A heterogeneous orientation criterion for crack modelling in cortical bone using a phantom-node approach

[EN] Cortical bone can be considered as a heterogeneous composite at microscopic scale, composed of osteons that act as reinforcement fibres embedded in interstitial matrix. Cement lines constitute the interface between osteons and matrix, and they often behave as the weakest links along which microcracks tend to propagate. However, current simulations of crack growth using XFEM combined with usual orientation criteria as implemented in commercial codes do not capture this behaviour: they predict crack paths that do not follow the cement lines surrounding osteons. The reason is that the orientation criterion used in the implementation of XFEM does not take into account the heterogeneity of the material, leading to simulations that differ from experimental results. In this work, a crack orientation criterion for heterogeneous materials based on interface damage prediction in composites is proposed and a phantom node approach has been implemented to model crack propagation. The method has been validated by means of linear elastic fracture mechanics (LEFM) problems obtaining accurate results. The procedure is applied to different problems including several osteons with simplified geometry and an experimental test reported in the literature leading to satisfactory predictions of crack paths.The authors gratefully acknowledge the funding support received from the Spanish Ministry of Economy and Competitiveness and the FEDER operation program in the framework of the projects DPI2013-46641-R, DPI2017-89197-C2 and RTC-2015-3887-8 and also from the Generalitat Valenciana through the Programme PROMETEO 2016/007.Marco, M.; Belda, R.; Miguélez, MH.; Giner Maravilla, E. (2018). A heterogeneous orientation criterion for crack modelling in cortical bone using a phantom-node approach. Finite Elements in Analysis and Design. 146:107-117. https://doi.org/10.1016/j.finel.2018.04.009S10711714

Surgery technique for ovine ruminal cannulation

The study of the ruminants' digestive system is of great interest to improve their productive efficiency. From 1928, in which Schalk and Amadon described the technique of cannulation in one stage for bovine and ovine, are developed numerous modifications of that technique as well as new others. A common problem is that can appear complications as movements of the cannula, increases in size of the fistula by necrosis of the tissue or ruminal fluid leak. The developed technique provides a simplification to the surgery, minimizes the complications and lengthens functional life of the cannula.El estudio del sistema digestivo de los rumiantes es de gran interés para conseguir mejorar su eficiencia productiva. Desde 1928, año en el que Schalk y Amadon describieron la técnica de canulación en una fase para su utilización en bovino y ovino, se desarrollan numerosas modificaciones de esta técnica así como otras nuevas. Un problema común es que pueden aparecer complicaciones como movimientos de la cánula, aumentos de tamaño de la fístula por necrosis o fugas de líquido ruminal. La técnica desarrollada aporta una simplificación a la cirugía, minimiza las complicaciones y alarga vida funcional de la cánula

Day-ahead allocation of operation reserve in composite power systems with large-scale centralized wind farms

This paper focuses on the day-ahead allocation of operation reserve considering wind power prediction error and network transmission constraints in a composite power system. A two-level model that solves the allocation problem is presented. The upper model allocates operation reserve among subsystems from the economic point of view. In the upper model, transmission constraints of tielines are formulated to represent limited reserve support from the neighboring system due to wind power fluctuation. The lower model evaluates the system on the reserve schedule from the reliability point of view. In the lower model, the reliability evaluation of composite power system is performed by using Monte Carlo simulation in a multi-area system. Wind power prediction errors and tieline constraints are incorporated. The reserve requirements in the upper model are iteratively adjusted by the resulting reliability indices from the lower model. Thus, the reserve allocation is gradually optimized until the system achieves the balance between reliability and economy. A modified two-area reliability test system (RTS) is analyzed to demonstrate the validity of the method.This work was supported by National Natural Science Foundation of China (No. 51277141) and National High Technology Research and Development Program of China (863 Program) (No. 2011AA05A103)

Experimental validation of finite elements model in hip fracture and its clinical applicability

