Insufficiency stress fractures.

Bones weakened by osteopenia have insufficient elastic resistance to withstand even the minimal mechanical stresses of normal daily activity. Repetitive subthreshold injury to these susceptible bones results in insufficiency-type stress fractures. The spine, pelvis, and lower extremities are commonly affected by these fractures. Insufficiency fractures create a diagnostic challenge for clinicians and radiologists alike. The radiographic evidence of the fracture is often so subtle that it escapes detection. Conversely, findings on other studies may be so striking that they suggest metastatic disease. Insufficiency fractures are often subjected to unnecessary biopsies, and they have been treated unwittingly with chemotherapy and radiation therapy. Radiologists are in a key position to prevent these errors. A thorough familiarity with the characteristic appearance and location of these fractures assures the correct diagnosis.