Overcoming the Challenge of Controlled Total Facetectomy in Uniportal Endoscopic Transforaminal Interbody Fusion: A Direct-Visualization Crown-Reaming Technique
Article information
Abstract
Endoscopic transforaminal lumbar interbody fusion (Endo-TLIF) is increasingly used as a minimally invasive fusion technique; however, controlled total facetectomy under endoscopic visualization remains technically demanding. Conventional reaming methods are often partially blind and fluoroscopy-dependent, and these limitations may increase the risk of neural irritation or endplate violation. We describe a direct-visualization crown-reaming technique for controlled total facetectomy and disc-space preparation during Endo-TLIF. Sequential foraminal enlargement and facetectomy are performed using a hollow crown reamer under continuous endoscopic visualization, allowing real-time identification of neural structures. Disc removal and endplate preparation are completed while preserving subchondral bone integrity, and the hollow reamer configuration permits simultaneous autologous bone graft collection. Direct-visualization crown reaming is a feasible technique for controlled total facetectomy during uniportal Endo-TLIF and may improve procedural control and facilitate neural structure identification. Further studies are warranted to evaluate its safety and potential clinical benefits.
INTRODUCTION
Uniportal endoscopic transforaminal lumbar interbody fusion (Endo-TLIF) has evolved as a minimally invasive alternative to conventional fusion techniques, offering reduced tissue trauma and faster recovery while maintaining comparable clinical outcomes [1-3]. The procedure is typically performed through Kambin’s triangle, a narrow anatomical corridor bordered by the exiting nerve root, traversing nerve root, and the superior endplate of the caudal vertebra. Within this confined space, controlled total facetectomy is essential to achieve adequate neural decompression and create sufficient working room for cage insertion [4].
Current endoscopic fusion techniques describe disc-space preparation using trephines or specialized reamers, which are introduced primarily under fluoroscopic guidance [1,2,5]. Although effective, these methods often rely on tactile feedback and indirect visualization during bone removal, which may increase the risk of neural irritation or unintended endplate violation. A technical gap, therefore, remains in achieving reproducible, controlled total facetectomy under continuous endoscopic visualization.
To address this limitation, we introduce a direct-visualization crown-reaming technique to facilitate controlled facetectomy and disc-space preparation entirely under endoscopic guidance.
CASE AND OPERATIVE PROCEDURE
1. Case Presentation
A 66-year-old female presented with chronic lower back pain associated with progressive neurogenic claudication. She reported a limited walking tolerance of approximately 15 minutes due to bilateral leg discomfort, more pronounced on the left. Radicular symptoms included numbness along the L3–5 dermatomal distribution, predominantly on the left. Neurological examination revealed decreased sensation in the L3–5 dermatomes, grade 4 weakness of the extensor hallucis longus bilaterally, preserved deep tendon reflexes, and no sphincter dysfunction.
Standing whole-spine radiographs demonstrated degenerative lumbar scoliosis with grade I spondylolisthesis at L3–4 and L4–5. Magnetic resonance imaging of the lumbar spine revealed severe central canal stenosis with associated facet hypertrophy and foraminal narrowing (Figure 1). Given the presence of multilevel instability, severe stenosis, and progressive neurological symptoms, uniportal Endo-TLIF with controlled total facetectomy at the affected levels was planned.
Preoperative imaging. (A and B) Standing whole-spine anteroposterior and lateral radiographs demonstrate overall alignment. (C) T2-weighted sagittal lumbar magnetic resonance imaging (MRI) shows degenerative changes and canal stenosis. (D and E) Dynamic lateral flexion and extension radiographs of the lumbar spine demonstrate segmental instability. (F) Axial T2-weighted MRI at L3–4. (G) Axial T2-weighted MRI at L4–5 demonstrates central canal and lateral recess stenosis.
