Spinal Cord Injury

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39 Spinal Cord Injury

Despite substantial improvements in emergency, diagnostic, and surgical care, spinal trauma continues to present a challenging spectrum of diseases for the neurosurgeon to manage. When spinal trauma results in a spinal cord injury (SCI), the emotional and financial toll inflicted on individuals and their families is enormous. Improvements in the quality of care delivered over the past few decades are partially reflected in the recognition that centers of excellence that focus on acute treatment and rehabilitation of the SCI patient are best equipped to deal with the magnitude of services these patients require.

Epidemiology

Spinal cord injury typically occurs in males at the peak of their productive lives. The incidence of traumatic SCI is approximately 11,000 new cases each year in the United States,¹ with a prevalence of 191,000. The prevalence of SCI patients is increasing steadily owing to improved survival in both the acute and chronic stages of the disease. The amount spent on the treatment of spinal cord injuries in the United States is approximately 5.6 billion dollars each year and rising annually.² The cost of caring for the individual spinal cord–injured patient is directly related to the injury level of the spinal cord and to the patient’s age, with the highest costs associated with older quadriplegic patients who are dependent on a ventilator.²

Etiology

Most spinal injuries result from high-speed motor vehicle accidents (Figure 39-1). Falls and work-related injuries are other important contributors. Spinal cord injury that is due to violence is on a dramatic rise secondary to increased incidence of assaults. These injuries include both blunt and penetrating injuries, such as gun and knife wounds. Sports-related injuries, which include football, horseback riding, and hockey injuries, are relatively rare but have received recent media attention.³^–⁴ Finally, recreational injuries from jet skis, snowmobiles, snow skiing, snowboarding, and parachuting, to name but a few, appear to be on the rise as “extreme sports” become more prevalent.

Figure 39-1 A, Sagittal T2-weighted MRI demonstrates a C6-C7 fracture-dislocation with severe cord compression in a patient who presented with complete C6 quadriplegia-ASIA. B, Patient was treated surgically to realign the spine and gained significant root recovery without any recovery of hand or lower extremity function.

Initial Management

Suspected SCI alters the basics of the “ABCs” of resuscitation in several important ways. With respect to airway management, suspected SCI dictates in-line immobilization of the spine at all times, so hyperextension of the neck is contraindicated. A jaw thrust must be used to open the airway, and required intubation must be done with the head/neck in a neutral position. This is an important point to remember because patients with a high SCI will have diminished or absent respiratory capacity and frequently require emergent intubation.

Aggressive resuscitation of SCI patients proceeds as with all trauma patients. As indicated earlier, however, upper SCI may be associated with neurogenic shock, requiring large-volume fluid replacement. Although pressors are likely to be required in the setting of neurogenic shock, field management is commonly limited to fluid resuscitation. High incidence of associated head injury often requires use of colloid solutions in addition to normal saline/lactated Ringer’s solution in an effort to adequately resuscitate the patient while minimizing exacerbation of cerebral edema.

Immobilization and Diagnostic Evaluation

Rigid immobilization is indicated if there is any doubt about the presence of SCI. Presence of altered mental status in any way dictates the use of “spinal cord precautions.” These include use of in-line immobilization, maintenance of neutral position, cervical immobilization with a rigid collar, and use of backboards for transport.

After initial resuscitative efforts, diagnostic studies are undertaken. Fine-cut helical computed tomography (CT) scan with coronal and sagittal reconstructions have supplanted plain radiographs in most trauma centers as an initial evaluation in detecting spine fractures. Additional spine studies may be obtained after the patient has been stabilized and more emergent diagnostic studies have been undertaken. During this time, rigid cervical collar and backboard immobilization must be continued.

Further diagnostic studies will be dictated by the findings of the initial and secondary surveys as well as findings of initial diagnostic studies. Several points are important to keep in mind. First, important information can be obtained from studies performed for other reasons. For example, routine chest and abdominal radiographs may provide important information regarding the presence of significant thoracic/lumbar spine injury. Although these do not replace subsequent “formal” spine studies, they are often obtained as part of the routine trauma workup and provide early clues to the presence of spine trauma and may help prioritize subsequent imaging studies (Figure 39-2). Radiographs and particularly the CT are the most sensitive tools in detecting a fracture of the spine, but occasionally it is difficult to clear the spine—even in the absence of a fracture—because an unstable ligamentous injury without fracture may exist.

