PATHOBIOLOGY OF ARTICULAR-CARTILAGE IN TRAPEZIOMETACARPAL OSTEOARTHRITIS .2. 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 intac t osteochondral specimens was analyzed and correlated with known patte rns of gross, histologic, and biochemical disease. The earliest change s were observed in the tangential surface lamina and occurred in areas of chondromalacia in the palmar contact area of the joint. Progressiv e disruption of this superficial fibrillar layer of the articular cart ilage was followed by disorganization of the underlying chondrocytes a nd matrix. In palmar regions with more advanced chondromalacia and los s of eosinophilic staining, free cellular elements and craters 20-30 m u m in diameter, resembling empty chondrocyte lacunae, appeared in con junction with the absence of any tangential surface meshwork. Eburnate d areas demonstrated no fibrillar or cellular elements. Disruption of the protective surface lamina of trapeziometacarpal articular cartilag e occurs in a geographic pattern corresponding to joint contact areas and regions of selective biochemical decomposition of proteoglycan mat rix. These observations support an interdependent relationship between mechanically induced abrasive surface wear and biochemical matrix deg radation in the production of the cartilage lesion of trapeziometacarp al osteoarthritis.