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

Background: Unstable C1 (atlas) fractures pose a substantial surgical challenge due to their proximity to critical neurovascular structures and the unique biomechanical role of the atlantoaxial complex. Disruption of the transverse atlantal ligament (TAL) destabilizes the C1 ring, and traditional fusion constructs sacrifice substantial cervical motion. C1-ring osteosynthesis with a rod and lateral mass screw construct offers a motion-preserving alternative, though screw placement can be technically demanding. In this report, we present the use of stereotactic navigation-assisted open reduction and internal fixation (ORIF) of the C1 ring to stabilize an unstable C1 fracture. Case Description: A 34-year-old man sustained a ring-expanding C1 fracture with TAL disruption after diving into a shallow pool. Imaging confirmed right-sided anterior and posterior arch fractures with lateral mass displacement and intrasubstance TAL tear. Given the unstable fracture pattern, surgical fixation was pursued to restore anatomic alignment and preserve motion. The patient underwent prone positioning, closed reduction with fluoroscopic guidance, and stereotactic navigation-assisted C1-ring osteosynthesis via a posterior approach. Intraoperative O-arm imaging confirmed accurate screw placement and anatomic reduction. Postoperatively, the patient demonstrated excellent recovery with maintained bony alignment, fracture healings, and near-complete return of cervical motion at 6.5 months. Conclusions: Navigation-assisted ORIF of unstable C1 fractures is a safe, effective, and motion-preserving strategy that achieves reliable reduction and stabilization. It represents a valuable alternative to fusion procedures in young patients in whom fusion carries very high morbidity. Stereotactic navigation enhances the accuracy and safety of lateral mass screw placement and may reduce complication risk. This case adds to the growing literature supporting posterior C1-ring osteosynthesis as a safe approach for select unstable atlas fractures.