Vol 8, No 1, January/February 2000 21 Over the past century, 223 million guns have been introduced into this country, including 77 million hand- guns, 66 million shotguns, and 79 million rifles (3 million of the assault type). 1,2 The presence of a firearm, now estimated to exist in half of all US households, 2 increases an individualÕs risk of killing or being killed by threefold and of dying by suicide by fivefold. 3,4 Two thirds of these weapons are loaded and stored within reach of a child. 2 This environment results in 150,000 to 500,000 missile injuries (half involving the extremities) 5 and 40,000 to 50,000 deaths annually. 4-6 Having increased fourfold since the 1950s, the latter figure approxi- mates the number of Americans lost during the Vietnam War, is nearly twice the number of persons who die of acquired immunodefi- ciency syndrome each year, and is three times the number of deaths associated with drunk driving. Gunshot wounds, including acci- dental, intentional, and self-inflicted injuries, are now the second leading cause of death and injury for the youth of this country, especially African-Americans, killing more teenage boys than all natural causes combined. 3,4 The homicide rate for males aged 15 to 24 in the United States is roughly 20 times higher Dr. Bartlett is Assistant Clinical Professor of Orthopaedic Surgery, University of Vermont College of Medicine, Burlington. Dr. Helfet is Director of the Orthopaedic Trauma Service, The Hospital for Special Surgery, New York. Dr. Hausman is Chief of The Hand Service, Mount Sinai Medical Center, New York. Dr. Strauss is Chief of Trauma, Mount Sinai Medical Center, New York. Reprint requests: Dr. Bartlett, University of Vermont, McClure Musculoskeletal Research Center, 440 Stafford Hall, Burlington, VT 05405-0084. Copyright 2000 by the American Academy of Orthopaedic Surgeons. Abstract As a result of the increasing number of weapons in this country, as many as 500,000 missile wounds occur annually, resulting in 50,000 deaths, significant morbidity, and striking socioeconomic costs. Wounds are generally classified as low-velocity (less than 2,000 ft/sec) or high-velocity (more than 2,000 ft/sec). However, these terms can be misleading; more important than velocity is the efficiency of energy transfer, which is dependent on the physical characteristics of the projectile, as well as kinetic energy, stability, entrance profile and path traveled through the body, and the biologic characteristics of the tissues injured. Although bullets are not sterilized on discharge, most low-velocity gunshot wounds can be safely treated nonoperatively with local wound care and outpa- tient management. Typically, associated fractures are treated according to accepted protocols for each area of injury. Treatment of low-velocity, low-energy fractures is generally dictated by the osseous injuries, as these are similar in many regards to closed fractures. Soft tissues play a more critical role in high- velocity and shotgun fractures, which are essentially open injuries. Aside from perioperative prophylaxis, antibiotics are probably required only for grossly contaminated wounds; however, because contamination is not always apparent, most authors still recommend routine prophylaxis. High-energy injuries and grossly contaminated wounds mandate aggressive irrigation and debridement, including a thorough search for foreign material. Open fracture protocols including external fixation or intramedullary nailing and intravenous antibiot- ic therapy for 48 to 72 hours should be instituted. If there is vascular damage, exploration and repair are best performed after prompt fracture stabilization. Evaluation of the Òfour CsÓÑcolor, consistency, contractility, and capacity to bleedÑprovides valuable information regarding the viability of muscle. Skin grafting is preferable when tension is required for wound closure, although other soft-tissue procedures, such as use of local rotation flaps or free tissue transfer, may be necessary, especially for shotgun wounds. Distal neurologic deficit alone is not an indication for exploration, as it often resolves without surgical intervention. J Am Acad Orthop Surg 2000;8:21-36 Ballistics and Gunshot Wounds: Effects on Musculoskeletal Tissues Craig S. Bartlett, MD, David L. Helfet, MD, Michael R. Hausman, MD, and Elton Strauss, MD than that in other industrialized nations. 3 The economic impact of gunshot trauma is also high. At an inner- city hospital, annual costs for the treatment of these injuries can easily reach $50 million. 3 Nationwide, the calculated costs of medical treat- ment, mental health care, emer- gency transport, police services, and insurance administration ex- ceed $2.7 billion annually, 5 most of which is borne by American tax- payers. 4,6 These figures do not include the costs related to addi- tional loss of productivity, the attendant pain and suffering, and the reduced quality of life, estimated at $63.4 billion each year. 5 For every gunshot homicide there are 3.3 nonfatal injuries. 3,5 One of these will be a brain or spinal cord injury, leading to lifetime expenditures in excess of $3 million. 