Overview
Gunshot wounds (GSWs) to the spine represent a major health problem in U.S. metropolitan areas as well as in military hospitals. With the perpetually escalating levels of violence, civilian GSWs to the spine have increased to 13% to 17% of all spinal cord injuries. Because of the high potential for severe functional impairment, these patients require major socioeconomic expenditures. Because of the high velocity of the ordnance, military GSWs to the spine are typically more severe and usually result in complete injuries, with decreased likelihood of neurologic recovery. In both civilian and military spinal GSWs, thoracic injuries are most common, followed by lumbosacral and cervical injuries.
Epidemiology
Civilian GSWs have reached epidemic proportions in the United States, being 90 times more frequent than in any other industrialized nation. GSWs to the spine have increased proportionally and now represent the second most common cause of spinal cord injury in metropolitan areas. The typical GSW patient is likely to be young, single, African American or Hispanic, male, and unemployed, with a history of previous violent injuries or encounters with the criminal justice system. Despite the fact that handguns represent only about 25% of the firearms in the United States, they are responsible for about 80% of GSW injuries. Because of the increasing incidence of GSWs to the spine, most level 1 trauma centers have now become well versed in the treatment of these types of patients.
In the past 10 years, the United States has been involved in two simultaneous conflicts within the global War on Terror: Operation Iraqi Freedom (2003 through 2012) and Operation Enduring Freedom. These two conflicts alone have resulted in over 50,000 casualties. Spine injuries are among the most disabling conditions affecting wounded soldiers. Associated injuries are frequent in this population, and these patients have higher rates of musculoskeletal, head, and chest trauma, as well as spine injuries at multiple levels, than their civilian counterparts. Delivery of medical care in a hostile combat environment can be challenging, and evacuation of the casualty and care provider to a safe location may take priority over a full medical evaluation while under fire.
Mechanisms of Injury
The energy of any moving object is determined according to the formula E = ½ mv 2 , where E is kinetic energy, m is mass, and v is velocity. Therefore the bullet energy impacted to tissues increases exponentially with the velocity. Most civilian firearms, typically pistols and handguns, have muzzle velocities of less than 2000 feet per second and are considered “low energy,” whereas military assault rifles, such as AK-47s and M-16s, have muzzle velocities greater than 2000 feet per second and are considered “high energy.” The closer the range of a gunshot, the less energy will be lost during transit; thus more energy will be transferred to the victim in close-range shootings. Fragmentation of the bullet on impact, as occurs with hollow-point bullets, results in multiple trajectories and increased damage to tissues.
Bullets may have a “jacket,” a thin metallic layer covering its surface. Fully jacketed bullets are designed to hit long-range targets, are highly precise, and may incur clean entry and exit wounds. Partially jacketed or nonjacketed bullets are designed to hit close-range targets and expand on impact, resulting in fragmentation and increased tissue damage.
Most bullets are made of a lead core, whereas the jackets are made of copper, brass, or nickel. These materials can be toxic, particularly if the bullets are lodged in the intervertebral disk. Lead toxicity has been reported and can be determined by periodic measurements of the lead level or by indirect effects, such as hematopoietic or axonal changes. In animal studies, copper has also been shown to be toxic to the brain and spinal cord tissue when in direct contact with tissues.
Prehospital and Emergency Room Management
The initial treatment of GSW victims targets the maintenance of airway, breathing, and circulation—the ABCs. All patients should receive tetanus prophylaxis as soon as possible, and specific issues must be addressed depending on the level of injury.
Cervical wounds are frequently complicated by airway injuries and often require immediate intubation or tracheostomy. Similarly, injuries to the major arteries in the neck result in pulsatile bleeding and may require placement of temporary stents to restore cerebral blood flow. Lesions of the pharynx and esophagus have a higher rate of infection and may mandate emergent surgical exploration and repair. These interventions should not be delayed by attempts to obtain radiographic clearance of the cervical spine in patients without neurologic deficit, because GSWs to the spine are rarely unstable. In patients with hypotension and bradycardia (i.e., neurogenic shock), the sympathetic input is diminished and should be treated with pressors rather than volume-replacement agents. Because the diaphragm is innervated by the C3–C5 spinal cord segments, patients with high cervical spinal cord injuries are usually unable to breathe and typically require immediate intubation for ventilation.
