Sacral insufficiency fractures: an often unsuspected cause of low back pain.

We describe a patient with sacral insufficiency fractures presenting as acute onset low back pain without antecedent trauma. Sacral insufficiency fractures are an often unsuspected cause of low back pain. The clinical presentation and plain radiograph findings can mimic metastatic disease, leading to unnecessary investigations and treatment. However, the location, linearity, and appearance of these fractures on computed tomography is very characteristic and obviates the need for further evaluation.