Current issues in arthrogenous inhibition.

Joint disease commonly results in severe weakness of associated muscles. Efforts to restore strength are often unsuccessful, even in the absence of pain. This is because of the underlying inhibition of motoneurones by afferent signals from in and around the affected joint, 'arthrogenous inhibition'. This phenomenon has received scant scientific attention, but several experimental techniques are now available with which it can be studied in man. Animal studies suggest possible neurophysiological mechanisms. Selective atrophy of different muscle fibre types, perhaps implying selective inhibition of different types of motor unit, remains unexplained, however. The severity of arthrogenous inhibition can be temporarily reduced by silencing afferent traffic but none of the techniques is yet generally applicable in practice. An alternative therapeutic approach is to produce involuntary muscle contractions by electrical stimulation. The effectiveness of therapeutic electrical stimulation may depend on the frequency and other characteristics of the stimulus.