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Imaging Update on Cervical Spinal Trauma, Instability Screening, and Clearance
Imaging Update on Cervical Spinal Trauma, Instability Screening, and Clearance Andrew P. White, MD,* Stewart Kerr, MD,† Richard C. Mendel, MD,‡ David Hannallah, MD,† and Alexander R. Vaccaro, MD, FACS§ Clinicians from varied specialties rely on cervical spine imaging techniques. The assessment of cervical spine instability after trauma is one typical scenario where imaging is a critical part of the evaluation. Screening for instability in nontraumatic clinical scenarios is also germane, however. Protocols to guide the clinician as to what imaging study is most useful to assess each patient circumstance have been refined in the past decade. This development has been driven, in part, by an evolution in modern imaging techniques. Changes in guidelines have also been motivated by the outcomes of large prospective series evaluating screening techniques. While various guidelines have been proposed by clinicians with varied perspectives and specialties, the recommendations are converging and have become remarkably similar to one another. As such, practical protocols for evaluating cervical spinal trauma, instability, and clearance can be proposed with expectation for wide applicability and good predictability. Semin Spine Surg 19:98-105 © 2007 Elsevier Inc. All rights reserved. KEYWORDS cervical imaging, trauma clearance, instability evaluation, screening utility of flexion– extension radiographs, cervical screening guidelines
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he incidence of cervical spinal fracture after blunt trauma is less than 5%1 and the radiographic finding of instability in degenerative, nontrauma patients is infrequent, with an incidence of about 1%.2 The performance of some type of cervical imaging technique for virtually every patient who presents to an emergency department or office with any neck-related complaint may be well motivated. The high frequency of cervical imaging is related to the considerable interest in detecting unstable cervical spine injuries which, if missed, may be associated with devastating complications. Injuries to the cervical spine may be purely ligamentous, isolated fractures, or a combined osteo-ligamentous disruption that can result in various degrees of instability. The radiological examination is a crucial part of nearly any injury detection protocol and is used in early treatment decision*Department of Orthopedic Surgery, Beth Israel Deaconess Medical Center, Boston, MA. †Department of Orthopaedic Surgery, Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, PA. ‡Department of Neurosurgery, Cooper University Hospital, Camden, NJ. §Departments of Neurosurgery and Orthopaedic Surgery, Jefferson Medical College and the Rothman Institute, Philadelphia, PA. Address reprint requests to Andrew P. White, MD, 834 Chestnut Street, Apt. 1114, Philadelphia, PA 19107. E-mail: [email protected]
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making. Images are used to assess the character of the injury, including bony displacement, angulation, and fragment size. These factors can be used to predict instability and to classify, prognosticate, and guide treatment. Cervical spine instability is frequently related to conditions other than acute trauma. Chronic instability in the setting of rheumatoid disease, congenital anomalies, remote trauma or surgery, and even degenerative disease may be commonly evaluated with cervical imaging techniques. The radiographic techniques used to evaluate the cervical spine as related to trauma, clearance, and instability will be considered in this review. New developments and new utilizations will be a focus.
Initial Cervical Imaging after Trauma Some type of imaging is performed for the vast majority of trauma patients. A certain subset of these patients, however, may be adequately evaluated for traumatic injury without advanced imaging techniques. It has been suggested that the patient who is alert, not intoxicated, and without a distracting injury, neurological deficit, neck pain, or tenderness can be clinically cleared without the need for cervical spine im-
Imaging update on cervical spinal trauma aging.3,4 Although this practice has been instituted for general practice in Canadian emergency departments,5 it may not be considered to be acceptable or to be a “standard of care” in all communities. While plain radiographs have traditionally been the first cervical imaging examination performed for patients with trauma, the increasing prevalence of high-quality computed tomographic (CT) scanners in United States hospitals has changed trauma screening techniques in the last decade. MacDonald and colleagues reported in 1990 that 99% of clinically significant injuries could be detected by three plain radiographic views.6 Another study similarly reported that plain radiography had a sensitivity and specificity of 93 and 95%, but only if the radiographs demonstrated the entire cervical spine from the occiput to the first thoracic vertebra.7 Others, however, have reported conflicting results. In 2006, Barrett and colleagues, in a report of the National Emergency X-Radiography Utilization Study (NEXUS), found that, from among 224 patients who had injuries identified on plain radiographs, there were 81 patients (36%) who had at least one secondary injury that was not identified on plain radiography, but only found on subsequent CT scan.8 Gale and colleagues recently found a still higher rate of cervical spine fractures missed by radiography alone.9 Using CT as a gold standard in their study, they retrospectively showed that the sensitivity and specificity of three radiographic views to detect cervical fractures was only 32 and 99%, respectively. This represented 13 missed fractures (of 19) in their patient cohort. The addition of selective CT as an adjunct to plain radiography has been shown to improve the sensitivity and specificity for detecting cervical spine injuries.10 This is particularly relevant to the evaluation of the upper cervical spine.11 For this reason, the standard Advanced Trauma Life Support protocol supports the use of plain radiographs as a screening tool with CT employed as an adjunct when the plain radiographs are inadequate or suggestive of injury or the patient has notable pain despite negative findings on the plain radiographs. If a head CT is performed as a part of the patient assessment, continuing the scan caudal to the C2 