2. Operative Technique
The patient was positioned prone on a radiolucent table, and the operative level was confirmed fluoroscopically. After insertion of a reference pin into the iliac crest, navigation guidance (Brainlab AG, Germany), integrated with the CIARTIC Move system (Siemens Healthineers AG, Germany), a self-driving 2-dimensional/3-dimensional mobile C-arm platform, was utilized to optimize anatomical orientation and trajectory planning. The procedure was performed using the EndoSurg Max and EndoSurg Plus endoscopic systems (unintech GmbH, Germany), including a crown reamer (internal diameter 10.2 mm, outer diameter 11.5 mm, length 128 mm) from the EndoPLIF instrument set (unintech GmbH). Erisma-LP MIS System instrumentation and Idys-TLIF polyetheretherketone (PEEK) implants (Clariance, France), designed for minimally invasive posterior lumbar interbody fusion procedures, were also utilized.
The working trajectory was planned just lateral to the pedicle of the cephalad vertebra at each level, corresponding to the conventional skin entry point commonly used for percutaneous pedicle screw insertion. Compared with the standard fluoroscopic landmark, the navigated guidance allowed slightly more lateral portal placement (Figure 2), creating a more medial working trajectory toward the facet complex and pedicle. This approach facilitated improved access to the surgical corridor and optimized implant trajectory during the procedure. The primary objective of the bony work was a controlled total facetectomy using a stepwise resection strategy. Resection of the inferior articular process (IAP) was initiated along the Wu-to-Kim line [6], progressing from the spinolaminar junction toward the isthmus. This was followed by resection of the tip of the superior articular process (SAP). The initial docking point was established directly on the facet joint surface. The tip of the SAP, corresponding anatomically to the level of the isthmus (Kim point) [6], was identified and confirmed using a navigated probe (Figure 2). Under continuous endoscopic visualization, surrounding bony margins were meticulously cleared to expose the entire facet joint and delineate the interlaminar window.
Surgical technique and direct-visualization crown-reaming protocol. (A and B) Fluoroscopy-guided standard portal entry placed lateral to the pedicle of the cephalad vertebra (yellow line) and a more lateral portal position under navigation guidance (blue line), enabling a medialized screw trajectory. (C and D) Intraoperative endoscopic views show initial docking on the inferior articular facet, with identification of the superior articular process tip at the isthmus level (Kim point, C) and spinolaminar junction (Wu point, D) using a navigated probe. (E) First crown reaming at the Wu point for central decompression and autologous bone harvest. (F) Second reaming at the midlamina, where the ligamentum flavum provides dural protection. (G) Lateral reaming to complete inferior articular process resection at the Kim point, achieving lateral decompression and preparing the corridor toward Kambin triangle.
3. Direct-Visualization Crown-Reaming Protocol
The direct-visualization crown-reaming protocol was performed in a stepwise, progressively lateralized manner to achieve a controlled total facetectomy and to safely create a corridor toward Kambin triangle.
The initial reaming step was initiated by docking the crown reamer at the Wu point (spinolaminar junction) of the cephalad level (Figure 2). The trajectory was directed medially toward the midline to accomplish central decompression while simultaneously harvesting autologous bone graft in a cylindrical fashion. To minimize slippage, the reamer was first rotated gently counterclockwise for 2 revolutions, applying minimal axial pressure, to create a pilot groove. Controlled clockwise rotation was then applied until a reduction in resistance was appreciated or a freely rotating bone core was observed within the reamer, indicating complete cortical separation. A half-pipe reamer was subsequently introduced to perform over-the-top decompression under continuous endoscopic visualization.
The second reaming was performed at the midportion of the cephalad lamina (Figure 2). At this level, the ligamentum flavum was typically encountered beneath the reamed surface, serving as a protective layer over the dura during bony decompression. A third reaming trajectory was then directed more laterally to address residual osseous structures. Finally, the reamer was positioned at the most lateral entry point to complete IAP resection, including the Kim point [6]. This progressive lateralization strategy allowed full mobilization of the facet complex and adequate expansion of the transforaminal working corridor. A diamond burr was used to refine any remaining portion of the IAP. Reaming was then initiated at the tip of the SAP and advanced carefully toward the ligamentum flavum. Reaming was discontinued upon approaching the far cortex adjacent to the dura. Cortical release was completed using a Kerrison punch or diamond burr under direct visualization to minimize the risk of neural injury. In this case, 6 cylindrical bone cores were harvested, yielding approximately 6 mL of autologous graft material for intradiscal use.
