A Chance fracture is a spinal injury resulting from severe, high-energy trauma to the back. This injury disrupts both the bony structure of a vertebra and the surrounding ligaments. It is a serious condition requiring prompt medical attention, as it can be easily overlooked in the setting of major trauma.
Defining the Injury and Affected Spinal Anatomy
A Chance fracture is anatomically defined as a flexion-distraction injury, meaning the spine is simultaneously bent forward and pulled apart. This pattern typically results in a unique horizontal split that runs through the vertebral body and its posterior elements, such as the pedicles and spinous process. The injury most frequently occurs at the thoracolumbar junction, which is the transitional area between the rigid thoracic spine (T12) and the more flexible lumbar spine (L1 and L2). This location is where stresses concentrate during extreme spinal movement.
This fracture is distinguished because the fracture line essentially splits the vertebra in two. The injury can be purely osseous (involving only the bone) or osteoligamentous (including tears to the strong ligaments and discs). Injuries involving soft tissue structures, like the posterior ligamentous complex, significantly impact spinal stability. The fracture is named after Dr. G.Q. Chance, a radiologist who first described this horizontal splitting fracture in 1948.
The Unique Mechanism of Injury
The mechanism involves an extremely rapid, forceful forward bending (flexion) of the upper body over a fixed point. This flexion combines with a powerful distraction force, pulling the posterior and middle parts of the vertebra away from each other. This injury pattern is often called a “seatbelt fracture” or “Seatbelt Syndrome.”
The classic cause is a motor vehicle collision, particularly a head-on impact, where the occupant is restrained only by an older or improperly worn lap-only seatbelt. During the sudden deceleration, the lap belt acts as a fulcrum, or pivot point, across the abdomen. The upper body is thrown forward, folding over the belt, which concentrates the tension and distraction force directly onto the thoracolumbar spine. This intense force causes the vertebra to fail horizontally under the tension, resulting in the characteristic split.
Identifying a Chance Fracture and Related Complications
A patient with a Chance fracture reports severe back pain. Neurological deficits, such as weakness or numbness in the legs, are not always present because the fracture tends to pull the spinal canal open rather than crush the spinal cord. Physicians may observe a distinct horizontal bruise across the abdomen, known as the “seatbelt sign,” which raises suspicion for this spinal injury.
Diagnosis relies on medical imaging, beginning with X-rays and progressing to a Computed Tomography (CT) scan for detailed bony anatomy and visualization of the horizontal fracture line. Magnetic Resonance Imaging (MRI) is also utilized to assess soft tissue damage, including ligamentous tears and potential injury to the spinal cord or nerve roots. Because of the mechanism of injury, up to 50% of patients with a Chance fracture also have associated internal (visceral) injuries to the abdomen. Common internal injuries include perforation of the bowel, mesenteric tears, or trauma to the pancreas and duodenum, requiring careful assessment.
Treatment and Recovery Outlook
The management of a Chance fracture depends on the stability of the injury and the presence of associated neurological deficits or internal injuries. Fractures that are purely bony, have minimal displacement, and involve no ligamentous damage are considered stable. Stable Chance fractures can be treated non-operatively using a cast or a rigid brace, such as a thoracolumbosacral orthosis (TLSO), which holds the spine in extension to promote bony fusion.
Surgical intervention is required for unstable fractures, including those with significant ligament disruption or neurological compromise. The surgery typically involves internal fixation using pedicle screws and rods to stabilize the spine, often followed by fusion. Recovery timelines vary, but patients treated non-operatively may wear a cast or brace for 8 to 12 weeks. Physical therapy helps the patient regain strength, flexibility, and mobility.