Fractures in the Horse. Группа авторов

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Fractures in the Horse - Группа авторов


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the neutral axis has the largest effect on resisting bending and torque loads. Two geometric properties, the area moment of inertia and the polar moment of inertia, quantify the contribution of geometry to a particular bone’s resistance to bending and torsion, respectively.

      Application of a load at a distance from the centre of a bone induces a bending moment. The bending moment is a product of the magnitude of the force applied and the length of the moment arm about which the force is applied. Moment arm length is the perpendicular distance from the line of action of the force to an axis of rotation. A longer moment arm increases the bending effect of the force applied.

Schematic illustration of example of a stress–strain curve of a bone sample.

      Source: Modified from Lopez [43].

Schematic illustration of compressive stress–strain behaviour of one compact and two trabecular bone samples demonstrating the influence of apparent density (P) on the material properties of bone.

      Source: Modified from Keaveny and Hayes [72].

Schematic illustration of factors influencing the deformation of bone subjected to a bending force include the magnitude of the bending moment (a product of the force applied (F) and the length of the moment arm), the elastic modulus of the bone material, and the area moment of inertia about a neutral axis.

      Although helpful in fostering a conceptual understanding, assumptions of cylindrical or elliptical geometry underestimate the complexity of bone structure [76]. Experimentally, finite‐element (FE) modelling, wherein geometry and material properties are obtained from quantitative computed tomography (QCT), is used to generate 3D models that more accurately predict the structural response of bones with irregular and variable cross‐sectional characteristics to different loading conditions [77, 78].

      Viscoelasticity

      Viscoelastic materials exhibit both viscous and elastic characteristics when loaded. Elasticity is the tendency of solid materials to return to their original shape after a deforming force is removed. Viscosity is a measure of a fluid’s resistance to flow (i.e. a viscous fluid will resist motion). Bone is a viscoelastic material because it contains water that can be displaced through the organic matrix. Viscoelasticity refers to the combination of elastic and viscous behaviour where the applied stress results in an instantaneous elastic strain followed by a viscous, time‐dependent strain. In other words, a viscoelastic material will return to its original shape after a deforming force has been removed (i.e. it will show an elastic response) even though it will take time to do so (i.e. it will have a viscous component to this response).

Schematic illustration of formulae for the area moment of inertia and the polar moment of inertia for a hollow cylindrical cross-section.

      Source: Modified from Morgan and Bouxsein [36].


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