Intraoperative evoked potential monitoring of the spinal cord. A restricted filter, scalp method during Harrington instrumentation for scoliosis.

Intraoperative monitoring of somatosensory evoked potentials (EPs) can improve the margin of safety during surgery around the spine. Several methods are available. The authors report their experience in monitoring 65 patients who underwent Harrington instrumentation and spinal fusion for correction of scoliosis. They studied the effects of changes in stimulating and recording parameters, seeking ways to reduce noise and variability in the EP signal. The authors were able to improve the quality of the monitoring records significantly by closer spacing of the scalp electrodes, bipolar rather than referential recording, faster rates of stimulation, and greater low-frequency filtering. The technique seems to be safe, easily performed, reproducible, and relatively inexpensive. It has produced no false-negative results to date, and it significantly reduced the incidence of false-positive results (false alarms) as compared with previously described techniques.