A patient presents with an acute inversion ankle sprain. Which ligament is most likely to be injured?

An acute inversion ankle sprain typically occurs when the foot rolls inward, which places stress on the lateral ligaments of the ankle. The calcaneofibular ligament is one of the key ligaments located on the lateral side of the ankle and is particularly susceptible to injury during this type of motion. When the inversion occurs, the calcaneofibular ligament is under tension and can be overstretched or torn, leading to pain and instability.

Understanding the anatomy of the ankle helps clarify why the calcaneofibular ligament is the most likely injury in this scenario. The long plantar ligament, tibionavicular ligament, and tibiocalcaneal ligament are located more medially or posteriorly and are less likely to be affected during an inversion injury, which primarily stresses the lateral structures.

In summary, the calcaneofibular ligament's position and function make it the most commonly injured ligament in acute inversion ankle sprains, rendering it the correct choice in this scenario.