Abstract
Background: Intraoperative neuromonitoring (IONM) is frequently used during spine surgery to mitigate the risk of neurological injuries. Yet, its role in anterior cervical spine surgery remains controversial. Without consensus on which anterior cervical spine surgeries would benefit the most from IONM, there is a lack of standardized guidelines for its use in such procedures. Purpose: We sought to assess the alerts generated by each IONM modality for 4 commonly performed anterior cervical spinal surgeries: anterior cervical diskectomy and fusion (ACDF), anterior cervical corpectomy and fusion (ACCF), cervical disk replacement (CDR), or anterior diskectomy. In doing so, we sought to determine which IONM modalities (electromyography [EMG], motor evoked potentials [MEP], and somatosensory evoked potentials [SSEP]) are associated with alert status when accounting for procedure characteristics (number of levels, operative level). Methods: We conducted a retrospective review of IONM data collected by Accurate Neuromonitoring, LLC, a company that supports spine surgeries conducted by 400 surgeons in 8 states, in an internally managed database from December 2009 to September 2018. The database was queried for patients who underwent ACCF, ACDF, anterior CDR, or anterior diskectomy in which at least 1 IONM modality was used. The IONM modalities and incidence of alerts were collected for each procedure. The search identified 8854 patients (average age, 50.6 years) who underwent ACCF (n = 209), ACDF (n = 8006), CDR (n = 423), and anterior diskectomy (n = 216) with at least 1 IONM modality. Results: Electromyography was used in 81.3% (n = 7203) of cases, MEP in 64.8% (n = 5735) of cases, and SSEP in 99.9% (n = 8844) of cases. Alerts were seen in 9.3% (n = 671), 0.5% (n = 30), and 2.7% (n = 241) of cases using EMG, MEP and SSEP, respectively. In ACDF, a significant difference was seen in EMG alerts based on the number of spinal levels involved, with 1-level ACDF (6.9%, n = 202) having a lower rate of alerts than 2-level (10.0%, n = 272), 3-level (15.2%, n = 104), and 4-level (23.4%, n = 15). Likewise, 2-level ACDF had a lower rate of alerts than 3-level and 4-level ACDF. A significant difference by operative level was noted in EMG use for single-level ACDF, with C2-C3 having a lower rate of use than other levels. Conclusions: This retrospective review of anterior cervical spinal surgeries performed with at least 1 IONM modality found that SSEP had the highest rate of use across procedure types, whereas MEP had the highest rate of nonuse. Future studies should focus on determining the most useful IONM modalities by procedure type and further explore the benefit of multimodal IONM in spine surgery.
Keywords: neuromonitoring, EMG, MEP, SSEP, anterior cervical
Introduction
In the 1970s, a rapid expansion of surgical interventions for spinal deformities coincided with a rise in spinal cord injuries associated with aggressive corrections. Developments in intraoperative neuromonitoring (IONM) such as the Stagnara wake-up test, a technique for monitoring cord injury through testing motor function, evolved into modern-day electromyography (EMG), motor evoked potentials (MEP), and somatosensory evoked potentials (SSEP) [2,29,35,38]. These IONM modalities are increasingly used during spine surgery to mitigate the risk of neurological injuries; a recent study found that the use of IONM for spine surgery increased by 296% from 2008 to 2014 [27].
One serious complication of anterior cervical spine surgery is iatrogenic injury to critical neurovascular structures, including the spinal cord, nerve roots, and blood vessels [7,19,24]. To reduce the risk of postoperative neurologic complications and to ensure the functional integrity of neurovascular structures, surgeons frequently use IONM modalities when performing anterior cervical spine surgery [19,32]. However, there is debate on its efficacy, especially during anterior cervical procedures [1,4,15,33]. Studies have shown SSEP and MEP monitoring during anterior cervical diskectomy and fusion (ACDF) surgeries have no effect on the rate of postoperative deficits and add unnecessary cost [1,4,33].
Meanwhile, proponents of IONM in anterior cervical procedures argue that multimodal monitoring and corresponding alerts are necessary for ACDF cases with underlying myelopathy or cord compression. Furthermore, proponents argue that IONM may alter the surgical course, thereby reducing intraoperative injury [5,6,9,22,26,28]. Thus, there is no consensus on which anterior cervical spine surgeries benefit the most from IONM; likewise, there are no guidelines for standardized use and performance of these procedures [26].
In this study, we intended to investigate patients who had undergone anterior cervical spinal surgery—ACDF, anterior cervical corpectomy and fusion (ACCF), cervical disk replacement (CDR), or anterior diskectomy—with at least 1 IONM modality to determine whether there are associations among IONM alerts and procedure characteristics such as the number of levels accessed.
Methods
Institutional review board (IRB) approval was obtained for this study. No informed consent was required.
