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Emergency Radiology |
1 From the Department of Radiology, University of North Carolina–Chapel Hill School of Medicine, CB #7510, 508 Old Infirmary Bldg, Chapel Hill, NC 27599-7510 (C.C.B.), and the Robert Wood Johnson Clinical Scholars Program (C.C.B., R.A.D.), Department of Radiology, Harborview Medical Center (C.C.B., F.A.M.), and Department of Medicine (S.D.R., R.A.D.), University of Washington School of Medicine, Seattle. Received December 23, 1997; revision requested March 23, 1998; final revision received November 23; accepted January 8, 1999. C.C.B. supported by the Seattle Veterans Affairs Medical Center-Robert Wood Johnson Clinical Scholars Program. Address reprint requests to C.C.B., Department of Radiology, Harborview Medical Center, Box 359728, 325 Ninth Ave, Seattle, WA 98104-2499.
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Abstract |
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 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: A decision analysis model was constructed to compare the incremental cost-effectiveness of radiography and CT as primary cervical spine screening modalities in trauma patients. Analyses were performed from a societal perspective, and probability and cost estimates from the literature and institutional experience were used. In separate cost-effectiveness analyses, hypothetical cohorts of trauma patients from three defined clinical scenarios were considered: high, moderate, and low risk for cervical spine fracture. Outcome measures included cases of paralysis prevented, total cost of screening strategies, and incremental cost-effectiveness ratios.
RESULTS: In high-risk patients, screening with CT is a dominant strategy that prevents cases of paralysis and saves money for society. In moderate-risk patients, screening with CT is cost-effective with reference-case assumptions and within the range of most sensitivity analyses. In the low-risk group, CT screening helps prevent cases of paralysis, but the incremental cost-effectiveness ratio is high (>$80,000 per quality-adjusted life year).
CONCLUSION: CT is the preferred cervical spine screening modality in trauma patients at high and moderate risk for cervical spine fracture.
Index terms: Cost-effectiveness • CT, helical, 31.12115 • Spine, CT, 31.12115 • Spine, fractures, 31.41 • Trauma
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The standard method of screening the cervical spine is a conventional radiographic series, which typically consists of lateral, anteroposterior, and odontoid views. Nonetheless, 5%–8% of patients with fracture may have normal radiographs (11–16). In addition, particular difficulty in positioning multiple-trauma patients may lead to a large number of inadequate radiographic examinations (17).
Computed tomography (CT) has been proposed as a method of screening trauma patients to exclude cervical spine fracture (12,18). The sensitivity of screening cervical spine CT is higher than that of radiography (12,19,20). Furthermore, in some trauma centers, performing screening CT of the cervical spine at the time of head CT may allow a more rapid radiologic exclusion of cervical spine fracture than performing conventional radiography (12). Higher direct medical costs and variable availability are the primary disadvantages of screening the cervical spine with CT. However, associating screening cervical spine CT with the head CT commonly performed in trauma patients may mitigate these factors.
Current standards of care dictate that all patients at risk for cervical spine fracture undergo radiologic screening. However, it is possible to define groups of patients in whom there is a higher probability of injury. We previously reported on a clinical prediction rule that can be used to stratify patients into various groups according to their level of probability for injury (21,22). The prediction rule was based on a case-control study involving 168 patients with cervical spine fracture and 304 control patients. By using the relatively simple clinical factors of mechanism of injury, age, presence of severe head injury, and presence of focal neurologic deficit, patients can be separated into groups that have a broad range of probabilities of cervical spine fracture. The use of a clinical prediction rule enables the tailoring of cervical spine screening imaging in patients with different levels of injury probability rather than the use of the same strategy for all patients.
In this study, we used cost-effectiveness analyses to compare the use of screening CT with the use of the standard radiographic screening protocol in evaluating blunt trauma victims with possible cervical spine fracture. The target population was patients who are screened for possible cervical spine fracture in trauma centers or emergency departments and who are already scheduled to undergo CT scanning of the head. We performed separate analyses for patients with different levels of probability of injury. Our purpose was to compare the cost-effectiveness of CT with that of radiography in screening for possible cervical spine fracture in trauma patients.
