Abstract

Background: We evaluated whether intraoperative neural monitoring (IONM), including somatosensory evoked potential monitoring (SEP), motor evoked potential monitoring (MEP), and electrophysiological monitoring (EMG), could reduce operative errors attributed to lumbar instrumented fusions, including minimally invasive (MI) transforaminal lumbar interbody fusion (TLIF)/open TLIF.

Methods: Operative errors included retraction/stretch or cauda equina neural/cauda equina injuries that typically occurred during misplacement of interbody devices (IBD) and/or malpositioning of pedicle screws (PS).

Results: IONM decreased the incidence of intraoperative errors occurring during instrumented lumbar fusions (MI-TLIF/TLIF). In one series, significant loss of intraoperative SEP in 5 (4.3%) of 115 patients occurred after placing IBD; immediate removal of all IBD left just 2 patients with new neural deficits. In other series, firing of trigger EMG’s (t-EMG) detected intraoperative PS malpositioning, prompted the immediate redirection of these screws, and reduced the need for reoperations. One t-EMG study required a reoperation in just 1 of 296 patients, while 6 reoperations were warranted out of 222 unmonitored patients. In another series, t-EMG reduced the pedicle screw breech rate to 7.78% (1723 PS) from a higher 11.25% for 1680 PS placed without t-EMG. A further study confirmed that MEP’s picked up new motor deficits in 5 of 275 TLIF.

Conclusion: SEP/MEP/EMG intraoperative monitoring appears to reduce the risk of surgical errors when placing interbody devices and PS during the performance of lumbar instrumented fusions (MI-TLIF/TLIF).However, IONM is only effective if spine surgeons use it, and immediately address significant intraoperative changes.

Keywords: Transforaminal Lumbar Interbody Fusions, Surgical errors, Malpositioning Pedicle Screws, Interbody Devices, Retraction Neural Injuries, Intraoperative Monitoring, Somatosensory Evoked Potentials (SEP), Electromyography (EMG), Motor Evoked Potentials (MEP), Minimally Invasive (MI) TLIF

INTRODUCTION

Can intraoperative neurophysiological monitoring (IONM) limit surgical errors (i.e. particularly attributed to placing interbody devices (IBD), or pedicle screws (PS)) during instrumented pedicle/screw fusions, including open/minimally invasive (MI) transforaminal lumbar interbody fusions (MI-TLIF/TLIF)?[ 1 - 11 ] In this review, intraoperative somatosensory evoked potential monitoring (SEP) largely monitored dorsal column dysfunction during cervical/thoracic surgery. However, even during lumbar surgery, motor evoked potential monitoring (MEP) best identified impending motor dysfunction, while electrophysiological monitoring (including triggered EMG (t-EMG)) most readily identified pedicle breaches. Real-time alerts provided by combinations of these 3 modalities helped surgeons limit/avert impending surgical errors/neurological damage (i.e., occurring due to excessive retraction, stretch, or compression requiring revision/removal of IBD and/or redirecting malpositioned PS) [ Table 1 ]. Nevertheless, IONM is only effective if spine surgeons use it and expeditiously change/alter/modify their operative technique in response to IONM alerts.

Table 1:

Added Safety and Efficacy for Intraoperative Neural Monitoring (IONM) of Transforaminal Lumbar Interbody Fusion (TLIF).

Multimodal IONM Limits Postoperative Deficits and Reoperation Rates

Multiple rather than single IONM modalities utilized during instrumented lumbar pedicle screw fusions (PS) utilized during MI-TLIF/TLIF, better identify impending intraoperative neural injury/surgical errors; however they must prompt surgeons to perform immediate intraoperative resuscitative maneuvers to limit/avoid new postoperative neurological deficits [ Table 1 ].[ 1 - 11 ] Gonzalez et al. (2009) stated multimodality IONM can; “...maximize the diagnostic efficacy in regard to sensitivity and specificity in the detection of impending neural injury; their hypothesis was that it would prove even more useful with more MI procedures being performed in the future.[ 5 ] Nixon et al. (2014) observed that 4 (1.2%) of 340 TLIF cases (primary surgeon Dr. Fessler) developed postoperative paraparesis, and stated; “Nonetheless, acknowledgment and open discussion of this serious complication is important for surgeon education”. However, these “complications” were most probably surgical errors.[ 9 ] Hofler and Fessler (2021) subsequently advocated using multimodal IONM to; “...aid with the avoidance of neurologic complications during lumbar instrumented fusions”.[ 6 ] However, they noted that IONM must be; “... followed by accurate recognition of the cause for these changes and appropriate responses by the surgeon, anesthesiologists, and monitoring personnel to correct the change”.

