Posterior inclinatory approach for degenerative foraminal stenosis with the biportal endoscopic technique: clinical and radiological outcomes

doi:10.21203/rs.3.rs-4683716/v1

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Posterior inclinatory approach for degenerative foraminal stenosis with the biportal endoscopic technique: clinical and radiological outcomes

https://doi.org/10.21203/rs.3.rs-4683716/v1

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Background

Although there are several surgical applications to treat foraminal stenosis, difficulties in some cases need novel access to decompression and preserve normal structure simultaneously. Biportal endoscopic spine surgery (BESS) presents a multitude of advantages, including enhanced flexibility, improved magnification, and an expanded field of view. We introduce a novel posterior inclinatory access in BESS (PIA-BESS) that is specifically designed to treat some specific degenerative foraminal stenosis and evaluate its clinical and radiological outcomes.

Methods

Between March 2021 and July 2023, 19 patients presenting with symptomatic nerve root involvement due to foraminal stenosis underwent the PIA-BESS surgical procedure. Preoperative and postoperative assessments involved magnetic resonance imaging (MRI) and computed tomography (CT) scans to measure changes in the cross-sectional area of the spinal canal and intervertebral foramen. Clinical outcomes were evaluated using the Oswestry Disability Index (ODI) scores and the visual analog scale (VAS) scores for buttock and radicular pain. The dynamic intervertebral angle (IVA) and vertebral slip rate, as determined from preoperative and postoperative X-rays, were employed to evaluate post-surgical vertebral stability.

Results

The intervertebral foraminal area increased significantly from the initial measurement of 32.26 ± 13.49 mm2 to 79.95 ± 19.78 mm2 (P<0.05). Similarly, the spinal canal area also showed a significant increase, from 105.37 ± 21.66 mm2 to 145.63 ± 17.86 mm2 (P<0.05). ODI scores reduced significantly from 73.27 ± 13.21 to 9.26 ± 7.65 (P<0.05), and VAS scores reduced significantly from 5.79 ± 1.08 to 0.84 ± 0.90 (P<0.05). Notably, there were significant differences between the pre-operation and post-operation measurements. However, no significant changes were observed in the dynamic IVA and vertebral slip rate.

Conclusions

The PIA-BESS approach is an effective and low-complication method for addressing stenosis in the lumbar foraminal region. It provides effective decompression for bony stenosis or extruded and sequestered discs in the foraminal region, while preserving the normal structure to maintain the spine stability.

Foraminal stenosis

Biportal endoscopic technique

Posterior inclinatory approach

Nerve root lesion

Foraminal stenosis is one of the common forms of lumbar degenerative disease. Statistical data from previous studies show that the incidence of this type of lumbar degenerative disease is between 8% and 11%, with the majority originating from the L5-S1 level (75%)[1, 2]. Conditions such as disc herniation, facet joint hypertrophy, and ligamentum flavum thickening often lead to symptoms from both traversing and exiting root nerve. Currently, treatment options include decompression combining intervertebral fusion and fixation and simple decompression.

Intervertebral fusion and instrumental fixation demonstrate efficacy–particularly in patients with lumbar instability, as a result of stabilization of the unstable lumbar vertebrae and provision of sufficient decompression. However, spinal fusion surgery is not without challenges, given it is associated with various reported complications such as pseudoarthrosis, instrumental failure, and adjacent segment disease[3].

The paraspinal surgical approach was first reported by Wiltse et al. in 1968[4] and improved in 1988[5]. This approach considered the classic surgical approach for lumbar foraminal lesions can be undertaken with microscopic or endoscopic assistance[6, 7].

It is an outside-in surgery that is suitable for extraforaminal lesions but limited to stenosis within the spinal canal.

Biportal endoscopic spinal surgery (BESS) is a type of full-endoscopic spinal surgery technology that has emerged in recent years. It offers a clear view of the surgical field under water medium, flexible operation under dual channels, an adaptable and variable surgical approach, and the use of more surgical instruments[8, 9]. Jon Park et al. reported the “four-level stenosis protocol” to evaluate the foraminal and lateral recess zones[10]. A contralateral sublaminar approach was recommended for the dominant foramen-to-extraforaminal stenotic pathology or disk extrusion at level 1 or 2 combined with lateral recess stenosis [11]. Despite these advantages, BESS suffers a limitation of a high possibility of incomplete decompression in the L5-S1 extraforaminal stenosis owing to its long bone work trajectory under the wide lamina.