Figure 39-2 This 45-year-old man sustained (A) an L4 fracture-dislocation and presented with a dense footdrop. He underwent (B) anteroposterior reconstruction with instrumentation.

Patients with a suspected spinal column injury who are unconscious, uncooperative, or intoxicated or who have associated traumatic injuries that distract from their assessment will often require further radiographic study of the cervical spine before the discontinuation of cervical spine immobilization. Several options exist and include (1) maintenance of the collar and/or spine precautions until the patient becomes coherent and responsive, (2) dynamic imaging of the spine with physician monitoring, and (3) magnetic resonance imaging (MRI) of the spine to rule out a purely ligamentous injury. Of the three options, we frequently use MRI to clear the spine because a completely negative MR image in the setting of trauma indicates that there is no instability of the cervical spine (Figure 39-3). Malalignment and evidence of spine trauma on these imaging studies frequently determines subsequent management and diagnostic decision making. Cervical subluxations often require the use of traction and/or manual reduction of the fracture-dislocation. Diazepam (Valium) or lorazepam (Ativan), along with careful neurologic monitoring, often in the intensive care unit (ICU) setting, is required because application of traction can realign the spine but can also result in neurologic deterioration.

Figure 39-3 A, Admission lateral radiograph of a 31-year-old man who was “cleared” in the emergency department after cervical spine series and CT failed to demonstrate a fracture. Patient had a Glasgow Coma Scale score of 11 on admission and significant facial fractures. B, He presented 1 year post admission with increasing neck pain and was diagnosed with a severe cervical kyphotic deformity with bilateral perched facets at C5-C6. MRI (gradient-echo sequence) done on admission in this obtunded patient would have easily demonstrated the posterior ligamentous injury between the C5 and C6 spinous process, which is relatively subtle on the admission lateral cervical spine radiograph seen in A.

Pediatric Spinal Cord Injury

Pediatric spine trauma is relatively uncommon, representing approximately 5% of all spinal cord injuries.⁵ For a specific discussion of pediatric SCI, please see Chapter 210. In addition, guidelines have been published on this topic.⁶

Pharmacotherapy

The concepts of primary and secondary SCI are important principles in understanding the pathophysiology and the role of pharmacotherapeutic agents in emergent treatment. The primary injury mechanism results from a mechanical insult that occurs at the time of impact and includes acute compression, impaction, distraction, laceration, and shear.⁷ Secondary injuries occur after the initial injury and account for some of the progressive pathologic changes associated with SCI.⁷ A number of drugs have been tested in the laboratory, but only a few of these agents have progressed to clinical trials to evaluate their efficacy. Five randomized controlled trials of pharmacotherapy for acute SCI have been conducted, focusing on the therapeutic effect of either corticosteroids or gangliosides.

Corticosteroids

A number of studies have shown improved neurologic recovery in animals with spinal cord injuries that have received either dexamethasone or methylprednisolone.⁸^–¹² Corticosteroid treatment initially held promise as a potential therapeutic agent for its putative role in reducing white matter edema and inflammation. Current evidence, however, suggests that the major mechanism of action is reduction of the effects of secondary injury—in particular, the destructive effects of lipid peroxidation on cell membranes.² Other actions include improving spinal cord blood flow, enhancing the postinjury activity of Na⁺/K⁺-ATPase, and facilitating the recovery of extracellular calcium ion.^8,¹³

