American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the early diagnostic imaging method for osteonecrosis of the femoral head?

1. CT scan

2. Plain radiographs

3. MRI

4. Ultrasound

The correct answer is: MRI

The early diagnostic imaging method for osteonecrosis of the femoral head is MRI. This is primarily due to MRI’s superior ability to detect subtle changes in bone marrow that occur in the initial stages of osteonecrosis. In its early stages, osteonecrosis can present without any visible changes on plain radiographs, which typically become apparent only in the later stages of the disease when the structural integrity of the bone is compromised. MRI, on the other hand, can identify edema and other intramedullary abnormalities that indicate the presence of osteonecrosis long before any architectural changes in the bone itself are visible on X-rays or CT scans. This makes MRI the most effective imaging modality for early diagnosis, allowing for timely intervention which can be crucial in preserving the integrity of the femoral head and preventing progression to more severe stages of the condition. While CT scans and plain radiographs are useful in evaluating advanced disease, they are not as sensitive in the early detection of osteonecrosis. Ultrasound may help in certain clinical settings but does not provide the detailed imaging needed to identify early changes associated with osteonecrosis.