Computer-navigated transfacet uniportal endoscopic lumbar interbody fusion: a novel technique and illustrative case series

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Abstract

Introduction

Uniportal endoscopic lumbar interbody fusion (U-ELIF) has emerged as a highly tissue-sparing alternative to minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF), offering reductions in muscle disruption, blood loss, pain, and hospital stay [1–3]. However, current U-ELIF approaches (trans-Kambin and interlaminar) have some limitations. The trans-Kambin approach carries a risk of injury to the exiting nerve root [1,4,5], while the interlaminar approach involves manipulation of the traversing nerve root or dural sac [6–8].

We describe a computer-navigated transfacet U-ELIF approach that accesses the disc space through the facet joint by creating a reproducible bony corridor, which provides intrinsic neural protection. Through this approach, disc preparation and interbody cage insertion using modern endoscopic instruments can be performed with high safety. Fig. 1 and Table 1 summarize the advantages and disadvantages of the various U-ELIF approaches.

Fig. 1

Approaches to uniportal endoscopic lumbar interbody fusion.

Table 1

Summary of uniportal endoscopic lumbar interbody fusion approaches

To our knowledge, this is the first technical report in literature describing a computer-navigated transfacet U-ELIF approach. We present a case series to demonstrate the feasibility and potential clinical utility of this approach.

Technical Notes

Surgical technique

Patient selection

Surgical indications include degenerative lumbar conditions, such as low-grade spondylolisthesis, spinal stenosis with instability, and mild-to-moderate central stenosis with foraminal stenosis [1]. Patients with facet joint widths of ≥12 mm are considered suitable candidates in order to accommodate the 11-mm endoscopic portal (Fig. 2).

Fig. 2

Magnetic resonance imaging showing facet width and transfacetal cage insertion trajectory.

Positioning and navigation setup

The procedure is performed under general anesthesia. Neuromonitoring electrodes are placed in the supine position before placing the patient in the prone position on a Jackson table. Baseline somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) are recorded after draping. Real-time SSEPs are monitored throughout the surgery, while MEPs are acquired at key stages (transfacet access, cage insertion, decompression, screw placement, and end of surgery). The navigation reference frame is secured to the cephalad spinal process through a mini-open midline incision. An O-arm fluoroscopic guidance system (Medtronic Inc., Minneapolis, MN, USA) provides intraoperative three-dimensional images for real-time navigation with the StealthStation S7 receiver (Medtronic Inc.).

Transfacet access

Guidewires for pedicle screws are placed with navigation through paramedian skin incisions. Separate 1.5-cm incisions are made along the same paramedian line for navigated Jamshidi needle entry through the midpoint of the facet joint into the disc. A 1.6-mm K-wire is placed to confirm the trajectory using computer navigation and fluoroscopy (Fig. 3). A 7.5-mm hand reamer is introduced over the K-wire to create a bony corridor, and it is subsequently dilated to fit an 11-mm endoscopic sleeve (Figs. 4, 5).

Fig. 3

(A–D) Computer-navigation of Jamshidi needle insertion into disc space via transfacet approach.

Fig. 4

(A) K-wire guided hand reamer. (B) Checking depth of hand reaming using navigation.

Fig. 5

Intraoperative navigation. (A) Start point of hand reamer. (B) Ideal depth of hand reaming, not breaching ventral cortex of facet joint.

Endoscopic disc preparation

A Vertebris uniportal endoscope (RIWOspine, Knittlingen, Germany) is inserted for visualization of the transfacet corridor and to confirm its integrity. The superior articular process protects the exiting nerve root, while the inferior articular process protects medial neural structures. Ventral cortex osteotomy with an Ultrasonic Osteotome (SMTP, Beijing, China) completes the corridor access (Fig. 6). Annulotomy and discectomy are performed through the safe transfacet corridor using radiofrequency, expandable shavers, and articulating curettes. An expandable trial is expanded under fluoroscopy guidance until a tactile feel of adequate expansion force with two fingers is acquired, which determines the cage size. Adequate endplate preparation is confirmed by halting irrigation to observe bone bleeding. A dry scope environment is created for cage insertion (Fig. 7).

Fig. 6

(A) I: medial cortex of facet joint. II: superolateral cortex of facet joint. III: transfacet bony corridor leading to ventral cortex of facet joint. IV: caudal pedicle. (B) Osteotomy of ventral cortex using Ultrasonic Osteotome (SMTP).

