This case illustrates a craniocervical junction distraction injury.

Craniocervical biomechanical continuity depends on the integrity of the skull base, atlas, and axis and their attaching ligaments. The articulations of the craniocervical junction are defined by the middle atlantoaxial joint, which consists of two synovial compartments that surround the dens and allow rotation of C1 and C2 with respect to each other, and the paired lateral atlantoaxial and atlanto-occipital articulations. These joints are supported by several ligaments, the most crucial of which are the tectorial membrane, the alar ligaments, and the transverse fibers of the cruciate ligament (transverse ligament) in maintaining craniocervical integrity.

The most prevalent cause of craniocervical junction injuries is high speed motor vehicle collisions. The injury mechanism is commonly severe hyperflexion accompanied by axial compression. In some cases, it is the result of hyperextension with axial compression and rotation. There is resulting dislocation of the craniocervical junction and atlanto-axial distraction. These are considered grossly unstable injuries since the rotational and shearing forces at the craniocervical junction disrupt the ligamentous continuity of the tectorial membrane, the alar ligaments, and the transverse ligament. Thus, there is loss of atlanto-axial continuity, and resultant separation.

Conventional radiographic and CT findings in craniocervical distraction injuries include:

• Prevertebral soft-tissue swelling
• Basion-dens interval > 12 mm
• Basion–posterior axial line interval > 12 mm anteriorly or >4 mm posteriorly
• Abnormal power’s ratio (used to diagnose occipitocervical dislocation)
  • Power’s ratio is the (distance from the basion to the posterior arch of C1) divided by the (distance from the anterior arch of C1 to the opisthion). A ratio of 1 is considered normal. Normal. If > 1.0, this is suggestive of anterior dislocation. A ratio < 1.0 is suspicious for:
• posterior atlanto-occipital dislocation
• odontoid fractures
• ring of atlas fractures
• Widening or incongruity of the articulation between the occipital condyles and the lateral masses of C1
• C1-C2 dislocation or subluxation and resultant widening of the C1-C2 facets
• Fractures of the bony structures of the craniocervical junction

MR imaging findings in craniocervical distraction injuries, usually best viewed sagittal or coronal MR imaging with T2-weighted or STIR sequences, include:

• Prevertebral soft-tissue swelling
• Interspinous, or nuchal ligament edema
• Fluid within the articular capsules
• Facet widening
• Epidural hematoma with/without resultant spinal cord injury

Craniocervical junction distraction injuries are often accompanied by significant neurologic and vascular compromise. Many patients sustaining these injuries die as a direct result or present with profound sensory and motor sequelae and/or deficits including ventilator-dependent quadriplegia. Early diagnosis, cervical spine stabilization and cardiorespiratory support are imperative for patient survival and/or recovery.

Case courtesy of Associate Professor Pramit Phal