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 Table of Contents  
Year : 2020  |  Volume : 1  |  Issue : 2  |  Page : 80-84

Role of intraoperative neuromonitoring in spine surgery: A retrospective study

Department of Orthopaedics, AIIMS, Rishikesh, Uttarakhand, India

Date of Submission21-May-2020
Date of Decision10-Jun-2020
Date of Acceptance08-Sep-2020
Date of Web Publication15-Dec-2020

Correspondence Address:
Dr. Pankaj Kandwal
Department of Orthopaedics, AIIMS, Rishikesh, Uttarakhand
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JME.JME_35_20

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Background: Iatrogenic neurological injury resulting during surgical intervention is a devastating complication not only for patient but also for the operating surgeon. Even with best efforts, the risk remains approximately 5%. Aims: This study aims to study the role of intraoperative neuromonitoring (IONM) in non-deformed spine surgeries and to find out the sensitivity and specificity. Settings and Design: Tertiary health-care centre. Retrospective study with data of the patients operated from January 2019 to January 2020 was reviewed and evaluated. Materials and Methods: Patients with spinal fractures, spondylodiscitis, bony tumours of spine and degenerative spinal disorders without neurological deficit were included. The patients with spinal deformity and with prior neurological deficits were excluded. Group A: the patients with no IONM signal drop during procedure, Group B: the patients who experienced significant drop in signal during surgery. Statistical Analysis Used: Data entry-MS Excel, Data analysis-SPSS 23.0 version for windows, descriptive statistics-mean ± numerical variable, null hypothesis-paired test-two sample for mean (<0.05 = significant). Results: Fifty-nine patients were included. Of 59, 50 patients had no significant drop, and 9 patients had permanent drop in signals. The mean blood loss in Group A was 735 ± 442.1 ml and was 978.9 ± 829 ml in Group B (P = 0.006). There was no signal drop in 39 patients. The sensitivity and specificity according to the above data in our series was 60% (confidence interval [CI] = 0.613–0.586) and 88% (CI = 0.891–0.886). Conclusions: IONM is fairly sensitive and very specific for detecting intraoperative neural compromise. There is significant correlation between the blood loss in the surgery and signal drop.

Keywords: Electromyography, intraoperative neuromonitoring, motor evoked potential

How to cite this article:
Ifthekar S, Ahuja K, Mittal S, Yadav G, Goyal N, Rana AS, Kandwal P. Role of intraoperative neuromonitoring in spine surgery: A retrospective study. J Med Evid 2020;1:80-4

How to cite this URL:
Ifthekar S, Ahuja K, Mittal S, Yadav G, Goyal N, Rana AS, Kandwal P. Role of intraoperative neuromonitoring in spine surgery: A retrospective study. J Med Evid [serial online] 2020 [cited 2023 Jun 3];1:80-4. Available from: http://www.journaljme.org/text.asp?2020/1/2/80/303571

  Introduction Top

Iatrogenic paraplegia after surgical intervention of the spine is a devastating complication not only for the patient but also gives sleepless nights to operating surgeon, and even after best efforts, the risk remains approximately 5%.[1] The advancement of the surgical techniques require the need for real-time monitoring of spinal cord and nerve roots during the surgical manoeuvres.[2],[3] This led to the development of more sophisticated methods which can give a real time feedback of the integrity of the spinal tracts and that led to the birth of concept of intraoperative neuromonitoring (IONM). IONM has varied options and each with a very specific application. Followings are some of the modalities: somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), electroencephalography, electromyography (EMGs), brainstem auditory evoked potentials and visual evoked potentials.[3]


This study aimed to study the role of IONM and its modalities and to report the sensitivity, specificity of IONM in detecting intraoperative neural injury in non-deformed spinal surgeries.

  Materials and Methods Top

This study was conducted in a tertiary health-care teaching hospital. A retrospective data of 59 patients operated for non-deformed spine in our institute from January 2019 to January 2020 were reviewed and the results were evaluated. Patients with fractures of spine, spondylodiscitis, bony tumours of spine, degenerative spinal disorders who were operated under neuromonitoring with intact neurology were included in the study. The patients operated primarily for deformity and the patients with prior neurological deficits were excluded from the study. All the patients were monitored with free running EMGs and MEP. SSEPs and transmitted EMGs were used as and when required. The muscles routinely used for monitoring were rectus abdominis (D10-L1), vastus lateralis (L3), tibialis anterior (TA) (L4), extensor hallucis longus (L5), abductor hallucis brevis (S1) in lower limb and trapezius (accessory nerve), deltoid (C5), biceps (C5C6), brachioradialis (C6), triceps (C7) and abductor pollicis brevis (C8T1) were used for upper limbs [Figure 1].
Figure 1: Application of motor evoked potential leads in lower limb myotomes

