Full-Endoscopic Trans-Kambin Triangle Lumbar Interbody Fusion : Surgical Technique

Summary

Here, we present a protocol to perform full-endoscopic trans-Kambin triangle lumbar interbody fusion (KLIF). The protocol utilizes a posterolateral approach via Kambin’s triangle for safe expandable cage insertion and neural decompression while preserving dorsal facet structure and minimizing soft tissue trauma.

Abstract

The goal of this protocol is to provide a reproducible method for performing full-endoscopic trans-Kambin triangle lumbar interbody fusion (KLIF). Lumbar interbody fusion (LIF) is a widely established surgical treatment for lumbar spinal instability and stenosis. While lateral access surgeries (e.g., Oblique Lateral Interbody Fusion (OLIF), Extreme Lateral Interbody Fusion (XLIF)) carry risks of injury to the psoas muscle and lumbar plexus, this article presents the protocol for KLIF, which offers an alternative lateral access route via Kambin’s triangle.

The procedure begins with percutaneous pedicle screw insertion, employing a specific screw locking sequence to facilitate vertebral reduction. The subsequent endoscopic phase strictly focuses on creating a safety aperture of at least 12 mm via controlled partial ventral facetectomy. This ensures sufficient space to accommodate the cannula and cage without injuring the exiting nerve root. The protocol emphasizes precise stepwise execution to ensure safe and reproducible outcomes. An expandable cage is then inserted to restore disc height. This technique is applicable for patients with degenerative lumbar conditions requiring minimally invasive lumbar interbody fusion with reduced soft tissue disruption.

Anatomically, KLIF is distinct from conventional TLIF, which typically requires facetectomy and retraction of the dural sac. KLIF utilizes a "facet-preserving" approach that accesses the disc lateral to the superior articular process, thereby minimizing bleeding and dural tear risks. Consequently, the procedure generally allows for a drain-free postoperative course. KLIF provides a minimally invasive and safe strategy for lumbar fusion. This protocol provides a standardized framework for performing KLIF and may support its adoption in minimally invasive spine surgery.

Introduction

Lumbar interbody fusion (LIF) is a widely established surgical treatment for lumbar spinal instability and stenosis. The goal of this protocol is to provide a reproducible, step-by-step method for performing KLIF. Over the years, various approaches have been developed, ranging from traditional Posterior LIF (PLIF) and Transforaminal LIF (TLIF) to more recent lateral approaches such as Oblique LIF (OLIF) and Extreme Lateral LIF (XLIF). While lateral approaches minimize paraspinal muscle damage, they introduce risks of injury to the psoas muscle, lumbar plexus, and major vessels. These limitations highlight the need for a minimally invasive approach that avoids both posterior muscle disruption and lateral visceral or neural complications.

However, despite the increasing adoption of minimally invasive fusion techniques, a standardized endoscopic approach for interbody fusion remains limited, creating a need for clearly defined procedural guidelines.

Full-endoscopic spine surgery (FES) has evolved significantly since its inception. Initially developed as percutaneous nucleotomy by Hijikata¹ and Kambin², it advanced to targeted discectomy techniques^3,4. Today, FES has become a versatile tool for bony decompression. Despite these advances, the application of full-endoscopic techniques to interbody fusion remains less standardized and continues to evolve. In 2020, the AOSpine consensus paper established the unified term "Full-Endoscopic Spine Surgery (FESS)" to standardize the nomenclature⁵.

The logical progression of FES is its application to spinal arthrodesis. Although various names such as "percutaneous endoscopic TLIF" (PETLIF)⁶ or "percutaneous endoscopic LIF" (PELIF)⁷ have been used in the literature, the fundamental concept relies on accessing the disc space via Kambin's triangle². Compared to conventional TLIF and OLIF approaches, this method aims to reduce tissue disruption while maintaining direct visualization and anatomical preservation.

To clarify the nomenclature based on anatomy, Kim et al. differentiated the techniques based on the extent of bony resection. Unlike conventional TLIF, which involves total facetectomy to insert a cage, KLIF preserves the dorsal facet joint structure by inserting the cage through Kambin's triangle with only partial ventral foraminoplasty. Based on this anatomical concept, we previously proposed the nomenclature KLIF to unify the terminology^8,9. This technique is particularly suitable for patients with degenerative lumbar conditions requiring interbody fusion, where preservation of posterior elements and minimization of soft tissue damage are desired.

