Emergency War Surgery NATO Handbook: Part I: Types of Wounds and Injuries: Chapter II: Missile-Caused Wounds

Discussion

United States Department of Defense

It becomes apparent from observing of data on the Wound Profiles that a projectile's striking velocity and mass determine only the potential for tissue disruption. For example, a shot through soft tissue of the average human thigh by a 7.62 NATO round loaded with the soft-point bullet (Figure 11) could result in an exit wound up to 13 cm in diameter with massive tissue loss. The same potential is available in the 7.62 NATO FMC military bullet (Figure 7), but the exit wound it causes in a comparable shot would most likely not exceed 2 cm in its largest dimension.

If one presented at the average large city hospital with a gunshot wound in the thigh (entrance and exit holes of less than l cm in diameter) and gave the history of being shot with a 22 Long Rifle bullet, the surgical treatment rendered would be minimal. The same would probably apply if the history were of a wound from a 38 Special or a 45 Automatic. If, however, the history was given that the wound had been made by an M-16, the victim would most likely be subjected to an excision of the entire bullet track and possibly even several cm of tissue on all sides of the track. Comparing the first 12 cm of penetration on the M-16 wound profile (Figure 12) with that of the other examples mentioned (Figures 4, 5, 6), shows that in such a wound the M-16 is unlikely to cause any more tissue disruption than the 22 Long Rifle. The reason for this is that the M-16 round does not fragment or yaw in the first 12 cm of soft tissue it traverses, nor does it develop its very significant temporary cavitation effects prior to 12 cm of penetration. The widespread belief that each and every wound caused by "high-velocity" projectiles must be treated by "radical debridement" is incorrect and results from failure to recognize the role of other variables, such as bullet mass and construction, in the projectile-tissue interaction.

Serious misunderstanding has been generated by looking upon "kinetic energy transfer" from projectile to tissue as a mechanism of injury. In spite of data to the contrary, many assume that the amount of "kinetic energy deposit" in the body by a projectile is directly proportional to the damage it does. Such thinking stops short of delving into the actual interaction of projectile and tissue that is the crux of wound ballistics. Wounds that result in a given amount of "kinetic energy deposit" may differ widely. The nondeforming rifle bullet of the AK-74 (Figure 9) causes a large temporary cavity which can cause marked disruption in some tissues (liver), but considerably lesser disruption in others (muscle, lung, bowel wall). The temporary cavitation produced by the M-16 (Figure 12), acting on tissue that has been perforated by bullet fragments, causes a much larger permanent cavity in tissues such as muscle and bowel wall and a similar disruption to that caused by the AK-74 in liver. A large slow projectile will crush a large amount of tissue (permanent cavity), whereas a small fast missile with the same kinetic energy will stretch more tissue (temporary cavity) but crush a proportionately smaller volume of tissue.

The "temporary cavity/energy deposit mystique" has spilled over into the field of weapons development and evaluation, where one large study rates handgun bullets based upon the unfounded assumption that the degree of incapacitation a bullet causes in the human target is directly proportional to the size of the temporary cavity produced by the bullet. Many soft tissues (muscle, skin. bowel wall, lung) are flexible and elastic, having the physical characteristics of a good energy absorber. The assumption that tissue must be damaged by the temporary displacement of cavitation makes no sense physically or biologically. Not surprisingly, law enforcement agencies are finding increasing numbers of cases in which handgun bullets chosen on the basis of such studies fail to perform as predicted.

In the missile-wounded combat casualty, determination of the missile's path through the body is a major concern. Since the majority of penetration projectiles follow a relatively straight course in tissue, an estimate of the missile's path can be made from the location of the entrance wound and the location of the exit wound or the position at which the expended projectile comes to rest within the body. In most cases, physical examination and biplanar X-rays establish these two points and allow clinical estimation of structures that might have been damaged. In some cases, oblique X-ray views will be needed and it may be impossible to determine with certainty whether penetration of a body cavity has occurred. When the question arises as to whether or not the peritoneal cavity has been perforated by abdominal wall wounds, experience has clearly demonstrated that it is better to look and see (by laparotomy) than to wait and see.

Bullet fragmentation and its correlative severe permanent tissue disruption (Figures 11, 12, 13) are especially useful roentgenographic signs. Rifle wounds of the chest wall in which a large disruption has occurred in the muscles of the shoulder girdle (M-16, AK-74, or AK-47 if it strikes bone) may be expected to have pulmonary contusion even without penetration of the pleural cavity. This may not be evident on X-rays taken shortly after wounding. The surgeon must be aware of this potentially life-threatening situation and assure adequate follow up observation and treatment. This is one of the more common situations in which occult damage from temporary cavity "blunt trauma" results in a clinical problem.

A point worth reiterating is that the surgeon is best advised to treat the wound and not the weapon!

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Operational Medicine 2001

Health Care in Military Settings

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