Penetrating gunshots to the head and lack of immediate incapacitation. I. Wound ballistics and mechanisms of incapacitation.

There are two distinct mechanisms of ballistic injury. Crushing of tissue resulting in a permanent tract is the primary factor in wounding of most tissues and most body regions. Temporary cavitation causes radial tissue displacement and subsequent shearing, compression and especially stretching of tissue analogous to blunt trauma. In contrast to the effect in elastic tissue, temporary cavitation can contribute substantially to wounding of inelastic tissue, such as the brain. This is the case in penetrating gunshot wounds to the head. Additionally, the penetration of the bony cranium can produce secondary missiles in the form of bone or bullet fragments and a tendency of the bullet to deformation and early yaw. Most important, wounding resulting from temporary cavitation is greatly augmented by the confined space provided by the unyielding walls of the skull. Bone contact and enhanced effects of temporary cavitation result in an enlarged zone of disintegrated tissue and in high intracranial peak pressures. Morphological signs of powerful intracranial pressure effects are cortical contusion zones, indirect skull fractures and perivascular haemorrhages remote from the tract. Depending on ballistic and anatomical parameters, the intracranial effect varies from slightly more severe injury than in isolated soft tissue to an "explosive" type of injury with comminuted fractures of the skull and laceration of the brain. Incapacitation is the physiologically based inability to perform complex and longer lasting movements independent of consciousness or intention. Immediate incapacitation is possible following cranio-cerebral gunshot wounds or wounds that disrupt the upper cervical spinal cord only. Rapid incapacitation can be produced by massive bleeding from major vessels or the heart. Immediate incapacitation is the result of primary intracranial effects of the bullet. A mechanism similar to commotion cerebri applied extracranially does not exist in cases of penetrating gunshot wounds to the head.