Production of split patterns on the articular cartilage surfaces of rats

A device has been designed to permit reproducible loads to be applied perpendicularly to the acutely curved cartilage surfaces of the diarthrodial joints of small animals. With this apparatus, a sharp, round pin has been used to cause splits in the hyaline articular cartilage of the lower end of the femurs of 37 Wistar rats. In the patellar groove, the splits form a longitudinal pattern. On the condylar surface, the pattern is fantail, radial or non-uniform. It is suggested that cartilage thickness, joint congruence and load per unit area, are variables related to the directional pattern of the splits. These variables, in turn, reflect the gross, microscopic and molecular anatomy of the cartilage. The effects pin-pricks are comples: they disrupt surface collagen bundles and other cartilage components. Experiments made to test the effects of drying, isotonic saline, hyaluronic acid and sodium hydroxide support the view that the state of hydration and fluid flow are important determinants of the shape of cartilage splits. However, sodium hydroxide-induced cartilage disruption, involving glycosaminoglycan loss, did not influence split configuration. Some preliminary evidence suggests that the process of crack propagation, by which splits form, may be related to the position and shape of chondrocyte lacunae. It is concluded that pin-prick testing offers a means by which the structural properties of the cartilage of small diarthrodial joints may be conveniently tested in vitro.