After complete exposure of Kambin triangle, annulotomy was performed. A Harrison cage glider [7] was introduced into the disc space with appropriate bevel orientation to protect the traversing nerve root. Endoscopic disc preparation was performed using progressively larger visualized disc shavers, increasing to 10 mm at L4–5 and 11 mm at L3–4. Endplate preparation was completed using disc shavers and visualization ring curettes, ensuring thorough removal of the cartilaginous endplate while preserving the subchondral bone under direct endoscopic inspection.
Autologous bone graft was packed intradiscally and within a banana-shaped PEEK cage (11 mm × 10 mm × 30 mm). The cage was inserted through the glider under fluoroscopic and navigational guidance. After confirmation of appropriate depth and position, the cage was advanced further and rotated to achieve a horizontal orientation. Final positioning was verified radiographically. The same procedure was repeated at L3–4 using a 10-mm disc shaver and a 10 × 10 × 30-mm PEEK cage. Percutaneous pedicle screws were subsequently inserted from L3 to L5 under navigation guidance. Bilateral rods were applied, and the set screws were tightened sequentially. Final torqueing facilitated restoration of segmental alignment and stabilization of the construction. The complete operative technique is demonstrated in Supplementary Video Clip 1.
4. Postoperative Course
Postoperative standing radiographs demonstrated satisfactory reduction of the spondylolisthesis in the sagittal plane with improved coronal alignment and maintained segmental stability (Figure 3). No radiographic evidence of cage subsidence, implant malposition, or instrumentation-related complications was observed. Clinically, the patient reported marked relief of calf tightness and improvement in lower-extremity numbness on postoperative day 1 without new neurological deficits. At the 3-month follow-up, motor strength had improved to grade 5 in all tested muscle groups, and the patient was able to ambulate independently without limitation, with complete resolution of neurogenic claudication symptoms.
Postoperative imaging. Comparison of preoperative (A and C) and postoperative (B and D) radiographs demonstrates satisfactory sagittal reduction with improved coronal alignment and no cage subsidence or hardware-related complications.
DISCUSSION
Controlled bone resection within Kambin triangle remains one of the most technically demanding steps in uniportal Endo-TLIF. Adequate total facetectomy is critical to ensure sufficient decompression and working space for cage insertion; however, the narrow transforaminal corridor and proximity of the exiting nerve root and dorsal root ganglion limit surgical maneuverability. Conventional endoscopic fusion techniques typically describe disc access and foraminal enlargement using trephines or specialized reamers introduced under fluoroscopic guidance. Although effective, these instruments are often advanced with partial visualization, relying on tactile feedback and imaging rather than continuous direct endoscopic monitoring. This may increase the risk of neural irritation, incomplete facetectomy, or unintended endplate violation.
The feasibility of direct-visualization bone reaming in the transforaminal corridor has been demonstrated previously for the treatment of lumbar disc herniation. In a retrospective study of 80 cases undergoing full-endoscopic foraminoplasty, a visualized bone reamer enabled controlled bony decompression under continuous endoscopic guidance, with favorable clinical outcomes and no increase in neural complications [8]. Building upon this concept, we extended the application of direct visualization reaming from limited foraminoplasty to controlled total facetectomy in Endo-TLIF. By performing facetectomy under continuous endoscopic monitoring, neural structures can be clearly identified throughout the reaming process, potentially improving procedural control and reproducibility. In addition, the hollow configuration of the crown reamer allows simultaneous autologous bone graft harvesting, which may enhance workflow efficiency.
