Neither the performance of CT in diagnosing penetrating gastrointestinal injury nor its ability to discriminate patients requiring either observation or surgery has been determined.

INTRODUCTION:Cerebral fat embolism syndrome (CFES) mimics diffuse axonal injury (DAI) on MRI with vasogenic edema, cytotoxic edema, and micro-hemorrhages, making specific diagnosis a challenge. The objective of our study is to determine and compare the diagnostic utility of the conventional MRI and DTI in differentiating cerebral fat embolism syndrome from diffuse axonal injury.METHODS:This retrospective study was performed after recruiting 11 patients with severe CFES and ten patients with severe DAI. Three trauma radiologists analyzed conventional MR images to determine the presence or absence of CFES and DAI. DTI analysis of the whole-brain white matter was performed to obtain the directional diffusivities. The results were correlated with clinical diagnosis to determine the diagnostic utility of conventional MRI and DTI.RESULTS:The sensitivity, specificity, and accuracy of conventional MRI in diagnosing CFES, obtained from the pooled data were 76, 85, and 80 %, respectively. Mean radial diffusivity (RD) was significantly higher and the mean fractional anisotropy (FA) was lower in CFES and differentiated subjects with CFES from the DAI group. Area under the receiver operating characteristic (ROC) curve for conventional MRI was 0.82, and for the differentiating DTI parameters the values were 0.75 (RD) and 0.86 (FA), respectively.CONCLUSIONS:There is no significant difference between diagnostic performance of DTI and conventional MRI in CFES, but a difference in directional diffusivities was clearly identified between CFES and DAI.

PURPOSE To retrospectively compare the diagnostic performance of arterial, portal venous, and dual-phase computed tomography (CT) for blunt traumatic splenic injury. MATERIALS AND METHODS Informed consent was waived for this institutional review board-approved, HIPAA-compliant study. Retrospective record review identified 120 blunt trauma patients (87 male [72.5%] 33 female [27.5%]; age range, 18-94 years) who had undergone dual-phase abdominal CT within 5 years, including 30 without splenic injury, 30 with parenchymal injury only, 30 with splenic active bleeding, and 30 with intrasplenic pseudoaneurysm. Six radiologists each performed blinded review of 20 different cases, and scored the presence of pseudoaneurysm, active bleeding, parenchymal injury, and hematoma; 20 cases were interpreted by all radiologists. Data analysis included calculation of diagnostic performance measures with confidence intervals, areas under receiver operating characteristic curves, and interobserver agreement/variability. RESULTS For intrasplenic pseudoaneurysm, arterial phase imaging was more sensitive (70% [21 of 30] vs 17% [five of 30]; P < .0002) and more accurate (87% [78 of 90] vs 72% [65 of 90]; P = .0165) than portal venous phase imaging. For active bleeding, arterial phase imaging was less sensitive (70% [21 of 30] vs 93% [28 of 30]; P = .0195) and less accurate (89% [80 of 90] vs 98% [88 of 90]; P = .0168) than portal venous phase imaging. For parenchymal injury, arterial phase CT was less sensitive (76% [68 of 90] vs 93% [84 of 90]; P = .001) and less accurate (81% [nine of 120] vs 95% [114 of 120]; P = .0008) than portal venous phase CT. For all injuries, dual-phase review was equivalent to or better than single-phase review. CONCLUSION For CT evaluation of blunt splenic injury, arterial phase is superior to portal venous phase imaging for pseudoaneurysm but inferior for active bleeding and parenchymal disruption; dual-phase CT provides optimal overall performance.

