Surgical Treatment of Penetrating Wounds of the Spine

Penetrating injuries to the spinal cord rank as the third leading cause of spinal cord injuries (SCIs), after motor-vehicle accidents and falls. Penetrating injuries account for almost 15% of new SCIs each year in the United States. Penetrating SCIs most commonly result from missile or stabbing injuries and predominantly occur in areas with a high rate of violent crime.

Most of the early experience with neurosurgical management of penetrating SCIs was gained during wartime. During World War I, the overall mortality rate from a missile injury causing complete myelopathy was 71.8%. This high rate of mortality after penetrating SCI was similar to mortality rates from any cause of complete myelopathy at the time. The optimal treatment of these patients, including resuscitation, surgical intervention, and postoperative care, was unknown. An operative mortality of 62% discouraged most surgeons from attempting intervention. If operative management was performed, neurosurgical treatment usually consisted of laminectomy in the case of incomplete myelopathy or debridement of entry and exit wounds in the case of complete myelopathy.

Numerous medical advances have since been made that have greatly lengthened the life expectancy of SCI victims. Many of these breakthroughs, including antibiotic therapy and advanced trauma life support, occurred during or after World War II. The mortality rate of penetrating SCI in World War II decreased to between 7.4 and 14.5%. Surgeons, however, remained pessimistic about operative intervention for these injuries until the Korean War. During this conflict, most penetrating spinal injuries underwent surgical exploration, with reports of improvement in some cases.

Further improvements in trauma resuscitation and surgical management of penetrating SCIs occurred during Operation Iraqi Freedom and Operation Enduring Freedom, where combat-related SCIs are at the highest rate in recorded history. In American troops deployed in these conflicts, 38% of penetrating spinal column injuries have a concomitant SCI.

The number of penetrating injuries to the spinal cord among civilians has sadly increased over the past several decades, and the treatment of civilian penetrating SCIs has not been as favorable as recent advances in wartime management. Among the industrialized nations, gunshot wounds are vastly more common in the United States. Stabbing injuries, however, are less common in the United States than in other countries. In South Africa, 25% of all SCIs are caused by stab wounds.

An understanding of the pathophysiology of this condition continues to evolve, although the available treatments remain quite limited.

39.2 Patient Selection

39.2.1 Physical Examination

Once the patient has been stabilized from a cardiopulmonary standpoint, a thorough history must be obtained. Information about the mechanism of injury, associated trauma, and type and caliber of weapon should be sought. This information is important prognostically and therapeutically as high-velocity bullets, most often used by the military, may cause direct or concussive injury to the spinal cord and nearby blood vessels. A concussive effect is caused by a missile passing close to, but not through, the spinal canal. The concussive injuries caused by shock waves may improve over time. Lower-velocity bullets, the type most commonly seen in civilian injuries, tend to cause damage by direct violation of the spinal cord; this usually results in an all-or-none effect with these weapons. Therefore, patients who suffer SCIs tend to have complete myelopathy. Consequently, the prognosis of myelopathy created by a low-velocity bullet is poor.

After a thorough history has been taken, a detailed neurologic examination must follow. One must immediately document the level of SCI and American Spinal Injury Association (ASIA) grade. Fifty percent of penetrating injuries occur in the thoracic region, 20% are cervical, and the other 30% occur in the thoracolumbar area. More than 50% of gunshot wounds to the spinal cord that cause SCIs result in a complete SCI. This percentage is higher in the thoracic spine. Entry and exit wounds must be inspected, with careful attention directed to the presence of obvious contamination or leakage of fluid from the wounds.

39.2.2 Radiologic Assessment

Standard anterior and posterior and lateral roentgenograms of the spine are mandatory and must be obtained as soon as possible. Notation should be made of the location of the bullets or other objects. The alignment of the spine and presence of fractures can also be evaluated at this time. A computed tomographic (CT) scan through the involved area should be performed in most patients. The levels scanned should include not only the level of the bullet but also the level of spinal cord dysfunction if the two levels are not concordant. This study effectively evaluates the spinal canal ( ▶ Fig. 39.1). CT myelogram may also be used to assess for neural compression or evidence of cerebrospinal fluid (CSF) leak.

Fig. 39.1 Penetrating spinal injuries may traverse the spinal cord completely (a), enter the spinal canal and lodge in the cord (b), or miss the cord altogether and damage only the spine or meninges (c).

The use of magnetic resonance imaging (MRI) in cases of retained missile in the vicinity of the spinal cord remains controversial. Despite the presence of metallic artifact, valuable information, such as the presence of extradural hematoma or spinal cord contusion, can be gained. This must be weighed against the risk of fragment migration, which could be catastrophic for a neurologically intact patient. The exact risk remains unknown, but series of patients with retained spinal bullets undergoing MRI have not demonstrated significant consequences. Myelopathy after penetrating injury may result from a compressive hematoma, which is a surgically treatable lesion. It is difficult to visualize a hematoma with any study other than MRI, although CT-myelogram may be used. MRI and myelogram may also be needed at later times if a CSF fistula is suspected.

