Abstract
Background To evaluate the clinical and radiological outcomes of biportal endoscopic lumbar interbody fusion (BE-LIF) using the 30-degree endoscope in patients with lumbar spondylolisthesis and severe disc height loss and to highlight its technical advantages in endplate preparation and contralateral decompression.
Methods This retrospective study included 21 patients with single-level Meyerding grade II spondylolisthesis and preoperative disc height <5 mm who underwent BE-LIF combined with percutaneous pedicle screw fixation between February 2023 and February 2025. Clinical outcomes were assessed using the visual analog scale for back and leg pain and the Oswestry Disability Index. Radiographic parameters, including vertebral slip, disc height, and foraminal height, were evaluated on standing lateral x-ray images, while fusion status was assessed using Bridwell grading on 6-month postoperative computed tomography scans.
Results At a mean follow-up of 11.7 ± 2.6 months, all patients demonstrated statistically significant clinical improvement, visual analog scale scores decreased from 7.2 ± 0.6 to 1.5 ± 0.5 for low back pain, from 7.5 ± 0.5 to 1.7 ± 0.6 for leg pain, and the Oswestry Disability Index improved from 42.6 ± 5.7 to 15.7 ± 2.5 (P < 0.001). Radiologically, vertebral slip was reduced from 11.3 ± 1.5 mm to 2.1 ± 0.4 mm. Anterior and posterior disc heights increased from 5.6 ± 0.6 mm and 4.9 ± 0.5 mm to 8.5 ± 1.2 mm and 8.3 ± 1.4 mm, respectively. Foraminal height improved from 9.8 ± 1.7 mm to 14.7 ± 2.8 mm. Fusion was confirmed in all cases (Bridwell grade I: 28.6%, grade II: 71.4%), with no cage subsidence or major complications reported.
Conclusion The use of the 30-degree endoscope in BE-LIF for spondylolisthesis with severe disc collapse provides enhanced visualization, facilitates safe and effective decompression, and results in favorable clinical and radiological outcomes.
Level of Evidence 3.
- Minimally invasive spine surgery
- biportal endoscopic lumbar interbody fusion
- lumbar spondylolisthesis
- disc height loss
Introduction
Lumbar interbody fusion combined with pedicle screw fixation is a well-established and effective surgical approach commonly performed to treat lumbar spondylolisthesis (LS).1,2 In recent years, the adoption of minimally invasive spine surgery has expanded significantly, supported by advancements in modern surgical instruments and imaging technologies.3–5 Among these techniques, biportal endoscopic spine surgery (BESS) offers several advantages, utilizing 2 independent channels, 1 for the endoscope and 1 for instruments, thereby enhancing visualization with high magnification and providing a flexible working environment.6–9
Numerous studies have demonstrated favorable outcomes using the biportal endoscopic lumbar interbody fusion (BE-LIF) technique in conjunction with percutaneous pedicle screw fixation (PPSF).10–13 However, most of these studies have focused on cases with stenosis, instability, or low-grade spondylolisthesis.13 In contrast, higher-grade spondylolisthesis with Meyerding grade II or above, especially when accompanied by severe disc height (DH) loss, poses a unique challenge for posterior access, particularly in achieving sufficient interbody graft placement and proper reduction.14–16 In these cases, the goals of surgery are 2-fold: adequate neural decompression and restoration of DH to facilitate both optimal clinical outcomes and successful interbody fusion. One of the most critical steps is meticulous endplate preparation, ensuring the bony endplate remains intact while thoroughly removing cartilaginous tissue.10,17 This not only increases the surface area for fusion materials but also helps mobilize the segment, making reduction easier and more controlled. The biportal endoscopic approach offers a favorable platform for performing these tasks under direct visualization.
Direct endoscopic visualization during BE-LIF is critically dependent on the appropriate choice of scope angle, which determines the quality of magnification, field of view, and the surgeon’s ability to accurately identify anatomical structures within a limited corridor.18–20 The 0-degree endoscope, commonly used in biportal endoscopic procedures, provides a direct, intuitive line of sight and produces familiar anatomical perspectives.21–23 However, this straight view is constrained by a limited field of vision and a narrow working angle, making it difficult to navigate or visualize structures obscured by hypertrophic bone, collapsed disc spaces, or distorted anatomy—especially in cases of high-grade spondylolisthesis or severe central canal stenosis.21,23
Recent studies have highlighted the potential of 30-degree endoscopes in overcoming these limitations by offering a wider and more dynamic viewing field, particularly when performing contralateral decompression or deep endplate preparation.21,22 Unlike 0-degree optics, the 30-degree scope can bypass obstructing elements and visualize around corners, which facilitates safer dissection and improved visualization of the collapsed disc space and contralateral anatomy.18,23 Nonetheless, angled scopes generate images from an oblique axis, which may distort depth perception and create unfamiliar perspectives if not carefully interpreted. As such, successful application of a 30-degree scope requires deliberate orientation and a thorough understanding of altered spatial relationships during operation.18,19,23 Integrating this scope into BE-LIF for advanced spondylolisthesis cases offers significant advantages but also demands a refined surgical strategy to maximize its benefits while minimizing potential pitfalls.
