Scanning electron microscopic study of age-related surface changes in rat femoral head articular cartilage.

The articular surface of the femoral heads of young (5 month-old) and old (21 month-old) female rats were examined with the use of the scanning electron microscope using an especially sensitive preparative technique in which the femoral heads were fixed in a glutaraldehyde-paraformaldehyde fixative, post-fixed in OsO4, dehydrated in ethanol and critical point dried. The articular surfaces of the young group were relatively smooth with only small ridges, which may represent superficial collagen fibrils embedded in a proteoglycan matrix. The old group's articular surfaces differed in 2 ways from the surfaces obtained from the young group. First, circumscribed depressions (roughly 20-25 micrometers in diameter) were found, which may represent the empty lacunae of superficial-layer chondrocytes. Secondly, the articular surface was 'roughened', apparently by numerous exposed collagen fibrils that may have been exposed as a result of a loss of superficial proteoglycans. It is concluded that our methodology of tissue preparations for observation with the scanning electron microscope is a sensitive and practical technique that could be useful for characterizing early morphological manifestations of articular cartilage degenerative changes.