OBJECT:The authors performed a study to determine if lesion expansion occurs in humans during the early hours after spinal cord injury (SCI), as has been established in rodent models of SCI, and to identify factors that might predict lesion expansion.METHODS:The authors studied 42 patients with acute cervical SCI and admission American Spinal Injury Association Impairment Scale Grades A (35 patients) and B (7 patients) in whom 2 consecutive MRI scans were obtained 3-134 hours after trauma. They recorded demographic data, clinical information, Injury Severity Score (ISS), admission MRI-documented spinal canal and cord characteristics, and management strategies.RESULTS:The characteristics of the cohort were as follows: male/female ratio 37:5; mean age, 34.6 years; and cause of injury, motor vehicle collision, falls, and sport injuries in 40 of 42 cases. The first MRI study was performed 6.8 ±2.7 hours (mean ± SD) after injury, and the second was performed 54.5 ± 32.3 hours after injury. The rostrocaudal intramedullary length of the lesion on the first MRI scan was 59.2 ± 16.1 mm, whereas its length on the second was 88.5 ± 31.9 mm. The principal factors associated with lesion length on the first MRI study were the time between injury and imaging (p = 0.05) and the time to decompression (p = 0.03). The lesion's rate of rostrocaudal intramedullary expansion in the interval between the first and second MRI was 0.9 ± 0.8 mm/hour. The principal factors associated with the rate of expansion were the maximum spinal cord compression (p = 0.03) and the mechanism of injury (p = 0.05).CONCLUSIONS:Spinal cord injury in humans is characterized by lesion expansion during the hours following trauma. Lesion expansion has a positive relationship with spinal cord compression and may be mitigated by early surgical decompression. Lesion expansion may be a novel surrogate measure by which to assess therapeutic effects in surgical or drug trials.

OBJECT:Pulmonary complications are the most common acute systemic adverse events following spinal cord injury (SCI), and contribute to morbidity, mortality, and increased length of hospital stay (LOS). Identification of factors associated with pulmonary complications would be of value in prevention and acute care management. Predictors of pulmonary complications after SCI and their effect on neurological recovery were prospectively studied between 2005 and 2009 at the 9 hospitals in the North American Clinical Trials Network (NACTN).METHODS:The authors sought to address 2 specific aims: 1) define and analyze the predictors of moderate and severe pulmonary complications following SCI; and 2) investigate whether pulmonary complications negatively affected the American Spinal Injury Association (ASIA) Impairment Scale conversion rate of patients with SCI. The NACTN registry of the demographic data, neurological findings, imaging studies, and acute hospitalization duration of patients with SCI was used to analyze the incidence and severity of pulmonary complications in 109 patients with early MR imaging and long-term follow-up (mean 9.5 months). Univariate and Bayesian logistic regression analyses were used to analyze the data.RESULTS:In this study, 86 patients were male, and the mean age was 43 years. The causes of injury were motor vehicle accidents and falls in 80 patients. The SCI segmental level was in the cervical, thoracic, and conus medullaris regions in 87, 14, and 8 patients, respectively. Sixty-four patients were neurologically motor complete at the time of admission. The authors encountered 87 complications in 51 patients: ventilator-dependent respiratory failure (26); pneumonia (25); pleural effusion (17); acute lung injury (6); lobar collapse (4); pneumothorax (4); pulmonary embolism (2); hemothorax (2), and mucus plug (1). Univariate analysis indicated associations between pulmonary complications and younger age, sports injuries, ASIA Impairment Scale grade, ascending neurological level, and lesion length on the MRI studies at admission. Bayesian logistic regression indicated a significant relationship between pulmonary complications and ASIA Impairment Scale Grades A (p = 0.0002) and B (p = 0.04) at admission. Pulmonary complications did not affect long-term conversion of ASIA Impairment Scale grades.CONCLUSIONS:The ASIA Impairment Scale grade was the fundamental clinical entity predicting pulmonary complications. Although pulmonary complications significantly increased LOS, they did not increase mortality rates and did not adversely affect the rate of conversion to a better ASIA Impairment Scale grade in patients with SCI. Maximum canal compromise, maximum spinal cord compression, and Acute Physiology and Chronic Health Evaluation-II score had no relationship to pulmonary complications.

This study investigated correlations between American Spinal Injury Association (ASIA) clinical injury motor scores in patients with traumatic cervical cord injury and magnetic resonance (MR) diffusion tensor imaging (DTI) parameters. Conventional imaging and DTI were performed to evaluate 25 patients (age, 39.7±13.9 years; 4 women, 21 men) with blunt spinal cord injury and 11 volunteers (age, 31.5±10.7 years; 3 women, 8 men). Cord contusions were hemorrhagic (HC) in 13 and non-hemorrhagic (NHC) in 12 patients. The spinal cord was divided into three regions to account for spatial and pathological variation in DTI parameters. Comparisons of regional and injury site mean diffusivity (MD), fractional anisotropy (FA), radial diffusivity ( λ(⊥)), and longitudinal diffusivity ( λ(‖)) were made with control subjects. ASIA motor scores were correlated with DTI using linear regression analysis. HC and NHC patients showed significant reduction (p<0.001) in MD and λ(‖) in all three regions. At the injury site, significant decreases in FA and λ(‖) were seen for both injury groups (p<0.001). λ(⊥) values were significantly increased only for patients with NHC (p<0.05). Significant reduction in FA and λ(‖) (p<0.0001) was observed at the whole cord level between the injured (NH and NHC) and control groups. Within the NHC group, strong correlations were observed between ASIA motor scores and average MD, FA, λ(⊥), and λ(‖) at the injury site. However, no correlation was observed within the HC group between any of the DTI parameters and ASIA motor scores. DTI parameters reflect the severity of spinal cord injury and correlate well with ASIA motor scores in patients with NHC.

