Averaged and depth-dependent anisotropy of articular cartilage by microscopic imaging

To identify the common connections among the averaged and depth-dependent anisotropic properties of articular cartilage by performing a meta-analysis of several published multidisciplinary imaging results. The imaging techniques involved include microscopic magnetic resonance imaging (microMRI), polarized light microscopy (PLM), Fourier-transform infrared imaging (FTIRI), and transmission electron microscopy (TEM).

Several physical properties of cartilage are incorporated in this meta-analysis. These tissue properties include T(2) anisotropy from microMRI, angle and retardance from PLM, infrared anisotropy from FTIRI, and image morphology from TEM. Because the specimens in these studies all came from the same type of canine humeral joints, it is possible to correlate these multidisciplinary tissue properties using a common platform.

An ellipse model was used to identify the connections among these tissue properties in terms of the anisotropy of articular cartilage, in each histological zone as well as for the entire noncalcified tissue. It was found that many aspects of these tissue properties can be interpreted beyond their usual meanings as measured, based on 3 features of an ellipse: the concentration, the orientation, and the anisotropy.

The ellipse model is a useful graphical concept in cartilage imaging since it helps to bring together the measured physical/morphological/chemical quantities in these imaging tools and the anisotropic structure of articular cartilage. Two possible mechanisms for the angular transition of collagen fibrils in cartilage are discussed.