High Speed Video Analysis of Thoracolumbar Burst Fractures

Introduction Following a burst fracture, decompressive surgery is often recommended on the basis of imaging alone. There is, however, little evidence that the removal of intra-canal bone fragments is of neurological benefit to the patient (1). Further, there is doubt as to whether the fragment position seen on post-injury CT scans represents the true extent of the occlusion produced during the fracture process (2). The aim of this study was to develop an experimental method for examining the events that are likely to cause neurological injury at the time of fracture. A new technique, using high-speed video to film inside the spinal canal during the fracture event, is described. Methods A rig was built to create reproducible burst fractures by dropping a mass of up to 7kg from a maximum height of 2m onto three-vertebra spinal segments. The thoracolumbar spines were harvested from calves aged 21 days. During preparation, the spinal cord was removed and the ends of the specimens were fixed in polymethylmethacrylate holders that allowed unimpeded access to the spinal canal. In order to film the fracture process, a high-speed video (Kodak HS4540, Roper Scientific MASD, CA, USA) was used. The system was capable of recording 3072 frames of 256 x 256 pixels at a speed of 4500 frames/second. The spinal canal was illuminated via a mirror above the specimen using a 50W light source. The camera was positioned in line with a second mirror below the specimen so that the cross-section of the canal could be seen (Figure 1). A second camera was used to film the outside of the specimen to determine if buckling occurred during the impact process. After capture, the frames were downloaded to a PC and analysed using a custom written algorithm in an image analysis package (Image-Pro Plus 3.0, Media Cybernetics, MD, USA) to determine the canal cross-sectional area as a function of time during the fracture event. To validate the results, CT scans were taken of nine of the specimens and compared with the final video images taken during the test.