Question

A 6 year old child presents with pain in the hip in the femoral triangle region and limitation of movements. X-ray does not reveal any abnormality. What is the next step?

• A. USG
• B. MRI
• C. Aspiration
• D. Traction

Hint:

Early Perthes disease can have a normal X-ray; pick the most sensitive imaging for avascular necrosis.

Answer 1

The Correct Option is B

Step 1: Identify the clinical picture. A 6 year old with hip pain referred to the femoral triangle (groin) and restricted hip movements, with a normal plain X-ray, is the classic early presentation of Perthes disease (Legg-Calve-Perthes disease), an idiopathic avascular necrosis of the femoral head.
Step 2: Understand why the X-ray is normal. In the very early (avascular) stage of Perthes disease, plain radiographs are frequently normal because bony changes such as a small epiphysis, increased density, crescent sign and fragmentation take weeks to appear.
Step 3: Choose the most sensitive next investigation. MRI detects early marrow ischaemia and avascular necrosis before any change is visible on X-ray, making it the investigation of choice when the X-ray is normal but Perthes is suspected.
Step 4: Eliminate the other options. USG only shows a joint effusion and is non-specific, aspiration is reserved for suspected septic arthritis, and traction is a treatment, not a diagnostic step.
Step 5: The correct answer is MRI (option 2).