Navigation-assisted C1-ring osteosynthesis for an unstable atlas fracture: a case report

Introduction

C1 (atlas) fractures typically result from axial loading or hyperextension forces transmitted from the occiput to the upper cervical spine, disrupting the atlas ring (1-3). Their relevance in modern healthcare has grown as advanced imaging has expanded the detection of both high- and low-energy injury patterns. Epidemiologic studies demonstrate a bimodal age distribution, with peaks in young adults and the aging population (4,5). Clinically, C1 fractures are significant because resulting instability can threaten neurologic structures and often requires nuanced decision-making between motion-preserving and fusion-based stabilization. These injuries also impose substantial healthcare costs through the need for advanced imaging, prolonged immobilization, and occasionally, complex surgical intervention.

The C1 vertebra is a ring-shaped structure which consists of an anterior and posterior arch and two lateral masses; these comprise the vertebral foramen and surround the spinal cord (1,2). The lateral masses of C1 form articulations with the occipital condyles, and the dens of C2 articulates with the posterior aspect of the anterior arch of C1 (1,2). This region connects the skull to the spine and, importantly, through the C1–C2 (first and second cervical vertebrae) joint, generates 50% of flexion and extension and rotational range of motion of the head and upper cervical spine (3). Due to the highly mobile nature of the C1–2 joint, it is anchored by strong ligamentous connections including the transverse odontoid, anterior atlantoaxial, posterior atlantoaxial, alar, and transverse atlantal ligaments (TALs) (1,2). Of these, the TAL, provides the greatest support in articulation between C1 and C2. In atlas fractures—which account for 10.6% of cervical fractures and between 1–3% of all spinal fractures—the TAL is susceptible to tears, and loss of integrity of the TAL compromises the stability of the atlantoaxial joints (6-8).

On plain radiographs with an open mouth odontoid view, TAL injuries can be assessed by the Rule of Spence, which identifies injury with lateral mass displacement exceeding 6.9 mm (9-12). Alternatively, measurements of the atlantodens interval greater than 3 mm in adults can indicate TAL injury (13-16). X-ray evaluation of suspected TAL injuries have largely been supplanted by magnetic resonance imaging (MRI), which is additionally able to confirm injury to the TAL and is the preferred method to determine ligamentous injury (16).

Unstable C1 fractures represent a challenging subset of upper cervical spine injuries due to their proximity to vital neurovascular structures and the highly mobile nature of the atlantoaxial joint. While stable C1 fractures can be managed with immobilization with halo vest orthosis (HALO) placement or a hard cervical collar, disruption of the TAL—the primary stabilizer of the atlantoaxial complex—renders the ring unstable and typically requires surgical stabilization. Treatment of unstable atlas fractures remains controversial. Posterior C1–C2 or occipitocervical fusions offer reliable stabilization but sacrifice substantial cervical rotation (3). C1-ring osteosynthesis with lateral mass screws and single level rod fixation has emerged as a motion-preserving alternative, aiming to restore ring integrity while maintaining native occiput-C2 articulation (17). However, this technique poses technical challenges, particularly regarding the safe and accurate placement of lateral mass screws in close proximity to the spinal canal and vertebral arteries.

Given the limited literature on open reduction and internal fixation (ORIF) for unstable C1 fractures, the objective of this case report is to detail our surgical technique, highlight the clinical outcome, and contribute to the growing body of evidence on motion-preserving management strategies. Reports describing the use of stereotactic navigation in this setting are even more limited. Therefore, we aim to demonstrate its utility in facilitating accurate lateral mass screw placement while minimizing the risk to adjacent neurovascular structures. We present this article in accordance with the CARE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-25-174/rc).

Case presentation

All procedures performed in this study were in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Ethics Committee of the University of Michigan (No. HUM00276242). Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

A 34-year-old male sustained cervical spine trauma after diving into a shallow pool. He presented to the emergency department with neck pain and limited range of motion. He was otherwise neurovascularly intact and normoreflexive. Initial radiographic evaluation included a computed tomography (CT) scan of the cervical spine, which demonstrated fractures through the right anterior and posterior arches of C1, accompanied by lateral displacement of the right lateral mass (Figure 1). There was no evidence of facet dislocation or fracture involving the odontoid process. A CT angiogram of the cervical spine revealed no evidence of arterial injury or vascular compromise. MRI of the cervical spine showed an intrasubstance tear of the right transverse ligament, supporting the diagnosis of an unstable C1 fracture (Figure 2). Given the degree of displacement and ligamentous compromise, conservative treatment with external immobilization alone was deemed insufficient to ensure stability and healing. Surgical intervention was recommended to provide anatomic reduction and rigid fixation. The patient was subsequently indicated for C1 ORIF with navigation assistance vs. C1–C2 fusion, with the operative goal of performing osteosynthesis if possible.

