Intraoperative neuromonitoring practice patterns in spinal deformity surgery: a global survey of the Scoliosis Research Society

Timing of intraoperative neurophysiological monitoring (IONM) recovery and clinical recovery after termination of pediatric spinal deformity surgery due to loss of IONM signals

BACKGROUND CONTEXT

Intraoperative neurophysiological monitoring (IONM) is used to reduce the risk of spinal cord injury during pediatric spinal deformity surgery. Significant reduction and/or loss of IONM signals without immediate recovery may lead the surgeon to acutely abort the case. The timing of when monitorable signals return remains largely unknown.

PURPOSE

The goal of this study was to investigate the correlation between IONM signal loss, clinical examination, and subsequent normalization of IONM signals after aborted pediatric spinal deformity surgery to help determine when it is safe to return to the operating room.

STUDY DESIGN/SETTING

This is a multicenter, multidisciplinary, retrospective study of pediatric patients (<18 years old) undergoing spinal deformity surgery whose surgery was aborted due to a significant reduction or loss of IONM potentials.

PATIENT SAMPLE

Sixty-six patients less than 18 years old who underwent spinal deformity surgery that was aborted due to IONM signal loss were enrolled into the study.

OUTCOME MEASURES

IONM data, operative reports, and clinical examinations were investigated to determine the relationship between IONM loss, clinical examination, recovery of IONM signals, and clinical outcome.

METHODS

Information regarding patient demographics, deformity type, clinical history, neurologic and ambulation status, operative details, IONM information (eg, quality of loss [SSEPs, MEPs], laterality, any recovery of signals, etc.), intraoperative wake-up test, postoperative neurologic exam, postoperative imaging, and time to return to the operating were all collected. All factors were analyzed and compared with univariate and multivariate analysis using appropriate statistical analysis.

RESULTS

Sixty-six patients were enrolled with a median age of 13 years [IQR 11-14], and the most common sex was female (42/66, 63.6%). Most patients had idiopathic scoliosis (33/66, 50%). The most common causes of IONM loss were screw placement (27/66, 40.9%) followed by rod correction (19/66, 28.8%). All patients had either complete bilateral (39/66, 59.0%), partial bilateral (10/66, 15.2%) or unilateral (17/66, 25.8%) MEP loss leading to termination of the case. Overall, when patients were returned to the operating room 2 weeks postoperatively, nearly 75% (40/55) had monitorable IONM signals. Univariate analysis demonstrated that bilateral SSEP loss (p=.019), bilateral SSEP and MEP loss (p=.022) and delayed clinical neurologic recovery (p=.008) were significantly associated with having unmonitorable IONM signals at repeat surgery. Multivariate regression analysis demonstrated that delayed clinical neurologic recovery (> 72 hours) was significantly associated with unmonitorable IONM signals when returned to the operating room (p=.006). All patients ultimately made a full neurologic recovery.

CONCLUSIONS

In children whose spinal deformity surgery was aborted due to intraoperative IONM loss, there was a strong correlation between combined intraoperative SSEP/MEP loss, the magnitude of IONM loss, the timing of clinical recovery, and the time of electrophysiological IONM recovery. The highest likelihood of having a prolonged postoperative neurological deficit and undetectable IONM signals upon return to the OR occurs with bilateral complete loss of SSEPs and MEPs.

Does an improvement in cord-level intraoperative neuromonitoring data lead to a reduced risk for postoperative neurologic deficit in spine deformity surgery?

PURPOSE

To determine if an improvement in cord-level intraoperative neuromonitoring (IONM) data following data loss results in a reduced risk for new postoperative motor deficit in pediatric and adult spinal deformity surgery.

METHODS

A consecutive series of 1106 patients underwent spine surgery from 2015 to 2023 by a single surgeon. Cord alerts were defined by Somatosensory-Evoked Potentials (SSEP; warning criteria: 10% increase in latency or > 50% loss in amplitude) and Motor-Evoked Potentials (MEP; warning criteria: 75% loss in amplitude without return to acceptable limits after stimulation up 100 V above baseline level). Timing of IONM loss and recovery, interventions, and baseline/postoperative day 1 (POD1) lower extremity motor scores were analyzed.

