Abstract Background: The mechanical fixation of the spine in patients with osteoporotic vertebral degeneration is a challenge for surgeons, the vertebrae selected to insert the screws may fail, endangering health and even patient's life. Objective: The objective of the study was to study the effect of the variation of the bone density in the bone-screw interface from a three-dimensional model of the lumbar section. Materials and methods: The finite element method was used to model the behavior of the lumbar vertebral section when applying compression loads. Results: The stresses between 2 and 3 MPa were located on the contact surface with the screw, both in the vertebral body and in the apophysis, being slightly higher in the vertebral body. Conclusions: Regardless of bone density, the contact zones between the screws are susceptible to bone tissue failure. The posterior half of the vertebral body was the most sensitive to high values of stress, while in the areas furthest from the axis of the screw stress tended to their minimum.

Resumen Introducción: La fijación mecánica de la columna en pacientes con degeneración vertebral osteoporótica es un reto para los cirujanos, pues las vértebras seleccionadas para insertar los tornillos pueden fallar, poniendo en peligro la salud y la vida del paciente. Objetivo: Estudiar el efecto de la variación de la densidad ósea en la interfase hueso-tornillo, a partir de un modelo tridimensional de la sección lumbar. Materiales y métodos: Se emplea el método de los elementos finitos para modelar el comportamiento de la sección vertebral lumbar al aplicar cargas de compresión. Resultados: Los esfuerzos entre 2 y 3 MPa se ubicaron en la superficie de contacto con el tornillo, tanto en el cuerpo vertebral como en la apófisis, siendo ligeramente superiores en el cuerpo vertebral. Conclusiones: Independientemente de la densidad ósea, las zonas de contacto entre el tornillo son susceptibles al fallo del tejido óseo, debido a que están próximos al esfuerzo de fallo óseo de 2.37 ± 1.14 MPa reportado en la literatura. La mitad posterior del cuerpo vertebral fue la más sensible a sufrir valores altos de esfuerzos, mientras que en las zonas más alejadas del eje del tornillo los esfuerzos tendieron a su magnitud mínima.

Abstract The calcaneo-stop implant for the children´ flatfoot correction is a common treatment method. The objective of the paper is to determine the behavior of the calcaneo-stop by using two biocompatible materials. The Finite Element Method (FEM) was used. The materials analyzed were AISI 316L steel and Ti-6Al-4V titanium alloy. It was considered in the definition of the load model the biomechanics of the foot and the weight of boys and girls of 10 and 12 years old by using the Cuban anthropometric model. It was obtained that the implant´s model guarantees the mechanical resistance for both investigated materials. The difference between the two stresses was 4.44 MPa, which represented a percentage difference of 5%. Both materials had enough reserve in their tensional behavior since their stress was lower than the yield stress of each material, and they guarantee the mechanical resistance of the calcaneus stop design.

Resumen Uno de los métodos de corrección del pie plano en los niños es mediante el implante calcáneo-stop. El objetivo del trabajo fue determinar el comportamiento del calcáneo stop al emplear dos materiales bio-compatibles en su fabricación. Se utilizó el Método de Elementos Finitos (MEF). Los materiales analizados fueron el acero AISI 316L y la aleación de titanio Ti-6Al-4V. Las cargas fueron calculadas teniendo en cuenta la biomecánica del pie y el peso de niños y niñas de 10 y 12 años utilizando el modelo antropométrico cubano. Se obtuvo como resultado que el modelo del implante garantiza la resistencia mecánica para ambos materiales investigados. La diferencia entre ambas tensiones es de 4,44 MPa, lo que representa una diferencia porcentual del 5 %. Ambos materiales poseen reserva suficiente en su resistencia mecánica, pues son menores las tensiones máximas que el límite elástico del material y garantizan la resistencia mecánica del diseño de calcáneo-stop

