Flexion-distraction injuries (FDI) of the spine occurs as a result of high-energy forces applied to the trunk (and spine). Usually there is a flexion force against the chest strong enough to break the back. The distraction force can dislodge the facet (spinal) joints enough to cause them to cross over each other and get locked.
Most often there are other injuries as well. The chest and lungs can be damaged at the same time the spine is injured. In the case of a car accident, the lap belt can cause additional abdominal injuries.
A flexion-distraction injury at the junction of the thoracic and lumbar spine (T12-L2) is called a Chance fracture. The fracture was first described by Dr. G. Q. Chance in 1948. Chance fractures were more common before the advent of lap and shoulder seat belts in the 1980s.