11 Spinal Cord Injury and Central Cord Syndrome
Abstract
Corresponding to the marked growth of the aging population is an unfortunate increase in the incidence of older adults who suffer spinal cord injury (SCI). Age-related changes in the vertebral column as well as the spinal cord itself lead to a different presentation of SCI in older adults. Falls, the leading cause of older adult SCI, have a propensity to result in central cord syndrome from hyperextension at the time of the trauma. Management of SCI is challenging because older adults are likely to present with co-morbidities. In addition to co-morbidities present on admission, potential SCI complications from cardiac, pulmonary, skin, renal, and urinary systems can further complicate patient care. All treatment plans and potential complications require management tailored to the individual patient, not to chronological age alone. Conservative and surgical management strategies should always be carefully considered and individualized to patients and their goals of care.
Key Points
There is an increasing incidence of SCI in older adults, with falls being the leading causes of injury
The pathophysiology of spinal cord injury in the older adult differs from younger patients due to age-related changes of the spinal column
Central cord syndrome occurs in older adults more frequently and is associated with cervical hyperextension injuries
Management of older adult SCI patients is complicated by their increased incidence of co-morbidities.
Cardiac, pulmonary, renal, urinary, integument complications are the most frequent complications seen in older adult SCI patients.
Conservative and surgical treatments can be considered, and management should be individualized to patients and their goals of care
11.1 Epidemiology
There is an estimated global incidence of 67.9 cases of SCI per million population, with a prevalence as high as 116.3/million in the aging population (ago > 65). 1 The economic burden of SCI is an estimated four billion dollars in the United States. 2 Although North American has seen an overall decrease in traumatic SCI due to motor vehicle accidents, the incidence of SCI has not decreased. 3 Globally, in the last decade there is an epidemiological shift in the age of SCI from a younger to an older population, with the average age increasing from 29 years to over 40 years. 4 , 5 , 6 It is estimated that patients over 70 years of age will account for the majority of new traumatic spinal cord injuries by 2032. 7
The most common etiology of SCI is physical trauma, which accounts for an estimated 90% of all SCI. 3 In North America, motor vehicle accidents are the primary cause of SCI among all age groups. While falls are the overall second leading cause of all SCIs it is the leading cause of spinal cord injuries in the aging population. 3 Nontraumatic causes of SCIs account for about 10% of all injuries and can include spinal column degeneration, infection and abscess formation, tumors, and congenital malformation. 3
Registry data has been helpful in better understanding the differences between the older and the younger population with respect to SCI. In Canada, the Rick Hansen Spinal Cord Injury Registry is a prospective observational registry that collects data from people who have had an SCI. 8 The participating centers in the registry are nationwide and include 18 acute care and 13 rehabilitation hospitals. Recent registry analysis of 1,232 Canadian SCI patients from 2004 to 2013 found an epidemiological divide between the etiology and epidemiology of patients over the age 70 when compared to patients under the age of 70. 9 Older adult patients were more likely to be injured by a fall (83%, compared to 39% of those under the age of 70). Older adults were also found to be less severely injured over all, with 58.2% having Injury Severity Scores (multi-trauma) less than 25 compared to 39.1% for those under age 70. The Injury Severity Score is a standard trauma score that indicates the degree of trauma to major body regions. A score of 25 or more can affect care and is indicative of major trauma to another region in addition to the spine. 10 Older adult patients were also more likely to be American Spinal Injury Association (ASIA) grade C or D (71% vs. 47%) and also more likely to be injured in the cervical level (78% vs. 62%). 9
Despite being less injured overall, with less severe spinal cord injuries as assessed by ASIA grade, the mortality rate was significantly greater among patients over 70 years of age (4.2% vs. 0.6% in younger patients). In the following sections, we will review how the pathophysiology and management of SCI may be contributing to this increased mortality.
11.2 Pathophysiology and Biomechanical Considerations
Damage from SCI can be classified as primary or secondary injury. Primary injury is characterized as the damage which occurs immediately following the insult to the cord. The physical forces associated with the mechanical trauma include laceration, compression, distraction, and shear. Most spinal cord injuries are caused by a direct insult to the spinal cord as a result of a contusion or traction, and transection of the spinal cord is rare. 3
Secondary injury is the cascade of events that is initiated by the trauma and results in biochemical and pathological changes that damage axons and neurons secondarily that would have otherwise survived. One of the major treatment aspects to limiting secondary injury is stabilizing the spinal column and removing spinal cord compression such that additional injury does not occur. Other secondary injury mechanisms involve systemic effects, local vascular effects, electrolyte changes, and biochemical changes. Systemic effects of spinal cord injury can result in hypotension and hypoxia due to loss of innervation to supply muscles of vascular tone and muscles for respiration. These systemic effects can lead to loss of autoregulation and loss of microcirculation. The initial trauma can also result in hemorrhage, which can further reduce blood flow and cause ischemic injury.
