1 Introduction

Degenerative lumbar spinal stenosis is one of the most common diseases of the spine. Lumbar foraminal stenosis, or extraforaminal stenosis, is a common cause of spinal cord radiculopathy with a frequency of about 8–11%. It is caused by ligamentous and osseous structure hypertrophy, therefore, causing the canal space of the exiting nerve root to become narrower.^1–4 In addition, a decrease in intervertebral disc height also causes a decrease in the dimension of the canal space. Several techniques including partial pediculectomy, fusion, foraminotomy, and facetectomy have been introduced to solve this problem. There are currently two major surgical treatment options for this disease: one is decompression with fusion and the other is simple decompression.^5–7 The micro decompression technique to protect facet joints without fusion was first introduced by Wiltse and Spencer, several authors have modified it, and has since been modified by several authors. This operation improved the conditions of about 80% of patients and is considered to be a good surgical treatment for lumbar foraminal stenosis or far lateral stenosis. Alternatively, interbody fusion surgery can definitively expand the intervertebral space to resolve foraminal stenosis without foraminotomy.⁷ However, fusion surgery may cause complications such as adjacent segment disease and pseudoarthrosis.^8–10 Thus, several authors introduced the decompression of foraminal stenosis using uniportal endoscopy of the docking type,^2,3 At the L5-S1 level, the disadvantage is that proper decompression is not possible due to the difficulty of access created by the prominence of iliac crest. Recently, biportal arthroscopic spinal surgery has been reported by several authors,^11–13 and has started to get spotlighted. The literature on the far lateral approach of biportal endoscopy is still lacking. In this report, we would like to introduce far lateral approach of biportal arthroscopic spinal surgery using 30° arthroscopy as an alternative to open surgery for L5-S1 foraminal stenosis without instability and central stenosis.

2 Material and methods

12 consecutive patients were involved in this study. Preoperative lumbar plain x-ray including flexion extension view, CT, and MRI were checked in all patients. These patients were diagnosed with foraminal stenosis at L5-S1. Patients who did not respond to conservative treatment including medication and physiotherapy despite 6 weeks of conservative treatment were involved. The clinical outcomes including Modified Macnab criteria, VAS, operation time, and complication rate were analyzed from patients who were treated by biportal arthroscopic spinal surgery using 30° arthroscopy.

2.1

2.1 Case

An 80-year-old woman visited our outpatient clinic complaining of leg pain that began 2 months prior to her visit. In a neurologic examination, there were no motor weaknesses, patient appealed paresthesia with radiating pain in left side lower extremity. A plain x-ray showed degenerative spondylosis but no scoliosis or prominent instability. Magnetic resonance imaging showed no stenosis of the central canal, but the foraminal stenosis of left L5-S1 was observed due to the presence of an asymmetrical left posterolateral disc protrusion (Fig. 1.A). The patient was treated with conservative therapy including selective root block and medication. In spite of conservative therapy, symptoms were not controlled within 6 weeks. She was scheduled to undergo surgery to decompress L5-S1 left foramen and relieve neurologic symptoms. At the time of surgery, the patient underwent biportal endoscopic spinal surgery using the far lateral approach in a prone position under general anesthesia. The patient had improved symptoms prior to surgery. Magnetic resonance imaging and computerized tomography of the patient revealed that the foraminal stenosis was decompressed (Fig. 1.B.).

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Fig. 1 A. Preoperative magnetic resonance imaging demonstrated the foraminal stenosis of left L5-S1 was caused by the presence of an asymmetrical left posterolateral disc extrusion. B. Postoperative magnetic resonance imaging revealed that left L5-S1 foraminal stenosis due to posterolateral disc extrusion was well decompressed, the superior articular process of S1 was partially removed and the enlargement of the L5-S1 foramen was confirmed by computerized tomography after surgery.

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2.2

2.2 Operation technique

2.2.1

2.2.1 Basic setup

Instruments including basic spine instruments, 30° 4 mm arthroscopy which were commonly used in joint arthroscopy, radioflequency catheter, 4.2 mm arthroscopic burr, and a shaver were used in operation. The procedures were operated under general anesthesia. The patients were positioned prone along with the abdomen free. Level confirmation was conducted under intraoperative fluoroscopy.