The KLIF technique utilizes the endoscopic view to safely navigate Kambin's triangle, which lies immediately posterior to the psoas major muscle. Therefore, a detailed and standardized protocol is necessary to ensure safe and reproducible implementation of this technique. Unlike OLIF or XLIF, the KLIF surgical field is devoid of major vessels and organs, potentially reducing the risk of vascular and visceral complications compared to lateral approaches. This protocol provides a comprehensive and reproducible step-by-step guide for performing KLIF, highlighting key technical steps required for safe cage insertion through Kambin’s triangle.

Protocol

All procedures described herein were performed in accordance with the ethical standards of the institutional and/or national research committee (Ethics Committee of Tokushima University Hospital, Approval No.:3642) and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all subjects involved in the study.

Figure 1: Schematic overview of the KLIF surgical workflow. The diagram illustrates the seven main stages of the procedure: (1) Patient positioning and neuromonitoring setup, (2) Percutaneous pedicle screw insertion with selective locking sequence, (3) Endoscopic approach to Kambin’s triangle, (4) Foraminoplasty to achieve the 12 mm safety aperture, (5) Disc preparation and distractor expansion, (6) Bone grafting and expandable cage insertion, and (7) Final screw locking and wound closure. The inset highlights the 12 mm safety aperture measurement at Kambin’s triangle. Please click here to view a larger version of this figure.

NOTE: Figure 1 provides a comprehensive schematic overview of the KLIF surgical workflow, which is divided into seven distinct stages. We strongly recommend referring to this workflow before proceeding with the detailed protocol steps.

1. Preoperative preparation and positioning

NOTE: Figure 2 provides a schematic overview of all instruments used in this protocol (pencil dilator, oblique cannula, open square cannula, and S-guide)

Figure 2: Key instruments used in the KLIF procedure. (A) Pencil dilator for initial disc space access. (B) Oblique cannula (working channel, elevator type; Ø8.0 mm, length 165 mm). (C) Open square cannula (8 × 10 mm) for cage insertion. (D) Safe guide wire (S-guide). Please click here to view a larger version of this figure.

1. Administer general anesthesia to the patient using endotracheal intubation. Administer intravenous prophylactic antibiotics (e.g., cefazolin 1–2 g) within 60 min before skin incision.
2. Place the patient in the prone position on a radiolucent operating frame (e.g., a prone-positioning radiolucent frame) to allow the abdomen to hang freely, thereby reducing epidural venous pressure.
3. Set up the C-arm fluoroscope to ensure clear anteroposterior (AP) and lateral views of the target intervertebral disc level can be obtained without obstruction.
4. Set up the neuromonitoring system for transcranial motor evoked potentials (TcMEP) and free-run electromyography (EMG) to monitor the exiting nerve root (ENR) throughout the procedure.
5. Confirm baseline neuromonitoring signals before proceeding. Pad all pressure points (chest, anterior superior iliac spines, knees) to prevent pressure injury.
6. Confirm the target disc level under fluoroscopy using anatomical landmarks (iliac crest at L4–L5) and verify true AP and lateral projections by aligning the endplates and centering the spinous process.