Electrolyte changes have also been studied with respect to spinal cord injury. Injury can cause an increase in intracellular calcium which can disrupt important cellular processes and can activate destructive processes. Other biochemical changes include the accumulation of neurotransmitters such as the catecholamines, norepinephrine and dopamine. Excitotoxicity is another secondary injury mechanism where neurons are damaged and killed by the overactivation of receptors for the excitatory neurotransmitter glutamate, such as the NMDA receptor and AMPA receptor. Other biochemical secondary injury mechanisms include free radical production, lipid peroxidation, eicosanoid production, pro-inflammatory cytokine release, edema, loss of energy metabolism and apoptosis. Several treatment strategies for spinal cord injury have focused on limiting secondary injury and have undergone or are undergoing clinical trials. 11
Older adult patients are at increased risk for SCI due to age related degeneration. Degeneration of the spine increases with patient age due to a combination of increased structural load, repetitive microtrauma, and age-related changes to bone, muscle, and intervertebral disc physiology. 12 These degenerative processes typically begin with intervertebral disc wearing, through the loss of proteoglycans and water. Aging and natural wear on intervertebral discs can cause loss of elasticity with progressive loss of disc height and integrity causing disc budging or protrusion. This loss of disc height contributes to the loss of tensile properties of the ligamentum flavum, with buckling of the ligamentum flavum further contributing to narrowing of the spinal canal. Cervical spinal canal space can also be limited by osteophyte development, 12 with hypertrophy of the uncovertebral joints and facet joints and ossification of the posterior ligament. Aging is also associated with loss of vertebral height, further contributing to spinal canal stenosis. 13 Injury can occur with hyperextension, because with extension, there can be further buckling of the ligamentum flavum. This results in an additional 2 to 3 mm loss of the anteroposterior diameter, causing an acute compression of the spinal cord parenchyma and resulting in a central cord injury 3 (Fig. 11‑1). Older adult patients with either a narrow spinal canal or large spinal cord (cord-canal mismatch) are at an increased risk for developing spinal cord injury, even in the context of minor spinal cord trauma due to these age-related changes. 14 , 15
11.3 Common Injury Types
Complete spinal cord injuries result in a complete loss of motor and sensory function below the level of injury. An incomplete injury preserves some motor or sensory function below the injury level, such as voluntary anal contraction, palpable or visible muscle contraction below the injury level, or sensation below the injury level. An incomplete injury can be mild, such as an altered sensation to a dermatome. The American Spinal Injury Association (ASIA) impairment scale (Fig. 11‑2) is used to classify the severity of the deficit. Incomplete spinal cord injuries can further be classified as incomplete spinal cord injury syndromes, with central cord syndrome being the most common syndrome seen in older adults. One of the key elements to the evaluation of an SCI patient is the assessment of voluntary anal contraction as it can significantly impact prognosis. Other syndromes, such as anterior cord syndrome, Brown-Sequard syndrome, or posterior cord syndrome (Table 11‑1, Table 11‑2) can also occur.
11.3.1 Central Cord Syndrome
Central cord syndrome is the most common incomplete cervical spinal cord injury affecting older adults. 3 Central cord syndrome was first described by Schneider and colleagues in 1954 as a syndrome characterized by a disproportionately greater motor impairment of the upper extremities compared to the lower extremities, bladder dysfunction, and varying levels of sensory loss below the level of the lesion. 16 They also proposed that the pathophysiology of this syndrome was because of mechanical compression injuring the central portion of the spinal cord disrupting the medial lamination of the cortical spinal tracts that control the hand and upper extremity function, but sparing the lateral tracts serving the sacral and lower extremities. However, this pathophysiological mechanism has not been substantiated because the anatomic distribution and function of the corticospinal tract is controversial. 17 , 18 , 19
Central cord type injuries without traumatic fractures tend to be associated with a stenotic central canal of mean diameter less than 14mm. 20 Patients with greater degrees of canal stenosis have been found to have poorer neurologic recovery. 20 Unlike complete spinal cord injury, which is perceived to be a disorder of the younger population, incomplete spinal cord syndromes like central cord syndrome affect a greater proportion of aging spinal cord injury patients. 9 The pathophysiology of central cord syndrome also shows a bimodal distribution, with the younger population (< 50 years of age) getting injured due to severe spinal column traumatic injuries and the aging population (> 50 years of age) more likely to be injured due to a hyperextension injury in a narrow spondylotic canal. 20
A recent summary of postmortem evaluations and observations suggests that the greater selective loss of upper extremity than lower extremity motor function is due to selective injury to lateral white matter columns of the spinal cord 3 , 21 , 22 , 23 and not through the direct loss of motor neurons to the hands or the precise anatomic lamination or location of the corticospinal tracts referred to by Schneider. Histologic evaluation of three patients with central cord injuries found that there was evidence of axonal and myelin loss of the lateral white matter tracts. At 6 weeks post injury, there was considerable loss of the lateral white matter columns, with Wallerian degeneration and marked axonal breakdown. 19 It appears that the greater selective loss of upper than lower extremity function is associated with the selective injury to the lateral white matter columns.
