Deformation of cartilaginous collagen fiber network under pressure: a load-bearing MRI study

Introduction The complex organization of collageneous fiber network in joint cartilage and its load conditioned behaviour determines the biomechanical properties of this tissue. It has been shown that the state of health of the cartilage has an influence on the deformation mechanisms of the collagen network under compressive load [1, 2]. Thus, the compression tests could be a successful tool to detect slight arthrotic changes in the cartilage. Many authors assessed the deformation of collagen fiber network under pressure by means of different microscopic techniques. Kääb et al. reported the crimping form of statically compressed fibres (Fig.1a) [3], whereas Thambyah and Broom declare ‘chevron-like’ bending of fibrous structure under loading (Fig.1b) [2]. Nötzli and Clark have also found that the changes of the collagen fibres form include both bending and crimping [1]. MR appearance of the cartilage is changing under loading conditions because the signal intensity is altering by the collagen network deformation. The reason behind this effect is the MR intensity dependence on the orientation of collagen fibrils in the static magnetic field B0 [4], which has been described trough a mean fiber orientation θ and an opening angle α [5]. In general, the intensity dependence on the angles θ and α can be described with the help of following expression: