Abstract
Background Two widely used full-endoscopic lumbar interbody fusion (FE-LIF) techniques include the facet-preserving trans-Kambin approach, performed via a transforaminal corridor, and the facet-sacrificing endoscopic posterolateral transforaminal lumbar interbody fusion, which utilizes an interlaminar route. More recently, several authors have introduced an emerging transfacet endoscopic approach as an alternative, minimally invasive strategy for LIF. However, the majority of these studies have relied on direct decompression of neural elements, and the effectiveness of indirect decompression following transfacet endoscopic fusion has not yet been established.
Surgical Technique This study describes a keyhole transfacet FE-LIF technique that employs indirect decompression to decompress neural elements. A limited facetectomy is performed using an endoscopic round burr to create a keyhole transfacet osseous corridor, allowing disc removal, endplate preparation, and interbody cage insertion without direct visualization or manipulation of the exiting or traversing nerve roots. When necessary, supplemental endoscopic direct decompression can be performed following cage placement in the same setting.
Clinical Application This study highlights the cases of 4 patients with diverse degenerative lumbar spine pathologies: low-grade degenerative spondylolisthesis, low-grade isthmic spondylolisthesis with severely collapsed disc space, segmental coronal lumbar deformity with severe spinal canal stenosis, and pseudarthrosis following prior lumbar interbody fusion surgery. All patients underwent keyhole transfacet FE-LIF with an indirect decompression technique and had a minimum follow-up of 1 year.
Conclusion This study describes the surgical technique for indirect decompression performed in a prone position using keyhole transfacet endoscopic fusion, presents early clinical application, and reports short-term radiographic observation associated with this technique.
Clinical Relevance The keyhole transfacet endoscopic fusion offers a minimally invasive approach for achieving indirect decompression in the prone position in patients with various lumbar degenerative spinal conditions. In addition, adjunctive direct decompression can be performed in the same setting after cage insertion when indicated.
Level of Evidence 5.
Introduction
Endoscopic spine surgery has demonstrated favorable outcomes in the management of various spinal disorders.1,2 More recently, these techniques have been adapted for lumbar interbody fusion (LIF) to minimize surgical morbidity and facilitate faster recovery.3,4 Full-endoscopic lumbar interbody fusion (FE-LIF) employs a uniportal endoscopic approach to achieve interbody fusion. Kim et al described 2 principal posterior approaches for FE-LIF: the facet-preserving trans-Kambin (KLIF) technique and the facet-sacrificing endoscopic posterolateral transforaminal lumbar interbody fusion (EPTLIF).5 The KLIF technique utilizes a transforaminal route through Kambin’s triangle to access the disc space, often requiring adjunctive foraminoplasty to accommodate cage insertion. This approach primarily depends on indirect decompression to relieve neural elements without entering the spinal canal.6 In contrast, EPTLIF is performed via an interlaminar approach and typically involves direct decompression, including complete facetectomy and resection of the ligamentum flavum, similar to minimally invasive transforaminal lumbar interbody fusion (MI-TLIF).7
More recently, several studies have reported encouraging results using an emerging transfacet (or transarticular process) endoscopic approach. This technique accesses the target disc through a transfacet osseous corridor; however, most reported methods involve varying degrees of articular process resection to directly expose and decompress the neural elements.8–10
In this article, we present the keyhole transfacet FE-LIF technique for the treatment of various degenerative lumbar spinal conditions, including a case of pseudarthrosis following prior LIF. To our knowledge, this is the first study that demonstrates the initial and short-term radiographic observation of indirect decompression achieved through a transfacet endoscopic fusion approach.
Technical Notes
This is a technical description and case illustration outlining the surgical steps of the keyhole transfacet FE-LIF procedure. Patients’ medical records and radiographic data were retrospectively reviewed. Institutional Review Board approval was obtained from Samut Sakhon Hospital (SKH REC 41/2569/V.1) prior to data collection, and the requirement for informed consent was waived.
Surgical Techniques
Patient Positioning and Incisions
Under general anesthesia, the patient was positioned prone on a radiolucent operating table. Neurophysiologic monitoring was not utilized. The C-arm fluoroscope was positioned on the contralateral side of the planned endoscopic transfacet approach. Skin entry points for percutaneous pedicle screw insertion were marked bilaterally at the target level using fluoroscopic guidance (eg, L4–L5 in this description). Following standard skin preparation and draping, the procedure commenced with four 2-cm skin incisions. Guide needles were advanced through the pedicles of L4 and L5 bilaterally, and guidewires were then inserted into the vertebral bodies. The needles were subsequently removed while maintaining the guidewires in place, with their external ends secured within the operative field.
Subsequently, the fascial incision at the cranial pedicle screw entry site on the endoscopic access side (eg, the left L4 incision in this illustration) was extended caudally to facilitate insertion and maneuverability of the working cannula and endoscope. A pencil-tip dilator was then advanced and docked onto the left L4–5 facet joint through the extended fascial opening, with the position confirmed on lateral fluoroscopy. A beveled-tip working sleeve was subsequently introduced over the dilator (Figure 1A).
Docking the working sleeve on the L4–L5 facet joint (A), identification of the facet joint capsule (B), and the dorsal surface of the facet joint line (C, red asterisk). Drilling along the facet joint line (D), visualization of the lateral extension of the ligamentum flavum within the keyhole transfacet corridor (E), exposure of the posterolateral disc beneath the ligamentum flavum (F), and guidewire insertion into the disc space (G and H). IAP, inferior articular process; SAP, superior articular process; LF, ligamentum flavum.
Identifying the Facet Joint Capsule and Bony Facet Joint Line
A full-endoscopic system (VERTEBRIS, RIWOspine GmbH, Knittlingen, Germany) was used, featuring an outer diameter of 9.3 × 7.4 mm, a working channel of 5.6 mm, a working length of 177 mm, and a 20° angled lens. The procedure began with endoscopic soft tissue clearance to expose and identify the facet joint capsule (Figure 1B and Video 1). The capsule was then incised using an endoscopic punch to reveal the dorsal surface of the facet joint line, corresponding to the articulation between the L4 inferior articular process (IAP) and the L5 superior articular process (SAP) in this case (Figure 1C).
Endoscopic Keyhole Transfacet Bone Work
Endoscopic bone work was then initiated using a 5.5-mm round burr to drill along the facet joint line (Figure 1D). The transfacet drilling was performed in a posterolateral-to-anteromedial trajectory, directed toward the posterolateral aspect of the disc space, thereby creating a keyhole working corridor through a limited facetectomy. When indirect decompression alone was intended, bone removal was preferentially carried out lateral to the facet joint line to preserve the medial wall of the IAP, avoiding violation of the ipsilateral lamina and the ligamentum flavum overlying the traversing nerve root. The preserved medial wall of the IAP serves as a protective barrier for the traversing nerve root during trialing and cage insertion. The cranial and caudal limits of the bony resection were intermittently verified with lateral fluoroscopy to ensure they did not extend beyond the disc space. In addition, the superior wall of the facet joint, the lateral aspect of the SAP, and the pars interarticularis were preserved to protect the exiting nerve root.
The limited facetectomy was continued as described until the ventral cortex of the facet joint was reached, allowing identification of the lateral extension of the ligamentum flavum within the foraminal zone, located beneath the facet joint and overlying the posterolateral aspect of the disc (Figure 1E). The bony work was then further extended within the transfacet corridor to create a 10- to 12-mm working space, sufficient for insertion of a custom-made double-tip Harrison cage glider. Care was taken to avoid violation of the superior margin of the inferior pedicle during this step. Finally, the exposed ligamentum flavum was resected to access the target disc space (Figure 1F).
Discectomy and Endplate Preparation
Disc work was initiated using an endoscopic arrowhead annulus knife to perform the annulotomy and establish a working tract within the disc, typically directed toward the midline. A guidewire was then advanced into the disc space through the endoscopic working channel (Figure 1G), with its position confirmed on both lateral and anteroposterior fluoroscopic views (Figure 1H). The endoscope and working sleeve were subsequently withdrawn, and an initial dilator was introduced into the disc space over the guidewire (Figure 2A), after which the guidewire was removed. The cage glider sleeve was then compressed around the dilator (Figure 2B) and advanced along it until the glider tips were positioned at the posterior aspect of the disc space in a craniocaudal orientation (Figure 2C). Finally, the initial dilator was removed, leaving the glider in place (Figure 2D).
