Wave Change of Intraoperative Transcranial Motor-Evoked Potentials During Corrective Fusion for Syndromic and Neuromuscular Scoliosis

Wave Change of Intraoperative Transcranial Motor-Evoked Potentials During Corrective Fusion for... Abstract BACKGROUND There is little information on intraoperative neuromonitoring during correction fusion surgery for syndromic scoliosis. OBJECTIVE To investigate intraoperative TcMEPs and conditions (body temperature and blood pressure) for syndromic scoliosis. METHODS The subjects were 23 patients who underwent 25 surgeries for corrective fusion using TcMEP. Patients were divided into groups based on a decrease (DA+) or no decrease (DA−) of the amplitude of the TcMEP waveform of ≥70%. The groups were compared for age, sex, disease, type of surgery, fusion area, operation time, estimated blood loss, body temperature, blood pressure, Cobb angle, angular curve (Cobb angle/number of vertebra), bending flexibility, correction rate, and recovery. RESULTS The mean Cobb angles before and after surgery were 85.2° and 29.1°, giving a correction rate of 68.2%. There were 16 surgeries (64.0%) with intraoperative TcMEP wave changes. The DA+ and DA− groups had similar intraoperative conditions, but the short angular curve differed significantly between these groups. Amplitude deterioration occurred in 4 cases during first rod placement, in 8 during rotation, and in 3 during second rod placement after rotation. Seven patients had complete loss of TcMEP. However, most TcMEP changes recovered after pediclectomy or decreased correction. The preoperative angular curve differed significantly between patients with and without TcMEP changes (P < .05). CONCLUSION Intraoperative TcMEP wave changes occurred in 64.0% of surgeries for corrective fusion, and all but one of these changes occurred during the correction procedure. The angular curve was a risk factor for intraoperative motor deficit. Risk factors, Wave changes of intraoperative transcranial motor-evoked potentials, Syndromic scoliosis, Short angular curve ABBREVIATIONS ABBREVIATIONS AP anterior-posterior AUCs areas under the ROC curve ICC intraclass correlation coefficient ROC receiver operating characteristics TcMEP transcranial motor-evoked potential UHMW ultrahigh molecular weight. Neural complications are severe risks in surgery with instrumentation for scoliosis correction.1-3 The incidence of neurological deficit after this surgery has been widely studied3-6 and has been associated with type of procedure, curve magnitude, instrumentation type, combined approach, and decreased spinal cord perfusion due to hypotension or significant hemorrhage in surgery for idiopathic scoliosis.4 Syndromic scoliosis is generally defined as scoliosis associated with a systemic disease, including Down syndrome, Rett syndrome, achondroplasia, Ehlers–Danlos syndrome, Prader–Willi syndrome, Friedrich ataxia, Marfan syndrome, neurofibromatosis, and osteogenesis imperfecta.7 The rate of neurological deficit with syndromic scoliosis is more frequent than that with idiopathic scoliosis.7-10 Intraoperative spinal cord monitoring is important to reduce neurological complications in syndromic scoliosis.11 Transcranial motor-evoked potential (TcMEP) monitoring is a simple and increasingly used approach with high sensitivity and specificity that is particularly effective for the corticospinal tract.12-14 In this approach, decreased spinal cord perfusion during correction can be detected as a signal change intraoperatively or after surgery as loss of neural function with delayed onset. However, there is little information on intraoperative neuromonitoring and conditions (body temperature and blood pressure) during correction fusion surgery for syndromic scoliosis. An improved understanding of wave changes in surgery for syndromic scoliosis is an important step in reducing neural complications. Therefore, this study was performed to investigate TcMEP wave changes during correction fusion surgery for syndromic scoliosis. METHODS Patients A total of 110 consecutive patients aged <20 yr old underwent correction and fusion surgery under intraoperative neurophysiological TcMEP monitoring at our hospital from 2005 to 2013. Among these patients, there were 23 with syndromic scoliosis, including 8 cases with an etiology of cerebral palsy, 7 of neurofibromatosis type 1, 4 of Marfan syndrome, and 1 each of Down syndrome, Ehlas–Danlos syndrome, Sotos syndrome, and Noonan syndrome. Eight cases were treated preoperatively with Halo-ring traction. For the thoracic main curve, ultrahigh molecular weight (UHMW) polyethylene tape was used on the concave side of the scoliosis. Translation and rotation forces were used with direct vertebral rotation with a concave rod, using pedicle screws inserted at the apex.15 For the lumbar curve, segmental screw fixations were performed. Radiographic data were evaluated using Spinal Deformity Group parameters.16 Certified radiology technicians took standard pre- and postoperative upright anterior-posterior (AP) and lateral standing radiographs and AP supine traction radiographs on long cassettes. Medical records and radiographs were reviewed by 2 spine surgeons. In this review, Cobb angles of the major thoracic and lumbar curves were measured to calculate the correction rate: (preoperative Cobb angle – postoperative Cobb angle)/(preoperative Cobb angle) × 100%. Preoperative flexibility was measured using the Cobb angle for side bending: (preoperative Cobb angle – Cobb angle for side bending)/(preoperative Cobb angle) × 100%. Patients were divided into groups based on a decrease (DA+) or no decrease (DA–) of amplitude of the TcMEP waveform of ≥70%, based on use of a similar criterion in a nationwide, prospective multicenter study in Japan.17-19 Age, sex, disease, surgical method, fusion area, operation time, estimated blood loss, change of body temperature, blood pressure (during the correction procedure in the DA– group and at the time of amplitude change in the DA+ group), preoperative Cobb angle of the main curve, preoperative flexibility under traction, short angular curve (preoperative Cobb angle of the main curve/number of vertebra) that means severe curve with the spinal cord in the canal, postoperative Cobb angle, and correction rate were compared retrospectively between the DA+ and DA– groups. The timing of procedures was also investigated in the DA+ group. The study was approved by our IRB and informed consent was obtained from all patients. Anesthetic Management Benzodiazepine suppresses latency and amplitude and thus was used minimally, if at all, as a preanesthetic medication. Induction was achieved with propofol (3-4 mg/kg), fentanyl (2 mg/kg), and vecuronium (Fuji Pharma Co, Ltd, Tokyo, Japan; 0.12-0.16 mg/kg), and anesthesia was maintained using propofol (50-100 μg/kg/min) and fentanyl (1-2.5 μg/kg/h). Normal end-tidal CO2 was maintained throughout surgery. Stimulating and Recording