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A prospective multicenter observational study.The aim was to investigate the validity of transcranial motor-evoked potentials (Tc-MEP) in cervical spine surgery and identify factors associated with positive predictive value when Tc-MEP alerts are occurred.The sensitivity and specificity of Tc-MEP for detecting motor paralysis are high; however, false-positives sometimes occur.The authors examined Tc-MEP in 2476 cases of cervical spine surgeries and compared patient backgrounds, type of spinal disorders, preoperative motor status, surgical factors, and the types of Tc-MEP alerts. Tc-MEP alerts were defined as an amplitude reduction of more than 70% from the control waveform. Tc-MEP results were classified into two groups: false-positive and true-positive, and items that showed significant differences were extracted by univariate analysis and detected by multivariate analysis.Overall sensitivity was 66% (segmental paralysis: 33% and lower limb paralysis: 95.8%) and specificity was 91.5%. Tc-MEP outcomes were 33 true-positives and 233 false-positives. Positive predictive value of general spine surgery was significantly higher in cases with a severe motor status than in a nonsevere motor status (19.5% vs . 6.7%, P =0.02), but not different in high-risk spine surgery (20.8% vs . 19.4%). However, rescue rates did not significantly differ regardless of motor status (48% vs . 50%). In a multivariate logistic analysis, a preoperative severe motor status [ P =0.041, odds ratio (OR): 2.46, 95% confidence interval (95% CI): 1.03-5.86] and Tc-MEP alerts during intradural tumor resection ( P0.001, OR: 7.44, 95% CI: 2.64-20.96) associated with true-positives, while Tc-MEP alerts that could not be identified with surgical maneuvers ( P =0.011, OR: 0.23, 95% CI: 0.073-0.71) were associated with false-positives.The utility of Tc-MEP in patients with a preoperative severe motor status was enhanced, even in those without high-risk spine surgery. Regardless of the motor status, appropriate interventions following Tc-MEP alerts may prevent postoperative paralysis.

A prospective, multicenter study.This study clarified the uses and limitations of transcranial motor-evoked potentials (Tc-MEPs) for nerve root monitoring during adult spinal deformity (ASD) surgeries.Whether Tc-MEPs can detect nerve root injuries (NRIs) in ASD surgeries remains controversial.We prospectively analyzed neuromonitoring data from 14 institutions between 2017 and 2020. The subjects were ASD patients surgically treated with posterior corrective fusion using multichannel Tc-MEPs. An alert was defined as a decrease of ≥70% in the Tc-MEP's waveform amplitude from baseline, and NRI was considered as meeting the focal Tc-MEP alerts shortly following surgical procedures with postoperative nerve root symptoms in the selected muscles.A total of 311 patients with ASD (262 women and 49 men) and a mean age of 65.5 years were analyzed. Tc-MEP results revealed 47 cases (15.1%) of alerts, including 25 alerts after 10 deformity corrections, six three-column osteotomies, four interbody fusions, three pedicle screw placements or two decompressions, and 22 alerts regardless of surgical maneuvers. Postoperatively, 14 patients (4.5%) had neurological deterioration considered to be all NRI, 11 true positives, and three false negatives (FN). Two FN did not reach a 70% loss of baseline (46% and 65% loss of baseline) and one was not monitored at target muscles. Multivariate logistic regression analysis revealed that risk factors of NRI were preexisting motor weakness ( P0.001, odds ratio=10.41) and three-column osteotomies ( P =0.008, odds ratio=7.397).Nerve root injuries in our ASD cohort were partially predictable using multichannel Tc-MEPs with a 70% decrease in amplitude as an alarm threshold. We propose that future research should evaluate the efficacy of an idealized warning threshold (e.g., 50%) and a more detailed evoked muscle selection, in reducing false negatives.

Study design A prospective, multicenter study. Objective To evaluate the usefulness of transcranial motor-evoked potentials (Tc-MEPs) during supine-to-prone position change for thoracic ossification of the posterior longitudinal ligament (T-OPLL). Summary of background data Supine-to-prone position change might be a risk of spinal cord injury in posterior decompression and fusion surgeries for T-OPLL. Methods The subjects were 145 patients with T-OPLL surgically treated with posterior decompression and fusion using Tc-MEPs in 14 institutes. Tc-MEPs were monitored before surgery from supine-to-prone position and intraoperatively in 7 institutes and only intraoperatively in the other 7 institutes because of disapproval of the anesthesia department. In cases of Tc-MEP alert after position change, we adjusted the cervicothoracic posture. When the MEP did not recover, we reverted the position to supine and monitored the Tc-MEPs in supine position. Results There were 83 and 62 patients with/without Tc-MEP before position change to prone (group A and B). The true-positive rate was lower in group A than group B, but without statistical significance (8.4% vs 16.1%, p = 0.12). In group A, 5 patients who had Tc-MEP alert during supine-to-prone position change were all female and had larger body mass index values and upper thoracic lesions. Among the patients, 3 underwent surgeries after cervicothoracic alignment adjustment, and 2 had postponed operations to 1 week later with halo-vest fixation because of repeated Tc-MEP alerts during position change to prone. The Tc-MEP alert at exposure was statistically more frequent in group B than in group A (p = 0.033). Conclusion Tc-MEP alert during position change is an important sign of spinal cord injury due to alignment change at the upper thoracic spine. Tc-MEP monitoring before supine-to-prone position change was necessary to prevent spinal cord injury in surgeries for T-OPLL.Level of Evidence: 4.

