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.

Figure 1 Schematic representation of the three-column model of the spine. The anterior column consists of the anterior longitudinal ligament (ALL) and the anterior half of the vertebral body/intervertebral disc complex. The middle column is composed of the posterior half of the vertebral body/intervertebral disc complex and the posterior longitudinal ligament (PLL). The posterior column includes the intact vertebral arch and associated ligamentous structures.

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).

Figure 2 The American Spinal Injury Association (ASIA) Impairment Scale, and ASIA neurological classification scheme for spinal cord injury (SCI). The Impairment Scale is a permutation of the original Frankel Scale for SCI. The actual ASIA classification scheme includes the ASIA Impairment Scale and ASIA motor/sensory indices, as well as the Functional Independence Measure (FIM), which is not pictured. (The American Spinal Cord Injury Association [ASIA] and The International Medical Society of Paraplegia [IMSOP].)

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.

Figure 3 Lateral radiograph of the nonpathologic cervical spine, demonstrating normal alignment of (A) the anterior vertebral bodies, (B) the posterior vertebral bodies, (C) the laminar-facet line, and (D) the spino-laminar line.