EXPERIMENTAL IMPACT INJURY TO THE CERVICAL-SPINE - RELATING MOTION OFTHE HEAD AND THE MECHANISM OF INJURY

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 injur y to the cervical spine have been associated with flexion and extensio n motions of the head and neck, However, the classification of the mec hanisms is not always in agreement with the patient's account of the i njury or with lacerations and contusions of the scalp, which indicate the site of the impact of the head, Eleven specimens were dropped in a n inverted posture with the head and neck in an anatomically neutral p osition, Forces, moments, and accelerations were recorded, and the imp acts were imaged at 1000 frames per second, The velocity at the time o f 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 di d not correspond to the mechanism of the injury to the cervical spine, Injury occurred 2.2 to 18.8 milliseconds after impact and before noti ceable motion of the head, However, the classification of the mechanis m of the injuries was descriptive of the local deformations of the cer vical spine at the time of the injury, Accordingly, it is a useful too l in describing the local mechanism of injury Buckling of the cervical spine, involving extension between the third and sixth cervical verte brae and flexion between the seventh and eighth cervical vertebrae, wa s observed, Other, more complex, buckling deformations were also seen, suggesting that the deformations that occur during impact are so comp lex that they can give rise to a number of different mechanisms of inj ury: 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 i njury, are not a reliable indicator of the mechanism of injury. The me chanism of injury is descriptive of local deformations of the cervical spine and forces at the instant of injury, Although it is a useful to ol 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 ) tile head, The complex buckling of the cervical spine that results f rom a vertical impact of the head may cause concomitant flexion and ex tension in different regions of the cer,icd spine, Treatment should be based on the local mechanism, with the understanding that this type o f impact may involve multiple, sometimes non-contiguous, mechanisms of injury.