Cerebral contusions: re-evaluation of the mechanism of their development.

At the present writing, the biomechanics of "coup-contrecoup" contusions may be summarized as follows: 1) "Coup" contusions are caused by the slapping effect of discrete areas of inbeding bone during impact. "Contrecoup" contusions are caused by the movements of the brain against irregular and rough bony enviornment. 2) When the head is relatively fixed, a blunt discrete impact causes a "coup" lesion with no "contrecoup" effect. 3) When the head is free to move, a blunt impact will cause a contrecoup lesion or lesions and no "coup" effect. 4) "Fracture contusion" is caused by the slapping effect of the fracture site on the outbending cerebral surface. In such cases, occassionally the dura may be torn. 5) Deeper contusions in the substance of the brain are due to inertial stresses from relative movements and pressure gradients. 6) Contusions of the cerebral tonsils are due to their relative movements at the posterior fossa-foramen magnum junction.