Scanning electron microscopy and replica studies of articular surfaces of guinea-pig synovial joints.

Many attempts have been made during the past 20 years to explain the remarkable lubricating qualities of synovial fluid (Dowson, 1966-67; McCutcheon, 1966-7) but, until recently, relatively little attention has been paid to the precise threedimensional form of the articulating surfaces between which the fluid is interposed. Indeed, McCall (1968) stated that the literature contained no light microscope photographs of synovial joint surfaces. The advent of the scanning electron microscope has made the incident light microscope almost obsolete in this respect: the scanning microscope combines great depth of focus with the capacity to photograph large portions of tissue at low magnification. These properties have appealed to students of synovial joint function and observations from several centres have now begun to suggest some of the structural appearances which may be encountered at human joint surfaces. It seemed equally important to learn more of the surface of the synovial joints of the common laboratory animals and, since the guinea-pig and rat were being used extensively in these laboratories for investigations of experimental arthritis, it was decided to define the appearances encountered when scanning electron microscopy was used to survey the main joints of these animals. In the present paper a first investigation of the upper and lower femoral and upper tibial surfaces of the guinea-pig is reported. The photographs obtained by scanning electron microscopy are compared with those made with incident light and with replicas of the joint surfaces prepared by a 2-stage technique and viewed by conventional transmission electron microscopy.