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Cervical Spine Injury:

A Clinical Decision Rule to Identify High-Risk Patients for Helical CT Screening

OBJECTIVE.

We aimed to validate the routine use of a clinical decision rule to direct di-agnostic imaging of adult blunt trauma patients at high risk for cervical spine injury.

MATERIALS AND METHODS.

We previously developed and have since routinelyused a prediction rule based on six clinical parameters to identify patients at greater than 5%risk of cervical spine injury to undergo screening helical CT of the cervical spine. During a 6-month period, 4285 screening imaging studies of the cervical spine were performed in adultblunt trauma patients. Six hundred one patients (398 males, 203 females; age range, 16–100years; median age, 38 years) underwent helical CT, and the remainder underwent 3684 con-ventional radiographic examinations. Clinical and report data were extracted from the radiol-ogy department database, medical records, and the hospital trauma registry. Abnormalfindings were independently confirmed by additional imaging studies, autopsy results, or clin-ical outcome.

RESULTS.

The true-positive cervical spine injury rates in helical CT– and conventionalradiography-screened patients who presented directly to our trauma center were 40 (8.7%) of462 and seven (0.2%) of 3684, respectively. The cervical spine injury rate in patients whowere transferred from outside institutions to our trauma center and who underwent helical CTwas 37 (26.6%) of 139. This figure included 20 patients already known to have cervical spinefracture.

CONCLUSION.

The clinical decision rule can distinguish patients at high and low riskof cervical spine injury, thus supporting its validity.

pinal cord injury and paralysisare important health burdens inthe United States, with an annual

incidence of 40 per 1 million population.Most cases are caused by blunt force cervicalspine trauma [1, 2]. Radiography, despite itsrecognized limitations [3], is the standardimaging technique for screening patients forsuspected neck injury that may be clinicallyoccult. A minimum standard examinationcomprises a lateral radiograph that com-pletely shows C7 and anteroposterior andopen-mouth odontoid views [4]. Recent in-terest has been shown in the technique of he-lical CT to screen for cervical spine injury[5]. Advantages of helical CT over radiogra-phy may include improved accuracy andfaster diagnosis [6]. However, helical CT ofthe cervical spine is more expensive thanconventional radiography, carries a higherradiation dose, and may be warranted only inhigh-risk patients. Recent work from our in-

stitution, using decision-tree analysis model-ing and considering all long-term costs andoutcomes, has shown that screening helicalCT can be more cost-effective than conven-tional radiography, provided that contempo-raneous head CT is performed and that theprobability of cervical spine fracture in thescreened population exceeds approximately5% [7]. Thus, the optimal imaging strategyfor a particular patient will depend on thatindividual’s probability of injury.

Unfortunately, reliable predictors of cervi-cal spine injury have proven difficult to iden-tify, although several authors have proposedmethods for stratifying patients into broadcategories of risk [3, 8, 9]. We developed aclinical decision rule (Appendix), based onpublished and retrospective local institutionaldata, that was designed to select adult pa-tients with blunt trauma who are at greaterthan 5% risk for cervical spine fracture to un-dergo screening helical CT [10]. Guidelines

Julian A. Hanson

1

C. Craig Blackmore

1,2

Frederick A. Mann

1

Anthony J. Wilson

1

Received July 2, 1999; accepted after revision August 31, 1999.

1

Department of Radiology, Harborview Medical Center, University of Washington School of Medicine, 325 Ninth Ave, Seattle, WA 98104. Address correspondence to C. C. Blackmore.

2

Department of Radiology, University of North Carolina, Manning Dr., Chapel Hill, NC 27599.

AJR

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0361–803X/00/1743–713

© American Roentgen Ray Society

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for clinical prediction rules call for their vali-dation on study populations other than thosefrom which they were derived [11, 12].

The objective of this study was to testwhether clinical predictors of injury can beused to select high-risk patients for imaging.We evaluated a strategy of using a clinicaldecision rule to stratify patients to undergoeither helical CT or conventional radiogra-phy for cervical spine screening. In thisstudy we determined the yield (true-positiverate) for cervical spine injury for patients se-lected for helical CT and for those selectedfor radiography. In so doing, we validatedthe clinical decision rule.

Materials and Methods

In July 1997, we introduced a policy of usinghelical CT as the primary cervical spine imagingtechnique for high-risk adult blunt trauma patients.Screening helical CT of the cervical spine was tobe performed only in combination with head CTand was to be preceded by emergent cross-tablelateral cervical spine radiography performed in theresuscitation area. Patients were required to fulfillat least one of the six criteria that constituted theclinical decision rule (Appendix). The selection ofthese six clinical parameters was based on priorstudies and local observations [10]. The parame-ters were chosen for being readily available to theclinician at the time of initial patient assessment.The requirement to undergo contemporaneoushead CT was a condition of our previous cost-ef-fectiveness analysis [7].