[ES] La fractura de la extremidad proximal de fémur es objeto de interés en inves-tigación. La complejidad del entramado óseo y la ineficiencia estructural asociada alenvejecimiento hacen que existan muchas variables todavía por comprender desde el puntode vista experimental, pero no existe un modelo de investigación estructural y biomecánico dela fractura de cadera claramente definido.La hipótesis de este trabajo es que es posible desarrollar un modelo de experimentacióncomputacional que caracterice el hueso de la extremidad proximal del fémur como un materialheterogéneo a partir de la traslación directa de los parámetros mecánicos obtenidos de piezasanatómicas de experimentación.Material y método:Trabajo experimental que compara la experimentación real en cadáver yun modelo numérico basado en análisis de elementos finitos (AEF). Las variables que se hanempleado son: punto de inicio de la fractura, su propagación, carga progresiva y la carga máximahasta fractura.Al modelo computacional se trasladaron los parámetros mecánicos reales obtenidos de laspiezas anatómicas basándose en la relación entre las unidades Hounsfield de la TA C de altaresolución y la densidad mineral ósea de cada elemento virtual, mientras que la propagaciónde la fractura se modeló mediante desarrollo computacional propio del equipo investigador,con disminución de las propiedades mecánicas de los elementos da ¿nados conforme avanza lalínea fractuaria.Resultados: El modelo computacional fue capaz de determinar el punto de inicio de la fractura,con una discreta tendencia a la medialización anatómica de dicho punto respecto a lo ocurridode manera experimental. El grado de correlación fue muy alto al comparar el valor real dedeformación progresiva de las muestras frente al obtenido por el modelo computacional. Sobre32 puntos analizados, se obtuvo una pendiente de 1,03 en regresión lineal, con un error relativoentre las deformaciones del 6% y un coeficiente de Pearson de R2=0,99. El modelo computacionalinfraestimó discretamente la carga máxima de fractura, con un error relativo aproximado al10%.Conclusión: El modelo computacional de AEF desarrollado por este equipo investigador mul-tidisciplinar se puede considerar, en conjunto, un modelo completo de AEF de la extremidadproximal del fémur con aplicabilidad clínica futura al ser capaz de simular e imitar el compor-tamiento biomecánico de fémures humanos contrastado con un modelo experimental clásicorealizado en piezas anatómicas. Sobre esta base podrán evaluarse interacciones cualitativasy cuantitativas que lo consoliden como un potente banco de ensayos de experimentacióncomputacional sobre el fémur proximal humano[EN] Fracture of the proximal extremity of the femur is the subject of research interest. The complexity of the bone framework and the structural inefficiency associated with ageing leave many variables yet to be understood from an experimental perspective. However, there is no clearly defined structural and biomechanical research model for hip fracture. The hypothesis of this paper is that it is possible to create a computational experimentation model that characterises the bone of the proximal extremity of the femur as a heterogeneous material from directly translating the mechanical parameters obtained from anatomical experimentation specimens. Material and method An experimental paper comparing real experimentation on cadavers and a numerical model based on finite element analysis (FEA). The variables uses were: the start point of the fracture, propagation of the fracture, progressive load and maximum load until fracture. The real mechanical parameters obtained from the anatomical specimens were translated to the computational model based on the relationship between the Hounsfield units of the high resolution CAT scan and the bone mineral density of each virtual element, whereas the propagation of the fracture was modelled by the research team's own computational design, reducing the mechanical properties