When you fall directly onto your ankle, what type of injury is most likely?

Ankle Inversion Injury: Most Common Injury Type

When you fall onto your ankle, you most commonly sustain a lateral ankle sprain affecting the anterior talofibular ligament (ATFL), which accounts for 25% of all musculoskeletal injuries and 50% of sports-related injuries. 1, 2

Mechanism of Injury

The typical injury occurs through forced plantar flexion and inversion (supination) of the ankle as your body's center of gravity rolls over the ankle joint. 3 This explosive inversion motion happens at the subtalar joint and tears the ATFL because it possesses the lowest ultimate load among the lateral ligaments. 4

Specific Ligament Injury Pattern

• The ATFL is injured first and most frequently in approximately 80% of lateral ankle sprains. 2, 3
• The calcaneofibular ligament (CFL) is the second most commonly injured, often in combination with ATFL tears. 3, 5
• The posterior talofibular ligament (PTFL) is rarely injured except in severe trauma. 3
• Complete ruptures of all three lateral ligaments (luxatio pedis supinatoria) are extremely rare. 5

Beyond Simple Ligament Sprains

A critical pitfall is assuming ankle sprains only involve lateral ligament injury. 6 Falls onto the ankle can also cause:

• Osteochondral lesions of the talus (cartilage and bone damage beneath the joint surface). 1, 6
• Anterior or posterior ankle impingement (soft tissue or bone pinching). 6
• Subtalar and transverse tarsal joint injuries that coexist with ankle ligament damage. 6
• Occult fractures including lateral process of talus ("snowboarder's fracture"), fifth metatarsal base, or malleolar fractures. 1
• Syndesmotic injuries (high ankle sprains), though these typically occur with different mechanisms (dorsiflexion-eversion-external rotation) rather than simple inversion falls. 1, 2

Clinical Grading

Lateral ankle sprains are classified into three grades of increasing severity:

• Grade I: Mild sprain with microscopic ligament damage. 1
• Grade II: Moderate sprain with partial ligament tears. 1
• Grade III: Severe sprain with complete ligament rupture. 1

Diagnostic Approach

When point tenderness exists over the malleoli, inability to bear weight immediately after injury occurs, or the patient cannot walk four steps, radiographs are required per Ottawa Ankle Rules to exclude fracture. 1 However, delayed physical examination at 4-5 days post-injury provides optimal sensitivity (84%) and specificity (96%) for detecting complete ATFL rupture using the anterior drawer test, as acute swelling obscures early clinical assessment. 1, 7