Analysis of the passive biomechanical behavior of a sheep-specific aortic artery in pulsatile flow conditions.

In this work, a novel numerical-experimental procedure is proposed, through the use of the Cardiac Simulation Test (CST), device that allows the exposure of the arterial tissue to in-vitro conditions, mimicking cardiac cycles generated by the heart. The main goal is to describe mechanical response of the arterial wall under physiological conditions, when it is subjected to a variable pressure wave over time, which causes a stress state affecting the biomechanical behavior of the artery wall. In order to get information related to stress and strain states, numerical simulation via finite element method, is performed under a condition of systolic and diastolic pressure. The description of this methodological procedure is performed with a sample corresponding to a sheep aorta without cardiovascular pathologies. There are two major findings: the evaluation of the mechanical properties of the sheep aorta through the above-mentioned tests and, the numerical simulation of the mechanical response under the conditions present in the CST. The results state that differences between numerical and experimental circumferential stretch in diastole and systole to distinct zones studied do not exceed 1%. However, greater discrepancies can be seen in the distensibility and incremental modulus, two main indicators, which are in the order of 30%. In addition, numerical results determine an increase of the principal maximum stress and strain between the case of systolic and diastolic pressure, corresponding to 31.1% and 14.9% for the stress and strain measurement respectively; where maximum values of these variables are located in the zone of the ascending aorta and the aortic arch.

Short CRP for Anterior Canalithiasis: A New Maneuver Based on Simulation With a Biomechanical Model.

Introduction/Objective: Anterior canalithiasis is an uncommon and challenging diagnosis. This is due in part to the difficulty of defining the affected side, the extreme positioning required to carry out described therapeutic maneuvers, and the infrequent use of specific maneuvers. Our objective is to present a new treatment alternative for anterior canalithiasis which is based on the well-known canalith repositioning procedure (CRP) described by Epley and which is used routinely in the treatment of both posterior and anterior canalithiasis. Analysis of the standard CRP for anterior canalithiasis with a biomechanical model validates that this new maneuver is an enhanced treatment option for anterior canalithiasis. We call the new maneuver the "short CRP." Methods: A previously published 3D biomechanical model of the human labyrinths for the study of BPPV was used to analyze the conventional CRP in the treatment of anterior canalithiasis. The expected position of free otoliths near the anterior ampulla of the anterior semicircular duct was followed while recreating the sequential positions of the CRP. Although the standard CRP was possibly effective, certain enhancements were evident that could increase successful repositioning. These enhancements were incorporated into the modification of the CRP presented here as the "short CRP" for anterior canalithiasis. Results: The traditional CRP used for posterior canalithiasis can also be used for anterior canalithiasis. Although in the traditional CRP the head hangs 30° below horizontal, our simulation shows that a 40° head-hang below horizontal is an enhancement and may ensure progression of anterior otolith debris. Elimination of Position 4 of the classic CRP, in which the face is turned 45° toward the floor, was also seen as an enhancement as this position is predicted to cause retrograde movement of otoliths back into the anterior canal if the patient tucks the chin in position 4 or when sitting up. Conclusion: A modification of the CRP called the "short CRP" can be used to treat anterior canalithiasis. Model analysis predicts possible increased efficacy over the standard CRP. Model analysis of existing BPPV treatments is a valuable exercise for examination and can lead to realistic enhancements in patient care.

Biomechanical Evaluation With a Novel Cadaveric Model Using Supination and Pronation Testing of a Lisfranc Ligament Injury.

BACKGROUND: Lisfranc joint injuries can be due to direct or indirect trauma and while the precise mechanisms are unknown, twisting or axial force through the foot is a suspected contributor. Cadaveric models are a useful way to evaluate injury patterns and models of fixation, but a frequent limitation is the amount of joint displacement after injury. The purpose of this study was to test a cadaveric model that includes axial load, foot plantarflexion and pronation-supination motion, which could re-create bone diastasis similar to what is seen in subtle Lisfranc injuries. Our hypothesis was that applying pronation and supination motion to a cadaveric model would produce reliable and measurable bone displacements. METHODS: Twenty-four fresh-frozen lower leg cadaveric specimens were used. The medial (C1) and intermediate (C2) cuneiforms and the first (M1) and second (M2) metatarsal bones were marked. A complete ligament injury was performed between C1-C2 and C1-M2 in 12 specimens (group 1), and between C1-C2, C1-M2, C1-M1, and C2-M2 in 12 matched specimens (group 2). Foot pronation and supination in addition to an axial load of 400 N was applied to the specimens. A 3D digitizer was used to measure bone distances. RESULTS: After ligament injury, distances changed as follows: C1-C2 increased 3 mm (23%) with supination; C1-M2 increased 4 mm (21%) with pronation (no differences between groups). As expected, distances between C1-M1 and C2-M2 only changed in group 2, increasing 3 mm (14%) and 2 mm (16%), respectively (no differences between pronation and supination). M1-M2 and C2-M1 distances did not reach significant difference for any condition. CONCLUSIONS: Pronation or supination in addition to axial load produced measurable bone displacements in a cadaveric model of Lisfranc injury using sectioned ligaments. Distances M1-M2 and C2-M1 were not reliable to detect injury in this model. CLINICAL RELEVANCE: This new cadaveric Lisfranc model included foot pronation-supination in addition to axial load delivering measurable bone diastasis. It was a reliable Lisfranc cadaveric model that could be used to test different Lisfranc reconstructions.

