Central Cord Syndrome

Central cord syndrome is present in 9% of all traumatic cord injuries and is the most common of the spinal cord syndromes. This is a condition first reported by Thornburn in 1887 and then popularized by Schneider et al. in 1954. Hyperextension in the cervical spine, with some preexisting cervical spondylosis, is usually responsible for this type of injury. Imaging the cervical spine in patients with central cord syndrome will reveal stenosis from spondylosis, fracture subluxation, or sequestered disk, with no spinal stenosis. Schneider proposed that these injuries resulted from acute compression from preexisting bone spurs anteriorly and hypertrophied ligamentum flavum posteriorly, and contributed to hematomyelia and central cord necrosis (Fig. 50C.1). Schneider witnessed weakness in the upper extremities greater than the lower extremities, as well as a variable degree of sensory disturbances and loss of bladder control. It was proposed that pyramidal signs due to involvement of the anterior horn cells led to weakness in the arms greater than the legs, secondary to the topography of the corticospinal tracts. Because of their good recovery, Schneider was in favor of taking a more conservative approach toward treating these patients. In his case series, he did note that the majority of his patients had permanent disability in their hands that rarely recovered. An alternative explanation takes into account the belief that a greater focus of the corticospinal tracts is dedicated to supplying the distal musculature in the upper extremity (Levi et al., 1996). Thus, injury to the corticospinal tract produces more significant weakness in the upper extremity, with concentration in the hands. Correlations of magnetic resonance imaging (MRI) (Quencer et al., 1992) and histopathology (Martin et al., 1992; Jimenez et al., 2000) fail to suggest hematomyelia from Schneider’s hypothesis. There is in fact minimal disruption of the central gray matter. Axonal disruption and swelling is more widespread in the white matter.

Fig. 50C.1 Central cord syndrome. Described classically as injury to corticospinal tracts supplying arm and hand function, which is topographically located medial to the fibers supplying the lower extremity.

(Reprinted with permission from Tator, C.H., 1994. Classification of spinal cord injury based on neurological presentation, in: Narayan, R.J., Wilberger, J.E., Jr., Povlishock, J.T. (Eds.), Neurotrauma. McGraw-Hill, New York, pp. 1059-1073.)

Anterior Cord Syndrome

Anterior cord syndrome occurs with injuries to the ventral two-thirds of the cord, while sparing the posterior column (Fig. 50C.2). It is present in 2.7% of all traumatic SCIs (McKinley et al., 2007). Motor function is lost distal to the site of the injury. Spinothalamic function may be disrupted, leading to hyperesthesia and hypoalgesia below the level of the lesion. Though this syndrome is classically described for anterior spinal artery compromise, in the setting of trauma, it is due to flexion injuries or retropulsed disk or bone. Anterior cord syndrome carries a worse prognosis than other cord syndromes.

Fig. 50C.2 Anterior cord syndrome. Anterior cord damage results in injury to corticospinal and spinothalamic tracts. There is preservation of dorsal columns.

(Reprinted with permission from Tator, C.H., 1994. Classification of spinal cord injury based on neurological presentation, in: Narayan, R.J., Wilberger, J.E., Jr., Povlishock, J.T. (Eds.), Neurotrauma. McGraw-Hill, New York, pp. 1059-1073.)

Posterior Column Syndrome

Posterior column syndrome is a rare condition with an incidence of less than 1%. This syndrome has been linked to neck hyperextension injuries. Injuries occur to the posterior aspect of the cord (Fig. 50C.3). Since the posterior columns are injured, there is usually a loss of position sense, with retained spinothalamic function. Motor function can be affected as well. Although this syndrome has been mentioned in the literature, it has been recently omitted from the International Standards for Neurological and Functional Classification of SCI (revised 2006) and is not currently recognized as a separate syndrome.

Fig. 50C.3 Posterior cord syndrome. Posterior cord damage results in dorsal columns injury and preservation of spinothalamic tracts.

(Reprinted with permission from Tator, C.H., 1994. Classification of spinal cord injury based on neurological presentation, in: Narayan, R.J., Wilberger, J.E., Jr., Povlishock, J.T. (Eds.), Neurotrauma. McGraw-Hill, New York, pp. 1059-1073.)

Brown-Séquard Syndrome

Brown-Séquard syndrome accounts for 1% to 4% of all traumatic SCIs. Injuries affect the lateral half of the cord (Fig. 50C.4). It occurs most frequently in the cervical spine and is usually due to penetrating injuries and (less commonly) blunt trauma including disk herniations. In cases of blunt trauma, Brown-Séquard syndrome usually occurs in the context of hyperextension injuries, though it has been observed in flexion injuries, locked facets, and compression-related injuries. Below the level of the lesion, it classically manifests with ipsilateral pyramidal deficit, loss of ipsilateral tactile discrimination, position sense, and vibratory sensation, and loss of pain and temperature sensation on the contralateral aspect of the body one to two dermatomes below the level of the injury.

Fig. 50C.4 Brown-Séquard syndrome. Corticospinal tracts, dorsal columns, and spinothalamic tracts are injured from hemisection of the cord. Spinothalamic tracts cross in the ventral white commissure to the opposite side of the cord and course rostrally. Dorsal column and corticospinal tracts are impaired on the ipsilateral side.

(Reprinted with permission from Tator, C.H., 1994. Classification of spinal cord injury based on neurological presentation, in: Narayan, R.J., Wilberger, J.E., Jr., Povlishock, J.T. (Eds.), Neurotrauma. McGraw-Hill, New York, pp. 1059-1073.)

There is rarely this classic presentation of Brown-Séquard syndrome, however. More frequently, patients presenting with Brown-Séquard syndrome present with a variation of the classic syndrome, termed Brown-Séquard plus (Taylor and Gleave, 1957). With Brown-Séquard plus, there is asymmetrical hemiplegia as well as hypalgesia more prominent on the less paretic side. Patients presenting with a clinical picture consistent with a classic Brown-Séquard syndrome injury have a worse prognosis than patients presenting with a variation of the syndrome, but the overall prognosis is good. Brown-Séquard has the best functional motor recovery when compared to other clinical spinal cord syndromes. Most subjects obtain bowel and bladder continence. Patient having predominantly more weakness in the upper extremities compared to the lower extremities have a favorable outcome in regard to ambulating. The symptoms of Brown-Séquard syndrome may appear instantaneously or in a delayed fashion. Furthermore, they may occur in conjunction with other spinal cord syndromes.

Cervicomedullary Syndrome

Cervicomedullary syndrome injuries appear in the upper cervical cord and extend to the medulla. Because of its location, the clinical manifestations of this syndrome include respiratory compromise, hypotension, tetraparesis (often mimicking a central cord syndrome with arms effected more than legs), hyperesthesia, and the onion-skin or Déjerine pattern of sensory loss over the face. Lower medullary and high cervical cord injuries will tend to effect the perioral distribution, whereas a more caudal cervical segment will tend to affect the peripheries of the face. Facial sensation is involved because the spinal trigeminal nucleus and tract are located in the upper cervical cord. The proposed mechanism of injury includes a variety of injuries to the atlantoaxial complex as well as injuries resulting from compression via burst fractures or herniated disks.

Conus Medullaris Syndrome

There is high probability that injuries to the thoracolumbar region can involve the conus medullaris. The conus medullaris represents the transition of the spinal cord from the central nervous system to the peripheral nervous system. The location of this region is highly variable—between the T12-L1 disk space to the middle third of L2 in the majority of the population (Fig. 50C.5). Thus, injury to the spinal column at the T12-L1 junction portrays inaccuracies regarding the exact injury to the neurological system. The lumbar parasympathetic fibers, sacral sympathetic fibers, and sacral somatic nerves originate in the conus medullaris. The classic presentation entails lower-extremity weakness, absent lower-limb reflexes, and saddle anesthesia. There is usually mixed upper motor neuron and lower motor neuron involvement. Loss of the bulbocavernosus and anal reflexes is permanent, differentiating conus medullaris syndrome from SCIs that have a return of these reflexes within 48 hours of the injury. Patients typically have an areflexic bowel and bladder (low-pressure, high-capacity bladder). The most common injuries to the vertebral column resulting in this condition are burst fractures or fracture-dislocation. There is no strong clinical evidence favoring surgical intervention over nonsurgical intervention for conus medullaris injuries. Furthermore, if surgical intervention is performed, there is no compelling evidence to suggest that earlier decompression affects functional outcome.

Fig. 50C.5 Conus medullaris syndrome. T2 sagittal magnetic resonance imaging study showing a T12 burst fracture resulting in conus medullaris syndrome.

Cauda Equina Syndrome

The cauda equina is defined as the region of the neuroaxis occupied by the filum terminale. The only neurological structures in this region include the lumbar and sacral roots. Injuries in this location are typically a pure lower motor neuron injury (Fig. 50C.6). Findings often include absent bulbocavernosus reflex, absent deep tendon reflexes, flaccid urinary bladder, and reduced lower-extremity muscle tone. It is differentiated from conus medullaris syndrome by the presence of asymmetrical weakness and the absence of upper motor neuron involvement (Table 50C.2). Like conus medullaris syndrome, burst fracture and fracture-dislocation are the most common vertebral column injuries associated with this condition. Cauda equina injuries have better recoveries owing to the resiliency of the roots to injuries and the greater regeneration capacity of the roots compared to the spinal cord. The sacral roots, however, are very delicate, and injuries to them may be permanent. In general, cauda equina syndrome in the setting of herniated disk pathology is treated early (within 24 hours) if possible to prevent residual symptoms (Kennedy et al., 1999). Functional outcome in a traumatic setting, however, is similar to conus medullaris syndrome. There is no strong evidence correlating functional outcome to surgical decompression, nor is there any evidence that suggests cauda equina injuries fare better with early versus late decompression.

Fig. 50C.6 Cauda equina syndrome. T2 sagittal magnetic resonance imaging study showing an L3 burst fracture resulting in cauda equina syndrome.