3 Because gun- shot trauma exacts such an enor- mous toll from both the individual and society, the surgeon should take an active interest in both its prevention and its treatment. An understanding of ballistics and the wounding characteristics of various weapons will also facilitate proper evaluation and care. Ballistics By convention, bullet wounds are generally classified as low- or high- velocity injuries. Low-velocity wounds (Fig. 1) are less severe, are more common in the civilian popu- lation, and are typically attributed to projectiles with muzzle velocities below 1,000 to 2,000 feet per second (fps). Tissue damage is usually more substantial with higher-velocity (greater than 2,000 to 3,000 fps) mil- itary and hunting weapons. While convenient, the terms Òlow-velocityÓ and Òhigh-velocityÓ can be very misleading. 7,8 Shotguns, for exam- ple, are technically low-velocity weapons, but are responsible for substantial rates of major soft-tissue, nerve, vascular, bone, and joint in- jury, 6,9,10 resulting in a mortality rate nearly twice that attributable to other weapons. More appropriate are the designations Òlow-energyÓ and Òhigh-energy,Ó which are de- scriptive of the amount of damage to the tissues. To appreciate this distinction, the factors that affect the transmission of the wounding capacity of a missile to the tissues must be considered. Pulling the trigger of a firearm releases its firing pin, which strikes the primer. When crushed, the primer ignites, producing an in- tense flame, which enters the main chamber of the cartridge case and ignites the powder. The ensuing generation of a large quantity of gas and heat (up to 5,200¡F) pro- duces a pressure as great as 25 tons per square foot, which ejects the bullet. 11 Next, the gases trapped in the bore (the evenly hollowed-out inner portion of the barrel) expand and reach a velocity greater than that of the projectile, further accel- erating and destabilizing it for a short distance. 12 The wounding capability of the bullet is directly related to its ki- netic energy, determined by the formula E = M/2 ×V 2 , where E rep- resents energy; M, mass; and V, velocity. Before World War II, bullet and weapon construction focused on mass, favoring heavier projectiles of large caliber (diame- ter of the bullet or rifle bore in millimeters or as a decimal frac- tion of an inch). However, in- creasing mass only produces lin- ear increases in kinetic energy, but increasing velocity does so expo- nentially. In fact, at the speed of sound (4,760 fps), the rate of ener- gy conversion into mechanical disruption of tissue can become proportional to the third power of velocity or even higher. 13 There- fore, over the past five decades, greater emphasis has been placed on lighter, spin-stabilized missiles traveling at high velocities. The inertia of a projectile acts through its center of mass, which lies along its line of flight. 12 Re- tarding forces act at the center of pressure, which lies in front of the center of mass (tip of the bullet) in a nose-on flight. Any degree of deviation of the longitudinal axis of the bullet from its line of flight is known as yaw, the square of which proportionally affects its rate of deceleration. 12 The nonspinning bullet is inherently unstable and will have a propensity to tumble. To best minimize this occurrence and achieve gyroscopic stability, Ballistics and Gunshot Wounds Journal of the American Academy of Orthopaedic Surgeons 22 Figure 1 Anteroposterior (AP) view of the right humerus of a 29-year-old man after a small-caliber, low-velocity gunshot wound with resultant radial nerve neu- rapraxia. Initial treatment included a coap- tation splint and discharge home on a regi- men of oral antibiotics. At 3 weeks, the plaster splint was replaced by a Sarmiento brace, in which uneventful healing was completed. The nerve palsy slowly re- solved over the ensuing 4 months. the bullet should be long, thin, and spun on its axis by helical grooves in the bore of the firearm (barrel rifling). 12-14 The highly complex action of spin on a yawing bullet (precession), combined with a sec- ond complicated motion of higher frequency and lower amplitude (nutation), will cause the missile to rotate in a rosette pattern of mo- tion, (analogous to a spinning top), imparting stability. 12 More important than velocity is the efficiency of energy trans- fer, 8,10,11,13,14 which is dependent on six factors: (1) The amount of kinetic energy possessed by the projectile at the time of impact, such that the longer the range (distance from the target), the lower the velocity at impact. 13 (2) The stability and entrance profile of the projectile. At a yaw of 90 degrees (sideways), max- imal energy transfer is achieved. 8,14 Yaw tends to decrease over longer distances, 12 allowing the bullet to hit its target nose-on; at impact, however, wobbling and then tum- bling occur. (3) The caliber, con- struction, and configuration of the bullet, which can be by far the most important factors predicting its effects. 7,11,13 (4) The distance and path traveled within the body. Penetrating (not exiting) missiles deliver their total contained kinetic energy; perforating (exiting) mis- siles transfer significantly less. 11,12 (5) The biologic characteristics of the tissues impacted. 11,15 (6) The mechanism of tissue disruption (e.g., stretching, tearing, crushing). 7 On the basis of the interactions between these many factors, differ- ent injury patterns will occur or even coexist. Inefficient energy transfer by a high-velocity bullet might produce only minimal dam- age. In contrast, complete release of energy by a low-velocity projec- tile can inflict devastating wounds. Thus, Cooper and Ryan 14 have warned that one should Òtreat the wound [and] not the weapon.