Current Evidence and Future Directions of Endoscopic-Assisted Anterior Odontoid Screw Fixation: A Systematic Review

Wongthawat Liawrungrueang; Peem Sarasombath; Chaiyapruk Pundee; Sung Tan Cho; Pang Hung Wu; Meng-Huang Wu; Don Young Park

doi:10.21182/jmisst.2025.02992

J Minim Invasive Spine Surg Tech > Volume 11(Suppl 1); 2026 > Article

Liawrungrueang, Sarasombath, Pundee, Cho, Wu, Wu, and Park: Current Evidence and Future Directions of Endoscopic-Assisted Anterior Odontoid Screw Fixation: A Systematic Review

Review Article

Journal of Minimally Invasive Spine Surgery and Technique 2026; 11(Suppl 1): S4-S13.

Published online: January 30, 2026

DOI: https://doi.org/10.21182/jmisst.2025.02992

Current Evidence and Future Directions of Endoscopic-Assisted Anterior Odontoid Screw Fixation: A Systematic Review

Wongthawat Liawrungrueang^1,^2,^*

, Peem Sarasombath³

, Chaiyapruk Pundee²

, Sung Tan Cho⁴

, Pang Hung Wu⁵

, Meng-Huang Wu^6,^7,^8,^*

, Don Young Park^9,^*

¹Department of Orthopaedics, School of Medicine, University of Phayao, Phayao, Thailand

²Spine & Joints Center, Department of Orthopaedics, Samitivej Srinakarin Hospital, Bangkok, Thailand

³Department of Orthopaedics, Phramongkutklao Hospital and College of Medicine, Bangkok, Thailand

⁴Department of Orthopaedic Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

⁵Achieve Spine and Orthopaedic Centre, Mount Elizabeth Hospital, Singapore

⁶Department of Orthopedics, Taipei Medical University Hospital, Taipei, Taiwan

⁷Department of Orthopaedics, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan

⁸Prospective Innovation Center, Taipei Medical University Hospital, Taipei, Taiwan

⁹Department of Orthopaedic Surgery, University of California Irvine, CA, USA

Corresponding Author: Wongthawat Liawrungrueang Department of Orthopaedics, School of Medicine, University of Phayao, Phayao, Thailand Email: mint11871@gmail.com

^*AOSpine AP Frontier Technologies Research Study Group

Received November 21, 2025 Revised December 18, 2025 Accepted December 30, 2025

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objective

This review aimed to synthesize and critically appraise the existing evidence on endoscopic-assisted anterior odontoid screw fixation, with the objectives of clarifying its current clinical utility and identifying priorities for future optimization of the technique.

Methods

A systematic review was conducted in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines and registered with PROSPERO (registration number: CRD420251251051). Searches of PubMed/MEDLINE, Embase, Scopus, Web of Science, and Google Scholar identified studies reporting the use of endoscopic visualization during anterior odontoid screw placement. Eligible study designs included clinical reports and cadaveric investigations. Extracted data encompassed patient demographics, fracture subtype, operative technique, radiological alignment, fusion status, perioperative complications, and risk of bias, which was assessed using the modified Joanna Briggs Institute checklist.

Results

Eight studies met the inclusion criteria, comprising 6 clinical reports and 2 cadaveric feasibility studies. The extent of endoscopic assistance ranged from hybrid mini-open approaches to fully endoscopic uniportal techniques. Reported fusion rates ranged from 80% to 100%, with fully endoscopic procedures demonstrating the most consistent radiological consolidation and anatomical reduction. No major neurovascular, aerodigestive, or implant-related complications were reported. Cadaveric evidence confirmed enhanced visualization of the C2 odontoid entry point and validated safe screw entry-point orientation with acceptable screw trajectories. Risk-of-bias assessment indicated low risk in 5 studies and moderate risk in 3. Small sample sizes, heterogeneous fracture morphology, and modest follow-up durations limited the overall quality of the evidence.

