Given that gunshot wounds reportedly affect the foot nearly five percent of the time, these authors provide an overview of ballistics associated with gunshot wounds as well as keys to injury assessment, surgical debridement and wound stabilization.
Gunshot wounds and firearm injuries are common and place a continuous burden on hospital resources and the community. Although gunshot wounds are less common in America than in other parts of the world, the Centers for Disease Control and Prevention (CDC) reported 73,883 non-fatal injuries and 32,163 deaths in 2011 due to firearms in the United States alone.1,2 Studies have also found gunshot wounds to involve the extremities more than any other parts of the body, affecting the foot approximately 5 percent of the time.3-7
The treatment of gunshot wounds in the lower extremity can become challenging due to the extent of injury and loss of muscle, tendon, bone, skin, nerves and vascular supply.8 Many of these wounds require specialized fixation techniques, soft tissue reconstruction and extensive wound care, making an understanding of ballistics, the mechanism of injury and wound characteristics important when evaluating firearm injuries.3,8,9
Understanding The Principles Of Ballistics With Gunshot Wounds
When discussing ballistics in relation to wounds, it is important to understand the related nomenclature in this field. Ballistics is the science of mechanics that deals with the flight behavior and effects of projectiles.7 When discussing ballistics, a missile is the projectile that transmits damaging energy to the casualty or target. It is important to understand the term “missiles” is not referring to rocket-propelled explosives but to bullets, fragments and pellets fired from a weapon.
In firearm ballistics, there is a distinction between low- and high-velocity weapons with a velocity of more than 2,000 ft./sec. typically being designated as high velocity. Generally, high velocity corresponds to a kinetic energy greater than 750 ft./lbs. commonly produced by hunting and military rifles.8 To gain perspective, a projectile must travel a speed of 163 ft./sec. to penetrate skin and 200 ft./sec. to break bone.10 Handguns and shotguns are low-velocity weapons. Nevertheless, they can act like high-velocity weapons at close range, which is a distance of less than 14 feet.9,11
When missiles penetrate tissue, the injury is directly proportionate to the amount of energy that transfers to the target. One can determine the kinetic energy of a missile by the velocity (v) and mass (m) of the missile in which kinetic energy = 1/2mv2.3,9,12 While velocity is the most important factor, the efficiency of energy transfer depends on many aspects including the characteristics of the missile and tissue one encounters.9,13,14
Missile characteristics affecting energy transfer include the missile’s mass, shape, stability, path, deformation and fragmentation.9,14 The caliber of a missile describes the diameter of the barrel the missile travels through. Due to the high tolerance of both the barrel and the missile, the diameter of the missile and barrel are essentially the same.7 Larger caliber missiles are greater in size, have more mass and can cause substantial tissue damage. When the initial diameter of a missile increases by 2.5 times, the area of tissue damage increases by 625 times.3 This increase can greatly raise the stopping power of the missile. However, due to their size and weight, larger caliber missiles also lose velocity, which relatively quickly makes them less efficient at longer distances.7
Jacketing a missile is a process in which the manufacturer will cover the lead missile in copper. This allows for an increase in accuracy and velocity of the missile. Often, these rounds are referred to as a “full metal jacket.” Hollow-point rounds are manufactured with a hollow or depression at their tip. These rounds can be devastating to tissue because upon striking the target, the tip of the bullet expands. This allows the missile to lose less velocity traveling from the muzzle to the target while creating a greater surface area upon striking the target. This increase in surface area slows the missile down, making it less likely to exit the target and allowing for maximum energy transfer.
