American Board of Internal Medicine (ABIM) Certification Practice Exam

In which stage of osteonecrosis is an MRI particularly useful for diagnosis?

1. Chronic stage

2. Early stage

3. Critical stage

4. Terminal stage

The correct answer is: Early stage

MRI is particularly useful for diagnosing osteonecrosis in the early stage due to its ability to detect changes in bone marrow before any visible changes occur on X-rays. In the early phase of osteonecrosis, the bone starts to undergo ischemic changes, which lead to the formation of edema within the marrow. MRI is highly sensitive in identifying these subtle changes, specifically revealing areas of low signal intensity that correspond to necrotic bone. During the chronic stage, changes can often be identified on X-rays, making MRI less critical for diagnosis; it may instead be used to assess the extent of the disease. In the critical and terminal stages, osteonecrosis typically presents with well-defined, more obvious signs that can be evaluated through other imaging techniques. Thus, the early stage is where MRI shines in its ability to provide an early diagnosis, guiding timely intervention to prevent further deterioration of the condition.