Chance fracture

Pure bony Chance fracture

In a classic pure bony Chance fracture, the injury line passes strictly through the bone structures at a single level: the vertebral body, pedicles (pedicles), and spinous process. The posterior ligamentous complex remains completely intact.

The prognosis for this injury variant is considered favorable because bone tissue has a better healing potential compared to ligaments. Nevertheless, patients typically require surgical spinal fixation to stabilize the segment.

There is an important variant where the fracture line shifts and passes through the pars interarticularis. In this case, the posterior ligaments of an adjacent (usually superior) level, such as the interspinous ligament, may be involved. Detecting this nuance on tomograms is critical, as it directly determines the required scope and extent of surgical fixation.

Soft-tissue Chance injury

A soft-tissue Chance injury is a flexion-distraction trauma where the posterior bony structures remain intact, but a rupture of the posterior ligaments occurs.

Diagnosing this condition presents major challenges. On standard radiographs or baseline CT, this injury can easily be confused with a simple flexion-compression fracture, in which the ligaments are spared.

Biomechanics and diagnostic features:

• The degree of bony compression of the vertebral body is usually minimal. This is because flexion occurs around an anteriorly displaced fulcrum.
• In elderly patients with osteoporosis, compression can occur with minimal physical effort, whereas in young patients, such trauma always indicates significant force.
• The main diagnostic sign is the presence of a kyphotic spinal deformity. In the soft-tissue Chance variant, the kyphosis angle is disproportionately large (much greater) than would be expected given such a minor degree of vertebral compression.

Imaging of ligamentous injuries

Cross-sectional imaging methods are used to assess the integrity of the ligamentous apparatus.

1. MRI. Traditionally remains the most accurate and sensitive method for direct visualization of ligamentous ruptures, such as the interspinous ligaments or ligamentum flavum. On T2-weighted images, the rupture is often accompanied by a hyperintense (bright) signal in the injured area.
2. MSCT (Multislice CT). Allows for both indirect and direct evaluation of posterior ligamentous structures. The natural contrast here is the epidural adipose tissue adjacent to the ligamentum flavum. An intact ligament always has a smooth contour. If the contour is irregular, it is a direct indication of a rupture.

Of particular importance is the dirty fat sign. It occurs when ligament rupture leads to hemorrhage into the surrounding epidural fat, causing the fat to lose its normal low (dark) attenuation on CT scans.

Differential diagnosis: Burst fractures

It is crucial to distinguish Chance fractures from burst fractures, as treatment strategies differ. Burst fractures occur under the action of an axial compressive force, for example, from a fall from a height (often associated with bilateral calcaneal fractures) or when force is applied to the vertex of the head.

The vertebral body, pedicles, and posterior elements form a single bony ring. In a burst mechanism, the body fracture is often accompanied by the destruction of posterior elements.

Key radiographic differences:

• On anteroposterior (AP) views, widening of the interpedicular distance is visualized.
• On the lateral view, the main distinguishing feature is determined—loss of height of the posterior wall of the vertebral body (flattening of both the anterior and posterior walls occurs).

The preservation and normal height of the posterior wall of the vertebral body in Chance fractures fundamentally distinguishes them from burst injuries.

Class and exam questions

What else to study on this topic

• Biomechanics of the fulcrum effect in seatbelt trauma
• Anatomy and CT Imaging of the Ligamentum Flavum
• Pathogenesis of cervical spine burst fractures
• Associated trauma: the link between spinal and calcaneal fractures in falls
• MRI protocols for assessing the ligament apparatus (T2 and STIR sequences)

Other topics in the "Spine" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.