body will then include the atlanto-axial articulation and improve the detection of upper cervical injuries, for example. CT scanning should also be used if it is not possible to achieve adequate plain radiographs. McCullogh and colleagues recently published a landmark study where they considered whether or not plain radiographs were useful at all when a modern spiral CT scan was obtained.12 In their review, 48% of the emergency department plain radiographs were deemed technically adequate. Overall, the plain radiographs had a sensitivity of 45% and a specificity of 97%, while the subset of technically adequate plain radiographs had a somewhat improved sensitivity of 52% and specificity of 98%. Both the sensitivity and specificity of helical CT, however, was 98%, which was statistically significantly different as compared with that of the radiographs. Most importantly, among the patients in whom an injury had been identified on CT, 48% of them were missed on technically adequate plain radiographs. CT alone missed
99 one of the injuries; this was an odontoid fracture that was easily seen on retrospective review of the original CT images. This was likely missed due to reader oversight and not related to the sensitivity of the imaging technique. The authors concluded that, when performing modern spiral CT scanning for cervical trauma, the use of plain radiographs may be safely omitted. The utility of plain radiographs should not be completely overlooked, however. The standard AP, neutral lateral, and open mouth odontoid views should remain part of the initial imaging protocol, even for patients who will undergo CT and MR imaging. These familiar radiographs are often used in the initial decision-making process. The initial injury plain radiographs also become an essential part of the medical record and are subsequently used in follow-up evaluations, to compare with later plain radiographs. The comparative utility of CT scanning to plain radiography alone is currently being reflected in modified diagnostic protocols. The results of a new protocol to evaluate cervical spine injuries in blunt trauma were reported in 2005. Under this protocol, any patient without clinical evidence of neurologic injury, alcohol or drug intoxication, or distracting injury underwent cervical spine evaluation by clinical examination and plain radiographs. Patients who did not meet these criteria underwent cervical helical CT scanning, and for patients who had neurologic deficits, an MRI was also obtained. Using this protocol to evaluate 2584 patients, the authors reported an injury detection sensitivity of 99% and a specificity of 100%. The risk of missing a cervical spine injury in these blunt trauma patients was 0.04% and no spine injuries were missed in patients with head injuries.13 While there is no current consensus in the peer-reviewed literature as to the most appropriate cervical imaging study for every patient scenario, several guidelines and recommendations have been reported. Many of these guidelines are rather similar to one another. The Spine Trauma Study Group, established in 2002, is an international panel of orthopedic and neurological surgeons each with extensive experience in spinal trauma. The group recently published their suggested protocol for initial spinal imaging in the setting of blunt trauma based on published efficacy and cost-effectiveness information and on the opinions its members.14 They recommended that plain radiographs be used for the initial radiographic evaluation of the spine after acute trauma. CT scanning was recommended to define the detail of every spinal injury detected on plain radiographs and was recommended to be used as a screening tool after radiographs for any patient with neck pain, tenderness, neurological deficit, or any unconscious or unexaminable patient (Fig. 1). MRI was also recommended for every radiographic abnormality, and for every patient who was unexaminable or with a neurological deficit. This proposed use of CT and MR is likely to be very effective; it is essentially the same as that of Sanchez and coworkers, who reported 99% sensitivity and 100% specificity in diagnosing cervical injuries after blunt trauma.13
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Figure 1 This figure depicts a protocol for the initial spine imaging after trauma, as recommended by The Spine Trauma Study Group. (Reprinted with permission.14)
Technical Considerations for Cervical Spine Imaging In order for accurate diagnoses to be made with high sensitivity, variability in imaging techniques and variability in image quality must be limited as much as possible. An acceptable lateral cervical radiograph, for example, should demonstrate overlap of the left and right lateral masses. A true lateral radiograph will improve the sensitivity of detecting a rotational injury, for example, as discrepancy in rotation can be more easily recognized.
An adequate radiograph must also clearly image the caudal limits of the cervical spine, including the C7-T1 disk. Indeed, a fracture of C7 or a dislocation at C7-T1 accounted for 17% of all cervical injuries in a review of 818 patients from the NEXUS.15 Oblique views may be helpful to visualize the cervico-thoracic junction when individual patient anatomy precludes an adequate view of the top of T1. Nearly all spine surgeons are familiar with cases where a very serious cervical spine injury was overlooked when a technically inadequate lateral radiograph was accepted (Fig. 2).
Figure 2 Inadequate initial cervical radiographs (A) contributed to the failure to identify an unstable cervical injury. This patient presented to an outside hospital with neck pain but without any recognized neurological deficit. She was admitted to the hospital for care of other injuries. Her cervical injury was not identified until several days after admission, after a progressively worsening neurological deficit had developed and a CT scan was obtained (B). The intraoperative lateral radiograph demonstrates the spine caudal to the obvious abnormality (C).
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Figure 3 This patient presented with an incomplete spinal cord injury. The initial radiographs demonstrated no specific morphologic abnormalities (A, B) and the CT scan images (C-F) demonstrated grossly well-aligned vertebrae with a unilateral facet fracture. A subsequent MRI (G and H) revealed the offending pathology, however, as a large C6-C7 disk herniation, effacing the thecal sac and compressing the cervical spinal cord.
