**Core Concept**
The clinical presentation of an elderly patient with a history of fall, inability to move, and tenderness in Scarpa's triangle suggests a hip fracture, but the absence of a visible fracture on X-ray indicates a need for further evaluation. This scenario highlights the importance of distinguishing between overt and occult fractures in the elderly population.

**Why the Correct Answer is Right**
The correct answer involves a diagnosis of femoral neck fracture, which is a common cause of hip pain in elderly patients. The patient's presentation, including the mechanism of injury (fall), inability to move, and tenderness in Scarpa's triangle, is consistent with a femoral neck fracture. Scarpa's triangle is a region of tenderness over the femoral neck, and its presence suggests a femoral neck fracture, especially in the absence of a visible fracture on X-ray. This diagnosis is supported by the fact that occult fractures (fractures not visible on X-ray) are more common in elderly patients due to osteoporosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the underlying cause of the patient's symptoms, which is likely a femoral neck fracture.

**Option B:** This option is incorrect because it does not take into account the patient's clinical presentation, including the mechanism of injury and the presence of tenderness in Scarpa's triangle.

**Option C:** This option is incorrect because it does not consider the possibility of an occult fracture, which is a common occurrence in elderly patients with hip pain after a fall.

**Clinical Pearl / High-Yield Fact**
A key clinical pearl in this scenario is to remember that occult fractures are more common in elderly patients with hip pain after a fall. In such cases, a thorough clinical evaluation, including a detailed history and physical examination, is essential to establish the diagnosis.

**Correct Answer: C. MRI of the hip to rule out occult fracture.**