Figure 1 Axial CT image at the C1 level demonstrates atypical Jefferson fracture with multiple displaced fractures involving the right lateral aspects of the anterior and posterior arches of the C1 vertebra (small arrows). There is an intact left transverse atlantal ligament (large arrow). CT, computed tomography.

Figure 2 Axial T2-weighted turbo spin-echo MRI image demonstrates intact left transverse atlantal ligament (large arrow), with complete tear of the right transverse atlantal ligament (small arrow). MRI, magnetic resonance imaging.

The patient was positioned prone on a radiolucent operating table with careful padding to avoid pressure injuries. Prior to surgical incision, the surgical team performed a closed reduction maneuver using positioning and axial traction of the cervical spine. With the head secured in a Mayfield clamp, gentle longitudinal traction was applied carefully with neuromonitoring to reduce the displaced lateral masses of C1 with ligamentotaxis. The neck was carefully extended and positioned to optimize reduction of the fracture under fluoroscopy.

Following this manual reduction, an intraoperative O-arm three-dimensional (3D) CT spin was obtained to verify the adequacy of fracture realignment prior to proceeding with open instrumentation. This real-time imaging confirmed near-anatomic reduction of the C1 ring and proper alignment of fracture fragments, providing confirmation that the closed reduction was successful and that the surgical plan for ORIF without fusion could proceed.

A stereotactic navigation system was registered using the intraoperative O-arm images, allowing precise anatomical guidance for screw placement and fracture fixation. A midline posterior cervical incision was made extending from the occiput to the C2 spinous process. Subperiosteal dissection exposed the posterior arch of C1 while preserving surrounding musculature to minimize postoperative morbidity. Under navigation guidance, bilateral screws were placed into the lateral masses of C1 along a safe trajectory to avoid injury to the vertebral artery and spinal cord (18). Rods were then contoured and secured to maintain rigid fixation of the C1 ring. A final O arm spin confirmed anatomic reduction and stable fixation. The wound was irrigated and closed in layers. The patient tolerated the procedure well without intraoperative complications. Post fixation, a HALO vest was applied to provide supplemental external immobilization during the initial healing phase.

Immediate postoperative imaging confirmed anatomic reduction and appropriate hardware positioning (Figure 3). The patient was discharged home on postoperative day 2 with instructions to maintain HALO immobilization and avoid neck movements that could risk pin loosening.

Figure 3 Post-operative upright AP (A), lateral (B), and odontoid (C) view radiographs demonstrating osteosynthesis of C1 vertebral body. AP, anteroposterior.

At 3 weeks postoperatively, anterior HALO pin migration was noted, necessitating HALO removal and transition to a Miami J collar. Despite this complication, the fracture was maintained in stable alignment without neurological deficits. The surgical wounds had healed well without concern for infection.

During the 3-month postoperative visit, the patient had stated he discontinued use of the Miami J collar two weeks prior and reported intermittent neck discomfort, characterized by soreness, tightness, and cramping; however, symptoms had improved overall. He noted difficulty with lateral range of motion and had not yet initiated formal physical therapy. He was advised to begin gentle range of motion exercises independently, and a physical therapy prescription was provided. At 6.5 months post-operatively, a CT scan was obtained to evaluate bony healing, which demonstrated stable fracture alignment without hardware failure (Figure 4). The patient continued to report gradual improvement in neck pain, tightness, and stiffness. By 6.5 months, he had near-normal cervical range of motion and had returned back to almost all activity. At his 1-year follow-up, he reported maintaining excellent neck range of motion in all planes and continuing physical therapy to support it. He remained unrestricted in his activities and, in recent weeks, had been able to tolerate waterskiing and rollercoasters without issue.