This study analyzes the strategic advantages of using the 30-degree endoscope in performing BE-LIF for patients with spondylolisthesis accompanied by severe DH loss. We also present preliminary clinical and radiographic outcomes associated with this approach.
Methods
This retrospective cohort study enrolled patients who underwent single-level BE-LIF between February 2023 and February 2025. The study was conducted in accordance with the principles outlined in the Declaration of Helsinki and received ethical approval from the Institutional Review Board. Due to the retrospective nature of the study, the requirement for obtaining informed consent from individual participants was waived.
Inclusion Criteria and Patient Selection
Patients were eligible for inclusion if they had a confirmed diagnosis of LS presenting with significant clinical symptoms, including low back pain, radicular leg pain, and motor or sensory impairment. Radiological confirmation was based on magnetic resonance imaging and dynamic flexion–extension x-rays, which correlated with clinical findings and demonstrated single-level spondylolisthesis graded as Meyerding grade II and accompanied by severe DH loss. Severe DH loss was defined as a preoperative DH of less than 5 mm on lateral standing x-ray, calculated as the average of anterior and posterior disc space measurements. All included patients had failed conservative treatment for a minimum of 6 weeks and subsequently underwent BE-LIF combined with PPSF performed by the same lead surgeon. Exclusion criteria included coexisting spinal conditions such as infection, neoplasms, traumatic injury, or a history of prior lumbar spine surgery.
Surgical Technique
Anesthesia and Patient Positioning
All procedures were performed under general endotracheal anesthesia with the patient positioned prone on a radiolucent spine table equipped with a Wilson frame, which helped minimize intra-abdominal pressure. The table height was adjusted to optimize the use of intraoperative fluoroscopy, allowing for clear acquisition of both anteroposterior and lateral imaging. A 30-degree endoscope was utilized throughout the procedure to enhance visualization of the surgical field. All surgeries were performed by a single right-handed surgeon.
Skin Incisions and Portal Creation
The target surgical level was localized using both anteroposterior and lateral fluoroscopic views. A 1.5-cm longitudinal incision was made for the working portal, positioned along the line connecting the lateral margins of the pedicles and centered at the level of the lower endplate. The viewing portal was placed approximately 2.5 to 3 cm away, cranially on the left side and caudally on the right, to facilitate subsequent PPSF. Following fascial incision, serial dilators were used to carefully detach the multifidus muscle from the cranial lamina and access the intermuscular plane between the multifidus and longissimus muscles. Fluoroscopic triangulation was confirmed with the distal tip of the dilators directed to the spinolaminar junction, and the working portal oriented parallel to the disc space. This alignment is critical, as it optimizes the approach to the disc space and facilitates safe and efficient access for subsequent decompression and interbody fusion.
Unilateral Laminectomy
With continuous irrigation established via both portals, the initial bony landmark was identified at the junction between the inferior border of the cranial lamina and the base of the spinous process, known as the spinolaminar junction. A 4-mm diamond burr was then used to perform stepwise thinning of the cranial lamina until the insertion point of the ligamentum flavum (LF) was visualized. Once the LF attachment was reached, the burr was redirected laterally to thin the isthmus. The inferior articular process (IAP) was then separated using an osteotome and entirely removed. To further expand the working space and clearly expose Kambin’s triangle, the apex of the superior articular process (SAP) was drilled until the superior border of the pedicle was visible. All harvested bone fragments were collected and reserved for autologous grafting.
Endplate Preparation
The LF overlying the SAP was partially detached using a Penfield dissector to create an access window to the disc space (Figure 1A). Most of the LF, especially around the traversing nerve root (TNR) and exiting nerve root (ENR), was preserved to serve as a protective barrier for neural elements during deep disc space manipulation. Disc material and cartilaginous endplates were removed using angled curettes and chisels. Special attention was paid to avoid damaging the bony endplates by advancing the scope deeper and carefully inspecting the endplate surfaces. The anterior and lateral regions of the disc space were thoroughly prepared to optimize the fusion environment and facilitate spondylolisthesis reduction (Figure 1B).
(A) Adequate exposure of Kambin’s triangle (outlined in white) is achieved by burring the apex of the superior articular process (SAP). The ligamentum flavum (LF) is preserved and serves as a natural protective barrier for neural elements, particularly toward the spinal canal and exiting nerve root (ENR). (B) Clear visualization of both endplates is obtained through a 30-degree endoscope during the endplate preparation stage. (C) Bone graft materials and the transforaminal lumbar interbody fusion cage are inserted. The preserved LF provides a natural shield for neural structures, eliminating the need for a retractor during cage insertion. (D) The entire grafting process is performed under direct endoscopic visualization, ensuring accurate placement, maximizing contact surface area, and avoiding endplate injury. (E) Percutaneous pedicle screw fixation is performed, followed by spondylolisthesis reduction using a levering technique.