Insertion of the initial dilator over the guidewire (A), double-tip custom-made cage gliders (B), and placement of the cage glider within the transfacet bony corridor (C and D). Disc work and endplate preparation (E), cage insertion through the cage glider (F), and confirmation of final cage position using anteroposterior and lateral fluoroscopy (G).
Discectomy and endplate preparation were then performed through the cage glider under lateral fluoroscopic guidance using pituitary rongeurs and appropriately sized paddle distractors (Figure 2E). Care was taken to avoid over-distraction of the disc space and violation of the bony endplates. Following these steps, the endoscope can be reintroduced to directly visualize the prepared endplates and, if necessary, complete any remaining endplate preparation (Video 1).
Trialing and Interbody Cage Insertion
Sequentially larger trial spacers were inserted through the cage glider into the prepared disc space until an interference fit was achieved, guiding selection of the appropriate cage size. In this case, a conventional transforaminal lumbar interbody fusion (TLIF) polyetheretherketone cage filled with demineralized bone matrix was used as the interbody device. The prepared cage was then advanced into the disc space via the cage glider (Figure 2F). Final cage positioning was confirmed on both anteroposterior and lateral fluoroscopic views prior to removal of the insertion handle. (Figure 2G).
Adjunctive Direct Decompression (If Indicated)
Following cage insertion, the endoscope can be reintroduced to assess cage positioning and confirm the integrity of the operated facet joint. Additional direct decompression may be performed at this stage if indicated. Video 2 demonstrates this step in another patient. Percutaneous pedicle screw and rod placement was then completed, followed by standard wound closure. A surgical drain is not routinely used, even when adjunctive direct decompression is performed.
Illustrative Cases
Case 1
A 60-year-old woman presented with chronic low back pain and bilateral L5 radicular symptoms, more pronounced on the left side. Radiographs demonstrated low-grade degenerative spondylolisthesis at L4–5 (Figure 3A) and corresponding magnetic resonance imaging (MRI) revealed severe spinal canal stenosis, with a thecal sac cross-sectional area (CSA) of 59.6 mm² (Figure 3B).
Preoperative lumbar radiographs (A) and magnetic resonance images (MRI) (B). Postoperative lumbar radiographs (C), early postoperative MRIs (D), and 1-year follow-up MRIs (E).
The patient underwent keyhole transfacet FE-LIF at L4–5 without direct decompression. The endoscopic transfacet approach was performed on the left side, corresponding to the side of more severe radicular symptoms. Postoperative radiographs are shown in Figure 3C. The early postoperative MRI demonstrated an increase in the thecal CSA to 90.5 mm², representing a 51.8% improvement (Figure 3D). The 1-year follow-up MRI revealed further spinal canal remodeling at the operated level, with a thecal sac CSA of 145.9 mm², corresponding to a 244.8% increase from the preoperative value (Figure 3E).
Case 2
A 51-year-old man presented with chronic low back pain and right-sided L5 radicular symptoms. Plain radiographs demonstrated grade 2 isthmic spondylolisthesis at L4–5 with a severely collapsed disc space (Figure 4A). MRI revealed severe bilateral foraminal stenosis at the same level (Figure 4B). The keyhole transfacet endoscopic approach was performed at L4–5 on the right side, corresponding to the patient’s symptomatic side.
Preoperative lumbar radiographs (A) and parasagittal magnetic resonance images (MRIs) (B). Postoperative lumbar radiographs (C) and 1-year follow-up parasagittal MRIs (D).
