When to X-ray an Ankle After Injury
X-ray an ankle after injury when the Ottawa Ankle Rules criteria are met: 1) inability to bear weight immediately after injury, 2) point tenderness over the medial malleolus, posterior edge or inferior tip of the lateral malleolus, talus, or calcaneus, or 3) inability to ambulate for 4 steps in the emergency department. 1
Ottawa Ankle Rules (OAR) - The Gold Standard
The Ottawa Ankle Rules have been extensively validated and are the most accurate clinical decision rules for determining when ankle x-rays are necessary after trauma. They demonstrate:
- Sensitivity: 92-100% (extremely reliable at ruling out fractures)
- Specificity: 16-51% (moderately effective at identifying true positives) 1
Key Components of the Ottawa Ankle Rules:
For ankle zone assessment, x-ray is required if:
- Pain in the malleolar region AND
- Either:
- Bone tenderness at the posterior edge or tip of either malleolus
- Inability to bear weight both immediately after injury AND in the emergency department
For midfoot zone assessment, x-ray is required if:
- Pain in the midfoot region AND
- Either:
- Bone tenderness at the navicular bone or base of 5th metatarsal
- Inability to bear weight both immediately after injury AND in the emergency department 1
Special Considerations
When to Bypass the OAR and Order X-rays Directly:
- Patients with neurologic disorders or peripheral neuropathy
- Children under 5 years of age (OAR validated only for ages 5 and older)
- Multiple trauma patients
- Altered mental status
- Injuries >1-3 weeks old with persistent pain 1
Follow-up Imaging:
If initial x-rays are negative but pain persists for more than 1 week but less than 3 weeks:
- MRI without IV contrast OR
- CT without IV contrast 1
These advanced imaging options are particularly important for detecting:
- Occult fractures
- Osteochondral injuries
- Ligamentous tears
- Syndesmotic injuries 2
Benefits of Implementing the OAR
Proper implementation of the OAR can:
- Reduce unnecessary radiographs by 25-36% 3, 4
- Decrease emergency department wait times by up to 20 minutes 1
- Maintain 100% sensitivity for clinically significant fractures 5
- Reduce healthcare costs 3
Pitfalls to Avoid
- Don't rely solely on ability to bear weight: Some patients with fractures can still walk
- Don't miss posterior malleolar fractures: Consider a 50° external rotation lateral view if there is posterior ankle pain following forced plantar flexion 6
- Don't skip palpation of all required areas: Ensure complete assessment of all bony landmarks specified in the OAR
- Don't apply OAR to patients with altered sensation: Patients with neuropathy or neurologic disorders require direct imaging 1
The Ottawa Ankle Rules represent the most evidence-based approach to determining the need for ankle radiography after injury, with multiple validation studies confirming their effectiveness in reducing unnecessary imaging while maintaining excellent sensitivity for detecting clinically significant fractures.