Femoral nerve neuromonitoring for lateral lumbar interbody fusion surgery

Prone Transpsoas Lumbar Interbody Fusion for Degenerative Disc Disease

Background

Prone transpsoas lumbar interbody fusion (PTP) is a newer technique to treat various spinal disc pathologies. PTP is a variation of lateral lumbar interbody fusion (LLIF) that is performed with the patient prone rather than in the lateral decubitus position. This approach offers similar benefits of lateral spinal surgery, which include less blood loss, shorter hospital stay, and quicker recovery compared with traditional open spine surgery. PTP offers additional benefits over traditional lateral positioning, with a more familiar patient position for spine surgeons, the ability to perform simultaneous posterior decompression and fusion without repositioning, and improved sagittal alignment.

Description

PTP is performed with the patient under general anesthesia and with use of somatosensory evoked potentials (SSEP) and electromyography (EMG) neuromonitoring. The patient is positioned prone with the aid of specialized patient positioners. Once the patient is positioned and draped, the disc space of interest is marked with use of fluoroscopic guidance. An incision is made, and blunt dissection is performed through the external oblique, internal oblique, and transversalis muscles. The psoas muscle is palpated, and dilators are placed at the target disc level under fluoroscopic guidance, with care taken to protect the peritoneum and lumbar plexus. Specialized retractors are then positioned. Anulotomy and disc removal, disc space preparation, trialing, and final interbody placement are performed. The procedure ends with obtaining hemostasis and closure of the incision.

Alternatives

Before surgery is performed, nonoperative treatment should be attempted, including the use of nonsteroidal anti-inflammatory drugs, physical therapy, and spinal injections. Surgical alternatives include posterior lumbar laminectomy with or without fusion, as well as other procedures in the anterior column, such as LLIF, anterior lumbar interbody fusion, oblique lumbar interbody fusion, transforaminal lumbar interbody fusion, and posterior lumbar interbody fusion. These alternatives must be considered, especially when working at the L4-S1 disc spaces, because of potential limitations to lateral surgery, such as in cases of high-riding iliac crests, a rising psoas, and previous abdominal surgery.

Rationale

Lateral spinal surgery evolved as a means to approach the anterior column of the spine in order to treat various spine disorders, such as degenerative disc disease, tumors, infection, and spinal deformity. With the PTP procedure, the patient is in the prone rather than the lateral decubitus position, which allows the psoas muscle to retract more posteriorly because it is under tension, pulling the lumbar plexus away from the target point of the procedure. In addition, the prone position results in improved sagittal alignment compared with the lateral position. With respect to sagittal alignment, the PTP procedure allows for more appropriate balancing, which improves clinical outcomes. The peritoneum is also farther away from the operative zone during PTP, providing a safer corridor away from the bowel and ureter. For these reasons, PTP can potentially lead to improved outcomes compared with a lateral procedure performed with the patient in the lateral decubitus position, while also minimizing the risk of bowel and bladder injury and neurapraxia. In addition, PTP eliminates the need for repositioning or staged procedures. For instance, posterior laminectomies and fusions can be efficiently performed with the patient in the prone position, possibly simultaneously with the PTP procedure, whereas repositioning and redraping would be required with a lateral approach.

Expected Outcomes

PTP has several advantages over traditional posterior spinal surgery. These include a shorter hospital stay, decreased blood loss, and faster return of mobility. Specifically compared with a lateral approach with the patient in the lateral decubitus position, PTP may result in better segmental lordosis and spinopelvic alignment. To date, overall outcomes are otherwise similar between lateral decubitus and prone transpsoas approaches.