To address the severely collapsed disc space, an endoscopic diamond round burr was used to drill the posterior aspect of the disc and remove syndesmophytes. Then, after positioning the cage glider, sequentially larger paddle distractors were employed to gradually restore disc height. Trial spacers, aided by the distraction capability of the double-tip cage glider, further facilitated disc space opening and appropriate cage size selection. In such cases, an expandable cage is preferred. For this patient, an expandable TLIF cage (AccelFix-XT, L&K Biomed Co., Ltd., Yongin-si, Korea) was utilized, with an initial contracted height of 8 mm, a length of 27 mm, and 0° lordosis, prefilled with demineralized bone matrix. Following insertion, the cage was expanded to a height of 10 mm upon reaching the device’s torque limit.
Postoperative radiographs and 1-year follow-up MRI (Figures 4C and D) showed an increase in foraminal height and area bilaterally at the operated level.
Case 3
A 68-year-old man presented with chronic low back pain, bilateral radicular leg symptoms, and neurogenic claudication. Plain radiographs demonstrated a lumbar coronal deformity with a 23° curve from L1 to L4, without global coronal imbalance. Lateral listhesis was noted at the right side of L3–4, along with disc space narrowing at L3–4 and L4–5 on the coronal plane (Figure 5A). MRI revealed severe spinal canal stenosis at L3–4 and moderate stenosis at L4–5 (Figure 5B).
Preoperative lumbar radiographs (A) and magnetic resonance images (MRIs) (B). Postoperative lumbar radiographs (C). Early postoperative (D) and 1-year follow-up MRIs of L3–4 (E). Early postoperative (F) and 1 year follow-up MRIs of L4–5 (G). Surgical wounds following the procedure (H).
For this patient, a bilateral endoscopic approach was performed with the goal of correcting the segmental coronal deformity. Following insertion of pedicle guidewires from L3 to L5 bilaterally, the procedure began with a keyhole transfacet endoscopic approach at L4–5 on the left side. After completing cage placement at this level, the operative setup was repositioned to the contralateral side, and a transfacet approach was subsequently performed at L3–4 on the right. Expandable cages were utilized at both levels to facilitate insertion and restore disc height in the narrow disc spaces. An 8° lordotic cage was selected for each level, with expansion from an initial height of 8 mm to 12 mm achieved intraoperatively.
Figure 5C showed the postoperative radiographs. The early postoperative and 1-year follow-up MRIs of L3–4 (Figure 5D and E) and L4–5 (Figure 5F and G) demonstrated the initial improvement of the thecal sac CSA and the spinal canal remodeling from the indirect decompression effect.
Case 4
A 60-year-old woman had previously undergone open stand-alone posterior lumbar interbody fusion (PLIF) on the left side (Figure 6A) 7 years prior to presentation at our spine clinic. Although she initially experienced symptomatic improvement, she gradually developed recurrent low back pain and bilateral L4 and L5 radicular symptoms. Plain radiographs obtained at our clinic demonstrated implant subsidence (Figure 6B), and MRI revealed bilateral foraminal stenosis at L4–5, along with right-sided lateral recess stenosis (Figure 6C).
Immediate postoperative lumbar radiographs following prior open posterior lumbar interbody fusion at L4–5 (A), preoperative lateral lumbar radiograph (B), and magnetic resonance images (C) before the full-endoscopic lumbar interbody fusion (FE-LIF) procedure. Intraoperative cage insertion during the keyhole transfacet FE-LIF (D). Postoperative lumbar radiographs (E) and 1-year follow-up computed tomography (F). Surgical wounds following the FE-LIF procedure (G), with the red arrow indicating the endoscopic access incision.
Keyhole transfacet FE-LIF at L4–5 was performed without direct decompression to address the patient’s pseudarthrosis. The endoscopic transfacet approach was undertaken on the right side to utilize the relatively preserved disc space for cage insertion adjacent to the prior implant and to avoid scar tissue at the previously operated left facet joint (Figure 6D). During endplate preparation and trialing, disc space distraction was limited due to the segmental stiffness. Therefore, an interference-fit static cage was selected rather than an expandable cage to minimize the risk of intraoperative subsidence associated with over-distraction.
Figure 6E shows the postoperative radiographs. At 1-year follow-up, computed tomography demonstrated bridging bone between the inferior endplate of L4 and the superior endplate of L5 (Figure 6F). Figure 6G illustrates the surgical wounds following the FE-LIF procedure.