Methods A D185 MultiPulse Stimulator (Digitimer Ltd, Welwyn Garden City, Hertfordshire, England) was used for transcranial stimulation, using 4 to 5 stimuli in a row at 2-ms intervals, a stimulus of 300 to 600 V, and a 100-ms epoch time with 20 individual recorded responses. The point of stimulation in the International 10-20 System was 2-cm anterior and 3-cm lateral from the Cz location. Motor-evoked potentials were recorded from the upper and lower extremities via a pair of needle electrodes, using Neuropack MEB-2200 v. 04.02 (Nihon Kohden, Tokyo, Japan), with monitoring of as many muscles as possible among the deltoid and hypothenar from the upper extremities, and bilateral adductor longus, quadriceps femoris (quad), hamstrings, tibialis anterior, gastrocnemius, and abductor hallucis from the lower extremities (quad, hamstrings, tibialis anterior, and gastrocnemius until 2009), depending on the spinal level of surgery. Only MEP data from lower extremity muscles were used for analysis. Multimodal monitoring was performed in all cases. Monitoring and Alert Parameters TcMEP values at baseline were recorded immediately after surgical exposure of the spine, and then signals were obtained after screwing, fixing of UHMW polyethylene tape on the concave side, rod placement on the concave side, rotation, and rod placement on the other side. A final TcMEP test was performed after wound closure. TcMEP peak-to-peak amplitudes are shown in μV. If a decrease in TcMEP of ≥70% occurred, the surgeons were notified of this as a minor neurophysiological change. A decrease from baseline of 90% or a slip below 5 μV was considered to be a major change indicating possible motor tract injury, and surgery was stopped for a few minutes to allow recovery of the neurophysiological signal. Additional procedures, such as removal of the rod or increasing blood pressure, were also performed. Receiver operating characteristics (ROC) analysis was conducted for each short angular curve for each decrease in the amplitude of TcMEP ≥70%. Statistical Analysis SPSS ver. 19 (SPSS Inc, IBM Inc, Armonk, New York) was used for data analysis. Values are presented as mean ± SD. Differences between the 2 groups were analyzed by the Mann–Whitney U test and Fisher exact test. The cutoff amplitude for each short angular curve for each decreased amplitude of TcMEP ≥ 70% was determined using ROC analysis. Sensitivity and specificity at optimal cutoff values were calculated. Areas under the ROC curve (AUCs) of >0.9, 0.7-0.9, 0.5-0.7, 0.5 were interpreted to indicate high accuracy, moderate accuracy, low accuracy, and a chance result, respectively.20 The intraclass correlation coefficient (ICC) was used to evaluate intra- and interobserver reliability of the measurements of the 3 imaging modalities, with values of <0.40, 0.40-0.59, 0.60-0.74, and 0.75-1.00 considered to be poor, fair, good, and excellent, respectively.21P < .05 was taken to be significant in all analyses. RESULTS Descriptive Data A total of 25 surgeries were performed on 23 patients (15 males and 8 females) with a mean age of 15.8 yr (range: 5-17 yr) at surgery. One male and one female underwent 2 surgeries each because of proximal adjacent kyphosis and progression of non-fused thoracic spine, respectively. The average follow-up period was 5.1 yr (range: 2-10 yr). Eight patients received preoperative halo-traction. Two were treated with anterior vertebral body-screw fixation, 11 with posterior correction fusion followed by anterior release and bone graft, and 12 with posterior correction fusion. The total operation time was 482 min (188-781 min) and total EBL was 1965 ml (428-4179 ml; Table 1). TABLE 1. Demographic and Clinical Data Age (years)  16  Gender male/female (n)  14/7  Preoperative Cobb angle (°)  81.6  Traction Cobb angle (°)  55.1  Flexibility (%)  33.4  Age (years)  16  Gender male/female (n)  14/7  Preoperative Cobb angle (°)  81.6  Traction Cobb angle (°)  55.1  Flexibility (%)  33.4  View Large TABLE 1. Demographic and Clinical Data Age (years)  16  Gender male/female (n)  14/7  Preoperative Cobb angle (°)  81.6  Traction Cobb angle (°)  55.1  Flexibility (%)  33.4  Age (years)  16  Gender male/female (n)  14/7  Preoperative Cobb angle (°)  81.6  Traction Cobb angle (°)  55.1  Flexibility (%)  33.4  View Large Rates of Successful Derivation and TcMEP Deterioration In the 25 surgeries, 284 muscles in the lower extremities were monitored, and acceptable baseline TcMEP responses were obtained from 270 (95%). Intraoperative electrophysiological deterioration, which was defined as a decrease from baseline TcMEP amplitude of ≥70%, occurred in 16 surgeries (64%, DA+ group). There were 7 cases with an etiology of cerebral palsy, 4 of neurofibromatosis type 1, 2 of Sotos syndrome, and 1 each of Down syndrome, Ehlas-Danlos syndrome, and Noonan syndrome. There were no significant differences in age, sex, disease, surgical methods, operation time, EBL, change of body temperature, blood pressure at correction, preoperative Cobb angle of the main curve, preoperative flexibility, postoperative Cobb angle, and correction rate between the DA+ and DA− groups, but the short angular curve (preoperative Cobb angle of the main curve/number of vertebra) and the fusion area did differ significantly between the 2 groups (P < .05; Table 2). The AUC for the ROC curve was 0.75 and the cutoff amplitude was 14.19° (Figure 1). Eight cases in the DA+ group had pre- and intraoperative traction, and 5 of these cases had signal changes. There was 1 nonambulatory case with CP in the DA+ group. The intra- and interobserver reliabilities were excellent (ICC: 0.776, 0.757, respectively). FIGURE 1. View largeDownload slide ROC analysis for each short angular curve for each decreased amplitude of the TcMEP ≥ 70%. The cutoff angle was 14.19°, at which the sensitivity was 0.625 and the specificity was 0.929. FIGURE 1. View largeDownload slide ROC analysis for each short angular curve for each decreased amplitude of the TcMEP ≥ 70%. The cutoff angle was 14.19°, at which the sensitivity was 0.625 and the specificity was 0.929. TABLE 2. Incidence of Intraoperative Wave Deterioration Using the 70% Criterion Deterioration Syndrome  +(n = 16) CP 7, NF-1 4, Sotos 2, E-D 1, Down 1, Noonan 1  − (n = 9) Marfan 4, NF-1, 3, CP 1, down 1  P  Age (years)  12.9 ± 3.5  14.3 ± 14.1  .15  Sex (male/female) (n)  10/6  6/3  .6  Preop. Halo-traction (n)  5  3  .9  Pre Cobb angle (°)  79.4 ± 15.7  85.4 ± 30.9  .6  Flexibility (%)  36.4 ± 12.3  28.2 ± 12.3  .15  Angular curve (°)  19.3 ± 7.0  14.1 ± 3.1  .03  Sagittal Cobb angle (°)  25.9 ± 5.4  27.7 ± 5.3  .44  Body temperature (°C)  36.8 ± 0.5  36.9 ± 0.5  .99  Blood pressure (mmHg)  89.5 ± 8.2  91.9 ± 7.3  .22  Surgical methods (A/AP/P)  0/6/10  2/5/2  ns  Operation time (min)  477 ± 151  485 ± 167  .91  EBL (ml)  1689.6 ± 890  2395.4 ± 1254  .19  Post Cobb angle (°)  24.9 ± 15.8  35.0 ± 21.3  .25  Correction rate (%)  69.9 ± 15.3  61.0 ± 17.8  .27  Syndrome  +(n = 16) CP 7, NF-1 4, Sotos 2, E-D 1, Down 1, Noonan 1  − (n = 9) Marfan 4, NF-1, 3, CP 1, down 1  P  Age (years)  12.9 ± 3.5  14.3 ± 14.1  .15  Sex (male/female) (n)  10/6  6/3  .6  Preop. Halo-traction (n)  5  3  .9  Pre Cobb angle (°)  79.4 ± 15.7  85.4 ± 30.9  .6  Flexibility (%)  36.4 ± 12.3  28.2 ± 12.3  .15  Angular curve (°)  19.3 ± 7.0  14.1 ± 3.1  .03  Sagittal Cobb angle (°)  25.9 ± 5.4  27.7 ± 5.3  .44  Body temperature (°C)  36.8 ± 0.5  36.9 ± 0.5  .99  Blood pressure (mmHg)  89.5 ± 8.2  91.9 ± 7.3  .22  Surgical methods (A/AP/P)  0/6/10  2/5/2  ns  Operation time (min)  477 ± 151  485 ± 167  .91  EBL (ml)  1689.6 ± 890  2395.4 ± 1254  .19  Post Cobb angle (°)  24.9 ± 15.8  35.0 ± 21.3  .25  Correction rate (%)  69.9 ± 15.3  61.0 ± 17.8  .27  CP, cerebral palsy; E-D, Ehlas-Danlos; NF-1, neurofibromatosis type 1 View Large TABLE 2. Incidence of Intraoperative Wave Deterioration Using the 70% Criterion Deterioration Syndrome  +(n = 16) CP 7, NF-1 4, Sotos 2, E-D 1, Down 1, Noonan 1  − (n = 9) Marfan 4, NF-1, 3, CP 1, down 1  P  Age (years)  12.9 ± 3.5  14.3 ± 14.1  .15  Sex (male/female) (n)  10/6  6/3  .6  Preop. Halo-traction (n)  5  3  .9  Pre Cobb angle (°)  79.4 ± 15.7  85.4 ± 30.9  .6  Flexibility (%)  36.4 ± 12.3  28.2 ± 12.3  .15  Angular curve (°)  19.3 ± 7.0  14.1 ± 3.1  .03  Sagittal Cobb angle (°)  25.9 ± 5.4  27.7 ± 5.3  .44  Body temperature (°C)  36.8 ± 0.5  36.9 ± 0.5  .99  Blood pressure (mmHg)  89.5 ± 8.2  91.9 ± 7.3  .22  Surgical methods (A/AP/P)  0/6/10  2/5/2  ns  Operation time (min)  477 ± 151  485 ± 167  .91  EBL (ml)  1689.6 ± 890  2395.4 ± 1254  .19  Post Cobb angle (°)  24.9 ± 15.8  35.0 ± 21.3  .25  Correction rate (%)  69.9 ± 15.3  61.0 ± 17.8  .27  Syndrome  +(n = 16) CP 7, NF-1 4, Sotos 2, E-D 1, Down 1, Noonan 1  − (n = 9) Marfan 4, NF-1, 3, CP 1, down 1  P  Age (years)  12.9 ± 3.5  14.3 ± 14.1  .15  Sex (male/female) (n)  10/6  6/3  .6  Preop. Halo-traction (n)  5  3  .9  Pre Cobb angle (°)  79.4 ± 15.7  85.4 ± 30.9  .6  Flexibility (%)  36.4 ± 12.3  28.2 ± 12.3  .15  Angular curve (°)  19.3 ± 7.0  14.1 ± 3.1  .03  Sagittal Cobb angle (°)  25.9 ± 5.4  27.7 ± 5.3  .44  Body temperature (°C)  36.8 ± 0.5  36.9 ± 0.5  .99  Blood pressure (mmHg)  89.5 ± 8.2  91.9 ± 7.3  .22  Surgical methods (A/AP/P)  0/6/10  2/5/2  ns  Operation time (min)  477 ± 151  485 ± 167  .91  EBL (ml)  1689.6 ± 890  2395.4 ± 1254  .19  Post Cobb angle (°)  24.9 ± 15.8  35.0 ± 21.3  .25  Correction rate (%)  69.9 ± 15.3  61.0 ± 17.8  .27  CP, cerebral palsy; E-D, Ehlas-Danlos; NF-1, neurofibromatosis type 1 View Large Amplitude deterioration occurred during exposure in 1 case, in rod placement on the concave side before rotation in 4 cases, in rotation in 8 cases, and in rod placement on the convex side after rotation in 3 cases (Table 3). A 100% loss in TcMEP amplitude occurred in all muscles in 7 cases and in one leg in 3 cases. One case with an amplitude decrease during exposure recovered without an additional procedure. Of the 3 cases with an amplitude decrease during rod placement before rotation, 2 recovered in 10 min and the third, in which amplitude did not recover, had transient motor deficit after surgery. Seven of 8 cases with an amplitude decrease during rotation and all 3 with an amplitude decrease during rod placement after rotation recovered without an additional procedure. The 1 case that required an additional procedure is described in the next section. TABLE 3. Timing of Amplitude Change Procedure  n  Recover  Motor deficit  Exposure  1  1  0  Rod placement before derotation  4  3  1  Derotation  8  8  0  Rod placement after derotation  3  3  0  Procedure  n  Recover  Motor deficit  Exposure  1  1  0  Rod placement before derotation  4  3  1  Derotation  8  8  0  Rod placement after derotation  3  3  0  View Large TABLE 3. Timing of Amplitude Change Procedure  n  Recover  Motor deficit  Exposure  1  1  0  Rod placement before derotation  4  3  1  Derotation  8  8  0  Rod placement after derotation  3  3  0  Procedure  n  Recover  Motor deficit  Exposure  1  1  0  Rod placement before derotation  4  3  1  Derotation  8  8  0  Rod placement after derotation  3  3  0  View Large Illustrative Case The patient was a 15-yr-old boy in the DA+ group. The preoperative Cobb angle of the main curve was 114° at T5-L1 (Figure 2A). Surgery for posterior correction and fusion at T4-L5 was performed. TcMEP amplitude decreased to 100% from baseline after rotation (Figure 2B, arrowhead). The amplitude recovered following removal of the rod and pediclectomy at the concave site of spinal cord kinking (Figure 2B, arrow). Surgery was finished with moderate correction with a stable amplitude (Figure 2C) and without a neurological deficit. FIGURE 2. View largeDownload slide The patient was a 15-yr-old boy in the DA+ group. A, The preoperative Cobb angle of the main curve was 114° at T5-L1. Surgery for posterior correction and fusion at T4-L5 was performed. B, TcMEP amplitude decreased to 100% from baseline after rotation (arrowhead). The amplitude recovered following removal of the rod and pediclectomy at the concave site of spinal cord kinking (arrow). C, Surgery was finished with moderate correction within a stable amplitude and no neurological deficit. FIGURE 2. View largeDownload slide The patient was a 15-yr-old boy in the DA+ group. A, The preoperative Cobb angle of the main curve was 114° at T5-L1. Surgery for posterior correction and fusion at T4-L5 was performed. B, TcMEP amplitude decreased to 100% from baseline after rotation (arrowhead). The amplitude recovered following removal of the rod and pediclectomy at the concave site of spinal cord kinking (arrow). C, Surgery was finished with moderate correction within a stable amplitude and no neurological deficit. DISCUSSION Correction of scoliosis may encounter a critical phase, and safe procedures are needed to minimize postoperative motor and sensory deficits.22,23 This had led to recognition of the importance of spinal cord monitoring. Spinal cord monitoring of somatosensory-evoked potentials was suggested in scoliosis surgery by the Scoliosis Research Society as a standard of care in 1992,6 and such monitoring is now common in surgery for spinal deformity. Waveform changes in 11 (12%) of 92 scoliosis cases and no motor deficits using SC-TNP were described by Kamata et al24; and in another 102 scoliosis cases, Tsuji et al25 found Br(E)-MsEP waveform changes in 20 (19.6%), and 3 cases with transient motor deficits. These reports included syndromic scoliosis among cases of general spinal deformity, but there have been no studies of syndromic scoliosis alone. Therefore, in the current study, waveform deterioration in spinal cord monitoring was examined during surgery for syndromic scoliosis. In this study, a decrease from baseline TcMEP amplitude of ≥70% occurred in 16 surgeries (64%). A short angular curve was a risk factor for amplitude change, and a 14° curve per