P31-20 Intraoperative cranial nerve monitoring with corticobulbar motor evoked potentials

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P31-17 Analysis of the target-reaching movement in patients with cervical myelopathy K. Igarashi1 , S. Shibuya2 , H. Sano1 , M. Takahashi1 , M. Hasegawa1 , S. Ichimura1 , K. Satomi1 , Y. Ohki2 1 Department of Orthopaedic Surgery, Kyorin University School of Medicine, Japan, 2 Department of Integrative Physiology, Kyorin University School of Medicine, Japan Objective: In animal studies, it is shown that proximal (target-reaching) and distal (grasping) movements of the upper extremity are differently affected by spinal pyramidotomy. We analyzed the target-reaching movement in patients with cervical myelopathy, and examined if it is useful to evaluate symptoms, and to predict recovery after the decompression surgery. Methods: Twenty-eight pre-operative patients and 15 age-matched controls participated in the experiments. Some patients returned to the experiments, up to 1 year after the surgery. They performed targetreaching movements, cued by sound. Three-dimensional positions of the index finger were sampled by an electromagnetic motion tracking system. By analyzing the movement, reaction time, movement time and accuracy of touch position (TP) were obtained, as well as time for online correction (CT) induced by sudden target jump. The parameters were compared with scores of conventional tests; the JOA score, 10-second grip and release test, the manual muscle testing, and motor evoked potential induced by transcranial magnetic stimulation of the motor cortex. Results: All patients mainly claimed clumsiness in the hand movement pre-operatively, and showed significantly deteriorated scores in conventional tests. They also showed poor online adjustments of the reaching movement. It was reflected in long CT and variable TP, though the other parameters were not affected significantly. However, CT was not correlated with any score from conventional tests. After the surgery, CT immediately returned to the normal level, while the JOA score, which mainly evaluate hand functions, improved gradually during months. When including post-operative data, CT and JOA score were correlated, and recovery of the latter could be predicted better if including CT immediately after the surgery. Conclusions: The target-reaching movement is useful to evaluate deficits that cannot be detected by conventional tests. Post-operative JOA score suggests that recovery in hand functions partly depends on mechanisms for the reaching movement. P31-18 Spinal cord lesions during scoliosis surgery: our experience and neurophysiologic identification of the lesion level 1

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E. Montes , G. De Blas , I. Regidor , M. Villadoniga , E. Hevia , C. Barrios3 , J. Burgos4 1 Clinical Neurophysiology Department, Hospital Ramon y Cajal, Madrid, Spain, 2 Orthopedics Department, Hospital La Fraternidad, Madrid, Spain, 3 Orthopaedics and Trauma Unit, Department of Surgery, Valencia University Medical School, Valencia, Spain, 4 Pediatric Orthopedics, Hospital Ramon y Cajal, Madrid, Spain Objectives: To describe the cases where spinal cord injury was detected during spine surgery and to determine the level of the injury, in order to identify the cause and to try to correct it during the surgery. Methods: Loss of motor evoked potentials suggestive of spinal cord injury was detected in 9 patients of 372 scoliosis surgery in our institution. We found different mechanisms of spinal cord injury: Direct trauma to the spinal cord in two cases, after extirpation of hemivertebra in other 2 cases and unknown in 5 cases. Pedicular screws stimulation was performed to assess stimulation thresholds and to try to identify those screws invading the spinal canal. Also epidural somatosensory evoked potentials (SEP) were obtained by posterior tibial nerve stimulation and ascending epidural electrode recording trying to identify the level of spinal cord injury. Results: Disappearing of SEP during surgery confirmed spinal cord lesion at the same level of injury in the patients with direct trauma. Patients developed postoperative paraplegia, and recovered completely two months after surgery. Both hemivertebra patients showed immediate loss of SEP at the level of the malformation, but had complete recovery of motor evoked potentials after spinal fixation and stabilization during the surgery. In the 5 patients with the unknown cause of the injury, we found screws with stimulation thresholds between 5 and 8 mA in 3 patients, and between 8 and 12 mA (uncertainty threshold) in 2 patients. After removing

