| Summary: | Articular cartilage tissue exhibits a spatial dependence in material properties that govern mechanical behaviour. A mathematical model of cartilage tissue under one dimensional confined compression testing is
developed for normal tissue that takes account of these variations in material properties. Modifications to
the model representative of a selection of mechanisms driving osteoarthritic cartilage are proposed, allowing
application of the model to both physiological and pathophysiological, osteoarthritic tissue. Incorporating
spatial variations into the model requires the specification of more parameters than are required in the absence of these variations. A global sensitivity analysis of these parameters is implemented to identify the
dominant mechanisms of mechanical response, in normal and osteoarthritic cartilage tissue, to both static
and dynamic loading. The most sensitive parameters differ between dynamic and static mechanics of the
cartilage, and also differ between physiological and osteoarthritic pathophysiological cartilage. As a consequence changes in cartilage mechanics in response to alterations in cartilage structure are predicted to be
contingent on the nature of loading and the health, or otherwise, of the cartilage. In particular the mechanical response of cartilage, especially deformation, is predicted to be much more sensitive to cartilage stiffness
in the superficial zone given the onset of osteoarthritic changes to material properties, such as superficial
zone increases in permeability and reductions in fixed charge. In turn this indicates that any degenerative
changes in the stiffness associated with the superficial cartilage collagen mesh are amplified if other elements
of osteoarthritic disease are present, which provides a suggested mechanism-based explanation for observations that the range of mechanical parameters representative of normal and osteoarthritic tissue can overlap
substantially.
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