- Department of Neuroscience, Winthrop University Hospital, Mineola, NY, USA
Mark M. Stecker
Department of Neuroscience, Winthrop University Hospital, Mineola, NY, USA
DOI:10.4103/2152-7806.98579Copyright: © 2012 Stecker MM. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Stecker MM. A review of intraoperative monitoring for spinal surgery. Surg Neurol Int 17-Jul-2012;3:
How to cite this URL: Stecker MM. A review of intraoperative monitoring for spinal surgery. Surg Neurol Int 17-Jul-2012;3:. Available from: http://sni.wpengine.com/surgicalint_articles/a-review-of-intraoperative-monitoring-for-spinal-surgery/
Background:Intraoperative neurophysiologic monitoring (IONM) is a technique that is helpful for assessing the nervous system during spine surgery.
Methods:This is a review of the field describing the basic mechanisms behind the techniques of IONM. These include the most often utilized trancranial motor evoked potentials (Tc-MEPs), somatosensory evoked potentials (SSEPs), and stimulated and spontaneous EMG activity. It also describes some of the issues regarding practices and qualifications of practitioners.
Results:Although the anatomic pathways responsible for the Tc-MEP and SSEP are well known and these clinical techniques have a high sensitivity and specificity, there is little published data showing that monitoring actually leads to improved patient outcomes. It is evident that IONM has high utility when the risk of injury is high, but may be only marginally helpful when the risk of injury is very low. The monitoring team must be well trained, be able to provide the surgeon feedback in real time, and coordinate activities with those of the surgical and anesthesia teams.
Conclusions:Although IONM is a valuable technique that provides sensitive and specific indications of neurologic injury, it does have limitations that must be understood. Maintaining a high quality of practice with appropriately trained personnel is critical.
Keywords: Intraoperative neurophysiologic monitoring, motor evoked potentials, somatosensory evoked potentials, spine
Intraoperative neurophysiologic monitoring (IONM) is a valuable technique for assessing the nervous system. It replaces the neurologic examination when the patient is under general anesthesia and cannot cooperate with a face-to-face examination. It allows for assessment of many neural structures including the neuromuscular junction, peripheral nerve, spinal cord, brainstem, and cortex during surgery. One goal of this review is to summarize the techniques used for IONM of the spine. The most commonly employed techniques during spinal procedures are: (1) transcranial motor evoked potentials (Tc-MEPs), (2) upper and lower somatosensory sensory evoked potentials (upper and lower SSEP), (3) pedicle screw simulation, and (4) spontaneous electromyography (EMG). A number of other techniques have been used over the years that include direct spinal cord stimulation and reflex monitoring.
This review is broken up into three sections: one discusses the basic techniques used, another one discusses the application of these techniques in different common surgical procedures of the spine, and the third one discusses the typical qualifications for personnel involved in IONM.
Trancranial motor evoked potentials
Tc-MEPs have been used to perform intraoperative monitoring for more than 20 years.[
Basic physiology of Tc-MEPs in the awake patient
In a normal awake patient, electrical stimulation of the cortex/subcortical white matter with a single electrical pulse produces a number of responses that can be recorded by an epidural electrode placed over the upper thoracic spinal cord [
Trancranial motor evoked potentials and anesthesia
The clinical importance of the physiology described above is that a single stimulus applied to the scalp of an awake person may produce a muscle contraction because of the train of D- and I-waves reaching the anterior horn cell. However, under general anesthesia, a single stimulus may not be effective since the I-waves are diminished and the anterior horn cell sees only the single D-wave. In addition, during general anesthesia, there is a reduction in spontaneous activity in the interneurons of the spinal cord, reducing the overall level of excitation reaching the anterior horn cell. During clinical IONM studies, these problems are overcome by using trains of stimuli rather than single stimuli [
Stimulus parameters and trancranial motor evoked potentials
The train stimuli used during TC-MEP range in amplitude from about 75 to 900 V, with maximal currents up to 0.9 A. The stimulation voltage and current required is markedly dependent on the type of electrode used. The highest current levels are required if EEG cup electrodes are used. Lower thresholds are seen with subdermal needle electrodes and corkscrew electrodes. The duration of each pulse is between 50 and 500 msec.[
Safety and complications of trancranial motor evoked potentials
Safety and the prevention of complications are important issues when discussing motor evoked potentials.[
Electrode locations for performing trancranial motor evoked potentials
Stimulating electrodes are typically placed over the C1 and C2 locations (located midway between the traditional C3 and C4 electrode positions and Cz in the 10–20 system) which are near the motor cortex. Other locations including more lateral placements may optimize stimulation in some patients. Midline stimulation may be helpful at times for eliciting responses from the lower extremities. However, even with these placements, the point of maximal stimulation is not the cortex, but the deep white matter likely in the corona radiate.[
The muscle MEP is the most commonly used Tc-MEP. Recordings are of high amplitude and can be obtained with a single trial. Thus, they can provide the surgeon with nearly instantaneous information, unlike the SSEP which requires prolonged averaging. The problem with the muscle MEP is that the waveform is complex. Thus, many schemes have been devised to try to determine when there is a significant change.
