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

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

Structural health monitoring using ultrasonic guided-waves and the degree of health index

This paper proposes a new damage index named degree of health (DoH) to efficiently tackle structural damage monitoring in real-time. As a key contribution, the proposed index relies on a pattern matching methodology that measures the time-of-flight mismatch of sequential ultrasonic guided-wave measurements using fuzzy logic fundamentals. The ultrasonic signals are generated using the transmission beamforming technique with a phased-array of piezoelectric transducers. The acquisition is carried out by two phased-arrays to compare the influence of pulse-echo and pitch-catch modes in the damage assessment. The proposed monitoring approach is illustrated in a fatigue test of an aluminum sheet with an initial notch. As an additional novelty, the proposed pattern matching methodology uses the data stemming from the transmission beamforming technique for structural health monitoring. The results demonstrate the efficiency and robustness of the proposed framework in providing a qualitative and quantitative assessment for fatigue crack damage

Señal ultrasónica guiada de monitorización de fatiga en placa metálica

Corresponding author: Dr. Sergio Cantero Chinchilla. [email protected] // [email protected] Involved institutions: University of Nottingham (UK), University of the Basque Country (ES), Technological Institute of Aragón (ES), University of Granada (ES).Ultrasonic guided-wave test data taken from a fatigue test experiment over a notched aluminium plate. Data summary.- Ultrasonic guided-wave test data: Frequency of excitation: 300 kHz (radial mode of vibration) Shape: sinusoid of 4 cycles Amplitude: 45 Vpp Sampling frequency: 60 kHz Fatigue test data.- Load type: Tension-Tension (using Instron 8850 servo-hydraulic fatigue testing machine) Minimum load: 1kN Maximum load: 10kN Frequency: 6Hz Number of cycles: 100 000 Specimen information.- Aluminum plate Alloy: QQA250/5 ‘O’ 2024 Dimensions: 245mm x 500mm x 1mm Central notch length: 22.5mm (centered with respect to the test sample centerline and machined using a laser cutting procedure) Further description.- The fatigue test has been performed using a middle tension [M(T)] specimen with a centered crack and loaded in tension using a positive loading ratio. A fatigue pre-cracking procedure was applied to develop a fresh and straight crack front to mitigate the effect of the machined started notch. The detection and monitoring of the crack onset and growth was carried out using two phased-arrays of six piezoelectric wafer active sensors (PWAS), one set as transmitter, the other as receiver. Piezoelectric ceramic disc transducers of 7mm diameter and 0.5mm thickness have been used in this fatigue test. They PWAS were placed symmetrically with regards to the sample centerline and bonded to the aluminum surface using a 3M Scotch-Weld DP490 epoxy adhesive (TradeMarks). File naming convention: “P_AL_S01_BF6.mat” or “P_AL_S01_BF6_XXX.mat” with XXX=1000, 2000, 3000, 100 000; P stands for Plate; AL stands for Aluminum; S01 stands for specimen 01; BF6 stands for Beamforming using 6 transducers; XXX are the number of cycles at which the fatigue test stopped and the ultrasonic guided-wave tests were performed (every 1000 fatigue cycle). Note 1: The file “P_AL_S01_BF6.mat” contains the data with the structure in pristine state. Note 2: The files “P_AL_S01_BF6_XXX.mat” contains the data after XXX fatigue cycles. Further details about the internal data structure of the MAT-files included within the Readme file within the dataset