How do I differentiate between a fracture and an ankle sprain?

How to Rule Out Broken Bones vs Ankle Sprain

Use the Ottawa Ankle Rules to determine if X-rays are needed—order radiographs only if the patient cannot bear weight immediately after injury, cannot take 4 steps in the emergency department, or has point tenderness over specific bony landmarks (medial malleolus, posterior edge or inferior tip of lateral malleolus, talus, or calcaneus). 1

Clinical Decision Algorithm for Fracture vs Sprain

Step 1: Apply Ottawa Ankle Rules Systematically

The Ottawa Ankle Rules have excellent sensitivity (92-100%) for detecting fractures, meaning they reliably rule out fractures when negative. 1, 2 Order ankle X-rays if any of the following criteria are met:

• Inability to bear weight immediately after injury or in the emergency department 1, 2
• Point tenderness over the medial malleolus 1
• Point tenderness over the posterior edge or inferior tip of the lateral malleolus 1
• Point tenderness over the talus 1
• Point tenderness over the calcaneus 1
• Point tenderness at the base of the fifth metatarsal 2
• Point tenderness over the navicular bone 2

The Ottawa Ankle Rules correctly ruled out fracture without radiography in 299 out of 300 patients (99.7% accuracy). 3

Step 2: Recognize Exclusionary Criteria That Override the Rules

Always obtain radiographs regardless of Ottawa Ankle Rules if the patient has: 1

• Peripheral neuropathy (including diabetic neuropathy) 1
• Inability to cooperate with examination 1
• Intoxication preventing reliable assessment 1
• High-energy trauma or polytrauma 1
• Medial tenderness, bruising, or swelling suggesting increased fracture risk 1

Step 3: Order Appropriate Imaging When Indicated

When X-rays are warranted, order a standard three-view ankle series (anteroposterior, lateral, and mortise views). 1 Weight-bearing radiographs are preferred when possible, as they provide critical information about fracture stability, particularly for malleolar fractures. 3, 1

Common pitfall to avoid: Do not routinely order foot or knee radiographs with ankle inversion injuries—the yield is extremely low. 3, 1

Step 4: Assess for Ligament Injury When Fracture is Ruled Out

If radiographs are negative or not indicated by Ottawa Ankle Rules, the injury is likely a ligament sprain. However, physical examination in the first 48 hours cannot reliably distinguish between simple distortion and complete ligament rupture due to excessive swelling and pain. 2

Re-examine the patient 4-5 days post-injury when the anterior drawer test has optimized sensitivity (84%) and specificity (96%). 3, 2 The combination of four findings indicates likely lateral ligament rupture: 3, 2

• Hematoma present
• Pain on palpation around distal fibula
• Positive anterior drawer test
• Significant swelling

Step 5: Consider Advanced Imaging for Persistent Symptoms

If pain persists 1-3 weeks after negative radiographs, order MRI without contrast (most sensitive for occult fractures and bone marrow edema) or CT without contrast (excellent for detecting subtle cortical fractures). 1

Reserve MRI for specific clinical scenarios: 2

• Suspected high-grade ligament injuries
• Osteochondral defects
• Syndesmotic injuries
• Occult fractures
• Persistent symptoms after initial treatment period

Key Clinical Distinctions

Fracture Red Flags

• Inability to bear weight immediately after injury 1, 2
• Bony point tenderness over specific landmarks 1
• High level of pain, rapid onset of swelling 3
• Coldness or numbness in the injured foot 3

Sprain Characteristics

• Typical inversion injury in plantar-flexed position 3
• Most commonly affects anterior talofibular ligament 4
• Can bear weight (though painful) 1
• Tenderness over ligaments rather than bone 3

Special Considerations

Snowboarder's fracture warning: Lateral talar process fractures are overlooked on routine radiographs 40-50% of the time and may be misdiagnosed as lateral ankle sprains. 3 Consider X-rays even with borderline Ottawa Ankle Rules findings if there is swelling inferior to the lateral malleolus in snowboarders. 1

Pediatric patients: Recent evidence shows that in children and adolescents, ATFL sprains and osteochondral avulsions are more common than previously thought, challenging the traditional assumption that most lateral ankle injuries in this population are Salter-Harris type I fractures. 5