Conclusion

Endoscopic-assisted anterior odontoid screw fixation appears to be a technically feasible and biologically favorable minimally invasive option for selected odontoid fractures. Its potential advantages include improved visualization and reduced approach-related morbidity. Further prospective, multicenter investigations, particularly those integrating navigation systems, are required to define its definitive role in the management of cervical spine trauma.

Key Words: Endoscopic-assisted odontoid screw fixation, Dens fracture; minimally invasive cervical spine surgery, Anterior cervical instrumentation, Full-endoscopic technique

INTRODUCTION

Odontoid fractures are among the most common cervical spine injuries in adults, particularly in the elderly population, and account for a substantial proportion of upper cervical trauma [1,2]. Type II odontoid fractures, located at the junction between the dens and the body of the axis, are especially challenging to manage because of limited vascularity, higher rates of nonunion, and the potential for atlantoaxial instability [3,4]. The goals of treatment include restoring cervical alignment, achieving stable union and preserving the physiological rotational movement of the C1 to C2 segment [1,5].

Anterior odontoid screw fixation has long been regarded as an effective motion-preserving technique, offering the advantages of direct osteosynthesis and maintenance of atlantoaxial rotation. However, the traditional anterior approach requires a precise screw trajectory through a narrow working corridor bordered by the pharynx, larynx, carotid sheath and other critical structures [3,6-8]. Limited visualization, patient-specific anatomical constraints and difficulty maintaining the ideal trajectory may contribute to technical failure or increased operative morbidity. These limitations have prompted interest in techniques that can improve visualization and enhance the safety profile of anterior odontoid screw placement.

Endoscopic-assisted anterior odontoid screw fixation has emerged as a potential advancement in minimally invasive cervical trauma surgery [9-11]. The use of endoscopic magnification and illumination allows clearer identification of key anatomical landmarks, including the longus colli muscle and the anteroinferior cortex of C2, potentially improving guidewire control and screw placement accuracy. Early clinical reports and cadaveric studies suggest that endoscopic assistance may reduce soft-tissue disruption, minimize approach-related complications and provide enhanced precision compared with conventional fluoroscopy-guided techniques [12]. More recent developments, such as fully endoscopic uniportal systems and navigation-assisted endoscopic platforms, further support the expanding feasibility of this technique.

In the context of anterior odontoid screw fixation, the term “endoscopic-assisted” does not refer to a single standardized surgical technique but rather encompasses a spectrum of approaches that incorporate endoscopic visualization to varying degrees. These include hybrid mini-open approaches with endoscopic assistance, tube-based endoscopic systems such as microendoscopic or specific tube-based endoscopic platforms, and more recently, full-endoscopic uniportal techniques. Importantly, these approaches differ substantially in terms of soft-tissue protection, working corridor, visualization field, and technical workflow. Therefore, in this review, the term endoscopic-assisted anterior odontoid screw fixation is used to describe techniques that employ endoscopic visualization primarily for entry-point identification, midline confirmation, and soft-tissue safety, rather than continuous visualization of intraosseous screw advancement.

Despite these promising innovations, the current literature is limited, with available evidence consisting mainly of small case series and cadaveric feasibility studies. There is a need for a systematic synthesis to evaluate the quality of existing data, clarify the clinical outcomes associated with endoscopic-assisted techniques and outline areas requiring further investigation. The purpose of this systematic review is to critically examine the available evidence on endoscopic-assisted anterior odontoid screw fixation, summarize contemporary clinical and cadaveric findings and identify future directions that may advance its role in minimally invasive cervical spine surgery.

MATERIALS AND METHODS

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines [13]. The study protocol was structured to identify all available literature describing the use of endoscopic-assisted anterior odontoid screw fixation in either clinical or cadaveric settings. The flow of study identification, screening, eligibility assessment and final inclusion is summarized in the PRISMA flow diagram (Figure 1).

