CHAPTER 26 SPINE: SPINAL CORD INJURY, BLUNT AND PENETRATING, NEUROGENIC AND SPINAL SHOCK
In the acute setting, spinal cord injury (SCI) represents a complex management issue, with optimal patient care depending on the smooth execution of diagnostic and therapeutic interventions, involving several different disciplines within the medical field. These include emergency medical system (EMS) personnel, emergency department (ED) staff, radiologists, orthopedic and neurological surgeons, intensivists, and physiotherapists. Of these, the immediate interventions employed within hours of injury often dictate the overall prognosis, and provide the patient with the best opportunity to improve long-term functional outcome. For this reason, adequate spinal immobilization, prompt diagnosis, and early consultation of the appropriate surgical service are measures that every ED physician should strive to incorporate into the evaluation each individual trauma patient. This chapter focuses on the epidemiology, classification, and management of SCI, as well as the complications that are typically encountered in both the acute and chronic spine-injured patient. It is through a healthy understanding of the diagnostic and therapeutic guidelines and recommendations that the morbidity and mortality associated with SCI can continue to trend downward, as it has consistently over the past 30 years.
INCIDENCE
Spinal cord injury as a whole most often afflicts young men between the ages of 16 and 30. The mean age is 29.7 years, and there is an 82% male gender bias, likely reflecting the greater tendency of young males to engage in risk-related activities.1–3 Injury most often occurs in the warmer summer months, especially during the weekend, with 53% of all SCI occurring between Friday and Sunday.4 With regard to specific etiologies of SCI, results often vary from one trauma center to the next, based largely on the socioeconomic setting of the respective institution. Vehicle trauma is common to both rural and urban healthcare centers as the leading cause of SCI. Prevention programs, including mandatory seatbelt laws, coupled with evolving innovations in automobile safety have served to drastically reduce the overall proportion of SCI attributable to motor vehicle accidents in recent years. In one 10-year period between 1980 and 1990, the overall proportion of SCI caused by vehicle trauma decreased from 47.2% to 38.1%.2 In rural centers, falls account for the second highest cause of SCI. Whereas in urban centers, violence has rivaled vehicle trauma as the leading cause of SCI. Specifically, gunshot wounds (GSW) from handguns represents approximately 90% of all SCI resulting from violence in urban centers, with an over-representation of minorities in these specific cases. Sports-related injuries continue to play a significant role in the overall incidence of SCI, regardless of the socioeconomic setting. In a study focusing on sports-related SCI out of the University of Alabama, Birmingham, the following sports contributed most to SCI in descending order: diving/surfing, football, winter sports, gymnastics, wrestling, and horseback riding.5 With the ever-increasing geriatric population, and youth violence on the rise, it is likely that falls and penetrating SCI will represent an increasing proportion of total SCI cases in years to come.
SCI represents a major economic burden on the healthcare industry for a variety of reasons. At the core of the problem is the fact that SCI patients not only represent an acute management challenge, with the average first year postinjury costs ranging from $123,000 to $417,000 depending on the neurologic level of injury, but they also represent a chronic financial burden, when long-term direct and indirect costs are factored in.2,6 Whereas direct costs are absorbed as a direct result of the injury, including rehospitalizations, nursing home care, durable equipment, and attendant care, indirect costs are more esoteric, and include loss of future wages, fringe benefits, and productivity. While it is indeed a triumph of modern medicine and critical care that greater than 95% of SCI patients survive their initial hospitalization, with an overall lifespan now approaching that of the average citizen, these factors have only further contributed to the escalating direct and indirect costs associated with the life-long care for SCI patients.1,2 The young average age of SCI patients at the onset of injury contributes further to the economic impact of SCI, with the estimated lifetime direct and indirect costs in excess of $2.5 million for high cervical injury patients (injury between C1 and C4).2
MECHANISM OF INJURY
First described by Denis,7 the three-column model of spinal anatomy divides the spine into three distinct longitudinally-oriented anatomical columns (Figure 1). The anterior column includes the anterior longitudinal ligament (ALL), the anterior half of the vertebral body, and the intervertebral disc. The middle column consists of the posterior half of the vertebral body/intervertebral disc and posterior longitudinal ligament (PLL). Finally, the posterior column represents all bony/ligamentous elements posterior to the PLL (pedicles, lamina, spinous process, ligamentum flavum, and the interspinous ligament). By definition, SCI resulting in disruption of at least two of these three columns is considered an unstable injury. This somewhat simplistic representation of spinal anatomy serves to provide a mental framework for appreciating spine biomechanics and the potential injuries that may result from various blunt and penetrating forces to the spinal column.