11.4 Treatment Options
Treatment patterns and clinical outcomes can vary with respect to patient age. The initial management of SCI is focused on basic life support and preventing further injury. Protection and maintenance of airway, breathing, and circulation should be performed, as per trauma management guidelines, ideally concurrently with immobilization of the bony spine. Of particular note in elderly patients is that the patient’s spine should be immobilized in neutral alignment for the specific patient. In some older adult patients with kyphotic deformities or those with ankylosing spondylitis, extension of the neck to obtain what would be neutral alignment for an individual without kyphosis can result in increased spinal cord injury and neurological deficits. 24 In these patients, the spine should be maintained in its preinjury kyphotic alignment, which can be obtained with the aid of immobilization devices such as blankets under the head, sandbags or halo orthoses. 25 In the context of serious spinal cord injury, the patient may experience hypoventilation and neurogenic, spinal shock (hypotension and bradycardia) for which the patient would need respiratory and hemodynamic stabilization.
11.4.1 Neurological Assessment
After acute respiratory and hemodynamic stabilization of the spinal cord injury patient, neurologic examination is required. A full neurologic exam, following the International Standards for Neurological Classification of Spinal Cord Injury should be completed, including motor function, light touch sensory function, pin prick sensory function, voluntary anal contraction and bulbocavernosus reflex, in order to properly determine the severity of spinal cord injury and to guide management. While this examination may be challenging in polytrauma patients, it is important for prognostication, as perineal sensation and voluntary anal contraction function can be present even if there is no motor or sensory function of the lower extremities and can significantly impact prognosis for improvement in neurological function. Presence of any sensation or motor function below the level of injury renders the patient an incomplete spinal cord injury, and there is a significantly increased rate of improved neurologic function in incomplete patients versus complete patients. 3
11.4.2 Imaging
Recommendations for radiographic imaging from the American Association of Neurological Surgeons and Congress of Neurological Surgeons Joint Guidelines Committee for the radiographic assessment of spinal cord injuries have been published. 26 In the patient with a suspected spinal cord injury, high-quality computed tomography (CT) imaging of the cervical spine is recommended. Only if high-quality CT imaging is not available would a 3-view cervical spine series (anteroposterior, lateral, and odontoid views) be recommended. These X-rays should be supplemented with CT (when it becomes available) to further define areas that are suspicious or not well visualized on the plain cervical X-rays.
Magnetic resonance imaging (MRI) can be helpful to identify soft tissue injuries that may not otherwise be seen with CT, such as disc protrusions, hemorrhage, ligamentous hypertrophy and cord contusions. In regards to central cord injury, common radiographs of central cord-injured patients may not show cervical fractures; because the injury mechanism is believed to result from a hyperextension injury with compression of the spinal cord an MRI would be required to assess these patients. Acute MRI imaging performed after a central cord injury can provide detailed images of the spinal cord parenchyma. Specific imaging sequences such as T2-weighted gradient echo studies have shown hyperintense signal at the level of injury as well as the ability to assess the presence of intraparenchymal hemorrhage and spinal canal stenosis.
11.4.3 Acute Stabilization
Conservative options may be considered, more so in the older adult due to the increase in surgical risks that is associated with the increase in aging comorbidities. Conservative, non-operative management options can include bed rest, traction or bracing. Bed rest with immobilization of the fracture can result in numerous complications, including pneumonia, pressure ulcers, gastrointestinal bleeding, urinary tract infections, deep vein thrombosis, pulmonary embolism, spasticity, and deconditioning. Traction can be used to reduce a fracture or dislocation or to decompress the spinal cord and can be performed using serial weights with clinical and radiological (radiographs or fluoroscopic) examination or with manual traction. Lastly, bracing for cervical injuries can allow for immobilization of the fracture and mobilization of the patient, which can decrease the risks associated with bed rest. Bracing options include rigid cervical spine collars and halo-vest immobilization for cervical injuries and thoracolumbosacral orthoses and Jewett bracing for thoracolumbar injuries. Fracture healing can occur with ultimately no further need of the brace. However, with ligamentous injuries, bracing does not repair the ligamentous injury and surgery may be required for definitive repair.