Shotgun missiles have unique characteristics. They fire a large single projectile known as a slug or a significantly large mass of pellets referred to as shot.12 At close range, the wadding from the shotgun acts as a single projectile.9,15 However, as the range increases, the wad expands and the velocity of the pellets decreases substantially. Even with this decrease in velocity, these pellets still may cause great damage to the target because they rarely exit the casualty. Slugs are more accurate and do not lose as much velocity at range. Their soft lead composition allows for easy deformation and it is not uncommon for them to break into large pieces within the body. This is known as a lead snowstorm.12
After leaving the barrel, the missile’s motion occurs in three dimensions. The yaw of a missile greatly affects the amount of damage it causes. (Yaw is the angle that the long axis of the missile deviates during travel.)3 When the yaw becomes so severe that the missile begins to move end over end, it is known as tumbling. When a bullet has severe yaw or starts to tumble, the profile of the missile increases, causing greater energy transfer to the casualty.7
A Closer Look At Tissue Damage In Gunshot Wounds
Due to substantial variables involved in missiles, the designation of a high-energy wound remains subjective and ultimately depends on the physical examination.9 If this designation depends on velocity alone, it only recognizes potential injury and not actual tissue damage.9,14 There is little ability to clinically estimate the amount of energy transferred.9,14
As missiles travel through a target, they produce two types of cavity. The permanent cavity results from direct crushing of tissue by the missile. The diameter of this cavity equates the diameter of the projectile. Tissue within the permanent cavity is destroyed and devitalized. Along with the permanent cavity, a temporary cavity occurs as well.3,7 The temporary cavity results from a momentary acceleration of the surrounding tissue in all directions away from the permanent cavity.7 The temporary cavity occurs by the permanent cavity pushing the surrounding tissue outward.13
Once the missile passes through the tissue, a vacuum forms behind it. The vacuum often pulls foreign debris such as dirt, clothing particles and bacteria into the wound.3 The size of the cavity depends on the missile’s kinetic energy that transfers to the tissue.9 Larger missiles that shatter, deform or tumble tend to have slower exit velocity, resulting in a larger cavity.16 The temporary cavity collapses due to the vacuum effect. Then it reforms and collapses repeatedly with decreased amplitude until all motion ceases. The cells within this temporary cavity are damaged due to the stretching and tearing of the surrounding tissue.
In uncomplicated, low-velocity gunshot wounds, the amount of tissue damage may only be a few cells deep outside of the permanent cavity.9 Lower kinetic energy wounds usually have similarly sized entry and exit wounds. On the other hand, in more complicated or high-velocity wounds, tissue damage can be extensive and the exit wound is typically larger than the corresponding entrance wound.
Tissue characteristics also affect the injury pattern. Tissues that have more elasticity and relatively low density such as skin can be spared from serious injury with gunshot wounds.9,13,14 In contrast, dense organs with less elasticity such as bone absorb more energy, resulting in more damage. When a missile strikes bone, fracture, missile deformation, missile fragmentation and secondary missile production may all occur.7 The high ratio of bone to soft tissue within the foot and ankle is the main reason missile injuries are so devastating to this region.
Keys To Initial Documentation And Management Of Injuries
Although accidental gunshot wounds are common, when evaluating these wounds, it is necessary to document injuries objectively and clearly.17 Although emergency physicians typically manage these wounds, a detailed description of the wound is important. Incorrect documentation can have medicolegal implications. Accordingly, one should refrain from opinion on and differentiation of entry or exit wounds.17 Instead, note the size, shape, anatomic location and associated findings including powder or soot burns.17
The distance from the end of the barrel to the target is typically less than three feet if a powder burn is visible.3 Photographing the wound may prove to be useful. If one must remove clothing from a victim, avoid disturbing any missile holes in shoes or clothing. One should save all missile fragments, document them and handle them with care.17
The management of a firearm injury to the lower extremity is an emergency but comes secondary to treatment of the patient as a whole.18 After stabilizing the wound, one should obtain an accurate history if possible. The history should include the type and caliber of missile, the type of weapon used, the distance from the weapon to the patient and the position of the victim when the incident occurred.3
A Guide To Injury Assessment
Firearm injuries are unique because of the variability of action and anatomy involved. The victim’s clinical examination will reveal skin wounds and the approximate location of fractures. One must determine the patient’s distal neurovascular status as soon as possible. Clinically, if one suspects vascular insult because of the inability to palpate pulses, a white or blue discoloration of the skin or excessive bleeding, then angiography may be beneficial.