The first NASCIS trial (NASCIS I) examined low- (100 mg) and high- (1000 mg) dose methylprednisolone given for 10 days. Unfortunately, this trial had no control group, and no significant difference in outcome was found except for an increased number of wound infections among patients in the high-dose group.¹⁴ The second NASCIS trial (NASCIS II) was a prospective, randomized, double-blind, multicenter trial that demonstrated improved neurologic outcomes after 6 weeks, 6 months, and 1 year in patients with nonpenetrating SCI who had received a regimen of methylprednisolone, which included a bolus dose of 30 mg/kg.¹⁵ Improvement in motor and sensory scores associated with administration of methylprednisolone was only observed if the drug was given within 8 hours of injury when compared with naloxone or a placebo. Results of this study have been criticized.^16,¹⁷ Some of the criticisms relate to difficulties in randomization, reporting methods, analysis of benefit limited to small subgroups within the larger study, and lack of replication of results by a completely independent group of investigators, among others. However, the administration of methylprednisolone is believed to reduce the amount of secondary injury that occurs after SCI and has become an important tool in the treatment of SCI in most North American centers. The results of NASCIS III have been published and compared the dosage of methylprednisolone used in the NASCIS II protocol with a longer dosing regimen (48 hours) as well as with a 21-aminosteroid. The 21-aminosteroids (lazaroids), a new class of steroids that are potent inhibitors of lipid peroxidation, lack much of the glucocorticoid activity of many of the traditional steroid compounds. Results of the study suggested that when patients are seen within 3 hours of their injury, they should receive a bolus dose of methylprednisolone (30 mg/kg intravenously [IV]) followed by 23 hours of treatment (5.4 mg/kg/h IV). Patients seen between 3 and 8 hours should receive the same bolus followed by a longer dosing regimen (48 hours). Complications from 48 hours of treatment included a significant increase in severe sepsis and pneumonia.¹⁸ Neurosurgical guidelines for management of spine trauma recommend methylprednisolone as a treatment option, recognizing that the risks of use have been more clearly demonstrated than benefit.^19,²⁰

Gangliosides

Gangliosides are complex sialic acid–containing glycosphingolipids which are present in high concentrations in neural membranes. These compounds are involved in a variety of cell-surface phenomena such as cell-substrate binding and receptor functions.²¹ Basic research in the past 15 years has demonstrated that these compounds can (1) promote the survival of neurons in cell culture; (2) increase the number, length, and branching of neuronal processes in cell culture; and (3) improve functional recovery after a variety of traumatic and ischemic insults to the peripheral and central nervous system. A limited number of animal studies have examined the role of gangliosides after SCI and have shown only a modest effect on the regeneration of serotonergic neurons.²² A recent prospective, randomized, double-blind, single-center study found a beneficial effect in functional neurologic outcomes when the ganglioside GM¹ was administered within 72 hours of human SCI.²³ However, a multicenter trial demonstrated no statistically significant benefit with administration of this agent at 26 and 52 weeks after injury.²⁴

Hypothermia

Two recent studies were published on the safety and feasibility of mild to moderate intravascular cooling for SCI. Levi et al. reported on a series of 14 patients with American Spinal Injury Association (ASIA) classification A complete cervical cord injuries who underwent a protocol to achieve temperatures of 33.5°C via a closed-loop delivery system. Researchers found good correlation between intravascular and intrathecal cerebrospinal fluid temperature.²⁵ Average time between inductions of hypothermia was 9.17 ± 2.24 hours (mean ± SEM); time to target temperature was 2.72 ± 0.42 hours; duration of cooling at target was 47.6 ± 3.1 hours; and average total length of time of cooling was 93.6 ± 4 hours. A subsequent paper summarized the complications and neurologic outcomes seen in the SCI patients treated with hypothermia and compared them to age- and injury-matched controls. The hypothermia group ASIA conversion rate to a higher grade was approximately 42%, with a similar frequency of complications to institutional controls.²⁶ This pilot study suggested that systemic intravascular cooling can be accomplished with minimal variations in temperature and few adverse events, and may pave the way for larger multicenter SCI trials to test the efficacy of mild to moderate hypothermia in SCI.²⁷

Intensive Care Unit Management

Spinal cord injury is associated with profound effects on all vital systemic functions. Through primarily class III medical evidence, numerous reports indicate lower morbidity and mortality rates in patients with SCI managed with ICU monitoring and aggressive medical management of these changes.²⁸^–³⁶ At the least, these studies taken together indicate that a systematic approach must be taken to evaluate and treat each of the potential complications. Early and late complications will be seen, and the degree of involvement of each system is usually correlated with the level and severity of injury.