Total facetectomy plays a pivotal role in TLIF by permitting adequate neural decompression and facilitating cage insertion through an expanded transforaminal corridor. From a biomechanical perspective, removal of the facet joint disrupts the posterior tension band and reduces segmental stability [9]; however, this destabilization is intended to be compensated by interbody support and supplemental fixation. The quality and precision of facetectomy, therefore, have important mechanical consequences. Incomplete resection may restrict cage trajectory and limit optimal cage positioning, potentially compromising load distribution across the endplate [10]. Conversely, excessive or uncontrolled bone removal may damage adjacent stabilizing structures or violate the subchondral endplate, increasing the risk of cage subsidence. Controlled facetectomy under direct endoscopic visualization may offer biomechanical advantages by enabling targeted resection while preserving nonessential supporting structures. Precise removal of the IAP and hypertrophic superior facet allows adequate decompression without unnecessary collateral bone loss. Moreover, maintaining subchondral endplate integrity during subsequent disc-space preparation is critical for preserving axial load-bearing capacity. By transforming facetectomy from a partially blind maneuver into a visually guided process, direct-visualization crown reaming may improve cage trajectory alignment, optimize footprint contact, and potentially enhance segmental stability after fusion. Further biomechanical and radiologic studies are warranted to clarify whether this technical refinement translates into reduced subsidence rates and improved fusion mechanics.
In contemporary full-endoscopic TLIF, high-speed endoscopic burrs are widely utilized for precise and controlled facetectomy and can also facilitate adequate autologous bone graft harvesting through adjunctive techniques, such as fascial incision and en bloc extraction of larger bone fragments by temporarily removing the working sheath to expand the surgical corridor. While this burr-based approach allows for flexibility and controlled decompression, it is inherently characterized by a layer-by-layer bone removal process from the superficial cortex toward deeper structures, which may result in incremental loss of cortical and cancellous bone prior to effective graft collection and may require additional procedural steps. In contrast, the reaming technique described in the present study offers a more direct transcortical trajectory using crown reamers, enabling simultaneous facetectomy and bone harvesting, with potentially reduced bone loss and improved efficiency in graft acquisition. This streamlined workflow may also decrease the need for repeated instrument exchanges and facilitate shorter operative time, particularly in cases with marked facet hypertrophy and well-defined anatomical landmarks. However, burr-based techniques retain a clear advantage in terms of precision, especially in anatomically constrained regions or in close proximity to neural elements, where fine control is essential [4]. Furthermore, although burr-based bone harvesting with sheath-assisted fragment extraction can yield substantial graft volume, it may require additional soft tissue disruption and procedural steps. Conversely, the reaming technique introduces specific technical challenges, particularly the need for accurate interpretation of tactile feedback during penetration of the far cortex, beyond which critical neurovascular structures may be at risk, thereby reflecting a potentially steeper learning curve. Accordingly, in our practice, reaming is preferentially employed in patients with severe facet hypertrophy where efficient bone removal and graft harvesting are prioritized, whereas burr-based facetectomy combined with conventional bone harvesting techniques may be more suitable in cases requiring meticulous decompression, anatomical variability, or when enhanced procedural control is necessary to ensure neural safety.
An additional theoretical advantage of the crown-reaming technique is the ability to preserve and simultaneously collect local autologous bone graft during facetectomy. Similar to chisel or osteotome-based bone harvesting strategies described in unilateral biportal endoscopic (UBE) surgery, the hollow crown reamer may allow retrieval of relatively large cancellous and cortical bone fragments while maintaining continuous visualization during resection. Compared with high-speed burr-based facetectomy, this approach may potentially reduce excessive bone pulverization and improve the efficiency of local graft collection. However, unlike chisels used in UBE surgery, crown reaming remains a rotational drilling technique and still requires careful trajectory control and continuous endoscopic monitoring to avoid neural irritation or unintended bony violation. Therefore, the potential graft preservation benefit remains theoretical and requires further clinical validation.
This report should be interpreted within the limitations of a technical video manuscript and preliminary clinical experience. The current study primarily aims to demonstrate the surgical workflow, anatomical landmarks, and technical feasibility of direct-visualization crown reaming for controlled total facetectomy during uniportal Endo-TLIF. In addition, the current experience is limited to carefully selected degenerative cases, and the applicability of this technique in more complex settings, such as severe foraminal stenosis, dysplastic facet anatomy, revision surgery, severe instability, and osteoporosis, requires further investigation. Future prospective comparative studies with larger patient cohorts and longer follow-up are necessary to better define the safety profile, reproducibility, indications, and clinical relevance of this technique.
