Fig. 29.1
Gunshot wound to the skull. (a) Entrance wound on exterior of skull (b) exit wound on interior of skull with bevealing
Beveling can be found evenly distributed around the wound, indicating a more or less perpendicular entrance. In cases of tangential impacts, the amount of beveling may be asymmetrical with greater amount opposite the entrance of the bullet. Tangential bullets may also produce what are known as “keyhole defects” [2]. As the bullet enters the bone tangentially, chipping will occur on the entrance side and the stresses on the opposite side will cause fracture propagation in the outer table causing a large area of beveling. Internal beveling will also be present which can confirm the wound as entrance. Directionality of the bullet through the skull can also be determined based on the presence of this finding.
A bullet may pass through one portion of the body and reenter into another. The most common occurrence is when an arm is struck and the bullet perforates through and then enters the thorax [1]. This phenomenon can result in both an atypical entrance wound on the thorax as well as an atypical shoring exit wound on the arm if pressed against the body. The reentry wound is often oval or crescent in shape and may not have a ring of abrasion.
29.1.4 Distance
The range of fire, or muzzle to target distance, is often the next determination made in gun shot wound cases. Approximate distances can be established based on the presence or absence of debris from the muzzle. If close enough, this debris can be deposited into the skin and clothing of the victim. Typically four ranges have been delineated: contact, near contact, close and distant.
Contact shots will show the presence of gun shot residue (GSR) and soot on the margins of the wound. The hot gases expelled by the gun will burn the soot into the tissues and it cannot be washed away. This should not be confused with bullet wipe. Bullet wipe is the presence of debris that is transferred to the clothing or skin as the bullet passes through. This can happen in both close and distant range firings.
When the muzzle has been placed close to the skin but not in hard contact, loose or near contact wounds may be seen. Loose contact wounds are represented by a deposition of soot around the entrance wound, which can be wiped away. Near contact wounds have a larger ring of soot and with a larger inner ring of seared tissue, due to the dispersion of powder, that is not easily wiped away.
The presence of stippling or tattooing is an indication that the distance to muzzle was of close range. This distance is from 0.012 m (5 in) to approximately 0.457 m (18 in). Stippling is cause by the gunpowder particles striking the skin and causing punctate abrasions. Unlike the deposition of soot, stippling cannot be washed away. If the muzzle is fired at an angle to the skin, there will be a greater dispersion of stippling in the direction of the firing.
When the muzzle of the gun is greater than 0.457 m (18 in) away, stippling will not be present. However, the lack of stippling alone should not determine distance since clothing and intermediate objects may mask its presence. The size and shape of the entrance wound in distant shots will be more representative of the bullet.
29.1.5 Direct Versus Indirect Fractures
Skeletal injuries to long bones in the extremities can be caused by both direct impact and indirect impact [3]. Indirect fractures are the result of a projectile passing close to a bone but not directly striking it. They are characterized by a simpler fracture pattern and less medullary contamination when compared with direct fractures [4]. Approximately 10 % of all long bone fractures are indirect. Direct fractures occur when a bullet strikes bone with enough force to cause a fracture [5]. In contrast, these fractures are more complex and generally have more comminution.
Between 1968 and 1970, Huelke et al. authored three papers to describe the “bio-ballistics” of direct fractures of the femur. Using stainless steel spheres, the authors conducted direct impacts to both unembalmed and embalmed femoral specimens. One of the basic findings was that both the unembalmed and embalmed specimens responded the same in terms of energy loss versus impact velocity. The authors reported that given the same velocity, the diameter and not the mass of the sphere was the main factor determining damage. Cavitation and shock waves were discussed as the reason for this finding. Although, it was reported that cavitation did not appear until the velocity was 600 and 800 ft/s for spheres measuring .406 and .250 in. respectively [6].
