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
   • Creates a bigger exit point, or
   • Remains in the body
3. The projectile can change direction
   • Creates further damage

Physical Impairments and Complications

Impacts of the Gunshot Injuries

Gunshot wounds can result in a spectrum of injuries that include the following:

• Diffuse soft-tissue damage
• Muscle damage
• Nerve injury
• Vascular injury/Hemorrhage
• Bone injury
• Severe pain

Diffuse soft-tissue damage

Soft tissue damage is the result of the primary cavity or temporary cavitation. Tissues in the primary cavity are directly injured by the contact of the projectile and extreme kinetic energy transfer. Tissue in the temporary cavity "is destroyed by projectile compression and shearing that leaves a projectile trail."

The type of tissue damage include partial or complete damage like ruptures, lacerations, internal burns and scarring in the later stages. The following factors will determine the extend of the wound depth and damaged area:

• Projectile impact: velocity, mass, shape, calibre, material, yawing and impact distance:
  • Mass/shape: as the projectile diameter or length becomes bigger they are likely to cause more damage
  • Velocity: as the velocity increases, the amount of kinetic energy dramatically increases, causing more harm.
  • Impact distance: as the projectiles have longer distances, they lose more of its kinetic energy, can create lesser harm, where even smaller projectiles from close distances can cause excessive damage.
  • Yaw is "the angle between the long axis of the bullet and its direction of flight." As the distance increases, the projectile loses its stability and starts to yaw off. It can also increase the cross-sectional area and create more damage.
• Tissue impact: density, elasticity, and thickness. High elasticity and low density equal less damage.
  • Skin have a large amount of elasticity and relatively low density
  • Lungs have a much lower density and absorb less energy
  • Bones are dense and absorb more energy
• The entry and exit points and trajectory within the body
  • If close to the nervous plexus, it can create more severe damage
  • If close to main arteries or veins, it can produce more complicated clinical presentations
• Projectile fragmentation
  • More fragments results in more than one trajectory within the body and that means more severe internal issues to manage in the following days and months

Muscle Damage

"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."

Skeletal muscles can be affected by laceration, contusion or crush injury, denervation, haemorrhage or ischaemia, burns, and volumetric muscle loss. The primary trauma can be complicated by secondary trauma that can include the following:

• Infection and sepsis as a result of contamination with bullet or debris accumulated on clothing or skin
• Surgical debridement of damaged tissue
• Excessive physical movement

Immobilisation and nutrient deficiency are considered common side effects leading to volumetric muscle loss.

Nerve Injury

The following are the mechanisms of gunshot-related peripheral nerve injury:

• direct transection of the nerve
• indirect injury by producing thermal damage, shock waves, laceration secondary to fracture fragment displacement
• compression due to swelling or subacute scar formation

The most frequently affected nerves in the upper extremities are ulnar nerve and brachial plexus.

As a result of soft tissue cavitation, the gunshot-related injuries can induce axonotmesis and neuropraxia.Axonotmesis "describes the range of peripheral nerve injuries that are more severe than a minor insult, such as those resulting in neurapraxia, yet less severe than the transection of the nerve, as observed in neurotmesis." Neuropraxia is the "focal segmental demyelination at the site of injury without disruption of axon continuity and its surrounding connective tissues."

Haemorrhage

Vascular injury can lead to the blood loss defined as a haemorrhage. Haemorrhage can be internal or external. The most common sign of vascular injury is hematoma. In addition, hemorrhagic area can be found surrounding irreversible damaged tissue following gunshot injury. This extra vacation zone "is characterized by interstitial bleeding but absence of macroscopically evident tissue destruction."

Bone Injury

• Drill-hole
  • Low-energy ballistic penetration
  • Affect metaphyseal region of long bones
  • Limited extension of fracture lines
• Comminuted fractures
  • High-energy ballistic penetration
  • Secondary effect of cavitation associated with the fluid properties of bone marrow

Pain

• Peripheral nerve injury can cause neuropathic pain
  • caused by axonal or neuronal dysfunction that disrupts the myelin sheath in both the central and peripheral nervous systems,24 in which inflammatory and immunological mechanisms play a key role25 from ectopic generation of nerve impulses for small-gauge type C and Aδ fibers. In addition to the thermal injury and cavitations caused by the passage of the projectile, pain can also result from the compression of the neural elements by fibrosis, which responds well to excision of the tissue.

"chronic pain was observed in 538 of 769 patients (70% 95% CI 66.7%-73.1%). Those patients who were wounded in 3 or more anatomical parts of the body had a higher percentage of chronic pain—71.2% (95% CI 63.4%-78.5%) than in patients with gunshot wounds in 1 or 2 anatomical parts of the body, here the frequency of chronic pain was 69.7% (95% CI 66.0%-78.5%). That is, the probability of chronic pain increases in patients who received gunshot wounds in a larger number of anatomical parts of the body." the presence of a neuropathic component of pain in such patients, suggesting that the likelihood of receiving a negative result of pain treatment in patients with gunshot wounds is associated with the presence of a neuropathic component of pain.

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