Interpretative criteria for the muscle MEP
One criterion is the threshold criterion proposed by Calancie.[
The effect of pre-operative damage to the motor pathways and the trancranial motor evoked potentials
It should also be noted that the state of the motor pathways prior to surgery is very critical to the generation of the muscle MEP. If there is injury pre-operatively, even if the patient has good strength pre-operatively, the MEPs may be difficult to obtain. This is because activation of the anterior horn cell requires a highly synchronized volley of inputs that can easily be desynchronized by a minor disruption of conduction.
Because the D-wave has a simple morphology and is insensitive to anesthesia, criteria for interpretation are much simpler than for the muscle MEP. It is generally considered[
Upper and lower extremity somatosensory evoked potentials
The SSEP [
Anatomy of the somatosensory evoked potential
Impulses from the upper and lower extremity travel back to the spinal cord utilizing different pathways. The impulses from the upper extremity are conducted to the spinal cord through the peripheral nerve and brachial plexus where the ERB’ s point potential is generated. These fibers synapse in the dorsal column nuclei, where in response to upper extremity stimulation, the N13 potential is seen. The fibers then pass through the medical lemniscus in the brainstem and reach the thalamus where the upper extremity SSEPs generate part of the N20 potential. Arriving at the primary sensory cortex, the upper extremity SSEPs generate a cortical N20 and P22.
From the lower extremity, somatosensory potentials travel past the popliteal fossa where the popliteal potential is generated before they reach the lumbosacral plexus. As the impulses from the lower extremity enter the cauda equina, a lumbar potential (N21) is generated. Both the popliteal and lumbar potentials can be difficult to record, especially in patients who are overweight. The orthodromic action potentials then travel along the dorsal root and enter the spinal cord posteriorly. Most of the fibers monitored with this technique travel in the dorsal columns although there is evidence that some do travel in the dorsal spinocerebellar pathways.[
Of note, the slower conducting fibers in the spinothalamic pathways are not monitored by this technique.
Criteria for change in somatosensory evoked potentials
In comparison with the Tc-MEPs, SSEP responses are very low in amplitude and require prolonged averaging. Therefore, depending on the ambient level of noise, the time required to determine if a significant change has occurred may be 3–5 minutes or more. SSEP responses have a simple waveform, and so are simpler to quantify than the muscle MEPs. Injury to the large fiber dorsal column pathways is typically expected when there is a >50% decrease in amplitude or 10% increase in latency of any of the above potentials. Interpretation of what represents a significant change remains controversial because of intraobserver variability and because the optimal criteria for determining when there is a significant change are very dependent on the type of procedure.[
The recording of spontaneous EMG activity from a muscle provides information on the state of the peripheral nerves that innervate that muscle. Compression or stretch of a nerve as well as hypothermia and ischemia produce depolarization of the axons resulting in the appearance of spontaneous action potentials. These action potentials subsequently produce contractions of muscle fibers that can be recorded by electrodes placed in the muscle.
Theoretical limitations of spontaneous EMG recording
There are a number of important clinical issues regarding these responses. The first is that the spontaneous activity in the different axons during injury is not synchronized so that there is generally no large-scale muscle movement; rather, there may be only contractions of a few fibers at a time. Thus, the placement and type of the recording electrodes is critical since spontaneous activity may be noted in one location and not another within the same muscle.[
Patterns of spontaneous electromyography activity associated with nerve damage
One of the critical issues is which patterns of EMG activity are most highly associated with damage to the nerve.[
Pros and cons of using spontaneous EMG activity
The most useful characteristic of spontaneous EMG activity is that it is instantaneous. Alternatively, the most disadvantageous factors attributed to spontaneous EMGs include its extreme sensitivity to neuromuscular blockade, complex criteria for significant abnormality, and dependence on anesthesia.[
For instrumented spinal fusions, electrical stimulation facilitates proper screw placement. The most common use is to determine whether a screw that has already been placed is properly located. The basic principle[
Factors that may confound the interpretation of triggered electromyography responses
Although the technique for interpreting triggered EMG responses appears simple, there are a number of potential issues that may confound the evaluation of results. The first is that if the nerve root has been previously injured, the threshold will rise, and it is possible that a high threshold may be recorded even when the screw is electrically near the nerve. If the monitorist is not certain that the nerve root under study is uninjured, it is sometimes possible to stimulate the nerve root directly. For spinal nerve roots, the threshold for stimulation is typically at a current of approximately 2 mA. Significantly higher thresholds might indicate nerve damage that could falsely elevate the threshold for stimulation of the pedicle screw.[
Threshold levels vary with spinal location
It is also important to know that the[
Other monitoring techniques to facilitate screw placement
There are other techniques that may assist the surgeon with placement of pedicle screws. These involve continuous stimulation of the tools producing the screw holes and testing the screw holes before the screw is placed.[
H-reflexes and F-waves
There has been significant interest in using H-reflexes and F-waves as a means to monitor the function of the spinal cord and proximal nerve roots during spine surgery. As in