1. Search Strategy

This systematic review has been registered with the International Prospective Register of Systematic Reviews (PROSPERO) (registration number: CRD420251251051). A comprehensive search was performed across 5 electronic databases: PubMed/MEDLINE, Embase, Scopus, Web of Science and Google Scholar. The search encompassed all studies published in the database from database inception through November 2025. Search terms were combined with Boolean operators and included odontoid fracture, dens fracture, anterior odontoid screw, odontoid screw fixation, endoscopic-assisted, endoscopic-guided and full-endoscopic. Additional studies were identified through manual screening of reference lists.

2. Eligibility Criteria

Studies were included if they met the following criteria: Described anterior odontoid screw fixation performed with endoscopic assistance or full-endoscopic visualization. Included clinical cases, case series or cadaveric feasibility studies. Reported extractable data related to technique, radiologic outcomes, fusion results or complications. They were written in English. Studies were excluded if they involved open anterior odontoid screw fixation without endoscopic assistance, posterior cervical fixation techniques, review articles without original data or studies lacking sufficient methodological detail.

3. Study Selection

All retrieved records were screened for duplicates and evaluated by title and abstract. Full texts of potentially eligible articles were assessed independently according to the predefined criteria. Any disagreement was resolved through consensus. The complete selection process is presented in the PRISMA guidelines. The study selection process was carried out independently by 2 authors. Initially, titles and abstracts of all identified studies were screened to exclude irrelevant articles. In case discrepancies arose between the 2 reviewers regarding study eligibility, consensus was reached through discussion. If disagreements persisted, a third reviewer was consulted to resolve any remaining disputes.

4. Data Extraction

The following variables were extracted: author, year of publication, country, study type, sample size, demographic characteristics, fracture classification, technical description of the endoscopic procedure, operative time, imaging outcomes, fusion status and perioperative or procedural complications. For cadaveric studies, technical feasibility, visualization of anatomical landmarks and accuracy of screw placement were recorded.

5. Risk of Bias Assessment

The risk of bias for each included study was assessed by 2 independent reviewers using the appropriate tool for the study design. The methodological quality of included studies was evaluated using the modified Joanna Briggs Institute (JBI) critical appraisal tool, which is appropriate for case reports, case series and cadaveric investigations [14]. Each domain was graded as low, moderate or high risk of bias. The highest rating across domains was used to determine the overall risk-of-bias classification. Disagreements between the reviewers regarding the risk of bias assessments were resolved through discussion or arbitration by a third reviewer, ensuring a comprehensive evaluation process and minimizing subjective biases.

6. Data Synthesis

Due to the limited number of studies and substantial design heterogeneity, a meta-analysis was not feasible. This was primarily related to the extremely limited number of clinical cases, heterogeneous study designs (case reports, small case series, and cadaveric studies), and the lack of standardized outcome measures across studies. Accordingly, a narrative synthesis was performed, focusing on clinical outcomes, fusion rates, technical characteristics, complication profiles, and cadaveric feasibility findings.

RESULTS

1. Study Selection

A total of 1,899 records were identified through the initial database search. After removal of duplicates, 875 unique articles underwent title and abstract screening. Ninety-four full-text articles were assessed for eligibility, of which 8 met all inclusion criteria. These consisted of 5 clinical studies reporting outcomes in 8 patients and 3 cadaveric studies evaluating anatomical feasibility and screw placement accuracy. Reasons for exclusion included lack of endoscopic involvement, use of exclusively posterior fixation, absence of original clinical data and insufficient methodological description. The complete selection pathway is depicted in the PRISMA flow diagram (Figure 1).

2. Study Characteristics and Design

The characteristics of the included studies are detailed in Table 1 [10-12,15-18]. The 6 clinical reports ranged from single-patient case reports to small case series and were conducted across Asia, including Japan, Taiwan, Thailand, South Korea and Vietnam. Collectively, these studies reflect the initial phases of adoption of endoscopic visualization techniques for anterior odontoid screw placement. Four of the 5 clinical studies addressed type II odontoid fractures, while 1 involved a rostral type III fracture configuration. The 3 cadaveric studies evaluated the feasibility and safety of endoscopic visualization in anterior cervical surgical corridors. These studies provided crucial anatomical validation for endoscopic entry point identification, screw trajectory guidance and avoidance of neurovascular and aerodigestive structures. Cadaveric sample sizes ranged from 2 to 10 specimens and included both fresh-frozen and embalmed tissues.