of the damaged elements as the fracture line advanced. Results The computational model was able to determine the start point of the fracture, with a slight tendency towards anatomical medialisation of this point compared to what happened experimentally. The degree of correlation was very high on comparing the real value of progressive deformation of the samples compared to that obtained by the computational model. Over 32 points analysed, a slope of 1.03 in lineal regression was obtained, with a relative error between the deformations of 16% and a Pearson's coefficient of R2=.99. The computational model slightly underestimated the maximum fracture load, with a relative error of approximately 10%. Conclusion The FEA computational model developed by this multi-disciplinary research team could be considered, as a whole, a complete FEA model of the proximal extremity of the femur with future clinical applicability since it was able to simulate and imitate the biomechanical behaviour of human femurs contrasted with a traditional experimental model made from anatomical specimens. On this basis, qualitative and quantitative interactions can be assessed which consolidate it as a powerful computational experimentation test bench for the human proximal femur.Larrainzar-Garijo, R.; Caeiro, J.; Marco, M.; Giner Maravilla, E.; Miguélez, M. (2019). Validación experimental de un modelo de análisis de elementos finitos en fractura de cadera y su aplicabilidad clínica. Revista Española de Cirugía Ortopédica y Traumatología. 63(2):146-154. https://doi.org/10.1016/j.recot.2018.05.006146154632Cristofolini, L., Juszczyk, M., Martelli, S., Taddei, F., & Viceconti, M. (2007). In vitro replication of spontaneous fractures of the proximal human femur. Journal of Biomechanics, 40(13), 2837-2845. doi:10.1016/j.jbiomech.2007.03.015Santoni, B. G., Nayak, A. N., Cooper, S. A., Smithson, I. R., Cox, J. L., Marberry, S. T., & Sanders, R. W. (2016). Comparison of Femoral Head Rotation and Varus Collapse Between a Single Lag Screw and Integrated Dual Screw Intertrochanteric Hip Fracture Fixation Device Using a Cadaveric Hemi-Pelvis Biomechanical Model. Journal of Orthopaedic Trauma, 30(4), 164-169. doi:10.1097/bot.0000000000000552Haynes, R. C., Pöll, R. G., Miles, A. W., & Weston, R. B. (1997). Failure of femoral head fixation: a cadaveric analysis of lag screw cut-out with the gamma locking nail and AO dynamic hip screw. Injury, 28(5-6), 337-341. doi:10.1016/s0020-1383(97)00035-1Krischak, G. D., Augat, P., Beck, A., Arand, M., Baier, B., Blakytny, R., … Claes, L. (2007). Biomechanical comparison of two side plate fixation techniques in an unstable intertrochanteric osteotomy model: Sliding Hip Screw and Percutaneous Compression Plate. Clinical Biomechanics, 22(10), 1112-1118. doi:10.1016/j.clinbiomech.2007.07.016Basso, T., Klaksvik, J., Syversen, U., & Foss, O. A. (2014). A biomechanical comparison of composite femurs and cadaver femurs used in experiments on operated hip fractures. Journal of Biomechanics, 47(16), 3898-3902. doi:10.1016/j.jbiomech.2014.10.025Loh, B. W., Stokes, C. M., Miller, B. G., & Page, R. S. (2015). Femoroacetabular impingement osteoplasty. The Bone & Joint Journal, 97-B(9), 1214-1219. doi:10.1302/0301-620x.97b9.35263Tsai, A. G., Reich, M. S., Bensusan, J., Ashworth, T., Marcus, R. E., & Akkus, O. (2013). A fatigue loading model for investigation of iatrogenic subtrochanteric fractures of the femur. Clinical Biomechanics, 28(9-10), 981-987. doi:10.1016/j.clinbiomech.2013.09.009Knobe, M., Altgassen, S., Maier, K.