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Critical Considerations In Cervical Spine Injury
The authors review cervical spine anatomy, the most common stable and unstable injuries to the area, the latest imaging guidelines, special concerns relating to children with neck injury, and recent findings about methylprednisolone therapy.
By Selma Mizouni, MD, and Barry J. Knapp, MD, FACEP
An estimated 10,000 persons sustain a spinal cord injury (SCI) in the United States every year, resulting in severe morbidity and mortality. About 90% of these injuries are related to blunt trauma. Cervical spine injuries (CSIs) often cause catastrophic disruption in the lives of both the patient and his family. Patient outcomes range from an asymptomatic presentation to quadriplegia to instant death. A delay in diagnosis can significantly worsen neurologic compromise.
The majority of CSI patients are male (4:1 ratio), with bimodal peaks between 15 to 24 years of age and then 50 years and older. Common mechanisms of injury include motor vehicle accidents (MVAs, 50%), falls (25%), and sports-related injuries (10%).
Up to one third of CSIs occur at the level of C1-C2, and about half occur at the level of C5-C7. Higher CSIs—at the craniocervical or atlantoaxial junction, for example—tend to have poor outcomes. Up to 20% of all spinal fractures are multiple and 5% are at discontinuous levels. Discovery of a spine injury at one level must prompt imaging of the rest of the spine.
As many as 10% of unconscious patients who present to the emergency department following an MVA have a CSI. Current literature cites the incidence of CSIs to be 4.3% in major trauma centers. Not all patients with a CSI will have obvious neurologic deficits. Unstable bony injury can occur without spinal cord damage. Actual spinal cord injury will occur in 1.3% of all trauma patients. In this article, we will review the anatomy of the cervical spine, common fractures, and current imaging and treatment recommendations.
Anatomy of the cervical spine
The cervical spine consists of seven vertebrae numbered one to seven, separated by the intervertebral disks. A typical cervical vertebra has a body, with two transverse processes, one spinous process, two transverse foramina, and one vertebral foramen. The vertebral arteries run through the transverse foramina; the spinal cord runs through the vertebral foramen.
The seven vertebrae are joined by a complex network of ligaments that figure in the traditional division of the cervical spine into three distinct columns: anterior, middle, and posterior. The anterior column consists of the vertebral body, anterior annulus fibrosus, and anterior longitudinal ligament. The middle column consists of the posterior wall of the vertebral body, posterior annulus fibrosus, and posterior longitudinal ligament. The posterior column consists of the bony complex of the vertebral arch and posterior ligamentous process. Disruption of two of these columns will result in an unstable cervical injury.
The top vertebra (C1) is called the atlas. It lies on the axis of C2, which has a stool-like protrusion called the odontoid process (or dens). A vertical projection that lies just posterior to the anterior arch of C1, the odontoid process has ligamentous attachments to the base of the skull and articulates with C1. The atlas and axis permit flexion, extension, and rotary movements. The spinal cord is made up of neuronal cell bodies and axons organized into several tracts: the spinothalamic (pain and sensation), corticospinal (motor function), and posterior columns (position sense, vibratory sensation, and deep pressure). The spinal nerve roots run through the intervertebral foramina. Damage to the spinal cord occurs in two phases. The initial damage is a direct consequence of a mechanical traumatic impact that causes hemorrhaging into the cord and the formation of edema. Secondary tissue degeneration caused by hemorrhage and edema occurs within hours, resulting in further compromise of blood flow. The severity of the injury determines the prognosis for recovery of function. A neurologic lesion is considered complete when there is an absence of sensory and motor function below the level of injury. Spinal shock needs to be considered during the initial evaluation of a CSI. This condition, which may occur in the early period after a CSI, presents as a complete loss of reflex activity in association with motor or sensory loss. The return of spinal reflexes, usually within 24 to 48 hours, signals the end of spinal shock. Neurologic deficits that persist after this period often remain permanent. Some improvement and recovery can be expected in patients with partial deficits. Damage to specific regions of the cervical spine result in predictable physical findings. Individual dermatomes, reflexes, and muscle tone will indicate the location of the spinal lesion.
COMMON UNSTABLE INJURIES
Unstable injuries that may result from a CSI include atlanto-occipital and facet dislocations. Various fractures may also occur, including flexion teardrop fractures, Jefferson fractures, odontoid fractures involving C2, hangman's fractures, and cervical burst fractures.
Atlanto-occipital dislocation. This complex injury occurs at the junction between the atlas and the skull. Most frequently, it is an anterior dislocation that causes a prevertebral hematoma and usually results in instant death.