2. Percutaneous pedicle screw (PPS) placement

1. Under fluoroscopic guidance, identify the pedicle entry point on the AP view at the junction of the transverse process and the superior articular process (approximately the 10 o’clock position for the right pedicle and 2 o’clock for the left). Insert a cannulated pedicle access needle (bone biopsy needle) into the pedicle and confirm on AP view that the needle tip is within the pedicle shadow before advancing. Then insert guide wires into the pedicles of both the cranial and caudal vertebrae at the target level. Confirm parallel alignment with the disc on the lateral view.
2. Make skin incisions appropriate for the screw size and insert the cannulated percutaneous pedicle screws (PPS) over the guide wires. Confirm screw trajectory on both AP and lateral fluoroscopy: on AP view, the screw tip must not cross the medial pedicle wall; on lateral view, the screw should terminate within the anterior third of the vertebral body.
3. Thread the pre-contoured titanium rods into the tulip heads of the pedicle screws using a rod-passing instrument. Confirm bilateral rod seating under lateral fluoroscopy before locking.
4. Perform the screw locking sequence based on the direction of the vertebral slippage to facilitate reduction.
   1. For Anterior Slippage (Anterolisthesis) of the Cranial Vertebra: Tighten the set screws of the caudal screws to the final torque (final locking). Keep the set screws of the cranial screws loosely tightened (temporary fixation).
   2. NOTE: This configuration allows for the reduction of the anterior slippage when the cranial set screws are finally locked after cage insertion (Figure 3).
   3. For Posterior Slippage (Retrolisthesis) of the Cranial Vertebra: Tighten the set screws of the cranial screws to the final torque (final locking). Keep the set screws of the caudal screws loosely tightened (temporary fixation).
      NOTE: This configuration allows for the reduction of the posterior slippage aligned with the rod curvature when the caudal set screws are finally locked after cage insertion.

Figure 3: Percutaneous Pedicle Screw (PPS) fixation setup. Lateral fluoroscopic view showing the setup after percutaneous pedicle screw (PPS) insertion and before endoscopic insertion. For the correction of L4 anterior slippage, the caudal (L5) screws are "Final Locked", while the cranial (L4) screws are kept in a "Loose" (temporary fixation) state. Please click here to view a larger version of this figure.

3. Endoscopic approach to Kambin's triangle

1. Determine the skin entry point for the endoscopic approach, typically located 8–12 cm lateral to the midline, targeting Kambin’s triangle at an angle of approximately 20°–30° to the horizontal plane. Confirm the planned trajectory on both AP and lateral fluoroscopy before needle insertion; on the AP view, the target should be the superolateral aspect of the disc at the outer margin of the pedicle shadow.
2. Under fluoroscopic guidance, insert an 18 G spinal needle into the center of the target intervertebral disc via Kambin’s triangle.
3. Remove the inner stylet and inject 2 mL of indigo carmine dye through the needle to stain the nucleus pulposus and the inner annulus fibrosus.
4. Insert a guide wire through the needle and remove the needle, leaving the guide wire in place.
5. Make an approximately 8 mm skin incision at the wire entry point.
6. Insert a tapered dilator (diameter approx. 7 mm) over the guide wire.
7. Advance the dilator until it touches the annulus fibrosus.
8. Insert the initial oblique cannula (working channel, elevator type; Ø8.0 mm, length 165 mm) over the dilator and dock it firmly on the superior articular process (SAP).
9. Remove the dilator, leaving the guide wire and cannula in place.
10. Confirm the needle position via lateral (Figure 4A) and AP (Figure 4B) fluoroscopy.
11. Connect the full-endoscopic camera system and irrigation pump to the cannula. Set the continuous saline irrigation pressure to 20–30 mmHg to maintain a clear endoscopic field. Confirm adequate flow and visualization before advancing the endoscope into the disc space.

4. Foraminoplasty: Expanding the safety window

1. Insert the endoscope (25° or 30° viewing angle) into the cannula under continuous saline irrigation.
2. Use a bipolar radiofrequency probe to clear soft tissues on the surface of the SAP and identify the ENR located cranially and ventrally.
3. Insert a high-speed endoscopic drill equipped with a 3 mm diameter diamond burr through the working channel.
4. Drill the ventral aspect of the SAP to widen Kambin's triangle. The high-speed drill’s setting is typically 64,000 rpm with a 3 mm diamond burr.
   CAUTION: Exercise extreme caution to avoid contact with the ENR during drilling. Always keep the nerve root under direct visualization or protected by the cannula.
5. The "12 mm Rule": Continue drilling until the distance between the remaining facet bone and the ENR is at least 12 mm.
6. Use the 3 mm diamond burr as a measuring tool; ensure that a width equivalent to four burr diameters (3 mm × 4) is available at the disc surface (Figure 4C).
   NOTE: This 12 mm clearance is critical to safely accommodate the subsequent oblique cannula and the fusion cage without compressing the nerve root.

