Spinal cord monitoring during surgery by direct recording of somatosensory evoked potentials. Technical note.

A simple method of spinal cord monitoring that can be readily used during surgery for spinal disorders in children or adults is described. A spinal subdural recording electrode is placed rostral to the site of surgery and the peroneal nerve is stimulated in the popliteal fossa; in this way, large-amplitude polyphasic spinal somatosensory evoked potentials (SEP's) can be directly recorded. The large amplitude of the spinal SEP's recorded intrathecally facilitates spinal cord monitoring by allowing: 1) rapid acquisition of the evoked response, which provides continuous monitoring during surgery; 2) relatively easy interpretation of the signal, there being no significant ultrashort- or long-latency components to the waveform; and 3) signal acquisition in an electrical environment that would be unacceptable using standard methods of spinal and cortical SEP recording.