A novel C-Arm-free navigation-guided endoscopy-assisted extraforaminal decompression for L5 radiculopathy with far-out syndrome: a surgical technical note

Introduction

In 1917, Bertolotti introduced the term “Bertolotti syndrome” to describe low back pain associated with a lumbosacral transitional vertebra (LSTV), a condition that remains an enigma (1). Wiltse et al. later described L5–S1 extraforaminal stenosis (far-out syndrome), in which the L5 nerve root is compressed between an enlarged L5 transverse process and the sacral ala distal to the foramen (2). The most commonly used classification for LSTV is the Castellvi system, in which type II refers to incomplete unilateral (IIa) or bilateral (IIb) lumbarization/sacralization, characterized by an enlarged transverse process forming a diarthrodial joint with the sacrum (3). Management typically begins with non-steroidal anti-inflammatory drugs (NSAIDs), targeted physiotherapy, and image-guided injections or radiofrequency denervation (4,5). Refractory cases may require resection of the pseudo-articulation, segmental fusion when there is significant degeneration, or focused decompression in the setting of nerve root entrapment (6,7).

Traditional microscopic foraminotomy has been considered the gold standard for treating far-out syndrome (8). With advances in endoscopic spine surgery, full-endoscopic and unilateral biportal endoscopic (UBE) techniques have been increasingly used to address foraminal and extraforaminal stenosis, offering excellent illumination, magnification, and access to deeper pathology with minimal soft-tissue disruption (9-11). However, most described techniques depend on C-arm fluoroscopy for level confirmation, trajectory planning, and portal adjustment—steps that become difficult when a hypertrophic L5 transverse process and sacral ala obscure conventional landmarks. Concerns regarding cumulative radiation exposure to patients and surgeons have further driven a shift toward navigation-based workflows that reduce or eliminate intraoperative fluoroscopy (12). O-arm based three-dimensional navigation provides real-time multiplanar visualization of bony anatomy and instrument trajectories, enabling precise access to the extraforaminal corridor and controlled bone resection while preserving stabilizing structures (13).

To date, reports of navigation with UBE for far-out syndrome have been reported (14). The objective of this report is to describe a C-arm-free navigation-guided endoscopy-assisted extraforaminal decompression technique for L5 far-out radiculopathy. We aim to demonstrate how this approach enables accurate lesion localization, precise portal placement, and targeted L5 root decompression using navigated burrs, and to outline the surgical workflow and clinical experience supporting its feasibility and potential advantages over conventional fluoroscopy-dependent methods. We present this article in accordance with the SUPER reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-233/rc).

Preoperative preparations and requirements

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. This study was conducted with the approval of the Ethics Committee of Okayama Rosai Hospital, a tertiary hospital (approval No. 577). Written informed consent was obtained from the patient.

Patient history

Case presentation

A 74-year-old woman presented to our hospital with severe right L5 radicular pain and intermittent claudication limited to less than 300 m. She had undergone L3–5 interbody fusion at another hospital 8 years earlier and remained asymptomatic for 2 years postoperatively. Thereafter, she gradually developed recurrent right lower limb radicular pain and was treated conservatively for 10 months. A right L5 selective nerve root block provided transient but clear relief and confirmed L5 as the affected nerve root.

Her neurological examination revealed hypoesthesia and pain along the lateral aspect of the right lower leg (L5 dermatome), with weakness of the extensor hallucis longus muscle [manual muscle testing (MMT) 4/5]. There was no hyperreflexia in either lower limb and no urinary disturbance.

Preoperative imaging

Plain lumbar radiographs showed L3–5 interbody fusion and bilateral L5 transverse processes articulating with the S1 ala (Figure 1). The L2/3 disc space was narrowed, and the L5–S1 level was mobile. Computed tomography (CT) confirmed the presence of a Castellvi type IIb LSTV and showed severe stenosis in the far-out region of the right L5–S1 area (Figure 2). Magnetic resonance imaging (MRI) showed extraforaminal compression of the right L5 nerve root between the right L5 transverse process and the sacral ala, consistent with far-out syndrome (Figure 3).

Figure 1 Preoperative lumbar radiographs. (A) Anteroposterior, (B) neutral lateral, (C) flexion lateral, and (D) extension lateral views demonstrating prior L3–5 lumbar interbody fusion performed at another hospital.

Figure 2 Preoperative lumbar CT images. (A) Coronal reconstructed CT; (B) axial CT at L5/S1; (C) three-dimensional reconstructed CT. Red arrows indicate right extraforaminal stenosis, and blue arrows indicate spinal implants. CT, computed tomography.