RESULTS

IONM Cord loss was noted in 4.8% (53/11,06) of patients and 34% (18/53) with cord alerts had a POD1 deficit compared to preoperative motor exam. MEP and SSEP loss attributed to 98.1% (52/53) and 39.6% (21/53) of cord alerts, respectively. Abnormal descending neurogenic-evoked potential (DNEP) was seen in 85.7% (12/14) and detected 91.7% (11/12) with POD1 deficit. Abnormal wake-up test (WUT) was seen in 38.5% (5/13) and detected 100% (5/5) with POD1 deficit. Most cord alerts occurred during a three-column osteotomy (N = 23/53, 43%); decompression (N = 12), compression (N = 7), exposure (N = 4), and rod placement (N = 14). Interventions were performed in all 53 patients with cord loss and included removing rods/less correction (N = 11), increasing mean arterial pressure alone (N = 10), and further decompression with three-column osteotomy (N = 9). After intervention, IONM data improved in 45(84.9%) patients (Full improvement: N = 28; Partial improvement: 17). For those with full and partial IONM improvement, the POD1 deficit was 10.7% (3/28) and 41.2% (7/17), respectively. For those without any IONM improvement (15.1%, 8/53), 100% (8/8) had a POD1 deficit, P < 0.001.

CONCLUSION

A full or partial improvement in IONM data loss after intraoperative intervention was significantly associated with a lower risk for POD1 deficit with an absolute risk reduction of 89.3% and 58.8%, respectively. All patients without IONM improvement had a POD1 neurologic deficit.

Neuromonitoring for spine surgery in children

Neuromonitoring or electrophysiologic monitoring is now an essential component of pediatric spine surgery due to the high number of spinal deformity indications in asymptomatic patients, for whom any neurological complication would be disastrous. Technological advances have led to the development of compact monitors that allow surgeons themselves to monitor the motor evoked potentials (MEP) perioperatively. This shift happened because it was difficult to always have a neurophysiologist in the operating room. Unfortunately, this also means that multimodal monitoring (sensory, mixed, D-wave, electromyography, pedicle screws) is much more difficult to implement. There are absolute indications, such as any spinal deformity without neurological deficit and relative indications, which are more difficult to interpret. Technical incidents frequently occur before the start of the surgery. If no replacement device is available, the procedure must be cancelled unless the patient's life or function are at risk. At least two monitoring systems should be available at every facility to avoid having to cancel surgery for purely technological reasons. Once the surgical procedure has started, the absence of MEP recruitment curves in the upper and lower limbs is likely due to the anesthesia depth; the surgery should be stopped until this problem is corrected. When there is a true intraoperative alert (MEPs disappear in the lower limbs only), we propose taking the following steps, depending on whether the spine is stable or unstable: remove the causal implant, remove all hardware, preserve any stabilization devices, initiate an intraoperative wake-up test, verify conditions under which the intervention should continue. Level of evidence: V.

Influences of Increasing Pedicle Screw Diameter on Widening Vertebral Pedicle Size during Surgery in Spinal Deformities in Children and Adolescents without Higher Risk of Pedicle and Vertebral Breaches

BACKGROUND

A very common technique for treating spinal deformities in children and adolescents is the use of segmental screws. In order to obtain proper stability and the best possible correction, the screws must first be precisely inserted. Additional factors influencing the quality and success of the operation are the size and quality of the bone, the skills of the surgeon, and biomechanical factors, i.e., the width and length of the screws used during surgery. Our study was focused on evaluating the effect of increasing the diameter of the instrumented pedicles by pedicle screws and assessing the safety of expanding these pedicles with screws of various sizes in children with spinal deformities during the growth period, using preoperative magnetic resonance imaging and postoperative computed tomography (CT) to assess and compare preoperative size measurements from MRI to postoperative CT measurements.

