Diagnostic imaging of foot and ankle injuries in children

Ankle and tarsal bone injuries

In pediatric ankle trauma, the distal tibia is frequently involved. A characteristic variant is a spiral fracture, classified as a type II injury according to the Salter-Harris system (the fracture extends through the physeal plate and into the metaphysis, sparing the epiphysis).

Tarsal bone fractures have specific features:

• Talus: Fractures of the talar neck require heightened vigilance as they are associated with an extremely high risk of avascular necrosis due to its unique blood supply.
• Cuboid, navicular, and cuneiform bones: Isolated injuries to these structures are relatively rare. When they do occur, they typically appear radiologically as simple avulsion fractures.
• Stress fractures: Pediatric patients actively involved in sports can develop stress (fatigue) fractures, which can occur in literally any tarsal or metatarsal bone.

Differential diagnosis: base of the 5th metatarsal

One of the most common diagnostic pitfalls in pediatric radiology is evaluating the base of the 5th metatarsal. In this area, it is essential to clearly distinguish between normal anatomy and traumatic injury.

For correct image interpretation, keep in mind the relative positions of the structures (diaphysis, metaphysis, epiphysis, and apophysis):

1. Normal apophysis: The shadow of the 5th metatarsal apophysis is always oriented longitudinally. It runs strictly parallel to the long axis (diaphysis) of the metatarsal bone itself.
2. Fracture: A true fracture of the base of the 5th metatarsal has a transverse fracture line relative to the bone axis.

Understanding this spatial difference helps avoid the overdiagnosis of fractures where only a physiological growth zone is present.

Associated high-energy injuries: Cervical spine

Since severe foot trauma often results from motor vehicle accidents (MVAs), part of the polytrauma assessment must include evaluating other areas, primarily the cervical spine.

Although spinal injuries account for less than 10% of all spinal trauma and less than 2% of all pediatric fractures, their clinical significance is immense. The spectrum of injuries ranges from fractures and ligamentous disruptions to direct spinal cord trauma.

Imaging algorithm (NICE, 2016):

• In the absence of neurological deficits, initial diagnosis is performed using standard radiography.
• The choice between CT and radiography is dictated by specific clinical findings.
• In children under 16 with any neurological signs of spinal cord injury, MRI is strictly mandatory.

SCIWORA syndrome and normal anatomical variants

The pediatric spine possesses unique biomechanics: the osteoligamentous complex is significantly more elastic and flexible than the spinal cord it encloses. During forceful flexion-extension forces, SCIWORA (Spinal cord injury without radiographic abnormality) syndrome may develop. In this condition, the bones and ligaments remain intact on radiographs, but the spinal cord sustains critical damage. MRI allows these changes to be detected, although in rare cases, even the scan may appear normal despite pronounced clinical symptoms.

During imaging of the cervical spine, it is important not to mistake trauma for normal variants:

• Pseudosubluxation: Physiological displacement of up to 4 mm, most commonly at the C2/C3 and C3/C4 levels.
• Spinolaminar line: A line along the anterior contours of the spinous processes of C1–C3. Normally, it lies no more than 2 mm from the C2 junction. If C2 is displaced posteriorly by 2 mm or more, this indicates true subluxation or fracture.
• Pseudojefferson fracture: A normal radiographic appearance mimicking trauma on an open-mouth odontoid view.

Class and exam questions

What else to study on this topic

• Salter-Harris classification of pediatric fractures
• Avascular necrosis of the tarsal bones: pathogenesis and radiological presentation
• Mechanisms of avulsion fractures of the tarsal bones
• Algorithms for assessing the spinolaminar line and other radiomorphometric parameters
• Indications for MRI in spinal trauma according to NICE guidelines (2016)

Other Topics in "Pediatric Diagnostic Radiology"

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