Biomechanics of the Spine
Prior to delving into potential mechanisms of SCI, a healthy understanding of the biomechanics of the spine is imperative. As is frequently the case, there is often a certain degree of discrepancy between the actual level of deforming injury to the spine, and the resultant radiographic findings and neurologic deficits associated with the injury. Multiple mechanisms are often simultaneously involved in producing SCI. In their simplest forms, the four types of injurious forces that may be imparted to the intact spinal column are (1) flexion and extension (deflexion) injuries, (2) vertical compression and longitudinal distraction trauma, (3) rotational injuries, and (4) injuries with combined mechanisms.1,6
Regarding flexion-extension injuries, the spinal cord is often damaged by compression, transverse/longitudinal shear, torsion, and rotational forces. These injuries typically involve the cervical spine, and often result in disk protrusion, and/or interspinous/anterior column/posterior column ligamentous tears. When an associated disk protrusion and/or subluxation is present, there is a high incidence of concomitant local cord damage with mainly central cord necrosis and hemorrhage seen. In children under the age of 8, extreme hyperflexion injuries are often associated with complete cord transection, secondary to the physiologic high cervical ligamentous laxity normally found in the pediatric population.8–10
Hyperextension (retroflexion) injuries most often result in damage to the spinal cord at the C5–C6 level, as extension is maximal at this specific level from a biomechanical perspective. These injuries are often associated with bony dislocation, ventral fracture-dislocation, avulsion of articular processes, disruption/displacement of the intervertebral disks, and disruption of the anterior longitudinal ligament/posterior longitudinal ligament, all of which result in significant compromise of the anteroposterior diameter of the spinal canal and subsequent central cord lesions.9
Compression and longitudinal distraction injuries are most often seen in the setting of vertical stress to the spinal column secondary to the falls on the head, buttocks, or neck. They also often occur with an acute increase in axial load forces during a motor vehicle accident (MVA). Radiographically, these injuries are typically characterized by vertebral body flattening, end-plate fractures, and acute disk herniations. Often, there is associated retropulsion of bony fragments/disk material into the spinal canal, and varying degrees of resultant cord compression. When the mechanism of injury involves a fall, the majority of these injuries occur at the thoracolumbar junction, the most mobile segment of the spinal column. Conversely, the lower cervical spine is more often involved in cases where a vertical axial load is imparted the spinal column.
Similar to compression/longitudinal distraction injuries, rotational injuries of the spine most often involve the thoracolumbar junction and upper lumbar spine. By definition, they may involve all parts of the vertebral body, including the pedicles, articulating facets, and ligamentous complex. These injuries often result in unilateral or bilateral dislocation, or stable/unstable fracture dislocation due to interlocking of the vertebral bodies and distraction of the intervertebral disks.9,11
Mechanism of Injury
Spinal cord trauma is a broad term describing an injurious event that results in disruption of the functional and/or anatomic integrity of the spinal cord at a particular level(s). Although isolated lumbar spine injuries represent a significant proportion of SCI, the majority of debilitating SCI involve trauma to the cervical and thoracic spine. It is for this reason that the focus of this discussion will be injury of the spine from the cervical spine down to the thoracolumbar junction. With respect to the general mechanism of injury, all SCI can be categorized in one of three subgroups: (1) direct (penetrating) SCI, (2) indirect (blunt) SCI, or (3) combined direct/indirect SCI. Depending on the underlying mechanism of injury involved, the pathogenesis of SCI can be further subclassified. Primary traumatic lesions are due to direct mechanical disruption of the cord parenchyma, typically occurring at the time of the original injury. Secondary traumatic (reactive) lesions do not develop directly from the injurious stimulus, but instead evolve as a consequence of injury-related factors, including the development of edema, ischemia, improper immobilization with secondary mechanical injury, and other biochemical disorders. Finally, common to both primary and secondary traumatic lesions is the potential for delayed neurologic sequelae, including scar formation, secondary degeneration, or regenerative phenomena.9
Penetrating Spinal Cord Injury
