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Summary

Here, we present the third channel-assisted UBE technique, which allows for the vertical removal of herniated disc fragments. This technique can effectively address the limitations of traditional UBE techniques. This article will systematically elaborate on this procedure.

Abstract

Unilateral biportal endoscopic (UBE) spine surgery is an emerging minimally invasive surgical (MIS) technique that has gained popularity for treating lumbar spinal stenosis, particularly in Eastern Asia. The traditional UBE technique, with two portals on one side, can achieve successful unilateral laminotomy for bilateral decompression (ULBD) and, therefore, demonstrates favorable clinical outcomes. However, in the case of lumbar spinal stenosis combined with contralateral disc herniation, it is very difficult to remove the contralateral disc herniation, especially the loose disc fragment within the deep disc. Here, a third channel of the traditional UBE technique was developed to do the discectomy within the ipsilateral endoscopic vision, with which the instruments can go vertically into the contralateral disc, allowing easy discectomy. This technique can not only achieve adequate decompression of the bilateral spinal canal but also effectively remove contralateral herniated disc fragments. This technique avoids performing another UBE procedure on the opposite side, which can potentially shorten the duration of the operation, minimize blood loss and tissue damage, and ensure sufficient neural decompression. This paper will introduce the indications and surgical operation procedures, as well as present a classical case report and follow-up data, to facilitate the application of the third channel-assisted UBE (T-UBE) technique for spine surgeons.

Introduction

In the field of spine surgery, minimally invasive spine surgical (MISS) techniques have evolved significantly in recent years, transitioning from open surgery to microscopic, microendoscopic, and endoscopic surgery. Endoscopic spine surgery is an advanced form of MISS technique that has been widely used to treat spinal diseases and achieve satisfactory clinical outcomes¹. Compared with traditional open surgery, it has the advantages of less tissue damage, less bleeding, quicker recovery, and fewer postoperative complications².

Endoscopic spine surgery can be performed using single or two portals. Unilateral biportal endoscopic (UBE) spine surgery is an innovative type of MISS technique that was first reported for performing lumbar discectomy in Argentina. It has since been refined to also perform decompression or fusion surgery in South Korea³. The surgical procedure of the UBE technique is similar to conventional open surgery. However, the UBE technique is less invasive and provides a clearer field of view compared to traditional open surgery^4,5.

The conventional UBE technique not only enables unilateral decompression but also achieves bilateral decompression for spinal stenosis^6,7. In 2019, Heo et al.⁸ reported that the UBE technique could significantly expand the stenotic dural areas through unilateral laminotomy for bilateral decompression (ULBD). This technique also preserved more of the ipsilateral facet joint by undercutting the medial facet joint, compared to conventional microscopic decompression. In 2021, Kim et al.⁹ described a new decompression procedure for UBE in cases of asymmetric spinal stenosis using a contralateral approach. The contralateral approach UBE technique was able to achieve adequate decompression of the contralateral recess and spinal stenosis. It had advantages such as better manipulative freedom, a more accessible target approach, and more facet preservation.

The advantage of the UBE technique is dorsal and lateral spinal decompression through the endoscopic ULBD procedure. However, It is challenging to perform ventral neural decompression or discectomy when there is bilateral recess stenosis or disc herniation. Although bilateral UBE can be performed, it will significantly prolong the operation time, increase intraoperative bleeding, and elevate the risk of dural injury. Here, a third channel was developed in the UBE technique to perform the discectomy within the same endoscopic field of view. This allows the instruments to be inserted vertically into opposite discs, making the discectomy process easier. This technique can not only achieve adequate decompression of the bilateral spinal canal but also effectively remove contralateral herniated disc fragments.

Protocol

The Institutional Review Board of the Third Affiliated Hospital at Sun Yat-sen University approved the protocols (ID:[2022]02-356-01). All included patients were required to sign an informed consent form.

1. Surgical indications

1. Include patients with lumbar spinal stenosis who have contra-lateral recess stenosis or disc herniation or who have contra-lateral neural compression.