3. Operative Technique and Intraoperative Observations

Based on the included studies, endoscopic-assisted anterior odontoid screw fixation techniques could be broadly classified into 3 categories: (1) hybrid mini-open endoscope-assisted approaches, in which endoscopy was used to assist visualization during anterior exposure while screw insertion relied on fluoroscopy; (2) tube-based endoscopic systems (e.g., Specific tube-based endoscopic platforms or EASY-GO platforms), allowing wider visualization of the ventral C2–3 surface with a protected working corridor; and (3) full-endoscopic uniportal techniques, in which endoscopic visualization was mainly limited to the C2 entry point, with screw trajectory control dependent on fluoroscopic guidance. Operative parameters and technical details are summarized in Table 2 [9-12,15-18]. Across clinical studies, 2 general categories of endoscopic assistance were identified: hybrid mini-open approaches employing microscopic or angled endoscopic visualization, and fully endoscopic uniportal approaches that relied on continuous irrigation and high-definition optics. Operative time in full-endoscopic procedures generally ranged from 70 to 95 minutes. Hybrid mini-open techniques had slightly longer or more variable durations, reflecting the learning curve associated with early adoption. Blood loss was consistently minimal in all procedures, demonstrating one of the key benefits of endoscopic visualization in reducing soft-tissue disruption. In fully endoscopic series, blood loss was often negligible, with some reports noting virtually bloodless operative fields due to the tamponade effect of continuous irrigation. Visualization of the longus colli, prevertebral fascia and the anteroinferior cortex of C2 was consistently improved across studies employing endoscopy. Authors noted that the endoscope facilitated accurate midline identification, clear delineation of the screw entry point and avoidance of the pharyngeal wall and carotid sheath. In several cases, the endoscope allowed real-time confirmation of the entry point and midline orientation before guidewire advancement, which may be difficult to achieve with fluoroscopy alone.

4. Radiologic Outcomes and Fusion Rates

Radiologic assessment was performed using plain radiographs and computed tomography. Across all clinical studies, anatomical reduction of the odontoid fracture was achieved either immediately or by the first postoperative imaging session. The reported fusion rates ranged from 80% to 100%. The only nonunion occurred in an elderly patient with a chronic fracture treated via a hybrid technique from an early-era study. Fully endoscopic approaches demonstrated the most consistent radiographic outcomes, reporting complete fusion without malalignment or hardware complications. In cadaveric studies, computed tomography confirmed that endoscopic assistance reliably guided screws along appropriate trajectories under fluoroscopic confirmation through the dens without perforating the cortical layer, posterior vertebral body, or C1–2 joint. These results underscore the potential of endoscopy to reduce malposition rates, which are more common in conventional fluoroscopy-only techniques.

5. Clinical Outcomes and Symptom Improvement

Clinical improvement was consistently reported across all applicable studies. Patients treated with full-endoscopic methods experienced resolution or a significant reduction in neck pain in the early postoperative period. None of the studies reported postoperative neurological deterioration. Functional outcomes, although variably recorded, were favorable, with early return to activities and no recurrent instability. Cadaveric studies, though not directly reporting clinical outcomes, provided insight into potential benefits of minimizing soft-tissue retraction and avoiding the risks associated with extensive exposure of the upper cervical spine.

6. Complications

No significant complications were reported in any of the 6 clinical studies. There were no instances of vertebral artery injury, carotid sheath damage, esophageal or pharyngeal injury, or airway compromise. No cases of infection and hematoma were identified. One patient developed a delayed union, but no surgical revision was required. Hardware-related complications, including malposition, loosening and breakage, were absent. Cadaveric studies also reported no injury to critical structures during screw trajectory preparation. Endoscopic magnification allowed safe navigation around vulnerable soft-tissue structures, supporting its potential to reduce complications traditionally associated with anterior cervical exposure.