METHODS

We obtained data for evaluation from the available medical records and treatment histories of patients aged 2 to 18 who underwent surgical treatment of spinal deformities in the years 2016-2023. In 230 patients (28 male and 202 female), 7954 vertebral bodies were scanned by preoperative MRI, and 5080 pedicle screws were inserted during surgery, which were then assessed by postoperative CT scan. For the most accurate assessment, patients were classified into three age groups: 2-5 years (Group 1), 6-10 years (Group 2), and 11-18 years (Group 3). In addition, we studied implant subgroups: vertebral bodies with inserted pedicles of screw sizes 5.0 mm and 5.5 mm (Group S), and pedicles of screw sizes 6.0 mm, 6.5 mm, and 7.0 mm (Group L).

RESULTS

The morphology of pedicles (Lenke classification) analyzed before surgery using MRI was 55.2% type A, 33.8% type B, 4.7% type C, and 6.3% type D. The postoperative lateral and medial breaches were noted, and these did not cause any complications requiring revision surgery. The mean pedicle diameter before surgery for T1-L5 vertebral pedicles was between 3.79 (1.44) mm and 5.68 (1.64) mm. The mean expanding diameter of pedicles after surgery for T1-L5 vertebral pedicles ranged from 1.90 (0.39) mm to 2.92 (0.28) mm, which corresponds to the extension of the pedicle diameter in the mean range of 47% (4.1)-71% (3.0). We noted that the mean vertebral pedicle expansion was 49% in Group 1, 52% in Group 2, and 62% in Group 3 (N.S.), and the mean expansion for 7.0 mm screw pedicles was 78%.

CONCLUSIONS

Our study confirms that there is a wide range of expansion of the vertebral pedicle during screw insertion (up to 78%) with a low risk of lateral or medial breaches and without an increased risk of complications. The larger the diameter of the screw inserted into the pedicle, the more the pedicle expands. Pedicle measurements by preoperative MRI may be helpful for sufficient reliability in preoperative planning.

The Use of Intraoperative Neuromonitoring for Cervical Spine Surgery: Indications, Challenges, and Advances

Intraoperative neuromonitoring (IONM) has become an indispensable surgical adjunct in cervical spine procedures to minimize surgical complications. Understanding the historical development of IONM, indications for use, associated pitfalls, and recent developments will allow the surgeon to better utilize this important technology. While IONM has shown great promise in procedures for cervical deformity, intradural tumors, or myelopathy, routine use in all cervical spine cases with moderate pathology remains controversial. Pitfalls that need to be addressed include human error, a lack of efficient communication, variable alarm warning criteria, and a non-standardized checklist protocol. As the techniques associated with IONM technology become more robust moving forward, IONM emerges as a crucial solution to updating patient safety protocols.

The role of counter-torque holders in tightening of pedicle screw-rod constructs: a biomechanical study in a porcine model

BACKGROUND CONTEXT

Pedicle screw-rod assembly procedures following pedicle screw insertion include contouring and placing rods into screw tulips, introducing set screws into the tulip along the screw thread, applying a counter-torque holder and tightening all the set screws clockwise. Even if an appropriate pedicle screw is implanted, screw dislodgement after tightening of the tulip and set screw is not uncommon. Pedicle wall violation resulting from excessive rotational force due to inadequate use of a counter-torque holder might be the reason. However, the strain change in the pedicle during tulip-set screw tightening and the role of counter-torque have never been investigated.

PURPOSE

This study determined differences in the strain change in the outer and inner pedicle walls during tulip-set screw tightening; additionally, the influence of counter-torque on pedicle wall violation was elucidated.

STUDY DESIGN

A controlled biomechanical study; the strain values of outer and inner pedicle walls in cadaveric porcine L4-L5 vertebrae during tulip-set screw tightening with or without a counter-torque holder were measured.

METHODS

Twelve L4-L5 fresh-frozen porcine lumbar vertebrae were implanted with screw-rod constructs; the set screw was randomly locked into the tulip in the right L5, right L4, left L5 and left L4 testing groups. The maximal values from eight strain gauges (P-R-O: outer cortex of right pedicle in proximal vertebra; P-R-I: inner cortex of right pedicle in proximal vertebra; D-R-O: outer cortex of right pedicle in distal vertebra; D-R-I: inner cortex of right pedicle in distal vertebra; P-L-O: outer cortex of left pedicle in proximal vertebra; P-L-I: inner cortex of left pedicle in proximal vertebra; D-L-O: outer cortex of left pedicle in distal vertebra; D-L-I: outer cortex of left pedicle in proximal vertebra) for each specimen during tightening to 12 Nm were measured.

