This file prepared by V E R I C O M M BBS (510) 891-0303. EMERGENCY WAR SURGERY Missile-Caused Wounds Certain fundamental knowledge concerning wound ballistics is essential to the military surgeon. The term "wound bal- listics" is defined as the study of the motion of missiles within the body and the wounding capacity of various missiles. Iden- tification of causative agents of wounds is important for two reasons--mmedical and tactical. From the medical standpoint, the surgeon must know the wounding capacity of the weapon to assist in evaluating the extent of injury to achieve the most effective therapy. From the tactical point of view, the effective ness of special weapons can be gaged correctly by careful and astute observation of the nature of the wounds produced by these weapons. FUNDAMENTALS OF WOUND BALLISTICS The wounding potential of any missile is the summation of numerous factors which together constitute the principles of wound ballistics. The behavior of the missile in relation to wounding capacity includes the following: 1. The amount of energy transmitted to the body upon im- pact by a missile is determined in part by the mass and size of the missile, but chiefly by its velocity. 2. The amount of energy expended is expressed by the formula: 2 2 m(v - v ) 1 2 KE = ---------- 2g where KE refers to kinetic energy, m refers to mass, v1, stands for the initial velocity, v2 stands for the final velocity, and g refers to acceleration due to gravity. As this formula shows velocity is the most important factor in the production of the kinetic energy expended in the body upon wounding. 3. The behavior of the missile upon penetration is influ- enced by the density of the tissues injured and the elasticity of the skin and other tissues. 4. The direction of the transmitted energy is determined by the shape of the bullet, its motion in flight, and stability at the time of impact. Mass and Size of the Missile The number of high-velocity bullet wounds has been increas- ing in succeeding wars of modern times; the increase resulted from the use of high-velocity small arms and automatic weapons together with reintroduction of the Claymore mine which upon detonation, emits numerous spherical missiles at high velocity. The AK-47 Russian military rifle utilized bullets weighing 122 grains as compared to the U.S. high-velocity M-16 rifle bullet weighing 55 grains. Artillery, mortar, an mine fragments are irregular and vary not only in size and shape but also in velocity. Both bullets and fragments are considered to be primary missiles. Secondary missiles include shell wadding, clothing, building material, rocks, and other objects which are converted into wounding missiles by the effects of the primary missile. Velocity Velocity, the most important factor in wounding, is expressed in feet per second or in meters per second. The terms "high velocity" and "low velocity" are arbitrary. Any missile travel- ing more than 2,000 feet per second can be considered a high- velocity missile, although often 2,500 feet per second is chosen as the dividing line. Civilian injuries usually are inflicted with low-velocity weapons. The .38 caliber pistol, for example, has a muzzle velocity of approximately 680 feet per second. This weapon can be compared to the high-velocity military rifle bul- let (M-16 bullet) which has a muzzle velocity of approximately 3,250 feet per second. The kinetic energy theory of wounding capacity indicates that the energy expended is directly propor- tional to the mass and to the square of the effective velocity. Thus, doubling of the velocity quadruples the kinetic energy of the missile. Rifles employed in World War I had an average velocity of 2,3OO feet per second (700 meters per second), while those employed in the Vietnam conflict developed a muzzle velocity in excess of 3,200 feet per second (976 meters per second). Low-velocity missiles.--The mechanism by which a low- velocity missile produces a wound is relatively simple. In knife or bayonet wound, for example, only those tissues with which the blade comes into contact are severed. No significant energy is imparted to the nearby tissues, and the damage, for all practical purposes, is entirely localized. The low-velocity bullet or fragment also creates local damage and has been shown to push the tissue aside. In all wounds produced by low-velocity missiles, therefore, only minimal debridement is required. The impact of high-velocity missiles which become spent also produces wounds equivalent to those produced by low-velocity missiles. High-velocity missiles.