Ó Weapons and Ammunition Although handguns are typically low-energy weapons, with muzzle velocities below 1,400 fps, 11,13 they are still the most frequently used firearms in fatal injuries. 1,5 Exam- ples include the .38-caliber revolver (600 to 870 fps), the 9-mm pistol, and the .45-caliber semiautomatic weapon (860 fps). A small-caliber short-barreled type, common in urban areas and costing less than $50, is the ÒSaturday Night Special.Ó Named for their rifled barrel, rifles include low-velocity types, such as the rarely fatal air rifle 11,13 and the .22 (1,100 to 1,255 fps). 11,13 Higher-velocity military (assault) rifles include the M-16 (3,250 fps) 11 and the AK-47 (2,340 fps). 7 Even at 300 yd, bullets fired from these par- ticular weapons retain nearly half of their original muzzle velocity. Although the M-16 round has ap- proximately the same caliber and weight as the .22, it is fired at a velocity three times greater than that of the latter, producing nearly ten times the amount of kinetic energy (Fig. 2). Assault rifles have been involved in 16% of homicides in New York City but fewer than 2% of homicides in more rural areas. 1 More common in rural areas, shotguns fire a Òmissile,Ó consisting of a few to hundreds of lead pellets, at a velocity of 1,000 to 1,500 fps. 13 Because of its high efficacy of energy transfer at close-range, the shotgun is the most formidable and destruc- tive of all small arms. A sawed-off shotgun offers the advantage of concealment and more rapid dis- persion of pellets, increasing the probability of striking the target. 6,13 Damage is based on the choke, load, barrel length (federal law requires a minimum of 18 inches), smooth bore, wadding, powder charge, and range. 6,16 The choke is a partial constriction of the bore at the muzzle that condenses and con- trols the shot pattern. The tighter the choke, the smaller the spread of pellets and the greater the length of the shot column. ÒGauge,Ó which refers to the number of lead balls of the given bore diameter that are required to weigh 1 lb, is an archaic term. 11 The load is composed of different sizes of shot, packed into what is usually a plastic shell. The role of wadding is to fill up dead space in the shell, protect the pow- der and shot, and seal the bore dur- ing firing to keep gas behind the pellets. 11 It is commercially pro- duced from paper, cardboard, felt, plastic, or composite materials. The quantity and type of gun- powder affect the initial kinetic ener- gy of the bullet. Gunpowder (black powder) was originally composed of a mixture of saltpeter (potassium nitrate), charcoal, and sulfur and was measured in drams. Modern smokeless powder, invented in 1884 and modified much since then, is measured in dram-equivalents. 11,16 Craig S. Bartlett, MD, et al Vol 8, No 1, January/February 2000 23 Figure 2 AP view of the right distal femur of an 18-year-old woman with a high-velocity M-16 rifle wound. Note the Òlead snowstormÓ pattern and severe com- minution. The arteriogram revealed no gross arterial damage. Bullets are composed primarily of lead combined with varying amounts of other metals depend- ing on their desired final hardness (0.5% antimony, 0.3% copper, and 0.05% other metals in one common formulation). 17 They can be modi- fied in many ways to improve energy transference, including full or partial (soft-point) metal jacket- ing, partial metal jacketing with a cavity at the tip (hollow point), controlling expansion with use of aluminum, scoring, bonding, com- bining multiple projectiles into one cartridge, and adding an explosive charge. 7,11,14,18 The com- mon failure of explosive bullets to detonate on impact presents con- tinuing danger to both medical personnel and patients. Magnum shells and cartridges contain a heavier than standard powder charge, which increases projectile energy by 20% to 60%. 6 Scoring the bullet (e.g., the dumdum) makes it more likely to fragment when subjected to strong in-flight physical forces. 13,18 A bullet com- posed of bonded fragments of iron or lead (e.g., .22-caliber frangible) will disintegrate on striking a hard surface. Fully jacketed bullets are uti- lized primarily in assault rifles. These have a lead or steel core, which is covered by an outer jacket of cupronickel or gilding metal (copper or zinc) to minimize defor- mation. Therefore, they invariably exit the victim if he is the primary target within a few hundred yards of the muzzle. In contrast, both soft-nose and hollow-point bullets flatten out on impact, the latter expanding up to twice their origi- nal diameter and quadrupling the amount of tissue struck. 7 At high velocities, these bullets also shed as they travel through the body, creat- ing a characteristic radiographic Òlead splatterÓ or Òlead snowstormÓ pattern 11 (Fig. 2). Most hunting bullets also exit the body. 11 Shot shells are handgun car- tridges with bird shot encased in plastic. The plastic contains the shot until impact, often producing fatal results at distances of less than 10 ft. 11,18 In contrast, a shotgun slug (a single large projectile mounted into a shotgun shell) can produce massive internal injuries compara- ble in severity to those of high- velocity rifle bullets. The Bullet Wound An impact velocity of only 150 to 170 fps is required to penetrate skin. 6,12 Most entrance wounds, regardless of range, are oval to cir- cular with a punched-out clean appearance and are often sur- rounded by a zone of reddish dam- aged skin (the abrasion ring). 