Biomechanical aspects of cervical trauma

Abstract

The biomechanical expert opinion on the injury mechanism is necessary in few cases only. However, the judgement of these cases is extremely compromised if mechanically wrong terms are introduced in the clinical report. Since the injury mechanism in the neck is very complex the clinical physician should concentrate on the clinical findings familiar to him; usually the clinician lacks technical case documentation and specific training in injury biomechanics. The relevant mechanisms of neck injuries are an indirect trauma induced by a) a head contact leading to compression, hyperflexion, hyperextension and/or hypertranslation and b) a non-head-contact mechanism (hyperflexion or hyperextension, hypertranslation, acceleration). A non-contact mechanism occurs e.g. during a rear end impact without head restraint (hyperextension) or a frontal collision of a belted occupant (hyperflexion) without head impact. The term "whiplash" is misleading and incorrect: It presumes a virtually non existing two phase movement back and forth (or vice versa) like during the development of the crack of the whip. Secondly, it mixes the physical criterion mechanism with the anatomical or morphological criterion injury e.g. distortion, sprain etc. A (head)-contact mechanism is due to a corresponding momentum exerted from the head on the neck. Again, the anatomical or morphological terms are equal, but the mechanism is different. During a contact mechanism as well as during a non-contact mechanism not only a hyperflexion or a hyperextension can occur; in the first phase of the impact also a shearing force between the upper vertebral bodies (CO-C2) may load the intervertebral structures by hypertranslation.