-J., Gradl-Dietsch, G., Kaczmarek, C., Nebelung, S., … Buecking, B. (2017). Screw-blade fixation systems in Pauwels three femoral neck fractures: a biomechanical evaluation. International Orthopaedics, 42(2), 409-418. doi:10.1007/s00264-017-3587-yGarcía-Aznar, J. M., Bayod, J., Rosas, A., Larrainzar, R., García-Bógalo, R., Doblaré, M., & Llanos, L. F. (2008). Load Transfer Mechanism for Different Metatarsal Geometries: A Finite Element Study. Journal of Biomechanical Engineering, 131(2). doi:10.1115/1.3005174Cilla, M., Checa, S., Preininger, B., Winkler, T., Perka, C., Duda, G. N., & Pumberger, M. (2017). Femoral head necrosis: A finite element analysis of common and novel surgical techniques. Clinical Biomechanics, 48, 49-56. doi:10.1016/j.clinbiomech.2017.07.005Schileo, E., Taddei, F., Cristofolini, L., & Viceconti, M. (2008). Subject-specific finite element models implementing a maximum principal strain criterion are able to estimate failure risk and fracture location on human femurs tested in vitro. Journal of Biomechanics, 41(2), 356-367. doi:10.1016/j.jbiomech.2007.09.009Giner, E., Arango, C., Vercher, A., & Javier Fuenmayor, F. (2014). Numerical modelling of the mechanical behaviour of an osteon with microcracks. Journal of the Mechanical Behavior of Biomedical Materials, 37, 109-124. doi:10.1016/j.jmbbm.2014.05.006Morgan, E. F., & Keaveny, T. M. (2001). Dependence of yield strain of human trabecular bone on anatomic site. Journal of Biomechanics, 34(5), 569-577. doi:10.1016/s0021-9290(01)00011-2Go´mez-Benito, M. J., Garcı´a-Aznar, J. M., & Doblare´, M. (2005). Finite Element Prediction of Proximal Femoral Fracture Patterns Under Different Loads. Journal of Biomechanical Engineering, 127(1), 9-14. doi:10.1115/1.1835347Dragomir-Daescu, D., Salas, C., Uthamaraj, S., & Rossman, T. (2015). Quantitative computed tomography-based finite element analysis predictions of femoral strength and stiffness depend on computed tomography settings. Journal of Biomechanics, 48(1), 153-161. doi:10.1016/j.jbiomech.2014.09.016Rezaei, A., Giambini, H., Rossman, T., Carlson, K. D., Yaszemski, M. J., Lu, L., & Dragomir-Daescu, D. (2017). Are DXA/aBMD and QCT/FEA Stiffness and Strength Estimates Sensitive to Sex and Age? Annals of Biomedical Engineering, 45(12), 2847-2856. doi:10.1007/s10439-017-1914-5Khoo, B. C. C., Brown, K., Cann, C., Zhu, K., Henzell, S., Low, V., … Prince, R. L. (2008). Comparison of QCT-derived and DXA-derived areal bone mineral density and T scores. Osteoporosis International, 20(9), 1539-1545. doi:10.1007/s00198-008-0820-yKhoo, B. C. C., Brown, K., Zhu, K., Pollock, M., Wilson, K. E., Price, R. I., & Prince, R. L. (2011). Differences in structural geometrical outcomes at the neck of the proximal femur using two-dimensional DXA-derived projection (APEX) and three-dimensional QCT-derived (BIT QCT) techniques. Osteoporosis International, 23(4), 1393-1398. doi:10.1007/s00198-011-1727-6Dall’Ara, E., Eastell, R., Viceconti, M., Pahr, D., & Yang, L. (2016). Experimental validation of DXA-based finite element models for prediction of femoral strength. Journal of the Mechanical Behavior of Biomedical Materials, 63, 17-25. doi:10.1016/j.jmbbm.2016.06.004LOUBONNICK, S. (2007). HSA: Beyond BMD with DXA. Bone, 41(1), S9-S12. doi:10.1016/j.bone.2007.03.007Marco, M., Larraínzar, R., Giner, E., Caeiro, J. R., & Miguélez, H. (2016). Análisis de la variación del comportamiento mecánico de la extremidad proximal del fémur mediante el método XFEM (eXtended Finite Element Method). Revista de Osteoporosis y Metabolismo Mineral, 8(2), 61-69. doi:10.4321/s1889-836x2016000200003Lenich, A., Bachmeier, S., Prantl, L., Nerlich, M., Hammer, J., Mayr, E., … Füchtmeier, B. (2011). Is the rotation of the femural head a potential initiation for cutting out? A theoretical and experimental approach. BMC Musculoskeletal Disorders, 12(1). doi:10.1186/1471-2474-12-79Kurz, S., Pieroh, P., Lenk, M., Josten, C., & Böhme, J. (2017). Three-dimensional reduction and finite element analysis improves the treatment of pelvic malunion reconstructive surgery. Medicine, 96(42), e8136. doi:10.1097/md.0000000000008136Vercher, A., Giner, E., Arango, C., Tarancón, J. E., & Fuenmayor, F. J. (2013). Homogenized stiffness matrices for mineralized collagen fibrils and lamellar bone using unit cell finite element models. Biomechanics and Modeling in Mechanobiology, 13(2), 437-449. doi:10.1007/s10237-013-0507-

