The value of intraoperative neurophysiological monitoring in tethered cord surgery

The value of intraoperative neurophysiological monitoring (IONM) with surgical detethering in dysraphic patients has been questioned. A retrospective analysis of our series of 65 patients is presented with special focus on technical set-up and outcome. All patients were diagnosed with a tethered cord (TC) due to spinal dysraphism. A high-risk group (HRG) was determined consisting of 40 patients with a lipomyelomeningocele and/or a split cord malformation sometimes in combination with a tight filum terminale. The surgical procedure was a detethering operation in all cases performed by a single surgeon during a 9-year period (1999-2008). A standard set-up of IONM was used in all patients consisting of motor-evoked potentials (MEP) evoked by transcranial electrical stimulation (TES) and electrical nerve root stimulation. In young patients, conditioning stimulation was applied in order to improve absent or weak MEPs. IONM responses could be obtained in all patients. Postoperative deterioration of symptoms was found in two patients of whom one patient belonged to the HRG. Mean maximal follow-up of all 65 patients was 4.6 years (median 4.1 years). Long-term deterioration of symptoms was found in 6 of 65 patients with a mean follow-up of 5 years (median 5.3 years). The use of IONM is feasible in all TC patients. The identification of functional nervous structures and continuous guarding of the integrity of sacral motor roots by IONM may contribute to the safety of surgical detethering

Influence of the montage of stimulation electrodes for intraoperative neuromonitoring during orthopedic spine surgery

Purpose: In transcranial electrical stimulation, induced motor evoked potentials (MEPs) are influenced by the montage of stimulation electrodes. Differences are to be examined between coronal and sagittal stimulation. Methods: Forty-five patients with idiopathic scoliosis were included. Coronal and sagittal montages were obtained by electrode placement at C3C4 and Cz'F using large contact electrodes. Corkscrew and short needle electrodes were additionally placed at C3C4 in five patients. Voltage motor thresholds (MTvoltage) and MEP amplitudes at 2 times MTvoltage (MEP2MTvoltage) were obtained of upper and lower extremity muscles. Differences of MTvoltage and MEP2MTvoltage at Cz'F and C3C4 and between electrodes were analyzed. Results: MEP2MTvoltage benefits from coronal positioning. Correlations between MTvoltage and impedance were not significant for large electrodes at Cz'F, very low for C3C4, and high for short needles or corkscrew electrodes. MTvoltage of short needles and corkscrews was up to 200% higher compared with MTvoltage of long needles. MTcurrent is increased by 20% to 30% and 2% to 10% for the arm and leg muscles, respectively. Conclusions: Biphasic stimulation at C3C4 is advised when constant voltage stimulation is used to monitor the spinal cord during orthopedic spine surgery. MTvoltage of corkscrew and small needle electrodes are highly sensitive to electrode impedances

Ultrasound myography:Application in nerve conduction velocity assessment and muscle cooling

A new application of ultrasound for studying muscle twitch induced by electrical stimulation is described and some preliminary results are presented. The method, called "ultrasound myography" (UMG), uses Doppler ultrasound to measure muscle movement velocity. The Doppler signals were measured simultaneously with the electromyography (EMG) signals from the thenar muscle of a healthy subject. Averaged EMG and full-wave rectified UMG responses to repeated electrical stimuli were measured after cooling of the hand and adaptation to room temperature. Latency times over the wrist of cold hands adapted to a surrounding temperature of 8°C were 4.5 ms and 16.9 ms for the EMG and averaged rectified UMG responses, respectively. Both latency times decreased considerably after 1 h adaptation to a room temperature of 21°C:20% for the EMG response and 35% for the UMG response. The conduction velocities of the median nerve in the forearm determined by both methods yield comparable results. The results of both methods are discussed. It is concluded that UMG possibly offers a new method in clinical practice for the assessment of nerve conduction velocities in the forearm, and basically is a new simple-to-use technique for noninvasive analysis of deep biomechanical processes. © 1993

Intraoperative neurophysiology in tethered cord surgery:Techniques and results

©AANS, 2017. OBJECTIVE The aim of this study was to establish optimal electric stimulation parameters for intraoperatively monitoring the bulbocavernosus reflexes (BCRs) in infants. METHODS The authors retrospectively reviewed the medical records of all infants (age < 24 months) who had undergone an untethering operation for tethered cord syndrome between May 2013 and February 2014 at a single institution and whose baseline BCR had been elicited during surgery. Using different combinati ons of stimulation parameters-number of stimulation pulses: 4 or 8 pulses, interpulse interval: 1, 2, or 5 msec, and polarity of stimulation: biphasic or monophasic-the authors compared the relative mean amplitude of 10 BCR responses (rmaBCRs) to each combination of parameters. RESULTS The rmaBCRs were larger with the 8-pulse stimulations than with the 4-pulse stimulations (p < 0.0001). There was a tendency, though not statistically significant, for larger rmaBCRs to be obtained with the longer interpulse interval in the 8-pulse stimulation (p = 0.1289). The biphasic stimulation produced larger rmaBCRs than the monophasic stimulation (p = 0.0005). CONCLUSIONS Biphasic 8-pulse stimulations with 5-msec or 2-msec intervals yield the largest BCR responses. Considering that an 8-pulse stimulation with 5-msec intervals may overlap the onset of the BCR, a biphasic 8-pulse stimulation with 2-msec intervals is recommended as the optimal stimulation paradigm to monitor intraoperative BCRs in infants