Direct spinal cord stimulation
Spinal cord stimulation techniques, originally championed by Owen,[
Detecting intraoperative spinal cord injury
Although it does have some limitations, neurophysiologic monitoring is a relatively new technique that can be very helpful in preventing injury to the nervous system. The first limitation relates to the overall frequency of neurologic injury during an operation. If the frequency of injury during a particular surgery is extremely low, the type of monitoring utilized must be highly sensitive and specific in order to provide useful information. When the frequency of injury is relatively high, monitoring need not have the same sensitivity and specificity in order to be helpful. This is illustrated in
Illustration of the effect that the a priori probability P(I) has on the probability that a warning is associated with true injury when a warning is made with every injury (100% sensitive) and varying levels of false-positive warnings P(W/NI). W = warning, I = injury, NI = no injury, P(W/NI) is the conditional probability of a warning when there is no injury
In scoliosis surgery, the risk of spinal cord injury is much higher than with the ACDF, roughly 0.3–0.8%. Thus, the likelihood that monitoring will be helpful is increased.[
Results of Selected Studies of intraoperative neurophysiologic monitoring in spinal surgeries. No attempt was made to be exhaustive. It should be noted that due to differences in criteria used for interpretation and different presentation of results, the numbers obtained from different studies are not always comparable. There are also significant differences between the differing surgical populations and different definitions of a neurologic deficit, anesthesia used and monitoring technique
The Neurophysiology Research and Education Consortium (
Intraoperative monitoring for peripheral nerve injury
There are a number of types of peripheral nerve injury that may occur during spine surgery. Injury may occur during positioning to the ulnar nerve[
When should monitoring be used?
One important question in the current climate of cost-effective medicine is determining which spine surgeries should be monitored. One answer to this question is that every case should be monitored because even if there is a tiny chance that a patient could benefit, then some patients will have improved outcomes. Beyond this, there are a number of cost-effectiveness arguments that can be applied. One of the arguments relates to the cost of responding to a warning. Each time a warning is issued by the monitoring team, a number of events occur. This includes the surgical and anesthesia teams double checking what they are doing. Very commonly attempts will be made to increase the blood pressure, administer medications, or change the level of anesthesia. Thus, there is a cost in terms of OR time and medications involved with a response to a warning. The cost of this is Co(W), the operative cost of responding to a warning. The total cost would be Co(W) × P(W), where P(W) is the probability that a warning is issued. In addition, there is a cost to providing the monitoring for each case Cm, which is not dependent on the rate of issuing a warning. The cost saved by responding to a warning is the cost of an injured patient C(I) multiplied by the chance that monitoring will prevent an injury. This is the probability that a warning is issued P(W) times the conditional probability that the warning is associated with a true injury P(I/W) (probability of injury given a warning) times the probability that a true warning can be acted on to prevent injury PC. Thus, the total cost of monitoring is Cm + Co(W) × P(W) – C(I) × P(I/W)P(W) × PC. If this number is positive, then monitoring is not cost effective. If it is negative, then monitoring is cost effective. Consider some very rough estimates. For a scoliosis procedure, the cost of providing a warning may be $1000 [both Co(W) and Cm] and the cost of an injury being permanent paraplegia might be $10,000,000. If PC is say 0.5 (the surgeon can prevent injury in half of cases where there is a true injury), then since P(I/W) is on the order of 0.24 (above), then the above equation for total cost will read as 1000 – P(W) × 1,250,000. Thus, if P(W) is greater than about 0.1%, monitoring is cost effective. Using the numbers quoted above for scoliosis, monitoring would be very cost effective, but at least for the investigators cited above regarding ACDF, the advantage would be marginal. In surgical procedures where the cost of an injury is less, monitoring becomes cost effective by this calculation only when the risk of injury is high.
This is not the complete calculation for the cost effectiveness of monitoring because it did not include the advantages that might be gained if the costs of monitoring were used for another service that might benefit the patient. In fact, the cost estimated above needs to be compared not to zero but to the cost that might be saved by using the amount Cm for another patient care expense that could also help prevent injury. Consider the case of a surgeon who performs three spine surgeries a week. The total cost of monitoring for these cases would be conservatively estimated at $150,000/year. This might be enough for the surgeon to hire an additional physician's assistant and a nurse just to take care of these three patients every week. It is hard to estimate the advantage that hiring these additional medical personnel would have, but it is clear that the advantage will be more in the medically ill elderly patient than in the medically healthy young person. This is especially true since there is a known 2–10% rate of making errors in writing medication orders,[
IONM is performed at two levels. The first is a technical level that involves placement of electrodes, setting up monitoring equipment, and performing the testing as described above. The other level is the interpretative level that involves deciding which testing is appropriate for a given surgical case and elucidating the clinical meaning of any change in the waveforms during the procedure.