This part continues the paper presented earlier in the Tutorials section. The purpose is to show the use of the Chi-square (X2) control chart as a way of monitoring processes like the bag-filling operations of colored candies. In Part 1 we described the bag-filling process and expained how control charts can be used to check the stability of that process. A typical bag of colored candies should have about the same proportional count of pieces of six different colors. To find out what the color distributions for colored candies should be, contact the candy companies (e.g .• Mars Inc., Hershey Foods Corporation, etc.). Suppose the colors in each bag are red, yellow. green. orange, light (tan) and dark brown_ Monitoring the process for each color reqUires six separate control charts. filling walls with costly paper. Others have used single-color pieces to demonstrate statistical process control. e.g., Kohn and Dorner (1992). Kullberg (1992). and Wortham (1992). These examples focused on one color and i9nored the other colors. The motivation for considering the X2 control chart is to form a composite chart that monitors all the colors while preserving the information of these colors. See Duncan (1950) and Marcucci (1985) for more information. The X2 is an old statistical tool used to test (a) goodness-of-m of probability distributions. (b) homogeneity of proportions. and, (c) independence of (two or more) cross-classified variables in contingency tables. Schlotzhauer (1991) described various X2

Object The objective of this study was to elucidate the relationship between admission demographic data, validated injury severity measures on imaging studies, and clinical indicators on the American Spinal Injury Association (ASIA) motor score, Functional Independence Measure (FIM), manual dexterity, and dysesthetic pain at least 12 months after surgery for acute traumatic central cord syndrome (ATCCS) due to spinal stenosis. Methods Over a 100-month period (January 2000 to April 2008), of 211 patients treated for ATCCS, 59 cases were due to spinal stenosis, and these patients underwent surgical decompression. Five of these patients died, 2 were lost to follow-up, 10 were not eligible for the study, and the remaining 42 were followed for at least 12 months. Results In the cohort of 42 patients, mean age was 58.3 years, 83% of the patients were men, and 52.4% of the accidents were due to falls. Mean admission ASIA motor score was 63.8 (upper extremities score, 25.8 and lower extremities score, 39.8), the spinal cord was most frequently compressed at skeletal segments C3–4 and C4–5 (71%), mean midsagittal diameter at the point of maximum compression was 5.6 mm, maximum canal compromise (MCC) was 50.5%, maximum spinal cord compression was 16.5%, and length of parenchymal damage on T2-weighted MR imaging was 29.4 mm. Time after injury until surgery was within 24 hours in 9 patients, 24–48 hours in 10 patients, and more than 48 hours in 23 patients. At the 1-year follow-up, the mean ASIA motor score was 94.1 (upper extremities score, 45.7 and lower extremities score, 47.6), FIM was 111.1, manual dexterity was 64.4% of baseline, and pain level was 3.5. Stepwise regression analysis of 10 independent variables indicated significant relationships between ASIA motor score at follow-up and admission ASIA motor score (p = 0.003), MCC (p = 0.02), and midsagittal diameter (p = 0.02); FIM and admission ASIA motor score (p = 0.03), MCC (p = 0.02), and age (p = 0.02); manual dexterity and admission ASIA motor score (p = 0.0002) and length of parenchymal damage on T2-weighted MR imaging (p = 0.002); and pain level and age (p = 0.02) and length of parenchymal lesion on T2-weighted MR imaging (p = 0.04). Conclusions The main indicators of long-term ASIA motor score, FIM, manual dexterity, and dysesthetic pain were admission ASIA motor score, midsagittal diameter, MCC, length of parenchymal damage on T2-weighted MR imaging, and age, but different domains of outcome were determined by different predictors.