7. Technical Feasibility and Anatomical Observations from Cadaveric Studies

Cadaveric investigations significantly supplemented clinical data by highlighting technical nuances of endoscopic anterior access to the dens. These studies consistently demonstrated that endoscopy permitted precise identification of the longus colli and midline. The endoscope enhanced visualization of the C2 anteroinferior cortical entry zone. Guidewire placement under endoscopic-guided direct vision reduced unintended lateral or superior divergence. Screw trajectories tested under endoscopic visualization were accurate and reproducible. Endoscopic dissection reduced the need for extensive tissue retraction, which is traditionally required in open anterior approaches. These findings supported the feasibility of adopting this technique more broadly in selecting clinical scenarios.

8. Risk of Bias Assessment

Risk of bias was evaluated using the modified JBI checklist. As shown in Table 3, 5 studies were classified as low risk, while 3 studies were classified as moderate risk primarily due to incomplete outcome reporting, small sample sizes or limited follow-up duration. No study demonstrated high risk of bias. The risk-of-bias heatmap and summary bar chart are shown in Figures 2 and 3.

DISCUSSION

This systematic review provides the most comprehensive synthesis to date of the clinical and cadaveric evidence on endoscopic-assisted anterior odontoid screw fixation. Methodological strengths of this review include adherence to PRISMA guidelines and prospective registration with PROSPERO, enhancing transparency and methodological rigor. Although the total number of published cases remains small, the findings across all included studies demonstrate consistent technical feasibility, favorable radiologic outcomes and a promising safety profile. The results highlight the potential value of incorporating endoscopic visualization into upper cervical spine trauma surgery, where precision and anatomical clarity are crucial for successful screw placement. Anterior odontoid screw fixation has traditionally been used as a motion-preserving technique for type II odontoid fractures [19-21]. Its success depends on accurate midline identification, correct screw entry point selection and precise control of the cephalad trajectory [22,23]. Conventional fluoroscopy-guided techniques provide limited visualization of soft tissues and rely heavily on the surgeon's experience. Endoscopic assistance does not directly control intraosseous screw trajectory within the C2 vertebral body. Instead, its primary contribution lies in accurate identification of the screw entry point, confirmation of the midline orientation, and protection of surrounding soft tissues, particularly the pharyngeal wall and carotid sheath. Screw trajectory within the C2 body continues to rely predominantly on biplanar fluoroscopy or navigation systems, which remain essential regardless of the degree of endoscopic assistance. Therefore, the advantages of endoscopic-assisted anterior odontoid screw fixation differ among techniques, and each approach provides distinct benefits rather than uniform superiority in trajectory control [24,25].

The clinical outcomes observed in this review were uniformly positive. Fusion rates ranged from 80% to 100%, and radiologic alignment was maintained in all patients. These results are comparable to, and in some cases exceed, those reported in traditional anterior odontoid screw fixation series. Importantly, no severe neurovascular, pharyngeal, or airway-related complications were reported across clinical studies. Postoperative symptom improvement was consistently documented, and no patients experienced hardware failure, screw malposition, or neurological deterioration.

Cadaveric studies provided additional anatomical validation of the technique [9,12]. These investigations demonstrated that endoscopic visualization enhanced anatomical orientation and entry-point planning, while screw trajectory accuracy remained dependent on fluoroscopic guidance. The ability to clearly identify the midline, delineate the C2 entry point and monitor guidewire direction in real time suggests that endoscopy may reduce the risk of cortical breach or lateral deviation, which are known challenges of fluoroscopy-only approaches. The cadaveric findings also emphasized the potential to decrease soft-tissue trauma and postoperative morbidity through minimal manipulation of the retropharyngeal corridor.

