A scanning electron microscopic study of the degenerative cartilage in patellar chondropathy

Patellar chondropathy as cartilage degeneration localized in patellar cartilage in young persons is characterized by cartilaginous changes, such as softening, swelling, and fissuring. With a view to structural characterization of early cartilaginous degeneration before erosion, the morphology of affected cartilage was studied under a scanning electron microscope. The surface network of cartilage constituting fibrils had an edematous change, presenting with fibrillation on the medial facet, whereas many fibrils of the central ridge had a collagen bundle, and fissuring of varying size was observed. It appeared that a mechanical force (shearing) acting on the site of the central ridge was associated with the formation of a collagen bundle and its destruction. On the lateral facet, fibrils were arranged perpendicular to the joint surface; the superficial layer of fibrils was worn by hyper-pressure acting on the lateral facet. On the fractured surface, the coarseness of collagen fibrils showed changes that varied with the site and stage of cartilage degeneration. Frequent changes were signs of fibril loosening (coarsening), such as reduction in fibril density (i.e., edematous change), collagen fibril aggregation, and fissuring, and longitudinal restructuring of fibrils. The patellar cartilage in the patients of this series showed a structure adapted to the mechanical force. The initial structural changes of cartilage consisted of collagen fibril aggregation and reduction in fibril density. These changes give rise to matrix rarefaction, which in turn causes cartilage degeneration to progress. These changes were concurrent in both the superficial and middle layers and were not localized as basal degeneration.