Insertion of Graft Materials and Cage
Autologous bone was collected using a Kerrison rongeur from the cranial and caudal lamina, as well as from the base of the spinous process. The previously removed IAP was meticulously cleaned of soft tissue and prepared for grafting. A multilayer bone grafting technique was employed, beginning with the placement of fine hydroxyapatite mixed with small autograft fragments into the anterior portion of the disc space. Next, the entire IAP was inserted, serving as a structural barrier to prevent migration of the graft materials. Finally, a transforaminal lumbar interbody fusion (TLIF) cage packed with additional autologous bone was inserted. We used the Zyston Curve PEEK TLIF cage (Zimmer Biomet) with a 32-mm footprint and 0 degrees of lordosis in all cases. All steps were performed under direct endoscopic visualization and confirmed with fluoroscopic guidance. To enhance visual clarity and surgical precision, irrigation pressure was reduced during this stage (Figure 1C and D).
Neural Decompression (Ipsilateral and Contralateral)
Following cage placement, neural decompression was extended to both the ipsilateral and contralateral sides. Under the enhanced visualization provided by the 30-degree endoscope, the “over-the-top” technique was employed. A Penfield dissector was used to gently detach the contralateral LF from its attachments before removing it in 2 separate pieces. A chisel with an appropriate angle was utilized to resect the contralateral SAP. This step ensured thorough decompression of both the ENRs and TNRs and facilitated further vertebral reduction during the final fixation phase.
PPSF and Spondylolisthesis Reduction
Ipsilateral pedicle screws were first inserted percutaneously through the original viewing and working portal incisions, followed by placement of contralateral screws in a similar manner. Rods were then inserted bilaterally. Under fluoroscopic guidance, spondylolisthesis reduction was performed by first tightening the caudal screws and then levering the cranial vertebra upward using a controlled technique. The maneuver was executed simultaneously on both sides to ensure balanced and symmetrical reduction. Final alignment and overall construct stability were confirmed using intraoperative fluoroscopic imaging (Figure 1E).
Wound Closure and Postoperative Care
After confirming proper implant positioning, the skin incisions were closed in layers using absorbable sutures for the fascia and subcutaneous tissue and nonabsorbable sutures for the skin.
Postoperatively, patients were encouraged to begin early mobilization with a lumbosacral orthosis, typically starting on the second postoperative day after drain removal. Intravenous antibiotics were administered for the first 24 hours. Routine follow-up included both clinical and radiographic evaluations at regular intervals, with fusion status assessed by computed tomography (CT) at 6 months postoperatively.
Measurement of Outcomes
Clinical outcomes were assessed using the visual analog scale (VAS) for both low back pain and radicular leg pain, as well as the Oswestry Disability Index (ODI), to evaluate functional disability. These scores were recorded preoperatively and at the final follow-up visit. Operative parameters, including operative time, estimated blood loss, length of hospital stay, and perioperative complications, were also documented. Radiological assessments were based on plain standing radiographs. The degree of spondylolisthesis was graded preoperatively according to the Meyerding classification. DH was measured pre- and postoperatively at the anterior, middle, and posterior portions of the disc space on lateral radiographs. Additional parameters, including lumbar lordosis (LL), segmental lordosis (SL), and foraminal height, were also evaluated (Figure 2). Postoperative fusion status was assessed postoperatively using CT at 6 months and classified according to the Bridwell interbody fusion grading system (Figure 3).
Radiographic measurement methods on lateral lumbar spine x-ray images used to evaluate spondylolisthesis. (A) Lumbar lordosis (LL), segmental lordosis (SL), and vertebral body slip (BS). (B) Anterior disc height (ADH), posterior disc height (PDH), and foraminal height (FH). (C) Postoperative radiograph.
Illustrative case of a 52-year-old female patient with Meyerding grade II L4–L5 spondylolisthesis and severe disc height loss. (A) Preoperative lateral radiograph. (B) Intraoperative fluoroscopic image and postoperative computed tomography (CT) at 3 mo demonstrating early bone bridging primarily within the intra-cage zone. (C) CT at 6 mo showing stable fusion in the intra-cage zone, with additional bone bridging observed in the extra-cage zone along the anterior vertebral body margin.
Statistical Analysis
Statistical analysis was performed to evaluate both clinical and radiological outcomes. Continuous variables, including VAS, ODI scores, and radiological measurements, were expressed as means ± SDs, while categorical variables were reported as frequencies and percentages. Pre- and postoperative clinical and radiological variables were compared using paired sample t tests. A P value of <0.05 was considered statistically significant. All statistical analyses were performed using SPSS Statistics version 28.0 (IBM Corp., Armonk, NY, USA).
Results
Patient Demographics and Baseline Characteristics
A total of 21 patients with LS and severe DH loss underwent single-level BE-LIF combined with PPSF (Table 1). The mean follow-up duration was 11.7 ± 2.6 months. The average patient age was 62.4 ± 9.5 years, with 13 women (61.9%) and 8 men (38.1%). Comorbidities, as defined by the modified 5-item frailty index, were present in 33.3% of patients, while 66.7% were diagnosed with osteoporosis. The distribution of affected levels was as follows: L4 to L5 in 11 patients (52.4%), L5 to S1 in 7 patients (33.3%), and L3 to L4 in 3 patients (14.3%).
