Correlating Tissue Mechanics and Spinal Cord Injury: Patient-Specific Finite Element Models of Unilateral Cervical Contusion Spinal Cord Injury in Non-Human Primates.

Non-human primate (NHP) models are the closest approximation of human spinal cord injury (SCI) available for pre-clinical trials. The NHP models, however, include broader morphological variability that can confound experimental outcomes. We developed subject-specific finite element (FE) models to quantify the relationship between impact mechanics and SCI, including the correlations between FE outcomes and tissue damage. Subject-specific models of cervical unilateral contusion SCI were generated from pre-injury MRIs of six NHPs. Stress and strain outcomes were compared with lesion histology using logit analysis. A parallel generic model was constructed to compare the outcomes of subject-specific and generic models. The FE outcomes were correlated more strongly with gray matter damage (0.29 < R2 < 0.76) than white matter (0.18 < R2 < 0.58). Maximum/minimum principal strain, Von-Mises and Tresca stresses showed the strongest correlations (0.31 < R2 < 0.76) with tissue damage in the gray matter while minimum principal strain, Von-Mises stress, and Tresca stress best predicted white matter damage (0.23 < R2 < 0.58). Tissue damage thresholds varied for each subject. The generic FE model captured the impact biomechanics in two of the four models; however, the correlations between FE outcomes and tissue damage were weaker than the subject-specific models (gray matter [0.25 < R2 < 0.69] and white matter [R2 < 0.06] except for one subject [0.26 < R2 < 0.48]). The FE mechanical outputs correlated with tissue damage in spinal cord white and gray matters, and the subject-specific models accurately mimicked the biomechanics of NHP cervical contusion impacts.

Finite- and Fixed-Time Cluster Synchronization of Nonlinearly Coupled Delayed Neural Networks via Pinning Control.

In this article, the cluster synchronization problem for a class of the nonlinearly coupled delayed neural networks (NNs) in both finite- and fixed-time cases are investigated. Based on the Lyapunov stability theory and pinning control strategy, some criteria are provided to ensure the cluster synchronization of the nonlinearly coupled delayed NNs in both finite-and fixed-time aspects. Then, the settling time for stabilization that is dependent on the initial value and independent of the initial value is estimated, respectively. Finally, we illustrate the feasibility and practicality of the results via a numerical example.

Further results on finite-time synchronization of delayed inertial memristive neural networks via a novel analysis method.

In this paper, we propose a novel analysis method to investigate the finite-time synchronization (FTS) control problem of the drive-response inertial memristive neural networks (IMNNs) with mixed time-varying delays (MTVDs). Firstly, an improved control scheme is proposed under the delay-independent conditions, which can work even when the past state cannot be measured or the specific time delay function is unknown. Secondly, based on the assumption of bounded activation functions, we establish a new Lemma, which can effectively deal with the difficulties caused by memristive connection weights and MTVDs. Thirdly, by constructing a suitable Lyapunov functions and using a new inequality method, novel sufficient conditions to ensure the FTS for the discussed IMNNs are obtained. Compared with the existing results, our results obtained in a more general framework are more practical. Finally, some numerical simulations are given to substantiate the effectiveness of the theoretical results.

Anterior Vertebral Body Growth Modulation: Assessment of the 2-year Predictive Capability of a Patient-specific Finite-element Planning Tool and of the Growth Modulation Biomechanics.

STUDY DESIGN: Numerical planning and simulation of immediate and after 2 years growth modulation effects of anterior vertebral body growth modulation (AVBGM). OBJECTIVE: The objective was to evaluate the planning tool predictive capability for immediate, 1-year, and 2-year postoperative correction and biomechanical effect on growth modulation over time. SUMMARY OF BACKGROUND DATA: AVBGM is used to treat pediatric scoliotic patients with remaining growth potential. A planning tool based on a finite element model (FEM) of pediatric scoliosis integrating growth was previously developed to simulate AVBGM installation and growth modulation effect. METHODS: Forty-five patients to be instrumented with AVBGM were recruited. A patient-specific FEM was preoperatively generated using a 3D reconstruction obtained from biplanar radiographs. The FEM was used to assess different instrumentation configurations. The strategy offering the optimal 2-year postoperative correction was selected for surgery. Simulated 3D correction indices, as well as stresses applied on vertebral epiphyseal growth plates, intervertebral discs, and instrumentation, were computed. RESULTS: On average, six configurations per case were tested. Immediate, 1-year, and 2-year postoperative 3D correction indices were predicted within 4° of that of actual results in coronal plane, whereas it was <0.8 cm (±2%) for spinal height. Immediate postoperative correction was of 40%, whereas an additional correction of respectively 13% and 3% occurred at 1- and 2 year postoperative. The convex/concave side computed forces difference at the apical level following AVBGM installation was decreased by 39% on growth plates and 46% on intervertebral discs. CONCLUSION: This study demonstrates the FEM clinical usefulness to rationalize surgical planning by providing clinically relevant correction predictions. The AVBGM biomechanical effect on growth modulation over time seemed to be maximized during the first year following the installation. LEVEL OF EVIDENCE: 3.

Hybrid Constructs for Performing Three-level Hybrid Surgery: A Finite Element Study.