Respiratory System

Respiratory complications are a major source of morbidity and mortality after SCI, with an 18% to 30% mortality rate reported in patients with tetraplegia.^32,³⁷ In a study by Hachen and associates,^28,³⁰ most early deaths were related to pulmonary complications, with the likelihood of severe insufficiency related to SCI severity. Whereas most cervical spinal cord injuries occur below C4, with the phrenic nerves continuing to innervate the diaphragm, the respiratory system is frequently severely affected, particularly after cervical spinal cord injuries. Specifically, marked reductions in (forced) vital capacity, inspiratory capacity, and expiratory flow rates frequently result in hypoxemia.^28,^32,³⁸^–⁴¹ These changes may be attributed to variable paralysis of the intercostal muscles and accessory muscles of respiration. Loss of abdominal muscle tone and ileus also reduce the mechanical efficiency of breathing.

In general, there is a period of grace in which the patient with a cervical SCI will maintain his or her respiratory status. However, respiratory failure can ensue 24 to 48 hours after admission. Additional injuries such as rib fractures, hemothorax, and so on can accelerate this respiratory deterioration. Preparation for such events should be undertaken early so that if intubation is required, it can be done with stabilization using in-line traction, often supplemented by fiberoptic technique using a bronchoscope. Measurements of arterial blood gases, negative inspiratory force, and forced vital capacity may provide a method of early detection of respiratory failure.

The most common respiratory complications include atelectasis, pneumonia, pulmonary embolus, pulmonary edema, and acute respiratory distress syndrome. In addition to difficulty with taking deep breaths and coughing, patients are often unable to clear airway secretions. Accumulation of secretions and/or mucus plugs can result in respiratory failure. Prevention includes respiratory treatment with bronchodilators, frequent pulmonary toilet, chest physiotherapy, increasing airway humidity, intubation, and mechanical ventilation including the use of continuous positive airway pressure. The use of the RotoRest bed significantly decreases pulmonary complications associated with SCI ^32,⁴² because it improves pulmonary blood flow and reduces the incidence of pulmonary emboli.

Pulmonary infections frequently complicate spinal cord injuries. Within days of admission, the normal flora of the oral cavity will contain increasing numbers of nosocomial organisms. Hospital-acquired pulmonary infections are heralded by fever, increased white blood cells both in the sputum and in the peripheral blood, and changes on the chest radiograph. After obtaining appropriate cultures, commencement of broad-spectrum antibiotics should be instituted.

Most patients can be discontinued or weaned from the ventilator after they have been medically stabilized, which usually means treatment of pulmonary infections, reestablishment of euvolemia, enhancement of respiratory muscle function, and nutritional supplementation to offset the high caloric requirements of the trauma. Initially, weaning the intermittent mandatory ventilation rate is followed by weaning of the positive airway pressure (either continuous or end-expiratory). With prolonged periods of ventilation (>2 weeks), and/or multiple failed extubations, one should consider a tracheostomy. The likelihood of requiring a tracheostomy increases after a high SCI, preexisting pulmonary disease, and the age of the patient. Tracheostomy effectively reduces the physiologic dead space. Northrup and colleagues ⁴³ have demonstrated that a tracheostomy can be performed before anterior cervical instrumentation of the spine, with a low risk of infection; but in our patient population, early surgery for stabilization is advocated, and consequently, few patients undergo tracheostomy before anterior cervical stabilization surgery.

Cardiovascular System

Significant confusion arises when the term spinal shock is used after SCI. The misunderstanding regarding its use stems from multiple causes. First, many physicians use the terms spinal shock and neurogenic shock interchangeably. Neurogenic shock, however, refers to a condition characterized by hypotension and bradycardia resulting from interruption of the sympathetic nervous system pathways within the spinal cord. The incidence of significant neurogenic shock increases with injuries above the T6 level, because unopposed vagal tone slows the heart and reduces systemic vascular resistance, resulting in venous pooling. The condition responds to administration of fluids and/or colloids and occasionally requires the use of pressors. Neurogenic shock is distinct from hypovolemic shock, which may occasionally occur concomitantly in the multitrauma patient with SCI who has evidence of either external or internal bleeding. Whereas isolated hypovolemic shock is characterized by hypotension with tachycardia, relative bradycardia (for a given degree of hypotension) is to be expected in the setting of multitrauma with SCI.

