Validation of chevron-like deformations of collagen fiber network in articular cartilage by means of load-bearing μMRI

Introduction: The load-dependent collageneous fiber organization in the joint cartilage determines the biomechanical properties of this tissue. It has been shown that the deformation mechanisms of the collagen network under compressive load depend on the morphological and structural intactness of the cartilage [1, 2]. Thus, the analysis of load-reactions of joint cartilage could be a successful tool to detect (slight) arthritic changes. The deformation of collagen fiber network under pressure was detected by means of different microscopic techniques. The compression causes the bending and crimping of collagen fiber [1, 3]. Thambyah and Broom declare a chevron-type shear discontinuity of the fiber orientation in the transitional zone under load in case of an intact tangential surface zone (Fig.1a) [2]. On the other hand, when the tangential layer was disrupted – which was caused by arthritis – the characteristic kink of the chevron model was not observed (Fig.1b). This demonstrates the important functional role of the articular surface for strain-limiting and stress transmission. It was shown that the collagen matrix deformation under load can be observed by means of angle-sensitive T2-weighted MRI [4-5]. With this method, the bending and crimping of the collagen fiber in compressed cartilage could be assumed [6]. In the present study, the feasible deformation mechanisms of collageneous ultrastructure – particularly the fiber bending and crimping – were analyzed by means of load-bearing MRI with the aim to detect the chevron-type shear discontinuity as an imprint of intact tangential layer.