5. Disc preparation and expansion

1. Once the 12 mm safety window is confirmed, remove the endoscope, leaving the oblique cannula in place.
2. Insert the pencil dilator through the cannula.
3. Loosen the set screws of the PPS that were left temporarily tightened (not finally locked) in step 2.4.
4. Under AP and lateral fluoroscopic guidance, advance the pencil dilator to the center of the disc by tapping it with a mallet (Figure 4D).
5. Confirm that the disc height is distracted by the pencil dilator.
6. Insert the initial cannula into the disc along the pencil dilator (Figure 4E).
7. Temporarily tighten the PPS set screws to hold the distracted height.
8. Remove as much residual disc fiber as possible from inside the disc using a rongeur through the cannula (Figure 4F).
9. Insert the safe guide wire (S-guide) into the disc. Remove the oblique cannula, leaving the S-guide in place.
10. Assemble the 8 × 10 mm distractor and T-handle. Pass the assembled distractor through the safe guide wire to expand the disc height. Loosen the set screws that were temporarily tightened (Figure 5A).
11. Rotate the distractor 90° to vertically expand the intervertebral disc space and facilitate reduction of the vertebral slippage (Figure 5A). NOTE: For a left-sided approach with anterolisthesis, rotate clockwise; for retrolisthesis, rotate counter-clockwise.
12. Tighten the set screws to fix the distracted position once the disc height is expanded and the slippage is reduced (Figure 5B).
13. Rotate the distractor back 90°, returning it to its original 8 mm width orientation.
    NOTE: For small patients, use an 8 × 8 mm distractor; for larger patients requiring greater expansion, use an 8 × 10 mm or 10 × 12 mm distractor.
14. If the disc height is collapsed and distractor insertion is difficult, insert a starting rod through the safe guide wire first. Use a mallet to gently advance if needed.
    PAUSE POINT: After successful disc distraction, verify disc height restoration under lateral fluoroscopy before proceeding to cannula insertion.
15. Remove the handle from the distractor. Orient the U-shaped opening of the 8 × 10 mm open square cannula toward the facet joint (cranially) and insert it along the distractor under fluoroscopic guidance (Figure 5C).
    NOTE: Use an 8 × 8 mm cannula for small patients or a 10 × 10 mm cannula for larger patients.
16. Confirm cannula placement within the disc space on AP and lateral fluoroscopy. Re-attach the handle to the distractor and remove the distractor, leaving the open square cannula in place.
17. If neuromonitoring signals react to standard cannula insertion, switch to an alternative-orientation open square cannula (Rescue Square Cannula) inserted in the opposite orientation to protect the nerve root.
18. Perform curettage inside the disc using a motorized shaver and ring curette to remove residual disc material (Figure 5D).
    NOTE: The indigo, carmine dye injected in step 3.3 stains disc material blue, aiding identification of disc tissue.
19. Remove the safe guide wire when transitioning to the ring curette. Re-insert the endoscope after curettage to inspect the disc space.
20. Perform a complete discectomy using endoscopic forceps and shavers under direct endoscopic visualization.
21. Thoroughly decorticate the cartilaginous endplates of both the cranial and caudal vertebrae using a motorized shaver until punctate bleeding bone is exposed to facilitate fusion.
    CAUTION: Preserve the bony cortical rim of the endplates to prevent cage subsidence.
    NOTE: Adequate preparation is confirmed when a uniformly bleeding bony surface is visible on the endoscopic view.

Figure 4: Establishment of the 12 mm safety aperture and endoscopic setup. (A) Lateral fluoroscopic view, demonstrating endoscopic targeting of Kambin’s triangle. (B) Anteroposterior fluoroscopic view confirming instrument positioning. (C) Endoscopic view illustrating the 12 mm safety aperture, corresponding to approximately four 3 mm drill diameters. (D) Lateral fluoroscopic view showing insertion of a pencil dilator into the intervertebral disc. (E) Anteroposterior fluoroscopic view demonstrating placement of the working cannula within the disc space. (F) Endoscopic view of intradiscal preparation. Please click here to view a larger version of this figure.

