Recent advancements in spinal endoscopic techniques have positioned full-endoscopic lumbar interbody fusion (endo-LIF) as a promising alternative to open and minimally invasive transforaminal lumbar interbody fusion (TLIF), offering comparable long-term outcomes. The endoscopic approach features smaller incisions, minimal muscle disruption, reduced blood loss, and superior short-term outcomes [1,2]. However, the technical complexity and steep learning curve of endo-LIF present a significant risk of nerve root injury, particularly for less experienced surgeons [3,4]. This underscores the importance of employing the correct surgical technique for nerve root protection.

Two commonly employed approaches in endo-LIF are full-endoscopic facet-sparing TLIF (FE fs-TLIF) and full-endoscopic facet-resecting TLIF (FE fr-TLIF) [5–11]. FE fs-TLIF involves a partial facetectomy and discectomy via the Kambin triangle, whereas FE fr-TLIF requires a complete facetectomy and discectomy through an extended Kambin triangle, resembling the approach used in conventional open TLIF [12]. Due to the diverse anatomical considerations of these approaches—including surgical incision, operative route, extent of facet resection, and cage entry point—FE fs-TLIF is associated with a higher incidence of exiting nerve root irritation, while FE fr-TLIF presents an increased risk of traversing root and thecal sac injury [12–14]. Nerve root injury can result in prolonged hospitalization and adversely impact clinical outcomes [9,12,15].

Literature and clinical experience indicate that the highest risk for nerve root injury arises during discectomy, endplate preparation, and cage insertion [9,14]. Therefore, developing effective methods to protect the nerve root during these steps is crucial, although there is a lack of technical guidelines focusing on these skills. Kim et al. [9] introduced a dedicated working glider to prevent nerve root irritation during endo-LIF procedures. A previous cadaveric study revealed that the selection of cage glider designs and surgical steps should be individualized to the specific approach, differentiating between FE fs-TLIF and FE fr-TLIF [16]. These studies suggest that diverse cage designs play a crucial role in nerve root protection during endo-LIF surgery. To ensure tailored nerve root protection, this study discusses the surgical tips and the selection of appropriate cage gliders for these two approaches, focusing on the use of bullet-shaped (straight) or banana-shaped cages during discectomy and cage implantation.

This study provides a comprehensive review of the surgical techniques utilized in the two approaches to uniportal full endo-LIF. It identifies the most critical timepoints for nerve root irritation during the operation, offering critical guidance for spine surgeons. Furthermore, the study explores a range of surgical techniques for inserting banana-shaped and bullet-shaped cages, expanding upon the existing literature on open TLIF procedures [19]. In FE fs-TLIF, irrespective of whether a banana-shaped or bullet-shaped cage is being inserted, a one-tip cage glider is recommended for protecting the exiting nerve root. This preference is based on the preserved bony structure, minimal traversing root irritation risk, and potential for stabbing injury to the nerve with the use of a two-tip cage glider. During banana-shaped cage implantation in FE fr-TLIF, a two-tip cage glider should be used for protecting both nerve roots. This is necessitated by the lateral tilt of the cage holder during insertion, which heightens the risk of exiting root irritation. In comparison, one-tip and two-tip gliders are both recommended in FE fr-TLIF when using a bullet-shaped cage. The proper insertion of the cage glider tips and the corresponding rotation technique are also elucidated. A summary of these key points is listed in Table 1.

The choice between FE fs-TLIF and FE fr-TLIF should be guided not by a rigid doctrine but rather by careful consideration of individual patient factors and pathology-specific requirements. In our clinical practice, we consider three primary factors when selecting between FE fs-TLIF and FE fr-TLIF. First, patient comorbidities play a crucial role in the selection process. For older patients or those with high surgical risk, FE fs-TLIF under local anesthesia is often preferred. Second, radiological findings aid in determining the need for direct decompression. FE fr-TLIF is particularly more suitable in patients with facet joint hypertrophy, facet cysts, or ligamentum flavum pathology. Third, sagittal alignment goals are a key consideration influencing cage selection. FE fr-TLIF permits the placement of larger cages owing to the wider surgical corridor, which can enhance spinal alignment [20]. Overall, we advocate for a flexible and tailored approach to each patient’s anatomy and clinical needs to achieve both surgical safety and optimal outcomes.