We conducted a retrospective review of IONM data collected by Accurate Neuromonitoring, LLC, a company that provides IONM support to 400 surgeons in more than 100 U.S. hospitals and ambulatory centers. The database was queried for patients who underwent ACDF, ACCF, CDR, or anterior diskectomy and used at least 1 IONM modality (EMG, MEP, SSEP). In addition, an IONM report was available for each case, detailing patient monitoring strategies, baseline/intraoperative responses, and conclusions of any critical changes. Patient age was the only demographic data available in the database, nor did it include information on patient diagnoses, comorbidities, preoperative clinical data, complications, or clinical follow-up. Patients were excluded from the study if they had incomplete procedural information, concurrent thoracic or lumbar spine procedures, multiple anterior cervical procedures (ie, concomitant ACDF and CDR), or if they were undergoing tumor resection or concomitant posterior cervical approaches.
A total of 8854 patients were included; the average age was 50.6 ± 11.2 years old. Procedures included ACCF (n = 209), ACDF (n = 8006), CDR (n = 423), and anterior diskectomy (n = 216). A majority of these cases were single-level surgeries. In fact, 70.8% (n = 148) of ACCFs, 46.3% (n = 3707) of ACDFs, 60.3% (n = 255) of CDRs, and 49.5% (n = 107) of anterior diskectomies were single-level cases.
All data were collected and managed using Research Electronic Data Capture (REDCap) hosted at Weill Cornell Medicine Clinical and Translational Science Center supported by the National Center for Advancing Translational Science of the National Institute of Health under award number: UL1 TR002384. REDCap is a secure, web-based software platform designed to support data capture for research studies [20,21].
For each case, patient age, procedure type, and the number of spinal levels involved in surgery were recorded. The use of specific IONM modalities and the incidence of IONM alerts were collected. Differences in use and alerts based on the type of procedure, the number of levels, and the cervical level were analyzed. When analyzing the association with level of surgery, only single-level cases were analyzed because we were unable to decipher at which level an alert occurred in patients undergoing multilevel procedures.
This methodology is in accordance with a study previously published by our group assessing IONM use and alerts in patients undergoing lateral lumbar interbody fusion [3].
When comparing use and alerts by number of surgical levels and among different procedure types, the number of levels for ACCF were counted per motion segment (ie, partial corpectomy and fusion of 1 disk space was designated as 1-level surgery; a true 1-level ACCF, such as complete corpectomy of one vertebral body and fusion of 2 disk spaces, was designated as a 2-level surgery, etc.) This was done to allow for comparisons between procedures as the number of levels for all the other procedure types are counted per disk space. When comparing use and alerts by level of surgery, true 1-level ACCFs (complete corpectomy of 1 vertebral body and fusion of 2 disk spaces) were studied and the level of surgery was designated by the level of the corpectomy (ie, C3-C5 ACCF was recorded as surgery at C4).
Statistical Analysis
Categorical variables were summarized as “count (percentage)” and were compared using χ2 and Fisher exact tests. A P value <.0001 was considered statistically significant. Analyses were performed using the IBM Statistical Package for the Social Sciences (SPSS) version 27.
Results
Of the 8854 patients who had undergone ACCF, ACDF, CDR, or anterior diskectomy with at least 1 IONM modality, EMG was used in 81.3% (n = 7203), MEP in 64.8% (n = 5735), and SSEP was used in 99.9% (n = 8844) (Table 1). Alerts were seen in 9.3% (n = 671) of EMG, 0.5% (n = 30) of MEP, and 2.7% (n = 241) of SSEP (see Supplemental Figures).
Table 1.
IONM modality by utilization and alerts.
| IONM modality | |||
|---|---|---|---|
| EMG | MEP | SSEP | |
| Modality used | 7203/8854 (81.3 %) | 5735/8854 (64.8) | 8844/8854 (99.9) |
| • Alert | • 671/7203 (9.3 %) | • 30/5735 (0.5) | • 241/8844 (2.7) |
| • No alert | • 6532/7203 (90.7 %) | • 5705/5735 (99.5) | • 8603/8844 (97.3) |
| Modality not used | 1651/8854 (18.7 %) | 3119/8854 (35.2) | 10/8854 (0.1) |
IONM Intraoperative neuromonitoring, EMG electromyography, MEP motor evoked potentials, SSEP somatosensory evoked potentials.