these screws, motor evoked potentials were recovered in all cases and patients were postoperatively asymptomatic. Conclusion: In our experience, all the cases of intraoperative spinal cord injury during scoliosis surgery were caused by mechanical mechanisms. Neurophysiological techniques allow us to locate the level of spinal cord injury and its cause, in order to correct it intraoperatively in most cases. P31-19 The usefulness and pitfall of intraoperative spinal cord monitoring M. Ando1,2 , K. Maio1 , S. Sasaki1 , T. Tamaki1 , M. Yoshida2 1 Department of Orthopedic Surgery, Wakayama Rosai Hospital, Wakayama, Japan, 2 Department of Orthopedic Surgery, Wakayama Medical University, Wakayama, Japan Introduction: As there are risks to damage neural tissues in the spinal cord, the spinal cord monitoring has been performed in the spinal surgery. Objective: The purpose of this study is to assess the usefulness and limitation of intraoperative spinal cord monitoring. Methods: In 150 patients (male 70, female 80, mean age 67 years old) the spinal cord monitoring was performed during spinal surgery using a single or a combined monitoring method. Monitoring methods included spinal cord evoked potentials after electrical stimulation to the spinal cord [Sp(E)-SCEP, sensory related potential], muscle evoked potential after stimulation to the brain [Br(E)-MsEP, motor related potential]. Evaluation: The critical point of the evoked potentials were decided as follows. In Br(E)-MsEP, complete diminishing of the potential was thought to be a significance change. Decrement of the spike wave below 50% to the control was decided to be a critical point of Sp(E) SCEP. The relationships between significant change of the evoked potentials and postoperative neurological changes were evaluated. Results: In this series, true positive was 1 case, true negative 147 cases, false positive 1 case and false negative 1 case. In the meningioma of the thoracic spinal cord case, Br(E)-MsEP showed no significant changes of the potentials. However the patient complained the dysfunction of the posterior column after surgery. This case was false negative. Discussion: Br(E)-MsEP is relatively easy to be elicited by using high voltage output stimulator and is a good indicator of motor function. However this potential is sometimes unstable on the condition of anesthesia. To minimize the effect of anesthesia and to avoid false negative case in which selective part of the spinal cord is damaged, it is recommended to perform multimodality monitoring using Sp(E)-SCEP and D wave. P31-20 Intraoperative cranial nerve monitoring with corticobulbar motor evoked potentials C. Dong1 , R. Akagami1 , B. Westerberg2 Division of Neurosurgery, Department of Surgery, University of British Columbia, Vancouver, Canada, 2 Division of Otolaryngology, Department of Surgery, University of British Columbia, Vancouver, Canada

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Objective: Standard EMG monitoring techniques cannot provide ongoing functional assessment of cranial nerves during skull base surgery. A novel method of cranial nerve monitoring with corticobulbar motor evoked potentials (CB MEPs) was developed to overcome the difficulties with EMG techniques and its efficacy was evaluated. Methods: 291 consecutive patients undergoing microsurgical resection of cerebellopontine angle tumors were included in the study. CB MEPs were elicited with localized contralateral transcranial electrical stimulation. MEPs were recorded from the ipsilateral orbicularis oris muscle in all of 291 patients to monitor facial nerve function and from the ipsilateral cricothyroid or vocalis muscle in 23 of these patients to assess the function of the vagus nerve. Direct distal cranial nerve activation was excluded by demonstration of the absence of single pulse responses and by the onset latency consistent to a central origin. The amplitude of MEPs was calculated as a percentage of baseline and correlated with postoperative facial and vagus nerve function. Results: Valid facial and vagus nerve MEPs were obtained throughout the procedure in 98% and 95% of the patients monitored, respectively. MEP responses tended to be polyphasic and showed large variability. In 30% of these patients, stimulus triggered EMG was unable to be obtained early in the procedure from direct proximal facial nerve stimulation. Using a 50% baseline MEP amplitude criterion, significant facial deficits were predicted with a sensitivity of 0.91 and a specificity of 0.96. Vagus nerve

