What imaging is needed for a deep tissue injury to the ankle?

Imaging for Deep Tissue Injury to the Ankle

For deep tissue injury to the ankle, radiography with three standard views (anteroposterior, lateral, and mortise) is the appropriate initial imaging study when fracture is suspected based on Ottawa Ankle Rules criteria. 1

Ottawa Ankle Rules Assessment

The decision to obtain imaging should be guided by the Ottawa Ankle Rules (OAR), which have 92-99% sensitivity for detecting ankle fractures 1:

• Obtain radiographs if ANY of the following are present:

  • Inability to bear weight immediately after injury
  • Point tenderness over the medial malleolus
  • Point tenderness over the posterior edge or inferior tip of lateral malleolus
  • Point tenderness over the talus or calcaneus
  • Inability to walk 4 steps in the emergency department

• No imaging is needed if:

  • Patient can bear weight
  • No point tenderness over the malleoli, talus, or calcaneus
  • Patient can walk 4 steps

Standard Radiographic Protocol

When indicated by positive OAR findings:

1. Three standard views should be obtained 1:

   • Anteroposterior (AP)
   • Lateral
   • Mortise views (AP with 15-20° internal rotation)
   • Include the base of the fifth metatarsal bone distal to the tuberosity

2. Weight-bearing radiographs are preferred when possible, especially with fractures of uncertain stability 1

   • A medial clear space <4 mm confirms stability
   • Increased instability is associated with:
     • Medial tenderness, bruising, or swelling
     • Fibular fracture above the syndesmosis
     • Bi- or trimalleolar fractures
     • Open fracture
     • High-energy injury

Advanced Imaging Considerations

When radiographs are negative but clinical suspicion remains high:

1. CT Imaging 1, 2:

   • Indicated for:
     • Complex injuries
     • Posterior malleolar fractures
     • Posterior pilon variant fractures
     • Preoperative planning
     • High-energy trauma or polytrauma patients
   • Particularly useful in patients with diabetes or neuropathy
   • MDCT has superior sensitivity compared to radiography for calcaneal (87%), talar (78%), and midfoot fractures (25-33%) 2

2. MRI Imaging 1, 3:

   • Indicated when:
     • Radiographs are negative but clinical suspicion of fracture remains high
     • Suspicion for ligamentous tears in inversion injuries
     • Occult injuries are suspected

3. Special Views for specific clinical scenarios 1:

   • Broden view: For lateral process fracture of the talus ("snowboarder's fracture")
   • Anterior talofibular ligament view: For distal fibular avulsion fractures
   • Gravity stress view: For supination-external rotation injuries with suspected deltoid ligament disruption

Common Pitfalls and Caveats

1. Avoid manipulation of the ankle prior to radiographs (unless neurovascular deficit or critical skin injury) 1

2. Do not routinely order foot or knee radiographs with ankle radiographs for inversion injuries (low yield) 1

3. Beware of missed fractures in:

   • Snowboarder's fractures (lateral talar process) - overlooked in 40-50% of routine radiographs 1
   • Posterior malleolar fractures - more common in older females and diabetic patients 1

4. Consider patient factors that may require different imaging approaches:

   • Patients with diabetic neuropathy or neurologic compromise may have fractures despite no pain, point tenderness, or walking difficulty 1
   • Children under 5 years of age require different assessment (OAR not validated) 1

5. Medial clear space >4mm correlates with disruption of both deltoid and tibiofibular ligaments 4

By following these evidence-based guidelines, appropriate imaging can be obtained to accurately diagnose deep tissue injuries to the ankle while minimizing unnecessary radiation exposure and healthcare costs.