Technical considerations have also developed with the evolution of CT scanning for spinal trauma. Modern helical CT scanners, for instance, reduce the risk of missing a subtle fracture in the axial plane “between slices” and allow for improved quality of coronal and sagittal reformatted images, as well. Use of nonhelical CT is discouraged; studies of patients with traumatic cervical spine injuries showed that nonhelical CT missed certain fractures that plain radiographs detected.16,17 An adequate CT scan for trauma should collect data at 1.5-mm intervals, from the base of the occiput to T4. Both coronal and sagittal images should be reformatted as a standard part of the examination. To best utilize the coronal reformats to evaluate the occipitocervical junction, the images should be reformatted in the plane parallel to the odontoid, rather than parallel to the lower cervical vertebrae. This best allows for comparison to the familiar open mouth radio-
graphic view, for both injury detection and measurement. Sagittal reformats are particularly useful to recognize and assess injuries to the lateral masses, as well as any displaced fracture in the sagittal plane. Cervical spine CT scanning for trauma evaluation is attractive for many reasons. Its high sensitivity for injury detection, speed of examination, and convenience when concurrently obtaining the typical CT of the chest, abdomen, and pelvis for trauma, all make the CT a very useful tool. It should not be used ubiquitously, however, due to both its added cost and associated radiation exposure to the skin and thyroid gland. The radiation delivered to the thyroid gland by a cervical spine spiral CT scan is 26.0 mGy, as compared with 1.80 mGy for a three-view radiographic series, representing a 14-fold increase.18 An alternative, lower dose (14.1 mGy) protocol for helical CT of the cervical spine has demonstrated
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Figure 3 (continued)
equivalent technical adequacy and diagnostic accuracy as a standard (26.0 mGy) protocol.19 Considering that this alternative technique would reduce the excess thyroid cancer mortality for 25-year-old men from 96.7 (standarddose CT) to 52.4 (lower-dose CT) per 100,000 patients, it may be considered a superior technique. Of note, the excess thyroid cancer mortality for radiographs alone, which deliver a 1.8 mGy thyroid dose, is 6.7 per 100,000 patients. The use of magnetic resonance imaging (MRI) in cervical trauma is well utilized in North America. MRI obtains image data directly in any plane without the degradation that can be seen when reformatting cervical spine CT scans. It can best be used to evaluate potential soft-tissue injuries, including that to the ligament, disks, and neural elements.20 MRI is superior to CT in identifying and characterizing an epidural mass, such as a disk extrusion or epidural hematoma. The utility of MR imaging in distinguishing between cord contusion, hemorrhage, or transection has important prognostic significance.21 The extent of intramedullary signal changes on MRI also has important physiologic and prognostic significance.22 The T1-weighted MR image gives excellent spatial resolution and a good survey of marrow signal but does not differentiate well tissues of the posterior longitudinal ligament, a desiccated disk herniation, and cerebrospinal fluid, which all appear as low-intensity signal. Consequently, a T2-weighted
sequence using fast spin-echo technique is typically used to evaluate for central canal and thecal sac compromise. In addition to the fast spin-echo sagittal T2, a true T2-weighted sequence in the axial plane should be performed to evaluate intramedullary tissue. Fat suppression of the T2-weighted sequences is useful in the trauma evaluation since it will make edema or hemorrhage in ligaments, bone, and the spinal cord more evident. To detect acute ligamentous, disk, or neural injury with the highest sensitivity, Short Tau Inversion Recovery (STIR) sequences should be included. STIR sequences are similar to a fat-suppressed T2 but further highlight acute soft-tissue edema. Magnetic resonance angiography (MRA) is being used to evaluate cervical spinal trauma patients with greater frequency in the last decade. It is now recognized that the vertebral arteries may be injured with an incidence as high as 25 to 46% following cervical trauma.23,24 While controversial, there may be a benefit to anticoagulation in the perioperative period for the asymptomatic patient with unilateral vertebral artery injury to prevent propagation of thrombosis.25 MRA has been demonstrated to be as sensitive as conventional angiography in detecting vertebral artery injuries.26 For these reasons, MRA has become part of the standard imaging protocol for cervical spinal trauma evaluation at many regional spinal cord injury centers in the United States.
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Figure 4 This elderly patient with ankylosing spondylitis (AS) presented with neck pain and a normal neurological examination. His plain radiographs demonstrated the characteristic bony changes of AS, but did not reveal a fracture. A helical CT scan with sagittal reformats (A) demonstrated a fracture at the C6-C7 level. This is a transverse fracture, with disruption of the anterior and posterior elements at the same vertebral level. This fracture morphology is often seen in spinal conditions associated with extensive and multilevel fusions, where the fracture biomechanics behave more like a long bone than a normal segmented vertebral column. The subsequent fat-suppressed T2 MRI (B) confirms the transverse pattern of bony injury and reveals the transverse injury to posterior ligamentous tissues, indicating a highly unstable injury.
Imaging Measurement Techniques The accurate description of cervical injuries has not been well standardized. For example, while posttraumatic subaxial kyphosis may be readily recognized by nearly all observers, the degree of kyphosis as measured by each observer is likely to reveal a wide range of techniques and a wide range of values. The literature is replete with varied methods of cervical radiographic measurement. To use the previous example, cervical sagittal alignment has been reported in the literature using a wide variety of methods.27-30 While the Cobb technique may be the most popular, the Harrington posterior vertebral body tangent technique may be more reproducible between observers.27 Cannada and colleagues also reported that measuring the distance between spinous processes was more reliable than using the Cobb technique for detecting cervical pseudarthroses.31 White and colleagues, however, recently demonstrated that measuring cervical sagittal angle using the Cobb technique was more accurate, with a significantly improved intraobserver correlation, as compared with two other methods, including the posterior vertebral body tangent method.2 The Spine Trauma Study group recently published a consensus statement on measurement techniques for lower cervical spine injuries. They recognized that a standard set of imaging measurement techniques does not exist and that
many spine surgeons have developed their own techniques, leading to a high degree of variability. The group performed a literature review to compile a list of useful lower cervical spine image measurement techniques and then developed a consensus among members as to the most useful techniques. To measure lower cervical kyphosis, for example, a consensus was developed that the Cobb method was the most useful, using the inferior endplate of the vertebral body caudal to the injured level and the superior endplate of the body cranial to the injured vertebrae. Consensus was also developed for measurements of vertebral body height loss, vertebral translation, canal compromise, and facet fracture articular apposition.32 These techniques are proposed to be the most useful, but prospective studies will be needed to evaluate the utility of each.
The Role of MRI in Imaging Traumatic Fractures and Dislocations The reduction of a cervical fracture or dislocation with traction may be associated with a risk of neurological injury if a concomitant disk herniation becomes impinged on the spinal cord with reduction (Fig. 3).33 For this reason, some have advocated MRI before attempting a closed reduction. There have been no documented cases, however, of permanent spi-
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104 nal cord injury in an awake, cooperative, neurologically intact patient who underwent a carefully observed closed reduction. In fact, Vaccaro and coworkers reported a series of successful closed reductions of facet dislocations, with no neurological injuries, even in two awake patients known to have disk herniations before reduction.34 Given the potential risk, however, closed reduction without previous MRI should only be undertaken in a patient who is awake, alert, and able to cooperate with the neurologic examination. An early closed reduction, before an MRI is obtained, may be advisable for the alert patient with a complete or high-grade incomplete injury since such a patient may have much to gain and little to lose in terms of early closed decompression of the spinal cord.35 In a patient who cannot be reliably followed with serial neurological examinations, however, a MRI should be obtained before reduction.