Surgical options of decompression should be considered if there is failure of the conservative options and progressive neurological deterioration. Surgery can also quickly decompress the spinal cord and fuse the unstable spine to allow for early mobilization of the patient to prevent the complications associated with bedrest. While surgical decompression and fusion can stabilize the unstable spine and relieve spinal cord compression, the success rates are mitigated in patients with comorbidities and/or high anesthesia risks.
There are many different surgical approaches used to treat spinal cord injuries, with a unified goal of neural element decompression and stabilization of the vertebral column. Spinal cord decompression and fracture reduction is intended to relieve pressure on the damaged spinal cord and nerve roots, with the goal of reducing secondary spinal cord damage by minimizing edema and ischemia. Decompression is also utilized to remove disc herniation, ligamentum flavum, hematoma, fractured bone, infection, or tumor.
Depending on the stability of the vertebral column, a fusion combined with a decompression may be required. A spinal fusion joins two or more vertebrae and prevents movement between the fused vertebrae. There are many different types and approaches for spinal fusion that can be used to stabilize the injured spine. Most techniques will involve instrumentation to stabilize the spine and the use of a bone graft to fuse the vertebrate and are detailed in other chapters.
In a nation-wide study on the trends of treating central cord syndrome, Brodell and colleagues found that almost 40% of aging patients presenting with central cord syndrome underwent surgery, in which anterior cervical decompression and fusion was the most common surgical treatment, accounting for almost 50% of patients, while posterior cervical decompression and fusion was used in 18% of the surgical patients. Posterior cervical decompression without fusion was used in 17% of patients. 27
11.5 Benefits and Risks
Management of SCI has been examined in the older adult. Aging patients have been found to have a greater morbidity, and in-hospital and postdischarge mortality. 9 Older patients have also been found to have poorer functional outcome when compared to younger populations, especially after cervical spinal cord injury. 3 The causes of poor surgical outcome are not clear, as the aging population may not be treated with surgical intervention as often because of the history of poor results, compliance with the patient’s goals of care, or because surgical intervention is more likely to lead to poor results.
Ahn et al looked at the effect of older age on treatment decisions and outcomes in patients with traumatic spinal cord injury in a study involving the Rick Hansen Spinal Cord Injury Registry. 9 This study was a prospective, multicenter observational registry which looked at patients from 18 acute care and 13 rehabilitation hospitals across Canada from 2004 to 2013. Of the 1,440 patients included in the analysis, it was found that there were differences in the spinal cord injuries sustained in patients younger than 70 years of age compared to those 70 years of age or older. Older patients were more likely to be injured by a fall, to be less severely injured overall—with Injury Severity Scores less than 25—to have less severe American Spinal Cord Injury Association Impairment (AIS) grades of C or D, and to have an injury at the cervical level. Despite generally having less severe injuries, they tended to have more postoperative complications, such as urinary tract infections, pneumonia, pressure ulcers and deep vein thromboses. They also had a longer acute length of stay and higher in-hospital mortality. Interestingly, the length of stay at rehabilitation hospitals did not differ significantly between the older and younger groups.
While the older-aged patients were less likely to receive acute surgical treatment, age was no longer a factor when neurologic severity and level were adjusted, as surgery was more likely if the injury was from a high-energy trauma or if the patient had an AIS grade of A or B. Patients aged 70 years or more experienced a significantly longer time from injury to arrival at a participating acute care hospital (median 14.5 vs. 8 hours) and there was a significantly longer time from admission to surgery (37 vs. 19 hours). While there was a significant delay from injury to arrival at an acute care hospital and a significant delay from admission to surgery, it is unclear whether or not these delays were associated with the increased mortality that was found to be significantly greater among older than younger patients.