2.2.2

2.2.2 Landing of extra foramen

In order to perform this operation, we need to basically create two portals. Additionally we can make a portal for water outflow. The proximal portal should be made 2 cm away from the L5 pedicle, and the distal portal was made on the sacral ala (Fig. 2.A). The two portals were 0.5 cm in diameter, enough to insert instruments and endoscope. Two portals are made with a diameter of about 0.5 cm and should have a diameter sufficient to insert instruments and endoscope. The proximal portal was used as the viewing portal and the distal portal was used as the working portal. After inserting a scope into the viewing portal and inserting a muscle detacher into the working portal, the muscle separation was started from the L5 transverse process using the triangulation technique, and the muscle was detached in the order of L5 pedicle, L5 S1 facet joint, and ala to create a primary space (Fig. 2.B). When approaching the transverse process, it is helpful to orient the 30° arthroscopic arrow to 6 o’clock. Tarsus muscles and tissues blurring the field of vision were removed using radioflequency catheter or shaver, and a radioflequency catheter was used to ensure a clear field of view when there was active bleeding (Fig. 3.A). If the water flow is congested, the visual acuity deteriorates rapidly, so a 5.0 mm plastic cannula can be used or an additional portal can be made (Fig. 3.B).

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Fig. 2 A. Location of portal for L5-S1 far lateral approach, Left side. R, right, L, Left. B. Step to create a working space of L5-S1 far lateral approach. R, right, L, Left.

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Fig. 3 A. Radioflequency catheter was used to ensure a clear field of view at L5-S1 foramen. B. When the water flow is congested, the visual field can be rapidly deteriorated and the water flow can be secured using the plastic cannula. C. Partial removal of superior articular process using osteotome allows foraminal decompression at 12 O’clock direction of arthroscopy. D. The foraminal ligament is removed above the root after removal of the superior articular process. E. Pituitary were used to remove disc fragments that were ruptured under the root. F. The operation was completed after confirming space of the same size as the root dimension. G, H. The 30° arthroscopy has the great advantage of being able to view inside more than those of 0° arthroscopy and work even closer to the pedicle, more vertically to the vertebra, rotated in the 12 o’clock direction.

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2.2.3

2.2.3 Decompression of foramen

After a sufficient working space was created, the half of the superior articular process in the thickened facet joint was removed using an arthroscopic burr and osteotome, and the remaining part of the inside was removed using kerrison punch and pituitary punch (Fig. 3.C). At the unroofing of the foramen, a 30° arthroscopy was rotated at 12 o'clock to gain more visibility. When 0° arthroscopy and 30° arthroscopy were compared at the same position, at 0° it was not visible due to the facet joint, but at 30° we could see more inside the foramen. The ligamentum flavum was removed from the distal portion of the L5 transverse process using curret and kerrison punch in the proximal to distal direction (Fig. 3.D). After completion of the flavectomy, the root and epidural fat were identified, and the outer layer of the annulus was identified just distal to the root, followed by annulotomy using a radioflequency catheter. At the time of discectomy, the 30° arthroscopy was rotated to 6 o'clock and the field of view was secured so that the floor could be seen. More curret and pituitary were used to remove disc fragments that were ruptured under the root (Fig. 3.E). After confirming that the space of the same size as the root dimension was secured, the operation was completed after inserting the drain tube (Fig. 3.F).

3 Result

The mean operation time was 55 min (range: 45–70). There were no infections, dura tears, or neurologic complications. Of the 12 cases, 8 cases were on the left side and 4 were on the right side. The mean leg VAS of patients improved from 7.5 to 1.8 after surgery. At the final follow-up, all twelve cases were recorded with excellent on the Modified Macnab criteria.

