Disc Injuries in Rear Impacts
Discinjuries following rear-end impacts are often observed in clinical practice by physicians, many following in the low-speed delta-V range. I have seen many disc bulging or herniation cases over the years in the delta-V range of 4 to 10 mph. Most of these disc cases had preexisting degeneration in the spine noted with imaging studies or out-of-position issues leading to susceptibility. Smith evaluated 72 real-world rear impacts with accident reconstruction to determine the delta-Vs and the types of injuries that were diagnosed by physicians. Discbulges or herniations were found in the cervical spine with delta-Vs as low as 8km/h and in the lumbar spine as low as 11.3 km/h. Yoganandan et al. exposed four entire human cadavers to rear impacts with 4.4 to 6.8m/sec (9.8 to 15.2 mph) delta-V and a mean of 3.3 or 4.5g acceleration. After single impact, the cervical spine was analyzed for any traumatic findings using standard radiology and CT scanning. X-ray and CT analysis only found an avulsion fracture of the C5 body and C5-C6 disc distraction injury without a fracture. Then the specimens underwent cry sectioning to determine if any soft tissue injuries occurred that were not noted in the radiological evaluation. Cryosectioning revealed the following: annular tears at C5-C6, diastasis of C1-C2 and C5-C6 zygapophysical joints with associated tears of capsular ligaments, tears of C6-C7 ligamentum flavum, and tear/rupture of C5-C6 anterior longitudinal ligament.