Viscoelastic deformation of articular cartilage during impact loading

Abstract

Articular cartilage is a highly hydrated fibre composite material that provides a resilient, low-friction bearing surface covering bones where they articulate. The literature suggests that the tissue becomes increasingly elastic, less viscoelastic, as the loading rate increases, i.e. hysteresis, the energy lost between loading and unloading, will decrease with increasing strain-rate. Here we show, using a controlled impact, that hysteresis increases with strain rate. No fluid was lost during the deformation and the ratio of the radial to the axial strains, Poisson's ratio, measured using high-speed video recording, increased as the tissue was deformed, starting close to zero and tending towards that for an isovolumetric deformation. The decreasing coefficient of restitution, a measure of the hysteresis, was modelled using a non-linear viscoelastic element, as a first approximation. These results indicate that the tissue remains viscoelastic with increasing strain rate, dissipating energy which might otherwise generate cracks in the matrix.