RESULTS

The maximal strain values of the ipsilateral strain gauges in all testing groups were almost significantly higher when a counter-torque holder was not used than when one was used. The strain values in the adjacent pedicle of specimens without a counter-torque holder were significantly increased: P-R-O and P-R-I in the right L5 group; D-R-I in the right L4 group; P-L-I and P-L-O in the left L5 group; D-L-O and D-L-I in the left L4 group.

CONCLUSIONS

The constraint effect of counter-torque during tulip-set screw tightening is necessary. Clockwise rotational force with a fragile lateral pedicle wall suggests that caution is required when using a counter-torque holder to tighten the right L5 and left L4 constructs.

CLINICAL SIGNIFICANCE

A counter-torque holder is important during tulip-set screw tightening; improper use may lead to adjacent pedicle wall violation, sequentially resulting in pedicle screw loosening.

Current Trends in Intraoperative Spinal Cord Monitoring: A Survey Analysis among Japanese Expert Spine Surgeons

Introduction

Although intraoperative spinal neuromonitoring (IONM) is recommended for spine surgeries, there are no guidelines regarding its use in Japan, and its usage is mainly based on the surgeon's preferences. Therefore, this study aimed to provide an overview of the current trends in IONM usage in Japan.

Methods

In this web-based survey, expert spine surgeons belonging to the Japanese Society for Spine Surgery and Related Research were asked to respond to a questionnaire regarding IONM management. The questionnaire covered various aspects of IONM usage, including the preferred modality, operation of IONM, details regarding muscle-evoked potential after electrical stimulation of the brain (Br(E)-MsEP), and need for consistent use of IONM in major spine surgeries.

Results

Responses were received from 134 of 186 expert spine surgeons (response rate, 72%). Of these, 124 respondents used IONM routinely. Medical staff rarely performed IONM without a medical doctor. Br(E)-MsEP was predominantly used for IONM. One-third of the respondents reported complications, such as bite injuries caused by Br(E)-MsEP. Interestingly, two-thirds of the respondents did not plan responses to alarm points. Intramedullary spinal cord tumor, scoliosis (idiopathic, congenital, or neuromuscular in pediatric), and thoracic ossification of the posterior longitudinal ligament were representative diseases that require IONM.

Conclusions

IONM has become an essential tool in Japan, and Br(E)-MsEP is a predominant modality for IONM at present. Although we investigated spine surgeries for which consistent use of IONM is supported, a cost-benefit analysis may be required.

Comprehensive Perioperative Approach to Complex Spine Deformity Management

OBJECTIVE

Study perioperative strategies for optimizing neuroprotection in complex spine deformity correction surgery.

METHODS

We report the case of a patient with severe lumbar dextroscoliosis, thoracolumbar junction hyperkyphosis with a 40-degree Cobb angle levoconvex scoliosis who underwent spinal deformity correction with loss of neuromonitoring during surgery. We performed a literature review on perioperative management of complex spine deformity.

RESULTS

A 50-year-old man presented with lumbar pain and right L4 radiculopathy. Surgical intervention for deformity correction and decompression was indicated with T4-L4 posterior instrumentation L2/L3 and L3/L4 transforaminal lumbar interbody fusion. Surgery was aborted due to the loss of neuromonitoring. Postsurgery, the patient had left sensory deficit and the neurocritical care team clinically suspected and deduced the anatomic location of the spinal cord compression. Magnetic resonance imaging confirmed a T10-T11 hyperintensity suggestive of cord ischemia due to osteophyte compressing the spinal cord. The patient underwent a second corrective surgery with no intraoperative events and has no long-term neurological sequela.

CONCLUSIONS

This case illustrates that a comprehensive perioperative approach and individualized risk factor assessment is useful in complex spine deformity surgery. Further research is needed to determine how this individualized comprehensive approach can lead to intraoperative and postoperative countermeasures that improved spine surgery outcomes.

LEVEL OF EVIDENCE

Level V.