CONCLUSION
Direct-visualization crown reaming is a technically feasible approach for controlled total facetectomy during uniportal Endo-TLIF. Continuous endoscopic visualization throughout the reaming process may improve procedural control, facilitate neural structure identification, and allow simultaneous harvesting of local autologous bone graft. Further studies with larger cohorts and longer follow-up are warranted to better define the reproducibility, safety profile, and potential clinical benefits of this technique in Endo-TLIF procedures.
WRITTEN TRANSCRIPT
00:00 Title Slide
Overcoming the Challenge of Controlled Total Facetectomy in Uniportal Endoscopic Transforaminal Lumbar Interbody Fusion: A Direct-Visualization Crown Reaming Technique.
00:09 Introduction
Uniportal endoscopic TLIF requires controlled total facetectomy within the narrow transforaminal corridor of Kambin triangle, where neural structures are closely adjacent. Previous transforaminal foraminoplasty has demonstrated that bone removal using a direct-visualization reamer can be performed safely under continuous endoscopic guidance. Building on this concept, we applied a direct-visualization crown-reaming technique to achieve controlled total facetectomy during Endo-TLIF. This visually guided approach may improve surgical precision, optimize cage trajectory, and preserve endplate integrity with potential biomechanical benefits. The following video demonstrates the key operative steps.
00:47 Case Presentation
A 66-year-old woman presented with progressive low back pain and neurogenic claudication, limited to 15 minutes of walking. She had L3–5 numbness and grade 4 weakness of the extensor hallucis longus bilaterally, without sphincter dysfunction.
01:02 Preoperative Radiographs
Standing whole-spine radiographs show degenerative lumbar scoliosis with grade I spondylolisthesis at L3–4 and L4–5.
01:10 Dynamic Radiographs
Dynamic lateral flexion-extension radiographs of the lumbar spine demonstrated radiographic instability at the affected levels.
01:17 Preoperative MRI
Magnetic resonance imaging of the lumbar spine revealed severe stenosis at L3–5 with associated facet hypertrophy and foraminal narrowing.
01:24 Surgical Planning
The patient was positioned prone on a radiolucent table. After confirming the operative level with fluoroscopy, the portal entry point was determined under radiographic guidance. The standard trajectory was planned just lateral to the pedicle of the cephalad vertebra at each segment (yellow line), corresponding to the same skin entry point typically used for percutaneous pedicle screw insertion.
The image demonstrates a more laterally positioned portal entry point under navigation guidance (blue line). This lateralized starting point facilitates a more medialized screw trajectory, potentially improving pedicle screw purchase and biomechanical stability.
01:57 Facet Exposure and Landmark Identification
The initial docking point was established on the facet joint. Bony margins were then carefully cleared to fully expose the entire facet joint and interlaminar window. The tip of the SAP, corresponding to the level of the isthmus called Kim point [6], was identified and confirmed using a navigated probe.
02:16 The Protocol of Visualization Crown Reamer
Once the anatomical boundaries were clearly visualized, controlled facetectomy was initiated under direct endoscopic guidance. Our objective was to resect the IAP by cutting from the Wu-to-Kim point [6], followed by resection of the SAP tip. This stepwise facetectomy allowed clear identification and widening of the working corridor toward Kambin triangle, thereby preparing an adequate pathway for TLIF cage insertion.
02:45 First Reaming: Spinolaminar (Wu Point)
The first reaming step was initiated by docking the crown reamer at the Wu point (spinolaminar junction) of the cephalad level. The initial trajectory was directed medially toward the midline to achieve central decompression while harvesting autologous bone graft in a cylindrical fashion. To prevent slippage, the reamer was gently rotated counterclockwise for 2 rounds with minimal pressure to create a preliminary groove. Subsequently, clockwise rotation was applied in a controlled manner until reduced resistance was felt or a free bone core was observed rotating within the reamer, indicating complete cortical separation.