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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For patients clinically deemed to require imaging of the cervical spine, we developed an imaging algorithm in which screening cervical spine CT would be substituted for conventional radiography (Fig 1). As described below (in the Probability Estimates section), three sample populations with different risks of cervical spine fracture were defined on the basis of the mechanism of injury and clinical factors that would be available to the emergency department or trauma center physician at the time of the imaging decision (Table 1). These clinical scenarios were determined by means of development and bootstrap validation of a clinical prediction rule from a previously reported retrospective case-control study (21) conducted at our institution. The scenarios selected represented a range of pretest probabilities for injury and thus were representative of the range of patients in whom CT screening might be considered. For each of these clinical scenarios, the cost-effectiveness of CT versus that of radiography for cervical spine screening in trauma patients was determined.
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Decision Analysis Model
A computer-based decision analysis model (TreeAge Software, Williamstown, Mass) was constructed to compare the CT screening algorithm with the conventional radiographic screening protocol (Fig 2). By using probability and cost estimates for each possible outcome, incremental cost-effectiveness ratios were calculated for the use of screening CT compared with the use of radiography. The results were expressed as dollars per quality-adjusted life year (QALY), which represents the additional benefit in terms of longevity and quality of life per additional dollar spent on cervical spine screening when the CT scanning strategy is used.
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Probability Estimates
The cost-effectiveness model was dependent on six probability estimates: probability of fracture, sensitivity of radiography, specificity of radiography, sensitivity of CT, specificity of CT, and probability of paralysis from undetected fracture. Sensitivity was defined as the ability of the screening examination to enable the identification of patients with fractures, or the number of true-positive results divided by the number of patients with fracture. Specificity, on the other hand, was defined as the ability of the screening test to enable correct classification of patients without fracture as individuals with normal spines, or the number of true-negative results divided by the total number of patients without disease (23). Probability estimates were derived from the medical literature and from the collection of original data, as described below. Because the cervical spine radiographic protocol is the current standard of care and the CT screening protocol is less well accepted, we intentionally chose values that are more favorable to radiography when uncertainty existed.
To determine the risk of cervical spine fracture, we adapted a clinical prediction rule that we had developed previously (21,22). The original clinical prediction rule was derived to estimate the risk of fracture in all trauma patients. However, for consideration of CT cervical spine screening in the present study, the relevant population consisted of only those patients scheduled to undergo head CT. To estimate the risk of fracture in the head CT population, we performed a case-control study with 224 patients (161 men and 63 women aged 18–88 years [mean age, 42.8 years]) with cervical spine fracture and 379 control patients (275 men and 104 women aged 18–94 years [mean age, 35.7 years]). The control patients were randomly selected from trauma patients who underwent head CT as part of their emergency department evaluation. Both groups were selected from victims of nonpenetrating trauma who were (a) examined at our institution between 1992 and 1995, (b) aged 18 years or older, and (c) not transferred from another institution. The purpose of this clinical prediction rule was to influence cervical spine imaging decision making at the initial patient presentation in the emergency department or trauma center. Therefore, the information used for the clinical prediction rule was only that which would be available at the initial evaluation.
Because patients who were transferred from another institution might have undergone a previous examination or intervention, there would be potential for selection bias if they were included. Accordingly, we included only those patients who had undergone the initial examination at our center and excluded all those who were transferred from another facility. One hundred twenty-three (55%) of the 224 patients and 76 (20%) of the 379 control subjects in this analysis also were included in the previous study from which the original clinical prediction rule was derived. For each case and control subject, information regarding the presence or absence of clinical predictors of cervical spine fracture was noted by one of two trained chart abstractors, who were one of the authors (C.C.B.) and a research assistant. To avoid ascertainment bias, we selected clinical predictors from information that is determined before the diagnosis of cervical spine fracture is made. These predictors included age, mechanism of injury, obvious head or facial injury, and loss of consciousness. Head injury was determined both clinically and with the findings of head CT, which would, by design, precede the screening cervical spine CT. To determine agreement, both reviewers assessed 29 (5%) of the 603 charts. Data from the chart review forms were then entered into a database by using double-key entry with verification.