Compartment syndrome may also occur with gunshot wounds. If the physician suspects increased compartment pressures, take measurements and if the pressures are elevated, perform an appropriate fasciotomy as a medical emergency.
Flush the gunshot wound with sterile saline and do a preliminary cleaning of the wound. Then take anaerobic and aerobic wound cultures, and consider appropriate routine tetanus prophylaxis.3 One needs to ensure immediate hemorrhage control and stabilization of the lower limb before taking radiographs.18 Radiographs allow for identification of gas, fractures, bone fragments, the extent of soft tissue injury, the location of retained missiles and other retained foreign bodies such as fragments of sock and shoe material.
At this stage in treatment, clinicians can make a judgment as to the probable degree of energy transfer within the wound. Peripheral nerve damage can be difficult to evaluate initially. Due to tissue damage and pain, the patient may be unwilling to attempt to move his or her foot to evaluate motor function and assist in the determination of sensation. As with vascular evaluation, the physician may have an index of suspicion of nerve damage based on the proximity of the wound to the peripheral nerves.
Pertinent Pearls For Surgical Debridement And Wound Stabilization
The wound may be classified as either a high or low velocity missile wound.18 When it comes to gunshot wounds involving fractures, treat them as open fractures.19 The Gustilo and Anderson classifications are useful when managing these wounds.3,20 We can usually consider low-velocity wounds less than eight hours old as type I open injuries, allowing for immediate wound closure following fracture stabilization.21 Low-velocity wounds older than eight hours are type II injuries. For high- and low-velocity wounds classified as Gustilo type II and III wounds, one can allow delayed closure.3 Wound closure typically occurs three to 10 days following debridement if there are no clinical signs of infection.22
In low-velocity missile wounds, minimal excision of the devitalized skin margins with irrigation of the resulting defect is sufficient.18 This is due to the lack of or minimal formation of temporary cavity involved in low-velocity missile wounds.23 High-velocity missile wounds require more extensive debridement. Excise the permanent wound tract as well as the muscle at a variable distance. Determine this by evaluating the consistency, color, contractility and capillary bleeding of the surrounding muscle. Remove all necrotic tissue and devitalized muscle.18
In both low- and high-velocity missile wounds of the lower extremity, fractures are common. At the time of debridement, one may utilize either internal or external fixation to stabilize unstable or displaced type I fractures caused by a low velocity missile.3 In type II or III fractures common with high-velocity missile wounds, incorporate external fixation away from the wound site until the wound is sterile. If there is a defect present between two main fracture fragments, the use of antibiotic beads or a polymethyl methacrylate spacer impregnated with antibiotics may maintain length.18
After the wound is free of infection and contamination, the surgeon may utilize internal fixation and bone grafting can take place if necessary. Stabilization and fixation of the fractures can be challenging because of variability and extensive damage. All types of fixation including Kirschner wires, Steinman rods, bone screws and plates, and external fixators may be necessary. It is not unusual for a patient to undergo multiple surgeries if the soft tissue and bone damage are extensive. In regard to high-velocity missile wounds, arthrodesis or amputation may also be necessary.24
An intra-articular injury is not always obvious. When there is doubt about joint penetration, the wound and joint require exploration, debridement with copious lavage and removal of any foreign debris. Intra-articular fractures, air within the joint and intra-articular hematomas are all indications that a joint has been infiltrated. If missile fragments remain within the joint, it can cause mechanical trauma with subsequent arthritis and loss of function. Also, any lead from the missile within the joint is absorbed and may cause lead toxicity.24-27
Although there is a possibility of lead toxicity from retained missile fragments anywhere within the body, it is unusual for lead absorption to occur in an extra-articular manner. When it comes to non-articular missile fragments, they do not require surgical removal and most often provide insignificant long-term complications.27 In addition, in cases of shotgun injuries, it may be impossible to remove all of the buckshot.
