The influence of microscopic technology on knowledge of cartilage surface structure.

FIG. 1 Proposed mechanisms of joint lubrication (Redrawn after Walker and others, 1968) (Lancet, 1969; Dowson, Wright, and Longfield, 1969) and a further possibility, 'weeping' lubrication, has been proposed (McCutchen, 1959, 1962). More recently, the role ofelectrostatic forces at articulating surfaces has been investigated (Roberts, 1971). In each of these hypothetical mechanisms the thesis had been accepted that these, surfaces are 'strikingly smooth' (Davies, 1969). The demonstration that normal load-bearing surfaces might not, after alf, be smooth (Dowson, Longfield, Walker, and Wright, 1968; Gardner and Woodward, 1968; Jones and Walker, 1968; Walker, Dowson, Longfield, and Wright, 1968; Inoue, Kodama, and Fujita, 1969; Walker, Sikorski, Dowson, Longfield, Wright, and Buckley, 1969), dramatically changed the theoretical approach to articulation mechanisms. A suggestion emerged (Fig. 2), supported by substantial data obtained with cartilage in vitro, that pools oflubricant, trapped betweenopposing undulationsonthecartilage surfaces, could lose fluid, concentrate hyaluronateprotein, and ensure efficient lubrication by a unique 'boosted' system (Longfield, Dowson, Walker, and Wright, 1969). Much of the support for this proposed mechanism of 'boosted lubrication' would be lost if it could be shown that the gentle surface undulations detected by talysurf tracings and identified by scanning electron microscopy were artefacts caused by the methods used to isolate and manipulate cartilage in vitro. During the past 2 years it has therefore been a main interest of this laboratory to examine loadbearing cartilaginous surfaces in detail under conditions that approximate as closely as possible to