Management of Penetrating Injuries to the Spine

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Chapter 180 Management of Penetrating Injuries to the Spine

Michelle J. Clarke, R.a.j. Narayan, Timothy F. Witham

Penetrating spinal injuries (PSIs) encompass a range of traumatic etiologies, from nonmissile injuries such as knife wounds to high-velocity missile injuries such as rifle shots. Unfortunately, the incidence of PSIs may be increasing.^1,² In addition, there has been a shift from stab wounds to gunshot wounds. There may also be an increase in missile velocity, possibly due to greater civilian access to high-powered weapons.³ Because of the range of injuries, no single management paradigm is applicable to all patients. A lack of randomized trials also makes it harder to make definitive statements regarding optimal management.

The majority of treatment recommendations have resulted from knowledge gained on the battlefield. Traditionally, civilian missile-penetrating traumas have been low-velocity injuries, such as those seen with handguns. However, urban centers are treating more high-velocity injuries similar to military-grade weapons. These high-velocity injuries result in greater concussive injury, tissue damage, and wound contamination.⁴ In contrast, low-velocity injuries result in localized injury with pathophysiology related to direct trauma, not the concussive element of a supersonic ballistic missile.

Surgical decision making revolves around risk–benefit analysis, weighing potential gains in neurologic function against surgical risk in patients who may improve with conservative management alone. Regardless of treatment decisions, patients with incomplete injuries often improve, while patients with cord transections do not. Anatomic disruption from the initial injury may result in various complications that include cerebrospinal fluid (CSF) leakage, infection, spinal instability, and iatrogenic neurologic injury. Thus, the purpose of this chapter is to assist the clinician in providing the optimal treatment for a given patient.

Incidence and Classification

Currently, the annual incidence of spinal cord injury (SCI) in the United States is estimated to be 40 per 1 million people, or 12,000 new cases each year ^5,⁶ The majority of SCIs are the result of motor vehicle accidents and falls; however, violence (primarily gunshot wounds) results in 15% of injuries. Prior to 1980, violence accounted for 13.3% of SCIs, and this rate peaked in the 1990s at 24.8% before declining to 15.1% in 2005.⁶ In less developed countries or those with strict gun laws, nonmissile PSIs are proportionally more common.⁷ According to the National Spinal Cord Injury Database, the mean age of PSI is 29.7 years, with a 4:1 male predominance.⁸

As with any SCI, PSIs should be described by both anatomic level and degree of neurologic impairment. Anatomically, 20% of injuries are reported in the cervical spine, 50% in the thoracic spine, and 30% in the lumbar spine, which partially reflects the relative lengths of the spine segments.⁸^–¹³ Approximately 40% of patients are shot in the back, while 19% are shot anteriorly.¹⁴ Management and prognosis of injuries is highly dependent on associated injuries, which vary based on trajectory. Associated injuries are reported in 25% of civilian missile (handgun) injuries and 67% of military missile (high-velocity rifle) injuries.² Injuries to the neck, chest, and abdomen take precedence over spine injury during initial management if vascular or visceral injury threatens patient survival.

It must be determined whether the injury is complete or incomplete and whether it involves the cauda equina. If incomplete or involving the cauda equina, motor, sensory, and sphincter function below the level of injury must be recorded. The American Spinal Injury Association’s International Standards for Neurologic Classification of SCI provides the best assessment of neurologic impairment.¹⁵ Patients injured by missiles are more likely to suffer a complete SCI than those suffering from nonmissile injuries. Of patients suffering from missile injuries as reported in the literature, 49% to 83% had complete injuries, 12% to 43% had incomplete injuries, and 17% to 20% had cauda equina injuries.^10,^14,¹⁶^–¹⁸ Of patients suffering from nonmissile injuries, 21% to 33% had complete injuries and 67% to 79% had incomplete injuries.¹⁰^–¹² Data comparison is limited, because some authors did not consistently categorize injuries to the cauda equina separately.

Clinical Evaluation

In any PSI, initial evaluation must follow advanced trauma life support (ATLS) guidelines; thus, neurologic examination can occur only after the patient is hemodynamically stable and airway control has been secured. Until the patient is clinically and radiographically cleared, care should be taken to avoid unnecessary movement of the spine. Thus, depending on the situation, a cervical collar, backboard, log-roll, and awake fiberoptic intubation should be considered to avoid iatrogenic neurologic deterioration. Spinal instability is a rare complication of gunshot wounds and is even less common with stab wounds.¹⁹ Some centers advocate not immobilizing the patient in the prehospital setting, given that immobilization may complicate or delay care of medically urgent associated injuries.^5,²⁰^–²²

Following the primary survey, an accurate neurologic examination should be performed, along with subsequent serial evaluations. Confounding factors such as intubation, associated injuries, alcohol or drug impairment, and traumatic brain injury may make examination difficult. In addition, by merely observing in the clinical examination, entry and exit points may be misleading, as bullets and fragments may ricochet or cavitation may cause more damage than initially anticipated.

