Syndesmotic (High Ankle) Sprain
Based on the clinical presentation—positive squeeze test, positive external rotation stress test, anterior upper ankle tenderness, and pain with fibular compression—this patient most likely has a syndesmotic injury (high ankle sprain).
Clinical Reasoning
The constellation of findings strongly points to syndesmotic disruption rather than a typical lateral ankle sprain:
Key Diagnostic Features Present:
- Positive squeeze test: Squeezing the fibula and tibia below the knee causes pain in the superior ankle—this is highly specific (88% specificity) for syndesmotic injury 1
- Positive external rotation stress test: This test has the fewest false-positive results among syndesmotic tests and demonstrates good reliability 2
- Anterior upper ankle tenderness: Tenderness over the anterior aspect of the syndesmosis is a hallmark finding 3
- Absence of malleolar/lateral ligament tenderness: No tenderness of the medial malleolus, lateral malleolus, or typical lateral ligament structures argues against a standard lateral ankle sprain
Why Not a Lateral Ankle Sprain:
The negative findings are crucial here. In typical lateral ankle sprains, you would expect:
- Tenderness over the anterior talofibular ligament (ATFL) or lateral malleolus
- Positive anterior drawer or talar tilt tests (though pain may limit these)
- The absence of these findings, combined with the positive syndesmotic tests, shifts the diagnosis away from lateral ligament injury
Diagnostic Accuracy Considerations
Important caveat: While the squeeze test is highly specific (88%), its sensitivity is only 30% 4. The external rotation stress test has 20% sensitivity but 84.8% specificity 4. This means:
- A positive test strongly suggests syndesmotic injury (high specificity)
- A negative test does NOT rule it out (low sensitivity)
- No single clinical test is sufficiently accurate in isolation 5
The combination of multiple positive tests increases diagnostic confidence. Research shows that syndesmotic injury is 4 times more likely when both syndesmosis ligament tenderness AND a positive external rotation stress test are present 1.
Next Steps
Per ACR guidelines, MRI ankle without IV contrast is the most appropriate next imaging study 6. The guidelines specifically state that for acute trauma with radiographs negative for osseous injury but physical examination demonstrating alignment abnormality suggesting syndesmotic/ligamentous injury, MRI is usually appropriate 6.
MRI has:
- 100% reported accuracy for tibiofibular ligament tears 7
- Superior soft-tissue evaluation compared to CT 6
- Ability to detect syndesmotic injury even when radiographs appear normal 6
Clinical pearl: Syndesmotic injuries are often missed on initial evaluation. They account for approximately 18% of ankle sprains but can occur even in Grade I sprains 4. The injury may not be apparent on plain radiographs, making advanced imaging essential when clinical suspicion is high 3.
Why This Matters for Outcomes
Undiagnosed syndesmotic injuries lead to:
- Chronic ankle instability
- Prolonged recovery times
- Potential need for surgical intervention if instability persists
- Adverse long-term outcomes if the normal tibiofibular relationship is not restored 3
The key is that failure to diagnose and stabilize syndesmotic disruption adversely affects outcome 3, making accurate early diagnosis critical for preventing chronic morbidity and optimizing quality of life.