Which imaging modality is most sensitive for early osteomyelitis?

• A. X-ray
• B. CT scan
• C. MRI
• D. Ultrasound

Answer: (C)

The main idea is that osteomyelitis starts in the bone marrow, so early detection hinges on seeing marrow changes. MRI is the most sensitive at this stage because it images the marrow directly and can pick up edema and inflammatory changes long before any cortical bone destruction becomes visible on X-ray or CT. On MRI, infected marrow typically shows low signal on T1 and high signal on T2/STIR, with enhancement after contrast, highlighting active infection and surrounding soft-tissue involvement. This makes MRI capable of identifying osteomyelitis within the first days to weeks, when other modalities often appear normal.

X-ray often looks normal early because it only shows bone changes after the disease has progressed to cortical destruction or periosteal reaction, which takes time. CT does better for cortical bone detail and bony sequestra but is less sensitive to early marrow edema. Ultrasound is useful for soft tissue and fluid collections but does not reliably assess bone marrow or early osteomyelitis.