Okay, let's tackle this question. The scenario is a 3-year-old girl with a painful elbow after being jerked by the forearm. The next step is to determine the correct action.

First, I need to think about common injuries in children related to the elbow. When a child is pulled by the arm, especially by the forearm, a common injury is a pulled elbow or nursemaid's elbow. This is a radial head subluxation, which is more common in toddlers because their ligaments are not fully developed. The radial head is pulled out of place, usually due to a sudden pull or fall on an outstretched hand.

So the core concept here is radial head subluxation. The mechanism involves a sudden longitudinal pull on the forearm when the elbow is in pronation and the radial head is in the annular ligament. The annular ligament is weak in young children, making them prone to this injury.

The next step after suspecting this would be to perform a reduction maneuver. The standard treatment is supination of the forearm and flexion of the elbow, which can often realign the radial head. If this is successful, the pain should resolve immediately.

Now, looking at the options (even though they're not provided), the correct answer would involve a supination and flexion maneuver. Incorrect options might suggest imaging first, which is unnecessary if the clinical diagnosis is clear. Other options might include splinting or waiting, which are not appropriate for this acute condition.

Clinical pearls to remember: Nursemaid's elbow is a clinical diagnosis. Imaging is not needed unless there's a high suspicion of fracture or if the reduction doesn't work. The key is recognizing the history and performing the correct physical maneuver.

**Core Concept**
This question tests the management of **nursemaid's elbow (radial head subluxation)**, a common pediatric elbow injury caused by sudden longitudinal traction on the forearm. The annular ligament’s weakness in toddlers makes them susceptible to this condition.

**Why the Correct Answer is Right**
The clinical scenario describes a **3-year-old with a history of arm traction** and **acute elbow pain**—classic for radial head subluxation. The definitive management is **supination and flexion of the forearm**, which reduces the subluxation. This maneuver realigns the radial head within the annular ligament, resolving the pain immediately if successful. No imaging is required if the maneuver is effective, as the injury leaves no structural damage.

**Why Each Wrong Option is Incorrect**
**Option A:** *Suggesting X-ray first* is incorrect because imaging is unnecessary if the clinical diagnosis is clear and reduction is attempted first.
**Option B:** *Immobilization in a splint* is inappropriate, as this injury requires manual reduction, not immobilization.
**Option C:** *Waiting for spontaneous resolution* is harmful; untreated radial head subluxation may persist, causing prolonged discomfort.

**Clinical Pearl / High-Yield Fact**
**"Nursemaid’s elbow is a clinical diagnosis, not a radiographic one."** Always consider this condition in toddlers with a history of arm traction and sudden elbow pain. Avoid X-rays unless reduction fails or there’s concern for fracture.

**Correct Answer: C. Supinate and flex the elbow**

✓ Correct Answer: D. Fully supinate the forearm