A statistically significant difference was noted among procedures for EMG use (P < .0001), with EMG being used in 85.6% (n = 179) of ACCF, 80.4% (n = 6440) of ACDF, 90.1% (n = 381) of CDR, and 94.0% (n = 203) of anterior diskectomy cases (Table 2). Specifically, EMG use was significantly lower for ACDF compared with CDR and anterior diskectomy. Similarly, a statistically significant difference was noted among procedures for MEP use (P < .0001) with MEP being used in 79.4% (n = 166) of ACCF, 64.7% (n = 5183) of ACDF, 78.3% (n = 331) of CDR, and 25.0% (n = 54) of anterior diskectomy cases. Specifically, MEP use was lower for anterior diskectomy compared with all other procedures, and lower for ACDF compared with ACCF and CDR. Similar findings were also seen in the 1-level (P < .0001) and 2-level (P < .0001) subgroups for EMG and MEP use. There was no significant difference in SSEP use; SSEP was used in 100.0% (n = 209) of ACCF, 99.9% (n = 7998) of ACDF, 100.0% (n = 423) of CDR, and 99.1% (n = 214) of anterior diskectomy cases. There was no difference in rates of use for any IONM modality by number of levels of surgery (see Supplemental Tables).
Table 2.
IONM modality utilization by procedure and number of levels.
| EMG utilization by number of levels | ||||||||
|---|---|---|---|---|---|---|---|---|
| EMG utilization No. (%) |
1 (%) | 2 (%) | 3 (%) | 4 (%) | 5 (%) | Unspecified | P value | |
| ACCF (n = 209) |
179/209 (85.6) |
23/29 (79.3) |
128/148 (86.5) |
24/27 (88.9) |
1/2 (50.0) |
1/1 (100.0) |
2/2 (100.0) |
.483 |
| ACDF (n = 8006) |
6440/8006 (80.4) |
2941/3707 (79.3) |
2721/3337 (81.5) |
682/844 (80.8) |
64/76 (84.2) |
3/3 (100.0) |
29/39 (74.4) |
.140 |
| Disk replacement (n = 423) |
381/423 (90.1) |
228/255 (89.4) |
144/157 (91.7) |
6/8 (75.0) |
— | — | 3/3 (100.0) |
.260 |
| Diskectomy (n = 216) |
203/216 (94.0) |
97/107 (90.7) |
79/82 (96.3) |
19/19 (100.0) |
5/5 (100.0) |
— | 3/3 (100.0) |
.223 |
| P value | <.0001 | <.0001 | <.0001 | .129 | — | — | — | — |
| MEP utilization by number of levels | ||||||||
| MEP utilization No. (%) |
1 (%) | 2 (%) | 3 (%) | 4 (%) | 5 (%) | Unspecified | P value | |
| ACCF (n = 209) |
166/209 (79.4) |
20/29 (69.0) |
120/148 (81.1) |
22/27 (81.5) |
1/2 (50.0) |
1/1 (100.0) |
2/2 (100.0) |
.471 |
| ACDF (n = 8006) |
5183/8006 (64.7) |
2356/3707 (63.6) |
2221/3337 (66.6) |
530/844 (62.8) |
51/76 (67.1) |
1/3 (33.3) |
24/39 (61.5) |
.041 |
| Disk replacement (n = 423) |
331/423 (78.3) |
206/255 (80.8) |
118/157 (75.2) |
6/8 (75.0) |
— | — | 1/3 (33.3) |
.433 |
| Diskectomy (n = 216) |
54/216 (25.0) |
24/107 (22.4) |
21/82 (25.3) |
5/19 (26.3) |
4/5 (80.0) |
— | 0/3 (0.0) |
.039 |
| P value | <.0001 | <.0001 | <.0001 | .001 | — | — | — | — |
| SSEP utilization by number of levels | ||||||||
| SSEP utilization No. (%) |
1 (%) | 2 (%) | 3 (%) | 4 (%) | 5 (%) | Unspecified | P value | |
| ACCF (n = 209) |
209/209 (100.0) |
29/29 (100.0) |
148 /148 (100.0) |
27/27 (100.0) |
2/2 (100.0) |
1/1 (100.0) |
2/2 (100.0) |
1.000 |
| ACDF (n = 8006) |
7998/8006 (99.9) |
3703/3707 (99.9) |
3334/3337 (99.9) |
843/844 (99.9) |
76/76 (100.0) |
3/3 (100.0) |
39/39 (100.0) |
.997 |
| Disk replacement (n = 423) |
423/423 (100.0) |
255/255 (100.0) |
157/157 (100.0) |
8/8 (100.0) |
— | — | 3/3 (100.0) |
1.000 |
| Diskectomy (n = 216) |
214/216 (99.1) |
105/107 (98.1) |
82/82 (100.0) |
19/19 (100.0) |
5/5 (100.0) |
— | 3/3 (100.0) |
.572 |
| P value | .004 | <.0001 | .951 | .996 | — | — | — | — |
IONM Intraoperative neuromonitoring, EMG electromyography, ACCF anterior cervical corpectomy and fusion, ACDF anterior cervical diskectomy and fusion, MEP motor evoked potentials, SSEP somatosensory evoked potentials.