The clinical prediction rule previously derived for all trauma patients was then applied to the trauma and head CT data set, and the odds ratio for cervical spine fracture was determined for several clinical scenarios. To calculate the absolute risk of fracture for each of the clinical scenarios, we used likelihood ratios adapted from the clinical prediction rule and the baseline probability of fracture in trauma patients who undergo head CT, which was directly measured at our institution. Confidence intervals (CIs) were calculated by using bootstrap modeling of the baseline risk of fracture and the likelihood ratios for each of the clinical scenarios. Bootstrap modeling is a method of randomly resampling from a given experimental sample to simulate the drawing of multiple samples from the underlying population. It is used to ensure that a clinical prediction rule is not overfit to the data from which it was derived but rather generalizable to other similar samples (24). On the basis of the clinical prediction rule results, we selected three clinical scenarios to represent conditions with high, moderate, and low risk for cervical spine fracture.
The sensitivity of cervical spine radiography was estimated on the basis of values from literature reports (11,14–16,20,25). First, we used the 
2 test to exclude heterogeneity (P = .24); then we pooled the reported sensitivities (26,27). A computerized search of the English-language literature was conducted. References of the located articles were then searched for additional relevant sources. For inclusion, the number of true-positive and false-negative images had to be reported in the study, and the eventual clinical presentation with fracture had to be used as the reference standard. Studies in which CT scanning was used as the reference standard were excluded, because, to our knowledge, there is no information on the natural history of such injuries. We do not know on the basis of the existing literature whether such injuries will become clinically relevant. Accordingly, fractures discovered at CT with no associated clinical findings were excluded from estimates of the sensitivity of radiography. By excluding these CT-based studies, the derived sensitivity of radiography was higher, and the bias was more conservative in favor of the radiographic protocol.
The specificity of cervical spine radiography was measured directly from the medical records of randomly selected trauma patients who were examined at our institution, fit into the described clinical scenarios, and had undergone cervical spine radiography. For each patient, we determined whether cervical spine CT had been performed and whether a cervical spine fracture had been identified at this examination. The group of patients who had undergone cervical spine CT but did not have fractures constituted the false-positive cases for specificity determination. This "false-positive" group was heterogeneous and included patients with equivocal or inadequate radiographs and patients in whom the radiographs were thought to be abnormal. However, because the radiographs obtained in all of these patients led to CT scanning, they were considered to be false-positive for decision-making purposes. This study has been reported in greater detail previously (17).
The sensitivity of CT was determined by reviewing the literature, with simple pooling of the available data. Research articles in which there was a defined cohort of patients who underwent screening CT were included in the analysis (12,18). In addition, because of the low number of published studies, we included unpublished data representing the continuation of the largest published series in which CT and radiography are directly compared (Nunez D.B., personal communication, May 1997). For determination of the sensitivity of CT, the eventual clinical presentation or identification of fracture by using any other imaging modality was considered the reference standard. To our knowledge, no estimates of the specificity of CT are available in the literature. An estimate of specificity was determined from the authors' experience and from consultations with physicians at other trauma centers. This estimate was tested over a broad range in the sensitivity analysis to allow for the added uncertainty of this method of estimation.
The probability of severe secondary deficit (ASIA grade C or worse) was obtained from the medical literature. Three studies (7,9,28,29) have been published encompassing 137 cervical spine fractures of which there was a delay in diagnosis. In these studies, a range in probability of severe neurologic sequelae of 0% to 18% is reported. Heterogeneity in the methodology of these studies limits the ability to combine the data. Accordingly, a conservative estimate between the measured probabilities (5%) was chosen as the reference value of probability, and a broad range was considered in the sensitivity analysis (1%–15%).
Cost Estimates
Cost estimates for radiologic procedures were derived from the 1995 Medicare relative value unit (RVU) reimbursement schedules (30). The reference-case estimate for the cost of cervical spine radiography was the global reimbursement for a four-view cervical spine study (1.38 RVUs); the reimbursement for two- and six-view studies were included in the sensitivity analysis. The cost of full cervical spine CT scanning, which was not performed in conjunction with head CT, also was determined from the RVU schedule (7.74 RVUs).