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Patients monitored under IONM were grouped into two groups. The patients with no IONM signal drop during the procedure were grouped into Group A and the patients with any IONM signal drop during the procedure (either transient or permanent) were grouped into Group B. A comparison was done between these two groups keeping the duration of surgery and blood loss as variables. Independent t-test was used to find the P value. A P < 0.05 was considered significant correlation. A consistent amplitude decrease of 80% or more was taken as significant,[4] the morphology of the waveform and latency of the MEPs were also considered. An alert on the monitor demands immediate check of equipment and leads, elevation of mean arterial pressure (MAP) to more than 80 mm Hg, warming the patient to 36°C, wound exploration to rule out graft or implant malposition, hematoma formation, or change in spinal alignment. The anaesthetic agents were also reviewed and depth of anaesthesia was assessed. The operative field and patient were examined for sources of external pressure on the carotid arteries or peripheral nerves. After all these measures, if the signals remained depleted, then a significant positive signal drop was noted and the post-operative power was correlated with the intraoperative drops. The specificity, sensitivity, positive predictive value and negative predictive value were calculated and noted.

  Results Top

A total of 59 cases of non-deformed spine were operated under neuromonitoring. The mean age of the patients was 41.9 ± 17.7 years (13 years–70 years). Of 59 patients, there were 35 males and 24 females. Aetiology wise: 27 were infective spondylodiscitis (pyogenic and tubercular), 17 degenerative spine, 9 cases of traumatic spinal injuries, 3 cases of tumours and 3 congenital spinal conditions which were monitored during surgery. Procedures performed: 15 patients underwent posterior decompression, posterior instrumented fusion and anterior column reconstruction, 17 patients were treated with posterior decompression and instrumented fusion alone, 2 patients underwent complex iliolumbar fixation, 9 patients underwent anterior cervical decompression and fusion, 6 patients were treated by posterior cervical decompression and fusion, 2 patients underwent tumour excision, 1 patient was treated with anterior lumbar decompression and fixation for spinal fracture and 7 underwent minimally invasive spinal instrumentation. In our operative group, 50 patients did not show any significant drop in the signal throughout the procedure. Amongst 9 patients who had significant drop in IONM signals, 2 underwent minimally invasive spine surgery (MIS TLIF), 6 underwent posterior decompression and instrumented fusion and 1 underwent posterior cervical decompression and instrumentation. Forty-eight patients who witnessed no significant drop in signals and did not have any post-operative neurological deficits were labelled as true negatives. Two patients had normal monitoring through the procedure but there was weakness noted in the post-operative period. These two patients were labelled as false negatives. Three patients had intra operative signal drop which was significant according to the criteria described above and all three had post-operative neurological deficits, these 3 cases were labelled as true positives. Six cases showed significant drop in signals intraoperatively but there was no post-operative weakness and these were labelled as false positives [Figure 2] and [Table 1]. In these cases, the drop was seen during the latter half of the surgeries when manipulation was done or during decompression. The signals most commonly dropped during a bolus of anaesthetic infusion and this could be diagnosed by dropped potentials even in the control leads. The sensitivity and specificity according to the above data in our series was 60% (confidence interval [CI] = 0.613–0.586) and 88% (0.891–0.886). A 95% CI was taken where 1-a was taken as 0.05. The positive predictive value in the operated group was 33% (CI = 0.343–0.323) and the negative predictive value was 96% (CI = 0.961–0.958). We did not perform a wake up test in any of our cases and the neurology was assessed only when the patient was out of anaesthesia. Total intravenous anaesthesia was used in all our cases.
Figure 2: Graphical representation of true positives and true negatives: intraoperative neuromonitoring (+ve) positive means patients who had significant drop of signals, intraoperative neuromonitoring (-ve) negative means patients who did not experience drop of signals

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Table 1: Details of true positive, negative; false-positive, negative; positive predictive and negative predictive value

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Further analysing the results, the patients were split into two groups, Group A (n = 50) who never experienced any drop in signals and Group B (n = 9) who experienced some signal drop during monitoring either significant and persistent or insignificant and recoverable. In Group A, the mean duration of surgery was 238.13 ± 117.04 min, whereas it was 270 ± 110.9 min in Group B (P = 0.07). The mean blood loss in Group A was 735 ± 442.1 ml where as it was 978.9 ± 829 ml in Group B (P < 0.05).