Imaging High-Risk Patients When evaluating patients with an increased risk for missed injuries, a heightened suspicion must be exercised. In concordance, an increased reliance on advanced imaging methods should be undertaken. Spondyloarthropathies such as ankylosing spondylitis and diffuse idiopathic skeletal hyperostosis are common examples of disorders where evaluating physicians must maintain the assumption that a potentially devastating injury exists (Fig. 4) until it has been ruled out by virtually every useful imaging method.36 Other conditions that should be carefully scrutinized for suspected cervical spine injury include pain in the setting of a congenital or acquired cervical spine fusion, and connective tissue disorders associated with ligamentous laxity.
mobility may be observed in patients presenting with radicular and degenerative diseases, but the potential utility of identifying such hypomobility has not been documented.42 One recent study has addressed the utility of flexion extension films to detect instability in the degenerative population. Investigators examined 206 sets of cervical F/E radiographs to determine the percentage of lateral F/E radiographs that revealed pathology not appreciated on neutral lateral radiographs. This study also determined the frequency that these supplemental views led to a change in the management of these patients. In this population, 1% had spondylolisthesis noted only on the F/E images and 3% had a change in their neutral view spondylolisthesis. None of these findings led to a change in clinical management.2 The authors commented that this data, combined with the extra cost and radiation exposure associated with additional views, led them to no longer regard dynamic radiographs as a useful part of the initial imaging for the patient with degenerative cervical conditions.
Conclusion The importance of imaging to evaluate the cervical spine for instability is well established. Specific imaging recommendations are changing, however, as techniques evolve and as investigators continue to report the utility of various protocols. While current protocols may be reliable and well accepted, it is anticipated that as our field becomes more focused on cost containment and interested in high efficiency evaluation, protocols and guidelines are likely to continue to change.
References
Screening Utility of Flexion–Extension Radiographs In the absence of findings on plain radiography and CT scanning, some authors have previously recommended flexion– extension (F/E) radiographs to be performed in the emergency department for patients presenting with cervical symptoms.37,38 Others have discouraged this practice in the acute setting, citing that instability might be missed secondary to muscular guarding.39,40 For this reason, initial bracing is recommended for the patient with cervical symptoms but no radiographic abnormalities until delayed F/E radiographs can be obtained several weeks after an injury. While the utility of F/E radiographs in the subacute evaluation of the spine trauma patient is established, the role of dynamic radiographs in the nontrauma population is poorly defined. One recent investigation reviewed AP and neutral lateral radiographs of patients with no history of trauma and concluded that the use of routine cervical radiographs as a screening tool is not justified for the nontraumatic patient population.41 The authors did, however, recommend the use of cervical films in the nontraumatic setting for patients with localizing signs or symptoms of dysfunction. This study did not consider the potential utility of F/E radiographs. Hypo-
1. Grossman MD, Reilly PM, Gillett T, et al: National survey of the incidence of cervical spine injury and approach to cervical spine clearance in U.S. trauma centers. J Trauma 47:684-691, 1999 2. White AP, Biswas D, Smart LR, et al: Utility of flexion-extension radiographs in evaluating the degenerative cervical spine. Spine J 6:14S, 2006 3. Hoffman JR, Wolfson AB, Todd K, et al: Selective cervical spine radiography in blunt trauma: methodology of the National Emergency X-Radiography Utilization Study (NEXUS). Ann Emerg Med 32:461469, 1998 4. Hoffman JR, Mower WR, Wolfson AB, et al: Validity of a set of clinical criteria to rule out injury to the cervical spine in patients with blunt trauma. National Emergency-Radiography Utilization Study Group. N Engl J Med 343:94-99, 2000 5. Stiell IG, Wells GA, Vandemheen KL, et al: The Canadian C-spine rules for radiography in alert and stable trauma patients. JAMA 286:18411848, 2001 6. MacDonald RL, Schwartz ML, Mirich D, et al: Diagnosis of cervical spine injury in motor vehicle crash victims: how many X-rays are enough? J Trauma 30:392-397, 1990 7. Nguyen GK, Clark R: Adequacy of plain radiography in the diagnosis of cervical spine injuries. Emerg Radiol 11:158-161, 2005 8. Barrett TW, Mower WR, Zucker MI, et al: Injuries missed by limited computed tomographic imaging of patients with cervical spine injuries. Ann Emerg Med 47:129-133, 2006 9. Gale SC, Gracias VH, Reilly PM, et al: The inefficiency of plain radiography to evaluate the cervical spine after blunt trauma. J Trauma 59: 1121-1125, 2005 10. Berne JD, Velmahos GC, El-Tawil Q, et al: Value of complete cervical
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helical computed tomographic scanning in identifying cervical spine injury in the unevaluable blunt trauma patient with multiple injuries: a prospective study. J Trauma 47:896-903, 1999 Barba CA, Taggert J, Morgan AS, et al: A new cervical spine clearance protocol using computed tomography. J Trauma 51:652-657, 2001 McCulloch PT, France J, Jones DL, et al: Helical computed tomography alone compared with plain radiographs with adjunct computed tomography to evaluate the Cervical spine after high-energy trauma. J Bone Joint Surg Am 87:2388-2394, 2005 Sanchez B, Waxman K, Jones T, et al: Cervical spine clearance in blunt trauma: evaluation of a computed tomography-based protocol. J Trauma Injury Infect Crit Care 59:179-183, 2005 France JC, Bono CM, Vaccaro AR: Initial radiographic evaluation of the spine after trauma: when, what, where and how to image the acutely traumatized spine. J Orthop Trauma 19:640-649, 2005 Goldberg W, Mueller C, Panacek E, et al: Distribution and patterns of blunt traumatic cervical spine injury. Ann Emerg Med 38:17-21, 2001 Acheson MB, Livingston RR, Richardson ML, et al: High-resolution CT scanning in the evaluation of cervical spine fractures: comparison with