Anterior arch fracture:
Hyperextension injury
Transverse stable fracture through inferior/mid anterior arch
Due to avulsion at attachment site of atlanto-odontoid ligament/longus colli muscle
Best seen on lateral view as transverse displaced fracture through anterior arch inferiorly Associated with focal prevertebral soft tissue swelling
Differential includes secondary ossification centre
Posterior arch fracture:
Hyperextension injury
Due to compression of posterior arch of C1 between occiput and C2 spinous process
Vertical stable fracture of the posterior arch, if isolated
Best seen on lateral view; usually not associated with prevertebral soft tissue swelling; if seen indicates complex injury
Frequently associated with Jefferson fracture, odontoid fracture, 2nd & 3rd vertebral bodies and hence CT is indicated
References:
Rao SK et al. Spectrum of Imaging Findings in Hyperextension Injuries of the Neck. RadioGraphics 2005;25:1239-1254
