Mechanism Hyperflexion

ANTERIOR SUBLUXATION Anterior subluxation is also known as hyperflexion sprain. The posterior ligamentous structures fail because of the hyperflexion of the cervical spine. A pure subluxation injury has no associated fractures. Radiographic findings can include a "fanning" or widening of the spinous processes at the level of injury. The disc space may be widened posteriorly and narrowed anteriorly. Abrupt angulation change of more than 11 degrees at a single interspace may also signal an injury21 (Fig 264-3).

Cervical spine radiographs may be normal if the hyperflexion sprain has not caused a fracture and the subluxation has been reduced. Flexion and extension views should be obtained in awake and cooperative patients to further evaluate for injury. Flexion views will exaggerate the radiographic abnormalities and extension views will reduce them. Anterior subluxation is a stable injury but mandates consultation to institute proper treatment, ensure absence of any associated spinal injuries, and prevent the development of delayed instability and pain syndromes.

BILATERAL INTERFACETAL DISLOCATION (BID) BID occurs when disruption to all ligamentous structures due to hyperflexion allows the articular masses of the involved vertebra to dislocate superiorly and anteriorly over into the intervertebral foramen inferior to the involved vertebra ( Fig 2.64:5). Radiographically, the vertebra can be seen dislocated anteriorly to at least 50 percent its width. The injury is mechanically unstable and usually presents with neurologic findings. 16 A "perched" vertebra is seen in partial BID, when the articular masses of the involved vertebra are perched on the superior articular processes of the subjacent vertebra. This configuration is also mechanically unstable but may not present with neurologic compromise.16 Using the term locked facets to describe a BID is misleading because the injury is unstable. Immediate specialist referral is necessary to reduce the dislocation.

SIMPLE WEDGE FRACTURE A wedge fracture of a vertebra is caused by compression between two other vertebrae. The superior end plate fractures while the inferior surface of the vertebra remains intact (Fig.264:6). The posterior ligaments may be disrupted, leading to an increase in the distance between spinous processes. Posterior element disruption makes the injury unstable. The simple wedge fracture is differentiated from a burst fracture by the absence of a vertical fracture of the vertebral body. Immediate specialist consultation is necessary if stability of the posterior ligament is not assured. 16

CLAY-SHOVELER'S FRACTURE An avulsion of the spinous process of the lower cervical vertebrae, classically C7, is known as a clay-shoveler's fracture ( Fig. 264:7). Intense flexion against contracted posterior erector spinal muscles causes avulsion of the spinous process. An isolated clay shoveler's fracture is mechanically stable. Conservative treatment with ice, analgesia, rest, and early referral is indicated. 16

FLEXION TEARDROP FRACTURE Extreme flexion can cause the flexion teardrop fracture (Fig.264-8). The associated anterior cord syndrome is due to impingement of the spinal cord by the fracture hyperkyphosis. There is complete disruption of all ligamentous structures at the level of the injury. The "teardrop" is the anteroinferior portion of the vertebral body, which is separated and displaced from the remaining portion of the vertebra. This injury is mechanically unstable and requires immediate attention from a spine specialist.16

FIG. 264-8. Flexion teardrop fracture.
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