Penetrating Injuries to the Cervical Spine

h1 class=”calibre8″>16 Penetrating Injuries to the Cervical Spine

Christine Hammer and James S. Harrop

Abstract

Penetrating injuries to the cervical spine occur most frequently among males in the second to fourth decade of life, generally as a result of interpersonal violence. Mechanisms of injury range from common missile injuries, such as gunshot wounds, to less common missile injuries such as those from nail guns or military-grade explosive devices. Knife stab wounds, or stab wounds, are the most common nonmissile form of penetrating injuries. Less common are accidents or injuries involving objects capable of penetrating the skin (e.g., needles, wood or glass fragments, etc.). Cervical spine instability is relatively uncommon, and thus penetrating injuries to the cervical spine are often able to be treated conservatively without surgery or rigid immobilization. Retained fragments carry some risk of infection, but surgery is reserved for those who have failed conservative antibiotic therapy. Steroid use has been a point of controversy, therefore, routine use of steroids for penetrating injuries to the cervical spine is not recommended.

Keywords: penetrating injuries, cervical spine, stability, instability, immobilization, decompression, fusion, spinal cord injury, gunshot wounds, GSWs, stabbing, knife

16.1 Introduction

The National Spinal Cord Injury Statistics Center (NSCISC) estimates that in the United States, spinal cord injuries (SCI) occur at a rate of 54 cases per one million individuals; there are approximately 17,000 new cases of SCI each year. ¹ Injuries involving the cervical spine make up over half of these instances. ² However, penetrating injuries involving the cervical spine are a relatively uncommon cause of SCI. This is due not only to the rarity of this type of injury, but also to the infrequent association of SCI with penetrating injuries to the cervical spine. ³ For example, at one of the busiest trauma centers in the United States, on average there are only 10 gunshot wounds (GSWs) annually involving the cervical spine, with less than half of victims surviving the initial injury. ⁴ Furthermore, other studies have shown that less than 10% of all penetrating injuries involving the cervical spine are associated with SCI. Estimates of cervical spine instability range from 0.2 to 4%, a relatively small number of which go on to require immobilization via surgery or orthosis. ⁴

Historically, approximately 80% of all new SCI cases occurred in males. ⁵ In the past few decades, however, there has been a trend toward an increasing incidence of SCIs in females. ⁵ With regard to data specifically addressing injuries to the cervical spine, including penetrating injuries, males are still most commonly involved. ⁶ In the United States, non-Hispanic blacks account for a disproportionate fraction of cases of SCI compared to their representation among the general population. ¹ While SCI is estimated to occur most commonly during the second to fourth decade, there is a bimodal distribution with a second smaller peak occurring in those over the age of 65 years. ⁷ The average age of cervical spine injury has been increasing in the recent years, mirroring the steadily increasing average age of the general population. The age distribution of patients with penetrating injuries to the cervical spine is clustered within the second to fourth decade. ⁸

Overall, SCIs most commonly result from motor vehicle accidents, falls, acts of violence, and sports/recreation activities in descending order. ⁹ However, the most commonly reported mechanism of injury among individuals presenting with penetrating injuries to the cervical spine are acts of violence, followed by accidents. Depending on geographic location, this may involve either missile or nonmissile objects, with GSWs being more common in the United States, whereas stab wounds (SWs) predominate in developing countries. ⁴

16.2 Mechanisms of Injury

Penetrating injuries to the neck are defined as injuries occurring between the clavicles and the base of the skull. This space is broken down into three zones and injury in any of these three zones may result in injury to the spine (▶ Fig. 16.1). ¹⁰

Fig. 16.1 Cervical zones.

Zone 2 is the largest and most accessible zone of the neck. Surgical access to zone 3 is limited by the mandible, and access to zone 1 may be impeded by the sternum and clavicles. In addition to the spine, mediastinal structures may be at risk of injury when injuries to zone 1 are present. Skull base and craniofacial injuries may accompany penetrating trauma to zone 3. Penetrating injuries involving the cervical spine may be broadly classified into missile (GSWs) or projectile (i.e., nonmissile [SWs]) injuries. ¹¹ In layman’s terms, missile injuries usually involve bullets or shots, nail guns, or other ballistic sources (e.g., arrows, explosion-related fragments, etc.). Nonmissile injuries include nonballistic SW injuries, including those induced via knives and other objects, which are used intentionally or accidentally. ¹²

Classical mechanics relates the kinetic energy of a projectile to its mass and velocity by the formula KE = 1/2mv ²; thus, the most important factor predicting the capacity to injure is the projectile’s muzzle velocity. Military-grade weapons have a much greater muzzle velocity than civilian weaponry such as the handgun. ¹³ Beyond the injury caused by the projectile itself, additional kinetic energy is transferred to the tissue in the form of a secondary cavitation wave, causing further destruction in an ellipsoid shape both larger than and remote from the path of the projectile itself. Temporary cavitations are created more commonly by high-velocity projectiles (which travel at 2,000–3,000 feet/second), whereas projectiles from typical civilian handguns and shotguns leave the muzzle at 1,000 to 2,000 feet/second. ¹³ However, upon striking bone, a projectile typically deforms and expands, leading to increased damage. ¹⁴ This is the same principle exploited by the hollow-point bullet. Laboratory studies have shown that energies of 6.8 J are required to penetrate bone; the maximum energy transferred during a stabbing may range from 64 to 115 J. ¹⁵

