To establish the current practice of spinal cord monitoring in units carrying out scoliosis surgery in the UK. To illustrate the benefit of routinely monitoring motor evoked potentials (MEPs). Questionaire: Nationwide survey of spinal monitoring modalities used by spinal units carrying out deformity surgery. 10 out of 27 units routinely measure motor evoked potentials (MEPs), the remainder use only sensory potentials (SEPs). There is significant variability in use of monitoring around the UK and we have compared this to the practice elsewhere in the world. We report the case of a thirteen year old girl who underwent posterior instrumentation for correction of an idiopathic scoliosis. Intra-operatively there was a significant reduction in the amplitude of the MEPs without any corresponding change in the SEPs. These changes reversed when the correction was released. The surgery was abandoned and was carried out as a staged procedure, initially anteriorly then posteriorly. There was no loss of motor potentials during either operation and no post operative neurological abnormalities. We propose that the changes noted initially were due to transient ischaemia of the cord which would not have been detected without MEPs and may have led to long term sequelae. This highlights the safety benefit of routinely using MEPs in scoliosis surgery. Nationally there is wide variation in the monitoring of spinal cord function during scoliosis surgery. We feel that monitoring of motor potentials is a vital component in ensuring scoliosis surgery is as safe as possible

Purpose: Pinch strength has been shown to be a predictor of the ability to grip objects and perform functional hand-related tasks. As the sole flexor of the thumb IP joint, the flexor pollicus longus (FPL) muscle has previously been shown to play an essential role in directing thumb tip force as well as contribute to overall pinch strength. The relative contribution of FPL to pinch strength is unknown however. As the FPL may be affected in several acute and chronic conditions, determining the contribution of FPL to pinch strength may be useful in planning as well as evaluating treatment options. The purpose of this study was to estimate the contribution of FPL to pinch strength in-vivo using an EMG-guided, selective motor blockade, test-retest protocol. Method: 11 healthy volunteers were recruited to participate in the study. All participants completed a brief questionnaire regarding prior hand injuries and subsequently underwent a physical examination to assess baseline hand function. Baseline pinch strength was recorded using three different pinch techniques: key pinch, 3-point chuck grasp, and tip pinch. Participants then underwent EMG-guided lidocaine blockade of the FPL muscle. Motor evoked potentials as well as skin potentials were used to confirm adequate FPL blockade. The physical exam was repeated as were pinch strength measurements. Post block splinting was necessary to stabilize the thumb IP joint. Grip strength, in addition to clinical examination, was utilized pre and post block to assess for inadvertent blockade of other muscle groups or nerves. A final clinical evaluation was conducted at study completion to note any complications or adverse effects. Results: All three types of pinch strength showed a significant difference between pre and post measurements (p< 0.01). The mean differences pre and post were 9.7N,6.4N, and 5.2N in key, 3-point chuck, and tip pinch respectively (p< 0.01). The relative contribution of FPL for each pinch type was 53.2%,39.5%, and 44.3%. EMG, motor evoked potentials, and skin potentials confirmed adequate paralysis of the FPL. Physical examination did reveal decreased sensation in median and radial nerve distributions in some individuals, however the effect on observed motor function was negligible. Grip strength decreased by only 4N post blockade confirming no clinically significant median nerve motor blockade. The protocol was well tolerated and no serious complications were noted. Conclusion: Using an in-vivo model we were able to estimate the contribution of FPL to overall pinch strength. In our study, FPL’s contribution to pinch strength was estimated to be 9.7N,6.4N, and 5.2N in key, 3-point chuck, and tip pinch respectively (p< 0.01). The relative contribution of FPL for each pinch type was 53.2%, 39.5%, and 44.3%. Inherent limitations in study design may have tended to overestimate the contribution of FPL to pinch. This information may be useful in planning and evaluating treatments for acute and chronic conditions affecting FPL function

There is an inherent risk of iatrogenic new neurological deficit (NND) arising at the spinal cord, cauda equina and nerve root during spinal surgery. Intraoperative neurophysiological monitoring (IONM) can be employed to preserve spinal cord function during spinal surgery. IONM techniques include somatosensory and motor evoked potentials, amongst others. A Canadian survey of 95 spinal surgeons showed that 62.1% used IONM and a similar survey in France of 117 spinal surgeons showed that only 36% used IONM. Unavailability was a common reason for its disuse. Current literature by the British Society of Clinical Neurophysiology has outlined the importance of IONM in preventing NND and the need for the implementation of guidelines for IONM. The lack of an established guideline has resulted in a varied approach in the use of IONM in England. There has been no previous attempt to ascertain the current use of IONM in England. Our study is aimed at assessing the variability of the use of IONM in England as well as identifying the rationale amongst surgeons that dictate their use of IONM. We are in the process of investigating the indications of use of IONM for cervical and lumbar spine procedures in 252 spinal surgeons from 33 hospitals with spinal services. Our survey will illustrate the current use of IONM in spinal surgery in England. It will highlight some of the reasons for the variability of use of IONM and identify factors that can contribute to a more standardised use of IONM in spinal surgery

