Physical Mechanisms of Soft Tissue Injury from Penetrating Ballistic Impact

Most civilian nonfatal gunshot injuries and murders involve handguns. Gunshot wounds are often classified as being due to high-velocity or low-velocity projectiles, e.g. rifle or handgun rounds. However, this is a historical distinction, and there is overlap in energy that can be delivered to tissue by modern rifle and handgun rounds. Also, the same diameter (caliber) bullet can have different impact energies depending on the firearm used. A clearer, physical basis for understanding wounding potential is needed. All bullets lose energy as they travel through tissue, and the local rate of energy loss determines the magnitude of the forces and thus the extent of wounding. The ways the local forces between the bullet and tissue cause injury are often described as 1) permanent cavitation (the hole left after tissue is damaged due to the intense stress field close to the bullet path), 2) temporary cavitation (tissue stretching out of the way due to large retarding forces for a few milliseconds until snapping back into place due to elasticity) and 3) remote injury effects beyond the reach of the temporary cavity due to propagation of a ballistic pressure wave. Regardless of impact energy, if the retarding force is comparable for a given bullet path, the wound will be comparable. Use of the imprecise terms 'high-velocity' and 'lowvelocity' impacts, lack of appreciation for the relationship between change in kinetic energy and forces between a bullet and tissue, and inconsistent explanations of the ballistic pressure wave in the literature have hindered a more general understanding of gunshot injury ballistics. Because of variations in energy actually lost as a bullet penetrates and variations in the anatomical location of the penetration, ballistic information can be a valuable guide for the surgeon but does not substitute for careful assessment of the wound.