Clusterization of knee joint hyaline cartilage of intact rats and rats with experimental osteoarthritis

To reveal and study the structural changes of clusters (mosaic) organization of hyaline cartilage in case of osteoarthritis we carried out experiments on its modeling using bilateral transection of anterior cruciate ligaments in 28 knee joints of 14 white rats. The autopsy material at 4, 8 and 12 weeks after ligament transaction, and 12 samples from 6 intact rats (control group) completed pool for studying the cartilage morphology. The degree of osteoarthritis progression was evaluated using a semiquantitative scale by Kraus. Quantitative morphology included the estimation of surface factor, cartilage thickness, average chondrocyte density, and matrix optical density in Safranin O staining. The chondrocyte density was calculated to identify microcluster variety in the matrix. The expression of aggrecan and lubricin revealed by immunohistochemical assays made it possible to assess the chondrocyte synthetic ability in the corresponding zones of the cartilage. As a result, we have to conclude that the experimental osteoarthritis is accompanied by changes of cartilage microcluster organization. It becomes more homogeneous with less of dense and lubricin production in the superficial zone. Large clusters with a peculiar hypercellularity and heterogeneity of the density matrix are formed in the deep zone. Structural relations with the underlying bone are disordered, single osteophytes appear. The received data may particularly explain the mechanisms of osteoarthritis progression.