How do I determine if a pediatric patient's Salter-Harris type 2 (fracture of the growth plate) fracture of the thumb is displaced?

Determining Displacement in Pediatric Salter-Harris Type 2 Thumb Fractures

Obtain a standard three-view radiographic examination (PA, lateral, and oblique) of the thumb to assess for displacement, as this is the initial imaging modality recommended by the American College of Radiology for all suspected thumb fractures. 1, 2

Radiographic Assessment of Displacement

Initial Imaging Protocol

• Order "hand" or "thumb" radiographs specifically (not "finger") to ensure complete first ray coverage including the carpometacarpal joint 1
• Three views are mandatory: posteroanterior, true lateral, and oblique projections, as two views alone are inadequate for detecting thumb fractures 1, 2
• Standard radiographs detect most fractures, dislocations, and bony avulsions in pediatric patients 1

Defining Displacement on Radiographs

Measure the displacement in millimeters on the radiographs, as specific thresholds guide treatment decisions:

• <2 mm displacement: Generally considered minimally displaced and can be managed with casting 3
• 2-4 mm displacement: Intermediate zone where treatment decisions vary based on clinical factors 3, 4
• >3-4 mm displacement: Typically requires closed or open reduction 3, 4

Additional Radiographic Findings to Assess

• Articular step-off >2 mm indicates operative management 1
• Rotational deformity: Even 5 degrees of angulation can cause evident rotational deformity that should be assessed clinically and confirmed radiographically 5
• Metaphyseal fragment position: In Salter-Harris type 2 fractures, assess the Thurston-Holland fragment for displacement 6, 5

When Initial Radiographs Are Equivocal

Advanced Imaging Indications

If clinical suspicion remains high despite negative or equivocal radiographs, proceed directly to MRI without IV contrast rather than casting and waiting 10-14 days 1:

• MRI has 100% sensitivity for detecting occult fractures with bone marrow edema patterns 7, 2
• MRI is particularly useful for assessing ligamentous injuries and Salter-Harris type 1 fractures that may not be visible on plain films 7, 2

CT Considerations

• CT is rarely indicated for acute thumb Salter-Harris fractures but may be useful for complex intra-articular fractures requiring surgical planning 2
• CT has increased sensitivity for detecting nondisplaced fractures compared to conventional radiography 7

Clinical Assessment Complements Imaging

Physical Examination Findings

• Assess for rotational deformity clinically: Have the child make a fist and observe whether all fingernails align in the same plane 5
• Focal bony tenderness over the growth plate suggests fracture even if radiographs appear normal 2
• Visible deformity or significant mechanism of injury warrants immediate imaging 2

Common Pitfalls to Avoid

• Do not rely on two-view radiographs alone, as this misses a significant proportion of thumb fractures 1, 2
• Do not delay advanced imaging in equivocal cases, as this can lead to functional impairment and missed diagnoses 1
• Do not assume all growth plate injuries are visible on initial radiographs: 41% of toddler's fractures show evidence only on follow-up films 7
• Watch for open fractures: Salter-Harris type 2 fractures of the thumb can present as open fractures with nailbed injuries (Seymour fractures) requiring urgent management 6