Okay, let's tackle this question. The patient is a footballer with a twisting injury to the right ankle. The key points here are the location of the swelling—medial malleolus—and the absence of a fracture on X-ray. The question is asking which structure could be injured.

First, I need to recall the common structures around the ankle. The medial malleolus is part of the tibia, and the structures in that area include the medial collateral ligament (also known as the deltoid ligament), tendons, and possibly the medial ligaments. Since there's no fracture, it's more likely a ligamentous injury.

The deltoid ligament is a strong ligament on the medial side of the ankle. Injuries here are common in inversion sprains, but wait—wait, inversion usually affects the lateral ligaments. Wait, maybe I'm mixing this up. Let me think. When you twist your ankle, inversion (turning the foot inward) typically causes lateral ligament injuries, like the anterior talofibular ligament. But the question mentions swelling around the medial malleolus. So if the injury is on the medial side, maybe it's a medial ligament (deltoid) sprain. But how does that happen? Medial ligament injuries are less common than lateral ones. They usually occur from eversion injuries, which would push the foot outward, stressing the medial structures. So in a twisting injury, if the foot is everted, that could tear the deltoid ligament.

But the question says it's a twisting injury. Let's consider the mechanism. If the foot is twisted, depending on the direction, it could lead to either lateral or medial injuries. For example, a sudden twisting motion during a football maneuver might cause the foot to evert, leading to a medial ligament injury. Alternatively, maybe there's a medial collateral ligament tear.

Wait, the medial malleolus is part of the tibia. The deltoid ligament connects the medial malleolus to the navicular, calcaneus, and talus. So a sprain here would cause medial swelling. Since X-rays don't show a fracture, it's a soft tissue injury. So the injured structure is likely the deltoid ligament.

Now, looking at the options (even though they aren't listed here), the correct answer would be the deltoid ligament. The other options might be other ligaments or structures. For example, lateral ligaments would cause lateral swelling, tendons like the posterior tibial tendon might be involved, but if the injury is at the medial malleolus, the primary structure is the deltoid.

I need to make sure about the mechanism. If it's a twisting injury causing medial swelling without fracture, the most common medial injury is the deltoid ligament. So the answer is the deltoid ligament. The other structures like the lateral collateral ligament or others would present with different symptoms. So the correct answer is the deltoid ligament.

**Core Concept**
Ankle injuries involving the medial malleolus without fractures typically involve ligamentous structures. The **deltoid ligament** (medial collateral ligament) is the primary medial stabilizer of the ankle, often injured in eversion or twisting mechanisms.

**Why the Correct Answer is Right**

✓ Correct Answer: A. Deltoid Ligament