2. Surgical method

1. Perform bilateral endoscopic spinal canal decompression via UBE-ULBD technique and endoscopic discectomy via T-UBE.

3. Preoperative procedure

1. Anesthesia and surgical position:
   1. Under general anesthesia, position the patient prone on a spinal frame, avoiding any discomfort. Flex the lumbar spine slightly to open up the interlaminar space.
      NOTE: General anesthesia with endotracheal intubation or combined spinal-epidural anesthesia is used for surgical procedures to minimize intraoperative pain.
2. Desired portals position (L4-5, for example):
   1. Obtain a standard anteroposterior (AP) X-ray view, and let the target intervertebral space be vertical to the ground in the X-ray lateral view by adjusting the surgical table.
   2. Mark the bilateral pedicles of L5 and the ipsilateral pedicle of L4. Draw a line along the midline of the L4/5 intervertebral disc and the posterior midline of the spine.
   3. On the ipsilateral side, mark two incisions 1.5 cm above and below the midline of the intervertebral disc for manipulation and endoscopic portal, respectively. Locate the third channel incision on the contra-lateral midline of the L4/5 intervertebral disc space.

4. Surgery procedure (L4-5, for example)

1. Sterilize the surgical site with iodine tincture and 75% alcohol, and prepare the site with waterproof drapes.
2. Establish UBE endoscopic channel and ipsilateral working channel.
   1. Insert two syringe needles from the medial edge of the line of the ipsilateral pedicle shadow, one at 15 mm cranial and the other at 15 mm caudal, to the midline of the L4/5 intervertebral disc. The inserted needles will form a triangle and meet at the L4/5 interlaminar.
   2. Then, make two 8-10 mm longitudinal skin incisions for endoscopic and manipulated portals based on the location of the aforementioned needles.
   3. After dissecting the extralaminal soft tissue with a curette, insert serial dilators to expand the surgical field. Then, establish the endoscopic channel and working channel, converging along the sublaminar edge.
3. Establish endoscopic operating space (Figure 1A-C)
   1. Insert a 30-degree endoscope via the viewing channel, connected to a continuous gravity saline irrigation positioned 50-60 cm high above the patient.
   2. After that, insert the surgical instruments and a radiofrequency ablation blade via the working channel to remove the soft tissue on the laminar surface until exposure of the lower edge of the L4 lamina, the ligamentum flavum, and the medial edge of the ipsilateral L4/5 facet joint. Establish the endoscopic operating space.
4. Ipsilateral laminotomy and neural decompression (Figure 2A-D, Figure 3A-D)
   1. Remove the ipsilateral lower part of the L4 lamina, the upper part of the L5 lamina, and the medial inferior facet by a 3.5-mm high-speed drill (8000 rotations/s) and Kerrison punches until the ligamentum flavum is fully mobilized.
   2. Then, separate the ligamentum flavum from the dural sac and gradually remove it from the cranial to the caudal end with Kerrison punches or forceps.
   3. After that, carefully remove the medial facet joint of L4/5 and the hyperplastic facet joint bone with a soft-tissue protection drill or punches until the traversing nerve root is completely decompressed.
   4. Ensure that more than 50% of the medial facet is preserved, avoiding the possibility of spinal instability.
5. Contra-lateral dorsal neural decompression (Figure 4A-E)
   1. Remove the base of the L4 spinous process with a drill (8000 rotations/s) and adjust the working channel obliquely towards the contralateral spinal canal.
   2. Undercut the medial part of the contralateral L4 inferior facet, fully expose the contralateral ligamentum, separate from the dural sac, and remove it using Kerrison punches (4 mm) until adequate dorsal neural decompression.
6. Contralateral third channel-assisted discectomy (Figure 5A-C, Figure 6A-E)
   1. Make an 8-mm longitudinal skin incision adjacent (5 mm) to the spinous process at the midline of the contralateral disc. Insert a K-wire, followed by serial dilators under endoscopic view, to establish the contra-lateral working channel.
   2. After the thecal sac and contra-lateral traversing nerve root (L5) are retracted and well protected, expose the contralateral herniated disc fragment. Then, insert forceps or other instruments vertically into the contra-lateral disc space and remove the herniated disc tissues through the third channel.
   3. At last, use a blunt nerve hook to explore the dural sac and bilateral nerve roots to ensure sufficient spinal decompression.
7. Place a drainage tube outside the lamina and suture each incision to complete the operation.
   NOTE: The surgical instruments used in the T-UBE technique are essentially the same as those used in the conventional UBE technique and traditional open spinal surgery. There is no need to purchase specialized instruments. T-UBE instruments include a 30-degree, 4-mm-diameter arthroscope, an endoscopic sheath, standard laminectomy instruments such as Kerrison punches, forceps, and nerve hooks, as well as a bipolar flexible radiofrequency probe, and a 3.5-mm radiofrequency electrode.