6. Bone grafting and cage insertion

1. Prepare the autologous bone graft (harvested from the iliac crest) and/or allograft bone substitute.
2. Insert the bone funnel into the open square cannula.
3. Fill the anterior and lateral disc space with the bone graft material using the bone tamp and a mallet.
4. Select the appropriate size of the expandable interbody fusion cage and attach it to the inserter.
   NOTE: Ensure the cage is in its collapsed (non-expanded) state before insertion.
5. Under AP and lateral fluoroscopic guidance, insert the expandable cage into the disc space (Figure 5E, 5F).
6. Expand the cage to the desired height to properly restore the intervertebral disc height and foraminal height (Figure 5G).
7. Monitor the EMG signals continuously during cage insertion and expansion; pause if any sustained neuro-irritation is detected.
8. Confirm the final cage position and expansion height fluoroscopically. Verify that the cage covers ≥ 40% of the disc area on AP view and that foraminal height is restored on lateral view.
   PAUSE POINT: Confirm cage positioning under fluoroscopy before proceeding to final screw locking.
   NOTE: If cage position is suboptimal, partially collapse and reposition the cage before re-expanding and re-confirming position. Ensure the cage is located centrally or slightly anteriorly within the disc space.
9. Remove the cage inserter and the open square cannula.

7. Final fixation and closure

1. Confirm the final position of the cage and pedicle screws using AP and lateral fluoroscopy.
2. Fully tighten the set screws of the PPS construct to the manufacturer-specified final torque using a torque-limiting driver (e.g., 90 in-lb [approximately 10 N·m] for the Posterior fixation system Spinal System; refer to the applicable device IFU) (Figure 5H).
   NOTE: As described in step 2.4, this final tightening facilitates the reduction of the vertebral slippage.
3. (Optional) If central stenosis or lateral recess stenosis persists, perform additional endoscopic decompression (ventral facetectomy or laminotomy) at this stage.
4. Irrigate the surgical wounds with saline solution.
5. Close the fascia layer with absorbable suture (e.g., 2-0 polyglycolic acid). Close the skin with non-absorbable sutures or skin staples. Apply a sterile dressing. No drain is typically required.
6. Position the patient supine in the post-anesthesia care unit for monitoring.
   NOTE: A postoperative suction drain is typically not required due to minimal bleeding and because the procedure does not involve retraction or exposure of the dural sac.

Figure 5: Sequential steps of disc distraction, cage insertion, and reduction. (A) Fluoroscopic view showing insertion of the distractor with the cranial screw in a loose state. (B) Rotation of the distractor by 90° to expand the intervertebral disc space, with subsequent locking of the cranial screw to maintain distraction. (C) Reorientation of the distractor and insertion of the open square cannula. (D) Intradiscal tissue removal using a curette. (E) Lateral fluoroscopic view of expandable cage insertion in the collapsed state. (F) Anteroposterior fluoroscopic view showing cage placement. (G) Expansion of the cage to restore disc height. (H) Final reduction achieved by tightening of the cranial set screw, resulting in posterior translation of the L4 vertebra. Please click here to view a larger version of this figure.

Results

A representative case is a 72-year-old woman diagnosed with L4 degenerative spondylolisthesis and L4/5 central spinal canal stenosis. She presented with a 10-year history of lower back and leg symptoms, which had worsened significantly over the past two years. Her primary complaints were pain radiating from both buttocks to the lateral aspect of the thighs and lower legs, along with numbness in the soles of both feet. She exhibited intermittent claudication with a walking distance of approximately 150 m. Standing postures, such as washing dishes, exacerbated her symptoms. Neurological examination revealed normal muscle strength (Manual Muscle Testing (MMT) 5/5 in all lower limb muscles) but hypoactive Achilles tendon reflexes and mild bladder/rectal disturbance. Preoperative imaging should be evaluated for degree of slippage, disc height, and severity of stenosis to guide surgical planning, including cage height selection and foraminoplasty extent. Preoperative X-ray and MRI demonstrated L4 anterior slippage and severe central stenosis at the L4/5 level (Figure 6A-D). These imaging findings met the inclusion criteria for KLIF, characterized by moderate-grade spondylolisthesis with preserved disc space allowing safe access through Kambin’s triangle.

