Arthrosis is characterized by destructive lesions of cartilage occuring in the pressure areas of the articular surfaces and leading to the denudation and erosion of the sub-chondral bone. At a further stage these lesions are distinguished from cartilage lesions due to aging and correspond to the progressive erosion of a tissue whose cells present mainly signs of degeneration and whose tissue contains few proteoglycans. The histologic appearance of the initial lesions of the cartilage remains a matter of controversy and ambiguity. Some look like fissures in relatively healthy tissues where the cells show signs of proliferation and hyperactivity. Others correspond to the fragmentation of tissues whose cells and connective tissues are severely damaged. The first biochemical changes of cartilage in arthrosis associate a disorder of proteoglycan aggregation and an increase in the water content. The modifications of proteoglycans could be due to the action of proteolytic enzymes or to a lack of synthesis due to changes in chondrocyte glycotransferase. The biochemical changes could be the cause of cartilage destruction following pressures, since they can decrease the resistance of the tissue. They could nevertheless, be secondary to rupture lesions of the collagen, due only to stress. Arthrosis can then be secondary to either a special weakness of the cartilage or abnormal stress factors.