Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine
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Proc Inst Mech Eng H · Jan 2002
Comparative StudyPrediction of skin burn injury. Part 2: Parametric and sensitivity analysis.
Part 2 of this paper presents an analysis of variance (ANOVA) for investigating the precedence of the various parameters, and the effects of varying these parameters, in assessment of burn injury resulting from the exposure of skin surface to heat sources. A one-dimensional model based on the finite difference method (FDM), as implemented in a spreadsheet software application, is applied to the assessment of burn injury. Henriques' theory of skin burns is used for determining the spatial and temporal extent of tissue damage. ⋯ It was also found that fat thermal conductivity and blood perfusion rate have no obvious effect on injury threshold. A two-dimensional analysis was further conducted to determine the sensitivity of the predicted injury to the values of frequency factor, P, and apparent activation energy, deltaE, used in the models. Part 1 of this study details the development of the computer models based on the one- and two-dimensional bioheat equations.
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Proc Inst Mech Eng H · Jan 2002
Comparative StudyPrediction of skin burn injury. Part 1: Numerical modelling.
Skin burn injury and heat tolerance in man is a complex interaction of physical heat exchange processes and the potential for physiological adjustments. In recently developed one-dimensional finite difference and two-dimensional finite element bioheat transfer based numerical models of the skin, the prediction of the thermal efficacy of cooling treatment was evaluated. With the use of a standard Arrhenius model for damage rate, the extent of burn injury was computed from the transient temperature solution. ⋯ Numerical data obtained in the current study suggest that non-thermal factors must be considered in the calculation of the efficacy of postburn cooling therapy. However, when dealing with living tissue, any numerical model can provide only an approximation to conditions in real exposures. Together with analysis of variance, the models were used for investigating the precedence of the various parameters and the effects of varying these parameters on assessment of burn injury resulting from exposure of skin surface to heat sources (Part 2).
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Proc Inst Mech Eng H · Jan 2002
Patient-specific spine models. Part 1: Finite element analysis of the lumbar intervertebral disc--a material sensitivity study.
If patient-specific finite element models of the spine could be developed, they would offer enormous opportunities in the diagnosis and management of back problems. Several generic models have been developed in the past, but there has been very little detailed examination of the sensitivity of these models' characteristics to the input parameters. This relationship must be thoroughly understood if representative patient-specific models are to be realized and used with confidence. ⋯ All loading modes were sensitive to the annulus properties with stiffnesses varying by up to +/-16 per cent. The model also revealed that for a particular compressive deformation or flexural or torsional rotation, the disc bulge was not sensitive to any of the material properties over the range of properties considered. The annulus stresses did differ significantly as the material properties were varied (up to 70 per cent under a compressive load and 60 per cent during disc flexion).
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Proc Inst Mech Eng H · Jan 2000
ReviewBiological reactions to wear debris in total joint replacement.
The vast majority of total hip prostheses currently implanted consist of a hard metal or ceramic femoral head articulating against an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. Over the last 10 years, evidence has accumulated to show that these prostheses are prone to failure due to late aseptic loosening and few survive beyond 25 years. With an increasing need to implant hip prostheses in the younger, more active patient the need to understand the mechanisms of failure and to develop artificial hip joints using alternative materials have become major issues in the orthopaedic community. ⋯ For metal-on-metal prostheses, the prospects for increasing the osteolysis free life of the implant are good but additional biological problems associated with the nanometre size and reactivity of the wear particles in vivo may emerge. For the ceramic-on-ceramic prostheses, although initial prospects are encouraging, more data are needed on the characteristics of the wear particles generated in vivo before predictions can be made. It is concluded that the pre-clinical testing of any new materials for joint replacement must include an analysis of the wear particle characteristics and their biological reactivity in addition to the usual assessment of wear.
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Proc Inst Mech Eng H · Jan 2000
Comparative StudyA comparative joint simulator study of the wear of metal-on-metal and alternative material combinations in hip replacements.
While total hip replacement represents the major success story in orthopaedic surgery in the twentieth century, there is much interest in extending even further, early in the twenty first century, the life of implants. Osteolysis has been identified as a major factor limiting the life of prostheses, with indications that fine polyethylene wear debris, generated primarily at the interface between the femoral head and the acetabular cup, promotes the process. There is therefore considerable interest in the introduction of alternative wear resistant systems to limit the deleterious effects of wear. ⋯ The number of metallic particles may exceed the number of polyethylene wear particles from an otherwise similar metal-on-polyethylene joint by a factor of 10(3). A detailed discussion of the size and morphology of wear debris and tissue reaction to various forms of debris is beyond the scope of this paper, but the biological response to polymeric, metallic and ceramic wear debris forms a major subject for further study. The present investigation nevertheless confirms the potential of carefully designed and manufactured metal-on-metal total replacement joints for the treatment of diseased and damaged hips.