March 19, 2016
14 min read

Intraoperative spinal neuromonitoring proves to be a new, yet controversial field

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Intraoperative neuromonitoring is used during spine surgery to monitor and limit possible injury to a patient’s nervous system. Sometimes, however, it is deemed unnecessary and may add expense to already expensive procedures.

Intraoperative neuromonitoring can provide valuable information for a surgeon who performs complex spine surgery procedures and may prevent injury to a patient. However, according to some spine surgeons, this monitoring tool is not necessary or overly helpful in every spine surgery they perform.

For simple procedures, such as anterior cervical discectomy and fusion (ACDF), intraoperative neuromonitoring may just add to the overall cost without providing much of a benefit, Frank La Marca, MD, associate professor of neurosurgery, orthopedics and biomedical engineering at the University of Michigan, in Ann Arbor, Mich., told Spine Surgery Today.

Frank La Marca, MD, said spine surgeons must be aware that a patient’s neuromonitoring data can be affected by the anesthesia used during surgery.

Smaller, less complicated procedures, such as microdiscectomies or laminectomies, typically do not require or need intraoperative neuromonitoring, he said. Sometimes, however, spine surgeons may feel pressured to use neuromonitoring due to the malpractice mindset in today’s health care environment, La Marca noted.

Pressure to monitor

Should a patient suffer a debilitating injury to his or her neurological system and intraoperative monitoring was not used during the surgery — even if the procedure was one in which the literature says monitoring will not be beneficial — many lawyers will often stick to this point if a malpractice suit is ever brought against the operating surgeon, according to La Marca.

“Many surgeons think: ‘If I don’t use this, they’ll blame me for it.’ It can drive overutilization of the technique and certainly increase overall costs. Neuromonitoring is one of these. I often will review defense cases for doctors who have been accused of not using monitoring in cases where monitoring would not have had any particular influence on any outcome. Lawyers hook on to that, and expert witnesses testify to the contrary, even if there is no evidence-based medicine to support it,” La Marca said.

Lawrence G. Lenke

There also are surgeons who believe intraoperative neuromonitoring does not provide the type of information that can be used to prevent injury, therefore its use remains controversial among spine surgeons, said La Marca, who uses intraoperative neuromonitoring for oncology, deformity and other complex or prolonged cases.

“It is controversial. In the case of intramedullary tumors, some feel by the time you have a change in neuromonitoring, the damage is done. But there are also data to show, and we feel likewise, that it can give you the idea that when you are closer to neural tissue than the tumor itself, it will let you know when to possibly back down,” he said.

Necessity for deformity correction

For complex surgeries, such as spinal deformity correction, neuromonitoring is invaluable, according to Lawrence G. Lenke, MD, of Columbia University Medical Center, in New York City.

“Basically, we use neuromonitoring 100% of the time for any type of spinal deformity surgery. Obviously, some cases are much higher risk than others for having neurologic complications. Any time we are correcting a deformity there is some potential risk to the neurologic system, so that is why it is imperative we use it. In addition, we also use it because patients have issues just with being positioned in surgery and the time they are undergoing the surgery can create peripheral nerve issues, brachial plexopathies, and the monitoring can pick those up,” Lenke told Spine Surgery Today.

There are no reasons to not use monitoring during a spinal deformity procedure, Lenke said. By monitoring the nervous system, surgeons are protecting the spinal cord and nerves during the corrective surgery and protecting the whole body from any type of nerve palsy or problem during a prolonged procedure, he said.

Andres A. Gonzalez

“Neuromonitoring is useful for any type of true spinal surgery where you are going in to treat a diagnosis you have confirmed. Anything from a straightforward lumbar discectomy, all the way to a 10-hour spinal reconstruction, to me there is no reason to not use the monitoring. It provides you with helpful information. It does not hinder our operative field at all, does not increase infection rates and I cannot see a reason why you would not want to use it and make spine surgery as safe as possible. There is plenty of literature to support that statement,” Lenke said.

Common monitoring methods

The three most commonly used neuromonitoring modalities during spinal surgery are transcranial motor evoked potentials (MEPs), somatosensory evoked potentials (SSEPs) and stimulated and spontaneous electromyography, according to studies by Stecker in Surgical Neurology International in 2012 and by Andres A. Gonzalez, MD, MMM, FACNS, of the University of Southern California Department of Neurology, and colleagues in Neurosurgical Focus in 2009.

Transcranial MEPs have become popular and most effective in the last 5 years to 10 years, based on the literature.

Lenke said transcranial MEPs monitoring not only provides important and accurate information on the state of the motor tracts of the spinal cord, but also can provide detailed information on the individual motor groups of the lower extremities and upper extremities, which are innervated by specific nerves, Lenke said.