Patient demographics and baseline characteristics.
Perioperative Parameters
The mean operative time for the entire procedure, including both interbody fusion and PPSF, was 211.0 ± 36.5 minutes. The average intraoperative blood loss was 231.0 ± 53.7 mL. The mean duration of hospital stay was 7.6 ± 1.9 days. No intraoperative complications such as incidental durotomy or nerve root injury were observed. Additionally, there were no perioperative complications related to wound infection or instrumentation.
Clinical Outcomes
Preoperatively, the majority of patients (61.9%) presented with combined sensory and motor disturbances. Clinical outcomes showed progressive improvement at all recorded time points, including prior to discharge, at 6 months postoperatively, and at the final follow-up (Table 2).
Clinical outcomes.
At final follow-up, all clinical outcome measures demonstrated statistically significant improvement. The mean VAS score for low back pain decreased from 7.2 ± 0.6 to 1.5 ± 0.5 (P < 0.001), and the VAS score for leg pain improved from 7.5 ± 0.5 to 1.7 ± 0.6 (P < 0.001). Similarly, the ODI improved markedly, from 42.6 ± 5.7 preoperatively to 15.7 ± 2.5 (P < 0.001) at the final follow-up.
Radiological Outcomes
Radiographic evaluations demonstrated significant improvements in multiple parameters following surgery (Table 3). The degree of vertebral body slip was markedly reduced from a preoperative mean of 11.3 ± 1.5 mm to 2.1 ± 0.4 mm postoperatively (P < 0.001). Both anterior and posterior DH significantly increased, with anterior DH improving from 5.6 ± 0.6 mm to 8.5 ± 1.2 mm, and posterior DH from 4.9 ± 0.5 mm to 8.3 ± 1.4 mm (both P < 0.001). Foraminal height also increased substantially, from 9.8 ± 1.7 mm preoperatively to 14.7 ± 2.8 mm postoperatively (P < 0.001).
Radiological outcomes.
In contrast, changes in spinal alignment parameters such as LL and SL were not statistically significant. LL remained stable, changing from 44.8° ± 4.9° preoperatively to 44.7° ± 3.6° postoperatively (P = 0.918), while SL changed from 18.6° ± 2.7° to 18.9° ± 2.2° (P = 0.437).
Routine postoperative CT images at 6 months confirmed solid interbody fusion in all cases. Bridwell grade I fusion was observed in 28.6% of patients, while grade II fusion was noted in 71.4%. No cases of cage subsidence greater than 2 mm were detected.
Discussion
Endoscopic lumbar interbody fusion, including both uniportal and biportal approaches, has gained significant traction as an effective technique for managing lumbar spinal instability while preserving paraspinal musculature and bony structures.9,24 Among these, BE-LIF has emerged as a widely adopted and reliable method, supported by growing clinical evidence—particularly for the treatment of degenerative spondylolisthesis.7,10,25–28 Our findings further support the safety and efficacy of BE-LIF, when combined with PPSF, in patients with spondylolisthesis and severe intervertebral DH loss, a population known to present technical challenges. Clinically, patients experienced early and sustained improvements in axial back pain, radicular symptoms, and functional disability. Both VAS and ODI scores improved significantly and were already evident prior to discharge, allowing patients to begin early ambulation and physical rehabilitation as early as postoperative day 2, in accordance with our institutional protocol. All patients were discharged only after appropriate wound healing and skin suture removal. These clinical benefits were maintained at 6-month follow-up, with no serious complications reported, indicating the durability and safety of the procedure.
