BackgroundTotal Ankle Replacement (TAR) has become a common surgical procedure for severe Osteoarthritis of the ankle. Unlike hip and knee, current TARs still suffer from high failure rates. A key ...

Evaluation of a new morphological approximation of the articular surfaces of the ankle joint

\n Compliant mechanisms are typically designed for varying stiffness from nearly zero to rigid. However, targeted design for fine-tuning within an application's sensitive range of stiffness remains more desirable for practical implementation in accurate loading or positioning systems. To achieve various competing objectives, a “generalized spiral spring” (GSS) is proposed which achieves small size and other objectives by using a reduced number of parameters as provided by the spiral shape description of the components. An analytical model based on virtual work and curved beam theory is developed for accurate prediction of the stiffness. Moreover, finite element (FE) models are also developed for verification of the proposed designs. Multiobjective design optimization (MDO) is conducted to maximize the linearity in the stiffness versus control parameter (CP) response and improve resolution. The proposed analytical model is validated experimentally and computationally. This approach may be used to achieve finesse by accurate positioning with force control for industrial robots and elegant prostheses.

Generalized Spiral Spring: A Bioinspired Tunable Stiffness Mechanism for Linear Response With High Resolution

This paper briefly reviews the different methodology, technology, challenges, and outcomes of various studies related to TAR prosthesis based on numerical and experimental techniques. Very less in-vitro experimental studies on TAR have been found than finite element (FE) studies. Due to the invasive nature of the experimental approach, inadequacy and less clinical information, computational modelling has been widely used by the researchers. This paper critically examines the part related to FE modelling and experimental analysis. Some recommendation related to modelling of bones, cartilages, ligaments, muscles, and implant-bone interface condition were discussed for better understanding the results and better clinical significance.

Experimental and finite element investigation of total ankle replacement: A review of literature and recommendations.

Multidirectional mechanical properties and constitutive modeling of human adipose tissue under dynamic loading.

Tuning bifurcation loads in bistable composites with tunable stiffness mechanisms

e-Spring: Circular arch mechanism for large and linear tunable stiffness control based on tuning deformation mode contributions

The most common physical injuries are injuries of the lower extremity. In fact, controlled studies on highly physically active groups such as athletes and military personnel show that five injury types are repeatedly cited as accounting for over 50 percent of all training injuries: stress fractures, overuse injuries of the knee, Plantar Fasciitis, Achilles Tendonitis, and ankle sprains [1-5].

Three-dimensional finite element analysis (3D FEA) of the foot in the standing position allows researchers to analyze the relationship between foot behavior and orthotic designs, which may help to relieve or prevent such injuries. Various 3D FEA models of the foot in the standing position show very different boundary conditions, including: fixing the fibula and tibia at different points between the ankle and knee, fixing the talus, and applying slip/no-slip conditions in the articular surfaces [6-12]. This may have a large effect on overall foot stiffness and the strain of the Plantar Aponeurosis.

This study is developed to investigate the influence of these boundary conditions on the overall foot stiffness and strain in the Plantar Aponeurosis in the standing position.

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Effects of boundary conditions on foot behaviour in the standing position in 3D finite element foot model

Development of a simplified, reproducible, parametric 3D model of the talus.

Recent research has shown that hyperelastic properties of the plantar soft tissue consisting of adipose tissue and fibrous septa change from region to region. However, relatively little research has been conducted to develop analytical or computational models to describe the region-specific behavior of the plantar soft tissue. The objective of the research is to develop a region-specific constitutive model of the plantar soft tissue. Plantar soft tissue specimens were dissected from six regions [subcalcaneal (CA), sublateral (LA), subnavicular (Nav), 1st, 3rd, and 5th submetatarsal (M1, M3, M5)] from cadaveric foot samples, and a picrosirius red staining technique was used to visualize the collagen fibers in fibrous septa. The volume fractions of adipose tissue and fibrous septa and the volume fractions of the principal orientations of the fibrous septa were calculated with the intensity gradient method. Region-specific constitutive models were then developed in finite element analysis considering the microstructure of the plantar soft tissue. The hyperelastic region specific material properties of the plantar soft tissue were validated with experimental unconfined compression tests and indentation tests from the literature. The results show that the models give reasonable predictions of the stiffness of the soft tissue within a standard deviation of the tests. The region-specific constitutive models help to explain how changes in the constituents are related to mechanical behavior of the soft tissue on a region specific basis.

Region-specific constitutive modeling of the plantar soft tissue

Experimental measurements of stresses and strains for lower extremity injuries (LEI) are invasive, and therefore, predictions require physiologically accurate 3D finite element (FE) models of the foot and ankle. In previous models, skin is typically neglected. However, experimental studies have shown that skin is much stiffer than soft tissue. In this study, the material sensitivity of skin on foot arch deformation is investigated. A finite element model of the foot is developed, incorporating bones, soft tissue, ligament, articulating surfaces, plantar aponeurosis, skin and plantar plate. Balanced standing is simulated without skin or with three different skin mechanical properties. By including different skin models, the foot static vertical stiffness, navicular displacement and plantar aponeurosis strain change significantly, when compared with the model without skin. The study shows that skin, showing a much stiffer behaviour than soft tissue, should not be neglected in the foot modelling. Further, the plantar plate considered in this model can give merit to modelling injuries such as plantar plate tearing.

Haihua Ou

Papers

e-Spring: Circular arch mechanism for large and linear tunable stiffness control based on tuning deformation mode contributions

Effects of boundary conditions on foot behaviour in the standing position in 3D finite element foot model

Development of a simplified, reproducible, parametric 3D model of the talus.

Region-specific constitutive modeling of the plantar soft tissue

Effect of Skin on Finite Element Modeling of Foot and Ankle During Balanced Standing