[Stress on the radiocarpal joint. CT studies of subchondral bone density in vivo]

Most concepts about the mechanism of load transmission through the radiocarpal joint have been mostly acquired from the study of cadaveric specimens. Apart from this, however, it is possible to derive direct knowledge about the actual mechanical conditions of a joint from certain morphological parameters, particularly by analysis of the subchondral mineralization. CT-osteoabsorptiometry (CT-OAM) has provided a non-invasive investigative tool by which the distribution of subchondral mineralization within the radiocarpal joint can be determined. Seventeen wrist-joints in healthy young subjects were investigated by means of CT-OAM, and the results evaluated both topographically and quantitatively. In most cases, two density maxima were found on the articular radial surface, one corresponding to the scaphoid and one to the lunate. These matched the positions of pressure peaks described in reports of research on mechanical models. The density maximum on the articular surface of the radius opposing the scaphoid is, however, rather more dorsally placed, whereas that opposing the lunate lies palmar to the radioulnar midline. This explains the transmission of force to the forearm and the geometrical configuration of the joint components. On the other hand, our quantitative results do not confirm the existence of a generally greater degree of mineralization of either one of the joint compartments. We cannot confirm theories attributing transmission of the main force through either the scaphoid or the lunate. We assume rather that the type of stress indicated by the predominantly monocentric density maxima either on the scaphoid or the lunate surface of the radius, together with the equally balanced bicentric degree of mineralization, are to be regarded as physiological.