Facet dislocation. The result of extreme flexion of the head and neck without axial compression, a facet dislocation can be either unilateral or bilateral. Unilateral facet dislocations without disk widening or subluxation are stable injuries. However, bilateral facet dislocations disrupt the anterior ligament, intervertebral disk, and posterior ligament, creating a vertebral misalignment of more than 3 mm. The three types of bilateral facet dislocations, in order of increasing severity, are the subluxed facets, perched facets, and locked facets.
Flexion teardrop fractures. One of the most severe of all CSIs, flexion teardrop fractures tend to be extremely unstable. They are caused by severe flexion forces that disrupt all ligaments as well as the intervertebral disk at the level of injury. The anteroinferior portion of the vertebral body is fractured, with concomitant posterior displacement of the fracture into the spinal canal. This type of injury often presents with acute anterior cord syndrome, marked by quadriplegia and loss of anterior column senses with retention of posterior column senses.
Jefferson fractures. Owing to its ring shape, the atlas will fracture at more than one point, which is called a Jefferson fracture. The mechanism of injury is axial loading. This often occurs when a person dives head first into a swimming pool or surf and hits the bottom. It can also occur when a heavy object strikes a person on top of the head.
Odontoid fractures. Odontoid fractures involving C2 account for approximate-ly 15% of cervical spine fractures. Not uncommonly, fractures of the anterior ring of C1 occur simultaneously. Anderson and D'Alonzo classified odontoid fractures based on the anatomic location of the fracture. A type I fracture (5% of odontoid fractures) is an avulsion injury to the tip of the odontoid and is potentially unstable. A type II fracture (60%) occurs at the base of the odontoid and is very unstable. A type III fracture (30%) is a fracture through the base of the odontoid into the body of the axis; this type of fracture has the best prognosis. A rare type of odontoid fracture is a vertical fracture, which occurs less than 5% of the time.
Odontoid fractures result from a complex combination of forces that combine flexion, extension, and rotation. Clinical presentation will include pain and an inability to move the neck. A common complaint is the sensation of instability, as if the head is not being supported by the neck. Patients may hold their head with their hands to prevent any motion.
Hangman's fracture. Also called traumatic spondylolisthesis of C2, a hangman's fracture is a bilateral C2 pedicle fracture with variable anterior displacement of C2 on C3. It is a common CSI in fatal MVAs; only atlanto-occipital dislocations occur more often. This fracture is a hyperextension injury that occurs frequently in MVAs involving rapid deceleration. Vertebral and craniofacial arterial injuries are commonly seen with hangman's fracture. Neurologic sequelae from spinal cord pathology can be spared due to the autodecompression of the spinal canal that takes place secondary to bilateral pedicle fractures. Only 5% of patients will require intraoperative neurosurgical stabilization. Most patients can be managed with halo immobilization.
Cervical burst fracture. A burst fracture occurs when axial forces cause the collapse of an entire vertebral body. This is often seen in patients who have fallen from a height. Fracture fragments commonly extend into the spinal canal, producing neurologic sequelae. This fracture should not be confused with an anterior wedge fracture, in which there is loss of only anterior vertebral body height.
COMMON STABLE INJURIES
Stable injuries that may occur as a result of a CSI include clay-shoveler's, compression wedge, and extension teardrop fractures. Clay-shoveler's fracture. A clay-shoveler's fracture is a stable fracture caused by aggressive neck flexion. Avulsion of bone off the spinous process occurs. This type of fracture is most often seen in the lower cervical spine. Neck immobilization is not mandatory but often helps to alleviate pain.
Compression wedge fractures. These fractures occur with hyperflexion and involve compression of the anterior portion of the vertebral body. There is generally no posterior ligamentous disruption and thus no neurologic injury.
Extension teardrop fractures. These are often stable injuries as well. With forced extension, the anterior longitudinal ligament pulls the anteroinferior corner of the vertebral body away from the remainder of the vertebra. This injury most commonly occurs at the level of C2. IMAGING OF CERVICAL SPINE INJURIES
Over the past decade there has been a dramatic change in the approach to imaging studies of acute cervical spine trauma. This change is driven by the increasing availability of computed tomography (CT) and magnetic resonance imaging (MRI), as well as recognition of the limitations of plain films. It has been shown that plain films miss between 5% to 8% of cervical spine fractures.