Active Disturbance Rejection Control for Robot Manipulator

Active Disturbance Rejection Control (ADRC) is a control methodology used in chemical processes, aircraft, motors, and other systems. This paper compares the results of an ADRC controller to a Proportional Integral Derivative controller (PID), applied to two degrees of freedom robots. A Linear Extended State Observer (LESO) is used to reconstruct the state variables and unknown parameters needed to control the position of each link. The ADRC can achieve the tracking position and estimate the velocity of each link. The results of the simulation program are shown

Analysis of mechanical behavior variation in the proximal femur using X-FEM (Extended Finite Element Method)

Introducción: El fémur humano ha sido ampliamente estudiado desde hace muchos años de manera experimental con análisis in vitro, y ahora, gracias a los avances de la informática, también se puede analizar de manera numérica. Algunos autores han demostrado la capacidad del método de los elementos finitos para predecir el comportamiento mecánico de este hueso, pero todavía son muchas las posibilidades recurriendo a la sinergia entre el método de los elementos finitos y ensayos experimentales. En este trabajo, por ejemplo, se estudia cómo afectan distintas simulaciones de osteoporosis a las cargas de fractura del fémur. El objetivo de este estudio es predecir la fractura de cadera, tanto la carga a la que se produce ésta como la propagación de la fisura sobre el hueso. Aplicando el método de los elementos finitos al campo de la biomecánica se puede realizar una simulación que muestre el comportamiento del hueso bajo diferentes condiciones de carga. Material y métodos: A partir de imágenes DICOM de tomografía computarizada de la extremidad proximal del fémur derecha de un varón se ha obtenido la geometría del hueso. Mediante un programa informático se han generado las propiedades mecánicas dependientes de la densidad mineral ósea de cada vóxel, y posteriormente se ha utilizado un código de elementos finitos para aplicar diferentes configuraciones de carga y estudiar los valores de fractura del hueso. El modelo numérico ha sido validado a través de un artículo de la literatura científica. Resultados: La carga de fractura en configuración de caída lateral es aproximadamente la mitad que la carga en el caso de la posición normal, lo cual concuerda con diferentes estudios experimentales presentes en la literatura científica. Además se han estudiado diferentes condiciones de carga en situaciones cotidianas, en las que se ha observado que la carga de fractura es mínima en la posición monopodal. También se han simulado condiciones de osteoporosis en las que se ha comprobado cómo desciende la carga de fractura al disminuir las propiedades mecánicas óseas. Conclusiones: Mediante el método de los elementos finitos en conjunto con una imagen médica DICOM es posible el estudio de la biomecánica de la cadera y obtener una estimación del fallo del hueso. Además se pueden aplicar diferentes configuraciones de carga y variar las propiedades mecánicas del hueso para simular el comportamiento mecánico de éste bajo condiciones osteoporóticas.Introduction: For years, the human femur has been extensively studied experimentally with in vitro analysis. Nowadays, with computer advances, it can also be analyzed numerically. Some authors report the usefulness of finite method in predicting the mechanical behavior of this bone. There are many possibilities using the synergy between the method finite element and experimental trials. In this paper, for example, we study how they affect different osteoporotic simulations involving femur fracture loads. The aim of this study is to predict hip fracture, both the load to which this occurs as the propagation of the crack in the bone. By applying the finite element method to the field of bio-mechanics, simulation can be carried out to show the behavior under different bone load conditions. Material and methods: Using DICOM images, CT scan of the proximal end of the right femur of a male has been obtained bone geometry. By a computer program they have been generated dependent mechanical properties of the BMD each voxel, and then used a finite code to apply different load configurations and study values bone fracture elements. The numerical model has been validated in the literature. Results: Load breaking in lateral fall configuration is approximately half the load in the case of the normal position, which agrees with different experimental studies published. In addition, we have studied various load conditions in everyday situations, where it was observed that the load fracture is minimal in mono-podal position. Osteoporotic conditions have also been simulated which confirmed that the load fracture has been reduced by decreasing mechanical properties. Conclusions: By using the finite element method in conjunction with DICOM medical imaging, it is possible to study the biomechanics of the hip and obtain an estimate of bone failure. In addition, different load configurations can be applied and vary the mechanical properties of bone to simulate the mechanical behavior of low osteoporotic conditions.S

