The Feasibility of Endoscopic-Assisted Anterior Odontoid Screw Fixation in Ankylosing Spondylitis
Article information
Abstract
This study aimed to describe the technical feasibility and clinical outcome of endoscope-assisted anterior odontoid lag screw fixation in a patient with ankylosing spondylitis, in whom the conventional open anterior approach was limited due to cervical rigidity. A 56-year-old man with longstanding ankylosing spondylitis presented with severe neck pain and right-sided tingling sensations following trauma. Imaging revealed a type III odontoid fracture. Because of rigid cervical alignment, adequate neck extension required for the conventional open anterior approach was not achievable. Endoscope-assisted anterior odontoid screw fixation was performed using a biplane C-arm. The procedure involved endoscopic dissection of the prevertebral corridor and insertion of the cannulated lag screw under fluoroscopic guidance. The screw was successfully placed across the fracture site without intraoperative complications. Postoperative imaging confirmed appropriate screw trajectory and fracture reduction. The patient’s pain improved immediately, allowing early ambulation. He was discharged uneventfully, and follow-up examinations demonstrated stable fixation. Endoscope-assisted anterior odontoid lag screw fixation appears to be a safe and effective alternative for treating odontoid fractures in patients with ankylosing spondylitis. This technique minimizes soft-tissue injury and facilitates optimal screw trajectory in cases where rigid cervical alignment precludes the conventional open approach.
INTRODUCTION
Odontoid process fractures are classified by Anderson and D’Alonzo [1]. Type II fractures, occurring at the base of the dens, are unstable and have a high risk of nonunion. Grauer et al. [2] further subdivided type II fractures into subtypes IIa, IIb, and IIc. Of these, IIa and IIb are considered ideal indications for anterior odontoid screw fixation, which achieves direct fracture compression and preserves atlantoaxial motion [3-5].
Anterior odontoid screw fixation was first introduced in the 1980s [6,7]. The conventional anterior open approach, while technically straightforward, is associated with drawbacks including large incision, significant prevertebral soft-tissue dissection, and postoperative complications such as dysphagia and prevertebral swelling [8].
Endoscopic-assisted anterior odontoid screw fixation has emerged as a minimally invasive alternative, offering smaller incisions, direct visualization, and reduced soft-tissue injury [9-12]. We performed endoscopic anterior odontoid screw fixation for an odontoid fracture in a patient with ankylosing spondylitis, where adequate surgical positioning was challenging.
CASE REPORT
A 56-year-old man with longstanding ankylosing spondylitis presented with severe neck pain and right-sided tingling sensation following a slip-down injury. Computed tomography (CT) revealed a type III odontoid fracture according to the Anderson–D’Alonzo classification. He also had a concomitant right temporal contusion (Figure 1). Despite the fracture pattern, severe neck pain precluded ambulation, prompting surgical fixation.
Preoperative imaging findings. (A) Lateral cervical spine radiograph showing rigid cervical alignment in a patient with longstanding ankylosing spondylitis. (B) Sagittal computed tomography (CT) image demonstrating a type III odontoid fracture. (C) Coronal CT image confirming the fracture configuration and alignment of the odontoid process. (D) Axial CT image at the level of the odontoid fracture. (E) Sagittal cervical spine magnetic resonance imaging showing the fracture and surrounding soft tissue structures. (F) Axial brain CT image revealing a concomitant right temporal contusion.
Rigid ankylosis of the cervical spine prevented extension, and preoperative planning confirmed that the conventional open anterior approach would not allow an adequate screw trajectory due to thoracic cage interference (Figure 2). Therefore, an endoscope-assisted anterior approach was chosen.
Assessment of the anterior surgical corridor. Preoperative lateral cervical radiograph obtained in maximal cervical hyperextension. The orange dotted lines indicate the feasible anterior surgical corridor that is anatomically unobstructed by the mandible and sternum. The yellow dotted line represents the actual screw insertion trajectory. The green dotted line shows the conventional open anterior approach corridor, which was not feasible in this patient due to rigid cervical alignment.
