FIREARM AND PROJECTILE DESIGN

Although there are many variables, the muzzle velocity (speed of the bullet as it leaves the barrel) and the bullet characteristics such as mass and deformability are the most important determinants of the wound that a particular weapon will produce (Table 1). The muzzle velocity is determined by the caliber of the bullet, the capacity of the casing (amount of powder), and gun barrel length. The bullet’s velocity rapidly increases as it travels down the barrel, but gradually slows upon meeting air resistance once it has exited. Handguns generally accept smaller bullets with less powder and have shorter barrels than rifles, and therefore produce projectiles of considerably less velocity (Table 2).

Table 1 Factors Involved in Wound Ballistics

Table 2 Muzzle Velocity by Gun and Bullet Type

The mass of the bullet is determined by its caliber (diameter), length, and the density of its metal components. Because of its heavier mass, and therefore its increased energy per given velocity, lead is the principal element of most bullets. Lead, however, is a relatively soft metal that deforms readily during high-velocity flight. “Jacketed” bullets have a lead body covered with metal alloys that prevent deformation during flight, and therefore help the bullet retain speed and accuracy over a long distance. Conventionally jacketed bullets will deform when they strike dense tissue, but bullets with thicker jackets are intended to retain their shape and therefore penetrate deeply into large game animals such as elephants (Figure 1). Bullets that deform upon striking the body will cause considerably more collateral tissue damage by direct contact, cavitation, and shock waves than nondeformable bullets. Fragmentation of bullets will also occur when the bullet strikes bone and will add to the damage by shredding surrounding tissue (Figure 2).

Figure 1 Full-metal-jacket .308 caliber rifle bullet that has opened upon impact with a game animal (left) compared with same caliber bullet with a thicker jacket that has passed undeformed through the animal (right). Notice the grooves on the base of each bullet caused by the internal rifling of the barrel.

(Bullets courtesy of Gerald Warnock, MD, Portland, OR.)

Figure 2 (A) Close range .30-06 hunting rifle wound to the right forearm. (B) Radiograph of same injury showing extensive bony comminution and bullet fragmentation. (C) Radiograph of same patient’s pelvis demonstrating extensive fragmentation of the bullet. This patient required lower abdominal wall reconstruction.

According to The Hague Declarations of 1899, military rifle bullets “which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core” are banned. This prohibition was designed to reduce the severity of wounds, and therefore the suffering of soldiers on the battlefield, but does not apply to combatants of noncontracting organizations and does not apply to bullets commonly used for hunting. In fact, “full-metal-jacket” (FMJ) bullets are prohibited for game hunting in many jurisdictions. For this reason, hunting rifle wounds may be more severe than those resulting from an equivalent military rifle. The exception to this principle is the assault rifle, which although its bullet is jacketed, causes severe wounds from the bullet’s tendency to tumble in tissue.

HANDGUNS

Handguns are commonly used in urban areas because they are lightweight and can be concealed. Fortunately, handguns cannot produce as highly accelerated and accurate a projectile as rifles. The amount of gunpowder packed into a handgun bullet casing must be limited to avoid barrel damage and permit the shooter to fire the weapon supported only by their arms and hands. Experienced marksmen can master the handgun under controlled circumstances, but both police and criminals probably strike their target less than half the time in the field. Accuracy is dramatically decreased with distance. The majority of handgun wounds, therefore, are generated from 10 yards or less.

The immediate danger of a handgun wound stems from direct injury to vital organs such as are found in the head, neck, or chest. The probability of proximity injury to vasculature is less with handgun wounds than it is with rifle or automatic weapon injuries, but should still be considered. Because the velocity of a handgun bullet is less as the bullet strikes the tissue, the bullet is less likely to deform or fragment and tissue cavitation may be slight. Jacketed handgun bullets cause even less collateral damage than the nonjacketed, and in some cases may penetrate the tissue and subsequently exit the body with much of their destructive potential intact.

