Chapter 19: CLINICAL FORENSIC MEDICINE

Clinical Summary

Gunshot injuries can be accurately identified and classified as entrance, atypical entrance, exit, or atypical (grazing) wounds based upon their physical characteristics. Wounds are not classified based upon their size. Physical findings in and around these wounds may offer evidence as to the actual mechanism of injury, supporting or refuting the initial history given to the provider. As most physical findings are transient in nature (cleaned, debrided, or eventually healed), the emergency physician must be diligent in recognizing and documenting them at the time of presentation. The physician’s failure to accurately document the physical characteristics of the wounds or correctly interpret the physical findings can compromise the legal process and obstruct justice.

Entrance Wounds

Gunshot wounds of entrance are divided into four categories based on their range of fire: distant, intermediate, close, and contact. Range-of-fire is the distance from the gun’s muzzle to the victim’s skin or clothing.

The size of the entrance wound bears no relation to the caliber of the inflicting bullet. Entrance wounds over elastic tissue will contract around the tissue defect and have a diameter much less than the caliber of the bullet.

Distant Wounds: The distant wound is inflicted from a range sufficiently distant that the bullet is the only component expelled from the muzzle that reaches the skin. There is no visible tattooing or soot deposition associated with a distant entrance wound. As the bullet penetrates the skin, friction between it and the epithelium results in the creation of an “abrasion collar” (Fig. 19.1). The width of the abrasion collar will vary with the angle of impact. Elongated abrasion collars from projectiles that enter on an angle may produce a collar with a “comet tail” (Fig. 19.2). Most entrance wounds will have an abrasion collar; however, gunshot wounds to the palms and soles are exceptions—their entrance wounds appear slit-like. Bullets that pass through an intermediate object, a door or windshield for example, will become deformed or misshapen (Fig. 19.3). A misshapen bullet creates an irregular abrasion collar (Fig. 19.4) as compared to the smooth abrasion collar created by a nondeformed bullet (Fig. 19.1).

Intermediate-Range Wounds: Tattooing is pathognomonic for an intermediate-range gunshot wound and presents as punctate abrasions from contact with partially burned or unburned grains of gunpowder (Fig. 19.5). This tattooing cannot be wiped away. Clothing and hair, as intermediate objects, may prevent the gunpowder grains from making contact with the skin. Tattooing can, but rarely does, occur on the palms and soles owing to the thickness of their epithelium.

Tattooing has been reported with a range of fire as close as 1 cm and as far away as 4 feet. The density of the abrasions and the associated pattern will depend upon the barrel length, muzzle-to-skin distance, type of gunpowder (ball, flattened ball, or flake), presence of intermediate objects, and caliber of the weapon. Spherical powder travels farther and has greater penetration than flattened ball or flake powder. “Pseudotattooing” (Fig. 19.6) is punctate abrasions from fragments created when bullets pass through intermediate objects like wood or glass.

Close-Range (Near-Contact) Wounds: “Close range” is defined as the maximum range at which soot is deposited on the clothing (Fig. 19.7) or wound (Fig. 19.8) and typically is a muzzle-to-victim distance of 6 inches or less. On rare occasions, however, soot has been found on victims as far as 12 inches from the offending weapon. The concentration of soot will vary inversely with the muzzle-to-victim distance and its appearance will be affected by the type of gunpowder and ammunition used, the barrel length, the caliber, and the type of weapon.

Contact Wounds: A contact wound occurs when the barrel or muzzle is in contact with the skin or clothing as the weapon is discharged. Contact wounds can be described as tight, where the muzzle is pushed hard against the skin, or loose, where the muzzle is incompletely or loosely in contact with the skin or clothing. Wounds sustained from tight contact with the barrel can vary in appearance from a small hole with seared, blackened edges (from the discharge of hot gases and an actual flame), to a gaping, stellate wound (from the expansion of the skin from gases) (Figs. 19.9 and 19.10). Large stellate wounds are often misinterpreted as exit wounds based solely upon their size and without adequate examination of the wound characteristics.

