AEMCA Practice Exam

What characterizes a chance fracture in the spine?

1. Neck hyper-flexion injury

2. Anterior column compression with posterior columns failing under tension

3. Direct trauma from an object

4. Overextension without prior compression

The correct answer is: Anterior column compression with posterior columns failing under tension

A chance fracture is specifically characterized by anterior column compression with the posterior columns failing under tension. This type of fracture typically occurs due to a flexion-distraction mechanism, which applies force that compresses the vertebral body (anterior column) while simultaneously exerting tension on the posterior elements, leading to fracture. The mechanism of injury usually involves a hyper-flexion event such as being involved in a motor vehicle accident, where the torso flexes forward rapidly while the pelvis remains anchored (like when the seatbelt restrains the lower body). This creates a situation where the anterior portion gets compressed, resulting in a fracture, while the posterior structures, such as the lamina and spinous processes, may become disrupted due to the tensile forces. The other answers describe different types of injuries or mechanisms that do not apply specifically to chance fractures. For example, a neck hyper-flexion injury typically leads to different fracture patterns and instability, while direct trauma from an object is more associated with blunt force injures resulting in other fracture types. Lastly, overextension without prior compression does not accurately represent the mechanism involved in the formation of a chance fracture, as it does not involve the characteristic flexion-distraction forces.