As seen in Table 3, EMG alerts were seen in 12.8% (n = 23) of ACCF, 9.3% (n = 596) of ACDF, 11.8% (n = 45) of CDR, and 3.4% (n = 7) of anterior diskectomy cases; MEP alerts were seen in 2.4% (n = 4) of ACCF, 0.5% (n = 25) of ACDF, 0.3% (n = 1) of CDR, and 0.0% (n = 0) of anterior diskectomy cases; and SSEP alerts were seen in 7.2% (n = 15) of ACCF, 2.6% (n = 208) of ACDF, 3.1% (n = 13) of CDR, and 2.3% (n = 5) of anterior diskectomy cases. Despite differences in use rates, there were no significant differences in the rates of alerts between procedure types (Supplemental Figure 2).
Table 3.
IONM alert by procedure and number of levels.
| EMG alert (%) | Alert by number of levels | |||||||
|---|---|---|---|---|---|---|---|---|
| 1 (%) | 2 (%) | 3 (%) | 4 (%) | 5 (%) | Unspecified | P value | ||
| ACCF (n = 179) |
23/179 (12.8) |
3/23 (13.0) |
15/128 (11.7) |
5/24 (20.8) |
0/1 (0.0) |
0/1 (0.0) |
0/2 (0.0) |
.775 |
| ACDF (n = 6440) |
596/6440 (9.3) |
202/2941 (6.9) |
272/2721 (10.0) |
104/682 (15.2) |
15/64 (23.4) |
0/3 (0.0) |
3/29 (10.3) |
<.0001 |
| Disk replacement (n = 381) |
45/381 (11.8) |
26 /228 (11.4) |
17/144 (11.8) |
2/6 (33.3) |
— | — | 0/3 (0.0) |
.261 |
| Diskectomy (n = 203) |
7/203 (3.4) |
4/97 (4.1) |
2/79 (2.5) |
0/19 (0.0) |
1/5 (20.0) |
— | 0/3 (0.0) |
.168 |
| P value | .003 | .011 | .121 | .138 | — | — | — | — |
| MEP alert (%) | Alert by number of levels | |||||||
| 1 (%) | 2 (%) | 3 (%) | 4 (%) | 5 (%) | Unspecified | P value | ||
| ACCF (n = 166) |
4/166 (2.4) |
1/20 (5.0) |
3/120 (2.5) |
0/22 (0.0) |
0/1 (0.0) |
0/1 (0.0) |
0/2 (0.0) |
.886 |
| ACDF (n = 5183) |
25/5183 (0.5) |
13/2356 (0.6) |
9/2221 (0.4) |
3/530 (0.6) |
0/51 (0.0) |
0/1 (0.0) |
0/24 (0.0) |
.933 |
| Disk replacement (n = 331) |
1/331 (0.3) |
0/206 (0.0) |
1/118 (0.8) |
0/6 (0.0) |
— | — | 0/1 (0.0) |
.406 |
| Diskectomy (n = 55) |
0/55 (0.0) |
0/24 (0.0) |
0/21 (0.0) |
0/5 (0.0) |
0/4 (0.0) |
— | 0/1 (0.0) |
1.000 |
| P value | .007 | .049 | .018 | .980 | — | — | — | — |
| SSEP alert (%) | Alert by number of levels | |||||||
| 1 (%) | 2 (%) | 3 (%) | 4 (%) | 5 (%) | Unspecified | P value | ||
| ACCF (n = 209) |
15/209 (7.2) |
1/29 (3.4) |
12/148 (8.1) |
2/27 (7.4) |
0/2 (0.0) |
0/1 (0.0) |
0/2 (0.0) |
.907 |
| ACDF (n = 7998) |
208/7998 (2.6) |
80/3703 (2.2) |
102/3334 (3.1) |
24 /843 (2.8) |
2/76 (2.6) |
0/3 (0.0) |
0/39 (0.0) |
.210 |
| Disk replacement (n = 423) |
13/423 (3.1) |
6/255 (2.4) |
7/157 (4.5) |
0/8 (0.0) |
— | — | 0/3 (0.0) |
.424 |
| Diskectomy (n = 214) |
5/214 (2.3) |
3/105 (2.9) |
2/82 (2.4) |
0/19 (0.0) |
0/5 (0.0) |
— | 0/3 (0.0) |
.875 |
| P value | .001 | .418 | .007 | .445 | — | — | — | — |
IONM Intraoperative neuromonitoring, EMG electromyography, ACCF anterior cervical corpectomy and fusion, ACDF anterior cervical diskectomy and fusion, MEP motor evoked potentials, SSEP somatosensory evoked potentials.