Summary
All patients underwent the keyhole transfacet FE-LIF successfully with no perioperative complications observed. Clinical outcomes are summarized in Table 1.
Clinical outcomes.
Discussion
With advances in endoscopic instrumentation and surgical techniques, endoscopic fusion procedures, including FE-LIF, have gained increasing popularity as minimally invasive options for treating degenerative lumbar spine disorders.4 Compared with MI-TLIF and open TLIF, these approaches are associated with reduced soft tissue injury, lower blood loss, and faster early recovery.11,12 The most commonly utilized FE-LIF techniques are the KLIF and EPTLIF.5,6 The KLIF technique employs a transforaminal route through Kambin’s triangle beneath the facet joint to access the disc space. In cases with a narrow working corridor, additional foraminoplasty or partial resection of the ventral SAP may be required to facilitate disc preparation and cage insertion. This approach primarily relies on indirect decompression achieved through interbody cage placement without direct exposure of the spinal canal.13 Clinical outcomes reported for KLIF are comparable to those of other LIF techniques.12,14 While the incidence of dural injury is low, neurological complications—particularly involving the exiting nerve root—have been reported at rates of up to 22.5%. Additionally, KLIF can be technically challenging at the L5/S1 level in patients with a high iliac crest.6 Furthermore, a Kambin’s triangle measuring less than 9 mm may limit the feasibility of this approach.15
EPTLIF represents another widely used FE-LIF technique. In this approach, the working corridor is established through an interlaminar route with complete facetectomy, similar to MI-TLIF.5,16 This facilitates direct decompression of neural elements and permits insertion of a larger interbody cage. Additionally, the endoscopic view allows direct visualization of the endplates during disc removal and preparation. The posterolateral endoscopic TLIF approach has also gained traction among surgeons utilizing biportal endoscopic systems.17,18 Favorable outcomes have been reported with EPTLIF, even in complex cases such as severely collapsed disc spaces, degenerative scoliosis, and grade II spondylolisthesis.7,19–21 However, despite these advantages, notable complications—including neurological injury and incidental durotomy—remain relatively common.20,22
In 2020, Khalifeh et al introduced the transfacet technique as an alternative approach for performing MI-TLIF in patients with degenerative lumbar conditions and low-grade spondylolisthesis, reporting encouraging outcomes.23,24 Their technique involved initial bilateral pedicle screw placement, followed by creation of a working corridor through the ipsilateral facet joint under microscopic visualization. An articulating expandable interbody device was then inserted to achieve indirect decompression. Additionally, a contralateral facet joint release was performed to enhance disc space distraction and increase the available fusion surface area.
Since then, several authors have described uniportal endoscopic transfacet or transarticular process techniques, in which bony work is initiated at the dorsal aspect of the facet joint.8–10,25,26 Most of these approaches have relied on direct decompression to address neural compression. Lewandrowski et al reported a uniportal endoscopic transfacet technique for direct spinal decompression in 65 patients with severe lumbar spinal stenosis.26 They observed a low rate of neurological complications, including 7.7% transient postoperative dysesthesia, with no incidental durotomies or nerve root injuries. The reduced manipulation of both traversing and exiting nerve roots in the transfacet approach may account for the lower incidence of dysesthesia compared with transforaminal techniques. Additionally, no postoperative instability was observed at 2-year follow-up.