Transcranial MEPs are among the most valuable of the neuromonitoring techniques employed during surgery and done following spinal cord injury or spine trauma, Sanjay S. Dhall, MD, of the University of California, San Francisco, said.

“What we have found in recent years is often the more valuable of the two types of evoked potentials are the motor evoked potentials, mainly because for both the patient and surgeon that is often what we are most concerned with, and what is most catastrophic to lose — a patient’s motor function. Motor evoked potentials have become powerful and important for a variety of types of spine surgery,” Dhall told Spine Surgery Today.

Motor evoked potentials in trauma

Transcranial MEPs also are invaluable for patients with a spinal cord injury or spine trauma, according to Dhall.

George I. Jallo

The example he gave is of a patient who comes into the emergency room with a broken neck or broken back. The patient is not moving. Surgeons can take the patient into the OR and get a set of baseline MEPs once the patient is under anesthesia, Dhall said. These baseline numbers then serve as a guideline for the procedure and will provide real-time feedback to the surgeon regarding any damage being done to the patient, he added.

“What we find sometimes is some of these people may not be moving upon our examination, but they show some motor evoked function in the arms and legs, or the extremity they are not moving. What we find is those people tend to go on to recover from their spinal cord injury. On the other hand, those who do not have any motor evoked potentials tend not to recover. So it seems to be a good way to test for some residual function that we may not be able to see clinically,” Dhall said.

He said MEPs should be used for both elective and emergency surgeries, particulary when a procedure is going to be near the spinal cord, or in the thoracic or cervical spine.

Surgery carries risk

Intraoperative monitoring should be used with any cervical, thoracic or lumbar spine procedure, or if there is a risk to any of those related nerves or nerve roots or the spinal cord itself, Gonzalez told Spine Surgery Today.


Gonzalez will even use intraoperative neuromonitoring for an ACDF.

“Every surgery carries some degree of risk. In the spectrum of operations from small nerve to large brain tumor surgeries, all surgeries carry different percentages of risk of injury. In the case of spine surgery particularly, what intraoperative monitoring is interested in is reducing the risk to the nervous system, namely the risk to the spinal cord and nerve roots. The goal of neuromonitoring is to reduce this as much as we can. We would like the risk to be zero,” Gonzalez said.

Great value from monitoring

A study Gonzalez and colleagues conducted reviewed the different types of intraoperative neuromonitoring used for various spine procedures. In regard to cervical and thoracic procedures, Gonzalez and colleagues noted the use of SSEPs and MEPs offer great value in providing a global assessment of spinal cord function.

“In a recent study looking at the value of multimodality monitoring in cervical spine surgery, somatosensory evoked potentials were reported to have a sensitivity of 52% and a specificity of 100% in detecting postoperative neurological deficits, whereas motor evoked potentials were reported to offer a sensitivity of 100% and a specificity of 96%. Taken together, these results imply that somatosensory evoked potential/motor evoked potential monitoring offers the most comprehensive way to selectively screen for and identify impending spinal cord injury while minimizing false-positive interpretations,” Gonzalez and colleagues wrote.

Complex procedures

For spine tumor removal or spinal cord tumor removal, intraoperative monitoring is an absolute necessity, George I. Jallo, MD, of All Children’s-Johns Hopkins Medicine, in St. Petersburg, Fla., told Spine Surgery Today.

“I use monitoring any time I am working around the spinal cord, so for me it is tumors inside the cord, or outside the spinal cord, but inside the dura. Then in children with congenital conditions, such as a tethered cord, where there is fat attached to the spinal cord or nerves, and other cases where we need to monitor the motor or sensory pathways, I will use monitoring. I will also use it for brain tumors involving the motor cortex, brainstem tumors and if I am going to be close to the motor pathways, such as the basal ganglia location. The reason I use it, to me it is like a Global Positioning System [GPS]. If you have it, why not use it? It will help guide you during the operation about the integrity of these pathways,” he said.

Intraoperative neuromonitoring is only as effective as the team using it, Jallo noted. The real-time data need to be correctly interpreted by the neurophysiologist or whoever is in charge of reading the data for the procedure.

Neuromonitoring: A team effort

Most surgeons who frequently use neuromonitoring will gain the necessary experience to understand the language amongst the team members, Jallo said. The technology is very dependent upon the preoperative neurological function and the anesthesia, he noted.

“The tool is only as good as the person, physician or whoever is going to interpret the recordings. There are some people who use neuromonitoring for legal purposes, but not for the information it provides. Essentially, neurophysiological monitoring is present, but no interpretation or management decision done is based on the data. You are going through the motions and not using it to its full potential,” Jallo said.