To determine whether neurophysiological electrical pedicle testing (EPT) is a useful aid in the detection of malpostioned pedicle screw tracts. EPT data from 246 screws in 32 spinal operations on 32 patients over a 5 year period (2009–2014) were recorded and analysed. In addition to physical palpation, a ball-tipped electrode delivered stimuli and the output was recorded by evoked electromyogram (EMG). When breach threshold values were recorded, the surgeon rechecked the tract for breaches and responded appropriately. In addition, standard motor evoked potential (MEP) and sensory evoked potential(SEP) spinal cord monitoring was performed. There were 24(9.8%) pedicle breaches by tract testing and 8(3.3%) by screw testing. In 11 instances in 7 patients where the tract testing showed a breach, the tract was redirected and subsequent screw testing showed adequate integrity of the pedicle. The total time for tract and screw testing was 25 seconds. There were no associated changes in MEP or SEP monitoring with any of the recorded pedicle breaches and none of the patients had any post-operative neurological deficit. EPT for the pedicle screw and tract is a safe, simple, practical and reliable technique which improves the accuracy of screw placement. Further studies would be required to confirm (and possibly revise) the threshold levels and to demonstrate whether EPT reduces the risk of misplaced screws or post-operative neurological deficit

Introduction. Changes in the central nervous system (CNS) pathways controlling trunk and leg muscles in patients with low back pain and radiculopathy have been observed and this study investigated whether surgery impacts upon these changes. Methods. Parameters of corticospinal control were examined on 3 occasions in 22 patients prior to, at 6 and 26 weeks following lumbar decompression surgery and in 14 control subjects at the same intervals. Electromyographic activity was recorded from tibialis anterior (TA), soleus (SOL), rectus abdominis (RA), external oblique (EO) and erector spinae (ES) muscles at the T12 & L4 levels in response to transcranial magnetic stimulation of the motor cortex. Results. In the surgical group, asymmetries in the size of motor evoked potentials (MEPs) in TA (P=0.001) and in the cortical silent periods (cSP) were found between the left and right sides in SOL (P=0.005) and ES at L4 (P=0.014) prior to surgery. This was not observed at 6 or 26 weeks. Abdominal responses could be evoked in 12 patients and there was a significant reduction in the cSP contralateral to the pain in EO (P=0.034) and RA (P=0.041) at 6 weeks. These parameters remained stable in controls over time. Discussion. The fact that changes appear to stabilise at 6 weeks is of interest as this parallels clinical outcome studies. Current work is ongoing to examine these excitability changes in both inhibitory and excitatory cortical pathways in these patients, and to what extent they may be related to clinical outcome

Introduction: Changes in the central nervous system (CNS) pathways controlling trunk and leg muscles in patients with low back pain and sciatica have been demonstrated. The aim of this study is to investigate whether these changes are altered by surgery. Methods: Corticospinal excitability was examined on 2 occasions in 15 patients prior to and 6 weeks following lumbar decompression surgery and 7 control subjects – at the same time intervals. This was achieved by recording electromyographic (EMG) activity from tibialis anterior (TA), soleus (SOL), rectus abdominis (RA), external oblique (EO) and erector spinae (ES) muscles at the T12 & L4 levels in response to transcranial magnetic stimulation (TMS) of the motor cortex. Results: A significant asymmetry in the cortical silent period (cSP) between the side ipsilateral to the pain and the contralateral side was found pre- but not post surgery in ES at L4 (P=0.012) and SOL (P=0.039). An asymmetry in the size of motor evoked potentials (MEPs) was also found in TA (P=0.009) which was no longer significant post surgery. Abdominal responses could be recorded in 10 subjects, where significant decreases in contralateral cSP in EO (P=0.021) and RA (P=0.033) were found. In controls no significant differences or changes were found. Discussion: These results show significant asymmetries in the CNS control of trunk and leg muscles in patients prior to surgery to relieve pain which are resolved by the surgery. The degree of change in asymmetry may reflect the variability in surgical outcome. This work is currently ongoing. Conflicts of Interest: None. Funded by: the DISCS foundation