Appropriate imaging studies are needed to fully understand the path of the penetrating object and the resultant anatomic damage, even in asymptomatic patients.²³ Plain radiographs may be helpful in identifying metallic fragments, even if an exit wound is clearly seen (Fig. 180-1). Computed tomography (CT) is useful to assess bone damage and canal compromise (both by fracture and by weapon fragments) and to give an initial evaluation of alignment. CT myelogram may also be useful in determining canal and foraminal compromise, or root avulsion injuries. Unfortunately, metal artifact from bullet/knife fragments may make these tests difficult to interpret; yet these same fragments would likely preclude magnetic resonance imaging (MRI). MRI may be useful to assess ligamentous and spinal cord damage, as well as hemorrhage in all compartments (extradural, intradural, and intramedullary) if it is verified that there are no metal fragments. Further tests to determine spinal stability may be needed if clinical or radiographic evidence suggests this may be a problem. Injuries with a “side-to-side” trajectory may be more likely to cause instability.²⁴ Clinical judgment regarding additional tests, including thoracic, abdominal, and vascular imaging studies, should be exercised based on the clinical picture and the suspected trajectory of the penetrating object. In cases of suspected peripheral nerve injury, electromyelography and nerve conduction studies are seldom useful in the acute setting.

FIGURE 180-1 Anteroposterior (A) and lateral plain (B) radiographs of the cervical spine in a 41-year-old man who was rendered immediately quadriplegic following a gunshot wound to the neck. A large-caliber bullet is present at C5-C6. No surgical intervention was undertaken.

Clinical Management

In the majority of patients suffering from PSI, conservative (nonoperative) treatment is indicated. Historically, surgical indications included decompression and débridement of neural tissue, removal of bony or metallic fragments, dural repair, correction of spinal instability, and relief of pain. Currently, absolute indications are probably limited to spinal instability, intractable CSF leak, and clear demonstration of a projectile, bone fragment, or hematoma that is resulting in ongoing deficit or pain. Once the patient has undergone a thorough evaluation, operative versus conservative management is decided case by case. The main factors influencing this decision are the extent of neural element compression and the patient’s potential for functional neurologic recovery.

Surgical decompression should be considered in cases of intradural or extradural neural compression from the missile, bone, disc, hematoma, gross contamination, or in-driven foreign bodies. Although PSI may result in spinal instability, this is rare. More relevant is iatrogenic instability resulting from a surgical procedure to decompress the neural elements. Such a situation must be addressed during preoperative planning. Patients with known or planned iatrogenic instability should be considered for stabilization or fusion. Removal of debris or washout of the wound to prevent infection is usually not indicated in missile injuries, because the explosive force of the firing weapon effectively “sterilizes” the bullet. The exception may be stab wounds or cases in which there is gross contamination.²⁵

The degree of neurologic compromise and potential for functional recovery is important in determining the aggressiveness of treatment. In patients who are neurologically well, local wound care alone may be appropriate. In patients with complete injuries, surgery is usually not performed unless they have spinal instability or a late complication. In patients with incomplete deficits, surgery in the setting of a compressive lesion may result in functional recovery and should be considered (Fig. 180-2).

FIGURE 180-2 Axial CT of the upper thoracic spine that demonstrates intracanalicular bone and bullet fragments. This 54-year-old man was running from his assailants when he was shot in the back. The bullet entered the interscapular region on the left side at the T5 level, resulting in paraparesis. After a T3 to T6 laminectomy with removal of bone and bullet fragments, he had partial, but remarkable, motor and sensory recovery.

The cauda equina is a special case, as root sparing and recovery is comparable to a peripheral nerve injury (Figs. 180-3 and 180-4). Also, almost all patients enjoy some recovery of nerve root function regardless of management.¹⁴ Thus, some practitioners recommend conservative treatment for these injuries,^18,²⁶ while others favor surgical intervention.^13,^16,²⁷ The advantage of surgical intervention is the removal of blood products and necrotic debris, which may decrease the incidence of scarring, arachnoiditis, and chronic pain syndromes.