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Management of Penetrating Injuries to the Spine
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. Historically, most literature on the treatment of PSIs came from the battle fields. However, with the rise of violence throughout the world, the incidence of PSIs in the urban population continues to increase. Injuries sustained from the direct path of the offending weapon can cause substantial damage in addition to the damage done by the concussive effect. This leads to an increased incidence of complete neurologic deficit in PSIs compared to blunt injuries. Complete spinal cord injuries (SCIs) are significant healthcare burdens as the expected lifetime healthcare cost for a 25-year-old with tetraplegia is greater than $4.7 million per patient. The enormous cost burden, combined with the opportunity to improve neurologic outcome, make appropriate initial surgical therapy for these patients extremely important.
Most experiences with the management of PSIs has been gained during wartime. Throughout the 19th century and into World War I (WWI), PSIs came with a high mortality rate, typically greater than 50%, which discouraged many from performing any surgical interventions. The British Medical Research Council, in a review of WWI PSIs, concluded that the only indication for laminectomy was for an incomplete lesion with progressive neurologic loss. With improved mortality rates during WWII, publications favored aggressive surgical debridement and intradural exploration even in those patients with complete neurologic injuries. The treatment paradigm of civilian PSIs, however, is less clear. Reports vary widely as to the proper management of such injuries, but certain guiding principles can be gleaned from the available data. Effective treatment relies on a thorough understanding of the principles of ballistics and tissue injury. Determinants of surgical decision for a patient with a PSI include the neurologic status of the patient, stability of the spine, velocity of the weapon, path of the bullet or weapon, and location of any retained fragments. The decision to perform surgery should carefully weigh the benefits of potential neurologic recovery with the risks of surgical complication in patients who may improve with conservative management. The goal of this chapter is to help guide the clinicians in providing the best clinical care for these patients based on current literature.
Epidemiology
It is estimated that the annual incidence of SCI is approximately 54 cases per one million people in the United States, with PSIs accounting for 13% to 17% of all SCIs and an incidence rate of 4 to 7 new cases per million persons per year. Gunshot wounds account for the majority of penetrating injuries with stab wounds accounting for only 0.3% of injuries. Gunshot wounds used to represent 13% of all SCI, after motor vehicle accidents (38%) and falls (16%). However, as gun violence has increased in prevalence, gunshot injuries have surpassed falls to become the second most common cause of SCI. The mean age of injury is reported between 20.7 and 29.7 years with a 4:1 male predominance. , According to studies conducted in the United States, between 47% and 53% of penetrating SCIs are African Americans, 28% to 45% Hispanics, 4% to 18% Caucasians, and the rest miscellaneous. , Anatomically, 20% involve the cervical spine, 50% the thoracic spine, and 30% the lumbar spine.
Ballistics and Pathophysiology
Spinal cord injury caused by stab wound (SCISW) is most commonly inflicted with knives and may damage the spinal cord directly or indirectly. The direct injury may range from dural tear to total cord transection. Spinal cord contusion may be caused indirectly from the weapon impacting the cord against the bony spinal canal. In this type of nonmissile penetrating trauma, the bony elements of the spine often deflect injuries, decreasing the chance of complete cord injury. The knife usually enters the spinal canal in the gutter between the spinous process and transverse process, leading to an incomplete spinal cord injury. Similar to gunshot wounds, stab wounds most often involve the thoracic spine (63.8%), followed by the cervical spine (29.6%), and finally the lumbar spine (6.7%). Complete cord injury is more common in thoracic spine injuries than cervical or lumbar.
A fundamental understanding of ballistics is necessary to understand the wounding potential of a gunshot injury (GSI). Several factors that affect the severity of spinal GSIs include the velocity, path, size of the projectile, and distance between the firearm and target. Bullets damage tissues and structures by three known mechanisms: direct impact injury of the bullet along its path, pressure or shock waves created by the bullet impacting on tissue, and the cavitation after affect. High-velocity missiles, usually in the military setting, can produce spinal injury from their concussive effect without directly penetrating of the spinal canal. These types of injuries may have a slightly better prognosis. Low-velocity missiles are more likely to injure the spinal cord directly along its path and often present as complete myelopathies.
