INTRODUCTION
Degenerative lumbar spondylolisthesis (DLS) is a disorder that presents the displacement of one vertebral body over the one below. Patients with DLS may have any combination of low back pain (LBP), buttock pain, neurogenic claudication, and radiculopathy [1-4]. They are generally older than 50 years, which is a differential aspect from congenital spondylolisthesis, and DLS occurs mainly at the L4–5 level as opposed to its isthmic counterpart, which occurs most commonly at the L5–S1 level [1,2]. DLS often has multiple pathologies combined with forward displacement, including facet hypertrophy, diffuse disc degenerative bulging, and buckling of the ligamentum flavum, which are highly related to spinal canal stenosis, and DLS is a major cause of LBP with spinal canal stenosis among the elderly [1,2,5]. Surgical procedure is commonly recommended in patients with uncontrolled pain with conservative treatment [6], and surgery showed superior to nonoperative care for managing DLS in the randomized, controlled study of Weinstein et al. [7]
The current review of instrumented fusion with canal decompression has been widely used to treat DLS [8]. In the United States, DLS accounts for the most significant proportion of lumbar fusion surgery, and the number more than doubled from 2004 to 2015 [9,10]. However, instrumented fusion has an issue related to the hospital cost and the cost-effectiveness compared to the decompression alone without fusion procedure [9]. In addition, fusion can have adjacent segment disease (ASD) after surgery during the follow-up periods, which needs revision surgery. In some countries, approximately 50% of patients undergo decompression alone [11], and well-designed studies [12-14] and systemic reviews [15,16] have recommended decompression alone. However, decompression alone is concerned with the fact that getting rid of bony, ligamentous elements and facet joints will cause iatrogenic segmental instability and progression of DLS. Therefore, instead of laminectomy, which was the conventional method of decompression, less invasive procedures that preserve the midline and the integrity of stabilizing structures of the segment are now commonly used [17-19].
This study focused on biportal endoscopic spinal surgery (BESS) and performed unilateral laminotomy for bilateral decompression (ULBD) for one segment of central canal stenosis with or without DLS. BESS has been reported to have many advantages as an endoscopic minimally invasive decompression procedure for treating spinal canal stenosis [20,21]. We hypothesized that endoscopic decompression of BESS also works for treating stenosis with DLS and stenosis without DLS.
MATERIALS AND METHODS
1. Study Design and Selection Criteria
This retrospective observational study evaluated the clinical and radiological outcomes of BESS in patients with central canal stenosis, with and without associated low-grade DLS. Data were collected from patients treated between January 2015 and December 2018, with a minimum follow-up period of 2 years. Ethical clearance was obtained from the Institutional Review Board (IRB) of Chungnam National University College of Medicine (IRB No. CNUH 2023-01-046), and all procedures adhered to the ethical standards outlined in the Declaration of Helsinki. Inclusion criteria included patients aged 18–80 years, radiological confirmation of moderate to severe central canal stenosis according to the Lumbar Central Canal Stenosis grading system [22], and a diagnosis of low-grade DLS (Meyerding grade I) [23]. In addition to central canal stenosis, patients with radiological evidence of lateral recess stenosis due to facet hypertrophy or ligamentous hypertrophy were included. However, severe foraminal stenosis, as classified by the Wildermuth grading system, was excluded from this study. Eligible patients experienced persistent symptoms, such as leg pain or neurogenic claudication, refractory to at least 3 months of conservative treatment, including physical therapy, nonsteroidal anti-inflammatory drugs, or epidural steroid injections. A total of 170 patients met the inclusion criteria. It was divided into 2 cohorts: group A, comprising 68 patients with central canal stenosis and low-grade DLS, and group B, consisting of 102 patients with central canal stenosis without DLS. For group A, the stability of the affected segment was confirmed by segmental stability, defined as a translation difference of ≤4.5 mm between flexion and extension lateral radiographs or an angulation of ≤15° on dynamic flexionextension radiographs [24,25]. Exclusion criteria included patients with high-grade spondylolisthesis (Meyerding grade II or higher), severe foraminal stenosis defined by the Wildermuth grading system [22,26], and previous lumbar spine surgery at the affected segment. Patients with coexisting pathological conditions, such as infections, tumors, trauma, or metabolic bone disorders, were also excluded. The study compared the outcomes of BESS in patients with central stenosis, with and without DLS, to assess the efficacy and stability of decompression without fusion in a minimally invasive approach.
