When is ankle imaging, such as X-rays (X-radiation) or Magnetic Resonance Imaging (MRI), necessary for ankle symptoms?

When to Get Ankle Imaging

Ankle imaging should be guided by the Ottawa Ankle Rules (OAR), with radiographs indicated for patients who cannot bear weight immediately after injury, have point tenderness over the malleoli/talus/calcaneus, or cannot walk four steps, while MRI should be used when radiographs are negative but clinical suspicion remains high. 1

Initial Radiographic Imaging

Ottawa Ankle Rules

• Radiographs are indicated as the initial imaging study when a patient meets any of the following Ottawa Ankle Rules criteria 1:

  • Inability to bear weight immediately after injury
  • Point tenderness over the medial malleolus, posterior edge or inferior tip of lateral malleolus, talus, or calcaneus
  • Inability to walk four steps in the emergency department

• The OAR have 92-99% sensitivity and 25-46% specificity for detecting ankle fractures 1

When Radiographs Are Not Indicated

• Imaging is usually not appropriate for patients who can walk and have no point tenderness over the malleoli, talus, or calcaneus 1
• Physical examination alone can eliminate the need for up to 50% of ankle radiographs in acute trauma 2

Standard Radiographic Protocol

• Three standard views should be included 1:
  • Anteroposterior view
  • Lateral view
  • Mortise view (to include the base of the fifth metatarsal bone)

Advanced Imaging

When to Order MRI

• MRI without IV contrast is indicated when 1, 3:

  • 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
  • Radiographs demonstrate potential osteochondral injury

• MRI is superior for detecting 1, 3:

  • Bone marrow edema indicating stress reaction or occult fracture
  • Subtle cortical disruptions not visible on radiographs
  • Associated ligamentous and tendon injuries

When to Order CT

• CT without IV contrast is indicated when 1:
  • Radiographs demonstrate a fracture and further evaluation of extent, displacement, comminution, or intra-articular extension is needed
  • Complex injuries such as subtalar, calcaneal, and talar fractures require preoperative planning
  • Polytrauma or complex comminuted injuries require multiplanar imaging

Ligament Injuries

• For suspected ligament injuries, clinical assessment using the anterior drawer test is optimized if delayed for 4-5 days post-injury (84% sensitivity, 96% specificity) 1
• MRI is indicated for suspected high-grade ligament injuries, osteochondral defects, syndesmotic injuries, and occult fractures (93-96% sensitivity, 100% specificity) 1

Special Considerations

Patients with Exclusionary Criteria

• For patients with neurologic disorders, peripheral neuropathy, or other conditions where OAR cannot be applied, radiographs should be the initial imaging study 1
• These patients may have no pain or point tenderness despite fracture due to poor pain proprioception 1

Timing of Imaging

• Avoid manipulation of the ankle prior to radiographs in the absence of neurovascular deficit or critical skin injury 4
• Manipulating ankle injuries before obtaining radiographs significantly increases the risk of requiring re-manipulation (44% vs 18%) 4

Common Pitfalls to Avoid

• Do not rely solely on radiographs when clinical suspicion for fracture remains high but initial radiographs are negative 3
• Hairline fractures may be radiographically occult in up to 50% of cases, particularly those involving the lateral talar process 3
• 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 3