RESUMO: Os cavalos com claudicação modificam o comportamento do andamento. Porém, uma leve modificação pode não ser identificada clinicamente. O objetivo desta pesquisa foi caracterizar as fases do andamento normal dos cavalos através da combinação de fotogrametria e acelerometria, para identificar alterações estruturais ou funcionais nos membros. O estudo foi conduzido em 23 cavalos Warmblood machos adultos. A partir da fotogrametria foi possível obter as variáveis cinemáticas das extremidades e a trajetória dos marcadores ao longo do tempo. Por outro lado, os acelerômetros triaxiais foram usados para capturar as componentes ortogonais da aceleração. Determinou-se que apenas 10 cavalos mostraram um padrão de marcha normal, e houve uma correspondência de 43% entre pareceres dos peritos e as técnicas de diagnóstico. De acordo com a classificação das fases da marcha de Stashak, as fases do ciclo da extremidade anterior foram 34/4/8/13/41 enquanto para a extremidade posterior foram 54/11/8/8/19. A amplitude de movimento (ROM) de pescoço, joelho e sesamóide foram 45,52±5,63°, 196,04±19,7° e 209±11,52°, respectivamente. Uma combinação dos métodos experimentais foi utilizada para identificar as fases do ciclo de marcha de cavalos saudáveis. Constatou-se correspondência na localização dos pontos de deslocamento máximo do membro com ambas as técnicas. A informação mais detalhada do movimento dos membros foi obtida usando a acelerometria. Estes métodos são aplicáveis em outras condições, quer a campo ou no laboratório.

ABSTRACT: Horses with lameness modify gait behavior, but when it is subtle, it may not be possible to identify it clinically. The objective of this research is to characterize the normal gait phases of walking Warmblood horses by combining photogrammetry and accelerometry to monitor lameness to indicate a structural or functional disorder in the extremities. The study was conducted in 23 adult male Warmblood horses. Photogrammetry was used to identify the kinematic variables of the limbs and the markers path over time; triaxial accelerometers were used to capture the orthogonal acceleration components. It was determined that only 10 horses showed a normal gait pattern, there was a 43% correspondence between the expert´s judgment and the diagnostic techniques. According to the Stashak classification of the gait phases, cycle phases to forelimb were 34/4/8/13/41, while for hind limb were 54/11/8/8/19 (% of the stride). The range of motion (ROM) of the neck, knee and fetlock joints was 45.52±5.63°, 196.04±19.7° and 209±11.52° respectively. A combination of experimental methods was used to identify the phases of gait cycle of healthy horses. There was a correspondence in the location of the points of maximum displacement of the limbs with both techniques. More detailed information on the limbs movement was obtained using the accelerometer technology. These methods are applicable to other conditions either outdoors or in the lab.

Abstract In this paper is presented a methodology to generate two-dimensional models of cancellous bone from images, with the main objective to achieve a closer representation to reality, in terms of the geometries that can be obtained. The methodology mainly uses Python™ language programming to establish instructions for using Abaqus™ graphical tools and therefore automatically generate the trabecular structure from the original image. As a first step, each trabecula of the image is idealized as an ellipse and each one is taken as basis for generating the geometries of pores and trabeculae in the model. A simulation of a compression test is also presented for three models made with this methodology, where finite element software was used. It is concluded that the methodology allows getting a very similar trabecular structure to the real one.

Resumen En este trabajo se presenta una metodología para generar modelos bidimensionales de hueso esponjoso a partir de imágenes, con el objetivo principal de alcanzar una representación más cercana a la realidad en cuanto a las geometrías que se pueden obtener. La metodología usa principalmente el lenguaje de programación Python® para establecer instrucciones de usar las herramientas gráficas de Abaqus® y con esto generar de manera automática la estructura trabecular de la imagen original. Como un primer paso, se idealiza cada trabécula de la imagen como una elipse, y cada elipse se toma como base para generar las geometrías de poros y trabéculas del modelo. También se presenta la realización de un ensayo de compresión para tres modelos hechos con esta metodología, donde se usó paquetería de elementos finitos. Se concluye que la metodología permite obtener una estructura trabecular muy similar a la real.