plain film examinations. AJR Am J Roentgenol 148:1179-1185, 1987 Pech P, Kilgore DP, Pojunas KW, et al: Cervical spinal fractures: CT detection. Radiology 157:117-120, 1985 Rybicki F, Nawfel RD, Judy PF, et al: Skin and thyroid dosimetry in cervical spine screening: Two methods for evaluation and a comparison between a helical CT and radiographic trauma series. AJR Am J Roentgenol 179:933-937, 2002 Shu KM, MacKenzie JD, Smith JB, et al: Lowering the thyroid dose in screening examinations of the cervical spine. Emerg Radiol 12:133136, 2006 Cohen WA, Giauque AP, Hallam DK, et al: Evidence-based approach to use of MR imaging in acute spinal trauma. Eur J Radiol 48:49-60, 2003 Flanders AE, Spettell CM, Tartaglino LM, et al: Forecasting motor recovery after cervical spinal cord injury: value of MR imaging. Radiology 201:649-655, 1996 Ishida Y, Tominaga T: Predictors of neurologic recovery in acute central cervical cord injury with only upper extremity impairment. Spine 27: 1652-1658, 2002 Parbhoo AH, Govender S, Corr P: Vertebral artery injury in cervical spine trauma. Injury 32:565-568, 2001 Friedman D, Flanders A, Thomas C, et al: Vertebral artery injury after acute cervical spine trauma: rate of occurrence as detected by MR angiography and assessment of clinical consequences. AJR Am J Roentgenol 164:443-447, 1995 Biffl WL, Moore DE, Elliot JP, et al: The devastating potential of blunt vertebral arterial injuries. Ann Surg 231:672-681, 2000 Phan T, Huston J, Bernstein MA, et al: Contrast-enhanced magnetic resonance angiography of the cervical vessels: experience with 422 patients. Stroke 32:2282-2286, 2001
105 27. Harrison DE, Harrison DD, Cailliet R, et al: Cobb method or Harrison posterior tangent method: which to choose for lateral cervical radiographic analysis. Spine 25:2072-2078, 2000 28. Troyanovich SJ, Stroink AR, Kattner KA, et al: Does anterior plating maintain cervical lordosis versus conventional fusion techniques? A retrospective analysis of patients receiving single-level fusions. J Spinal Disord Tech 15:69-74, 2002 29. Loder RT: The sagittal profile of the cervical and lumbosacral spine in Scheuermann thoracic kyphosis. J Spinal Disord 14:226-231, 2001 30. Hilibrand AS, Tannenbaum DA, Graziano GP, et al: The sagittal alignment of the cervical spine in adolescent idiopathic scoliosis. J Pediatr Orthop 15:627-632, 1995 31. Cannada LK, Scherping SC, Yoo JU, et al: Pseudarthrosis of the cervical spine: a comparison of radiographic diagnostic measures. Spine 28:4651, 2003 32. Bono CM, Vaccaro AR, Fehlings M, et al: Measurement techniques for lower cervical spine injuries; consensus statement of the Spine Trauma Study group. Spine 5:603-609, 2006 33. Eismont FJ, Arena MJ, Green BA: Extrusion of an intervertebral disc associated with traumatic subluxation or dislocation of cervical facets: case report. J Bone Joint Surg Am 73:1555-1560, 1991 34. Vaccaro AR, Falatyn SP, Flanders AE, et al: Magnetic resonance evaluation of the intervertebral disc, spinal ligaments, and spinal cord before and after closed traction reduction of cervical spine dislocations. Spine 24:1210-1217, 1999 35. Hart RA, Vaccaro AR, Nachwalter RS: Cervical facet dislocation: when is magnetic resonance imaging indicated? Spine 27:116-117, 2002 36. Harrop JS, Sharan A, Anderson G, et al: Failure of standard imaging to detect a cervical fracture in a patient with ankylosing spondylitis. Spine 30:E417-E419, 2005 37. Bachulis BL, Long WB, Hynes GD, et al: Clinical indications for cervical spine radiographs in the traumatized patient. Am J Surg 153:473-478, 1987 38. Lewis LM, Docherty M, Ruoff BE, et al: Flexion-extension views in the evaluation of cervical-spine injuries. Ann Emerg Med 20:117-121, 1991 39. Wang JC, Hatch JD, Sandhu HS, et al: Cervical flexion and extension radiographs in acutely injured patients. Clin Orthop Relat Res 111-116, 1999 40. Insko EK, Gracias VH, Gupta R, et al: Utility of flexion and extension radiographs of the cervical spine in the acute evaluation of blunt trauma. J Trauma 53:426-429, 2002 41. Johnson MJ, Lucas GL: Value of cervical spine radiographs as a screening tool. Clin Orthop Relat Res 102-108, 1997 42. Dvorak J, Panjabi MM, Grob D, et al: Clinical validation of functional flexion/extension radiographs of the cervical spine. Spine 18:120-127, 1993
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he incidence of cervical spinal fracture after blunt trauma is less than 5%1 and the radiographic finding of instability in degenerative, nontrauma patients is infrequent, with an incidence of about 1%.2 The performance of some type of cervical imaging technique for virtually every patient who presents to an emergency department or office with any neck-related complaint may be well motivated. The high frequency of cervical imaging is related to the considerable interest in detecting unstable cervical spine injuries which, if missed, may be associated with devastating complications. Injuries to the cervical spine may be purely ligamentous, isolated fractures, or a combined osteo-ligamentous disruption that can result in various degrees of instability. The radiological examination is a crucial part of nearly any injury detection protocol and is used in early treatment decision*Department of Orthopedic Surgery, Beth Israel Deaconess Medical Center, Boston, MA. †Department of Orthopaedic Surgery, Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, PA. ‡Department of Neurosurgery, Cooper University Hospital, Camden, NJ. §Departments of Neurosurgery and Orthopaedic Surgery, Jefferson Medical College and the Rothman Institute, Philadelphia, PA. Address reprint requests to Andrew P. White, MD, 834 Chestnut Street, Apt. 1114, Philadelphia, PA 19107. E-mail: [email protected]
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making. Images are used to assess the character of the injury, including bony displacement, angulation, and fragment size. These factors can be used to predict instability and to classify, prognosticate, and guide treatment. Cervical spine instability is frequently related to conditions other than acute trauma. Chronic instability in the setting of rheumatoid disease, congenital anomalies, remote trauma or surgery, and even degenerative disease may be commonly evaluated with cervical imaging techniques. The radiographic techniques used to evaluate the cervical spine as related to trauma, clearance, and instability will be considered in this review. New developments and new utilizations will be a focus.