Figure 3 Preoperative MRI. (A) Right parasagittal T2-weighted image, (B) left far-sagittal T2-weighted image, (C) coronal T2-weighted image, and (D) axial T2-weighted image at the L5/S1 level. Red arrows indicate right L5/S1 extraforaminal stenosis. MRI, magnetic resonance imaging.

After obtaining informed consent, posterolateral endoscopic extraforaminal decompression under navigation guidance was performed. This technique was performed in the bioclean room of Okayama Rosai Hospital, Japan, a tertiary care referral hospital. The necessary equipment for this procedure includes a radiolucent carbon operating table, ProAxis (Mizuho, USA), O-arm system (Medtronic, USA), lumbar microendoscope, Metrx (Medtronic, USA), neuromonitoring, Medtronic Nim Eclipse IONM system (Medtronic, USA), and navigated instruments. The surgery was performed by the two senior surgeons (S.A. and M.T.).

Step-by-step description

Patient positioning and equipment

Under general anaesthesia, the patient was placed in the prone position on a radiolucent carbon operating table (ProAxis, Mizuho, USA) (Figure 4A). A percutaneous reference frame was anchored 2 cm anterior to the left posterior superior iliac spine (PSIS) and an intraoperative O-arm scan (Medtronic, USA) was obtained for navigation registration on the StealthStation S8 platform (Medtronic, USA) (Figure 4B). Navigation accuracy was verified using a navigated pointer on multiple palpable bony landmarks. Accuracy checks were repeated at key transitions and reference frame was protected from inadvertent contact during further steps.

Figure 4 Intraoperative setup. (A) Patient positioning; (B) O-arm based navigation.

A 30° lumbar microendoscope, Metrx (Medtronic, USA) was used for visualization. Intraoperative neuromonitoring using the Medtronic Nim Eclipse IONM system (Medtronic, USA) was employed to minimize the risk of nerve root injury.

Surgical approach

With the surgeon standing on right side of patient, skin entry point was planned using the navigation system. Navigated first dilator was used and sequential dilatation was performed to reach the target extraforaminal corridor (Figure 5). After progressive dilation, a 16-mm working tube was inserted and secured with a flexible arm. The site of compression of the right L5 nerve root in the extraforaminal corridor was identified and confirmed using a navigated pointer (Figure 6).

Figure 5 Intraoperative navigation-guided access. The skin entry point is planned using the navigation system, and sequential navigated dilatation is performed to reach the target extraforaminal corridor. (A) Intraoperative image; (B) sagittal image of navigation; (C) coronal image of navigation.

Figure 6 Intraoperative confirmation of the compression site. Compression of the right L5 nerve root is identified and confirmed using a navigated pointer. (A) Intraoperative image; (B) endoscopic image; (C) sagittal image of navigation; (D) coronal image of navigation.

Extraforaminal decompression

The hypertrophic L5 transverse process was visualized compressing the L5 nerve in the extraforaminal space. A high-speed navigated diamond burr was used to resect the transverse process partially and decompress the L5 nerve root. Following bony decompression, perineural soft tissues in the extraforaminal region were carefully dissected and released. The exiting right L5 nerve root was fully decompressed under endoscopic visualization (Figure 7).

Figure 7 Intraoperative decompression of the right L5 exiting nerve root. (A) Intraoperative image; (B) endoscopic image; (C) sagittal image of navigation; (D) coronal image of navigation.

Intraoperative navigation integrity was maintained by finalising patient positioning before registration, preserving rigid fixation of reference frame and maintaining continuous optical line of sight and rechecking accuracy at each workflow transition.

No intraoperative complications (cerebrospinal fluid leaks, L5 nerve injury) occurred. Neuromonitoring signals (motor evoked potentials) remained same throughout the procedure. The operative time was 78 minutes, and the estimated blood loss was 50 mL. Postoperative radiogram, MRI, and CT confirmed adequate decompression of the extraforaminal region (Figures 8,9). Clinically, the patient reported marked improvement in right L5 radicular pain with resolution of preoperative numbness on standing and disappearance of intermittent claudication. Low back pain was better, and she was mobilized with a brace on postoperative day 1. Muscle strength of the right extensor hallucis longus improved to MMT grade 5 by the time of discharge, and no new neurological deficits or perioperative complications were observed.

Figure 8 Postoperative radiogram and MRI. (A) Anteroposterior lumbar radiogram, (B) lateral lumbar radiogram, (C) coronal T2-weighted image, (D) left parasagittal T2-weighted image, (E) axial T2-weighted image at L5/S1 level. Red arrows indicate adequate nerve decompression. MRI, magnetic resonance imaging.