Case example [Figure 3]: 35-year-old female experienced drop in MEP signals in the right vastus lateralis, TA and abductor hallucis brevis while undergoing posterior decompression and instrumentation for tubercular spondylodiscitis.
Figure 3: A 35-year-old female underwent posterior decompression and instrumentation for tubercular spondylodiscitis. (a) Baseline motor evoked potential graph, (b) drop in motor evoked potential signals in the right vastus lateralis, tibialis anterior and abductor hallucis brevis

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  Discussion Top

Improvement in technology and better instruments has provided the spine surgeons with variety of options to treat large number of spinal disorders. However, these surgeries are fraught with complications and should neurological deficit occur, it is nightmare for both patient and surgeon. Technology has progressed to address this concern where a continuous and real time feedback is given to the surgeon regarding the neural pathways. The various modalities are as follows.

SSEPs record specifically the ascending dorsal tracts of the cord and provide no information on the integrity of the descending anterior tracts. This is a limitation of this technique.[5] There is a time lag to evaluate the change in waveform of SSEPs.[6] A decrease in SSEP amplitude of more than 50% and increase in SSEP latency of more than 10% of baseline are generally accepted as the 'alarm criteria' for neural compromise.[5]

MEPs can be generated by transcranial electrical stimulation (TES) and transcranial magnetic stimulation. TES is commonly employed for the generation of MEPs as it is more resistant to anaesthesia.[7] The motor pathways are fed by the anterior spinal artery and are more sensitive to spinal cord ischemia and are more clinically relevant.[7] A study by Pelosi et al. suggested that some changes in MEP waveform may be because of haemodynamic alterations or changes in cortical rather than spinal level.[8] The high extracranial current can cause forceful jaw closure due to contraction of temporalis, which in turn can cause mouth and lip injury.[9]

Nerve root injuries are some of the most common neurologic deficits seen after spine surgeries, consisting around 60% of all new neurological deficits.[10] Free-running EMG can find out mechanical or metabolic irritation of the nerve.[11],[12],[13],[14]

The mean age group of the patients who were neuromonitored in our operative group was 41.9 years and mean duration of surgery was 231.5 min. A study done by Quraishi et al. included 102 consecutive patients whose mean age group was 41.5 years which was very similar to our group.[15] Although the age does not have significant effect on the results of neuromonitoring, the majority of the population undergoing spinal surgeries for non-deformed spine are adults and elderly population. A combined monitoring of more than 200 h was done to know the short comings and future prospects for improvement. The patient conditions associated with a higher incidence of neurologic injury include combined anterior and posterior approach and high degree of kyphosis.[16] Although the risk for neurologic injury in non-deformed spine is low compared to the deformed spine, free running EMGs and MEPs give a good idea about impending neurological injury resulting from mal position of screw and manipulation occurring during fusion surgeries. The use of transcranial MEP is in doubt for monitoring individual spinal nerve roots because of radicular overlap, variation across different patients and limited sampling from single muscle recordings. Multichannel tc-MEP recordings that span adjacent myotomes may help in resolving these limitations.[17],[18] Liebermann et al. in his study stated that the neurologic deficit was not related to age, gender or type of corrective surgery. In our study, there was a significant correlation (P < 0.05) between drop in signals and the amount of blood loss. As the blood loss increased, there was a transient or persistent signal loss. Measures such as fluid administration, vasopressor support helps in recovery of the signals.[19] The neurological signal loss can be prevented by maintaining the MAP above 85 mm hg and this was indirectly suggested by the fall in IONM as the blood loss increased. In the absence of any recognisable event during surgery causing drop in signal and an increased blood loss, signal drop can be taken as the one due to blood loss and surgeon can wait for spontaneous recovery. The sensitivity in our study was 60% and specificity was 88%. The low sensitivity may be attributed to the small number of patients in our series and the value changes as the sample size increases. Eggspuehler et al. studied 217 patients and demonstrated a specificity of 98%.[2] Sutter et al. did a study in which he monitored 1017 patients with multimodality techniques i.e., for 4731 h. He reported a sensitivity of 89% and specificity of 99%.[20] Quraishi et al. studied 102 patients and described a sensitivity and specificity of 67% and 98%, respectively.[20] As the number of patients increases the sensitivity increases as seen in the above studies, but the multimodality monitoring techniques have a high specificity even in limited number of patients. So, with multimodality monitoring techniques, if the signals do not show any consistent fall, more often than not the patient will not have any post-operative neurological deficit. The negative predictive value in our patients was 96% which again is a good indicator of preserved neurology if there is no significant intra operative drop in signals.

The accuracy of diagnosing intraoperative neural injury lies in setting the lower limit below which the signal drop is taken as significant. Failure to set the standard lower limit can be a cause for a lot of signal drop alarms during the procedure. We had few cases in which there was a global signal drop where even the control leads showed drop in the amplitude and increased latency of signals. The electrodes may be misplaced during the procedure. Any signal drop should also be correlated with the proper positioning of electrodes and any decision regarding the signal drop should be taken only after all the available methods to improve the spinal cord perfusion have been exhausted.


small sample size.

