Neurophysiological assessment of electrode placement in the spinal cord.

The use of neurophysiological techniques in addition to radiographic methods to determine the location of electrodes to be introduced into the epidural space for spinal cord stimulation is beneficial. Information on the distribution of paresthesias and muscle twitches provides an indication of the level and lateral location in relation to the midline of the spinal cord. For electrodes placed posteriorly, the threshold currents necessary for sensation are lower than those for muscle responses. Somatosensory evoked potentials resulting from epidural stimulation demonstrate effective depolarization of ascending structures. Evoked potentials recorded from the electrodes in response to peripheral nerve or spinal cord stimulation at a distant segment illustrate the possibility of activation of underlying generators of the spinal cord.