Initial Cervical Imaging after Trauma Some type of imaging is performed for the vast majority of trauma patients. A certain subset of these patients, however, may be adequately evaluated for traumatic injury without advanced imaging techniques. It has been suggested that the patient who is alert, not intoxicated, and without a distracting injury, neurological deficit, neck pain, or tenderness can be clinically cleared without the need for cervical spine im-
Imaging update on cervical spinal trauma aging.3,4 Although this practice has been instituted for general practice in Canadian emergency departments,5 it may not be considered to be acceptable or to be a “standard of care” in all communities. While plain radiographs have traditionally been the first cervical imaging examination performed for patients with trauma, the increasing prevalence of high-quality computed tomographic (CT) scanners in United States hospitals has changed trauma screening techniques in the last decade. MacDonald and colleagues reported in 1990 that 99% of clinically significant injuries could be detected by three plain radiographic views.6 Another study similarly reported that plain radiography had a sensitivity and specificity of 93 and 95%, but only if the radiographs demonstrated the entire cervical spine from the occiput to the first thoracic vertebra.7 Others, however, have reported conflicting results. In 2006, Barrett and colleagues, in a report of the National Emergency X-Radiography Utilization Study (NEXUS), found that, from among 224 patients who had injuries identified on plain radiographs, there were 81 patients (36%) who had at least one secondary injury that was not identified on plain radiography, but only found on subsequent CT scan.8 Gale and colleagues recently found a still higher rate of cervical spine fractures missed by radiography alone.9 Using CT as a gold standard in their study, they retrospectively showed that the sensitivity and specificity of three radiographic views to detect cervical fractures was only 32 and 99%, respectively. This represented 13 missed fractures (of 19) in their patient cohort. The addition of selective CT as an adjunct to plain radiography has been shown to improve the sensitivity and specificity for detecting cervical spine injuries.10 This is particularly relevant to the evaluation of the upper cervical spine.11 For this reason, the standard Advanced Trauma Life Support protocol supports the use of plain radiographs as a screening tool with CT employed as an adjunct when the plain radiographs are inadequate or suggestive of injury or the patient has notable pain despite negative findings on the plain radiographs. If a head CT is performed as a part of the patient assessment, continuing the scan caudal to the C2 body will then include the atlanto-axial articulation and improve the detection of upper cervical injuries, for example. CT scanning should also be used if it is not possible to achieve adequate plain radiographs. McCullogh and colleagues recently published a landmark study where they considered whether or not plain radiographs were useful at all when a modern spiral CT scan was obtained.12 In their review, 48% of the emergency department plain radiographs were deemed technically adequate. Overall, the plain radiographs had a sensitivity of 45% and a specificity of 97%, while the subset of technically adequate plain radiographs had a somewhat improved sensitivity of 52% and specificity of 98%. Both the sensitivity and specificity of helical CT, however, was 98%, which was statistically significantly different as compared with that of the radiographs. Most importantly, among the patients in whom an injury had been identified on CT, 48% of them were missed on technically adequate plain radiographs. CT alone missed
99 one of the injuries; this was an odontoid fracture that was easily seen on retrospective review of the original CT images. This was likely missed due to reader oversight and not related to the sensitivity of the imaging technique. The authors concluded that, when performing modern spiral CT scanning for cervical trauma, the use of plain radiographs may be safely omitted. The utility of plain radiographs should not be completely overlooked, however. The standard AP, neutral lateral, and open mouth odontoid views should remain part of the initial imaging protocol, even for patients who will undergo CT and MR imaging. These familiar radiographs are often used in the initial decision-making process. The initial injury plain radiographs also become an essential part of the medical record and are subsequently used in follow-up evaluations, to compare with later plain radiographs. The comparative utility of CT scanning to plain radiography alone is currently being reflected in modified diagnostic protocols. The results of a new protocol to evaluate cervical spine injuries in blunt trauma were reported in 2005. Under this protocol, any patient without clinical evidence of neurologic injury, alcohol or drug intoxication, or distracting injury underwent cervical spine evaluation by clinical examination and plain radiographs. Patients who did not meet these criteria underwent cervical helical CT scanning, and for patients who had neurologic deficits, an MRI was also obtained. Using this protocol to evaluate 2584 patients, the authors reported an injury detection sensitivity of 99% and a specificity of 100%. The risk of missing a cervical spine injury in these blunt trauma patients was 0.04% and no spine injuries were missed in patients with head injuries.13 While there is no current consensus in the peer-reviewed literature as to the most appropriate cervical imaging study for every patient scenario, several guidelines and recommendations have been reported. Many of these guidelines are rather similar to one another. The Spine Trauma Study Group, established in 2002, is an international panel of orthopedic and neurological surgeons each with extensive experience in spinal trauma. The group recently published their suggested protocol for initial spinal imaging in the setting of blunt trauma based on published efficacy and cost-effectiveness information and on the opinions its members.14 They recommended that plain radiographs be used for the initial radiographic evaluation of the spine after acute trauma. CT scanning was recommended to define the detail of every spinal injury detected on plain radiographs and was recommended to be used as a screening tool after radiographs for any patient with neck pain, tenderness, neurological deficit, or any unconscious or unexaminable patient (Fig. 1). MRI was also recommended for every radiographic abnormality, and for every patient who was unexaminable or with a neurological deficit. This proposed use of CT and MR is likely to be very effective; it is essentially the same as that of Sanchez and coworkers, who reported 99% sensitivity and 100% specificity in diagnosing cervical injuries after blunt trauma.13
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Figure 1 This figure depicts a protocol for the initial spine imaging after trauma, as recommended by The Spine Trauma Study Group. (Reprinted with permission.14)
Technical Considerations for Cervical Spine Imaging In order for accurate diagnoses to be made with high sensitivity, variability in imaging techniques and variability in image quality must be limited as much as possible. An acceptable lateral cervical radiograph, for example, should demonstrate overlap of the left and right lateral masses. A true lateral radiograph will improve the sensitivity of detecting a rotational injury, for example, as discrepancy in rotation can be more easily recognized.
