Pathology of Firearm Injuries Study Notes

Dr. Ajith Tennakoon - Former Chief Consultant JMO and Head of the Institute of Forensic Medicine and Toxicology, Colombo.

Dependent Factors:
- The transfer of kinetic energy from the projectile (missile) to the tissue of the host organ.
- Kinetic energy is quantified using the formula: $E = \frac{1}{2} mv^2$ where:
- $E$ = energy
- $m$ = mass of the projectile
- $v$ = velocity of the projectile.
Effects of Velocity:
- Velocity alone primarily causes lacerations and crushing of tissues.
Tissue Disruption:
- Shockwave compression effects disrupt tissues ahead of the projectile path.
- Mechanical acceleration of molecules adjacent to the bullet track creates a temporary cavity in the tissues.
- Movement of the missile creates a vacuum effect and suction, often pulling dirt and clothing into the wound.
- Secondary injuries can arise from bone fragments and damaged blood vessels resulting from the initial injury.

Characteristics:
- Comprise one or more metal barrels with a wider diameter.
- The inner surface of the barrel is smooth, lacking grooves.
- Typically fire multiple pellets, which can vary in number.
- The barrel design can be parallel or choke toward the end to enhance shot tightness.

Components:
- Cartridge: Constructed from cardboard or plastic and fitted into a metal base.
- Contains a percussion detonator within the metal base, explosive propellant, a wad, pellets, and is covered by a cardboard or plastic disc.

Contributors to Wound Appearance:
- Flame and hot gases: Causes burning near the wound.
- Soot and smoke: Results in blackening of the wound.
- Unburnt and burning propellant particles: Leads to tattooing effects on the skin.
- Carbon monoxide: Produces characteristic cheery pink discoloration in the tissue.
- Wad: Can create a separate wound channel.
- Lead pellets as projectiles: Cause physical damage.
- Detonator constituents: May require chemical analysis for identification.
- Fragments of cartridge cases: Can be found within the wound.

Contact Wounds:
- Characteristics include a circular shape matching the barrel size on soft tissues and stellate or ragged edges over bone.
- Edges may be crenated or inverted.
- Soiling and burning may be minimal or absent on the outside, but can be observed on the inside in cases of tight contact.
- Loose contact results in visible burning and blackening.
Close Contact Wounds:
- Signs include:
- Singed hair and burning of surrounding skin.
- Tattooing and cherry pink tissue coloration around the wound.
- Minimal blackening of the tissue.
- Abrasion-like patterns and presence of wad within the wound.
Intermediate (Short to Mid Range) Wounds:
- Typically lack blackening or burning.
- Tattooing may be observed.
- Wounds may show a "rat hole" appearance leading to a "satellite pallet" appearance.
Distant Range Wounds:
- Features include no central hole.
- Maximum spread of pellets occurs with no wad marks.
- Spread measurement correlates roughly to the range of fire in yards.

Characteristics:
- Wound characteristics can vary:
- Circular symmetrical shape at a right angle discharge.
- Elliptical appearance depending on the angle of discharge.
- Wound track indicates the projectile's path.

Shotgun Exit Wounds:
- Exit wounds are less common and usually represent a low velocity impact from pellets.
- Wound appearance varies based on anatomical location.
- Commonly lead to irregular lacerations or diffused internal tracks without cavitation effects.
- Secondary injuries can occur from bone fragments.

Characteristics of Rifled Weapons:
- Designed to fire a single projectile at a time, either single-shot or automatic.
- Muzzle velocity can vary between 1500 to 5000 feet per second.
- Barrels are thicker and feature spiral grooves that impart a spin to the bullet.
Types of Rifled Firearms:
- Handguns: Pistols and Revolvers.
- Rifles.
- Air rifles.
- Military-grade weapons.

Composition:
- Metal cylinder with one closed end containing a percussion detonator.
- Filled with explosive propellant and firmly braced bullet at the open end.

Contact Wounds (Rifled Weapon)
- Smaller circular entry in firm contact with soft skin.
- Insufficient blackening and burning inside the wound.
- Cherry pink coloration indicating heat and gas exposure.
- Muzzle imprint creating distinctive patterns.
- Stellate or cruciate wound patterns over bony surfaces.
Close Range Wounds:
- Involve similar characteristics to shotgun exits, including circular shapes and inverted edges.
- Signs of burning and tattooing are prevalent.
- Abrasion or collar markings may accompany the wounds.
Intermediate Range Wounds:
- Features smaller entry wounds relative to the missile size.
- Includes signs of abrasion color and tattooing, along with dirt or grease rings.
Distant Range Characteristics:
- Small circular entry with potential for abrade color and grease rings.
- Unusual shapes may occur due to extreme trajectories.

Perforating Wounds: Bullet enters and exits the body.
Penetrating Wounds: Bullet enters but does not exit, remaining within the body.
Grazed Wounds: Entrance and exit are interconnected superficially without engaging subcutaneous tissues.
Tangential Wounds: Wound channel extends into subcutaneous tissue without opening the skin at entry and exit.

Examples:
- Grazed, tangential, and superficial perforating wounds.
- Secondary injuries resulting from bone fragments, ricochet bullets, or back spatters.
- Re-entry wounds involve a bullet piercing one body part before entering another body part.

Occurs when a bullet strikes the skull at an angle, splitting into fragments. Produces an entrance wound that is externally beveled. The round part of the defect with inward beveling indicates the weapon's placement during fire.

Changes to the exit wound that mimic entrance wounds can occur due to firm surfaces at the point of contact, which abrades the everted skin.

These comprehensive insights into the pathology of firearm injuries reveal the complexities involved in understanding ballistic trauma and require careful analysis in forensic contexts.