Injury Pattern Patterned Injury

3.4.1. Injury Patterns

Many wounds caused by blunt trauma are nonspecific in determining the nature of the blunt surface that caused those injuries. An injury pattern is defined as a predictable but nonspecific injury having a characteristic distribution consistent with a particular traumatic event (Fig. 13). Blunt trauma injury patterns are seen in certain types of deaths.

3.4.1.1. Chronic Alcoholism

Chronic alcoholics, when intoxicated, fall repeatedly. They are predisposed to bleeding because of abnormal coagulation caused by cirrhosis (Fig. 7). Multiple blunt trauma injuries (e.g., contusions) on the extremities, torso, and face suggest assault (Fig. 14; ref. 30). There may be associated internal injuries that heighten concern. The finding of external and internal trauma of different ages, supported by toxicological analysis and investigation of the circumstances of the death, provides reassurance.

3.4.1.2. Hypothermia

Hypothermia occurs when the body temperature drops to less than 35°C (95°F [31-33]). Poor indoor heating, cold water immersion (see Chapter 5, Subheading 4.5.),

Fig. 14. Multiple contusions. Chronic alcoholic subject to repeated falls. (A) Forehead. (B) Elbow. (C) Knee and shin. (Courtesy of Dr. A. Tuck, London Health Sciences Centre, London, Ontario, Canada.)

and outdoor exposure are common scenarios (31,34). Certain predisposing factors play a role. Persons at the extremes of age are vulnerable (Fig. 5; refs. 31 and 34-36). Underlying disease or injury render an individual more vulnerable. Ischemic heart disease is a setting for cold-induced arrhythmia (36). Endocrine dysfunction (e.g., hypothyroidism, diabetes mellitus) alters perception of cold and decreases the ability to compensate (31). Neuropsychiatric illness (e.g., schizophrenia, dementia) can blunt the desire to seek shelter from the cold (31,37,38). Intoxicated individuals, either in wet clothes or dressed inadequately, are typical victims of cold weather exposure (31,34-36,38,39).

These cases can display a pattern of blunt trauma injuries. Abrasions occur commonly on the extremities, but other body sites may be involved (Figs. 5, 9, 15; refs. 35, 36, and 38). These scrapes can be caused by falling or rubbing. Their distribution on the dorsum of the hand suggests an altercation (Fig. 15). Suspicions are heightened if clothes have been removed. Paradoxical undressing varies from removal of footwear to complete nudity, which suggests sexual assault (Fig. 5; refs. 35,36, and 38-40). This phenomenon is the result of cold-induced vasoconstriction that is followed by vasodila-tion from loss of vascular tone (35,36,38,40). The result is a false sense of warmth, and there even may be evidence of rolling around in the snow (35,39). Paradoxical undressing occurs in the setting of dementia and suicide (37,39). Hypothermic victims can also be found in unusual locations (e.g., lying under a bed) because of "terminal burrowing behavior" (38).

Associated external findings include frostbite, edema of the face and extremities, and red livor mortis (Fig. 16; refs. 35, 36, and 41). Areas of purple or red-purple discoloration, particularly on the knees and elbows in nonlivid areas, have been described and

Fig. 15. Hypothermia death. Victim found lying face down on ice. Subtle abrasions on dorsum of hand from rubbing (see Fig. 9).
Fig. 16. Ischemic changes of right foot owing to frostbite.
Fig. 17. Hypothermia. Gastric erosions arranged in a rectangular distribution (arrow).

may be a postmortem change (35,36,41). When the body is thawed, veins are accentuated on extremities, and marbling caused by decomposition is enhanced (41).

Internal findings may be few. Acute changes include superficial gastric erosions, pancreatic hemorrhage, pulmonary edema, and "striped" hemorrhages in the iliopsoas muscles (Fig. 17; refs. 35, 36, 38, 40, and 41). Stomach lesions are likely caused by ischemia from vasoconstriction (40). A prolonged survival period can be complicated by coagulopathy, rhabdomyolysis, and renal failure (see Chapter 8, Heading 13; and ref. 31).

