methods</p> <p>A finite element model of a low-grade L5-S1 spondylolisthesis was constructed, including the morphology of the spine, pelvis and rib cage based on measurements from biplanar radiographs of a patient. Variations provided on this model aimed to study the effects on low grade spondylolisthesis as well as reproduce high grade spondylolisthesis. Normal and shear stresses at the lumbosacral junction were analyzed under various pelvic incidences, sacral slopes and slip percentages. Their influence on progression risk was statistically analyzed using a one-way analysis of variance.</p> <p>Results</p> <p>Stresses were mainly concentrated on the growth plate of S1, on the intervertebral disc of L5-S1, and ahead the sacral dome for low grade spondylolisthesis. For high grade spondylolisthesis, more important compression and shear stresses were seen in the anterior part of the growth plate and disc as compared to the lateral and posterior areas. Stress magnitudes over this area increased with slip percentage, sacral slope and pelvic incidence. Strong correlations were found between pelvic incidence and the resulting compression and shear stresses in the growth plate and intervertebral disc at the L5-S1 junction.</p> <p>Conclusions</p> <p>Progression of the slippage is mostly affected by a movement and an increase of stresses at the lumbosacral junction in accordance with spino-pelvic parameters. The statistical results provide evidence that pelvic incidence is a predictive parameter to determine progression in isthmic spondylolisthesis.</p

    Finite element modelling of hybrid stabilization systems for the human lumbar spine

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    Intersomatic fusion is a very popular treatment for spinal diseases associated with intervertebral disc degeneration. The effects of three different hybrid stabilization systems on both range of motion and intradiscal pressure were investigated, as there is no consensus in the literature about the efficiency of these systems. Finite element simulations were designed to predict the variations of range of motion and intradiscal pressure from intact to implanted situations. After hybrid stabilization system implantation, L4-L5 level did not lose its motion completely, while L5-S1 had no mobility as a consequence of disc removal and fusion process. BalanC hybrid stabilization system represented higher mobility at the index level, reduced intradiscal pressure of adjacent level, but caused to increment in range of motion by 20% under axial rotation. Higher tendency by 93% to the failure was also detected under axial rotation. Dynesys hybrid stabilization system represented more restricted motion than BalanC, and negligible effects to the adjacent level. B-DYN hybrid stabilization system was the most rigid one among all three systems. It reduced intradiscal pressure and range of motion at the adjacent level except from motion under axial rotation being increased by 13%. Fracture risk of B-DYN and Dynesys Transition Optima components was low when compared with BalanC. Mobility of the adjacent level around axial direction should be taken into account in case of implantation with BalanC and B-DYN systems, as well as on the development of new designs. Having these findings in mind, it is clear that hybrid systems need to be further tested, both clinically and numerically, before being considered for common use

    Is there any advantage of using stand-alone cages? A numerical approach

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    Background: Segment fusion using interbody cages supplemented with pedicle screw fixation is the most common surgery for the treatment of low back pain. However, there is still much controversy regarding the use of cages in a stand-alone fashion. The goal of this work is to numerically compare the influence that each surgery has on lumbar biomechanics. Methods: A non-linear FE model of the whole lumbar spine was developed to compare between two types of cages (OLYS and NEOLIF) with and without supplementary fixation. The motion of the whole spine was analysed and the biomechanical environment of the adjacent segments to the operated one was studied. Moreover, the risk of subsidence of the cages was qualitatively evaluated. Results: A great ROM reduction occurred when supplementary fixation was used. This stiffening increased the stresses at the adjacent levels. It might be hypothesised that the overloading of these segments could be related with the clinically observed adjacent disc degeneration. Meanwhile, the stand-alone cages allowed for a wider movement, and therefore, the influence of the surgery on adjacent discs was much lower. Regarding the risk of subsidence, the contact pressure magnitude was similar for both intervertebral cage designs and near the value of the maximum tolerable pressure of the endplates. Conclusions: A minimally invasive posterior insertion of an intervertebral cage (OLYS or NEOLIF) was compared using a stand-alone design or adding supplementary fixation. The outcomes of these two techniques were compared, and although stand-alone cage may diminish the risk of disease progression to the adjacent discs, the spinal movement in this case could compromise the vertebral fusion and might present a higher risk of cage subsidence

    Alterations in lumbar spine mechanics due to degenerative disc disease

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    2010 Fall.Includes bibliographical references.Degenerative disc disease is a major source of low back pain. It is hypothesized to significantly alter the biomechanics of the lumbar spine both at the tissue and motion segment (multi-vertebral) levels. However, explicit correlations between the former and the latter has not been established, and this critical link is only possible through modeling the intervertebral disc tissue behavior within a constitutive framework and implementing it in a finite element model of the lumbar spine. In order to develop a better appreciation of the biomechanics of disc degeneration, the main objectives of this dissertation work were to investigate the degenerative disease related mechanical alterations on lumbar spine through finite element modeling and experimentation, and evaluate the contemporary treatment strategies. To meet this objective, a finite element model of the healthy human lumbar spine was generated based on computed tomography (CT) imagery. Mesh convergence was verified based on strain energy density predictions. Kinematic and mechanical predictions of clinical interest, including range of motion and intradiscal nuclear pressure, were validated under pure moment loading. The mechanical properties of healthy and degenerated annulus fibrosus tissue were quantified using an orthotropic continuum model, with empirical determination of the requisite material coefficients derived from biaxial and uniaxial tension tests. The resultant material models were implemented into the validated finite element model in order to simulate disc degeneration at the L3-L4 level. At the tissue level, degeneration was found to significantly increase the dispersion in the collagen fiber orientation and the nonlinearity of the fiber mechanical behavior. At the motion segment level, degeneration increased the mobility of the spine, with concomitant increases in the local stress predictions in the annulus and facet force transmission. Our results were in good agreement with the clinical findings of instability and injury to the intervertebral disc due to degeneration. Total disc replacement was also considered as a treatment option within the aforementioned finite element framework. The model predictions indicated that single and two-level disc replacement restored motion at the treated levels, while linearizing the kinematic response and increasing the facet force transmission. The data reflect that the successful surgical outcome is most likely obtained when maximum preservation of native disc tissue is achieved during implantation of the prosthetic device

    Finite element simulation of daily activities held by the intervertebral disc

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    The spine is a complex system, capable of maintaining stability and simultaneously performing movements and the lumbar region is fundamental for this ability. The present work aims to validate a Finite Elements (FE) model of a lumbar motion segment, through numerical simulation of the required mobility on the intervertebral disc, accordingly to some daily activities. For this study, only the simplest motion on the spine was simulated: flexion, extension and lateral bending. The biomechanical response of the FE model has proved to be suitable for predictions on flexion, but on extension and lateral flexion unexpected extension angles were obtained. These results showed the need of improvements in the mesh geometry, along with the introduction of a model considering of the external ligaments restraining effect, in order to get a more reliable and closer to reality simulation of the all biomechanical system
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