Browsing by Subject "bone"

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    A Non-linear Visco-elastic Model for Dynamic Finite Element Simulation of Bovine Cortical Bone
    (2021) Blignaut, Caitlyn; Ismail, Ernesto; Cloete, Trevor
    Modelling and simulation of the human body during an impact situation such as a car accident, can lead to better designed safety features on vehicles. In order to achieve this, investigation into the material properties and the creation of a numerical model of cortical bone is needed. One approach to creating a material model of cortical bone suitable for these situations is to describe the material model as visco-elastic, as reported by Shim et al. [1], Bekker et al. [2] and Cloete et al. [3]. The work by Shim et al. and Bekker et al. developed three-dimensional models, but do not accurately capture the transition in behaviour in the intermediate strain rate region, while Cloete et al. developed a phenomenological model which captures the intermediate strain rate behaviour in one dimension. This work aims to verify and extend these models. The intermediate strain rate regime (1 s−1 to 100 s−1 ) is of particular interest because it is a key characteristic of the behaviour of cortical bone and several studies have been conducted to gather experimental data in this region [3, 4, 5, 6]. The behaviour can be captured using non-linear viscoelastic models. This dissertation focuses on the development and implementation of a material model of cortical bone based on non-linear visco-elastic models to capture the intermediate strain rate regime behaviour. The material model was developed using uni-axial test results from cortical bone. The model by Cloete et al. has been improved and extended, and issues of local and global strain rate with regards to the viscosity have been clarified. A hereditary integral approach was taken in the analysis and implementation of discrete models and was found to be consistent with mathematical models. The model developed was extended to three dimensions in a manner similar to that of Shim et al. and Bekker et al. for implementation in commercial finite element software (LS-Dyna and Abaqus).
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    Healthy lifestyle interventions in general practice Part 13: Lifestyle and osteoporosis
    (South African Academy of Family Physicians, 2011) Schwellnus, M P; Patel, D N; Nossel, C; Dreyer, M; Whitesman, S; Micklesfield, L; Derman, E W
    Osteoporosis is defined as a systemic skeletal disease that is characterised by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fractures. Therefore, the diagnosis of osteoporosis is based on measurement of bone mineral density (BMD) using central (axial) dual energy X-ray absorptiometry (DXA), and clinical evidence of a fragility fracture (history or radiological evidence). Osteoporosis is a major public health problem, affecting about 30% of postmenopausal women of Caucasian origin, and 70% of those aged 80 years. The risk factors for osteoporosis include lifestyle factors, genetic/ethnic factors, specific diseases causing secondary osteoporosis, ageing factors, qualitative factors, and drugs that are toxic to bone. In addition, there are specific additional risk factors for falls that need to be considered. It is well established that lifestyle factors, including physical activity, nutritional intervention, psychosocial intervention, smoking cessation and other lifestyle factor interventions are key elements in the prevention and management of osteoporosis. Guidelines for these lifestyle interventions in the prevention and management of osteoporosis are reviewed.