Penetrating trauma is an injury that occurs primarily by an object piercing the skin or entering a tissue of the body. The severity of the injury is determined largely by the velocity of the object that enters the body. High-velocity objects are usually projectiles such as bullets from high-powered rifles, such as assault rifles[1] or sniper rifles. Bullets classed as medium-velocity projectiles include those from handguns, shotguns,[1] and submachine guns. Low-velocity items, such as knives, are usually propelled by a person's hand, and usually do damage only to the area that is directly contacted by the object.[1] In addition to causing damage to the tissues they contact, medium- and high-velocity projectiles cause a cavitation injury: as the object enters the body, it creates a pressure wave which forces tissue out of the way, creating a cavity that can be much larger than the object itself.[1] The tissues soon move back into place, eliminating the cavity, but the cavitation frequently does considerable damage first.[1] Cavitation can be especially damaging when it affects delicate tissues such as the brain, as occurs in penetrating head trauma.
