USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What is the most common cause of ankle sprain due to inversion of a plantar-flexed foot?

1. Anterior Talofibular Ligament damage

2. Presence of ecchymosis at the anterolateral aspect of the ankle

3. Medial collateral ligament tear

4. Rupture of the Achilles tendon

The correct answer is: Anterior Talofibular Ligament damage

The most common cause of an ankle sprain resulting from inversion of a plantar-flexed foot is damage to the anterior talofibular ligament. When the foot is in a plantar-flexed position and subjected to an inversion force, the lateral ankle ligaments, particularly the anterior talofibular ligament, are placed under excessive stress. This ligament is the most commonly injured structure in acute ankle sprains due to its anatomical location and role in stabilizing the ankle during such movements. During inversion, the foot rolls inward, and if the force is significant, it can lead to microtears or complete tears of the anterior talofibular ligament. This type of injury is prevalent in sports and activities involving quick changes in direction or jumping, leading to a rapid pivoting motion of the ankle. While the presence of ecchymosis may indicate injury, it does not specify the exact ligament involved and is more of a clinical finding than a cause. A medial collateral ligament tear, often associated with eversion injuries, does not relate to inversion sprains. Lastly, rupture of the Achilles tendon typically involves a different mechanism, primarily affecting the posterior leg and not specifically characterized by ankle inversion. Thus, the primary injury seen in this scenario is indeed damage to