The delays in older patients may be because older patients require a more complex management plan for their comorbid conditions, and clinicians may prefer to manage incomplete cervical spinal cord injuries with a period of initial observation to assess neurologic improvement, especially in patients with central cord injury. However, even with the adjustment for injury severity, neurologic level and trauma severity, there was a delay in time to surgery associated with age. The delay to surgery may also be accounted for insofar as older patients may require more time to optimize their medical status for surgery with measures such as reversing anticoagulation, assessing for cardiovascular risk, and planning for prolonged ventilation. However, in the Ahn et al study, the comorbidity scores for the older and younger patients in the study were similar, suggesting that advanced age alone was associated with delays in both triage and surgical management.
Another significant factor may be because there are more central cord injuries in older adults compared to the younger population. Because the prognosis of patients with central cord injury can be quite good, 26 the delays to surgical intervention may have been because surgeons were waiting to see if there was significant recovery and only operating if there was a plateau in recovery and the patient was optimized. Indeed, Ahn et al 9 found that those with thoracolumbar injuries had the shortest delay to surgery. While age did appear to be associated with delayed triage and treatment, it is unclear as to whether such delays are fundamentally responsible for increases in morbidity and mortality. While decompression may decrease the complications associated with prolonged bedrest, rushing to surgery prior to optimization for surgery in older adults may increase morbidity and mortality from other comorbidities.
Schneider originally observed the natural history of central cord injuries and concluded that good neurologic recovery can be achieved without surgical intervention. Although the initial presentation of central cord syndrome, quadriplegia with perianal and sacral sparing can be quite severe, the prognosis is good when compared to that of complete spinal cord injuries, as 75% of patients can have partial recovery of motor function. 3 Patients with traumatic central cord syndrome usually have some degree of progressive return or recovery of neurologically function, even with conservative treatment alone. Age of the patient at the time of injury seems to have an effect on neurological recovery; unfortunately, patients aged 50 and over tend to recover slower and only achieve limited recovery when compared to patients in the younger population. 21 , 22 Numerous studies have supported this conclusion. 21 , 28 , 29 However, more recent studies have shown that patients who underwent surgical decompression may have a more rapid initial neurologic improvement and shorter hospitalization and rehabilitation periods. 30
As discussed previously, older adults disproportionately had more cervical spine fractures than any other age group. The management options in aging patients with cervical spine fractures include prolonged bed rest, rigid-collar orthosis or halo vest immobilization and operative fixation, with the later three treatments being the most commonly performed. Prolonged bedrest is often not well tolerated in the aging population because of the risk of increased morbidities, including spasticity, decubitus ulcers, gastrointestinal bleeding, and/or urinary tract infections. 31 Osteoporosis, reduced recovery capacity, and medical comorbidities have also been postulated to contribute to a higher risk for negative outcomes. 31
11.6 Pitfalls, Complications, and Avoidance
While there is an increase in comorbidities in older adults, 32 it is not clear that this will translate into increased complications in older adults, and so vigilance should be paid to avoid complications. A trend for an increased incidence of secondary complications in older adults has been reported, with the most common secondary complications being infections, psychiatric disorders, pressure sores, and cardiovascular complications. 32 The elderly were also found to have an increase in major postoperative complications (e.g.., urinary tract infection, pneumonia, pressure ulcer, or deep vein thrombosis). Spinal cord injury complications and their possible avoidance are reviewed below.
11.6.1 Cardiovascular
The increase in cardiovascular disease in older adults is of significant concern, as SCI can critically impact even healthy cardiovascular systems. Acute SCI above the level of T6 can involve the descending pathways to sympathetic neurons. This results in impairment in the control of the autonomic nervous system (ANS) and can cause bradycardia, arterial hypotension, and autonomic dysreflexia, which are components of neurogenic shock. 33 An estimated 68% of patients with ASIA A and B develop arterial hypotension, and 35% of all patients need vasopressor support. Additionally, 16% of these patients have been reported to experience cardiac arrest. 34
The management of these patients must balance adequate perfusion and oxygenation of the spinal cord with the complications associated with maintaining that perfusion. Fluids are often the first line to treat the hypotension associated with trauma and spinal cord injury. However, in patients with limited cardiac function, excessive fluid resuscitation may result in congestive heart failure (CHF). Development of CHF further limits systemic oxygenation, adequate perfusion and thus spinal cord oxygenation. Vasopressors, a mainstay in the treatment of the arterial hypotension and bradycardia associated with high SCI, may also stress an already compromised heart, leading to cardiac ischemia and infarction. Thus, to prevent potential cardiac complications, clinicians may be less aggressive with maintaining mean arterial blood pressures at 85 to 90 mm Hg for the first seven days after SCI— which has been described as a level III recommendation in the current guidelines for the clinical management of acute SCI. 35 A low threshold for cardiology consultation is warranted.
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