The influence of air bags and restraining devices on extremity injuries in motor vehicle collisions

The association between knee airbag deployment and knee-thigh-hip fracture injury risk in motor vehicle collisions: A matched cohort study

INTRODUCTION

In the U.S. alone, an estimated 30,000 knee-thigh-hip (KTH) injuries occur annually in frontal motor vehicle collisions. These fractures typically occur through occupant contact with the vehicle's knee bolster. Research has suggested that knee airbags (KABs) can mitigate the forces sustained during this contact, resulting in decreased injury risk; however, previous research has been limited by small sample sizes or by occurring in a controlled setting. The objective of the current study is to determine the effectiveness of KABs on KTH fracture risk using nationally representative, real-world data.

METHODS

Using combined data from the Crash Injury Research and Engineering Network and the National Automotive Sampling Survey, a matched cohort study was conducted among front-seat occupants of vehicles involved in a frontal collision occurring from 2000 to 2009. Occupants exposed to a KAB deployment were matched to occupants with no KAB deployment based on age ±5 years, sex, seatbelt use, vehicle seating position (i.e., driver or front passenger), car vehicle body type, collision impact, and sampling weight. A Cox proportional hazards model was used to calculate risk ratios (RRs) and associated 95% confidence intervals (95% CI) to estimate the association between KAB deployment and lower extremity fracture risk.

RESULTS

There was no association between KAB deployment and risk of lower extremity fracture (RR 0.83, 95% CI 0.52-1.31). A notable pattern in fracture risk, though not statistically significant, was observed, with a decreased risk of hip (RR 0.72, 95% CI 0.26-1.97) and thigh fracture (RR 0.81, 95% CI 0.32-2.05), and an increased risk of tibia/fibula (RR 1.23, 95% CI 0.52-2.90) and foot fracture (RR 1.96, 95% CI 0.72-5.32).

CONCLUSIONS

The results of the current study suggest that KABs are not associated with the risk of lower extremity fractures. However, given the small sample size of the current study, it is difficult to definitively say whether the observed injury pattern is representative of the true pattern.

Risk factors for 24-hour mortality after traumatic rib fractures owing to motor vehicle accidents: a nationwide population-based study

BACKGROUND

Accurate identification of patients at high risk of death as a result of major chest trauma is essential within a trauma system. We used 3-year population-based data in Taiwan to evaluate risk factors associated with 24-hour mortality among adults with obvious rib fractures and needing hospitalization after traffic accidents.

METHODS

Pooled data from Taiwan's National Health Insurance Research Database for the years 2002 through 2004 were used. A total of 18,856 patients hospitalized with rib fractures after traffic accidents were included. Multivariate logistic regression using generalized estimating equations was performed to explore the relationship between 24-hour mortality and patients' age, sex, and comorbid conditions, as well as hospital characteristics, adjusting for social factors and any clustering of the sampled patients by hospital.

RESULTS

Of patients in the sample, 459 (2.4%) died within 24 hours of admission. Patients who had six or more rib fractures were three times more likely to die within 24 hours of admission compared with patients with only one rib fracture (odds ratio [OR], 3.16; p < 0.001). The adjusted odds of death within 24 hours were higher for patients who had hemopneumothorax (OR, 3.15; p < 0.001), extremity fractures (OR, 1.74; p < 0.001), pelvic fractures (OR, 2.92; p < 0.001), head injuries (OR, 4.29; p < 0.001), spleen injury (OR, 1.83; p < 0.05), hepatic injury (OR, 4.39; p < 0.001), heart injury (OR, 4.48; p < 0.001), and diaphragm injury (OR, 3.16; p < 0.05) compared with patients who had none of these injuries.

CONCLUSIONS

We concluded that more than six ribs fractured, heart injuries, hepatic injuries, head injuries, and advanced age are the most important determinants of 24-hour mortality after thoracic trauma from traffic accidents.

