Posterior bow and vanishing line signs in diagnosis of burst fractures of the spine on plain radiographs

It is not uncommon to misdiagnose a burst fracture as a wedge compression fracture initially on plain film, resulting in a late progressive deformity and neurologic damage. The purpose of this study was to analyze the sensitivity, specificity and positive predictive value of plain radiographs in the diagnosis of thoracic and lumbar burst fractures using the posterior bow (PB) and vanishing line (VL) signs. Seven independent examiners, comprising three chief orthopedic residents, two radiologic third-year residents and two emergency attending physicians (orthopedists), randomly reviewed 26 sets of admission anteroposterior and lateral thoracolumbar spine radiographs taken in association with back injuries. They were asked to decide whether patients had a burst or a wedge compression fracture. All patients had computed tomography (CT) scans for diagnostic confirmation. The overall initial sensitivity using discriminant analysis in the diagnosis of burst fractures was 80%. This increased to 90% after the examiners were requested to use the PB and VL signs. The specificity decreased slightly from 75% to 71%, while the positive predictive value remained at 88%. Overdiagnosis of wedge compression fractures as burst fractures occurred, especially when the quality of the films was not ideal. We conclude that, with careful reading, the PB and VL signs help in identifying burst fractures on the initial plain film evaluation.