Cortical step sign in spinal clearance on trauma computed tomography – Indicator of acute thoracolumbar compression fracture

Abstract

Introduction Differentiating an acute from chronic compression fracture of the thoracolumbar (TL) spine can pose a dilemma for radiologists interpreting spinal imaging following trauma. Mild wedging of the vertebrae can be due to spondylosis or osteoporosis, whilst acute simple compression fractures may not always be associated with loss of body height. In this observational study, we hypothesize that the presence of a vertebral body cortical step is a reliable sign of an acute compression fracture on Computed Tomography (CT) scans. Methods In a retrospective review of thoracolumbar CT scans following trauma, two observers analysed for the presence of a cortical step at the anterior or posterior vertebral body cortex, fracture morphology and associated injuries. A ‘cortical step’ is defined as a break of hyperdense cortex on CT scans, intervening non-sclerosed trabecular bone, and sharp overlap of the underlying cortex. MRI of the spine was used as gold standard. Results 187 consecutive CT scans over 2 years were assessed. Sensitivity, specificity and accuracy of cortical step sign were 100%, 90.2% and 97% in diagnosing an acute thoracolumbar compression fracture, respectively. The interobserver reliability was high (kappa = 0.97). False positive cortical step was seen in Kummel’s disease and large Schmorl’s nodule. Conclusion Our results demonstrate high sensitivity and specificity of ‘cortical step sign’ in diagnosing acute vertebral body compression fractures of TL spine on CT scans in patients with trauma. This sign can be useful to radiologists for safe clearance of the thoracolumbar spine following trauma, helping distinguish acute trauma from chronic causes of vertebral body height loss.