The Medicare RVU schedule does not have a code for screening cervical spine CT at the time of head CT. However, the assumption that the incremental cost of cervical spine CT at the time of head CT is less than that of the independently performed, full-cost cervical spine CT examination is a key component in the argument for cervical spine screening with CT. This economic advantage of performing more than one examination in a scanning session is recognized by the RVU schedule in other cases. For example, the RVU cost of one cervical spine examination, performed with and without contrast material, is considerably less than the sum of the costs of the individual studies performed independently. We estimated the incremental RVU technical cost of obtaining a CT scan of the cervical spine in a patient who is already positioned in the scanner for head CT to be 1.78 RVUs, which is equivalent to the incremental technical component of the RVU cost of obtaining a CT scan of the cervical spine without contrast material in a patient already positioned for CT of the cervical spine with contrast material. The professional component of the RVU cost of cervical spine CT is not affected by the method of acquiring the scan and therefore remains 1.75 RVUs. The total cost of screening cervical spine CT at the time of head CT is therefore the sum of the professional and technical components, or 3.53 RVUs. For sensitivity analysis, we tested the effect of a 50% over- or underestimation of the cost.
Estimates of the lifetime costs of spinal cord injury were derived from the literature (4,6,31–34). Direct medical costs in the 1st year and in all subsequent years, as well as rehabilitation and home care costs, were included. Indirect costs such as lost wages were excluded. All costs reported in the literature were adjusted to 1995 dollars by using the medical care consumer price index (U.S. Bureau of Labor Statistics) and a standard Medicare reimbursement rate of $34 per RVU. Costs occurring beyond the base year of the analysis were discounted by using a 3% discount rate (35,36).
Survival Analysis
The mean age of the patients with cervical spine fracture at our institution who were eligible for this study was 43 years. The life expectancy of a 43-year-old person in the United States who sustains a spinal cord injury is 14 years (37,38), which was used as the time horizon to estimate lifetime medical costs. The life expectancy of patients without spinal cord injury (39 years) was derived from life tables and used to estimate the number of years of life lost by sustaining a spinal cord injury.
Quality of Life Determination
The Health Utilities Index Mark 2 (39) was used to estimate the utility adjustment for life with a severe neurologic deficit. Six scenarios that typify the injury level and severity in patients with cervical spine fracture were devised. Three physiatrists with expertise in the care of patients with spinal cord injury were then asked to select the specific level of health status defined by the Health Utilities Index for each of seven attributes that is most representative of a typical patient's health status in a given scenario. The resultant levels of health status were converted into utility scores (39), which were then combined by using the relative population frequency of each of the scenarios for weighting. The average and range of the three physiatrists' scores were used as the utility adjustment reference standard and sensitivity analysis range, respectively.
QALYs were calculated from the measurements of life expectancy and utility adjustment for life with cervical spinal cord injury. To account for the time value of benefits and comply with the recent recommendations of the U.S. Public Health Service for the standardization of cost-effectiveness analysis methodology, QALYs, like costs, were discounted, with 3% as the reference-standard discount rate (35). The baseline utility in the absence of spinal cord injury was assumed to be 1.0. Because all patients may not be in perfect health, an estimated baseline utility of 0.9 was explored in the sensitivity analysis.
Sensitivity Analyses
Univariate sensitivity analyses were performed over the range of plausible estimates for all variables, including the discount rate. Table 2 lists the range of values included in the sensitivity analysis for each probability and cost estimate. In addition, we studied the effects of a systematic overestimation of the sensitivity and specificity of radiography and CT and of a systematic underestimation of the sensitivity and specificity of radiography and CT by using multivariate sensitivity analyses. Finally, to further test the stability of the results, we performed Monte Carlo simulations of 1,000 iterations by using triangular distributions for the major variables. This is a method of repeatedly testing the outcome of the simulation model by using random selection of a value for each of the variables from within their probable ranges (40).
