A transmission electron microscopic comparison of the articular surface of cartilage processed attached to bone and detached from bone.

The purpose of this study was to ascertain whether the surface asperities detected with the transmission electron microscope in shavings of young adult articular cartilage detached from bone reflect an in vivo condition or are artefacts. With this in view shavings of rabbit articular cartilage processed in the conventional manner were compared with pieces of cartilage attached to bone processed by a new method which we have evolved. An undulating surface and asperities up to about 0.3 micrometer deep were found in cartilage shavings processed in the conventional manner, but such asperities were not seen on cartilage processed attached to bone. We have therefore concluded that such asperities are artefactual and that they are engendered by cartilage curling. Cartilage processed attached to bone has an amazingly smooth surface; any so-called 'asperities' are less than 0.03 micrometer in depth and are confined to the surface coat which seems to be of a transient nature. On rare occasions, however, focal areas of roughening were found, where the asperities reached a depth of about 0.15 micrometer. Several past studies (reviewed in this paper) have shown that virtually all the asperities seen with the scanning electron microscope on the articular surface are artefacts of tissue processing. We have now shown that even most of the much smaller asperities seen with the transmission electron microscope are also artefacts. Therefore one has to conclude that the articular surface of young adults is remarkably smooth and that the surface asperities must be attributed to artefacts, ageing or pathological changes.