**Core Concept**
Pulled elbow, also known as radial head subluxation, is a common injury in young children where the head of the radius bone partially dislocates from its normal position in the elbow joint. This occurs due to a sudden pull on the extended arm, causing the radius to slip out of place.

**Why the Correct Answer is Right**
The mechanism of injury involves a sudden traction force on the extended arm, which causes the annular ligament surrounding the head of the radius to tear, allowing the radius to subluxate. This injury is more common in children due to their softer bones and weaker ligaments. The radial head subluxation is usually reduced by a simple maneuver called the "nurse's elbow," where the child's arm is flexed and pronated to return the radius to its normal position.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because pulled elbow specifically refers to radial head subluxation, not dislocation or fracture of the elbow joint.

**Option B:** This option is incorrect because the mechanism of injury involves a sudden traction force on the extended arm, not a direct blow to the elbow.

**Option C:** This option is incorrect because while it is a common injury in young children, pulled elbow is not typically associated with a fall or direct trauma to the elbow.

**Clinical Pearl / High-Yield Fact**
A classic clinical pearl to remember is that pulled elbow occurs in children due to their softer bones and weaker ligaments, making it essential for parents and caregivers to be aware of this common injury and know how to properly reduce it.

**Correct Answer: D. Radial head subluxation.**