High-Velocity Bone Trauma

An excerpt from Forensic Anthropology: A Comprehensive Introduction

Edited by Natalie R. Langley & MarisaTeresa A. Tersigni-Tarrant

Bone is a viscoelastic material and behaves like a brittle or ductile material, depending on the rate, duration, and velocity of a given load or force. High-velocity loading causes bone to react as a brittle material: the bone does not undergo plastic deformation but instead fails almost instantaneously and shatters like glass. The undeformed bone fragments produced by the fractures can be reassembled easily, much like fitting the pieces of a puzzle together (Figure 1) (Berryman et al. 2012a).


Figure 1—High-velocity trauma. Cranial vault reconstructed with adhesive after a gunshot wound shattered the vault bones into many fragments. (Courtesy of Natalie Langley, Forensic Anthropology Center, University of Tennessee, Knoxville.)

In terms of extrinsic variables, the wounding capacity of a bullet is derived from the kinetic energy transferred to the body tissues (Berryman et al. 2012a). Kinetic energy is equal to (m * v2)/2, where m is the mass of the moving object and v is its velocity. Since velocity is squared, higher-velocity projectiles have the capacity to be exponentially more destructive than lower-velocity projectiles. If a bullet exits the body, some of the wounding power exits as well, and only a portion of its kinetic energy is transferred to the body tissues. Given this, bullet design plays a significant role in the “stopping power” and lethalness of projectile injuries (e.g., hollow point bullets designed to deform and remain in the body are more lethal than jacketed bullets that may exit).

Gunshot wounds in the cranium typically are easiest to interpret. The cranial vault is a relatively rigid and closed structure, owing to its primary role to protect the brain. Many handgun injuries have entrance and exit wounds with signature features that make them easily distinguishable from one another and permit the anthropologist to ascertain the bullet’s trajectory. In addition, increased intracranial pressure caused by the entrance wound creates more extensive fracturing around this injury. These fractures relieve a significant portion of the intracranial pressure, and the fracturing associated with the corresponding exit wound is usually less severe. A “textbook” cranial gunshot wound has internal beveling associated with the endocranial surface of the entrance defect and external beveling on the ectocranial surface of the exit defect (Figure 2). These trademarks are most obvious on the flat bones of the cranial vault because of the material properties of these bones: two layers of cortical bone (the endo- and ectocranial surfaces), with a layer of dense spongy bone (referred to as diploë) between them.


Figure 2—(a) Entrance wound with radiating fractures and (b) Associated exit wound with external beveling and radiating and concentric fractures. (Courtesy of Natalie Langley, Forensic Anthropology Center, University of Tennessee, Knoxville.)

 

Of course, there are exceptions to all rules, which is why it is imperative to interpret skeletal trauma in light of the interaction of intrinsic and extrinsic variables and with an understanding of what might happen if one variable presents in an atypical manner. For example, a bullet that strikes the cranial vault with a tangential trajectory creates a “keyhole” defect. Keyhole entrance wounds have external beveling on one edge of the defect and a well-defined circular outline on the other side (Figure 3) (Dixon 1982; Berryman and Symes 2002). However, the bullet trajectory is evident, even in these atypical wounds: the “entrance” is elucidated by the unbeveled edge, and the “exit” is marked by external beveling. Radiating fractures may also initiate from the initial bullet impact site and advance in the direction of the bullet’s path (Berryman et al. 2012). Keyhole defects also have been reported in association with exiting bullets (Dixon 1984). Another exception to the typical beveling pattern observed in cranial gunshot wounds is observable in the thin bones of the facial skeleton, with their numerous sinuses and lack of diploë. These bones do not exhibit beveling and may fracture extensively and be effectively shattered (Berryman et al. 2012a).


Figure 3—Keyhole defect. Keyhole defect on the frontal bone. The arrow indicates the approximate direction of the bullet’s path: posterior to anterior, as indicated by the external beveling on the anterior margin. (Courtesy of Natalie Langley, Forensic Anthropology Center, University of Tennessee, Knoxville.)

Fracture lines may also assist in distinguishing an entrance wound from an exit wound or elucidate the sequence of multiple injuries. As mentioned earlier, the extent of fracturing is more severe for entrance wounds. In addition, fracture lines do not cross existing fractures, so fractures from an exit wound terminate into fractures from the corresponding entrance wound, because the entrance fractures traverse the vault faster than the bullet travels through the skull. Likewise, fractures from subsequent injuries terminate into previous fractures. This concept was introduced in 1903 by a forensic pathologist named Puppe, who recognized that intersecting fractures can be used to determine the sequence of blunt trauma impacts in the skull. Madea and Staak (1988) generalized Puppe’s theory to gunshot trauma (Berryman et al. 2012a).

