Transtubular Endoscopic Posterolateral Decompression for L5-S1 Lumbar Lateral Disc Herniation

Summary

Presented here is a novel technique of C-arm free transtubular posterolateral decompression for lumbar foraminal stenosis and lateral disc herniation under O-arm navigation.

Abstract

We report a novel technique for C-arm free transtubular L5 nerve decompression under CT-based navigation to reduce the radiation hazard. This procedure is performed under general anesthesia and neuromonitoring. The patient is placed in a prone position on an operating carbon table. A navigation reference frame is placed percutaneously into the contralateral sacroiliac joint or spinous process. Then, CT scan images are obtained. After instrument registration, the L5-S1 foraminal level is confirmed with a navigated probe, and the entry point is marked. Using an approximately 2 cm skin incision, the subcutaneous tissue and muscles are dissected. The navigated first dilator is aimed at the L5-S1 Kambin's triangle, and sequential dilation is performed. The 18 mm tube is used and fixed to the frame. The bone around the Kambin's triangle is removed with a navigated burr. For lateral disc herniation, the L5 nerve root is identified and retracted, and the disc fragment is removed. The navigation-guided tubular endoscopic decompression is an effective procedure. There is no radiation hazard to the surgeon or the operating room staff.

Introduction

Diagnosis and surgeries for lumbar foraminal stenosis (LFS) and lumbar lateral disc herniation (LLDH) at the L5-S1 level are challenging for spine surgeons because of this level's unique structure¹. The iliac crest, broad L5 transverse process (TP), small space between the sacral ala and the L5 TP, and osteophytes make the operating window very narrow². If the bony resection is not enough, inadequate decompression to the L5 nerve root may lead to residual symptoms. Massive bony removal causes postoperative instability. These issues limit surgeons' competencies with foraminal/extraforaminal L5 root decompression. Several reports have shown good results with minimally invasive spine surgeries, such as microscopic or endoscopic procedures in this area to decompress the L5 nerve root^3,4. Recently, the use of navigation for foraminal decompression of the L5 root has been reported with good surgical outcomes⁵.

Fully endoscopic discectomy is becoming popular for removing lateral lumbar disc herniation⁶. Furthermore, microendoscopic procedures in combination with navigation can help the surgeon to decompress the L5 root with precision². Usually, these techniques require intraoperative C-arm usage. The goal of this method is to decompress the L5 root precisely with minimum bony resection without a C-arm.

The indications for this technique are extraforaminal lumbar disc herniation and herniation/stenosis of the lateral half of the foraminal lumbar disc. The contraindications are herniation/stenosis of the medial one-third of the foraminal lumbar disc because the scope cannot reach the targeted area².

Protocol

This study was approved by the ethics committee of Okayama Rosai Hospital (No. 305).

1. Patient history taking

1. Ensure that the patient has a herniated disc that causes severe sciatica. Usually, the patient will have a history of some prodromal low back pain. They may correlate their symptoms with an episode of trauma.
2. Ask the patient to describe their radiating leg pain, including its location. Also ask them about the activities that make it better or worse when LFS or LLDH is suspected.

2. Physical examination

1. To determine the nerve level, check for the signs of the loss of sensation and weakness in the leg.
2. Perform a range of lumbar motion tests by asking the patient to bend forward and backward.
   1. Check for the induction of low back pain in the patient with a herniated disc when forward bending is done.
   2. Elevate the patient's leg in a supine position. If the angle between the bed and the leg is less than 70° due to sciatica, this is a strong suggestion that the patient has a herniated disc, which means the straight leg raise (SLR) test is positive.
      NOTE: The SLR test is very useful to distinguish between lumbar canal stenosis (SLR-) and lumbar disc herniation (SLR+).
3. Perform deep tendon reflex, and check muscle weakness in the patient.
4. Perform the Kemp test⁷. Fix the patient's opposite ilium from the side being tested with one hand in a standing position. Grab the patient's shoulder with the other hand and lead the patient to extension, ipsilateral side bending, and rotation.
   NOTE: LFS is characterized by exacerbation with foraminal narrowing caused by lumbar extension (Kemp's sign)⁷. If the Kemp test is positive, foraminal nerve compression by disc herniation or stenosis is likely.

