**Question:** A 22-year-old football player is admitted to the hospital with pain and swelling over the lateral aspect of the ankle. The emergency department doctor diagnosed an inversion sprain. Which ligament was most likely injured?

**Core Concept:** Inversion ankle sprain is a common sports injury where the ankle rolls inward, causing stretching or tearing of the ligaments on the outer side of the ankle. In this case, the main affected ligament is the **Anterior Talofibular Ligament (ATFL)**, one of the three primary ligaments in the ankle joint.

**Why the Correct Answer is Right:** The ATFL is primarily responsible for stabilizing the ankle joint during inversion movements. When this ligament gets stretched or torn, it leads to the characteristic symptoms of pain, swelling, and instability in the lateral aspect of the ankle. Inversion sprains are common in sports like football where the foot is planted and the ankle is forced inward, putting excessive strain on the ankle ligaments.

**Why Each Wrong Option is Incorrect:**

A. Lateral Collateral Ligament (LCL): This ligament is involved in stabilizing the ankle joint during eversion (ankle turning outward) and is not directly affected in an inversion sprain.

B. Posterior Talofibular Ligament (PTL): The PTL is involved in stabilizing the ankle joint during eversion, just like the LCL. Both ligaments are not the primary target in an inversion sprain.

C. Ankle Fractures: Although fractures can occur along with sprains, the question specifically asks for the most likely ligament injured in an inversion sprain. Ankle fractures are typically caused by high-energy injuries and are not the primary answer in this context.

D. Calcaneal Fractures: Similar to fracture, fractures of the calcaneus (heel bone) are unrelated to the lateral ankle sprain and do not represent the primary concern in this situation.

**Clinical Pearl:** Inversion ankle sprains are common sports injuries and occur frequently in football players. Prompt diagnosis and treatment are essential to prevent complications such as chronic ankle instability and long-term pain. Early immobilization, rest, and physiotherapy can lead to a successful recovery.