11 While powder tattooing of the skin implies a close-range wound, the fact that there are different forms of propellant powder makes this an unreliable finding. Also indicative of a close-range injury is a cherry- hue appearance of underlying muscle due to carboxyhemoglobin, formed by carbon monoxide re- lease during combustion. 11 Damage is created by several mechanisms, including the actual passage of the missile through tis- sue, a secondary shock wave, and cavitation. On striking its target, the bullet creates a temporary cavi- ty at the entry site due to stretching forces and the vacuum created by its passing. The volume of this cav- ity is proportional to the energy transferred by the missile (Fig. 3) 12 ; a maximum size of 10 to 40 times the diameter of the bullet is reached in 1 to 4 msec, 11,13,19,20 with internal pressures reaching 100 to 200 atm. 20 This violent event in high-velocity injuries over 2,500 fps can create damage of an almost explosive nature. 12 During the 10- to 30-msec life- time of the temporary cavity, 20 its vacuum may pull foreign material into the wound. 12,13 However, most bullets are pointed and transfer little from the entry site. 14 A Òtail splashÓ or Òsplash backÓ effect at high velo- cities can cause backward hurling of injured tissue. 8,11,20 After the bullet passes, the temporary cavity col- lapses and re-forms repeatedly with diminishing amplitude, leaving a smaller permanent cavity. 13,20 The more the elastic capacity of the sur- rounding tissue has been exceeded, the greater the size of this perma- nent cavity. Wang et al 15 separate the wound area into three zones: (1) a primary wound track (the permanent cavi- ty); (2) a contusion zone of muscle adjacent to the track; and (3) a con- cussion zone (variable outside con- gestion). In uncomplicated low- velocity civilian gunshot wounds, this area is essentially only a few cells deep. 21 Therefore, these wounds rarely require full explo- ration. 22 However, the volume of devitalized muscle grows with increasing energy, becoming visual- ly apparent at velocities over 1,000 fps and resulting in extensive bruis- ing at velocities over 2,000 fps. 8,12 After impact by a high-velocity, rapidly decelerating, deforming, and disintegrating projectile, tissue destruction may extend up to sever- al centimeters radially from the track. 13 Fascial planes may serve as channels for the dissipation of explosive force, leading to signifi- cant remote tissue damage. 14 As a result, disruption of muscle capil- lary blood supply, rupture of gas- containing viscera, and fractures can occur even without a direct im- pact. 11,12 Energy loss by the bullet and tis- sue disruption along the wound track are not uniform, due to varia- tions in tissue density and the behavior of the bullet as it travels from one structure to another. 15 Soft, bulky, homogeneous solid organs, such as liver, spleen, and Ballistics and Gunshot Wounds Journal of the American Academy of Orthopaedic Surgeons 24 muscle (specific gravities of 1.01 to 1.04), are violently disrupted when transferred kinetic energy exceeds the elastic limits of the tissue. 13,20 Histologically, swelling of muscle fibers to as much as five times nor- mal size can be observed, with clot- ting of muscle cytoplasm, loss of striations, and interstitial extravasa- tion of blood. Lactate levels increase to as much as six times normal, and depletion of adenosine triphosphate, creatine phosphate, and glycogen occurs. 23 These changes result in local edema, which may lead to a compartment syndrome, further in- creasing the insult to the soft tissues. 7 Bone (specific gravity of 1.11) can be shattered beyond recognition, but less dense and more elastic tissues, such as skin and lung (with much lower specific gravities of 0.2 to 0.5), may be virtually unscathed. 11,14,20 Although capillaries are prone to rupture, larger arteries (unless directly struck) are remarkably resis- tant to injury. 12 Likewise, larger nerve trunks, while susceptible to neurapraxic lesions, are rarely com- pletely disrupted. 12 Exit wounds can appear stellate, slitlike, crescentic, circular, or com- pletely irregular. 11 With greater velocities, bullet deformation, and tumbling within the body, these typically become larger and more irregular than entrance wounds. 13 For example, a full-metal-jacket bullet will produce a small cylin- drical cavity until it begins to tum- ble. When this occurs, massive amounts of kinetic energy are re- leased, widening the cavity and exit wound. However, a retro- grade effect can occur if the bullet slows and releases a large amount of energy immediately after impact (as may occur with rapidly expand- ing hunting ammunition). This will form a track with a cone based at the entry site. 11,13 Thus, contrary to popular opinion, an exit wound is not necessarily larger than the corresponding entrance wound. In contrast to entrance wounds, cavity formation at the exit site may allow substantial quantities of material to be sucked into the wound, particu- larly when the velocity exceeds 2,000 fps. 11 The Shotgun Wound Complicated formulas exist to de- termine the range of a shotgun wound. However, it may be easily estimated by measuring the diame- ter of the spread on the patient. As the shot pellets travel from 2 to 100 yd, they separate slightly less than 1 in/yd. 6,16 Soft-tissue shotgun injuries can be graded from the most extreme (type III) to benign (type 0) 6 (Fig. 4). Type III (Òpoint blankÓ) wounds are due to impact from a range of less than 3 yd and are extensive, with the concentrated cloud of shot potentially destroying everything in its path. Wound diameters of 6 in or less often herald injury to deeper structures. 