Giving the above shortcomings, based on BESS technology, we have developed a new posterior inclinatory approach (PIA-BESS), which can effectively decompress the ipsilateral foramen-to-extraforaminal stenotic pathology combined with lateral recess stenosis. The purpose of this study is to evaluate the effectiveness of this surgical method.

We conducted this study in compliance with the principles of the Declaration of Helsinki. This retrospective clinical research was approved by the Institutional Review Board of the Fourth Affiliated Hospital of Zhejiang University. All patients who underwent PIA-BESS surgery for lumbar foraminal stenosis signed an informed consent form before the surgery.

Between March 2021 and July 2023, a surgical team led by Dr. Qingfeng Hu performed a total of 934 BESS surgical procedures for lumbar degenerative diseases. Out of these 934 patients, 19 individuals with unilateral degenerative foraminal stenosis, with or without combined lateral recess stenosis, were treated using PIA-BESS and included in this study. Patients` demographic characteristics, classification of pathologies, distribution of operation levels, operative time, and surgical complications were reviewed.

Preparation for Surgery

The inclusion criteria for patients were as follows: the presence of (1) unilateral radiculopathy induced by osseous foraminal narrowing, with or without concurrent lateral recess stenosis, or (2) intervertebral disc herniation or fragments within the foramen causing nerve root symptoms. The exclusion criteria were as follows: the presence of (1) Patients with lumbar instability, (2) Patients with bilateral lower limb neurological symptoms, (3) Patients with central spinal stenosis, or (4) Patients with severe kyphosis or scoliosis.

Patients underwent routine assessments, utilizing anteroposterior, lateral, oblique, and dynamic radiographic examinations, to evaluate the alignment of the spine, disc space height, the extent of foraminal osseous encroachment, and the presence of instability. Additional radiological investigations, including magnetic resonance imaging (MRI) and computed tomography (CT) scans, were performed to ascertain the degree of foraminal stenosis and procure precise information about the facet joint - such as the level of joint hypertrophy, tropism, the size and form of the bony spur, as well as the inclination angle of the spinous process. This comprehensive evaluation enabled the surgeon to determine the extent of facet joint resection and the optimal approach angle for achieving ideal decompression while ensuring the preservation of segmental stability.

We use a 30° 4-mm-diameter arthroscope (Smith & Nephew, USA) (Fig. 1a)., a 90° 3.75mm radiofrequency ablator, and a 1.4-mm micro ablator radiofrequency probe (Bonss Medical, Jiangsu Bonss Medical Technology Company., Ltd., China) (Fig. 1b). We also used ordinary instruments in the BESS such as different kinds of Kerrison rongeur, 3mm-diameter straight and curved round burr, and 3-mm curved chisels, pituitary forceps, and cannula for water outflow. (Fig. 1c, d, e, f)

Surgical procedures

Skin incision and establishment of portals

Patients generally undergo surgery in a supine position after general anesthesia. An anterioposterior(AP) view from the C-arm is obtained to locate the entries for the working and viewing portals (Fig. 2a). Two longitudinal surgical incisions, approximately 0.5cm long, are made 5-10mm lateral to the spinous process. Two Kirschner wires are inserted diagonally outward from the incision and anchored at the level of the intervertebral foramen (Fig. 2b,c). The surgeon stands on the patient's healthy side (Fig. 2d) for the procedure. After determining the position under fluoroscopy, an operating channel and an endoscopic observation channel are established along the position of the Kirschner wire (Fig. 2e,f).

Bone work and flavectomy

Soft tissues overlying the lamina and the ligamentum flavum were ablated to expose the bone edge in the targeted interlaminar space (Fig. 3a). A high-speed burr was utilized to partially resect the lamina (Fig. 3b). The shaping of the lamina required burring upward to the endpoint of the ligamentum flavum, to expose the entire ligament (Fig. 3c). Subsequently, the ligamentum flavum was removed and the facet joint and the dural sac could be visualized via the endoscope (Fig. 3d).