Compared to conventional open procedures such as TLIF or posterior lumbar interbody fusion, BE-LIF offers several distinct advantages.27,29 Traditional approaches require extensive muscle dissection and retraction, which increase postoperative pain, prolong recovery time, and raise the risk of long-term muscle atrophy. Minimally invasive microscopic tubular-assisted fusion addresses some of these limitations but remains constrained by restricted visualization and fixed instrument trajectories. In contrast, BE-LIF, with complete separation of the working and viewing portals combined with magnified endoscopic visualization, maximizes preservation of the paraspinal muscles while still allowing precise access to the surgical target. This configuration enables highly flexible instrument maneuvering, facilitates accurate execution of surgical steps, and ultimately contributes to achieving surgical goals while minimizing complications.26,28,30,31 However, the application of BE-LIF in cases of high-grade spondylolisthesis (Meyerding grade ≥ II) or with severe intervertebral DH loss remains technically demanding. These challenges often require more time-consuming steps, particularly during endplate preparation and reduction of the slip. The collapsed disc space and distorted anatomical landmarks further complicate surgical orientation and precision. As a result, operative time and intraoperative blood loss in our cohort were relatively higher compared to previously published BE-LIF studies that involved more general populations with varying degrees of instability.10,29,32
Radiologically, the procedure achieved key surgical objectives. Restoration of both anterior and posterior DH, as well as foraminal height, was consistently observed, contributing to indirect decompression of the ENRs.10,31 Vertebral slip was effectively reduced through PPSF-assisted correction. Fusion outcomes were favorable, with all cases achieving Bridwell grade I or II fusion at 6 months and no instances of cage subsidence greater than 2 mm were recorded. These results reflect both the mechanical integrity of the construct and the meticulous preparation of the endplates.10,17,33,34 It is worth noting that cases of spondylolisthesis with severe DH loss are often accompanied by advanced disc collapse and Modic endplate degeneration.35,36 In such conditions, clear visualization and careful preservation of the bony endplate during meticulous removal of the cartilaginous layer play a critical role in reducing the risk of cage subsidence.31,33 This is one of the key advantages of endoscopic techniques, which provide direct, magnified visualization of the disc space.10,34
Endoscopic visualization in modern surgery has evolved remarkably over the past century, driven by continuous innovations in optical engineering.18,20,23,37 One of the most significant milestones was the introduction of the Hopkins rod-lens system, which replaced traditional air-filled lenses with solid glass rods separated by air spaces, markedly improving light transmission and image clarity.20,23,37 This design, later commercialized by Karl Storz, became the foundation of modern rigid endoscopy and enabled the development of various angled optics ranging from 0° to 120° for diverse surgical needs.20,37 Among these, 0° forward-viewing and 30° forward-oblique endoscopes are the most commonly used standards. While the 0° endoscope provides a straightforward and intuitive field of vision suitable for surgeons with limited endoscopic experience, the 30° endoscope offers a wider and more flexible visual field through simple rotation, facilitating visualization of lateral and deep structures without changing portal position.18,23 These technological advances laid the groundwork for modern spinal endoscopy, where angled optics have become increasingly important for complex decompression and fusion procedures.19,21,22
In addition to the general benefits of BESS, the use of a 30-degree endoscope offers several specific technical advantages that enhance the safety and efficacy of BE-LIF,21,22,38 particularly in anatomically challenging cases such as spondylolisthesis with severe DH loss.10,17
One of the most notable benefits of the 30-degree endoscope is the significant expansion of the visual field.17,19,21–23 Unlike a 0-degree scope, the angled view allows surgeons to visualize the anterior and lateral regions of the disc space more effectively, which is especially valuable in deep and narrow surgical corridors, such as those seen in collapsed discs or advanced degenerative conditions (Figure 4). This enhanced visualization facilitates thorough removal of cartilaginous endplate while preserving the integrity of the underlying bony endplate—an essential factor in reducing the risk of cage subsidence and promoting successful fusion.10,17 Moreover, by rotating the angled scope, surgeons can dynamically adjust the viewing angle without changing portal positions, allowing these maneuvers to be performed safely, precisely, and under continuous endoscopic guidance.19,22,23 This flexibility enhances the quality of endplate preparation and contributes to long-term construct stability.
Illustration of the differences in viewing angles and fields of vision between 0- and 30-degree endoscopes. (A) Schematic showing the principle of viewing direction and field coverage for 0-, 15-, and 30-degree endoscopes. (B) The 30-degree scope allows expansion of the visual field by simple rotation of the endoscope. C) When used dynamically, the 30-degree scope enables maximized visualization across the entire working area.
Furthermore, the 30-degree scope improves the efficiency of contralateral decompression using the “over-the-top” technique, allowing for a wider viewing angle while preserving more of the bony structures, especially the spinous process and contralateral lamina.21,22 This is beneficial for reducing surgical trauma while still achieving complete decompression of both TNR and ENR.
In cases of high-grade spondylolisthesis, where anatomical distortion such as posteriorly displaced facet joints can obscure the working space, the enhanced visualization provided by the 30-degree scope becomes even more critical. It is well recognized that for right-handed surgeons performing BESS, approaching from the left side often provides better soft tissue preservation and a clearer working corridor. However, in the setting of spondylolisthesis with DH collapse, the facet joint complex tends to shift posteriorly, creating a mechanical obstruction that limits the advancement of instruments through the working portal toward the deep portion of the disc space (Figure 5D). To overcome this challenge, we adjust the trajectory of the working portal incision more cranially, aligning it more parallel to the disc space (Figure 5A). As a consequence, the viewing portal must also be repositioned more cranially to maintain the optimal distance of 2.5 to 3 cm between the 2 portals, preserving true triangulation (Figure 5B and C). Under these modified portal positions, the field of view becomes more oblique and limited, particularly when using a 0-degree scope. In this configuration, visualizing the entire disc space, especially the cranial endplate, becomes difficult. The 30-degree scope effectively addresses this limitation by enabling angled visualization that compensates for the altered geometry, providing clear and comprehensive endplate exposure (Figure 5E).
