The role of cutaneous afferents in position sense, kinaesthesia, and motor function of the hand.

In reconstructive surgery and rehabilitation work, for decades it has been a basic problem for the author to discover which of the peripheral receptor systems provide the primary information on position, motion and degree of load (proprioception). At one time, joint receptors were accepted as the dominant source and more recently musculocutaneous receptors, whereas little attention has been given to cutaneous factors. A number of clinical observations, however, have indicated the importance of cutaneous afferents and this prompted the present study. There are no means of isolating the joint receptors in order to test them alone, but the fact that very good kinaesthesia can be present in their absence militates against their importance. The cutaneous and musculotendinous factors were therefore studied independently in the forearm and hand in test subjects, partly by means of an extensive nerve blocking technique, but also in experiments of the type devised by Gelfan and Carter (1967). The latter proved to be much less simple than had earlier been claimed. The results of the experiments indicated that no kinaesthetic information reaching conscious level could be shown to arise from the musculocutaneous system, whereas the cutaneous afferents appeared to provide the dominant input. As this system can be readily examined and can be moved surgically to parts in need of proprioception, the practical consequences are obvious. It was also observed that signals arising from skin that is displaced over contracting muscle bellies or moving tendons remote from the activated parts of the limb could constitute an important source of error, overlooked in earlier studies.