OBJECTIVE:Craniocervical distraction injury is a class of injuries that involve the skull base, the atlas, and the axis. Although these injuries often are overt imaging and clinical findings, the injury can be masked during unreliable physical examinations and difficult to identify during diagnostic imaging. The goal of this study was to identify on coronal and sagittal CT multiplanar reformations precise measurements and qualitative relations between anatomic landmarks that can help in establishing the diagnosis of craniocervical distraction injury.MATERIALS AND METHODS:We performed a retrospective review of the cases of 35 patients with craniocervical distraction injury admitted to our trauma center from 2000 to 2006. Two independent radiologists made several qualitative and quantitative anatomic assessments on reformatted CT images through the craniocervical junctions (skull base through C2) of the 35 patients and of 50 other patients sustaining blunt trauma who were discharged without findings of cervical spinal injury. Logistic regression, recursive partitioning, and multivariate analysis were performed in an attempt to find measurements that differentiated the groups.RESULTS:Among the patients with craniocervical distraction injury, statistically significant positive correlations were found in several measurements, including midline occiput-C1 spinolaminar distance (p=0.0016), midline C1-C2 spinolaminar distance (p<0.0001), basion-dens distance (p<0.0001), sum of condylar displacement (p=0.0002), and basion-posterior axial line distance (p<0.0001).CONCLUSION:Several quantitative parameters on sagittal and coronal multiplanar CT reformations can be used to differentiate patients with craniocervical distraction injury from patients without this injury.

OBJECT:This retrospective comparative cohort study was aimed at discovering the risk factors associated with subdural hygroma (SDG) following decompressive craniectomy (DC) to relieve intracranial hypertension in severe head injury.METHODS:Sixty-eight of 104 patients who had undergone DC during a 48-month period and survived > 30 days were eligible for this study. To assess the dynamics of subdural fluid collections, the authors compared CT scanning data from and the characteristics of 39 patients who had SDGs with the data in 29 patients who did not have hygromas. Variables significant in the appearance, evolution, and resolution of this complication were analyzed in a 36-week longitudinal study.RESULTS:The earliest imaging evidence of SDG was seen during the 1st week after DC. The SDG volume peaked between Weeks 3 and 4 post-DC and was gradually resolved by the 17th week. Among the mechanisms of injury, motor vehicle accidents were most often linked to the development of an SDG after DC (p < 0.0007), and falls were least often associated (p < 0.005). Moreover, patients with diffuse brain injury were more prone to this complication (p < 0.0299) than those with an evacuated mass (p < 0.0001). There were no statistically significant differences between patients with and without hygromas in terms of age, sex, Glasgow Coma Scale score, intraventricular and subarachnoid hemorrhage, levels of intracranial pressure and cerebral perfusion pressure, timing of decompression, and the need for CSF diversion. More than 90% of the SDGs were ipsilateral to the side of the craniectomy, and 3 (8%) of 39 SDGs showed evidence of internal bleeding at approximately 8 weeks postinjury. Surgical evacuation was needed in 4 patients with SDGs.CONCLUSIONS:High dynamic accidents and patients with diffuse injury were more prone to SDGs. Close to 8% of SDGs converted themselves into subdural hematomas at approximately 2 months postinjury. Although SDGs developed in 39 (approximately 60%) of 68 post-DC patients, surgical evacuation was needed in only 4.

OBJECTIVES:To investigate whether locking screws offer any advantage over nonlocking screws for plate fixation of humeral shaft fractures for weight-bearing applications.DESIGN:: Mechanical evaluation of stiffness in torsion, bending, and axial loading and failure in axial loading in synthetic and cadaveric bone.SETTING:Biomechanical laboratory in an academic medical center.METHODS:: We modeled a comminuted midshaft humeral fracture in both synthetic and cadaveric bone. Humeri were plated posteriorly. Two study groups each used identical 10-hole, 3.5-mm locking compression plates that can accept either locking or nonlocking screws. The first group used only nonlocking screws and the second only locking screws. Stiffness testing and failure testing were performed for both the synthetic bones (n = 6) and the cadaveric matched pairs (n = 12). Fatigue testing was set at 90,000 cycles of 440 N of axial loading.MAIN OUTCOME MEASURES:Torsion, bending, and axial stiffness and axial failure force after cyclic loading.RESULTS:With synthetic bones, no significant difference was observed in any of the 4 tested stiffness modes between the plates with locking screws and those with nonlocking screws (anteroposterior, P = 0.51; mediolateral, P = 0.50; axial, P = 0.15; torsional, P = 0.08). With initial failure testing of the constructs in axial loading, both plates failed above anticipated physiologic loads of 440 N (mean failure load for both constructs >4200 N), but no advantage to locking screws was shown. The cadaveric portion of the study also showed no biomechanical advantage of locking screws over nonlocking screws for stiffness of the construct in the 4 tested modes (P > 0.40). Fatigue and failure testing showed that both constructs were able to withstand strenuous fatigue and to fail above anticipated loads (mean failure >3400 N). No difference in failure force was shown between the 2 groups (P = 0.67).CONCLUSIONS:Synthetic and cadaveric bone testing showed that locking screws offer no obvious biomechanical benefit in this application.

