Current Biomechanical Theories

The linear acceleration theory was first evoked about one century ago. Relative movements and secondary impacts occur between the skull and the brain during a head impact. The pressure increases in the superficial cerebral structures below the impact zone, proportionally to the head linear acceleration (4). This theory explains the superficial cerebral lesions' occurrence. It cannot explain the preferential DAI localisation in the deep cerebral structures (8), neither the traumatic deep cerebral hematoma. It cannot axplain neither why the loss of consciousnes and the memory troubles are the most frequent clinic signs occuring after head trauma - despite the fact that the resposible cerebral structures are deeply located.

According to the rotational movements' theory evoked in 1943 by Holbourn (5), DAI and deep cerebral hematoma are caused by the tensile strains occuring between superficial and deep cerebral structures during the head circular movements. In a large series of experiments on primates, Thibault and Gennarelli particularly supported the role of the rotational movements in the DAI occurrence (6).

The consequences of the skull's vibrations are poorly understood. It is probable that the low-frequency skull vibrations (below 200 Hz) mainly cause deep cerebral lesions, while high-frequency vibrations have more consequences on the superficial cerebral structures (7).

In real life head trauma all these phenomena coexist. In the mean time, DAI and brain concussion also occured in pure linear accelerated experimental head trauma (5) even if under the current approach, the linear acceleration theory cannot explain how deep cerebral structures can be injured while superficial cerebral structures are respected.

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