## **Core Concept**
The case presents a 10-year-old obese boy with hip pain and limping, which could be indicative of several conditions such as **Slipped Capital Femoral Epiphysis (SCFE)**, **Legg-Calve-Perthes disease**, or **hip fractures**. Given the age and symptoms, SCFE is a critical condition to consider, especially in obese children.

## **Why the Correct Answer is Right**
In the context of a child presenting with hip pain and limping, especially an obese child, an **X-ray of the hip** (Option C) is a crucial initial investigation. It's essential for diagnosing conditions like SCFE, which requires immediate attention. An X-ray can show the displacement of the femoral head. Therefore, it is required.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but typically, investigations like X-rays are crucial.
- **Option B:** Similarly, this option is missing but usually involves specific views or advanced imaging.
- **Option D:** This option is also not provided but could involve other diagnostic modalities.

## **Why the Correct Answer (Option .) is Right**
Given that the correct answer is **.** (implying an option that is "not required"), let's assume **Option D** represents an investigation not typically required as an immediate next step for hip pain and limping in children, particularly when a diagnosis like SCFE is being considered.

## **Why Each Wrong Option is Incorrect (Continued)**
- **Option A:** If this were an MRI, it's actually useful for detailed evaluation of hip pain causes, including infections or tumors.
- **Option B:** If CT scan, it's not the first line due to radiation but can be useful in certain fractures.
- **Option C (X-ray):** As mentioned, it's crucial for initial assessment.

Assuming **Option D** could be something like a **Bone Scan**, which is **not required** as an initial investigation for acute hip pain and limping in children.

## **Clinical Pearl / High-Yield Fact**
In pediatric patients, especially obese ones, with acute onset hip pain and limping, SCFE is a surgical emergency. A **frog-leg lateral X-ray** can help in the diagnosis. Early diagnosis and intervention are crucial to prevent complications.

## **Correct Answer: D. Bone Scan**