2. Surgical Procedure
All surgeries were performed by a senior spine surgeon (HJL) with extensive experience in minimally invasive spinal procedures. Under general anesthesia, patients were positioned prone on a radiolucent operating table. A biportal endoscopic approach was utilized for ULBD. Two small portals were created: one for the endoscope and the other for surgical instruments. This technique allowed for direct visualization and decompression of the neural elements with minimal disruption to the paraspinal musculature and ligamentous structures. The surgical procedure utilized a 0° angled endoscope with a diameter of 4.0 mm, which provided a wide and clear visualization of the operative field. The saline irrigation pressure was maintained between 30–50 mmHg throughout the procedure to ensure a clear view while minimizing the risk of excessive fluid extravasation and intracranial hypertension. Adequate hemostasis was achieved using radiofrequency ablation. Key surgical nuances included meticulous preservation of the facet joint integrity to maintain spinal stability. The decompression procedure focused on removing hypertrophied ligamentum flavum and performing a partial medial facetectomy, as necessary, to relieve neural compression. Bone removal was performed in a stepwise fashion using a highspeed burr and Kerrison rongeurs, ensuring adequate decompression without over-resection of stabilizing structures. The contralateral decompression was carefully performed by tilting the endoscope and adjusting the working portal to facilitate complete bilateral decompression through a unilateral approach. Continuous saline irrigation was used to prevent heat buildup and optimize visualization to enhance surgical efficiency. Postoperatively, patients were encouraged to ambulate within 1–2 days, and the majority were discharged after 7–10 days (institutional protocols and regional practices) of observation and rehabilitation program, depending on individual recovery progress.
3. Clinical and Radiological Evaluation
Clinical outcomes were assessed preoperatively and at the final follow-up using the following standardized measures: visual analogue scale (VAS), Oswestry Disability Index (ODI), and Modified MacNab used to categorize patient satisfaction and overall outcome as excellent, good, fair, or poor based on symptom relief and functional improvement. Radiological outcomes were evaluated using dynamic flexion-extension radiographs to assess sagittal translation and segmental stability preoperatively and at the final follow-up. Magnetic resonance imaging (MRI) was performed preoperatively and postoperatively to verify decompression adequacy and rule out any residual stenosis or complications.
4. Statistical Analysis
Statistical analyses were conducted using the SPSS ver. 11.0 (SPSS Inc., Chicago, IL, USA). Continuous variables were expressed as mean±standard deviation, and categorical variables were presented as frequencies and percentages. Paired t-tests were used to compare each group’s preoperative and postoperative clinical scores. Independent t-tests were employed to evaluate differences between groups A and B. A chi-square or Fisher exact test was used for categorical variables as appropriate. A p-value <0.05 was considered statistically significant for all analyses.
RESULTS
1. Demographics and Characteristics
A total of 170 patients met the study criteria and were divided into 2 groups: group A (68 patients) with central stenosis and low-grade DLS and group B (102 patients) with central stenosis without DLS. The demographic data, disease characteristics, and intraoperative information for both groups are presented in Table 1. Group A had a mean age of 67.3±10.9 years, significantly older than group B, with a mean age of 56.0±18.7 years (p<0.001). The male-to-female ratio did not differ significantly between the 2 groups (p=0.27). The American Society of Anesthesiologists physical status classification was higher in group A (1.9±0.6) compared to group B (1.61±0.7), indicating a statistically significant difference (p<0.001). The median length of hospital stay was 10 days for both groups, with no significant difference observed (p=0.77). The median follow-up period was comparable between group A (1,052 days) and group B (1,039.5 days), with p=0.78. Mean operative time and estimated blood loss (EBL) per procedure level did not significantly differ between groups, with operative times of 62±3.8 minutes for group A and 63±7.2 minutes for group B (p=0.55) and EBL of 51±5.3 mL for group A and 59±5.8 mL for group B (p=0.74). The distribution of operated segments also varied between the groups. In group A, the L4–5 segment was the most frequently operated level (76.5%), while in group B, 55.9% of surgeries were at L4–5, and 29.4% were at L5–S1. No intraoperative complications, such as dural tears, were reported in either group.