level of curve was the threshold for a greater risk for amplitude change in TcMEP. To our knowledge, this is the first study of the incidence of TcMEP amplitude change and related risk factors in syndromic scoliosis. Qui et al3 identified congenital scoliosis, scoliosis with hyperkyphosis, a combined procedure, scoliosis with a Cobb angle >90°, and revision surgery as risk factors for neurological deficits after scoliosis correction. There was a tendency for an increased correction rate in the DA+ group, and overcorrection may also partly account for the signal changes. TcMEPs were recorded in patients who received a total intravenous anesthesia regimen to optimize response amplitudes and reduce response variability. TcMEPs are mediated by pathways with critical synaptic junctions in the spinal cord.26 Both anterior horn motor neurons in the spinal cord and particularly spinal motor interneurons have a high metabolic rate, which increases the vulnerability of the anterior horn gray matter and spinal motor system to ischemic injury.27 TcMEPs have greater sensitivity to ischemic changes in the spinal cord and facilitate a more rapid reaction.26 Transient ischemia of the spinal cord in the spinal canal due to correction of a short angular curve may cause an amplitude change. TcMEPs may also be influenced by blood pressure and temperature, but these parameters at the time of correction or amplitude change had no association with amplitude change in this study. Intraoperative spinal cord injury due to ischemia may not always affect blood pressure and body temperature, but transient ischemia due to low blood pressure results in amplitude change. Most amplitude changes occurred in rod placement before rotation or during rotation. Therefore, translation during rod placement before rotation and in rotation for each vertebra at the location of deformity may both be associated with spinal cord ischemia. Amplitude change during rod placement after rotation might suggest delayed-onset expression causes spinal cord ischemia after rotation. Undercorrection or rod removal is required if there is no recovery of amplitude in a few minutes. It is also important to perform pediclectomy at the concave site of the angular curve when there has been an amplitude change during correction in syndromic scoliosis with a short angular curve. Limitations A limitation of the study was the use of a nonparametric test in statistical analysis in a case series with <30 subjects. Use of a larger cohort could help to confirm the risk factors for wave changes in intraoperative TcMEP during corrective fusion for syndromic scoliosis. CONCLUSION A clinical study of TcMEP amplitudes in surgery for correction of syndromic scoliosis showed that a short angular curve is a risk factor of amplitude change. Undercorrection with rod removal should be performed if amplitude does not recover in a few minutes. It may also be important to perform pediclectomy at the concave site of the angular curve in a case with an amplitude change during correction of syndromic scoliosis with a short angular curve. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Winter RB. Neurologic safety in spinal deformity surgery. Spine . 1997; 22( 13): 1527- 1533. Google Scholar CrossRef Search ADS PubMed  2. Mooney JF 3rd, Bernstein R, Hennrikus WL Jr, MacEwen GD. Neurologic risk management in scoliosis surgery. J Pediatr Orthop . 2002; 22( 5): 683- 689. Google Scholar PubMed  3. Qiu Y, Wang S, Wang B, Yu Y, Zhu F, Zhu Z. 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Spinal cord evoked potential monitoring after spinal cord stimulation during surgery of spinal cord tumors. Neurosurgery . 1993; 33( 3): 451- 459. Google Scholar PubMed  23. Ulkatan S, Neuwirth M, Bitan F, Minardi C, Kokoszka A, Deletis V. Monitoring of scoliosis surgery with epidurally recorded motor evoked potentials (D wave) revealed false results. Clin Neurophysiol . 2006; 117( 9): 2093- 2101. Google Scholar CrossRef Search ADS PubMed  24. Kamata M, Suzuki N, Ono T et al.   Intraoperative spinal cord monitoring in scoliosis surgery: wave form changes by technical procedures. Seikeigeka . 1999; 50: 249- 254. 25. Tsuji T, Kawakami N, Goto M et al.   Compound muscle action potential monitoring during operation of spinal deformity. Nihonsekitui sekizuibyo-gakkai zassi . 2006; 17: 426. 26. Schwartz DM, Auerbach JD, Dormans JP et al.   Neurophysiological detection of impending spinal cord injury during scoliosis surgery. J Bone Joint Surg Am . 2007; 89( 11): 2440- 2449. Google Scholar PubMed  27. de Haan P, Kalkman CJ, de Mol BA, Ubags LH, Veldman DJ, Jacobs MJ. Efficacy of transcranial motor-evoked myogenic potentials to detect spinal cord ischemia during operations for thoracoabdominal aneurysms. J Thorac Cardiovasc Surg . 1997; 113( 1): 87- 101. Google Scholar CrossRef Search ADS PubMed  Operative Neurosurgery Speaks! Audio abstracts available for this article at www.operativeneurosurgery-online.com. Operative Neurosurgery Speaks (Audio Abstracts) Listen to audio translations of this paper's abstract into select languages by choosing from one of the selections below. Chinese: Lin Song, MD Department of Neurosurgery Beijing Tiantan Hospital Capital Medical University Beijing, China Chinese: Lin Song, MD Department of Neurosurgery Beijing Tiantan Hospital Capital Medical University Beijing, China Close English: Oluwakemi Aderonke Badejo, MBBS, FWACS Department of Surgery College of Medicine University of Ibadan Ibadan, Nigeria English: Oluwakemi Aderonke Badejo, MBBS, FWACS Department of Surgery College of Medicine University of Ibadan Ibadan, Nigeria Close French: Michael Bruneau, MD, PhD Department of Neurosurgery Erasme Hospital Brussels, Belgium French: Michael Bruneau, MD, PhD Department of Neurosurgery Erasme Hospital Brussels, Belgium Close Italian: Daniele Bongetta, MD Department of Neurosurgery Fondazione IRCCS Policlinico San Matteo Pavia, Italy Italian: Daniele Bongetta, MD Department of Neurosurgery Fondazione IRCCS Policlinico San Matteo Pavia, Italy Close Portuguese: Andrei Joaquim, MD, PhD Department of Neurology Division of Neurosurgery University of Campinas (UNICAMP) Campinas, Brazil Portuguese: Andrei Joaquim, MD, PhD Department of Neurology Division of Neurosurgery University of Campinas (UNICAMP) Campinas, Brazil Close Spanish: Alejandro Enriquez-Marulanda, MD Department of Neurosurgery Hospital Virgen del Rocío Sevilla, Spain Spanish: Alejandro Enriquez-Marulanda, MD Department of Neurosurgery Hospital Virgen del Rocío Sevilla, Spain Close Japanese: Soichi Oya, MD, PhD Department of Neurosurgery Saitama Medical Center/University Saitama, Japan Japanese: Soichi Oya, MD, PhD Department of Neurosurgery Saitama Medical Center/University Saitama, Japan Close Russian: Roman Kovalenko, MD Federal Almazov North-West Medical Research Centre St. Petersburg Russian Federation Russian: Roman Kovalenko, MD Federal Almazov North-West Medical Research Centre St. Petersburg Russian Federation Close Korean: Tae Gon Kim, MD Division of Vascular Section Department of Neurosurgery Bundang CHA Hospital Seongnam, Republic of Korea Korean: Tae Gon Kim, MD Division of Vascular Section Department of Neurosurgery Bundang CHA Hospital Seongnam, Republic of Korea Close Greek: Marios Themistocleous, MD Department of Neurosurgery Aghia Sophia Children's Hospital Athens, Greece Greek: Marios Themistocleous, MD Department of Neurosurgery Aghia Sophia Children's Hospital Athens, Greece Close Copyright © 2018 by the Congress of Neurological Surgeons http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Operative Neurosurgery Oxford University Press

