Assessment of biomechanical properties of the extracellular and pericellular matrix and their interconnection throughout the course of osteoarthritis

During osteoarthritis (OA)-triggered cartilage degeneration, the chondrocytes spatially rearrange from single to double strings, and then to small and finally big clusters. Both the extracellular matrix (ECM) and the pericellular matrix (PCM) progressively degrade in osteoarthritis, changing the overall mechanical properties of the cartilage. We investigated the mechanical properties particularly elasticity of the ECM and PCM and their interconnection as a function of chondrocyte spatial organisation. Human articular cartilage samples from 30 patients were categorised according to their cellular pattern. Elasticity of the ECM and PCM was assessed by means of atomic force microscopy (AFM). Significant decreases were observed in the elasticity of both the ECM and the PCM with each change of cellular pattern, except from single to double strings in the ECM (p = 0.072). Spatial reorganisation strongly correlated with the elasticity of the ECM (r = −0.768, p < 0.001) and of the PCM (r = −0.729, p < 0.001). The ECM/PCM ratio remained unchanged (r = −0.099, p = 0.281). This study is the first to describe and quantify the differences in the elastic moduli of the ECM in relation to the PCM on the basis of chondrocyte spatial arrangement. This study shows that the elastic changes of the ECM and the PCM occur simultaneously, unidirectionally, and to a comparable degree.