16 The presence of soot is evidence of a blast from a range of 1 ft or less. 11 Massive soft-tissue destruction and bacterial contami- nation from wadding require ag- gressive treatment and often long hospital stays. Type II (close-range) wounds, due to impact from a range of 9 to 21 ft, are almost as severe and penetrate deep to the fascia. These are less likely to have embedded wadding, which tends to fall away after distances greater than 6 ft. 6,11 Type II and III wounds are asso- ciated with high rates of commin- uted fractures (32% to 48%), major soft-tissue disruption (43% to 59%), vascular injury (23% to 35%), and peripheral nerve damage (21% to 58%). 9,10,24 Furthermore, vascular Craig S. Bartlett, MD, et al Vol 8, No 1, January/February 2000 25 A B Figure 3 Blocks of gelatin perforated by .30-caliber missiles at less than 1,000 fps (A) and at 2,800 fps (B). Arrows indicate missile tracks. (Reproduced with permission from Ziperman HH: The management of soft tissue missile wounds in war and peace. J Trauma 1961;1:361-367.) and neural injuries frequently coexist, and multiple injuries are often pres- ent. Such global trauma leads to amputation rates as great as 20% to 50% 10,24 and high mortality rates. In injuries from distances greater than 7 yd, a large cloud composed of widely scattered missiles pro- duces many small holes but rarely major soft-tissue disruption. 6 Such injuries can often be treated simply as multiple low-velocity wounds 6 and are grouped as type I (long- range), which penetrate to the sub- cutaneous tissues and deep fascia, and type 0, which involve only skin penetration. Beyond 20 to 50 yd (maximal range), the rapidly decel- erating and poorly shaped (aerody- namically) spherical pellets create negligible damage. 13 Bone Involvement Bone is a specialized form of dense connective tissue composed of cal- cium salts embedded in a matrix of collagenous fibers, which is rarely damaged without concomitant muscle injury. A minimum velocity of 195 to 200 fps is necessary for a bullet to breach its cortex. 6,20 The clinical and radiographic appear- ance of the entrance hole is usually a punched-out round to oval shape with a sharp beveled edge. In con- trast, the exit site typically has an excavated, conelike appearance with a variable amount of com- minution. 11 Generally, the greater the velocity of the missile, and therefore the greater its contained kinetic energy, the greater the com- minution at both entry and exit sites (Fig. 2). Lower-velocity projectiles can produce many different fracture patterns, either incomplete or com- plete. There are three types of incomplete fractures 13,25 : (1) the Òdrill-holeÓ fracture, which usually occurs through the soft metaphy- seal region of long tubular bones, and is characterized by entrance and exit holes with diameters close to the diameter of the bullet; (2) the unicortical (ÒdivotÓ) fracture, which involves a portion of bone removed from the main structure and occasionally a nondisplaced fracture line extending from the divot; and (3) the chip fracture, more common in stab wounds and rarely seen after bullet injuries. Complete fractures are more fre- quent in diaphyseal bone and in- clude patterns such as the single and double ÒbutterflyÓ fractures. Their spectrum ranges from frac- tures secondary to indirect forces to highly comminuted patterns. On impact, bone fragments are pro- pelled toward the periphery of the temporary cavity. Although these can become secondary missiles, causing damage to more distant structures, more commonly they quickly retract to the parent bone. 11 Frequently, other secondary mis- siles include articles of clothing, such as buttons and belt buckles. 13 Physeal damage has been noted in 16% of skeletally immature patients who sustain a gunshot wound. 26 This is usually due to di- rect damage as the bullet passes near a growth plate, which is easily noted on initial radiographs. How- ever, physeal injury can theoretically occur remote from the site of the wound track, leading to unforeseen growth arrest. 27 Joint Involvement and Metal Intoxication A bullet passing through a joint can damage bone, cartilage, ligaments, and menisci. Tornetta and Hui 28 noted a 42% incidence of meniscal injury and a 15% incidence of chon- dral damage in knee joints violated by low-velocity projectiles. Articu- lar damage may be crippling, with loss of normal anatomic contours leading to severe posttraumatic degenerative arthritis. Contamina- tion by bullet fragments can result in joint sepsis, rapid chondrolysis, and joint destruction. Lead intoxication (plumbism) can manifest from 2 days to 40 years after a gunshot injury. 