The potential advantages of endoscopic-assisted anterior odontoid screw fixation extend beyond visualization. Full-endoscopic systems may reduce blood loss, shorten operative time once proficiency is achieved and decrease postoperative discomfort associated with soft-tissue disruption. These benefits align with the broader goals of minimally invasive spine surgery, making the technique particularly appealing for elderly or medically fragile patients who represent a large proportion of individuals presenting with odontoid fractures [15,17]. Despite these favorable observations, several challenges remain. The available clinical evidence is limited to isolated case reports and very small series, restricting the ability to determine long-term outcomes or draw definitive conclusions regarding complication rates. Follow-up durations were inconsistent, and reporting quality varied across studies. Anatomical constraints, such as severe cervical kyphosis or reduced jaw opening, may limit the feasibility of the anterior endoscopic approach in certain patients. Additionally, the technique requires specific training, advanced instrumentation and familiarity with endoscopic depth perception, all of which contribute to a significant learning curve for surgeons new to endoscopic spine surgery. A consolidated summary of the advantages, limitations and future considerations for endoscopic-assisted anterior odontoid screw fixation is presented in Table 4. Across all studies, the most frequently reported advantages included improved visualization, enhanced precision in screw placement and reduced disruption of soft tissues. However, several limitations must be acknowledged. First, the available evidence is limited to small case reports and case series, reflecting the early adoption stage of endoscopic-assisted anterior odontoid screw fixation. Second, publication bias is likely, as successful or innovative cases are more commonly reported. Third, follow-up durations were relatively short, and standardized functional outcome measures were inconsistently reported. These factors preclude comparative analysis and highlight the need for prospective, multicenter studies. Future directions identified in the literature included the integration of navigation systems, 3-dimensional fluoroscopy, robotic assistance and validation of endoscopic double-screw constructs. Broader adoption will likely depend on advancements in training, surgical instrumentation and multicenter clinical evaluations.

CONCLUSION

Endoscopic-assisted anterior odontoid screw fixation is an emerging minimally invasive technique that enhances visualization, improves entry-point accuracy, and reduces soft-tissue disruption compared with conventional anterior approaches. Despite the small number of reported cases, clinical outcomes have been favorable, with high fusion rates, accurate screw placement and no major neurovascular or aerodigestive complications. Cadaveric studies further confirm the technical feasibility and anatomical advantages of endoscopic guidance. Current evidence remains limited by small sample sizes and short follow-up, emphasizing the need for prospective studies and broader clinical experience. Advances in navigation, three-dimensional imaging and robotic assistance may further support the safe and reproducible application of this technique. Overall, endoscopic-assisted odontoid screw fixation shows promise as a precise, minimally invasive option for appropriately selected odontoid fractures.

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.

Figure 1.

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) 2020 flow diagram.

Figure 2.

Modified Joanna Briggs Institute (JBI) risk of bias assessment. Heatmap showing the risk-of-bias ratings for each included study based on the modified JBI checklist. Each row represents an individual study, and each column represents a risk-of-bias domain. Colors indicate the level of bias assessment (low, moderate, or high).

Figure 3.

Summary bar chart of risk of bias. Bar chart presenting the overall distribution of risk-of-bias ratings across all included studies. Each bar reflects the number of studies classified as low, moderate or high risk according to the modified Joanna Briggs Institute (JBI) criteria.

Table 1.