Thoracic GSWs are usually associated with lung injuries (hemothorax and/or pneumothorax) or cardiovascular injuries (heart perforation, cardiac tamponade, aortic disruption). The treatment of these lesions takes precedence over those of the spinal cord injury.
Lumbar and sacral GSWs are typically associated with abdominal and pelvic injuries, respectively. Particular attention should be given to colonic perforations, because they carry a higher risk of infection if not treated with the appropriate antibiotics for an adequate period of time.
Neurologic Evaluation
The neurologic examination begins with removing all the patient’s clothing and log-rolling the patient to protect the spinal cord in case of an unstable injury. The number of entrance and exit wounds is recorded, and the difference between the two accounts for the number of bullets retained in the body. Entry wounds typically have clean and well-defined margins, whereas exit wounds have a ragged, “blown out” appearance. After local wound care, the wounds can be marked with radiopaque markers for later radiographic deduction of the missile paths.
Physical examination is focused on the level of injury and the presence of neurologic function below it. In the conscious patient, it is easy to determine the motor strength as well as sensory impairment. Comatose or sedated patients can be evaluated by their response to painful stimuli in the upper and lower extremities. Deep tendon reflexes are usually absent below the level of injury in patients with complete neurologic deficit (i.e., spinal shock). Particular attention should be given to the presence of the rectal sphincter tone and the bulbocavernosus reflex, which will determine whether the patient has a complete versus incomplete injury.
Radiologic Evaluation
The initial radiologic evaluation typically consists of plain radiographs, anteroposterior (AP) and lateral, of the involved areas. If the wounds are tagged with radiopaque markers, the bullet trajectories can be inferred, as can the potential tissue damage incurred on that path. Bullet fragments retained in the body can also be identified. If spinal instability is suspected (e.g., a patient has neurologic symptoms), particularly in the cervical spine, active flexion–extension films can be obtained.
The radiologic examination of choice for GSW to the spine is computed tomography (CT). Thin-slice (1 to 2 mm) CT images permit accurate bullet localization within the spinal segment as well as assessment of associated bony destruction. Coronal and sagittal reconstruction allows evaluation of the integrity of the three spinal columns and of the presence of focal kyphosis and/or scoliosis at the injured level.
Magnetic resonance imaging (MRI) has the potential of inducing bullet migration and thus worsening neurologic deficit. However, several studies have attested to the safety of MRI use in patients with spinal GSW. Advantages of MRI over CT include better definition of the soft tissues (disks, spinal cord, spinal nerves) and less artifact from the bullet.
Indications for Surgical Intervention
Preoperatively, all patients should receive broad-spectrum antibiotics. In cases of colonic perforation, antibiotics should be continued for 7 to 14 days and should include Gram-negative and anaerobic coverage. In patients with visceral perforation and concomitant spinal injury, it appears that surgical débridement of the spinal lesion and bullet removal from the spine do not improve the outcome. Steroids are not indicated in GSW to the spine, because they do not improve neurologic function but do increase the rate of complications.
Cerebrospinal Fluid Fistula
Cerebrospinal fluid (CSF) fistulas are easily recognized by the clear nature of the fluid persistently coming out of a GSW entry or exit wound. In cases of occult leaks, β-2 transferrin analysis can confirm the diagnosis, because this protein is specific to CSF. Occasionally, patients may exhibit mental status changes and even cranial nerve palsies as a result of extreme loss of CSF.
The first line of treatment for CSF leaks is placement of a lumbar drain. This allows for controlled drainage of 10 to 15 mL/hour, or until severe headache ensues, and sealing of the defect created by the GSW. Because of the risk of meningitis if left untreated, if the CSF leak persists, a laminectomy is typically required that should include repair of the dural defect, either primarily or with a dural graft. Lumbar drainage is usually continued postoperatively to facilitate the sealing of the dural repair.
Spinal Instability
A GSW to the spine rarely leads to instability. In the awake patient with no neurologic symptoms, it is safe to assume that the cervical spine is stable and to proceed with the emergent care without obtaining “radiographic clearance.” In these cases, immobilization in a hard cervical collar for 2 weeks allows for the pain and spasms to subside and permits a better evaluation by flexion–extension radiographs. Spinal instability is more likely in high-energy injuries, because missiles moving at higher speeds have a wider circumference of damage because of the shock wave.