Objective. After automakers were allowed the option of using sled tests for unbelted male dummies to certify the frontal crash performance of vehicles, most frontal air bags were depowered, starting in model year 1998, to reduce deaths and serious injuries arising from air bag deployments. Concern has been expressed that depowering air bags could compromise the protection of adult occupants. This study aimed to determine the effects of changes in air bag designs on risk of death among front-seat occupants.Methods. Deaths among drivers and right-front passengers per involvement in frontal police-reported crashes during calendar years 1998-2004 were compared among vehicles with sled-certified air bags ( model years 1998-2004) and first-generation air bags ( model years 1994-97). Frontal crash deaths were identified from the Fatality Analysis Reporting System. National estimates of police-reported crashes were derived from the National Automotive Sampling System/General Estimates System. Sled certification status for model years 1998-2004 was ascertained from published federal data and a survey of automobile manufacturers. Passenger cars, pickup trucks, sport utility vehicles, and minivans were studied. Stratified analyses were done to compute risk ratios (RR) and 95% confidence intervals ( 95% CI) for driver and right-front passenger deaths by air bag generation and crash, vehicle, and driver characteristics.Results. In frontal crashes, overall RRs were 0.89 for driver deaths ( 95% CI= 0.74-1.08) and 0.89 for right-front passenger deaths ( 95% CI= 0.74-1.07) in sled-certified vehicles compared with first-generation air bag-equipped vehicles. Child right-front passengers ( ages 0-4, 5-9) in vehicles with sled-certified air bags had statistically significant reductions in risk of dying in frontal collisions, including a 65% reduced risk among ages 0-4 ( RR= 0.35; 95% CI= 0.21-0.60). No differences in effects of sled-certified air bags were observed between drivers ages 15-59 and 60-74 in sled-certified vehicles, both of whom had RRs slightly below 0.90 ( non-significant). Among occupants killed in sled-certified vehicles, police-reported belt use was somewhat higher than in first-generation vehicles.Conclusions. No differences in risk of frontal crash deaths were observed between adult occupants with sled-certified and first-generation air bags. Consistent with reports of decreases in air bag-related deaths, this study observed significant reductions in frontal deaths among child passengers seated in the right-front position in sled-certified vehicles. Higher restraint use rates among children in sled-certified vehicles and other vehicle design changes might have contributed partially to these reductions.

Objective. This study aimed to determine whether a persuasive educational intervention could increase licensure among motorcycle owners. Unlicensed motorcycle operators appear to be disproportionately involved in police-reported motorcycle crashes in Maryland, accounting for about 27% of motorcycle operators in police-reported crashes, although unlicensed owners comprise 17% of primary motorcycle owners. Methods. A randomized controlled trial was conducted among unlicensed owners. Linking Maryland records of registered motorcycles with license files, 8,499 unlicensed owners who had no licensed co-owners were identified. Half were randomized to receive a persuasive educational mailing in early June 2005 from Maryland Motor Vehicle Administration (MVA). Motorcycle licenses can be attained by passing an accredited motorcycle training class or passing knowledge and skills tests administered by the state driver licensing agency. Licensure rates and motorcycle class enrollment were followed for 6 months post-intervention. Results. As of December 16, 2005, 280 intervention group owners had obtained Class M motorcycle licenses and 158 had obtained Class R motorcycle learner's permits. The comparison group obtained 209 M licenses and 122 R permits. The overall success rate in the intervention group, defined as obtaining Class M or R, was 10.4% compared with 7.9% in the comparison group (licensure ratio (LR) = 1.33; 95% confidence interval (CI) = 1.16–1.52). The intervention was most successful among men, whose LR for obtaining M licenses was 1.45 (95% CI = 1.21–1.75). LRs were higher among owners ages 40–48 and 49+ receiving the intervention compared with younger groups. Motorcycle training class enrollment rates were higher in the intervention group, particularly among those taking a course for riders with intermediate skills (enrollment ratio = 2.24; 95% CI = 1.41–3.55). Conclusion. The intervention appeared to increase licensure, yet the licensure rate remained low among the intervention group. Potential risks and benefits of increasing the percentage of motorcyclists who are licensed need to be studied.