SURGICAL TECHNIQUE
The procedure was performed with the patient in a supine position, with the neck in mild extension achievable under anesthesia. Biplanar C-arm fluoroscopy was used for continuous anteroposterior and lateral guidance. Intraoperative assessment demonstrated that the feasible anterior approach corridor, measured between the mandible and sternum without obstruction, was extremely narrow, approximately 18° (Figure 3). In general, the typical anterior approach corridor in nonankylosed patients ranges from 25° to 35°, depending on neck extension. In contrast, this patient’s limited extension due to ankylosis resulted in a markedly reduced 18° angle, emphasizing the utility of endoscopic assistance. A 1.0–1.5 cm skin incision was made at the C4–5 level, and minimal blunt dissection was performed obliquely along the potential space between the carotid sheath and trachea-esophageal complex, aided by a guide instrument and finger compression, until the anterior vertebral surface was reached. An 18-gauge spinal needle was then inserted into the prevertebral space above the C3 body or C3–4 disc space, and after confirming the absence of bleeding, a mixture of normal saline and contrast media (5–7 mL) was injected to expand the prevertebral space. A guidewire was passed through the needle, which was then removed, and further blunt dissection was performed at the C2–3 level using an obturator over the guidewire. A working cannula was then introduced through the obturator.
Intraoperative setup. (A) Intraoperative photograph showing the patient positioned supine with biplanar C-arm fluoroscopy. (B) The image demonstrating the feasible anterior surgical corridor between the mandible and sternum. The red line indicates the available approach angle, which measures approximately 18°.
A 6.3-mm TESSYS transforaminal endoscopic system was advanced through the cannula, marking the beginning of the endoscopic procedure. Using fluoroscopy, the bony entry point at C2 was identified. Hemostasis was achieved using an Ellman radiofrequency probe, and a partial C2–3 annulotomy was performed targeting the anterior inferior annular ligament of C2 body. Drilling was performed just below the anterior edge of the C2 endplate at the midline to prepare the entry point. A Kirschner wire was inserted through the endoscopic working channel, crossing the fracture line from the odontoid tip in a posterosuperior direction under fluoroscopic guidance to ensure a midline trajectory. After confirming its position, the tract was cannulated and tapped, and a lag screw of appropriate length (4.0mm x 36mm cannulated lag screw) was inserted across the fracture line to achieve reduction using the traditional guide instrument with an open cannulated screw system (Medtronic Sofamor Danek, USA) (Figure 4).
Endoscopic-assisted anterior odontoid screw insertion. (A) Intraoperative photograph obtained after creation of the prevertebral corridor, demonstrating the application of the endoscopic device through the working sheath. (B) Intraoperative photograph showing insertion of a lag screw of appropriate length across the odontoid fracture to achieve fixation and fracture reduction.
Following confirmation of proper screw placement both endoscopically and fluoroscopically, the working cannula was removed. Hemostasis was secured, and the wound was closed in layers with a submuscular vacuum-assisted drain placed.
RESULTS
The screw was accurately positioned, achieving satisfactory fracture compression.
Intraoperative blood loss was minimal, and there were no neurovascular or visceral complications. The patient’s neck pain markedly improved, enabling early ambulation. He was discharged without complications, and postoperative radiography confirmed appropriate screw placement and alignment (Figure 5).
Postoperative radiographic assessment. (A) Lateral cervical radiograph obtained postoperatively showing the odontoid lag screw in an optimal position. (B) Anteroposterior cervical radiograph confirming satisfactory screw alignment and fracture compression.
At 6 months postoperatively, CT imaging demonstrated partial bony union at the fracture site (Figure 6). Dynamic radiographs showed no evidence of instability, and the patient remained asymptomatic, reporting no neck pain or neurological deficits (Figure 7).
Six-month follow-up computed tomography (CT). Six-month postoperative CT images demonstrating partial bony union at the odontoid fracture site. Sagittal (A) and coronal (B) views.
Six-month follow-up dynamic radiographs. Dynamic cervical spine radiographs obtained at 6 months postoperatively showing no evidence of instability. Flexion (A), neutral (B), and extension (C) views.
DISCUSSION
Anterior odontoid lag screw fixation is widely accepted for type II odontoid fractures because it provides rigid fixation while preserving atlantoaxial rotation [3,4]. However, this technique requires sufficient cervical extension to access the C2–3 disc space and align the screw trajectory. In patients with ankylosing spondylitis, rigid spinal deformity often makes this impossible, thereby limiting the feasibility of the conventional open anterior approach.
Endoscopic assistance addresses these challenges by offering several advantages:
(1) Facilitating access: The endoscope enables direct visualization within a narrow corridor, reducing the need for excessive retraction of the trachea and esophagus.