Figure 6: Preoperative imaging of the representative case (A) Preoperative anteroposterior (AP) radiograph. (B) Preoperative lateral radiograph. (C) Preoperative sagittal T2-weighted MRI. (D) Preoperative axial T2-weighted MRI. Please click here to view a larger version of this figure.

The patient underwent L4/5 KLIF following the protocol described above. The successful outcome was attributed to strict adherence to key protocol steps, particularly adequate foraminoplasty to achieve the 12 mm safety aperture and precise cage placement under fluoroscopic guidance. The postoperative course was uneventful. No intraoperative complications such as nerve injury or excessive bleeding were observed, indicating procedural safety. Pain improvement was assessed using the Visual Analog Scale (VAS) for leg and back pain. Her bilateral leg pain improved significantly immediately after surgery (preoperative VAS leg pain score: 8/10; postoperative VAS leg pain score at 6 months: 1/10; preoperative VAS back pain score: 7/10; postoperative VAS back pain score: 2/10). Successful outcomes were defined by appropriate cage positioning (centrally or slightly anteriorly within the disc space on AP/lateral fluoroscopy), restoration of disc height, reduction of vertebral slippage, and adequate decompression of neural elements on postoperative MRI. Postoperative imaging confirmed successful cage placement and reduction of the slippage (Figure 7A, B). Postoperative imaging should be assessed for central cage positioning, restoration of disc and foraminal height, and absence of residual neural compression. Furthermore, MRI demonstrated effective decompression of spinal canal stenosis (Figure 7C, D). These findings indicate that the KLIF protocol effectively achieves both mechanical stabilization and neural decompression. The surgical wounds were minimal, demonstrating the minimally invasive nature of the procedure (Figure 8). In suboptimal cases, inadequate foraminoplasty or improper cage positioning may result in insufficient decompression or persistent symptoms, highlighting the importance of strict protocol adherence.

Overall, this representative case demonstrates that the KLIF protocol enables effective neural decompression, stable interbody fusion cage placement, and minimal soft tissue disruption when key procedural steps—including precise foraminoplasty, systematic screw locking, and meticulous endplate preparation—are followed.

Figure 7: Postoperative imaging of the representative case (A) Postoperative anteroposterior (AP) radiograph. (B) Postoperative lateral radiograph. (C) Postoperative sagittal T2-weighted MRI. (D) Postoperative axial T2-weighted MRI. Please click here to view a larger version of this figure.

Figure 8: Postoperative cosmetic outcome. Macroscopic view of the patient's back. The surgical wounds are minimal. The rectangular area labeled "PPS" indicates the small incisions for Percutaneous Pedicle Screw insertion, and the circled area labeled "Endoscope" indicates the portal for the trans-Kambin triangle approach. Please click here to view a larger version of this figure.

Discussion

KLIF offers a distinct alternative to conventional fusion techniques. Based on our comprehensive reviews^10,11, the KLIF procedure offers four distinct advantages compared to other fusion surgeries.

Minimally Invasive Cage Insertion
The use of a specialized open square cannula (8 mm x 10 mm) allows for cage insertion through a small skin incision (approximately 12–15 mm). This minimizes muscle damage compared to other fusion techniques^10,12.

Avoidance of Major Visceral Complications
Unlike Anterior LIF (ALIF), XLIF, and OLIF, which require careful navigation around major vessels, the ureter, or the bowel, the KLIF corridor is devoid of these intraperitoneal or retroperitoneal organs^10,12. The ENR is the primary concern, which is visualized and protected throughout the procedure.

Reduced Risk of Hematoma and Dural Injury
Conventional TLIF or PLIF often necessitates laminectomy or total facetectomy, which can increase the risk of postoperative hematoma or dural tears¹³. Since KLIF does not require such extensive bony resection, these risks are significantly minimized^8,10. Consequently, the use of a postoperative suction drain is generally unnecessary (drain-free).

Lower Surgical Site Infection (SSI) Rate
Minimally invasive approaches are expected to reduce surgical site infection (SSI) rates by limiting tissue exposure and dead space. A systematic review by Parker et al. compared minimally invasive TLIF (MIS-TLIF) to open TLIF and demonstrated a significantly lower cumulative incidence of SSI (0.6% vs. 4.0%)¹⁴. In our systematic review¹¹ and other reported KLIF series (e.g., Nagahama et al⁶., Nakamura et al⁷.), no SSIs were observed, suggesting that full-endoscopic KLIF may further reduce infection risks. These findings indicate a potential reduction in infection risk, although further comparative studies are required.