Background:. Spinal deformity surgery carries the risk of loss of neurological function which may be permanent. Although the overall the incidence is low it is much higher in complex congenital deformities or those with pre-existing myelopathy. Intra-operative spinal cord monitoring allows this risk to be reduced by providing feedback to the surgeon while the corrective manoeuvres are performed. Although ideally a trained technician with multimodal monitoring is recommended, it is often not an option in a resource limited environment and surgeon operated technology is used. Aim:. to evaluate the use of surgeon operated trans-cranial motor evoked potentials (tcMEP) in spinal deformity surgery. Methods:. A retrospective review was conducted on a single surgeon series of 108 consecutive cases utilising the NIM system (Medtronic). Percutaneous needles were employed in the scalp, both hands and feet to allow the upper limbs to act as controls. Forty-nine patients were 13 years old or less, 47 were 14–18, and 12 adults. The cohort consisted of 54 AIS, 27 neuromuscular scoliosis, 14 congenital, 2 old TB and 11 miscellaneous. The vast majority were posterior based procedures. Results:. In 4 cases initial traces could not be obtained. One was a severe myelopathy and further efforts to monitor were abandoned. In one case the anaesthetist had broken protocol and once converted to TIVA the traces improved. Two others were poor initially but improved as the case progressed. In 8 cases intra-operative traces were lost. One was thought to be due to hypothermia and the patient woke intact. Two were unrelated to surgical intervention and recovered spontaneously with patients waking intact. Four cases deteriorated during the corrective manoeuvre (one delayed) and recovered with reduction of correction. One case required removal of instrumentation after repeated loss each time rods were inserted and awoke with a weak leg but recovered and was re-operated two weeks later. Conclusion:. Surgeon operated tcMEP's allows feedback in terms of safety of deformity correction with a 100% negative predictive value and an 8% incidence of signal loss during correction allowing immediate remedial action

Purpose: Despite advances in surgical technique, neurological injury remains a potentially devastating complication of spinal deformity correction surgery. The purpose of the study is to describe surgical and patient factors associated with “electrophysiologic (EP) events” and neurogenic deficits. Method: A retrospective chart review, looking at “EP events” during surgery, was conducted on 162 patients who received surgical treatment of their pediatric spine deformity from 1999 to 2004. Results: Ninety three percent of cases (n=151) were successfully monitored by either somatosensory evoked potential (SEP) or motor evoked potential (MEP) monitoring. All three neurologic deficits that occurred in this study cases were successfully detected by EP monitoring (0.02%, p=.002). In those 151 cases that were successfully monitored, “EP events” were occured in twenty (13.2%) cases. The most common cause was systemic change (45%) and curve correction (40%). In those 20 cases, when corrective actions were made (n=15) “EP events” reversed to baseline values in all cases. When no corrective actions were taken (N=5) there was no reversals of “EP events” to baseline. Patients with kyphosis had a trend toward significantly higher rates of “EP events” (p=.174) and patients who had cardiopulmonary comorbidities had significantly higher rates of “EP events” (p=.007). Conclusion: Consistent with existing literature, the EP monitoring was successful in the vast majority of deformity surgeries. “EP events” were able to be reversed with corrective action and to predict neurologic deficits. Our study found that patients with kyphosis and/or cardiopulmonary comorbidities have higher risk of significant “EP events” during the surgeries

Objectives. To determine the limits of spinal displacement before the onset of neurophysiological changes during spinal surgery. Assessing if the type of force applied or the section of the adjacent nerve roots increases the tolerance to displacement. Methods. Experimental study in 21 domestic pigs. Three groups were established according to the displacing force applied to the cord: separation (group 1, n=7), root stump pull (group2, n=7) and torque (group3, n=7). Successive records of cord-to-cord motor evoked potential were obtained. The displacing force was removed immediately when neurophysiological changes observed. The experiment was repeated after sectioning the adjacent nerve roots. Results. The diameter of the dura in the study area was 7.2 ± 1 mm. Group 1: evoked potential changes appeared with displacement of 10.1 ± 1.6 mm with roots unharmed and 15.3 ± 4.7 mm (p <0.01) with section of four adjacent roots. Group 2: evoked potential disturbance at 17.5 ± 4.7 mm, which increased to 23.5 ± 2.1 mm (p <0.05) after cutting the two contralateral roots. Group 3: cord allowed torque of 95.3° ± 9.2 increasing to 112.4 ° ± 7.1 ° if the contralateral roots were cut. Except in two cases in group 3 (torsion), the potentials were normalized immediately after releasing the deforming force. Discussion. This experimental study shows that it is possible to surgically displace the medulla a distance superior to the diameter of the dura without detecting neurophysiological changes. The limits of cord displacement may be increased by the section of the adjacent nerve roots and if the tensile force is applied by traction of the root stumps. These findings support the neurological safety of spine deformity correction by isolated posterior approach, obviating the morbidity related to an additional anterior procedure