4 Discussion

Open decompression surgery using the Wilte approach is a conventional treatment for extraforaminal or foraminal stenosis.¹⁴ Open microforamotomy reports a success rate of 58%–80% and is reported to have poor outcomes compared to other spinal surgeries.¹⁵ However, excessive dissection of the paraspinal muscle may cause back pain or muscle atrophy. Minimal invasive technique using endoscopy has been attempted by several authors in extraforaminal or foraminal decompression. Recent advances in optics and endoscopy devices have allowed better vision and more precise operation, and good results of decompression surgery in foramen or extraforaminal stenosis using endoscopy have been reported.^2,3,16 The primary advantage of endoscopy-based spinal surgery in minimally complicated and minimally invasive tissues has been reported in several papers.^3,16 The recently introduced floating-type biportal arthroscopic spinal surgery has advantages over the conventional one portal endoscopic surgery in the far lateral approach.

First, one portal endoscopic decompression’s disadvantage is of a possible injury to the exiting nerve root during procedure if the foraminal space is severely narrow and the working cannula is not positioned appropriately. Unlike the docking type, the floating-type biportal arthroscopic technique can be used with various surgical instruments that can not be used in one portal type such as kerrison rongeur, pituitary forcep, burr, or ostetome regardless of size. It also has the advantage of covering a wide working space because it does not stay in one compartment with docking.

Second, the far lateral stenosis caused by L5-S1 level of hypertrophied sacral ala is limited by the one portal technique, whereas the biportal arthroscopic technique is relatively easy to solve the body decompression by sacral ala instrument such as osteotome.

Third, as a condition for successful decompression, the superior articular process in the foramen must be completely removed until the ligamentum flavum is exposed, and the exiting root must be fully decompressed from the entrance of the foramen to the extraforaminal area. However, in the case of open microscopic decompression or one portal endoscopic decompression, access to the inside of the L5-S1 foramen is not easy due to iliac crest. However, in biportal arthroscopic decompression, multiple sites can be accessed through triangulation and portal switching. When using a 30° arthroscopy, various views can be obtained through rotation. Especially, foramen unroofing is advantageous. In the case of a 30° arthroscopy, an approach to the foramen is possible if the distance from the lateral border of the pedicle to the portal site is about 2 cm.

If the 30° arthroscopy is rotated in the 12 o’clock direction, the field of view can be secured by an upward angle of 30° instead of a vertical angle of 0° scopy.

Therefore, when compared with 0° scopy or conventional one portal endoscopy, the 30° arthroscopy has the great advantage of being able to work even closer to the pedicle, more vertically to the vertebra (Fig. 3.G. and H.).

Because of these advantages, the biportal arthroscopic technique using 30° arthroscopy allows foraminal decompression while avoiding iliac crest at L5-S1 level.

There are some points to be considered when performing biportal arthroscopic spinal surgery using the far lateral approach.

The limitation of this study is its limited case of six patients, which is not statistically significant. Because the follow-up period has not been long so far, there is a lack of long term outcomes of clinical score and radiologic data.

A larger number of patients and long-term follow-ups may be required to further assess this technique.

Technical tips of biportal 30° arthroscopic spinal surgery at far lateral approach•If water outflow is reduced or poor, water congestion can result in muscle edema, resulting in a dramatically deteriorated visual field. Unlike the interlaminar approach, the far lateral approach requires more attention to outflow maintenance because the back muscle thickness is relatively thick.•When creating a working portal, cross-cut the fascia, and use a root retractor or insert a cannula into the working portal to maintain the flow.•When accessing the bottom of the transverse process, rotating the direction of the arthroscopy to 6 o’clock helps in working and visibility.•When performing foraminotomy, if the direction of arthroscopy is changed to near 12 o’clock, the field of view can be secured to the inside of the foramen.•The radial artery is an important structure located in the upper part of the foramen. It is a structure that always meets during foraminal decompression using the far lateral approach. It is recommended to refrain from working with an arthroscopic shaver near the foramen, as this may cause the visual field to deteriorate rapidly due to heavy blood flow.

5 Conclusion

The biportal arthroscopic decompression of the foraminal stenosis of L5-S1 using 30° arthroscopy was first described in this article. Far lateral approach of biportal arthroscopic spinal surgery with 30° arthroscopy is an alternative minimally invasive method that can decompress foraminal stenosis.

Conflict of interest

None.