Representative Results

The T-UBE technique will be demonstrated in a typical case. A 65-year-old male complained of low back pain with bilateral numbness in his lower limbs for 10 months. The numbness is more pronounced on the right side and is accompanied by intermittent claudication, which occurs after walking 50 m. The symptoms on the left side were relieved by analgesic and neurotrophic drug treatment, but the symptoms on the right side persisted. Physical examination revealed mild tenderness of the spinous process and pain upon percussion at the lumbar L4-5 level. There was a slight limitation in lumbar flexion and extension. The patient also exhibited mild hypoesthesia on the dorsum of the right foot and grade 5 extensor strength in both hallux. The right straight leg raise test (SLR) was negative, while the left SLR was positive at 60°. The preoperative visual analog scale (VAS)¹⁰ scores for low back pain and leg pain were both 5, and the Oswestry disability index (ODI)¹¹ score was 42% (Figure 7). The preoperative X-ray showed lumbar degeneration but no instability (Figure 8A–D). Magnetic resonance imaging (MRI) revealed L4-5 spinal stenosis, right facet cyst formation, left disc herniation, and severe bilateral nerve compression (Figure 9A–C). Computed tomography (CT) showed L4-5 central canal and bilateral recess spinal stenosis, as well as severe bilateral nerve compression (Figure 9D–F). The diagnosis was lumbar spinal stenosis (bilateral at L4/5) and left-sided lumbar disc herniation (at L4/5). The patient underwent surgical treatment for T-UBE L4/5 spinal canal decompression (ULBD) with contralateral discectomy through the third channel.

The patient started walking on the second day after the surgery, and the symptoms in his lower limbs nearly disappeared. Physical examination showed that the muscle strength of the lower limbs was grade V, and the sensation was the same as before the operation. The bilateral SLR test was negative. The VAS score for low back pain was 1, for leg pain was 0, and the ODI was 6% on postoperative day 3. Follow-up at 3 months, the VAS score for low back pain was 0, the VAS score for leg pain was 0, and the ODI was 4%. Follow-up at 6 months showed that the VAS for low back pain and leg pain was 0, and the ODI was 4%. The postoperative modified Macnab score was excellent. Postoperative CT showed adequate bilateral decompression at the L4-5 level, with more than 50% preservation of facet joints, thus avoiding the possibility of lumbar instability. Postoperative MRI showed adequate bilateral decompression at the L4-5 level using a unilateral approach. The procedure successfully removed the contralateral disc herniation, and there was no compression of the dural nerve (Figure 10). The dural sac area increased from 63.55 mm² (preoperative, Figure 9C) to 100.80 mm² (postoperative, Figure 10B). Additionally, the nerve root sedimentation sign changed from positive before the surgery to negative after the surgery.

Figure 1: Establish endoscopic operating space (A) Photograph capturing the operator's involvement during the procedure. (B) Utilization of a radiofrequency ablation blade to delicately remove soft tissue from the laminar surface. (C) Visual exposure of the lower edge of the L4 lamina and the medial aspect of the L4/5 right facet joint. Please click here to view a larger version of this figure.

Figure 2: Performing ipsilateral laminotomy. (A) Schematic representation of the procedure's microscopic operating space setup. (B) Operator engagement documented through gross photography. (C) Systematic grinding of the L4 lamina's lower inner edge to the tip of the ligamentum flavum insertion utilizing a micropowered burr, operating at a rotation rate of 8000 rotations per second. (D) Employing a micropowered burr to meticulously remove the lateral margin of the L4 inferior facet. Please click here to view a larger version of this figure.

