## **Core Concept**
The patient is presenting with thigh pain after long-term treatment with alendronate, a bisphosphonate used for osteoporosis management. Bisphosphonates are known to affect bone remodeling and have been associated with atypical femoral fractures (AFFs), particularly with long-term use.

## **Why the Correct Answer is Right**
The correct answer, **MRI of the thigh**, is the next appropriate investigation because it can help identify stress fractures or atypical femoral fractures early in the process, before they become overtly apparent on plain radiographs. MRI is highly sensitive for detecting bone marrow edema, which is an early sign of stress reactions in the bone, such as those leading to atypical femoral fractures. Early detection allows for timely intervention, which may prevent a complete fracture.

## **Why Each Wrong Option is Incorrect**
- **Option A (X-ray of the thigh):** While an X-ray is a reasonable initial imaging modality for evaluating thigh pain, it might not detect early stress reactions or fractures, especially if they are not yet causing significant cortical disruption.
- **Option B (CT scan of the thigh):** A CT scan provides more detail than an X-ray but exposes the patient to more radiation. It is not typically the first choice for evaluating suspected stress fractures or atypical femoral fractures.
- **Option D (Bone scan):** A bone scan can show areas of increased bone turnover but is less specific than MRI for characterizing the nature of the bone lesion or fracture.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that patients on long-term bisphosphonate therapy are at risk for atypical femoral fractures. A high index of suspicion and early MRI evaluation can be lifesaving and prevent progression to a complete fracture. Clinicians should consider obtaining imaging studies, preferably MRI, in patients with persistent thigh or groin pain who are on bisphosphonates.

## **Correct Answer:** . MRI of the thigh