Key points
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Principles of wound decontamination, not actual debridement of tissue, should be reinforced to prevent loss of anterior/posterior and/or horizontal projections of the soft tissue.
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The permanent cavity is the site of initial permanent tissue destruction.
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Final determination of the degree of tissue loss can only be made after anatomic reconstruction of the underlying facial skeleton.
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A key consideration of treatment is to have re-established the bony projection and angular shape of the facial skeleton as soon as possible, but definitively within 10 to 14 days, before the development of intractable facial scarring and contracture, or the formation of soft/hard tissue infection.
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Microvascular transfer of tissue to the head and neck region can generally be accomplished within 2 weeks of injury, allowing adequate time for the viability of the recipient tissue to be established and to eradicate any infection.
Causes of avulsive injuries
Shearing, or cutting, injuries created by blades or saws, tearing wounds caused by industrial machinery, and bites inflicted by animals are capable of creating avulsive defects and contaminated crush injuries of the craniomaxillofacial unit. Although large domestic animals can bite with forces as great as 450 lb/in, animals in the wild, such as bears or jaguars, can have bite forces in excess of 1700 lb/in ( Fig. 1 ). This form of crush injury is contaminated by a wide range of microorganisms, including viruses, bacteria, and mycobacteria. Significant areas of soft tissue overlying the facial skeleton may be avulsed, crushed, or bruised, compromising vascular supply and delaying initiation of the body’s host defense mechanism. Gross contaminates on machinery parts, including industrial residue and/or microbial sources from virtually limitless sites of origin, serve as infectious reservoirs further complicating the normal healing cascade.
Industrial or agricultural accidents possess the potential to create severe crush or avulsive wounds of the soft and hard tissues of the maxillofacial complex. Whether low or high velocity, the sheer mass of the injury platform associated with industrial machinery creates tissue injury patterns characteristics of a high-energy impact. As seen in firearm and ballistic injuries, if the injury pattern is consistent with a high-energy impact, the degree of tissue disruption occurring in the hard and/or soft tissues may result in separation from the native tissue bed and avulsion. If the wounding mechanism is a crush injury, the soft tissue overlying the bone can sustain catastrophic compromise to the vascular pedicle, resulting in soft and/or hard tissue necrosis. This necrosis, resulting in either partial loss of tissue/physical structure, or complete loss of the anatomic component, has the same physical outcome as avulsion.
A general understanding of energy/ballistics, either firearm related or in circumstances where objects otherwise strike and wound the victim, is necessary to adequately treat avulsive soft tissue injuries. A “round” is the comprehensive description of a unit of firearm ammunition. Each round consists of the following:
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Projectile
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Casing
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Propellant
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Primer
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. 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.
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. 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 because the surgical management of a wound caused by a .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.
Handguns are handheld firearms, with a barrel length generally 10.5 inches or less, which usually fire projectiles of a lower velocity and caliber. Handgun injuries generally have a tendency to “push-away,” or stretch soft tissues, including vessels or nerves, as opposed to avulsive loss. The characteristic low-velocity wound has a small rounded, or slightly ragged entrance wound, causing fragmentation of teeth and bony comminution, often exhibiting no exit wound ( Fig. 2 ). If an exit wound does occur, it is generally slit-shaped or stellate. Rifles are long guns with barrel lengths generally more than 24 inches. At distance, rifle wounds create a low-energy transfer similar to those seen with handguns. At close range the wounding characteristics are different because of the increased potential injury associated with velocity and high-energy transfer ( Fig. 3 ). The presence of an exit wound is usually found, which may be stellate and larger than the entry wound. The existence of avulsive soft/hard tissue wounds and significant fragmentation of the bone is are characteristic findings of rifle wounds. A shotgun is a long gun that may fire a single pellet, or numerous pellets, at a low velocity. The gauge of the shotgun is classified as the number of lead balls/pellets placed together equaling the interior diameter of the barrel, which would weigh one pound. For contact with close range injuries, the effect of the gas that is discharged under pressure into the wound also needs to be considered. This scenario is extremely important in shotgun and improvised explosive blast wounds because of the higher degree of contamination and presence of propelled gas and shock waves. Powder gases are expelled from the muzzle of the weapon after combustion of the gunpowder and follow the projectile out of the barrel. When the muzzle of the weapon is in contact with the target, this is an additional source of tissue displacement, injury, and thermal burning.
Shotgun pellet injuries essentially depend completely on the distance the weapon is from the target at the time of discharge. Sherman and Parrish devised a classification system to describe shotgun wounds in relation to the distance from the target. Type I injury occurs from a distance longer than 7 yards; type II injury is sustained when the discharge is within 3 to 7 yards; type III injury is within 3 yards. Type III injuries usually sustain dramatic soft and hard tissue injuries and avulsion of tissue, whereas type I injuries may be minimal ( Fig. 4 ). Because victims often have difficulty in determining how far away the shotgun was at the time of discharge, Glezer and colleagues revised this classification system and directed their attention to the size of the pellet scatter. Type I injuries occur when pellet scatter is within an area of 25 cm 2 ; type II injuries are within 10 cm 2 to 25 cm 2 ; type III injuries have pellet scatter less than 10 cm 2 . Although the Glezer classification originally was developed for abdominal injuries, the information is transferable to other areas of the body, and determinations of tissue injury is correlated directly to the size of the pellet scatter. Intuitively, the closer the shotgun is to the patient, the more dramatic the hard and soft tissue damage is. For rifles and handguns, the practical clinical difference in whether the weapon was 10 feet, 100 feet, or 1000 feet away from the patient otherwise has no bearing on surgical and medical treatment.