Figure 4 Post-operative CT scan with 3D reconstruction (A), axial (B), and coronal (C) cuts demonstrating stable osteosynthesis hardware placement with interval C1 fracture healing and reduction of C1–C2 articulation. 3D, three-dimensional; CT, computed tomography.

Discussion

Atlas fractures typically result from hyperextension or axial loading injuries to the cervical spine (1,3). While they are most frequently seen in elderly individuals, recent epidemiological studies describe a bimodal age distribution, with peaks occurring in young adults and again at 80–84 years (4). In younger patients, high-energy mechanisms such as motor vehicle accidents or diving injuries are common, while low-energy falls account for most fractures in the elderly (5). Although the incidence of atlas fractures has been rising—likely due to an aging population and increasing rates of osteoporosis—these injuries remain rare, representing just 3–13% of cervical spine fractures and 1.3–2% of all spinal injuries (4,19-22). Unstable variants, characterized by TAL disruption, are even less common (1). Historically, instability has been inferred from lateral mass displacement greater than 6.9 mm on open-mouth odontoid radiographs (or 8.1 mm with magnification) (9-12) or an atlantodens interval exceeding 3 mm (13-15). However, these radiographic criteria have largely been supplanted by MRI, which offers superior visualization of ligamentous injury.

Due to their infrequency, no definitive treatment algorithm exists for unstable C1 fractures. Non-operative strategies—including soft collar and HALO immobilization—have been used but are associated with complications such as malunion, nonunion, late instability, and inadequate restoration of C0–C2 (occiput to second cervical vertebra) height, often necessitating delayed surgery (23,24). Surgical stabilization via occiput-C2 or C1–C2 fusion provides reliable fixation but at the cost of significant motion loss. These segments account for approximately 50% of cervical spine range of motion, making fusion a poor choice for younger, active patients (1,3,25).

To preserve motion, newer techniques have been developed over the past two decades. Ruf et al. described an anterior transoral approach with C1-ring osteosynthesis and reported favorable range of motion and stability outcomes on dynamic MRI (26). However, the approach was criticized for its high infection risk and questionable biomechanical rationale, especially following TAL rupture (24,27,28). Subsequently, Li et al. proposed a posterior approach using skull traction and C1 lateral mass screws connected by rods to achieve reduction and stabilization (28). This technique addressed the need to restore C0–C2 height and ligamentous tension—a concept they referred to as the “buoy phenomenon”. Just as a buoy drifts when its anchor rope loses slack, TAL rupture and vertebral body collapse can allow anterior and lateral displacement of the C1 ring. Posterior fixation counteracts this mechanism by reestablishing height and tension in the ligamentous complex, including the cruciate, tectorial, and alar ligaments (28). Compared to anterior fixation, this posterior technique offers several advantages: improved fracture visualization, consistent bony union, fewer complications, and preservation of motion. Subsequent studies have validated this approach, showing excellent healing without evidence of instability or hardware failure (24,29-32).

Stereotactic navigation has further enhanced the precision of C1-ring osteosynthesis. Kumar et al. emphasized its utility in improving the accuracy of lateral mass screw placement (31,33). Although its impact on operative time remains debated, several studies demonstrate superior screw accuracy with navigation. In one large cohort of patients, comprised of 193 patients undergoing spine surgery requiring screw placement, the screw malposition rate was significantly lower in the navigation group (1%) compared to the freehand group (10.5%), and no patients in the navigation group required revision surgery for screw malposition (34). The authors also noted that operative time improved with growing familiarity with the system (34). Park and Choi similarly reported successful screw placement and anatomic reduction of the C1 ring using intraoperative navigation (24).

Our case illustrates the application of these principles in a healthy 34-year-old patient with an unstable C1 fracture sustained during a diving injury. Given his age and desire to preserve cervical motion, we pursued a posterior C1-ring fixation with stereotactic navigation. Postoperative CT confirmed optimal screw positioning within the lateral masses, and follow-up imaging showed no evidence of loosening or instability. This case supports the growing body of evidence favoring posterior C1-ring osteosynthesis as a safe, effective, and motion-sparing option for select patients with unstable atlas fractures.

