Introduction to Gunshot Injury Rehabilitation

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Definition of the Gunshot Injury

Gunshot injury is "the penetrating injury and its related consequences caused by a projectile from a firearm."

Epidemiology

Epidemiology of the gunshot injuries is difficult to assess and it varies based on the population, conflict setting, country, characteristics of the conflict, and time it occurred.

• In the USA in 2020 there were over 45 thousands deaths attributable to gun-related injuries, and every one person out of five individuals is going to present with a gunshot injury.
• 50.5% of deaths in Guatemala, Brazil, Colombia, Venezuela, Mexico and the USA is caused by firearm offences.
• Civilians and local combatants in armed conflict countries are affected by:
  • 22% gunshot wounds
  • 42.2% of injuries occurred in urban and 26.7% of injuries in semi-urban settings
  • 7.5% of injuries occurred in rural settings

• Gunshot wounds are the second most common mechanism of injury among US military personnel during armed conflict.

Firearms and Gunshot Injuries

Factors responsible for the wounding potential of a firearm include the following:

• The type of the firearm (muzzle velocity)
• The type of bullet
  • The larger the bullet, the slower its speed
• The distance to the target
• The size of pellets

Based on the muzzle velocity, the firearms can be divided into the low-velocity, medium-velocity , or high velocity firearms.

Low-Velocity Firearms

• Muzzle velocity less than 1200 feet
• Include small handguns and pistols
• Cause Gustilo-Anderson type I and type II injuries
  • Type I
    • Low energy
    • Wound size less than one centimetre
    • Minimal soft tissue damage and fracture comminution
    • Wound is clean
    • No neuromuscular injury
  • Type II
    • Moderate energy
    • Wound size between 1 and 10 centimetre
    • Moderate soft tissue damage and fracture comminution
    • Moderate wound contamination
    • No neuromuscular injury

Firearm example: shotgun is technically defined as low velocity, yet this device inflicts devastating wounds when fired at close range due to high-energy transfer.

Medium-Velocity Firearms

• Muzzle velocity between 1200-2000 feet per second
• High-calibre handguns and also shotguns
• Wound severity depends on the type of firearms used
• Shotgun causes more severe wound, regardless of the distance due to hundreds of small fragments inside the body.

Firearm example: shotguns and magnum handguns.

High-Velocity Firearms

• Muzzle velocity greater than 2000 feet per second
• Associated with more substantial tissue damage
• Cause Gustilo-Anderson type III wounds
  • Type III (A,B, or C)
    • High energy
    • Wound size usually greater than 10 centimetre
    • Extensive soft tissue damage
    • Severe fracture comminution
    • Extensive wound contamination
    • Periosteal stripping present
    • May require flap coverage (IIIB and IIIC)
    • Exposed fracture with arterial damage that requires repair may be present (IIIC)

Firearm example: rifles.

Mechanism of Gunshot Injury

1. The projectile hits the body
   • Transfers its kinetic energy and heat to the tissues on its way.
   • Creates a permanent cavity approximately at the size of the projectile's cross-sectional area.
   • Creates vortex effect: the spiral-shaped pattern of "dark residue surrounding a central bullet defect" also known as a comet-tailing.
   • Vortex effect causes stretching of the tissue based on the projectile's size creating a temporary cavity. This cavity occurs momentarily and contracts back.
2. The projectile exits the body by creating a bigger exit point or remains in the body.
3. The projectile can change direction and create further damage.

Physical impairments and Complications

"Gunshot injuries commonly result in diffuse soft-tissue damage, volumetric muscle loss, hemorrhage, fracture, and severe pain"

"The main mechanisms underlying penetrating ballistic tissue wounds associated with bullets include: (1) permanent cavitation, whereby tissue is destroyed by projectile compression and shearing that leaves a projectile trail; and (2) temporary cavitation, caused by tissue distention due to high-energy pressure vibrations from the projectile’s trail . Other issues, such as localised frictional heat stress, may exacerbate these primary insults. The extent of the firearm wound (i.e., depth and area damaged) is highly dependent upon projectile-tissue characteristics, whereby both the projectile (e.g., velocity, mass, shape, calibre, material, yawing and impact distance) and tissue impacted (e.g., density, elasticity, and thickness) interact to define the full extent and nature of injury. In general, skeletal muscle is suggested to be more sensitive to permanent cavitation, with temporary cavitation thought to induce less damage (unless the vasculature is disrupted) due to skeletal muscle’s inherent elasticity"

In regards to skeletal muscle impacted by a projectile or blast injury, damage is inflicted via various routes with laceration, contusion/crush injury, denervation (i.e., neural deficits), haemorrhage/ischaemia (i.e., vascular impediments) burns, and VML in particular of concern (Fig. ​(Fig.1).1). Both primary firearm or blast wounds can be aggravated by secondary trauma that further complicates severity of the injury, including development of infection/sepsis (caused in some cases by contamination with bullet/shotgun wadding, or other debris collected from clothing or skin), surgical debridement of damaged tissue (optimally performed within 6–8 h of trauma), and/or excessive physical movement.

Immobilisation, systemic inflammation, hyperglycaemia/insulin resistance, and nutrient deficiency are common side effects induced by ballistic trauma7, which are well-established mediators of muscle wasting in both the acute and chronic setting

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