ULTRASTRUCTURAL-STUDY OF CHONDROCYTES FROM FIBRILLATED AND NON-FIBRILLATED HUMAN OSTEOARTHRITIC CARTILAGE

Knee articular cartilage samples obtained by arthroscopy from ten pati ents with well defined knee osteoarthritis (OA) were studied by light and transmission electron microscopy. The morphological phenotype of c ells from fibrillated and non-fibrillated regions of OA cartilage was characterized. Three different cell sub-populations were identified. T ype 1 cells were found in the superficial and upper middle zones and c omprised single chondrocytes and cells organized in aggregates or 'clo nes' that showed a typical chondrocyte phenotype. Type 2 cells display ed a secretory phenotype. Type 3 cells comprised chondrocytes undergoi ng a degenerative process and were distributed throughout all zones of the cartilage. Changes in the cytoskeletal arrangement, presence of a bundant filopodia, peripheral localization of centrioles, and presence of primary cilia were found in many chondrocytes suggesting that they are active motile cells. No mitotic figures were found in this study. Morphometrical analysis was performed to determine the total number o f cells and the number of chondrocytes per lacuna in the superficial a nd upper middle zones of fibrillated and non-fibrillated OA cartilage. There were no statistically significant differences in the total numb er of cells. In contrast, fibrillated OA cartilage contained a statist ically significantly higher percentage of lacunae containing four of m ore chondrocytes than non-fibrillated OA cartilage samples. The absenc e of mitotic figures and the presence of motile elements in many chond rocytes raise the possibility that cell aggregates or 'clones' in dama ged OA cartilage originate by an active process of cell migration rath er than by cellular division.