The practice of monitoring
Practitioners at these two levels, however, cannot practice solely within the narrow boundaries described above. The practitioners who perform the technical level of monitoring must understand the interpretative process or else they will not be able to function efficiently. By the same token, interpreting providers must understand all aspects of the equipment being used and the technical problems that might arise which could interfere with signal acquisition.
Working with a team
Because responses to changes in the monitored waveforms need to be acted on quickly in order to prevent injury, it is critical that this team be highly trained, and work well with both the surgical and anesthesia teams. This, in particular, means that it is not optimal for a new monitoring team to arrive in the OR and just start working with a particular surgeon and anesthesiologist. It is important that the surgeon and monitoring team share expectations and protocols in advance. There must also be ongoing discussions between the monitoring team, and surgical and anesthesia teams beyond the contact that occurs during provision of services to individual patients in order to enhance quality assessment (QA) and quality improvement (QI) activities. This will also be an important venue in which to bring forward new monitoring techniques and new clinical problems, for joint discussion.
Credentials for intraoperative monitoring at the technical level
What are the credentials and training considered to be important for the technical level of monitoring, as defined by national societies? The appropriate credential is the Certification in Neurophysiologic Intraoperative Monitoring (CNIM) through the American Board of Registration of Electroencephalograpic and Evoked Potential Technologists (ABRET) (
Interpretation of intraoperative neurophysiologic monitoring and the practice of medicine
It is useful to begin by recalling a statement of the AMA House of Delegates Resolution 201 June 2008: “…it is the policy of the American Medical Association that supervision and interpretation of intraoperative neurophysiologic monitoring constitutes the practice of medicine, which can be delegated to nonphysician personnel who are under the direct or online real time supervision of the operating surgeon or another physician trained in, or who has demonstrated competence, in neurophysiologic techniques and is available to interpret the studies and advise the surgeon during the surgical procedures.” It is important to dissect this statement. Every state has laws that define what constitutes the practice of medicine. In the state of New York, according to the 2010 New York Code Title 8 Article 131-6521: “The practice of the profession of medicine is defined as diagnosing, treating, operating or prescribing for any human disease, pain, injury, deformity or physical condition.” Similar statements are issued by other states. The AMA policy is consistent with this definition of the practice of medicine. However, a physician is not the only person who can make a diagnosis or treat a patient. For example, a physical therapist may treat a patient with back pain. The general principle under which providers whose activities are not explicitly prescribed by the state medical code function is by delegation from a physician. It has always been the ability of the physician to delegate medical activities to non-licensed providers, provided that they have appropriate training and supervision and that there are no regulations that forbid the delegation of the particular service to a specified provider. It is thus important for an operating surgeon who delegates the interpretation of intraoperative monitoring to a non-physician check relevant law in the state and make sure that the person to whom this service is delegated has the appropriate credentials, education, and training. It is also important to recognize that the physician delegating that service remains responsible for it.
The state of Ohio presents an interesting application of the above principles in regard to diagnostic electromyography (EMG). The state allows the physician to delegate nerve conduction studies to non-physicians because definite criteria for performance and interpretation exist but not EMG because it cannot “safely be performed according to exact, unchanging directions” (State Medical Board of Ohio-Your Report-Summer 1999).
There are outstanding non-physician practitioners of IONM whose interpretative skills can provide great benefit to the patient, but it is very important to be sure, based upon state laws and regulations, that the process of delegation is consistent with good medical practice and consistent with state law.
Credentials for interpreting IONM
What are the credentials and training considered to be important for the interpretative level by national societies? There are a number of board certifications that directly apply to the field of IONM. The first is the American Board of Neurophysiologic Monitoring (ABNM) (
Policies for practicing intraoperative monitoring
Regarding policies for the practice of intraoperative monitoring, the ASNM (
Ttrancranial motor evoked potential
Tc-MEP using muscle responses (muscle MEP) provides an effective means of monitoring motor pathways in the spinal cord. Although optimal warning criteria have not been elucidated, simple criteria such as disappearance of the response are very useful guides. Care must be taken to prevent injury and to assure that anesthesia does not affect the muscle MEP responses. Significant changes in the muscle MEP during scoliosis surgery bear a strong correlation with cord injury. Although D-wave monitoring is limited to cervical and upper thoracic cord and requires an epidural recording electrode, it is helpful in addition to muscle MEP monitoring because it is not anesthesia dependent, is not dependent on neuromuscular blockade, and has simple criteria for interpretation.
Tc-MEP using muscle responses (muscle MEP) provides an effective means of monitoring motor pathways in the spinal cord. Although optimal warning criteria have not been elucidated, simple criteria such as disappearance of the response are very useful guides.
Care must be taken to prevent injury and to assure that anesthesia does not affect the muscle MEP responses.
Significant changes in the muscle MEP during scoliosis surgery bear a strong correlation with cord injury.
