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Year |
2001 |
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Question Number |
45 |
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Category |
Select |
Question
Which of the following statements best describes the mechanism that occurs during flexion-distraction (Chance-type) injuries of the thoracolumbar spine?
1. The anterior column fails first because the axis of rotation is within the disk space
2. The anterior column fails first because the axis of rotation is posterior to the facet joints
3. The posterior column fails first because the axis of rotation is anterior to the vertebral body
4. The posterior column usually remains intact and is protected by the facet joints
5. The middle column fails in compression with retropulsion of the vertebral body.
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Answer (click for answer)
Answer: 3
Explanation: "The axis of rotation of the applied force in this type of injury pattern is located anterior to the vertebral body, usually on the anterior abdominal wall (seat belt injury)." The posterior elements will fail under a tensile load and is the initial site of injury. The forces then extend through the disk space or vertebral body. A Chance type fracture involves a line of force that passes through the bony elements alone.
Reference: Beaty JH (ed): Orthopaedic Knowledge Update 6. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp653-671.