Study Design: Prospective observational study. Objective: To establish the sensitivity, specificity and cost-effectiveness of motor evoked potential (MEP) monitoring of lower lumbar nerve roots during instrumented spinal fusion. Subjects: 161 patients undergoing elective lumbar spinal fusion monitored with the Neurosign 800 machine. Outcome Measures: MEP evidence of pedicle breaches and nerve root over-distraction. Symptoms and signs of new neurological deficits postoperatively. EMG confirmation of neurological deficits in symptomatic post-operative patients. Results: True positive results consisted of pedicle breaches detected in 15 patients (9.3%). Nerve root irritation on distraction was found in 9 patients (5.6%). These results allowed modification of the surgical technique to prevent subsequent neural injury. True negative results on active pedicle probing occurred in 134 patients (83.2%) and in 146 patients (90.7%) on passive monitoring. False positive results were detected in 7 patients (4.3%). Four patients had electrical connection problems and in three patients pedicle probing was positive but direct screw testing was negative. True negative results consisted of a failure of monitoring to detect clinically significant neurological events in five patients (3.1%). In four the symptoms and signs were transient, resolving within six weeks of surgery. In one, revision decompression of the L5 nerve roots was required. Conclusions: MEP monitoring in our hands has a specificity of 95.4% and a sensitivity of 75%. The cost per case is around £75

Introduction. Changes in central nervous system (CNS) pathways controlling trunk and leg muscles in patients with low back pain(LBP) and lumbar radiculopathy have been observed and this study investigated whether surgery impacts upon these changes in the long term. Methods. 80 participants were recruited into the following groups: 25 surgery(S), 20 chronic LBP(CH), 14 spinal injection(SI), and 21 controls(C). Parameters of corticospinal control were examined before, at 6, 26 and 52 weeks following lumbar decompression surgery and equivalent intervals. Electromyographic(EMG) activity was recorded from tibialis anterior(TA), soleus(SOL), rectus abdominis(RA), external oblique(EO) and erector spinae(ES) muscles at the T12&L4 levels in response to transcranial magnetic stimulation of the motor cortex. Motor evoked potentials (MEP) and cortical silent periods(cSP) recruitment curves(RC) were analysed. Results. Trunk muscles in all patients had reduced raw EMG (P<0.001), increased motor thresholds (MTh;P<0.001) and MEP RC slopes. MTh in ESL4 correlated with back pain in all patients (r=0.201, P=0.016) and soleus MTh laterality with disability in surgery patients (r=0.49, P=0.018). S&SI patients displayed bilaterally increased soleus cSP (p<0.001), MEP latencies on the painful side (P<0.001), and cSP asymmetry (cSPA;P<0.001). cSPA resulted from abnormal soleus late responses on the painful side, indicating compromised agonist-antagonist control in patients with radiculopathy. In contrast to SI, surgery significantly reduced soleus cSPA and MEP latencies at 6 weeks (P≤0.034). Discussion. These results show long term changes in CNS control of trunk and leg muscles in radiculopathy and LBP, which are only partly reversed by surgery, and may provide future therapeutic targets to address the altered inhibitory processes within the brain. No conflicts of Interest. Sources of funding: The DISCS foundation. This abstract has not been previously published in whole or substantial part nor has it been presented previously at a national meeting

Summary Statement. The spinal cord showed marked sensibility to acute compression causing complete and irreversible injury. On the contrary, the spinal cord has more ability for adaptation to slow progressive compression mechanisms having the possibility of neural recovery after compression release. Introduction. The aim of this experimental study was to establish, by means of neurophysiologic monitoring, the degree of compression needed to cause neurologic injury to the spinal cord, and analyze whether these limits are different making fast or slow compression. Material and Methods. Spinal cord was exposed from T7 to T11 in 5 domestic pigs with a mean weight of 35 kg. The T8 and T9 spinal roots were also exposed. A pair of sticks, attached to a precise compression device, was set up to both sides of the spinal cord between T8 and T9 roots. Sequentially, the sticks were approximated 0.5 mm every 2 minutes causing progressive spinal cord compression. An acute compression of the spinal cord was also reproduced by a 2.5 mm displacement of the sticks. Cord to cord motor evoked potentials were obtained with two epidural catheters, stimulating proximal to T6 and recording below the compression level, distal to T10, for each sequential approach of the sticks. Results. The mean width of the dural sac was 7.1 mm. For progressive compression, increasing latency and decreasing amplitude of the evoked potentials were observed after a mean displacement of the sticks of 3.2 ± 0.9 mm, the evoked potential finally disappearing after a mean displacement of 4.6 ± 1.2 mm. The potential returned 16.8 ± 3.2 minutes after the compression was stopped in every case. The evoked potentials immediately disappeared after an acute compression 2.5 ± 0.3 mm, without any sign of recovering after 30 minutes. Conclusion. The proposed experimental model replicates the mechanism of a spinal cord injury caused by medially displaced screws into the spinal canal, causing therefore lateral compression to the spinal cord. The spinal cord showed marked sensibility to acute compression, which caused complete and irreversible injury. On the contrary, the spinal cord has more ability for adaptation to progressive and slow compression mechanisms. From a clinical point of view, it seems mandatory to avoid maneuvers of rapid mobilization or acute, even minimal, contusions of the thoracic cord