Avaliação biomecânica das lesões ligamentares do complexo articular de Lisfranc: novo modelo cadavérico utilizando estresse em supinação e pronação / Biomechanical evaluation of ligament injuries of the Lisfranc joint complex: new cadaveric model using stress in supination and pronation

Introdução: as lesões no complexo articular de Lisfranc ocorrem devido a trauma direto ou indireto, no qual forças de torção ou axiais são transmitidas ao pé. Os modelos cadavéricos são úteis para avaliar padrões de lesões e modelos de fixação, mas frequentemente a quantidade de deslocamento articular após a lesão torna-se um limitador. O objetivo deste estudo foi testar um modelo cadavérico que inclui carga axial, flexão plantar do pé e movimentos de pronação-supinação, recriando diástase óssea semelhante ao observado em lesões sutis de Lisfranc na prática clínica. Nossa hipótese é de que a aplicação do movimento de pronação e supinação em um modelo cadavérico produziria deslocamentos ósseos confiáveis e mensuráveis. Métodos: foram utilizadas 24 amostras cadavéricas frescas congeladas amputadas abaixo do nível do joelho. Os ossos cuneiformes medial e intermédio, o primeiro e o segundo metatarsos, foram marcados. Uma lesão ligamentar completa foi realizada entre os cuneiformes medial e intermédio e entre o cuneiforme medial e o segundo metatarso em 12 amostras (grupo 1) e adicionou-se a lesão dos ligamentos entre o primeiro metatarso e o cuneiforme medial e entre o segundo metatarso e o cuneiforme intermédio em 12 amostras correspondentes (grupo 2). Pronação e supinação do pé, além de uma carga axial de 400 N, foram aplicadas às amostras, utilizando-se o Instrom Testing Machine. Um digitalizador tridimensional (3D) foi utilizado para medir as distâncias entre os ossos. Resultados: para o grupo de lesão parcial (grupo 1), as distâncias referentes aos ossos nos quais os ligamentos foram seccionados apresentaram aumento na condição lesionada tanto em pronação quanto em supinação, como esperado. Em relação à distância entre o cuneiforme intermédio e o primeiro metatarso e entre o primeiro e o segundo metatarsos, observou-se diminuição na condição lesionada em pronação e aumento em supinação. Para o grupo de lesão completa (grupo 2), as distâncias referentes aos locais de secção dos ligamentos apresentaram aumento na condição lesionada tanto em pronação quanto em supinação, como esperado. No tocante à distância entre o cuneiforme intermédio e o primeiro metatarso e entre o primeiro e o segundo metatarsos, verificou-se o mesmo padrão de comportamento das lesões parciais. Conclusão: o modelo biomecânico cadavérico para lesões do complexo articular de Lisfranc desenvolvido neste estudo simula o mecanismo de estresse clínico da lesão e o tipo de lesão mais comum, exibe variações de distâncias fidedignas e mensuráveis e foi desenvolvido para permitir o teste do tratamento da lesão sem interferência nos dispositivos de aferição, podendo se constituir em excelente método para a comparação de técnicas de fixação das lesões ligamentares tarsometatarsais.

Introduction: Lesions in the Lisfranc joint complex occur due to direct or indirect trauma, where a torsional or axial force is transmitted to the foot. Cadaveric models are a useful way to assess injury patterns and fixation models, but a frequent limitation is the amount of joint dislocation after injury. The aim of this study was to test a cadaveric model that includes axial load, plantar flexion of the foot and pronation-supination movement, recreating bone diastasis similar to that observed in subtle Lisfranc lesions in clinical practice. Our hypothesis is that the application of pronation and supination motion in a cadaveric model would produce reliable and measurable bone displacements. Methods: Twenty-four fresh frozen cadaveric leg samples were used. The medial (C1) and intermediate (C2) cuneiform bones, the first (M1) and second (M2) metatarsal bones were marked. A complete ligament injury was performed between C1-C2 and C1-M2 in 12 samples (Group 1) and between C1-C2, C1-M2, C1-M1 and C2-M2 in 12 corresponding samples (Group 2). Foot pronation and supination, in addition to an axial load of 400 N, were applied to the samples. A 3D scanner was used to measure the distances between the bones. Results: For the partial lesion group (Group 1), in which the ligaments between C1-C2 and C1-M2 were injured, these distances increased in the injured condition in both pronation and supination, as expected. Regarding the distance C2-M1 and M1-M2, there was a decrease in the injured condition in pronation and an increase in supination. For the complete lesion group (Group 2), in which the ligaments between C1-C2, C1-M2, C1-M1, and C2-M2 were injured, these distances increased in injured condition both in pronation and supination, as expected. Regarding the behavior of distances C2-M1 and M1-M2, the same behavior pattern was observed as in partial injuries. Conclusion: The cadaveric biomechanical model for Lisfranc joint complex injuries developed in this study simulates the mechanism of clinical stress of the lesion and the most common type of lesion, exhibits reliable and measurable distances, and allows lesion treatment without compromise, being, possibly, an excellent method for comparing tarsometatarsal ligament injury fixation methods.