Conclusions

Open reduction internal fixation (ORIF) of unstable C1 fractures, as demonstrated in this case and supported by existing literature, reliably achieves anatomic reduction and preserves cervical range of motion in both lateral rotation and flexion-extension. As such, ORIF may represent a superior alternative to C1–C2 or occiput-C2 fusion in appropriately selected patients—particularly those who are otherwise healthy and for whom non-operative management is not reasonable. Based on our experience and published data, we recommend the use of stereotactic navigation to enhance the accuracy and safety of lateral mass screw placement.

Acknowledgments

The authors would like to thank Kristi Overgaard for her assistance with manuscript preparation and submission.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-25-174/rc

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-174/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-25-174/coif). B.P.R. reports receiving institutional funding from the University of Michigan RAC Orthopedic Research Grant unrelated to the current manuscript. R.D.P. receives consulting fees unrelated to this study from Globus Medical. I.S.A. receives consulting fees unrelated to this study from Kuros, Globus Medical, and OrthoFix. The other 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 Declaration of Helsinki and its subsequent amendments. This study was approved by the Ethics Committee of the University of Michigan (No. HUM00276242). Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

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. Mead LB 2nd, Millhouse PW, Krystal J, et al. C1 fractures: a review of diagnoses, management options, and outcomes. Curr Rev Musculoskelet Med 2016;9:255-62. [Crossref] [PubMed]
2. Aleem I, Rosenbaum S, Currier BL. Anatomy of the cervical spine. In: Heary RF. editor. Cervical trauma: surgical management. New York: Thieme; 2019:1-13.
3. Kim D, Viswanathan VK, Munakomi S, et al. C1 Fractures. 2024 Jun 13. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–.
4. Matthiessen C, Robinson Y. Epidemiology of atlas fractures--a national registry-based cohort study of 1,537 cases. Spine J 2015;15:2332-7. [Crossref] [PubMed]
5. Lyons JG, Mian HM. Epidemiology of atlas fractures in the United States: A 20-year analysis. J Craniovertebr Junction Spine 2022;13:85-93. [Crossref] [PubMed]
6. Kakarla UK, Chang SW, Theodore N, et al. Atlas fractures. Neurosurgery 2010;66:60-7. [Crossref] [PubMed]
7. Chan KS, Shlobin NA, Dahdaleh NS. Diagnosis and management of isolated C1 fractures: A systematic review. J Craniovertebr Junction Spine 2022;13:233-44. [Crossref] [PubMed]
8. Cloney MB, El-Tecle N, Dahdaleh NS. Traumatic atlas fracture patients comprise two subpopulations with distinct demographics and mechanisms of injury. Clin Neurol Neurosurg 2022;221:107414. [Crossref] [PubMed]
9. Heller JG, Viroslav S, Hudson T. Jefferson fractures: the role of magnification artifact in assessing transverse ligament integrity. J Spinal Disord 1993;6:392-6.
10. Liu P, Zhu J, Wang Z, et al. "Rule of Spence" and Dickman's Classification of Transverse Atlantal Ligament Injury Revisited: Discrepancy of Prediction on Atlantoaxial Stability Based on Clinical Outcome of Nonoperative Treatment for Atlas Fractures. Spine (Phila Pa 1976) 2019;44:E306-14. [Crossref] [PubMed]
11. Kopparapu S, Mao G, Judy BF, et al. Fifty years later: the "rule of Spence" is finally ready for retirement. J Neurosurg Spine 2022;37:149-56. [Crossref] [PubMed]
12. Spence KF Jr, Decker S, Sell KW. Bursting atlantal fracture associated with rupture of the transverse ligament. J Bone Joint Surg Am 1970;52:543-9.
13. Ryken TC, Aarabi B, Dhall SS, et al. Management of isolated fractures of the atlas in adults. Neurosurgery 2013;72:127-31. [Crossref] [PubMed]