Spinal shock encompasses a number of different neurologic manifestations of SCI with varying time courses. Traumatic injuries to the spinal cord interrupt and/or temporarily damage a number of descending and ascending pathways. The most common initial presentation of a complete SCI with respect to reflex and autonomic function is a period of areflexia and flaccidity that is gradually replaced by hypertonia, exaggerated reflexes, and (in many cases) spasticity. The transition period may last from days to weeks. The immediate onset of hyperreflexia and spasticity is uncommon; when it occurs, it is a bad prognostic sign. The period of transition in reflex and autonomic function is often referred to as spinal shock. Concomitant changes in motor and sensory function are also common.

Animal studies indicate that ischemia underlies many of the secondary mechanisms of post SCI, often dictating the resultant deficits.^28,⁴⁴^–⁴⁶ Human studies suggest a direct correlation between the severity of SCI and the incidence and severity of cardiovascular problems.^28,⁴⁷ Together, this suggests that reducing the magnitude of secondary injury should be at the forefront of medical management of SCI.

The typical patient with SCI without associated vascular or visceral injury presents to the emergency department with a mean arterial blood pressure of 80 mm Hg and a heart rate of 65 beats/min.³⁵ Persistent bradycardia is a frequent finding and is often profound enough to produce hemodynamic compromise.^28,⁴⁸ The patient’s blood pressure may respond to volume resuscitation, but often these patients require low-dose pressors. Aggressive medical management, including volume expansion and maintenance of mean arterial blood pressure greater than 85 mm Hg, is believed to potentially enhance neurologic outcome by maximizing spinal cord perfusion at the injury site and thus reducing the likelihood of secondary injury.⁷ Invasive hemodynamic monitoring will demonstrate a normal cardiac index with a low systemic vascular resistance. In the elderly patient with SCI, careful attention to volume replacement is required so as not to precipitate heart failure.

Gastrointestinal System

Hypoactive bowel sounds and impaired peristalsis are a common accompaniment after SCI, owing to the lack of sympathetic modulation. To avoid gastric and small-bowel dilatation, it is wise to delay enteral feeding. In any patient in whom gastric distention impairs respiratory function, a nasogastric tube is indicated. Most cervical cord injuries require nasogastric suction because of impaired bowel motility, air swallowing producing gastric distention, and respiratory compromise due to paralysis of intercostal muscles.

Patients with spinal cord injuries are at high risk of developing gastric and duodenal stress ulcers. Use of steroids compounds the risk of developing significant gastrointestinal hemorrhage. All patients with spinal cord injuries should receive at minimum an H₂ blocker to prevent this dreaded complication. The reported risk of gastrointestinal hemorrhage in NASCIS II for the control group was 3% and for the methylprednisolone group, 4.5%.¹⁵

Urinary System

During the period of spinal shock after a cervical or thoracic SCI, the urinary bladder is atonic and flaccid. Over time it becomes an upper motor neuron bladder with small capacity. An indwelling Foley catheter is initially placed. After 3 to 4 days this is switched to intermittent bladder catheterization to maintain urinary volumes below 500 mL. Urinary tract infections are common, and if any fevers occur, urine cultures must be obtained and antibiotics selected based on culture sensitivities. Patients with spinal injuries above T6 may also develop autonomic dysreflexia if the bladder becomes overdistended or sometimes with catheterization; sympathetic overactivity and thus headaches, hypertension, sweating, and reduced body temperature result. Long-term complications include chronic infections, obstructive uropathy, and renal calculi; if left untreated, renal failure may develop.

Integument

The SCI patient is extremely susceptible to developing decubiti. Frequent log rolling is invaluable in preventing skin breakdown. Specialized beds to turn SCI patients (e.g., RotoRest ⁴² [KCI,] can reduce the incidence of skin breakdown by preventing pressure on a single area. Early intervention for skin breakdown frequently involves application of the DuoDERM patch (ConvaTec, Princeton, New Jersey) to prevent progression.