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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statistic, was excellent ( = 0.80) (41). Patients who sustained severe head injury were selected as the reference group at high risk for cervical spine fracture (fracture risk = 11.2%; 95% CI = 9.4%, 15.3%). Patients with focal neurologic deficit and those older than 50 years with a high-energy mechanism of injury were included in the high-risk group in the sensitivity analysis. Patients aged 50 years or younger with a high-energy mechanism were selected as the reference group at moderate risk for cervical spine fracture (fracture risk = 4.2%, 95% CI = 2.7%, 6.9%). Patients older than 50 years with a moderate-energy mechanism were included in the moderate-risk group in the sensitivity analysis. Finally, patients aged 50 years or younger with a moderate-energy mechanism were selected as the reference group at low risk for cervical spine fracture (fracture risk = 2.1%; 95% CI = 1.6%, 3.2%). Patients with a low-energy mechanism were included in the low-risk group in the sensitivity analysis. The results of the cost-effectiveness analysis of each reference-case clinical scenario are shown in Table 3; the incremental summary analysis, in Table 4; and the univariate sensitivity analysis, in Table 5.
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Moderate-Risk Patients
In the moderate-risk group (high-energy mechanism and age 50 years or younger), the use of screening CT was more expensive than was the use of radiography at reference-case estimates. However, the CT screening strategy did prevent an additional 8.5 cases of paralysis at an incremental cost-effectiveness ratio of $16,500 per QALY. Throughout the range of the sensitivity analysis, the incremental cost-effectiveness ratio for screening CT in the moderate-risk group was less than $50,000 per QALY, except at the lowest estimate of paralysis risk and highest cost estimate for screening CT. At a probability of paralysis from missed fracture of 1%, the incremental cost-effectiveness ratio for screening CT scan was $180,000 per QALY. The incremental cost-effectiveness ratio for CT crossed the $50,000 per QALY mark at a probability of paralysis of approximately 2.8%.
At multivariate sensitivity analysis based on the highest estimates of sensitivity and specificity, screening CT in the moderate-risk group had an incremental cost-effectiveness ratio of $26,000 per QALY. At the lowest estimates of sensitivity and specificity, the cost-effectiveness ratio was $7,600 per QALY. The relatively low cost-effectiveness ratio in this worst-case scenario was primarily due to the lower sensitivity of radiography. Although this worst-case scenario also included low estimates for radiography specificity and for CT sensitivity and specificity, the most important factor was the lower radiography sensitivity, which caused the cost-effectiveness ratio to decrease. In the Monte Carlo simulations, the CT strategy was dominant in 380 (38%) of the 1,000 iterations, and the incremental cost-effectiveness ratio for screening with CT was less than $50,000 per QALY in 940 (94%) of the iterations.
Low-Risk Patients
On the basis of the data from this study, in the low-risk group—that is, those patients younger than 50 years with a moderate-energy mechanism—the use of CT screening is more expensive and prevents fewer additional cases of paralysis. In our hypothetical cohort of 100,000 low-risk patients, 4.2 additional cases of paralysis were prevented. The incremental cost-effectiveness ratio of such a strategy was $84,000 per QALY. Incremental cost-effectiveness ratios at extreme ranges of the sensitivity analysis varied from $12,000 to $526,000 per QALY. Finally, multivariate sensitivity analyses based on the highest and lowest sensitivity and specificity demonstrated cost-effectiveness ratios of $72,000 per QALY and $90,000 per QALY, respectively.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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In the moderate-risk group, including younger patients with a high-energy mechanism of injury and older patients with a moderate-energy mechanism, screening CT was more expensive than radiography, with a cost-effectiveness ratio of $16,500 per QALY at the reference-case assumptions. The absolute threshold for what constitutes a cost-effective intervention remains controversial. However, society has expressed a willingness to fund interventions that cost less than $20,000 per QALY (42,43), and many authors would consider $50,000 per QALY a reasonable threshold (44,45). Because the cost per QALY in the moderate-risk group was less than $20,000 with the reference-case assumptions and less than $50,000 per QALY in most of the sensitivity analyses and Monte Carlo simulations, the bulk of the evidence supports CT screening in this group. However, in this group in particular, because the determination of the most cost-effective screening study is less well defined, the individual experience at each institution also is important for selection of the optimal imaging strategy.