Foraminoplasty

Partial resection of the superior articular process is performed using a burr or a lamina rongeur, to expose the foraminal area. Tools such as disc forceps, Kerrison rongeur, and high-speed burr are then used to remove any protruding nucleus pulposus, osteophytes, or hypertrophied ligamentum flavum within the foraminal area (Fig. 4a,b). After the removal of the compressive elements, the course of the exiting nerve roots can be visualized (Fig. 4c,d).

Nerve root exploration and decompression

Following the course of the exiting nerve root, thorough exploration and decompression are carried out until the nerve is in a tension-free state. A nerve retractor may be used to gently manipulate the nerve root (Fig. 5a), confirming its tension-free state before concluding the procedure. Intraoperative X-ray confirms the position of the retractor within the foramen (Fig. 5b), ensuring that the foraminal nerve root canal has been adequately decompressed.

Clinical and radiology evaluation

All patients were followed up for at least six months after the surgery. The clinical results were evaluated and compared preoperatively and 6 months postoperatively using the Oswestry Disability Index (ODI) and the visual analog scale (VAS) scores for buttock and radicular pain.

For patients with intervertebral foraminal stenosis mainly caused by bone stenosis, we compared preoperative and postoperative CT scans to evaluate the surgical decompression effect. For patients with intervertebral foraminal stenosis mainly caused by free nucleus pulposus, we use preoperative and postoperative MRI to evaluate the surgical decompression effect. We measured the cross-sectional area of the intervertebral foramen (CSA-IVF) at the sagittal level of the pedicle (Fig. 6a, b), and the cross-sectional area of the spinal canal (CSA-SC) at the axial level of the foramina (Fig. 6c, d). The measured area is expressed in square millimeters.

To evaluate the stability of the vertebra, we analyzed the dynamic intervertebral angle (IVA) and slip rate based on X-ray imaging obtained before the surgery and at the 6-month follow-up. These assessments provided insights into the long-term stability of the spinal structure.

Statistical analyses

Statistical calculations, including means and standard deviations, were obtained using SPSS version 17.0. Paired t-tests were used to compare the differences in each parameter of the perioperative outcome. P-values of less than 0.05 were considered to indicate statistical significance.

Over the duration of two years, 19 patients (13 men and 6 female) were enrolled in our study. The mean age was 67.21 ± 9.56 years. Of these 19 patients, 1 patient received decompression at L3-4, 8 patients at L4-5, and 10 patients at L5-S1. In 5 patients, foraminal stenosis was mainly caused by disc herniation and displacement. Further, in 14 patients, foraminal stenosis was mainly caused by osseous structure hypertrophy, thickened ligamentum flavum, and other degenerative hyperplasia (Table 1).

Table 1

Demographic Data of the Patients(n = 19)
Characteristic	Value
Age (year)	67.21 ± 9.56
Sex, male: female	13:6
Level
L3-4	1
L4-5	8
L5-S1	10
Sides
Left	7
Right	12
Diagnosis
DH	5
DFS	14
Operation time(min)	78.63 ± 21.11
Hospital stay(day)	5.84 ± 1.38

DH: disc herniation

DFS: degeneration of foramen stenosis

We used the ODI and VAS score systems to evaluate the clinical effect. At the 6-month follow-up, patients reported a remarkable reduction in back and leg pain. ODI scores reduced from 73.27 ± 13.21 to 9.26 ± 7.65.(P<0.05), while VAS scores reduced from 5.79 ± 1.08 to 0.84 ± 0.9.(P<0.05).

We measured the cross-section area of the spinal canal in the axial image at the level of the foramina and the cross-section area of the intervertebral foraminal in the sagittal image at the level of the pedicle (Fig. 6). As shown in Table 2, the area of the spinal canal increased from 105.37 ± 21.66mm² to 145.63 ± 17.86mm² and the intervertebral foraminal area increased from 32.26 ± 13.49 mm² to 79.95 ± 19.78 mm². There were significant differences between the pre-operation and post-operation areas.

According to the radiology measurements, there were no significant differences in the dynamic IVA and dynamic slip rate before and after the surgery. Therefore, we can conclude that the PIA-BESS approach for foraminal stenosis did not cause iatrogenic vertebral instability.

