Disc Injuries in Side Impacts
Side impacts may cause disc injuries to the cervical or back regions. In most cases, there is violent rotational movement of the vehicle and occupant during the impact, causing torsion to the neck and back. In addition, most occupants will have his/her heads turned looking at the bullet vehicle or turned to alert other occupants, resulting in a pre-twisting of the spine will cause annular disc fibers to become taut. One study that confirmed disc injuries conducted near-sided cadaver testing in 14 side impact tests with a delta-V of 50 km/h into a barrier. The most common injury noted in the cervical spine was intervertebral disc hemorrhages (55%), followed by ligamentum flavum injuries.
Disc Injuries in Rear Impacts
Disc injuries 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. Disc bulges 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.