The purpose of this study was to analyze, with use of an impact model, the relationships among motion of the head, local deformations of the cervical spine, and the mechanisms of injury; the model consisted of the head and neck of a cadaver. Traditionally, the mechanisms of injury to the cervical spine have been associated with flexion and extension motions of the head and neck. However, the classification of the mechanisms is not always in agreement with the patient's account of the injury or with lacerations and contusions of the scalp, which indicate the site of the impact of the head. Eleven specimens were dropped in an inverted posture with the head and neck in an anatomically neutral position. Forces, moments, and accelerations were recorded, and the impacts were imaged at 1000 frames per second. The velocity at the time of impact was on the order of 3.2 meters per second. The angle and the padding of the impact surface varied.
Observable motion of the head did not correspond to the mechanism of the injury to the cervical spine. Injury occurred 2.2 to 18.8 milliseconds after impact and before noticeable motion of the head. However, the classification of the mechanism of the injuries was descriptive of the local deformations of the cervical spine at the time of the injury. Accordingly, it is a useful tool in describing the local mechanism of injury. Buckling of the cervical spine, involving extension between the third and sixth cervical vertebrae and flexion between the seventh and eighth cervical vertebrae, was observed. Other, more complex, buckling deformations were also seen, suggesting that the deformations that occur during impact are so complex that they can give rise to a number of different mechanisms of injury.
Clinical Relevance: Classic concepts of flexion and extension of the head as a mechanism of injury do not apply to a vertical impact of the head. Motions of the head, which often are used to classify the injury, are not a reliable indicator of the mechanism of injury. The mechanism of injury is descriptive of local deformations of the cervical spine and forces at the instant of injury. Although it is a useful tool for describing local mechanisms of injury, care should be taken not to confuse the mechanism of injury at the level of the motion segment with the mechanism as it applies to loads on (and resulting motions of) the head.
The complex buckling of the cervical spine that results from a vertical impact of the head may cause concomitant flexion and extension in different regions of the cervical spine. Treatment should be based on the local mechanism, with the understanding that this type of impact may involve multiple, sometimes non-contiguous, mechanisms of injury.