Full-Endoscopic Translaminar Decompression for Lumbar Foraminal Stenosis Using a 5.2-mm Working Channel Endoscope: A Short-Term Clinical Report

Kento Takebayashi; Hiroki Iwai; Hirohiko Inanami; Hisashi Koga

doi:10.21182/jmisst.2024.01830

Abstract

This report examined the short-term clinical outcomes of full-endoscopic translaminar decompression for lumbar foraminal stenosis using a 5.2-mm working channel endoscope. Eighteen patients treated between January and December 2023 were retrospectively analyzed. The mean operative time was 60.7 minutes, and the mean length of hospital stay was 3.3 days. Preoperative and 3-month postoperative leg pain, assessed by the Numerical Pain Rating Scale, improved markedly, with the mean score decreasing from 6.7 to 1.8 postoperatively. No complications such as dural injury, hematoma, or iatrogenic instability were observed. The modified technique offers the advantage of shorter operative time, which is achieved by using high-torque drills and large forceps. Caution must be exercised to prevent iatrogenic instability due to excessive bone resection. Further research is required to validate the long-term efficacy and safety of this treatment strategy. Nonetheless, utilizing a 5.2-mm working channel endoscope for translaminar decompression appears to be a promising option for the treatment of lumbar foraminal stenosis.

Key Words: Minimally invasive, Endoscopy, Lumbar vertebrae, Spinal stenosis

INTRODUCTION

Lumbar foraminal stenosis can be treated with full-endoscopic spine surgery (FESS) via the posterolateral (PLA) or translaminar (TLA) approach. Initially, TLA using a 4.1-mm working channel endoscope posed challenges, such as longer operative times and limited tool availability for bone removal and yellow ligament resection [1-4]. To overcome these hurdles, a slightly wider diameter endoscope with a 5.2-mm working channel, which is commonly used for lumbar spinal canal stenosis, has been adapted for the treatment of foraminal stenosis. This report outlines the short-term clinical outcomes associated with this approach.

MATERIALS AND METHODS

1. Indication

The TLA is particularly suitable for treating foraminal stenosis from the medial part of the foramen at the L5–S1 level because the transverse diameter of the foramen is anatomically elongated, presenting relative difficulty. Additionally, the iliac crest often hampers disc puncture, which is the initial step in the PLA. We conducted a retrospective analysis of 18 cases involving TLA for lumbar foraminal stenosis using a 5.2-mm working channel endoscope between January and December 2023. The parameters evaluated included operative time, hospital stay, local disc wedging angle (assessed using radiography), preoperative and 3-month postoperative leg pain (assessed using the Numerical Rating Scale [NRS]), and complications.

2. Surgical Procedure

Patients under general anesthesia were positioned prone, with reversed muscle relaxants, and motor-evoked potential (MEP) monitoring was initiated. A 10-mm skin incision was made 15–20 mm lateral to the midline, using a fluoroscope to ensure accurate positioning.

The obturator was positioned on the dorsal surface of the lamina. Because fenestration is mainly performed in the isthmus of the lamina, the obturator was inserted parallel to the endplate at the level of the foramen while monitoring lateral fluoroscopy. A 10-mm diameter working sheath was placed at the deepest insertion site at a 30° angle (Figure 1A and B). Subsequently, an endoscope with a working channel diameter of 5.2 mm is introduced (TOKIBO Co., LTD, Tokyo, Japan). Water pressure is set as in normal FESS.

After inserting the endoscope, forceps and a bipolar radiofrequency electrode system (Elliquence, Baldwin, NY, USA) were used to expose the lamina isthmus. The instrument positioning was confirmed using a lateral fluoroscopic view. If anatomical orientation is difficult to obtain, anterior-posterior fluoroscopic view should be reviewed as appropriate. The lamina was thinned using a 3.5-mm diameter (NSK-Nakanishi Japan, Tokyo, Japan) diamond bar on a high-speed drill. The area of bone resection should be approximately 10 mm × 10 mm instead of focusing on a single deep point. Severe degeneration may require drilling of the tip of the inferior articular process of the rostral lamina. After exposing the inner cortical bone of the lamina, resection of the inner cortical bone began at the site covering the superior articular process to provide guidance and ensure safe progression (Figure 2A). The yellow ligament of the dorsal foramen was detached from the attachment of the cephalocaudal lamina and resected with a Kerrison rongeur (Figure 2B). After the removal of the yellow ligament, the nerve root was visible (Figure 2C). In cases requiring discectomy, as much of the disc as possible was removed.

