A Mobile Outside-in Technique of Transforaminal Lumbar Endoscopy for Lumbar Disc Herniations

Summary

Here we present a protocol of a novel outside-in technique of transforaminal endoscopic discectomy for lumbar disc herniations. The technical aspects of the technique, the wide indications of use, and the results of the treatment in 184 patients are described in detail.

Abstract

Percutaneous endoscopic transforaminal lumbar discectomy (PETLD) has now become a standard of care for the management of lumbar disc disease. There are two techniques for the introduction of a working cannula with respect to disc—outside-in and inside-out. The aim of this prospective study is to describe the technical aspects of a novel mobile outside-in method in dealing with different types of disc prolapse. A total of 184 consecutive patients with unilateral lower limb radiculopathy due to lumbar disc prolapse were operated on with the mobile outside-in technique of PETLD. Their clinical outcomes were evaluated based on the type of disc prolapse they had, a visual analog scale (VAS) leg pain score, the Oswestry Disability Index (ODI), and the Macnab criteria. The completeness of the decompression was documented with a postoperative magnetic resonance imaging. The mean age of the patients was 50 ± 16 years and the male/female ratio was 2:1. The mean follow-up was 19 ± 6 months. A total of 190 lumbar levels were operated on (L1–L2: n = 4, L2–L3: n = 17, L3–L4: n = 27, L4–5: n = 123, and L5–S1: n = 19). Divided into types, the patient distribution was central: n = 14, paracentral: n = 74, foraminal: n = 28, far lateral: n = 13, superior-migrated: n = 8, inferior migrated: n = 38, and high canal compromise: n = 9. The mean operative time was 35 ± 12 (25 - 56) min and the mean hospital stay was 1.2 ± 0.5 (1–3) days. The VAS score for leg pain improved from 7.5 ± 1 to 1.7 ± 0.9. The ODI improved from 70 ± 8.3 to 23 ± 5. According to the Macnab criteria, 75 patients (40.8%) had excellent results, 104 patients (56.5%) had good results, and 5 patients (2.7%) had fair results. Recurrence (including early and late) was seen in 15 out of the 190 levels that were operated on (7.89%). This article presents a novel outside-in approach that relies on a precise landing within the foramen in a mobile manner and does not solely depend upon the enlargement of the foramen. It is more versatile in application and useful in the management of all types of disc prolapse, even in severe canal compromise and high migration.

Introduction

Chronic low back pain and leg pain are common ailments in any society. The treatment modalities to combat degenerative lumbar disc diseases have been continuously evolving. The armamentarium has been wide, from open surgery and fixation to microlumbar discectomy, and now the endoscopic route^1,2,3,4. The transforaminal pathway, initially suggested by Parvez Kambin, is now gradually becoming a standard of care^5,6,7. The advantages of full-endoscopic spine surgeries are less soft-tissue dissection, less blood loss, reduced hospital admission days, an early functional recovery, and an enhancement in the quality of life⁸.

The traditional outside-in approach of PETLD, given by Schubert and Hoogland⁴, deals with the introduction of a working cannula in the foramen and then an enlargement of the foramen by using reamers. The rationale behind the novel technique of the outside-in approach mentioned here is that it does not solely depend on enlarging the foramen in all cases. The technique focuses on the precise placement of the working cannula within the foramen and then guiding the movement of the cannula toward the target fragment, under endoscopic vision^9,10. Anatomically, there are three different routes into the transforaminal space, and if used effectively, percutaneous endoscopic spine surgery with the outside-in technique can be applied to a wider range of lumbar disc herniation. Central, paracentral, and high canal compromised Lumbar Disc Herniation (LDH) is approached by the intervertebral route; foraminal, superiorly migrated, and far lateral LDH is approached by the foraminal route, and inferiorly migrated LDH is approached by the suprapedicular route⁶. The advantage of this technique is that it preserves the normal anatomical structures with less discal injury, the epidural exposure is easy, and the manipulation of a working cannula in the foramen is not difficult. The technique described differs from the earlier one because it provides a precise vision of the structures within the foramen and focuses on the accurate placement of the cannula within the foramen, rather than on enlarging the foramen. The technique is equally safe as inside-out technique and provides an easy handling of structures, especially the extruded fragments. The goal of this study is to prove the versatility of this novel approach in managing different types of disc prolapse as central, paracentral, foraminal, far lateral, and up and down migration, and in high-canal compromise cases. The technique, however, demands a longer learning curve and so beginners need to be patient while learning.

Protocol

The protocol follows the guidelines of Nanoori Hospital's human research ethics committee. A written informed consent was obtained from all the patients with unilateral lower limb radiculopathy due to lumbar disc prolapse. The exclusion criteria were the presence of segmental instability, spondylolisthesis (more than grade 1), and the presence of significant spinal stenosis.

