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The biomechanical responses of a skin layer to surface loadings
Abstracts-International
Society of Biomechanics XIII Congress 1991
TENSILE PROPERTfES OF TW1STE.J ANTERIOR CRYCIATE LIGAMENTS Arthur F.T. flak , David Fang , Yvonne Yuan , and Andy C.W. Yeung' 'Rehabilitation Engineering Centre, Hong Kong Polytechnic, Kowloon, Hong Kong 'Department of Orthopaedics, Hong Kong University, Hong Kong The objective of this research is to determine the effects of a 45' tibia1 internal or external rotation on the structural behavior of ACL under tension. Twenty eight knees were tested. Six pairs were used to study the effects of 45' internal tibia1 rotation. Contralaterals were tested in neutral as controls. Another six pairs were for the 45' external rotation study. The tests were done at room temperature at a rate of 26mn/sec. Using group t statistics, the hypothesis that there are no differences in the maximum force between the neutral, IR or ER cases cannot be rejected at 95% confidence limit. Paired t statistics also fail to reject the above hypothesis. These statements are true also for the structural stiffness. It is interesting to note that the maximum force and structural stiffness are significantly highest for those failed at mid substance than those with failures involving either insertion sites, with confidence limit at 95%. It is also interesting to note that all rotated specimens failed either at the femoral or tibia1 insertion sites, except only for one IR specimen.
THE BIOMECHANICf\L RESPONSES OaFA SKIN LAYQTO SURFACE LOADINGS Arthur F.T. Mak , Qinque Wang , Lidu Huang 'Rehabilitation Engineering Centre jong Kong Polytechnic, Hong Kong Department of Fine Mechanical Engineering Shanghai University of Sciences and Technology, Shanghai, China This paper is to present an analysis of how a hydrated soft tissue layer like that of the skin biomechanically respond to pressure loadings applied on the layer surface. These results will provide a rational basis for the design of an active seating system to prevent pressure sore'. The skin together with its underlying soft tissues are modeled as a hydrated biphasic poroelastic layer adhered to a rigid impervious base simulating the effects of the bony substratum. The epidermal surface is taken to be impervious. The shear modulus and the Poisson's ratio are taken to be 66KPa and 0.16 respectively. Hydraulic permeability is taken as 3.5x10-'4m4/Ns. Two problems are presented: Problem 1: A uniform pressure distribution of radius 'a' is applied onto the surface in a fast rampstep manner simulating a classical creep situation. Problem 2: A pressure loading of a cosine profile is applied to an area of radius 'a' in a cyclic manner following a triangular saw pattern.
THE FEASIBILITY AND TIMING OF GRADUAL SCREWREMOVAL DURING FRACTURE HEALING WITH INTERNAL PLATING Arthur F.T. Mak and Ernest T.H. Wong Rehabilitation Engineering Centre, Hong Kong Polytechnic, Kowloon, Hong Kong This is to explore the feasibility of gradual screw removals during the course of fracture healing as a means to reduce the rigidity of the internal plate screw fixation system as healing proceeds, expose more bone to more normal physiological loadings, and allow the screw holes to be filled one pair at a time, thus lessening the adverse effects of stress concentration. A three dimensional model of a plated long bone was set up using NISA II. The diaphysis is modelled as a hollow cylindrical structure. The model consisted of 846 8-node quadratic solid elements with a total of 4512 degrees of freedom The results show that theoretically, the distal screw can be safely retrieved without jeopardizing the remaining screws as the Young's modulus of the fracture union reaches l/100 of normal bone. The results also demonstrate the relative insensitivity of the results to the positioning of the screws, both with respect to the screw stresses as we1 1 The results support a feasible as the strain energy density in the fracture union. The clinical advantage claimed still remains to be schedule of gradual screw removals. proven in later animal studies.
809
Society of Biomechanics XIII Congress 1991
TENSILE PROPERTfES OF TW1STE.J ANTERIOR CRYCIATE LIGAMENTS Arthur F.T. flak , David Fang , Yvonne Yuan , and Andy C.W. Yeung' 'Rehabilitation Engineering Centre, Hong Kong Polytechnic, Kowloon, Hong Kong 'Department of Orthopaedics, Hong Kong University, Hong Kong The objective of this research is to determine the effects of a 45' tibia1 internal or external rotation on the structural behavior of ACL under tension. Twenty eight knees were tested. Six pairs were used to study the effects of 45' internal tibia1 rotation. Contralaterals were tested in neutral as controls. Another six pairs were for the 45' external rotation study. The tests were done at room temperature at a rate of 26mn/sec. Using group t statistics, the hypothesis that there are no differences in the maximum force between the neutral, IR or ER cases cannot be rejected at 95% confidence limit. Paired t statistics also fail to reject the above hypothesis. These statements are true also for the structural stiffness. It is interesting to note that the maximum force and structural stiffness are significantly highest for those failed at mid substance than those with failures involving either insertion sites, with confidence limit at 95%. It is also interesting to note that all rotated specimens failed either at the femoral or tibia1 insertion sites, except only for one IR specimen.
THE BIOMECHANICf\L RESPONSES OaFA SKIN LAYQTO SURFACE LOADINGS Arthur F.T. Mak , Qinque Wang , Lidu Huang 'Rehabilitation Engineering Centre jong Kong Polytechnic, Hong Kong Department of Fine Mechanical Engineering Shanghai University of Sciences and Technology, Shanghai, China This paper is to present an analysis of how a hydrated soft tissue layer like that of the skin biomechanically respond to pressure loadings applied on the layer surface. These results will provide a rational basis for the design of an active seating system to prevent pressure sore'. The skin together with its underlying soft tissues are modeled as a hydrated biphasic poroelastic layer adhered to a rigid impervious base simulating the effects of the bony substratum. The epidermal surface is taken to be impervious. The shear modulus and the Poisson's ratio are taken to be 66KPa and 0.16 respectively. Hydraulic permeability is taken as 3.5x10-'4m4/Ns. Two problems are presented: Problem 1: A uniform pressure distribution of radius 'a' is applied onto the surface in a fast rampstep manner simulating a classical creep situation. Problem 2: A pressure loading of a cosine profile is applied to an area of radius 'a' in a cyclic manner following a triangular saw pattern.
THE FEASIBILITY AND TIMING OF GRADUAL SCREWREMOVAL DURING FRACTURE HEALING WITH INTERNAL PLATING Arthur F.T. Mak and Ernest T.H. Wong Rehabilitation Engineering Centre, Hong Kong Polytechnic, Kowloon, Hong Kong This is to explore the feasibility of gradual screw removals during the course of fracture healing as a means to reduce the rigidity of the internal plate screw fixation system as healing proceeds, expose more bone to more normal physiological loadings, and allow the screw holes to be filled one pair at a time, thus lessening the adverse effects of stress concentration. A three dimensional model of a plated long bone was set up using NISA II. The diaphysis is modelled as a hollow cylindrical structure. The model consisted of 846 8-node quadratic solid elements with a total of 4512 degrees of freedom The results show that theoretically, the distal screw can be safely retrieved without jeopardizing the remaining screws as the Young's modulus of the fracture union reaches l/100 of normal bone. The results also demonstrate the relative insensitivity of the results to the positioning of the screws, both with respect to the screw stresses as we1 1 The results support a feasible as the strain energy density in the fracture union. The clinical advantage claimed still remains to be schedule of gradual screw removals. proven in later animal studies.
809