Table 50C.2 Similarities and Differences between Conus Medullaris Syndrome and Cauda Equina Syndrome

Cervical Spine Fractures

Thoracolumbar Injuries

In general, the thoracic and lumbar spine is divided into three segments: an anterior column, middle column, and posterior column. The anterior column extends from the anterior longitudinal ligament to the middle of the vertebral body. The middle column is defined as the portion between the middle of the vertebral body to the posterior longitudinal ligament. The posterior column is the remaining extent of the vertebrae. The classification of thoracolumbar fractures utilizes the three-column model of the spine. A CT scan can provide precise information regarding the extent of injury. There are four major categories of thoracolumbar spine fractures (Fig. 50C.7). Compression fractures involve compression of the anterior body, leading to wedging. Compression of the anterior and middle column is seen in burst fractures. With burst fractures, radiographic indications for surgery are typically loss of vertebral height of 50%, 30 degrees of kyphosis, or 50% canal compromise from retropulsion of elements. There may be neurological deficits associated with retropulsion. Seat belt injuries involve the middle and posterior column. Patients are generally neurologically intact. However, these injuries are typically deemed unstable fractures and should be treated with surgical stabilization. In fracture-dislocation injuries, involvement of all three columns is seen. The radiographic appearance of these injuries suggests a flexion-rotation, sheer, or flexion-distraction mechanism. These fractures are highly unstable and require surgical intervention.

Fig. 50C.7 Computed tomography of various thoracolumbar fractures. A, Compression fracture. B, Burst fracture. C, Seat belt injuries. D, Fracture-dislocation.

Penetrating Spinal Cord Injuries

The majority of penetrating SCIs are due to gunshot wounds to the spine and second only to automobile accidents in causing spinal cord–related disability. Stab wounds to the spine are less commonly seen and present with Brown-Séquard features. When making an evaluation of gunshot injuries to the spine, the trajectory of the bullet must be considered in addition to the physical location of the bullet. It is important to assess whether bowel penetration and contamination is present. The destructive nature of a bullet is related to direct injury from the bullet itself, the shock waves it creates, and temporary cavitation. These factors are dependent on the size and velocity of the missile. On examination, injuries can present one level higher than the observed location of the bullet. CT scan can assess for instability and be more helpful than MRI, which can also be safely done. MRI will not typically influence acute treatment decisions unless an evolving hematoma is present. There has been debate over whether patients benefit from laminectomy and bullet removal with incomplete injuries. The National Institute of Disability and Rehabilitation Research suggests that there is no benefit from such heroic measures. However, patients with incomplete injuries with neurological deterioration should undergo decompression. The other indication for decompression includes injuries located at or below the level of the conus. Spinal nerve roots have a greater capacity to recover after decompression. There are cases of late neurological deterioration occurring as late as 17 years post injury (Ajmal et al., 2009). In these cases, improvement of symptoms can be seen after excision of the bullet and the surrounding reactive tissue. Spinal instability should warrant surgical stabilization. Infection can be common with a contaminated bullet causing viscus perforation and entering the spine. In a civilian population, long-term antibiotics (2-week course) have been shown to have favorable outcomes (Roffi et al., 1989). Steroids should be avoided for penetrating spine injuries.

Management in the Field

Initial evaluation of patients should begin with standard Advance Life Support Trauma protocol to address airway, breathing, and circulation. Trauma patients with significant multiple injuries, neurological deficits, loss of consciousness or altered mental status, or posterior midline tenderness should be treated as having SCI until further evaluation can be safely done at the hospital. They should be placed in a rigid cervical collar with sand bags on either side of the head. These patients should be carefully transported on a backboard and log rolled when turning to avoid any additional injuries. The head is typically taped down on the backboard. To avoid potential injury, intubation should be done with the chin lift method, not the jaw thrust technique.

Initial Hospital Assessment

Once the patient arrives at the hospital, a more detailed history and physical can be obtained. Paramedics are usually helpful in providing a detailed summary of events compiled from multiple sources at the scene of the injury. The history should focus on the timing and the potential mechanisms of injury. Information regarding the forces to the spine can be inferred from a clear description of the details of the event. The trauma team should repeat assessment of airway, breathing, and circulation while the patient is connected to monitors. Nasogastric tube and Foley catheters can be placed at this time. Blood work should include a basic metabolic panel, complete blood cell count, coagulopathy panel, type and screen, and toxicology panel. A detailed physical examination to determine the completeness and level of injury is essential. This will include an evaluation of muscle stretch reflexes as well as the abdominal cutaneous, cremasteric, and sacral reflexes. Rectal tone should be assessed in all patients. During this time, an evaluation should be made as to whether steroids should be initiated. Radiographic imaging should be done to assess location of injuries. Based on the clinical manifestations and imaging findings, a decision should be made regarding immediate closed reduction, emergent decompression and stabilization, or conservative management.

Radiographic Evaluation

Plain Radiography

Initial radiographic evaluation of the spine should be done with plain x-rays. The decision to obtain cervical spine imaging is based on the NEXUS (National Emergency X-Radiography Utilization Study) criteria (Hoffman et al., 2000), a set of five screening assessments created to help guide physicians in making a decision to exclude low-risk/low-yield patients from undergoing cervical radiography. Patients meeting all the criteria in Box 50C.2 can bypass imaging. This study reported a 99% sensitivity and a 12.9% specificity in diagnosing SCIs when using these criteria. More recently, the Canadian C-Spine Rule was noted to be superior to the NEXUS criteria in terms of sensitivity and specificity for alert, stable patients in whom cervical spine injury is a concern (Stiell et al., 2003). Screening criteria include high-risk factors, low-risk factors, and ability to actively rotate the neck. Using the Canadian C-spine Rule, patients older than age 65 who are subject to a “dangerous mechanism” or experience paresthesias (high-risk criteria) should receive plain radiography. Those not meeting any of the high-risk criteria are assessed further. If this subgroup of patients have delayed pain in the neck, posterior neck tenderness, cannot tolerate sitting or ambulatory position at any time after injury, or are involved in an accident that is more than a simple rear-end motor vehicle collision (low-risk criteria), then imaging should be obtained. If they lack any of the listed findings, they are further assessed for their ability to rotate the head. Plain radiography should be obtained for patients incapable of rotating their head 45 degrees in either direction.

Box 50C.2 NEXUS Criteria

No posterior midline cervical spine tenderness

No evidence of intoxication

A normal level of alertness

No focal neurological deficit

No painful distracting injuries

NEXUS, National Emergency X-Radiography Utilization Study.

Typical plain radiography of the cervical spine should include anteroposterior (AP), open odontoid, and lateral views with flexion-extension. An adequate lateral C-spine x-ray should visualize the area between the occiput and the top of T1. A so-called swimmer’s view may be helpful to view the caudal portion of the cervical spine. Four lines should be drawn on a lateral C-spine x-ray to evaluate for subluxation or fractures: (1) anterior vertebral body line, (2) posterior vertebral body line, (3) spinal laminar line, and (4) posterior spinous line (Fig. 50C.8). Findings showing more than 3.5 mm of subluxation or kyphotic angulation greater than 11 degrees to adjacent vertebral body segments can imply instability. Subluxation on the order of 25% or 50%, respectively, suggests unilateral or bilateral jumped facets. Mild flexion distraction injuries can be suggested by enlargement of the interspinous distance. The atlantodental interval (ADI) is a measure taken from the anterior margin of the dens to the closest portion of the anterior arch of C1. A value greater than 3 mm can suggest transverse ligament disruption. The Powers ratio is defined as a ratio of the distance from the basion to the posterior arch of the atlas divided by the distance from the opisthion to the anterior arch of the atlas. Atlanto-occipital dissociation can be suggested with a Powers ratio greater than 1. Prevertebral soft-tissue swelling should also be noted on the lateral C-spine x-rays. The upper limit of normal at the level of C3 is 4 mm. The amount of lateral mass overhang of C1 on C2 seen on the odontoid views can be measured to assess the integrity of the transverse ligament. A sum of lateral mass overhang greater than 7 mm is suggestive of transverse ligament disruption.

Fig. 50C.8 Evaluation of alignment of the cervical spine. A, Anterior vertebral body line. B, Posterior vertebral body line. C, Spinal laminar line. D, Posterior spinous process.

Complete x-rays of the whole spine should performed if any abnormalities of the spine are detected on imaging, since noncontiguous spine injuries are seen in 10.5% of cases (Vaccaro et al., 1992). Plain radiographs of the thoracic and lumbar spine should include AP and lateral films to assess for alignment, kyphosis, disk height, and fractures. Thoracic fractures can be missed on x-rays and may require a CT or MRI if injury is suspected in this region. Scoliosis films can detect present deformity and sagittal imbalance but more importantly can be used as a baseline study for assessing progressive posttraumatic kyphosis.

Cardiovascular Management in the Intensive Care Unit Setting

Cardiovascular disease is a significant contributor to death in acute and chronic SCI patients. Hypotension, cardiac arrhythmias, and autonomic dysreflexia in the acute stage result from loss of supraspinal sympathetic influence. To gain an appreciation of this topic, a thorough understanding of neuroanatomy and pathophysiology is needed.

Signals from various locations in the brain influence at least two key areas of the hypothalamus that modulate cardiovascular control: the dorsomedial hypothalamus and the paraventricular nucleus. The dorsomedial hypothalamus exerts its influence on vasomotor regulation and thus arterial blood pressure via the rostral ventrolateral medulla (and to a lesser extent the raphe pallidus) and cardiac regulation of heart rate via the raphe pallidus. The vagus nerve provides afferent signals from atrial stretch fibers to the nucleus solitarius. This information is then conveyed to the paraventricular nucleus, which in turn induces secretion of oxytocin and vasopressin. As the paraventricular nucleus processes information regarding volume through its atrial reflex, sympathetic activation in the kidneys and heart occur to alter volume status and heart rate. Signals between the brain and cardiovascular system are modulated through the autonomic nervous system. Excitatory input to the nucleus solitarius comes from sympathetic afferents originating in mechanoreceptors in the skeletal muscle, chemoreceptors in the arteries, and cardiopulmonary receptors. Inhibitory signals to the nucleus solitarius are derived from parasympathetic centers. These signals originate in the baroreceptors of the aortic arch and carotid artery, the atria, the great veins, and systemic and pulmonary vessels and travel through the vagus and glossopharyngeal nerves to exert their influence. Efferent sympathetic signals travel via preganglionic and postganglionic neurons. In general, a preganglionic sympathetic neuron arises centrally and terminates in a paravertebral ganglion of the sympathetic chain located just lateral to the vertebral bodies outside the central nervous system. The postganglionic neuron originates at this ganglion and terminates in the effector organ. The exception is in the abdomen and pelvis, where the splanchnic nerve carries preganglionic fibers which cross the paravertebral ganglia to terminate at the prevertebral ganglion. Postganglionic neurons originating from these ganglia give rise to axons that travel en route to the abdominal viscera using arterial walls as a guide to their destination. The heart is innervated by both parasympathetic and sympathetic nerves. Sympathetic preganglionic neurons supplying the heart arise from T1 to T6 and synapse on postganglionic neurons in the middle cervical and stellate ganglia. Parasympathetic neurons stem from the motor nucleus of the vagus nerve and the nucleus ambiguus, which supply the heart via the recurrent laryngeal and vagus nerves. The parasympathetic neurons synapse with the postganglionic neurons present in the epicardium or cardiac walls in the vicinity of the sinoatrial or atrioventricular node.