Study design A prospective multicenter observational study. Objective To elucidate the efficacy of transcranial motor-evoked potentials (Tc(E)-MEPs) in degenerative cervical myelopathy (DCM) surgery by comparing cervical spondylotic myelopathy (CSM) to cervical ossification of the posterior longitudinal ligament (OPLL) and investigate the timing of Tc(E)-MEPs alerts and types of interventions affecting surgical outcomes. Summary of background data Although CSM and OPLL are the most commonly encountered diseases of DCM, the benefits of Tc(E)-MEPs for DCM remain unclear and comparisons of these two diseases have not yet been conducted. Methods We examined the results of Tc(E)-MEPs from 1176 DCM cases (840 CSM /336 OPLL) and compared patients background by disease, preoperative motor deficits, and the type of surgical procedure. We also assessed the efficacy of interventions based on Tc(E)-MEPs alerts. Tc(E)-MEPs alerts were defined as an amplitude reduction of more than 70% below the control waveform. Rescue cases were defined as those in which waveform recovery was achieved after interventions in response to alerts and no postoperative paralysis. Results Overall sensitivity was 57.1%, and sensitivity was higher with OPLL (71.4%) than with CSM (42.9%). The sensitivity of acute onset segmental palsy including C5 palsy was 40% (OPLL/CSM: 66.7%/0%) whereas that of lower limb palsy was 100%. The most common timing of Tc(E)-MEPs alerts was during decompression (63.16%), followed by screw insertion (15.79%). The overall rescue rate was 57.9% (OPLL/CSM: 58.3%/57.1%). Conclusion Since Tc(E)-MEPs are excellent for detecting long tract injuries, surgeons need to consider appropriate interventions in response to alerts. The detection of acute onset segmental palsy by Tc(E)-MEPs was partially possible with OPLL, but may still be difficult with CSM. The rescue rate was higher than 50% and appropriate interventions may have prevented postoperative neurological complications.Level of Evidence: 3.

STUDY DESIGN Prospective multicenter study. OBJECTIVE To examine transcranial motor evoked potential (Tc-MEP) waveforms in intraoperative neurophysiological monitoring (IONM) in surgery for intradural extramedullary (IDEM) tumors, focused on the characteristics for cervical, thoracic and conus lesions. SUMMARY OF BACKGROUND DATA IDEM tumors are normally curable after resection, but neurological deterioration may occur after surgery. IONM using Tc-MEPs during surgery is important for timely detection of possible neurological injury. METHODS The subjects were 233 patients with IDEM tumors treated surgically with Tc-MEP monitoring at 9 centers. The alarm threshold was ≥70% waveform deterioration from baseline. A case with a Tc-MEP alert that normalized and had no new motor deficits postoperatively was defined as a rescue case. A deterioration of manual muscle test (MMT) score ≥1 compared to the preoperative value was defined as postoperative worsening of motor status. RESULTS The 233 patients (92 males, 39%) had a mean age of 58.1 ± 18.1 years, and 185 (79%), 46 (20%) and 2 (1%) had schwannoma, meningioma, and neurofibroma. These lesions had cervical (C1-7), thoracic (Th1-10), and conus (Th11-L2) locations in 82 (35%), 96 (41%) and 55 (24%) cases. There were no significant differences in preoperative motor deficit among the lesion levels. Thoracic lesions had a significantly higher rate of poor baseline waveform derivation (0% cervical, 6% thoracic, 0% conus, p

STUDY DESIGN Prospective multicenter study. OBJECTIVE The purpose of the study is to examine cases with poor baseline waveform derivation for all muscles in multichannel monitoring of transcranial motor-evoked potentials (Tc-MEPs) in spine surgery. SUMMARY OF BACKGROUND DATA Intraoperative neuromonitoring (IONM) is useful for identifying neurologic deterioration during spinal surgery. Tc-MEPs are widely used for IONM, but some cases have poor waveform derivation, even in multichannel Tc-MEP monitoring. METHODS The subjects were 3625 patients (mean age 60.1 years, range 4-95; 1886 females, 1739 males) who underwent Tc-MEP monitoring during spinal surgery at 16 spine centers between April 2017 and March 2020. Baseline Tc-MEPs were recorded from the deltoid, abductor pollicis brevis, adductor longus, quadriceps femoris, hamstrings, tibialis anterior, gastrocnemius, and abductor hallucis (AH) muscles after surgical exposure of the spine. RESULTS The 3625 cases included cervical, thoracic, and lumbar lesions (50%, 33% and 17%, respectively) and had preoperative motor status of no motor deficit, and motor deficit with manual muscle testing (MMT) ≥3 and MMT

Study design Prospective, multicenter, observational study. Objective The aim of this study was to investigate the efficacy of intervention after an alert in intraoperative neurophysiological monitoring (IONM) using transcranial motor-evoked potentials (Tc-MEPs) during surgery for thoracic ossification of the posterior longitudinal ligament (T-OPLL). Summary of background data T-OPLL is commonly treated with posterior decompression and fusion with instrumentation. IONM using Tc-MEPs during surgery reduces the risk of neurological complications. Methods The subjects were 79 patients with a Tc-MEP alert during posterior decompression and fusion surgery for T-OPLL. Preoperative muscle strength (manual muscle testing [MMT]), waveform derivation rate at the start of surgery (baseline), intraoperative waveform changes; and postoperative motor paralysis were examined. A reduction in MMT score of ≥1 on the day after surgery was classified as worsened postoperative motor deficit. An alert was defined as a decrease in Tc-MEP waveform amplitude of ≥70% from baseline. Alerts were recorded at key times during surgery. Results The patients (35 males, 44 females; age 54.6 years) had OPLL at T1-4 (n = 27, 34%), T5-8 (n = 50, 63%), and T9-12 (n = 16, 20%). The preoperative status included sensory deficit (n = 67, 85%), motor deficit (MMT ≤4) (n = 59, 75%), and nonambulatory (n = 26, 33%). At baseline, 76 cases (96%) had a detectable Tc-MEP waveform for at least one muscle, and the abductor hallucis had the highest rate of baseline waveform detection (n = 66, 84%). Tc-MEP alerts occurred during decompression (n = 47, 60%), exposure (n = 13, 16%), rodding (n = 5, 6%), pedicle screw insertion (n = 4, 5%), posture change (n = 4, 5%), dekyphosis (n = 2, 3%), and other procedures (n = 4, 5%). After intraoperative intervention, the rescue rate (no postoperative neurological deficit) was 57% (45/79), and rescue cases had a significantly better preoperative ambulatory status and a significantly higher baseline waveform derivation rate. Conclusion These results show the efficacy of intraoperative intervention following a Tc-MEP alert for prevention of neurological deficit postoperatively.Level of Evidence: 2.