29 Its most common causes include bullet fragments within a joint space, bone, or (rarely) intervertebral disk. 11,22,30 Lead fragments in soft tissues are quickly covered by avascular scar tissue, 29 which pre- vents their migration and perhaps uptake by the body. However, intra-articular lead dissolves in synovial fluid and may be deposit- ed in subsynovial tissues, leading to chronic irritation, arthritis, and (rarely) systemic effects (such as neurotoxicity, anemia, nausea and emesis, abdominal colic, and renal disease). Furthermore, toxicity Ballistics and Gunshot Wounds Journal of the American Academy of Orthopaedic Surgeons 26 6 ft 12 ft 24 ft Figure 4 Diameter of the spread of a shot column as range increases. Top, Type III (point-blank) pattern. Center, Type II (close-range) pattern. Bottom, Type I (long-range) pattern. (Reprinted with per- mission from DeMuth WE Jr: The mecha- nism of shotgun wounds. J Trauma 1971;219-229.) may rapidly accelerate in the pres- ence of metabolic disorders, alco- holism, or acute infection. 13 Two deaths have been reported. 11 The use of chelating agents is the initial treatment for lead intoxication. Bullet removal is usually neces- sary. 13,29 Copper, another metal common in firearm projectiles, is also neuro- toxic. 17 However, unlike lead, cop- per causes considerable local soft- tissue inflammation, necrosis, and erosion. Nickel can also be inflam- matory. Zinc and aluminum be- have similarly to lead in the soft tissues. 17 The Wandering Missile Vascular embolization by bullets, shot, or fragments occurs in rare instances. 11,13,31,32 The .22-caliber bullet is the most commonly in- volved projectile. Almost one fifth of cases involve the neck or upper extremities. 32 Migration of missiles into the portal system, pericardial space, spinal cord, kidneys, ureters, urethra, and lungs has also been observed. 6,31 Contamination and Infection Contrary to popular belief, bullets are not sterilized on discharge. 11,12,19,33,34 Furthermore, shotgun wadding has been associated with a high degree of wound contamination, 10,34 espe- cially in the case of older ammuni- tion, in which the wadding was often composed of clostridia-laden cattle hair and jute, and modern Òhome loadsÓ created with a variety of substances. Additional sources of infection include clothing frag- ments, skin flora, and other contam- inants. Therefore, primary closure is contraindicated. Injuries to the abdomen or bony pelvis are of par- ticular concern, because of their close association with bowel injury, which dramatically increases the risk of sepsis. 30 Nonviable muscle, especially in an anaerobic environment, is an ideal pabulum for the growth of many types of bacteria, especially clostridia. 12,13 Following a gunshot wound, the number of aerobes in devitalized muscle has been observed to be 10,000 organisms per gram of tissue at 6 hours and 100,000 at 12 to 24 hours, with the quantity of anaerobes at 6 hours falling within this range. 35 There- fore, debridement is optimally per- formed within 6 to 8 hours of injury. However, this timing is inexact due to the degree of tissue destruction, the presence of shock, and host re- sistance. 35 When there is too much devital- ized tissue to be absorbed or too great a bacterial load, the body will attempt to wall off the necrotic mass with a fibrin barrier and expel it after approximately 10 days. 7 However, without access to the outside, this mass will form an abscess. Incomplete removal of debris, such as shotgun wadding, can also result in abscess formation and chronic drainage. In these cases, imaging of the abscess with contrast material may help locate any foreign material before explo- ration. Most gunshot wounds are not complicated by infection, but infec- tions by certain pathogens are asso- ciated with increased morbidity. Clostridial infection can range from cellulitis to diffuse myonecrosis (gas gangrene). It usually develops over 3 days, but may occur within 6 hours of injury. Less commonly, streptococcal infection develops over the course of 3 to 4 days, with systemic reactions not appearing until late. Although rare, wound botulism can occur even in clinical- ly clean wounds, and should be suspected in the presence of bulbar and descending symmetric motor paralysis. 36 Assessment In a study of 16,316 patients with gunshot wounds of the extremities, Ordog et al 2 noted a 17% overall incidence of vascular injury based on positive findings by exploration and/or arteriography. However, the presence of a vascular injury is dependent on the location of the wound (Table 1), its severity, and the type of weapon used. Such details should be considered when Craig S. Bartlett, MD, et al Vol 8, No 1, January/February 2000 27 Table 1 Relationship of Wound Location and Incidence of Vascular Injury * Location of Wound Incidence of Vascular Injury, % Lateral thigh <1 Medial or posterior thigh 7-9 Popliteal fossa 9-10 Calf or leg 18-22 Upper arm or shoulder 9-10 Medial or posterior upper arm 6-8 Forearm or antecubital fossa 17-22 * Adapted with permission from Ordog GJ, Balasubramanium S, Wasserberger J, Kram H, Bishop M, Shoemaker W: Extremity gunshot wounds: Part one. Identification and treatment of patients at high risk of vascular injury. J Trauma 1994;36:358-368. Based on correlation with arteriography. attempting to identify the presence of a potentially limb- or even life- threatening condition. Most vascular injuries after pen- etrating trauma are manifested by ÒhardÓ physical findings, which permit a rapid and accurate diagno- sis. 2,13,37 These include a pulse deficit; a cold, lifeless extremity; cyanosis distal to the wound; a bruit or thrill; pulsatile or uncon- trollable bleeding; and a large or expanding hematoma or pseudo- aneurysm. A progressive neurologic deficit may signal the presence of the latter. ÒSoftÓ signs of a vascular injury include a history of hemor- rhage, hypotension, or a static neu- rologic deficit. Unfortunately, even after complete arterial disruption, a weak but palpable pulse might still be present. Accurate pulse assess- ment of a traumatized limb with normal perfusion can be hindered by edema, a hematoma, dressings, or splints. 