There can be an impairment of sympathetic control with high thoracic or cervical cord injuries. In general, complete cervical injuries are associated with the highest risk of needing vasopressor support (Ploumis et al., 2010). With unopposed parasympathetic activity from the vagus nerve, bradycardia, hypotension, and other arrhythmias result. Lesions higher than T6 will also affect the supraspinal influence to the splanchnic bed, as well as the vascular supply to the lower extremity. As a result of the denervated sympathetic vascular bed, there is potential for up-regulation or hypersensitivity of denervated peripheral α-adrenoreceptors. Furthermore, there is evidence to suggest that there is decreased presynaptic noradrenaline uptake. Following the obvious disruption of descending cardiovascular pathways that takes place with acute injuries, there are a series of known changes in the autonomic system that contribute to abnormal cardiovascular control. They include (1) morphological changes in the preganglionic sympathetic neurons, (2) the formation of inappropriate connections, (3) altered responsiveness and transmission of signal to vascular smooth muscle, and (4) abnormal spinal efferents.

Significant cardiovascular abnormalities have been correlated with the severity of the injury. Two abnormalities commonly reported are bradycardia and hypotension. Hypotension responds well to volume, though some patients require pressors to maintained elevated mean pressures. Bradycardia can be life threatening and require atropine. The 2-week period following an injury is the time when patients are most susceptible to cardiovascular instability, either from cardiac arrhythmias or episodes of hypotension requiring intervention.

Studies have demonstrated that aggressive medical management of hypotension may be beneficial in improving neurological recovery. One particular study focused on keeping mean arterial pressure (MAP) elevated above 85 mm Hg and early open or closed reduction for bilateral jumped facets (Wolf et al., 1991). This study showed a favorable outcome with these measures. Another study has shown beneficial neurological outcome for patients receiving invasive hemodynamic monitoring and given volume and pressor support to maintain adequate cardiac output and MAP above 90 mm Hg (Levi et al., 1993). A study performed under a prospective setting tested the hypothesis that MAP parameters above 85 mm Hg during the first several days of injury were associated with better outcomes (Vale et al., 1997). This study’s authors noted that 9 of 10 ASIA A cervical injury patients required pressors versus 9 of 29 patients with complete thoracic injuries. In addition, 3 of 10 ASIA A cervical injury patients regained ambulatory capacity at the 1-year follow-up point, while 2/10 patients regained bowel and bladder control. The incomplete cervical injury group had 23 of 25 and 22 of 25 patients recover ambulatory capacity and bladder function, respectively. They further grouped patients into an early, middle, or late period when surgical intervention was performed and found no statistical correlation between timing of surgery and neurological outcome. Their study stressed the importance of aggressive volume resuscitation and blood pressure control in influencing outcome.

A low resting blood pressure and orthostatic hypotension is common following cervical and high thoracic injuries. Although it is generally accepted that reduced sympathetic output to the cardiovascular system leads to a low baseline blood pressure in SCI patients, orthostatic hypotension is an incompletely understood phenomenon. It is possible that there is excessive pooling of blood in the viscera and organs secondary to a lack of a reflex vasoconstrictor activity from an ineffective baroreceptor response. Furthermore, with the absence of muscular activity in the lower extremity, there is less recirculation of blood in the venous pool. Additional explanations include reduced plasma volumes from hyponatremia and a cardiac deconditioned patient. Orthostatic hypotension can limit patient participation in rehabilitation. There is some evidence to suggest persistence of this phenomenon past the acute period. Although bradycardia is the most common arrhythmia present in the acute setting, various other arrhythmias are noted and include atrioventricular block, cardiac arrest, ventricular tachycardia, supraventricular tachycardia, and repolarization changes. Autonomic dysreflexia is common in the chronic phases of SCI and will be discussed in detail in later sections; this syndrome should be anticipated and immediate treatment provided if needed.

Current recommendations based on the 2002 American Association of Neurological Surgeons and the Congress of Neurological Surgeons (AANS/CNS) guidelines, as well as those developed by the Consortium for Spinal Cord Medicine, focus on providing acute critical care for patients who have suffered SCI. This entails transferring these patients to ICU centers, preferably with dedicated SCI units for cardiac and hemodynamic monitoring where cardiac arrhythmias and neurogenic shock can be detected in a timely fashion and treated appropriately. The primary treatment for hypotension is fluid resuscitation to restore preload. Once intravascular volume is restored, pressors should be initiated to keep MAP above 85 mm Hg for 1 week. Pressors should be used with invasive monitoring such as an arterial line and central venous catheters to allow for accurate readings. Dopamine has α-adrenergic, β-adrenergic, and dopaminergic agonist activity. It can counteract hypotension and bradycardia by increasing heart rate and contractility, thus increasing cardiac output. However, the α-mediated vasoconstriction effects are variable. Phenylephrine is a pure α-agonist useful in restoring systemic vascular resistance and increasing MAP. It is less potent than norepinephrine. With a lack of β-adrenergic activity, it can potentially cause reflex bradycardia due to increased end-systolic volume. Patients being treated with phenylephrine may have a difficult time with fluid resuscitation because of the increased partition coefficient of intravascular volume. Norepinephrine is a more logical choice than phenylephrine because of its combined α- and β-adrenergic agonist properties. Preload is restored through decreased venous capacitance. Norepinephrine has some inotropic activity to counteract hypotension and bradycardia. Epinephrine is used in refractory cases because of its potent effects in causing renal, splanchnic, and peripheral ischemia. Vasopressin is usually used in conjunction with norepinephrine and dopamine in septic patients; its role in SCI is yet to be defined. Milrinone and dobutamine can be used to promote cardiac output, but their vasodilatory effects make them less than ideal agents for treating hypotension. No individual pressor is considered the gold standard for treating hypotension in the setting of SCI, and each case should be considered individually (Ploumis et al., 2010).

Respiratory Management in the Intensive Care Unit Setting

Respiratory derangements in SCI patients depend on the extent and level of injury. The innervation of the diaphragm from the phrenic nerve is supplied by C3, C4, and C5. Injuries at or above the C2 level require immediate ventilatory support. Patients with injuries between C3 and C5 may need initial ventilatory support, but as inflammation subsides in the cord, they may regain ventilatory strength and have effective recruitment of accessory muscles. Age and preexisting comorbidities can greatly affect outcomes. Patients can still require ventilatory support with injuries below C5. There is a restrictive respiratory pattern encountered in SCI patients that can result from immobilization or additional physical injuries in the trauma patient such as contusion, pneumothorax, hemothorax, and flail chest; all these can lead to additional compromise. One study has shown a decrease in functional vital capacity (FVC) and expiratory flow rate immediately after injury (Ledsome and Sharp, 1981). Patients with FVC less than 25% had a greater chance of requiring ventilatory support. The authors attributed hypoxemia (Pao₂ <80 mm Hg) to a ventilation/perfusion mismatch. They found supplemental oxygen to be beneficial in treating hypoxemia. Other challenges of the restrictive respiratory patterns associated with SCI are decreased compliance, increased effort in breathing, and difficulties in clearing secretions and producing an effective cough. Thus, additional complications such as retained secretions, atelectasis, and pneumonia occur. Complicating factors in the treatment of respiratory problems stem from pulmonary and fat emboli, which can contribute to poor respiratory function.

In acute SCI patients, atelectasis is the most common respiratory-related complication. It can progress to significant pneumonia and respiratory failure. Certain measures can prevent and treat atelectasis: intermittent positive-pressure breathing (IPPB), inflation by inflating bags, or the incorporation of sighs into mechanical ventilation settings. Bronchospasm can result from autonomic changes in acute injury. They are typically seen in the face if IPPB especially in asthmatics and bronchodilator use should be encouraged. Ipratropium has been shown to increase FVC in about half of patients with tetraplegia. Larger tidal volumes (>20 mL/kg) have been shown to decrease atelectasis. Pulmonary edema can occur from fluid overload; other less common causes include cardiogenic failure and pulmonary sources such as acute respiratory distress syndrome, infection, and trauma. Less obvious causes may be excessive antidiuretic hormone secretion or autonomic changes that exacerbate pulmonary edema. Secretions in the acute periods are usually excessive and have a different chemical content, suggesting a neuronal influence. The increase in secretions can be noted as early as the first hour. Mucus plugs can form in conjunction with decreased cough and bronchospasm. Aggressive measures taken by the respiratory therapist have been shown to decrease the incidence of pneumonia and bronchoscopy use in the acute period. Some clinicians have even advocated early fiberoptic bronchoscopy and bronchial lavage to promote clearance of secretions (McMichan et al.,1980). Warm air, bronchodilators, and mucolytics can help improve respiratory status. Intrapulmonary percussive ventilation is a device that delivers high-frequency pulsations to loosen secretions and provide aerosolized medications to the lungs. Manually assisted coughing with a provider or via a device can clear bronchopulmonary secretions. Additional measures include a rotational bed and postural drainage. Although suctioning is widely used and a mainstay of treatment, it can complicate matters by causing hypoxia, hypotension, infection, tracheal mucus drainage, vagus nerve stimulation, and increased mucus production. Its effectiveness can be limited by patient fears and anxieties.

Pneumonia is a common complication related to the use of mechanical ventilation, with a risk of 1% to 3% per day of mechanical ventilation (Ball et al., 2001). The culprits of ventilator-associated pneumonia occurring within the first 4 days are usually Haemophilus influenzae and Staphylococcus pneumoniae. Only when Pseudomonas aeruginosa is suspected should double coverage with antipseudomonal β-lactam agents and aminoglycosides be considered. Prevention of aspiration and monitoring for its effects are essential for optimal care. Patients with diabetes can have preexisting gastric atony. A nasogastric tube is needed to treat an ileus. Patients on tube feeds require monitoring of their gastric residual content after feeding.