Introduction Transcranial motor evoked potentials are routinely used at The Children’s Hospital at Westmead to monitor the spinal cord in spinal surgery. This study is a prospective review of all spinal cord monitoring procedures from 1999 to 2004 in patients undergoing elective spinal deformity correction surgery at The Children’s Hospital at Westmead and Westmead Hospital. Spinal cord monitoring with Somatosensory Evoked Potentials (SSEP) and MEP has been widely used in combination during spinal surgery with good sensitivity and specificity. The use of CMAP as the only modality has not been widely used and its efficacy has not been fully elucidated. Using MEP and CMAP only may increase the sensitivity of spinal cord monitoring compared with combined SSEP and MEP monitoring. Methods The intra-operative monitoring outcomes were compared with patient’s post-operative clinical outcomes. The sensitivity and specificity were calculated and determined for our monitoring protocol. Results Transcranial MEPs were measured in 146 patients in 175 procedures. In 2 patients (2 procedures) we were unable to record any CMAPS. There were 15 intra-operative monitoring changes (8.7%). There were no new post-operative neurological deficits. Our results compare favourably to the literature with respect to the false-negative rate or new neurological events. Discussion Using our anaesthetic protocol and spinal monitoring criteria, we were able to successfully monitor patients undergoing elective spinal deformity correction surgery for a variety of diagnoses. The monitoring criteria are sufficiently strict to achieve a sensitivity of 1.0 (95%CI = 0.66–1.00) and a specificity of 0.97 (95%CI = 0.83–0.99). Monitoring of CMAPs alone has been adequate to avoid clinical neurological deficits

Introduction: Conventional reduction techniques for high-grade isthmic spondylolisthesis do not address important anatomical constraints on the L5 and S1 nerve roots, thereby leading to a significant risk of neurological deficit. We describe a novel three-stage reduction technique carried out in one operative session that respects these anatomical constraints. We report the results in seven cases. Methods: Between 2000 and 2006, four female and three male adolescents with high-grade spondylolisthesis (grade 3 or greater) underwent this 3 stage procedure which included: I) extensive posterior decompression of L5 and S1 nerve roots plus sacral dome osteotomy. II) anterior L5/S1 discectomy. III) reduction of spondylolisthesis with pedicle screw fixation and posterior lumbar interbody fusion using interbody cages. Somatosensory and motor evoked potentials were used during the procedure. Patients were followed up for a mean of 4 years (range1–6). Sagittal balance was restored and assessed by measuring sacral slope, lumbosacral angle, pelvic incidence and pelvic tilt. Results: The mean age at surgery was 14.7 years (range 12–17) and average duration of symptoms was 13.7 months (range6–24). Mean operative time was 6.5 hours (range 5–8), with a mean blood loss of 2242cc (range1400–4200). The mean pre-op slip angle was 57°(range 45°–100°) and the mean post-op slip angle was 37.5°(range28°–57°). Anatomical reduction was achieved in six patients and one patient with spondyloptosis was reduced to grade 2. Sagittal balance was restored in all patients. There were no permanent neurological complications. One patient with grade 4 spondylolisthesis developed transient right L5 nerve root palsy which fully recovered within 3 months. Conclusion: The safety and efficacy of this 3 stage reduction and stabilization procedure showed that immediate reduction of high grade spondylolisthesis with minimal risk of neurological deficit is possible. The procedure is technically demanding and should be performed by spinal surgeons familiar with the principles of anterior and posterior fusion