More recent work has studied the pathophysiology of indirect fractures of long bones to isolate variables involved with the production of a fracture. By using both strain gage technology and high-speed video, the temporal relationship between the passage of a bullet and occurrence of long bone fracture has been determined [7]. Dougherty et al. (2011) further analyzed the parameters associated with the production of long bone fracture. Using cadaveric specimens, it was determined that indirect fractures were of a simple (oblique or spiral) pattern (Fig. 29.2). For those specimens with fractures, the average wound track to bone distance was 9.68 mm. In contrast, the non-fractured specimens demonstrated a significantly shorter wound track to bone distance of 15.15 mm (p = 0.036). In addition, there were no fractures reported when 9-mm bullets with an average velocity of 263 m/s (862 ft/s) were used or when the M995 bullet velocity was below 975 m/s (3,200 ft/s) [8].
Fig. 29.2
Spiral fracture caused by temporary cavity formation
29.2 Behind Armor Blunt Trauma
29.2.1 Body Armor: Torso
Of approximately 1,200 officers killed in the line of duty since 1980, it is estimated that more than 30 % could have been saved by body armor [9]. According to the James Guelff Body Armor Act, the risk of dying from gunfire is 14 times higher for an officer not wearing a vest [9]. In addition, the US Department of Justice estimates that 25 % of state, local, and tribal law enforcement officers are not issued body armor. Since establishing the IACP (International Association of Chiefs of Police)/DuPont™ Kevlar® Survivors’ Club® in 1987; over 3,000 law enforcement personnel have survived both ballistic and non-ballistic incidents because they were wearing body armor [10].
Body armor is comprised of fibers that have been woven together into sheets. Numerous sheets are used to make up one ballistic panel. The sheets work individually and together to help prevent the penetration of the bullet. Some materials that are used include: Kevlar®, Spectra® Fiber, Aramid Fiber, and Dyneema. The material fibers work to absorb and spread the energy over the entire torso so all of the energy from the impact is not focused on one area of the body, resulting in serious injury.
The current standard for certifying the protective ability of the thoracic armor (NIJ Standard-0101.06) was released in 2008 by the National Institute of Justice. This Ballistic Resistance of Body Armor standard has been revised several times since the original version was released in 1972. Part of the standard since its inception is the measurement of the deformation behind a backing material, also known as Backface Signature (BFS). This testing method provides a discrete value by which the failure of the vest can be determined. A failure is indicated by a deformation of the backing material greater than 44 mm or a penetration of the vest. A penetration of the vest can be due to the projectile itself, a fragment of the projectile or a fragment from the vest.
There are five types of armor that are covered in the current standard (IIA, II, IIIA, III, IV). Each type has a specified threat level that must be used during the certification testing (Table 29.1). Shot patterns on the vest are also specified.
Table 29.1
NIJ P-BFS performance test summary
Armor type | Test round | Test bullet | Bullet mass | Conditioned armor test velocity | New armor test velocity |
|---|---|---|---|---|---|
IIA | 1 | 9 mm FMJ RN | 8.0 g (124 gr) | 355 m/s (1,165 ft/s) | 373 m/s (1,225 ft/s) |
2 | .40 S&W FMJ | 11.7 g (180 gr) | 325 m/s (1,065 ft/s) | 352 m/s (1,155 ft/s) | |
II | 1 | 9 mm FMJ RN | 8.0 g (124 gr) | 379 m/s (1,245 ft/s) | 398 m/s (1,305 ft/s) |
2 | .357 Magnum JSP | 10.2 g (158 gr) | 408 m/s (1,340 ft/s) | 436 m/s (1,430 ft/s) | |
IIIA | 1 | .357 SIG FMJ FN | 8.1 g (125 gr) | 430 m/s (1,410 ft/s) | 448 m/s (1,470 ft/s) |
2 | .44 Magnum SJHP | 15.6 g (240 gr) | 408 m/s (1,340 ft/s) | 436 m/s (1,430 ft/s) | |
III | 1 | 7.62 mm NATO FMJ | 9.6 g (147 gr) | 847 m/s (2,780 ft/s) | – |
IV | 1 | .30 Caliber M2 AP | 10.8 g (166 gr) | 878 m/s (2,880 ft/s) | – |
Special | – | Each test threat to be specified by armor manufacturer or procuring organization | |||
The current 0101.06 standard also includes a ballistic limit determination test. This test involves altering the velocity of the ammunition in order to determine a velocity at which there is a 50 % chance of penetration. The number of minimum shots required depends on the level of armor being tested. Type II through Type IIIA requires a minimum of 12 shots, while there are a minimum of 6 shots required for Types III and IV.
