Contemporary Problems in Trauma Surgery
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Principles of Ballistics Applicable to the Treatment of Gunshot Wounds Kenneth G. Swan, MD, FACS, * and Roy C. Swan, MDt
Ballistics is the science of the motion of a projectile through the barrel of a firearm (internal ballistics), during its subsequent flight through air or space (external ballistics), and during its final, complicated motion after striking the target (terminal ballistics). Wound ballistics is a special case of terminal ballistics in which the target is animal tissue. 2. 6, 10, 11, 13, 16, 17 Internal and external ballistics are nearly exact sciences, whereas terminal ballistics is so complex as to be, at best, sets of approximations. Nonetheless, the principles of wound ballistics enter usefully into an evaluation of a gunshot wound and its treatment. This is becoming increasingly apparent as the development of firearms in recent decades has moved toward progressively smaller projectiles with increasingly higher velocities. Internal ballistics considers the conversion of chemical energy of the propellant (gunpowder in the case of firearms) to the kinetic energy of the bullet. It considers the time course and interrelations of pressure, volume, and velocity in the bore of the firearm and the induction of "spin" of the bullet to achieve stability in flight by the rifling (helical grooves) in the bore (internal surface) of the gun barrel. When a cartridge (packaged gunpowder, propellant, primer, and bullet) is loaded into the chamber (breech end of the gun barrel) and its primer is struck mechanically, the resulting spark ignites the propellant and starts the controlled burning of this propellant in the chamber. As the precisely sized and shaped grains of propellant are volatilized and ignited at an accelerating rate, the inertia and resistance of the bullet are overcome, and it accelerates toward the muzzle. The volume behind the accelerating bullet increases, but the tendency of the pressure to fall is more than offset by the rapidly increasing total surface of the gas-emitting grains and the corresponding accelerating rate of burning. The rate of increase in pressure and the increase in the velocity continues until maxima are reached when *Professor and Chief, Section of General Surgery, and Director of Thoracic Surgery, University of Medicine and Dentistry of New Jersey, Newark, New Jersey tJoseph C. Hinsey Professor of Anatomy and Cell Biology Emeritus, Cornell University Medical College, New York, New York
Surgical Clinics of North America-Vol. 71, No.2, April 1991
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the bullet is about one third the distance toward the muzzle. Beyond this, pressure falls to about 20% of the maximum attained (tens of thousands of pounds per square inch), and the bullet leaves the muzzle still accelerating under the rapidly falling pressure of gas, which begins to escape from the muzzle. The bore of the rifle or handgun is drilled to produce a helix of alternating grooves and ridges (lands) called the rifling of the gun barrel, with a pitch, typically, of about one turn per 10 inches along the barrel from breech to muzzle. On ignition, the relatively hard steel ridges and grooves of the bore impress a corresponding pattern in the soft metal of the cylindrical part of the bullet so that it is accelerated not only linearly but also angularly. The resulting "spin" imparts stability to the trajectory of the bullet and tends to suppress erratic flight, typically in the form of yaw (the angle between the long axis of the bullet and its line of flight) and tumbling (forward rotation, end over end, around the bullet's center of mass).
EXTERNAL BALLISTICS As the accelerating bullet is forced through the muzzle, the turbulence of the emerging gas will induce slight yaw (only a few degrees) and a corresponding increase in resistance to the bullet. These latter factors will increase progressively and, over a long range (distance between muzzle and target), lead to a substantial drop in velocity.
TERMINAL (WOUND) BALLISTICS A low-velocity «1000 ftls or 305 m/s), 22-caliber* (5.6-mm-diameter bullet) pistol wound of soft tissue, such as the calf, will exhibit an entrance and an exit wound smaller than the diameter of the bullet and a track of tissue damage not much greater in diameter (Fig. lA). Usually, this wound will not require debridement. A higher-velocity (>3000 ftls or 914 m/s) gunshot wound, such as that resulting from a bullet of the same caliber from the current US military rifle (Colt M-16 A2) or a comparable military or sporting rifle, may exhibit a similar entrance, but the exit may range from the same to several times the diameter of the bullet (Fig. IB and C). Conversely, there may be no exit (Fig. ID) or an enormous exit (Fig. lC), depending on the shape and construction of the bullet and the tensile strength and density of the tissue it encounters.6 The track of this highvelocity, rapidly decelerating, deforming, and disintegrating projectile may be surrounded by tissue destruction extending as much as several centimeters radially from the track secondary to a momentary intense compression and subsequent stretching of surrounding tissue to many times its normal dimensions (Fig. IE). Figure 2A shows the entrance wound of a 32-caliber bullet fired from *For definition, see AppendiX.
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Figure 1. The ballistic effects of various bullets on simulated human tissue. See text for details.
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Figure 2. The effects of a 32-caliber pistol round fired from 3 m away. A, Entrance wound in patient's left Hank. B, Anteroposterior radiograph of the pelvis. The bullet is located just above the right superior pubic ramus. C, A lateral radiograph reveals the bullet to be in the mid pelvis.
a handgun at close range into the left flank of a victim. There was no exit wound, and radiographically (anteroposterior), the round was located in the pelvis just above the right superior pubic ramus (Fig. 2B). A lateral radiograph (Fig. 2C) revealed the round to be in the middle of the patient's pelvis. This relatively small (71 grains) bullet traveling relatively slowly (less than 1000 ftls) expended all of its kinetic energy (130 ft-lbs) in the Table 1. Ballistic Properties of Handguns and Their Bullets CALIBER'
25 32 38 45
BULLET WEIGHT (GRAINS)t
MUZZLE VELOCITY
(FTlS)
50
820
71
910
158 250
870
*Size in hundredths of an inch. tl grain = 60 mg. *At the muzzle.
860
KINETIC ENERGY* (Ff-LBS)
75 130 267 413
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victim where it came to rest. These ballistic data are summarized in Table 1. Not surprisingly, the internal damage to the patient was slight. Although the potential for life-threatening injury to vital structures such as the aorta and inferior vena cava is real, the actual damage to this patient was restricted to a small entrance and an equally small exit wound in the distal small bowel. Each wound was oversewn with several fine silk sutures, and the patient made an uneventful recovery. Contrast this experience with that caused by a comparable bullet fired from a rifle into the pelvis of a victim 50 m away. Figure 3A shows the entrance wound of an AK-47 rifle round in a patient's right buttock. The rifle bullet (Table 2) is slightly smaller in diameter than the handgun bullet (0.30 versus 0.32 inches), but the rifle bullet is heavier, 122 versus 71 grains. More important than these differences is the much greater muzzle velocity of the rifle round (2300 ftls) versus that of the handgun round (910 ftls). Despite a significant difference in ranges (3 versus 50 m), the degre~ of damage caused by the rifle round reflected its much greater kinetic energy, which amounted to a tenfold difference at the muzzles of the two weapons (1470 versus 130 ft-Ibs). The handgun round expended all of its kinetic energy in its victim and thus maximized its potential, mathematically, for tissue destruction. Such was not the case with the rifle round. Figure 3B shows the exit wound caused by the rifle round. Although not large (several centimeters), it is jagged, irregularly round, and avulsive. An overlying dressing is blood soaked, indicating the extensive damage to subcutaneous tissues and their blood vessels caused by the exiting missile. Figure 3C is an anteroposterior radiograph of the patient's pelvis: Multiple metallic fragments are dispersed within that cavity. A small hole is seen in the left sacroiliac region where the bullet penetrated the bony pelvis, crossing from right to left. At laparotomy, multiple injuries were encountered. Sigmoid colostomy was required for a wound of the rectosigmoid colon, and suprapubic cystostomy and bladder repair were necessitated by injuries to that structure. Multiple injuries to the small bowel required multiple repairs of enterotomies, as well as resection of a segment of ileum (Fig. 3D). The much more extensive damage caused by the rifle round was attributable to its fragmentation on striking and penetrating the bony pelvis, producing secondary missiles, albeit too small to be identifiable radiographically or surgically. Even the amount of tissue destruction was not the full potential of the bullet. An exit wound, however small, indicates that a significant portion of the bullet's kinetic energy remained after injuring the victim. This hypothesis is supported by the observation that only a relatively small amount of the original bullet is observed radiographically in the patient. As velocity of a missile increases, so does the probability of multiple organ injuries. This result is secondary to the larger area of injury caused by cavitation within the target, fragmentation of the missile, and secondary missiles, usually of bone. Of the principles basic to an understanding of the form and extent of damage in gunshot wounds, the first is the dissipation of the kinetic energy of a projectile in tissues. A second principle concerns the production of secondary missiles. A third concerns the phenomenon of cavitation.