STUDY DESIGN Prospective multicenter study. OBJECTIVE The aim of this study was to evaluate transcranial motor evoked potential (Tc-MEP) waveform monitoring in spinal surgery for patients with severe obesity. SUMMARY OF BACKGROUND DATA Spine surgeries in obese patients are associated with increased morbidity and mortality. Intraoperative Tc-MEP monitoring can identify neurologic deterioration during surgery, but has not been examined for obese patients. METHODS The subjects were 3560 patients who underwent Tc-MEP monitoring during spine surgery at 16 centers. Tc-MEPs were recorded from multiple muscles via needle or disc electrodes. A decrease in Tc-MEP amplitude of ≥70% from baseline was used as an alarm during surgery. Preoperative muscle weakness with manual muscle test (MMT) grade ≤4 was defined as a motor deficit, and a reduction of one or more MMT grade postoperatively was defined as deterioration. RESULTS The 3560 patients (1698 males, 47.7%) had a mean age of 60.0 ± 20.3 years. Patients with body mass index >35 kg/m2 (n = 60, 1.7%) were defined as severely obese. Compared with all other patients (controls), the rates of preoperative motor deficit (41.0% vs. 29.6%, P

Study design Prospective multicenter observational study. Objective To evaluate transcranial motor-evoked potentials (Tc-MEPs) baseline characteristics of lower limb muscles and to determine the accuracy of Tc-MEPs monitoring based on preoperative motor status in surgery for high-risk spinal disease. Summary of background data Neurological complications are potentially serious side effects in surgery for high-risk spine disease. Intraoperative spinal neuromonitoring (IONM) using Tc-MEPs waveforms can be used to identify neurologic deterioration, but cases with preoperative motor deficit tend to have poor waveform derivation. Methods IONM was performed using Tc-MEPs for 949 patients in high-risk spinal surgery. A total of 4454 muscles in the lower extremities were chosen for monitoring. The baseline Tc-MEPs was recorded immediately after exposure of the spine. The derivation rate was defined as muscles detected/muscles prepared for monitoring. A preoperative neurological grade was assigned using the manual muscle test (MMT) score. Results The 949 patients (mean age 52.5 ± 23.3 yrs, 409 males [43%]) had cervical, thoracic, thoracolumbar, and lumbar lesions at rates of 32%, 40%, 26%, and 13%, respectively. Preoperative severe motor deficit (MMT ≤3) was present in 105 patients (11%), and thoracic ossification of the posterior longitudinal ligament (OPLL) was the most common disease in these patients. There were 32 patients (3%) with no detectable waveform in any muscles, and these cases had mostly thoracic lesions. Baseline Tc-MEPs responses were obtained from 3653/4454 muscles (82%). Specificity was significantly lower in the severe motor deficit group. Distal muscles had a higher waveform derivation rate, and the abductor hallucis (AH) muscle had the highest derivation rate, including in cases with preoperative severe motor deficit. Conclusion In high-risk spinal surgery, Tc-MEPs collected with multi-channel monitoring had significantly lower specificity in cases with preoperative severe motor deficit. Distal muscles had a higher waveform derivation rate and the AH muscle had the highest rate, regardless of the severity of motor deficit preoperatively.Level of Evidence: 3.

Study design Retrospective observational study. Objective We investigated whether bone turnover markers could be a useful indicator for prediction of nonunion. Summary of background data Nonunion is a major complication of lumbar spinal fusion surgery. The involvement of bone turnover in the process of bony union in spinal fusion surgery is, however, poorly understood. Methods Of the 74 patients analyzed, 13 were diagnosed with nonunion. We evaluated the significance of the following risk factors: age, sex, number of fused segments, serum levels of total alkaline phosphatase, procollagen type 1 amino-terminal propeptide (P1NP), tartrate-resistant acid phosphatase 5b (TRACP-5b), and albumin, and history of diabetes mellitus, cigarette smoking, or alcohol use. We also defined the bone turnover ratio (BTR) as a value that equals serum TRACP-5b concentration divided by serum P1NP concentration to evaluate patients' individual bone turnover balance and investigated the significance of BTR as a risk factor. Results Univariate analysis showed that older age, malnutrition, and lower P1NP are risk factors for nonunion. Stepwise logistic regression analysis revealed that in the presence of lower P1NP, higher TRACP-5b becomes a risk factor. Furthermore, we identified BTR as the most significant risk factor for nonunion. The optimum cut-off value of BTR by receiver-operating characteristic curve was 11.74. Conclusion These findings show a relation between bone turnover and nonunion after spinal fusion surgery. The measurement of bone turnover markers could potentially be used to predict nonunion after spinal fusion surgery. Level of evidence 4.

Study design Prospective multicenter study. Objective The aim of this study was to study the incidence of nonneurologic adverse events related to transcranial electric stimulation (TES) for intraoperative spinal cord monitoring (IOM) with motor-evoked potentials (MEPs) (Tc(E)- MEPs) and determine the need for safety precautions. Summary of background data Tc(E)-MEPs monitoring requires high-voltage multipulse TES that causes widespread muscle contraction and movement. Improved awareness of TES-induced movement-related adverse events is needed. Methods We analyzed data from 2643 patients who underwent high-risk spinal surgery with intraoperative Tc(E)-MEPs at 11 spinal centers from 2010 to 2016. Information about neurologic and non-neurologic postoperative complications was collected, including type of surgical procedure, operative time, estimated blood loss, and treatment for postoperative adverse events. Results A 70% drop in Tc(E)-MEPs amplitude, which was the alarm criterion to interrupt surgery, predicted postoperative motor deficits with 93.5% sensitivity, 91.0% specificity, a false-positive rate of 8.2%, and a false-negative rate of 0.3%. Non-neurologic adverse events developed in 17 (0.64%) patients and were most commonly because of bite injuries (0.57%), including 11 cases of tongue laceration, two cases of lip laceration, and two cases of tooth breakage. Four (0.15%) tongue lacerations required surgical repair with sutures and two tooth breakages required dental treatment. One patient had hair loss corresponding to the TES site. One patient, who underwent additional IOM with transpharyngeal stimulation, had severe nasal hemorrhage following electrode placement by nasal route, which resolved spontaneously. Non-neurologic adverse events did not significantly affect the accuracy of IOM assessment. Neither operative times nor blood loss significantly influenced the occurrence of adverse events. Conclusion During TES-IOM, both the surgeon and monitoring team must consider the possibility-although rare-of non-neurologic adverse events, particularly bite injuries. Such complications can be minimized by using a soft bite-block and frequently evaluating the intraoral integrity of the anesthetized patient. Level of evidence 4.