Wave Change of Intraoperative Transcranial Motor-Evoked Potentials During Corrective Fusion for Syndromic and Neuromuscular Scoliosis

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Copyright © 2018 by the Congress of Neurological Surgeons
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2332-4252
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Abstract

Abstract BACKGROUND There is little information on intraoperative neuromonitoring during correction fusion surgery for syndromic scoliosis. OBJECTIVE To investigate intraoperative TcMEPs and conditions (body temperature and blood pressure) for syndromic scoliosis. METHODS The subjects were 23 patients who underwent 25 surgeries for corrective fusion using TcMEP. Patients were divided into groups based on a decrease (DA+) or no decrease (DA−) of the amplitude of the TcMEP waveform of ≥70%. The groups were compared for age, sex, disease, type of surgery, fusion area, operation time, estimated blood loss, body temperature, blood pressure, Cobb angle, angular curve (Cobb angle/number of vertebra), bending flexibility, correction rate, and recovery. RESULTS The mean Cobb angles before and after surgery were 85.2° and 29.1°, giving a correction rate of 68.2%. There were 16 surgeries (64.0%) with intraoperative TcMEP wave changes. The DA+ and DA− groups had similar intraoperative conditions, but the short angular curve differed significantly between these groups. Amplitude deterioration occurred in 4 cases during first rod placement, in 8 during rotation, and in 3 during second rod placement after rotation. Seven patients had complete loss of TcMEP. However, most TcMEP changes recovered after pediclectomy or decreased correction. The preoperative angular curve differed significantly between patients with and without TcMEP changes (P < .05). CONCLUSION Intraoperative TcMEP wave changes occurred in 64.0% of surgeries for corrective fusion, and all but one of these changes occurred during the correction procedure. The angular curve was a risk factor for intraoperative motor deficit. Risk factors, Wave changes of intraoperative transcranial motor-evoked potentials, Syndromic scoliosis, Short angular curve ABBREVIATIONS ABBREVIATIONS AP anterior-posterior AUCs areas under the ROC curve ICC intraclass correlation coefficient ROC receiver operating characteristics TcMEP transcranial motor-evoked potential UHMW ultrahigh molecular weight. Neural complications are severe risks in surgery with instrumentation for scoliosis correction.1-3 The incidence of neurological deficit after this surgery has been widely studied3-6 and has been associated with type of procedure, curve magnitude, instrumentation type, combined approach, and decreased spinal cord perfusion due to hypotension or significant hemorrhage in surgery for idiopathic scoliosis.4 Syndromic scoliosis is generally defined as scoliosis associated with a systemic disease, including Down syndrome, Rett syndrome, achondroplasia, Ehlers–Danlos syndrome, Prader–Willi syndrome, Friedrich ataxia, Marfan syndrome, neurofibromatosis, and osteogenesis imperfecta.7 The rate of neurological deficit with syndromic scoliosis is more frequent than that with idiopathic scoliosis.7-10 Intraoperative spinal cord monitoring is important to reduce neurological complications in syndromic scoliosis.11 Transcranial motor-evoked potential (TcMEP) monitoring is a simple and increasingly used approach with high sensitivity and specificity that is particularly effective for the corticospinal tract.12-14 In this approach, decreased spinal cord perfusion during correction can be detected as a signal change intraoperatively or after surgery as loss of neural function with delayed onset. However, there is little information on intraoperative neuromonitoring and conditions (body temperature and blood pressure) during correction fusion surgery for syndromic scoliosis. An improved understanding of wave changes in surgery for syndromic scoliosis is an important step in reducing neural complications. Therefore, this study was performed to investigate TcMEP wave changes during correction fusion surgery for syndromic scoliosis. METHODS Patients A total of 110 consecutive patients aged <20 yr old underwent correction and fusion surgery under intraoperative neurophysiological TcMEP monitoring at our hospital from 2005 to 2013. Among these patients, there were 23 with syndromic scoliosis, including 8 cases with an etiology of cerebral palsy, 7 of neurofibromatosis type 1, 4 of Marfan syndrome, and 1 each of Down syndrome, Ehlas–Danlos syndrome, Sotos syndrome, and Noonan syndrome. Eight cases were treated preoperatively with Halo-ring traction. For the thoracic main curve, ultrahigh molecular weight (UHMW) polyethylene tape was used on the concave side of the scoliosis. Translation and rotation forces were used with direct vertebral rotation with a concave rod, using pedicle screws inserted at the apex.15 For the lumbar curve, segmental screw fixations were performed. Radiographic data were evaluated using Spinal Deformity Group parameters.16 Certified radiology technicians took standard pre- and postoperative upright anterior-posterior (AP) and lateral standing radiographs and AP supine traction radiographs on long cassettes. Medical records and radiographs were reviewed by 2 spine surgeons. In this review, Cobb angles of the major thoracic and lumbar curves were measured to calculate the correction rate: (preoperative Cobb angle – postoperative Cobb angle)/(preoperative Cobb angle) × 100%. Preoperative flexibility was measured using the Cobb angle for side bending: (preoperative Cobb angle – Cobb angle for side bending)/(preoperative Cobb angle) × 100%. Patients were divided into groups based on a decrease (DA+) or no decrease (DA–) of amplitude of the TcMEP waveform of ≥70%, based on use of a similar criterion in a nationwide, prospective multicenter study in Japan.17-19 Age, sex, disease, surgical method, fusion area, operation time, estimated blood loss, change of body temperature, blood pressure (during the correction procedure in the DA– group and at the time of amplitude change in the DA+ group), preoperative Cobb angle of the main curve, preoperative flexibility under traction, short angular curve (preoperative