Important Tips

Make sure to adjust the table to waist height and keep your elbows at 90° of flexion while working on localization of the disc space. When doing disc work through the retractor, either raise the bed or sit in a chair to make sure that the disc space is at eye level, so that you are not straining your neck.During dissection, utilize finger dissection and avoid the use of electrocautery as it can cause neurapraxia and result in flaccid oblique musculature and subsequent pseudohernia.To reduce the risk of peritoneal injury, a 2-incision technique can be performed: Place a finger in an accessory posterior incision (either a midline incision or the percutaneous screw incision) to initially palpate the tip of the transverse process. Next, slide your finger into the retroperitoneal space and feel the psoas medially. Place another finger through the lateral incision, and touch both fingers together to ensure you are in the retroperitoneal space with your dilators.Another trick is to start the incision more posteriorly, as gravity will force you more anteriorly during localization.When placing the cage, the goal is to have it as anterior as possible in order to gain maximal lordosis and to span the apophyseal ring to reduce the risk of subsidence. In addition, placement of the widest possible cage can help reduce subsidence, with 18-mm cages showing greater subsidence than 22-mm cages.

Acronyms and Abbreviations

PTP = prone transpsoas lumbar interbody fusionLLIF = lateral lumbar interbody fusionALIF = anterior lumbar interbody fusionOLIF = oblique lumbar interbody fusionTLIF = transforaminal lumbar interbody fusionMRI = magnetic resonance imagingNSAID = nonsteroidal anti-inflammatory drugCT = computed tomographyEMG = electromyographyAP = anteroposteriorK-wire = Kirschner wireIV = intravenousSSEP = somatosensory evoked potentials.

Transabdominal motor evoked potential neuromonitoring of lumbosacral spine surgery

BACKGROUND CONTEXT

Transcranial Motor Evoked Potentials (TcMEPs) can improve intraoperative detection of femoral plexus and nerve root injury during lumbosacral spine surgery. However, even under ideal conditions, TcMEPs are not completely free of false-positive alerts due to the immobilizing effect of general anesthetics, especially in the proximal musculature. The application of transcutaneous stimulation to activate ventral nerve roots directly at the level of the conus medularis (bypassing the brain and spinal cord) has emerged as a method to potentially monitor the motor component of the femoral plexus and lumbosacral nerves free from the blunting effects of general anesthesia.

PURPOSE

To evaluate the reliability and efficacy of transabdominal motor evoked potentials (TaMEPs) compared to TcMEPs during lumbosacral spine procedures.

DESIGN

We present the findings of a single-center 12-month retrospective experience of all lumbosacral spine surgeries utilizing multimodality intraoperative neuromonitoring (IONM) consisting of TcMEPs, TaMEPs, somatosensory evoked potentials (SSEPs), electromyography (EMG), and electroencephalography.

PATIENT SAMPLE

Two hundred and twenty patients having one, or a combination of lumbosacral spine procedures, including anterior lumbar interbody fusion (ALIF), lateral lumbar interbody fusion (LLIF), posterior spinal fusion (PSF), and/or transforaminal lumbar interbody fusion (TLIF).

OUTCOME MEASURES

Intraoperative neuromonitoring data was correlated to immediate postoperative neurologic examinations and chart review.

METHODS

Baseline reliability, false positive rate, true positive rate, false negative rate, area under the curve at baseline and at alerts, and detection of preoperative deficits of TcMEPs and TaMEPs were compared and analyzed for statistical significance. The relationship between transcutaneous stimulation voltage level and patient BMI was also examined.

RESULTS

TaMEPs were significantly more reliable than TcMEPs in all muscles except abductor hallucis. Of the 27 false positive alerts, 24 were TcMEPs alone, and 3 were TaMEPs alone. Of the 19 true positives, none were detected by TcMEPs alone, 3 were detected by TaMEPs alone (TcMEPs were not present), and the remaining 16 true positives involved TaMEPs and TcMEPs. TaMEPs had a significantly larger area under the curve (AUC) at baseline than TcMEPs in all muscles except abductor hallucis. The percent decrease in TcMEP and TaMEP AUC during LLIF alerts was not significantly different. Both TcMEPs and TaMEPs reflected three preexisting motor deficits. Patient BMI and TaMEP stimulation intensity were found to be moderately positively correlated.