Although D-wave monitoring is limited to cervical and upper thoracic cord and requires an epidural recording electrode, it is helpful in addition to muscle MEP monitoring because it is not anesthesia dependent, is not dependent on neuromuscular blockade, and has simple criteria for interpretation.
Somatosensory evoked potentials
Upper and lower SSEP can be used to monitor the dorsal column (and possible dorsal spinocerbellar) sensory pathways during spine surgery. Changes in the SSEP have a high specificity but low sensitivity for detecting spinal cord injury.
Upper and lower SSEP can be used to monitor the dorsal column (and possible dorsal spinocerbellar) sensory pathways during spine surgery.
Changes in the SSEP have a high specificity but low sensitivity for detecting spinal cord injury.
Continuous and triggered EMG activity
Continuous EMG is one technique that detects peripheral nerve injury quickly and easily. Its use is limited by the fact that not all injuries produce spontaneous EMG activity. It is also limited by the fact that the criteria for determining which types of activity are associated with significant injury. Triggered EMG is an excellent technique for determining whether lumbar pedicle screws are properly placed. Use of the technique for screws in other locations may be helpful although normative data are less clear. Multimodality monitoring (SSEP + Tc-MEP + EMG) provides the surgeon with optimal information about the state of the nervous system. This helps to increase sensitivity and provide the surgeon with additional information on the specificity of any warnings issued.
Continuous EMG is one technique that detects peripheral nerve injury quickly and easily. Its use is limited by the fact that not all injuries produce spontaneous EMG activity. It is also limited by the fact that the criteria for determining which types of activity are associated with significant injury.
Triggered EMG is an excellent technique for determining whether lumbar pedicle screws are properly placed. Use of the technique for screws in other locations may be helpful although normative data are less clear.
Multimodality monitoring (SSEP + Tc-MEP + EMG) provides the surgeon with optimal information about the state of the nervous system. This helps to increase sensitivity and provide the surgeon with additional information on the specificity of any warnings issued.
Use of monitoring
IONM has a high sensitivity and specificity for detecting injury. In procedures where there is a high risk of severe injury, monitoring is clearly critical to improving outcomes. The advantage of monitoring during procedures with a low risk of injury or where the expected injuries are minor is not well defined.
IONM has a high sensitivity and specificity for detecting injury.
In procedures where there is a high risk of severe injury, monitoring is clearly critical to improving outcomes.
The advantage of monitoring during procedures with a low risk of injury or where the expected injuries are minor is not well defined.
It is critical for IONM to be helpful that it be performed by practitioners skilled at both the technical and interpretative aspects of monitoring. The activities of the monitoring team must integrate well with those of the surgical team and the anesthesia team, and should involve joint QA and QI activities. The monitoring team must be able to respond quickly to changes in the recorded signals and provide the surgeon with appropriate interpretations in real time. The surgeon and/or hospital responsible for the monitoring services must be sure that each provider has adequate training and supervision and all delegation of interpretations is consistent with each state's practice of medicine regulations.
It is critical for IONM to be helpful that it be performed by practitioners skilled at both the technical and interpretative aspects of monitoring.
The activities of the monitoring team must integrate well with those of the surgical team and the anesthesia team, and should involve joint QA and QI activities.
The monitoring team must be able to respond quickly to changes in the recorded signals and provide the surgeon with appropriate interpretations in real time.
The surgeon and/or hospital responsible for the monitoring services must be sure that each provider has adequate training and supervision and all delegation of interpretations is consistent with each state's practice of medicine regulations.
