Unstable Transverse Split Fracture of the Anterior Arch of the Atlas

Study Design: A case report Objectives: To report a case of delayed instability of the atlantoaxial joint after a transverse split fracture of the anterior arch of the atlas (C1) in a 65-year-old man Summary of Literature Review: A transverse split fracture of the anterior arch of the atlas (C1) is an uncommon type of C1 fracture. The mechanism of injury is not well-known, but is thought to be related to hyperextension of the neck. In our experience, such an injury poses a risk of transverse atlantal ligament injury and subsequent progression of instability in the atlantoaxial joint. Materials and Methods: A 65-year-old man was admitted to the trauma center with multiple injuries to the entire body after a rear-end collision. The patient was initially diagnosed with a transverse split fracture of the C1 anterior arch with an intact odontoid process shown on cervical computed tomography. C1-2 alignment was within the acceptable range, and the patient had no neurological deficit except mild posterior neck pain. Conservative treatment was maintained using a Philadelphia brace for the initial 3 months. However, delayed instability of the atlantoaxial joint was noted on plain radiographs taken at a 6-month follow-up. Therefore, C1-2 posterior instrumentation and fusion were performed using bilateral C1 posterior arch screws and bilateral C2 pedicle screws. Results: The patient’s neck pain was relieved after surgery, and the stability of the atlantoaxial joint was radiologically maintained until 2 years of follow-up. Conclusions: Even if neurological deficits and malalignment are not present, and there is no pathologic soft tissue swelling in a transverse split fracture of the C1 anterior arch, the surgeon should consider the possibility of the progression of C1-2 instability.