Intracytoplasmic filaments in the cells of adult human articular cartilage.

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Abstract
Samples of articular cartilage from the knee joint of human adults were studied with the electron microscope. Particular attention has been paid to the presence of filaments within the cytoplasm of the chondrocyte. In the electronmicrographs examined many of the chondrocytes contain one or more filamentous areas. The filaments lie directly within the cytoplasm and are not enclosed in membrane-bound vacuoles. They are usally closely packed and tend to be aligned in parallel arrays. No evidence of periodicity or banding was seen. The filaments are typically perinuclear in situation; much less commonly they are seen in a more peripheral part of the cytoplasm. Cells with filamentous areas were found both in the surface layer Of adult human articular cartilage and in its deeper layers. They were encountered both in cartilage samples with an intact articular surface and in samples showing osteo-arthritic fibrillation. The relationship of filament accumulation to the general state of the cytoplasm was investigated. The presence of filaments in small quantity was not evidence that a chondrocyte was degenerate. The accumulation of filaments in unusually large amounts can generally be classified as one of the patterns of degenerative change which occur in adult human articular chondrocytes.