CONCLUSIONS

These findings demonstrate the high reliability and predictability of TaMEPs and the potential added value when TaMEPs are incorporated into multimodality IONM during lumbosacral spine surgery.

Comprehensive Mapping and Dynamic Monitoring of the Temporal Branch of the Facial Nerve in Complex Cranial Reconstruction Surgery and Revision Cranioplasty

Facial nerve (FN) injury is a significant risk during complex cranial reconstruction surgeries, especially in revision cases where normal anatomy is distorted. The authors introduce a technique to mitigate FN injury, including preoperative FN mapping, intraoperative FN mapping, and continuous FN monitoring. Preoperative mapping uses a handheld ball-tip stimulator to elicit compound muscle action potentials (CMAP) in the frontalis muscle. Needle electrodes are placed above the orbital margin to record responses, starting at the stylomastoid foramen and extending until the entire temporal branch is mapped. Intraoperatively, continuous mapping is achieved using an electrified insulated suction device, allowing dynamic mapping during soft tissue dissection. Continuous monitoring involves placing stimulation electrodes near the stylomastoid foramen and recording CMAP responses from the frontalis and orbicularis oculi/orbicularis oris muscles. The authors tested this technique in 5 patients. The authors successfully mapped the temporal branch of the FN with isolated frontalis CMAP recordings in all patients. Intraoperative FN mapping and continuous monitoring were successfully performed in all cases. Two patients experienced complete cessation of FN CMAPs, which resumed upon loosening the tension on the myocutaneous flap held by fishhooks. One patient showed a 39% decrement in frontalis CMAP that did not recover. Despite these issues, all patients had intact FN function postoperatively and at follow-up. Our technique shows promise in mitigating FN injury during complex cranial reconstruction and cranioplasty revision surgery. Further research with a larger cohort is needed to confirm efficacy and statistical significance.

Female Sex and Supine Proximal Lumbar Lordosis Are Associated With the Size of the LLIF "Safe Zone" at L4-L5

STUDY DESIGN

Retrospective chart review.

OBJECTIVE

Identify demographic and sagittal alignment parameters that are independently associated with femoral nerve position at the L4-L5 disk space.

SUMMARY OF BACKGROUND DATA

Iatrogenic femoral nerve or lumbar plexus injury during lateral lumbar interbody fusion (LLIF) can result in neurological complications. The LLIF "safe zone" is the anterior half to two third of the disk space. However, femoral nerve position varies and is inconsistently identifiable on magnetic resonance imaging. The safe zone is also narrowest at L4-L5.

METHODS

An analysis of patients with symptomatic lumbar spine pathology and magnetic resonance imaging with a visibly identifiable femoral nerve evaluated at a single large academic spine center from January 1, 2017, to January 8, 2020, was performed. Exclusion criteria were transitional anatomy, severe hip osteoarthritis, coronal deformity with cobb >10 degrees, > grade 1 spondylolisthesis at L4-L5 and anterior migration of the psoas.Standing and supine lumbar lordosis (LL) and its proximal (L1-L4) and distal (L4-S1) components were measured. Femoral nerve position on sagittal imaging was then measured as a percentage of the L4 inferior endplate. A stepwise multivariate linear regression of sagittal alignment and LL parameters was then performed. Data are written as estimate, 95% CI.

RESULTS

Mean patient age was 58.2±14.7 years, 25 (34.2%) were female and 26 (35.6%) had a grade 1 spondylolisthesis. Mean femoral nerve position was 26.6±10.3% from the posterior border of L4. Female sex (-6.6, -11.1 to -2.1) and supine proximal lumbar lordosis (0.4, 0.1-0.7) were independently associated with femoral nerve position.

CONCLUSIONS

Patient sex and proximal LL can serve as early indicators of the size of the femoral nerve safe zone during a transpsoas LLIF approach at L4-L5.