At this stage, a half-pipe reamer was introduced to perform over-the-top decompression under direct endoscopic visualization.
04:02 Second Reaming: Laminar and IAP
The second reaming was performed at the midportion of the cephalad lamina. At this level, a thick ligamentum flavum was typically encountered beneath the reamed bone surface, serving as a protective layer over the dura during bone work.
04:46 Third Reaming: Through Facet Including SAP
A third reaming trajectory was then directed more laterally to address any remaining bony structures.
04:52 Lateral Reaming: IAP Resection at the Kim Point
Finally, the reamer was positioned at the most lateral entry point to complete IAP resection, including the Kim point (isthmus). Bone fragments floated with the reamer, indicating complete cortical separation. This step finalized the lateral decompression and facilitated full mobilization of the facet complex in preparation for corridor expansion toward Kambin triangle.
05:22 Autologous Bone Graft Harvest
In this case, 6 cylindrical bone cores were harvested, yielding approximately 6 mL of autologous graft material for intradiscal packing.
05:33 Annulotomy and Disc Access
After full exposure of Kambin triangle, annulotomy was performed. The disc shaver was introduced under direct endoscopic visualization through the front of endoscopic working channel and connected to the handle posteriorly.
05:47 Sequential Disc Shaving
Sequentially larger disc shavers were used under visualization, up to 10 mm at L4–5 and 11 mm at L3–4.
05:57 Reverse Curettage
Reverse curettage can be used to remove anterior bony spurs compressing the thecal sac.
06:06 Straight Curettage
Straight curettage facilitates removal of the cartilaginous endplate.
06:15 Endplate Preparation
Final endplate preparation was performed under direct endoscopic visualization, ensuring complete removal of the cartilaginous endplate while preserving the subchondral bone.
06:27 Cage Insertion and Pedicle Screw Fixation
A Harrison cage glider [7] was inserted into the disc space with appropriate bevel orientation to protect the traversing nerve root. Autologous bone graft was packed into the disc space. The cage was inserted through a cage glider under fluoroscopic guidance, advanced into the disc space, rotated to a horizontal orientation, and final position confirmed radiographically. At L4–5, a banana-shaped PEEK cage (11 mm × 10 mm × 30 mm) was inserted. The same procedure was repeated at L3–4 using a 10-mm disc shaver and a 10 × 10 × 30-mm PEEK cage. Percutaneous pedicle screws were then inserted using a Jamshidi needle under navigation guidance. Final set screw tightening restored segmental alignment.
07:17 Postoperative Radiographs
Follow-up radiographs demonstrated satisfactory sagittal reduction of the spondylolisthesis with improved coronal alignment.
07:24 Postoperative Course
At the 1st postoperative week, the patient reported relief of calf tightness and decreased lower-extremity numbness. At the 3-month follow-up, motor strength had improved to grade 5 in all tested muscle groups. The patient was able to ambulate without limitation and reported resolution of neurogenic claudication symptoms.
07:35 Conclusion
Controlled facetectomy under direct endoscopic visualization enables complete facet resection with adequate autologous bone graft harvest. Continuous visual guidance improves anatomical clarity during reamer use and may reduce fluoroscopic radiation exposure. Although our preliminary experience indicates that this technique is feasible and safe, further comparative studies are required to confirm its potential advantages over conventional trephine- or fluoroscopy-guided methods in terms of complications, subsidence, and long-term fusion outcomes.
Supplementary Material
Supplementary Video Clip 1 is available at https://doi.org/10.21182/jmisst.2026.03489.
Supplementary Video Clip 1.
Intraoperative video demonstrating the direct-visualization crown-reaming technique for controlled total facetectomy during endoscopic transforaminal lumbar interbody fusion.
Notes
Conflicts of Interest
The authors have nothing to disclose.
Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Acknowledgments
The narration in the supplementary video was produced using the integrated text-to-speech feature provided by CapCut (ByteDance Ltd.).
Ethics Statement
Written informed consent was obtained from the patient prior to participation in this study. The study protocol was reviewed and approved by the institutional review board (IRB) of Chulabhorn Royal Academy (IRB No. 072/2569).