[Morphological studies on structure and function of the superficial zone of the articular cartilage]

Mechanical response of the superficial zone of articular cartilage was examined with a cryoscanning electron microscope. The superficial zone to which no load was applied had a smooth surface, and the thickness of the zone was from 150 to 280 microns. The loaded zone was compressed to several micra in thickness within the first 2 seconds. The superficial zone was shown to respond sensitively to mechanical stresses. To elucidate the structure of the superficial zone each of three major constituent elements was separately removed, and the morphological changes were observed. From the results the superficial zone was considered to have a honeycomb structure which had fluid-containing hyaluronate within. In the lubrication experiment the friction coefficient increased remarkably when the zone was destroyed by scrubbing off or by collagenase digestion. The honeycomb structure of the superficial zone was thought to play an important role in animal joint lubrication.