Tomografía computarizada y sólidos virtuales para obtener modelos biomecánicos computacionales / Computed tomography and virtual solids to obtain computational biomechanical models

Uno de los padecimientos más comunes de los huesos es la fractura, definida como la pérdida de la continuidad del material óseo. Implantes y prótesis son utilizados para tratar algunas de ellas. Actualmente, antes de usar uno de estos dispositivos, se prueban modelos virtuales de los mismos utilizando un programa de diseño asistido por computadora. Para dichas pruebas, se requieren también modelos virtuales de los huesos. Los modelos óseos son obtenidos aplicando técnicas de segmentación de imágenes a las tomografías computarizadas (TC). Este trabajo presenta un procedimiento para la obtención de modelos biomecánicos hueso-implante a partir de las TCs y sólidos virtuales, teniendo en cuenta la estructura real de los huesos, compuesta de tejido cortical y trabecular. Para realizar los análisis de verificación del procedimiento se utilizó un modelo de un implante DHS y de una prótesis de cadera(AU)

One of the most common bone conditions is fracture, defined as the loss of the continuity of the bone material. Implants and prostheses are used to treat some of them. Currently, before using one of these devices, virtual models are tested using a computer-aided design program. For these tests, virtual models of the bones are also required. Bone models are obtained by applying image segmentation techniques to computed tomography (CT). This paper presents a procedure for obtaining biomechanical bone-implant models from the CTs and virtual solids, taking into account the real structure of the bones, composed of cortical and trabecular tissue. A DHS implant model and a hip prosthesis were used to perform the procedure verification tests(AU)

Mechanical characterisation of Dacron graft: Experiments and numerical simulation.

Experimental and numerical analyses focused on the mechanical characterisation of a woven Dacron vascular graft are presented. To that end, uniaxial tensile tests under different orientations have been performed to study the anisotropic behaviour of the material. These tests have been used to adjust the parameters of a hyperelastic anisotropic constitutive model which is applied to predict through numerical simulation the mechanical response of this material in the ring tensile test. The obtained results show that the model used is capable of representing adequately the nonlinear elastic region and, in particular, it captures the progressive increase of the rigidity and the anisotropy due to the stretching of the Dacron. The importance of this research lies in the possibility of predicting the graft׳s mechanical response under generalized loading such as those that occur under physiological conditions after surgical procedures.

ANÁLISIS BIOMECÁNICO DE LA EPIFISIOLISIS DE LA CABEZA FEMORAL: COMPARACIÓN ENTRE FÉMURES SANOS Y ENFERMOS

En este trabajo se desarrolla un análisis por elementos finitos cuyo objetivo principal es determinar las diferencias de tensiones en la placa de crecimiento que se producen entre fémures sanos, con epifisiolisis unilateral y con epifisiolisis bilateral, para evaluar sus posibles causas. Se elaboraron los modelos de elementos finitos correspondientes a 45 pacientes. Los resultados mostraron un patrón de esfuerzos similar en todos los grupos de fémures y, además, la aparición de tensiones mayores en el grupo con epifisiolisis con respecto al grupo control. Se observó también que el valor del ángulo axial-fisis dependía significativamente del tipo de fémur analizado, y, además, una mayor influencia de los factores geométricos en la incidencia de la enfermedad, en comparación con la del índice de masa corporal.

In this work, a finite element analysis (FEA) is accomplished to study the differences of stresses in the growth plate, that are produced in healthy and unhealthy femurs, and to evaluate the possible causes of this illness. Finite element models of 45 patients were developed. The results demonstrated a similar pattern of stresses in all the groups of femurs and also the appearance of greater stresses in the group with slipped capital femoral epiphysis than in the control group. It was also observed a strong dependency on the value of the axial-fisis angle from the group of femur analyzed and a bigger influence of the geometric factors than of the body mass index, in the incidence of the illness.