High Ankle Sprain vs. ATFL Avulsion: Critical Distinction
No, a high ankle sprain (syndesmotic injury) does NOT involve the anterior talofibular ligament (ATFL)—these are anatomically and mechanically distinct injuries that should never be confused. 1, 2
Anatomical and Mechanical Differences
High ankle sprains and lateral ankle sprains are completely separate entities:
High ankle sprains involve the syndesmotic ligaments (anterior tibiofibular ligament, posterior tibiofibular ligament, transverse ligament, and interosseous ligament) located between the distal tibia and fibula, proximal to the ankle joint 2, 3
Lateral ankle sprains involve the ATFL, which connects the talus to the fibula and is the most commonly injured ligament in ankle hyperinversion injuries 1, 4
The American College of Radiology explicitly warns against confusing these two injury patterns—lateral ankle sprains result from inversion mechanisms, while high ankle sprains result from dorsiflexion-eversion-external rotation forces 1
Your Specific Clinical Scenario
An ATFL injury with a small avulsion fragment off the fibula represents a lateral ankle sprain, NOT a high ankle sprain:
The avulsion fragment indicates the ATFL and calcaneofibular ligament (CFL) have torn with a piece of bone attached 5
These avulsion fragments typically measure 4-9 mm in width and 4-7 mm in length, with both the ATFL and CFL attached to the fragment 5
This injury pattern results from inversion stress and represents the severe end of the lateral ligament injury spectrum 5
Critical Clinical Implications
The distinction matters enormously for treatment and prognosis:
Lateral ligament avulsion fractures (your scenario) require primary screw fixation of the fragment to the fibula to prevent chronic instability, as motion between the fragment and fibula prevents spontaneous healing 5
Syndesmotic injuries require entirely different management focused on restoring tibiofibular relationship and may need syndesmotic screw fixation or suture-button devices 2
Untreated syndesmotic injuries lead to widening of the ankle mortise—just 1 mm of widening decreases tibiotalar contact area by 42%, leading to early osteoarthritis 3
Diagnostic Approach
MRI is the reference standard for definitively distinguishing these injuries:
MRI accurately identifies ATFL tears with 77-92% diagnostic accuracy and can visualize the avulsion fragment with surrounding bone marrow edema 1, 4
MRI is also the gold standard for grading syndesmotic ligament injuries (grades 1-3), which is critical for treatment planning 4, 6
The American College of Radiology notes that 15% of syndesmotic ligament injuries show no fracture on radiography, making MRI essential when clinical suspicion is high 4
Common Pitfall to Avoid
Do not assume all fibular avulsion fractures represent syndesmotic injury:
Avulsion fractures at the distal fibula tip where the ATFL attaches are lateral ligament injuries requiring fragment fixation 5
Syndesmotic avulsion fractures occur more proximally at the anterior or posterior tibiofibular ligament attachments 3
Clinical examination has limited value in differentiating acute ATFL rupture from syndesmotic injury—imaging is mandatory when either is suspected 7