Forensic medicine: Gun Shot Wounds

Depending on where you are working, gun shot wounds (GSWs) may be a rarity or so common that almost everyday you will see a patient with a GSW in the emergency room. GSWs generally have a bad prognosis with a high incidence of gangrene and anaerobic infection. On top of that there is likely to be a criminal investigation regarding the shooting, so knowledge of how to describe a lesion and preserve evidence is incredibly important. 

When talking about GSWs you first need to consider the construction of the bullet and the mechanics of gunfire. Projectiles are most often made of lead and may be jacketed or not, the jacket is often made of an alloy like brass (copper and zinc alloy). Here in Italy, unjacketed projectiles are illegal.

The bullet contains the projectile, jacket and a small amount of gunpowder which produces the explosion behind which propels the projectile.  The gunpowder usually contains the following chemicals; Barium, Antimony and Lead. These chemicals are what forensics pathologists look for when they look for evidence, they can sometimes even type the gun with knowledge of the chemical ratio.

On pressing the trigger there is a small explosion and most of the gunpowder is burnt to produce gas, however some powder will not burn and be fired along with the projectile.

So when the bullet exits the muzzle of the gun, gas and small fragments of unburnt powder also exits the gun like a kind of small pepper spray, there is also residue and grease from the barrel that is fired along with everything else.

A shotgun bullet is slightly different in that the projectile is actually a collection on small pellets (the shot) as the pellets leave the barrel of the gun they spread out so a GSW from a close range shotgun shot (it forms a large hole) is different to a long range shotgun shot (many small holes).

Bullets may penetrate the body and may exit or stop within the body. They can ricochet off bone and some are actually made to bounce more in the body cavities (nasty). The bullet entry hole is usually much bigger than the actual bullet because as the bullet travels through the air it spins and oscillates (again some are designed to do this more, for more damage). It can sometimes be very difficult to tell the difference between the entrance and exit wound because of this. Bullets may even break and leave multiple exit wounds from a single a entry point or multiple entries. Usually an entrance wound is a round discontinuation with no loss of tissue. The residues from the gun will be on the skin surface around the entrance wound. Its important to use tape or a stub to collect the residue from the skin surface. In fact you should keep anything used to clean the wound and the victims clothes as well as they will contain very important residue.

There are four things you can see with a GSW and it depends on the distance of the victim from the gun.

•        Entry/exit wound

•        Tattooing

•        Smoke stains

•        Burns.

At long distance there will be only the entry and exit wounds from the bullet. As the victim is closer to the attacker tattooing can be seen caused by small pieces of unburnt gunpowder that produce small black spots (penetrating skin) or red spots (excoriations).

At even closer range the smoke from the gun can produce smoke stains on the skin, colouring the skin around the entry wound black. At even closer range than this the flame from the gunshot can burn the skin.

All these residues are collected and mapped and compared often with shooting experiments to determine firing range and gun type (each gun has its own distinct pattern of residue spread).

If the gun is fired at point blank on contact with the skin, a so called contact wound is produced. This is often stellate in shape, the flaps are caused by the pressure of air as it escapes around the gun, it can look like a blunt force injury so be careful in your description.

If the bullet penetrates a flat bone it can be easy to spot the entry and exit side from bevelling of the bone edge (the bone will be bevelled on the exit side of the bone and diameter of the hole as the entry side has a smaller diameter to the exit side. Exit wounds can be very messy and may sometimes look like a blunt force injury, sometimes if the victim is against a surface where the bullet exits eg. A wall, material from the wall behind can be found in the wound. 

In terms of treatment, GSWs must be treated with thorough debridement and delayed primary suture in the same way as battle injuries (future post). It must never be closed straight away! The debridement should be extra thorough taking extra care to remove fragments of clothing and soil from the wound. 

Clinically you can divide GSWs into low velocity and high velocity injuries. Low velocity injuries can cause little soft tissue damage as long as they remain stable (remember that oscillation and cartwheeling of the bullet will cause more damage). High velocity injuries act like a small explosion and many tissue planes are separated providing easy access for infections. There is often foreign material in the wound further enhancing chance of infection.