38 Generally, arteriography is ex- tremely sensitive, quite specific for identification of vascular injury, and useful for surgical planning for treat- ment of complex wounds (Fig. 2). 2,13 It is particularly helpful after shot- gun injuries, because of the frequent occult vessel damage. 6 However, this imaging modality is expensive, has inherent risks, and is sensitive enough to detect occult findings that may resolve spontaneously. 2 Due to these limitations, arteriography may ultimately be replaced by noninva- sive duplex ultrasonography, a modality just as sensitive but with- out the associated complications. 2,38 When the physical examination indi- cates the presence of a well-localized arterial injury, preoperative arteriog- raphy is unnecessary. 2,38 In contrast, the absence of ÒhardÓ findings of vascular injury warrants a period of observation. In addition to appropriate ex- tremity imaging, it is important to obtain radiographs one body cavity above and one body cavity below any entrance or exit wound. 13 Clothing, most wadding, and even some metal jackets may be difficult to see on plain films, making a care- ful inspection mandatory. Clues that suggest the presence of a cloth foreign body include radiographic evidence of an irregular or spurred bullet, a relatively large entrance wound for the estimated caliber and range, and the absence of a frag- ment of the patientÕs clothing at the entrance site. 13 Careful evaluation is also crucial when any metal frag- ments lie in proximity to a joint space. Although the presence of joint violation or an intracapsular bullet can usually be determined on the basis of the fracture pattern, the plain-radiographic appearance, and the results of joint aspiration (if nec- essary), the most sensitive test remains a fluoroscopically assisted arthrogram. 39 If this is impractical or inconclusive, a computed tomo- graphic scan should be obtained. There are several important med- icolegal issues that pertain to evalu- ation and treatment. Care must be taken to preserve evidence by cut- ting aroundÑnot throughÑbullet holes in the patientÕs clothing. The location, size, shape, and nature of both the entrance and exit wounds must be precisely documented. Medical teams have often been inat- tentive on this point, with one study noting that fewer than 3% of charts have an adequate description of the wound. 7 Bullets should be marked only on the nose or base to preserve the rifling characteristics, and any wadding or loose pellets should be retained for evidentiary purposes. 11 Electrodiagnostic studies in the early postinjury period cannot dis- tinguish between a neurapraxic lesion and transection. Follow-up studies at 6 weeks and 3 months can show signs of early recovery, but their utility is limited. 24,40 The presence of spontaneous fibrilla- tions and muscle irritability is a sign of muscle denervation, indi- cating axonal disruption. In gener- al, expectations of these studies exceed their capabilities. Conservative Treatment of Low-Energy Wounds Most low-velocity gunshot wounds may be safely treated nonopera- tively, with simple local wound care (superficial irrigation and careful cleaning followed by a dressing, with or without antibi- otics) and outpatient management (Fig. 5). 2,19,33,34,41,42 These Òminor woundsÓ include low-energy un- contaminated injuries of skin, sub- cutaneous tissue, and muscle and fractures not requiring operative stabilization. Tetanus prophylaxis with a reinforcing booster of 0.5 mL of tetanus toxoid is indicated for all gunshot-wound patients who are not completely immu- nized (fewer than three immuniza- tions) or who have uncertain im- munization histories. 37,43 Anyone who has not had an immunization within 5 years requires a booster. Those not previously immunized will also require a minimum of 250 to 500 units of human tetanus im- mune globulin. 13,37,43 Aside from perioperative prophy- laxis, antibiotics are probably re- quired only for grossly contaminated wounds (Table 2). 19,21,33,34,37,41,42,44-48 Dickey et al 33 reported similar rates of infection in a prospective random- ized study of 73 patients treated with or without antibiotics. However, because contamination is not always apparent, most authors still recom- mend routine prophylaxis. 