Numerous strategies for nerve root protection have been developed for both preoperative and intraoperative phases [13]. Preoperatively, well-trained and experienced endoscopic spine surgeons have been demonstrated to achieve better clinical outcomes [21]. In some patients, an adequate Kambin triangle—bounded by the exiting nerve root, facet joint, and lower vertebral endplate—may be absent, especially in the upper lumbar levels. Thus, preoperative comprehensive imaging evaluations with computed tomography or magnetic resonance imaging are crucial for comprehensive surgical planning [15]. Advanced imaging facilitates preoperative planning by helping to assess the extent of facetectomy required, determine the optimal size of the working portal, and individualize the endoscopic approach angle [22]. Optimizing perioperative preparation is also vital for nerve root protection. Precise perioperative local anesthesia and neurophysiological monitoring equipment help mitigate the incidence of nerve root injury [13,23–26]. Surgical skill plays a pivotal role in ensuring nerve protection, with techniques such as the outside-in approach for inferior articular facetectomy, accurate docking points for the guidewire or working cannula, and proper execution of foraminoplasty being strongly recommended [18,27–30]. However, existing literature demonstrates a relative paucity of studies specifically addressing the risk of nerve root injury during the steps of cage insertion despite its clinical significance [9,13]. In our study, we aimed to address this knowledge gap by elucidating the surgical techniques for facilitating appropriate selection and use of cage glider selection.

During TLIF, achieving reliable fusion and restoring lumbar lordosis while minimizing cage subsidence and pseudoarthrosis remains a top priority for surgeons. Hence, numerous studies have examined the influence of diverse artificial disc designs, such as bullet-shaped and banana-shaped cages, on interbody fusion outcomes [31–33]. Although a consensus has not been established, several studies highlight the potential advantages of banana-shaped cages over bullet-shaped ones in restoring disc height, segmental lordosis, and lumbar lordosis. These benefits are theorized to stem from the anterior placement of the banana-shaped cage in the intervertebral space [19]. Furthermore, the anterior placement of banana-shaped cages is believed to lower the risk of subsidence due to the higher mechanical strength of the apophyseal ring [34]. In FE fs-TLIF, there are increased concerns regarding the higher risk of cage subsidence and suboptimal sagittal alignment restoration, which are attributed to the use of smaller cages necessitated by the relatively narrow surgical corridor [12]. The adoption of banana-shaped cages may address these limitations, potentially enhancing radiological and clinical outcomes in FE fs-TLIF and FE fr-TLIF. However, to date, only a limited number of case reports have explored the use of banana-shaped cages in uniportal full-endoscopic fusion surgery [35]. To address this gap, our team developed and introduced a preliminary surgical technique for the application of banana-shaped cages in endoscopic TLIF. This technique is grounded in single-center clinical experience and cadaveric anatomical studies, offering a foundation for future research to evaluate the safety and efficacy of banana-shaped cages in endoscopic fusion procedures.

This study has several limitations. First, the surgical techniques for nerve root protection during FE fs-TLIF and FE fr-TLIF are primarily derived from cadaveric findings and accumulated clinical experience. While these anatomical studies offer valuable insights into safe cage insertion, their effectiveness in real-world clinical settings remains to be validated. Currently, there is a paucity of clinical outcome data, especially concerning the use of banana-shaped cages under full-endoscopic guidance. To date, only a single well-designed cohort study has demonstrated a reduction in postoperative neurapraxia with bullet-shaped cages in full-endoscopic fusion surgery employing this technique [36]. To overcome this limitation, we conducted prospective clinical studies to assess outcomes such as nerve injury rates and recovery, with a particular emphasis on the use of banana-shaped cages. The results of these studies are expected to be published soon. Second, the precise risk of injury to exiting nerve roots during the insertion of banana-shaped cage is still unknown. Only a few studies have examined the potential risk [14,19]. However, we believe that despite the limited evidence, heightened awareness of this issue may help minimize the occurrence of complications to the greatest extent possible. Third, our study does not cover the full spectrum of currently available cage options. Devices such as OLIF-type cages and expandable cages exhibit distinct biomechanical properties and insertion profiles that may substantially affect the choice of neural protection strategies. To address this limitation, we plan to include these alternative cage designs in future cadaveric and clinical studies on endoscopic lumbar fusion. Lastly, the recommended surgical steps of cage glider insertion were partly based on cadaveric evaluations, which might not fully represent the clinical situation due to differences in soft tissue characteristics. However, given the limited nerve root visualization and the challenges associated with performing repeated trials of cage glider insertion during clinical practice, cadaveric anatomic dissection remains a valuable resource for advancing surgical knowledge.

In conclusion, appropriate cage glider selection and insertion techniques play an important role in safeguarding nerve roots during FE fs-TLIF and FE fr-TLIF. The selection of a one-tip or two-tip cage glider, along with the appropriate rotational technique, should be individualized to diverse approaches and cage types to augment surgical safety and optimize clinical outcomes.