Respiratory failure is defined as a Pco₂ over 50 mm Hg or Po₂ less than 50 mm Hg on room air, or the requirement of ventilatory support in the setting of a high cervical injury. It is prevalent in 40% of subjects with C1-C4 injuries, 25% of subjects with C5-C8 injuries, and 9.9% of subjects with thoracic injuries (Jackson and Groomers, 1994). Patients with injuries in the high cervical cord may suffer neurological deterioration in subsequent days as the injury ascends superiorly in the cord. There is no standard protocol in providing ventilatory support to this group of patients, but simple principles can be used. Patients with high cervical injuries will typically need full ventilatory support with controlled mechanical ventilation. SCI patients who are alert and maintain the capacity to initiate respiratory effort may require intubation, especially when FVC decreases to less than 10 to 15 cm³/kg. Patients with low FVC may have difficulties producing an effective cough and compromised bronchial hygiene. They do not require controlled ventilatory settings that promote ventilator dyssynchrony. Instead, they can benefit from pressure support modes to reduce ventilation/perfusion mismatches. Invasive respiratory support can incapacitate an individual’s defense mechanisms. The clearing mechanism of the cilia and the cough reflex become impaired. In addition, speech can be affected. Because of this, it may be beneficial to use noninvasive support. Patients with intact respiratory musculature but with decreased compliance from associated injuries may benefit from noninvasive support such as bilevel positive airway pressure (BiPAP) or continuous positive airway pressure (CPAP).

There is considerable debate over where to place tidal volume for SCI patients. Higher tidal volumes can be used to prevent atelectasis. Typically, tidal volume averages no higher than 6 to 8 mL/kg are used to avoid barotrauma, but one study suggested that tidal volumes as high as 20 mL/kg are needed to avoid atelectasis and prevent prolonged weaning times (Peterson et al., 1997). Regardless, tidal volumes can be increased in a manner to resolve atelectasis on chest x-ray. Peak pressure should never exceed 40 mm Hg.

Patients requiring long-term ventilatory support may need a tracheostomy to avoid subglottic stenosis and sinusitis. Tracheostomy is easier to tolerate, facilitates improved pulmonary hygiene, produces less dead space and less airway resistance, and creates more favorable conditions for weaning. Furthermore, tracheostomy allows for earlier initiation of rehabilitation. The decision to place a tracheostomy should not extend past 1 to 2 weeks. In the event anterior cervical surgery is performed, a time period of 2 weeks between surgery and tracheostomy placement is suggested. Attempts to extubate should not be made prematurely. When there are higher comorbidities such as baseline respiratory disease, acquired pneumonia, complicated ICU care, smoking history, age older than 45, or complete injuries, early tracheostomy placement should be considered.

Medical Management

Secondary injuries that occur in the spinal cord lead to deleterious and unwanted permanent damage. Steroids have been studied extensively as pharmacotherapy to hinder unwanted sequelae. Early animal models suggested benefit in impeding secondary injury, and this has translated into clinical studies in humans to assess steroid efficacy and safety. To date, results from these studies have not led to U.S. Food and Drug Administration (FDA) approval of steroids in the treatment of SCIs. The AANS and CNS have advocated methylprednisolone and GM-1 ganglioside use in SCI subjects as an option but not a standard of care.

There have been at least four prospective randomized trials studying steroid effects, with great controversy in interpretation of the methods and results from these studies. The National Acute Spinal Cord Injury Study (NASCIS) I trial compared two sets of patients receiving methylprednisolone (Bracken et al., 1985). One group received 100 mg of methylprednisolone followed by 25 mg every 6 hours for 10 days. The other arm used doses with 10 times that magnitude. Patients were followed up to 1 year after treatment, and results failed to show any significant difference between the two arms despite lacking a placebo. Following this study, NASCIS II was performed to include three groups: a placebo group, an opiate antagonist group using naloxone, and a methylprednisolone group that received a 30 mg/kg bolus over an hour, followed by 5.4 mg/kg/h for the next 23 hours (Bracken et al., 1990). Patients receiving methylprednisolone before 8 hours after injury were separated from patients receiving treatment after 8 hours following their injury. The authors suggested that patients with acute SCIs treated within 8 hours of the accident benefited from methylprednisolone. Furthermore, they pointed out that patients treated with methylprednisolone after 8 hours did significantly worse than the placebo group. The original author performed an ad hoc subgroup analysis to support his conclusions (Bracken et al., 1992). Although the entire patient sample consisted of 487 patients, this study showed encouraging results from a subgroup of patients receiving treatment within 8 hours of injury. This was not the case for patients receiving treatment 8 hours after injury. Since that time, there have been many critical analyses of the methods, statistical analysis, and scientific interpretation of the study. One of the most critical arguments stems from the lack of functional measures to assess outcome. Independent chart analysis shows that the placebo group treated within 8 hours of injury had similar recovery patterns to the corresponding methylprednisolone group for the first 6 weeks. Afterwards, the recovery plateaued. Most clinicians feel that incomplete injuries that show functional improvement at 6 months continue an ongoing trend of recovery. Chart analysis also showed that the placebo group treated within 8 hours of injury did worse than the group treated with placebo 8 hours after injury. In addition, the placebo group treated after 8 hours from the onset of injury had similar results to the methylprednisolone group treated within 8 hours of the injury. The study lacked any information regarding the timing or type of surgical interventions that were performed for these patients. Statistical tools have been criticized as being excessive, confusing, and difficult to replicate by professional statisticians. Furthermore, data from this study have never been made available for independent review. Only one study has attempted to model the NASCIS II study (Otani et al., 1994). Their results mirrored the NASCIS II data. Although results were published as Class I–level evidence, their methodology was not well reported, and they deviated from classical standards of a prospective randomized double-blinded study. NASCIS III attempted to evaluate the effects of methylprednisolone administered in a 24-hour versus 48-hour setting (Bracken et al., 1997). An added treatment arm received 48 hours of tirilazad, a medication with antioxidant properties. All patients received a bolus of 30 mg/kg followed by 5.4 mg/kg/h for the 24- and 48-hour methylprednisolone groups, or 2.5 mg of tirilazad every 6 hours. The authors noted neurological improvement at the 6-week and 6-month postinjury period for the 48-hour methylprednisolone group if medication was given between 3 and 8 hours post injury. Randomization bias was noted in NASCIS III, and there were no criteria established for a minimal motor deficit needed for participation in the study. Patients who had no motor deficits were included in the study, complicating matters.

Potential side effects related to methylprednisolone use in SCI patients include pulmonary embolism, sepsis, pneumonia, gastrointestinal hemorrhage, and wound infection. Recently, steroids have been demonstrated to increase the risk of major complications (Dimar et al., 2010). Because these side effects are substantial, methylprednisolone is used with reservations today.

GM-1 ganglioside is the only other medication tested through clinical trials. In vitro studies have been promising, showing neuritic sprouting and reduced apoptosis. Clinical trials were performed to test its effects in the clinical setting. A small single-center prospective, randomized, placebo-controlled study showed significant motor improvement at 1 year. A follow-up study with a large multimember prospective, randomized, placebo-controlled study failed to confirm these results. Thus, this agent has not been used in clinical practice but is listed as an option in clinical practice by the AANS and CNS.

Three additional agents considered to have neuroprotective effects were studied prospectively with randomized double-blinded clinical trials. Thyroid releasing hormone (TRH) has been tested in humans for its antagonistic effect on secondary injury mediators. Only one clinical trial tested this hypothesis in humans (Pitts et al., 1995). This study showed a statistically significant improvement for patients with incomplete SCI who received TRH, but the study was limited in statistical power by virtue of its small study size. Gacyclidine is an NMDA receptor antagonist known to compete against glutamate. Studies have not shown a significant benefit for incomplete cervical injuries at 1 year post injury (Tadie et al., 1999). Nimodipine has been studied for its ability to impede calcium-dependent injury in the secondary stages. Despite animal studies showing benefit, human controlled trials failed to show any benefit (Petitjean et al., 1998).

Nutritional Support

The nutritional requirements of acute SCI patients are vastly different from those of trauma patients without SCI. Immediately following an injury, especially in cases of high cervical injury, there is a period of reduced metabolic activity. However, there is a catabolic cascade that occurs. Whereas the resting energy expenditure (REE) of head injury patients may be 140% to 200% of the predicted normal basal energy expenditure (BEE), the REE of SCI patients is approximately 56% to 90% of the predicted normal BEE. Indirect calorimetry has been advocated as a more accurate measure to assess caloric needs of this population. Muscle mass is lost during this period from denervation, promoting a negative nitrogen balance. Achieving nitrogen balance is an unrealistic goal and should not be the objective.

Compromised gastrointestinal and immune integrity alter normal physiology and factor into the timing of initiating a diet. It is generally acceptable to provide early nutritional support to meet caloric requirements, counteract losses of muscle mass, and maintain gastrointestinal and immune integrity. There has also been evidence to refute fears that early feeding leads to increased septic complications (Dvorak et al., 2004), but the clinician should always be cognizant of a paralytic ileus, which can promote aspiration in light of cervical immobilization and swelling.

Nonsurgical Management

Spinal orthoses have been used to apply external forces to the spine to correct or prevent deformity and provide indirect stabilization of the spine while allowing the bone to fuse. Spinal immobilization techniques have been practiced throughout history and have been shown to be effective in achieving bony fusion. Although bracing and bedrest often provide the desired result in the long term, this is not always a practical method of achieving fusion. Medical complications associated with bedrest include pulmonary embolism, hospital-acquired infections, pressure ulcers and skin breakdown, and detrimental psychological effects. Furthermore, bedrest may be financially taxing and require prolonged hospital stays. Bedrest also limits early rehabilitation. For these reasons, in every case, the decision to brace is based on multiple factors and may not be dependent on the types of fractures present. Furthermore, the orthoses chosen must restrict movement, provide spinal realignment, and maintain trunk support. In general, orthoses are worn for a 3-month period to allow proper promotion of bony fusion.

Spinal orthoses of the cervical spine range from soft collars to external splinting techniques such as the halo vest. The cervical soft collar provides negligible resistance to motion and is primarily used as a reminder to patients to limit motion or for comfort by providing support to the cervical musculature. Hard cervical collars (Aspen, Miami J, Philadelphia) take into account the base of the skull, jaw, and shoulder to provide resistance for the cervical spine. Cervicothoracic orthoses (Yale, Somi, 4-poster, Guilford) provide a three-point bending movement as a means to restrict motion in the mid- to low cervical region. They provide added resistance to flexion, extension, and rotation compared to conventional hard collars but inadequate prevention of lateral flexion. They can also be uncomfortable to wear. When cervical collars are worn, they may produce a parallelogram-like bracing effect seen as a ventral and dorsal translation of the head. Halo bracing is still considered the most effective method of restricting motion (flexion/extension, lateral bending, and rotation) in the cervical spine. They reduce the parallelogram-like bracing effects at the expense of a snaking effect. The snaking effect is demonstrated with segmental movement in each single cervical level but with minimal overall movement between the occiput and lower cervical spine. The Minerva jacket is fitted by an orthotics expert and provides contact support through a thermoplastic shell, which is fitted around with a circumferential headband extending down to the thorax. These devices are known for minimizing the snaking effect but have the disadvantage of being in direct contact with the skin and causing skin breakdown, discomfort, warmth, and limited mobility of jaw movements. The halo device lacks direct contact with skin and soft tissue, leading to less skin breakdown. It also allows the jaw to be free so that easier speaking and eating may occur. Halo devices are associated with pin-site infection and require tightening of pins.