Prospective multicenter study.To analyze the incidence of intraoperative spinal neuromonitoring (IONM) alerts and neurological complications, as well as to determine which interventions are most effective at preventing postoperative neurological complications following IONM alerts in high risk spinal surgeries.IONM may play a role in identifying and preventing neural damage; however, few studies have clarified the outcomes of intervention after IONM alerts.We analyzed 2867 patients who underwent surgery for high risk spinal pathology using transcranial electrical motor-evoked potentials from 2010 to 2016. The high-risk spinal surgery cases consisted of 1009 spinal deformity cases, 622 cervical ossification of posterior longitudinal ligament (OPLL) cases, 249 thoracic-OPLL cases, 771 extramedullary spinal cord tumor cases, and 216 intramedullary spinal cord tumor (IMSCT) cases. We set a 70% amplitude reduction as the alarm threshold for transcranial electrical motor-evoked potentials and analyzed the outcomes of the interventions following monitoring alerts and postoperative neurological deficits.The true positive, false positive, true negative, false negative, and rescue cases of IONM comprised 126, 234, 2362, 9, and 136 cases, respectively. Most alerts and interventions occurred during correction and release in deformity cases, posterior decompression and dekyphosis in OPLL cases, and tumor resection and surgery suspension with steroid injection in spinal cord tumor cases; however, individual interventions varied. The rescue rates (number of patients rescued with intervention after IONM alert/number of true positive cases plus rescue cases) for deformity, cervical-OPLL, thoracic--OPLL, extramedullary spinal cord tumor, and IMSCT cases were 61.4% (35/57), 82.1% (32/39), 40% (20/50), 52.5% (31/59), and 31.6% (18/57), respectively.Our prospective multicenter study identified potential neural damage in 9.5% of cases and 52% rescue cases using IONM. Although the rescue ratios for t-OPLL and IMSCT were relatively low, appropriate intervention immediately after an IONM alert may prevent neural damage even in high-risk spinal surgeries.3.

Study design A retrospective observational study. Objective We evaluated the prevalence and clinical characteristics of tandem spinal stenosis (TSS) in patients with cervical myelopathy including ossification of the posterior longitudinal ligament of the cervical spine (C-OPLL). Summary of background data Concurrent cervical and lumbar spinal canal stenosis is generally reported as TSS. Most previous studies have used magnetic resonance imaging to evaluate spinal stenosis in the cervical and lumbar spine. Methods The authors performed a retrospective analysis of the outcomes of 297 myelography and cervical surgeries performed in myelopathic patients. We compared the non-TSS group (n = 125) with the TSS group (n = 172) in terms of multiple clinical parameters. In each group, we compared the cervical non-OPLL cases with the cervical OPLL cases. Moreover, we investigated the ratio and clinical outcomes of additional lumbar surgeries performed for TSS patients. Results One hundred seventy-two cases (57.9%) were considered TSS. Forty-one patients (13.8%) underwent a lumbar operation during the follow-up period. The TSS group included a greater number of OPLL patients, elderly patients, diabetes mellitus, hypertension, and non-smokers than the non-TSS group. The postoperative C-JOA score and the C-JOA recovery rate in the TSS group were significantly lower than the non-TSS group. In the TSS group, the non-C-OPLL patients were significantly older than the C-OPLL patients. The C-OPLL patients had higher postoperative C-JOA scores than the non-C-OPLL patients in both the TSS and non-TSS groups. The additional lumbar surgery effectively improved both the C-JOA and L-JOA scores in TSS patients. Conclusion The prognosis for TSS patients with myelopathy was worse than that for patients with isolated cervical lesions. Younger C-OPLL patients, even those with TSS, showed higher recovery rates than non-C-OPLL patients. Aging and coexistent lumbar lesions may influence the recovery process following surgery for cervical myelopathy. Level of evidence 4.

Study design Retrospective single-center study. Objective To investigate whether a preoperative index predicts clinical outcome after laminoplasty for cervical spondylotic myelopathy. Summary of background data This is the first study using the modified K-line, which connects the midpoints of the spinal cord at the C2 and C7 levels on midsagittal magnetic resonance imaging, to assess the relationship between postoperative clinical outcome and anticipated degree of spinal cord shifting. Methods Sixty-one consecutive patients who underwent laminoplasty for the treatment of cervical spondylotic myelopathy between 2000 and 2011 at our hospital were retrospectively reviewed. The interval between the preoperative mK-line and the anterior structure of the spinal canal at each segment of the C3 to C6 levels (INTn, n = 3-6) were measured on sagittal T1-weighted magnetic resonance imaging, and the sum of the INTn (INTsum) was then calculated. The degree of posterior cord shift was defined as follows: %Csum = ΣCn; Cn = (Bn-An) × 100/An (n = 3-6; An and Bn represent the preoperative and postoperative intervals between the midpoint of the spinal cord and the anterior impingement at each segment on sagittal T1-weighted magnetic resonance imaging, respectively). In addition, we defined INTmin as the minimum interval of the INTn in each patient. All patients were divided into lordotic and nonlordotic groups on the basis of lateral neutral radiography. The Japanese Orthopaedic Association (JOA) scoring system and recovery rate of the JOA score for cervical myelopathy was evaluated as clinical outcomes. Results The recovery rate of the JOA score was 48.1%. The lordotic and nonlordotic groups contained 38 and 23 patients, respectively. Linear regression analysis revealed that INTmin was significantly correlated with the recovery rate of the patients in the nonlordotic group, whereas INTsum was not associated with recovery of the JOA score. Conclusion We identified INTmin as a predictive factor for clinical outcomes in patients with nonlordotic alignment after laminoplasty. Level of evidence 4.