Fig. 7

Endplate preparation view. (A) Irrigation. (B) Dry scope. I: medial. II: caudal endplate. III: lateral. IV: cephalad endplate.

Interbody cage insertion

Morselized autologous bone mixed with Novosis recombinant human bone morphogenetic protein-2 (CBGIO, Seoul, Korea) is packed anteriorly for improved osteoinductive properties and fusion rates [9]. An expandable FlareHawk cage (Accelus, Palm Beach Gardens, FL, USA) is impacted into the disc space through the transfacet bony corridor. Fluoroscopy is performed before, during, and after cage expansion to ensure satisfactory position, expansion, and locking (Fig. 8).

Fig. 8

(A) Insertion of unexpanded interbody cage. (B) Expansion of interbody cage. (C) Oblique view confirming deployment of locking mechanism.

Endoscopic decompression

In patients with significant ipsilateral lateral recess compression, the endoscope is reintroduced to complete the ipsilateral facetectomy and flavectomy. The uniportal endoscope can be wanded to an “over-the-top” position and moved toward the contralateral side for contralateral decompression as required [10].

Pedicle screw insertion

Percutaneous pedicle screws are inserted using the previously navigated guidewires in a typical fashion [11]. Final construct position and screw depth are confirmed with fluoroscopy.

Pearls and pitfalls

The pearls and pitfalls of our approach are summarized in Table 2.

Table 2

Pearls and pitfalls of computer-navigated endoscopic transfacet access

Discussion

U-ELIF has gained momentum as an ultra-minimally invasive alternative to MIS-TLIF, enabling direct endplate visualization and minimizing the risk of endplate violation and cage subsidence [1,3,12–14]. While trans-Kambin and interlaminar U-ELIF techniques have been shown to achieve comparable results [15], both approaches carry notable limitations that restrict their applicability. The interlaminar approach, although intuitive and familiar, necessitates dural or traversing nerve root retraction to access the disc space, increasing the risk of tears or injuries [6–8]. The trans-Kambin approach spares central neural structures, but has anatomical constraints and may compromise the exiting nerve root [5,16].

The transfacet approach addresses these limitations by utilizing a safe bony corridor through the facet joint, preserving the inherent protective anatomy of the facet complex. This approach leverages “Kambin’s prism” concept [17] and reorients access through a wider base of this prism. This concept parallels transfacet access used in MIS-TLIF [18], but when used in U-ELIF, it offers the surgeon protection of neural structures while maintaining the benefits of endoscopic surgery with greater soft tissue preservation.

The transfacet approach can be challenging, especially in patients with altered anatomy resulting from degenerative changes. The use of real-time computer navigation ensures reliable trajectory acquisition and improves reproducibility across patients. Although additional setup time is required, computer navigation has been shown to reduce the total operative time and increase the accuracy of the surgery [19,20].

Intraoperative neuromonitoring is the standard practice for most minimally invasive procedures in our institution. Its setup and use typically add 15–20 minutes to the total operative time. However, the benefits of enhanced neurological safety and associated cost-effectiveness outweigh this limitation [21,22].

There are several limitations to this technique. First, this is a novel technique with no long-term data on outcomes. Second, the technique requires familiarity with both computer navigation and uniportal endoscopy, which may be associated with a learning curve [23]. Third, the approach is best suited for patients with facet joint widths of ≥12 mm to accommodate the 10–11-mm working channels of uniportal endoscopic systems. Despite its limitations, the benefits of endoscopic surgery associated with its ultra-minimally invasive profile have been well documented, and thus, this technique has a good outlook.

Future directions may involve integration of the approach into robotic systems, where the transfacet bony corridor eliminates the need for retraction or protection of neurogenic structures, allowing disc access, cage preparation, and cage insertion to be automated by robotic surgery. Further development in robotics, coupled with real-time navigation, may enable fully automated ultra-minimally invasive procedures in the future.

In conclusion, computer-navigated transfacet U-ELIF is a promising novel technique that leverages bony corridors and advanced surgical technologies to improve neural safety while preserving the advantages of endoscopic fusion. Larger studies are warranted to assess the long-term outcomes and broader applicability of this approach.

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