In the 6-month period from January 1 throughJune 30, 1998, 4285 adult trauma patients whopresented to our high-volume urban trauma centerunderwent an imaging screening study of the cer-vical spine. Indications for cervical spine imagingare based on the injury mechanism and include allmotor vehicle, pedestrian, and other traffic acci-dents; falls; and serious assaults. Six hundred oneof these 4285 patients (398 males, 203 females;age range 16–100 years; median age, 38) under-went helical CT of the cervical spine. Once we es-tablished our imaging policy and high-risk criteria,the ultimate choice of imaging technique was atthe discretion of the clinical trauma service. In thehelical CT group, the median patient Injury Sever-ity Score was 15, with a range of 1–75 (data avail-able in 530 [88%] of 601 cases). The InjurySeverity Score is a summary statistic for gradinganatomic severity of injury and predicting out-come for polytrauma patients. Individual injuriesare given a score of 1 (minor) to 6 (lethal) on thebasis of tables from the International Classifica-tion of Diseases [13]. The Injury Severity Score isthe sum of the squares of the three highest injuryscores for the face, head and neck, chest, abdomenand pelvic contents, extremities and pelvic girdle,and integument.

The screening helical CT technique involved 3-mm collimation helical scanning at a pitch of 1.5from T4 to the occiput, performed in two acquisitions(Fig. 1A). The upper thoracic region was included inthe scanning protocol to visualize this frequently ob-scured zone and thus to hasten radiographic spineclearance. Peak kilovoltages of 140 and 120 withmilliampere-seconds of 280 and 170 were used forthe upper thoracic and cervical spine segments, re-spectively. Axial images were reconstructed with thebone algorithm at 1.5-mm intervals with sagittal (Fig.1B) and coronal reformations. Reporting was basedon alternate images recorded on hard-copy film, withthe full set of images available for review at a work-station when necessary.

Report data were obtained from the radiology de-partment database (IDXrad Radiology InformationSystem; IDX Systems, Burlington, VT). Scan find-ings were classified into four groups on the basis oforiginal reports: definite or possible cervical spinefracture or ligament injury; other fractures involvingthe upper thoracic spine, proximal ribs, mandible, orskull base; no acute traumatic abnormalities; andtechnically inadequate. CT criteria used to suggestpossible ligamentous injury were based on sagittaland coronal reformations and included abnormalwidening of articulations at the craniocervical junc-tion, focal kyphosis with splaying of spinolaminardistances, and widening or subluxation of facetjoints. Contemporaneous cervical spine and cranialCT imaging studies were identified.

Definite or possible cervical spine injuries wereindependently confirmed using a combination of ad-ditional imaging (dedicated axial 1-mm collimationCT, cervical spine MR imaging, or supplementaryconventional radiography), surgical findings, or post-mortem results. Possible ligamentous injuries wererefuted in alert patients by results of flexion and ex-tension radiographs and normal clinical examination.Patients with obtusion underwent MR imaging.

Patients’ clinical data were extracted from thehospital trauma registry (a general database of allhospital trauma admissions), the regional spinetrauma database (maintained jointly by the depart-ments of neurosurgery, orthopedics, and rehabilita-tion medicine, and covering local admissions andregional referrals), and the medical record database(an on-line compilation of patient data includingtranscripts of discharge summaries and outpatientnotes). In each case the appropriateness of cervicalspine screening CT was retrospectively assessedfrom information contained in the discharge sum-mary and outpatient records; unless fulfillment of atleast one of the decision rule parameters was re-corded, it was assumed that the patient had not satis-fied screening CT criteria. One hundred thirty-nine(23%) of 601 patients who were transferred to ourtrauma center from outside institutions underwenthelical CT and were analyzed as a separate group.

Results

Four hundred sixty-two (77%) of 601 pa-tients presented directly to our trauma center

and underwent screening helical CT, with atrue-positive yield for cervical spine injury of40 (9%) of 462 (Fig. 2). Thirty-seven (93%) ofthese 40 injuries were fractures. After exclusionof patients with isolated transverse and spinousprocess fractures (

n

= 10), the screening injuryyield was 30 (7%) of 462. One hundred seven(23%) of the 462 patients were retrospectivelyjudged not to fulfill criteria for screening heli-cal CT, either because a full conventional radi-ography cervical spine series had been initiallyperformed, the patient had not undergone con-temporaneous cranial CT, or the trauma mech-anism did not meet the clinical decision rulespecifications. In the remaining 355 of 462 pa-tients, the true-positive injury detection ratewas 35 (10%) of 355 (Fig. 2).