Study design A retrospective single-center study. Objective To clarify preoperative factors predicting unsatisfactory indirect decompression after laminoplasty in patients with cervical spondylotic myelopathy. Summary of background data Many authors have shown that inadequate indirect decompression after laminoplasty can inhibit neural recovery and should be considered a complication. We previously demonstrated that residual anterior compression of the spinal cord (ACS) impaired recovery of upper extremity motor function. Although the K-line has been established as a predictive index indicating that laminoplasty is required in patients with ossification of the posterior longitudinal ligament, it remains unclear what preoperative factors can predict insufficient posterior cord decompression in patients with cervical spondylotic myelopathy. Methods Forty-six consecutive patients who underwent laminoplasty for the treatment of cervical spondylotic myelopathy at our hospital were reviewed. A modified K-line was defined as the line connecting the midpoints of the spinal cord at C2 and C7 on a T1-weighted sagittal magnetic resonance image. We also determined the minimum interval between the tip of local kyphosis and a line connecting the midpoint of the cord at the level of the inferior endplates of C2 and C7 (INTmin) on the midsagittal image. Data analysis involved logistic regression and receiver operating characteristic curve analysis to select the most valuable index for predicting postoperative ACS. Results Ten patients had ACS immediately after laminoplasty. Logistic regression analysis showed that INTmin was a significant predictive factor for the occurrence of postoperative ACS (odds ratio = 0.485; 95% confidence interval = 0.29-0.81; P = 0.02). Receiver operating characteristic curve analysis showed an area under the curve of 0.871. A cutoff of 4.0 mm had a sensitivity of 80% and a specificity of 80.6% for prediction of postoperative ACS. Conclusion The parameter INTmin correlated with the occurrence of postoperative ACS. A cutoff point of 4.0 mm is most appropriate for alerting spine surgeons to a high likelihood of postoperative ACS.

Study design Retrospective case-control study. Objective The purpose of this study was to examine the factors of postoperative paralysis in patients who have undergone thoracic ossification of posterior longitudinal ligament (OPLL) surgery. Summary of background data A higher percentage of thoracic OPLL patients experience postoperative aggravation of paralysis than cervical OPLL patients, including patients that presented great difficulties in treatment. However, there were a few reports to prevent paralysis thoracic OPLL. Methods The 156 patients who had received thoracic OPLL surgery were selected as the subjects of this study. The items for review were the duration of disease; the preoperative muscle strength (Muscle Manual Testing); OPLL levels (T1/2-4/5: high, T5/6-8/9: middle, and T9/10-11/12: low); the spinal canal occupancy ratio; the ratio of yellow ligament ossification as a complication; the ratio of transcranial-motor evoked potential (Tc-MEP) derivation; the preoperative/postoperative kyphotic angles in the thoracic vertebrae; the correction angle of kyphosis; the duration of surgery; and the amount of bleeding. The subjects were divided into two groups based on the absence or presence of postoperative paralysis to determine the factors of postoperative paralysis. Results Twenty-three patients (14.7%) exhibited postoperative paralysis. Multivariate analysis identified factors associated with postoperative paralysis: the duration of disease (odds ratio, OR = 3.3); the correction angle of kyphosis (OR = 2.4); and the ratio of Tc-MEP derivation (OR = 2.2). Conclusion The risk factors of postoperative paralysis are a short duration of disease and a small correction angle of kyphosis. In addition, ratios of Tc-MEP derivation below 50% may anticipate paralysis. Level of evidence 4.

STUDY DESIGN A retrospective single-center study. OBJECTIVE To investigate how functional recovery is influenced by anterior compression of the spinal cord (ACS) and instability at the level of ACS after laminoplasty in patients with cervical spondylotic myelopathy. SUMMARY OF BACKGROUND DATA There have been many reports that patients whose spinal cord cannot be decompressed sufficiently after laminoplasty are likely to show unsatisfactory neurologic outcomes. Notably, postoperative ACS is well known to cause problems. Clinically, however, it remains unknown how functional recovery is inhibited by postoperative ACS. METHODS Sixty-four consecutive patients who underwent expansive laminoplasty for the treatment of myelopathy at our hospital between 1998 and 2005 were reviewed. All 64 patients were available for follow-up. The average follow-up period was 97 months (60-156 months). Patients were divided into 2 groups: the ACS(+) group comprised 16 patients who had ACS 3 years postoperatively, and the ACS(-) group comprised 48 patients with no ACS. Clinical outcome was compared in terms of the Japanese Orthopaedic Association score (mean total score, mean score of each item, and recovery rates). RESULTS Demographics were similar between the 2 groups. Mean Japanese Orthopaedic Association score at final follow-up was 12.1 points (recovery rate 34.0%) in the ACS(+) group and 13.8 points (recovery rate 56.6%) in the ACS(-) group, and there was a significant difference in recovery rate between the groups (P < 0.05). Notably, a significant difference was found between the 2 groups in improvement of upper extremity motor function (P < 0.05). In addition, we found that not only the presence of ACS but also postoperative hypermobility of the intervertebral segment with ACS influenced clinical outcome negatively. CONCLUSION These results demonstrate that ACS after laminoplasty could be a risk factor for clinical outcome and might prevent improvement in upper extremity motor function in patients with myelopathy.

STUDY DESIGN The authors measured conductive cervical spinal cord evoked magnetic fields (SCEFs) after thoracic spinal cord stimulation in cats and visualized spinal cord activities. OBJECTIVE To evaluate the usefulness of magnetic field measurement. SUMMARY OF BACKGROUND DATA Magnetic field measurement has several theoretical advantages compared with electric potential measurement. Although biomagnetometers for the brain and heart are already on the market and are widely used, methods for magnetic field measurement of the spinal cord have not been established. METHOD Cervical laminectomy was performed on adult cats under anesthesia and the dural tube was exposed. Electrical stimuli were applied to the lower thoracic spinal cord by a catheter epidural electrode. SCEFs were recorded using a biomagnetometer specially designed for recording spinal cord action potentials. SCEFs were measured at 35 different points over the cervical spine and isomagnetic field maps of SCEFs were constructed. Thereafter, the spinal cord was transected completely at C5 and SCEFs were measured again. RESULTS The detected SCEFs showed a clear biphasic configuration. The first deflection of the magnetic fields from the left side was directed outward, but the right-side deflection was directed inward. The second deflection showed reversed polarity. The isomagnetic field maps of SCEFs clearly demonstrated the quadrupolar pattern and propagated at a conduction velocity of 80-120 m/s. After spinal cord transection, the propagation of SCEFs stopped at the transection site, and the SCEFs could not be obtained above the site. CONCLUSIONS The authors concluded that magnetic field measurement is useful for evaluation of spinal cord function. Moreover, it was apparent that SCEFs could indicate conduction block in the spinal cord.