In a tight-contact wound, all materials—the bullet, gases, soot, incompletely combusted gunpowder, and metal fragments—are driven into the wound. If the wound overlies thin or bony tissue, the hot gases will cause the skin to expand to such an extent that it stretches and tears. These tears will have a triangular shape, with the base of the tear overlying the entrance wound. Larger tears are associated with ammunition of .32 caliber or greater, or magnum loads.

Stellate tears are not pathognomonic for contact wounds. Tangential wounds, ricochet or tumbling bullets, and some exit wounds may also be stellate in appearance. These wounds are distinguished from tight-contact wounds by the absence of soot and powder within the wound. In some tight-contact wounds, expanding skin is forced back against the muzzle of the gun, causing a characteristic pattern contusion called a muzzle contusion (Fig. 19.9). An outline of the barrel can also be imprinted on the overlying clothing and is associated with contact wounds through clothing (Fig. 19.11). These patterns are helpful in determining the type of weapon (revolver or semiautomatic) used to inflict the injury and should be documented prior to wound debridement or surgery.

With a loose-contact wound, where the muzzle is angled or held loosely against the skin, soot and gunpowder residue will be present in and around the wound. The angle between the muzzle and skin will determine the soot pattern. A perpendicular, loose-contact or near-contact injury results in searing of the skin and deposition of the soot evenly around the wound. A tangential loose or near-contact injury produces an elongated searing pattern and deposit of soot around the wound.

“Bullet wipe” is a residue from soot, soft lead, or lubricant, which may leave a gray or black rim or streak on the skin or clothing overlying an entrance wound (Fig. 19.7). This discoloration may also be found around the abrasion collar but is usually more prominent on clothing.

Exit Wounds

Determining whether a wound is an entrance or an exit wound should be based on the physical characteristics and physical evidence associated with the wound and never upon the size of the wound. The size of the exit wounds are the result of a bullet pushing and stretching the skin from inside outward. The skin edges are generally everted, with sharp but irregular margins (Figs. 19.12, 19.13, 19.14). Abrasion collars, soot, searing, and tattooing are not associated with exit wounds. Soot can be seen at an atypical exit wound site if the entrance wound is close to the associated exit wound. Soot can be propelled through the wound from entrance to exit when the wound track is extremely short. If this is noted, the soot deposition will be more pronounced at the entrance and only faintly observed within the exit wound.

Exit wounds assume a variety of shapes and appearances and are not consistently larger than their corresponding entrance wounds. The size of an exit wound is determined primarily by the amount of energy transmitted to underlying tissue, bone for example, which is extruded from the wound. A bullet’s size, shape, and attitude as it exits as well as postinjury tissue swelling will affect its size. A bullet’s usual nose-first attitude can change upon entering the skin to a tumbling and yawing one. A bullet with sufficient energy to exit the skin in a sideways attitude or one that has increased its surface area by mushrooming may produce an exit wound larger than its entrance wound. Energy transferred to bone, with resultant ballistic fracture, may also result in an exit wound larger than the entrance wound (Fig. 19.14). A “false abrasion collar” or “shored exit” wound may mimic an entrance wound. This occurs when the epithelium is pressed against a supporting surface such as a floor, wall, chair, firm mattress, or wallet (Figs. 19.15 and 19.16).

Graze Wounds

Graze wounds are considered atypical and result from tangential contact with a passing bullet. The direction of the bullet’s path may be determined by careful wound examination. The bullet produces a trough and may cause the formation of skin tags on the lateral wound margins (Fig. 19.17). The base of these tags points toward the weapon and away from the direction of bullet travel.

Evidence Collection

Preservation of clothing, bullets, and cartridge cases is critical to the investigation of gun violence. Clothing should be place in separate paper bags and bullets in breathable containers. The microscopic marks on the exterior surface of a bullet can be used to identify the offending weapon. The use of booties on the ends of hemostats can prevent the loss of essential evidence and preserve these unique identifying microscopic marks from being altered or permanently destroyed (Fig. 19.18).

Pearls

1. Distant-range gunshot wounds are inflicted from a distance of greater than 4 feet and there is no tattooing, soot, or searing associated with the wound.