Historically, the management of penetrating spinal cord injury (PSI) was a task relegated mainly to military physicians, as the majority of these injuries occurred in the setting of active combat. Unfortunately, the emergence of violence as a leading cause of SCI in many urban centers over the past 20 years, has served to underscore the importance of emergency room physician familiarity with the acute management of these injuries in civilian practice. In general, PSI can be classified as either gunshot wound–related (GSW-PSI) or lacerating (non-GSW) PSI. Both types of PSI most commonly involve the thoracic spine, and seldom involve more than one vertebral segment.12 Depending on the series, 52%–57% of all PSI results in complete neurological deficit (no sacral motor/sensory sparing), although lacerating PSI often results in incomplete neurologic injury.13–15 Although by definition, PSI implies direct dural/parenchymal disruption, in some cases the pathogenesis of PSI resembles that of a concussive model. This has been demonstrated in numerous military-based studies in which normal-appearing dura was encountered at the time of laminectomy in numerous cases.16–19
Blunt Spinal Cord Injury
In clinical practice, closed injuries of the spine are typically the most frequent type of SCI encountered. They often occur in the setting of MVA, industrial accidents, falls, and sport-related activities. In these cases, underlying injury to the spinal cord may occur in the presence/absence of concomitant soft tissue injuries, including fracture dislocation and subluxation of the spine. Biomechanics and mechanism of injury play a central role in the type and extent of spinal cord injury incurred. A thorough understanding of the potential types of mechanical forces distributed throughout the spine at the time of injury is paramount in order to be able to anticipate the evolution of secondary reactive lesions following the initial insult. In general, closed SCI can be distilled down into two broad categories. The first involves indirect cord injury arising from blunt trauma without space-occupying or penetrating lesions within the spinal canal. This type of injury is frequently observed in cases where the mechanism of injury involves longitudinal shearing/distraction, flexion, rotation, rotation-flexion, and/or posteroanterior acceleration.9 The second type of closed SCI involves direct cord injury secondary to blunt or penetrating forces resulting in canal compromise from a variety of space-occupying lesions. These include bony/ligamentous damage, fracture dislocation, or subluxation. It is important to note that SCI is rarely confined to the anatomic point of impact. In approximately 15% of SCI cases, lesions are observed at multiple levels due to both primary and secondary traumatic changes.20
SEVERITY/GRADING OF SPINAL CORD INJURIES
The neurologic level of injury (NLI) is a specific term that refers to the most caudal spinal cord level at which normal motor/sensory function persists following SCI. Although some degree of correlation often exists between the anatomic and neurologic level of injury, this relationship is not always consistent. Several factors including the spinal segment involved, and the underlying mechanism of injury, contribute to the ultimate NLI, once secondary traumatic lesions have manifested. Overall, according to the American Spine Injury Association (ASIA) database, approximately 53% of SCI patients are tetraplegic, 46% are paraplegic, and the remaining 1% experience complete recovery by the time they are discharged from the hospital. The classification of SCI can be further categorized as complete or incomplete injury, referring to the absence/presence of sacral motor/sensory sparing, respectively. The most common neurologic category is incomplete tetraplegia (31.2%), followed by complete paraplegia (26%), complete tetraplegia (21.9%), and incomplete paraplegia (20%).1,2
Neurological and Functional Outcome Scales
Numerous classification schemes have been devised to describe patients with SCI over the years. Generally speaking, two types of assessment scales exist, neurological examination scales and functional outcome scales. It is now generally accepted that the most meaningful description of SCI in the acute setting occurs when a neurological assessment tool is applied in conjunction with a functional outcome assessment scheme, in order to provide perspective on the significance of any neurological recovery on the day-to-day life of SCI patients. The first standardized neurological assessment scale for SCI was proposed by Frankel and associates in 1969.21 In this scheme, a five-grade scale (A to E) is employed to discriminate SCI patients on the basis of differing degrees of motor/sensory function preserved after their injury. Frankel grade A patients are those with complete motor and sensory lesions. Grade B patients have sensory only functions below the level of injury. Grade C patients have some degree of motor and sensory function below the level of injury, but their retained/recovered motor function is useless. Grade D patients have useful, but abnormal, motor function below the level of injury. And grade E patients are fortunate enough to experience complete motor/sensory recovery prior to discharge from the hospital. The main deficiencies involving the Frankel scale proved to be the difficulty involved in discerning grade C from grade D patients, as well as the relatively poor interobserver reliability with practical application of the scale. Despite these shortcomings, the Frankel scale provided an important classification framework from which several contemporary classification schemes have been derived. In fact, the ASIA impairment scale, largely regarded as the most studied and useful of the SCI neurological classification schemes, is essentially a permutation of the original Frankel scale, in which objective parameters are provided to better assess the significance of retained motor function between grade C and grade D patients.22