  Conclusions Top

IONM is fairly sensitive and very specific for detecting intraoperative neural compromise in spine surgery. Evidence-based protocols need to be standardised to set the minimum criteria below which a positive signal drop should be accounted. There is a significant correlation between the amount of blood loss in the surgery and the signal drop noticed. There is a scope for further exploration and advancement in this field with considerably good sample size.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Murphy RF, Mooney JF 3rd. Complications following spine fusion for adolescent idiopathic scoliosis. Curr Rev Musculoskelet Med 2016;9:462-9.  Back to cited text no. 1
Eggspuehler A, Sutter MA, Grob D, Jeszenszky D, Dvorak J. Multimodal intraoperative monitoring during surgery of spinal deformities in 217 patients. Eur Spine J 2007;16 Suppl 2:S188-96.  Back to cited text no. 2
Kim SM, Kim SH, Seo DW, Lee KW. Intraoperative neurophysiologic monitoring: Basic principles and recent update. J Korean Med Sci 2013;28:1261-9.  Back to cited text no. 3
Langeloo DD, Lelivelt A, Louis Journée H, Slappendel R, de Kleuver M. Transcranial electrical motor-evoked potential monitoring during surgery for spinal deformity: A study of 145 patients. Spine 2003;28:1043-50.  Back to cited text no. 4
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. Electroencephal Clin Neurophysiol Evoked Potentials Sect 1995;96:6-11.  Back to cited text no. 5
Dinner DS, Lüders H, Lesser RP, Morris HH, Barnett G, Klem G. Intraoperative spinal somatosensory evoked potential monitoring. J Neurosurg 1986;65:807-14.  Back to cited text no. 6
Sloan TB, Heyer EJ. Anesthesia for intraoperative neurophysiologic monitoring of the spinal cord. J Clin Neurophysiol 2002;19:430-43.  Back to cited text no. 7
Pelosi L, Lamb J, Grevitt M, Mehdian SMH, Webb JK, Blumhardt LD. Combined monitoring of motor and somatosensory evoked potentials in orthopaedic spinal surgery Clinical Neurophysiology: Official Journal of the International Federation of Clinical Neurophysiology 2002;113:1082-91.  Back to cited text no. 8
MacDonald DB. Safety of intraoperative transcranial electrical stimulation motor evoked potential monitoring. J Clin Neurophysiol 2002;19:416-29.  Back to cited text no. 9
Dawson EG, Sherman JE, Kanim LE, Nuwer MR. Spinal cord monitoring. Results of the scoliosis research society and the European spinal deformity society survey. Spine (Phila Pa 1976) 1991;16:S361-4.  Back to cited text no. 10
Harper CM, Daube JR. Facial nerve electromyography and other cranial nerve monitoring. J Clin Neurophysiol 1998;15:206-16.  Back to cited text no. 11
Devlin VJ, Schwartz DM. Intraoperative neurophysiologic monitoring during spinal surgery. J Am Acad Orthop Surg 2007;15:549-60.  Back to cited text no. 12
Calancie B, Lebwohl N, Madsen P, Klose KJ. Intraoperative evoked EMG monitoring in an animal model. A new technique for evaluating pedicle screw placement. Spine (Phila Pa 1976) 1992;17:1229-35.  Back to cited text no. 13
Raynor BL, Lenke LG, Kim Y, Hanson DS, Wilson-Holden TJ, Bridwell KH, et al. Can triggered electromyograph thresholds predict safe thoracic pedicle screw placement? Spine (Phila Pa 1976) 2002;27:2030-5.  Back to cited text no. 14
Quraishi NA, Lewis SJ, Kelleher MO, Sarjeant R, Rampersaud YR, Fehlings MG. Intraoperative multimodality monitoring in adult spinal deformity: Analysis of a prospective series of one hundred two cases with independent evaluation. Spine (Phila Pa 1976) 2009;34:1504-12.  Back to cited text no. 15
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.  Back to cited text no. 16
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Coe JD, Arlet V, Donaldson W, Berven S, Hanson DS, Mudiyam R, et al. Complications in spinal fusion for adolescent idiopathic scoliosis in the new millennium. A report of the Scoliosis Research Society Morbidity and Mortality Committee. Spine (Phila Pa 1976) 2006;31:345-9.  Back to cited text no. 18
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Sutter M, Eggspuehler A, Grob D, Jeszenszky D, Benini A, Porchet F, et al. The diagnostic value of multimodal intraoperative monitoring (MIOM) during spine surgery: A prospective study of 1,017 patients. Eur Spine J 2007;16 Suppl 2:S162-70.  Back to cited text no. 20


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1]


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