What defines an ankle sprain?

Definition of an Ankle Sprain

An ankle sprain is defined as an injury to one or more ligaments in the ankle, typically occurring when the ankle is forced into an abnormal position, most commonly through an inversion injury in the plantar-flexed position. 1

Types and Grading of Ankle Sprains

• The most common type is a lateral ankle inversion sprain, which accounts for the majority of ankle sprains 1
• Ankle sprains can be classified into three grades based on severity:
  • Grade I: Mild stretching of the ligament without macroscopic tearing, minimal swelling and tenderness, no joint instability
  • Grade II: Partial tearing of the ligament, moderate pain, swelling and tenderness, mild to moderate joint instability
  • Grade III: Complete rupture of the ligament, severe swelling and pain, significant joint instability 1

Anatomical Considerations

• The most commonly injured ligaments are the lateral stabilizing ligaments:
  • Anterior talofibular ligament (ATFL) - most frequently injured
  • Calcaneofibular ligament (CFL)
  • Posterior talofibular ligament (PTFL) 1, 2
• High ankle (syndesmotic) sprains involve injury to the posterior and anterior tibiofibular ligaments, occurring through dorsiflexion and eversion of the ankle with internal rotation of the tibia 1

Mechanism of Injury

• Lateral ankle sprains typically occur through:
  • Forced plantar flexion and inversion of the ankle
  • Incorrect foot positioning at landing with a medially-deviated vertical ground reaction force
  • Explosive supination or inversion moment at the subtalar joint occurring in a very short time (approximately 50 ms) 1, 3
• Delayed reaction time of the peroneal muscles (60-90 ms) contributes to the inability to prevent the sprain 3

Clinical Presentation

• Key physical examination findings associated with more severe (grade III) sprains include:
  • Significant swelling
  • Hematoma formation
  • Pain on palpation
  • Positive anterior drawer test 1
• The presence of all four findings above has been associated with a 96% likelihood of lateral ligament rupture 1
• The anterior drawer test detects excessive anterior displacement of the talus onto the tibia, indicating a torn anterior talofibular ligament 1
• A crossed-leg test can detect a high ankle sprain, indicated by pain in the syndesmosis area when pressure is applied to the medial side of the knee 1

Diagnostic Considerations

• Diagnosis is primarily clinical, based on history and physical examination 1
• The Ottawa Ankle and Foot Rules can help determine the need for radiography, with high sensitivity (99.7%) for ruling out fractures 1
• Reexamination 3-5 days after injury, when pain and swelling have improved, is important to distinguish partial tears from complete ligament ruptures 1

Common Pitfalls in Diagnosis

• Excessive reliance on imaging when not indicated by Ottawa Rules 4
• Failure to recognize high ankle (syndesmotic) sprains, which require different management 1
• Not considering the possibility of associated injuries, such as osteochondral lesions or peroneal tendon injuries 4
• Inadequate follow-up assessment after initial swelling has subsided, which is crucial for accurate grading 1

Understanding the definition and characteristics of ankle sprains is essential for proper management and prevention of chronic instability, which affects approximately 20% of patients with acute ankle sprains 2.