OBJECTIVE: To systematically investigate the effect of 3-level hybrid constructs on the cervical spine biomechanics based on a validated model of the C3-C7 segments. METHODS: Three hybrid constructs with 2 U-shaped dynamic cervical implants and 1 cage were simulated. The 3 constructs were 1) Cage-U-U (cage implanted at the C3-C4 level and U-shaped dynamic cervical implants implanted at the C4-C5 and C5-C6 levels), 2) U-Cage-U, and 3) U-U-Cage. Biomechanical parameters including moments, cervical motions, and stresses in the facet and implants were analyzed in flexion and extension. RESULTS: The flexion and extension motions at artificial cervical disc replacement levels increased for all hybrid constructs when compared with those of intact model. However, the maximum increase was 52% with U-U-Cage model. At the unoperated adjacent level, the maximum motion increase in extension was 23% with the U-U-Cage model. Also, the U-U-Cage and U-Cage-U model generated more than 40% increase in terms of flexion motion at the adjacent level. The facet stress at the adjacent level increased by 28%, 20%, and 39% with the Cage-U-U, U-Cage-U, and U-U-Cage models, respectively. The moments required to reach the same motion as the intact model were significantly increased. CONCLUSIONS: The study showed that the U-U-Cage model lead to more compensation in terms of motion and facet stress. Furthermore, the present results imply that when conducting the hybrid surgery, the segmental motions should be taken into account. Performing anterior cervical discectomy and fusion at the level whose motion is relatively small may decrease the compensation required at the adjacent level.

Análisis de la variación del comportamiento mecánico de la extremidad proximal del fémur mediante el método XFEM (eXtended Finite Element Method) / 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 (AU)

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 (AU)

Assessment of bone quality and strength with new technologies.

PURPOSE OF REVIEW: To give an overview of advanced in-vivo imaging techniques for assessing bone quality beyond bone mineral density that have considerably advanced in recent years. RECENT FINDINGS: Quantitative computed tomography and finite element analysis improve fracture risk prediction at the spine, and help to better understand the pathophysiology of skeletal diseases and response to therapy by quantifying bone mineral density in different bone compartments, determining bone strength, and assessing bone geometry. With new high-resolution techniques, trabecular structure at the spine, forearm, and tibia, and cortical porosity at the forearm and tibia can be measured. Hip structure analysis and trabecular bone score have extended the usefulness of dual X-ray absorptiometry. SUMMARY: New advanced three-dimensional imaging techniques to quantify bone quality are mature and have proven to be complimentary methods to dual X-ray absorptiometry enhancing our understanding of bone metabolism and treatment.

Distribuição de tensões em um modelo tridimensional do primeiro pré-molar superior com esmalte anisotrópico ou isotrópico: análise comparativa pelo método de elementos finitos / Stress distribution in a premolar 3D model with anisotropic and isotropic enamel: finite element method analysis

A distribuição das tensões ao longo da estrutura dentária é determinada pela direção, o tipo e a magnitude das cargas que incidem na superfície oclusal e pelas características das estruturas de suporte. Este estudo teve como objetivo analisar, através do Método de Elementos Finitos, a distribuição de tensões na estrutura dentária, em um modelo tridimensional (3D) do primeiro pré-molar superior submetido a diferentes tipos de carregamentos, considerando o esmalte anisotrópico ou isotrópico...

Finite element analysis of the spine: towards a framework of verification, validation and sensitivity analysis.

A number of papers have recently emphasised the importance of verification, validation and sensitivity testing in computational studies within the field of biomechanical engineering. This review examines the methods used in the development of spinal finite element models with a view to a standardised framework of verification, validation and sensitivity analysis. The scope of this paper is restricted to models of the vertebra, the intervertebral disc and short spinal segments. In the case of single vertebral models, specimen-specific methods have been developed, which allow direct validation against experimental tests. The focus of intervertebral disc modelling has been on representing the complex material properties and further sensitivity testing is required to fully understand the relative roles of these input parameters. In order to construct complex multi-component short segment models, many geometric and material parameters are required, some of which are yet to be fully characterised. There are also major challenges in terms of short segment model validation. Throughout the review, areas of good practise are highlighted and recommendations for future development are proposed, taking a step towards more robust spinal modelling procedures, promoting acceptance from the wider biomechanics community.

Finite element modelling of a residual lower-limb in a prosthetic socket: a survey of the development in the first decade.

A review is presented of the existing finite element models developed from 1987 to 1996 for the biomechanics of lower-limb prostheses. Finite element analysis can be a useful tool in investigating the mechanical interaction between the residual limb and its prosthetic socket, and in computer-aided design and computer-aided manufacturing of prosthetic sockets. Various assumptions and simplifications are made in these models to simplify the actual problem with complex geometry, material properties, boundary and interfacial conditions, as well as loading situations. The analyses can provide the information on the stress distribution at the stump/socket interface and within the residual limb tissues. More recently, nonlinear models have been developed taking into consideration the process of socket rectifications, the slip/friction conditions and material large deformation. The models so far developed have provided some basic understanding of the biomechanics. Comparison of the predictions of these models with experimental measurements indicated that the predicted stresses were within the ranges measured, although one-to-one correspondence was difficult to achieve. Further research is still required in order to improve these models to obtain higher precision in the results taking into account nonlinear and dynamic effects.