Pathobiology of articular cartilage in trapeziometacarpal osteoarthritis. II. Surface ultrastructure by scanning electron microscopy.

Regional variation in the surface ultrastructure of hyaline cartilage in the osteoarthritic trapeziometacarpal joint was studied by means of scanning electron microscopy. Articular surface degeneration on intact osteochondral specimens was analyzed and correlated with known patterns of gross, histologic, and biochemical disease. The earliest changes were observed in the tangential surface lamina and occurred in areas of chondromalacia in the palmar contact area of the joint. Progressive disruption of this superficial fibrillar layer of the articular cartilage was followed by disorganization of the underlying chondrocytes and matrix. In palmar regions with more advanced chondromalacia and loss of eosinophilic staining, free cellular elements and craters 20-30 microns in diameter, resembling empty chondrocyte lacunae, appeared in conjunction with the absence of any tangential surface meshwork. Eburnated areas demonstrated no fibrillar or cellular elements. Disruption of the protective surface lamina of trapeziometacarpal articular cartilage occurs in a geographic pattern corresponding to joint contact areas and regions of selective biochemical decomposition of proteoglycan matrix. These observations support an interdependent relationship between mechanically induced abrasive surface wear and biochemical matrix degradation in the production of the cartilage lesion of trapeziometacarpal osteoarthritis.