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Figure 3. The victim of an AK47 gunshot fired from a distance of 50 m. A, Entrance wound (arrow) is located in the patient's right buttock. He is being sigmoidoscoped in the search for a rectal injury, the treating physician having identified blood on rectal examination. B, Exit wound (arrow) in the victim's left lower abdominal quadrant. A blood-soaked dressing has been laid back. (Illustration continued on opposite page)
DISSIPATION OF KINETIC ENERGY The extent and degree of damage in wounds are proportional to the amount of kinetic energy of the missile dissipated in the wound. A rifled bullet (see Appendix) fired at low velocity, spinning with its long axis parallel to the trajectory, may pass rather cleanly through tissue and exit retaining much of the kinetic energy it had on impact. A high-velocity rifle bullet of the same caliber will more likely strike with its long axis at a slight angle to its trajectory-S and, as a consequence of this and of its great velocity, deform and even disintegrate in the tissue (see Fig. IE). The much greater tissue resistance to this high-velocity, deformed, and "tilted" missile and its fragments leads to the degradation of an enormous amount of kinetic energy. The tissue damage is proportionately greater. The kinetic energy of a missile is proportional to the mass of the missile times the square of its velocity (KE - MV2). Tissue damage is proportional to the difference between the kinetic energy the missile has on impact and that on exit. The design of bullets has been directed toward maximizing the difference between the kinetic energy of impact and that of exit, and thus increasing the damage these bullets inflict. When exit velocity is reduced to zero, by whatever means, then maximal dissipation of kinetic energy has occurred, and tissue destruction or wound damage has reached
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Figure 3 (Continued). C, Anteroposterior radiograph indicates multiple metallic fragments, primarily on the left side of the pelvis. A small defect (arrow) in the left sacroiliac portion of the pelvis indicates where the bullet, striking the right buttock, traversed from right to left and penetrated the bony pelvis to the left of the midline. D, A segment of small bowel removed from the patient displays multiple defects characteristic of the effects of a fragmented bullet within the abdomen. A curved clamp is positioned for size comparison.
the maximum for that particular bullet and specific target. These principles are expressed mathematically as follows: [tissue damage - kinetic energy dissipation] [or] [dKE = V2 M (Ventrance2 - Vexif)] where M equals the mass of the missile and V equals its velocity.l Table 2. Ballistic Properties of Rifles and Their Bullets CALIBER"
22 223 30 308
MODEL
Long rifle M-16 AK-47 M-14
BULLET WEIGHT (GRAINS)
MUZZLE VELOCI1Y
KINETIC ENERGY
(FflS)
(FflLBS)t
40
1255
141
55
3240
122 147
2300
1289 1470 2520
2750
*In hundredths (two digits) or thousandths (three digits) of an inch. tAt the muzzle.
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SECONDARY MISSILES A second principle of wound ballistics is that a bullet or its fragments may impart sufficient kinetic energy to dense tissue such as bone and, occasionally, metal (from buttons and buckles of wearing apparel) that secondary missiles are created. These can become highly destructive (see Fig. IF). Not only may they be more destructive than the primary missile, but they take erratic, unpredictable, and unexpected courses. Recognition of potential damage to tissue by secondary missiles is particularly applicable to wounds of the face, wherein teeth may lie in the path of the primary missile. As secondary missiles, these structures often cause more damage to the brain and eyes than does the primary missile. At high velocities, bullets tend to yaw or tumble in tissue, increasing their profiles (i. e., their projected transverse areas perpendicular to the missile track), tending to increase the rate of dissipation of kinetic energy, thus increasing the probability of fragmentation of the primary missile and formation of secondary missiles. 8. II
CAVITATION A third principle of wound ballistics is the phenomenon of cavitation, first recognized by Woodruff in 1898. 18 Low-velocity missiles tend to push tissue aside, producing a path of destruction only slightly greater than the diameter of the missile (see Fig. lA). At higher velocities, the kinetic energy of the bullet is dissipated in part by an acceleration of tissue forward and laterally away from the bullet and track, generating in milliseconds a cavity filled with water vapor at subatmospheric pressure. At high velocity, this cavity continues to enlarge even after the bullet has passed (Fig. IG). The resultant stretching, compressing, and shearing of tissue may produce damage extending several centimeters lateral to the bullet and its track. Vessels, nerves, and other structures that were never in direct contact with the missile may be damaged. Within milliseconds, the cavity collapses because of tissue recoil and atmospheric pressure, only to re-form and collapse repeatedly at rapidly diminishing amplitudes after the bullet has passed. Contaminating foreign material such as pieces of clothing may be sucked through the entrance wound as well as the exit wound. At higher velocities, the entrance wound may be larger than the bullet, as the cavity tends to form earlier and closer to the point of impact. The lateral extent of tissue damage will, of course, be greater. If the path of the bullet through tissue is relatively short, the bullet may exit just as the degradation of its kinetic energy is beginning to increase rapidly through yaw and deformation. 7 In such a situation (see Fig. Ie), the exit wound may be larger and ragged compared with the modest wound of entrance. In longer paths through tissue, the maximal rate of degradation of kinetic energy may occur deep within, creating surprisingly extensive damage through cavitation but leaving entrance and exit wounds appearing as innocuous as those caused by low-velocity missiles (see Fig. IB). If the
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bullet yaws, tumbles, deforms, and fragments, cavitation may be extensive and asymmetric, but the wound of entrance may be modest, jlnd there may be no exit wound (Fig. IE). In tissues of relatively low tensile strength, such as in parenchymal organs like the liver, cavitation develops more readily and extensively than in tissues of greater tensile strength, such as bone or tendon. Intermediate in vulnerability to damage by cavitation is striated muscle. Tissue disruption by cavitation is enhanced by the microscopic mix of connective tissue with more cellular tissue and the consequent shearing of tissue by cavitation developing in any microscopic region. If missile velocities in tissue exceed the speed of sound (approximately 4600 ftls or 1400 m/s), transonic shock waves may be produced, which mayor may not cause adqitional tissue damage. 14. ~5 A comparison of two patients whose chest wounds were caused by rifles exemplifies these ballistic principles. Figure 4A is a photograph of ,a young man who attempted suicide with a 22-caliber rifle. A small entrance wound is seen in the superior aspect of the left side of his chest. Figure 4B shows the exit wound in the left shoulder region posteriorly. It, too, is small; it also is irregular (not round). On the left subclavian arteriogram, the subclavian, axillary, and proximal brachial arteries were normal, and no injury (e.g., intimal defect, false aneurysm, arteriovenous fistula) was identified. In addition, no bony injury was seen (Fig. 4C). Multiple metallic fragments were observed inferior to the left clavicle and superior to the subclavian and axillary arteries. A left brachial, axillary, and subclavian venogram revealed no apparent irljury to these veins (Fig. 4D). In this study, the left upper extremity is abducted, elevating the left clavicle and revealing to better advantage the multiple metallic fragments in the wound. These differ in size and shape. The largest is the probable size of the fragment that exited posteriorly, indicating that only a portion of the bullet's kinetic energy was expended in traversing the patient's torso. Thus, only a portion of the potential for tissue destruction was exerted. All rifle rounds should be considered "high velocity" in that the potential for tissue damage is greater than that of a comparable bullet fired from a handgun. The latter, in general, is "low velocity." Even though bone was not struck, the bullet exhibited by this case fragmented, increasing kinetic energy dissipation and cavitation. Nonetheless, this wound was successfully treated nonoperatively. The patient seen in Figure 5A sustained an AK-47 assault rifle wound of the left side of the chest. The skin about the entrance wound is tattooed, blackened, and burned by the residue of ignited powder near the muzzle of the rifle. The presence of these "powder burns" indicates the probable range to be within a few feet and distinguishes an entrance from an exit wound. The fact that the powder burn is greatest along the lateral aspect of the wound (Fig. 5B) suggests that the rifle was fired from an acut~ angle with respect to the frontal presentation of the victim. In this case, the implication is that the rifleman was to the left of the victim. Although this is seemingly in conflict with the location of the exit woun~ (Fig. 5C), the principle of ricochet makes a bullet or muzzle path difficult to predict with certainty. The exit wound is a large, irregular, avulsive wound located in the left shoulder posteriorly. A closer view (Fig. 5D) reveals a large cavity,
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Figure 4. A young man sustained a 22-caliber rifle wound of the superior portion of the left side of the chest in an apparent suicide attempt. A, The entrance wound is seen just inferior to the left clavicle. B, An exit wound is located posteriorly along the medial aspect of the left shoulder. C, An arteriogram of the left subclavian, axillary, and proximal brachial arteries reveals no apparent injury. Multiple metallic fragments are seen between the left clavicle and these arteries. No fracture is apparent. D, A left brachial, axillary, and subclavian venogram is unremarkable with the exception of multiple metallic fragments seen to better advantage with the patient's left arm abducted.
with skeletal muscle extruding from the depths where gas bubbles from injured pulmonary parenchyma are apparent. Figures 5E and F are anteroposterior and lateral radiographs of the patient's chest. A thoracostomy tube is seen. The injuries include multiple rib fractures and contusions of both lobes of the left lung. No metallic foreign bodies are seen, indicating that the bullet left the patient in its entirety. Whether it was fragmented is unknown. However, the size of the exit wound suggests that it resulted from secondary missiles of bone and multiple fragments of metal. The cavitary nature of the wound is evident on inspection of the exit alone.
