Congenital defect of the posterior arch of C1: a case report.

Odontoid fractures are one of the most common injuries to the cervical spine in geriatric patients. Congenital C1 arch absence, however, is a very rare anomaly found in the population. We describe the first reported case of a congenital C1 posterior arch absence and C1 anterior cleft presenting with odontoid fracture. We present the case of a 58-year-old male who was found to have a comminuted type III odontoid fracture with significant angulation and displacement. CT scan demonstrated this fracture and also demonstrated congenital cleft of his left anterior arch and absence of left C1 posterior arch. Given his anatomic anomaly, we elected to perform occipitocervical fusion. The patient underwent occipito-cervical fusion to avoid iatrogenic vertebral artery injury. He was also immobilized in a halo vest given patient-specific social factors and compromised bone quality. The patient had no intra- or post-operative complications, but a prolonged hospital stay due to alcohol withdrawal. At 3-month postoperatively the patient had no neck pain and return to baseline function. This case highlights the importance of obtaining a CT scan preoperatively to not only to further characterize the fracture but also for surgical planning and recognition of anatomic anomalies as this may significantly impact the operative strategy.