One hundred thirty-nine (23%) of 601 pa-tients were transferred to our trauma centerfrom outside institutions and underwentscreening CT. In 20 patients already known tohave a fracture, helical CT evaluation of thecomplete cervical spine revealed an additional12 fractures or dislocations in nine cases(45%). All but one of these additional frac-tures occurred at levels contiguous with theknown injury. Cervical fractures were de-tected in 17 (14%) of the remaining 119 trans-ferred patients.

Thus, of the 84 patients in whom a cervicalspine injury was confirmed, 57 (68%) were di-agnosed on screening helical CT and seven(8%) on conventional radiographs, and 20(24%) were initially identified from prior imag-ing at referring hospitals. The overall true-posi-tive detection rates for cervical spine injury inhelical CT– and radiography-screened patientswere 77 (13%) of 601 and seven (0.2%) of3684, respectively (Fig. 2). The most commonabnormalities identified on helical CT werefractures or subluxations involving the C3–C7pedicles, facets, or laminae (Table 1).

Furthermore, 54 (9%) of 601 patients werefound to have fractures of the upper thoracicspine, proximal ribs, mandible, or skull base(Table 2). Eleven (2%) of 601 patients had frac-tures of the upper thoracic vertebrae, seven ofwhich involved the body or bony neural arch.

Discussion

Little published data exist on helicalscreening CT of the complete cervical spine.Its use was first described in 1994 by Nunez etal. [6], who reported the results of screeningcervical spine CT in 800 high-risk blunttrauma patients (defined as those with a re-vised trauma score of 3 or less who requiredCT evaluation as part of the initial trauma im-

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aging workup. (The revised trauma score is aphysiologic measure of injury severity that isbased on respiratory rate, the Glasgow Comascale, and systolic blood pressure). In thestudy by Nunez et al., the researchers found68 fractures in 46 (5.8%) of the 800 patientsstudied. Thirty-nine (57%) of these 68 frac-tures were detected on CT but not on standardradiography. These authors observed that theintroduction of a CT screening policy was as-sociated with a reduction in the time requiredfor patient imaging evaluation in their emer-gency department.

We implemented a cervical spine traumascreening policy using a modified CT proto-col with narrower collimation and more ex-tensive spinal coverage. We designed aclinical decision rule to particularly focus oncervical trauma risk factors. In the group ofpatients who directly presented to our traumacenter and who were selected to undergoscreening helical CT on the basis of this deci-sion rule, the cervical spine injury rate was8.7%. Recent work has suggested that helicalCT could be a cost-effective strategy in popu-lations with fracture risk exceeding approxi-mately 5% [7]. Thus, the clinical decision rulewas sufficiently useful to serve as a tool whenselecting patients for screening helical CT. In

Fig. 1.—Screening helical CT technique used to evaluate for cervical and upper thoracic spinetrauma.A, Lateral cervical and upper thoracic scan projection shows levels and angulation for helical CTcoverage. Reconstruction interval = 1.5 mm.B, Midline sagittal reformation obtained from helical data set shows upper cervical spine.

BA

Fig. 2.—Decision tree shows radiologic screening yields according to imaging technique and patient subset (directadmission to Harborview Medical Center [HMC] or transfer). +ve = true-positive study for cervical spine injury.

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addition, we observed a very low incidence(0.2%) of cervical spine injury in the largegroup of 3684 patients who underwent con-ventional cervical radiography and who didnot satisfy high-risk criteria.

Helical CT imaging revealed a substantialnumber of additional injuries remote from thecervical spine. Of particular importance were11 cases of vertebral fracture in the upper tho-rax, a segment of the spine often difficult tovisualize on conventional radiographs. Thisconsideration had prompted the inclusion ofthe upper four thoracic vertebrae in the designof the screening CT protocol.

The cost-effectiveness of the screening CTstrategy is based on preventing delayed casesof paralysis by improved detection of unstableinjuries [7]. The risk of preventable paralysisis estimated from conventional radiographicstudies of misdiagnosed fractures. Extrapola-tion of the same risk to CT data requirescaution. Although helical CT may be moresensitive than conventional radiography forcervical spine fracture in general, it is the di-agnostic yield for unstable injuries that deter-mines the rate of avoidable neurologic deficitand thereby the justification for CT screening.The clinical significance of some screeningCT–detected abnormalities remains unclear.CT reveals minimally symptomatic andasymptomatic nondisplaced spinous and

transverse process fractures that may have norisk for neurologic injury and that may havebeen previously overlooked in conventionalradiographic series that relied on clinical pre-sentation with fracture as the diagnostic goldstandard. Although these injuries might be in-significant in terms of the need for surgicalstabilization, their presence reflects substan-tial absorbed energy, and it may be importantto detect them as markers for more severe lig-amentous, disk, brachial plexus, or vertebralartery injury [14].