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Although the pulmonary lesion would respond to tube thoracostomy and nonoperative management of ventilation and oxygenation, as well as antimicrobial therapy, the exit wound required radical debridement of devitalized soft tissues. In this case, no significant neurovascular injury or additional skeletal fracture was apparent. As in a previous case, this AK-47 round dissipated only a portion of its kinetic energy, because it exited, possibly intact, probably with significant velocity. It undoubtedly would have been a copper-jacketed round, in conformity with accords reached at the Hague Peace Conference of 1899, which stipulate that lead or other metallic bullets be protected against deformation so as to minimize their lethality in time of international conflict. 12 This apparent paradox brings reality to the premise that bullets fired in peacetime are often more destructive of tissue than those fired in war. The former generally are not copper jacketed and thus are more likely to deform during terminal ballistics and dissipate considerably more kinetic energy. This is an importaI).t distinction between civilian and military gunshot wounds, and one that has obvious clinical relevance. Critical application of these three principles-the relation between the mass and velocity of the projectile and its potential for imparting destructive forces to tissues, the production of secondary missiles, and the mechanism of cavitation-will guide the surgeon in his or her appraisal of the extent of damage, the need for debridement, and the potential for infection, as well as the possibilities for reconstruction. Obviously, management can be more effective if the surgeon can obtain appropriate information regarding the nature of the weapon inflicting the damage. In this discussion, we have separated our considerations of these three principles of wound ballistics. In actuality, they are complexly interrelated. 3, 4 For example, the rate of dissipation of kinetic energy in tissue and the degree of cavitation are functions of the shape of the bullet and its velocity on impact. Again, at a given velocity, the smaller the mass is, the greater is its tendency to yaw, tumble, and fragment.
SHOTGUNS The foregoing discussion has considered the wound baiIistics of a single bullet fired from a handgun or a rifle. The inside of a shotgun barrel is smooth ("smooth bored"): it is not helically grooved to impart spin and stability to a bullet, as in a rifle or handgun. A shotgun fires a "missile" consisting of a few to hundreds oflead or steel spheres (pellets) at relatively high muzzle velocity (1000-1500 ftls) and with massive wounding capacity at a range ofless than 4 to 5 yards (3.6-4.5 m). Because of the unfavorable aerodynamic shape of a spherical pellet compared with a pointed bullet, shotgun pellets decelerate rapidly, degrading kinetic energy to heat as their trajectories diverge after leaving the muzzle of the shotgun. Beyond 50 yards, the wounding capacity of these dispersed pellets generally is negligible (except for an eye or laryngeal wound), compared with effective ranges (see Appendix) of hundreds to thousands of yards in the case of a highpowered rifle. The effective range of a i2-gauge shotgun generally is from 20 to 50 m, depending on the several variables mentioned above. By contrast, the
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Figure 5. A soldier who sustained an AK-47 gunshot wound to the left side of his chest. A, The entrance wound is seen anteriorly. B, The entrance wound seen close up. It is surrounded by powder burns, more prominent to the left side of the patient, suggesting a tangential wound. C, The exit wound in the left posterior axillary line is large and irregular. D, The exit wound seen close up. Its cavitary nature is evident. Skeletal muscle is extruding from the depths of the wound, where gas bubbles indicate the presence of a pulmonary parenchymal injury. (Illustration continued on opposite page)
effective range of a rifle is measured in hundreds of meters (M-16: 300 m). The high muzzle velocity, the large total weight of the pellets (traveling as a single mass and not yet dispersing), and the rapid deceleration of the nonaerodynamic spherical pellets yield, at a range of 1 to 2 yd (0.9-1.8 m), a single large ragged entrance wound, severe and extensive tissue destruction, and, usually, in wounds of the trunk, no exit wound. At a range of 3 to 4 yd (2.7-3.6 m) and depending on the gauge and shot number, the entrance wound will be larger and will probably be surrounded by several single pellet wounds, each of which may show significant deformation. Beyond 20 yd (18 m), the pattern of pellet dispersion may be 1 to 3 ft (0.30.9 m) in diameter, with the likelihood that only a few pellets will hit the target and be modestly destructive. Thus, range is the most critical determinant of the wounding capacity of a shotgun. Gauge indicates the diameter of the bore of a shotgun and the diameter of the corresponding shotgun cartridge (or shell). Although measured in
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Figure 5 (Continued). E, Anteroposterior radiograph reveals a left-sided thoracostomy tube in place. There are multiple rib fractures, and contusion of both the upper and the lower lobes of the left lung is evident. F, A lateral radiograph confirms the presence of pulmonary contusion.
hundredths or thousandths of an inch, these diameters also are expressed in gauge numbers, ranging from 12 (the largest) to 410 (the smallest). Twelve (0.729 inch) and twenty (0.615 inch) are the gauges in most common use (see Appendix). Shot number indicates the diameter and number of pellets in a given cartridge: the higher the number, the smaller and more numerous the pellets. In a given gauge, the total weight of the pellet in a cartridge is constant. Shot numbers range from 12, the smallest (0.05 inches in diameter), to 00 (double 0 buckshot; 0.33 inches). Thus, for example, a 12-gauge shotgun cartridge loaded with No.9 shot for a 12-gauge shotgun bore contains 585 pellets, each 0.08 inches in diameter, for a total weight of lead of 1 oz; and a 20-gauge cartridge loaded with No.9 shot contains 512 pellets, for a total weight of 0.875 oz. Ballistic data are summarized in Table 3. However quaint, this classification is generally accepted. A "sawed-off" shotgun, that is, a shotgun whose barrel has been shortened by about 1 ft for criminal or riot control purposes, offers the advantage of a more rapid dispersion of the pellets and an increased probability of at least some of the pellets hitting the target, as well as the advantage of easier concealment. Figure 6A exhibits a 35-year-old man who sustained a 410 shotgun wound to the right anterior aspect of his chest from a distance of 3 m. There was no exit wound. A right thoracostomy tube was inserted because of decreased breath sounds on auscultation. Four hundred milliliters of blood, along with air, was evacuated. On closer inspection (Fig. 6B), the wound appeared to be slightly tangential, and its cavity extended toward the midline. The extent of the damage is seen in part radiographically (Fig. 6C), and the pellet size was determined to be No.9. The kink in the chest tube was corrected. Because the pellets appeared to be intra-abdominal as well as intrathoracic, and because the patient had symptoms and signs of
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Table 3. Ballistic Properties of Shotguns and Their Pellets* MUZZLE
PELLETS
GAUGE
Quantity
Size (inches)
No.