2. Clinical and Radiographic Outcomes
Both groups demonstrated significant improvements in clinical outcomes at the final follow-up, as measured by the VAS for back and leg pain, the ODI, and Modified MacNab criteria. Table 2 summarizes the preoperative and final follow-up scores for each group. In group A, the mean VAS score for back pain improved significantly, decreasing from 3.8±2.4 preoperatively to 1.9±2.0 at the final follow-up (p=0.02). The mean VAS score for lower extremity pain also showed a notable reduction, from 6.4±1.8 preoperatively to 2.3±2.0 (p<0.01). ODI scores improved from 48.9±15.7 preoperatively to 23.1±17.5 at the final follow-up (p<0.01). According to the Modified MacNab criteria, 27.9% of patients in group A achieved excellent outcomes, 42.6% had good outcomes, 22.1% had fair outcomes, and 7.4% reported poor outcomes. In group B, similar improvements were observed. The mean VAS score for back pain decreased from 3.9±2.5 preoperatively to 1.7±1.9 at the final follow-up (p=0.02), while the mean VAS score for lower extremity pain reduced from 6.6±2.0 to 2.2±2.2 (p<0.01). ODI scores in group B significantly improved from 62.0±19.1 preoperatively to 20.4± 16.7 (p<0.01). Modified MacNab criteria results showed that 32.4% of patients in group B had excellent outcomes, 32.4% had good outcomes, 29.4% had fair outcomes, and 5.9% had poor outcomes. Radiographic assessments indicated no significant changes in sagittal translation in either group, suggesting that spinal stability was preserved postoperatively. Group A’s sagittal translation remained stable from 5.25±4.6 mm preoperatively to 5.31±7.2 mm at follow-up (p=0.77). Similarly, in group B, sagittal translation remained stable from 0.8±2.5 mm preoper-atively to 0.9±3.1 mm at the final follow-up (p=0.82). Additionally, neurogenic claudication symptoms significantly improved in both groups, with the incidence dropping to 10% in group A and 9.8% in group B at the final follow-up.
3. Comparison of Patient Outcomes
Intergroup comparison of clinical outcomes and complications was reported in Table 3. At the final follow-up, both groups showed similar improvements in clinical outcomes, with no statistically significant differences observed in the VAS scores for back and lower extremity pain, ODI scores, or Modified MacNab satisfaction ratings between groups A and B. These findings indicate that BESS provided comparable symptom relief and functional improvement in patients with central canal stenosis, regardless of low-grade DLS. While the preoperative ODI score was higher in group B (62.0±19.1) compared to group A (48.9±15.7) (p<0.001), the final ODI scores were similar between the groups, with group A at 23.1±17.5 and group B at 20.4±16.7 (p=0.34). Additionally, the Modified MacNab criteria outcomes did not differ significantly between the groups, reinforcing that both cohorts benefited equally from the procedure. No major complications, such as dural tears, infections, or reoperations, were observed in either group, and no cases of ASD were noted over the follow-up period.
DISCUSSION
The present study provides compelling evidence that BESS with decompression alone is an efficacious and minimally invasive intervention for managing low-grade DLS accompanied by central stenosis [21,27]. The substantial improvements in pain and functional outcomes, as evidenced by reductions in VAS and ODI scores, indicate that decompression without fusion can effectively alleviate symptoms and enhance the quality of life in a carefully selected patient population. The necessity of fusion in the surgical treatment of DLS remains a contentious issue, primarily due to the potential complications associated with the procedure, such as ASD and increased perioperative morbidity. While fusion provides segmental stability, it has drawbacks, including the potential for accelerated degeneration of adjacent levels [16,28]. Our results demonstrated no significant changes in sagittal translation at the final follow-up, suggesting that decompression alone does not exacerbate segmental instability in stable DLS. Interestingly, while it is generally expected that patients with DLS exhibit greater sagittal translation, our findings showed no significant difference between groups A (DLS) and B (non-DLS) in Table 2. This could be attributed to the strict inclusion of Meyerding grade I cases, where vertebral slippage remains minimal, along with adaptive stabilization mechanisms such as facet joint hypertrophy and ligamentous thickening, which may restrict excessive motion. Furthermore, variations in sagittal translation measurement on dynamic flexion-extension radiographs, influenced by patient positioning and degenerative stiffness, may have contributed to the observed findings. Additionally, in Table 2, the preoperative sagittal translation value of 5.2 mm does not indicate instability but represents the absolute distance between the upper and lower vertebral segments. Our study defined instability as an increase in more than 4.5 mm translation between dynamic lateral x-rays (flexion-extension). This distinction ensures that the inclusion criteria remain consistent with the study design. These findings highlight that decompression alone provides substantial symptom relief while preserving spinal stability, reinforcing its role as a viable alternative to fusion for appropriately selected patients. This study’s findings, which demonstrated no significant changes in sagittal translation at the final follow-up in either group, suggest that decompression alone does not exacerbate segmental instability in stable DLS.