Analogous to the Frankel scale as a neurologic examination tool in SCI is the Functional Independence Measure (FIM) as a functional outcome scale. The FIM is an 18-item, seven-level scale designed to assess the severity of patient disability, estimate the burden of care, and to prognosticate on medical rehabilitation and overall functional outcome. Specifically, the FIM complements neurological assessment by providing scores for activities of grooming, bathing, eating, dressing the upper body, dressing the lower body, and toileting.22
Concomitant assessment of both the neurological and functional deficits in acute SCI is imperative in assessing the impact of injury on the patient as a whole. Additionally, linkage of these independent scales allows clinicians to specifically evaluate whether therapeutic interventions resulting in improvement of the gross neurological assessment score also result in enhanced functional recovery for the patient. It is on the basis of functional outcome that the overall significance of various therapeutic interventions can be truly assessed. Omission of such functional outcome assessment in the National Acute Spinal Cord Injury Study (NASCIS) I and II clinical trials assessing the benefit of acute methylprednisolone (MP) therapy in acute SCI patients is often cited as a critical shortcoming of the design study, rendering the interpretation of improved neurological outcome scores essentially impossible. A recent meta-analysis of the current literature regarding classification schemes for SCI prompted the Section on Disorders of the Spine and Peripheral Nerves of the American Association of Neurological Surgeons (AANS) and the Congress of Neurological Surgeons (CNS) to recommend the ASIA standards for neurological and functional classification of SCI as the preferred neurological examination for clinicians involved in the evaluation and management of acute SCI.22 This recommendation was based largely on the finding that the ASIA scale provided the greatest discrimination in grouping subjects with SCI into mixed-injured categories, with a relatively high degree of interobserver reliability. Similar to the other SCI classification schemes, the ASIA scale has undergone several revisions since its inception in 1984. Currently, the scale now consists of several components, including the ASIA impairment scale, the ASIA motor index score, the ASIA sensory score, and the FIM (Figure 2).
Spinal Cord Syndromes
Several spinal cord syndromes have been described in the setting of acute SCI. Central cord syndrome typically occurs with a cervical region injury leading to greater weakness in the upper limbs than the lower limbs, associated with sacral sparing. Brown-Sequard syndrome is classically seen in the setting of penetrating SCI resulting in a hemisection lesion of the cord. It is typically associated with a relatively greater ipsilateral proprioceptive and motor loss, with contralateral loss of sensitivity to pain and temperature below the NLI. Conversely, anterior cord syndrome is associated with a lesion causing variable loss of motor function and sensitivity to pain and temperature, while posterior tracts including proprioception are spared. Conus medullaris syndrome is associated with injury to the sacral cord and lumbar nerve roots, leading to areflexic bladder, bowel, and lower extremity, while sacral segments may occasionally demonstrate preserved reflexes. Finally, cauda equine syndrome is due to injury involving the lumbosacral nerve roots within the spinal canal, resulting in areflexic bladder, bowel, and lower extremities. Similar to the various brainstem vascular syndromes (e.g., Wallenberg’s syndrome), spinal cord syndromes often do not present with the classic textbook constellation of signs/symptoms. However, as is the case with brainstem vascular syndromes, an understanding of the various spinal cord syndromes serves to provide a rough neuroanatomical framework regarding the complex structural organization intrinsic to the spinal cord.
DIAGNOSIS
The organization of the central nervous system provides the physician with the opportunity to localize traumatic lesions to the spinal cord with a relatively high degree of accuracy, based on careful neurologic examination alone. However, adequate presurgical care, as well as optimal surgical planning, are both heavily dependent upon accurate imaging of the spine. For decades, plain roentgenograms of the spine have been an invaluable localization tool in SCI for several reasons. First, unlike other more sophisticated imaging modalities, the technology and resources required are not typically a limiting factor. Second, the portability of x-ray technology and the relative ease of acquisition provide the physician the opportunity to rapidly attain important anatomic information, even under the most hectic conditions. Lastly, plain films of the spine can provide a whole host of information regarding underlying SCI, including the presence/absence of fractures, subluxation/dislocation, and spinal canal patency (Figure 3). Although soft tissue structures are not well-visualized with standard x-ray technology, malalignment/angulation of the spine detected on a plain film may hint to underlying acute ligamentous or disk injury.