1. Patient Position and Skin Marking

1. Place the patient in the prone position on the radiolucent operating table with the spine in slight flexion.
   NOTE: Indications for surgery in patients are as follows: intractable, frequently unilateral radiculopathy resistant to conservative measures (for at least 6–8 weeks), with or without associated axial back pain, a positive tension sign on physical examination, and radiculopathy correlating with radiographic evidence on confirmatory MRI studies.
2. Mark the midline of the spine, as well as the extent of the iliac crest, with a marking pen under an image intensifier.
3. Mark the paraspinal skin entry point along the center of the disc space using the manual back assessment method⁶: check the borderline between the back muscles and the abdominal muscles. Mark the skin entry points just medial to this borderline in mid-disc level both in Antero-Posterior (AP) and lateral X-rays.

2. Local Anesthesia and Incision

1. Infiltrate subcutaneous local anesthetic (2 mL of 1% lidocaine) around the entry point and then perform the skin incision of about 1 cm and infiltrate the trajectory with the local anesthetic (3 mL of 1% lidocaine) through a 23 G needle.
2. Insert an 18 G spinal needle through the skin incision at a 25–35° angle to horizontal.
3. Pass the needle under the image intensifier through the fascia and the back muscles. Then, dock the needle at Kambin's triangle near the intervertebral disc.
   NOTE: Kambin's triangle is present at the posterolateral aspect of the disc. The hypotenuse is the exiting nerve root, the base is the superior border of the inferior vertebra, and the height is the thecal sac/traversing nerve root.
4. Check the free epidural space in Kambin's triangle by injecting 1.5 mL of contrast dye under the image intensifier. Provide local anesthesia in Kambin's triangle by injecting 8–10 mL of 1% lidocaine in the foraminal space followed by a booster injection of 2–4 mL of 1.6% lidocaine (8 mL of 2% lidocaine with 2 mL of saline plus 0.05 mL of epinephrine) 4–5 min after the initial injection.

3. Discography

1. Insert the needle in the discal space under fluoroscopy and perform discography by injecting 2 mL of 0.8% indigo carmine mixed with contrast.

4. Insertion of Endoscope

1. Insert a guide wire in the discal space through the needle and then remove the needle.
2. Through the inserted guide wire, slide the obturator in Kambin's triangle and anchor it over the surface of the disc space.
3. Insert the working cannula through the obturator and, thereafter, introduce the endoscope into the Kambin's triangle.
   NOTE: The working cannula is the beveled type with an 8 mm outer diameter. The endoscope has a 30° viewing angle, a 7.3 mm outer diameter, a 4.7 mm-diameter working channel, and 251 mm of total length. The entire procedure is performed using constant saline irrigation.

5. Surgical Procedure

1. Observe the epidural fat and soft tissues in the Kambin's triangle through the endoscope prior to the entry into the disc (Figure 1A).
2. Clear the soft tissue and blood vessels over the annulus using the radiofrequency coagulator. Perform the annular fenestration with an annular cutter and enter the annulus under endoscopic vision.
   NOTE: To avoid any injury to the exiting and traversing nerve root during the approach, the operation proceeds with continuous feedback from the patient.
3. Obtain a half-and-half view of the epidural space and the disc space by inserting the bevel type of the cannula in the fenestrated annulus.
   NOTE: In the dorsal half of the half-and-half, the posterior longitudinal ligament, the epidural space, and the traversing nerve root and dura can be seen. In the ventral half, the annulus and the disc ventral to the posterior longitudinal ligament can be seen.
4. Lever the working cannula downwards to achieve an exact half-and-half view⁷ (Figure 2A and 2B).
   NOTE: Using the bevel-type working cannula, it is not easy for beginners to manipulate the exiting nerve root safely, so a round working cannula can also be used (Figure 3).

6. Targeted Fragmentectomy

1. After decompressing the protruded disc sufficiently, change the trajectory of working toward the symptomatic disc area.
   NOTE: The working channel is directed toward the suprapedicular notch in the inferior-migrated disc, the epidural space in the high-canal compromised disc and foraminal space in the superior-migrated disc (Figure 3).
2. Confirm that all free fragments of the disc are removed by checking the free-floating dural sac, the exiting root, and the traversing root, and free the epidural space by rotating the working channel and the endoscope.
   NOTE: All patients undergo MRI on the day following the surgery (Figure 4 and Figure 5).

Results

Outcome Evaluation:

The outcome of the surgery was measured by the VAS leg pain score¹¹, the ODI¹², and the Macnab criteria¹³. These were measured in the preoperative period and during follow-up visits (1 week after the surgery, 3 months after the surgery, and at the last follow-up).

Discussion

The study is based on the prospective analysis of 184 patients with lumbar disc disease that were managed at our institute. X-ray imaging, computed tomography (CT), and magnetic resonance imaging (MRI) were done in all cases to confirm the diagnosis and to rule out other pathologies. The findings demonstrated on the CT and MRI scans were correlated with a neurologic examination. After the proper diagnosis, patients were operated on with the mobile outside-in technique of PETLD. The exclusion criteria were the presence of...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Contrast dye injection	Iobrix injection, Taejoon pharm,Seoul, Korea	S.No. 1
0.8% indigo carmine	Carmine, Korea United Pharmaceutical, Yoenki, Korea	S.No. 2
30° endoscope	Joimax GmbH, Germany	S.No. 3
Radiofrequency coagulator	Elliquence, New York, USA	S.No. 4
Drill	Primado 2 NSK, Tochigi, Japan	S.No. 5