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A parametric study of the axisymmetric loading of an anisotropically elastic limb model by a tourniquet

University of British Columbia

The clinical use of tourniquets has an associated nerve palsy incidence rate of approximately 0.1%. The mechanism of damage is thought to be some form of mechanical deformation. No previous work, has quantified such a mechanism. In this work, an axially compressive damage mechanism is proposed and supported by an order-of-magnitude analysis comparing it with other proposed mechanisms. Earlier attempts to model the application of a tourniquet to a limb have either not modelled the applied pressure adequately or have not made clear the connection between the mechanical properties being modelled and the induced damage. The model proposed in this paper incoporates anisotropic elastic parameters in a stress function formulation for a linearly elastic material with small deformations assumed. An analytical solution technique is developed for rectangular regions. The solution technique was applied to a close-to-isotropic case (the technique degenerates when pure isotropy is assumed) and the results were compared with an experimental investigation. Good agreement was obtained with most of the important features noted in the experimental literature, and a region of high negative axial strain was found to correlate well with observations of the locations and characteristics of the nerve lesions. A sensitivity analysis showed that the solution was relatively insensitive to the anisotropic parameters. Because of this insensitivity and the correlation of the regions of negative axial strain with the regions of damage, the model was used to suggest improvements in current tourniquet cuff designs. It was found that a smoother applied pressure distribution (sinusoidal as oposed to rectangular), a wider cuff, and an elimination of shear stress between the cuff and the skin all contributed to a decrease in the maximum negative axial strain. The last effect was not quantified, but reductions of 50-70% could be achieved by taking the first two measures.

Text

2010-07-10

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http://hdl.handle.net/2429/26296

Mechanical Engineering

University of British Columbia

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