Variation in articular cartilage in rats between 3 and 32 months old. A histomorphometric and scanning electron microscopy study.

In this study we assess the thickness, the cellular density, the cell sizes and the collagen of the three superficial cartilage zones and the morphology of the articular surface of the femoral trochlea in rats with 3, 12 and 32 months of age. The cartilage was studied using light microscopy and scanning electron microscopy. The quantitative results are expressed as means +/- SEM. The data were compared statistically (P < 0.05). Both the thickness and the cellular density significantly diminish with age, in the three cartilage zones studied. The reduction of cellular density is more pronounced in the superficial and intermediate zones of the cartilage (zones I and II, respectively). In zone III (deep zone), the cellular density declines only as from 12 months of age. The area of the chondrocytes diminishes in the superficial and deep zones, but only as from 12 months old. In the intermediate zone, there is no chondrocyte hypotrophy with age. The types of collagen in the zones of the cartilage change with age. In the superficial zone, the collagen type I predominates at 3 months of age while the collagen type II predominates at 12 and 32 months of age. In the intermediate and deep zones, the collagen type I that predominates at 3 months of age is substituted by the collagen type III at 12 and 32 months of age. The articular surface in the 3-month-old rats is relatively smooth, presenting few undulations. In 12-month-old animal cartilages, few fissures and craters are found. In the 32-month-old animals, it was observed a higher number of this kind of degenerative changes and with a more severe look.