Ultrastructural observations on fibril profiles in normal and degenerative human articular cartilage.

Ultrastructural changes in collagen fibril morphology in human osteoarthritis have not been critically analyzed. In this study, fibril profiles in healthy and fibrillated articular cartilage samples obtained from specimens resected during prosthetic arthroplasty were examined by transmission electron microscopy. Collagen fibrils were deposited parallel to the articular surface in the tangential zone, but were aligned radially to the surface in the deeper layers. In the 3 zones studied, fibril volume density was similar despite interzonal variation in mean fibril diameter values. The pattern of collagen deposition in degenerative samples correlated to some extent with the severity of surface fibrillation seen by light microscopy. Samples in which fibrillation was confined to the superficial zone contained fibril profiles similar in size and orientation to those seen in control samples. Where fibrillation extended to the deeper zones, volume density and mean fibril diameter values decreased accordingly. The data suggest that fibril profile differences may reflect variations in matrix proteoglycan levels between normal and degenerative samples.