Sacral insufficiency fractures presenting as acute low-back pain. Biomechanical aspects.

Sacral insufficiency fractures are an often unsuspected cause of low-back pain in elderly women with osteopenia who have sustained unknown or only minimal trauma. The authors describe 10 cases of spontaneous sacral insufficiency fractures, confirmed by computed tomography, characterized by the onset of acute low-back pain. Differential clinical and radiographic diagnosis of these fractures is often difficult. Recognition of the characteristic scintigraphic patterns in sacral fractures, which are frequent in osteopenic patients, could avoid mistaken diagnoses and unnecessary tests or treatment. One of the striking feature of these sacral fractures is their invariable location. The fractures extend vertically in the sacral alae, parallel to the sacroiliac joints. They are located just lateral to the margins of the lumbar spine. This distribution suggests that such fractures could be partially caused by weight-bearing transmitted through the spine.