The surgeon, anesthesiologist, neurophysiologist and surgical team must be on the same page in terms of the goal of the procedure and the intraoperative neuromonitoring alarms that may lead to a permanent deficit rather than a temporary or recoverable deficit, he said.

Evoked potentials frequently used

Many surgeons will only use somatosensory evoked potential neuromonitoring and neglect MEPs neuromonitoring. Furthermore, spine surgeons believe that if the sensory pathways are unharmed, then the motor pathway will be unharmed, as well, Jallo said. This theory, he noted, is incorrect.


“For some people, they believe sensory pathway is enough. If there is no damage to the sensory pathway, they are assuming the motor pathway will be intact. I do not believe that,” Jallo said. “You can have no changes in the sensory pathway, and a patient wakes up paralyzed, and vice versa. As the motor and sensory pathways are distinct within the spinal cord, I rely on both modalities for my spinal cord tumor surgeries.”

Anesthesia and its effect

But, La Marca said, anyone who uses an intraoperative neuromonitoring modality for any type of spine surgery knows certain types of anesthesia affect the data received.

Sanjay S. Dhall

Anesthesiologists and surgeons must be focused on what they are monitoring for in a procedure to ensure the type of anesthetics used do not muddle the incoming data, he said.

“You have to be in tune with the anesthesiologist when using neuromonitoring because there are types of anesthetics, particularly paralytics, which you cannot use when using motor evoked potentials. Not using paralytics will make a patient a bit ‘lighter’ and can also increase the muscle tone during the surgery. It is a tradeoff. If anesthesiologists are not careful, they can give you some false readings or mask abnormalities and then you are trying to troubleshoot when you are not getting the readings that you expect to get. It is important to be one with the anesthesiologist when using these techniques,” La Marca said.

Inhalants tend to interfere

Gonzalez agreed with La Marca and said the correct anesthesia is crucial when it comes to intraoperative neuromonitoring. Anesthesiologists must be in concert with the surgeon, as well as the goals of the neuromonitoring process during any procedure.

“Anesthetics that commonly affect your monitoring include halogenated agents, such as isoflurane, that affect the transmission of signals from the nervous system and attenuate the responses. There are other agents, such as muscle relaxants, that do not affect the neurons themselves, but affect the actual muscle. If we are trying to get muscle responses, it will make the muscle responses go flat,” Gonzalez said.

Importantly, intravenous anesthetics tend to not interfere with intraoperative neuromonitoring as much as inhalants, he noted. To ensure none of these agents are used, surgeons must be in constant communication with the anesthesiologists. If these are used, the agents must be used during times when monitoring is not relevant or used at doses that will not significantly impact the ability to monitor those patients, according to Gonzalez.

Monitoring: An emerging area

Intraoperative neuromonitoring is a valuable tool for a variety of spinal procedures, but its use in simple procedures, like laminectomy, has yet to be established, Gonzalez noted.

“The field is relatively new compared to other fields in medicine. Similarly, there are fewer than a dozen fellowship programs in the nation that provide specific training in the field of intraoperative monitoring. So it is a relatively new field in many ways. I think it is important to know that until the 1970s, we had no monitoring. We had nothing,” Gonzalez said.

The future of intraoperative neuromonitoring may actually be outside of the OR, Dhall said, and in the intensive care unit. Real-time data to determine if damage to the spinal cord is occurring would be helpful to his work, he said.

“There is a potential that we can take this out of the OR and allow us to alter our management based on that. For example, if we can take motor evoked monitoring to the intensive care unit and use it for someone with an acute spinal cord injury, we can actually use that to guide our management. There may be potential in the future to use that to determine if the patient is getting enough blood and oxygen to the spinal cord based on whether that evoked potential changes,” Dhall said.


Standard of care

Intraoperative neuromonitoring is the standard of care for deformity correction surgeries, but not a standard of care for degenerative spine surgery procedures, Lenke said.

He noted the use intraoperative neuromonitoring should be expanded worldwide for spine surgery procedures, particularly due to its ability to monitor a patient’s individual nerve roots, which would prove helpful when more advanced surgeries are performed in developing countries.

“I often hear there is no money in the budget to have the monitoring personnel or the monitoring system brought in to help and it infuriates me because if you are able to do these complex spinal surgeries, you have the whole operating setup, the instrumentation, the personnel. There is no reason you should not be able to have your own monitoring technician and machines, as well, in there to make surgery as safe as possible,” Lenke said. – by Robert Linnehan

Disclosures: Dhall reports he receives speaking honoraria from DePuy Synthes Spine and Medtronic. Lenke reports he is a consultant for Medtronic and a royalty bearer. Gonzalez, Jallo and La Marca report no relevant financial disclosures.


Should intraoperative neuromonitoring be used for all anterior cervical discectomy and fusion cases, regardless of how straightforward the case appears to be?