Advantages of endplate visualization in a case of Meyerding grade II L4–L5 spondylolisthesis with severe disc space narrowing, operated by a right-handed surgeon standing on the patient’s left side. (A) Intraoperative lateral fluoroscopy shows optimal working portal placement, aligned parallel to both endplates. This alignment is critical for effective manipulation and smooth cage insertion. (B) Anteroposterior (AP) intraoperative fluoroscopic view showing the scope portal positioned approximately 3 cm cranial to the working portal. (C) Lateral fluoroscopic image demonstrating precise endplate cartilage removal using a small chisel, made easier by the initial parallel alignment of the working portal to the disc space. (D) Illustration showing that when using a 0-degree scope, full visualization of the endplate typically requires placing the working portal more caudally, which may compromise access due to posterior facet joint obstruction. (E) With a 30-degree scope, the working portal can remain parallel to the disc space, while the scope portal is positioned more cranially (dashed green line). By rotating the angled lens, the surgeon can maintain full visualization of both endplates.
Similarly, when approaching from the patient’s right side, the working portal is also oriented parallel to the disc space to facilitate cage insertion (Figures 6A through D). In this setup, the viewing portal is positioned 2.5 to 3 cm caudally to maintain adequate triangulation. However, in cases of spondylolisthesis, the posterior translation of the facet joint complex can obstruct the view of the caudal endplate, particularly when using a 0-degree endoscope. The straight visual axis limits the ability to fully assess and prepare the caudal endplate, which is essential for optimal cage positioning and fusion (Figure 6E). This limitation is effectively overcome by using a 30-degree scope. By simply rotating the angled scope, the visual field can be expanded toward the caudal direction, allowing complete and safe endplate preparation (Figure 6F).
Advantages of endplate visualization in a case of Meyerding grade II L5–S1 spondylolisthesis with severe disc space narrowing, operated by a right-handed surgeon standing on the patient’s right side. (A) Intraoperative anteroposterior (AP) fluoroscopic view showing the working portal placed cranially, with the scope portal positioned approximately 3 cm caudally. (B) Lateral fluoroscopic image demonstrating that the working portal is aligned parallel to both endplates. (C) Cartilaginous endplate removal using a small chisel. (D) Intraoperative estimation of cage size, performed under clear endoscopic visualization combined with fluoroscopy, ensuring endplate integrity is preserved while achieving sufficient loosening to facilitate reduction. (E) When using a 0-degree scope, visualization of the caudal endplate—especially its deeper portion—becomes limited due to the straight-line viewing axis. (F) In contrast, the 30-degree scope provides an expanded field of view, allowing clear visualization of the entire caudal endplate, even in deeper zones.
Despite these advantages, the use of the 30-degree endoscope requires specific training and experience.21–23,38 The angled view alters spatial perception and may initially challenge orientation, particularly for surgeons accustomed to working with 0-degree scopes or microscopes.18,23 However, once mastered, the 30-degree scope becomes a powerful tool for maximizing visualization, expanding surgical indications, and improving technical confidence in complex BE-LIF cases.
In summary, BE-LIF combined with PPSF appears to be a safe and effective approach for treating LS with severe DH loss, showing encouraging short-term clinical and radiological outcomes. The use of a 30-degree endoscope may offer additional advantages in this context, including improved visualization for contralateral decompression and more controlled endplate preparation, which are especially beneficial in anatomically challenging cases. However, these findings should be interpreted with caution due to several limitations. This was a single-center study with a relatively small sample size, focused specifically on a subgroup of severe DH loss, and all procedures were performed by a single experienced surgeon familiar with endoscopy technique. Moreover, the absence of a comparative group using a 0-degree scope limits our ability to draw definitive conclusions about the relative benefits of the 30-degree system. Further prospective, multicenter studies with larger and more diverse populations are needed to validate these results and better define the role of angled endoscopy in advanced lumbar fusion surgery.
Conclusion
BE-LIF using the 30-degree endoscope is a promising minimally invasive technique for the treatment of LS with severe DH loss. The angled visualization offers significant advantages in accessing deep and narrow disc spaces, facilitating safe decompression, meticulous endplate preparation, and accurate cage placement. Although further studies with larger sample sizes and comparative designs are warranted, the current findings suggest that the 30-degree scope may enhance the effectiveness and applicability of BE-LIF in anatomically challenging cases.
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
Institutional Review Board This study was conducted in accordance with the Declaration of Helsinki and with approval from the Ethics Committee and Institutional Review Board of Xuyen A General Hospital Medical Research Council (Institutional Review Board approval, No. 05/2025/QD-BVXA).