410t
67 197 512 225 585
0.13 0.11 0.11 0.11 0.08
6 9 6 9
20 20 12 12
4
Weight (oz)
Velocity (]tIs)
Kinetic Energy (ft/lbs)
0.500 0.875 0.875 1.000 1.000
1150 1200 1200 1200 1200
385 800 800 2100 2100
*These are estimates and averages of a spectrum of weights and velocities for each gun and its cartridges. t410 "gauge" is actually 410 caliber.
an acute abdomen, exploratory laparotomy was performed, and wounds of the right hepatic lobe were observed (Fig. 6D). Multiple pellets were removed, and the diaphragm was noted to be perforated in several places. The wound of entrance was then debrided, and the plastic shot carrier (Fig. 6E), not seen radiographically, was removed. In this case, despite the small gauge, extensive damage to soft tissue resulted. When shotguns are wounding agents, care must be taken to search for foreign bodies such as wadding and, in this case, plastic containers. Such foreign bodies are sources of wound contamination and subsequent abscess if not identified and removed. Because they are not apparent radiographically, they may be missed if a high index of suspicion is not applied. Such wounds are appropriately treated with pulsed jet lavage, which helps to remove pellets as well as uncover the foreign body. 16 Figure 7A reveals entrance and exit wounds of the right upper extremity of a 27-year-old man who was shot from a distance of about 5 m by a 20-gauge shotgun. His arms were extended and abducted as he faced his assailant. Although only a portion of the pellet mass struck him, there were these two wounds, entrance posteriorly and exit medially. Arteriography (Fig. 7B) revealed an abrupt cutoff of contrast agent near the origin of the right brachial artery. Multiple pellets of No.9 shot were positioned near the entrance and exit wounds. Large defects in the brachial artery and vein were found at operation but could be repaired satisfactorily with autologous saphenous vein; however, injuries to the median and ulnar nerves could not be repaired. Injury to the underlying muscle was significant and necessitated extensive debridement. A third type of shotgun wound is illustrated by Figure SA. A 16-yearold sustained wounds to both thighs from a 12-gauge shotgun said to have been fired from "one car-length." Both thighs were tense, although there was no apparent neurovascular damage clinically. A lateral radiograph of the left lower extremity (Fig. SB) reveals an intact femur, soft-tissue disruption throughout, and multiple metallic densities of No. 6 shot posterior to the femur. Figure se views the right lower extremity radiographically from the lateral aspect and reveals most of the pellets to be posterior to the femur. A digital subtraction right femoral arteriogram (Fig. SD and E) was normal. Nonetheless, the patient underwent thorough debridement of both thighs (Fig. SF) because of extensive damage to the
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Figure 6. A 35-year-old man sustained a 410 shotgun wound to the right side of his chest from a distance of approximately 3 m. A, Thoracostomy tube has been inserted. B, A close-up of the entrance wound reveals that the missiles were directed toward the midline. C, Anteroposterior radiograph of the chest reveals multiple small (No.9) shot. The kinked thoracostomy tube was later corrected. There is extensive contusion of the right lung, and the pellets appear to be intra-abdominal. D, Exploratory laparotomy was performed because of the presence of an acute abdomen and because the pellets were thought to be intra-abdominal. A wound of the right lobe of the liver was identified (arrow). E, A close-up view of the chest dUring debridement reveals a plastic "shot" carrier in the depths of the wound (arrow).
quadriceps musculature. Delayed primary closure of both wounds was carried out 5 days later. MEDICOLEGAL CONSIDERATIONS
In cases of gunshot wounding, medicolegal considerations frequently depend on some knowledge of ballistics. Law-enforcement officials are often
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Figure 7. Entrance and exit wounds (A) in the right arm of a 27-year-old man were produced by a 20-gauge shotgun fired tangentially and from a distance of 5 m. B, Arteriography reveals a cutoff (arrow) in the proximal right brachial artery. No reconstitution of How is seen. Multiple pellets of No.9 shot are located about the entrance and exit wounds.
frustrated by the apparently careless manner in which critical information or evidence is handled, even by experienced medical and paramedical personnel, in the emergency room as well as the operating room. In this regard, certain principles deserve reiteration and emphasis, because the present legal climate of this country places stringent constraints on the lawenforcement community.9 "Each instance of a frustration of justice due to careless handling of evidence by a surgical team is an irony not to be tolerated." At a bare minimum, the medical team receiving a patient who has sustained a gunshot wound should: (1) exert care not to destroy the clothing worn by the patient, and in particular, to cut around and not through bullet holes; (2) carefully preserve and turn over to appropriate law-enforcement officials any weapon, and more specifically, any metallic foreign body obtained from the patient, such as a bullet or its fragments; (3) describe as precisely as possible and even photograph prior to debridement (a diagram for the patient's personal record is an appropriate alternative) any entrance or exit wound; and (4) query the police and witnesses as to the nature of the weapon (firearm, caliber) and distance (range). Although the medical team is not expected to assume the role of sleuth, its cooperation may prove critical in the pursuit of justice.
Figure 8. A I6-year-old sustained frontal shotgun wounds from a single I2-gauge cartridge containing No.6 shot from a distance of "one car-length." A, Both thighs were tense, but no neurovascular injury was evident clinically. B, A lateral radiograph of the left lower extremity reveals no fracture but multiple metallic densities of No. 6 shot located posterior to the femur. Extensive soft-tissue disruption is apparent, but no fracture is observed. C, A lateral radiograph of the right lower extremity reveals multiple metallic densities of No.6 shot, located mostly posterior to the right femur, which is free of fracture. D, A right femoral digital subtraction arteriogram reveals no injury to the superficial artery in the region of the pellets. E, A continuation of the right femoral digital subtraction arteriogram to include the proximal popliteal artery reveals no vascular injury. F, Wounds of both thighs are opened widely and debrided of underlying devitalized soft tissue. Delayed primary closure was accomplished successfully 5 days later.
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Figure 8 (See legend on opposite page)
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REFERENCES 1. Adams DB: Wound ballistics: A review. Milit Med 27:831-835, 1982 2. Amato JJ, Billy IJ, Lawson NS, et al: High velocity missile injury: An experimental study of the retentive forces of tissue. Am J Surg 127:454-459, 1974 3. Barach E, Tomlanovich M, Nowak R: Ballistics: A pathophysIologic examination of the wounding mechanisms of firearms. 1. J. Trauma 26:232-235, 1986 4. Barach E, Tomlanovich M, Nowak R: Ballistics: A pathophysiologic examination of the wounding mechanism of firearms. II. J Trauma 26:374-383, 1990 5. Berlin RH, Janzon B, Liden E, et al: Wound ballistics of Swedish 5.56-mm assault rifle AK 5. J Trauma 28 (suppl):76-83, 1988 6. Berlin RH, Janson B, Rybeck B, et al: A proposed standard methodology for estimating the wounding capacity of small calibre projectiles or other missiles. Acta Chir Scand Suppl 508:11, 1982 7. Fackler ML, Breteau JP, Courbil LJ, et al: Open wound drainage versus wound excision in treating the modern assault rifle wound. Surgery 105:576-584, 1989 8. Fackler ML, Surinchak JS, Malinowski JA, et al: Bullet fragmentation: A major cause of tissue disruption. J Trauma 24:35-39, 1984 9. Harris LS: Editorial comment. J Trauma 17:871, 1977 10. Janzon B, Seeman T: Muscle devitalization in high-energy missile wounds, and its dependence on energy transfer. J Trauma 25:138-144, 1985 11. Liu YA, Wu BJ, Xie ZC, et al: Wounding effects of two types of bullets in soft tissue of dogs. Acta Chir Scand Suppl 508, 1982 12. Ragsdale B: Gunshot wounds: A,historical perspective, Milit Med 149:301-315, 1984 13. Ryan JM, Cooper GJ, Maynard RL: Wound ballistics: Contemporary and future research. J R Army Med Corps, 134:119-125, 1988 14. Suneson A, Hansson HA, Seeman T: Pressure wave injuries to the nervous system caused by high-energy missile extremity impact I: Local and distant effects on the peripheral nervous system-A light and electron microscopic study on pigs, J Trauma 30:281-294, 1990 15. Suneson A, Hansson A, Seeman T: Pressure wave injuries to the nervous system caused by high-energy missile extremity impact II: Distant effects on the central nervous system-A light and electron microscopic study on pigs. J Trauma 30:295-306, 1990 16. Swan KG, Swan RC: Gunshot Wounds: Pathophysiology and Management, ed. 2. Chicago, Year Book Medical Publishers, 1989 17. Wang ZG, Qian CW, Zhan DC, et al: Pathological changes of gunshot wounds at various intervals after wounding. Acta Chir Scand Suppl 508:197-210, 1982 18. Woodruff CEo The causes of the explosive effect of modern small caliber bullets. NY Med J 67:593-601, 1898
Address reprint requests to Kenneth G. Swan, MD, FACS Section of General Surgery University of Medicine & Dentistry of New Jersey Newark, New Jersey 07103
APPENDIX Definitions of Weapons Terminology Caliber is the diameter of a bullet or rifle bore in hundredths (two digits) or thousandths (three digits) .of an inch. Gauge number is derived from the number of lead spheres of a diameter equal to the diameter of the bore making up 1 lb of lead. Range is defined as effective, maximal effective, and maximal. The last is the distance the unimpeded pellet or slug will travel when the weapon is fired at an appropriate acute angle with the horizontal. This is the definition of trajectory. The maximal effective range is the distance from which a marksman can be expected to strike a target (accuracy) and inflict a potentially mortal wound (lethality). The effective range is the same predicted result when the weapon is fired by less than a marksman. A rifted bullet is an elongated projectile to which spin on the long axis has been imparted by helical grooves in the barrel of the firearm.
