Characteristics of Ballistic and Blast Injuries

Key points

  • The permanent cavity is the site of initial permanent tissue destruction.

  • Deformation of the projectile after impacting hard tissues causes an increase in the size of the permanent cavity.

  • After striking bone, fragmentation of the projectile and/or bone can result in the formation of numerous secondary projectiles each producing additional wounding potential, enlarging the size of the permanent cavity.

  • The ultimate fate and compositional makeup of the projectile is more important than its velocity or caliber.

  • Soft tissue injuries inherent in ballistic trauma may exhibit avulsive loss, sequential necrosis over days to weeks, and compromised vascularity, negating/delaying potential microvascular or pedicled soft tissue reconstruction.

Introduction

Ballistic injury patterns to the craniomaxillofacial region present a unique, and challenging, dilemma for the facial trauma surgeon. The tissue disruption associated with ballistic injury to the head and neck region can be daunting, and the identification of normal anatomic planes, potentially lost within bleeding, destroyed soft and hard tissues can challenge the skills of even the most experienced facial trauma specialist. Although classically considered under the purview of the military trauma surgeon, ballistic and blast injuries also are routinely treated by the civilian surgeon because of the incidence of intentional and unintentional firearm injuries and industrial accidents. A basic understanding of the definitions and characteristic clinical findings of ballistic and blast wounds should be an important tool in the armamentarium of the practicing craniomaxillofacial trauma surgeon.

Introduction

Ballistic injury patterns to the craniomaxillofacial region present a unique, and challenging, dilemma for the facial trauma surgeon. The tissue disruption associated with ballistic injury to the head and neck region can be daunting, and the identification of normal anatomic planes, potentially lost within bleeding, destroyed soft and hard tissues can challenge the skills of even the most experienced facial trauma specialist. Although classically considered under the purview of the military trauma surgeon, ballistic and blast injuries also are routinely treated by the civilian surgeon because of the incidence of intentional and unintentional firearm injuries and industrial accidents. A basic understanding of the definitions and characteristic clinical findings of ballistic and blast wounds should be an important tool in the armamentarium of the practicing craniomaxillofacial trauma surgeon.

Introduction to commonly used ballistic terms

Any introduction to the study of ballistic injuries should provide a review of commonly used terms. Table 1 provides the necessary background information to recognize the terminology associated with ballistics, and how those components correlate to an understanding of ballistic injuries:

Table 1
Commonly used terms in ballistics
Components of ammunition
Cartridge/Round A unit of firearm ammunition
Projectile The component of the round that is expelled toward the target, sometimes referred to as the “bullet”
Magnum A cartridge loaded with either a greater volume or more powerful propellant than the original cartridge design, imparting greater velocity to the projectile
Components of weapon
Rifling Helical grooves in the barrel of a weapon, which imparts spin along the long axis of the projectile
Caliber The internal diameter of the barrel of a weapon, usually measured in millimeters or fractions of an inch
Gauge/Bore The total number of round lead balls that would fill the diameter of the barrel and weigh 1 pound
Associated terms seen in ballistic literature
Yaw Movement along the longitudinal access of the projectile
Precession Rotation of the projectile around the center of mass
Nutation Small circular movement along the projectile tip
Magnus effect Lateral crosswind effect of a spinning projectile in flight
Coriolis effect Spherical shape and rotational properties of the Earth, and its orbit, as it applies to the projectile

As historical concepts of ballistics teach that impact kinetic energy is equal to one-half the mass of the projectile times velocity squared (KE = ½ MV 2 ), one would wrongly assume caliber (size) of the projectile and velocity are the sole components of injury calculation. Actually, the increased energy transmitted from a high-velocity projectile does not necessarily translate to increased wounding capacity, as will be noted throughout the remainder of this article, and the physical properties of the projectile, and its fate on striking the victim, are more important than the caliber. Caliber alone has no alteration to the surgical treatment of the injury, and primarily serves to satisfy the curiosity of the attending medical staff. By understanding the basic mechanical properties of the projectile expelled toward the target, the correlation of velocity and subsequent energy transfer, and the anatomic properties of the head and neck, the craniomaxillofacial trauma surgeon will have a better understanding of the consequences of ballistic injury to the facial skeleton ( Box 1 ).

Box 1

  • Velocity

  • Profile

  • Shape

  • Stability

  • Fragmentation

  • Expansion

  • Secondary impact

Factors affecting energy transfer between a projectile and body tissue

Yaw, precession, and nutation are frequently referenced when initially studying ballistics. Yaw and precession decrease as the distance of the bullet from the barrel increases, and along with nutation, are terms generally associated with shooting from a distance, as seen in military-grade artillery weaponry ( Fig. 1 ). Illustrative examples of yaw are exaggerated in excess of 30° for graphic representation, while in actuality the degree of yaw is generally less than 1° to 2°, affording tight control of the projectile in flight and allowing the projectile to hit what the firearm is aimed toward. Should the yaw be as exaggerated as seen in most artistic renderings, the projectile would be uncontrollable because of tumbling along the path of fire. A clear clinical example of the effects of yaw and precession is that when examined on a shooting range, projectile holes in targets are consistently circular in nature, indicating the spherical shape of the projectile, not a ragged opening consistent with “tumbling” or excessive yaw. Of interest, projectiles do tumble within the body of the target, causing increased damage after striking hard tissue, or with deformation of the projectile. Although these terms have practical applications in weaponry, the clinical significance of these items in craniomaxillofacial ballistic trauma is negligible at best.