Data Availability Statement The data used in this research were acquired from a public resource.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2025 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
References
- 1.↵Mobbs RJ , Phan K , Malham G , Seex K , Rao PJ . Lumbar interbody fusion: techniques, indications and comparison of interbody fusion options including PLIF, TLIF, MI-TLIF, OLIF/ATP, LLIF and ALIF. J Spine Surg. 2015;1(1):2–18. 10.3978/j.issn.2414-469X.2015.10.05
- 2.↵Verma R , Virk S , Qureshi S . Interbody fusions in the lumbar spine: a review. HSS J. 2020;16(2):162–167. 10.1007/s11420-019-09737-4
- 3.↵Choi JY , Park SM , Kim HJ , Yeom JS . Recent updates on minimally invasive spine surgery: techniques, technologies, and indications. Asian Spine J. 2022;16(6):1013–1021. 10.31616/asj.2022.0436
- 4.↵Goldberg JL , Härtl R , Elowitz E . Minimally invasive spine surgery: an overview. World Neurosurg. 2022;163:214–227. 10.1016/j.wneu.2022.03.114
- 5.↵Prabhu MC , Jacob KC , Patel MR , Pawlowski H , Vanjani NN , Singh K . History and evolution of the minimally invasive transforaminal lumbar interbody fusion. Neurospine. 2022;19(3):479–491. 10.14245/ns.2244122.061
- 6.↵Prabhu MC , Jacob KC , Patel MR , Pawlowski H , Vanjani NN , Singh K . History and evolution of the minimally invasive transforaminal lumbar interbody fusion. Neurospine. 2022;19(3):479–491. 10.1016/j.semss.2024.101084
- 7.↵Kang MS , Heo DH , Kim HB , Chung HT . Biportal endoscopic technique for transforaminal lumbar interbody fusion: review of current research. Int J Spine Surg. 2021;15(suppl 3):S84–S92. 10.14444/8167
- 8.↵Park M-K , Son S-K . Biportal endoscopic lumbar interbody fusion: review of current evidence and the literature. J Minim Invasive Spine Surg Tech. 2021;6(Suppl 1):S171–S178. 10.21182/jmisst.2021.00066
- 9.↵Ahn Y , Youn MS , Heo DH . Endoscopic transforaminal lumbar interbody fusion: a comprehensive review. Expert Rev Med Devices. 2019;16(5):373–380. 10.1080/17434440.2019.1610388
- 10.↵Pao JL . Biportal endoscopic transforaminal lumbar interbody fusion using double cages: surgical techniques and treatment outcomes. Neurospine. 2023;20(1):80–91. 10.14245/ns.2346036.018
- 11.↵Zhu C , Liang J , Pan H , Zhang W . Far lateral lumbar interbody fusion with unilateral pedicle screw fixation and double traversing cages using a biportal endoscopic technique. Acta Neurochir (Wien). 2023;165(8):2165–2169. 10.1007/s00701-023-05702-7
- 12.↵Heo DH , Eum JH , Jo JY , Chung H . Modified far lateral endoscopic transforaminal lumbar interbody fusion using a biportal endoscopic approach: technical report and preliminary results. Acta Neurochir (Wien). 2021;163(4):1205–1209. 10.1007/s00701-021-04758-7
- 13.↵Heo DH , Lee DC , Kim HS , Park CK , Chung H . Clinical results and complications of endoscopic lumbar interbody fusion for lumbar degenerative disease: a meta-analysis. World Neurosurg. 2021;145:396–404. 10.1016/j.wneu.2020.10.033
- 14.↵Kumar M , Rai V , Joshi A , Nalin S , Gandhi MK . Reduction of high-grade spondylolisthesis using minimally invasive spine surgery-transforaminal lumbar interbody fusion “trial-in-situ” technique: a technical note with case series. Asian Spine J. 2024;18(5):712–718. 10.31616/asj.2024.0224
- 15.↵Rajakumar DV , Hari A , Krishna M , Sharma A , Reddy M . Complete anatomic reduction and monosegmental fusion for lumbar spondylolisthesis of Grade II and higher: use of the minimally invasive “rocking” technique. Neurosurg Focus. 2017;43(2):E12. 10.3171/2017.5.FOCUS17199
- 16.↵Harakuni T , Iwai H , Oshima Y , et al . Full-endoscopic lumbar interbody fusion for treating lumbar disc degeneration involving disc height loss: technical report. Medicina (Kaunas). 2020;56(9):478. 10.3390/medicina56090478
- 17.↵Park H-J , Shin JI , You K-H , et al . Biportal endoscopic transforaminal lumbar interbody fusion: how to improve fusion rate? Int J Spine Surg. 2024;18(5):582–588. 10.14444/8648
- 18.↵Liu CY , Wang MY , Apuzzo MLJ . The physics of image formation in the neuroendoscope. Childs Nerv Syst. 2004;20(11–12):777–782. 10.1007/s00381-004-0930-6
- 19.↵Klangsin S , Ngaojaruwong N , Tintara H . Comparison of 30-degree and 0-degree laparoscopes in the visualisation of the inferior epigastric vessel, rectus abdominis muscle and bladder dome in gynaecologic laparoscopy. J Obstet Gynaecol. 2022;42(6):2203–2207. 10.1080/01443615.2022.2036957
- 20.↵Gaab MR . Instrumentation: endoscopes and equipment. World Neurosurg. 2013;79(2 Suppl):S14.e11–S14.e21. 10.1016/j.wneu.2012.02.032
- 21.↵Kim N , Jung SB . Percutaneous unilateral biportal endoscopic spine surgery using a 30-degree arthroscope in patients with severe lumbar spinal stenosis: a technical note. Clin Spine Surg. 2019;32(8):324–329. 10.1097/BSD.0000000000000876
- 22.↵Kim JE , Choi DJ . Unilateral biportal endoscopic decompression by 30° endoscopy in lumbar spinal stenosis: technical note and preliminary report. J Orthop. 2018;15(2):366–371. 10.1016/j.jor.2018.01.039
- 23.↵Phillips BB . General principles of arthroscopy. Campbell’s Operative Orthopaedics. 3; 2003:2497–2514.