Experimental validation of finite elements model in hip fracture and its clinical applicability

La fractura de la extremidad proximal de fémur es objeto de interés en investigación. La complejidad del entramado óseo y la ineficiencia estructural asociada al envejecimiento hacen que existan muchas variables todavía por comprender desde el punto de vista experimental, pero no existe un modelo de investigación estructural y biomecánico de la fractura de cadera claramente definido. La hipótesis de este trabajo es que es posible desarrollar un modelo de experimentación computacional que caracterice el hueso de la extremidad proximal del fémur como un material heterogéneo a partir de la traslación directa de los parámetros mecánicos obtenidos de piezas anatómicas de experimentación. Resultados: El modelo computacional fue capaz de determinar el punto de inicio de la fractura, con una discreta tendencia a la medialización anatómica de dicho punto respecto a lo ocurrido de manera experimental. El grado de correlación fue muy alto al comparar el valor real de deformación progresiva de las muestras frente al obtenido por el modelo computacional. Sobre 32 puntos analizados, se obtuvo una pendiente de 1,03 en regresión lineal, con un error relativo entre las deformaciones del 6% y un coeficiente de Pearson de R2=0,99. El modelo computacional infraestimó discretamente la carga máxima de fractura, con un error relativo aproximado al Conclusión: El modelo computacional de AEF desarrollado por este equipo investigador mul-tidisciplinar se puede considerar, en conjunto, un modelo completo de AEF de la extremidad proximal del fémur con aplicabilidad clínica futura al ser capaz de simular e imitar el compor-tamiento biomecánico de fémures humanos contrastado con un modelo experimental clásico realizado en piezas anatómicas. Sobre esta base podrán evaluarse interacciones cualitativas y cuantitativas que lo consoliden como un potente banco de ensayos de experimentación computacional sobre el fémur proximal humano.Fracture of the proximal extremity of the femur is the subject of research interest. The complexity of the bone framework and the structural inefficiency associated with ageing leave many variables yet to be understood from an experimental perspective. However, there is no clearly defined structural and biomechanical research model for hip fracture. The hypothesis of this paper is that it is possible to create a computational experimentation model that characterises the bone of the proximal extremity of the femur as a heteroge-neous material from directly translating the mechanical parameters obtained from anatomical experimentation specimens. Material and method: An experimental paper comparing real experimentation on cadavers and a numerical model based on finite element analysis (FEA). The variables uses were: the start point of the fracture, propagation of the fracture, progressive load and maximum load until fracture. The real mechanical parameters obtained from the anatomical specimens were transla-ted to the computational model based on the relationship between the Hounsfield units of the high resolution CAT scan and the bone mineral density of each virtual element, whereas the propagation of the fracture was modelled by the research team's own computational design, reducing the mechanical properties of the damaged elements as the fracture line advanced. Results: The computational model was able to determine the start point of the fracture, with a slight tendency towards anatomical medialisation of this point compared to what happened experimentally. The degree of correlation was very high on comparing the real value of progres-sive deformation of the samples compared to that obtained by the computational model. Over 32 points analysed, a slope of 1.03 in lineal regression was obtained, with a relative error bet-ween the deformations of 16% and a Pearson's coefficient of R2=0,99. The computational model slightly underestimated the maximum fracture load, with a relative error of approximately 10%. Conclusion: The FEA computational model developed by this multi-disciplinary research team could be considered, as a whole, a complete FEA model of the proximal extremity of the femur with future clinical applicability since it was able to simulate and imitate the biomechanical behaviour of human femurs contrasted with a traditional experimental model made from anato-mical specimens. On this basis, qualitative and quantitative interactions can be assessed which consolidate it as a powerful computational experimentation test bench for the human proximal femur

The cut-out phenomenon in intertrochanteric femur fracture: analysis using a finite element model

