New mechanism for inducing closed head injury in the rat.

Due to the frequency of closed head injuries and cost of treatment, there is great interest in the mechanical parameters involved in provoking the injury. A new device has been developed to produce closed head injury due to impact-induced angular acceleration in the rat. A 488-gram mass was propelled down a 2-meter drop tube by springs at a velocity of 21 mph (9.5 m/s), depending on strength and displacement of the springs. The projectile then impacts a lever arm protruding laterally from an aluminum helmet fixed at the anterior face with a ball-bearing pivot allowing only lateral rotation, which has been shown to cause severe brain injury. A sodium silicate elastomeric material with a thickness of 1 cm was placed at the impact interface to increase the contact time between the projectile and the lever arm. Biomechanical results from a lumped parameter mathematical model and testing indicated an angular acceleration of 300,000 +/- 20,000 rad/s2, angular velocity of 300 +/- 50 rad/s, and impact duration of 2.0 +/- 0.3 ms. When scaled to the human, the results indicated an angular acceleration of 4,100 rad/s2, angular velocity of 32 rad/s, and impact duration of 20 ms, consistent with values associated with classical concussion. Magnitudes and durations at these levels have not been produced in the rat by rotational loading caused by impact, and due to the flexibility of the design, these parameters can be further increased.