Thoracolumbosacral orthoses are useful for compression fractures and nonoperative burst fractures; they mainly target fractures between T10 and L2. In principle, they apply a three-point fixation. The Jewitt device uses one posterior pad on the midthoracic region and two anterior pads on the sternum and pubic symphysis. This device is useful in limiting flexion and extension motion but ineffective in limiting rotation and lateral bending. Since sternal fixation is the most cephalad region of support for this brace, the amount of segmental motion above T6 can be increased. Thus, the Jewitt brace is contraindicated for fractures superior to T6. Custom-molded clamshell thermoplastic devices provide the added benefit of limiting lateral bending and rotation and distributing pressure over a wider surface area. They can be used for fractures extending from T3 to L3. Lumbosacral orthoses have been used to treat fractures distal to this region and are less effective. Their use is controversial, since their effectiveness is limited by the inadequate effective fixation of the pelvis to manage low fractures. Lengthening the brace downward toward the inguinal region or distal to the iliac crest can prevent an individual from sitting. As a result, some lumbosacral orthoses include a hip spica cast to provide partial compensation of movement.

Closed reduction has been used to provide spinal realignment in the setting of facet fracture, jumped facets, subluxation, or spinal deformity as a primary means of realignment before open reduction is attempted. Successful reduction of jumped facets can be safely done. It has been shown that patients who undergo successful closed reduction can have better outcomes than those patients requiring surgery (Papadopoulos et al., 2002). Patients must be awake and cooperative and provide a reliable neurological exam. Traction is performed with the patient in supine position. The head is placed in Gardner Wells tongs or a halo ring attached to a set of weights by a rope suspended off the side of the bed via a pulley mechanism. A distracting force is applied with added weights. The initial weight for traction is usually 3 lbs multiplied to the level of injury in the cervical spine. Weight is added in 5- to 10-lb increments, spinal alignment is checked with fluoroscopy, and a neurological exam is performed at 10- to 15-minute intervals. In general, there is no defined upper limit of traction that should be applied. Subjective pain and neurological deficit should discourage any further traction. Furthermore, if the weight applied shifts the patient in bed, traction should be halted. Once spinal realignment is achieved, the patient may either be locked into the halo vest or taken to the operating room in traction, where surgical stabilization can be achieved.

Surgical Management

Indications for surgery include decompression, stabilization, and correction of deformity. In a general sense, White and Panjabi define spinal stability as the “ability of the spine under physiological loads to limit patterns of displacement so as not to damage or irritate the spinal cord or nerve roots and, in addition, to prevent incapacitating deformity or pain due to structural changes” (White and Panjabi, 1990). The initial radiographic workup may suggest spinal instability, but more often, clinical judgment based on history and physical examination in conjunction with follow-up imaging can help establish a more definitive diagnosis of spinal instability. For acute fractures and dislocations, the timing of events in relation to the presentation and the completeness of the injury should be noted. Traditionally, complete injuries (ASIA A) were typically treated with the goal of surgical stabilization; there is definitely a stronger argument for early decompression for incomplete versus complete injuries. Prospective randomized trials done with animals show neurological improvement with early surgical decompression for SCI (Rabinowitz RS et al., 2008). Initial prospective randomized trials suggest that patients undergoing early surgical decompression (<72 hours post injury) do not fare better than patients undergoing late decompression (>5 days post injury) (Vaccaro et al., 1997). The benefit from surgical decompression is likely to be greater if done sooner than the 72-hour time window. In a systemic review of the literature, early decompression was found to have better neurological outcomes than late decompression if done within 24 hours of the injury (La Rosa et al., 2004). Surgery in the early period has been shown to be safe when there are stable hemodynamic parameters with monitoring and expert surgical and anesthesia staff are present (Fehlings and Perrin, 2006). Early results from the Surgical Treatment for Acute Spinal Cord Injury Study (STASCI) suggested improved neurological outcome for early decompression done within 24 hours post injury (Fehlings et al., 2008). Although traumatic central cord injuries are included in the STASCI study, the timing of surgery in traumatic central cord syndrome may be more controversial. Cervical pathology contributing to traumatic central cord syndrome are divided into one of three categories: (1) cervical spondylosis in the setting of segmental spinal stenosis or anterior pathology from disk/osteophyte complex; (2) fracture subluxations, and (3) disk sequestration with no evidence of spinal stenosis. Favorable results in motor recovery and cost effectiveness have been recorded for decompression of disk herniation and fractures causing central cord syndrome (Guest et al., 2002). A recent study showed no difference in outcome for patients with acute traumatic central cord syndrome treated with surgical decompression when comparing the timing of surgery, the surgical approach, or the type of cervical pathology (Chen et al., 2009). Currently, prospective randomized trials are underway to assess whether patients undergoing early decompression (<5 days) fare better than patients undergoing late decompression for traumatic central cord syndrome.

The decision to operate is based on the type of injury, timing of presentation, completeness of the injury, medical comorbidities, and other traumatic injuries that may prevent early decompression. There is questionable benefit for surgical decompression performed for complete injuries presenting within 24 hours. Urgent surgical decompression should be offered to patients with incomplete injuries presenting within a 24-hour period post injury. Bilateral jumped facets causing incomplete injury and injuries associated with progressive neurological deterioration warrant a more aggressive approach to surgery.

Recently the Spine Study Trauma Group attempted to provide a standard protocol to guide physicians in treating thoracolumbar fractures. As a result, the Thoracolumbar Injury Severity Score (TLISS) and Thoracolumbar Injury Classification and Severity Score (TLICS) were introduced (Tables 50C.4 and 50C.5). The TLISS is an algorithm that assigns a score based on mechanism of injury, posterior ligamentous injury, and neurological deficits (Vaccaro et al., 2005). There was concern that substantial variability existed among observers as they attempted to postulate the mechanisms of injury and assign an additive score for this category. The TLICS was then created to focused on fracture morphology (Lee et al., 2005). Insofar as the reliability of these two systems is untested and has never been clinically validated, clinicians should not rely solely on the TLICS and TLISS algorithms to guide their decision making.

Table 50C.4 Thoracolumbar Injury Severity Score

Table 50C.5 Thoracolumbar Injury Classification and Severity Score

Patients with compression fractures of the thoracolumbar spine not requiring open surgical intervention may qualify for vertebral augmentation procedures. Vertebroplasty is a percutaneous procedure that uses a specially formulated acrylic bone cement injected into a fractured vertebra to provide stabilization. Kyphoplasty is a procedure that uses an inflatable percutaneous balloon to restore height and reduce complications from cement leakage. There is a theoretical restoration of vertebral body height and reduction of kyphotic deformity with this procedure. In general, patients qualifying for vertebroplasty must have acute or subacute fractures and no posterior vertebral body breech. Two recent prospective randomized trials failed to show any improvement of pain with vertebroplasty (Buchbinder et al., 2009; Kallmes et al., 2009). Although kyphoplasty has been shown to reduce local kyphotic deformity, there does not seem to be a positive effect seen on a global scale (Korovessis et al., 2008; Pradhan et al., 2006).

Spinal Cord Injury and Bladder Function

The bladder maintains storage and release of urine through influences from the central nervous system. In the past, renal failure has been a leading cause of death in the SCI patient. With improved management of urological dysfunction in SCI patients, mortality has been greatly reduced. Specific objectives for a bladder management program entail efficient storage and emptying while maintaining low pressures and preventing overdistention of the bladder. These measures can prevent complications from high intravesicular pressure. It is to the patient’s benefit to maintain a bladder regimen that allows them to integrate into society. Urinary tract infections (UTIs) should be prevented.

Understanding the physiology and anatomy of the lower urinary tract is important to recognize available treatment options. Peripheral innervation of the bladder can de divided into autonomic and somatic pathways. Parasympathetic pathways excite the smooth muscle of the bladder and inhibit firing to the urethral sphincter smooth muscle. Cholinergic neurons rising from the intermediolateral region at S2 through S4 stimulate the bladder wall via the pelvic nerves. The urethral sphincter is relaxed by means of nitric oxide release. Hypogastric nerves carry sympathetic fibers supplied by the thoracolumbar region (T10-L2) and prevertebral inferior mesenteric ganglia. Noradrenaline acts on β-adrenergic receptors of the bladder wall, causing an inhibitory effect. Sympathetic modulation of the bladder neck and urethra is excitatory and works via α₁– and α₂-adrenergic receptors. Somatic fibers originate in the Onuf nucleus in the anterolateral horn of the spinal cord at S2-S3 and provide excitatory signals to the urethral sphincter. Fibers traveling through the pudendal nerves release acetylcholine which acts on nicotinic receptors. Afferent signals travel back via the pelvic nerves. They are composed of Aδ and C fibers. Aδ fibers respond to stretch, and C fibers respond to noxious stimuli and inflammatory elements. Afferent signals travel to the pontine micturition center (PMC), periaqueductal gray matter, or ventral posterior nucleus of the thalamus and eventually reach the cerebral cortex. Additional regions that exert influence on lower urinary tract control include the medullary raphe nuclei, the locus coeruleus, the paraventricular nucleus of the hypothalamus, and the anterior hypothalamus. Efferent signals originate from suprapontine regions such as the frontal cortex and periaqueductal gray matter. They project to the PMC, which regulates reflex micturition via somatic, sympathetic, or parasympathetic pathways. When the bladder fills, a negative feedback mechanism is in place to promote storage of urine. However, once the bladder pressure meets a certain threshold, a supraspinal inhibitory response supersedes, causing micturition to take place. The inhibitory response is derived from the PMC.

