What is the most common mechanism of an ankle syndesmosis injury?

The most common mechanism of an ankle syndesmosis injury is external rotation. This type of injury typically occurs when the foot is planted and the body rotates, causing a shearing force at the syndesmosis, which is the fibrous joint connecting the two bones of the lower leg—the tibia and fibula. This mechanism can result in a torn ligament at the syndesmosis, leading to instability and pain in the ankle.

Ankle eversion typically affects the ligaments on the lateral aspect of the ankle and is more associated with sprains than syndesmosis injuries. Ankle inversion, similarly, also primarily impacts the lateral ligaments and tends to lead to more common ankle sprains. Direct impact can cause various ankle injuries but does not specifically target the syndesmosis as the primary injury mechanism.

Therefore, understanding that external rotation creates a specific type of stress on the ankle's interosseous ligament effectively distinguishes it from the other options.