Figure 9 Postoperative image. (A) Coronal reconstruction CT, (B) right far-lateral sagittal reconstruction CT, (C) axial CT at L5/S1 level. A blue arrow indicates pedicle screw. Red arrows demonstrate good extraforaminal decompression. CT, computed tomography.

At the 6-month follow-up, she was able to walk more than 1 km without claudication. Sensory disturbance in the L5 dermatome had almost completely resolved, and she reported complete resolution of her preoperative symptoms. The VAS score for leg pain improved from 65 mm preoperatively to 23 mm at 1-year final follow-up.

Postoperative considerations and tasks

• Immediate post op neurological examination;
• Mobilization on postoperative day 1 with a lumbar brace;
• Postoperative CT to check for adequacy of decompression;
• Look for red flag signs (new radiculopathy or suspicious hematoma).

Tips and pearls

• Meticulous planning is needed on preoperative CT/MRI to understand the extent of the pseudo-articulation, and the exact course of the L5 nerve root in the foramen and far-out zone.
• Navigation should be used to design the portal trajectory: an entry point that directly targets the extraforaminal corridor should be used. The cranial and lateral portals facilitate access to the pseudo-articulation without excessive muscle dissection.
• The navigated burr should be used gradually to thin the hypertrophic L5 transverse process, sacral ala, and pseudo-articulation under navigation guidance, then complete removal with punches. A protective bony layer must be kept between the burr and the exiting L5 root until the final stages.
• Iatrogenic instability should be avoided by limiting bone removal to the pseudo-articulation, osteophytes, and compressive bands, while preserving facet and pars.
• Bleeding should be controlled early with low-pressure irrigation, bipolar coagulation, and hemostatic agents along epidural veins, avoiding blind coagulation near the root and dorsal root ganglion.

Discussion

LSTV describe a congenital variation in spinal anatomy in which the elongated transverse process of the last lumbar vertebra wholly or partially fuses with the first sacral segment (15). Reported LSTV prevalence ranges from 4% to 35.9%, with recent studies suggesting it is roughly 10–20% in the general population (16). Bertolotti syndrome, a form of LSTV, is an essential but often overlooked cause of chronic lower back pain in young and middle-aged adults (17). Quinlan et al. reported Bertolotti syndrome in 4.6% (35/769) of patients, with higher frequency in patients less than 30 years (18).

The pathogenesis of Bertolotti syndrome is complex and multifactorial. Several mechanisms have been proposed, including pain originating from arthritic changes in the pathological joint (19), pain related to accelerated disc degeneration at the level above the LSTV (18), and nerve root impingement in the extraforaminal zone (20). Additional contributing factors may include segmental hypermobility, abnormal torque, altered mechanical loading, and weakening of the iliolumbar ligament associated with the LSTV (18,21).

In patient with symptomatic pathology, management typically includes resection of the pseudo-articulation between the L5 transverse process and the sacral ala with or without fusion between L5 and S1 (17). This can be accomplished by open, minimally invasive, or endoscopic techniques. With the recent paradigm shift toward endoscopic spine surgery, an increasing number of endoscopic approaches have been introduced for the treatment of far-out syndrome (22,23). The evolution of endoscopic techniques for Bertolotti syndrome and far-out syndrome is summarised in Table 1.

Most of these techniques rely heavily on C-arm fluoroscopy for level confirmation, trajectory planning, and intraoperative adjustment. In the deep extraforaminal “far-out” corridor, this dependence on two-dimensional fluoroscopic imaging makes the procedure technically demanding. It contributes to cumulative radiation exposure for both the surgeon and the patient. Spine surgeons, in particular, receive some of the highest occupational fluoroscopy exposure because of frequent fluoroscopic imaging which leads to increased risks of malignancy, cataract, and other radiation-related health effects (12). Only a few studies have described the use of navigation in combination with endoscopy-assisted techniques for the management of far-out syndrome (26). Real-time navigation in fully endoscopic procedures is inherently constrained by the single working channel and the need for continuous endoscope manipulation, making stable reference registration and reliable instrument tracking difficult (27).

Our technique demonstrates that integrating intraoperative O-arm based three-dimensional navigation with endoscopy-assisted technique enhances anatomical orientation and allows precise targeting of the extraforaminal corridor, controlled bone resection at the pseudo-articulation, and effective neural decompression without any radiation exposure. Also, ours is the first technique to use navigated burrs in the management of far-out syndrome. Navigated burrs enabled accurate targeting and precise control over the depth and extent of resection in our case.