2. Intermediate-range gunshot wounds are inflicted at a distances up to 4 feet and characteristically are associated with tattooing from partially burned and unburned gunpowder impacting the skin.

3. Near or close-contact gunshot wounds are defined as the maximum range at which soot is deposited on the wound or clothing and typically occur at a distance of 6 inches or less.

4. Contact gunshot wounds (barrel is in contact with the skin or clothing at time of discharge) vary in size but will include triangular tears, searing of the skin, and soot within or around the wound.

5. Abrasion collars, soot, searing, and tattooing are associated with entrance wounds.

6. Determination of whether a wound is an entrance or exit wound should only be based on the physical characteristics of the wound and clothing and not on the size of the wound.

7. The size of an exit wound is determined by: (1) energy transferred from the bullet to underlying tissue (bone pushed out), (2) bullet shape (mushroomed) and configuration, and (3) swelling of underlying tissue.

8. Emergency physicians should attempt to recognize, document, preserve, and collect short-lived evidence whenever the clinical situation allows.

Every “weapon” (hand, belt, hot iron, knife, electrical cord, baseball bat, tire iron) can leave a mark, design, or pattern stamped or imprinted upon or just below the level of the epithelium. The imprints of these weapons are called pattern injuries, which are considerably reproducible. These injuries can be categorized into three major classifications according to their source: sharp-force, blunt-force, and thermal-pattern injuries.

Clinical Summary

There are two types of sharp-force injuries: incised and stabbed. The incised wound is longer than it is deep. The stab wound is defined as a puncture wound that is deeper than it is wide (Figs. 19.19, 19.20, 19.21). The wound margins of sharp-force injuries are clean and lack the abraded edges of lacerations from blunt forces. Forensic information can be gathered during the examination of a stab wound. Some characteristics of a knife blade, single- or double-edged, can be determined by visual inspection. Characteristics such as serrated versus sharp can be determined if the blade was drawn across the skin during insertion or withdraw from the victim. Serrated blades do not always leave these characteristic marks.

When a patient presents with superficial and/or parallel incisions, the wounds must be considered intentionally self-inflicted until proven otherwise (Figs. 19.22 and 19.23). The emergency physician should obtain a more detailed history, including the number of “swipes” the alleged assailant made with the knife. Accidental, self-inflicted incised wounds on the palm or palmar aspect of the fingers are common on the hands of suspects in violent stabbings (Fig. 19.24). The suspects’ hand slips down the handle and makes contact with the knife blade when the blade impacts a firm object, like bone (Fig. 19.25).

Pearls

1. Incised wounds have sharp wound margins and are longer than they are deep. Incisions result from contact with a sharp-edged implement: glass, knife blade, razor blade, or scalpel.

2. Stab wounds are puncture wounds that are deeper than they are long.

3. Knife-blade characteristics (single or dual edged, serrated or smooth) can frequently be determined by a visual inspection of the wound.

4. Superficial and/or parallel incisions should be assumed to be self-inflicted.

Clinical Summary

The most common blunt force injury is the contusion (Fig. 19.26). The pattern contusion is one that helps identify the causative weapon. A blow from a linear object leaves a contusion that is characterized by a set of parallel lines separated by an area of central clearing (Fig. 19.27). The blood underlying the striking object is forcibly displaced to the sides, which accounts for the pattern’s appearance. Pattern injuries that an emergency physician should recognize include those caused by the hand (slap marks [Fig. 19.27], fingertip contusions [Fig. 19.28], grab marks, ligature marks [Fig. 19.30], fingernail abrasions), solid objects (baseball bat, tire iron, 2 by 4, belt, shoe, comb), and bite marks.

Other manifestations of blunt-force trauma to the skin are the abrasion and the laceration. A weapon with a unique shape or configuration may stamp a mirror image of itself on the skin (Fig. 19.29) and provide the emergency physician with additional information on the mechanism of the injury. The color of a contusion cannot be used to accurately date its age.

