The classic mechanism involves the patient being thrown forward across an intact lap-belt, resulting in a hyperflexion force acting around a center of rotation anterior to the spinal column at the belt.
This results in distraction forces at all three columns of the spine
- The posterior elements are torn apart through either the facet joints or the bone itself
- The middle column is torn apart through either the posterior disc or the posterior vertebral body
- The anterior column is either disrupted in severe injuries or left as a hinge that cannot resist either flexion or rotational displacement
There could be associated injuries frequently due to violent compression of viscera between the spinal column and lap belt. Rates of intra-abdominal hollow viscus injury is reported as high as 50%.
Flexion distraction injuries can be either single level or two level.
This kind of injury passes through the posterior ligamentous structures and the underlying disc at the same level, or through the posterior lamina, pedicle, and vertebral body in the same transverse plane. These injuries disrupt only a single motion segment.
These injuries begin posteriorly at one level of lamina or facet joint, then proceed anteriorly in an oblique fashion so that the injury passes out of the vertebral body into an adjacent disc or through the disc into an adjacent body. In these injuries, two adjacent motion segments are disrupted, and stabilization requires addressing both levels of injury.
With most car manufacturers today providing lap-shoulder belts as standard equipment, there is a lower incidence of flexion-distraction injuries.
Imaging for Flexion Distraction Injuries
Xrays are the basic investigations to assess flexion distraction injuries. Computed tomography and MRI are used for better delineation of fractures and to know the health of the spinal cord. In case of surgery preoperative CT or MRI images can be used to find whether pedicles of the injured vertebra are intact or not.
Nonoperative Treatment of Flexion Distraction Injuries
There is very little role of non operative treatment in these injuries. One of the rare indication is a reducible fracture through the bone. In this situation, the fracture can be reduced and maintained in a brace or cast. Reduction is performed by applying hyperextension forces to the spinal column and this is followed by casting or bracing in hyperextension.
Patient should be followed up with serial xrays to ensure maintenance of the reduction. External immobilization is recommended for a minimum of 3 months.
Surgical Treatment of Flexion Distraction Injuries
If the injury is ligamentous or osseoligamentous [involves bone and ligament], surgical stabilization is indicated. The primary goal of surgery in flexion-distraction injuries is restoration of alignment and stability rather than decompression. In cases where direct neural compression from a herniated disc or hematoma is responsible for the neurological deficit, decompression becomes an important objective.
Therefore posterior reduction and compressive stabilization is usually sufficient.
As anterior column is not destabilized, doing an anterior surgery in flexion distraction injuries is not a good idea as it would lead to greater destabilization.
The surgery usually done is decompression, reduction of the fracture, fixation with pedicle screw system and posterior segment fusion.
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