Nonetheless, several measures designed to increase the wounding potential or “stopping-power” of handguns are available and will be encountered. These include “hollow-point” bullets designed to expand (Figure 3, right) and Glaser Safety Slugs® designed to disintegrate into tiny pellets after impact (Figure 4). The Glaser Safety Slug® is marketed to law enforcement and security personnel who need to immobilize a human target in a crowded environment such as an airport or an airplane without concern of overpenetration or ricochet into innocent bystanders. “Magnum” handguns have extra powder and longer barrels that will produce a devastating wound at close range. Fortunately, magnum editions are not as commonly seen as regular handguns because they are expensive, heavy, and difficult to master.

Figure 3 .45 caliber full-metal-jacket handgun bullet (left) and 10-mm “hollow-point,” partially jacketed bullet (right)

(Bullets courtesy of Bruce Ham, MD, and Gerald Warnock, MD, Portland, OR.)

Figure 4 Radiograph of chest and upper abdomen of patient shot with a Glaser Safety Slug®. Note the midline larger projectile with multiple accompanying pellets in the right upper quadrant. This patient sustained colon, gastric, renal, splenic, diaphragmatic, and pancreatic injuries as well as paraplegia from the main projectile striking the spinal cord. Since the main projectile passed through the colon, it was electively removed posteriorly.

Indications for operation of handgun wounds of the neck, chest, and abdomen would include mandatory exploration for Zone II neck injuries, selective exploration of the chest based on hemorrhage, and mandatory exploration of all abdominal penetrations except tangential injuries that do not penetrate the fascia and selective liver injuries. Patients with bullet entrance sites below the nipple on the chest require abdominal exploration if the abdomen is tender, a diagnostic peritoneal lavage is suspicious, or the diaphragm is not well visualized on radiograph. Stable patients with right upper quadrant wounds may be selectively evaluated by CT scan and managed nonoperatively if the bullet clearly injures only the liver. Laparoscopy may be used to evaluate the diaphragm in stable, nontender patients with chest wounds or as an adjunct to nonoperative management of liver penetrations that result in bile leaks.

HUNTING RIFLES

Civilian rifle wounds, such as those resulting from hunting accidents, are among the most destructive injuries seen by surgeons. The increased amount of gunpowder contained in the bullet case and the enhanced length of the barrel that exposes the bullet to the force of the powder blast for a longer distance leads to dramatically more projectile acceleration than is possible with a handgun (Figure 5). Rifling, the barrel’s internal spiraling grooves, causes the bullet to spin and consequently improves distance and accuracy. The average muzzle velocity of a 30-06 hunting rifle is 890 m/sec and may maintain up to 90% of its kinetic energy at 100 m. A rifle wound to an extremity, whether close range or distant, will destroy soft tissue, bone, and vessels, and cause dramatic hemorrhage that may need to be controlled with direct pressure or a tourniquet at the scene (see Figure 2).

Figure 5 Various rifle bullets compared. Left to right: .223 caliber FMJ (M-16 assault rifle), 30-30 soft point, 6-mm soft point, 30-06 soft point, .308 caliber military-style FMJ (7.62 mm NATO), .458 caliber FMJ magnum, .375 caliber FMJ magnum, .378 caliber FMJ hollow tip, World War II–era .47 caliber FMJ. FMJ, full metal jacket.

(Bullets courtesy of Bruce Ham, MD, and Gerald Warnock, MD, Portland, OR.)

Because of the potential for extensive damage to an extremity struck by a rifle bullet, plain radiographs looking for fractures, operative wound exploration with debridement, and intraoperative angiograms are highly recommended. Even if the overlying skin is uninjured, the soft tissue hidden beneath may be irreversibly damaged. All devascularized tissue and pieces of clothing should be removed. Serial debridements at daily intervals may be necessary to identify all devascularized tissue. Abdominal gunshot wounds from hunting rifles are best managed by open abdomen techniques with second-look operations if several organs are simultaneously injured.

