## **Core Concept**
The patient's presentation suggests a hip injury, likely a femoral neck fracture, given the mechanism of injury (fall), the position of the leg (external rotation), inability to move the leg, and tenderness in Scarpa's triangle (also known as the femoral triangle). The absence of a visible fracture line on X-ray does not rule out a fracture, especially if it is an incomplete or stress fracture, or if the X-ray is not sensitive enough to detect the fracture.

## **Why the Correct Answer is Right**
The most appropriate next step in management, given the clinical suspicion of a femoral neck fracture despite a negative X-ray, is to perform an MRI (Magnetic Resonance Imaging). MRI is highly sensitive and specific for detecting fractures, including those not visible on plain radiographs. It can identify occult fractures (those not visible on X-ray) and provide detailed images of the soft tissues and bone marrow, which can be helpful in planning treatment.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is blank and cannot be evaluated.
- **Option C:** CT (Computed Tomography) scans can provide more detailed images of bone than X-rays but are not the first choice for evaluating suspected femoral neck fractures when MRI is available. CT scans involve more radiation and may not provide the same level of detail about soft tissues and bone marrow as MRI.
- **Option D:** This option is blank and cannot be evaluated.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that a high index of suspicion for occult hip fractures should be maintained in elderly patients who present with hip pain or an inability to bear weight after a fall, even if initial X-rays appear normal. MRI is the diagnostic modality of choice in such cases due to its high sensitivity and specificity for detecting fractures.

## **Correct Answer:** . MRI