1. Amassian V, Deletis V, Shils J.editors. Animal and human motor system neuorphysiology related to intraoperative monitoring. Neurophysiology in Neurosurgery. San Diego California: Academic Press; 2002. p. 3-23
2. Anderson DG, Wierzbowski LR, Schwartz DM, Hilibrand AS, Vaccaro AR, Albert TJ. Pedicle screws with high electrical resistance: A potential source of error with stimulus-evoked EMG. Spine (Phila Pa 1976). 2002. 27: 1577-81
3. Baars JH, Kalisch D, Herold KF, Hadzidiakos DA, Rehberg B. Concentration-dependent suppression of F-waves by sevoflurane does not predict immobility to painful stimuli in humans. Br J Anaesth. 2005. 95: 789-97
4. Bar-On Z, Zeilig G, Blumen N, Ohry A, Azaria M. Paraplegia following surgical correction of scoliosis with Cotrel-Dubousset instrumentation. Bull Hosp Jt Dis. 1995. 54: 32-4
5. Bell CM, Bajcar J, Bierman AS, Li P, Mamdani MM, Urbach DR. Potentially unintended discontinuation of long-term medication use after elective surgical procedures. Arch Intern Med. 2006. 166: 2525-31
6. Bigelow DC, Patterson T, Weber R, Stecker MM, Judy K. Comparison of endotracheal tube and hookwire electrodes for monitoring the vagus nerve. J Clin Monit Comput. 2002. 17: 217-20
7. Bose B, Wierzbowski LR, Sestokas AK. Neurophysiologic monitoring of spinal nerve root function during instrumented posterior lumbar spine surgery. Spine (Phila Pa 1976). 2002. 27: 1444-50
8. Burke D, Hicks R, Stephen J, Woodforth I, Crawford M. Assessment of corticospinal and somatosensory conduction simultaneously during scoliosis surgery. Electroencephalogr Clin Neurophysiol. 1992. 85: 388-96
9. Calancie B, Harris W, Brindle GF, Green BA, Landy HJ. Threshold-level repetitive transcranial electrical stimulation for intraoperative monitoring of central motor conduction. J Neurosurg. 2001. 95: 161-8
10. Calancie B, Madsen P, Lebwohl N. Stimulus-evoked EMG monitoring during transpedicular lumbosacral spine instrumentation.Initial clinical results. Spine (Phila Pa 1976). 1994. 19: 2780-6
11. Chen ZY, Wong HK, Chan YH. Variability of somatosensory evoked potential monitoring during scoliosis surgery. J Spinal Disord Tech. 2004. 17: 470-6
12. Chung I, Glow JA, Dimopoulos V, Walid MS, Smisson HF, Johnston KW. Upper-limb somatosensory evoked potential monitoring in lumbosacral spine surgery: A prognostic marker for position-related ulnar nerve injury. Spine J. 2009. 9: 287-95
13. Darden BV, Hatley MK, Owen JH. Neurogenic motor evoked-potential monitoring in anterior cervical surgery. J Spinal Disord. 1996. 9: 485-93
14. de Blas G, Barrios C, Regidor I, Montes E, Burgos J, Piza-Vallespir G. Safe pedicle screw placement in thoracic scoliotic curves using t-EMG: Stimulation threshold variability at concavity and convexity in apex segments. Spine (Phila Pa 1976). 2012. 37: E387-95
15. Delank KS, Delank HW, Konig DP, Popken F, Furderer S, Eysel P. Iatrogenic paraplegia in spinal surgery. Arch Orthop Trauma Surg. 2005. 125: 33-41
16. Deletis V, Deletis V, Shils J.editors. Intraoperative neuorphysiology and methodologies used to monitor the functional integrity of the motor system. Neurophysiology in Neurosurgery. San Diego, California: Academic Press; 2002. p. 25-51
17. Deletis V, Isgum V, Amassian VE. Neurophysiological mechanisms underlying motor evoked potentials in anesthetized humans. Part 1. Recovery time of corticospinal tract direct waves elicited by pairs of transcranial electrical stimuli. Clin Neurophysiol. 2001. 112: 438-44
18. Eggspuehler A, Sutter MA, Grob D, Jeszenszky D, Porchet F, Dvorak J. Multimodal intraoperative monitoring (MIOM) during cervical spine surgical procedures in 246 patients. Eur Spine J. 2007. 16: S209-15
19. El-Hawary R, Sucato DJ, Sparagana S, McClung A, Van Allen E, Rampy P. Spinal cord monitoring in patients with spinal deformity and neural axis abnormalities: A comparison with adolescent idiopathic scoliosis patients. Spine (Phila Pa 1976). 2006. 31: E698-706
20. Fehlings MG, Brodke DS, Norvell DC, Dettori JR. The evidence for intraoperative neurophysiological monitoring in spine surgery: Does it make a difference?. Spine (Phila Pa 1976). 2010. 35: S37-46
21. Forbes HJ, Allen PW, Waller CS, Jones SJ, Edgar MA, Webb PJ. Spinal cord monitoring in scoliosis surgery.Experience with 1168 cases. J Bone Joint Surg Br. 1991. 73: 487-91
22. Hendey GW, Barth BE, Soliz T. Overnight and postcall errors in medication orders. Acad Emerg Med. 2005. 12: 629-34
23. Holland NR, Lukaczyk TA, Riley LH, Kostuik JP. Higher electrical stimulus intensities are required to activate chronically compressed nerve roots.Implications for intraoperative electromyographic pedicle screw testing. Spine (Phila Pa 1976). 1998. 23: 224-7