(2) Optimizing trajectory: Endoscopic placement naturally aligns with the lag screw insertion angle, overcoming the anatomical restrictions imposed by rigid cervical kyphosis.
(3) Minimizing morbidity: The minimally invasive approach involves a small incision, reduced soft-tissue trauma, and a lower risk of postoperative swelling or dysphagia.
Previous studies have demonstrated the safety and efficacy of endoscopic-assisted odontoid fixation [9-12]. However, this case particularly highlights the usefulness of this technique in patients with ankylosing spondylitis, where the conventional anterior approach is often technically prohibitive.
1. Patient Selection
Ideal candidates for endoscopic-assisted anterior odontoid screw fixation include those with reducible type II or III fractures, preserved fracture alignment, and no evidence of severe comminution. In patients with ankylosing spondylitis, this technique is particularly advantageous when cervical rigidity precludes the conventional open anterior approach.
2. Contraindications and Learning Curve
This technique may not be appropriate for patients with extensive anterior soft-tissue scarring, prevertebral infection, or high-risk airway compromise. Moreover, the learning curve can be steep, requiring familiarity with endoscopic anatomy, instrument handling, and fluoroscopic navigation. Once mastered, however, the technique allows precise screw placement even in cases with severe cervical rigidity.
A comparative summary of the conventional open and endoscopic-assisted anterior approaches is presented in Table 1.
Comparison between the conventional open anterior approach and endoscopic-assisted anterior odontoid screw fixation
CONCLUSION
Endoscope-assisted anterior odontoid lag screw fixation is a feasible and effective minimally invasive technique. In patients with ankylosing spondylitis, it not only reduces tissue trauma but also simplifies screw trajectory, thereby enabling safe fixation in anatomically challenging conditions. This technique represents a valuable alternative to traditional open anterior or posterior fusion methods.
WRITTEN TRANSCRIPT
0:00 Operating Room Setup
This is the operating room setup.
Biplane fluoroscopy has been arranged and the surgical drapes are in place.
0:12 Prevertebral Corridor Access
After confirming the target surgical level, the obturator is advanced through the prevertebral corridor using a retractor. The trachea and esophagus are gently mobilized medially, creating a narrow but sufficient working channel into this corridor.
0:19 Prevertebral Space Expansion
Contrast-mixed saline is carefully injected to expand the prevertebral space and establish a safe endoscopic field.
0:24 Guidewire Placement and Access Widening
Once the corridor has been created, a guide K-wire is advanced until it touches the anterior surface of the bone. The obturator is reintroduced along this wire, and blunt dissection is carried out to widen the access route.
0:36 Endoscope Insertion
A working sheath is then docked, through which the endoscope is inserted, providing direct visualization of the surgical field under endoscopic view.
0:44 Soft Tissue Dissection and Entry Preparation
Soft tissue dissection is performed using an Ellman radiofrequency probe. A partial discectomy is carried out, and drilling of the superior endplate of C3 is performed to prepare a precise bony entry point for screw insertion.
1:03 K-Wire Advancement Across the Fracture
With the entry point prepared, a K-wire is advanced across the odontoid fracture under strict biplanar C-arm guidance.
1:23 Tract Preparation
After the K-wire is carefully advanced up to the tip of the odontoid, the tract is tapered and prepared along the guide through this channel.
1:31 Lag Screw Insertion
A lag screw of appropriate size is inserted across the fracture line, allowing compression of the fracture gap and achieving firm fixation and fusion.
2:07 Final Confirmation and Hemostasis
Following screw placement, the endoscope is used to directly confirm the position of the implant. Bleeding control is meticulously performed, and finally, a Hemovac drain is inserted before wound closure.
2:20 Procedure Completion
This completes the procedure of endoscope-assisted anterior odontoid screw fixation, enabling safe and minimally invasive stabilization, even in the setting of ankylosing spondylitis with rigid cervical alignment.
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.
Acknowledgments
The authors gratefully acknowledge the support of the staff at the Department of Neurosurgery, Daegu Catholic University College of Medicine, for their assistance with patient management and intraoperative procedures. We also thank the radiology team for their valuable contributions to preoperative planning and postoperative imaging.
Informed Consent
Informed consent was waived due to the retrospective and anonymized nature of this study.