CASE REPORT
The patient was a 67-year-old man with no medical comorbidities. He was involved in a motor vehicle accident, sustaining a right-sided head impact. Computed tomography and magnetic resonance imaging (MRI) showed C1–2 rotatory dislocation with right C2 facet fracture and locking (Figure 1). Imaging also revealed hypoplasia of the left vertebral artery (VA), which was taken into consideration during surgical planning to avoid vascular injury (Figure 2). No neurological deficits were noted. MRI excluded cord compression (Figure 3). Holter traction for 3 days failed to achieve reduction, and severe neck pain persisted (Figure 4). Surgical reduction and fusion were planned.
SURGICAL TECHNIQUE
1. Patient Positioning and Portal Planning
Under general anesthesia, the patient was positioned prone with the head securely fixed using a Mayfield clamp. Initial attempts at reduction of fracture under traction were unsuccessful.
The incision for the instrument portal was planned using anterior-posterior (AP) and lateral fluoroscopic views, referencing the lateral margin of the C1 lateral mass in AP view and the inclination of the C1 lateral mass and C2 pedicle in lateral view. Even during the right-sided procedure, the surgeon operated from the patient’s left side (Figures 5 and 6).
Instrument portal: A 1.5-cm longitudinal incision was made.
Endoscopic portal: A separate 7-mm incision was created 2.5 cm rostral (cranial) to the instrument portal to allow endoscopic access.
2. Endoscopic-Assisted Reduction of Locked C1–2 Facets and Facet Joint Preparation for Fusion
The obturator was advanced toward the bony landmark at the spinolaminar junction of the C2. Soft tissue dilation was carefully performed through the splenius capitis, semispinalis capitis, and obliquus capitis muscles. Continuous irrigation was used to create the endoscopic working space. The junction of the C2 lamina and inferior articular process was then fully exposed and the C2 pedicle superomedial margin was identified.
Intraoperatively, the obliquus capitis inferior muscle was found interposed between the locked facets, preventing reduction, with the C2 nerve root also trapped. The inferior margin of the C1 posterior arch was drilled to widen the corridor. After muscle division, the facet gap became visible, allowing insertion of a curette between the locked facets; rotation of the curette achieved joint reduction and widened the facet space. However, the C2 nerve root was too bulky, obstructing direct access to the facet surface. Therefore, the right C2 nerve was transected just proximally to the dorsal root ganglion (DRG), and a cage trial was used to distract the facet space further.
Under continuous saline irrigation and high-definition endoscopic visualization, the facet cartilage was removed and the subchondral bone was exposed using a curette and drill, creating an optimal fusion bed in a bloodless and safe field.
3. Instrumentation
The medial wall of the C1 lateral mass and superior–medial pedicle wall of C2 were palpated to avoid canal violation. Pilot holes for the C1 lateral mass and C2 pedicle screws were drilled under endoscopic and fluoroscopic guidance (Figure 7). A 5-mm polyetheretherketone (PEEK) cage filled with Demineralized Bone Matrix was inserted into the facet joint (Figure 8). OASYS polyaxial screws (3.5 mm × 30 mm; Stryker, USA) were placed, and rods were inserted and secured with nuts. The same procedure was performed on the opposite side, and the contralateral C2 nerve was preserved. Bilateral drains were placed (Figure 9).
4. Outcome
The patient’s visual analogue scale pain score improved from 8 preoperatively to 2 on postoperative day (POD) 1. The patient was discharged on POD7 without complications. At 3 months, he remained pain-free with stable fixation and no loss of reduction (Figure 10).
DISCUSSION
This case demonstrates the feasibility and efficacy of unilateral biportal endoscopy (UBE)-assisted posterior C1–2 reduction and arthrodesis for irreducible traumatic atlantoaxial rotatory dislocation (AARD) with facet fracture and locking. Delayed or neglected traumatic AARD in adults is associated with worse clinical outcomes and increased surgical complexity [1]. Early surgical intervention as demonstrated in this case may therefore improve pain control and stabilization while reducing operative morbidity [2].
The Harms technique, as a well-established method for posterior C1–2 fusion, offers several notable advantages. It provides robust 3-dimensional stabilization of the atlantoaxial complex through polyaxial screw and rod constructs, allowing for strong fixation even in cases with significant ligamentous disruption or bony instability [3]. Additionally, it has a well-documented track record of high fusion rates and reliable long-term outcomes, particularly in traumatic or degenerative pathologies of the upper cervical spine. The familiarity of the technique among spine surgeons and its reproducibility across diverse patient anatomies further reinforce its role as a standard approach in complex C1–2 stabilization [4].
Compared to traditional open surgical techniques such as the Harms method, which employs polyaxial screws and rods via a larger exposure [5], UBE technique offers significant advantages including enhanced magnified visualization, reduced muscle trauma, and a clear, bloodless surgical field facilitated by continuous saline irrigation to decrease venous bleeding [6]. These features enable meticulous facet release and precise preparation of the joint surfaces, which are critical for successful arthrodesis.