The procedure ended upon confirming nerve root decompression from the center to the periphery. Decompression of the nerve root may increase MEP responses in the corresponding nerve root region. No drains were placed, and bed rest was discontinued three hours after surgery. The patient was discharged on the following day. Preoperative magnetic resonance imaging (Figure 3A and B) and postoperative computed tomogarphy demonstrating the extent of bone removal in the right L5–S1 foraminal stenosis (Figure 4A–C) are shown.

RESULTS

Of the 18 patients, 16 were men and two were women (mean age, 72.2 years). The operative levels were L4–5 in three cases and L5–S1 in 15 cases. The mean local disc wedging angle was 1.3°. The mean operative time was 60.7 minutes; blood loss was negligible in all patients. The mean length of the hospital stay was 3.3 days. No complications such as dural injury, hematoma, or iatrogenic instability were observed. The mean preoperative and 3-month postoperative NRS scores for leg pain significantly improved from 6.7 to 1.8 (p<0.05) (Table 1).

DISCUSSION

Surgical treatment for lumbar foraminal stenosis is generally interbody fusion, but recently there have been various reports on decompression procedures, including microscopic [5], microendoscopic [6,7], and full-endoscopic procedures (single [8-14] and biportal [15]). All reports have shown good clinical results; however, the most minimally invasive decompression technique is the single-portal full-endoscopic procedure.

In treating lumbar foraminal stenosis using full-endoscopic single-portal surgery, selecting the decompressive approach is pivotal and is typically guided by the vertebral arch width. The TLA suits wider arches, whereas the PLA suits narrower arches without iliac crest interference. Extraforaminal lesions such as far-out syndrome require PLA, which is inaccessible to the TLA. Preoperative imaging and electrophysiological studies are crucial for an accurate diagnosis.

Surgical strategies vary based on the foraminal stenosis categories (anteroposterior and circumferential), each requiring tailored decompression techniques. Patients with stenosis, mainly in the anteroposterior direction, can be decompressed relatively easily. However, patients with focal scoliosis often have symptoms related to stenosis in the cephalocaudal direction, requiring partial excision of the bulging disc, vertebral body, and pedicle, which is more difficult to perform. Conditions reported to increase the reoperation rate include local disc wedging and Cobb angle change of 3° or more between supine and standing position [16,17]. Fusion surgery should be considered in such cases.

TLA, utilizing a 5.2-mm working channel endoscope, reduces the operative time with high-torque drills and large forceps. However, caution is essential in preventing iatrogenic instability caused by excessive bone resection.

This study has several limitations. These include the retrospective nature of the study, small number of cases, short follow-up period, and selection bias due to relatively mild local scoliosis in many cases. Future studies are expected to increase the number of cases, conduct long-term follow-up, and conduct comparative and prospective studies using a PLA.

CONCLUSION

The short-term clinical results of full-endoscopic translaminar decompression for lumbar foraminal stenosis using a 5.2-mm working channel endoscope were promising. Further studies are required to validate the long-term efficacy and safety of this technique.

NOTES

Conflicts of interest

The authors have nothing to disclose.

Funding/Support

This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Figure 1.

The location and angle of the endoscope. Anterior-posterior (A) and lateral (B) views.

Figure 2.

Intraoperative image of right L5–S1 full-endoscopic discectomy via the translaminar approach. (A) Exposure of the superior articular process (SAP) and yellow ligament (YL), and removal of the inferior articular process. (B) Removal of the YL using a Kerrison rongeur. (C) Decompressed nerve root (NR) visible after removal of the YL.

Figure 3.

Preoperative magnetic resonance image showing right L5–S1 foraminal stenosis. Sagittal (A) and axial (B) views.

Figure 4.

Postoperative computed tomography showing the range of bone removal. Sagittal (A) and axial (B) views. (C) Three-dimensional view. Arrowheads indicate the areas of removed bone.

Table 1.

Demographic and clinical characteristics of the patients

Age (yr)	Sex	Level	Preoperative NRS	Postoperative NRS	Operative time (min)	Hospital stay (day)
68	Male	L4–5	5	0	59	4
85	Male	L5–S1	8	1	52	4
61	Male	L5–S1	7	2	37	4
70	Male	L4–5	7	1	98	4
76	Male	L5–S1	10	2	51	3
68	Male	L5–S1	4	1	38	3
63	Male	L5–S1	6	1	65	3
79	Female	L5–S1	6	0	78	4
73	Male	L5–S1	8	4	42	3
66	Male	L5–S1	6	4	55	3
74	Male	L5–S1	7	2	55	3
79	Male	L5–S1	5	1	54	3
64	Female	L5–S1	8	3	47	3
74	Male	L5–S1	8	1	73	3
74	Male	L4–5	10	5	67	3
67	Male	L5–S1	8	3	85	3
83	Male	L5–S1	6	1	71	3
75	Male	L5–S1	3	0	66	3

NRS, Numerical Rating Scale.

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