Treating Gunshot Wounds In The Lower Extremity
Jacketing a missile is a process in which the manufacturer will cover the lead missile in copper. This allows for an increase in accuracy and velocity of the missile. Often, these rounds are referred to as a “full metal jacket.” Hollow-point rounds are manufactured with a hollow or depression at their tip. These rounds can be devastating to tissue because upon striking the target, the tip of the bullet expands. This allows the missile to lose less velocity traveling from the muzzle to the target while creating a greater surface area upon striking the target. This increase in surface area slows the missile down, making it less likely to exit the target and allowing for maximum energy transfer.
Shotgun missiles have unique characteristics. They fire a large single projectile known as a slug or a significantly large mass of pellets referred to as shot.12 At close range, the wadding from the shotgun acts as a single projectile.9,15 However, as the range increases, the wad expands and the velocity of the pellets decreases substantially. Even with this decrease in velocity, these pellets still may cause great damage to the target because they rarely exit the casualty. Slugs are more accurate and do not lose as much velocity at range. Their soft lead composition allows for easy deformation and it is not uncommon for them to break into large pieces within the body. This is known as a lead snowstorm.12
After leaving the barrel, the missile’s motion occurs in three dimensions. The yaw of a missile greatly affects the amount of damage it causes. (Yaw is the angle that the long axis of the missile deviates during travel.)3 When the yaw becomes so severe that the missile begins to move end over end, it is known as tumbling. When a bullet has severe yaw or starts to tumble, the profile of the missile increases, causing greater energy transfer to the casualty.7
A Closer Look At Tissue Damage In Gunshot Wounds
Due to substantial variables involved in missiles, the designation of a high-energy wound remains subjective and ultimately depends on the physical examination.9 If this designation depends on velocity alone, it only recognizes potential injury and not actual tissue damage.9,14 There is little ability to clinically estimate the amount of energy transferred.9,14
As missiles travel through a target, they produce two types of cavity. The permanent cavity results from direct crushing of tissue by the missile. The diameter of this cavity equates the diameter of the projectile. Tissue within the permanent cavity is destroyed and devitalized. Along with the permanent cavity, a temporary cavity occurs as well.3,7 The temporary cavity results from a momentary acceleration of the surrounding tissue in all directions away from the permanent cavity.7 The temporary cavity occurs by the permanent cavity pushing the surrounding tissue outward.13
Once the missile passes through the tissue, a vacuum forms behind it. The vacuum often pulls foreign debris such as dirt, clothing particles and bacteria into the wound.3 The size of the cavity depends on the missile’s kinetic energy that transfers to the tissue.9 Larger missiles that shatter, deform or tumble tend to have slower exit velocity, resulting in a larger cavity.16 The temporary cavity collapses due to the vacuum effect. Then it reforms and collapses repeatedly with decreased amplitude until all motion ceases. The cells within this temporary cavity are damaged due to the stretching and tearing of the surrounding tissue.
In uncomplicated, low-velocity gunshot wounds, the amount of tissue damage may only be a few cells deep outside of the permanent cavity.9 Lower kinetic energy wounds usually have similarly sized entry and exit wounds. On the other hand, in more complicated or high-velocity wounds, tissue damage can be extensive and the exit wound is typically larger than the corresponding entrance wound.