ASSAULT RIFLES

The M-16 (United States), AK-47 and AK-74 (Russia), Uzi and Galil (Israel), Fal (Belgium), and their variations are relatively lightweight, short-barreled military rifles that fire rapidly sequential, high-velocity bullets that tumble and yaw shortly after striking tissue. Military actions that rely on these weapons seek to rapidly disable as many combatants as possible. Although these rifles and their ammunition are no longer sold on the civilian market in most Western countries, rifles that the owner possessed prior to 1994 can be legally fired in the United States, such as in target practice. These are the most common assault rifles that will be encountered in military actions; it is estimated that tens of millions of AKs and Uzis have been manufactured and distributed around the world. The caliber of bullet used in assault rifles ranges from the smaller 5.45-mm (0.21-inch) AK-74, to the 0.223-inch M-16, to the 7.62-mm (0.3-inch) AK-47, to the 9-mm (0.35-inch) Uzi.

In general, these bullets will produce severe wounds that will require soft tissue debridement; however, surgeons who have operated on injuries caused by assault rifles have occasionally noted their surprise that more injury is not apparent. This is because both the M-16 and the AK-74 deliver an FMJ bullet not much larger than a .22-caliber small-game rifle. If a single bullet passes cleanly through an extremity, the surrounding tissue damage will not be as dramatic as what a deformable, larger-caliber hunting rifle bullet would cause.

The salient point for surgeons to remember about automatic or semi-automatic assault rifles is the difficulty there can be in determining the bullet’s trajectory after it strikes the victim. Abdominal wounds may contain several areas of bowel injury as well as solid organ disruptions. Thoracic penetrations need ultrasonic visualization of the pericardial space and esophageal contrast radiography if nonoperative therapy is chosen. Extremity wounds may require operative exploration and debridement and an angiogram is indicated if the ankle-brachial index (ABI) is 0.9 or less.

SHOTGUNS

Shotguns and their shells come in four main sizes: .410 juvenile, 20-gauge, 12-gauge, and the 10-gauge (Figure 6). Pellets are of variable sizes and are made of lead or steel. Heavier lead pellets scatter less than steel pellets, but are illegal for shooting waterfowl. Slugs are also available for shotguns and are commonly used for game hunting in some states, such as New Jersey (Figure 7). The shotgun is ineffective against humans at distances greater than 10 or 15 yards (30–45 feet), but close range (<4 feet) blasts are 85% fatal. These wounds are extremely morbid and often require several operations and multidisciplinary management. Pellets spread in every direction and strike multiple types of tissue, but fortunately because of their small mass the damage potential of the shot dissipates quickly. Pellets may enter arteries and veins and embolize peripherally or centrally. A search for the plastic insert dispelled from the shell and pieces of the patient’s clothing hidden in the wound is advised in close-range cases. There is no indication to remove all the pellets—lead poisoning does not occur from pellets or bullets left permanently in human tissue.

Figure 6 20-gauge, 12-gauge, and 10-gauge shotgun shells compared (left to right).

(Bullets courtesy of Gerald Warnock, MD, Portland, OR.)

Figure 7 Shotgun shell loaded with lead slug instead of pellets (left). Same type of slug removed from game animal. Note deformity of central zone from flight and contact.

(Bullets courtesy of Gerald Warnock, MD, Portland, OR.)

Thoracic wounds created by close-range shotgun blasts may be challenging to cover if part of the chest wall is lost—diaphragm transposition or emergent muscular flaps have been described. Abdominal wounds are best managed with serial operations and debridement through an open abdomen mesh prosthesis. Extremity shotgun blasts usually require wound exploration and debridement with intraoperative angiograms.