As seen in Table 3, a statistically significant difference was seen in EMG alerts based on number of levels for ACDF procedures (P < .0001), with 1-level ACDF (6.9%, n = 202) having a lower rate of alerts compared with 2-level (10.0%, n = 272), 3-level (15.2%, n = 104), and 4-level (23.4%, n = 15) ACDF, and 2-level ACDF having a lower rate of alerts compared with 3-level and 4-level ACDF. The EMG, MEP, and SSEP alerts did not vary by number of levels for any other procedure (Supplemental Figure 3).
As seen in Table 4, a statistically significant difference by operative level was noted in EMG use for single-level ACDF procedures (P < .0001), with C2-C3 having a lower rate of use compared with all other levels (C2-C3: 33.3%, C3-C4: 74.7%, C4-C5: 82.6%, C5-C6: 79.9%, C6-C7: 78.6%, C7-T1: 85.2%). There were no other statistically significant differences in use or alerts based on level of surgery for any procedure (Table 5).
Table 4.
IONM modality utilization by single-level procedures and cervical level.
| Utilization by cervical level | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Single-level procedures | EMG utilization No. (%) |
C1 (%) | C2 (%) | C3 (%) | C4 (%) | C5 (%) | C6 (%) | C7 (%) | Unspecified | P value |
| ACCF (n = 128) |
128/148 (86.5) |
— | — | 2/3 (66.7) |
33/40 (82.5) | 35/38 (92.1) |
49/57 (86.0) | 9/10 (90.0) | — | .610 |
| C1-C2 | C2-3 | C3-4 | C4-5 | C5-6 | C6-7 | C7-T1 | ||||
| ACDF (n = 2941) |
2941/3707 (79.3) |
— | 5/15 (33.3) | 283/379 (74.7) | 457/553 (82.6) | 1413/1769 (79.9) | 731/930 (78.6) | 52/61 (85.2) |
— | <.0001 |
| Disk replacement (n = 228) |
228/255 (89.4) |
— | — | 20/23 (87.0) |
29/32 (90.6) | 115/129 (89.1) | 64/71 (90.1) | — | — | .970 |
| Diskectomy (n = 97) |
97/107 (90.7) |
— | 1/1 (100.0) | 12/14 (85.7) | 14/16 (87.5) | 50/53 (94.3) |
19/22 (86.4) | 1/1 (100.0) |
— | .832 |
| Utilization by cervical level | ||||||||||
| Single-level procedures | MEP utilization No. (%) |
C1 (%) | C2 (%) | C3 (%) | C4 (%) | C5 (%) | C6 (%) | C7 (%) | Unspecified | P value |
| ACCF (n = 120) |
120/148 (81.1) |
— | — | 3/3 (100.0) |
35/40 (87.5) | 32/38 (84.2) |
41/57 (71.9) | 9/10 (90.0) |
— | .227 |
| C1-C2 | C2-3 | C3-4 | C4-5 | C5-6 | C6-7 | C7-T1 | ||||
| ACDF (n = 2356) |
2356/3707 (63.6) |
— | 9/15 (60.0) | 257/379 (67.8) | 347/553 (62.7) | 1125/1769 (63.6) | 580/929 (62.4) | 38/60 (63.3) |
0/2 (0.0) |
.592 |
| Disk replacement (n = 206) |
206/255 (80.8) |
— | — | 19/23 (82.6) | 24/32 (75.0) | 106/129 (82.2) | 57/71 (80.3) | — | — | .823 |
| Diskectomy (n = 24) |
24/107 (22.4) |
— | 0/1 (0.0) |
1/14 (7.1) |
6/16 (37.5) |
13/53 (24.5) |
4/22 (18.2) |
0/1 (0.0) |
— | .427 |
| Utilization by cervical level | ||||||||||
| Single-level procedures | SSEP utilization No. (%) |
C1 (%) | C2 (%) | C3 (%) | C4 (%) | C5 (%) | C6 (%) | C7 (%) | Unspecified | P value |
| ACCF (n = 148) |
148/148 (100.0) |
— | — | 3/3 (100.0) |
40/40 (10.00) | 38/38 (100.0) | 57/57 (100.0) | 10/10 (100.0) | — | 1.000 |
| C1-C2 | C2-3 | C3-4 | C4-5 | C5-6 | C6-7 | C7-T1 | ||||
| ACDF (n = 3703) |
3703/3707 (99.9) |
— | 15/15 (100.0) | 379/379 (100.0) | 553/553 (100.0) | 1766/1769 (99.8) | 929/929 (100.0) | 59/60 (98.3) |
2/2 (100.0) |
.006 |
| Disk replacement (n = 255) |
255/255 (100.0) |
— | — | 23/23 (100.0) |
32/32 (100.0) | 129/129 (100.0) | 71/71 (100.0) | — | — | 1.000 |
| Diskectomy (n = 105) |
105/107 (98.1) |
— | 1/1 (100.0) | 14/14 (100.0) | 16/16 (100.0) | 51/53 (96.2) |
22/22 (100.0) | 1/1 (100.0) |
— | .838 |
IONM Intraoperative neuromonitoring, EMG electromyography, ACCF anterior cervical corpectomy and fusion, ACDF anterior cervical diskectomy and fusion, MEP motor evoked potentials, SSEP somatosensory evoked potentials.