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Principles of Ballistics Applicable to the Treatment of Gunshot Wounds Kenneth G. Swan, MD, FACS, * and Roy C. Swan, MDt
Ballistics is the science of the motion of a projectile through the barrel of a firearm (internal ballistics), during its subsequent flight through air or space (external ballistics), and during its final, complicated motion after striking the target (terminal ballistics). Wound ballistics is a special case of terminal ballistics in which the target is animal tissue. 2. 6, 10, 11, 13, 16, 17 Internal and external ballistics are nearly exact sciences, whereas terminal ballistics is so complex as to be, at best, sets of approximations. Nonetheless, the principles of wound ballistics enter usefully into an evaluation of a gunshot wound and its treatment. This is becoming increasingly apparent as the development of firearms in recent decades has moved toward progressively smaller projectiles with increasingly higher velocities. Internal ballistics considers the conversion of chemical energy of the propellant (gunpowder in the case of firearms) to the kinetic energy of the bullet. It considers the time course and interrelations of pressure, volume, and velocity in the bore of the firearm and the induction of "spin" of the bullet to achieve stability in flight by the rifling (helical grooves) in the bore (internal surface) of the gun barrel. When a cartridge (packaged gunpowder, propellant, primer, and bullet) is loaded into the chamber (breech end of the gun barrel) and its primer is struck mechanically, the resulting spark ignites the propellant and starts the controlled burning of this propellant in the chamber. As the precisely sized and shaped grains of propellant are volatilized and ignited at an accelerating rate, the inertia and resistance of the bullet are overcome, and it accelerates toward the muzzle. The volume behind the accelerating bullet increases, but the tendency of the pressure to fall is more than offset by the rapidly increasing total surface of the gas-emitting grains and the corresponding accelerating rate of burning. The rate of increase in pressure and the increase in the velocity continues until maxima are reached when *Professor and Chief, Section of General Surgery, and Director of Thoracic Surgery, University of Medicine and Dentistry of New Jersey, Newark, New Jersey tJoseph C. Hinsey Professor of Anatomy and Cell Biology Emeritus, Cornell University Medical College, New York, New York
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the bullet is about one third the distance toward the muzzle. Beyond this, pressure falls to about 20% of the maximum attained (tens of thousands of pounds per square inch), and the bullet leaves the muzzle still accelerating under the rapidly falling pressure of gas, which begins to escape from the muzzle. The bore of the rifle or handgun is drilled to produce a helix of alternating grooves and ridges (lands) called the rifling of the gun barrel, with a pitch, typically, of about one turn per 10 inches along the barrel from breech to muzzle. On ignition, the relatively hard steel ridges and grooves of the bore impress a corresponding pattern in the soft metal of the cylindrical part of the bullet so that it is accelerated not only linearly but also angularly. The resulting "spin" imparts stability to the trajectory of the bullet and tends to suppress erratic flight, typically in the form of yaw (the angle between the long axis of the bullet and its line of flight) and tumbling (forward rotation, end over end, around the bullet's center of mass).
EXTERNAL BALLISTICS As the accelerating bullet is forced through the muzzle, the turbulence of the emerging gas will induce slight yaw (only a few degrees) and a corresponding increase in resistance to the bullet. These latter factors will increase progressively and, over a long range (distance between muzzle and target), lead to a substantial drop in velocity.
TERMINAL (WOUND) BALLISTICS A low-velocity «1000 ftls or 305 m/s), 22-caliber* (5.6-mm-diameter bullet) pistol wound of soft tissue, such as the calf, will exhibit an entrance and an exit wound smaller than the diameter of the bullet and a track of tissue damage not much greater in diameter (Fig. lA). Usually, this wound will not require debridement. A higher-velocity (>3000 ftls or 914 m/s) gunshot wound, such as that resulting from a bullet of the same caliber from the current US military rifle (Colt M-16 A2) or a comparable military or sporting rifle, may exhibit a similar entrance, but the exit may range from the same to several times the diameter of the bullet (Fig. IB and C). Conversely, there may be no exit (Fig. ID) or an enormous exit (Fig. lC), depending on the shape and construction of the bullet and the tensile strength and density of the tissue it encounters.6 The track of this highvelocity, rapidly decelerating, deforming, and disintegrating projectile may be surrounded by tissue destruction extending as much as several centimeters radially from the track secondary to a momentary intense compression and subsequent stretching of surrounding tissue to many times its normal dimensions (Fig. IE). Figure 2A shows the entrance wound of a 32-caliber bullet fired from *For definition, see AppendiX.
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Figure 1. The ballistic effects of various bullets on simulated human tissue. See text for details.
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Figure 2. The effects of a 32-caliber pistol round fired from 3 m away. A, Entrance wound in patient's left Hank. B, Anteroposterior radiograph of the pelvis. The bullet is located just above the right superior pubic ramus. C, A lateral radiograph reveals the bullet to be in the mid pelvis.
a handgun at close range into the left flank of a victim. There was no exit wound, and radiographically (anteroposterior), the round was located in the pelvis just above the right superior pubic ramus (Fig. 2B). A lateral radiograph (Fig. 2C) revealed the round to be in the middle of the patient's pelvis. This relatively small (71 grains) bullet traveling relatively slowly (less than 1000 ftls) expended all of its kinetic energy (130 ft-lbs) in the Table 1. Ballistic Properties of Handguns and Their Bullets CALIBER'
25 32 38 45
BULLET WEIGHT (GRAINS)t
MUZZLE VELOCITY
(FTlS)
50
820
71
910
158 250
870
*Size in hundredths of an inch. tl grain = 60 mg. *At the muzzle.
860
KINETIC ENERGY* (Ff-LBS)
75 130 267 413
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victim where it came to rest. These ballistic data are summarized in Table 1. Not surprisingly, the internal damage to the patient was slight. Although the potential for life-threatening injury to vital structures such as the aorta and inferior vena cava is real, the actual damage to this patient was restricted to a small entrance and an equally small exit wound in the distal small bowel. Each wound was oversewn with several fine silk sutures, and the patient made an uneventful recovery. Contrast this experience with that caused by a comparable bullet fired from a rifle into the pelvis of a victim 50 m away. Figure 3A shows the entrance wound of an AK-47 rifle round in a patient's right buttock. The rifle bullet (Table 2) is slightly smaller in diameter than the handgun bullet (0.30 versus 0.32 inches), but the rifle bullet is heavier, 122 versus 71 grains. More important than these differences is the much greater muzzle velocity of the rifle round (2300 ftls) versus that of the handgun round (910 ftls). Despite a significant difference in ranges (3 versus 50 m), the degre~ of damage caused by the rifle round reflected its much greater kinetic energy, which amounted to a tenfold difference at the muzzles of the two weapons (1470 versus 130 ft-Ibs). The handgun round expended all of its kinetic energy in its victim and thus maximized its potential, mathematically, for tissue destruction. Such was not the case with the rifle round. Figure 3B shows the exit wound caused by the rifle round. Although not large (several centimeters), it is jagged, irregularly round, and avulsive. An overlying dressing is blood soaked, indicating the extensive damage to subcutaneous tissues and their blood vessels caused by the exiting missile. Figure 3C is an anteroposterior radiograph of the patient's pelvis: Multiple metallic fragments are dispersed within that cavity. A small hole is seen in the left sacroiliac region where the bullet penetrated the bony pelvis, crossing from right to left. At laparotomy, multiple injuries were encountered. Sigmoid colostomy was required for a wound of the rectosigmoid colon, and suprapubic cystostomy and bladder repair were necessitated by injuries to that structure. Multiple injuries to the small bowel required multiple repairs of enterotomies, as well as resection of a segment of ileum (Fig. 3D). The much more extensive damage caused by the rifle round was attributable to its fragmentation on striking and penetrating the bony pelvis, producing secondary missiles, albeit too small to be identifiable radiographically or surgically. Even the amount of tissue destruction was not the full potential of the bullet. An exit wound, however small, indicates that a significant portion of the bullet's kinetic energy remained after injuring the victim. This hypothesis is supported by the observation that only a relatively small amount of the original bullet is observed radiographically in the patient. As velocity of a missile increases, so does the probability of multiple organ injuries. This result is secondary to the larger area of injury caused by cavitation within the target, fragmentation of the missile, and secondary missiles, usually of bone. Of the principles basic to an understanding of the form and extent of damage in gunshot wounds, the first is the dissipation of the kinetic energy of a projectile in tissues. A second principle concerns the production of secondary missiles. A third concerns the phenomenon of cavitation.