Overutilization of care

Intraoperative neurophysiological monitoring (i.e., recording motor evoked potentials [MEPs] and somatosensory evoked potentials [SSEPs]) is a tool that can be used to potentially avoid permanent neurological deficits during spinal procedures. Its use is especially widespread among neurological surgeons and has, in many aspects, come to be thought of as “standard of care” during almost any surgical procedure involving the spine. Certainly during complex spinal reconstruction or tumor resection procedures, intraoperative neuromonitoring can be invaluable in preventing or predicting neurological deficits. However, its utility during “standard” (one- or two-level) spinal decompression or fusion surgeries is questionable, not only in terms of clinical benefit to patients, but also with regard to financial expenditures associated with its use. This is particularly true with regard to cervical spine procedures, and in particular standard anterior cervical discectomy and fusion (ACDF) for degenerative cervical spondylosis in the non-myelopathic patient.

Frank L. Acosta

Indeed, the ACDF procedure is one of the oldest and most successful surgical interventions available to the spinal surgeon and has been utilized safely even before the advent of intraoperative neuromonitoring.  Nevertheless, many, if not the majority of spine surgeons, currently believe neurophysiological monitoring is an essential tool that must be utilized even for standard ACDF procedures. The reasons for this belief are likely multifactorial, but medicolegal considerations often play a large part in the decision to use neuromonitoring tools during even routine ACDF procedures.  That routine ACDFs can be done safely and effectively without intraoperative MEPs and SSEPs monitoring has been demonstrated not only by the fact that ACDFs have been performed long before neuromonitoring was available, but also by recent scientific manuscripts. A recent study by Cole and colleagues found intraoperative neuromonitoring did not correlate with reduced neurological complications after single-level ACDFs, but did significantly increase financial expenditures associated with the index procedure and hospital stay.

Ultimately, the decision to use intraoperative neurophysiological monitoring during routine ACDFs rests with the surgeon. However, particularly in our current era of health care and its emphasis on appropriate resource utilization, we must weigh the evidence of its true utility during such procedures against the financial burden it places on our health care system so as to avoid its over-use and the misconception that it is standard of care.

Frank L. Acosta, MD, is an associate professor of neurosurgery at Keck Medicine University of Southern California, in Los Angeles.

Disclosure: Acosta reports no relevant financial disclosures.

Cole T, et al. Spine. 2014;doi:10.1097/BRS.0000000000000593.


Necessary for all cases

Intraoperative neuromonitoring should be used for all anterior cervical cases because it provides many benefits to increase patient safety.
Transcutaneous MEPs (TCMEPs) of the anterior cord before and after positioning should be compared to minimize the risk of spinal cord injury in stenotic patients from hyperextension of the cervical spine. Spontaneous electromyography (sEMG) of the brachial plexus can detect potential plexus injury from excessive traction on the shoulders.
During the approach and retractor positioning, neuromonitoring of the endotracheal tube can identify a decrease in sEMG of the recurrent laryngeal nerve to minimize hoarseness and vocal complications. Excessive retraction or injury to the carotid sheath can be detected by decreased cortical upper extremity SSEPs, thereby decreasing the chance of stroke or other vascular complications.

During decompression, monitoring upper extremity sEMG can detect inadvertent nerve root injury. During graft insertion and instrumentation, TCEMEPs should be compared to baseline to protect against over distraction or hardware malplacement. An improvement in sEMG or SSEP levels from baseline can indicate successful decompression and appropriate foraminal height restoration.

Neil Badlani

Some argue that neuromonitoring should only be used for riskier cases. However, neuromonitoring increases safety in every case, so selecting certain cases over others implies that the safety of some patients is valued more. The increased cost is likely offset by improved patient outcomes through a reduction in complications and potential revision surgeries which leads to an increase in value. Furthermore, the repetition of using neuromonitoring for every case improves the efficiency and accuracy of the technique for the technician and surgical team.

There are potential medicolegal concerns if neuromonitoring is not used and a patient has a complication. While this should not be a driving force behind our decisions, it is our reality.

Fehlings and colleagues performed a systematic review of the literature in their study and concluded that multimodal monitoring is sensitive and specific for the detection of intraoperative injury. The main objective of intraoperative neurophysiological monitoring is to identify induced neurophysiological alterations so they can be detected as they occur and corrected during surgery, thus avoiding post-surgical complications.

Neil Badlani, MD, MBA, is an orthopedic spine surgeon at the Orthopedic Sports Clinic, in Houston.

Disclosure: Badlani reports no relevant financial disclosures.

Fehlings MG, et al. Spine. 2010;doi:10.1097/BRS.0b013e3181d8338e.

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