However, lead becomes soluble in organic acids such as synovial fluid, producing increased blood lead concentrations.27 The symptoms of lead intoxication are vague and multiple organs can be affected. The symptoms often include fatigue, malaise, joint pain, headaches, nausea, vomiting, constipation and changes in memory, behavior and attention span.24-27 Consequently, when a lead fragment is within a joint, the excision of the fragment is essential.14 A clinician should suspect lead poisoning in a patient with microcytic anemia, basophilic stippling and abdominal pain.9,27
Case Study: When A Patient Shoots His Foot And Goes On To Amputation
A 42-year-old male presented to the emergency department after accidentally shooting himself in the left foot with a shotgun. His medical history was positive for bipolar disorder, chronic obstructive pulmonary disease and a previous drug overdose. His surgical history was positive for previous treatment of a gunshot wound to his left foot two years prior to the current injury. He was taking venlafaxine (Effexor, Pfizer), quetiapine (Seroquel, AstraZeneca), diazepam (Valium, Hoffman-LaRoche) and carisprodol (Soma), and had no allergies to medications.
The initial evaluation revealed massive soft tissue damage to the dorsal and plantar aspect of his foot. The entry wound was located over the medial metatarsals and dorsalis pedis artery extending completely through the foot. The wounds consisted of irregular wound borders and devitalized tissue. Motor function and sensation were intact. The vascular exam indicated a capillary refill time of four seconds to the great toe. The patient graded his pain as 10 out of 10. Standard X-rays revealed comminution of the first and second metatarsals with most of the first metatarsal missing. There were also fractures of the third and fourth metatarsals, and proximal phalanges of the second, third and fourth toes. Numerous bone and missile fragments were scattered throughout the wound.
The patient started on IV antibiotic prophylaxis and went to surgery four hours after the injury occurred. The procedure involved taking deep aerobic and anaerobic cultures. We debrided all devitalized tissue, removing small, loose fragments of bone, missile fragments, debris and hematoma. After performing power antibiotic irrigation, we inserted drains and applied retention sutures.
Two days later, the patient went back to surgery. We performed further debridement and irrigation. There was no evidence of infection or ischemic changes. To stabilize the foot, we inserted Kirschner wires in the medullary canal of the second metatarsal and inserted an allogenic strut as a spacer where the first metatarsal would have been located. We used a Kirschner wire for stabilization.
After one week, his left great toe became gangrenous and we proceeded to perform an amputation. We subsequently irrigated the wound and performed primary closure as the tissue was healthy. The patient discharged himself from the hospital against medical advice and was reluctant to return for any follow-up visits. One month later, he presented to the emergency department with a wound dehiscence and infection of his left foot. His white blood cell count was 13,000. We administered IV antibiotics and performed a midfoot amputation the next day.
Gunshot injuries of the lower extremity remain a common entity. The high variability of modern weapons, anatomy, location and distance from the weapon to the casualty make these wounds difficult to manage methodically.
This case study displays that even with meticulous care and multiple surgeries, these wounds may still require amputation. However, with a working knowledge of ballistics and use of the principles involved in managing penetrating trauma and reconstruction of soft tissue and osseous defects, the podiatric surgeon can provide effective management of gunshot wounds to the foot and ankle.
Dr. James is a second-year podiatric surgical resident at Oakwood Annapolis Hospital, part of the Oakwood Healthcare System, in Wayne, Michigan.
Dr. Fallat is the Director of the Podiatric Surgical Residency with the Oakwood Healthcare System and the Section Leader of the Podiatry Department of Surgery at Oakwood Annapolis Hospital in Wayne, Michigan. He is a Fellow of the American College of Foot and Ankle Surgeons.
Dr. Morrison is the Associate Director of the Podiatric Surgical Residency with the Oakwood Healthcare System at Oakwood Annapolis Hospital in Wayne, Michigan. She is a Fellow of the American College of Foot and Ankle Surgeons.
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Editor’s note: For further reading, see “How To Diagnose And Treat Foreign Body Injuries” in the June 2003 issue of Podiatry Today, “Expert Insights On Managing Traumatic Wounds” in the November 2007 issue or “How To Achieve Optimal Treatment Of Puncture Wounds” in the January 2007 issue.
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