Matched-pair cohort studies involve pairs of cases where outcomes of interest (e.g., mortality, morbidity, injury, etc.) among persons exposed to risk factors are compared with persons not exposed. Matched cohort studies have been used in traffic-crash research, for example, to compare the injury risk of drivers and passengers from the same crash or vehicle. Matching in cohort studies helps reduce bias and confounding effects that may exist in estimating risk or hazard ratios. Only the data where one or both of the paired cases with the outcome of interest are used, which is useful when little or no information is available regarding pairs in which cases did not have the outcome. For example, this technique could be used to analyze a registry of disease or trauma cases, since no information would be available on the number of cases that are disease or trauma free. Mantel-Haenszel stratification, logistic and conditional Poisson regression, and Cox proportional hazard models are common methods used to analyze data from cohort studies. This paper will show how SAS procedures GENMOD (for conditional Poisson regression) and PHREG (for Cox proportional hazards regression) can be used to analyze matched-pair cohort data in traffic crash research.

OBJECTIVE. The purpose of this study was to compare the usefulness of two CT grading systems of blunt splenic trauma in predicting which patients need surgery or angioembolization.MATERIALS AND METHODS. Four hundred patients in hemodynamically stable condition admitted with blunt splenic injury were included in the study. All patients underwent contrast-enhanced MDCT. Grade of splenic injury was prospectively assigned according to the American Association for the Surgery of Trauma (AAST) splenic injury scale. Patients were treated with surgical intervention, splenic arteriography with or without embolization, or observation alone. All MDCT images were retrospectively reviewed and regraded according to a novel grading system that specifically incorporates the findings of active bleeding or splenic vascular injury, including pseudoaneurysm and arteriovenous fistula. Receiver operating characteristics curves were generated with both grading systems for all splenic interventions, and statistical analyses were performed.RESULTS. The area under the ROC curves for the new splenic grading system for splenic arteriography, surgery, and both interventions exceeded 80%. The area under the curve for the new splenic grading system was greater than that for the AAST injury scale for all interventions. Differences were found to be statistically significant for splenic arteriography (p=0.0036) and the combination of arteriography and surgery (p=0.0006).CONCLUSION. The proposed CT grading system is better than the AAST system for predicting which patients with blunt splenic trauma need arteriography or splenic intervention.

US air bag regulations were changed in 1997 to allow tests of unbelted male dummies in vehicles mounted and accelerated on sleds, resulting in longer crash pulses than rigid-barrier crashes. This change facilitated depowering of frontal air bags and was intended to reduce air bag-induced deaths. Controversy ensued as to whether sled-certified air bags could increase adult fatality risk. A matched-pair cohort study of two-vehicle, head-on, fatal collisions between drivers involving first-generation versus sled-certified air bags during 1998-2005 was conducted by using Fatality Analysis Reporting System data. Sled certification was ascertained from public information and a survey of automakers. Conditional Poisson regression for matched-pair cohorts was used to estimate risk ratios adjusted for age, seat belt status, vehicle type, passenger car size, and model year for driver deaths in vehicles with sled-certified air bags versus first-generation air bags. For all passenger-vehicle pairs, the adjusted risk ratio was 0.87 (95% confidence interval: 0.77, 0.98). In head-on collisions involving only passenger cars, the adjusted risk ratio was 1.04 (95% confidence interval: 0.85, 1.29). Increased fatality risk for drivers with sled-certified air bags was not observed. A borderline significant interaction between vehicle type and air bag generation suggested that sled-certified air bags may have reduced the risk of dying in head-on collisions among drivers of pickup trucks.