Figure 3: Achieving neural decompression. (A) Utilization of a nerve elevator to meticulously separate the ligamentum flavum at the lower edge of the L4 lamina and at its insertion point. (B) Careful removal of the ligamentum flavum from its cranial to caudal and lateral dimensions utilizing a 4 mm Laminar rongeur. (C) Removal of the ligamentum flavum within the right lateral recess at the L4/5 level, accompanied by the resection of hyperplastic cohesive facet joint bone and facet joint cyst. (D) Culmination of nerve root decompression to ensure comprehensive resolution. Please click here to view a larger version of this figure.

Figure 4: Contra-lateral dorsal neural decompression. (A) Controlled abrasion of a portion of the base of the L4 spinous process, employing a micropowered burr. (B) Precise exposure of the contralateral L4 inferior facet, culminating in the full visualization of the left border of the ligamentum flavum. (C) Meticulous removal of the left ligamentum flavum along with a section of the medial wall of the left facet at the L4/5 level, accomplished through the use of a 4 mm Laminar rongeur. (D) Attainment of dorsal decompression for the contralateral nerve root. (E) Schematic representation of the base of the L4 spinous process abrasion process. Please click here to view a larger version of this figure.

Figure 5: Establishing the third channel. (A–C) A sequence of sub-figures depicting the procedural progression of establishing the third channel. Please click here to view a larger version of this figure.

Figure 6: Contralateral third channel-assisted discectomy. (A) Gross photographic documentation of the operator's active involvement during the procedure. (B) Methodical retraction of the thecal sac and the left L5 nerve root utilizing a nerve retractor, leading to optimal exposure of the contralateral herniated disc. (C) Precise cutting of the disc using a sharp knife. (D) Removal of the nucleus pulposus achieved through the utilization of a nucleus pulposus forceps. (E) Successful realization of an adequate release of the nerve root. Please click here to view a larger version of this figure.

Figure 7: Visual analog scale (VAS) and Oswestry disability index (ODI) scores. (A) Visualization of the variations in Visual Analog Scale (VAS) scores pertaining to low back pain, both before surgery and throughout the postoperative follow-up. (B) Depiction of the alterations in VAS scores relating to leg pain, pre-surgery and during the postoperative follow-up. (C) Comprehensive representation of the shifts in Oswestry Disability Index (ODI) scores, prior to surgery and within the postoperative follow-up period. Please click here to view a larger version of this figure.

Figure 8: Preoperative radiographs. (A) Lumbar reoperative anteroposterior radiograph of the patient. (B) Preoperative lumbar lateral radiograph of the patient. (C) Preoperative lumbar hyperflexion radiograph of the patient. (D) Preoperative lumbar hyperextension radiograph of the patient. Please click here to view a larger version of this figure.

Figure 9: Preoperative MRI and CT. (A) Preoperative left sagittal MR image of the lumbar region for the patient. (B) Preoperative right sagittal MR image of the lumbar region for the patient. (C) Preoperative horizontal MR image of the L4/5 level for the patient. (D,E) Preoperative lumbar coronal CT images for the patient. (F) Preoperative horizontal CT image of the L4/5 level for the patient. Please click here to view a larger version of this figure.

Figure 10: Postoperative MRI and CT. (A) Postoperative sagittal MR image of the lumbar region for the patient. (B) Postoperative horizontal MR image of the L4/5 level for the patient. (C) Postoperative sagittal CT image of the lumbar region for the patient. (D) Postoperative horizontal CT image of the L4/5 level for the patient. Please click here to view a larger version of this figure.

Figure 11: The comparison between conventional UBE and T-UBE. Please click here to view a larger version of this figure.

Discussion

The UBE technique is an innovative endoscopic surgery that has rapidly advanced in recent years for the treatment of spinal disorders¹². In contrast to PELD, UBE does not require specialized instruments and is similar to conventional surgical procedures. This may reduce costs and eliminate the need for extensive training, particularly for surgeons experienced in arthroscopic surgery¹³. Therefore, the UBE technique has been widely used for discectomy, spinal canal decompression, and intervertebral fusion, particularly in East Asia. The benefits of this procedure include reduced damage to the paravertebral musculature, less bleeding, a clear surgical view, quicker recovery, and fewer postoperative complications¹⁴.

