An adolescent athlete has injured his ankle. He has right ankle pain, ecchymosis, and significant edema, and he is unable to bear weight at the time of the exam. Which diagnosis is least likely?

• A. An avulsion fracture
• B. Grade I sprain
• C. Grade II sprain
• D. Grade III sprain

Answer: (B)

Significant swelling and bruising with the inability to bear weight after an ankle injury points to a ligament injury beyond a mild stretch. A mild sprain typically shows only minimal swelling and little ecchymosis, with the joint still able to bear weight or with only mild difficulty. In contrast, what you’re seeing here—marked edema, ecchymosis, and clearly compromised weight-bearing—fits better with a partial tear or complete rupture of ankle ligaments, or even a nearby bone injury like an avulsion fracture, which is not unusual in adolescents.

So the scenario is far more consistent with a moderate to severe sprain or a fracture/physeal injury, not a mild one. That’s why the milder diagnosis is least likely.