Chance Fracture¶

Definition¶

A Chance fracture is a flexion-distraction injury of the thoracolumbar spine characterized by horizontal fracture planes extending through the vertebral body, pedicles, and posterior elements. First described by G.Q. Chance in 1948, these injuries involve failure of the posterior and middle columns under tension (distraction), with the anterior column acting as a fulcrum.

Mechanism of Injury¶

The classic mechanism is a head-on motor vehicle collision in which the occupant is restrained by a lap belt only (without a shoulder harness). The lap belt acts as a fulcrum at the anterior abdominal wall, and the upper body flexes forward violently, creating a distraction force that propagates from posterior to anterior through the spine.

The fulcrum of rotation is located at or anterior to the anterior vertebral body, so all three columns fail in tension (distraction) rather than compression.

Subtypes¶

Bony Chance Fracture (AO Type B1)¶

A purely osseous injury in which the horizontal fracture line extends through the spinous process, lamina, pedicles, and vertebral body. Because bone heals better than ligaments, purely bony Chance fractures have a better prognosis with conservative management.

Ligamentous (Soft Tissue) Chance Injury (AO Type B2)¶

The distraction force disrupts the posterior ligamentous complex, facet capsules, and intervertebral disc rather than fracturing through bone. This variant has a poorer prognosis because ligaments heal less reliably and the risk of delayed instability is higher. Surgical fixation is typically required.

Mixed Bony-Ligamentous¶

A combination of osseous and ligamentous disruption — the most common pattern in practice.

Imaging Findings¶

CT¶

Sagittal images — Horizontal fracture line extending through the posterior elements (spinous process, lamina) and vertebral body. The vertebral body fracture may be difficult to see if the fracture plane is purely horizontal (parallel to the axial slices).
Axial images — Fracture through the pedicles; widening of the facet joints
"Empty facet" sign may be present if there is facet joint widening
Associated vertebral body compression fracture (AO B2 + A type) is common

MRI¶

High STIR/T2 signal in the interspinous region, disc, and posterior ligaments indicating disruption
Disc space widening
Posterior element edema
Evaluates for spinal cord or cauda equina injury

Radiography¶

Horizontal fracture through the posterior elements visible on lateral view
Widened interspinous distance
The "seat belt" sign on the patient's abdomen should prompt thoracolumbar imaging

Clinical Pearl

Chance fractures are strongly associated with intra-abdominal injuries — the same lap belt mechanism that causes the spinal injury can cause bowel perforation, mesenteric tears, pancreatic injury, and splenic rupture. Up to 50% of patients with Chance fractures have concurrent abdominal injuries. A "seat belt sign" (ecchymosis across the abdomen) should trigger both spinal and abdominal CT evaluation.

Management¶

Purely bony Chance fractures — May be treated conservatively with hyperextension bracing (Jewett or CASH brace) for 8–12 weeks if well-aligned
Ligamentous or mixed injuries — Typically require surgical posterior fixation because ligaments heal unreliably
TLICS scoring is useful: distraction morphology (4 points) plus any PLC disruption (3 points) typically yields a score favoring surgery

Key Points¶

Chance fractures are flexion-distraction injuries, classically from lap belt restraint in motor vehicle collisions
The hallmark is a horizontal fracture line extending through the posterior elements and vertebral body
Purely bony injuries (AO B1) may heal conservatively; ligamentous injuries (AO B2) typically require surgery
Up to 50% of patients have associated intra-abdominal injuries — abdominal CT is mandatory
The thoracolumbar junction is the most common location
MRI is essential for assessing ligamentous versus bony disruption

References¶

Koay J, Davis DD, Hogg JP. Chance Fractures. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023. https://www.ncbi.nlm.nih.gov/books/NBK536926/
Tyroch AH, McGuire EL, McLean SF, et al. The association between Chance fractures and intra-abdominal injuries revisited: a multicenter review. Am Surg. 2005;71(5):434-438. https://pubmed.ncbi.nlm.nih.gov/15986977/
Reid AB, Letts RM, Black GB. Pediatric Chance fractures: association with intra-abdominal injuries and seatbelt use. J Trauma. 1990;30(4):384-391. https://pubmed.ncbi.nlm.nih.gov/2325168/
Mulpuri K, Reilly CW, Perdios A, Tredwell SJ, Blair GK. The spectrum of abdominal injuries associated with chance fractures in pediatric patients. Eur J Pediatr Surg. 2007;17(5):322-327. https://pubmed.ncbi.nlm.nih.gov/17968788/
Huecker MR, Stretanski MF. Seat Belt Injury. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025. https://www.ncbi.nlm.nih.gov/books/NBK470262/
Flanders A. Thoracolumbar injury. The Radiology Assistant. 2009. https://radiologyassistant.nl/neuroradiology/spine/thoracolumbar-injury
Chance fracture. Radiopaedia. https://radiopaedia.org/articles/chance-fracture?lang=us