The National Emergency X-radiography Utilization Study (NEXUS) provides emergency physicians with guidelines to determine the need for cervical imaging. According to the NEXUS guidelines, radiographs may be unnecessary for patients who meet all five of the following criteria:
• no posterior midline cervical spine tenderness
• no evidence of intoxication
• normal level of alertness
• no focal neurologic deficit
• no painful distracting injuries
The NEXUS study was conducted at 21 centers across the United States, involving 34,069 patients with blunt trauma undergoing cervical spine radiography. The study reported a 99.6% sensitivity for detecting clinically important injuries. Of those patients with a CSI, the mean age was 40 years. Because only 1.3% of fractures were in children eight years old or younger, it would be imprudent to broadly extrapolate the NEXUS criteria to the pediatric population. Critics of the NEXUS criteria argue that there is poor interobserver agreement regarding "no evidence of intoxication" and "no painful distracting injuries" because these were not well defined in the study.
More recently, a Canadian cervical spine guideline was developed, based on a convenience sample of 8924 adults (mean age, 37 years) who presented to the emergency department with blunt trauma to the head/neck, stable vital signs, and a Glasgow Coma Scale score of 15. The patients were evaluated by plain radiography, CT, and a structured follow-up telephone interview. Among the study sample, 151 (1.7%) patients had a clinically significant CSI, which was the main outcome measure.
The guideline consists of three key questions:
• Was there a high-risk factor involved (for example, age over 65, dangerous mechanism of injury, or paresthesias)?
• Was there a low-risk factor present indicating an ability to assess range of motion (such as a simple rear-end car accident, sitting position in the emergency department, being ambulatory at the time of injury, delayed onset of neck pain, or absence of midline cervical spine tenderness)?
• Can the patient actively rotate his neck 45° to each side?
This guideline was shown to have a 100% sensitivity and 42.5% specificity for identifying the 151 clinically significant CSIs. A recent Canadian study compared both the NEXUS and Canadian guidelines. It concluded that for alert patients with trauma who are in stable condition, the Canadian guideline is superior to NEXUS with respect to sensitivity and specificity for CSI, and applying it would result in reduced use of radiography. All patients at risk for cervical spine fracture should undergo radiologic screening. It is possible to identify groups in whom there is a higher probability of injury. For example, there is a high incidence of CSIs in the severe, blunt, multiple-injury patient requiring ICU admission as well as patients with altered mental status, including intoxication and head injury. Major trauma patients should be treated as having an unstable cervical fracture until proven otherwise. Helical CT scan has a higher sensitivity and specificity than plain cervical radiographs in the moderate- and high-risk trauma population. Computed tomography of the cervical spine has a sensitivity of 97% to 100%. Magnetic resonance imaging is highly sensitive in the detection of ligamentous injury, SCI, and soft tissue swelling. It is less sensitive at detecting bony injury. It is important to remember that not all cases of ligamentous injury result in instability. Both MRI and CT should be considered in the obtunded trauma patient before clearing the cervical spine. Cervical CT can be limited, however, in patients with severe degenerative disease, and MRI should be strongly considered in questionable cases. Cervical evaluation in children using MRI may have added importance. In children less than 10 years of age, the most common CSIs are ligamentous without fracture.
PEDIATRIC IMAGING MODALITIES
Pediatric CSIs are rare. However, the upper cervical vertebrae tend to be more vulnerable in children than adults, and interpretations of pediatric cervical spine plain films can be difficult. Normal variations include pseudosubluxation, absence of lordosis, epiphyseal variations, unfused synchondroses, and incomplete ossification. Cervical spine immobilization is harder to achieve in children because they tend to be uncooperative and cervical collars do not fit them properly. Assessment can be especially challenging if the child is not verbal. Open-mouth views can be impossible in young children because of their lack of understanding. Remember that a single lateral plain film is not adequate to rule out a CSI. An SCI without a radiographic abnormality is more common in children than adults. The incidence is thought to be 10% to 20% of all pediatric SCIs. There can be a delay of up to four days before the onset of objective signs of myelopathy. A history of transient neurologic symptoms should be taken seriously. Asymptomatic children with a low probability of injury can be cleared clinically. The presence of a neurologic deficit in stable children warrants MRI. The standard of care for pediatric patients who are unconscious or have impaired consciousness requires imaging by CT or MRI.