Our operative time of 78 minutes is comparable to that reported by Ha et al. for UBE decompression without navigation (68 minutes), with similarly low blood loss (30 vs. 50 mL in our case) (28). Clinically, our patient experienced rapid relief of radicular leg pain and improved walking tolerance, with postoperative imaging confirming complete extraforaminal decompression and no approach-related complications.

Technically, navigation and endoscopy are complementary. Navigation facilitates precise creation of an entry point that directly targets the extraforaminal L5 nerve root corridor, while the endoscope offers magnified visualization for meticulous bone removal and perineural dissection (25). This combination enables targeted removal of compressive osteophytes and fibrous tissue while allowing decompression of the L5 nerve root and preserving stability. In our experience, the ability to visualize the exiting nerve root continuously from the foramen into the far-out zone and to confirm its free pulsation under endoscopic view provides a reliable endpoint for adequate decompression.

This report has several limitations. First, as this is a technical note, we did not perform a direct comparison of our technique with fluoroscopy-based endoscopy, open decompression, or fusion procedures. Second, the need for O-arm imaging and navigation infrastructure may limit the applicability of this approach in resource-constrained settings. Third, the learning curve for this technique must be acknowledged: navigation-guided endoscopy for far-out syndrome requires familiarity with both technologies, including accurate interpretation of navigation images, maintenance of registration accuracy, and precise bony work under endoscopic visualization. For young surgeons, performing these cases under the guidance of a senior surgeon is highly valuable, particularly to develop familiarity about the extraforaminal anatomy.

Despite these limitations, our experience suggests that C-arm-free, navigation-guided endoscopy-assisted decompression is a feasible and attractive option for selected patients with far-out L5 radiculopathy.

Conclusions

This technical note illustrates that unilateral extraforaminal entrapment of the L5 nerve root can be effectively treated with C-arm-free, navigation-guided endoscopy-assisted decompression. Intraoperative O-arm based navigation enhances anatomical orientation, facilitates precise portal placement, and enables targeted bone resection. In our case, this workflow achieved rapid and durable relief of radicular symptoms through a minimally invasive corridor and eliminated the need for continuous fluoroscopic radiation.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the SUPER reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-233/rc

