In evaluating for sacral insufficiency fracture in an elderly patient with acute back pain, which imaging modality is commonly helpful when plain X-ray is unrevealing?

• A. Plain X-ray.
• B. MRI.
• C. CT scan.
• D. Bone scintigraphy.

Answer: (D)

When plain X-ray findings are unrevealing in an elderly patient with acute back pain, occult sacral insufficiency fracture is a key concern. Bone scintigraphy is highly sensitive for detecting occult fractures because it shows increased osteoblastic activity at the fracture site early in the healing process. In sacral insufficiency fractures, this typically manifests as focal radiotracer uptake in the sacrum, sometimes described as the H-sign, which can identify the fracture even when X-rays are normal. While MRI offers superior specificity and can visualize marrow edema and the fracture line directly, bone scintigraphy remains a practical and rapid option when X-rays are negative and MRI is not immediately available. CT can help delineate fracture lines but may miss early fractures without cortical disruption.