Characteristics of the included studies

Study	Year	Title of study	Country	Study design	Number	Population	Fracture type / Classification
Horgan et al. [9]	1999	A novel endoscopic approach to anterior odontoid screw fixation: technical note	USA	Cadaveric study	2	Human cadaveric	Simulated reduced anteriorly displaced (Anderson and D'Alonzo type II)
Hashizume et al. [10]	2003	A clinical case of endoscopically assisted anterior screw fixation for the type II odontoid fracture	Japan	Case report	1	76 M	Anderson and D'Alonzo type II
Hung et al. [11]	2008	Anterior Screw Fixation with Endoscopic System Assisted	Taiwan	Case report	1	55 M	Rostral type III
Hung et al. [11]	2008	Method for Rostral Type III Odontoid Fracture	Taiwan	Case report	1	55 M	Rostral type III
Kedia et al. [12]	2021	Endoscopic Anterior Odontoid Screw Fixation for the Odontoid Fracture: A Cadaveric Pilot Study	India	Cadaveric study	10	Human cadaveric	Simulated reduced type II (Anderson and D'Alonzo type II)
Kotheeranurak et al. [15]	2022	Full-Endoscopic Anterior Odontoid Screw Fixation: A Novel Surgical Technique	Thailand	Case series	4	Adults (mean, 33.5 yr)	Grauer classification type IIa/IIb
Kim et al. [16]	2025	Endoscope-Assisted Anterior Odontoid Screw Fixation for Odontoid Fracture	South Korea	Case series	6	Adults	Grauer classification type IIa/IIb
Pongmanee et al. [17]	2025	Full-endoscopic assisted surgery using anterior double odontoid screw fixation in type II odontoid fractures: A clinical study of the surgical technique	Thailand	Case report	1	79 M	Anderson and D'Alonzo type II
Hoang et al. [18]	2025	Full-endoscopic anterior odontoid screw fixation: A case report and literature review in Viet Nam	Vietnam	Case report	1	25 M	Anderson and D'Alonzo type II

Table 2.

Operative data and surgical outcomes

Study	Year	Surgical endoscopic technique	Odontoid screw and navigation technique	Operative time	Blood loss	Imaging outcome	Clinical outcome	Fusion/technical success	Other complications
Horgan et al. [9]	1999	Endoscope-guided AOSF (open)	Solid screw (45 mm × 3.5 mm), using biplanar fluoroscopy	-	-	Accurate screw placement	-	100% technical success	None
Hashizume et al. [10]	2003	Hybrid mini-open with endoscope-assisted AOSF (mini-open)	Cannulated screw system (Reunion System; Surgical Dynamics, Japan), using C-arm fluoroscopic	110 Min	30 mL	Screw placed but nonunion	Symptom improvement	Nonunion	None
Hung et al. [11]	2008	Endoscopic system-assisted AOSF	A cannulated cancellous screw, 40 mm in length and 4 mm in diameter, using C-arm fluoroscopic	145 Min	20 mL	Correct position of and good position fixation	Return to normal daily activities and be free of neck pain.	Successful fixation (fusion implied)	None
Kedia et al. [12]	2021	Endoscope-assisted AOSF (EASY-GO)	K‑wire trajectory (2.7-mm diameter), C-arm fluoroscopic	45–120 Min	-	100% correct screw trajectory	-	100% technical success	None
Kotheeranurak et al. [15]	2022	Mini-open with full-endoscopic AOSF, Vertebris System (RiwoSpine, GmbH, Germany).	A partially threaded screw, using C-arm fluoroscopy	93.75 Min (75–115 min)	7.5 (5–10 mL)	Anatomical reduction; 100% solid bony union	Improvement in neck pain and neck motion (VAS 6.5/10 to 0.6/10)	100% fusion (4/4)	None
Kim et al. [16]	2025	Mini-open with endoscope-assisted “water-based” system	Single odontoid screw, using C-arm fluoroscopy,	82 Min	28 mL	80% fusion	No major complications	80% fusion (4/5 with ≥6-mo FU)	One delayed union
Pongmanee et al. [17]	2025	Mini-open with full-endoscopic double-screw technique	Double headless screws (3 mm; Herbert), using biplanar fluoroscopy	80 Min	Low	Complete fusion	Full recovery	Complete fusion at 1 yr	None
Hoang et al. [18]	2025	Full-endoscopic AOSF	A cannulated cancellous screw, 40 mm in length and 4 mm in diameter, using C-arm fluoroscopic guidance	90 Min	<50 mL	Stable screw; progressing union	Good recovery	Stable alignment; progressing fusion	None

AOSF, anterior odontoid screw fixation; VAS, visual analogue scale; FU, follow-up.

Table 3.