An adequate radiograph must also clearly image the caudal limits of the cervical spine, including the C7-T1 disk. Indeed, a fracture of C7 or a dislocation at C7-T1 accounted for 17% of all cervical injuries in a review of 818 patients from the NEXUS.15 Oblique views may be helpful to visualize the cervico-thoracic junction when individual patient anatomy precludes an adequate view of the top of T1. Nearly all spine surgeons are familiar with cases where a very serious cervical spine injury was overlooked when a technically inadequate lateral radiograph was accepted (Fig. 2).
Figure 2 Inadequate initial cervical radiographs (A) contributed to the failure to identify an unstable cervical injury. This patient presented to an outside hospital with neck pain but without any recognized neurological deficit. She was admitted to the hospital for care of other injuries. Her cervical injury was not identified until several days after admission, after a progressively worsening neurological deficit had developed and a CT scan was obtained (B). The intraoperative lateral radiograph demonstrates the spine caudal to the obvious abnormality (C).
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Figure 3 This patient presented with an incomplete spinal cord injury. The initial radiographs demonstrated no specific morphologic abnormalities (A, B) and the CT scan images (C-F) demonstrated grossly well-aligned vertebrae with a unilateral facet fracture. A subsequent MRI (G and H) revealed the offending pathology, however, as a large C6-C7 disk herniation, effacing the thecal sac and compressing the cervical spinal cord.
Technical considerations have also developed with the evolution of CT scanning for spinal trauma. Modern helical CT scanners, for instance, reduce the risk of missing a subtle fracture in the axial plane “between slices” and allow for improved quality of coronal and sagittal reformatted images, as well. Use of nonhelical CT is discouraged; studies of patients with traumatic cervical spine injuries showed that nonhelical CT missed certain fractures that plain radiographs detected.16,17 An adequate CT scan for trauma should collect data at 1.5-mm intervals, from the base of the occiput to T4. Both coronal and sagittal images should be reformatted as a standard part of the examination. To best utilize the coronal reformats to evaluate the occipitocervical junction, the images should be reformatted in the plane parallel to the odontoid, rather than parallel to the lower cervical vertebrae. This best allows for comparison to the familiar open mouth radio-
graphic view, for both injury detection and measurement. Sagittal reformats are particularly useful to recognize and assess injuries to the lateral masses, as well as any displaced fracture in the sagittal plane. Cervical spine CT scanning for trauma evaluation is attractive for many reasons. Its high sensitivity for injury detection, speed of examination, and convenience when concurrently obtaining the typical CT of the chest, abdomen, and pelvis for trauma, all make the CT a very useful tool. It should not be used ubiquitously, however, due to both its added cost and associated radiation exposure to the skin and thyroid gland. The radiation delivered to the thyroid gland by a cervical spine spiral CT scan is 26.0 mGy, as compared with 1.80 mGy for a three-view radiographic series, representing a 14-fold increase.18 An alternative, lower dose (14.1 mGy) protocol for helical CT of the cervical spine has demonstrated
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Figure 3 (continued)
equivalent technical adequacy and diagnostic accuracy as a standard (26.0 mGy) protocol.19 Considering that this alternative technique would reduce the excess thyroid cancer mortality for 25-year-old men from 96.7 (standarddose CT) to 52.4 (lower-dose CT) per 100,000 patients, it may be considered a superior technique. Of note, the excess thyroid cancer mortality for radiographs alone, which deliver a 1.8 mGy thyroid dose, is 6.7 per 100,000 patients. The use of magnetic resonance imaging (MRI) in cervical trauma is well utilized in North America. MRI obtains image data directly in any plane without the degradation that can be seen when reformatting cervical spine CT scans. It can best be used to evaluate potential soft-tissue injuries, including that to the ligament, disks, and neural elements.20 MRI is superior to CT in identifying and characterizing an epidural mass, such as a disk extrusion or epidural hematoma. The utility of MR imaging in distinguishing between cord contusion, hemorrhage, or transection has important prognostic significance.21 The extent of intramedullary signal changes on MRI also has important physiologic and prognostic significance.22 The T1-weighted MR image gives excellent spatial resolution and a good survey of marrow signal but does not differentiate well tissues of the posterior longitudinal ligament, a desiccated disk herniation, and cerebrospinal fluid, which all appear as low-intensity signal. Consequently, a T2-weighted
sequence using fast spin-echo technique is typically used to evaluate for central canal and thecal sac compromise. In addition to the fast spin-echo sagittal T2, a true T2-weighted sequence in the axial plane should be performed to evaluate intramedullary tissue. Fat suppression of the T2-weighted sequences is useful in the trauma evaluation since it will make edema or hemorrhage in ligaments, bone, and the spinal cord more evident. To detect acute ligamentous, disk, or neural injury with the highest sensitivity, Short Tau Inversion Recovery (STIR) sequences should be included. STIR sequences are similar to a fat-suppressed T2 but further highlight acute soft-tissue edema. Magnetic resonance angiography (MRA) is being used to evaluate cervical spinal trauma patients with greater frequency in the last decade. It is now recognized that the vertebral arteries may be injured with an incidence as high as 25 to 46% following cervical trauma.23,24 While controversial, there may be a benefit to anticoagulation in the perioperative period for the asymptomatic patient with unilateral vertebral artery injury to prevent propagation of thrombosis.25 MRA has been demonstrated to be as sensitive as conventional angiography in detecting vertebral artery injuries.26 For these reasons, MRA has become part of the standard imaging protocol for cervical spinal trauma evaluation at many regional spinal cord injury centers in the United States.
