Following penetrating trauma, spinal motion restriction is associated with worse outcomes and therefore it should not be done routinely. Mechanism
As a missile passes through tissue, it decelerates, dissipating and transferring kinetic energy to the tissues. The velocity of the projectile is a more important factor than its mass in determining how much damage is done;  kinetic energy increases with the square of the velocity. In addition to injury caused directly by the object that enters the body, penetrating injuries may be associated with secondary injuries, due for example to a blast injury.The path of a projectile can be estimated by imagining a line from the entrance wound to the exit wound, but the actual trajectory may vary due to ricochet or differences in tissue density. In a cut, the discolouration and the swelling of the skin from a blow happens because of the ruptured blood vessels and escape of blood and fluid and other injuries that interrupt the circulation. Cavitation
Permanent
Low-velocity items, such as knives and swords, are usually propelled by a persons hand, and usually do damage only to the area that is directly contacted by the object. The space left by tissue that is destroyed by the penetrating object as it passes through forms a cavity; this is called permanent cavitation. Temporary
High-velocity objects are usually projectiles such as bullets from high-powered rifles, such as assault rifles or sniper rifles. Bullets classed as medium-velocity projectiles include those from handguns, shotguns, and submachine guns.
In addition to causing damage to the tissues they contact, medium- and high-velocity projectiles cause a secondary cavitation injury: as the object enters the body, it creates a pressure wave which forces tissue out of the way, creating a cavity which can be much larger than the object itself; this is called "temporary cavitation". The temporary cavity is the radial stretching of tissue around the bullets wound track, which momentarily leaves an empty space caused by high pressures surrounding the projectile that accelerate material away from its path.The characteristics of the tissue injured also help determine the severity of the injury; for example, the denser the tissue, the greater the amount of energy transmitted to it. Skin, muscles, and intestines absorb energy and so are resistant to the development of temporary cavitation, while organs such as the liver, spleen, kidney, and brain, which have relatively low tensile strength, are likely to split or shatter because of temporary cavitation. Flexible elastic soft tissues, such as muscle, intestine, skin, and blood vessels, are good energy absorbers and are resistant to tissue stretch. If enough energy is transferred, the liver may disintegrate. Temporary cavitation can be especially damaging when it affects delicate tissues such as the brain, as occurs in penetrating head trauma. Location
Head
While penetrating head trauma accounts for only a small percentage of all traumatic brain injuries (TBI), it is associated with a high mortality rate, and only a third of people with penetrating head trauma survive long enough to arrive at a hospital.