Trabajo premiado con una beca FEIOMM de Investigación Básica 2018.Objetive: This work aimed to analyze the cut‐out phenomenon, which involves oblique displacements and/or rotations of the femoral head around the cephalic component of the intramedullary nail. The analysis was carried out using finite element numerical models. This technique seeks to understand the failure of this type of fixation and establish what po‐sitioning of the system favors or prevents failure due to cut‐out. Material and methods: The study was carried out on a numerical model of the proximal limb of an artificial femur and an intramedullary nail type PFNA (proximal femoral nail anti‐rotation). In the numerical model, the position of the in‐tramedullary nail was varied in the anterior/posterior and superior/inferior directions to analyze the influence of the position on the cut‐out phenomenon. Stresses in critical areas and torque on the nail under normal position loading were analyzed. Results: The most critical position was the one in which the intramedullary nail is placed in the superior position, due to the high compressions that appear in the trabecular bone of the femoral head. The centered position of the nail de‐creased the risk of bone damage and the torque that the intramedullary nail has to support. Conclusions: This type of model allows us to simulate the influence of the nail position and obtain variables that are otherwise difficult to analyze. Although it is a simple model with static load, it confirms that a centered position of the intramedullary nail reduces the risk of cut‐out .Objetivo: El objetivo del trabajo fue analizar el fenómeno de cut-out, fenómeno que supone desplazamientos oblicuos y/o rotaciones de la cabeza femoral alrededor del componente cefálico del clavo intramedular. El análisis se llevó a cabo mediante modelos numéricos de elementos finitos. Con esta técnica se busca entender el fallo de este tipo de fijaciones y establecer qué posicionamiento del sistema favorece o evita el fallo por cut-out. Material y métodos: El estudio se realizó sobre un modelo numérico de la extremidad proximal de un fémur artificial y un clavo intramedular tipo PFNA (femoral proximal de antirrotación). En el modelo numérico se varió la posición del clavo intramedular en dirección anterior/posterior y superior/inferior para analizar la influencia de la posición en el fenómeno de cut-out. Se analizaron las tensiones en zonas críticas y par torsor sobre el clavo bajo una carga en posición normal. Resultados: La posición más crítica fue aquella en la que el clavo intramedular está colocado en la posición superior, debido a las altas compresiones que aparecen en el hueso trabecular de la cabeza femoral. La posición centrada del clavo disminuyó el riesgo de daño óseo y el par torsor que tiene que soportar el clavo intramedular. Conclusión: Este tipo de modelos permite simular la influencia de la posición del clavo y obtener variables que de otra manera son difíciles de analizar. Aunque se trata de un modelo sencillo con carga estática, confirma que una posición centrada del clavo intramedular disminuye el riesgo de cut-out.Los autores agradecen la financiación recibida a través de la Sociedad Española de Investigación Ósea y del Metabolismo Mineral con la Beca de Investigación 2018. También agradecen la financiación recibida a través del Ministerio de Ciencia e Innovación y el Programa FEDER a través de los proyectos DPI2017-89197-C2-1-R y DPI2017-89197-C2-2-R

Comparing inequalities in the labour market from a segmentation perspective

Production of INCASI Project H2020-MSCA-RISE-2015 GA 691004The purpose of this chapter is to carry out a comparative analysis of labour markets in Europe and Latin America from the perspective of segmentation in order to explain the processes of social inequality that arise in the workplace, in light of recent trends in global socio-economic changes. The chapter proposes two main objectives. The first is to perform a comparative descriptive analysis of the main features of labour markets among 60 European and Latin American countries. The second objective is to propose a model of comparative analysis of labour inequality from the theoretical perspective of the segmentation of the labour market and structural heterogeneity. We will focus our analysis by selecting two countries, Spain and Argentina, which both underwent a late development of capitalism. The following general hypothesis is formulated: Spain and Argentina, having clearly differentiated features in economic structure, level of development, institutional frameworks and socio-historical processes, show common dynamics in the structuring of the capitalist labour market between a primary and secondary segment. Using equivalent databases on the workforce a typology of segmentation of employment is constructed that show, in addition to the specificities of each country, the similarities in the structuring of the labour market