Atlantoaxial rotatory subluxation with ankylosis in an 11-year-old girl: a case report.

Study Design: Report of an 11-year-old girl with a left atlantoaxial rotatory subluxation and ankylosis found 20 months after she sustained a cervical injury.

Objective: To describe the radiographic characteristics of this rare deformity assessed with a combination of spiral CT scan with multiplanar three-dimensional reformations and functional CT scan.

Summary Of Background Data: Atlantoaxial rotatory subluxation is a well-known condition, but its association with lateral C1-C2 ankylosis has not been reported to our knowledge.

Methods: For a complete assessment of the dislocation, a combined morphologic volumetric and functional CT study was performed.

Results: Spiral CT showed an atlantoaxial rotatory subluxation with lateral C1-C2 ankylosis. CT study also demonstrated a lateral C1-C2 subluxation and an ipsilateral occipitoatlantal subluxation. Cervical MRI showed no spinal cord compression despite the seriousness of the dislocation process.

Conclusions: Whereas "classic" spiral study with multiplanar and three-dimensional reformations allows precise assessment of relationships between the upper cervical vertebrae, as well as bony changes, a functional CT study is essential for cervical biomechanic assessment of rotational instabilities of the craniovertebral junction and upper cervical spine.