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Figure 3. The victim of an AK47 gunshot fired from a distance of 50 m. A, Entrance wound (arrow) is located in the patient's right buttock. He is being sigmoidoscoped in the search for a rectal injury, the treating physician having identified blood on rectal examination. B, Exit wound (arrow) in the victim's left lower abdominal quadrant. A blood-soaked dressing has been laid back. (Illustration continued on opposite page)
DISSIPATION OF KINETIC ENERGY The extent and degree of damage in wounds are proportional to the amount of kinetic energy of the missile dissipated in the wound. A rifled bullet (see Appendix) fired at low velocity, spinning with its long axis parallel to the trajectory, may pass rather cleanly through tissue and exit retaining much of the kinetic energy it had on impact. A high-velocity rifle bullet of the same caliber will more likely strike with its long axis at a slight angle to its trajectory-S and, as a consequence of this and of its great velocity, deform and even disintegrate in the tissue (see Fig. IE). The much greater tissue resistance to this high-velocity, deformed, and "tilted" missile and its fragments leads to the degradation of an enormous amount of kinetic energy. The tissue damage is proportionately greater. The kinetic energy of a missile is proportional to the mass of the missile times the square of its velocity (KE - MV2). Tissue damage is proportional to the difference between the kinetic energy the missile has on impact and that on exit. The design of bullets has been directed toward maximizing the difference between the kinetic energy of impact and that of exit, and thus increasing the damage these bullets inflict. When exit velocity is reduced to zero, by whatever means, then maximal dissipation of kinetic energy has occurred, and tissue destruction or wound damage has reached
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Figure 3 (Continued). C, Anteroposterior radiograph indicates multiple metallic fragments, primarily on the left side of the pelvis. A small defect (arrow) in the left sacroiliac portion of the pelvis indicates where the bullet, striking the right buttock, traversed from right to left and penetrated the bony pelvis to the left of the midline. D, A segment of small bowel removed from the patient displays multiple defects characteristic of the effects of a fragmented bullet within the abdomen. A curved clamp is positioned for size comparison.
the maximum for that particular bullet and specific target. These principles are expressed mathematically as follows: [tissue damage - kinetic energy dissipation] [or] [dKE = V2 M (Ventrance2 - Vexif)] where M equals the mass of the missile and V equals its velocity.l Table 2. Ballistic Properties of Rifles and Their Bullets CALIBER"
22 223 30 308
MODEL
Long rifle M-16 AK-47 M-14
BULLET WEIGHT (GRAINS)
MUZZLE VELOCI1Y
KINETIC ENERGY
(FflS)
(FflLBS)t
40
1255
141
55
3240
122 147
2300
1289 1470 2520
2750
*In hundredths (two digits) or thousandths (three digits) of an inch. tAt the muzzle.
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SECONDARY MISSILES A second principle of wound ballistics is that a bullet or its fragments may impart sufficient kinetic energy to dense tissue such as bone and, occasionally, metal (from buttons and buckles of wearing apparel) that secondary missiles are created. These can become highly destructive (see Fig. IF). Not only may they be more destructive than the primary missile, but they take erratic, unpredictable, and unexpected courses. Recognition of potential damage to tissue by secondary missiles is particularly applicable to wounds of the face, wherein teeth may lie in the path of the primary missile. As secondary missiles, these structures often cause more damage to the brain and eyes than does the primary missile. At high velocities, bullets tend to yaw or tumble in tissue, increasing their profiles (i. e., their projected transverse areas perpendicular to the missile track), tending to increase the rate of dissipation of kinetic energy, thus increasing the probability of fragmentation of the primary missile and formation of secondary missiles. 8. II
CAVITATION A third principle of wound ballistics is the phenomenon of cavitation, first recognized by Woodruff in 1898. 18 Low-velocity missiles tend to push tissue aside, producing a path of destruction only slightly greater than the diameter of the missile (see Fig. lA). At higher velocities, the kinetic energy of the bullet is dissipated in part by an acceleration of tissue forward and laterally away from the bullet and track, generating in milliseconds a cavity filled with water vapor at subatmospheric pressure. At high velocity, this cavity continues to enlarge even after the bullet has passed (Fig. IG). The resultant stretching, compressing, and shearing of tissue may produce damage extending several centimeters lateral to the bullet and its track. Vessels, nerves, and other structures that were never in direct contact with the missile may be damaged. Within milliseconds, the cavity collapses because of tissue recoil and atmospheric pressure, only to re-form and collapse repeatedly at rapidly diminishing amplitudes after the bullet has passed. Contaminating foreign material such as pieces of clothing may be sucked through the entrance wound as well as the exit wound. At higher velocities, the entrance wound may be larger than the bullet, as the cavity tends to form earlier and closer to the point of impact. The lateral extent of tissue damage will, of course, be greater. If the path of the bullet through tissue is relatively short, the bullet may exit just as the degradation of its kinetic energy is beginning to increase rapidly through yaw and deformation. 7 In such a situation (see Fig. Ie), the exit wound may be larger and ragged compared with the modest wound of entrance. In longer paths through tissue, the maximal rate of degradation of kinetic energy may occur deep within, creating surprisingly extensive damage through cavitation but leaving entrance and exit wounds appearing as innocuous as those caused by low-velocity missiles (see Fig. IB). If the
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bullet yaws, tumbles, deforms, and fragments, cavitation may be extensive and asymmetric, but the wound of entrance may be modest, jlnd there may be no exit wound (Fig. IE). In tissues of relatively low tensile strength, such as in parenchymal organs like the liver, cavitation develops more readily and extensively than in tissues of greater tensile strength, such as bone or tendon. Intermediate in vulnerability to damage by cavitation is striated muscle. Tissue disruption by cavitation is enhanced by the microscopic mix of connective tissue with more cellular tissue and the consequent shearing of tissue by cavitation developing in any microscopic region. If missile velocities in tissue exceed the speed of sound (approximately 4600 ftls or 1400 m/s), transonic shock waves may be produced, which mayor may not cause adqitional tissue damage. 14. ~5 A comparison of two patients whose chest wounds were caused by rifles exemplifies these ballistic principles. Figure 4A is a photograph of ,a young man who attempted suicide with a 22-caliber rifle. A small entrance wound is seen in the superior aspect of the left side of his chest. Figure 4B shows the exit wound in the left shoulder region posteriorly. It, too, is small; it also is irregular (not round). On the left subclavian arteriogram, the subclavian, axillary, and proximal brachial arteries were normal, and no injury (e.g., intimal defect, false aneurysm, arteriovenous fistula) was identified. In addition, no bony injury was seen (Fig. 4C). Multiple metallic fragments were observed inferior to the left clavicle and superior to the subclavian and axillary arteries. A left brachial, axillary, and subclavian venogram revealed no apparent irljury to these veins (Fig. 4D). In this study, the left upper extremity is abducted, elevating the left clavicle and revealing to better advantage the multiple metallic fragments in the wound. These differ in size and shape. The largest is the probable size of the fragment that exited posteriorly, indicating that only a portion of the bullet's kinetic energy was expended in traversing the patient's torso. Thus, only a portion of the potential for tissue destruction was exerted. All rifle rounds should be considered "high velocity" in that the potential for tissue damage is greater than that of a comparable bullet fired from a handgun. The latter, in general, is "low velocity." Even though bone was not struck, the bullet exhibited by this case fragmented, increasing kinetic energy dissipation and cavitation. Nonetheless, this wound was successfully treated nonoperatively. The patient seen in Figure 5A sustained an AK-47 assault rifle wound of the left side of the chest. The skin about the entrance wound is tattooed, blackened, and burned by the residue of ignited powder near the muzzle of the rifle. The presence of these "powder burns" indicates the probable range to be within a few feet and distinguishes an entrance from an exit wound. The fact that the powder burn is greatest along the lateral aspect of the wound (Fig. 5B) suggests that the rifle was fired from an acut~ angle with respect to the frontal presentation of the victim. In this case, the implication is that the rifleman was to the left of the victim. Although this is seemingly in conflict with the location of the exit woun~ (Fig. 5C), the principle of ricochet makes a bullet or muzzle path difficult to predict with certainty. The exit wound is a large, irregular, avulsive wound located in the left shoulder posteriorly. A closer view (Fig. 5D) reveals a large cavity,
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Figure 4. A young man sustained a 22-caliber rifle wound of the superior portion of the left side of the chest in an apparent suicide attempt. A, The entrance wound is seen just inferior to the left clavicle. B, An exit wound is located posteriorly along the medial aspect of the left shoulder. C, An arteriogram of the left subclavian, axillary, and proximal brachial arteries reveals no apparent injury. Multiple metallic fragments are seen between the left clavicle and these arteries. No fracture is apparent. D, A left brachial, axillary, and subclavian venogram is unremarkable with the exception of multiple metallic fragments seen to better advantage with the patient's left arm abducted.
with skeletal muscle extruding from the depths where gas bubbles from injured pulmonary parenchyma are apparent. Figures 5E and F are anteroposterior and lateral radiographs of the patient's chest. A thoracostomy tube is seen. The injuries include multiple rib fractures and contusions of both lobes of the left lung. No metallic foreign bodies are seen, indicating that the bullet left the patient in its entirety. Whether it was fragmented is unknown. However, the size of the exit wound suggests that it resulted from secondary missiles of bone and multiple fragments of metal. The cavitary nature of the wound is evident on inspection of the exit alone.