Cobb angle of the main curve/number of vertebra) that means severe curve with the spinal cord in the canal, postoperative Cobb angle, and correction rate were compared retrospectively between the DA+ and DA– groups. The timing of procedures was also investigated in the DA+ group. The study was approved by our IRB and informed consent was obtained from all patients. Anesthetic Management Benzodiazepine suppresses latency and amplitude and thus was used minimally, if at all, as a preanesthetic medication. Induction was achieved with propofol (3-4 mg/kg), fentanyl (2 mg/kg), and vecuronium (Fuji Pharma Co, Ltd, Tokyo, Japan; 0.12-0.16 mg/kg), and anesthesia was maintained using propofol (50-100 μg/kg/min) and fentanyl (1-2.5 μg/kg/h). Normal end-tidal CO2 was maintained throughout surgery. Stimulating and Recording Methods A D185 MultiPulse Stimulator (Digitimer Ltd, Welwyn Garden City, Hertfordshire, England) was used for transcranial stimulation, using 4 to 5 stimuli in a row at 2-ms intervals, a stimulus of 300 to 600 V, and a 100-ms epoch time with 20 individual recorded responses. The point of stimulation in the International 10-20 System was 2-cm anterior and 3-cm lateral from the Cz location. Motor-evoked potentials were recorded from the upper and lower extremities via a pair of needle electrodes, using Neuropack MEB-2200 v. 04.02 (Nihon Kohden, Tokyo, Japan), with monitoring of as many muscles as possible among the deltoid and hypothenar from the upper extremities, and bilateral adductor longus, quadriceps femoris (quad), hamstrings, tibialis anterior, gastrocnemius, and abductor hallucis from the lower extremities (quad, hamstrings, tibialis anterior, and gastrocnemius until 2009), depending on the spinal level of surgery. Only MEP data from lower extremity muscles were used for analysis. Multimodal monitoring was performed in all cases. Monitoring and Alert Parameters TcMEP values at baseline were recorded immediately after surgical exposure of the spine, and then signals were obtained after screwing, fixing of UHMW polyethylene tape on the concave side, rod placement on the concave side, rotation, and rod placement on the other side. A final TcMEP test was performed after wound closure. TcMEP peak-to-peak amplitudes are shown in μV. If a decrease in TcMEP of ≥70% occurred, the surgeons were notified of this as a minor neurophysiological change. A decrease from baseline of 90% or a slip below 5 μV was considered to be a major change indicating possible motor tract injury, and surgery was stopped for a few minutes to allow recovery of the neurophysiological signal. Additional procedures, such as removal of the rod or increasing blood pressure, were also performed. Receiver operating characteristics (ROC) analysis was conducted for each short angular curve for each decrease in the amplitude of TcMEP ≥70%. Statistical Analysis SPSS ver. 19 (SPSS Inc, IBM Inc, Armonk, New York) was used for data analysis. Values are presented as mean ± SD. Differences between the 2 groups were analyzed by the Mann–Whitney U test and Fisher exact test. The cutoff amplitude for each short angular curve for each decreased amplitude of TcMEP ≥ 70% was determined using ROC analysis. Sensitivity and specificity at optimal cutoff values were calculated. Areas under the ROC curve (AUCs) of >0.9, 0.7-0.9, 0.5-0.7, 0.5 were interpreted to indicate high accuracy, moderate accuracy, low accuracy, and a chance result, respectively.20 The intraclass correlation coefficient (ICC) was used to evaluate intra- and interobserver reliability of the measurements of the 3 imaging modalities, with values of <0.40, 0.40-0.59, 0.60-0.74, and 0.75-1.00 considered to be poor, fair, good, and excellent, respectively.21P < .05 was taken to be significant in all analyses. RESULTS Descriptive Data A total of 25 surgeries were performed on 23 patients (15 males and 8 females) with a mean age of 15.8 yr (range: 5-17 yr) at surgery. One male and one female underwent 2 surgeries each because of proximal adjacent kyphosis and progression of non-fused thoracic spine, respectively. The average follow-up period was 5.1 yr (range: 2-10 yr). Eight patients received preoperative halo-traction. Two were treated with anterior vertebral body-screw fixation, 11 with posterior correction fusion followed by anterior release and bone graft, and 12 with posterior correction fusion. The total operation time was 482 min (188-781 min) and total EBL was 1965 ml (428-4179 ml; Table 1). TABLE 1. Demographic and Clinical Data Age (years)  16  Gender male/female (n)  14/7  Preoperative Cobb angle (°)  81.6  Traction Cobb angle (°)  55.1  Flexibility (%)  33.4  Age (years)  16  Gender male/female (n)  14/7  Preoperative Cobb angle (°)  81.6  Traction Cobb angle (°)  55.1  Flexibility (%)  33.4  View Large TABLE 1. Demographic and Clinical Data Age (years)  16  Gender male/female (n)  14/7  Preoperative Cobb angle (°)  81.6  Traction Cobb angle (°)  55.1  Flexibility (%)  33.4  Age (years)  16  Gender male/female (n)  14/7  Preoperative Cobb angle (°)  81.6  Traction Cobb angle (°)  55.1  Flexibility (%)  33.4  View Large Rates of Successful Derivation and TcMEP Deterioration In the 25 surgeries, 284 muscles in the lower extremities were monitored, and acceptable baseline TcMEP responses were obtained from 270 (95%). Intraoperative electrophysiological deterioration, which was defined as a decrease from baseline TcMEP amplitude of ≥70%, occurred in 16 surgeries (64%, DA+ group). There were 7 cases with an etiology of cerebral palsy, 4 of neurofibromatosis type 1, 2 of Sotos syndrome, and 1 each of Down syndrome, Ehlas-Danlos syndrome, and Noonan syndrome. There were no significant differences in age, sex, disease, surgical methods, operation time, EBL, change of body temperature, blood pressure at correction, preoperative Cobb angle of the main curve, preoperative flexibility, postoperative Cobb angle, and correction rate between the DA+ and DA− groups, but the short angular curve (preoperative Cobb angle of the main curve/number of vertebra) and the fusion area did differ significantly between the 2 groups (P < .05; Table 2). The AUC for the ROC curve was 0.75 and the cutoff amplitude was 14.19° (Figure 1). Eight cases in the DA+ group had pre- and intraoperative traction, and 5 of these cases had signal changes. There was 1 nonambulatory case with CP in the DA+ group. The intra- and interobserver reliabilities were excellent (ICC: 0.776, 0.757, respectively). FIGURE 1. View largeDownload slide ROC analysis for each short angular curve for each decreased amplitude of the TcMEP ≥ 70%. The cutoff angle was 14.19°, at which the sensitivity was 0.625 and the specificity was 0.929. FIGURE 1. View largeDownload slide ROC analysis for each short angular curve for each decreased amplitude of the TcMEP ≥ 70%. The cutoff angle was 14.19°, at which the sensitivity was 0.625 and the specificity was 0.929. TABLE 2. Incidence of Intraoperative