Table 5.
IONM alert by single-level procedures and cervical level.
| Single-level procedures | EMG alert (%) | Alert by cervical level | |||||||
|---|---|---|---|---|---|---|---|---|---|
| C1 (%) | C2 (%) | C3 (%) | C4 (%) | C5 (%) | C6 (%) | C7 (%) | P value | ||
| ACCF (n = 128) |
15/128 (11.7) |
— | — | 0/2 (0.0) |
6/33 (18.2) |
7/35 (20.0) |
1/49 (2.0) |
1/9 (11.1) |
.079 |
| C1-C2 (%) | C2-3 (%) | C3-4 (%) | C4-5 (%) | C5-6 (%) | C6-7 (%) | C7-T1 (%) | |||
| ACDF (n = 2941) |
202/2941 (6.9) |
— | 0/5 (0.0) |
23/283 (8.1) |
30/457 (6.6) |
87/1413 (6.2) |
60/731 (8.2) |
2/52 (3.9) |
.413 |
| Disk replacement (n = 228) |
26/228 (11.4) |
— | — | 2/20 (10.0) |
4/29 (13.8) |
11/115 (9.6) |
9/64 (14.1) |
— | .793 |
| Diskectomy (n = 97) |
4/97 (4.1) |
— | 0/1 (0.0) |
0/12 (0.0) |
2/14 (14.3) |
2/50 (4.0) |
0/19 (0.0) |
0/1 (0.0) |
.406 |
| Single-level procedures | MEP alert (%) | Alert by cervical level | |||||||
| C1 (%) | C2 (%) | C3 (%) | C4 (%) | C5 (%) | C6 (%) | C7 (%) | P value | ||
| ACCF (n = 120) |
3/120 (2.5) |
— | — | 0/3 (0.0) |
1/35 (2.9) |
0/32 (0.0) |
0/41 (0.0) |
2/9 (22.2) |
.003 |
| C1-C2 (%) | C2-3 (%) | C3-4 (%) | C4-5 (%) | C5-6 (%) | C6-7 (%) | C7-T1 (%) | |||
| ACDF (n = 2356) |
13/2356 (0.6) |
— | 0/9 (0.0) |
4/257 (1.6) |
2/347 (0.6) |
6/1125 (0.5) |
1/580 (0.2) |
0/38 (0.0) |
.259 |
| Disk replacement (n = 206) |
0/206 (0.0) |
— | — | 0/19 (0.0) |
0/24 (0.0) |
0/106 (0.0) |
0/57 (0.0) |
— | 1.000 |
| Diskectomy (n = 24) |
0/24 (0.0) |
— | — | 0/1 (0.0) |
0/6 (0.0) |
0/13 (0.0) |
0/4 (0.0) |
— | 1.000 |
| Single-level procedures | SSEP alert (%) | Alert by cervical level | |||||||
| C1 (%) | C2 (%) | C3 (%) | C4 (%) | C5 (%) | C6 (%) | C7 (%) | P value | ||
| ACCF (n = 148) |
12/148 (8.1) |
— | — | 0/3 (0.0) |
2/40 (5.0) |
4/38 (10.5) |
3/57 (5.3) |
3/10 (30.0) |
.087 |
| C1-C2 (%) | C2-3 (%) | C3-4 (%) | C4-5 (%) | C5-6 (%) | C6-7 (%) | C7-T1 (%) | |||
| ACDF (n = 3703) |
80/3703 (2.2) |
— | 1/15 (6.7) |
10/379 (2.6) |
15/553 (2.7) |
40/1766 (2.3) |
14/930 (1.5) |
0/60 (0.0) |
.315 |
| Disk replacement (n = 255) |
6/255 (2.3) |
— | — | 3/23 (13.0) |
1/32 (3.1) |
2/129 (1.6) |
0/71 (0.0) |
— | .008 |
| Diskectomy (n = 105) |
3/105 (2.9) |
— | 0/1 (0.0) |
0/14 (0.0) |
1/16 (6.3) |
2/51 (3.9) |
0/22 (0.0) |
0/1 (0.0) |
.851 |
IONM Intraoperative neuromonitoring, EMG electromyography, ACCF anterior cervical corpectomy and fusion, ACDF anterior cervical diskectomy and fusion, MEP motor evoked potentials, SSEP somatosensory evoked potentials.