29th International Congress of Clinical Neurophysiology MEPs remained above 50% of baseline in all of 23 patients and no patients had postoperative vagus nerve deficits. Conclusions: Reliable facial and vagus nerve MEPs could be recorded throughout the procedure during skull base procedures. CB MEP monitoring can circumvent difficulties of standard EMG monitoring techniques, provide ongoing evaluation of facial and vagus nerve function and predict outcome with sufficiently useful accuracy. P31-21 Recording triggered EMG thresholds from axillary chest wall electrodes. A new refined technique for accuracy of upper thoracic pedicle screw placement E. Montes1 , I. Regidor1 , G. De Blas1 , M. Villadoniga1 , C. Barrios2 , J. Burgos3 1 Clinical neurophysiology Department, Hospital Ramon y Cajal, Madrid, Spain, 2 Orthopaedics and Trauma Unit, Department of Surgery, Valencia University Medical School, Valencia, Spain, 3 Pediatric Orthopedics, Hospital Ramon y Cajal, Madrid, Spain Objective. To evaluate the sensitivity and safety of a new technique to record triggered EMG thresholds from axillary chest wall electrodes when inserting pedicle screws in the upper thoracic spine (T2-T6). Methods: A total of 237 (35%) thoracic screws were placed at T2-T6 levels in 92 patients with adolescent idiopathic scoliosis. A single electrode placed at axillary mid line was able to record potentials during surgery from all T2-T6 miotomes at each side. Screw position was evaluated after surgery using a CT-scan. Results: Malposition was detected in 35 pedicle screws (14.7%). Pedicle medial cortex was breached in 24 (10.1%). Six screws (2.5%) were located inside the spinal canal. Mean EMG threshold was 24.44±11.30 mA in well-positioned screws, 17.98±8.24 mA (p < 0.01) in screws violating the pedicle medial cortex, and 10.38±3.33 mA (p < 0.005) in screws located inside the spinal canal. Bellow 12 mA threshold, 33.4% of the screws (10/30) showed malposition. A 36% of the pedicle screws with t-EMG stimulations thresholds within the range 6 12 mA exhibited malposition. Conclusion: Assessment of upper thoracic pedicle screw placement by recording tEMG at a single axillary electrode was highly reliable. Thresholds below 12 mA should alert surgeon to suspect screw malposition. This technique simplify tEMG potentials recording for safety placement of pedicle screws at upper thoracic levels. P31-22 Intraoperative neurophysiologic monitoring in the endovascular and surgical treatment of pediatric arteriovenous malformations V. Nguyen1 , S. Cho1 , S. Chang2 , G. Steinberg2 , M. Marks3 , H. Do3 , J. Lopez1 1 Department of Neurology, Stanford University/Stanford Hospital & Clinics, Stanford, CA, USA, 2 Department of Neurosurgery, Stanford University/Stanford Hospital & Clinics, Stanford, CA, USA, 3 Department of Radiology, Stanford University/Stanford Hospital & Clinics, Stanford, CA, USA Objective: To evaluate the utility of intraoperative neurophysiologic monitoring (IONM) in the endovascular and surgical treatment of pediatric arteriovenous malformations (AVMs). Background: The usefulness of IONM has been described in the treatment of cerebrovascular diseases, including AVMs. Endovascular and surgical treatments of cerebral AVMs carry the risk of intraoperative cerebral ischemia or injury. There are no published studies on the use of IONM exclusively in the treatment of pediatric AVMs. Design/Methods: We reviewed 213 pediatric cerebral AVMs cases monitored between 1995 and 2009, ages 10 days to 18 years. 74 surgical resections and 139 endovascular embolizations were monitored using SSEPs, BAEPs, MEPs, EEG, and/or cranial nerve EMG. In patients under conscious sedation instead of general anesthesia, serial modified neurologic examinations were used as a supplemental monitoring technique. Results: There were 30 cases (14%) with intraoperative electrophysiologic or physical examination changes. Nine (30%) had “permanent” changes (not resolving by end-of-case), and 7 of those (78%) developed new post-procedure deficits, usually ischemic or hemorrhagic strokes. 21 (70%) had “transient” changes (resolving by end-of-case), and 5 of those (24%) developed new deficits. In the 183 cases without IONMchanges, 11 (5.16%) developed new neurologic deficits. Seven of those developed new deficits outside of the neurologic territory monitored

