Contact analysis of biphasic transversely isotropic cartilage layers and correlations with tissue failure

Failure of articular cartilage has been investigated experimentally and the oretically, but there is only partial agreement between observed failure an d predicted regions of peak stresses. Since trauma and repetitive stress ar e implicated in the etiopathogenesis of osteoarthritis, it is important to develop cartilage models which correctly predict sites of high stresses. Ca rtilage is anisotropic and inhomogeneous, though it has been difficult to i ncorporate these complexities into engineering analyses. The objectives of this study are to demonstrate that a transversely isotropic, biphasic model of cartilage can provide agreement between predicted regions of high stres ses and observed regions of cartilage failure and that with transverse isot ropy cartilage stresses are more sensitive to convexity and concavity of th e surfaces than with isotropy. These objectives are achieved by solving pro blems of diarthrodial joint contact by the finite-element method. Results d emonstrate that transversely isotropic models predict peak stresses at the cartilage surface and the cartilage-bone interface, in agreement with sites of fissures following impact loading; isotropic models predict peak stress es only at the cartilage-bone interface. Also, when convex cartilage layers contacted concave layers in this study, the highest tensile stresses occur in the convex layer for transversely isotropic models; no such differences are found with isotropic models. The significance of this study is that it establishes a threshold of modeling complexity for articular cartilage tha t provides good agreement with experimental observations under impact loadi ng and that surface curvatures significantly affect stress and strain withi n cartilage when using a biphasic transversely isotropic model. (C) 1999 El sevier Science Ltd. All rights reserved.