Du et al utilized an endoscopically guided trephine to resect the articular process, harvest autologous bone graft, and subsequently perform direct decompression of the traversing nerve root.9 Following this, a custom-designed endoscopic working tube was employed to protect both the exiting and traversing nerve roots during disc preparation and interbody cage insertion. Similarly, Jiao et al introduced the transarticular trephine plasty technique, which involves en bloc resection of the targeted articular process by first anchoring a Kirschner wire and coaxial trephine onto the facet joint.10 This approach creates a bony channel that facilitates access to Kambin’s triangle. Direct endoscopic decompression is then performed, followed by disc preparation and cage placement. Using the transarticular trephine plasty technique, the authors reported pedicle fractures in 2 of 39 patients during facet resection. Feng et al reported outcomes of single-level direct decompression in 49 patients using 3 endoscopic fusion techniques—PLIF, TLIF, and transarticular process LIF—demonstrating favorable efficacy with comparable postoperative recovery among the approaches.25 Ngoh et al utilized computer-assisted navigation to define the trajectory for transfacet access.27 The transfacet corridor was initially created using hand reamers and then completed with an endoscopic ultrasonic osteotome. The authors noted that patients with a narrow facet width (<12 mm) may not be ideal candidates for this technique, given the use of an 11 mm endoscopic working sleeve. Asawasaksakul et al demonstrated their modified transfacet FE-LIF approach for treating a patient with low-grade degenerative spondylolisthesis.8 In their technique, an endoscopic osteotome was used to harvest autologous bone graft, followed by creation of a keyhole facetectomy with a diamond round burr to access the disc space and facilitate cage insertion. The endoscope was subsequently reintroduced to perform additional direct decompression as needed.
In contrast to the aforementioned techniques, we do not routinely harvest local bone graft from the facet joint during transfacet bone work. Instead, drilling is initiated after exposure of the dorsal surface of the facet joint line. This approach allows precise control over the trajectory of the transfacet corridor from the dorsal facet surface to the target disc, facilitates preservation of the bony corridor walls during the limited facetectomy, and reduces the risk of inferior pedicle fracture.
In addition, we favor the use of a double-tip cage glider to facilitate interbody cage insertion. The glider tips, which dock at the posterior aspect of the disc space, help protect the bony endplates during cage delivery and also function as a disc distractor. This distraction capability aids in inserting a larger static cage, which is important for achieving effective indirect decompression through disc height restoration and ligamentotaxis. However, even with the double-tip cage glider, cage insertion through the transfacet corridor can be technically challenging in certain scenarios, such as a narrow or severely collapsed disc space. In such cases, we prefer the use of an expandable interbody device with an initial contracted height of 6 to 8 mm, allowing gradual expansion within the disc space after insertion. Several authors have incorporated cage gliders in endoscopic fusion procedures.8,28 Chuang et al introduced the GUARD technique, utilizing various custom-designed cage gliders to protect the traversing and exiting nerve roots while facilitating cage insertion in both facet-preserving and facet-resection endoscopic fusion surgeries.28 In contrast, we do not routinely use the cage glider as a neural protective device. In our transfacet technique, the risk of traversing and exiting nerve root injury is inherently reduced, as these neural elements are typically not exposed during the procedure. Instead, the preserved facet structures and the transfacet osseous corridor serve as a natural barrier, providing protection to the neural elements throughout the surgical process.
A comparison of the 3 FE-LIF techniques is summarized in Table 2.
Comparison of the full-endoscopic lumbar interbody fusion techniques.
The present study demonstrates the clinical application of the keyhole transfacet FE-LIF technique using an indirect decompression strategy across a range of lumbar degenerative conditions. These included a patient with bilateral leg pain and severe central canal stenosis due to low-grade degenerative spondylolisthesis treated with a unilateral endoscopic approach (case 1), a patient with severe foraminal stenosis associated with low-grade isthmic spondylolisthesis and a markedly collapsed disc space (case 2), and a patient with segmental lumbar coronal deformity accompanied by severe spinal canal stenosis (case 3), in whom a bilateral endoscopic approach was employed to facilitate deformity correction.
We also demonstrated radiographic evidence of indirect decompression following a transfacet or transarticular process FE-LIF technique in this study. We observed early postoperative expansion of the spinal canal, likely attributable to disc height restoration and ligamentotaxis, followed by further enlargement over time due to remodeling at 1-year follow-up. The indirect decompression effect on the spinal canal has been well described in lateral lumbar interbody fusion (LLIF).29,30 Disc height restoration achieved with LLIF cages leads to thinning of the ligamentum flavum, reduction of posterior disc bulging, and an increase in the thecal sac CSA in the early postoperative period. Over time, continued remodeling of the disc and ligamentum flavum contributes to further expansion of the spinal canal.30 In contrast, evidence supporting indirect decompression following endoscopic fusion remains limited. Wu et al reported outcomes of indirect decompression using a facet-sacrificing EPTLIF technique, in which the ligamentum flavum overlying the ipsilateral traversing nerve root and the contralateral ligamentum flavum were preserved.31 They demonstrated early improvement in spinal canal dimensions, followed by progressive remodeling of both the spinal canal and the contralateral foramen at final follow-up.
