"Dirty Fat Pad" Sign: A novel computed tomography (CT) indicator of injury to the posterior ligamentous complex in acute fractures of the thoracolumbar spine.

Abstract

To describe a CT finding which indicates Posterior Ligamentous Complex (PLC) injury in acute thoracolumbar spinal fractures and to determine if this has been described previously. The anomaly was first described by the senior author. We reviewed 1235 trauma CTs looking for this sign. We identified all thoracolumbar fractures and classified these as thoracic or lumbar fractures depending on the spinal level of the injured vertebra. We sought to determine if the 'dirty fat pad' sign was present on the mid-sagittal CT images of the spine. If present we looked to see if there was MRI confirmation of disruption of the posterior ligamentous complex. A literature review was performed of the MEDLINE, Embase Classic and EMBASE databases for descriptions of the appearance of the posterior ligamentous complex on CT following spinal trauma, from their respective inceptions in 1946 and 1974, to 21.11.25. We found 356 thoracolumbar fractures in the 1235 trauma CTs. Twenty scans showed the 'dirty fat pad' sign (5.6%). MRI in these cases confirmed the disruption of the posterior ligamentous complex. The literature review provided titles and abstracts describing CTs with spinal trauma. These papers were screened for relevance, and thirty-two texts then reviewed in full. No paper retrieved described the radiological appearance of the fat pads on CT or MRI, in health or injury. In our study we found that the 'dirty fat pad sign' was relatively uncommon. However, when seen, it did indicate disruption of the posterior ligamentous complex of the spine. We recommend the use of this sign and suggest it should be sought when reviewing acute trauma CTs. If present it would suggest ligamentous disruption thus guiding clinicians to provide more caution in protecting the patient during transfers and treatments.