Variation in articular cartilage in rabbits between weeks six and eight

Previous studies of variation in cartilage characteristics with age have involved comparison of young and adult individuals, but no data on short-term age-related change are available. Such data are important for studies of the response of cartilage to experimental stimuli in young rabbits, to distinguish the response to the stimuli from accompanying age-related changes.

We used light microscopy to study the thickness, cell density, and degree of histological definition of articular cartilage on the femoral trochlea of 6-, 7-, and 8-week-old rabbits.

Thickness and cell density both decline significantly with age. The decline in cell density is more marked in surface layers of cartilage and is accompanied by an increase in the safranin O-staining affinity of the extracellular matrix and an extension of this affinity towards the surface.

Our results indicate that the synthesis of matrix components becomes more important relative to proliferative activity. The traditionally defined histological layers (zones I, II, III, and IV) are not clearly distinguishable in rabbits of this age. In 6- and 7-week old animals only a "surface" (I/II) and a "deep" layer (III) can be distinguished. By 8 weeks, zones I and II are well defined but the mineralization front (marking the boundary between zones III and IV) is still absent.