Structural adaptations in compressed articular cartilage measured by diffusion tensor imaging

To demonstrate the use of diffusion tensor magnetic resonance micro-imaging to observe adaptations of collagen fibres to mechanical compression in articular cartilage.

Spin-echo and diffusion tensor images (156x156microm in-plane resolution, 2mm slice thickness) of bovine cartilage were obtained at a magnetic field of 7.0T in relaxed and compressed states. The parameters determined were: T2, maximum and mean diffusivity, direction of the maximum diffusion eigenvector and fractional anisotropy of diffusion.

A correlation was found between the compressive strain applied to the cartilage and the change in both magnitude and direction of the maximum diffusivity. Compression resulted in a decrease in both the maximum and mean eigenvalues, particularly in the surface and transitional zones, while the change in orientation of the eigenvectors corresponding to maximum diffusion was greatest in the transitional region. In this region, the average orientation of the principal eigenvectors with respect to the normal to the articular surface increased by up to 40 degrees, indicating that the collagen fibre bundles were oriented more parallel to the surface when compressed.

Diffusion tensor imaging can be used to monitor the changes in the direction of the collagen fibres due to compression. It may form the basis of a new non-invasive approach to functional evaluation of cartilage, with potential applications in the diagnosis and treatment of osteoarthritis.