Neuromonitoring Identifies Occlusion of Femoral Artery in STA-MCA Bypass Procedure: A Case Report

Intraoperative neurophysiological monitoring (IONM) is a technique used to assess the somatosensory and gross motor systems during surgery. While it is primarily used to detect and prevent surgically induced nervous system trauma, it can also detect and prevent injury to the nervous system that is the result of other causes such as trauma or ischemia that occur outside of the operative field as a result of malpositioning or other problematic physiologic states. We present a case study where a neuromonitoring alert altered the surgical procedure, though the alert was not correlated to the site of surgery. A 69-year-old male with a history of bilateral moyamoya disease and a left middle cerebral artery infarct underwent a right-sided STA-MCA bypass and encephaloduroarteriosynangiosis (EDAS) with multimodal IONM. During the procedure, the patient experienced a loss of motor evoked potential (MEP) recordings in the right lower extremity. Blood pressure was elevated, which temporarily restored the potentials, but they were lost again after the angiography team attempted to place an arterial line in the right femoral artery. The operation was truncated out of concern for left hemispheric ischemia, and it was later discovered that the patient had an acute right external iliac artery occlusion caused by a fresh thrombus in the common femoral artery causing complete paralysis of the limb. This case highlights the importance of heeding IONM alerts and evaluating for systemic causes if the alert is not thought to be of surgical etiology. IONM can detect adverse systemic neurological sequelae that is not necessarily surgically induced.

Elimination of Lumbar Plexus Injury by Changing the Entry Point and Traction Direction of the Psoas Major Muscle in Transpsoas Lateral Lumbar Spine Surgery

Background and Objectives: The lateral approach is commonly used for anterior column reconstruction, indirect decompression, and fusion in patients with lumbar degenerative diseases and spinal deformities. However, intraoperative lumbar plexus injury may occur. This is a retrospective comparative study to investigate and compare neurological complications between the conventional lateral approach and a modified lateral approach at L4/5. Materials and Methods: Patients with a lumbar degenerative disease requiring single-level intervertebral fusion at L4/5 were included and categorized into group X and group A. Patients in group X underwent conventional extreme lateral interbody fusion, while those in group A underwent a modified surgical procedure that included splitting of the anterior third of the psoas muscle, which was dilated by the retractor on the anterior third of the intervertebral disc. The incidence of lumbar plexus injury, defined as a decrease of ≥1 grade on manual muscle testing of hip flexors and knee extensors and sensory impairment of the thigh for ≥3 weeks, on the approach side, was investigated. Results: Each group comprised 50 patients. No significant between-group differences in age, sex, body mass index, and approach side were observed. There was a significant between-group difference in intraoperative neuromonitoring stimulation value (13.1 ± 5.4 mA in group X vs. 18.5 ± 2.3 mA in group A, p < 0.001). The incidence of neurological complications was significantly higher in group X than in group A (10.0% vs. 0.0%, respectively, p < 0.05). Conclusions: In our modified procedure, the anterior third of the psoas muscle was entered and split, and the intervertebral disc could be reached without damaging the lumbar plexus. When performing lumbar surgery using the lateral approach, lumbar plexus injury can be avoided by following surgical indication criteria based on the location of the lumbar plexus with respect to the psoas muscle and changing the transpsoas approach to the intervertebral disc.

