Introduction to Gunshot Injury Rehabilitation

Original Editor - Zafer Altunbezel

Top Contributors - Ewa Jaraczewska and Jess Bell  

Introduction

Gunshot injuries are one of the most common injury patterns in conflict settings, with civilians becoming more vulnerable in 21st-century armed conflicts. Gunshot injuries are high-energy injuries which can cause significant tissue damage, paralysis or death. The extent of the injury depends on a number of factors. Rehabilitation professionals should have an understanding of the potential consequences and appropriate management strategies throughout each phase of rehabilitation to enhance patient outcomes.

Definition of Gunshot Injury

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

Epidemiology

The epidemiology of gunshot injuries is difficult to assess, and it varies based on the population, conflict set, country, characteristics of the conflict, and time it occurred:

• Wild et al. aimed to describe "conflict-related injuries sustained by civilians and local combatants in twenty-first century conflict". They found that:
  • gunshot injuries caused 22% of injuries in civilians and local combatants
  • gunshot injuries are the second most common mechanism of injury among US military personnel during armed conflict, causing 19.9% of injuries
• Wild et al. also found that urban and semi-urban settings have higher rates of gunshot injuries
  • gunshot injuries accounted for 42.2% of injuries in urban settings
  • gunshot injuries accounted for 26.7% of injuries in semi-urban settings
  • gunshot injuries accounted for 7.5% of injuries in rural settings

• in the USA in 2020, over 45,000 deaths were attributed to gun-related injuries (i.e. 13.6 per 100,000 people)

Types of Firearms and Severity of Gunshot Injury

The wounding potential of a firearm depends on various factors, including:

• the type of the firearm (muzzle velocity)
• the type of bullet
• the distance to the target
• the size of the pellets

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

Classification

Gunshot injuries can be classified based on the type of firearm and the Gustilo-Anderson open fracture classification. You can find out more about this classification system here: Gustilo Classification.

Low-Velocity Firearms

Low-velocity firearms, including small handguns and pistols, have a muzzle velocity of less than 1200 feet. They tend to cause injuries that are similar to Gustilo-Anderson Type I and Type II injuries.

• Type I
  • low energy
  • wound size is less than one centimetre
  • minimal soft tissue damage and fracture comminution
  • wound is clean
  • no neuromuscular injury
• Type II
  • moderate energy
  • wound size is between 1 and 10 centimetres
  • moderate soft tissue damage and fracture comminution
  • moderate wound contamination
  • no neuromuscular injury

Medium-Velocity Firearms

Medium-velocity firearms, including high-calibre handguns and shotguns, have a muzzle velocity between 1200-2000 feet per second. However, wound severity depends on various factors, including the distance and projectile.

Example: shotguns are medium-velocity firearms, but because of the "large total mass of their lead pellets can increase their kinetic energy dramatically. [...] Depending on the distance to the target and the size of pellets, shotguns can reflect the wounding potential of high-velocity firearms or multiple low-velocity weapons. [...] Very close proximity of shotgun to the target (< 2 m) results in not only the pellet projection, but also shell fragments and wadding."

High-Velocity Firearms

High-velocity firearms, including military and hunting rifles, have a muzzle velocity greater than 2000 feet per second, and they are associated with more substantial tissue damage. They tend to cause Gustilo-Anderson Type III wounds.

• Type III (A, B, or C)
  • high energy
  • wound size is usually greater than 10 centimetres
  • extensive soft tissue damage
  • severe fracture comminution
  • extensive wound contamination
  • periosteal stripping present
  • may require flap coverage (III B and III C)
  • exposed fracture with arterial damage that requires repair may be present (III C)

Figure 1. Mechanism of gunshot injury.

Mechanism of Gunshot Injuries

• The projectile hits the body and transfers its kinetic energy and heat to the tissues
• This creates a permanent cavity approximately the size of the projectile's cross-sectional area
• The momentarily extreme pressure around the projectile's trajectory can create a vortex effect
• This vortex effect causes the tissue around the projectile's trajectory to momentarily stretch out, forming a temporary cavity, before contracting back
• The projectile may exit the body, usually creating a bigger exit point, remain in the body or change direction
• Sometimes the projectile fragments or explodes inside the body, causing further damage

Effects of Gunshot Injuries

"While the tissues in the primary cavity sustain direct injury due to energy transfer, surrounding tissues within the temporary cavity sustain secondary injuries due to burns and extreme stretching."

Figure 2. Cross-section of a gunshot injury.

Gunshot wounds can have a range of effects, including diffuse soft tissue damage, muscle damage, nerve injury, vascular injury / haemorrhage, bone injury and severe pain. These injuries are discussed in more detail below.

Soft-tissue Injury

The permanent cavity or temporary cavitation causes soft tissue damage:

• tissues in the primary (permanent) cavity are injured by the projectile and extreme kinetic energy transfer
• tissues in the temporary cavity are "destroyed by projectile compression and shearing that leaves a projectile trail"

There may be partial or complete damage to the soft tissues, including ruptures, lacerations, internal burns and scarring in the later stages.