The UBE technique has the distinct advantage of decompressing the spinal canal. Recently, two randomized controlled trials (RCTs) reported that the UBE technique has comparable clinical outcomes to traditional microscopic open surgery in the procedures of discectomy and spinal canal decompression. In 2020, Park et al.¹⁵ reported that UBE decompressive laminectomy is an alternative approach to microscopic open surgery in patients with symptomatic lumbar spinal stenosis, offering comparable clinical outcomes. More recently, Park et al.¹⁶ (from the same team) also reported that UBE discectomy was non-inferior to microscopic discectomy over a 12-month period. They concluded that UBE discectomy can be a relatively safe and effective surgical technique for lumbar disc herniation, with the added advantage of reduced muscle damage.

Compared to other minimally invasive surgical (MIS) techniques, Aygun et al. found that UBE was superior to microendoscopic discectomy (MED) in terms of improving the ODI and Zurich Claudication Questionnaire (ZCQ) over various follow-up periods. UBE surgery also resulted in shorter hospital stays, reduced operative times and blood loss, and higher patient satisfaction rates¹⁷. In another study, although back pain relief was better on post-op day 1, the UBE technique was reported to be similar to the MED technique regarding leg pain relief, long-term efficacy, and safety. As for percutaneous endoscopic lumbar discectomy (PELD), UBE was comparable to PELD in providing relief for low back or leg pain, demonstrating long-term effectiveness, and ensuring safety¹⁸.

Although the UBE technique has many advantages in surgical neural decompression of lumbar spinal stenosis, it still has some limitations. Age-related degeneration of the spine, including facet hypertrophy or ipsilateral spinous process deviation, may hamper ipsilateral access and require partial facetectomy to expose the lateral recess⁹. To overcome this limitation, Kim et al. reported that UBE decompression via the contralateral approach could offer more manipulative freedom and also allow safer decompression and facet preservation⁹. Although UBE can do very well with dorsal and lateral spinal decompression via endoscopic ULBD procedure, It is difficult to perform ventral neural decompression or discectomy when bilateral or contra-lateral recess stenosis or disc herniation exists.

In this study, we proposed the third channel-assisted UBE technique (T-UBE) to overcome this limitation. During the operation, the assistant utilizes a nerve hook to retract and protect the nerve root and dural sac via the original operation channel. Subsequently, the chief surgeon performs a discectomy through the third channel. The contralateral ventrally herniated intervertebral disc can be well exposed and easily removed, which can also be applied to contralateral stenosis decompression. In this situation, the T-UBE technique may prevent the need for an additional UBE operation on the opposite side. This can help to reduce the overall operation time, minimize soft tissue damage, and potentially lower the risk of nerve injury during surgery. Discectomy should not only remove the prolapsed or herniated nucleus pulposus tissue but also eliminate any loose nucleus pulposus tissue in the intervertebral disc¹⁹. The operating device is positioned vertically from the contralateral third channel in the T-UBE. In this way, the nucleus pulposus forceps can access the deep intervertebral disc and remove it, thereby reducing the recurrence rate of intervertebral disc herniation and avoiding dural sac injury caused by excessive inclination of the operating device. However, similar to conventional UBE decompression surgery, the T-UBE technique requires careful attention to preserving more than 50% of the bilateral facets, maintaining lumbar stability, and avoiding postoperative lumbar instability.

For cases of spinal stenosis combined with central disc herniation, the conventional UBE technique can effectively achieve spinal canal decompression and herniated disc resection through ULBD²⁰. For cases of spinal stenosis combined with contralateral paracentral or foraminal disc herniation, the conventional UBE technique is often hindered by the dural sac and contralateral nerve roots. It becomes challenging for the operating device to access the contralateral herniated disc or reach the deep disc without causing nerve injury. However, the T-UBE technique can address this limitation. Under the protection of the nerve retractor in the original operating channel, the operating device was inserted vertically through the third channel to successfully extract the herniated disc and remove the loose nucleus pulposus from the innermost part of the disc. This approach is more efficient and safer (Figure 11).