In addition, this study also illustrated the use of transfacet FE-LIF as a salvage revision procedure for pseudarthrosis following prior LIF. Several surgical strategies have been described for managing pseudarthrosis after LIF, including removal of the previously implanted cage via anterior or lateral approaches, or retention of the existing cage with performance of a contralateral TLIF.32,33 However, evidence supporting the role of endoscopic fusion in revision settings remains limited. Telfeian et al reported a successful awake transforaminal endoscopic fusion in a patient with pseudarthrosis, in which an expandable stand-alone cage was placed adjacent to a previously inserted TLIF polyetheretherketone cage.34 Similarly, in case 4 of the present study, we demonstrated that an interbody cage can be safely inserted adjacent to a prior PLIF cage using the proposed keyhole transfacet endoscopic approach.
Patient selection for indirect decompression using endoscopic fusion remains controversial, and high-quality evidence is still limited. Morimoto et al suggested that the KLIF may be preferable to LLIF in single-level degenerative spondylolisthesis, as it involves smaller skin incisions and may be technically more feasible in obese patients.13 However, LLIF may be more advantageous in multilevel degenerative disease, particularly when substantial deformity correction is required. Direct decompression techniques may be more appropriate in cases of ossified ligamentum flavum or severe central canal stenosis associated with marked ligamentum flavum hypertrophy. Wu et al recommended indirect decompression or ipsilateral direct decompression using facet-sacrificing EPTLIF for patients with predominantly unilateral degenerative pathology on MRI, while bilateral direct decompression was preferred in cases with severe central, bilateral recess, and foraminal stenosis.31 In our practice, we have adopted the patient selection criteria for indirect decompression with LLIF proposed by Yingsakmongkol et al35 to identify suitable candidates for this approach. Patients meeting the following criteria are considered appropriate and likely to achieve favorable outcomes: (1) dynamic clinical symptoms, (2) a disc height difference of ≥1 mm between supine and standing positions, (3) absence of static stenotic lesions such as bony lateral recess narrowing or facet cysts, and (4) no significant motor weakness. If these criteria are not satisfied, adjunctive direct decompression after cage insertion is performed at the surgeon’s discretion. Furthermore, in cases involving substantial coronal or sagittal deformity or multilevel degenerative lumbar disease, we generally favor indirect decompression using LLIF rather than the transfacet FE-LIF approach.
Limitations
This study has several limitations. First, it is a technical report with a small number of case illustrations and short-term, preliminary outcomes. Larger series with longer follow-up and comparative studies against established fusion techniques are needed to further validate this approach. Additionally, the use of a custom-made double-tip cage glider for cage delivery may limit reproducibility, as this instrument may not be readily available to all spine surgeons interested in adopting the technique.
Conclusions
The keyhole transfacet FE-LIF provides an alternative method for indirect decompression in the prone position by establishing a transfacet working corridor through a limited facetectomy and introducing an interbody cage via this bony pathway. This study demonstrates the preliminary feasibility of this technique in the management of a range of degenerative spinal conditions, including pseudarthrosis following prior LIF. In addition, adjunctive direct decompression can be performed in the same setting, if required, after cage insertion.
Supplementary material
Online Supplementary Video 1.
Left-sided endoscopic keyhole transfacet approach demonstrating the indirect decompression technique.Online Supplementary Video 2.
Endoscopic visualization of the disc space following interbody cage insertion, including an example of adjunctive direct decompression performed after cage insertion in another patient.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.
Ethics Approval Approval from the Institutional Review Board of Samut Sakhon Hospital (SKH REC 41/2569/V.1) was obtained before medical records were accessed. Informed consent was waived for this study.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2026 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
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