Finally, although screening with CT continues to prevent cases of paralysis in the low-risk group, the cost to society is high. In the low-risk reference group and in most of the ranges explored in the sensitivity analysis in this study, the cost of screening with CT was in excess of that which society is likely to be willing to pay. Therefore, CT is not cost-effective for screening low-risk patients.
Because cost-effectiveness is dependent on risk of fracture, use of screening CT should be limited to patients at moderate or high risk of fracture. In this study, we examined only three scenarios in detail; however, the results may be extended to other clinical scenarios with known fracture risk. For example, in the moderate-risk group, we considered patients aged 50 years or younger with a high-energy mechanism; however, the results were also relevant to those patients older than 50 years with a moderate-risk mechanism, in whom the risk of fracture was 5.5% (Table 1). Although assigning an absolute value to a QALY is controversial, a cutoff of $20,000 per QALY as cost-effective yields a fracture risk threshold of approximately 4%, above which CT is the cost-effective imaging choice. In this study, we defined several scenarios that fit this criterion; therefore, these results may serve as a foundation for evidence-based guidelines for cost-effective imaging.
We note the limitations of this study. The complexities of each clinical scenario were necessarily simplified to allow analysis. For example, minor neurologic abnormalities such as mild motor or sensory deficits were ignored. We also ignored the effects of treatment of incidental or clinically unimportant findings in either screening protocol. In addition, we assumed that screening cervical spine CT at the time of head CT has less direct medical cost than does a separate cervical spine CT examination and that all patients would undergo head CT. Although all patients in the high-risk group do undergo head CT for evaluation of their head injuries, this assumption may not hold in the low-risk group. To be complete, we included low-risk patients in the decision analysis model. However, the results indicated that screening cervical spine CT is not cost-effective in this group, even when head CT is performed.
In addition, we considered only patients who are victims of blunt trauma, because the treatment of patients with penetrating neck trauma may be quite different. Investigation of the use of CT in victims of penetrating trauma was beyond the scope of this analysis. Finally, there are assumptions intrinsic to this analysis that must be acknowledged. For example, we assumed that all unstable cervical spine fractures eventually become evident and are treated. In addition, we assumed that the treatment of cervical spine fracture will not be related to the initial imaging study.
This study, like all decision analysis models, is dependent on estimates and assumptions derived from various sources. To maximize the accuracy of such estimates, we attempted to locate and include all relevant estimates from the medical literature and performed primary data collection where necessary. Furthermore, sensitivity analyses were broad where the uncertainty was the greatest—for example, for the probability of paralysis. Our estimates of sensitivity might be high, given that the published literature comes from academic institutions that specialize in trauma care; thus, they may not represent the values obtained in common practice. However, any overestimation of the sensitivity would be expected to occur for both radiography and CT, and we expected the relationship between them to be similar. We included multivariate sensitivity analyses to explore this possibility and demonstrated no major change from the reference-case analysis findings. The multiple sensitivity analyses and Monte Carlo simulations used in this analysis are a way of determining how robust the results are, and they have a role that parallels that of statistical hypothesis testing in more traditional research designs.
Additional technology assessment is needed to confirm the superior sensitivity of CT over that of radiography and determine the optimal technique for CT screening. Furthermore, validation of the injury risk prediction rule in different settings would be useful to ensure that the fracture probabilities reported in this study are generalizable beyond the major urban trauma center setting from which they were derived. However, one barrier to the broader use of CT has been the higher cost. The results of this analysis demonstrated that, on the basis of current knowledge, CT is cost-effective in high- and moderate-risk patients when all costs are considered. We believe that CT should be the initial screening modality of choice in selected patients at major trauma centers in the United States.