In SCIs, neurogenic bladders are classified according to the location of the lesion. A lower motor neuron lesion is localized below the conus medullaris. In this situation, the bladder detrusor is areflexic or hyporeflexic but maintains a normal or underactive external sphincter. With this type of injury, there is still coordination between the bladder detrusor and the sphincter. Additional characteristics depend on the extent of involvement of the peripheral fibers and whether there is predominance of afferent or efferent fibers. With peripheral fiber loss, an absent sacral reflex (bulbocavernosus and cremasteric reflexes) may be observed. A purely motor neurogenic bladder will have preserved sensation. With afferent loss, there is impaired emptying consequent to diminished or absent sensation, and this can lead to chronic overdistention. Findings on urodynamic studies would reveal a low bladder pressure, absent electromyographic (EMG) activity, and altered functional bladder outlet mechanisms (Fig. 50C.9, A). As a result, a high postvoid residual would be expected. In upper motor neuron lesions, the sacral arc is preserved, but pontine modulation is disrupted. There is incoordination between the detrusor and sphincter, which is known as detrusor–external sphincter dyssynergia (DESD; Table 50C.6). With a preserved sacral reflex, there is urinary incontinence from reflexic contraction of the bladder when filling occurs and meets a certain threshold. Detrusor overactivity can been seen in suprasacral spinal lesion. When coupled with DESD, high intravesicular pressures result. As a result, urodynamic studies will confirm a baseline spontaneous activity of the bladder as well as simultaneous firing of the detrusor and external sphincter (see Fig. 50C.9, B). High intravesicular pressure and postvoid residuals occur from this abnormal activity. A highly compliant bladder, seen in lower motor injuries, can lead to overdistention injuries and require clean intermittent catheterization (CIC) to counteract the unwanted phenomenon. However, with a poorly compliant bladder, high pressures can lead to injuries in the upper urinary tract. A detrusor leak-point pressure (DLPP) determined from urodynamic studies will indicate the pressure at which leakage occurs in the bladder. This value is typically 40 cm H₂O. Vesicoureteral reflux from high DLPP can also complicate matters by causing UTI, pyelonephritis, or ischemic injuries. Chronically, this can lead to renal scarring.

Fig. 50C.9 Urodynamic studies of a neurogenic bladder. A, Atonic neurogenic bladder occurs from lower motor neuron injuries. B, Detrusor sphincter dyssynergia occurs from upper motor neuron injuries. C, Normal bladder.

Table 50C.6 Differences between Atonic Bladder and Detrusor External Sphincter Dyssynergia (DESD)

Helpful diagnostic studies include baseline urinalysis and creatinine test. The upper urinary tract should be assessed for structural stability. This includes renal ultrasound or radiography to look for hydronephrosis, renal stones, or tumor. CT is the most sensitive means to evaluate renal stones. A voiding cystogram can assess for vesicoureteral reflux, bladder hypertrophy, and bladder diverticula. A dimercaptosuccinic acid renogram can provide functional information. Cystoscopy can lead to direct visualization for determining causes of hematuria and irritation. In the long term, it is useful to evaluate bladder cancer and treat kidney stones. Baseline urodynamic studies should be obtained at 6 weeks post injury or when urinary incontinence occurs.

In the hospital setting, spinal shock will predominate and will manifest as an areflexic, acontractile bladder usually lasting 6 to 12 weeks, but it can last up to 12 months. During this time, Foley catheterization or CIC is used to maintain integrity of the urinary system. CIC should be performed every 4 hours to keep volumes in the bladder less than 500 mL. For long-term management, intermittent catheterization is the preferred method to drain the bladder, owing to the high complication rates from long-term use of indwelling catheters, which include infection, cancer, renal stones, alterations in bladder compliance, strictures, and diverticula. Indwelling catheters may be a reasonable option for patients who lack motivation or have limited hand function and are unable to receive adequate care by the caregiver. Lower motor neuron injuries may be treated by physical measures such as the Valsalva or the Credé maneuvers. The Valsalva maneuver increases intraabdominal pressure, whereas the Credé maneuver applies manual direct pressure to the suprapubic area. Reflex voiding involves suprapubic tapping as a method to stimulate the sacral reflux arc in supraspinal lesions to facilitate voiding. However, this is used in conjunction with transurethral sphincterotomy to allow bladder drainage at low pressures in order to avoid upper tract injuries.

Currently, the medications used to inhibit bladder overactivity include anticholinergics (oxybutynin, tolterodine), tricyclic antidepressants (TCAs, e.g., imipramine), and antispasmodic medications (baclofen, tizanidine). Intravesicular therapy with botulinum toxin A has been used and avoids the undesirable side effects associated with systemic pharmacological agents. The effects of botulinum A can last for 16 to 36 weeks to prevent bladder overactivity, lower bladder pressures, and alter maximum bladder capacity. This agent can also be used in the external sphincter.

A variety of surgical options exist when primary bladder management methods fail. Electrical stimulation of the sacral roots (S2-S4) promotes bladder contraction. Selective posterior sacral root rhizotomy can suppress hyperreflexic detrusor activity. Augmentation enterocystoplasty is a bladder augmentation procedure known to increase total bladder capacity by using the bowel to augment the bladder. Complications known to arise from this procedure include changes in bowel habits and metabolic derangements. An alternative method to accomplish augmentation entails detrusor myomectomy caused by the formation of a diverticula by weakening the muscle from an excision in the submucosa. Considerations for this procedure are made for patients with intractable detrusor hyperactivity, a lack of motivation for self-catheterization, a desire to convert from reflux voiding to self-catheterization, or high risk for developing upper urinary tract complications. Cutaneous conduits and urinary diversion have been used for detrusor overactivity. They provide external drainage of urine through the abdominal wall to an external collecting device. This is accomplished by connecting the ureters to an intestinal segment which is externalized. The ileal conduit does not serve as a storage reservoir, and there is no metabolic derangement, since there is only transient exposure of urine to the absorptive surface. Continent urinary diversions contain a reservoir that is attached to the urethra instead of the bladder or can be accessed through an abdominal stoma which is catheterized. Metabolic derangements can occur with prolonged contact of urine with the surface of the bowel. These procedures are useful for females and patients with structural abnormalities of the urethra or bladder, bladder cancer, and incontinence that prevents proper care of perineal decubiti. In general, females have more technical difficulties with intermittent catheterization and have no external incontinence device like the male condom catheter. They also experience urethral erosion from catheterization. Transurethral sphincterotomy is the preferred surgical method in patients with DESD refractory to anticholinergic medications. It is typically used for a male with quadriplegia or a high thoracic injury effecting hand function. Females are unable to have an external drainage device and thus do not qualify for this procedure.

Complications resulting from a neurogenic bladder are significantly lower with encouragement of CIC. Although symptomatic UTI should be treated, routine urine cultures are typically not warranted. Asymptomatic bacteruria is generally not an indication for treatment except in the case of urease-producing pathogens such as Proteus, Pseudomonas, or Klebsiella. Overall, there is a high incidence of renal stones for SCI patients, but urease-producing bacteria place patients at higher risk for developing stones. Acetohydroxamic acid can reduce the incidence of stone formation. Vesicoureteral reflux is a common complication that results from low bladder compliance and high intravesicular pressure, leading to upper urinary tract deterioration. This will eventually lead to a greater risk of infection, kidney stones, and renal failure. As discussed previously, upper urinary tract deterioration is typically treated conservatively but may require ureteral reimplantation. There is a higher frequency of bladder cancer occurring in this population, reported to be between 2% and 10%. The culprit is usually squamous cell carcinoma, but transitional cell carcinoma can occur. Squamous cell carcinoma is very aggressive and carries a poor prognosis. On presentation, it is typically found to be already metastatic. These patients typically present with hematuria and recurrent UTIs. Chronic indwelling catheters have been noted to be risk factors, so if long-standing indwelling catheter use is part of management, cystoscopy should be used as a screening measure.

Spinal Cord Injury and Bowel Function

Bowel dysfunction in SCI can lead not only to the inconvenience and embarrassment of fecal incontinence but also to significant physical distress. Common symptoms noted in these patients include ileus, gastric ulcers, GERD, volvulus, stercoral perforation, dyspnea, worsening spasticity, autonomic dysreflexia, constipation, diarrhea, nausea, pain, distention, hemorrhoids, loss of appetite, impaction, fecal incontinence, and delayed and unanticipated evacuation. Despite defecation occurring in SCI patients, more energy and time are required, and this can be both physically and emotionally taxing; assistance is often needed in half of this population. Manual stimulation and manual disimpaction are required in a great majority of patients. Not surprisingly, higher-level injury, complete injury, and nonambulatory states correlate with toilet dependency. To appreciate the pathophysiology that takes place in an SCI patient, it is important to understand the normal anatomy.

The boundaries of the colon are the ileocecal valve proximally and the anal sphincter distally. The internal anal sphincter (IAS) is composed of a layer of smooth muscle in continuity with the rectum. It is involved in maintaining continence of liquids and gas. The external anal sphincter (EAS) is continuous with the pelvic floor and consists of a circumferential band of striated muscle. It maintains continence of solids. The puborectalis muscle is attached to the pubic bones and tethers the rectum, providing a kink in the rectum when it contracts. These three muscles provide continence of the colorectal system. The IAS is in a resting state of contractions. During a Valsalva or cough, the EAS and puborectalis muscle contract to prevent incontinence. The nervous system is composed of an intrinsic and extrinsic nervous system. The intrinsic nervous system is composed of the Auerbach plexus, lying between the longitudinal and circular muscle layers; this system provides coordinated motility. The extrinsic nervous system provides influences from the parasympathetic, sympathetic, and somatic nerves. Parasympathetic innervation of the gastrointestinal system from the esophagus to the splenic flexure is supplied by the vagus nerve. From the descending colon to the rectum, the pelvic nerve provides parasympathetic innervation. Sympathetic innervation is derived from the superior and inferior mesenteric and hypogastric nerves. Somatic innervation from the pudendal nerve provides control of the pelvic floor. As stool advances in the rectum, distention is noted, leading to relaxation of the IAS. Voluntary contraction of the EAS prevents incontinence. When stool is involuntarily advanced into the rectum, defecation secondary to relaxation of the EAS and puborectalis muscle occurs.

Motility is dependent on three mechanisms in the colon: neurogenic, myogenic, and chemical. The small and large intestine are largely autonomous, with a minor influence from the central nervous system or autonomic nervous system. Enteric smooth-muscle cells have interconnected gap junctions allowing transmission of signals. Furthermore, intestinal muscle inherently possesses autorhythmicity that causes the colonic wall to contract. Chemical influences through neurotransmitters and hormones act on the central nervous system, autonomic nervous system, or directly on muscle cells. In response to a meal, the gastrocolonic reflex promotes colonic motility.

