What is a chance fracture?

What is a Chance Fracture?

A Chance fracture is a specific type of flexion-distraction injury of the spine characterized by horizontal disruption through the vertebral body and posterior elements (pedicles, lamina, and spinous processes), classically occurring at the thoracolumbar junction (typically L1-L3) and most commonly associated with lap belt injuries in motor vehicle accidents. 1, 2

Mechanism of Injury

• The injury occurs when the spine rotates about a fixed axis, such as a lap belt during sudden deceleration in a motor vehicle collision 1
• The mechanism is pure flexion-distraction, causing the spine to bend forward around the restraint point 2, 3
• While classically associated with seat belt use, Chance fractures can occur in unbelted passengers through similar flexion-distraction mechanisms 3

Defining Characteristics

The fracture has specific anatomical features that distinguish it from other spinal injuries 2:

• Horizontal splitting through the vertebral body and neural arches via the pedicles
• Minimal or no decrease in the anterior height of the involved vertebral body
• No forward or lateral displacement of the superior vertebra
• Location predominantly between L1 and L3 in the majority of cases

Classification Patterns

Four distinct patterns of Chance fractures have been identified, with varying stability 2, 4:

1. Type 1 (Unstable): Osseous disruption crosses the posterior arches, pedicles, and vertebral body 2
2. Type 2 (Unstable): Horizontal fracture involves both pedicles with anterior extension through the inferior third of the vertebral body 2
3. Type 3 (Unstable): Fracture with anterior vertebral extension through the superior third of the vertebra 2
4. Type 4 (Stable): Fracture with anterior horizontal vertebral disruption limited to the posterior half of the body 2

Clinical Recognition

A critical pitfall is that Chance fractures are frequently not recognized initially, leading to delayed diagnosis 4:

• Look specifically for the "seat belt sign" - abdominal bruising in a horizontal pattern across the lower abdomen 1
• Palpate for marked tenderness and visible kyphotic deformity at the thoracolumbar junction 1
• Maintain high suspicion in any restrained passenger involved in high-speed frontal collisions 1, 3

Associated Injuries

• Intra-abdominal injuries are common and may require immediate surgical intervention before addressing the spinal injury 1, 5
• The presence of abdominal trauma should heighten suspicion for Chance fracture in the appropriate mechanism 1, 3
• Cervical spine injuries can occur concomitantly and require evaluation 1

Treatment Approach

Management depends on fracture stability and associated injuries 5, 2, 4:

• Unstable fractures (Types 1-3) require surgical stabilization with open or percutaneous pedicle screw fixation 1, 5, 2
• Stable fractures (Type 4) may be managed conservatively with casting or bracing 2, 3
• Purely ligamentous injuries (Chance-type without bone involvement) are inherently unstable and typically require surgical fixation 1
• Surgical approaches allow early mobilization while minimizing morbidity, with percutaneous techniques reducing blood loss 5

Important Caveats

• The term "Chance fracture" technically refers to injuries with vertebral body fracture involvement; purely ligamentous flexion-distraction injuries are sometimes called "Chance-type injuries" but represent a distinct entity requiring surgical management 1
• These injuries are uncommon in the pediatric population but follow similar patterns when they occur 1
• Delayed recognition can lead to progressive deformity and neurological compromise, making early diagnosis critical 4