- 24.↵Pholprajug P , Kotheeranurak V , Liu Y , Kim JS . The endoscopic lumbar interbody fusion: a narrative review, and future perspective. Neurospine. 2023;20(4):1224–1245. 10.14245/ns.2346888.444
- 25.↵Ding Y , Chen H , Wu G , Xie T , Zhu L , Wang X . Comparison of efficacy and safety between unilateral biportal endoscopic transforaminal lumbar interbody fusion versus uniportal endoscopic transforaminal lumbar interbody fusion for the treatment of lumbar degenerative diseases: a systematic review and meta-analysis. BMC Musculoskelet Disord. 2024;25(1):1037. 10.1186/s12891-024-08146-x
- 26.↵Kang MS , You KH , Choi JY , Heo DH , Chung HJ , Park HJ . Minimally invasive transforaminal lumbar interbody fusion using the biportal endoscopic techniques versus microscopic tubular technique. Spine J. 2021;21(12):2066–2077. 10.1016/j.spinee.2021.06.013
- 27.↵Lin GX , Yao ZK , Zhang X , Chen CM , Rui G , Hu BS . Evaluation of the outcomes of biportal endoscopic lumbar interbody fusion compared with conventional fusion operations: a systematic review and meta-analysis. World Neurosurg. 2022;160:55–66. 10.1016/j.wneu.2022.01.071
- 28.↵Luan H , Peng C , Liu K , Song X . Comparing the efficacy of unilateral biportal endoscopic transforaminal lumbar interbody fusion and minimally invasive transforaminal lumbar interbody fusion in lumbar degenerative diseases: a systematic review and meta-analysis. J Orthop Surg Res. 2023;18(1):888. 10.1186/s13018-023-04393-1
- 29.↵Park MK , Park SA , Son SK , Park WW , Choi SH . Clinical and radiological outcomes of unilateral biportal endoscopic lumbar interbody fusion (ULIF) compared with conventional posterior lumbar interbody fusion (PLIF): 1-year follow-up. Neurosurg Rev. 2019;42(3):753–761. 10.1007/s10143-019-01114-3
- 30.↵Kim JE , Yoo HS , Choi DJ , Park EJ , Jee SM . Comparison of minimal invasive versus biportal endoscopic transforaminal lumbar interbody fusion for single-level lumbar disease. Clin Spine Surg. 2021;34(2):E64–E71. 10.1097/BSD.0000000000001024
- 31.↵Duong TVH , Tuan PA , Vu HV , et al . Effectiveness of biportal endoscopic lumbar interbody fusion using the multi-layer bone grafting technique: a retrospective study from vietnam. Asian Spine J. 2025;19(2):228–241. 10.31616/asj.2024.0522
- 32.↵Park DY , Upfill-Brown A , Curtin N , et al . Clinical outcomes and complications after biportal endoscopic spine surgery: a comprehensive systematic review and meta-analysis of 3673 cases. Eur Spine J. 2023;32(8):2637–2646. 10.1007/s00586-023-07701-9
- 33.↵Polikeit A , Ferguson SJ , Nolte LP , Orr TE . The importance of the endplate for interbody cages in the lumbar spine. Eur Spine J. 2003;12(6):556–561. 10.1007/s00586-003-0556-5
- 34.↵Calek AK , Cornaz F , Suter M , Fasser MR , Farshad M , Widmer J . Endplate weakening during cage bed preparation significantly reduces endplate load capacity. Eur Spine J. 2024;33(7):2621–2629. 10.1007/s00586-024-08289-4
- 35.↵Lan M , Ou Y , Wang C , et al . Patients with modic type 2 change have a severe radiographic representation in the process of lumbar degeneration: a retrospective imaging study. J Orthop Surg Res. 2019;14(1):298. 10.1186/s13018-019-1355-y
- 36.↵Mu X , Deng H , Wei X , Wei J , Caggiari G . Do modic changes contribute to lumbar instability or other way around? A retrospective study based on their types, extents, and affected lumbar segments. BMC Musculoskelet Disord. 2023;24(1):879. 10.1186/s12891-023-07011-7
- 37.↵Tosi U , Guadix SW , Cohen AR , Souweidane MM . Neuroendoscopy: how we got here. World Neurosurg. 2023;178:298–304. 10.1016/j.wneu.2023.07.124
- 38.↵Kim JE , Choi DJ . Unilateral biportal endoscopic spinal surgery using a 30° arthroscope for L5-S1 foraminal decompression. Clin Orthop Surg. 2018;10(4):508–512. 10.4055/cios.2018.10.4.508