Following SCI, there is a disruption of the extrinsic influences of the nervous system on the bowel. Initial studies evaluating bowel dysfunction in SCI patients showed decreased compliance and deficient postprandial motor and myoelectrical response in the colon (Glick et al., 1984). The term neurogenic bladder evolved to account for either a lower motor neuron (LMN) bowel syndrome producing areflexia or an upper motor neuron (UMN) syndrome producing hyperreflexia (Stiens et al., 1997). The LMN syndrome results from injury of the conus medullaris, cauda equina, or pelvic nerves, with decreased influence from the parasympathetic system. Thus, this injury pattern produces peristalsis leading to slow stool movement and constipation. Furthermore, a denervated EAS leads to fecal incontinence. A lesion proximal to the conus medullaris results in UMN bowel syndrome or hyperreflexic bowel, and this in turn leads to increased tone in the colonic wall, anus, and EAS. Reflex coordination and stool propulsion remain preserved from intact connections between the spinal cord and colon. Thus, with a tight EAS present, constipation predominates. Recently, this theory of UMN and LMN syndromes was tested as researchers characterized the motility of the bowel in more detail. Resting motility of the colon was present in lower levels of contractility than in normal subjects that was independent of the level or completeness of injury (Fajardo et al., 2003). Furthermore, a postprandial motor response was confined to the descending colon in SCI patients with lower levels of contractility than in normal subjects. Despite the efforts of research, there continues to be a great void in our understanding of the pathophysiological basis of bowel dysfunction in SCI patients.

A bowel management program in SCI patients involves diet modifications, monitoring adequate fluid intake, management of medications, and physical means to stimulate or promote defecation. Therapy should target satisfying the specific objectives of each individual. A few important principles are kept in mind when developing an individualized bowel management program. The goal of therapy is a well-formed fecal mass with appropriate volume and consistency. A regular elimination pattern is also preferred. The bowels should initiate propulsive motility when needed. If the bowel is able to achieve adequate filling, evacuation of stool should be spontaneous. Complete evacuation of stool contents should be the goal.

The methods to treat constipation in this population are difficult, since the pathophysiological mechanisms are not well defined. Physical measures include manual disimpaction and anorectal stimulation. In terms of diet, a well-balanced meal should consist of a wide variety of ingredients and good proportions of carbohydrates, proteins, and fats. The use of laxatives should be limited. Fiber and probiotic supplements should be used to enhance stool consistency. Scheduled emptying and deposition of suppositories will also lead to a regular frequency of evacuation. If these methods do not work, then medications are supplemented to the existing regimen. This includes macrogol, high doses of psyllium, prokinetics, digestive enzymes, and many other agents combined to provide a customized treatment for each individual. Transanal irrigation can be used if medications are not effective. Randomized trials comparing this intervention to other traditional conservative bowel management programs showed transanal irrigation to be beneficial in reducing constipation, reducing fecal incontinence, and improving quality of life (Christensen et al., 2006). When conservative measures fail, an enterostomy should be considered. Presently, two other surgical interventions are gaining attention and have been noted to improve bowel function in the SCI population: the sacral anterior root stimulator and the Malone anterograde continence enema (MACE).

Posttraumatic Syringomyelia

Syringomyelia is found in 21% to 28% of SCI patients (Brodbelt and Stoodley, 2003). Cystic changes are found in approximately 30% to 50% of all SCI patients. There have been many proposed mechanisms but no unified theory behind the formation of the initial cystic structure. The formation has largely been attributed to hematomyelia, inflammatory responses leading to edema in the cord, ischemia, or arachnoiditis. Enlargement, on the other hand, is generally thought to be due to changes in the compliance of the subarachnoid space or from spinal stenosis, arachnoid adhesions, or persistent cord compression impairing CSF circulation. Correlations exist between the presence of uncorrected kyphosis and stenosis and severity of symptoms. The cystic cavity, acting as a one-way valve, creates imbalance of CSF flow into the cavity. The proposed “slosh mechanism” attributes the growing collections to be secondary to the influences of respirations and blood pressure on CSF pressure.

Although present in a significant portion of SCI patients, only 3% to 4% of these patients suffer from symptoms related to syringomyelia. Symptoms of the syrinx can occur from 3 to 34 months following injury. Injury to the spinothalamic tracts leads to pain and a dull, aching, or burning sensation at or above the level of injury. There may also be a dissociated sensory loss (loss of pain and temperature sensation without loss of light touch or proprioception). Measures that increase intraabdominal pressure such as sneezing, coughing, or straining can increase the pain. Positional changes such as sitting can also increase pain. The intensity of pain is highly variable. Since a syrinx is typically unilateral, asymmetrical dysreflexia and ascending weakness may appear. Hyperhidrosis, autonomic dysreflexia, Horner syndrome, dysphagia, cardiopulmonary dysfunction, and bulbar signs and symptoms can present. Following an injury, spasticity can be more severe in those patients with syrinx. Although the condition is progressive in most patients, some may have stable or resolving symptoms and radiographic appearance of the syrinx.

CT in conjunction with myelogram have been helpful in the past to diagnosis subarachnoid adhesions, but modern-day imaging with MRI is more reliable in picking up the diagnosis. MRI is also helpful in showing that a syrinx can be multiple, asymmetrical, or loculated. Calculating its size and the percentage of involvement in an axial view can further help define a clear prognosis. Edema seen on MRI can portray future expansion. Newer technologies such as cine MRI may be helpful in localizing the obstruction or tethering or show communicating segments that may be helpful in planning a surgery.

While this problem is easy to diagnose with modern imaging, it is difficult to treat. Currently, 80% of patients who undergo a form of surgical intervention to treat their syrinx will have persistent or deteriorating findings on follow-up imaging. Modern-day therapies focus on one of four surgical options: shunting procedures, lysis of adhesions, correction of deformity or decompression, and cord transsection. Correction of deformity or decompression is usually the preferable option, with good results in reducing the size of the syrinx. The timing of surgery is controversial. Surgery is typically performed on those patients who are deteriorating neurologically or have increasing pain. Some clinicians believe that a symptomatic posttraumatic syrinx should be treated once it is diagnosed, since symptoms are often irreversible. Arachnolysis and duraplasty is another option that is preferable over shunting and serves to untether and decompress the spinal cord. Arachnoid adhesions prevent flow of CSF from occurring in the subarachnoid space. Surgery is focused on leaving the arachnoid intact while removing arachnoid scarring. The majority of cases will have a small rim of arachnoid scarring left. Caution should be exercised to prevent blood products from entering the cord. Artificial dural substrate is preferred to prevent scarring as well. Aspiration of a syrinx cavity in a posttraumatic patient is not recommended. Shunt, though a viable option, produces mixed results. Shunting should be reserved for situations in which patients fail arachnolysis and duraplasty or where tethering is not found. Syringoperitoneal or syringopleural shunts are commonly placed, though syringosubarachnoid shunts are becoming more common. Subarachnoid-to-peritoneal shunts have been used but with no evidence to support benefits. The shunt is typically placed on the caudal portion of the syrinx in a cranial trajectory, with the entry into the dorsal root entry zone or the posterior median sulcus to minimize spinal cord damage. Ultrasonography may be useful intraoperatively to locate the syrinx. For syringosubarachnoid shunts, the distal end must not be placed in a region occupied by arachnoiditis. Shunt failure rates are high; roughly half report failure. Myelotomies, cord transsections, and percutaneous aspirations provide no long-term solution. Recently there has been promise in fetal neural tissue implantation.

Medical therapies are aimed at treating the symptoms. Antispasmodic agents can be used when spasticity creates significant pain, functional disability, or interferes with quality of life. TCAs (amitriptyline) and anticonvulsants (gabapentin) help with the neuropathic pain. Anticholinergics can reduce excessive secretions and sweating.

Neuropathic Pain

Neuropathic pain from SCI can be disabling. It can affect quality of life by limiting sleep and activities of daily living and causing functional disability. Furthermore, the prognosis for a resolution of the pain syndrome is poor. It is estimated that 65% to 85% of those suffering from SCI will suffer from neuropathic pain and that a third of these patients will suffer from severe pain (Siddall et al., 2003). The discrepancy in estimates appears to be related to the nonuniform nomenclature used in the literature. Only recently has the International Association for the Study of Pain (IASP) established a Spinal Injury Pain Task Force. In general, four types of pain are considered. Pain is divided into visceral and musculoskeletal, as well as two major neuropathic categories. Musculoskeletal pain is often related to mechanical instability of the spine or muscle spasm. The first type of neuropathic pain deals with a dermatomal pattern at the level of the injury, and the second type is more diffuse and occurs below the level of the injury. To date, only one prospective study shows that at 5 years after the injury, 41% of study participants had at-level neuropathic pain, and 34% had below-level neuropathic pain (Siddall et al., 2003). There appears to be no correlation between completeness or level of injury and the development of postoperative pain.

The mechanism behind the development of pain is unclear. Traditional efforts to understand the cause of neuropathic pain have focused on the region in close proximity to the level of injury. However, contemporary views suggest that more “downstream” or “upstream” changes occur in the nerve roots or the brain. When incomplete injuries occur, transmission of nociceptive impulses can theoretically still occur through various residual pathways. Even in complete injuries, residual sensory pathways exist that may not be evaluated with standard physical examination and may serve as these residual pathways. Studies have shown that injections of local anesthetic at the rostral end of the injuries can bring pain relief (Davis et al., 1954; Pollock et al., 1951). More recent investigations have shown an increased sensitivity of nerve cells close to the level of injury. These nerve cells have a higher amount of background activity, greater amount of responsiveness to stimuli, and a longer duration of firing. Additional changes are suggested to occur at the molecular level and include changes to the level and function of neurotransmitters and their receptors. Glial activation occurs following injury, leading to increased secretion of prostaglandins and various cytokines. Structural changes are known to occur, with restructuring of connections in the dorsal horn. More recent work has focused on thalamocortical dysrhythmia and the plasticity and reorganizational changes that occur in the brain.

The methods of treating neuropathic pain are broad, but principles center around treating the underlying causes of pain. If this is not possible, treatment should focus on palliative measures. Symptomatic treatment is necessary for at-level and below-level neuropathic pain. Surgical options should always focus first on decompressing nervous tissue, untethering the spinal cord, or dealing with a syrinx formation. If these measures do not provide a satisfactory remedy to the pain, then disconnecting the site of abnormal activity is the next appropriate step. Lesions in the dorsal root entry zone can be used to destroy an area of hyperactive nerve cells in the dorsal horn cells in close proximity to the level of the injury. Most studies suggest that 50% to 85% of patients have a good amount of relief of pain from this procedure (Siddall, 2009). Electrophysiological techniques such as intramedullary recording of C-fiber evoked electrical hyperactivity may aide in targeting the lesion. Finally, some patients may benefit from cordotomy or cordomyelotomy.

