**Core Concept**
Inversion injuries to the ankle primarily affect the lateral ligament complex, with the anterior talofibular ligament (ATFL) being the most commonly injured structure due to its location and biomechanical role in stabilizing the ankle during inversion.

**Why the Correct Answer is Right**
The anterior talofibular ligament (ATFL) is the most frequently injured ligament in ankle inversion injuries. It is the most lateral and anterior of the three ligaments in the ankle, running from the fibula to the talus. During inversion, the talus moves posteriorly and laterally, stretching and tearing the ATFL. This ligament bears the majority of the mechanical load during such injuries, making it the most vulnerable. The injury is common in activities involving sudden twisting or stumbling, as in this case.

**Why Each Wrong Option is Incorrect**
Option B: The posterior talofibular ligament (PTFL) is a weaker, more posterior ligament and is rarely injured in inversion trauma. It does not bear the primary load during inversion.
Option C: The calcaneofibular ligament (CFL) is more posterior and medial than the ATFL and is involved in some cases, but it is less commonly injured than the ATFL in inversion.
Option D: The deltoid ligament is medial and is primarily involved in inversion injuries only in rare cases, such as severe trauma, and is not the most likely to be injured in a typical inversion fall.

**Clinical Pearl / High-Yield Fact**
In ankle inversion injuries, the anterior talofibular ligament (ATFL) is the most commonly injured ligament—accounting for over 80% of cases. This makes it the cornerstone of clinical assessment and imaging in such injuries.

✓ Correct Answer: A. A