Unilateral Endo-LIF in treating central lumbar spinal stenosis

Abstract

Purpose

To investigate the clinical efficacy and morphological alterations in the central canal following unilateral-approach endoscopic lumbar interbody fusion (Endo-LIF) for treating central lumbar spinal stenosis (CLSS) with neurogenic claudication.

Methods

From January 2021 to January 2023, 33 patients with CLSS who received unilateral Endo-LIF were retrospectively analyzed. A qualitative analysis of dural sac morphology was performed utilizing MRI scans. The dural sac cross-sectional area (DSCA), contralateral ligamentum flavum thickness (LFT) and contralateral foramen height (FH) were quantitatively measured. The clinical outcomes were assessed using the Visual Analog Scale (VAS), Oswestry Disability Index (ODI), and modified MacNab criteria.

Results

This study enrolled 33 patients with a mean follow-up period of 22.57 months. Qualitative central canal parameters significantly improved after unilateral-approach Endo-LIF (p < 0.001). Compared with preoperative value, significant increases in DSCA (90.7 ± 30.7%) and contralateral FH (19.7 ± 5.0%), and significant decreases in contralateral LFT (20 ± 4.0%) were found (p < 0.001). Postoperative VAS and ODI scores showed statistically significant decreases at all follow-up intervals (1, 3, and 12 months) and at final assessment (p < 0.05). The patients were rated as excellent in 19 cases and good in 12 cases (93.9%) based on the modified MacNab standard.

Conclusion

Unilateral-approach Endo-LIF can significantly improve the area of the central canal. Therefore, Endo-ILF unilateral direct decompression may be a promising option for CLSS with bilateral symptoms. (one side is mild).

Introduction

Degenerative lumbar spinal stenosis (DLSS) is a prevalent degenerative condition, which may lead to lower back, lower limb pain, and neurogenic intermittent claudication [1]. Anatomically, lumbar spinal stenosis can be classified into three distinct types: central canal stenosis, lateral recess stenosis, and foraminal stenosis [2]. The central lumbar spinal stenosis (CLSS) is the most common, which always presented neurogenic intermittent claudication and bilateral lower limb symptoms [3]; [4]. Surgical treatment can be considered after a failed trial of conservative therapy. Traditional surgery can be performed using bilateral or unilateral laminectomy or laminotomy. Recently, Full endoscopic “over-the-top” decompression, technically termed unilateral laminotomy for bilateral decompression, represents a minimally invasive surgical approach for CLSS [5–8]. The over-the-top procedure is technically demanding and prone to dural sac tears. To resolve this limitation, Kim et al. indicated that unilateral-approach minimally invasive surgery transforaminal lumbar interbody fusion (MIS-TLIF) significantly improved radiographic parameters of the central canal and contralateral neural foramen [9]. However, the necessity of bilateral direct decompression is still controversial for CLSS with bilateral symptoms (one side is mild).

In recent years, Endoscopic lumbar interbody fusion (Endo-LIF) has gained widespread adoption in spinal surgery owing to its demonstrated advantages including reduced intraoperative blood loss, minimized muscular trauma, and decreased postoperative hospitalization duration [10–12]. In our study, we aimed to investigate indirect decompression of central canal using radiographic measurement after Endo-LIF.

Methods

Subjects

A total of 61 patients performed unilateral-approach Endo-LIF in our hospital (Zhongda Hospital) from January 2021 to January 2023. The database inclusion criteria were: (1) The radiologic diagnosis was degenerative central lumbar spinal stenosis and lumbar instability; (2) patients had intermittent claudication and bilateral leg pain (the VAS score for one side was ≤ 4); (3) lack of efficacy at least 3 months conservative therapy. The exclusion criteria: (1) multiple-level surgery; (2) previous lumbar surgery, spinal tumors, fractures, infections and deformities; (3) incomplete medical data. Lumbar segmental instability was defined as dynamic radiography showing interbody displacement of > 4 mm or an angle change of > 10 mm[13]. CLSS was defined as DSCA ≤ 75 mm² on axial T2-weighted MRI. This study received ethical approval from our Institutional Review Board (2023ZDSYLL406). Patient informed consent documents were signed before the study. Of the 61 patients, 12 patients underwent preoperative MRI at other hospitals, 7 patients did not undergo postoperative MRI, and 9 patients were lost to follow-up. Consequently, 33 patients undergoing Endo-LIF were retrospectively enrolled in this study.

