Biomechanics of whiplash injury

The article reports a new hypothesis of whiplash injury based on a series o f experimental studies using isolated human cadaveric specimens. Although t he clinical symptoms of whiplash are widely known, the understanding of the underlying injury mechanism is poor. The prevailing view of neck-hyperexte nsion as the essential injury mechanisms was not supported by recent experi ments. In a series of experiments using eight human cadaveric specimens whi ch underwent experimental stepwise whiplash acceleration from 2.5 to 10.5 g functional radiographs and flexibility tests were performed at the end of each acceleration step. Ligament strains, vertebral alignment and elongatio n of the vertebral artery were monitored during the whiplash trauma by high speed cinematography and specially designed transducers. After the trauma C T- and MRI-scans were taken and specimens were sectioned using Cryomicrotom y. We found a distinct biphasic kinematic response of the cervical spine to whiplash trauma. In the first phase the spine formed an S-shaped curve wit h flexion at the upper levels and hyper-extension at the lower levels. This phase was found to be the vulnerable phase of whiplash trauma. The largest dynamic elongation of the capsular ligaments was observed at the C6-C7 lev el during this initial S-shaped phase of whiplash. The maximum elongation o f the vertebral artery could be observed synchronously in the first S-shape d curve of the cervical spine. In the second phase of whiplash all levels o f the cervical spine were extented, so that the head reached is maximum ext ension. No injuries were observed in the second phase. We propose, based on our experimental findings, that with low accelerations the anterior struct ures of the lower cervical spine are injuried during the first phase of whi plash, when the cervical spine forms an S-shaped curve and before the neck is fully extended. At higher trauma accelerations there is also a tendency for the injuries to occur at upper levels of the cervical spine. Based on o ur findings the traditional view of whiplash as hyper-extension injury can be modified by a differentiated, time dependent, biphasic biomechanical mod el of the injury, thus allowing better and more effective injury prevention , diagnosis and therapy.