Mechanism Hyperextension Injuries

HYPEREXTENSION DISLOCATION A hyperextension injury involves a complete tear of the anterior longitudinal ligament and intervertebral disk with disruption of the posterior ligamentous complex. Facial trauma with a central cord syndrome is the most common clinical presentation. Radiographically the vertebrae are normally aligned because the dislocation will be reduced. Diffuse prevertebral soft tissue swelling is usually present. Other signs include a disk-space widening anteriorly or a fracture of the anteroinferior end plate of the vertebrae.16 If the patient has no neurologic deficit and no evidence of fracture, flexion-extension films may be used to help define ligamentous instability. Any evidence of instability requires immediate specialist consultation.

AVULSION FRACTURE OF THE ANTERIOR ARCH OF ATLAS A hyperextension may avulse the inferior pole of the anterior tubercle of C1. This is most readily detected on the lateral view (Fig 264:13). The presence of perivertebral soft tissue swelling and absence of cortication distinguish it from the ununited secondary ossification center of the inferior pole of the tubercle. A fracture involving the entire anterior arch is unstable. Immediate specialist consultation is recommended. 16

EXTENSION TEARDROP FRACTURE A hyperextension mechanism may cause the anterior longitudinal ligament to avulse the inferior portion of the anterior vertebral body at its insertion ( Fig, 264-14). The most common location is at C2. The height of the fragment usually exceeds its width. This fracture is more common in older patients with osteoporosis. The extension teardrop fracture is unstable in extension and immediate specialist consultation is necessary. 16

FIG. 264-14. Extension teardrop fracture.

FRACTURE OF POSTERIOR ARCH OF THE ATLAS Hyperflexion of the cervical spine may compress the posterior arch of the atlas between the occipital bone and the spinous process of the axis. This is to be differentiated from the Jefferson fracture of C2. Prevertebral soft tissue swelling is much more prevalent with the more extensive Jefferson fractures. CT scanning will ultimately define which fracture is present. This fracture is frequently associated with other cervical spine fractures, and specialist consultation is recommended.

LAMINAR FRACTURE Isolated laminar fractures are caused by hyperextension and may be subtle on plain radiographs. Associated spinous process fractures may be present. CT scanning is required to define the extent of spinal cord involvement. This injury is considered stable; immediate specialist consultation is recommended.

HANGMAN'S FRACTURE The hangman's fracture is located in the pedicles of C2, with C2 displacing anteriorly on C3 ( Fig 264:15). The fracture is caused by an extension mechanism and is seen in judicial hangings. Suicidal hangings do not usually cause the extreme hyperextension seen in judicial hangings and do not cause a hangman's fracture. The same fracture is seen in motor vehicle and diving accidents where sudden hyperextension forces are applied in deceleration. Owing to the large diameter of the spinal canal at the level of C2, even displacement of C2 on C3 may not cause neurologic injury, and these patients may be neurologically intact. This injury is unstable and mandates immediate consultation.

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