Consequently, for patients without preoperative instability, BESS appears to be a viable alternative to fusion, effectively mitigating symptoms while preserving segmental motion and reducing the risk of ASD. The comparison analysis between patients with DLS and those with central stenosis without spondylolisthesis revealed no statistically significant differences in clinical outcomes at the final follow-up. This parity in outcomes underscores that low-grade DLS does not compromise the efficacy of decompression alone. While group B presented with a higher preoperative ODI score, likely reflective of a more significant baseline disability, both groups experienced comparable improvements postoperatively. These findings suggest that BESS is equally beneficial in managing symptomatic central stenosis, irrespective of low-grade spondylolisthesis.
Comparison with previous studies supports our findings that decompression alone is a viable option for selected patients with low-grade DLS. Försth et al. [13] and Austevoll et al. [12] conducted randomized controlled trials comparing decompression alone with fusion and found that decompression alone yielded comparable outcomes in pain relief and functional improvement while avoiding the risks of fusion. Additionally, Chang et al. [19] demonstrated that ULBD provided satisfactory symptom relief in patients with lumbar stenosis, irrespective of low-grade spondylolisthesis. This aligns with our results, which show significant improvement in pain and disability scores in both groups with and without DLS. Furthermore, Park et al. [20] highlighted that biportal endoscopic decompression achieved similar clinical outcomes to conventional microscopic decompression while offering advantages such as reduced tissue disruption, minimal blood loss, and faster postoperative recovery. Our findings further reinforce that BESS-ULBD is an effective technique for achieving adequate decompression without compromising spinal stability, particularly in the elderly population who may have higher surgical risks associated with fusion procedures. These findings suggest that BESS with decompression alone should be considered an effective alternative to fusion, particularly for patients without preoperative instability. The technique preserves spinal stability and provides substantial symptom relief, supporting its adoption as a standard minimally invasive approach for central canal stenosis with or without low-grade DLS.
BESS offers distinct advantages over traditional open decompression techniques. Its minimally invasive nature facilitates direct visualization and decompression of the neural elements while minimizing paraspinal musculature and ligamentous structure disruption. The clear and magnified endoscopic view with independent, various angular instrument movements enables us to perform the ULBD procedure precisely and meticulously [8,29]. The observed absence of major complications, such as dural tears or neurological deficits, and the low incidence of minor complications, such as superficial infections, attest to the safety profile of BESS [28,30-33]. Additionally, the lack of reoperations and the absence of adjacent segment pathology over the follow-up period further highlight the durability and stability of outcomes achieved through this approach. The authors showed the example of our illustrative case with A 60-year-old female presented with severe bilateral lower extremity radiating pain and neurogenic claudication. The patient’s symptoms had been progressively worsening over the past year, significantly impacting his quality of life. Preoperative imaging revealed low-grade DLS at the L4–5 level with severe central canal stenosis. The patient underwent ULBD using a BESS (Fig. 1). The comparison of preoperative and postoperative standard and dynamic x-rays (Fig. 2) showed no progressive listhesis. MRI of the lumbar spine later showed complete decompression of the stenotic lesion and adequate expansion of the thecal sac (Fig. 3). The patient reported significant leg pain relief and could resume daily activities without limitations. At the 2-year follow-up, no progression of segmental instability was observed, and the patient remained asymptomatic.
The limitations of this study were the retrospective design and the relatively small sample size, which may constrain the generalizability of the findings. Moreover, while the follow-up period adequately captures short-term and medium-term outcomes, it may not fully encompass the long-term sequelae, such as delayed instability or recurrent stenosis. Future research should include prospective studies with larger cohorts and extended follow-up durations to corroborate these results and further elucidate the long-term implications of decompression without fusion in treating DLS.
CONCLUSION
BESS with decompression alone offers an effective, minimally invasive alternative for managing stable low-grade DLS with central canal stenosis. This study demonstrated significant improvements in pain relief and functional outcomes without compromising spinal stability. The absence of major complications and the preservation of segmental motion suggest that decompression alone can achieve satisfactory results without the need for fusion. Although further research is needed to confirm these findings, BESS with decompression alone should be considered a viable option for appropriately selected patients.
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