Additionally, this technique facilitates reproducible execution of key procedural steps, including controlled foraminoplasty and systematic screw locking sequences, which contribute to the observed clinical advantages in patients with degenerative spondylolisthesis¹⁵. This protocol may be modified based on patient anatomy, such as adjusting the entry angle or extent of foraminoplasty in cases with severe foraminal stenosis. Compared to conventional TLIF and OLIF techniques, KLIF provides a more direct and tissue-sparing approach, although it may require higher technical expertise and specialized training.

Anatomically, this technique is distinct from conventional TLIF, which typically requires facetectomy that exposes the dural sac as the medial boundary. This method represents a significant advancement in minimally invasive spine surgery by enabling safe interbody fusion through a fully endoscopic approach while preserving anatomical structures. In contrast, KLIF preserves the facet joint structure to a greater degree (only partial resection) and accesses the disc via Kambin's triangle, where the medial wall comprises the SAP and dural sac. Therefore, the nomenclature "Trans-Kambin Triangle LIF" is anatomically more accurate than "Endoscopic TLIF"^8,9,12. Although the fundamental concept of trans-Kambin triangle endoscopic fusion has been introduced in the literature under various names (e.g., PETLIF, PELIF), the current protocol differs from previously reported techniques in several key aspects. First, KLIF explicitly defines the extent of bony resection as partial ventral foraminoplasty only, thereby preserving the dorsal facet joint structure, which distinguishes it from facet-sacrificing approaches. Second, the protocol incorporates a specific screw locking sequence tailored to the direction of vertebral slippage, enabling simultaneous decompression and reduction. Third, the use of an expandable cage inserted through an open square cannula via a strictly defined 12 mm safety aperture represents a standardized, reproducible workflow not fully described in earlier reports. These procedural distinctions are intended to address the lack of standardization in the field and to provide surgeons with a clearly defined, step-by-step protocol suitable for adoption. This method is particularly suitable for patients with degenerative spondylolisthesis and preserved disc space requiring minimally invasive fusion.

The success of this procedure relies on the establishment of a 12 mm safety aperture¹⁶. The most critical steps of this protocol include precise identification of Kambin’s triangle, controlled foraminoplasty to achieve a 12 mm safety aperture, and careful protection of the ENR during cage insertion. Enlarging Kambin's triangle to at least 12 mm via foraminoplasty is critical to accommodate the cage without compressing the ENR. Our results, showing only one transient nerve irritation in the early learning curve and none in subsequent cases, support the safety of this protocol when strictly followed. If inadequate visualization or nerve irritation occurs, repositioning of the working cannula and further controlled foraminoplasty may be required to safely expand the working corridor. In such cases, reposition the cannula, increase foraminoplasty width, and reassess under direct endoscopic visualization before proceeding.

Limitations include a steep learning curve typical of endoscopic surgery. Additional limitations include restricted visualization in cases of severe anatomical distortion, limited applicability in high-grade spondylolisthesis, and dependence on fluoroscopic guidance, which may increase radiation exposure. Surgeons should master basic endoscopic decompression before attempting KLIF. Additionally, short-term outcomes in this representative case were favorable; however, larger studies are required to confirm long-term efficacy.

