Fatigue fractures of the sacrum in children: two case reports and a review of the literature.

We present the clinical and radiological features of two children with fatigue fractures of the sacrum. Both patients were active, had no underlying bone disease and presented with insidious onset of low back pain. Plain radiography was non-contributory to the diagnosis. In both patients a focal area of increased activity was present in the lateral aspect of the sacrum on bone scintigraphy, which corresponded to linear medullary sclerosis in the sacral ala demonstrated by computed tomography. Magnetic resonance imaging in one patient revealed a linear signal void in the sacral ala on T1- and T2-weighted images. This was surrounded by diffuse low marrow signal on T1-weighted images, and increased marrow signal on T2-weighted images. Fatigue fractures of the sacrum should be considered in the differential diagnosis of low back pain in children. An awareness of their appearance on magnetic resonance imaging is important as this modality is increasingly utilised, particularly in children.