An electron microscopic study has been made of human articular cartilage from twenty patients aged fifteen to eighty-six years with osteoarthritic changes ranging from early to far advanced. Early changes in the matrix consist of minute surface irregularities and decreased electron density of the interfiber matrix, especially in the upper middle zones. With progression of the osteoarthritic lesion, buckling of the surface layer increases with the formation of clefts that penetrate the deeper zones. Collagen fibers are arranged parallel to the surface of these clefts and in the deeper zones these fibers are perpendicular to the joint surface.

The number of degenerating chondrocytes increases with the severity of the osteoarthritis and these cells often contain excessive numbers of intracellular filaments and lysosome-like structures. In advanced osteoarthritic lesions almost all cells appear to be degenerating.

As the osteoarthritis progresses from an early to a moderately advanced stage, viable chondrocytes and clones of chondrocytes become progressively enlarged, contain increased numbers of intracellular organelles indicative of increased synthetic and secretory activity, and demonstrate evidence of cell replication.

These ultrastructural findings are compared with those of normal human articular cartilage and their significance is discussed in the light of histochemical, biochemical, and metabolic studies of other investigators. The findings suggest that before the advanced stage is reached the osteoarthritic lesion represents an abortive attempt at repair and regeneration of the articular cartilage.