Chance Fractures

The injury. A Chance fracture is a flexion-distraction injury of the thoracolumbar spine, and the classic patient is a restrained occupant who flexes over a lap seatbelt during a motor vehicle accident. G.Q. Chance described it in 1948 and it was originally called the seatbelt fracture; its hallmark is the classic horizontal fracture line through the posterior elements.

Mechanism. The lap belt acts as a fulcrum. During rapid deceleration the upper body flexes forward while the pelvis stays restrained, and the resulting flexion-distraction force opens the posterior spine while the anterior column pivots over the belt.

Where, and in whom. The peak is L1-L3, at the thoracolumbar junction. A motor vehicle accident with a lap-belt restraint is the commonest mechanism, and a fall with flexion does the same thing. Children are at higher risk because the lap belt rides higher.

Where the rest of this sits. A Chance fracture is one pattern in the thoracolumbar fracture family, and the reason it is singled out is that it fails in distraction rather than compression - which is why a burst fracture with a similar-looking loss of height is a different injury with a different operation. And if there is a deficit the grading belongs to spinal cord injury.

What fails, and in which direction. In Denis's three-column terms the fulcrum is the anterior column, at lap-belt level, so everything behind it is loaded in tension.

Tension, not compression. The posterior elements fail in tension. A burst fracture is the opposite: every column fails in compression, and it is fixed in the opposite direction too.

Stability. The posterior ligamentous complex is disrupted by definition, which is why most Chance fractures are considered unstable.

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The classification that changes management is bony versus ligamentous, because it decides whether the injury can heal in a brace. Denis subdivides by what fails, and TLICS and the AO Spine system turn the findings into the decision to operate.

History. The answers that change what happens next:

• The MVA details, especially restraint type: lap belt or three-point
• Mechanism of impact
• Abdominal symptoms: pain, distension, vomiting
• Neurological symptoms

The spine. A widened interspinous space that can be felt is the classic finding, tenderness is focal at the fracture level, and a kyphotic deformity may be visible or palpable.

The abdomen. Transverse bruising across the abdomen is the seatbelt sign. This is a two-cavity injury pattern: the bruise raises suspicion for a Chance fracture and for intra-abdominal injury together, so the thoracolumbar spine and the abdomen and pelvis are both imaged, never one alone. Tenderness may be generalised or focal, distension may mean bleeding or an ileus, and guarding and rigidity are the signs of peritonitis.

Neurology. Complete lower limb motor and sensory testing, perianal sensation for sacral sparing, rectal tone, and reflexes, which may be hypo- or hyperreflexic depending on the level.

What travels with the fracture. The seatbelt injury spectrum runs through the abdomen as well as the spine, and these are the visceral injuries to look for.

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What the CT shows. The classic appearance:

• Horizontal fracture line through spinous process, laminae, transverse processes, pedicles and vertebral body
• Widened interspinous space at the injury level
• Empty facet sign if the facets are subluxed
• Minimal anterior column compression, which distinguishes it from a burst

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Non-union. Rare after a fusion that has been adequately compressed. The risk is higher where a ligamentous injury was treated non-operatively.

Bracing after surgery. Practice varies. Some use a TLSO for 6-12 weeks as comfort and a reminder, others rely on the instrumentation alone, and short segment fixation is generally stable enough for that.

Long-term. Watch for adjacent segment disease, which is less common than after a burst fracture because the construct is short, and ask about chronic pain.

After surgery. Fusion rates are high when the construct is adequately compressed, hardware failure is low because the anterior column is intact, alignment is restored well, and most patients return to normal function.

By type. A purely bony injury heals excellently, whether braced or fixed, and a ligamentous injury does excellently once fused. A ligamentous injury treated non-operatively does poorly, with chronic instability.

Neurology. Most Chance fractures are neurologically intact. Where there is a deficit the prognosis depends on its severity, and recovery at the cauda equina level is generally good.

The abdomen. An associated abdominal injury increases morbidity and may delay the spine surgery, and needs coordination with the general surgical team.

Global Epidemiology

Flexion-distraction (Chance) injuries are a minority of thoracolumbar fractures but carry a disproportionate burden of associated visceral and neurological injury. In the original lap-belt era series, 32 of 38 restrained occupants (84%) sustained abdominal injury, with bowel or mesenteric injury in 27 of 32 (Denis et al, 1983). In a prospective cohort, abdominal injury occurred in 64% of patients with a seatbelt sign versus 8.7% without, and small-bowel perforation in 21% of those with the sign (Chandler et al, 1997). In the paediatric population, a two-decade single-centre series found abdominal visceral injury in 42% and neurological injury in 27% of children with lumbar Chance fractures, with injuries occurring even when a three-point belt was correctly worn (Louman-Gardiner et al, 2008). The shift from lap-only to three-point restraints has reduced but not eliminated these injuries, particularly in rear-seat and incorrectly restrained children.

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