A Chance fracture is a specific injury to the spinal column characterized by the horizontal splitting of a vertebra. It is a type of flexion-distraction injury, meaning the spine is simultaneously bent forward and pulled apart by a sudden, forceful bending motion of the torso. Its potential for instability and association with other severe internal injuries makes prompt recognition and treatment important.
Anatomical Features of a Chance Fracture
The injury involves a distinctive horizontal fracture line running through the vertebral bone. It most commonly occurs at the thoracolumbar junction, the area where the rigid thoracic spine meets the more mobile lumbar spine, typically involving vertebrae between T11 and L4.
A Chance fracture is considered unstable because it disrupts all three columns of the spine, a model used to assess stability. The three columns are the anterior, middle, and posterior. In this fracture, the posterior and middle columns fail under tension, being pulled apart, while the anterior column often fails under compression.
The fracture line classically extends horizontally from the back to the front, passing through the posterior bony elements like the spinous process and pedicles, and continuing through the main vertebral body. The injury may be purely a fracture through the bone (osseous), involve a tear through the spinal ligaments (ligamentous), or be a combination of both (osteoligamentous).
The Mechanism of Injury
The unique pattern of the Chance fracture is caused by hyperflexion-distraction. It is commonly referred to as a “seatbelt fracture” because it was frequently seen in high-speed motor vehicle accidents involving older, two-point lap belts. During rapid deceleration, the upper body is violently thrown forward.
The lap belt acts as a rigid fulcrum, pinning the lower body while the upper body continues its forward momentum. This action causes the vertebra to be pulled apart, or distracted, over the fixed point of the belt, resulting in the horizontal splitting fracture. The force causes the posterior elements of the spine to fail under a stretching force.
A concerning aspect of this mechanism is the high risk of associated damage to abdominal organs. The force that fractures the spine can also compress or tear internal structures like the pancreas, duodenum, small bowel, and mesentery. Up to 50% of patients with a Chance fracture sustain significant intra-abdominal injuries, which can be life-threatening.
Recognizing and Diagnosing the Fracture
Patients with a Chance fracture typically present with severe back pain. A physical sign often looked for is the “seatbelt sign,” which is bruising or abrasions across the abdomen or lower chest corresponding to the path of the lap belt. While most patients do not have severe neurological deficits, some may experience weakness, numbness, or loss of bladder control due to spinal cord compression.
Initial diagnostic imaging often includes X-rays, but a Computed Tomography (CT) scan is the preferred method for fully characterizing the bony fracture detail. CT imaging is highly sensitive for identifying the horizontal fracture line and assessing for any associated intra-abdominal injuries. To evaluate soft tissue damage, such as ligamentous tears or injury to the spinal cord, a Magnetic Resonance Imaging (MRI) scan is often necessary.
Treatment and Recovery
Treatment depends on the stability of the injury and the presence of neurological deficits. For stable, purely bony fractures without significant ligamentous tearing, non-surgical management may be appropriate. This conservative route involves immobilizing the spine, often with a specialized brace called a thoracolumbosacral orthosis (TLSO), which holds the back in an extended position to promote healing.
Unstable fractures, or those with signs of spinal cord compromise or extensive ligament damage, typically require surgical stabilization. The most common procedure involves internal fixation, where metal rods and screws are used to stabilize the affected segment of the spine. This instrumentation provides immediate stability and allows the bone and ligaments to heal in the correct alignment.
Following treatment, recovery requires a period of restricted activity followed by physical therapy. Rehabilitation aims to restore muscle strength and mobility in the torso and back. Patients are monitored with follow-up imaging to ensure the fracture heals without developing a progressive curvature of the spine.