Traumatic simultaneous asymmetric hip dislocations and motor vehicle accidents

Hip dislocations are becoming more frequent with increasing numbers of motor vehicle accidents. Bilateral hip dislocations are a rare injury, and simultaneous asymmetric dislocations are even more rare. Of the 20 cases described in the English literature, 16 have been sustained by occupants of motor vehicle accidents. This article presents the first case of a female with traumatic simultaneous asymmetric hip dislocations, as well as the first patient with associated asymmetric acetabular wall fractures.

Injury risks between first- and second-generation airbags in frontal motor vehicle collisions

BACKGROUND

Airbags in vehicles manufactured after 1997 were depowered to decrease injury risks for infants/children and small adults. It is possible that compared to earlier airbags second-generation airbags provide less injury protection due to their depowered nature.

METHODS

A cohort study was conducted using 1995-2004 national data. Risk ratios (RRs) and 95% confidence intervals (CIs) compared injury risks for occupants involved in frontal collisions in vehicles wherein a first- or second-generation airbag deployed by body region and injury severity using the Abbreviated Injury Scale (AIS). Associations were adjusted for crash severity, seatbelt use, seat position, occupant location, and vehicle curb weight.

RESULTS

For upper extremity injuries reduced RRs were observed for AIS 1 or greater (RR=0.76, CI 0.67-0.86), AIS 2 or greater (RR=0.76, CI 0.58-1.00) and AIS 3 (RR=0.81, CI 0.64-1.03). Elevated risks were observed for AIS 5 thoracic injuries (RR=1.46, CI 1.04-2.07) but were made null when differences in age and gender were adjusted for.

CONCLUSIONS

Vehicles equipped with first- and second-generation airbags appear to offer similar protection for front-seated occupants. The observed decreased risks for upper extremity injury and increased risks for severe thoracic injuries warrant further attention.

[Knee injuries of vulnerable road users in road traffic]

BACKGROUND

The purpose of this study was to assess the risk of knee injuries among vulnerable road users, such as pedestrians, bicyclists and motorcyclists.

METHODS

Two different periods (years 1985-1993 and 1995-2003) were compared. Inclusion criteria were furthermore Abbreviated Injury Scale knee 2-3 (AIS(knee)). Technical analysis assessed the type of collision, direction and speed as well as the injury pattern, and different injury scores (AIS, ISS) were examined documented by the accident research unit, which analyses technical and medical data collected shortly after the accident at the scene. This study included 2,580 pedestrians, 2,279 motorcyclists and 4,322 bicyclists from a total number of 22,794 victims in 17,382 accidents.

RESULTS

Among vulnerable road users, 2% (196/9181 patients) had serious ligamentous or bony injuries of the knee. The risk of injury was higher for motorcyclists and bicyclists than for pedestrians. Knee injury severity was higher for pedestrians. Over the course of 18 years, the knee injury risk was significantly reduced in more recent times (35%>28%, p<0.0001). Improved aerodynamic design of car fronts reduced the risk for severe knee injuries significantly (p=0.0015).

CONCLUSIONS

The highest risk for knee injuries among vulnerable road users is encountered by motorcyclists followed by bicyclists and pedestrians. Over time, the knee injury risk for pedestrians could be significantly reduced due to aerodynamic changes of current car fronts. Further modification of the exterior car design might decrease the risk for knee injuries among vulnerable road users.

The interaction of 'occupant factors' on the lower extremity fractures in frontal collision of motor vehicle crashes based on a level I trauma center

BACKGROUND

To advance occupant protection through the improvement of safety countermeasures, it is necessary to understand the factors that affect human injury tolerance. This study investigated the effect of 'occupant factors' i.e. age, gender, height, weight, and body mass index (BMI) on the pattern of lower extremity injury after motor vehicle crashes (MVCs). The second objective was to identify factor(s) (including restraint systems and Delta V) that influence the severity of fractures (open versus close fractures) within the lower extremity area. The outcome of this study may have implications toward secondary prevention in MVCs.