14. Radcliff KE, Sonagli MA, Rodrigues LM, et al. Does C1 fracture displacement correlate with transverse ligament integrity? Orthop Surg 2013;5:94-9. [Crossref] [PubMed]
15. Jackson RS, Banit DM, Rhyne AL 3rd, et al. Upper cervical spine injuries. J Am Acad Orthop Surg 2002;10:271-80. [Crossref] [PubMed]
16. Dickman CA, Hadley MN, Browner C, et al. Neurosurgical management of acute atlas-axis combination fractures. A review of 25 cases. J Neurosurg 1989;70:45-9. [Crossref] [PubMed]
17. Shatsky J, Bellabarba C, Nguyen Q, et al. A retrospective review of fixation of C1 ring fractures--does the transverse atlantal ligament (TAL) really matter? Spine J 2016;16:372-9. [Crossref] [PubMed]
18. Butt BB, Piche J, Gagnet P, et al. Stereotactic navigation in anterior cervical spine surgery: surgical setup and technique. J Spine Surg 2020;6:598-605. [Crossref] [PubMed]
19. Smith RM, Bhandutia AK, Jauregui JJ, et al. Atlas Fractures: Diagnosis, Current Treatment Recommendations, and Implications for Elderly Patients. Clin Spine Surg 2018;31:278-84. [Crossref] [PubMed]
20. Ma W, Xu N, Hu Y, et al. Unstable atlas fracture treatment by anterior plate C1-ring osteosynthesis using a transoral approach. Eur Spine J 2013;22:2232-9. [Crossref] [PubMed]
21. Kandziora F, Chapman JR, Vaccaro AR, et al. Atlas Fractures and Atlas Osteosynthesis: A Comprehensive Narrative Review. J Orthop Trauma 2017;31:S81-9. [Crossref] [PubMed]
22. Marcon RM, Cristante AF, Teixeira WJ, et al. Fractures of the cervical spine. Clinics (Sao Paulo) 2013;68:1455-61. [Crossref] [PubMed]
23. Dvorak MF, Johnson MG, Boyd M, et al. Long-term health-related quality of life outcomes following Jefferson-type burst fractures of the atlas. J Neurosurg Spine 2005;2:411-7. [Crossref] [PubMed]
24. Park CK, Choi MK. Direct C1 posterior arch screws for reduction and osteosynthesis in the treatment of Jefferson fracture. Acta Neurochir (Wien) 2024;166:31. [Crossref] [PubMed]
25. Panjabi M, Dvorak J, Crisco J 3rd, et al. Flexion, extension, and lateral bending of the upper cervical spine in response to alar ligament transections. J Spinal Disord 1991;4:157-67. [Crossref] [PubMed]
26. Ruf M, Melcher R, Harms J. Transoral reduction and osteosynthesis C1 as a function-preserving option in the treatment of unstable Jefferson fractures. Spine (Phila Pa 1976) 2004;29:823-7. [Crossref] [PubMed]
27. Dickman C. Re: Ruf M, Melcher R, Harms J. Transoral reduction and osteosynthesis C1 as a function-preserving option in the treatment of unstable Jefferson fractures. Spine 2004;29:823-7. Spine (Phila Pa 1976) 2004;29:2196-7. [Crossref] [PubMed]
28. Li L, Teng H, Pan J, et al. Direct posterior c1 lateral mass screws compression reduction and osteosynthesis in the treatment of unstable jefferson fractures. Spine (Phila Pa 1976) 2011;36:E1046-51. [Crossref] [PubMed]
29. Yu JC, Niemeier TE, Manoharan SR. Unstable C1 Fracture Managed with Internal Fixation Using Lateral Mass Screws: A Case Report. JBJS Case Connect 2018;8:e9. [Crossref] [PubMed]
30. Bransford R, Chapman JR, Bellabarba C. Primary internal fixation of unilateral C1 lateral mass sagittal split fractures: a series of 3 cases. J Spinal Disord Tech 2011;24:157-63. [Crossref] [PubMed]
31. Kumar A, Onggo J, Fon LH, et al. Direct Fixation of C1 Jefferson Fracture Using C1 Lateral Mass Screws: A Case Report. Int J Spine Surg 2019;13:345-9. [Crossref] [PubMed]
32. Gelinas-Phaneuf N, Stienen MN, Park J. Posterior open reduction and internal fixation of C1 fractures: the C-clamp technique. Acta Neurochir (Wien) 2018;160:2451-7. [Crossref] [PubMed]
33. Buchholz AL, Morgan SL, Robinson LC, et al. Minimally invasive percutaneous screw fixation of traumatic spondylolisthesis of the axis. J Neurosurg Spine 2015;22:459-65. [Crossref] [PubMed]
34. Akgun MY, Manici M, Ates O, et al. Unlocking Precision in Spinal Surgery: Evaluating the Impact of Neuronavigation Systems. Diagnostics (Basel) 2024;14:1712. [Crossref] [PubMed]