Human lumbar spine biomechanics: study of pathologies and new surgical procedures

This thesis aims to shed light on the process that undergoes the lumbar spine as a result of intervertebral disc degeneration and different lumbar surgeries, paying special attention on the main risk factors and how to overcome them. Low back pain is the leading musculoskeletal disorder in all developed countries generating high medical related costs. Intervertebral disc degeneration is one of the most common causes of low back pain. When conservative treatments fail to relieve this pain, lumbar surgery is needed and, in this regard, lumbar fusion is the \textquotedblleft gold standard\textquotedblright technique to provide stability and neural decompression.Degenerative disc disease has been studied through two different approaches. An in-vivo animal model was reproduced and followed-up with MRI and mechanical testing to see how the water content decreased while the stiffness of the tissue increased. Then, degeneration was induced in a single disc of the human lumbar spine and the effects on the adjacent disc were investigated by the use of the finite element models. Further on, different procedures for segmental fusion were computationally simulated. A comparison among different intersomatic cage designs, supplemented with posterior screw fixation or placed in a stand-alone fashion, showed how the supplementary fixation drastically decreased the motion in the affected segment increasing the risk of adjacent segment disease more than a single placed cage. However, one of the main concerns regarding the use of cages without additional fixation is the subsidence of the device into the vertebral bone. A parametric study of the cage features and placement pointed to the width, curvature, and position as the most influential parameters for stability and subsidence.Finally, two different algorithms for tissue healing were implemented and applied for the first time to predict lumbar fusion in 3D models. The self-repairing ability of the bone was tested after simple nucleotomy and after instrumentation with internal fixation, anterior plate or stand-alone intersomatic cage predicting, in agreement with previous animal and clinical studies, that instrumentation may be not necessary to promote segmental fusion. In particular, the intervertebral disc height was seen to play an important role in the bone bridge or osteophyte formation.To summarize, this thesis has focused in the main controversial issues of intervertebral disc degeneration and lumbar fusion, such as degenerative process, adjacent segment disease, segment stability, cage subsidence or bone bridging. All the models described in this thesis could serve as a powerful tool for the pre-clinical evaluation of patient-specific surgical outcomes supporting clinician decisions. This thesis aims to shed light on the process that undergoes the lumbar spine as a result of intervertebral disc degeneration and different lumbar surgeries, paying special attention on the main risk factors and how to overcome them. Low back pain is the leading musculoskeletal disorder in all developed countries generating high medical related costs. Intervertebral disc degeneration is one of the most common causes of low back pain. When conservative treatments fail to relieve this pain, lumbar surgery is needed and, in this regard, lumbar fusion is the \textquotedblleft gold standard\textquotedblright technique to provide stability and neural decompression. Degenerative disc disease has been studied through two different approaches. An in-vivo animal model was reproduced and followed-up with MRI and mechanical testing to see how the water content decreased while the stiffness of the tissue increased. Then, degeneration was induced in a single disc of the human lumbar spine and the effects on the adjacent disc were investigated by the use of the finite element models. Further on, different procedures for segmental fusion were computationally simulated. A comparison among different intersomatic cage designs, supplemented with posterior screw fixation or placed in a stand-alone fashion, showed how the supplementary fixation drastically decreased the motion in the affected segment increasing the risk of adjacent segment disease more than a single placed cage. However, one of the main concerns regarding the use of cages without additional fixation is the subsidence of the device into the vertebral bone. A parametric study of the cage features and placement pointed to the width, curvature, and position as the most influential parameters for stability and subsidence. Finally, two different algorithms for tissue healing were implemented and applied for the first time to predict lumbar fusion in 3D models. The self-repairing ability of the bone was tested after simple nucleotomy and after instrumentation with internal fixation, anterior plate or stand-alone intersomatic cage predicting, in agreement with previous animal and clinical studies, that instrumentation may be not necessary to promote segmental fusion. In particular, the intervertebral disc height was seen to play an important role in the bone bridge or osteophyte formation. To summarize, this thesis has focused in the main controversial issues of intervertebral disc degeneration and lumbar fusion, such as degenerative process, adjacent segment disease, segment stability, cage subsidence or bone bridging. All the models described in this thesis could serve as a powerful tool for the pre-clinical evaluation of patient-specific surgical outcomes supporting clinician decisions. <br /

Biomechanical Comparison between Stand-alone Interbody Cages and their Benefits over Posterior Screw Fixation

Lumbar pain is one of the most common problems of population. Far too often it is caused by ageing and degeneration of intervertebral discs. Fusion techniques, as arthrodesis which used screw fixation, were the first surgeries used to avoid lumbar pathologies. However, arthrodesis reduced dramatically the spine movement.Stand-alone cage is a minimally invasive surgery alternative to lumbar fusion with posterior fixation. Despite their previous reported successful results (Ahmadian et al., 2014) some physicians continue questioning their effectiveness because of the risk of spine destabilization and cage migration (Oxland et al., 2000).The purpose of this research was to demonstrate that stand-alone cages introduced in a minimally invasive way are a good surgical solution for the IVD diseases.This main goal has been divided into three different partial goals: prove spinal stability, show the decompression on the neural region and compare the effects over the adjacent discs with and without posterior fixation. It is also of the interest of this work to compare between cage designs based on the above mentioned criteria