Although often criticized, the BFS test is based on research performed within the military in the 1970s [11–14]. This research involved a biomedical assessment of injuries resulting from specified ammunition striking a selected armor or a blunt impactor striking the body directly designed to mimic the bullet/armor/body interaction. Key areas of the torso were targeted including the lung and heart. The surrogate often used was an Angora goat, however some studies cite the use of a porcine or canine surrogate. Lung and heart injury as well as non-lethality were key parameters studied.
An extension of this research involved parametric modeling of blunt trauma lethality [11, 14]. Input parameters from the projectile such as mass, velocity, diameter and those of the armor; mass per unit area, were combined with the characteristics (mass and body wall thickness) of the subject being impacted. These input parameters were used then used to predict a level of lethality for the impact.
Newer models to predict the risk of injury as a result of BABT have been developed including biomechanical [15] and finite element models [16, 17]. These models have been developed to address the current limitations of the clay standard, however none have been incorporated into the current standard.
29.2.2 Case Studies: Torso
In an effort to determine the types of BABT injuries being sustained by law enforcement agents, a subset of data was collected from the IACP/DuPont™ Kevlar® Survivors’ Club® database. This database is maintained by IACP and represents those officers who have survived due to the fact they were wearing body armor. It includes not only the ballistic cases but also stab/slash and blunt force trauma. Survivors are asked to complete a questionnaire about their incident and the resulting injuries.
As part of a recent ongoing study, cases involving ballistic impacts to the torso were studied. Additional information was collected specific to their injuries including the medical record. Of the 77 cases collected, 71 had adequate data available. Data for each case were obtained through phone interviews, medical records, and police reports. Injured officers were between the ages of 22 and 54, with the average being 34 ± 8 years of age. From the 71 cases that were collected for this study, there were a total of 90 shots stopped by personal body armor. The majority of the shots impacted the anterior chest (74 %, n = 65), followed by abdomen (16 %, n = 12), posterior upper torso (9 %, n = 8), and posterior lower torso (6 %, n = 5).
The level of protection offered by a ballistic vest is an important element of officer safety. The NIJ body armor performance standard has been revised several times since its inception to reflect the growing threats faced by officers. As previously discussed, vests are certified using a combination of weapons and rounds that are commonly used by law enforcement and criminals. The most current standard classifies armor into five types: IIA, II, IIIA, III, and IV. The first three levels are soft armor that protect against various handgun and shotgun ammunitions, while the last two levels are hard plates used in conjunction with soft armor to protect against rifle and armor piercing rounds. The majority of officers in this study wore either a threat level IIA or II vest (Fig. 29.3). From all of the cases, 25 % of the officers had additional protection from a trauma plate or pack.
Fig. 29.3
Percentage of body armor threat level based on case studies
The injuries that occurred from the 90 shots stopped by the armor have been classified as blunt trauma and backface signature injuries (Table 29.2). The majority of the injuries resulting from impacts to the vest were categorized as blunt trauma injuries (60 %, n = 54). These include less severe injuries involving contusions, abrasions, and rib fractures. Backface signature (BFS) injuries were the next most common injury among the sample population (21 %, n = 19). BFS injuries occur when there is a penetrating injury to the chest even though the bullet is captured within the armor [18]. These injuries have become more prevalent in recent years due to the desired increased in flexibility of the armor systems.
Table 29.2
Summary of case study data
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