In this study, the most common types of in-jury revealed on CT were C3–C7 articularmass, pedicle, and lamina fractures or sublux-ations. Thirty-one such injuries were found in27 (4.5%) of 601 patients. Seventeen of these27 patients required stabilization with surgicalinstrumentation or halo fixation, or died. Theremaining 10 patients had minimally dis-placed

or nondisplaced fractures or sublux-ations that were stable on serial radiographicstudies and that were treated with cervicalbrace or collar immobilization for up to 12weeks. Isolated transverse or spinous processfractures were detected in 15 (2.5%) of 601patients, and the screening helical CT injuryyield remained high even after exclusion ofthese cases.

We observed “dilution” of the indicationsfor screening CT, with 107 (23%) of 462 pa-tients directly presenting to our trauma cen-ter judged in retrospect not to have satisfiedselection criteria. This indication drift, or de-viation from the standard protocol, may bedue to presumptions that screening CT is amore accurate, faster, and more convenienttechnique. Requesting trauma physiciansmay exercise clinical judgment on factorsnot included in the original prediction rule.For example, falls were all grouped togetherin the original prediction rule because wehad insufficient data to separate them. Intu-itively, however, one would expect falls from

great heights to be greater injury risk factorsthan falls from standing, and one might as-sign greater weight to a fall from someheight than that mandated by the predictionrule. Clinical judgments of this nature maycontribute to the cases in which the protocolwas not strictly followed. Some indicationdrift is probably inevitable in an effective-ness study such as this one. This bias to in-clude nonprotocol patients could reduce theoverall injury detection rate in the screenedpopulation. Despite this effect, the positivescan rate (8.7%) was sufficiently high for theimaging strategy to be cost-effective, as pre-dicted by modeling. Indeed, a higher positivescan rate of 9.9% was found in the 355 pa-tients who were retrospectively thought tosatisfy the decision rule.

The retrospective extraction of clinicaldata from the medical record, as performedin this study, is subject to limitations. Thepresence or absence of individual decisionrule criteria was not routinely recorded, so itwas not possible to correlate the associationbetween individual parameters and fracturerisk, or to further refine the decision rule.Furthermore, it may not be appropriate to useinformation compiled after the event (i.e.,medical records) to justify patient selectionfor helical CT, a decision that must be madein the immediate evaluation period.

In 20 patients with known cervical spinefractures (based on prior conventional radio-graphs), the helical CT study was used toscreen for a second injury. Almost 50% ofthis group (9/20) had at least one additionalunsuspected fracture. However, the clinicalimpact of these additional detected injurieswas limited because they were generallycontiguous with the known injury level andwould therefore have been diagnosed using aconventional targeted CT examination.

We noted a higher incidence of fracture inthe transferred (14.3%) than in the directlypresenting (8.7%) patients. The transferredpatients were a selected group with more se-vere injuries, which was reflected by higherinjury severity scores than those of the directadmission patients (median [range]: 17 [5–45] compared with 14 [1–75], respectively;

p

< 0.05, Mann-Whitney statistical analysis).In summary, this report supports the asser-

tion that simple clinical parameters can beused to stratify patients on the basis of theprobability of cervical spine injury. Suchstratification can be used to select appropri-ate patients for more cost-effective screeningfor cervical spine injury using helical CT.

aPatients admitted directly to Harborview Medical Center.

TABLE 1 Cervical Spine Injuries Revealed on Helical CT in 77 Patients

Injury HMC Patientsa Transferred Patients

Occipital, atlantal, or axial fracture or subluxation 3 2C1 fracture 0 6C2 fracture 9 15C3–C7 body fracture 4 10C3–C7 facet, pedicle, or lamina fracture or subluxation 16 15C3–C7 transverse or spinous process fracture 13 8

Total 45 56

TABLE 2 Additional Injuries Revealed on Helical CT in 54 Patients

Injury No.

Upper thoracic spine fracture 11Proximal rib fracture 32Skull base fracture 12Mandible fracture 3Hyoid fracture 1

Total 59

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APPENDIX: Clinical Decision Rule to Select High-Risk Patients to Undergo Helical CT of the Cervical Spine: Six Injury Mechanisms or Clinical Parameters

Injury mechanism parameters based on initial report of emergency transportation personnel, patient, or witnesses:

1. High-speed (

≥

35 mph [56 kmph] combined impact) motor vehicle accident

2. Crash with death at scene of motor vehicle accident

3. Fall from height (

≥

10 ft [3 m])

Clinical parameters based on primary patient survey:

4. Significant closed head injury (or intracranial hemorrhage seen on CT)

5. Neurologic symptoms or signs referred to the cervical spine

6. Pelvic or multiple extremity fractures

The presence of any one parameter places the patient in the high-risk category (>5% risk of cervical spine fracture) and indicates that thepatient should undergo helical CT. It is assumed that CT of the head will be performed contemporaneously.

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