Fig. 1
Yaw: Movement along the longitudinal access of the projectile; precession: rotation of the projectile around the center of mass; nutation: small circular movement along the projectile tip.

The magnus and coriolis effects are also frequently referenced in the discussion of ballistics, but again are isolated to the military applications of projectile flight, as well as the recreational aspects of long-range firing for hunting or competitive shooting. As the overwhelming majority of ballistic injuries to the head and neck region occur within relatively short distances, well within the effective range of the weapon and projectiles, these definitions and concepts have minimal to no correlation to the remainder of this article, or for the surgical management of these ballistic injuries.

Components of ballistic missiles

As previously described, the cartridge or round describes a unit of firearm ammunition. Each round consists of the following ( Fig. 2 ):

  • Projectile

  • Casing

  • Propellant

  • Primer

Fig. 2
( A ) Cross-sectional analysis of a cartridge and shotgun shell. ( B ) Cross-section of a full-metal jacketed rifle cartridge.

The components of a round provide a basic understanding of the principles of firearm injury. The projectile is the portion of the bullet that is expelled and strikes the target. The compositional makeup of the projectile (soft lead, hollow point, full copper covering, or multiple pellets, as seen in shotguns) has a direct correlation on the wounding potential of the weapon. As a projectile deforms after striking the victim, either as a result of metallurgic composition during manufacturing, or as a direct consequence of striking the underlying bone, the energy transfer to the victim, and potential injury to associated tissues, is increased. As noted earlier, the actual projectiles expelled by firearms are limited in type only by the imagination of the manufacturers and firearm enthusiast. The casing is the container packaging the projectile, propellant (gunpowder or cordite), and primer as a single unit for placement into the firing mechanism of the weapon. The propellant, such as gunpowder or cordite, is the accelerant that actually allows for expulsion of the projectile from the weapon. The more propellant in a cartridge, as is seen in magnum and rifle rounds, the greater velocity the projectile exhibits. Wadding, or wads, are generally plastic frameworks with a paper or felt insert that hold the various pellets (projectiles) together in relation to the propellant, allowing for accurate and safe release of all the projectiles simultaneously from the barrel in scattershot and shotgun cartridges. Without the presence of wadding, the gas produced by the propellant would push through the pellets, and not propel them as a unit. The primer is the only portion of the bullet with an explosive charge. As the primer is struck by the firing pin of the weapon, the explosive charge is activated, igniting the propellant and sending the projectile on its flight. Some cartridges are referred to as rimfire, as the priming mechanism is contained within the rim of the base rather than a separate primer in the center of the base. Generally, rimfire cartridges are less powerful and cannot be reloaded, whereas centerfire cartridges can have the primer replaced and reloaded with another projectile.

Rifles, handguns, and machine guns have rifled barrels; essentially, spiral grooves cut into the length of the interior of the bore of the barrel. The grooves impart spin upon the projectile, stabilizing it in flight and allowing the projectile to travel in a controlled manner to the target. The grooves are separated by segments of metal, called lands, which project into the middle of the barrel. The diameter of the barrel measured between the lands represents the caliber of the projectile. Caliber specifications based on nomenclature used in the United States can be difficult to comprehend, and utterly confusing to the health care team. The 0.30-06 and the Winchester 0.308 cartridges are both loaded with bullets that have a diameter of 0.308 inches. The ‘‘06″ in this term describes the year, 1906, when the cartridge was introduced to the market. The term ‘‘grains’’ originally was applied to black powder charges and refers to the weight of the powder in the cartridge, not the number of granules contained in the cartridge case. A 0.30–30 cartridge has a 0.308-inch-diameter bullet propelled by 30 grains of smokeless powder. As newer forms of gunpowder were developed, this powder charge was no longer used, but the terminology persists to this day. Additional misperceptions regarding caliber exists because the North Atlantic Treaty Organization (NATO) and US military projectiles are described using the metric system (7.62-mm or 9.00-mm rounds), whereas US civilian firearm munitions are generally referred to in measurements relating to inches (0.357 or 0.38). Unfortunately, no uniform mechanism exists for the description of firearm cartridges and manufacturers continue to inundate the market with further descriptions to add to the confusion, such as velocity, country of manufacture, number of grains of propellant, year of manufacture, and so forth ( Fig. 3 ). As noted earlier, the question regarding caliber is commonly asked in the management of ballistic injury. In reality, caliber has minimal practical impact in the care of the patient, as the surgical management of a wound caused by a 0.357 projectile is no different from a wound caused by a 9-mm round, and should be directed to the specific anatomic anomaly created by the projectile, not the weapon used. Experienced surgical providers cannot accurately determine the caliber of a weapon by visual examination of the wound alone, and would never alter the required treatment based on the diameter of the projectile.

Jan 23, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Characteristics of Ballistic and Blast Injuries
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