25. Jahangiri FR, Holmberg A, Vega-Bermudez F, Arlet V. Preventing position-related brachial plexus injury with intraoperative somatosensory evoked potentials and transcranial electrical motor evoked potentials during anterior cervical spine surgery. Am J Electroneurodiagnostic Technol. 2011. 51: 198-205
26. Journee H, Nuwer MR.editors. Motor EP physiology, risks and specific anesthetic effects. Handbook of Clinical Neurophysiology. Amsterdam, NL: Elsevier; 2008. 8: 218-34
27. Kalkman CJ, Drummond JC, Kennelly NA, Patel PM, Partridge BL. Intraoperative monitoring of tibialis anterior muscle motor evoked responses to transcranial electrical stimulation during partial neuromuscular blockade. Anesth Analg. 1992. 75: 584-9
28. Kelleher MO, Tan G, Sarjeant R, Fehlings MG. Predictive value of intraoperative neurophysiological monitoring during cervical spine surgery: A prospective analysis of 1055 consecutive patients. J Neurosurg Spine. 2008. 8: 215-21
29. Khan A, Pearlman RC, Bianchi DA, Hauck KW. Experience with two types of electromyography monitoring electrodes during thyroid surgery. Am J Otolaryngol. 1997. 18: 99-102
30. Komanetsky RM, Padberg AM, Lenke LG, Bridwell KH, Russo MH, Chapman MP. Neurogenic motor evoked potentials: A prospective comparison of stimulation methods in spinal deformity surgery. J Spinal Disord. 1998. 11: 21-8
31. Kothbaurer K, Deletis V, Shils J.editors. Motor evoked potential monitoring for intramedullary spinal cord surgery. Neurophysiology in Neurosurgery. San Diego, California: Academic Press; 2002. p. 73-92
32. Krammer MJ, Wolf S, Schul DB, Gerstner W, Lumenta CB. Significance of intraoperative motor function monitoring using transcranial electrical motor evoked potentials (MEP) in patients with spinal and cranial lesions near the motor pathways. Br J Neurosurg. 2009. 23: 48-55
33. Langeloo DD, Journee HL, de Kleuver M, Grotenhuis JA. Criteria for transcranial electrical motor evoked potential monitoring during spinal deformity surgery A review and discussion of the literature. Neurophysiol Clin. 2007. 37: 431-9
34. Leppanen RE, Abnm D. American Society of Neurophysiological M. Intraoperative monitoring of segmental spinal nerve root function with free-run and electrically-triggered electromyography and spinal cord function with reflexes and F-responses. A position statement by the American Society of Neurophysiological Monitoring. J Clin Monit Comput. 2005. 19: 437-61
35. Loder RT, Thomson GJ, LaMont RL. Spinal cord monitoring in patients with nonidiopathic spinal deformities using somatosensory evoked potentials. Spine (Phila Pa 1976). 1991. 16: 1359-64
36. MacEwen GD, Bunnell WP, Sriram K. Acute neurological complications in the treatment of scoliosis.A report of the Scoliosis Research Society. J Bone Joint Surg Am. 1975. 57: 404-8
37. Malhotra NR, Shaffrey CI. Intraoperative electrophysiological monitoring in spine surgery. Spine (Phila Pa 1976). 2010. 35: 2167-79
38. Manninen PH. Monitoring evoked potentials during spinal surgery in one institution. Can J Anaesth. 1998. 45: 460-5
39. Minahan RE, Riley LH, Lukaczyk T, Cohen DB, Kostuik JP. The effect of neuromuscular blockade on pedicle screw stimulation thresholds. Spine (Phila Pa 1976). 2000. 25: 2526-30
40. Montes E, De Blas G, Regidor I, Barrios C, Burgos J, Hevia E. Electromyographic thresholds after thoracic screw stimulation depend on the distance of the screw from the spinal cord and not on pedicle cortex integrity. Spine J. 2012. 12: 127-32
41. More RC, Nuwer MR, Dawson EG. Cortical evoked potential monitoring during spinal surgery: Sensitivity, specificity, reliability, and criteria for alarm. J Spinal Disord. 1988. 1: 75-80
42. Nash CL, Lorig RA, Schatzinger LA, Brown RH. Spinal cord monitoring during operative treatment of the spine. Clin Orthop Relat Res. 1977. 126: 100-5
43. Noonan KJ, Walker T, Feinberg JR, Nagel M, Didelot W, Lindseth R. Factors related to false- versus true-positive neuromonitoring changes in adolescent idiopathic scoliosis surgery. Spine (Phila Pa 1976). 2002. 27: 825-30
44. Nuwer MR, Dawson EG, Carlson LG, Kanim LE, Sherman JE. Somatosensory evoked potential spinal cord monitoring reduces neurologic deficits after scoliosis surgery: Results of a large multicenter survey. Electroencephalogr Clin Neurophysiol. 1995. 96: 6-11
45. Parker SL, Amin AG, Farber SH, McGirt MJ, Sciubba DM, Wolinsky JP. Ability of electromyographic monitoring to determine the presence of malpositioned pedicle screws in the lumbosacral spine: Analysis of 2450 consecutively placed screws. J Neurosurg Spine. 2011. 15: 130-5
