Occipital condylar fractures are frequently missed on standard radiographs and with the advent of CT imaging these fractures are more common than previously demonstrated. Three types have been described according to the classification system of Anderson and Montesano: type I is a comminuted fracture of the occipital condyle with minimal or no fragment displacement into the foramen magnum, type II is a basilar skull fracture extending into the occipital condyle, and type III is a fracture with a fragment displaced medially from the inferomedial aspect of the occipital condyle into the foramen magnum. Occipitoatlantal dislocation (OAD) is a rare devastating often fatal injury. Various radiographic criteria can be used to establish the diagnosis of OAD and direct measurement of occipitovertebral skeletal relationships altered by occipitoatlantal dissociation using the basionaxial and basion-dental intervals provides the most accurate imaging assessment of this injury. More survivors are reported because of improvements in diagnosis and treatment [16].

The unique anatomical relationship between the atlas and axis produces a variety of injury patterns not seen elsewhere in the spine. Injury to the C1/C2 complex accounts for about 25% of cervical spine injuries. Fractures of C2 occur most frequently, 55% of which involve the odontoid peg. Traumatic subluxation of C1 on C2 and rotatory fixation also occur with or without associated bone injury [17]. Atlantoaxial subluxation occurs when there is loss of integrity of the odontoid peg and/or the transverse ligament. Post-traumatic atlantoaxial subluxation is rare and even rarer without odontoid fracture.

Atlantoaxial dissociation is a general term used to encompass all types of atlantoaxial subluxation, dislocation and rotatory fixation. In the majority of atlantoaxial rotatory fixation (atlantoaxial rotatory subluxation, atlantoaxial dislocation), fixation occurs within the normal range of movement of the joint so the C1/C2 complex is not truly subluxed or dislocated. This entity is defined as persistent pathological fixation of the atlantoaxial joint in a rotated position such that the atlas and the axis move as a single unit rather than independently. It usually results from apparently insignificant cervical spine trauma. It is a rare condition occurring in children more than adults. Positional CT is required to differentiate atlantoaxial rotatory fixation from physiological atlantoaxial rotation and other causes of torticollis because these conditions can appear identical on static CT. CT is initially performed in the anatomical position. Further images are then obtained with the patient’s head turned as much as they can to the right and then to the left; this determines whether the atlas and axis rotate independently of each other, as is normal.

Fractures of the atlas (C1) account for 2–13% of cervical spine fractures and are generally not associated with neurological deficit. C1 fractures are frequently associated with fractures elsewhere in the cervical spine particu- larly at the C2 and C7 levels. C1 fractures have been classified into five types including fractures of the anterior arch, posterior arch, lateral mass, transverse process and the burst type (Jefferson) fracture. This classification also describes the mechanism of injury and the stability of each fracture type.

Dens fractures of the axis (C2) are most commonly described by the Anderson-D’Alonzo classification system, with three types depending on location of the fracture plane and level of involvement (tip, base or C2 body), which has important therapeutic and prognostic implications. The mechanism of injury resulting in an odontoid process fracture involves a combination of extreme flexion, extension or rotation, plus a shearing force. The majority of cases have no neurological injury but deficit may develop later due to atlantoaxial subluxation. Fractures of the ring of the axis can occur through the laminae, the inferior articular facets, the pars interarticularis, the superior articular facets, the pedicles and the posterior wall of the vertebral body. These fractures are invariably bilateral but not symmetrical. Traumatic spondylolisthesis (neural arch avulsion from body) of C2, known as „hanged man’s fracture”, is a group of injuries with variable mechanisms accounting for 4–23% of cervical spine fractures. Effendi and coworkers [18] produced a classification of fractures of the ring of the axis according to radiological displacement and stability. The type and degree of displacement of the C2 vertebral body, the state of the C2/C3 disc space and articular facets of C2/C3 are considered. Extension teardrop fractures and hyperextension dislocations account for about 20% of C2 injuries. The teardrop fracture is caused by avulsion of the anterior longitudinal ligament off the anteroinferior endplate of the vertebral body; a variant, hyperextension strain is the same mechanism, but only involves soft tissue injury without the osseous avulsion. Hyperextension dislocation injury also involves a fracture of the anteroinferior corner of a vertebral body. It most frequently involves the lower cervical vertebra, but is not rare at the C2/C3 level. Fractures involving both C1 and C2 occur less frequently than isolated C1 and C2 fractures.

There are multiple types of subaxial cervical spine injury (i.e., below C2). These injuries are best classified by the mechanism of injury. The mechanism of injury is described by the vector of the force that causes the subsequent injury. Many patients with cervical spine trauma have more than one injury and they tend to occur in „families” based on the mechanism. Hyperflexion injuries are the most common injuries to the spine. Injuries from hyperflexion mechanisms include hyperflexion sprains, a purely ligamentous injury, bilateral facet dislocations, anterior wedge compressions of the vertebral body, clay shovelers fractures and flexion teardrop fractures. The „flexion teardrop” fracture is an unstable fracture, and is the most devastating cervical spine injury compatible with life. This injury is caused by severe flexion with resultant disruption of all ligaments and their associated stability. The anterior vertebral body is comminuted, with a triangular fragment or „teardrop,” anteroinferiorly. The posterior portion of the vertebral body retropulses into the spinal canal causing injury to the spinal cord. Patients clinically present with acute anterior cord syndrome, characterized by complete paralysis, hypesthesia and hypalgesia to the level of injury, and preservation of dorsal column function. The addition of a rotational component and posterior distraction with hyperflexion injuries can result in unilateral facet dislocations. Axial loading and accompanying hyperflexion will lead to burst fractures. Forces acting along the coronal plane (i.e., a lateral flexion injury) give rise to lateral compression of the vertebral bodies. In general, hyperflexion injuries cause narrowing of the anterior interverterbal disc, with distraction of the posterior ligament complex and the posterior disc. Anterior translation of the vertebral body and posterior elements may also be present, distinguishing this injury from anterior subluxations caused by hyperextension injuries wherein the spinolaminar line is not usually displaced. Hyperextension injuries are more common in the cervical spine than in the thoracolumbar spine. Most of these fractures are due to hyperextension forces and are usually stable, such as the „extension teardrop” that classically occurs at the anteroinferior margin of C2.