PROTECTIVE VESTS

There are many varieties of “bullet-proof” vests manufactured with successive layers of synthetic materials such as Kevlar® (Dupont), which is a lightweight aramid fiber with extreme tensile strength. These vests are categorized according to their level of protection: Level I will protect the wearer from a .38 handgun at 259 m/sec, Level II from a 9-mm FMJ at 332 m/sec, and Level III from a 9-mm FMJ (assault rifle) at 427 m/sec. Protection from rifle bullets at higher velocities requires the addition of a ceramic plate to the vest. No vest is 100% effective, however. Even if the bullet does not penetrate, chest wall and pulmonary contusions can occur from the blunt force that is dissipated into the vest and onto the chest wall. Many varieties of “armor-piercing” bullets are manufactured for both handguns and rifles, and may be encountered in both military and nonmilitary situations, even though they are illegal for civilian use. These projectiles are jacketed and have a lead inner shell and a hardened steel or tungsten interior core. As the conventional portion of the projectile strikes the vest, it deforms and “softens up” the barrier. The hardened cores of these bullets pass through their softer shells to penetrate body and vehicular armor and even, in some cases, concrete walls.

LANDMINES AND IMPROVISED EXPLOSIVE DEVICES

The detonation of a concealed explosive device such as a conventional landmine or an improvised explosive device (IED) usually results in the immediate amputation or at least partial amputation of the triggering extremity. Exsanguination from major vessel injury is possible, and therefore a field tourniquet may be necessary. Fragments of metal and debris will also shower the contralateral extremity, perineum, torso, and face. The current military standard for operative management is damage control—repeated debridements of devascularized tissue and the use of external fixators for bone stability are recommended. Conventional landmines triggered by the foot will cause an umbrella effect that spares the skin and subcutaneous tissue of the lower leg while destroying underlying muscle and bone (Figure 8A). The overlying skin will hide significant destruction and contamination beneath (Figure 8B). Aggressive debridement to prevent infection tracking along the popliteal vessels and neural sheaths is advised. Robin Coupland of the International Red Cross makes an argument, however, to conserve the partially protected gastrocnemius muscle for reconstruction.

Figure 8 (A) “Umbrella” effect of foot-triggered mine on the lower leg. (B) Severe damage to the compartments of the lower leg may be concealed by overlying skin.

(From Coupland RM: War Wounds of Limbs: Surgical Management. Oxford, Butterworth-Heinemann, Ltd., 1993, with permission of the author and the International Committee of the Red Cross.)

RED CROSS WOUND CLASSIFICATION

Classification of wounds has merit since in practical terms it may be difficult to determine the exact type of weapon used. The International Committee of the Red Cross has adopted Coupland’s wound description method. There are six main criteria that are used to divide wounds into three grades and four types. At first glance the system seems formidable, but surgeons of the Red Cross, who classify about 4000 wounds per year, have accepted the system and are developing guidelines based on it. Wounds are scored on initial assessment or after surgery by entry size (centimeters), exit size (centimeters), cavity size (fingers), fractures, vital structures (brain, viscera, major vessels), and metallic body (intact bullet vs. fragments). The categories are E, X, C, F, V, and M, respectively (Figure 9). The advantages of uniform classification of wounds for research purposes are multiple.

Figure 9 Examples of wound scores obtained under International Red Cross Wound Classification.

(From Coupland RM: War Wounds of Limbs: Surgical Management. Oxford, Butterworth-Heinemann, Ltd., 1993, with permission of the author and the International Committee of the Red Cross.)

BULLET REMOVAL

Bullet removal is generally unnecessary and ideally would not be used as the only indication for a surgical procedure. An occasional patient is symptomatic enough from an irritating focus to tempt the surgeon to remove the projectile. Many a surgeon, however, has searched subcutaneous tissue in vain looking for a foreign body that seems to be just beneath the skin. Radiographic localization may be necessary.

The only risk of lead poisoning seems to be from bullets in contact with synovial fluid and by extrapolation, spinal cord fluid. Bullets that pass through colon and subsequently lodge in bone are at risk to cause osteomyelitis. Controversy exists as to the magnitude of the risk, but at our center we favor removal if possible. The alternative is irrigation of the tract and a minimum of 10 days of broad-spectrum intravenous antibiotics. Other true indications for bullet removal include removing bullet emboli in arteries and veins and bullets lodged in cardiac chambers.