C1-C2 Transorbital Fixation: Cadaveric Investigation and Technical Note

Objective: To assess the feasibility of anterior C1-C2 transarticular fixation via the combined medial TONES and endoscopic endonasal approach (MT/EEA). Methods: Four pre-scanned cadaveric heads were dissected in the anatomy laboratory using the combined MT/EEA. Image guidance was used to identify entry points and trajectory; however, instruments were not CT-navigated. Bilateral medial orbitotomies below the frontoethmoidal suture were performed via either a conjunctival precaruncular or a superior eyelid incision. The EEA entailed posterior septectomy and bilateral anterior ethmoidectomies. The nasopharyngeal mucosa, the pharyngobasilar fascia, and the longus capitis and rectus capitis anterior muscles covering the craniocervical junction were excised. Each MT provided access to the contralateral C1–C2 joint ([ Fig. 1 ]). In the first specimen, the screw tunnel was created through a posterior approach, and the screws were placed using the MT/EEA to confirm the adequacy of the corridor in terms of angle and exposure. Subsequently, three variants of screw entry and trajectory were performed purely via the MT/EEA, essentially employing a reverse, modified stand-alone Magerl technique. Results: The inferior margin of the condyle served as a surface landmark for determining the screw entry level on C1. The direction of drilling was from superior and inferior and medial to lateral. The first entry point was placed at the midpoint of the anterior arch of C1 along the craniocaudal axis, just medial to a theoretical vertical line drawn at the medial edge of the condyle–C1 joint on the coronal plane. The screws successfully transgressed the C1-C2 facets and the isthmus of C2. The second entry point -on another specimen- was placed on the upper half of the anterior arch of C1 along the craniocaudal axis, within two vertical lines bordering to the medial half of the craniocervical joint and extending on C1 on the coronal plane. The screws passed through the C1-C2 joint and the C2 isthmus, with one screw abutting the vertebral artery on one side. In the third paradigm the entry point was located at the midpoint of the anterior arch of C1 along the craniocaudal axis and at the same level as in the second specimen on the coronal plane. Due to increased downward angle, the screws traversed the C1-C2 joint, but not the isthmus, resulting in reduced bony purchase (Figs. 2, 3). Conclusion: The combined MT/EEA can be effectively utilized for the placement of C1-C2 transarticular screws, obviating the need for angled instruments. Future clinical applications may include managing surgical instability following EEA for craniocervical junction pathology. Nevertheless, a high-riding vertebral artery and a narrow C2 isthmus pose significant challenges to this technique. Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany