Traumatic vertical atlantoaxial instability in a case of atlanto-occipital coalition.

Study Design: This is a report of a woman with an atlanto-occipital coalition who experienced a traumatic vertical atlantoaxial facet dislocation and severe associated neurologic injury.
Objective: To describe the radiographic and pathoanatomic characteristics of the injury process.
Summary of Background Data: Severe injuries of the occipito-atlantoaxial complex are uncommon and only rarely are associated with patient survival. This is the first report of this particular injury.
Methods: Plain radiography and tomography demonstrated the facet dislocation and instability of the injury. Surgical exploration for repair of the torn dura mater and bony arthrodesis demonstrated the gross pathoanatomy.
Results: The patient's vertical atlantoaxial instability was stabilized, her dura mater reconstructed, and her necrologic status has improved to allow mobilization with a cane.
Conclusion: Vertical atlantoaxial instability has not been described previously. From the somewhat subtle radiographic findings, one might underestimate the severity of the neurologic damage. Aggressive work-up and management of this injury is suggested to avoid potential further necrologic sequelae.