Objective: To emphasize the need to provide a controlled method of intra-operative reduction to correct fixed cervical flexion deformities in ankylosing spondylitis and to describe the technique involved. Design: The treatment of severe fixed cervical flexion deformity in ankylosing spondylitis represents a challenging problem that is traditionally managed by a corrective cervicothoracic osteotomy. The authors describe a method of controlled surgical reduction of the deformity, which eliminates saggital translation and reduces the risk of neurological injury. Subjects: 2 male patients aged 39 and 45 years old with ankylosing spondylitis presented with severe fixed flexion deformity of the cervical spine. Both patients had previously undergone a lumbar extension osteotomy to correct a severe thoracolumbar kyphotic deformity. As a result of the fixed cervical flexion deformity, marked restriction in forward gaze with ‘chin on chest’ deformity, feeding difficulties and personal hygiene were encountered in both. Their respective chin-brow to vertical angle was 60 and 72°. Somatosensory and motor evoked potentials were used throughout surgery. A combination of cervical lateral mass screws and thoracic pedicle screws were used. Interconnecting malleable rods were then fixed at the cervical end, thereby allowing them to slide through the thoracic clamps thus achieving a safe method of controlled closure of the cericothoracic osteotomy. When reduction was achieved, definitive pre-contoured titanium rods were interchanged. Halo-jacket was not considered necessary in view of the segmental fixation used. Results: Good anatomical reduction was achieved, with near complete correction of the deformities, restoration of saggital balances and forward gazes. There were no neurological deficits in either patient and the postoperative recoveries were uneventful. Both osteotomies united with no deterioration noted at 2 years. Conclusions: We illustrate a controlled method of surgical reduction during corrective cervicothoracic osteotomy of fixed cervical kyphosis in ankylosing spondylitis. This has been achieved with the use of a combination of cervical lateral mass screws and thoracic pedicle screws with interconnecting malleable rods that were later replaced with titanium rods. The authors believe that the unique technique described remains a technically demanding but adequate and safe approach for correcting such challenging deformities

Objective: To demonstrate possible advantages of combined (motor and sensory) versus single modality (either motor or sensory) intraoperative spinal cord monitoring. Design: Retrospective and prospective clinical study. Materials and Methods: One hundred and twenty-six consecutive operations in 97 patients had peroperative monitoring the lower limb motor evoked potentials (MEPs) to multi- pulse transcranial electrical stimulation (TES), and tibial nerve somatosensory evoked potentials (SEPs). Seventy-nine patients had spinal deformity surgery, and eighteen had surgery for trauma, tumor or disc herniation. Results: Combined motor and sensory monitoring was successfully achieved in 104 of 126 (82%) operations. Monitoring was limited to MEPs alone in two, and SEPs alone in eighteen cases. Neither MEPs nor SEPs were obtainable in two cases with Friedreich’s ataxia. Significant evoked potentials (EP) changes occurred in one or both modalities in 16 patients, in association with instrumentation (10) or systemic changes (6). After appropriate remedial measures, SEPs recovered either fully or partially in all cases (8/8) and MEPs in 10/15. New neurodeficits developed post-operatively in six of the sixteen patients with abnormal EPs, including two in whom SEPs had either not changed or recovered fully after remedial measures. One patient developed S3–5 sensory loss despite full recovery of both SEPs and MEPs. Two patients without neurological consequences had persistent MEP changes. Normal MEPs (but not SEPs) at the end of the operation correctly predicted the absence of new motor deficits. There were no false negative MEP changes. Conclusion: MEPs are more sensitive than SEPs, but may rarely raise false positive alarm. SEPs are unaffected by anaesthetics and can be monitored more frequently. Combined monitoring is safe, complimentary to each other, and increases sensitivity and predictivity of adverse neorological consequences. True incidence of false positive MEP or SEP changes are difficult to define. Remedial measures after monitoring changes may help cord ischaemia to recover and absence of neurological deficit, therefore, may not indicate a false positive monitoring change

Introduction Spinal cord monitoring in posterior scoliosis surgery has become a standard of care. It has been our practice since 1999, to monitor the somato-sensory potential (SEP) and motor evoked potential (MEP) in all posterior cases. We report on and discuss the meaning of alteration in the spinal cord monitor signal that occurred in 15 cases from a total of 165 procedures. Methods This is a retrospective review of patients from a hospital database. Over a six year period, 167 posterior scoliosis instrumented fusion procedures were performed by paired combinations of the four authors. In 13 cases we have been alerted to a change in one or both signals during the procedure. Associated with these, were two cases of intra-operative cardiac arrest, and six cases of post-operative neurological deficit. All patients remain under continued regular review. Results In the two cases of intra-operative cardiac arrest, the SEP and MEP signals were lost approximately three minutes prior to the arrest. Both patients had neurological deficits post-operatively, one has totally recovered, and one has a residual complex regional pain syndrome of the right leg. This last patient is the only one of six who has not had complete resolution of the post-operative neurological deficit. In five of the six cases who sustained post-operative neurological deficits, the SEP and usually the MEP was lost and did not return. In the sixth case, the SEP did return. In the remaining seven cases, there were changes of decreased amplitude or increased latency in the SEP or MEP that did not appear to result in a postoperative clinical consequence, however; in two patients, signal changes were directly related to changes in blood pressure, and in two other patients, signal changes were directly related to concave hook placement. Discussion On review of the management and outcome of these cases, we conclude that profound hypotension will alter the SEP and may herald a catastrophic cardiovascular or neurological event. Furthermore, the modality of continuous spinal cord monitoring can provide specificity in the diagnosis of an actual or impending neurological insult and allow for appropriate and timely intervention. We believe spinal cord monitoring in the posterior approach for spinal deformity is an invaluable tool, and is in fact, mandatory for all idiopathic and ambulant non-idiopathic spinal deformities