3. Evaluation of radiograms (XP) and magnetic resonance imaging (MRI)

1. Perform anteroposterior and lateral radiography in a standing position to check lumbar deformity and spondylolisthesis. If the patient has severe deformity, spinal fusion is indicated.
2. Perform functional radiography in a standing position. Check the functional radiograms to confirm lumbar instability by measuring vertebral abnormal movement (Figure 1A, B).
   NOTE: If there is severe instability that indicates more than 10° or more than 3 mm slip at the L5-S1 level, L5-S1 fusion should be considered.
3. Perform MRI to accurately assess the nerve compression site.
   1. For lateral lumbar disc herniation (LLDH), take a coronal T2 weighted image to identify the location of the herniated disc (Figure 1C-E).

Figure 1: Preoperative radiograms and MRI. (A) Lateral extension radiogram, (B) Lateral flexion radiogram, (C) Parasagittal T2 weighted MRI image, (D) Coronal T2 weighted MRI image, (E) Axial T2 weighted MR imaging at the L5-S1. The arrow indicates FLDH. Please click here to view a larger version of this figure.

4. Evaluation of computed tomography (CT) and MRI-CT fusion images

1. Perform CT to check if there is a calcified disc (Figure 2A, D) or foraminal osteophyte (Figure 2B, C) not by the disc.
2. Take an MRI-CT fusion image to understand the exact 3D location of the herniated disc (Figure 3).

Figure 2: Preoperative CT. (A,B) Parasagittal reconstruction CT, (C) Coronal reconstruction CT, (D) Axial CT at L5-S1. The white arrows indicate calcified FLDH; a black arrow shows an osteophyte. Please click here to view a larger version of this figure.

Figure 3: CT MRI fusion images. (A) Posterior view, (B) Posterolateral view. The white arrow indicates FLDH. Please click here to view a larger version of this figure.

5. Patient positioning and neuromonitoring (NM)

1. Provide general anesthesia to the patient.
2. Then, place the patient in a prone position on a carbon table.
3. Ensure that the patient's eyes are not compressed with a special face cover. Pay attention to the bolster position not to compress the abdomen of the patient.
4. Perform neuromonitoring using a multi-modality intraoperative monitoring system that assesses spinal cord integrity and provides a warning of potential harm to critical neural pathways (Figure 4A).Transcranial motor evoked potentials (MEPs) generate a stimulus at the motor cortex.
   1. Use recording electrodes to measure the signals at predetermined peripheral upper and lower extremity muscle group sites.
      NOTE: If neuromonitoring is used, nerve decompression is also confirmed with this. For a muscle of which the innervated nerve is decompressed adequately, the amplitude of the MCV usually increases.

6. Intraoperative CT scan and spinal navigation

1. Place a navigation reference frame (RF) percutaneously into the spinous process or sacroiliac joint. Obtain intraoperative CT scan images with a mobile CT scanner (Figure 4B).
2. Transmit the CT 3D images to the navigation system automatically using a cable (Figure 4C).

Figure 4: Neuromonitoring, O-arm, and navigation. (A) Neuromonitoring, (B) O-arm, (C) Navigation. Please click here to view a larger version of this figure.

7. Navigated instrument registration

1. Register the navigated pointer, dilater, and high-speed burr by tapping the tip to the RF hole manually. Then, perform the accuracy check by touching the bony surface.

8. Incision and muscle dissection

1. With the help of a navigated pointer, confirm the location of the L5-S1 foraminal level by a 50-60 mm extended image from the pointer tip and mark the entry point for the skin incision (Figure 5A).
2. Make an approximately 2 cm longitudinal skin incision, and then dissect the subcutaneous tissue, lumbar iliocostalis, and multifidus muscle along the muscle fibers.
3. Dock the navigated first dilator at the base of the L5 transverse process using a navigation system (Figure 5B). Then, insert the sequential dilators (5.3 mm, 9.4 mm).
4. Insert the final tube (14 mm) and fix it to the flexible arm assembly firmly (Figure 5C). Confirm the position of the tube with a navigation system and the anatomy through endoscopy.

Figure 5: Skin incision and sequential dilation. (A) Navigated pointer, (B) Navigation monitor, (C) Tubular retractor. Please click here to view a larger version of this figure.

