Chance Fracture: Definition, Characteristics, and Management
A Chance fracture is a horizontal splitting injury of the spine caused by flexion-distraction forces, typically involving the thoracolumbar region, characterized by a horizontal fracture line extending through the posterior elements, pedicles, and vertebral body, often resulting from seat belt injuries during motor vehicle accidents.
Anatomical Characteristics and Classification
- Chance fractures are characterized by a horizontal splitting of the vertebra through the posterior elements, pedicles, and vertebral body without significant anterior vertebral height loss or displacement 1
- Four main patterns of Chance fractures have been identified:
- Pattern 1: Osseous disruption crossing posterior arches, pedicles, and vertebra (unstable) 1
- Pattern 2: Horizontal fracture through both pedicles with extension through inferior third of vertebral body (unstable) 1
- Pattern 3: Fracture with anterior extension through superior third of vertebra (unstable) 1
- Pattern 4: Fracture with horizontal disruption in posterior half of vertebral body (stable) 1, 2
Mechanism of Injury
- Chance fractures result from flexion-distraction forces, commonly known as "seat belt fractures" due to their association with improperly worn lap belts during motor vehicle accidents 3
- The mechanism involves hyperflexion around a fixed anterior point (such as a lap belt), creating tension forces that split the vertebra horizontally 1
- Most commonly affects the thoracolumbar junction (T12-L2), though they can occur at other levels 3
Epidemiology
- Chance fractures are relatively rare, representing approximately 0.6% of all spinal fractures 2
- They are frequently misdiagnosed or diagnosis is delayed due to their sometimes subtle radiographic appearance 2
- Often associated with abdominal injuries due to the common mechanism involving lap belts 4
Diagnostic Approach
- Initial evaluation should include plain radiographs, though they have limited sensitivity (30-70%) 5
- MRI is the preferred imaging modality for definitive diagnosis due to its high sensitivity and specificity in detecting the full extent of bony and soft tissue injury 5
- CT scanning provides detailed structural information about bone architecture and is useful for surgical planning 5
- Chance fractures may appear "benign" on initial imaging but can lead to chronic instability if not properly identified and treated 3
Treatment Options
Treatment depends on fracture stability:
Surgical options include:
Outcomes and Prognosis
- Surgical treatment allows early mobilization with stable fixation 4
- Minimally invasive approaches result in less blood loss, reduced soft tissue trauma, and fewer complications compared to open procedures 6
- With appropriate treatment, patients typically progress to osseous union without implant failure 4
- Most patients can return to their original occupations after treatment 3
Special Considerations
- Associated abdominal injuries are common and should be evaluated 4
- Neurological deficits are uncommon but should be assessed 3
- Implant removal may be performed after healing (approximately 9 months post-injury) 4
- Mean subsequent kyphosis after implant removal is minimal (approximately 1.4 degrees) 3
Pitfalls and Caveats
- Misdiagnosis is common due to the sometimes subtle radiographic appearance 2
- Failure to recognize the instability pattern can lead to chronic instability and long-term complications 3
- Pure ligamentous variants of seat-belt injuries may have greater risk of subsequent kyphosis 3
- All patients with diagnosed distraction injuries of the spine should receive appropriate stabilization to prevent long-term sequelae 3