Confirming a C5 Palsy with a Motor Evoked Potential Trending Algorithm during Insertion of Cervical Facet Spacers: A Case Study

The use of cervical facet spacers has shown favorable clinical results in the treatment of cervical spondylotic disease; however, there are limited data regarding neurological complications associated with the procedure. This case report demonstrates the specificity of multi-myotomal motor evoked potentials (MEPs) in detecting acute postoperative C5 palsy following placement of facet spacers. A posterior cervical fusion with decompression and instrumentation involving DTRAX (Providence Medical Technology; Lafayette, CA) was used to treat a patient with cervical stenosis and myelopathy. Intraoperative neurophysiological monitoring (IONM) consisting of MEPs, somatosensory evoked potentials (SSEPs), and free-run electromyography (EMG), was used throughout the procedure. Immediately following the placement of the DTRAX spacers at C4-5, a decrease in amplitudes from the right deltoid and biceps MEP recordings (>65%) was detected. All other IONM modalities remained stable; it is noteworthy that there was an absence of mechanically elicited EMG. A novel post-alert regression analysis trending algorithm of MEP amplitudes confirmed the visual alert. This warning along with an intraoperative computed tomography (CT) scan of the cervical spine subsequently resulted in the decision to remove one of the facet spacers. Surgical intervention did not result in recovery of the aforementioned MEP recordings, which remained attenuated at the time of wound closure. Postoperatively, the patient exhibited an immediate right C5 palsy (2/5). A post-surgery application of the trending algorithm demonstrated that it correlated to the visual alert until the end of monitoring.

Postoperative Femoral Nerve Palsy and Meralgia Paresthetica after Gynecologic Oncologic Surgery

Femoral nerve palsy and meralgia paresthetica following gynecologic cancer surgery are rare, but severe and long lasting. Here, we aimed to study their incidence, severity, possible risk factors and its time to remission. Between January 2008 and December 2017 976 gynecologic cancer patients were identified in our institutional database receiving surgery. Complete patient charts were reviewed retrospectively. Possible risk factors were analyzed by Fisher’s exact test. 441 (45.18%) out 976 were treated for Ovarian cancer. In total 23 patients were identified with a postoperative neurological leg disorder. A femoral nerve palsy was present in 15 patients (1.5%) and a meralgia paresthetica in 8 patients (0.82%). Three patients showed both disorders. Duration of surgery (p = 0.0000), positioning during surgery (p = 0.0040), femoral artery catheter (p = 0.0051), prior chemotherapy (p = 0.0007), nicotine abuse (p = 0.00456) and prior polyneuropathy (p = 0.0181) showed a significant association with a postoperative femoral nerve palsy. Nicotine abuse (p = 0.0335) and prior chemotherapy (p = 0.0151) were significant for the development of a meralgia paresthetica. Long lasting surgery, patient positioning and femoral arterial catheter placement are risk factors for a postoperative femoral nerve palsy in gynecologic cancer surgery. Polyneuropathy, nicotine abuse, and prior chemotherapy are predisposing risk factors for a femoral nerve palsy and a meralgia paresthetica. A resolution of symptoms is the rule for both disorders within different time schedules.

L4 Corpectomy: Surgical Approaches and Mitigating the Risk of Femoral Nerve Injuries

OBJECTIVE

Because of the challenging anatomic location, corpectomies are performed less often at the fourth lumbar vertebral body than at other levels. Our objective was to review the literature of L4 corpectomy and anterior column reconstruction.

METHODS

A literature search in the Medline/PubMed database was conducted following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to identify all relevant cases and cases series describing corpectomies of the L4 vertebral body using "lumbar" AND "corpectomy" as search terms. We present an illustrative case to describe the technique.

RESULTS

We identified 18 articles with 30 patients who met the search criteria. Including our case illustration, the most common approach used was the lateral retroperitoneal approach (n = 17, 54.8%), of which 8 (26.7%) were performed via a transpsoas approach. Seven (23%) patients underwent corpectomy through a posterior approach, 4 (12.9%) through an anterior retroperitoneal approach, and 3 (10%) through combined anterior and lateral retroperitoneal. The overall complications rate was 19.3% including 1 case each of femoral nerve injury and iatrogenic lumbar nerve root injury.

CONCLUSIONS

Corpectomies of the L4 vertebral body are challenging. None of the various approaches described clearly demonstrates any superiority in mitigating the risk of neural complications. Decision making about which surgical approach to use should be based on patient-specific characteristics.