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Figure 4 This elderly patient with ankylosing spondylitis (AS) presented with neck pain and a normal neurological examination. His plain radiographs demonstrated the characteristic bony changes of AS, but did not reveal a fracture. A helical CT scan with sagittal reformats (A) demonstrated a fracture at the C6-C7 level. This is a transverse fracture, with disruption of the anterior and posterior elements at the same vertebral level. This fracture morphology is often seen in spinal conditions associated with extensive and multilevel fusions, where the fracture biomechanics behave more like a long bone than a normal segmented vertebral column. The subsequent fat-suppressed T2 MRI (B) confirms the transverse pattern of bony injury and reveals the transverse injury to posterior ligamentous tissues, indicating a highly unstable injury.
Imaging Measurement Techniques The accurate description of cervical injuries has not been well standardized. For example, while posttraumatic subaxial kyphosis may be readily recognized by nearly all observers, the degree of kyphosis as measured by each observer is likely to reveal a wide range of techniques and a wide range of values. The literature is replete with varied methods of cervical radiographic measurement. To use the previous example, cervical sagittal alignment has been reported in the literature using a wide variety of methods.27-30 While the Cobb technique may be the most popular, the Harrington posterior vertebral body tangent technique may be more reproducible between observers.27 Cannada and colleagues also reported that measuring the distance between spinous processes was more reliable than using the Cobb technique for detecting cervical pseudarthroses.31 White and colleagues, however, recently demonstrated that measuring cervical sagittal angle using the Cobb technique was more accurate, with a significantly improved intraobserver correlation, as compared with two other methods, including the posterior vertebral body tangent method.2 The Spine Trauma Study group recently published a consensus statement on measurement techniques for lower cervical spine injuries. They recognized that a standard set of imaging measurement techniques does not exist and that
many spine surgeons have developed their own techniques, leading to a high degree of variability. The group performed a literature review to compile a list of useful lower cervical spine image measurement techniques and then developed a consensus among members as to the most useful techniques. To measure lower cervical kyphosis, for example, a consensus was developed that the Cobb method was the most useful, using the inferior endplate of the vertebral body caudal to the injured level and the superior endplate of the body cranial to the injured vertebrae. Consensus was also developed for measurements of vertebral body height loss, vertebral translation, canal compromise, and facet fracture articular apposition.32 These techniques are proposed to be the most useful, but prospective studies will be needed to evaluate the utility of each.
The Role of MRI in Imaging Traumatic Fractures and Dislocations The reduction of a cervical fracture or dislocation with traction may be associated with a risk of neurological injury if a concomitant disk herniation becomes impinged on the spinal cord with reduction (Fig. 3).33 For this reason, some have advocated MRI before attempting a closed reduction. There have been no documented cases, however, of permanent spi-
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104 nal cord injury in an awake, cooperative, neurologically intact patient who underwent a carefully observed closed reduction. In fact, Vaccaro and coworkers reported a series of successful closed reductions of facet dislocations, with no neurological injuries, even in two awake patients known to have disk herniations before reduction.34 Given the potential risk, however, closed reduction without previous MRI should only be undertaken in a patient who is awake, alert, and able to cooperate with the neurologic examination. An early closed reduction, before an MRI is obtained, may be advisable for the alert patient with a complete or high-grade incomplete injury since such a patient may have much to gain and little to lose in terms of early closed decompression of the spinal cord.35 In a patient who cannot be reliably followed with serial neurological examinations, however, a MRI should be obtained before reduction.
Imaging High-Risk Patients When evaluating patients with an increased risk for missed injuries, a heightened suspicion must be exercised. In concordance, an increased reliance on advanced imaging methods should be undertaken. Spondyloarthropathies such as ankylosing spondylitis and diffuse idiopathic skeletal hyperostosis are common examples of disorders where evaluating physicians must maintain the assumption that a potentially devastating injury exists (Fig. 4) until it has been ruled out by virtually every useful imaging method.36 Other conditions that should be carefully scrutinized for suspected cervical spine injury include pain in the setting of a congenital or acquired cervical spine fusion, and connective tissue disorders associated with ligamentous laxity.
mobility may be observed in patients presenting with radicular and degenerative diseases, but the potential utility of identifying such hypomobility has not been documented.42 One recent study has addressed the utility of flexion extension films to detect instability in the degenerative population. Investigators examined 206 sets of cervical F/E radiographs to determine the percentage of lateral F/E radiographs that revealed pathology not appreciated on neutral lateral radiographs. This study also determined the frequency that these supplemental views led to a change in the management of these patients. In this population, 1% had spondylolisthesis noted only on the F/E images and 3% had a change in their neutral view spondylolisthesis. None of these findings led to a change in clinical management.2 The authors commented that this data, combined with the extra cost and radiation exposure associated with additional views, led them to no longer regard dynamic radiographs as a useful part of the initial imaging for the patient with degenerative cervical conditions.
Conclusion The importance of imaging to evaluate the cervical spine for instability is well established. Specific imaging recommendations are changing, however, as techniques evolve and as investigators continue to report the utility of various protocols. While current protocols may be reliable and well accepted, it is anticipated that as our field becomes more focused on cost containment and interested in high efficiency evaluation, protocols and guidelines are likely to continue to change.
References
Screening Utility of Flexion–Extension Radiographs In the absence of findings on plain radiography and CT scanning, some authors have previously recommended flexion– extension (F/E) radiographs to be performed in the emergency department for patients presenting with cervical symptoms.37,38 Others have discouraged this practice in the acute setting, citing that instability might be missed secondary to muscular guarding.39,40 For this reason, initial bracing is recommended for the patient with cervical symptoms but no radiographic abnormalities until delayed F/E radiographs can be obtained several weeks after an injury. While the utility of F/E radiographs in the subacute evaluation of the spine trauma patient is established, the role of dynamic radiographs in the nontrauma population is poorly defined. One recent investigation reviewed AP and neutral lateral radiographs of patients with no history of trauma and concluded that the use of routine cervical radiographs as a screening tool is not justified for the nontraumatic patient population.41 The authors did, however, recommend the use of cervical films in the nontraumatic setting for patients with localizing signs or symptoms of dysfunction. This study did not consider the potential utility of F/E radiographs. Hypo-
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