In silico study of cuspid' periodontal ligament damage under parafunctional and traumatic conditions of whole-mouth occlusions. A patient-specific evaluation

Background and objective: Although traumatic loading has been associated with periodontal ligament (PDL) damage and therefore with several oral disorders, the damage phenomena and the traumatic loads involved are still unclear. The complex composition and extremely thin size of the PDL make experimentation difficult, requiring computational studies that consider the macroscopic loading conditions, the microscopic composition and fine detailed geometry of the tissue. In this study, a new methodology to analyse the damage phenomena in the collagen network and the extracellular matrix of the PDL caused by parafunctional and traumatic occlusal forces was proposed. Methods: The entire human mandible and a portion thereof containing a full cuspid tooth were separately modelled using finite element analysis based on computed tomography and micro-computed tomography images, respectively. The first model was experimentally validated by occlusion analysis and subjected to the muscle loads produced during hard and soft chewing, traumatic cuspid occlusion, grinding, clenching, and simultaneous grinding and clenching. The occlusal forces computed by the first model were subsequently applied to the single tooth model to evaluate damage to the collagen network and the extracellular matrix of the PDL. Results: Early occlusal contact on the left cuspid tooth guided the mandible to the more occluded side (16.5% greater in the right side) and absorbed most of the lateral load. The intrusive occlusal loads on the posterior teeth were 0.77–13.3% greater than those on the cuspid. According to our findings, damage to the collagen network and the extracellular matrix of the PDL could occur in traumatic and grinding conditions, mainly due to fibre overstretching (>60%) and interstitial fluid overpressure (>4.7 kPa), respectively. Conclusions: Our findings provide important biomechanical insights into the determination of damage mechanisms which are caused by mechanical loading and the key role of the porous-fibrous behaviour of the PDL in parafunctional and traumatic loading scenarios. Besides, the 3D loading conditions computed from occlusal contacts will help future studies in the design of new orthodontics appliances and encourage the application of computing methods in medical practice

The macular retinal ganglion cell layer as a biomarker for diagnosis and prognosis in multiple sclerosis: A deep learning approach

AbstractPurposeThe macular ganglion cell layer (mGCL) is a strong potential biomarker of axonal degeneration in multiple sclerosis (MS). For this reason, this study aims to develop a computer‐aided method to facilitate diagnosis and prognosis in MS.MethodsThis paper combines a cross‐sectional study of 72 MS patients and 30 healthy control subjects for diagnosis and a 10‐year longitudinal study of the same MS patients for the prediction of disability progression, during which the mGCL was measured using optical coherence tomography (OCT). Deep neural networks were used as an automatic classifier.ResultsFor MS diagnosis, greatest accuracy (90.3%) was achieved using 17 features as inputs. The neural network architecture comprised the input layer, two hidden layers and the output layer with softmax activation. For the prediction of disability progression 8 years later, accuracy of 81.9% was achieved with a neural network comprising two hidden layers and 400 epochs.ConclusionWe present evidence that by applying deep learning techniques to clinical and mGCL thickness data it is possible to identify MS and predict the course of the disease. This approach potentially constitutes a non‐invasive, low‐cost, easy‐to‐implement and effective method

Estudio y simulación mediante software de elementos finitos de las diferentes cirugías de disco intervertebral

La motivación principal de este proyecto es el estudio mediante técnicas ingenieriles de problemas asociados a la biomedicina, con el propósito de mejorar la calidad de vida de las personas que deben someterse a operaciones de implantes protésicos. Su finalidad fundamental es la determinación de la cirugía más adecuada a aplicar a un paciente aquejado de dolores lumbares. En primer lugar se ha modificado el modelo de elementos finitos de la columna lumbar desarrollada por Moramarco (1) validandolo con los datos existentes el la bibliografía (2). Este modelo supone una mejora significativa con respecto a los modelos computacionales que existentes ya que incorpora la geometría no sólo de vértebras y discos, sino de ligamentos y fibras en los tejidos, necesarios para la simulación correcta del movimiento. A continuación se ha simulado la degeneración del disco D45, variando sus propiedades y comparando los resultados con los efectos reales de la degeneración. Tras ver los problemas de las patologías lumbares se han realizado diferentes modelos en elementos finitos que permitan modelar las diferentes cirugías existentes, como son la artrodesis y los implantes intervertebrales con fijación posterior mediante tornillos. Una vez realizado el cálculo computacional de estos modelos se establece, por comparación con la columna lumbar sana, que disminuyen drásticamente el movimiento relativo en el segmento intervenido. Esta disminución de movimiento, conlleva un incremento de giro relativo en el resto de segmentos, lo cual provoca un aumento de tensiones. El incremento de tensiones en los discos adyacentes, puede provocar dolor y aumentar la probabilidad de propagación de la degeneración. Con el objetivo de conseguir una técnica quirúrgica que respete el movimiento natural de la columna, se ha simulado una cirugía en la que únicamente se introduzca el espaciador intervertebral, sin fijación posterior. Viendo los resultados de esta nueva técnica se concluye que aunque la fijación mediante tornillos consigue una perfecta estabilización de la columna, la mejor técnica desde el punto de vista biomecánico es el implante sin fijación posterior, que consigue estabilizar la columna sin modificar drásticamente el movimiento natural del paciente

