| Research Abstract |
The surface layr of the articular cartilage, which is devoid of collagen fibrils and cells, contributes to the lubrication of the joint and protects the cartilage from digestion by exogenous enzymes. The layr is mainly composed of proteoglycan, a major constituent of the cartilage. When the surface layyr was removed from the articular cartilage by scraping the articular surface of the rabbit knee, osteoarthrosis frequently developed in the joint. The development of osteoarthrosis was dependent on the scraped area. When the scraped area was large, the incidence of the development of osteoarthrosis was high. The purpose of the present study was to elucidate the pathogenesis of osteoarthrosis, especially the relationship between the development of osteoarthrosis and the surface layr of the articular cartilage. Two groups of rabbits were examined. In one group, only central one-third of the femoral articular surface was scraped in the right knee. In the other, almost the entire articular s
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urface of the femoral condyles was scraped. In the former group, animals did not develop osteoarthrosis in their right knees, while rabbits in the latter group frequently developed osteoarthrosis. In the cryo-scanning electron microscopy, in the group of the small scraped area, the surface layr was regenerated in the scraped area with in a week. At that point of time, lubrication of the joint, which had been impaired by the scraping, was restored to the normal level. Immuno-chemical examination revealed that the regenerated surface layr in the scraped area was composed of proteoglycan as the layr in the normal cartilage. Transmission electron microscopy showed enrichment of intracellular organs, indicating enhanced production of extracellular matrix by the chondrocytes in and around the scraped area. In the group in which almost entire articular surface of the knee joint was scraped, animals frequently developed osteoarthrosis of the knee joint. In the scraped area, the surface layr was not observed. The impaired lubrication of the joint was not improved, and the degenerative changes progressed. These results indicated that the development of osteoarthrosis after scraping the articular surface was related to the restoration of the surface layr which was dependent on the scraped area. When the scraped area was small, the surface layr is regenerated by activated secretion of chondrocytes and progressive osteoarthrotic changes do not occur. When the scraped area was large, the surface layr was not restored by the cells and the articular cartilage undergo progressive degeneration and destruction. Less
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