19,34,41,44,45 Hansraj et al 45 have suggested treatment for 2 days with an intra- venous antibiotic, such as cefazolin, for minor wounds with cortical bone defects. In their study, substitution of a long-acting, broad-spectrum cephalosporin (ceftriaxone) allowed discharge 1 day earlier than for patients treated with cefazolin, and Ballistics and Gunshot Wounds Journal of the American Academy of Orthopaedic Surgeons 28 Craig S. Bartlett, MD, et al Vol 8, No 1, January/February 2000 29 No Signs of vascular injury? No Proximate injury † ? Angiography ‡ Duplex Doppler Negative Observe Exploration* Positive NegativePositive NegativePositive Exploration* Angiography Yes Yes No Yes Signs of vascular injury? YesNo If proximate injury, † intraoperative angiography Low-energy wound Discharge home (if no other injuries) High-energy wound Exploration or intraoperative angiography Extremity gunshot injury with high-energy wound, severe contamination, joint penetration, unstable fracture requiring surgical stabilization, or clinically unstable patient with signs and symptoms of vascular injury? ABCs of trauma care Tetanus prophylaxis Initial local debridement in ED Cleanse with povidone and normal saline Sterile dressing Consider initial dose of cefazolin, 1 g Splint unstable fracture Definitive wound and fracture care: Local debridement in ED Irrigation of wound Splint or cast, as fracture dictates Ciprofloxacin, 750 mg PO bid x 3 days (alternative: cephalexin or dicloxacillin) Closure by secondary intention Definitive wound and fracture care: Irrigation and local debridement in OR Arthroscopy or arthrotomy for joint penetration Stabilize as fracture pattern dictates Cefazolin, 1 g IV q8h x 48-72 h Closure by secondary intention Definitive wound and fracture care: Irrigation and local debridement in OR Stabilize as fracture pattern dictates Cefazolin, 1 g IV q8h x 48-72 h Closure by secondary intention Definitive wound and fracture care: Irrigation and local debridement in OR Stabilize as fracture pattern dictates Cefazolin, 1 g IV q8h x 48-72 h Closure by secondary intention Aggressive irrigation and debridement in OR Excise contaminated tissue Explore wound tract External fixation common (possibly IM nail, rarely ORIF) IV antibiotics as per open-fracture protocols (type I, II, or III), continue at least 48-72 h, but also until wounds are clean (up to 1-2 weeks for severe contamination) Repeat surgical debridement q48h until wounds are clean Closure by secondary intention (possible skin graft or flap) Figure 5 Suggested treatment for gunshot wounds. Abbreviations: bid = twice a day; ED = emergency department; IM = intramuscular; IV = intravenous; OR = operating room; ORIF = open reduction and internal fixation; PO = by mouth; q8h = every 8 hours, * = guidelines for exploration: exploration is appropriate unless the injury involves only a single vessel below the trifurcation of the popliteal artery or distal to the midforearm (such an injury is not generally explored unless there is a diagnosis of compartment syndrome, arteriovenous fis- tula, or pseudoaneurysm); † = proximate injuries are defined as those in which the missile track passes within 1 inch of a known anatomic path of a major vessel; ‡ = if there are ÒsoftÓ signs of vascular injury, can consider duplex Doppler first. Ballistics and Gunshot Wounds Journal of the American Academy of Orthopaedic Surgeons 30 Table 2 Suggested Treatment Regimens for Gunshot Wounds * Authors Study Design Wound Type Antibiotic Regimen Hansraj et al 45 Prospective Low-velocity with minor fractures Ceftriaxone, 1g IV qd × 2 doses, or (excludes head, spine, feet) cefazolin, 1g IV q8h × 7 doses Ordog et al 37 Retrospective Minor (87% low-velocity, 4%-6% Usually cephalosporin or with fractures) dicloxacillin PO Geissler et al 41 Prospective Low-velocity with minor fractures Cefonicid, 1g IM × 1, or cefazolin, 1g q8h × 48 h Dickey et al 33 Prospective Low-velocity with minor fractures Cefazolin, 1g IV q8h × 24 h randomized Woloszyn et al 19 Retrospective Low-velocity fractures (13% IV antibiotics × 3d or cephalexin, required open reduction and 250-500 mg PO qid × 7-10 d internal fixation or arthrotomy) Brettler et al 48 Retrospective Low-velocity (53% with fractures, Cephalothin, 2 g IV initially, 15% requiring emergent surgery) then × 3 d (92% of patients), or other antibiotics (8%) Patzakis et al 34 Prospective All gunshot fractures Penicillin/streptomycin or randomized cephalothin, 100 mg/kg of body weight in divided doses q6h IV × 10-14 d Brien et al 44 Retrospective Low-velocity fractures First-generation cephalosporin plus aminoglycoside, IV × 72 h Molinari et al 46 Retrospective Low-velocity fractures Varying short courses of IV antibiotics Nowotarski et al 47 Retrospective Low- to medium-velocity fractures Cefazolin, IV × 48 h (average) Wright et al 21 Retrospective Low-velocity fractures First-generation cephalosporin, IV × 48 h Knapp et al 42 Prospective Low-velocity fractures Cephapirin, 2 g q4h plus randomized gentamicin, 80 mg q8h, or ciprofloxacin, 750 mg bid × 3 d * Abbreviations: bid = twice a day; ED = emergency department; IM = intramuscular; IV = intravenous; NS = normal saline; OR = operating room; PO = by mouth; q8h = every 8 hours; qd = every day; qid = four times a day. ÒMinorÓ fractures defined as stable fractures that did not require surgical stabilization (i.e., patients underwent closed fracture treatment). à Same wound care as would have been performed in ED for wounds with nonoperative fractures. ¤ Some patients counted more than once due to multiple fractures. ¦ Historical control (randomized retrospective). # No statistical significance between results for two treatments.