Deformation of chondrocytes in articular cartilage under compressive load: a morphological study

The main function of articular cartilage is to transmit load. The objective of this study was to describe the deformation of chondrocytes under static loading and its relation to collagen matrix deformation. Whole intact rabbit knee joints were loaded statically with either high or low magnitude and long or short duration. Specimens were cryopreserved while under load and prepared for morphological evaluation by field emission scanning electron microscopy. With this method an immediate preservation of the chondrocyte in its loaded state was possible. Static compression of articular cartilage produced a zone-specific deformation of chondrocyte shape, depending on the magnitude and duration of load. Under high-force and long-duration loading, the chondrocytes showed considerable deformation concomitant with the highly deformed collagen fibres. Chondrocyte deformation occurred mostly in the transitional and upper radial zones and less in the lower layers. There was no significant change of the chondrocyte shape in the tangential zone under high- or low-force short-duration loading. These results show that the chondrocytes undergo significant changes in shape ex vivo and that they are sensitive to differences in the magnitude and duration of loads being applied. Chondrocyte deformation is strongly linked to the deformation of the surrounding cartilage collagen matrix.