Study design A prospective clinical study. Objective To investigate the dynamic causative factor in the pathogenesis of myelopathy in patients with cervical ossification of the posterior longitudinal ligament (OPLL) using kinematic computed tomography (CT) myelography. Summary of background data Kinematic CT myelography is useful for dynamically evaluating the cervical spine with high-resolution images, particularly in bony compressive lesions. However, no studies have evaluated the dynamic factors in patients with OPLL using kinematic CT myelography. Methods From 2008 to 2013, 51 consecutive patients with OPLL who presented with myelopathy were prospectively enrolled in this study. The patients were examined with kinematic (flexion-extension) CT myelography using a multidetector CT scanner. The range of motion at C2-C7 from flexion to extension was measured in the sagittal view. The segmental range of motion, anterior-posterior diameter and cross-sectional area (CSA) of the spinal cord were measured at the level where the spinal cord was most compressed by OPLL. Results The neurological condition of the patients evaluated by Japanese Orthopaedic Association scores were 10.8 ± 2.4 points. The mean range of motion at C2-C7 and at the most compressed segment were 23.1 ± 11.7 and 7.0 ± 4.4°, respectively. Both the anterior-posterior diameter and the CSA at the most compressed levels were significantly decreased during neck extension compared with flexion. Interestingly, the anterior-posterior diameter and the CSA were decreased during neck flexion in 13.7% (7/51) of the patients. All 7 of these patients had massive OPLL with an occupying rate 60% or more. The dynamic change rate of CSA (flexion/extension) was significantly smaller in patients with an OPLL occupying rate 60% or more compared with patients with an occupying rate less than 60%. Conclusion Although spinal cord compression was increased during neck extension in most of the patients, greater levels of compression could be placed on the spinal cord during neck flexion when the patients had OPLL with a high occupying rate. Level of evidence 4.

STUDY DESIGN Retrospective analysis of prospectively collected data from consecutive patients undergoing 2 methods of transcranial electrical motor evoked potential (TCE-MEP) monitoring during cervical spine surgery. OBJECTIVE To investigate the efficacy of biphasic transcranial electric stimulation, the deviation rate, amplitude of TCE-MEPs, complications, and sensitivity and specificity of TCE-MEP monitoring were compared between the biphasic and conventional monophasic stimulation methods. SUMMARY OF BACKGROUND DATA With biphasic stimulation, unlike monophasic stimulation, measurement time can be reduced considerably because a single stimulation elicits bilateral responses almost simultaneously. However, no study has yet reported a detailed comparison of the 2 methods. METHODS Examination 1: Amplitude and derivation rate of TCE-MEPs was compared for monophasic and biphasic stimulation in the same 31 patients with cervical compression myelopathy. Examination 2: Sensitivity, specificity, and complications of TCE-MEP monitoring were compared in 200 patients with cervical compression myelopathy who received monophasic or biphasic stimulation (100 patients each) during intraoperative monitoring. RESULTS Examination 1: Derivation rates of biphasic stimulation in the deltoid, biceps brachii, abductor digiti minimi, and flexor hallucis brevis muscles were the same or higher than for monophasic stimulation. TCE-MEP amplitudes elicited by biphasic stimulation compared with monophasic stimulation were significantly larger in the biceps (paired t, P < 0.0001), but similar in the other 3 muscles. Examination 2: In the biphasic and monophasic stimulation groups, warnings were issued to surgeons in 10 and 11 cases, for a sensitivity of 100% for both groups and specificity of 97.8% and 96.7%, respectively. No complications related to stimulation were observed in any of the 200 patients. CONCLUSION Biphasic stimulation had similar or higher derivation rates and equivalent sensitivity and specificity than monophasic stimulation. No complications were observed for either stimulation method. Biphasic stimulation is an effective TCE-MEP monitoring method for cervical spine surgery that may also reduce measurement time. LEVEL OF EVIDENCE 4.

STUDY DESIGN A prospective analysis OBJECTIVE Our aim was to investigate the efficacy of new synthetic porous/dense composite hydroxyapatite (HA) for use in anterior cervical discectomy and fusion (ACDF). SUMMARY OF BACKGROUND DATA Iliac crest bone graft (ICBG) has been traditionally used as the "gold standard" for ACDF. The significant complication rate associated with harvesting tricortical ICBG, however, has encouraged development of alternative graft substitutes. METHODS The morphology of the porous/dense HA was observed by scanning electron microscopy (SEM), and the in vitro compressive strength of the composite HA was measured. From April 2005, 51 consecutive patients underwent 81 levels of ACDF using the composite HA with percutaneously harvested trephine bone chips. Clinical and radiological evaluation was performed during the postoperative hospital stay and at follow-up. Furthermore, the outcomes in ACDF using the composite HA were compared with those using tricortical ICBG. RESULTS The SEM images demonstrated 100- to 300-μm pores (approximately 40% of porosity) in the porous layers of the HA. The compressive strength of the composite HA was 203.1 ± 4.1 MPa. In the clinical study, the demographic data of the patients were similar in HA and ICBG groups. The fusion rates in HA group were comparable with those in ICBG group. The cervical lordosis was enhanced postoperatively in both groups and well preserved at 2-year follow-up without significant differences between the groups. The intraoperative blood loss in HA group was significantly lesser than that in ICBG group. Donor site complications were found in 29.2% of the patients in ICBG group, whereas no donor site morbidity was found in HA group. No major collapse or fragmentation of the composite HA was found. CONCLUSION The hybrid graft of composite HA and percutaneously harvested trephine chips seemed promising as a graft substitute for ACDF. LEVEL OF EVIDENCE 4.