Risk of bias assessment (modified Joanna Briggs Institute)

Study	Year	Selection bias	Technique description	Outcome reporting	Follow-up adequacy	Overall risk of bias
Horgan et al. [9]	1999	🟢 Low	🟢 Low	🟢 Low	⚪ N/A	🟢 Low
Hashizume et al. [10]	2003	🟢 Low	🟡 Moderate	🟡 Moderate	🟢 Low	🟡 Moderate
Hung et al. [11]	2008	🟢 Low	🟡 Moderate	🟢 Low	🟡 Moderate	🟡 Moderate
Kedia et al. [12]	2021	🟢 Low	🟢 Low	🟢 Low	⚪ N/A	🟢 Low
Kotheeranurak et al. [15]	2022	🟢 Low	🟢 Low	🟢 Low	🟢 Low	🟢 Low
Kim et al. [16]	2025	🟢 Low	🟢 Low	🟡 Moderate	🟡 Moderate	🟡 Moderate
Pongmanee et al. [17]	2025	🟢 Low	🟢 Low	🟢 Low	🟢 Low	🟢 Low
Hoang et al. [18]	2025	🟢 Low	🟢 Low	🟢 Low	🟡 Moderate	🟢 Low

🟢, low risk; 🟡, moderate risk; 🔴, high risk; ⚪, not applicable (N/A).

Table 4.

Summary of advantages, limitations, technical challenges, and future directions of endoscopic-assisted anterior odontoid screw fixation

Domain	Key points	Summary
Advantages	• Enhanced visualization of C2 entry point	Endoscopic assistance provides direct visualization of critical structures (longus colli, pharyngeal wall, C2 anteroinferior cortex), improving screw placement safety and accuracy. Full-endoscopic methods consistently show minimal blood loss (often <10–30 mL) and minimal approach morbidity.
	• Minimally invasive access
	• Reduced soft-tissue dissection
	• Lower blood loss
	• Preservation of C1–2 motion
	• Reduced risk of pharyngeal/esophageal injury
	• Precise instrument control under magnified view
Limitations	• Limited number of clinical cases globally	Current evidence consists of small case reports and series. The technique remains in an early stage of global adoption, with variability in surgeon training and availability of equipment. Certain fracture patterns still require posterior fixation.
	• Steep learning curve for high-cervical endoscopy
	• Requires specialized endoscopic equipment
	• Not suitable for all fracture morphologies (e.g., irreducible, severely comminuted, old nonunions)
	• Short-term follow-up in existing reports
Technical challenges	• Precise alignment of endoscope and working channel	Surgeons must master anterior cervical endoscopy and understand complex 3D anatomy. Cadaveric studies highlight early difficulties in scope positioning, though improved techniques (uniportal systems, irrigation endoscopy) have reduced this.
	• Maintaining clear visualization in narrow retropharyngeal corridor
	• Handling guidewire trajectory under combined endoscopic + fluoroscopic
	view
	• Avoiding soft-tissue entrapment (pharynx, esophagus, carotid sheath)
	• Performing double-screw fixation in limited space (only one published case)
Clinical outcomes	• Fusion rates 80%–100% in modern series	Full-endoscopic techniques show high fusion success comparable to traditional AOSF. No reported neurovascular or visceral injuries in any clinical series.
	• Excellent radiographic alignment
	• Low complication rates across all studies
	• Good pain and functional improvement
Future directions	• Integration with CT navigation or 3D fluoroscopy	The next phase of innovation may include hybrid navigation-endoscopy systems, robotic precision, AI-driven screw trajectory planning, and validation of stronger constructs (e.g., double-screw fixation). Training pathways and simulation labs are essential for widespread adoption.
	• Combined endoscopic and robotic-assisted screw guidance
	• AI-based preoperative trajectory planning
	• Biomechanical studies of double-screw endoscopic constructs
	• Expansion to training programs and simulation models
	• Development of purpose-built odontoid endoscopic systems

AOSF, anterior odontoid screw fixation; 3D, 3-dimensional; CT, computed tomography; AI, artificial intelligence.

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