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Reliability of intraoperative electrophysiological monitoring in selective posterior rhizotomy
S Mittal1, J P Farmer, C Poulin
1Division of Neurosurgery, Montreal Children's Hospital, McGill University Health Center, Quebec, Canada.
Object:
Selective posterior rhizotomy is a well-established treatment for spasticity associated with cerebral palsy. At most medical centers, responses of dorsal rootlets to electrical stimulation are used to determine ablation sites; however, there has been some controversy regarding the reliability of intraoperative stimulation. The authors analyzed data obtained from the 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 stimulation 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 were recorded by electromyography and were also assessed by a physiotherapist, and grades of 0 to 4+ were assigned. The difference in grades between the first and second stimulation trains was determined for 752 roots. Statistical analysis demonstrated a clear consistency in motor responses between 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. Furthermore, 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 reproducible and reliable for selection of abnormal rootlets. Intraoperative electrophysiological stimulation can be valuable in achieving a balance between elimination of spasticity and preservation of underlying strength.
Insights
Intraoperative electrical stimulation during selective posterior rhizotomy for cerebral palsy spasticity is reproducible. This technique reliably identifies abnormal nerve roots, balancing spasticity reduction with strength preservation.
Area of Science:
- Neurosurgery
- Neurology
- Pediatric Orthopedics
Background:
- Selective posterior rhizotomy (SPR) is a standard treatment for spasticity in cerebral palsy.
- Concerns exist regarding the reliability of intraoperative electrophysiological assessments for guiding SPR.
Purpose of the Study:
- To evaluate the reproducibility of motor responses to dorsal root stimulation during SPR.
- To determine if current techniques reliably identify abnormal nerve rootlets for ablation.
Main Methods:
- 77 patients undergoing SPR had dorsal roots (L-2 to S-2) stimulated.
- Stimulation was repeated to assess motor response consistency via electromyography and physiotherapy assessment.
- 752 roots were analyzed for changes in motor response grades between stimulation runs.
Main Results:
- Over 93% of dorsal roots showed no change or a one-grade difference between stimulation trials.
- Electromyography and clinical assessments demonstrated high consistency in motor responses.
- The majority of maximally abnormal responses (grade 4+) remained consistent upon repeat stimulation.
Conclusions:
- Current intraoperative electrophysiological stimulation techniques for SPR are reproducible and reliable.
- This method aids in selectively ablating abnormal rootlets while preserving motor function.
- SPR guidance using electrophysiology can effectively manage spasticity and maintain strength.