When examining skull fractures, it is also important to understand the sequence in which fractures are generated. Radiating fractures are the first fractures that form when a bullet enters the cranium. Multiple radiating fractures may extend from the gunshot wound in a stellate pattern. As the intracranial pressure increases, the cranial fragments between the radiating fractures are heaved outward, placing tensile strain on the inner table of the skull at a distance from the entrance site, which causes first-generation concentric fractures to propagate perpendicular to the radiating fractures. Second-generation concentric fractures may form, given sufficient energy and intracranial pressure (Figure 4).


Figure 4—Gunshot wound fractures. The cranial vault from Figure 1 is used to illustrate fracture generation from gunshot wounds. The red lines depict radiating fractures associated with the entrance wound. The blue lines show second- and third- generation concentric heaving fractures caused by the increased intracranial pressure from the entering projectile. The black lines indicate radiating fractures from the exit defect that terminate into fractures caused by the entrance. (Courtesy of Natalie Langley, Forensic Anthropology Center, University of Tennessee, Knoxville.)

 


Figure 5—(a) Defect on anterior bodies of the sixth and seventh thoracic vertebrae (note related fractures of transverse processes). (b) Gutter fracture, with arrow showing direction of the bullet’s path. (c) Exit defect on lamina of sixth thoracic vertebra (note radiating fractures and external beveling on the left margin of the defect). (d) Gunshot wound on the head of right seventh rib (direction of fire indicated by fragments displaced in direction of bullet’s path.)

Gunshot wounds in other areas of the body do not exhibit the same features as the cranial vault. The thoracic cage is composed of a more mobile set of skeletal elements connected by a variety of joints (intervertebral, sternocostal, and costovertebral joints), muscles (intercostal muscles and deep and superficial back muscles), and ligaments. Bullets may travel through intercostal spaces without wounding bones. Furthermore, intrathoracic pressure is not a significant factor in fracture production, and the lungs typically collapse once the pleural cavity is penetrated. The bones of the thoracic cage also have different material properties. The vertebrae and sternum are largely trabecular bones. Like the skull, the ribs are flat bones, but they are more elongated and tubular in shape. They also lack a layer of diploë between the dorsal and ventral layers of cortical bone and instead have a less dense layer of trabecular bone (Langley 2007). The rib cage is bordered posteriorly by the thin cortical bone of the scapular bodies and superiorly by the clavicles, and these bones may also be injured in gunshot wounds of the thorax. The unique intrinsic properties of the bony elements of the thoracic cage produce gunshot wounds with distinctive features.

It is not possible to determine the sequence of gunshot wounds in the thoracic cavity by examining the skeletal elements, but experts can deduce direction of fire. A case study on the exhumed remains of Dr. Carl Austin Weiss (accused assassin of Louisiana Governor Huey P. Long, who was shot at least 20 times in the chest) revealed several distinctive features associated with gunshot wounds in ribs that indicate direction of fire: radiating fractures, displaced bone fragments, depressed fractures, beveling, and overall fracture patterns (Ubelaker 1996) (Figure 6). Langley (2007) corroborated these observations in an analysis of 87 gunshot wounds to the chest. Depressed bone fragments around the entrance site and displaced bone splinters at the exit site occur frequently in the ribs and indicate direction of the bullet’s path through the rib (Langley 2007) (Figure 7). Owing to the more flexible nature of the chest cavity compared with the cranial cavity, significant intracavity pressure does not build up, and therefore, concentric heaving fractures are absent in gunshot wounds in ribs.


Figure 6—Gunshot wound in a rib. (a) Entrance defect on external surface, with radiating fractures. (b) Exit defect, with beveling on pleural surface of the same rib. (Courtesy of Natalie Langley.)


Figure 7—Displaced bone fragment. Bone fragment displaced in the direction of the bullet’s path through the rib (direction indicated with red arrow). (Courtesy of Natalie Langley.)

Gunshot wounds in long bones have received little attention in the research literature, but reports indicate that these injuries exhibit beveling, which can be used to interpret directionality. Impacts to bone shafts typically cause massive comminution. Because the fractures associated with the entrance defect travel around the bone shaft faster than the bullet, a distinct exit defect is absent (Langley 2007). Wounds on long bone epiphyses may exhibit more typical beveling, depressed fractures, or massive fragmentation, depending on the area struck and the velocity of the projectile. Angle of impact also affects the appearance of the beveling (Smith and Wheatley 1984), and keyhole fractures have been documented in long bone shafts (Berryman and Gunther 2000).