The disadvantage of the T-UBE technique is that it requires an additional surgical incision and needs an assistant to complete the procedure. Maybe an automatic nerve retractor can be developed to serve as a surgical aid in the future. In addition, the visual field of TUBE is easily affected by intraoperative bleeding, and even a little bleeding can interfere with the surgeon's operation. Some skills may be useful, such as avoiding a large fluctuation of blood pressure and controlling blood pressure to 100-110 mmHg during operation, maintaining relatively stable hydrostatic pressure by gravity water irrigation, intraoperative preventive hemostasis, static hemostasis or compressive hemostasis with gelatin sponge or hemostatic drugs. Furthermore, anticoagulants should be discontinued before surgery, and patients with cardiovascular diseases should receive heparin replacement therapy.

This study primarily introduces the surgical procedure and advantages of the T-UBE technique. This technique will be used for patients with lumbar spinal stenosis who have contralateral recess stenosis or disc herniation or who have contra-lateral neural compression. Nonetheless, it is pivotal to acknowledge that the current study presents only a limited number of clinical cases. To establish its true efficacy, an expanded array of cases and prospective studies are required.

In conclusion, the T-UBE technique, developed from the conventional UBE technique, can address the limitations of the conventional UBE technique. It improves the efficiency of spinal decompression, reduces operative time, minimizes tissue damage, and leads to better clinical outcomes. Therefore, it is expected to be a significant alternative to the conventional UBE technique.

Materials

Bone dissector	Hengsheng Medical Instrument Co., Ltd.	PMT-BLQ001	Used for soft tissue expansion and laminar bone surface soft tissue stripping. Curved streamline design, better hand holding, one device and two uses, one end as soft tissue expansion, the other end as bone tissue dissection, fully expand and dissect the lamina and facet soft tissue.
Electric surgical equipment for osseous tissue	Viewall	VP7110	Used to grind off vertebral plate and partial facet bone; in the device channel, it is used for processing bone tissue; grind bone tissue at high speed, without damage to soft tissues such as nerve vessel; even grind close to nerve root, without damage to nerve; it is safer and faster.
Expandable Channel	Hengsheng Medical Instrument Co., Ltd.	PMT-KZG001	Perform channel dilation
Handle of scalpel	Hengsheng Medical Instrument Co., Ltd.	PMT-DB001	Used to Install scalpel
Mouth gag	Hengsheng Medical Instrument Co., Ltd.	PMT-KKQ001	Used to handle annulus breaks prior to disc
Nerve hook	Hengsheng Medical Instrument Co., Ltd.	PMT-LG001	Used for traction of nerve root in surgery; under endoscopic surgical field, pull apart and protect nerve root in instrument channel and can simultaneously enter other instruments for processing intervertebral disc.
Nucleus pulposus forceps	Hengsheng Medical Instrument Co., Ltd.	PMT-SHQ003	Used for clamping soft tissue and nucleus pulposus tissue of intervertebral disc during operation. Different angles and sizes allow easier grasping of soft tissue in various locations during surgery, and the finger loop design is ergonomic and easy to perform, along with gunshot forceps.
Osteotome	Hengsheng Medical Instrument Co., Ltd.	PMT-GZ001	During the operation, handle the lamina and facet, osteotomes with different angles and sizes can efficiently and flexibly chisel the facet and laminar bone
Radiofrequency electrode	GAOTONG	DZX-T2430-A160	Used for hemostasis ablation, cutting and cleaning soft tissue under endoscope during operation
Rongeur	Hengsheng Medical Instrument Co., Ltd.	PMT-YGQ002	During the operation, the laminar and facet bones were bitten and cut, the bone window was enlarged, and different sizes and angles were different. The bitewing mouth of the large incision easily bitewed off different bony tissues and calcified tissues, greatly saving the operation time, gun design, better hand holding sensation, and more forceful biting of bony tissues during the operation
Scalpel	Hengsheng Medical Instrument Co., Ltd.	PMT-SSD001	Used to cut the annulus fibrosus
Tissue Liberator	Hengsheng Medical Instrument Co., Ltd.	PMT-BLQ002	Used for stripping soft tissue in surgery, bidirectionally at different angles; used for stripping and separating mucosal tissue under instrument channel.