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Although the pulmonary lesion would respond to tube thoracostomy and nonoperative management of ventilation and oxygenation, as well as antimicrobial therapy, the exit wound required radical debridement of devitalized soft tissues. In this case, no significant neurovascular injury or additional skeletal fracture was apparent. As in a previous case, this AK-47 round dissipated only a portion of its kinetic energy, because it exited, possibly intact, probably with significant velocity. It undoubtedly would have been a copper-jacketed round, in conformity with accords reached at the Hague Peace Conference of 1899, which stipulate that lead or other metallic bullets be protected against deformation so as to minimize their lethality in time of international conflict. 12 This apparent paradox brings reality to the premise that bullets fired in peacetime are often more destructive of tissue than those fired in war. The former generally are not copper jacketed and thus are more likely to deform during terminal ballistics and dissipate considerably more kinetic energy. This is an importaI).t distinction between civilian and military gunshot wounds, and one that has obvious clinical relevance. Critical application of these three principles-the relation between the mass and velocity of the projectile and its potential for imparting destructive forces to tissues, the production of secondary missiles, and the mechanism of cavitation-will guide the surgeon in his or her appraisal of the extent of damage, the need for debridement, and the potential for infection, as well as the possibilities for reconstruction. Obviously, management can be more effective if the surgeon can obtain appropriate information regarding the nature of the weapon inflicting the damage. In this discussion, we have separated our considerations of these three principles of wound ballistics. In actuality, they are complexly interrelated. 3, 4 For example, the rate of dissipation of kinetic energy in tissue and the degree of cavitation are functions of the shape of the bullet and its velocity on impact. Again, at a given velocity, the smaller the mass is, the greater is its tendency to yaw, tumble, and fragment.
SHOTGUNS The foregoing discussion has considered the wound baiIistics of a single bullet fired from a handgun or a rifle. The inside of a shotgun barrel is smooth ("smooth bored"): it is not helically grooved to impart spin and stability to a bullet, as in a rifle or handgun. A shotgun fires a "missile" consisting of a few to hundreds oflead or steel spheres (pellets) at relatively high muzzle velocity (1000-1500 ftls) and with massive wounding capacity at a range ofless than 4 to 5 yards (3.6-4.5 m). Because of the unfavorable aerodynamic shape of a spherical pellet compared with a pointed bullet, shotgun pellets decelerate rapidly, degrading kinetic energy to heat as their trajectories diverge after leaving the muzzle of the shotgun. Beyond 50 yards, the wounding capacity of these dispersed pellets generally is negligible (except for an eye or laryngeal wound), compared with effective ranges (see Appendix) of hundreds to thousands of yards in the case of a highpowered rifle. The effective range of a i2-gauge shotgun generally is from 20 to 50 m, depending on the several variables mentioned above. By contrast, the
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Figure 5. A soldier who sustained an AK-47 gunshot wound to the left side of his chest. A, The entrance wound is seen anteriorly. B, The entrance wound seen close up. It is surrounded by powder burns, more prominent to the left side of the patient, suggesting a tangential wound. C, The exit wound in the left posterior axillary line is large and irregular. D, The exit wound seen close up. Its cavitary nature is evident. Skeletal muscle is extruding from the depths of the wound, where gas bubbles indicate the presence of a pulmonary parenchymal injury. (Illustration continued on opposite page)
effective range of a rifle is measured in hundreds of meters (M-16: 300 m). The high muzzle velocity, the large total weight of the pellets (traveling as a single mass and not yet dispersing), and the rapid deceleration of the nonaerodynamic spherical pellets yield, at a range of 1 to 2 yd (0.9-1.8 m), a single large ragged entrance wound, severe and extensive tissue destruction, and, usually, in wounds of the trunk, no exit wound. At a range of 3 to 4 yd (2.7-3.6 m) and depending on the gauge and shot number, the entrance wound will be larger and will probably be surrounded by several single pellet wounds, each of which may show significant deformation. Beyond 20 yd (18 m), the pattern of pellet dispersion may be 1 to 3 ft (0.30.9 m) in diameter, with the likelihood that only a few pellets will hit the target and be modestly destructive. Thus, range is the most critical determinant of the wounding capacity of a shotgun. Gauge indicates the diameter of the bore of a shotgun and the diameter of the corresponding shotgun cartridge (or shell). Although measured in
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Figure 5 (Continued). E, Anteroposterior radiograph reveals a left-sided thoracostomy tube in place. There are multiple rib fractures, and contusion of both the upper and the lower lobes of the left lung is evident. F, A lateral radiograph confirms the presence of pulmonary contusion.
hundredths or thousandths of an inch, these diameters also are expressed in gauge numbers, ranging from 12 (the largest) to 410 (the smallest). Twelve (0.729 inch) and twenty (0.615 inch) are the gauges in most common use (see Appendix). Shot number indicates the diameter and number of pellets in a given cartridge: the higher the number, the smaller and more numerous the pellets. In a given gauge, the total weight of the pellet in a cartridge is constant. Shot numbers range from 12, the smallest (0.05 inches in diameter), to 00 (double 0 buckshot; 0.33 inches). Thus, for example, a 12-gauge shotgun cartridge loaded with No.9 shot for a 12-gauge shotgun bore contains 585 pellets, each 0.08 inches in diameter, for a total weight of lead of 1 oz; and a 20-gauge cartridge loaded with No.9 shot contains 512 pellets, for a total weight of 0.875 oz. Ballistic data are summarized in Table 3. However quaint, this classification is generally accepted. A "sawed-off" shotgun, that is, a shotgun whose barrel has been shortened by about 1 ft for criminal or riot control purposes, offers the advantage of a more rapid dispersion of the pellets and an increased probability of at least some of the pellets hitting the target, as well as the advantage of easier concealment. Figure 6A exhibits a 35-year-old man who sustained a 410 shotgun wound to the right anterior aspect of his chest from a distance of 3 m. There was no exit wound. A right thoracostomy tube was inserted because of decreased breath sounds on auscultation. Four hundred milliliters of blood, along with air, was evacuated. On closer inspection (Fig. 6B), the wound appeared to be slightly tangential, and its cavity extended toward the midline. The extent of the damage is seen in part radiographically (Fig. 6C), and the pellet size was determined to be No.9. The kink in the chest tube was corrected. Because the pellets appeared to be intra-abdominal as well as intrathoracic, and because the patient had symptoms and signs of
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Table 3. Ballistic Properties of Shotguns and Their Pellets* MUZZLE
PELLETS
GAUGE
Quantity
Size (inches)
No.