AIS has different image than paralytic scoliosis or scoliosis accompanying some diseases of the spinal cord in electromyographical and electroneurographical examinations (EMG and ENG). These differences are concerned to different progression, characteristic properties in skeletal system pathology or curves angles at the thoracic and lumbosacral spine. There are always two sites in patients with AIS where changes in transmission from the motor cortex to the motoneuronal centres in lumbosacral region appear. These phenomena were shown in motor evoked potentials studies which were induced with the magnetic field (MEP) in areas of motor cortex and recorded from centres of cervical and lumbosacral spinal cord as well as from muscles of upper and lower extremities. Changes in efferent transmission are greater twice in recordings from muscles of lower extremities and in oververtebral recordings at L5-S1 regions what suggests, that secondary slowing down takes place at the level of the apical thoracic vertebrae of primary curve (mostly at Th7–8), predominantly on the concave than convex side of scoliosis. MEP study confirmed a previous finding with somatosensory evoked potentials (SEPs) similarly about two focuses of disturbances in of afferent transmission on the spinal centres-supraspinal centres pathway. MEP showed changes in the efferent transmission on the supraspinal centres-spinal motor generator pathway. Such changes are not observed in scolioses other than idiopathic. Results of the complex neurophysiological studies suggest that the primary origin of AIS is the brain stem area at the level of thalamus where changes of afferent and efferent transmission are detected. There is a close relationship of this structure with the pineal gland and secretion of neurotransmitters at this level in correlation to disturbances in melatonin secretion and other neurohormones. Disorders in melatonin secretion and other neurohormones may induce a scoliosis what was shown in previous genetic and experimental neurophysiological studies on animals, together with cutting of the pineal stalk. Some aspects of this problem were also mentioned in our previous clinical neurophysiological studies [1–3]. Results of studies suggest that in patients with AIS, there are structural and functional changes in the area of thalamus, which cause disturbances in afferent and efferent transmission at this level. Pathology in the pineal secretion of neurohormones can be one of the factors influencing the formation and progression of AIS, as a disease of probably secondary origin to the functional changes in brain. Results of MEP studies discussed in this report confirm that the primary origin of AIS takes place at the level of the brain stem but not in the spinal cord

Purpose & Background: The spinal muscles are increasingly being linked to spinal complaints. However, little is known regarding the corticospinal control of these muscles. Corticospinal pathways can be activated using transcranial magnetic stimulation (TMS) applied over the motor cortex. This study uses TMS to assess corticospinal input to the paraspinal muscles in the thoracic region. Methods: Ten individuals (mean [± SD] age 33 ± 10 yrs; mean height 166 ± 10 cm; two left-handed; five male, five female) with no history of neurological disorder were recruited into this study and written informed consent obtained. Subjects lay prone in a relaxed position with the head unsupported. Surface electromyographic (EMG) recording electrodes were positioned bilaterally over the paraspinal muscles adjacent to thoracic spinal processes T1 and T2. TMS was applied using a MagStim 200 stimulator connected to a double cone coil with its cross-over positioned over the vertex so that the maximum induced current flowed in a posterior to anterior direction. The stimulus intensity was adjusted in steps of 5% of the maximum stimulator output (MSO), and ten stimuli were delivered at each strength. Threshold for a motor evoked potential (MEP) in each muscle was determined as the minimum intensity that would evoke MEPs to 50% of stimulus presentations. Latency of MEPs was determined by measuring the time between the stimulus and the start of the first deflection in the MEP. The procedure was repeated for the other pairs of thoracic segments between T3 and T12. Results: In all subjects, it was possible to evoke MEPs in relaxed paraspinal muscles at all thoracic levels. Mean (±SEM) threshold for evoking a MEP on the left side increased from 47 ± 2.5 %MSO at level T1 to 55 ± 2.5 %MSO at T12 (Pearson correlation, P< 0.05) but remained more constant (P> 0.05) on the right side (T1, 55 ± 3.9 %MSO; T12, 57 ± 3.3 %MSO). Over all levels tested, mean threshold for MEPs was 3.9 ± 0.6 %MSO higher on the right than the left side (Student’s paired t-test, P< 0.05). Mean latency of MEPs on the left increased from 11.9 ± 0.7 ms at level T1 to 15.5 ± 0.6 ms at T12 and on the right from 12.3 ± 0.5 ms at level T1 to 16 ± 0.7 ms at T12 (Pearson correlation, P< 0.05). Throughout the thoracic region, latency of MEPs was 0.8 ± 0.2 ms longer on the right than the left side (Student’s paired t-test, P< 0.05). Conclusion: The latency of MEPs increased as recordings were made from muscles innervated more caudally. Threshold for MEPs varied between subjects and at different spinal levels but our results indicate that it was higher at more caudal levels, perhaps suggesting weaker corticospinal innervation. Threshold was lower and latency shorter for muscles on the left side raising the interesting possibility that paraspinal muscles have some asymmetry in their corticospinal innervation. This study has provided us with baseline electrophysiological data allowing us to investigate the voluntary control pathways to muscles stabilising the thoracic spinal cord following trauma or disease

