Treating Gunshot Wounds In The Lower Extremity
Given that gunshot wounds reportedly affect the foot nearly five percent of the time, these authors provide an overview of ballistics associated with gunshot wounds as well as keys to injury assessment, surgical debridement and wound stabilization.
Gunshot wounds and firearm injuries are common and place a continuous burden on hospital resources and the community. Although gunshot wounds are less common in America than in other parts of the world, the Centers for Disease Control and Prevention (CDC) reported 73,883 non-fatal injuries and 32,163 deaths in 2011 due to firearms in the United States alone.1,2 Studies have also found gunshot wounds to involve the extremities more than any other parts of the body, affecting the foot approximately 5 percent of the time.3-7
The treatment of gunshot wounds in the lower extremity can become challenging due to the extent of injury and loss of muscle, tendon, bone, skin, nerves and vascular supply.8 Many of these wounds require specialized fixation techniques, soft tissue reconstruction and extensive wound care, making an understanding of ballistics, the mechanism of injury and wound characteristics important when evaluating firearm injuries.3,8,9
Understanding The Principles Of Ballistics With Gunshot Wounds
When discussing ballistics in relation to wounds, it is important to understand the related nomenclature in this field. Ballistics is the science of mechanics that deals with the flight behavior and effects of projectiles.7 When discussing ballistics, a missile is the projectile that transmits damaging energy to the casualty or target. It is important to understand the term “missiles” is not referring to rocket-propelled explosives but to bullets, fragments and pellets fired from a weapon.
In firearm ballistics, there is a distinction between low- and high-velocity weapons with a velocity of more than 2,000 ft./sec. typically being designated as high velocity. Generally, high velocity corresponds to a kinetic energy greater than 750 ft./lbs. commonly produced by hunting and military rifles.8 To gain perspective, a projectile must travel a speed of 163 ft./sec. to penetrate skin and 200 ft./sec. to break bone.10 Handguns and shotguns are low-velocity weapons. Nevertheless, they can act like high-velocity weapons at close range, which is a distance of less than 14 feet.9,11
When missiles penetrate tissue, the injury is directly proportionate to the amount of energy that transfers to the target. One can determine the kinetic energy of a missile by the velocity (v) and mass (m) of the missile in which kinetic energy = 1/2mv2.3,9,12 While velocity is the most important factor, the efficiency of energy transfer depends on many aspects including the characteristics of the missile and tissue one encounters.9,13,14
Missile characteristics affecting energy transfer include the missile’s mass, shape, stability, path, deformation and fragmentation.9,14 The caliber of a missile describes the diameter of the barrel the missile travels through. Due to the high tolerance of both the barrel and the missile, the diameter of the missile and barrel are essentially the same.7 Larger caliber missiles are greater in size, have more mass and can cause substantial tissue damage. When the initial diameter of a missile increases by 2.5 times, the area of tissue damage increases by 625 times.3 This increase can greatly raise the stopping power of the missile. However, due to their size and weight, larger caliber missiles also lose velocity, which relatively quickly makes them less efficient at longer distances.7