Clinical Evaluation
As with any trauma, initial management of PSI patients should follow the principles of standard trauma care as dictated by Advanced Trauma Life Support guidelines. When possible, information regarding the mechanism of injury, type of weapon, and proximity and direction of the shot should be obtained from witnesses, emergency medical personnel, or law enforcement officers. Once the patient is hemodynamically stable and other primary injuries have been addressed, a full neurologic assessment should be conducted and serial assessment should be performed, ideally by the same provider when possible. It should include evaluation of motor function, sensation, reflexes, rectal tone, and entrance and exit wounds. By convention, spinal cord injuries are identified by the lowest level of antigravity motor function. Complete injury and incomplete SCIs are differentiated by either no or some preservation of motor or sensory function more than three segments below the neurologic level of injury, respectively. The neurologic level is at least one level higher than the vertebral level of injury in 70% of injuries, as the same level as the vertebral level in 20% of injuries, and two levels lower than the vertebral level in 10% of injuries.
Approximately 25% of all missile injuries to the spinal cord will have an associated systemic injury, which may require more urgent attention than the underlying spine injury. Cervical spinal GSIs are commonly associated with damage to the airway, esophagus, or vascular injury to the carotid or vertebral arteries ( Fig. 165.1 ). Thoracic or thoracolumbar spinal GSI may involve injuries to the thoracic and abdominal viscera including lung, heart, GI tract, and the great vessels. , Patients with visceral injuries are often hemodynamically unstable and require urgent exploration which takes precedence over spine surgeries. The incidence of vertebral artery injury in penetrating cervical trauma is 1% to 8% and includes occlusions, arteriovenous fistulas, intimal tear, and pseudoaneurysm. , Historically, some clinicians have advocated for exploration of all wounds that penetrated the platysma, translated from military surgical practice, to avoid missed injury. However, this led to high negative exploration rates (53% to 56%). Therefore, management of these injuries have shifted to more selective approaches, initially using a “zone-based” algorithm of mandatory exploration for stable but symptomatic zone II patients and routine radiographic vascular studies for stable zone I and III injuries. While this approach yielded higher nonoperative rates, it was still associated with high negative exploration rates. With the development of newer and more widely available imaging modalities such as computed tomography angiography (CTA), recent literature advocates for individualized surgical planning based on selective use of investigative tools to diagnose internal organ injuries. Studies have shown that CTA achieved high sensitivity, specificity, and predictive values in detecting clinically significant injuries with positive results followed by confirmatory tests such as angiography, endoscopy, or bronchoscopy
Radiological Evaluation
Appropriate imaging studies are needed to fully understand the path of the penetrating object and the resultant anatomic damage. Two-view radiographs can identify the trajectory of the object and any associated fragments ( Fig. 165.2 ). However, the penetrating object may ricochet off of bone and not follow a straight course. Computer tomography (CT) is useful in delineating the anatomy of the bony injury and to localize the trajectory of the missile within the spinal canal ( Figs. 165.3 and 165.4 ). In patients with incomplete neurologic injury, CT myelogram may be helpful to assess or confirm neural compression ( Fig. 165.5 ). It can also be helpful in evaluating for a cerebrospinal fluid (CSF) fistula. The use of magnetic resonance imaging (MRI) in GSI to the spinal cord is controversial. While it can provide excellent spinal cord anatomy and visualize ligamentous injury, metal artifact from bullet or knife fragments may make these tests difficult to interpret. Furthermore, MRI is usually not used in these patients due to concerns for the migration of ferromagnetic missile fragments, although existing clinical studies in the literature on the use of up to 1.5 T MRIs in patients with retained bullet fragments have reported MRI use to be safe in these patients with no evidence of fragment migration or neurologic sequelae. , The most frequent complaint with MRI use is that the patient may feel a sensation of heat from the bullet. In patients with either clinical or radiographic concerns of instability, dynamic lateral view radiographs should be obtained.
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