Muscle Injury

"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, ischaemia, burns, and volumetric muscle loss. Primary trauma can be complicated by secondary trauma, including:

• infection and sepsis as a result of contamination from the bullet or debris accumulated on clothing or the skin
• surgical debridement of damaged tissue
• excessive physical movement

Immobilisation and nutrient deficiency can lead to volumetric muscle loss after a gunshot injury.

Nerve Injury

Gunshot injuries can cause:

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

Therefore, gunshot-related injuries can cause axonotmesis, neuropraxia and neurotmesis. 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." Neurotmesis is a "complete transection of a peripheral nerve."

The most frequently affected nerves in the upper extremities are the ulnar nerve and the brachial plexus. Sheilds et al. also note that, in gunshot injuries, "vascular injury and fractures increase the risk of nerve injury".

Vascular Injury / Haemorrhage

Blood vessels can be directly injured or affected by secondary circulatory compromise. Vascular injury can lead to blood loss or haemorrhage (internal or external). A haemorrhagic area can form around irreversibly damaged tissue following gunshot injury. This extra vacation zone "is characterized by interstitial bleeding but the absence of macroscopically evident tissue destruction."

Figure 3. Highly comminuted fracture-gunshot injury. Image courtesy of Dr. Matt Skalski, Radiopaedia.org; rID:46134

Bone Injury

Gunshot injuries usually result in comminuted, displaced fractures:

• caused by high-energy ballistic penetration
• a secondary effect of cavitation associated with the fluid properties of bone marrow
• associated with a high incidence of secondary complications, including infection and nonunion
  • the rate of infection is higher in patients with a skin flap
  • the rate of nonunion is higher in patients who have vascular injuries

A drill-hole effect is often caused by low-energy injuries to porous, low-density / cancellous bone:

• more common in the pelvis, distal femur, proximal humerus and spine
• low-energy ballistic penetration
• affects the metaphyseal region of long bones

Unicortical fractures:

• can be due to "low-energy missile impact that creates only a tangential bone defect"

Transverse or spiral fractures:

• can be caused by lower-energy gunshots to dense and highly-mineralised diaphyseal cortical bone

Gunshot injuries can result in secondary injuries (e.g. a fall), which can also result in fracture.

Pain

• Patients with gunshot wounds in a combat setting have a high risk of chronic pain, "45% higher than the general population in civilian trauma patients"
• 70% of individuals with gunshot injuries develop chronic pain
• Kuchyn and Horoshko found that individuals who were injured by gunshots in three or more areas had a higher percentage of chronic pain than those with injuries to one or two areas
• Complex regional pain syndrome (CRPS) can occur after traumatic events, including gunshot injuries

Determinants of Injury Severity

• Projectile: velocity, mass, shape, calibre, material, yawing and impact distance:
  • mass / shape: as projectile diameter / length increase, more damage is likely
  • velocity: as the velocity increases, the amount of kinetic energy dramatically increases, causing more harm
  • impact distance: as projectiles travel longer distances, they lose more of their kinetic energy and cause less harm, whereas even smaller projectiles from close distances can cause extensive 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. While this decreases the amount of kinetic energy transfer, it can increase the cross-sectional area, causing more damage
• Type of tissue: density, elasticity, and thickness
  • high elasticity and low density equal less damage
  • skin has a high degree 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 they are close to the nervous plexus, more severe damage can occur
  • if they are close to main arteries or veins, the clinical presentation can be more complicated
• Projectile fragmentation
  • more fragments = more than one trajectory within the body, which results in more severe internal issues to manage in the following days and months

Potential Challenges and Secondary Complications of Gunshot Injuries

The management of the secondary complications related to the gunshot injury is complex. Early intervention and in-depth knowledge are required to maximise rehabilitation outcomes.

Some secondary complications of gunshot injuries are listed below:

• joint contractures can develop as a result of periods of immobilisation after comminuted and complex open fractures that require external / internal fixation
• myofascial, chronic, or neuropathic pain can develop due to internal scarring, internal burns, wound or bone infection
• peripheral nerve injuries that are initially undetected due to heterogeneity and the conditions on the field may require referral to a specialist
• deep vein thrombosis or different types of embolism
• complex regional pain syndrome (causalgia) known as military pain syndrome - "tends to affect combat soldiers after they sustain wartime injuries from blasts and gunshots"
• central sensitisation
• mental health issues, including post-traumatic stress disorder, anxiety or depression, which tend to worsen over time with long-term declines in mental health status

Skills and Knowledge Required to Treat Gunshot Injuries

It is recommended that rehabilitation professionals treating gunshot injuries have a solid understanding of the following topics:

• neuroanatomy
  • to perform a neurological examination
  • to plan treatment
  • to recognise signs and symptoms that warrant referral to speciality services
• pain neuroscience
  • to provide pain education to help manage chronic / persistent pain
• clinical reasoning
  • to manage complex cases
  • to participate in / lead a multidisciplinary team
• manual skills
  • to help manage joint contractures, internal scarring, and neurogenic compromise

Resources

• Gun Shot Wounds