How selective is selective posterior rhizotomy?

Although selective posterior rhizotomy has become an increasingly utilized surgical treatment for spasticity, the procedure is unstandardized and is performed differently at various medical centers. Most surgeons use some form of direct dorsal rootlet stimulation with intraoperative multichannel electromyographic response monitoring. Electrophysiological monitoring offers the theoretical advantage of identifying pathologic reflex circuits for interruption while preserving those pathways that are "normal." However, the monitoring technique most commonly used has not been critically evaluated and, therefore, its value remains uncertain. In 22 selective posterior rhizotomy procedures performed for spastic cerebral palsy, the authors were unable to identify a single electromyographic response that could be called normal by presently accepted criteria. Dorsal rootlets were chosen for division on the basis of relative degrees of abnormality. Intraoperative electromyographic monitoring of a nonspastic patient produced tracings suggestive of spasticity by presently accepted criteria. These discrepancies suggest that current electrophysiological monitoring in selective posterior rhizotomy should be reevaluated.