Passive and Active t-EMG Limits Errors of Lumbar PS Fusions (MI-TLIF/Open TLIF)

Passive and active EMG (i.e., trigger EMG (t-EMG)) alerts increased the accuracy for detecting intraoperative PS misplacement, often prompting immediate screw redirection, and reducing the incidence of postoperative reoperations required to address malpositioned screws [ Table 1 ].[ 1 , 7 , 11 ] Bindal et al. (2007) performed 25 MI TLIF placing 105 PS.[ 1 ] “Passive EMGs” yielded no alerts during spinal decompressions, but did identify five alerts of; “...intermittent nerve root firing...” following placement of IBD; interestingly, none of these patients exhibited new postoperative neural deficits. They observed; “Using... the active stimulation protocol (t-EMG) 76.2% of screw placements required one or more changes to the trajectory of the pedicle access needle”. [ 1 ] With t-EMG, 25 postoperative X-rays and 20 CT scans (i.e., including.... visualization of 85 PS) showed only 3 lateral breaches which were clinically irrelevant. Kaliya-Perumal et al. (2017) documented that t-EMG used for 296 Group I patients to place 1856 PS yielded 145 (8.7%) screw alerts; PS were immediately repositioned, and just 1 patient required a second operation for a malpositioned screw.[ 7 ] Alternatively, 6 of their 222 Group II patients whose 1256 PS were placed without t-EMG required additional surgery. Yongjun et al. (2023) also found fewer (7.78%) misplaced PS using t-EMG monitoring in 374 patients to place 1723 PS vs. a higher 11.25% of misplaced PS occurring in 339 patients undergoing 1680 PS placement without the benefit of t-EMG.[ 11 ]

Significant SEP Decreases/Alerts During IBD Placement in 5 of 115 TLIF Patients Prompted Immediate IBD Removal and Averted Deficits in 3 Patients

When Duncan et al. (2012) performed 115 TLIF, 5 patients developed significant decreases (alerts) in SEP amplitude without EMG changes following the placement of IBD [ Table 1 ].[ 4 ] All 5 devices were immediately removed, and SEP changes reverted to normal (i.e., returned to baseline) prior to closing. Removing IBD due to these SEP alerts, therefore likely avoided neurological injuries in 3 patients, limiting postoperative neural deficits to just 2 patients.

IONM Reduces Errors Occurring in MI-TLIF/Open TLIF Surgery

MI-TLIF/Open TLIF studies documented the reduction of intraoperative errors utilizing IONM [ Table 1 ].[ 2 , 6 , 8 - 10 ] Nixon et al. (2014) found that 4 (1.2%) of 340 patients undergoing unilateral MI-TLIF (2002-2012) sustained new bilateral postoperative weakness/neurological deficits.[ 9 ] The authors concluded; “... the specific etiology or pathophysiology behind these complications remains relatively unknown (e.g., direct neural injury, traction injury, hypoperfusion, positioning complications, and others...).” Nevertheless, they likely mislabeled the 4 new postoperative instances of paralysis as “complications”, whereas they were probably due to surgeon error. With IONM, Schar et al. (2017) identified 5 (29%) new L5 radicular motor deficits in 17 patients (2005–2013) undergoing instrumented high-grade fusions for L5S1 isthmic spondylolisthesis; 4 of 5 patients fully recovered within 3 postoperative mos. (e.g., 1 was lost to follow-up).[ 10 ] They concluded that without IONM, more of these deficits would likely have been permanent/irreversible.[ 10 ] Kim et al. (2019) looked at the impact of using SEP/EMG to perform 275 TLIF vs. utilizing SEP/EMG with MEP for 66 TLIF.[ 8 ] They found MEPs were 80% sensitive/100% specific for the five new postoperative motor deficits. SEP failed to detect the 2 postoperative sensory deficits, and EMG had high false positive rates for either motor or sensory neural injuries; they, therefore, recommended adding MEP to SEP/EMG when performing TLIF to best detect impending motor injuries.[ 8 ] In 113 patients undergoing percutaneous endoscopic TLIF (PE-TLIF), Chen et al. (2021) found 12 (10.6% alerts) utilizing multimodal vs. single IONM; when alerts were immediately addressed intraoperatively, they resulted in just 7 transient minor postoperative neurological deficits.[ 2 ] It is worth repeating Hofler and Fessler’s conclusions in 2021 regarding the need to respond to significant IONM changes for PS placement.[ 6 ] They commendted that these changes should be; “...followed by accurate recognition of the cause for these changes and appropriate responses by the surgeon, anesthesiologists, and monitoring personnel to correct the change”.[ 6 ]

CONCLUSION

Significant intraoperative IONM alerts prompted immediate intraoperative resuscitative maneuvers (i.e. reduction of retraction, stretching, IBD removal and/or PS redictection/ repositioning) to limit operative errors attributed to instrumented lumbar PS fusions (MI-TLIF/Open TLIF) [ Table 1 ]. Appropriate responses to significant IONM alerts limited/avoided many postoperative neurological deficits, and reduced reoperation rates for compressive IBD and malpositioned screws [ Table 1 ].[ 1 - 11 ]

Declaration of patient consent

Patients’ consent not required as patients’ identities were not disclosed or compromised.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-Assisted technology for manuscript preparation

The author(s) confirms that there was no use of Artificial Intelligence (AI)-Assisted Technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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