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The objective of the present study was to determine the kinematics of the human head-neck complex with specific reference to posterior facet joints as a function of rear impact acceleration. Six intact human head-neck complexes were prepared by fixing the first thoracic vertebra in polymethylmethacrylate. The specimens were oriented such that the Frankfurt plane was horizontal and the cervico-thoracic disc was at an angle of 25 degrees to simulate the normal driving position. Retroreflective targets were inserted to the cervical vertebrae. The specimens were subjected to simulated rear impact accelerations using a minisled apparatus. A series of tests were conducted with velocities of 2.1, 4.6, 6.6, 9.3, and 12.4 km/h. In this study, to achieve the objective, results are presented on the facet joint motions at the C4–5, C5–6, and C6–7 levels as a function of change in velocity.

Inertial loading of the head-neck complex occurs in rear impacts wherein the head and neck of the occupant are initially subjected to rearward forces. Epidemiological evidence exists to demonstrate the significance and societal impact of these injuries [4]. From a clinical perspective, trauma secondary to inertial loads belongs to the lower end of the Abbreviated Injury Scale, and no specific diagnostic techniques are available to quantitatively document the injury. Furthermore, identification of the mechanisms of injury and derivation of injury thresholds are limited. In fact, there is a paucity of literature focusing on the reproduction of rear impact-induced neck injuries due to a single-event rear impact. Because the impact acceleration is transmitted to the head from the torso via the cervical column, the components of the human neck play a role in the mechanics of trauma.