Differential Diagnosis for Inversion Injury of the Right Ankle

Single Most Likely Diagnosis

• Ankle Sprain: This is the most common injury resulting from an inversion mechanism, leading to stretching or tearing of the lateral ankle ligaments. The presence of tenderness over the lateral aspect and soft tissue swelling over the lateral malleolus supports this diagnosis, despite the absence of a fracture.

Other Likely Diagnoses

• Ligamentous Injury (not necessarily a sprain): In addition to sprains, more severe ligamentous injuries could occur, including partial or complete tears of the lateral ligaments (anterior talofibular, calcaneofibular, or posterior talofibular ligaments).
• Peroneal Tendon Injury: The peroneal tendons run along the lateral aspect of the ankle and can be injured during an inversion mechanism, leading to pain and swelling in this area.
• Anterior Talofibular Ligament (ATFL) Injury: As the most commonly injured ligament in ankle sprains, an isolated ATFL injury could present with similar symptoms and findings.

Do Not Miss Diagnoses

• Osteochondral Defect of the Talus (despite the report): Although the X-ray did not demonstrate a talar dome osteochondral defect, clinical correlation is recommended, suggesting that this possibility should not be entirely ruled out without further evaluation, such as an MRI, especially if symptoms persist.
• Fracture (e.g., Avulsion Fracture): While the X-ray did not show an obvious fracture, minor bony irregularities or avulsion fractures could be missed. These require careful clinical evaluation and possibly additional imaging.
• Syndesmotic Injury: Although less common with a pure inversion mechanism, a syndesmotic injury (involving the ligaments connecting the tibia and fibula) could occur, especially with more severe trauma or in certain patient populations.

Rare Diagnoses

• Talar Fracture (other than osteochondral defect): Fractures of the talus can occur but are less common than other injuries in the context of an inversion mechanism.
• Calcaneal Fracture: While more typically associated with high-energy trauma or falls from a height, a calcaneal fracture could potentially occur with severe inversion injuries.
• Subtalar Dislocation or Instability: These are less common injuries that could result from severe trauma to the ankle, including inversion mechanisms, and might not be immediately apparent on initial X-rays.