**Question:** Best investigation for detection of stress fracture is?

A. Radiography
B. Magnetic Resonance Imaging (MRI)
C. Dual-energy X-ray absorptiometry (DEXA)
D. Ultrasonography

**Core Concept:** Stress fractures are microscopic cracks in bone caused by repetitive or excessive stress, often seen in athletes or individuals engaging in high-impact activities. They commonly occur in the weight-bearing bones such as the tibia, fibula, femur, and pelvis. Diagnosis of stress fractures is crucial for early intervention and prevention of further complications.

**Why the Correct Answer is Right:** Magnetic Resonance Imaging (MRI) is the best investigation for detecting stress fractures because of its high sensitivity and specificity. MRI can visualize bone marrow edema and surrounding soft tissue changes associated with a stress fracture, helping differentiate it from other causes of bone pain. MRI is particularly valuable in detecting stress fractures in patients with negative radiographs or when there is concern for soft tissue involvement.

**Why Each Wrong Option is Incorrect:**

A. Radiography: Although radiography is essential for detecting bony abnormalities, it has limited sensitivity in detecting early-stage stress fractures. Radiographs are often normal within the first two to three weeks of injury, and up to 30% of stress fractures may not be visible on plain radiographs.

B. Dual-energy X-ray absorptiometry (DEXA): DEXA is a bone densitometry test used to assess bone mineral density (BMD) and diagnose osteoporosis. DEXA is not suitable for detecting early-stage stress fractures, as it primarily assesses bone density and not bone abnormalities.

C. Ultrasonography: Ultrasonography is not a reliable option for diagnosing stress fractures due to its limited sensitivity in detecting early-stage stress fractures and its inability to visualize soft tissues and surrounding structures.

**Clinical Pearl:** A high index of suspicion, a detailed history, and a thorough physical examination are essential for diagnosing stress fractures, particularly when radiographs are inconclusive. MRI is recommended when there is suspicion of stress fracture, negative radiographs, or when soft tissue involvement is suspected.