Discussion
Our retrospective study reviewed a total of 8854 cases of anterior cervical surgery in which at least 1 IONM modality was used. We found that EMG, MEP, and SSEP were used in 81.3%, 64.8%, and 99.9% of cases, respectively. Our results further indicated that the incidence of alerts across all procedure types using EMG, MEP, and SSEP was <12%, <2%, and <7%, respectively.
The study has several limitations. First, we used a private IONM database that identified patients undergoing ACCF, ACDF, CDR, and anterior diskectomy, but there was no control group of patients who had surgery without IONM available for comparison. Second, because the database did not contain postoperative data, we do not know if the alerts prevented or missed postoperative neurologic complications. In addition, the database did not include granular details about the alerts, such as exactly when during the procedures the alerts occurred and whether they were associated with specific steps of the surgery. Furthermore, the database also lacked information regarding intraoperative patient positioning. Therefore, the potential relationship of these factors to neuromonitoring alerts could not be assessed. Finally, our record of IONM alerts based on cervical level is limited to patients undergoing single-level procedures, as we could not identify the level at which an alert occurred in patients undergoing multilevel procedures.
The use of EMG in minimally invasive spine surgery has been largely limited to its efficacy in determining safe pedicle screw placement [8]. Pedicle screw testing is conducted through stimulating the implanted screw and eliciting a response from the corresponding myotome; because the pedicle functions as an insulator, a higher response threshold indicates decreased likelihood of injury to the exiting nerve root [37]. The MEP monitoring is used to assess the functional intactness of descending motor pathways; a decreased amplitude of muscle MEP may be used to evaluate early ischemic or iatrogenic injury to the spinal cord [32]. Although MEPs are typically performed in a manner suitable for detecting spinal cord injury, detection of nerve root injury is not commonly attempted using MEP. Somatosensory evoked potential was first reported by Nash et al as a modality to monitor nerve injury in scoliosis surgery and has since been used frequently in cervical spine surgery; however, it is limited by a high rate of false-positive and false-negative alerts [9,30,31]. While various groups have comments on the benefits and shortcomings of IONM, consensus regarding the use of EMG, MEP, and SSEP in spine surgery is lacking, potentially due to lack of available data on the benefits and drawbacks of unimodal IONM [3,9,26].
The ACCF, ACDF, CDR, and anterior diskectomy procedures have been used to treat degenerative conditions of the spine for more than 70 years [17,34]. The IONM modalities have been frequently used to monitor these procedures to detect the risk of intraoperative injury to critical neurovascular structures [12,18]. A study by Clark et al [11] examined the role of IONM in cervical spondylotic myelopathy cases and found a correlation between the decreased incidence of MEP alerts and postoperative neurological deficits. A study by Kelleher et al [25] estimated 100% positive predictive values for both SSEP and MEP, as all intraoperative alerts were correlated with a surgical event or postoperative complication. Our results demonstrate that in anterior cervical spine surgeries using IONM, the most used modality was SSEP, followed by EMG and MEP; MEP had the greatest incidence of intraoperative alerts.
However, research has emerged questioning the utility of routine IONM in spine surgery [1,13,23]. Badhiwala et al [4] reviewed International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes from the Healthcare Cost and Utilization Project database and found that there was no correlation between use of IONM and reduced neurological complications following ACDF surgery. In fact, due to the lack of standardized guidelines on which IONM modality to employ for anterior cervical spine procedures, clinicians are choosing based on personal preference and medical/legal considerations [26].
The cervical spine is close to many important neurovascular structures, especially in its center. Complications after cervical spine surgery may include dysphagia, vascular injury, and dural penetration [36]. Dysphagia may occur from damage to the superior laryngeal nerve at the level of C3-C4, while vascular injury to the vertebral and/or carotid arteries is most common anterior to the transverse foramen of C7 or during lateral decompression maneuvers from C3-C6 [10]. Prior studies have noted that an increase in the number of operative levels in cervical spine surgery may lead to an increased risk of neurovascular injury [14,39]. In our study, EMG alerts were associated with a higher number of levels for ACDF procedures. This finding may support prior studies suggesting that an increase in the number of levels operated on may be associated with greater neurologic injury in ACDF procedures [16].
In conclusion, this retrospective review of anterior cervical spinal surgeries performed with at least 1 IONM modality found SSEP had the highest rate of use across procedure types (>99.0%), whereas MEP had the highest rate of nonuse across procedure types (35.2%). There was a significant difference in overall EMG and MEP use across procedure types, which was also noticeable in 1-level and 2-level procedures, whereas SSEP use had a significant difference across 1-level procedure types. The EMG alerts in ACDF procedures varied significantly by the number of levels operated upon. The EMG use in only 1-level ACDF procedures varied significantly by the operative level. Future studies should focus on the risks and benefits of multimodal IONM in spine surgery.