Surgical procedure (referred to our previously reported [14])

All surgical procedures were performed with patients in the prone position on a radiolucent operating table under general anesthesia. Under C-arm fluoroscopic guidance, four 1.5 cm longitudinal skin incisions were created over the targeted pedicles. Subsequently, puncture needles were percutaneously introduced through the pedicular trajectories into the vertebral bodies. Four guide wires replaced the puncture needles, bent 90° and held in place (Fig. 1A). The unilateral decompression was performed according to the preoperative dominant symptom, an 18G needle was fluoroscopically guided to the medial articular process using articular process (AP) projection. Then the incision was lengthened slightly (approximately 2 cm). Multiple different types of dilating catheters were gradually inserted to expand the surgical channel (Fig. 1B). After the catheters were withdrawn, the endoscope was inserted and isotonic saline irrigated continuously to clean operative area. Then, removed the medial AP by Kerrison rongeurs and endoscopic trephines (Fig. 1C). The procedure involved facetectomy and ipsilateral hemilaminectomy extending to the spinous process base. Following ligamentum flavum resection, exposure of the lumbar intervertebral disc, dural sac, and nerve root was achieved. Under endoscopic visualization, the working cannula (beveled tip oriented toward the spinal canal) provided direct exposure of the neural elements. A series of pituitary forceps were used to sufficiently decompress the nerve root. Then, reversed the cannula to protect the existing and traversing nerve root out of the endoscopic view, while lumbar intervertebral disc remained in endoscopic view. Intervertebral disc was removed until anterior longitudinal ligament using pituitary forceps and reamers. The cartilaginous endplates were decorticated using alternating rotational movements of the reamers and stripped away them with curettes (Fig. 1D).

Fig. 1.

The initial needles were sequentially exchanged for four guidewires, which were then secured to the surgical drape (A). Sequential dilating catheters were inserted (B). A series of endoscopic trephines (C). The tools for grind the nucleus pulposus and cartilaginous endplates (D). The nerve root and cage were checked (E). The appearance of incisions (F)

After preparing adequately the endplates, the local bone from vertebral plate and spinous process base with allogeneic cancellous bone were implanted through a funnel-shaped device after the endoscope was withdrawn. Subsequently, a suitable bullet-shaped PEEK cage (Capstone) stuffed with allogeneic and local bones was hammered into the intervertebral space. The endoscope and working tubes were removed again after nerve root and dural sac were checked (Fig. 1E). The procedure was completed with percutaneous pedicle screw fixation under fluoroscopic guidance (Fig. 2), followed by layered closure of the fascial and subcutaneous tissues with interrupted absorbable sutures (Fig. 1F).

Fig. 2.

Both postoperative lateral (A) and anteroposterior (B) radiographs confirmed correct implant positioning

Radiological evaluation

The dural sac morphology was graded with qualitative parameter, the dural sac cross-sectional area (DSCA), contralateral ligamentum flavum thickness (LFT) and contralateral foramen height (FH) were measured quantitatively. The CLSS was qualitatively graded on axial T2-weighted MRI according to the criteria by Lee et al. [15, 16] : grade 0 (Preserved cerebrospinal fluid (CSF) signal with clearly visible dural sac), grade 1 (Mild anterior CSF space obliteration with maintained separation of cauda equina nerve roots), grade 2 (Moderate anterior CSF space compromise with nerve root aggregation) or grade 3 (Severe anterior CSF space obliteration with complete cauda equina bundling). Quantitative measurements included: (1) DSCA (mm2): The area of dural sac was evaluated at the narrowest cross-sectional area on axial T2-weighted MRI (Fig. 3A). (2) contralateral LFT [17]: The LFT was quantified on axial T2-weighted MRI as the midpoint distance between: (a) The medial insertion at the spinous process base; (b) The lateral attachment at the facet joint capsule (Fig. 3B). (3) contralateral FH: the maximum length from the superior margin of the pedicle of the inferior vertebra to the inferior margin of the pedicle of the superior vertebra on sagittal T2-weighted MRI (Fig. 3C). Continuous trabecular bone crossing through the PEEK fusion cage. The measurements were performed by two doctors independently using MRI of the Picture Archiving Communication System (PACS).

Fig. 3.