9. Bone resection with the navigated high-speed burr

1. Check the level with the navigated probe. Check the L5-S1 level with a navigated pointer in the navigation monitor.
2. Remove the bone at the lower base of the transverse process and the lateral part of the facet joint with a navigated high-speed burr or conventional high-speed burr (Figure 6).
   NOTE: Further surgical steps are planned according to the disc herniation or canal stenosis.
3. In the case of canal stenosis, remove the bony element that compresses the nerve root completely.
   CAUTION: Before using the navigated instruments, the surgeon should check the accuracy of navigation because sometimes the reference frame is moved.

Figure 6: Navigated high-speed burr. (A,B): Intraoperative image, (B): Navigated high-speed burr. Please click here to view a larger version of this figure.

10. Endoscopic disc resection

1. For LLDH, identify the L5 nerve root and retract cranially by a nerve retractor. Then, remove the disc fragment using pituitary forceps carefully.
2. In the case of LFS, widen the L5 foramen using a navigated high-speed burr under navigation guidance.
3. Remove every compressing soft tissue and bony element by pituitary forceps and Kerrison rongeurs. Identify the L5 root by its surrounding perineural fat and vessels (Figure 7).

Figure 7: Nerve root decompression. (A) Endoscope image; identifying and decompressing the L5 root (white arrow); the inter-vertebral foramen is widened by burring down the osteophytes with the help of a navigated burr. (B) Navigation monitor; during operation, the surgeons can view the one monitor indicating four pieces of information simultaneously: the surgical field, intraoperative neuromonitoring, intraoperative navigation, and microendoscope view. Please click here to view a larger version of this figure.

11. Skin closure

1. After irrigation with saline water to remove the debris, place a wound suction tube at L5-S1.
2. Then, close the skin with an absorbable suture.
3. Postoperatively, remove the drain after 48 h.
   NOTE: Postoperative images are shown in Figure 8.

Figure 8: Postoperative images. (A) Axial CT image at L5-S1, (B) Parasagittal reconstruction CT, (C) Axial T2 weighted MR imaging at L5-S1. The white arrows indicate the decompression area. Please click here to view a larger version of this figure.

Representative Results

Eight cases (four men, four women) underwent surgery using this new technique. The average age was 72.0 years, and the average follow-up period was 1.5 years. There were five patients with L5/S1 foraminal stenosis, two patients with L5/S foraminal disc herniation, and one patient with L3/4 foraminal disc herniation. We could perform all surgeries without a C-arm. The average surgical time and blood loss were 143 min ± 14 min and 134 ± 18 mL, respectively.

The average recovery percentage obtained using the Japanese orthopedic association (JOA) score (back pain evaluation)⁸ was 72.3% (57%-88%). The visual analog scale (VAS) for leg pain was reduced from 63 mm to 12 mm on average. There were no surgical complications. None of the patients needed a revision surgery due to residual pain (Table 1).

Man	4
Woman	4
Age (year)	43-82 (average 72.0)
Surgical time (min)	143 +/- 14
Intraoperative blood loss (mL)	134 +/- 18
JOA recovery (%)	57-88 (average 72.8)
Complication	No

Table 1: Representative results of navigational decompression at L5-S1.

Discussion

L5 radicular symptoms are caused mainly by L4-L5 disc herniation or stenosis. These symptoms may also occur due to L5 lumbar foraminal stenosis or L5-S1 lateral lumbar disc herniation (LLDH)⁹. Of all the symptomatic lumbar disc herniations, L5-S1 FLDH accounts for approximately 3%¹⁰. For L5-S1 foraminal lesions, a posterolateral or transforaminal approach is recommended. For this approach, there are three main techniques, such as the microscopic, tube with endoscopic, and fully endoscopic approaches. Microendoscopic lumbar discectomy (MED) with a tube was introduced by Foley in 1997¹¹. This MED system uses a 16 mm or 18 mm tube with a small endoscope. Recently, spinal navigation has become more popular due to advanced technology¹². However, spinal navigation has been applied mainly for spinal fusion¹³ because the bony structure is easily recognized in the navigation monitor.