Wave Deterioration Using the 70% Criterion Deterioration Syndrome  +(n = 16) CP 7, NF-1 4, Sotos 2, E-D 1, Down 1, Noonan 1  − (n = 9) Marfan 4, NF-1, 3, CP 1, down 1  P  Age (years)  12.9 ± 3.5  14.3 ± 14.1  .15  Sex (male/female) (n)  10/6  6/3  .6  Preop. Halo-traction (n)  5  3  .9  Pre Cobb angle (°)  79.4 ± 15.7  85.4 ± 30.9  .6  Flexibility (%)  36.4 ± 12.3  28.2 ± 12.3  .15  Angular curve (°)  19.3 ± 7.0  14.1 ± 3.1  .03  Sagittal Cobb angle (°)  25.9 ± 5.4  27.7 ± 5.3  .44  Body temperature (°C)  36.8 ± 0.5  36.9 ± 0.5  .99  Blood pressure (mmHg)  89.5 ± 8.2  91.9 ± 7.3  .22  Surgical methods (A/AP/P)  0/6/10  2/5/2  ns  Operation time (min)  477 ± 151  485 ± 167  .91  EBL (ml)  1689.6 ± 890  2395.4 ± 1254  .19  Post Cobb angle (°)  24.9 ± 15.8  35.0 ± 21.3  .25  Correction rate (%)  69.9 ± 15.3  61.0 ± 17.8  .27  Syndrome  +(n = 16) CP 7, NF-1 4, Sotos 2, E-D 1, Down 1, Noonan 1  − (n = 9) Marfan 4, NF-1, 3, CP 1, down 1  P  Age (years)  12.9 ± 3.5  14.3 ± 14.1  .15  Sex (male/female) (n)  10/6  6/3  .6  Preop. Halo-traction (n)  5  3  .9  Pre Cobb angle (°)  79.4 ± 15.7  85.4 ± 30.9  .6  Flexibility (%)  36.4 ± 12.3  28.2 ± 12.3  .15  Angular curve (°)  19.3 ± 7.0  14.1 ± 3.1  .03  Sagittal Cobb angle (°)  25.9 ± 5.4  27.7 ± 5.3  .44  Body temperature (°C)  36.8 ± 0.5  36.9 ± 0.5  .99  Blood pressure (mmHg)  89.5 ± 8.2  91.9 ± 7.3  .22  Surgical methods (A/AP/P)  0/6/10  2/5/2  ns  Operation time (min)  477 ± 151  485 ± 167  .91  EBL (ml)  1689.6 ± 890  2395.4 ± 1254  .19  Post Cobb angle (°)  24.9 ± 15.8  35.0 ± 21.3  .25  Correction rate (%)  69.9 ± 15.3  61.0 ± 17.8  .27  CP, cerebral palsy; E-D, Ehlas-Danlos; NF-1, neurofibromatosis type 1 View Large TABLE 2. Incidence of Intraoperative Wave Deterioration Using the 70% Criterion Deterioration Syndrome  +(n = 16) CP 7, NF-1 4, Sotos 2, E-D 1, Down 1, Noonan 1  − (n = 9) Marfan 4, NF-1, 3, CP 1, down 1  P  Age (years)  12.9 ± 3.5  14.3 ± 14.1  .15  Sex (male/female) (n)  10/6  6/3  .6  Preop. Halo-traction (n)  5  3  .9  Pre Cobb angle (°)  79.4 ± 15.7  85.4 ± 30.9  .6  Flexibility (%)  36.4 ± 12.3  28.2 ± 12.3  .15  Angular curve (°)  19.3 ± 7.0  14.1 ± 3.1  .03  Sagittal Cobb angle (°)  25.9 ± 5.4  27.7 ± 5.3  .44  Body temperature (°C)  36.8 ± 0.5  36.9 ± 0.5  .99  Blood pressure (mmHg)  89.5 ± 8.2  91.9 ± 7.3  .22  Surgical methods (A/AP/P)  0/6/10  2/5/2  ns  Operation time (min)  477 ± 151  485 ± 167  .91  EBL (ml)  1689.6 ± 890  2395.4 ± 1254  .19  Post Cobb angle (°)  24.9 ± 15.8  35.0 ± 21.3  .25  Correction rate (%)  69.9 ± 15.3  61.0 ± 17.8  .27  Syndrome  +(n = 16) CP 7, NF-1 4, Sotos 2, E-D 1, Down 1, Noonan 1  − (n = 9) Marfan 4, NF-1, 3, CP 1, down 1  P  Age (years)  12.9 ± 3.5  14.3 ± 14.1  .15  Sex (male/female) (n)  10/6  6/3  .6  Preop. Halo-traction (n)  5  3  .9  Pre Cobb angle (°)  79.4 ± 15.7  85.4 ± 30.9  .6  Flexibility (%)  36.4 ± 12.3  28.2 ± 12.3  .15  Angular curve (°)  19.3 ± 7.0  14.1 ± 3.1  .03  Sagittal Cobb angle (°)  25.9 ± 5.4  27.7 ± 5.3  .44  Body temperature (°C)  36.8 ± 0.5  36.9 ± 0.5  .99  Blood pressure (mmHg)  89.5 ± 8.2  91.9 ± 7.3  .22  Surgical methods (A/AP/P)  0/6/10  2/5/2  ns  Operation time (min)  477 ± 151  485 ± 167  .91  EBL (ml)  1689.6 ± 890  2395.4 ± 1254  .19  Post Cobb angle (°)  24.9 ± 15.8  35.0 ± 21.3  .25  Correction rate (%)  69.9 ± 15.3  61.0 ± 17.8  .27  CP, cerebral palsy; E-D, Ehlas-Danlos; NF-1, neurofibromatosis type 1 View Large Amplitude deterioration occurred during exposure in 1 case, in rod placement on the concave side before rotation in 4 cases, in rotation in 8 cases, and in rod placement on the convex side after rotation in 3 cases (Table 3). A 100% loss in TcMEP amplitude occurred in all muscles in 7 cases and in one leg in 3 cases. One case with an amplitude decrease during exposure recovered without an additional procedure. Of the 3 cases with an amplitude decrease during rod placement before rotation, 2 recovered in 10 min and the third, in which amplitude did not recover, had transient motor deficit after surgery. Seven of 8 cases with an amplitude decrease during rotation and all 3 with an amplitude decrease during rod placement after rotation recovered without an additional procedure. The 1 case that required an additional procedure is described in the next section. TABLE 3. Timing of Amplitude Change Procedure  n  Recover  Motor deficit  Exposure  1  1  0  Rod placement before derotation  4  3  1  Derotation  8  8  0  Rod placement after derotation  3  3  0  Procedure  n  Recover  Motor deficit  Exposure  1  1  0  Rod placement before derotation  4  3  1  Derotation  8  8  0  Rod placement after derotation  3  3  0  View Large TABLE 3. Timing of Amplitude Change Procedure  n  Recover  Motor deficit  Exposure  1  1  0  Rod placement before derotation  4  3  1  Derotation  8  8  0  Rod placement after derotation  3  3  0  Procedure  n  Recover  Motor deficit  Exposure  1  1  0  Rod placement before derotation  4  3  1  Derotation  8  8  0  Rod placement after derotation  3  3  0  View Large Illustrative Case The patient was a 15-yr-old boy in the DA+ group. The preoperative Cobb angle of the main curve was 114° at T5-L1 (Figure 2A). Surgery for posterior correction and fusion at T4-L5 was performed. TcMEP amplitude decreased to 100% from baseline after rotation (Figure 2B, arrowhead). The amplitude recovered following removal of the rod and pediclectomy at the concave site of spinal cord kinking (Figure 2B, arrow). Surgery was finished with moderate correction with a stable amplitude (Figure 2C) and without a neurological deficit. FIGURE 2. View largeDownload slide The patient was a 15-yr-old boy in the DA+ group. A, The preoperative Cobb angle of the main curve was 114° at T5-L1. Surgery for posterior correction and fusion at T4-L5 was performed. B, TcMEP amplitude decreased to 100% from baseline after rotation (arrowhead). The amplitude recovered following removal of the rod and pediclectomy at the concave site of spinal cord kinking (arrow). C, Surgery was finished with moderate correction within a stable amplitude and no neurological deficit. FIGURE 2. View largeDownload slide The patient was a 15-yr-old boy in the DA+ group. A, The preoperative Cobb angle of the main curve was 114° at T5-L1. Surgery for posterior correction and fusion at T4-L5 was performed. B, TcMEP amplitude decreased to 100% from baseline after rotation (arrowhead). The amplitude recovered following removal of the rod and pediclectomy at the concave site of spinal cord kinking (arrow). C, Surgery was finished with moderate correction within a stable amplitude and no neurological deficit. DISCUSSION Correction of scoliosis may encounter a critical phase, and safe procedures are needed to minimize postoperative motor and sensory deficits.22,23 This had led to recognition of the importance of spinal cord monitoring. Spinal cord monitoring of somatosensory-evoked potentials was suggested in scoliosis surgery by the Scoliosis Research