--The most important point to be Iearned in the transition of the civilian physician to the mili- tary surgeon is that the high-velocity wound is a totally different entity. The kinetic energy of the missile upon impact becomes imparted to the tissues. These adjacent tissues are suddenly hurled forward, laterally, and then backward. This is the theory of the acceleration of particles. A large space or cavity is created approximately 3O to 40 times the size of the missile, in which pressures of 100 atmospheres (1,500 psi) have been recorded (fig. 1). This effect was first termed "cavitation" by Woodruff in 1898. The temporary cavity becomes a vacuum which draws in air from both the entrance and the exit site (fig. 2). Its maximal size is attained within a few milliseconds and it pulsates quickly to rest, forming the permanent cavity. This permanent wound tract is visible to the clinician and the damage at a distance may not be immediately apparent. The effect of this cavity becomes particularly more damaging when the bone is fragmented and acts as a secondary missile. Ex- perimentation has shown that the high-velocity missile neatly shears the tissue while the violence of the expansion of the missile tract, as the cavity is created, disrupts tissues, ruptures blood vessels and nerves, and may even fracture bones at dis- tances removed from the path of the missile. This force of the cavity simulates compression or crushing injuries similiar: to those sustained in brunt trauma. The explosive nature of high-velocity wounds was first ob- served by Huguier in 1848. Wilson stated in 1921 that a high- velocity rifle bullet passing near a blood vessel produces intimal lesions at a distance from the missile tract. This concept was reinforced during the Korean war when vessels, the external appearance of which was grossly normal, were actually throm- bosed. Recent experimentation has demonstrated that the force of kinetic energy may literally destroy a blood vessel when indirectly struck. Tissue Destruction The type of wound which results from a missile may be a simple contusion or a penetrating or perforating wound. In a penetrating wound, the kinetic energy is dissipated wholly into the tissues. In a perforating wound, the amount of energy imparted to the tissues is the difference between the kinetic energy remaining at the point of exit and that present at the wound of entrance. The density of the tissues struck deter- mines the nature of the wounds as described above. Kocher demonstrated in 1876 that tissues which contained large quan- tities of water were most severely damaged, and Daniel, in 1944 correlated the severity of high-velocity wounds with the specific gravity of the tissue involved. Muscle is severely damaged because of its relatively high homogenous density. In contrast, the lung sustains less extensive local destruction because of its low density, resulting in absorption of less energy and a smaller temporary cavity. Tissues of varying density, such as fascia or bone, may divert the direction of the missile, resulting in bizarre wound tracts. Ballistic Behavior of Missiles An understanding of the ballistic behavior of a missile is necessary to interpret accurately the mechanism of tissue de- struction. Aerodynamic forces act upon the spin-stabilized bullet during Right and may change the angle of obliquity on impact. The effects of such forces include yaw, tumbling, precession, and nutation. Yawing is the deviation of a bullet in its longitudinal axis from the straight line of flight (fig. 3) Tumbling is the action of forward rotation around the center of mass (fig. 4). A bullet will tumble if its overturning moment due to yaw is sufficiently large. Spin, which maintains the bullet in a point on position, may introduce two circular mo- tions: (1) precession, which is a circular yawing around the center of mass in a spiral fashion (fig. 5), and (2) nutation which is the rotational movement in small circles forward in a rosette pattern (fig. 6). The varying severity of wounds and amount of tissue destruc- tion by identical missiles with the same energy can be explained in most part, by the angle of the bullet to the tissues at the moment of impact. Thus, a nontumbling bullet entering the tissues at a right angle will be in minimal contact with the tissues; upon exit, the bullet will have imparted a lesser amount of its kinetic energy to the tissues. A bullet which strikes at an oblique angle and tumbles through the tissues, on the other hand, will have contacted more tissue and consequently will have imparted a greater amount ot its energy to the tissue, re- resulting in greater tissue destruction. External appearances of both exit and entrance wounds may be misleading. The wound of exit is usually larger than the wound of entrance. The alert military surgeon will realize that, though the wounds caused by large fragments may appear to be more formidable, the energy imparted by smaller missiles of higher velocity may actually create far more serious and lethal injuries. END