Simulación por EF de la mecánica de la masticación

El presente proyecto trata sobre la simulación por elementos finitos de la acción de masticación de una mandíbula perteneciente a una mujer adulta, en la etapa final de cierre, es decir, cuando los dientes del maxilar inferior y los del maxilar superior están en contacto. No solamente se realizará el estudio para una persona sana que puede hacer uso de todos los músculos que intervienen en la acción de masticación (maseteros y temporales), sino que también se barajarán hipótesis con sus respectivas pruebas y estudios para distintos casos en los que dichos músculos estuvieran afectados, ya sea por algún tipo de traumatismo, parálisis, etc

Estudio por elementos finitos de un puente de carretera

El objetivo de este proyecto es el cálculo de un puente de hormigón armado. En esta memoria se describe un modelado geométrico del puente, y una simulación por elementos finitos, registrando los valores obtenidos de tensión y deformación, y para finalmente proponer una armadura lo más realista posible. Se considerarán diferentes hipótesis de carga. Se compararán los resultados obtenidos, y se emplearán los casos más desfavorables para dimensionar la estructura. La estructura en sí, es un puente de carretera situado en la variante de la carretera A-130 de Monzón a Ontiñena en Pomar de Cinca (Huesca). El modelado se ha realizado con el programa informático de elementos finitos, Ansy

Neuro-occlusal stimulation, a crucial effect on the asymmetric development of the paediatric stomatognathic system.: A 3D morphological and insilico study.

A statistical study of the relationship between the neuro-occlusal stimulus produced in paediatric patients with unilateral bitting and the abnormal stomatognathic system growth is proposed to improve early treatments and avoid surgical treatments later in life. Therefore, 3D morphological and finite element analyses were performed to study malformations and function imbalances, respectively

Desarrollo de autorizaciones de uso en pórticos triarticulados

El proyecto consiste en la realizacion de las autorizaciones de uso para los pórticos triarticulados prefabricado

Estudio por elementos finitos de la biomecánica lumbar humana. Análisis de la degeneración discal

El dolor lumbar es una de las patologías crónicas más extendidas. Se dice que aproximadamente el 80% de la población va a padecer dolor lumbar o va a desarrollar una patología discal en algún momento de su vida. Algunos estudios clínicos han demostrado que el 90% de las patologías de la columna vertebral están localizadas en la columna lumbar. El uso de modelos matemáticos y simulación computacional puede servir de base para predecir la aparición y evolución de patologías lumbares. Por tanto, la metodología seguida para desarrollar este proyecto ha sido por medio de modelos computacionales de elementos finitos que pretenden simular la respuesta de los discos intervertebrales frente a distintos estados de carga y distintas patologías. Los discos intervertebrales están compuestos por tejido cartilaginoso y constan de tres regiones diferenciadas. La región interna o núcleo pulposo, una estructura altamente hidrofílica capaz de soportar el 75% de la carga, distribuyendo los esfuerzos de forma horizontal al anillo. La región externa del disco o anillo fibroso, compuesta por capas concéntricas de fibras de colágeno (cuya rigidez aumenta en las capas más exteriores) que encierran al núcleo. Y la placa terminal compuesta por una fina capa de cartílago hialino que separa el disco del cuerpo vertebral. La porosidad y permeabilidad de cada una de las partes del disco juegan un papel fundamental en su comportamiento. Debido a estas características del disco se consideran tres modelos distintos para la simulación del anillo fibroso: un primer modelo porohiperelástico fibrado en el que se incluye el caracter hidrofílico de los discos intervertebrales, un segundo modelo porohiperelástico no fibrado y un último modelo poroelástico. Se analizan cada modelo en función de los distintos discos lumbares y de la patología discal. Por otro lado, los 3 créditos ECTS correspondientes a trabajo clínico o de usuario final, han sido realizados en una empresa I+D de biotecnología (Alphasip S.L.). Estas prácticas están íntimamente relacionadas con las asignaturas de "caracterización nanométrica en biomedicina y nanosensores" y "sistemas de liberación de fármacos" impartidas en el master de Ingeniería Biomédica. El trabajo desempeñado en dicha empresa ha sido el siguiente: - Colaboración en la fabricación de biosensores de diagnóstico molecular. - Estudio del funcionamiento y correcta funcionalización de nanotubos de carbono en chips. - Control de calidad y stock de los biosensores. - Tratamiento y análisis de datos electrónicos. - Elaboración de programas informáticos para automatizar los análisis de datos. - Apoyo técnico. - Reuniones con científicos nacionales e internacionales así como con empresas privadas