Toxicological testing is necessary to determine whether the victim was intoxicated. Acetone, detected in the urine, may be a sign of cold-induced ketosis (38).

3.4.2. Patterned Injury

The finding of a patterned injury—i.e., the source of injury is reproduced on the skin surface—is less common but has important evidentiary value, particularly in homicide investigations (Figs. 18-23 and refs. 8 and 42-47). On occasion, the injury is the mirror image of the striking object (44). Linking a patterned skin wound with its injury source is done by various means (e.g., 1:1 transparent overlay, photographic comparison of wound and the object or its cast, ultraviolet light illumination [44-48]).

3.4.2.1. Human Bite Mark

A human bite can occur during a sexual assault, child abuse, certain types of sexual behavior, and self-defense. Some bite marks have more innocent explanations (e.g., self-inflicted, child biting child [12,49-56]). Human biting tears or crushes, resulting in contusions, abrasions, and lacerations in a circular or elliptical array (49,57). Often the bite mark is composed of two "U"-shaped marks, corresponding to the upper and lower teeth and separated by an open space (between 25 and 40 mm, or about 0.125 in.),

Fig. 18. Driver involved in near-side collision. (A) Multiple lacerations on left cheek. Reverse L-shaped laceration (arrow). Fragments of tempered glass embedded in wounds. (B) Characteristic rectangular fragments of broken tempered glass from a side window.
Fig. 19. Patterned abrasion on chest caused by steering wheel.
Fig. 20. Driver fatality. (A) Two parallel linear abrasions (arrows) on left cheek of driver. (Courtesy of Dr. C. McLean, London Health Sciences Centre, London, Ontario, Canada.) (B) Patterned injury caused by intrusion of A-pillar (A).
Fig. 21. Lower abdominal cutaneous injuries from lap belt ("seat-belt sign"). (A) Contusion. (B) Abrasion.

which can be contused from teeth pressure (49). Petechiae from sucking may be present (55). Usually, impressions are made by the anterior six teeth (canine to canine [49,55]). Studies of bite marks have shown that most victims of a criminal act are women (53,58). The breast is the most common location. Male victims are more frequently bitten on the arms (53,58). Male children can be bitten on their genitalia, and girls sustain bites to many locations. Multiple bite marks do occur (58).

If a bite mark is suspected, then consultation with a dentist specializing in forensic odontology is necessary (54,58,59). Examination of a bite mark is best done in situ (57). If a case involves an assault, then the bite mark is swabbed for saliva, for the purpose of DNA analysis (43,49,60). Tooth fragments or dental calculus can be found in

Fig. 22. "Secondary" impact by a pedestrian struck by a motor vehicle. (A) Impact with hood edge and front headlight. (B) Another case showing semicircular abrasion above right hip likely the result of headlight contact. (Courtesy of the Office of the Chief Medical Examiner, Chapel Hill, NC.)

Fig. 22. "Secondary" impact by a pedestrian struck by a motor vehicle. (A) Impact with hood edge and front headlight. (B) Another case showing semicircular abrasion above right hip likely the result of headlight contact. (Courtesy of the Office of the Chief Medical Examiner, Chapel Hill, NC.)

Fig. 23. Run-over. (A) Patterned abrasions on neck. (B) Weave pattern of sweatshirt.

the bite mark (54). Photographs (color, black and white) with a proper reference (American Board of Forensic Odontology) scale, and models of the suspect's dentition are required for comparison (49,61,62). The bite mark impression is a negative reproduction of teeth indentations, and is used to create a model (Fig. 24; refs. 59 and 62). A model of a suspect's dentition can be compared either directly with a photograph of a bite mark or indirectly by use of an overlay created by computer, photocopy, or hand-tracing (49,59,61,63-65). A bite mark is mimicked by other types of skin trauma (e.g., sharpforce trauma, cardiac defibrillation [49,57,66,67]). Although a bite mark is a patterned injury, it is not always unique to one individual (49,68).

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