Changes in the cartilage proteoglycans in relation to age and osteoarthrosis

Changes in the extracellular components of various connective tissues with time and continuous use, as well as within experimentally-induced and human pathological conditions, were studied by morphological, chemical and biochemical methods. Osteoarthrotic lesions were produced surgically by implantation of polyethylene sheets, by continuous compression of the knee joint, and by intraarticular papain injection. Results of the model experiments showed that, irrespective of the method used for the production of experimental cartilage lesions, the alterations are strikingly similar. Within connective tissues a gradual deterioration takes place, as measured by marked differences in the histological and histochemical patterns. The degradative changes occur primarily in the matrix, resulting in a significant decrease in proteoglycan content. Under conditions of stress, in young animals, chondrocytes seem to revert to the chondroblastic state, showing mitotic figures, and are capable of producing matrix much more rapidly than is normally seen. This increased activity might be regarded as a nonspecific "feed-back" response of cells, leading to a reparative normalization of the various destructive tissue alterations.