What type of Magnetic Resonance Imaging (MRI) should be ordered for a hairline fracture to the right ankle?

MRI for Hairline Fracture of the Right Ankle

For a suspected hairline fracture of the right ankle, standard radiographs should be ordered first, and if negative with persistent symptoms, an MRI without contrast is the most appropriate follow-up imaging study.

Initial Imaging Approach

• Radiographs (X-rays) should be the first imaging study ordered for suspected ankle fractures, including hairline fractures 1
• Standard ankle radiograph protocol includes three views: anteroposterior, lateral, and mortise views 1
• The Ottawa Ankle Rules should guide the decision to obtain initial radiographs based on:
  • Inability to bear weight immediately after injury
  • Point tenderness over the malleoli, talus, or calcaneus
  • Inability to walk four steps 1

When to Order MRI

• MRI should be ordered when:
  • Initial radiographs are negative but clinical suspicion for fracture remains high
  • Patient has persistent ankle pain for more than 1 week after injury despite negative radiographs 1
• MRI without IV contrast is the most sensitive imaging modality for detecting occult fractures with associated bone marrow edema patterns 1

Type of MRI to Order

• Order an MRI of the ankle without intravenous contrast 1
• This protocol is most sensitive for detecting:
  • Occult fractures not visible on radiographs
  • Bone marrow edema patterns associated with stress injuries
  • Associated soft tissue injuries that may accompany the fracture 1, 2

Benefits of MRI for Hairline Fractures

• MRI provides superior visualization of:
  • Bone marrow edema indicating stress reaction or occult fracture
  • Subtle cortical disruptions not visible on radiographs
  • Associated ligamentous and tendon injuries that may accompany the fracture 2, 3
• MRI has higher sensitivity than CT for detecting bone marrow abnormalities associated with occult fractures 1

Clinical Considerations

• Hairline fractures may be radiographically occult in up to 50% of cases, particularly those involving the lateral talar process 1
• Early detection of hairline fractures is critical for proper treatment planning and to prevent progression to complete fractures or chronic pain 1, 4
• MRI can help distinguish between a simple ankle sprain and an occult fracture, which have different treatment approaches 2, 3

Common Pitfalls to Avoid

• Do not rely solely on radiographs when clinical suspicion for fracture is high but initial radiographs are negative 1
• Do not delay appropriate imaging in patients with persistent symptoms, as early detection of hairline fractures leads to better outcomes 1, 4
• Avoid ordering CT as the next study after negative radiographs when suspecting a hairline fracture, as MRI is more sensitive for detecting bone marrow abnormalities 1