Radiographic ‘shadow sign’ can be used to verify metal implant type in pediatric scoliosis patients

The “shadow sign” in a radiographic image may help surgeons determine whether the spinal instruments in a patient are stainless steel or titanium, a recent study finds.

Between 2005 and 2009, Sean M. Jones-Quaidoo, MD, and colleagues showed 16 lateral pediatric scoliosis radiographs to 19 orthopedic surgery residents, one spine fellow and two spine attendings and asked them what type of metal implants were in each image. There were six patient images of each metal along with two images each of a replicate metal to determine intraobserver reliability, according to the abstract.

Researchers concluded that the shadow sign, which occurs when radioluscent titantium rods and screws imposed on a radiograph are vibrant enough to highlight the underlying components on the image, can be used to determine what kind of spinal instrument is present in a patient. Stainless steel rods, by contrast, are not visible through radiograph.

The researchers noted that when using the shadow sign, the level of experience in diagnosing spinal lateral radiographs was also beneficial in identifying the implant type.