Spinal instability should be suspected in patients with comminuted fractures that involve the anterior and posterior elements, particularly if associated with abnormal focal angulation or subluxation. Progressive angulation over the course of weeks or months can also be interpreted as instability. Occasionally, MRI can identify the degree of ligamentous injury and can indirectly assist in the determination of the degree of instability.
In patients with incomplete neurologic deficit, spine surgeons may choose to treat a potentially unstable fracture that may result in a worsening neurologic status if not surgically stabilized. This is particularly true for patients with retained bullet or bone fragments in the spinal canal, who can also undergo a surgical decompression at the same time.
In patients with complete neurologic deficit, the surgical goal is to provide sufficient spinal stability to allow the patient to undergo the strenuous physical therapy and retraining necessary to use their preserved motor function to accommodate daily needs.
The surgical approach typically involves instrumentation and depends on the particular configuration of the fracture. An unstable GSW that involves mostly the vertebral body can be addressed by performing a corpectomy and fixation, whereas those that predominantly involve the posterior elements are treated by a posterior multilevel fixation, with or without decompression. Occasionally, a circumferential fixation is required in severely comminuted fractures.
The timing of surgery is usually between 5 and 10 days from the injury. Earlier operations have a high risk of CSF fistulas, whereas operations later than 2 weeks have a higher incidence of arachnoiditis and infection.
Neurologic Deficit
Neurologic deficit is more often complete after a GSW to the spine (59%) than with blunt injuries (49%). The societal cost of these injuries is tremendous: not only do these patients have extensive stays in the intensive care unit (ICU), hospital, and rehabilitation facilities, they are frequently ventilator dependent for prolonged periods of time. In addition, they are typically young and were previously capable of independent living; often they are completely disabled after the GSW.
Neurologic deficit after GSW to the spine can be progressive, incomplete, or complete. Progressive or delayed new-onset neurologic deficit after GSW to the spine represents an indication for emergent decompression, but it is a relatively rare occurrence. Progressive neurologic deterioration may be due to a bullet or bone fragment in the spinal canal or to an expanding epidural hematoma. This neurologic progression is best detected if the serial examinations are documented in the chart following the same pattern of muscle groups (e.g., the American Spinal Injury Association [ASIA] scale chart), preferably by a single, experienced physician.
Incomplete neurologic deficit typically involves various degrees of weakness of the legs and/or arms below the injury level, but occasionally it may present as Brown-Sequard, central cord, anterior cord, or even cruciate hemiparesis syndromes. The role of surgical decompression in these patients is still a matter of debate. Some authors believe that decompressive operations should be done in all the patients with evidence of canal compromise, but others have suggested that removal of bullet or bone fragments is beneficial only in the T12–L4 region. Most authors have not found any benefit from spinal canal decompression after GSW. If surgery is performed, timing is optimal within the first 24 to 48 hours after injury.
Complete neurologic deficit is characterized by complete absence of motor or sensory function below the level of injury. Most of these patients do not benefit from surgical decompression, because their chances of neurologic recovery are minimal. The only possible exception is the rare patient with a GSW to the cervical spine and imaging evidence of compressive pathology by bone fragments or a bullet. Early decompression in these cases may provide recovery of one or two cervical spinal segments, with major positive effects on their future recovery of independence with activities of daily living (ADLs).
Special Indications
Disk Herniation
GSW to the spine may result in disk herniations with spinal canal or foraminal compromise. In these rare cases, the indications for surgery are the same as for other acute disk herniations: emergent diskectomy for decompression. Bullet removal in these cases is not necessary, unless it is technically easy to perform and does not jeopardize adjacent neural structures.
Lead Toxicity
Lead toxicity is an unusual occurrence reported in GSW with the bullet lodged in the intervertebral disk space. The diagnosis is based on the presence of anemia and other hematopoietic alterations and requires determination of blood lead levels. The treatment consists of bullet removal and administration of lead-chelating agents.
Bullet Migration
Another rare situation is that of documented bullet migration. When associated with increased or new-onset neurologic deficit, surgical removal of the bullet is usually indicated.
Related posts:
Craniovertebral Junction Instabilities and Surgical Fixation Techniques
Surgical Approaches to the Craniovertebral Junction in Rheumatoid Arthritis
Anterior and Posterior Cervicothoracic Junction Stabilization Techniques
Percutaneous and Endoscopic Diskectomy
Sacral Screw Fixation and Plating Techniques
Primary Malignant and Benign Tumors of the Spine
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