Handguns and rifle barrels have grooves that spiral the bullet, increasing the muzzle velocity and aiming precision. In contrast, shotguns are smooth bore weapons, and the barrel is not rifled. The ammunition differs greatly, as well, usually consisting of multiple pellets packed into a single shell. Of course, this classification system is simplistic, as some handguns can fire shotgun shells, and shotguns can fire single slugs. Nonetheless, conventional shotguns produce distinctive wounds, which can be distinguished readily from handgun injuries. The muzzle velocity of shotguns is comparable to handguns, but the pellets begin to disperse and decelerate quickly on exiting the barrel. The primary factor in the extent of injury produced by a shotgun blast is the distance from the muzzle to the target. At close ranges, the pellets enter the body as a conglomerate mass that imparts massive injury to surrounding tissues, causing extensive fracturing and fragmentation of osseous structures (especially the skull). At far distances, the shot disperses and enters the body at a considerably lower velocity, causing multiple separate injuries that are less destructive than handguns or rifles that fire solitary bullets (Berryman et al. 2012a) (Figure 8). At sufficient distances, shotgun pellets lack the energy to penetrate the body and may cause only minor injuries.


Figure 8—Shot dispersal pattern. At close distances, the shots are a conglomerate mass (far left). As distance between muzzle and target increases, the shots disperse (far right). (Courtesy of Natalie Langley.)

The Scientific Working Group for Anthropology (SWGANTH) trauma analysis document cautions against estimating caliper or gauge from wound dimensions. While it may be possible to discern large from small caliber cranial gunshot wounds, significant overlap in wound dimensions from various bullet calipers suggests that caliber estimation is not a sound practice (Ross 1996). Numerous confounding extrinsic variables can affect wound dimensions, including firing distance, angle of entry, body position at the time of impact, surface treatment and strength characteristics of the bullet, preexisting fractures, and intermediate targets that may deform the bullet (DiMaio 1993; Berryman et al. 1995). The SWGANTH also maintains that estimating muzzle to target distance is an unacceptable practice. In cases where gunshot injuries are suspected, but fracture patterns or injury features are not diagnostic, it is a good idea to X-ray the remains to check for radiodense particles (i.e., lead and other metals) that may have become embedded in the bone. Gunshot residues and primers may also be detectable on the bone (Berryman et al. 2010). In any event, the case report should avoid conjecture and state only what the bony evidence supports. Scaled photographs and diagrams with labeled fractures and defects are helpful. Descriptions of injury patterns and mechanisms are preferred to overly specific interpretations that may cause more harm than good in the outcome of a case.

References

Berryman HE, and Gunther WM. 2000. Keyhole defect production in tubular bone. J Forensic Sci 45(2):483–487.

Berryman HE, Kutyla AK, and Davis JR II. 2010. Detection of gunshot primer residue on bone in an experimental setting–An unexpected finding. J Forensic Sci 55:488–491.

Berryman HE, Shirley NR, and Lanfear AK. 2012a. High Velocity Trauma. In MT Tersigni-Tarrant, and NR Shirley (Eds.), Forensic Anthropology: An Introduction. Boca Raton, FL: CRC Press.

DiMaio VJ. 1993. Gunshot Wounds: Practical Aspects of Firearms, Ballistics, and Forensic Techniques, 2nd revised edn, New York: Elsevier Science Publishing Company.

Dixon DS. 1982. Keyhole lesions in gunshot wounds of the skull and direction of fire. J Forensic Sci 27:555–566.

Dixon DS. 1984. Exit keyhole lesion and direction of fire in a gunshot wound of the skull. J Forensic Sci 29:336–339.

Langley NR. 2007. An anthropological analysis of gunshot wounds to the chest. J Forensic Sci 52(3):532–537.

Madea B, and Staak M. 1988. Determination of sequence of gunshot wounds of the skull. J Forensic Sci Soc 28(5–6):321–328.

Ross AH. 1996. Caliber estimation from cranial entrance defect measurements. J Forensic Sci 41(4):629–633.

Smith HW, and Wheatley KK. 1984. Biomechanics of femur fractures secondary to gunshot wounds. J Trauma 24(11):970–977.

Ubelaker DH. 1996. The remains of Dr. Carl Austin Weiss: An anthropological analysis. J Forensic Sci 41(1):60–79.

 
< Prev   Next >






Item of Interest

The language barrier between English-speaking investigators and Spanish-speaking witnesses is a growing problem. (Updated 28 February 2011)

Read more...