Reliability of intraoperative electrophysiological monitoring in selectiveposterior rhizotomy

Object. Selective posterior rhizotomy is a well-established treatment for s pasticity associated with cerebral palsy. At most medical centers, response s of dorsal rootlets to electrical stimulation are used to determine ablati on sites; however, there has been some controversy regarding the reliabilit y of intraoperative stimulation. The authors analyzed data obtained from th e McGill Rhizotomy Database to determine whether motor responses to dorsal root stimulation were reproducible. Methods. A series of 77 patients underwent selective dorsal rhizotomy at a single medical center. The dorsal roots from L-2 to S-2 were stimulated to determine the threshold amplitude. The roots were then stimulated at 2 to 4 + times the highest threshold with a 1-second 50-Hz train. A second stimula tion run of the entire dorsal root was performed before it was divided into rootlets. Rootlets were individually stimulated and sectioned according to the extent of abnormal electrophysiological propagation. Motor responses w ere recorded by electromyography and were also assessed by a physiotherapis t, and grades of 0 to 4+ were assigned. The difference in grades between th e first and second stimulation trains was determined for 752 roots. Statistical analysis demonstrated a clear consistency in motor responses be tween the two stimulation runs, both in the electromyographic readings and the physiotherapist's assessment. More than 93% of dorsal roots had either no change or a difference of only one grade between the two trials. Further more, the vast majority of dorsal roots assigned a grade of 4 at the first trial maintained the same maximally abnormal electrophysiological response during the second stimulation run. Conclusions. This study indicates that currently used techniques are reprod ucible and reliable for selection of abnormal rootlets. Intraoperative elec trophysiological stimulation can be valuable in achieving a balance between elimination of spasticity and preservation of underlying strength.