Thromboembolic Complications

Patients with SCI are at high risk of lower-extremity venous thromboembolism, which may manifest as deep vein thrombosis (DVT) in the lower or upper extremities and lead to leg swelling and/or pulmonary embolism. Depending on injury severity, age, and diagnostic methods, incidence of thromboembolic events ranges from 7% to 100%.⁴⁹ The majority of these events occur within the first 3 months after injury, except in patients who are elderly, obese, or who have had prior thromboembolic events.⁴⁹

Numerous studies have addressed the issue of preventive measures for DVT. Prevention has traditionally included the administration of low doses of heparin (5000 units subcutaneously) twice daily or more. However, meta-analysis of available literature suggests that better alternatives include the combination of pneumatic compression stockings with low-molecular-weight heparin (Lovenox) or adjusted-dose heparin.⁴⁹

Current recommendations for evaluation of suspected thromboemboli include use of Doppler ultrasound for suspected DVT and venography if a strong clinical suspicion exists for DVT despite a negative ultrasound or if pulmonary embolism is suspected.^49,⁵⁰ Treatment of pulmonary emboli or above-knee DVT requires heparinization. Should there be a contraindication to heparinization, an inferior vena cava filter should be placed. Prophylactic placement of inferior vena cava filters has been advocated,^27,^49,^51,⁵² but these procedures are not without risk, and no study thus far compares success rates to the aforementioned conservative prevention modalities.^49,⁵³

Prognostic Factors for Recovery

The clinician uses the neurologic examination, patient age, and appearance of the spinal cord on MRI as well as other clinical data to guide the patient and his or her family on the expected outcome for a specific injury. In any traumatic SCI, it is important to ascertain whether the patient has a functionally complete or incomplete neurologic deficit. The distinction is important because the prognosis for neurologic recovery differs for these two conditions. Patients with no evidence of motor or sensory function below their spinal column injury are considered to have functionally complete injuries. Patients with no voluntary motor control and only slight sensory preservation in their lowest sacral dermatomes or some anal tone are still considered to have incomplete injuries. Functionally, patients with complete cervical spinal cord injuries who remain complete within the first 24 hours of admission are unlikely to regain significant ambulatory function (1% to 3%).^54,⁵⁵ However, most patients who enter the hospital with an incomplete neurologic injury obtain some degree of recovery. The level and degree of an incomplete injury also provides important prognostic information. Cervical injuries have a higher potential for recovery when compared with thoracic and/or thoracolumbar injuries. The less severe the SCI, the more likely the patient will recover.⁵⁶

The majority of injuries occur in males, with well over half the injuries occurring in the 16- to 30-year-old age group. Prognosis for recovery is inextricably linked to age, with younger patients fairing much better than their older counterparts for regaining neurologic function after SCI.^57,⁵⁸ The two most important potential neurologic explanations are the capacity of the “young” spinal cord to function with major deficiencies in the neural circuitry and the possibility of some spontaneous regeneration of the CNS after injury.⁵⁹ The reverse also appears to be true. It is well recognized that patients with stable incomplete injuries who age may lose function, and this may simply be the result of the loss of the last few functioning neurons or axons within the damaged region of spinal cord.⁶⁰ Neuronal loss is a normal part of the aging process for both the brain and spinal cord, and the clinical deterioration observed after SCI may be likened to the postpolio syndrome.

MRI after SCI allows visualization of the spinal cord in a noninvasive manner. The images provide immediate feedback to the surgeon about the degree of spinal cord compression, as well as information regarding the stability of the spinal column through an assessment of the integrity of the ligaments, disks, and surrounding soft tissues. In addition, intramedullary hemorrhage may be easily discerned, providing important prognostic information. Intramedullary hemorrhage is more commonly observed after neurologically complete injuries, and hemorrhage signifies a worse neurologic and functional outcome.^61,⁶² MRI of SCI is discussed in greater detail in Chapter 40.