Radiological diagnosis is not the only tool in detection, monitoring of progress and making easy to undertake a decision about the surgical scoliosis correction. The below presented algorithm of scoliosis monitoring with complex and repetitive (comparative) neurophysiological examinations facilitates the doctor’s decision about method of the conservative treatment or just the moment of surgical intervention [3, 14]. Neurogenic changes in muscles can be found in early stages of the spine deformation – usually when the Cobb’s angle is over 100 [1]. Vertebral rotation and curvature progression follow simultaneously leading to deformation of the spinal cord together with the local ventral roots compression and sometimes inflammation of them. The structure of the grey matter especially in the ventral horn changes its form more on the convex side of scoliosis. Cell bodies together with the axonal hillocks in the motoneuronal pools show deformations comparing to the analogical area of the concave side. This produce discrete unilateral axonopathy in both efferent fibers of peroneal and tibial nerves in scoliotic patients at the age of about 10. This can be found in electroneurographical (ENG) recordings of M and F potentials even at the angle of scoliosis of 100 [10, 14]. Both parameters of the amplitudes and conduction velocities in M-wave studies are decreased and the frequency of F wave recording is diminished what suggests pathological asymmetrical changes just at the level of the ventral root. That is why electromyographical (EMG) recordings show asymmetrical, according to the ventral root somatotopical innervation, selective (found only in some muscles) deficits in frequency and amplitude of motor units action potentials, predominantly in girls. These girls have scoliosis accelerating the most with angle changes of 50 per year [2] that rapidly deepens the neurogenic changes. Other significant evaluation of the scoliosis acceleration is using the somatosensory evoked potentials (SEPs) for recording progression of pathology in the afferent transmission within the long ascending spinal cord pathways running in dorsal, dorsolateral and lateral funiculi [4, 5]. Changes in parameters more amplitude than conduction velocity from SEPs studies recorded at the cervical level are more visible on the concave than convex side of scoliosis. These changes are correlated with increasing the Cobb’s angle at the apical thoracic vertebrae (Th7–8) while peripheral sensory transmission remains only slightly disturbed [6, 7]. These changes were found to be twice greater when recording of SEPs was performed over cranially on the contralateral side of the scalp to the stimulation site at the ankle (tibial nerve than peroneal nerve fibers excitation) both in mothers and their daughters [4]. This points at the strong inhibition of the afferent transmission at the level of the brain stem (probably thalamus or medial lemniscus). During the comparative SEPs recordings at the cervical level, when parameters of waves change dramatically (or even they disappear), this may suggest that the lateral angle of scoliosis exceeded 450 with great acceleration of the torsion [9]. Somatosensory evoked potential recordings during the surgical correction of scoliosis showed only rarely the immediate improvement of the afferent transmission [7, 8, 11]. However, they make sure a surgeon about lack of blockade within the spinal pathways which comes from derotation and distraction procedures performed on the spine during implantation of the corrective instrumentation. First visible results of improvement in the SEPs parameters recorded postoperatively are usually seen a week after the surgery [14]. The above analogical phenomena but referring to the efferent transmission were shown in motor evoked potentials studies which were induced with the magnetic field (MEP) in areas of motor cortex and recorded from centres of cervical and lumbosacral spinal cord as well as from nerves and muscles of upper and lower extremities [12,13, 15]. Usually when AIS reaches the Cobb’s angle of 200 at the age of 25 and does not progress more it can be assumed, that its development is finished. In these patients the signs of neurogenic changes found in EMG examinations performed in lower extremities, paravertebral and gluteal muscles do not progress, too [14]