Ligamentum flavum thickness (A) and dural sac cross-sectional area (B) were obtained at the facet joint level using axial T2-weighted MRI. Foramen height (C) was measured on sagittal T2-weighted MRI. LFT: ligamentum flavum thickness; FH: foramen height; DSCA: dural sac cross-sectional area

Clinical evaluation

Clinical evaluations were systematically assessed using visual analog scale (VAS) and Oswestry disability index (ODI) at preoperative baseline and postoperative intervals (1, 3, 12 months, and final follow-up). Surgical success was evaluated using the modified Macnab criteria at the final follow-up.

Statistical analysis

All data was statistically analyzed in SPSS 21.0 (SPSS, Chicago, USA). All the quantitative data conformed to the normal distribution (Shapiro–Wilk test) and were presented as X ± S. The categorical data were compared using the Fisher’s exact test, and the quantitative data were compared with the paired t test. The reliability of two orthopedic surgeons was determined using Kappa (К) values for categorical parameters and intraclass correlation coefficients (ICCs) for numerical parameters [18]. A p value < 0.05 was considered statistical significance.

Result

Sixty one patients who underwent Endo-LIF surgery, all of whom achieved favorable surgical outcomes. This study enrolled 33 patients with a mean follow-up period of 22.57 months (range 14–36 months). Diagnoses associated with the CLSS were lumbar spondylolisthesis in 19 cases, ligamentum flavum hypertrophy in 9 cases and degenerative central disc herniation in 5 cases. The direction of decompression was decided based on the preoperative dominant symptom. The fusion rate was 93.9% (31 patients) at 12 months in the study. The general information is shown in Table 1. One patient contralateral radiating pain relief was not obvious after surgery, which improved with percutaneous endoscopic contralateral foraminal decompression. For qualitative parameters (dural sac morphology), the interobserver К values was 0.82, indicating excellent agreement between observations. For quantitative parameters (DCSA, LFT and FH), the ICCs were 0.61–0.80, indicating good reproducibility. A representative patient is shown in Fig. 4.

Table 1.

The demographic data

Number of patients	33
Age (years)	60.76 ± 17.26
Gender (Male/Female)	14/19
BMI (kg/m2)	25.31 ± 5.15
Operation time(min)	207.5 ± 43.7
Blood loss(ml)	83.3 ± 28.9
Independent ambulation (h)	31.5 ± 11.8
postoperative hospitalization(days)	4.6 ± 1.5

Fig. 4.

A 67-year-old female patient with a 3-year history of chronic low back pain accompanied by bilateral lower extremity radicular symptoms. A: preoperative sagittal spinal canal diameter. B: preoperative central canal, the dural sac morphology was grade 3. C: preoperative central canal on the CT images. D: postoperative sagittal spinal canal diameter. E: postoperative central canal, the dural sac morphology was grade 1. F: postoperative CT imaging confirmed decompression ranges

Radiographic outcome

Qualitative changes of the central canal improved significantly after unilateral-approach Endo-LIF (p < 0.001). The quantitative parameters of DSCA (90.7 ± 30.7%) and contralateral FH (19.7 ± 5.0%) significantly increased after surgery compared to preoperatively (p < 0.001). The contralateral LFT (20 ± 4.0%) significantly decreased after surgery (p < 0.001, Table 2). The postoperative CT image is shown in Fig. 5.

Table 2.

Changes of qualitative and quantitative parameters

Dural sac morphology	Preoperative	Postoperative	P
			< 0.001
0 (normal)	0	7(21%)
1 (mild)	0	23(70%)
2 (moderate)	22(67%)	3(9%)
3 (severe)	11(33%)	0
DCSA (mm2)	60.30 ± 16.79	108.33 ± 10.31	< 0.001
contralateral LFT (mm)	4.24 ± 0.85	3.36 ± 0.57	<0.001
contralateral FH (mm)	15.92 ± 1.30	19.03 ± 1.50	<0.001

DCSA dural sac cross-sectional area, LFT ligamentum flavum thickness, FH Foramen height

Fig. 5.

A, D: The lateral and coronal CT image at 3 days after surgery; B, E: The lateral and coronal CT image at 3 months after surgery; C, F: The lateral and coronal CT image at 12 months after surgery

Clinical outcome

The VAS and ODI scores significantly descended postoperatively (p < 0.05, Fig. 6). At final follow-up, modified MacNab criteria demonstrated excellent outcomes in 19 patients and good outcomes in 12 patients (93.9%).