The greatest uncertainty in our decision analysis model was with regard to the probability of developing a severe neurologic deficit from an undiagnosed cervical spine fracture. We believe the estimates of Davis et al (9) and of Gerrelts et al (28) are most relevant because they were derived from trauma centers, where screening CT might be implemented. The pooled risk of paralysis from undetected fracture in these two studies was 15%. In both studies, roughly half of the injuries with diagnostic delay were missed on the initial radiographs, and in half, the delay was secondary to inadequate imaging. The rate of paralysis in both groups was similar. Davis et al (9) also reported that 71% of the missed injuries were unstable.
An Alberta, Canada study (29) involved patients who were transferred to a spine injury referral center. In that study, although 16 (14.2%) of 113 patients with a diagnostic delay developed secondary neurologic deficits, there were no severe deficits reported. However, those patients who were not transferred to the spinal injury center, including those who died as a result of the secondary deficit, those who sought care outside of the province, and those who could not be transferred because of other injuries, could have been missed. Although we believe that the Davis and Gerrelts study populations are more relevant to our analyses, to be conservative, we used a reference-case estimate of 5%, which is between that used in the Alberta study and that used in the Davis and Gerrelts studies (9,28,29). We used a wide range of estimates in the sensitivity analysis to accommodate the uncertainty in estimating this risk.
The estimate of the probability of developing a severe neurologic deficit was a key determinant of CT cost-effectiveness. However, in the high-risk group, the incremental cost-effectiveness of CT was still relatively low ($55,000 per QALY), even at the extreme of the sensitivity analysis range. In the moderate-risk group, the incremental cost-effectiveness ratio crossed out of the range that society would be willing to pay as the probability of paralysis decreased (<3%), which indicates that some uncertainty persists as to which strategy is favored in this group. Nonetheless, the best estimate of cost-effectiveness was that in the baseline case, which indicated that CT is the preferred strategy.
The standard of care has been radiography of the cervical spine; screening CT has been considered to be experimental. Therefore, in situations of substantial uncertainty, we selected estimates with a bias in favor of radiography. Furthermore, we ignored other possible advantages of CT scanning, including the decreased time required to "clear" the cervical spine of any fracture (12) and the possibility of clearing the spine in patients who are too unstable for prolonged examination in the radiography suite. Finally, we excluded lost wages from the cost analysis of spinal cord injury. In the high- and moderate-risk scenarios, CT was cost-effective, or dominant, despite this intentional bias.
In conclusion, the use of cervical spine CT to screen high- and moderate-risk patients prevents cases of paralysis and may save money for society. On the basis of our cost-effectiveness analysis, CT should be considered as the primary cervical spine screening modality in selected victims of major trauma who are examined in high-volume urban emergency departments and trauma centers.
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Acknowledgments |
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Footnotes |
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Abbreviations: ASIA = American Spinal Injury Association QALY = quality-adjusted life year RVU = relative value unit
Author contributions: Guarantors of integrity of entire study, all authors; study concepts and design, all authors; definition of intellectual content, all authors; literature research, C.C.B., F.A.M.; clinical studies, C.C.B.; data acquisition, C.C.B.; data and statistical analyses, C.C.B., S.D.R.; manuscript preparation, C.C.B., F.A.M.; manuscript editing and review, all authors.
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R. H. Daffner Helical CT of the Cervical Spine for Trauma Patients: A Time Study Am. J. Roentgenol., September 1, 2001; 177(3): 677 - 679. [Abstract] [Full Text] [PDF]
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C. C. Blackmore, W. N. Zelman, and N. D. Glick Resource Cost Analysis of Cervical Spine Trauma Radiography Radiology, September 1, 2001; 220(3): 581 - 587. [Abstract] [Full Text] [PDF]
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M. E. Singer and K. E. Applegate Cost-Effectiveness Analysis in Radiology Radiology, June 1, 2001; 219(3): 611 - 620. [Abstract] [Full Text] [PDF]
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 G. Little, M. Kelly, and E Glucksman Critical pitfalls in the immediate assessment of the trauma patient Trauma, January 1, 2001; 3(1): 43 - 51. [Abstract] [PDF]
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R. H. Daffner Cervical Radiography for Trauma Patients: A Time-Effective Technique? Am. J. Roentgenol., November 1, 2000; 175(5): 1309 - 1311. [Abstract] [Full Text] [PDF]
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