In general, it seems wise to avoid MRI in neurologically intact patients with a retained fragment near the spinal cord. Complete patients presenting acutely, however, may benefit from early identification and removal of a compressive hematoma. As such, MRI should be considered for these patients, if not otherwise contraindicated. The potential benefit of MRI, either acutely or delayed, in a patient with incomplete myelopathy must be carefully weighed against the theoretical risk of further injury from missile migration. Most incomplete patients do not require MRI. The cause for their myelopathy can often be determined from other studies.

39.2.3 Indications for Surgical Treatment

Reasons to consider surgery after penetrating injuries to the spine include restoration of neurologic function, prevention or treatment of infection, a migratory or compressive missile fragment, correction of spinal instability, and prevention or treatment of CSF fistulas. In the acute setting, it is most important to remember that two-thirds of patients with a penetrating spinal injury have an associated visceral injury. Attention to these other organs often supersedes attention to the spine. Acute spinal surgery after penetrating injury is also associated with an increased incidence of infection and complication; however, this risk diminishes about 1 week after the injury. It therefore seems prudent to delay surgery, if possible. Perhaps the only urgent surgery in this scenario is the rapid evacuation of a compressive lesion from an incomplete, yet deteriorating, patient.

Spinal stability is rarely compromised after penetrating injuries to the spine; however, these patients may have sustained other types of trauma, such as physical beating or vehicular trauma, which may have imparted upon them additional spinal injuries. In regard to management of spinal instability, the penetrating aspect of the injury is of less importance from a surgical perspective than the combinatorial degree of instability. Furthermore, penetrating spinal injury is not itself a contraindication to closed cervical traction.

Cauda equina lesions have a better prognosis for functional recovery after penetrating injuries. These should be surgically decompressed acutely, when appropriate. Isolated nerve root injuries may be decompressed if they cause long-term problems; acute surgery is rarely warranted.

39.3 Preoperative Preparation

Patients with SCIs are trauma patients and should be treated at a trauma center whenever possible. They may have other life-threatening injuries and require immediate evaluation by an experienced trauma team. The airway must first be secured. Endotracheal intubation, if necessary, should not be delayed. Respiration, arterial oxygen saturation, heart rate, and arterial blood pressure must then be rapidly assessed and treated, if necessary. All these factors affect spinal cord perfusion and are of primary importance in preserving neurologic function. Hypotension is a common finding in patients with SCI, and the cause may be difficult to ascertain. High thoracic and cervical SCIs may lower blood pressure by the diminution of sympathetic tone. Victims of gunshot wounds may also have hypotension resulting from blood loss or cardiovascular compromise. Hypotension resulting from volume loss characteristically produces tachycardia, whereas hypotension resulting from SCI most often causes bradycardia. Initial management of hypotension after SCI mandates aggressive fluid resuscitation, followed by the judicious use of vasopressors. Blood products should be administered as necessary. If indicated, Swan–Ganz catheterization and other types of invasive hemodynamic monitoring should not be delayed. Furthermore, a Foley catheter should be placed to allow for bladder decompression and monitoring of volume status.

The available data suggest that treatment with corticosteroids is relatively contraindicated. All types of penetrating injuries were excluded from the National Acute Cord Injury Study (NASCIS) trials. Other studies have evaluated the use of corticosteroids for penetrating SCIs and have found no benefit. This lack of proven efficacy, coupled with the potential for steroids to inflict harm, provides a relative contraindication to steroid administration in victims of penetrating SCI.

Prophylactic antibiotics should be given. The ideal length of administration is not known, but it seems prudent to continue treatment for at least 1 week. The agent should be chosen based on the other regions of the body injured and local hospital bacterial sensitivities. Tetanus immunization status should be documented on admission, and prophylaxis should be given if any doubt remains.

Finally, penetrating objects take an unpredictable course through the tissue they enter. The importance of maintaining a high index of suspicion for associated injuries and maintaining a close collaboration with the trauma team members cannot be overstated.

39.4 Operative Procedure

39.4.1 Surgery for Missile Injuries

An aggressive effort should be undertaken to establish the exact cause of SCI. Compressive hematomas should be evacuated without delay in incomplete patients because the potential exists for functional improvement if addressed promptly. The benefit of evacuating intramedullary hematomas is unknown but may be performed at the discretion of the surgeon ( ▶ Fig. 39.2). The indication to acutely remove compressive bony fragments remains unresolved as well. Animal models have demonstrated better recovery of neurologic function with quicker decompression of extradural compressive elements; however, no trials have evaluated this effect in humans. If not performed acutely, delayed decompression of bone or disk from the spinal cord may be attempted in cases of incomplete myelopathy. Delayed decompression of bone, in the case of complete myelopathy, will not restore neurologic function, but some have suggested that this procedure may help prevent development of a syrinx. Injuries involving direct traversement of the spinal cord by a missile are unlikely to benefit from any type of surgery. Durotomy and myelotomy do not, by themselves, improve the likelihood of recovery after SCI.