Head and Neck Response to Axial Impacts

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Abstract
Two series of impacts to the head in the superior-inferior direction using 19 unembalmed cadavers are reported. The first series of five tests was aimed at generating kinematic and dynamic response to sub-injurious impacts for the purpose of defining the mechanical characteristics of the undamaged head-neck-spine system in the S-I direction. The second series of fourteen tests was intended to define injury tolerance levels for a selected subject configuration. A 10-kg impactor was used to deliver the impact to the crown at a nominal velocity of 8 m/s for the first series, and between 7 and 11 m/s for the second series. Measurements made in the first series include the impact velocity, force, and energy, the head three-dimensional kinematics, forces and moments at the occipital condyles, and accelerations of the T1, T6, and T12 vertebrae. Impact impedance curves were also generated. Measurements made during the second series were the same as the first, except that no condyle reactions were calculated nor detailed autopsies were performed. Peak impact force was not found to be a reliable predictor of cervical injury. Furthermore, since such injury often occurred without skull fractures indicating that the neck may be more vulnerable to S-I impacts than the head itself, the Head Injury Criterion (HIC) would not be useful to determine the effectiveness of head protective devices in protecting the neck. On the other hand, both the time integral of the force and the maximum head velocity correlated well with cervical spine damage and thus they may be useful in predicting neck injury.

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