Pediatric Atlanto Axial Instability

Etiology: Ligamentous laxity causing C1-C2 instability
Imaging Radiograph: When measuring the atlanto-dens interval on lateral flexion and extension and neutral cervical spine radiographs
— If the atlanto-dens interval is greater than 5 millimeters on any view there is instability
— If there is greater than 1-2 millimeters of motion at the atlanto-dens interval on flexion when compared to extension there is instability
DDX:
Complications:
Treatment: Surgical fusion
Clinical: Often seen in Trisomy 21

Radiology Cases of Atlanto Axial Instability

Radiograph of atlanto axial instability — Lateral radiographs of the cervical spine show a mildly enlarged atlanto dens interval in neutral position (left), that increases significantly on flexion (center) and reduces on extension (right).

Flexion and extension radiographs of atlanto axial instability — Lateral radiograph of the cervical spine in extension (left) shows the atlanto dental interval to measure 0 mm. Lateral radiograph of the cervical spine in flexion (right) shows the atlanto dental interval to measure 7 mm.