seat belt fracture
ORTHOPAEDICS, PUBLIC SAFETY
Definition A horizontal fracture through the spinous process of lower vertebrae with little or no compression of the vertebral body*. Horizontal fractures of the posterior elements may be associated with a horizontal fracture through the vertebral body, or with disruption of the ligaments and intervertebral discs without fracture.
*The fulcrum of the flexion force is displaced forward to the object over which the body is flexed, and therefore, the compression forces are removed from the vertebral body and no significant compression fracture results from such injuries.
Mechanism Flexion of the trunk over an object that serves as a fulcrum, such as a seat belt.
Comment Described by GQ Chance in 1948 (aka Chance fractures), these fractures result in a horizontal splitting of the vertebra that begins with the spinous process or lamina and extends anteriorly through the pedicles and vertebral body which tends to have a wedge compression fracture, while the posterior elements of the vertebra are distracted. Despite the extent of damage to the vertebra, these fractures tend to be stable. They are most common in T12, L1, and L2–the thoracolumbar spine, the junction of the relatively rigid thoracic spine and the more flexible lumbar spine. They were known as “seat-belt” fractures with the advent of lap seat belts in cars, but are now rare, because today’s cars are fitted with shoulder/lap belt combinations. Most of these fractures are now linked to falls or crush type injuries where the thorax is acutely hyperflexed. About 50% of have associated intraabdominal injuries fractures of the pancreas, duodenum and mesentery contusions or rupture which must be surgically assessed.
Synonyms Chance fracture, distension fracture, flexion/distension fracture