TREATMENT OPTIONS
In the prehospital setting, in-line stabilization can be achieved with a cervical immobilizing device. Evaluation in the emergency department begins with the ABCs of advanced trauma life support guidelines. Control of the airway should be achieved via intubation for any hemodynamically unstable patient and should be strongly considered for complete injuries above C5. It is important to keep in mind that C3, C4, and C5 innervate the phrenic nerve, which supplies the diaphragm. Many patients can support breathing via accessory muscles initially but will quickly tire, putting them at risk for respiratory compromise. Because SCIs often cause hypotension, fluid administration is the initial treatment of choice. Hypotension can result from blood loss, neurogenic shock, or cardiac injury. Blood loss must be presumed to be the cause of hypotension until proven otherwise. While it is true that neurogenic shock presents with bradycardia and hypotension, it should be assumed that there is concomitant hemorrhagic shock and that the patient is unable to mount an appropriate tachycardic response. Emergency physicians can prevent secondary injury to the spinal cord by alleviating spinal cord compression and ensuring cervical spine immobilization. A neurosurgical consultation should be obtained in all patients in whom a cervical injury cannot be ruled out. The use of corticosteroids is still hotly debated among physicians who care for CSIs. The pathophysiological theory is that corticosteroids diminish inflammatory changes, edema, and lipid peroxidation associated with an SCI. The first National Acute Spinal Cord Injury Study (NASCIS I) evaluated the daily use of 1 gram of intravenous (IV) methylprednisolone versus 0.1 gram IV for 10 days in 330 patients with acute SCI. Neurologic recovery at several different time points was the same for both groups. During the first 14 days post-injury, subjects treated with high-dose methylprednisolone had more than three times the fatality rate of patients given standard-dose glucocorticoids, which led to an early termination of the trial. NASCIS II evaluated patients receiving placebo, naloxone, or a 30 mg/kg IV bolus of methylprednisolone, followed by a continuous infusion at 5.4 mg/kg/hr for an additional 23 hours. Improved outcomes were found only after subgroup analysis in patients treated with methylprednisolone less than eight hours post-injury. In the NASCIS III trial, patients were randomly allocated to three groups: 5.4 mg/kg/hr methylprednisolone for 24 hours, 5.4 mg/kg/hr methylprednisolone for 48 hours, and 2.5 mg/kg methylprednisolone every six hours for 48 hours. All patients received a 30-mg/kg bolus dose of IV methylprednisolone at the outset. No significant differences in motor scores were observed, but again a subgroup analysis demonstrated benefit from the 48-hour regimen in patients who received methylprednisolone within three to eight hours post-injury. NASCIS II and III have been used as evidence of the efficacy of corticosteroids in blunt SCI. Limitations in the design and analysis of the NASCIS trials, however, and failure to replicate their results have raised questions as to their validity. After the initial criticisms directed at the methodology and interpretation of the NASCIS II and III trials, critical reviews of the use of methylprednisolone have been conducted by the American Association of Neurologic Surgeons, the Congress of Neurologic Surgeons, the Canadian Spine Society, and the Canadian Neurologic Society. All have come to the conclusion that methylprednisolone should not be considered a part of the clinical or medicolegal standard of care for patients with acute SCIs, but rather that it should be a treatment option only. As the availability of immediate neurosurgical consultation is often limited, emergency physicians would be best advised to consider IV steroid use the current standard of care. Current guidelines for the use of methylprednisolone are as follows:
• Methylprednisolone must be started within 8 hours of the injury.
• A 30 mg/kg bolus dose should be administered intravenously over 15 minutes.
• Forty-five minutes later, a maintenance infusion of 5.4 mg/kg/hr for the next 23 hours should be started.
A neurosurgical or orthopedic spine specialist is best qualified to determine the stability of cervical injuries. Depending on the clinical scenario, a patient with an unstable cervical spine may be taken to the operating room for fixation or placed in a cervical halo. Subluxations of the cervical spine are uniformly reduced by a neurosurgical or orthopedic spine specialist. After Garner-Wells tongs are placed into the soft tissue of the temples, traction is applied using weights under fluoroscopy guidance. Inability to achieve adequate reduction is an indication for spinal decompression and fusion. Once the cervical spine is reduced, spinal orthoses are used to immobilize the fracture. Fixation points using the cranium and thoracic cages and cervical collars prevent flexion and extension of the cervical spine.
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Suggested Reading
Bracken MB: Steroids for acute spinal cord injury. Cochrane Database Syst Rev (3):CD001046, 2002.
Denis F: Spinal instability as defined by the three column spine concept in acute spinal trauma. Clin Orthop Relat Res (189):65, 1983.
Hadley MN, et al.: Pharmacological therapy after acute cervical spinal cord injury. Neurosurgery 50(3 Supplement):S63, 2002.
Hoffman JR, et al.: Validity of a set of clinical criteria to rule out injury to the cervical spine in patients with blunt trauma: National Emergency X-Radiography Utilization Study Group. N Engl J Med 343(2):94, 2000.
Stiell IG, et al.: The Canadian C-Spine Rule versus the NEXUS Low-Risk Criteria in Patients with Trauma. N Engl J Med 349(26):2510, 2003.
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