Table 2

Morphometric of radiology and clinical outcomes
	Preoperation	Postoperation	P value
The cross-sectional area of the spinal canal (CSA-SC) (mm2)	105.37 ± 21.66	145.63 ± 17.8	<0.05
Cross-sectional area intervertebral foramen (CSA-IVF) (mm2)	32.26 ± 13.49	79.95 ± 19.78	<0.05
ODI	73.27 ± 13.21	9.26 ± 7.65	<0.05
VAS	5.79 ± 1.08	0.84 ± 0.9	<0.05
IVA(°)	6.14 ± 1.44	5.95 ± 1.45	0.68
Slip (%)	3.78 ± 2.47	3.85 ± 2.53	0.94

Lumbar degenerative stenosis is a complex disease, and its treatment requires a comprehensive and accurate analysis of the specific condition of the patient by the physician. In cases where neurological roots are compressed because of concurrent lumbar instability, it is necessary to perform lumbar fusion with internal fixation during decompression. However, in most cases, fusion is required to compensate for the surgical instability resulting from wider laminectomy and foraminotomy, in addition to ensuring sufficient decompression for relieving neurological pain.

Endoscopic spinal surgery (ESS) has been developed with the aim of achieving successful decompression while preserving structural integrity to the greatest extent possible, aided by magnification and illumination. ESS provides the technical possibility and feasibility of addressing lumbar spinal stenosis (LSS) through decompression alone while aiming to preserve normal structures. For ESS, a more precise and targeted preoperative assessment is necessary. The presence of unilateral or bilateral symptoms in patients, the correlation between imaging findings and clinical symptoms, and consideration of the responsible segment and stenosis location are all crucial factors to be taken into account when formulating the surgical plan. The foraminal region poses considerable challenges owing to the obstruction caused by the pedicle and facet joints, making decompression alone a challenging task. Excessive bone removal during surgery can result in iatrogenic lumbar instability, while insufficient removal may lead to suboptimal therapeutic outcomes. Therefore, the selection of an appropriate surgical approach and technique is of utmost importance.

Seeking to address the above factors, this study introduces a new surgical approach. The study demonstrates that PIA-BESS is an effective and low-complication approach for addressing stenosis in the lower lumbar foraminal region. It provides effective decompression for bony stenosis in the foraminal region and for extruded and sequestered discs, while also enabling simultaneous exploration of the exiting and traversing nerve roots (Fig. 7). PIA-BESS enables a good surgical field of view without removing the root portion of the spinous process; only a small amount of lamina bone is removed, thus preserving the stability of the lumbar posterior column (Fig. 8). The PIA-BESS approach can avoid the removal of the bottom of the spinous process and reduce manipulation of the dural sac compared with the reported contralateral sublamina approach[7]. However, some considerations should be noted when performing this surgery. The surgeon should only work on the medial aspect of the facet joint and avoid excessive medial facet joint removal to decrease the risk of iatrogenic instability. Furthermore, we recommend that L4-5 and L5-S1 levels are suitable for the PIA-BESS approach, owing to their wide laminar space, to diagonalize targeting the foraminal region.

Despite the present technique representing a promising novel surgical approach for the treatment of foraminal stenosis, there are also some limitations. Firstly, we find that it is more convenient for a right-handed surgeon to deal with lesions on the right side (surgeon on the patient's left side). When it comes to the left-side lesions, the right-handed surgeon may encounter some difficulties. Furthermore, the characteristics of this technique make it suitable for treating lesions in the unilateral intervertebral foramen and lateral recess area, although managing the central spinal canal or bilateral lesions remains challenging.

Author Contribution

Zhengyu Xu wrote the main manuscript text. Qingfeng Hu offered the supervision and review the article. Xiaowei Jing and Guojun Wei cooperate the surgeries.

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No competing interests reported.

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Posterior inclinatory approach for degenerative foraminal stenosis with the biportal endoscopic technique: clinical and radiological outcomes

Status:

Version 1

Abstract

Background

Methods

Results

Conclusions

Figures

INTRODUCTION

MATERIALS AND METHODS

Preparation for Surgery

Surgical procedures

Clinical and radiology evaluation

Statistical analyses

RESULTS

DH: disc herniation

DFS: degeneration of foramen stenosis

DISCUSSION

Declarations

Author Contribution

References

Additional Declarations

Supplementary Files

Status:

Version 1