Endoscopic-assisted decompression for lumbar canal stenosis was first reported in 2007¹⁴. With this technique, the central canal stenosis was decompressed through a unilateral approach with a 25° angled scope. Lateral lumbar disc herniation was also treated with endoscopically assisted open removal¹⁵. However, C-arm is mandatory to approach to the exact location with these techniques.

With the microscopic decompression technique for LLDH, the skin incision is relatively long, and foraminal disc herniation is difficult to remove because it does not have adequate angle scope. The image quality of the microscope is very clear, but the instruments may disturb the surgical field compared with the endoscopic procedure. The significant removal of the facet joint may lead to postoperative spinal instability and may further accelerate the rate of degeneration¹⁶. On the contrary, limiting the bony removal to prevent instability may end up in inadequate nerve root decompression. Among them, the fully endoscopic transforaminal approach to L5-S1 foramen is one of the best options for these lesions because of its minimal invasiveness⁶. However, this technique has a steep learning curve, the navigation is not available, and a high iliac crest may disturb the transforaminal approach¹⁷.

With our new technique, O-arm navigation gives the minimally invasive surgeons 3D image guidance and, thus, helps in the accurate removal of bony elements. The minimum facet resection avoids additional postoperative spinal instability². Specifically, the use of the navigated burr helps real-time dynamic feedback during the resection of the bony spur. Another advantage is that this novel technique is performed only under navigation guidance, so there is no need to use a C-arm during surgery. We use a small field of view (FOV) and low-resolution mode, so one CT scan time is less than 30 s. The radiation per second of an O-arm 3D scan is four times that of fluoroscopy, so one O-arm scan is equivalent to approximately 1.5 min of fluoroscopy according to the radiation measurement¹².

There are several critical steps in our new technique. Firstly, the first navigated dilater should not be inserted too deep because it has a relatively small diameter and so might injure the L5 nerve root. Secondly, if the patient has severe symptoms, the L5-S1 foraminal area must be very narrow. So, adequate bony resection is necessary before removing the herniated disc materials. Finally, the most important step within the protocol is that a navigated pointer should be used frequently to check the location to not remove too much bony resection. If there is a concern that the navigational accuracy is compromised during surgery, another O-arm scan should be taken.

Some modifications of this technique are available. A fully endoscopic decompression can be also performed if a long navigated pointer and a navigated high-speed burr are made. For cervical disc herniation, keyhole foraminotomy with a tubular retractor and navigation is very useful technique. With this technique, the authors performed C-arm free navigated percutaneous vertebral biopsy¹³.

There are several limitations of the procedure. Herniation/stenosis of the medial one-third of the lumbar disc are relative contraindications for this technique because the scope cannot reach the targeted area. Another limitation is the additional stab incision for the application of the navigation reference frame. The accuracy of navigation may be compromised due to movement of the reference frame; a new scan may be needed insuch a situation.

Materials

Name	Company	Catalog Number	Comments
1488 HD 3-Chip camera system	Stryker	1000902487
16mm Endoscope Attachment, Sterile	Medtronic	9560160
18mm Endoscope Attachment, Sterile	Medtronic	9560180
4K 32" surgical display	Stryker	0240-031-050
Adjustable hinged operating carbon table	Mizuho OSI	6988A-PV-ACP	OSI Axis Jackson table
L10 AIM light source	Stryker	1000902487
METRx MED System Endoscope, Long	Medtronic	9560102
METRx MED System Reusable Endoscope	Medtronic	9560101	Metrx
METRx MED System Reusable Endoscope	Medtronic	9560101 M
METRx MED System Reusable Endoscope, Long	Medtronic	9560102
Navigated high speed bur	Medtronic	EM200N	Stelth
Navigated passive pointer	Medtronic	960-559
NIM Eclipse system	Medtronic	ECLC	Neuromonitouring
O-arm	Medtronic	224ABBZX00042000	Intraoperative CT
Stealth station navigation system Spine 7R	Medtronic	9733990	Navigation
Surgical Carts	Stryker	F-NSK-006-00
Tubular Retractor, 16mm	Medtronic	955-524
Tubular Retractor, 16mm, Long	Medtronic	9560216
Tubular Retractor, 18mm	Medtronic	9560118
Tubular Retractor, 18mm, Long	Medtronic	9560218