46. Pelosi L, Lamb J, Grevitt M, Mehdian SM, Webb JK, Blumhardt LD. Combined monitoring of motor and somatosensory evoked potentials in orthopaedic spinal surgery. Clin Neurophysiol. 2002. 113: 1082-91
47. Quinones-Hinojosa A, Lyon R, Zada G, Lamborn KR, Gupta N, Parsa AT. Changes in transcranial motor evoked potentials during intramedullary spinal cord tumor resection correlate with postoperative motor function. Neurosurgery. 2005. 56: 982-93
48. Romstock J, Strauss C, Fahlbusch R. Continuous electromyography monitoring of motor cranial nerves during cerebellopontine angle surgery. J Neurosurg. 2000. 93: 586-93
49. Roy EP, Gutmann L, Riggs JE, Jones ET, Byrd JA, Ringel RA. Intraoperative somatosensory evoked potential monitoring in scoliosis. Clin Orthop Relat Res. 1988. 229: 94-8
50. Sala F, Palandri G, Basso E, Lanteri P, Deletis V, Faccioli F. Motor evoked potential monitoring improves outcome after surgery for intramedullary spinal cord tumors: A historical control study. Neurosurgery. 2006. 58: 1129-43
51. Schieppati M, Ducati A. Effects of stimulus intensity, cervical cord tractotomies and cerebellectomy on somatosensory evoked potentials from skin and muscle afferents of cat hind limb. Electroencephalogr Clin Neurophysiol. 1981. 51: 363-72
52. Schwartz DM, Auerbach JD, Dormans JP, Flynn J, Drummond DS, Bowe JA. Neurophysiological detection of impending spinal cord injury during scoliosis surgery. J Bone Joint Surg Am. 2007. 89: 2440-9
53. Schwartz DM, Sestokas AK, Dormans JP, Vaccaro AR, Hilibrand AS, Flynn JM. Transcranial electric motor evoked potential monitoring during spine surgery: Is it safe?. Spine (Phila Pa 1976). 2011. 36: 1046-9
54. Schwartz DM, Sestokas AK, Hilibrand AS, Vaccaro AR, Bose B, Li M. Neurophysiological identification of position-induced neurologic injury during anterior cervical spine surgery. J Clin Monit Comput. 2006. 20: 437-44
55. Sherrington C.editorsThe integrative action of the nervous system. New Haven, CT: Yale University Press; 1906. p.
56. Slimp JC. Electrophysiologic intraoperative monitoring for spine procedures. Phys Med Rehabil Clin N Am. 2004. 15: 85-105
57. Sloan T, Deletis V, Shils J.editors. Anesthesia and motor evoked potential monitoring. Neurophysiology in Neurosurgery. San Diego, California: Academic Press; 2002. p. 452-74
58. Smith PN, Balzer JR, Khan MH, Davis RA, Crammond D, Welch WC. Intraoperative somatosensory evoked potential monitoring during anterior cervical discectomy and fusion in nonmyelopathic patients--A review of 1039 cases. Spine J. 2007. 7: 83-7
59. Stecker MM, Baylor K, Wolfe J, Stevenson M. Acute nerve stretch and the compound motor action potential. J Brachial Plex Peripher Nerve Inj. 2011. 6: 4-
60. Stecker MM, Cheung AT, Patterson T, Savino JS, Weiss SJ, Richards RM. Detection of stroke during cardiac operations with somatosensory evoked responses. J Thorac Cardiovasc Surg. 1996. 112: 962-72
61. Stecker MM, Robertshaw J. Factors affecting reliability of interpretations of intra-operative evoked potentials. J Clin Monit Comput. 2006. 20: 47-55
62. Sutter MA, Eggspuehler A, Grob D, Porchet F, Jeszenszky D, Dvorak J. Multimodal intraoperative monitoring (MIOM) during 409 lumbosacral surgical procedures in 409 patients. Eur Spine J. 2007. 16: S221-8
63. Szelenyi A, Langer D, Beck J, Raabe A, Flamm ES, Seifert V. Transcranial and direct cortical stimulation for motor evoked potential monitoring in intracerebral aneurysm surgery. Neurophysiol Clin. 2007. 37: 391-8
64. Toleikis RJ, Deletis V, Shils J.editors. Neurophysiological monitoring during pedicle screw placement. Neurophysiology in Neurosurgery. San Diego, California: Academic Press; 2002. p. 231-64
65. Toleikis JR. American Society of Neurophysiological Monitoring. Intraoperative monitoring using somatosensory evoked potentials. A position statement by the American Society of Neurophysiological Monitoring. J Clin Monit Comput. 2005. 19: 241-58
66. Toleikis JR, Skelly JP, Carlvin AO, Burkus JK. Spinally elicited peripheral nerve responses are sensory rather than motor. Clin Neurophysiol. 2000. 111: 736-42
67. Toleikis JR, Skelly JP, Carlvin AO, Toleikis SC, Bernard TN, Burkus JK. The usefulness of electrical stimulation for assessing pedicle screw placements. J Spinal Disord. 2000. 13: 283-9
68. Ulkatan S, Neuwirth M, Bitan F, Minardi C, Kokoszka A, Deletis V. Monitoring of scoliosis surgery with epidurally recorded motor evoked potentials (D wave) revealed false results. Clin Neurophysiol. 2006. 117: 2093-101
69. Uribe JS, Kolla J, Omar H, Dakwar E, Abel N, Mangar D. Brachial plexus injury following spinal surgery. J Neurosurg Spine. 2010. 13: 552-8