Fig. 6.

A: The VAS for back and leg pain. B: The ODI scores

Discussion

CLSS is a common anatomical typing of degenerative lumbar spinal stenosis, which compression source comes from disc herniation, facet and ligamentum flavum hypertrophy, and osteophyte formation [19]. The main clinical manifestations are neurogenic intermittent claudication. Total laminectomy was considered as the basic surgical procedure for the patients who have failed to respond to conservative treatment [20]. However, the stability of the lumbodorsal muscular was destroyed due to the extensive excision of the bony structure [21]. To resolve this deficiency, some researchers proposed the concept of “limited decompression[22, 23]. Poletti first reported unilateral laminotomy for bilateral ligamentectomy could restore the dural sac cross-sectional area and alleviate their symptoms [24]. Spetzger and Bertalanffy reported unilateral laminotomy for bilateral decompression of lumbar spinal stenosis, postoperative dural sac morphology as well as the patient’s symptoms achieved significant improvement [25].

With the promotion of the minimally invasive surgery, the surgical treatment of CLSS had developed from open surgery to percutaneous endoscopic technique [26]. In recent years, Endo-LIF had become popular due to faster recovery and less complications [11, 27]. Siepe CJ reported the surgical technique of the endoscopic bilateral decompression via over-the top technique [6]. Singhatanadgige showed unilateral direct decompression with contralateral indirect decompression in MIS-TLIF could improve the early clinical symptoms in patients with LSS [28]. Ding found that the position of the cage within the intervertebral space could influence the indirect decompression [29]. Limthongkul reported that unbuckling of the ligamentum flavum played an important role for improvement of spinal canal area after the indirect decompression [17]. Nevertheless, the necessity of contralateral direct decompression for CLSS is still controversial.

The mechanism of indirect decompression mainly comes from OLIF, which is thought to the result of excision of disc herniation, increase of lumbar intervertebral space and unfoldment of the ligamentum flavum [9, 30, 31]. In our procedure, we removed unilateral vertebral plate, part of the articular process and basilar part of spinous process at the approach side, which could expand the area of spinal canal and make the dural sac backwards. In our study, significant improvement in the central canal spaces was confirmed qualitatively and quantitatively. Therefore, Endo-PILF unilateral direct decompression may be a promising option for CLSS with bilateral symptoms.

In the research, we assessed clinical efficacy of unilateral-approach Endo-LIF for CLSS. This study indicated that the VAS and ODI scores significantly decreased after surgery. This demonstrated unilateral-approach Endo-LIF appeared to achieve a good clinical efficacy [32]. However, Endo-LIF inherently involves a limited bone graft volume, which may influence fusion quality, cage subsidence, and the durability of indirect decompression.

There are some limitations of our study. First, the study was a retrospective with small sample size (some patients’ information is incomplete), some selection bias could have occurred. Second, the measurement parameters were not compared with bilateral-approach or over-the-top procedure. Third, the follow-up was short. Although a high fusion rate is reported, the potential influence of limited graft volume on radiographic decompression and long-term fusion quality has not been evaluated, the longer follow-up is needed to confirm long-term fusion quality. Therefore, further prospective, randomized control trial and longer follow-up should be conducted to validate our views.

Conclusion

Unilateral-approach Endo-LIF can significantly improve the area of the central canal and contralateral foramen. Therefore, Endo-ILF unilateral direct decompression may be a promising option for CLSS with bilateral symptoms. (one side is mild).

Authors’ contributions

Conceptualization: Zeng-xin GaoFormal Analysis: Xingdong Cheng, Li JinInvestigation: Xu ShenMethodology: Zeng-xin GaoProject Administration: Xingdong Cheng, Xu ShenWriting – Original Draft: Xingdong Cheng, Xu ShenWriting – Review & Editing: Xingdong Cheng, Xu Shen, Li Jin.

Funding

Jiangsu Provincial Health Commission Project (LX2021015).

Data availability

The data that support the findings of this study are available from the corresponding author [Z Gao] upon reasonable request.

Declarations

Ethics approval and consent to participate

This study was authorized by the ethics committee of Zhongda hospital (2023ZDSYLL406). All patients signed an informed consent document. Our study adhered to the Declaration of Helsinki.

Consent for publication

N/A.

Competing interests

The authors declare no competing interests.