410t
67 197 512 225 585
0.13 0.11 0.11 0.11 0.08
6 9 6 9
20 20 12 12
4
Weight (oz)
Velocity (]tIs)
Kinetic Energy (ft/lbs)
0.500 0.875 0.875 1.000 1.000
1150 1200 1200 1200 1200
385 800 800 2100 2100
*These are estimates and averages of a spectrum of weights and velocities for each gun and its cartridges. t410 "gauge" is actually 410 caliber.
an acute abdomen, exploratory laparotomy was performed, and wounds of the right hepatic lobe were observed (Fig. 6D). Multiple pellets were removed, and the diaphragm was noted to be perforated in several places. The wound of entrance was then debrided, and the plastic shot carrier (Fig. 6E), not seen radiographically, was removed. In this case, despite the small gauge, extensive damage to soft tissue resulted. When shotguns are wounding agents, care must be taken to search for foreign bodies such as wadding and, in this case, plastic containers. Such foreign bodies are sources of wound contamination and subsequent abscess if not identified and removed. Because they are not apparent radiographically, they may be missed if a high index of suspicion is not applied. Such wounds are appropriately treated with pulsed jet lavage, which helps to remove pellets as well as uncover the foreign body. 16 Figure 7A reveals entrance and exit wounds of the right upper extremity of a 27-year-old man who was shot from a distance of about 5 m by a 20-gauge shotgun. His arms were extended and abducted as he faced his assailant. Although only a portion of the pellet mass struck him, there were these two wounds, entrance posteriorly and exit medially. Arteriography (Fig. 7B) revealed an abrupt cutoff of contrast agent near the origin of the right brachial artery. Multiple pellets of No.9 shot were positioned near the entrance and exit wounds. Large defects in the brachial artery and vein were found at operation but could be repaired satisfactorily with autologous saphenous vein; however, injuries to the median and ulnar nerves could not be repaired. Injury to the underlying muscle was significant and necessitated extensive debridement. A third type of shotgun wound is illustrated by Figure SA. A 16-yearold sustained wounds to both thighs from a 12-gauge shotgun said to have been fired from "one car-length." Both thighs were tense, although there was no apparent neurovascular damage clinically. A lateral radiograph of the left lower extremity (Fig. SB) reveals an intact femur, soft-tissue disruption throughout, and multiple metallic densities of No. 6 shot posterior to the femur. Figure se views the right lower extremity radiographically from the lateral aspect and reveals most of the pellets to be posterior to the femur. A digital subtraction right femoral arteriogram (Fig. SD and E) was normal. Nonetheless, the patient underwent thorough debridement of both thighs (Fig. SF) because of extensive damage to the
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Figure 6. A 35-year-old man sustained a 410 shotgun wound to the right side of his chest from a distance of approximately 3 m. A, Thoracostomy tube has been inserted. B, A close-up of the entrance wound reveals that the missiles were directed toward the midline. C, Anteroposterior radiograph of the chest reveals multiple small (No.9) shot. The kinked thoracostomy tube was later corrected. There is extensive contusion of the right lung, and the pellets appear to be intra-abdominal. D, Exploratory laparotomy was performed because of the presence of an acute abdomen and because the pellets were thought to be intra-abdominal. A wound of the right lobe of the liver was identified (arrow). E, A close-up view of the chest dUring debridement reveals a plastic "shot" carrier in the depths of the wound (arrow).
quadriceps musculature. Delayed primary closure of both wounds was carried out 5 days later. MEDICOLEGAL CONSIDERATIONS
In cases of gunshot wounding, medicolegal considerations frequently depend on some knowledge of ballistics. Law-enforcement officials are often
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Figure 7. Entrance and exit wounds (A) in the right arm of a 27-year-old man were produced by a 20-gauge shotgun fired tangentially and from a distance of 5 m. B, Arteriography reveals a cutoff (arrow) in the proximal right brachial artery. No reconstitution of How is seen. Multiple pellets of No.9 shot are located about the entrance and exit wounds.
frustrated by the apparently careless manner in which critical information or evidence is handled, even by experienced medical and paramedical personnel, in the emergency room as well as the operating room. In this regard, certain principles deserve reiteration and emphasis, because the present legal climate of this country places stringent constraints on the lawenforcement community.9 "Each instance of a frustration of justice due to careless handling of evidence by a surgical team is an irony not to be tolerated." At a bare minimum, the medical team receiving a patient who has sustained a gunshot wound should: (1) exert care not to destroy the clothing worn by the patient, and in particular, to cut around and not through bullet holes; (2) carefully preserve and turn over to appropriate law-enforcement officials any weapon, and more specifically, any metallic foreign body obtained from the patient, such as a bullet or its fragments; (3) describe as precisely as possible and even photograph prior to debridement (a diagram for the patient's personal record is an appropriate alternative) any entrance or exit wound; and (4) query the police and witnesses as to the nature of the weapon (firearm, caliber) and distance (range). Although the medical team is not expected to assume the role of sleuth, its cooperation may prove critical in the pursuit of justice.
Figure 8. A I6-year-old sustained frontal shotgun wounds from a single I2-gauge cartridge containing No.6 shot from a distance of "one car-length." A, Both thighs were tense, but no neurovascular injury was evident clinically. B, A lateral radiograph of the left lower extremity reveals no fracture but multiple metallic densities of No. 6 shot located posterior to the femur. Extensive soft-tissue disruption is apparent, but no fracture is observed. C, A lateral radiograph of the right lower extremity reveals multiple metallic densities of No.6 shot, located mostly posterior to the right femur, which is free of fracture. D, A right femoral digital subtraction arteriogram reveals no injury to the superficial artery in the region of the pellets. E, A continuation of the right femoral digital subtraction arteriogram to include the proximal popliteal artery reveals no vascular injury. F, Wounds of both thighs are opened widely and debrided of underlying devitalized soft tissue. Delayed primary closure was accomplished successfully 5 days later.
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Figure 8 (See legend on opposite page)
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REFERENCES 1. Adams DB: Wound ballistics: A review. Milit Med 27:831-835, 1982 2. Amato JJ, Billy IJ, Lawson NS, et al: High velocity missile injury: An experimental study of the retentive forces of tissue. Am J Surg 127:454-459, 1974 3. Barach E, Tomlanovich M, Nowak R: Ballistics: A pathophysIologic examination of the wounding mechanisms of firearms. 1. J. Trauma 26:232-235, 1986 4. Barach E, Tomlanovich M, Nowak R: Ballistics: A pathophysiologic examination of the wounding mechanism of firearms. II. J Trauma 26:374-383, 1990 5. Berlin RH, Janzon B, Liden E, et al: Wound ballistics of Swedish 5.56-mm assault rifle AK 5. J Trauma 28 (suppl):76-83, 1988 6. Berlin RH, Janson B, Rybeck B, et al: A proposed standard methodology for estimating the wounding capacity of small calibre projectiles or other missiles. Acta Chir Scand Suppl 508:11, 1982 7. Fackler ML, Breteau JP, Courbil LJ, et al: Open wound drainage versus wound excision in treating the modern assault rifle wound. Surgery 105:576-584, 1989 8. Fackler ML, Surinchak JS, Malinowski JA, et al: Bullet fragmentation: A major cause of tissue disruption. J Trauma 24:35-39, 1984 9. Harris LS: Editorial comment. J Trauma 17:871, 1977 10. Janzon B, Seeman T: Muscle devitalization in high-energy missile wounds, and its dependence on energy transfer. J Trauma 25:138-144, 1985 11. Liu YA, Wu BJ, Xie ZC, et al: Wounding effects of two types of bullets in soft tissue of dogs. Acta Chir Scand Suppl 508, 1982 12. Ragsdale B: Gunshot wounds: A,historical perspective, Milit Med 149:301-315, 1984 13. Ryan JM, Cooper GJ, Maynard RL: Wound ballistics: Contemporary and future research. J R Army Med Corps, 134:119-125, 1988 14. Suneson A, Hansson HA, Seeman T: Pressure wave injuries to the nervous system caused by high-energy missile extremity impact I: Local and distant effects on the peripheral nervous system-A light and electron microscopic study on pigs, J Trauma 30:281-294, 1990 15. Suneson A, Hansson A, Seeman T: Pressure wave injuries to the nervous system caused by high-energy missile extremity impact II: Distant effects on the central nervous system-A light and electron microscopic study on pigs. J Trauma 30:295-306, 1990 16. Swan KG, Swan RC: Gunshot Wounds: Pathophysiology and Management, ed. 2. Chicago, Year Book Medical Publishers, 1989 17. Wang ZG, Qian CW, Zhan DC, et al: Pathological changes of gunshot wounds at various intervals after wounding. Acta Chir Scand Suppl 508:197-210, 1982 18. Woodruff CEo The causes of the explosive effect of modern small caliber bullets. NY Med J 67:593-601, 1898
Address reprint requests to Kenneth G. Swan, MD, FACS Section of General Surgery University of Medicine & Dentistry of New Jersey Newark, New Jersey 07103
APPENDIX Definitions of Weapons Terminology Caliber is the diameter of a bullet or rifle bore in hundredths (two digits) or thousandths (three digits) .of an inch. Gauge number is derived from the number of lead spheres of a diameter equal to the diameter of the bore making up 1 lb of lead. Range is defined as effective, maximal effective, and maximal. The last is the distance the unimpeded pellet or slug will travel when the weapon is fired at an appropriate acute angle with the horizontal. This is the definition of trajectory. The maximal effective range is the distance from which a marksman can be expected to strike a target (accuracy) and inflict a potentially mortal wound (lethality). The effective range is the same predicted result when the weapon is fired by less than a marksman. A rifted bullet is an elongated projectile to which spin on the long axis has been imparted by helical grooves in the barrel of the firearm.
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