In this case, the right C2 nerve root was transected proximal to the DRG to allow safe access to the locked facet. Notably, at 3-month follow-up, the patient reported no occipital numbness, paresthesia, or sensory deficits in the C2 dermatome, indicating preservation of function and minimal morbidity. Previous studies have reported variable outcomes after C2 nerve root resection. Yeom et al. [7] observed that 29% of patients experienced new or increased occipital neuralgia within 1 month postoperatively, with some requiring medical management, while Badhiwala et al. [8] noted that although C2 root transection increased the incidence of occipital numbness, it did not significantly affect long-term functional outcomes. Similarly, Karthigeyan et al. [9] reported that some patients developed transient sensory deficits, which often improved over time. Taken together, these findings suggest that unilateral C2 nerve root sacrifice can be performed safely in selected patients, with low risk of persistent sensory impairment, consistent with the favorable outcome observed in our patient.
Prior systematic reviews comparing UBE discectomy and fusion techniques with conventional or minimally invasive methods in lumbar spine surgery have consistently reported that UBE achieves comparable or superior clinical outcomes with less tissue damage, lower blood loss, and faster recovery [10]. While these data primarily pertain to lumbar pathology, they support the rationale for applying UBE techniques to cervical spine fusion, particularly for complex pathologies such as irreducible AARD where minimizing soft tissue disruption is advantageous.
Recent studies comparing the efficacy and complication rates of UBE fusion versus other minimally invasive fusion techniques for lumbar degenerative diseases have demonstrated that UBE offers comparable or superior clinical outcomes with a favorable safety profile [11,12]. These findings support the observed absence of complications and the rapid postoperative recovery in the present case, reinforcing the clinical value of UBE-assisted C1–2 fusion as a minimally invasive yet effective surgical option.
Furthermore, advances in endoscopic spine surgery, such as the use of large interbody spacers in extreme transforaminal lumbar interbody fusion, highlight the evolving technical capabilities of endoscopic approaches to achieve robust spinal stability [13]. The insertion of a PEEK cage into the facet joint in this case parallels these developments, suggesting that endoscopic techniques can be successfully adapted to the cervical spine to provide effective arthrodesis while preserving surrounding tissues. This expands the potential application of minimally invasive endoscopic fusion strategies beyond the lumbar spine and underscores the importance of continuous technical innovation in spinal surgery.
UBE-assisted posterior C1–2 fusion may be particularly suitable for patients with irreducible AARD accompanied by facet fracture and locking, especially when nonsurgical reduction fails and VA anatomy is favorable. The technique allows precise facet release and safe instrumentation while minimizing soft tissue injury. However, its application has certain limitations. The procedure requires specialized endoscopic equipment and a steep learning curve, which may restrict widespread adoption. Furthermore, in cases with severe anatomical distortion, extensive fracture comminution, or high-riding vertebral arteries, UBE may be technically challenging, and traditional open posterior fusion techniques may be preferable. Careful patient selection, preoperative planning, and familiarity with both open and endoscopic approaches are therefore essential to maximize safety and efficacy.
CONCLUSION
UBE-assisted posterior C1–2 fusion might be a safe and effective technique for atlantoaxial instability including irreducible traumatic AARD with facet fracture and locking, providing stable reduction and favorable short-term outcomes.
WRITTEN TRANSCRIPT
0:00 Orientation and Initial Endoscopic Exposure
1st, we will show the surgical video of the patient's right side for orientation. Since the surgeon is standing on the patients left side and operating across, the left side corresponds to cranial and the lower side to medial. Under continuous saline irrigation, the endoscope is introduced. Stepwise dissection is carried out through the posterior cervical muscles. Exposing the C1 posterior arch and the C2 lamina.
0:34 Management of the Venous Plexus
The venous plexus is encountered and carefully coagulated to maintain a bloodless field with clear visualization.
0:59 Identification of the C1–2 Facet Joint
After drilling the lower part of the C1 posterior arch to expose the muscles and the nerve root, the gap between the facets is identified.
1:12 Reduction of the Locked C1–2 Facet and C2 Nerve Root Management
Accurate is then inserted into the facet gap and with gentle rotation, reduction of the dislocated joint is achieved, restoring alignment. The right C2 nerve root is found in trapped between the locked facets. For adequate visualization, the nerve is transected just proximal to the dorsal rootganglion.
1:37 Anatomical Landmark Identification and Screw Trajectory Planning
The superior medial wall of the C2 pedicle and the medial border of the C1 lateral mass are palpated to prevent canal violation and to ensure safe instrumentation. Attention is then directed to screw trajectory planning.
1:53 Facet Endplate Preparation and Pilot Hole Creation
Using cage trials and drills as needed, the end plate is prepared and pilot holesare created under combined endoscopic and fluoroscopic guidance. At each pilot site a path is preformed with an all under C-arm control.
2:13 Facet Cage Insertion and Screw Instrumentation
A 5-mm peak cage filled with demineralized bone matrix is then inserted into the distracted facet joint. The cage restores facet height and provides structural support for fusion. Screw instrumentation is subsequently performed. Polyaxial screws are placed into the C1 lateral mass and the C2 pedicle under fluoroscopic guidance. Screw placement is confirmed to be safe and accurate.
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