In conclusion, KLIF is a minimally invasive technique that enables safe and effective lumbar interbody fusion through a structured, reproducible protocol. This protocol provides a structured approach for performing KLIF with reproducible procedural steps. Its success depends on adherence to critical procedural steps, including precise access through Kambin’s triangle and maintenance of the safety aperture. With further refinement and broader clinical validation, this method has the potential to expand its role in minimally invasive spine surgery. Future applications of this technique may include its adaptation for multi-level fusion procedures and integration with navigation or robotic-assisted systems to further improve accuracy and safety.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
10K Arthroscope tube set	Zimmer Biomet	LC-10K0-100-00	Irrigation system console
10K Irrigation console	Zimmer Biomet	LC-10K0-000-00	Irrigation system console
1-Coarse Diamond Bur SPL (3.5)	Nakanishi	PDS-1CD330-35	High-speed drill
21G PTCD needle, 200 mm	Hakko Shoji	U5099-MM	Needle for local anesthesia
32-inch 4K LCD monitor	Sony	LMD-X3200MD	Monitor
Aquarius NET Server	TeraRecon	N/A	CT reconstruction and analysis software
Bone Funnel	MERA	501-BF0006	Used for bone graft insertion
Bone Tamp	MERA	501-BT0008	Used for bone graft compaction
Centricity™ Universal Viewer Zero Footprint Client	GE Healthcare	Version 6.0 SP11.2.2	MRI visualization and analysis software
CLICKLINE grasping forceps	Karl Storz	28163FSI	Intervertebral disc rongeur
Curved rongeur, WL 360 mm, φ2.5 mm	RIWOspine	89240.1044	Soft tissue rongeur
Dilator, Ø7.0 mm, effective length 225 mm (2 holes)	Elliquence	11-2311	Dilator
Distractor	MERA	501-DS0808T / 501-DS0810T / 501-DS1012T	Used to expand disc height (8×8, 8×10, 10×12 mm)
ENDOCAM® Logic 4K camera controller	Richard Wolf GmbH	55253011 86-103	Camera
ENDOCAM® Logic 4K camera head	Richard Wolf GmbH	85525942 86-104	Camera
Fiber light cable (φ3.5 mm/3.0 mm)	Richard Wolf GmbH	806635301 86-124	Camera
Floseal Hemostatic Matrix	Baxter	ADS201844 5mL Kit	Hemostatic agent
Guide wire	Nihon MDM	28163GWT	Dilator
Hammer	MERA	501-HM0001	Used for insertion of the safe guide
LED light source unit for endoscopy (LED 1.2 set)	Richard Wolf GmbH	51610011 86-164	Camera
Open-angle Cannula	MERA	501-OC0808S / 501-OC0810S / 501-OC1010S	Standard cannula for cage insertion
Primado2 Drill System	Nakanishi	P200-CU-100	High-speed drill
Primado2 Foot Controler	Nakanishi	FC-73	High-speed drill
Primado2 Slim motor handpiece	Nakanishi	P200-SMH-HS	High-speed drill
PTC needle type B, 18G × 200 mm	Hakkou Shoji	22411830	Dilator
RELINE® Spinal System	NuVasive		Posterior fixation system including pedicle screws (polyaxial/reduction), Ti/CoCr rods
Rescue-angle Cannula	MERA	501-RC0808L / 501-RC0810L / 501-RC0810R	Alternative cannula to avoid nerve root irritation
Ring Curette	MERA	501-CU0007A	Used for disc material removal
RISE® Ti Lumbar Cage System	Globus Medical		Expandable TLIF lumbar interbody cage with controlled disc height restoration
Rongeur, WL 360 mm, φ3.0 mm	RIWOspine	89240.1003	Soft tissue rongeur
Safe Guide (S-guide)	MERA	501-SW0012	Guide inserted through the FED cannula
Shaver	MERA	501-SV0008T / 501-SV0009T / 501-SV0010T / 501-SV0012T	Used for disc space preparation
Starting Paddle	MERA	501-SP0608T	Used in cases with low disc height
Step dilator set (5 pieces)	Elliquence	CSD-5	Dilator
Super Slim attachment 200	Nakanishi	P200-RA330-L	High-speed drill
Surgi-Max Air	Elliquence	IEC4-SP	Bipolar device
T-handle	MERA	501-TH0003T	Handle for operating the distractor
Trigger-Flex	Elliquence	DTF-40	Bipolar device
VERTEBRIS lumbar, 25°, 6.9 mm, WL 207 mm	RIWOspine GmbH	89210.1254	Rigid endoscope
Working channel, duckbill type, Ø8.0 mm, length 165 mm	Richard Wolf GmbH	11-2910	Duckbill cannula
Working channel, elevator type, Ø8.0 mm, length 165 mm	Richard Wolf GmbH	11-2916	Oblique cannula