S291 (e.g. hemianopsia or acalculia in a case monitored with SSEPs and MEPs). The other 4 cases had post-operative fluctuating ischemia (variable perfusion/edema). Conclusions: IONM is a useful tool in predicting new post-procedure deficits in the endovascular and surgical treatment of pediatric AVMs. Permanent IONM changes are associated with a greater risk of new postprocedure deficits, especially cerebral infarcts or hemorrhage. Surgical or endovascular management was altered in all instances where IONM changes were detected. Therefore, the lack of post-procedure deficits in some patients could be due to such interventions. P31-23 Nerve conduction measurements for anterior interosseous nerve palsy S. Nobuta1 Department of Orthopaedic Surgery, Tohoku Rosai Hospital, Sendai, Japan 1

Objective: To assess the diagnostic value of motor nerve conduction measurements for anterior interosseous nerve (AIN) palsy. Methods: Compound muscle action potential (CMAP) from pronator quadratus (PQ) muscle and flexor pollicis longus (FPL) muscle were recorded with surface electrodes by supramaximal stimulation of the median nerve at the elbow in ten patients with AIN palsy. All patients had complete or incomplete palsy of flexor pollicis longus and flexor profundus of the index finger. Parameters were latency and amplitude. The criterion in our hospital for the normal values of side-to-side latency difference and amplitude were below 0.24 ms and below 1.52 mV in PQ-CMAP, and they were 0.35 ms and 1.74 mV in FPL-CMAP. One patient had neurolysis surgery and nine patients were treated conservatively. PQ-CMAP and FPLCMAP were recorded in all patients initially, and all showed abnormality in CMAPs. Delayed latency and/or low amplitude was/were seen in eight patients for PQ-CMAP, and in six for FPL-CMAP. Specifically, four patients showed only abnormal PQ-CMAP, two only abnormal FPL-CMAP, and four indicated abnormality in both PQ- and FPL-CMAP. Results: Results from a mean follow up of seven months were complete recovery in three, partial recovery in six, and unchanged in one. After the treatment, seven patients showed abnormal PQ-CMAP, and/or FPLCMAP with three showing only abnormal PQ-CMAP, one only abnormal FPL-CMAP, and three abnormality in both PQ- and FPL-CMAP. The posttreatment mean PQ-CMAP latency shortened compared with the initial PQ latency, and the post-treatment mean FPL amplitude increased compared with the initial FPL amplitude. Conclusions: Recording and analysis of PQ- and FPL-CMAP with surface electrodes were simple and safe, and were important in the definite electrodiagnosis of AIN palsy. P31-24 Follow-up study of changes in cutaneous reflex in the peroneus longus after acute ankle sprain G. Futatsubashi1 , S. Sasada2 , T. Komiyama3 Graduate School of Education, Chiba University, Chiba, Japan, 2 United of Graduate School Education, Tokyo Gakugei University, Tokyo, Japan, 3 Department of Health and Sports Science, Faculty of Education, Chiba University, Chiba, Japan

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Objective: Previously, we investigated the modulation of cutaneous reflexes in muscles acting at the ankle joint in patients with ankle sprain, and found that the magnitude of middle latency (onset 70 ms) suppressive response of the peroneus longus (PL) was increased in patients with ankle sprain. However, the time course of changes in cutaneous reflexes after ankle sprain is unclear. Therefore, the present study investigated the modulation of cutaneous reflexes in the PL during the acute stage after ankle sprain. Methods: Participants were 6 males who had sustained acute inversion ankle sprain. The subjects were asked to perform different levels of isometric eversion while sitting (5 40% of maximum EMG amplitude). Cutaneous reflexes were elicited by applying non-noxious electrical stimulation to the sural nerve at the ankle joint (PTx2.5, 333 Hz, 5pulses). EMG signals were recorded from both sides of PL. EMG signals were full-wave rectified and averaged (20 30 times). The middle latency component (70 120 msec, MLR) of the cutaneous reflex was analyzed by off-line analyses. The experiments were performed 3 4 days, 1 week, 2 weeks and 4 weeks after acute ankle sprain. Data from patients with