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-233/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-233/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. This study was conducted with the approval of the Ethics Committee of Okayama Rosai Hospital, a tertiary hospital (approval No. 577). Written informed consent was obtained from the patient.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Bertolotti M. Contributo alla conoscenze dei vizi di differenzazione regionale del racide con speciale riguardo alla assimilazione sacrale della V. lombare. Radiologique Medica 1917;4:113-44.
2. Wiltse LL, Guyer RD, Spencer CW, et al. Alar transverse process impingement of the L5 spinal nerve: the far-out syndrome. Spine (Phila Pa 1976) 1984;9:31-41. [Crossref] [PubMed]
3. Castellvi AE, Goldstein LA, Chan DP. Lumbosacral transitional vertebrae and their relationship with lumbar extradural defects. Spine (Phila Pa 1976) 1984;9:493-5. [Crossref] [PubMed]
4. Jenkins AL 3rd, Chung RJ, O'Donnell J, et al. Redefining the Treatment of Lumbosacral Transitional Vertebrae for Bertolotti Syndrome: Long-Term Outcomes Utilizing the Jenkins Classification to Determine Treatment. World Neurosurg 2023;175:e21-e29. [Crossref] [PubMed]
5. Gabriel DC, Liu DS, Ang B, et al. Bertolotti Syndrome in the Pediatric Population: A Literature Review and Management Algorithm. J Am Acad Orthop Surg Glob Res Rev 2025;9:e25.00069.
6. Jancuska JM, Spivak JM, Bendo JA. A Review of Symptomatic Lumbosacral Transitional Vertebrae: Bertolotti's Syndrome. Int J Spine Surg 2015;9:42. [Crossref] [PubMed]
7. Zhu W, Ding X, Zheng J, et al. A systematic review and bibliometric study of Bertolotti's syndrome: clinical characteristics and global trends. Int J Surg 2023;109:3159-68. [Crossref] [PubMed]
8. Sasaki M, Aoki M, Matsumoto K, et al. Middle-term surgical outcomes of microscopic posterior decompression for far-out syndrome. J Neurol Surg A Cent Eur Neurosurg 2014;75:79-83. [Crossref] [PubMed]
9. Kim JH, Kim HS, Kapoor A, et al. Feasibility of Full Endoscopic Spine Surgery in Patients Over the Age of 70 Years With Degenerative Lumbar Spine Disease. Neurospine 2018;15:131-7. [Crossref] [PubMed]
10. Ahn JS, Lee HJ, Choi DJ, et al. Extraforaminal approach of biportal endoscopic spinal surgery: a new endoscopic technique for transforaminal decompression and discectomy. J Neurosurg Spine 2018;28:492-8. [Crossref] [PubMed]
11. Heo DH, Sharma S, Park CK. Endoscopic Treatment of Extraforaminal Entrapment of L5 Nerve Root (Far Out Syndrome) by Unilateral Biportal Endoscopic Approach: Technical Report and Preliminary Clinical Results. Neurospine 2019;16:130-7. [Crossref] [PubMed]
12. Tanaka M, Zygogiannnis K, Sake N, et al. A C-Arm-Free Minimally Invasive Technique for Spinal Surgery: Cervical and Thoracic Spine. Medicina (Kaunas) 2023;59:1779. [Crossref] [PubMed]
13. Hagan MJ, Remacle T, Leary OP, et al. Navigation Techniques in Endoscopic Spine Surgery. Biomed Res Int 2022;2022:8419739. [Crossref] [PubMed]
14. Kavishwar RA, Liang Y, Lee D, et al. O-Arm Navigation-Guided Unilateral Biportal Endoscopic Decompression of Far-Out Syndrome. Neurospine 2024;21:1149-53. [Crossref] [PubMed]
15. Hughes RJ, Saifuddin A. Imaging of lumbosacral transitional vertebrae. Clin Radiol 2004;59:984-91. [Crossref] [PubMed]
16. Tang M, Yang XF, Yang SW, et al. Lumbosacral transitional vertebra in a population-based study of 5860 individuals: prevalence and relationship to low back pain. Eur J Radiol 2014;83:1679-82. [Crossref] [PubMed]
17. Rakauskas TR, Gallup S, Mohamed AA, et al. An update on the prevalence and management of Bertolotti's syndrome. Front Surg 2024;11:1486811. [Crossref] [PubMed]
18. Quinlan JF, Duke D, Eustace S. Bertolotti's syndrome. A cause of back pain in young people. J Bone Joint Surg Br 2006;88:1183-6. [Crossref] [PubMed]
19. Jönsson B, Strömqvist B, Egund N. Anomalous lumbosacral articulations and low-back pain. Evaluation and treatment. Spine (Phila Pa 1976) 1989;14:831-4. [Crossref] [PubMed]
20. Ichihara K, Taguchi T, Hashida T, et al. The treatment of far-out foraminal stenosis below a lumbosacral transitional vertebra: a report of two cases. J Spinal Disord Tech 2004;17:154-7. [Crossref] [PubMed]
21. Kojo S, Takahashi K, Tsubakino T, et al. Lumbar radiculopathy due to Bertolotti's syndrome: Alternative method to reveal the "hidden zone" - A report of two cases and review of literature. J Orthop Sci 2024;29:366-9. [Crossref] [PubMed]
22. Park MK, Son SK, Park WW, et al. Unilateral Biportal Endoscopy for Decompression of Extraforaminal Stenosis at the Lumbosacral Junction: Surgical Techniques and Clinical Outcomes. Neurospine 2021;18:871-9. [Crossref] [PubMed]
23. Wu PH, Sebastian M, Kim HS, et al. How I do it? Uniportal full endoscopic pseudoarthrosis release of left L5/S1 Bertolotti's syndrome under intraoperative computer tomographic guidance in an ambulatory setting. Acta Neurochir (Wien) 2021;163:2789-95. [Crossref] [PubMed]
24. Paudel B, Kim HS, Jang JS, et al. Percutaneous Full Endoscopic Treatment of Bertolotti Syndrome: A Report of Three Cases with Technical Note. J Neurol Surg A Cent Eur Neurosurg 2017;78:566-71. [Crossref] [PubMed]
25. Kalanchiam GP, Moorthy V, Oh JYL. Robotic-assisted minimally invasive excision of Bertolotti syndrome: novel technique and feasibility. Eur Spine J 2025; Epub ahead of print. [Crossref]
26. Mehta R, Tanaka M, Oda Y, et al. Transtubular Endoscopic Posterolateral Decompression of the L5 Root under Navigation and O-arm: A Technical Note. Acta Med Okayama 2021;75:637-40. [Crossref] [PubMed]
27. Ahn Y. Full-Endoscopic Spine Surgery : Its Roles and Limitations. J Korean Neurosurg Soc 2025;68:511-27. [Crossref] [PubMed]
28. Ha JS, Sakhrekar R, Han HD, et al. Unilateral Biportal Endoscopy for L5-S1 Extraforaminal Stenosis (Far Out Syndrome) - Technical Note with Literature Review. J Orthop Case Rep 2024;14:187-93. [Crossref] [PubMed]