Supplemental Material
Supplemental material, sj-docx-1-hss-10.1177_15563316221110572 for The Role of Intraoperative Neuromonitoring Modalities in Anterior Cervical Spine Surgery by Akhil Avunoori Chandra, Avani Vaishnav, Pratyush Shahi, Junho Song, Jung Mok, R. Kiran Alluri, Darren Chen, Catherine Himo Gang and Sheeraz Qureshi in HSS Journal®: The Musculoskeletal Journal of Hospital for Special Surgery
Supplemental material, sj-jpg-2-hss-10.1177_15563316221110572 for The Role of Intraoperative Neuromonitoring Modalities in Anterior Cervical Spine Surgery by Akhil Avunoori Chandra, Avani Vaishnav, Pratyush Shahi, Junho Song, Jung Mok, R. Kiran Alluri, Darren Chen, Catherine Himo Gang and Sheeraz Qureshi in HSS Journal®: The Musculoskeletal Journal of Hospital for Special Surgery
Supplemental material, sj-jpg-3-hss-10.1177_15563316221110572 for The Role of Intraoperative Neuromonitoring Modalities in Anterior Cervical Spine Surgery by Akhil Avunoori Chandra, Avani Vaishnav, Pratyush Shahi, Junho Song, Jung Mok, R. Kiran Alluri, Darren Chen, Catherine Himo Gang and Sheeraz Qureshi in HSS Journal®: The Musculoskeletal Journal of Hospital for Special Surgery
Supplemental material, sj-jpg-4-hss-10.1177_15563316221110572 for The Role of Intraoperative Neuromonitoring Modalities in Anterior Cervical Spine Surgery by Akhil Avunoori Chandra, Avani Vaishnav, Pratyush Shahi, Junho Song, Jung Mok, R. Kiran Alluri, Darren Chen, Catherine Himo Gang and Sheeraz Qureshi in HSS Journal®: The Musculoskeletal Journal of Hospital for Special Surgery
Footnotes
The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Sheeraz A. Qureshi, MD, MBA, reports relationships with AMOpportunities, Globus Medical, Healthgrades, K2M, Lifelink.com, Minimally Invasive Spine Specialty Group, Paradigm Spine, RTI Surgical, Stryker, Spinal Simplicity, Tissue Differentiation Intelligence, Vital 5. The other authors declare no potential conflicts of interest.
Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study used REDCap (Research Electronic Data Capture) hosted at Weill Cornell Medicine Clinical and Translational Science Center supported by the National Center For Advancing Translational Science of the National Institute of Health (NIH) under award number: UL1 TR002384.
Human/Animal Rights: All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2013.
Informed Consent: Informed consent was not required for this study.
Level of Evidence: Level IV: Therapeutic Study.
Required Author Forms: Disclosure forms provided by the authors are available with the online version of this article as supplemental material.
Supplemental Material: Supplemental material for this article is available online.
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Supplementary Materials
Supplemental material, sj-docx-1-hss-10.1177_15563316221110572 for The Role of Intraoperative Neuromonitoring Modalities in Anterior Cervical Spine Surgery by Akhil Avunoori Chandra, Avani Vaishnav, Pratyush Shahi, Junho Song, Jung Mok, R. Kiran Alluri, Darren Chen, Catherine Himo Gang and Sheeraz Qureshi in HSS Journal®: The Musculoskeletal Journal of Hospital for Special Surgery
Supplemental material, sj-jpg-2-hss-10.1177_15563316221110572 for The Role of Intraoperative Neuromonitoring Modalities in Anterior Cervical Spine Surgery by Akhil Avunoori Chandra, Avani Vaishnav, Pratyush Shahi, Junho Song, Jung Mok, R. Kiran Alluri, Darren Chen, Catherine Himo Gang and Sheeraz Qureshi in HSS Journal®: The Musculoskeletal Journal of Hospital for Special Surgery
Supplemental material, sj-jpg-3-hss-10.1177_15563316221110572 for The Role of Intraoperative Neuromonitoring Modalities in Anterior Cervical Spine Surgery by Akhil Avunoori Chandra, Avani Vaishnav, Pratyush Shahi, Junho Song, Jung Mok, R. Kiran Alluri, Darren Chen, Catherine Himo Gang and Sheeraz Qureshi in HSS Journal®: The Musculoskeletal Journal of Hospital for Special Surgery
Supplemental material, sj-jpg-4-hss-10.1177_15563316221110572 for The Role of Intraoperative Neuromonitoring Modalities in Anterior Cervical Spine Surgery by Akhil Avunoori Chandra, Avani Vaishnav, Pratyush Shahi, Junho Song, Jung Mok, R. Kiran Alluri, Darren Chen, Catherine Himo Gang and Sheeraz Qureshi in HSS Journal®: The Musculoskeletal Journal of Hospital for Special Surgery