Pharmacological agents are at best a modest means of controlling pain. Only a third of patients have 50% pain reduction. Local and parenteral administration of lidocaine has been shown to be beneficial in treating neuropathic pain, but local administration is generally not long-lasting, and parenteral administration is typically impractical. NMDA antagonists such as ketamine work by reducing excitability, but ketamine, like lidocaine, confers no long-term relief and is not administered orally. Opioids, antiepileptics, and antidepressants increase inhibitory signals and limit excitability of neurons transmitting pain signals. Two randomized controlled studies show improvement of neuropathic pain following administration of parenteral morphine (Attal et al., 2002) and alfentanil (Elde et al., 1995). The evidence for using oral and transdermal varieties of narcotics is limited. Current recommendations for pharmacological treatment are directed at symptomatic relief and include first-line agents such as systemic lidocaine, gabapentin, and pregabalin. Although a recent randomized study failed to show benefit from the use of gabapentin in treating neuropathic pain (Rintala et al., 2007), pregabalin has been shown to be of benefit (Vraken et al., 2008). Other new agents that may be considered include lamotrigine and topiramate; topiramate in particular has had encouraging results (Harden et al., 2002). Second-line agents include TCAs, alone or in combination with antiepileptics. TCAs have been shown to have benefit in a subgroup of patients with depression. Both valproate and carbamazepine have been used to treat this condition as well. Third-line treatment options include ketamine, opioids, intrathecal baclofen and morphine, selective serotonin reuptake inhibitors (SSRIs), clonidine, or other antiepileptics. SSRIs are not proven to work. In patients with localized symptoms, topical lidocaine therapy may provide relief. Intrathecal medications have shown some promise. Intrathecal morphine and clonidine has provided short-term pain relief by acting on the opioid receptors of the dorsal horn of the spinal cord. Although intrathecal baclofen works well to treat spasticity, its role in neuropathic pain is still to be determined. A variety of neurostimulation modalities have been used but without good data proving efficacy. These include transcutaneous electrical nerve stimulation (TENS) and acupuncture, which have been shown to help with below-level neuropathic pain (Norrbrink, 2009). Spinal cord stimulators have been shown to be beneficial for at-level neuropathic pain and incomplete injuries (Ciono et al., 1995). Deep brain stimulators do not show good long-term results (Finnerup et al., 2001), while transcranial and epidural stimulation have mixed results (Nguyen et al., 1999).

Spasticity

Spasticity has been shown to affect more than 80% of SCI patients (Levi et al., 1995). It typically takes several months after the injury for symptoms to become obvious. The initial signs of spasticity include some early reflexes such as tendon reflex, flexor withdrawal reflex, and a Babinski sign. Over time, the threshold to bring about a reflex response decreases, so that even ephemeral stimuli can produce long-lasting flexor contraction. Extensor reflexes present later and co-contraction of combined flexor/extensor response becomes prominent. Spasms triggered by bladder distention or heat/cold sensations can cause severe pain and create enough intensity to expel an individual from their wheelchair. The symptoms of spasticity are debilitating and lead to a reduced quality of life by limiting activities of daily living, effecting sleep, causing pain, predisposing to unnecessary decubitus ulcers, infections, and contractures, creating a burden on caregivers, and limiting rehabilitation efforts. Although there are multiple definitions for spasticity, its characteristics were best expressed by Lance in 1980. He states that spasticity “is a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, as one component of the upper motor neuron syndrome” (Lance, 1980). To understand spasticity, it is necessary to understand the physiology behind motor activity. The afferent pathways rely on type Ia (muscle spindles) and type II (secondary spindle endings) fibers. Type Ia fibers synapse directly with alpha motor neurons or with interneurons. Type II synapse with interneurons of the ventral horn of the spinal cord. Interneurons receiving signals from afferent fibers fire when the muscle is being stretched. Upper motor neurons terminate on lower motor neurons, mainly the alpha motor neurons which provide innervation to the extrafusal fibers and gamma motor neurons which provide innervation to the intrafusal fibers.

Spasticity has been described in its individual components: intrinsic tonic spasticity, intrinsic phasic spasticity, and extrinsic spasticity. Intrinsic tonic spasticity refers to the increased tone or hyperexcitability state that results from the lower threshold and increased gain of the stretch reflex. Intrinsic phasic spasticity (tendon hyperreflexia and clonus) is thought to be due to inhibition of group Ia fibers, leading to excitability of tendon reflexes and coactivation of antagonistic muscles. The exact mechanism behind clonus is not clearly understood. The last component of spasticity is extrinsic spasticity. This component results in involuntary muscle spasms that mimic a reflex that occurs in response to noxious stimuli. The most common spasms are flexion spasms. They occur in response to perceived noxious stimuli to the skin, muscle, subcutaneous tissues, or joints.

For a short time following injury, there is flaccid paralysis and loss of deep tendon reflexes. Over time, changes occur which lead to spasticity. Hyperactivity of gamma motor neurons creates hypersensitivity of the stretch reflex. Following an injury, there is an initial period of down-regulation of neuronal membrane receptors. This is followed by up-regulation of receptors, which leads to hypersensitivity. Axonal sprouting occurs over time, explaining the temporal changes that occur with spasticity. This mechanism contributes to prolongation of the time-to-peak for excitatory postsynaptic potentials (EPSPs) and the disruption of balance between excitatory and inhibitory input. Alterations occur in the excitatory and inhibitory pathways. A phenomenon known as postactivation depression occurs normally as neurotransmitters become depleted. There is a reduction of postactivation depression as well as presynaptic inhibition following SCI. Normally Ia-reciprocal inhibition prevents simultaneous firing of antagonistic muscles. In SCI, this inhibition is reduced, leading to coactivation of antagonistic muscles. Other well-documented mechanisms that play a large role in spasticity include enhancement in the excitability of motor neurons and interneurons. Motor neuronal excitability arises from activation of persistent inward currents and alternations in the monoaminergic drive from the brainstem to the spinal cord. Altered muscular properties also lead to increased tone. Muscle fibers change, along with accumulation of connective tissue and fibrosis, which decreases the elastic properties of muscle. There is also atrophy and loss of muscle fibers and sarcomeres. Alterations in the contractile properties thus become evident.

The management of spasticity centers around reducing unwanted symptoms that limit quality of life. Treatment modalities are multidisciplinary and include physical therapy and rehabilitation, pharmacological interventions (oral and intrathecal), and surgical options. Physical techniques should target passive muscle stretching, with a goal of reducing muscle tone and maintaining flexibility and a wide range of motion. Orthoses can resist contractures and prevent muscle shortening. Treating muscle spasms pharmacologically is often difficult. Medications used to treat spasticity work by suppressing neuronal activity. Although they can benefit the aforementioned exaggerated responses, they can also amplify the negative symptoms—loss of finger dexterity, weakness, and selective use of specific muscle groups. Pharmacological treatments generally fall into three categories: γ-aminobutyric acid (GABA)ergic agents that act on interneurons, α₂-adrenergic agents, and peripheral-acting drugs that act at the neuromuscular level. Diazepam and baclofen work on the GABA_A and GABA_B receptors, respectively. Diazepam opens chloride channels and hyperpolarizes the presynaptic Ia afferent neurons. In turn, this affects the monosynaptic and polysynaptic reflexes. Diazepam is comparatively more useful in treating the hyperactive reflexes and painful spasms that follow SCI than those associated with stroke or multiple sclerosis. Clonazepam has a lower risk of dependence and causes less sedation. It can be used for nocturnal spasms. Baclofen, on the other hand, acts on both the presynaptic and postsynaptic terminals, affecting both monosynaptic and polysynaptic reflexes as well. On the presynaptic channel, it reduces the influx of calcium. On the postsynaptic channel, it allows the outflow of potassium. Baclofen is effective in reducing flexor spasms and is considered a first-line agent. Functional measures have not been shown to improve with either of the two GABAergic medications. Clonidine works by enhancing α₂-adrenergic–mediated presynaptic inhibition of sensory afferents. Ultimately this leads to suppression of the polysynaptic reflexes of the spine. Clonidine has been shown to improve walking in the incomplete SCI population. Tizanidine is an α₂-adrenergic agonist that inhibits release of excitatory amino acids from the presynaptic terminals and works on controlling muscle spasms. It has additional effects on glycine, another molecule with inhibitory properties. Dantrolene is a peripheral-acting drug that works by inhibiting calcium from the sarcoplasmic reticulum. It is less useful in SCI, because it leads to weakness, although it does reduce muscle tone, tendon reflexes, and clonus while increasing range of motion. Less common medications include cyproheptadine and cannabis. Intrathecal medications are useful when individuals fail to respond to oral agents or are unable to tolerate the side effects of oral agents. This method of delivery allows four times the dose to be delivered at the equivalent of 1% of the oral dose. Injections are used for the purpose of chemodenervation of local nerves and reserved for individuals with focal spasticity. The injections accomplish nerve block, motor point block, or chemical neurolysis. Agents used include phenol, ethanol, and botulinum toxin. Phenol and ethanol work in the short term by blocking sodium channels. The long-term effects are aimed at denaturing proteins and promoting fibrosis of the neural tissue, interrupting nerve conduction and hence the reflex arc. Patients who receive this therapy have preservation of motor strength, but there is some permanent denervation with each injection. Botulinum toxin has been hailed as the first choice for treating focal spasticity but can produce weakness in the treated muscle. Despite most SCI patients having generalized spasticity, botulinum toxin has the potential to be effective in facilitating rehabilitation and improving function when combined with other treatments. The effects of botulinum toxin appear in 24 to 72 hours after administration and have a duration of approximately 3 months.

It is necessary to make mention that not all surgical treatment options for spasticity apply to SCIs. Selective rhizotomy, while helpful for cerebral palsy, is not useful in SCI. With the exception of intrathecal baclofen pumps, most of the surgical treatment options are aimed at the muscle and tendon. Tenotomy is used in cases of severe spasticity. Tendon lengthening procedures and tendon transfer can reduce tension on the intrafusal fibers. Electrical stimulation can reduce the amount of spasticity and can be applied to the muscles, peripheral nerves, and epidural space or in the spinal cord. Electrical fields have also been used to modulate the rate of firing of motor neurons.