Society as a standard of care in 1992,6 and such monitoring is now common in surgery for spinal deformity. Waveform changes in 11 (12%) of 92 scoliosis cases and no motor deficits using SC-TNP were described by Kamata et al24; and in another 102 scoliosis cases, Tsuji et al25 found Br(E)-MsEP waveform changes in 20 (19.6%), and 3 cases with transient motor deficits. These reports included syndromic scoliosis among cases of general spinal deformity, but there have been no studies of syndromic scoliosis alone. Therefore, in the current study, waveform deterioration in spinal cord monitoring was examined during surgery for syndromic scoliosis. In this study, a decrease from baseline TcMEP amplitude of ≥70% occurred in 16 surgeries (64%). A short angular curve was a risk factor for amplitude change, and a 14° curve per level of curve was the threshold for a greater risk for amplitude change in TcMEP. To our knowledge, this is the first study of the incidence of TcMEP amplitude change and related risk factors in syndromic scoliosis. Qui et al3 identified congenital scoliosis, scoliosis with hyperkyphosis, a combined procedure, scoliosis with a Cobb angle >90°, and revision surgery as risk factors for neurological deficits after scoliosis correction. There was a tendency for an increased correction rate in the DA+ group, and overcorrection may also partly account for the signal changes. TcMEPs were recorded in patients who received a total intravenous anesthesia regimen to optimize response amplitudes and reduce response variability. TcMEPs are mediated by pathways with critical synaptic junctions in the spinal cord.26 Both anterior horn motor neurons in the spinal cord and particularly spinal motor interneurons have a high metabolic rate, which increases the vulnerability of the anterior horn gray matter and spinal motor system to ischemic injury.27 TcMEPs have greater sensitivity to ischemic changes in the spinal cord and facilitate a more rapid reaction.26 Transient ischemia of the spinal cord in the spinal canal due to correction of a short angular curve may cause an amplitude change. TcMEPs may also be influenced by blood pressure and temperature, but these parameters at the time of correction or amplitude change had no association with amplitude change in this study. Intraoperative spinal cord injury due to ischemia may not always affect blood pressure and body temperature, but transient ischemia due to low blood pressure results in amplitude change. Most amplitude changes occurred in rod placement before rotation or during rotation. Therefore, translation during rod placement before rotation and in rotation for each vertebra at the location of deformity may both be associated with spinal cord ischemia. Amplitude change during rod placement after rotation might suggest delayed-onset expression causes spinal cord ischemia after rotation. Undercorrection or rod removal is required if there is no recovery of amplitude in a few minutes. It is also important to perform pediclectomy at the concave site of the angular curve when there has been an amplitude change during correction in syndromic scoliosis with a short angular curve. Limitations A limitation of the study was the use of a nonparametric test in statistical analysis in a case series with <30 subjects. Use of a larger cohort could help to confirm the risk factors for wave changes in intraoperative TcMEP during corrective fusion for syndromic scoliosis. CONCLUSION A clinical study of TcMEP amplitudes in surgery for correction of syndromic scoliosis showed that a short angular curve is a risk factor of amplitude change. Undercorrection with rod removal should be performed if amplitude does not recover in a few minutes. It may also be important to perform pediclectomy at the concave site of the angular curve in a case with an amplitude change during correction of syndromic scoliosis with a short angular curve. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Winter RB. Neurologic safety in spinal deformity surgery. Spine . 1997; 22( 13): 1527- 1533. Google Scholar CrossRef Search ADS PubMed  2. Mooney JF 3rd, Bernstein R, Hennrikus WL Jr, MacEwen GD. Neurologic risk management in scoliosis surgery. J Pediatr Orthop . 2002; 22( 5): 683- 689. Google Scholar PubMed  3. Qiu Y, Wang S, Wang B, Yu Y, Zhu F, Zhu Z. 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Chinese: Lin Song, MD Department of Neurosurgery Beijing Tiantan Hospital Capital Medical University Beijing, China Chinese: Lin Song, MD Department of Neurosurgery Beijing Tiantan Hospital Capital Medical University Beijing, China Close English: Oluwakemi Aderonke Badejo, MBBS, FWACS Department of Surgery College of Medicine University of Ibadan Ibadan, Nigeria English: Oluwakemi Aderonke Badejo, MBBS, FWACS Department of Surgery College of Medicine University of Ibadan Ibadan, Nigeria Close French: Michael Bruneau, MD, PhD Department of Neurosurgery Erasme Hospital Brussels, Belgium French: Michael Bruneau, MD, PhD Department of Neurosurgery Erasme Hospital Brussels, Belgium Close Italian: Daniele Bongetta, MD Department of Neurosurgery Fondazione IRCCS Policlinico San Matteo Pavia, Italy Italian: Daniele Bongetta, MD Department of Neurosurgery Fondazione IRCCS Policlinico San Matteo Pavia, Italy Close Portuguese: Andrei Joaquim, MD, PhD Department of Neurology Division of Neurosurgery University of Campinas (UNICAMP) Campinas, Brazil Portuguese: Andrei Joaquim, MD, PhD Department of Neurology Division of Neurosurgery University of Campinas (UNICAMP) Campinas, Brazil Close Spanish: Alejandro Enriquez-Marulanda, MD Department of Neurosurgery Hospital Virgen del Rocío Sevilla, Spain Spanish: Alejandro Enriquez-Marulanda, MD Department of Neurosurgery Hospital Virgen del Rocío Sevilla, Spain Close Japanese: Soichi Oya, MD, PhD Department of Neurosurgery Saitama Medical Center/University Saitama, Japan Japanese: Soichi Oya, MD, PhD Department of Neurosurgery Saitama Medical Center/University Saitama, Japan Close Russian: Roman Kovalenko, MD Federal Almazov North-West Medical Research Centre St. Petersburg Russian Federation Russian: Roman Kovalenko, MD Federal Almazov North-West Medical Research Centre St. Petersburg Russian Federation Close Korean: Tae Gon Kim, MD Division of Vascular Section Department of Neurosurgery Bundang CHA Hospital Seongnam, Republic of Korea Korean: Tae Gon Kim, MD Division of Vascular Section Department of Neurosurgery Bundang CHA Hospital Seongnam, Republic of Korea Close Greek: Marios Themistocleous, MD Department of Neurosurgery Aghia Sophia Children's Hospital Athens, Greece Greek: Marios Themistocleous, MD Department of Neurosurgery Aghia Sophia Children's Hospital Athens, Greece Close Copyright © 2018 by the Congress of Neurological Surgeons

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Operative NeurosurgeryOxford University Press

Published: Mar 29, 2018

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