STUDY DESIGN A retrospective analysis of prospectively collected data from consecutive patients undergoing transcranial electrical motor-evoked potential (TCE-MEP: compound muscle action potentials) monitoring during cervical spine surgery. OBJECTIVE.: To divide the warning threshold of TCE-MEP amplitude changes on the basis of origin into the spinal tract and spinal segments and decide warning thresholds for each. SUMMARY OF BACKGROUND DATA The parameter commonly used for the warning threshold in TCE-MEP monitoring is wave amplitude, but amplitude changes have not been examined by anatomical origin. METHODS Intraoperative TCE-MEP amplitude changes were reviewed for 357 patients with cervical myelopathy. Most of the patients were monitored by transcranial electrical stimulated spinal-evoked potential combined with TCE-MEP. The warning threshold of TCE-MEP was taken as waveform disappearance. For each patient, amplitude changes were separated, according to origin, into the spinal tract and spinal segments and compared with clinical outcome. RESULTS Assessable TCE-MEP waves were obtained in 350 cases. Disappearance of TCE-MEP waves, which were innervated by the spinal levels exposed to the surgical invasion, was seen in 11 cases. Disappearance of TCE-MEPs, which were innervated by the spinal levels inferior to them, was seen in 43 cases. There was no postoperative motor deficit in those cases. However, such deficits caused by spinal segment injury were seen in 2 cases, which showed that intraoperative amplitude decreased to 4.5% and 27%. CONCLUSION If we had established the warning threshold as 30% of the control amplitude, we would likely have prevented both cases of postoperative motor deficits, but 106 (30.3%) cases would have become positive cases. If we had established the warning threshold separately as wave disappearance for the spinal tract and 30% of the control amplitude for the spinal segments, sensitivity and specificity would have been 100% and 83.7%, respectively. Dividing the warning threshold on the basis of origin of amplitude changes could reduce false-positive cases and prevent intraoperative injuries.

Study design A case report of a patient with adhesive arachnoiditis after combined spinal and epidural anesthesia. Objective To report an extremely rare case of paraplegia due to adhesive arachnoiditis with extensive syringomyelia (ES) and a giant anterior arachnoid spinal cyst (AASC) after spinal and epidural anesthesia for obstetric surgery. Summary of background data Progressive inflammation of the arachnoid mater due to trauma, infection, or hydrocortisone was reported as early as the 1970s. However, coexistence of ES and a giant AASC after spinal and epidural anesthesia is extremely rare. Methods A 29-year-old woman suffered from sudden anuresis 5 months after spinal and epidural anesthesia for a cesarean section and subsequently experienced paraplegia and numbness below the chest. Magnetic resonance imaging showed an AASC compressing the spinal cord at T1-T6 and an adhesive lesion at T7. Posterior laminectomy at T6-T7 and adhesiolysis for arachnoid adhesion at T7 were performed. Although there was slight recovery of locomotive function postoperatively, it gradually worsened until 3 years after surgery. Magnetic resonance imaging at that time demonstrated a giant AASC and ES at the lower-thoracic cord. The cord compressed by the AASC became thinner sagittally. Secondary surgery involving posterior laminectomy at T5-T6 and insertion of a cyst-peritoneal shunt into the AASC was performed. Results The patient could walk without a cane 3 years after the shunt operation, although numbness and motor weakness of the lower extremities remained. Magnetic resonance imaging 3 years after the shunt operation showed a reduction of the AASC and decompression of the cord despite no improvement in ES. Conclusion This is the first report of a patient with a giant AASC and ES caused by spinal and epidural anesthesia. Although the optimal surgical treatment for these conditions remains unclear, shunting of the cyst effectively prevented the progression of symptoms.

Study design A prospective, comparative study. Objective We developed a hybrid graft (HBG) of porous β-tricalcium phosphate ceramics/percutaneously harvested bone sticks/autologous bone marrow aspirate for lumbar posterolateral fusion (PLF). The aim of this study was to investigate the efficacy of the HBG as a substitute for conventional corticocancellous iliac autografts. Summary of background data Iliac crest bone graft (ICBG) has been traditionally used as the golden standard for lumbar spinal fusion. The significant complication rate associated with harvesting corticocancellous ICBG, however, has encouraged development of alternative graft substitutes. Methods From September 2005, 61 consecutive patients underwent decompressive laminotomy and 1-level instrumented PLF. Each patient in this study had the constructs of the HBG placed on 1 side of the intertransverse process gutter. An autologous local bone graft (LBG) harvested during decompressive laminotomy was placed on the other side as a control. Radiographic evaluation was performed at 6 months, 1 year after surgery, and subsequently on an annual basis. The fusion statuses on either side of vertebra were compared. Results The flexion-extension motion in the dynamic x-rays at the target level decreased over time. Only 1 case exhibited over 5° of angular motion 2 years after surgery. In the evaluation of fusion status, the fusion rate for the HBG side (68.9% at 6 months, 83.6% at 1 year, 93.5% at 2 years) was higher than that for the LBG side (49.2% at 6 months, 75.4% at 1 year, 89.1% at 2 years) with a significant difference at 6 months after surgery. No significant complications at the donor site were found postoperatively. Conclusion The HBG promoted posterolateral spinal fusion without significant donor site morbidity. Because of its efficacy and safety, this hybrid construct seems promising as an alternative to conventional iliac bone grafts for lumbar spinal fusion.

Study design Prospective, comparative clinical study. Objective To compare the clinical outcome of anterior decompression and fusion with floating method and laminoplasty in the treatment of cervical myelopathy caused by ossification of the posterior longitudinal ligament (OPLL). Summary of background data There have been no reports that have accurately and prospectively compared surgical outcomes after anterior decompression and posterior decompression. Methods For cervical myelopathy caused by OPLL, we performed anterior decompression and fusion with floating method (ADF) in 1997, 1999, 2001, 2003, and 2004 and French-door laminoplasty (LAMP) in 1996, 1998, 2000, and 2002 at one institution. Twenty patients in the ADF group and 22 patients in the LAMP group were evaluated for 5 years' follow-up. The following criteria were evaluated: operation time, blood loss, complications, and Japanese Orthopedic Association score. For radiographic evaluation, canal narrowing ratio of OPLL, lordotic angle at C2-C7, and postoperative progression of the ossified lesion were measured. Results The operation time in the ADF group was longer than that in the LAMP group. The average blood loss showed no statistical difference between the 2 groups. Complications occurred in 5 cases in the ADF group, but none occurred in the LAMP group. The mean Japanese Orthopedic Association score system for cervical myelopathy and the recovery rate in the ADF group were superior to those in the LAMP group, especially for cases with greater than 50% of the spinal canal compromised by OPLL or kyphotic alignment of the cervical spine, preoperatively. Postoperative progression of OPLL was observed in 5% of the ADF group and 50% of the LAMP group. Conclusion ADF is considered especially suitable for cases with massive OPLL and preoperative kyphotic alignment of the cervical spine, although it leads to a higher incidence of surgery-related complications compared with LAMP.

