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This type of displacement most often occurs in the upper cervical segment of the cord. A blow to the front of the head forces the neck into hyperextension. There is often nothing to restrain the head until the occiput hits the lower cervical spine.
Extension injuries are generally less serious than flexion injuries. In the neck, the arch of the atlas or of the axis may be fractured. The injury is stable as is a tear of the anterior longitudinal ligament. Fracture of the pedicle of C2, "hangman's fracture", is often unstable.
Thoracolumbar extension injuries are less common. They may result in a fractured lamina, or the vertebral body may fracture and the disc prolapse.