The material and design of the weapon impacts the extent of injury; from fragments to hollow-point bullets that explode on impact to length and materials involved, the type of bullet, for example, may impact surgical decisions. Most bullets have a lead core, but the jackets can be made of copper, brass, or nickel. Each of these materials are potentially toxic. Lead toxicity from bullets lodged within the spine has been reported. The necrotic effect of copper on brain tissue and rabbit spinal neurons has also been previously described. ¹⁶

16.3 Assessment and Management

16.3.1 Initial Assessment

Patients should be evaluated and stabilized per applicable basic or Advanced Trauma Life Support guidelines. Injury to any of the three zones of the neck may compromise the patient’s airway. Furthermore, zone 3 injuries may compromise the integrity of the skull base. Thus, the injury may preclude orotracheal or nasotracheal intubation. Each injury must be evaluated on a case-by-case basis, and the airway must be secured accordingly.

Blood loss may precipitate hypotension which can impact spinal cord perfusion and exacerbate the SCI. Thus, immediate cardiovascular assessment and stabilization is essential. Tetanus prophylaxis should be administered according to current trauma guidelines. ¹⁷ A complete neurological assessment should be performed to gain an understanding of the extent of neurological injury, if present. Key elements regarding assessment of penetrating injuries of the cervical spine include motor and sensory examination of upper and lower extremities as well as an anorectal exam (to assess for sacral involvement). Any obvious retained objects, such as a knife handle and blade, should be left in place until the trajectory, depth, and neurovascular structural involvement are assessed with imaging. ¹⁸ In addition, the foreign object may be providing some element of tamponade and, to prevent hemorrhage, should not be removed. ¹³

16.3.2 Radiography

X-ray and computed tomography (CT) are the mainstay imaging modalities for the primary evaluation of a penetrating injury to the cervical spine. Furthermore, CT angiography (CTA) may be indicated for evaluation of vascular structures of the neck (e.g., vertebral arteries [VA]/internal and external carotid arteries [ICA/ECA]) and the head. The Denver Screening Criteria (DSC) or the modified Memphis criteria may be used to guide use of CTA. ¹⁹ Signs and symptoms on DSC include the following:

Focal neurological deficits.
Arterial hemorrhage.
Cervical bruit or thrill (< 50 years of age).
Infarct(s) on head CT.
Expanding neck hematoma.
Neurological exam inconsistent with head CT findings.

In patients who sustained GSWs, artifacts may limit assessment of bone fractures. Additional evaluation of the discoligamentous complex through magnetic resonance imaging (MRI) may be contraindicated. ⁴ The safety of MRI is determined by the radiologist who must consider the location of fragments as they relate to veins, arteries, and neural elements. ⁴ A recent prospective study found that there was no migration of retained fragments in patients with cervical GSWs, thus providing some basis for selecting patients who may benefit from evaluation via MRI. ²⁰ Findings of penetrating SCI on an MRI include those similar to any SCI such as increased T2 signal within the spinal cord or short tau inversion recovery (STIR) signal within the disc or ligaments. ²¹

In addition to the spine and spinal cord, penetrating neck injuries pose a risk to the extracranial carotid and vertebral arteries. One should maintain a low threshold for radiographic evaluation of the craniocervical vasculature. Screening may initially be performed via CTA; however, any concerning finding should prompt the use of digital subtraction angiography (DSA). In a case series on 187 US service members that had undergone DSA for blunt or penetrating craniocerebral trauma suffered in the conflict in the Middle East between 2003 and 2008, Bell et al noted a 26.2% incidence of vascular injury. ⁶ Of the 15 patients that sustained perpetrating injuries to the neck, injuries that were observed included 4 ICA and 1 VA dissections, 5 ICA and 4 VA pseudoaneurysms, 1 ICA and 1 VA arteriovenous (AV) fistula, and 1 pseudoaneurysm of the ECA. Majority of these lesions were amenable to endovascular treatment. In the same series, carotid pseudoaneurysms were the most likely lesions to require open surgical management. In ▶ Fig. 16.2, we show the cervical spine CT images of a 30-year-old male who sustained multiple GSWs to the neck and trunk. Neurologically this patient presented with quadriparesis and was also found to be hemodynamically unstable with concern for possible internal carotid injury in addition to concern for other large vessel injury. In a joint procedure with both vascular and general surgery, the patient had a sternotomy during which bleeding was encountered with concern for innominate versus right common carotid injury. Vascular surgery identified more than 50% injury to the right common carotid; they resected the damaged tissue and reconstructed the vessel with a Dacron graft. Postoperatively, a CTA of the neck was performed which showed the origin of the right vertebral artery was obscured by bullet fragments with reconstitution at V4. This imaging showed that bilateral ECA and ICA were intact without evidence of extravasation.

Fig. 16.2 A 30-year-old male presenting with multiple gunshot wounds with injury to the right internal carotid artery. These cervical spine computed tomography (CT) images show multiple views of the gunshot wound injury involving the C6 level including obscuration of the right vertebral artery.

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