STUDY DESIGN A clinical prospective study. OBJECTIVE To assess whether clinical and radiologic outcomes differ between anterior decompression and fusion (ADF) and laminoplasty (LAMP) in the treatment of cervical spondylotic myelopathy (CSM). SUMMARY OF BACKGROUND DATA No reports to date have accurately and prospectively compared middle-term clinical outcomes after anterior and posterior decompression for CSM. METHODS We prospectively performed LAMP (n = 50) in 1996, 1998, 2000, and 2002, and ADF (n = 45) in 1997, 1999, 2001, and 2003. The Japanese Orthopedic Association (JOA) score, recovery rate, and each item of the JOA score were evaluated. For radiographic evaluation, the lordotic angle and range of motion (ROM) at C2-C7 and residual anterior compression to the spinal cord (ACS) after LAMP on magnetic resonance imaging were investigated. RESULTS Eighty-six patients (ADF n = 39; LAMP n = 47) could be followed for more than 5 years (follow-up rate 91.5%). Demographics were similar between the two groups. The mean JOA score and recovery rate in the ADF group were superior to those in the LAMP group from 2-year data collected after surgery. However, LAMP was safer and less invasive than ADF with respect to physical status and complications in the perioperative period. For individual items of the JOA score, the ADF group showed significantly more improvement of upper extremity motor function than the LAMP group (P < 0.05). There was a significant difference in maintenance of the lordotic angle in the ADF group compared with the LAMP group despite no difference in ROM.The LAMP group was divided into two subgroups: (1) LAMP(+) (n = 16) comprising patients who had ACS at 2 years after surgery, and (2) LAMP(-) (n = 31) comprising patients without ACS. Recovery rate differed significantly between the LAMP(+) and LAMP(-) groups despite there being no difference between the LAMP(-) and ADF groups. CONCLUSION The recovery rate of the JOA score in the ADF group was better than that in the LAMP group. The clinical outcomes after LAMP could be influenced by ACS.

Study Design. Retrospective case series.Objective. To investigate risk factors for early reconstruction failure of multilevel cervical corpectomy with dynamic plate fi xation.Summary of Background Data. For anterior cervical decompression and fusion, reinforcement by plate fi xation was performed to decrease early reconstruction failure and to increase the fusion rate. However, a relatively high complication rate such as graft dislodgement, has been reported in patients undergoing multilevel corpectomy and reconstruction. Risk factors associated with early reconstruction failure have not been explicitly described.Methods. In 30 instrumented multilevel corpectomy and reconstruction, medical records and radiographic studies were reviewed to investigate risk factors with regard to sagittal alignment of the cervical spine, graft subsidence, screws used in fi xation, endplate preparation, and intermediate screw for fi bular graft.Results. Reconstruction failures included anterior slipping at the bottom of the graft in 2 cases, fracture of the C7 vertebral body in 2 cases, and pullout of a screw in 2 cases. Four patients were found to have nonunion of the graft at the fi nal follow-up, but none had experienced early reconstruction failure. On radiologic measurement, the fusion area lordotic angle after surgery in the patients with reconstruction failures was signifi cantly larger than that of the patients with no complications. The postoperative C2–C7 lordotic angles of the patients with reconstruction failure were also larger, but this trend was not statistically signifi cant. No other factor, such as age and gender, type of screw used, intermediate screw or preservation of the endplates was related to reconstruction failures in this study.Conclusion. Postoperative cervical hyperlordosis may adversely affect graft stability in the early postoperative period of the surgery of corpectomy and reconstruction with dynamic plate fi xation.Key words: anterior cervical fusion, anterior cervical plate, complication, cervical myelopathy, ossifi cation of longitudinal ligament. Spine 2011;36:E582–E587

Study design Preoperative electrophysiological and neurologic findings from patients with cervical myelopathy were evaluated statistically to determine their predictive value relative to the success of eliciting intraoperative motor-evoked potentials. Objectives To determine which preoperative variables accurately predicted the success of eliciting an intraoperative muscle-evoked potential. Summary of background data Motor-evoked potential recorded from the muscles after transcranial electrical stimulation is one of the most widely used methods for intraoperative spinal cord monitoring. However, motor-evoked potentials recorded from lower limb muscles are not detectable in patients with severe cervical myelopathy. Therefore, it is helpful to know the probability of the intraoperative transcranial electrical stimulation-motor evoked potential elicitation before the operation. Methods There were 38 patients with cervical myelopathy. Before the operation, motor-evoked potentials following transcranial magnetic stimulation were recorded from the flexor hallucis brevis, and central motor conduction times were measured. Neurologic function was evaluated using the Japanese Orthopedic Association score. During the operation, transcranial electrical stimulation-motor evoked potential from the flexor hallucis brevis was recorded. The Japanese Orthopedic Association score, threshold intensity of magnetic stimulation, and central motor conduction times were statistically evaluated for their potential of being predictors. Results The intraoperative transcranial electrical stimulation-motor evoked potential was detectable in all cases in which the preoperative transcranial magnetic stimulation-motor evoked potential was elicited by a lower intensity than 50% of the maximum output of the stimulator. Therefore, simultaneous use of other methods of monitoring should be considered in such cases that need higher output. However, the Japanese Orthopedic Association score or central motor conduction times were not useful criteria. CONCLUSIONS.: The threshold intensity of the preoperative transcranial magnetic stimulation-motor evoked potential was helpful in predicting elicitation of the intraoperative transcranial electrical stimulation-motor evoked potential.