Pearls

1. A contusion is the most common blunt-force injury pattern in interpersonal violence.

2. Blood underlying the force of the contusion is displaced to either side of the object, causing a pattern contusion in the shape of that object. This pattern is recognized by the central clearing surrounded by linear parallel contusions.

3. Emergency physicians must be able to recognize the pattern injuries caused by the hand (Fig. 19.27), solid objects, and bites.

4. Emergency physicians should not attempt to date the age of a contusion based upon its color or stage of resolution.

Clinical Summary

Manual strangulation is one of the most lethal forms of intimate partner violence and demonstrates the abuser’s power and control over the victim. The brain will suffer an anoxic injury when the flow of oxygenated blood is stopped by occlusion of the carotid arteries. Strangulation victims report visual and auditory changes just prior to a loss of consciousness. The loss of bladder control indicates a deep anoxic insult to the brain of at least 15 seconds in duration. The loss of bowel control occurs with carotid artery occlusions of greater than 30 seconds. The jugular veins can be occluded with 4 psi, the carotids with 11 psi, and the trachea with 34 psi. Occlusion of venous return can cause capillary rupture from increased pressure and the development of petechial hemorrhage (Figs. 19.32, 19.33, 19.34). Petechial hemorrhages can develop in any vascularized tissue, including the brain. The most sensitive areas for petechial development include the conjunctiva, sclera, and intraoral mucosa. The use of an oral-pharyngeal scope (Fig. 19.35) often reveals vocal cord injury and the presence of petechial hemorrhage in the posterior pharynx. With simultaneous occlusion of both the arterial and venous systems, it is possible to induce fatal and nonfatal strangulation events without petechial hemorrhage and evidence of external trauma.

Pearls

1. Strangulation is associated with a 700% increased risk of interpersonal homicide.

2. Application of a ligature (Figs. 19.30, 19.31) will leave a characteristic mark due to pressure applied over a small surface area.

3. Strangulation-induced petechial hemorrhage, from the rupture of venous vessels, may be found in the conjunctiva (Fig. 19.32), the soft palate, the posterior pharynx (Fig. 19.33), and above and below the area where pressure was applied (Fig. 19.34). Petechial hemorrhage is NOT required to prove strangulation. The majority of fatal strangulations exhibit no external evidence of trauma.

4. A victim of strangulation can be rendered unconscious in less than 8 seconds with bilateral occlusion of the carotid arteries. The carotids will be occluded with 11 pounds of pressure. Obtaining a history of neurological changes—loss of hearing, vision, consciousness, and bowel or bladder control—confirms neurologic injury and an anoxic insult to the brain.

Clinical Summary

Thermal pattern injuries are commonly seen in cases of abuse and assault especially when the victims are children and the elderly. A detailed history of the incident should include the position of the patient relative to the thermal source. This will help determine whether the injury was inflicted or accidental. Thermal injuries characterized by a distinct pattern that frequently present to emergency departments are those caused by cigarettes (Fig. 19.26), flatirons (Fig. 19.37), curling irons (Fig. 19.38), and scalding hot water (Fig 19.40). Water burns will be of two natures: immersion and splash. A sharp or clear line of demarcation between burned and unburned tissue characterizes an immersion or dipping burn. In contrast, splash burns are characterized by an irregular or undulating line or by isolated areas of thermal injury, usually round or oval in shape, caused by droplets of hot liquid. The severity of the scald injury depends upon two variables: the length of time that the skin was in contact with the offending substance and the temperature of the substance itself. Tap or faucet water causes full-thickness thermal damage in 1 second at 70°C (158°F), and 180 seconds at 48.9°C (120°F). Law-enforcement agencies should routinely measure the household’s or institution’s water temperature in any investigation involving a scald injury of a child, a developmentally delayed person, or an elderly one. The water temperature will give authorities an estimate of the duration of the insult and therefore the degree of malice of intention on the part of the assailant.

Pearls

1. A thermal-pattern injury is a common form of abuse seen in infants, institutionalized patients, and the elderly.

2. Emergency physicians must recognize thermal-pattern injuries of abuse.