METHODS

One-hundred and thirty-seven front-seat occupants involved in MVCs with frontal impact admitted to the University of Michigan trauma center as part of the Crash Injury Research and Engineering Network (CIREN) project were evaluated. Injuries were classified according to location (knee, thigh, hip [KTH]; lower leg [LL], foot and ankle [FA]). All the relevant variables mentioned above were analyzed.

RESULTS

KTH fractures were the most common region (49.5%) affected, followed by fractures to the FA (38.4%) and LL region (12.1%). Female occupants, being generally shorter than their male counterpart, sustained a significantly higher percentage of FA fractures (44% vs. 29.5%, p < 0.05). Male occupants sustained more KTH fractures (58.3% vs. 44%, p < 0.05). Results demonstrated that there were significantly higher percentages of 'open' fractures in the below knee area (FA [53.8%], LL [24.4%], and KTH [21.8%]; p < 0.05). Of all those variables tested (age, gender, height, weight, BMI, restraint systems, and Delta V), occupant's height had a significant effect on the severity of fractures sustained.

CONCLUSION

The interactive effect observed for height and gender on the pattern of lower extremity fracture is principally related to the body habitus and that gender may be a 'proxy' variable. The 'human factor' plays a vital role in influencing the pattern of injury in a MVC. This study strongly supports the fact that occupants with dissimilar body habitus interact differently with the interior cabin of the vehicle, thus, the performance of the active and passive safety systems.

Upper extremity fracture patterns following motor vehicle crashes differ for drivers and passengers

PURPOSE

Injury patterns of occupants in motor vehicle crashes are changing, with upper extremity injury becoming more common in patients treated at trauma centres. Although not life threatening, upper extremity injuries may result in long-term disability, including chronic deformity, neurovascular compromise and degenerative arthritis. The purpose of this study was to compare upper extremity injury in drivers and passengers using the Crash Injury Research Engineering Network (CIREN) database.

METHODS

CIREN data were used to compare upper extremity skeletal injury patterns and sources for drivers and passengers in frontal and side impacts. Occupant variables (age, gender, co-morbidity, avoidance maneuvers and restraint use) and crash variables (direction of impact, delta V and vehicle crush) were considered in the analysis.

RESULTS

Only 24.8% of all occupants in the CIREN database had upper extremity injuries. One-half of upper extremity injuries to drivers were forearm fractures compared to one-third for passengers. Occupants in side impacts were more likely (OR=5.05) to have clavicle fractures, even while controlling for driver versus passenger status and safety belt use. Air bags were more likely to be a source of forearm fracture (OR=2.31) when controlling for driver versus passenger status, direction of force, sex and age compared to other sources. Only 10% of driver fractures with air bag deployment in frontal impacts were associated with air bag fling.

CONCLUSIONS

This study found that drivers and passengers have different upper extremity injury patterns but the direction of impact also plays an important role.

The association between restraint system and upper extremity injury after motor vehicle collisions

OBJECTIVES

This study was designed to investigate the relationship between upper extremity (UE) injuries and occupant restraint systems among front seat occupants who were involved in frontal motor vehicle collisions (MVCs).

DESIGN

Case-control.

SETTING

The 1995 through 2002 National Automotive Sampling System (NASS) Crashworthiness Data System (CDS).

PARTICIPANTS

Subjects were identified from the NASS-CDS. All cases sustained an UE injury with a > or = 2 Abbreviated Injury Scale Score.

OUTCOMES

Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated comparing risk of UE in 3 mutually exclusive restraint system groups (seatbelt-only, airbag-only, seatbelt-airbag-combined) to the unrestrained group. Data analysis was adjusted for significant occupant, vehicle, and collision characteristics.

RESULTS

Seatbelt-only occupants had a reduced UE injury risk (OR, 0.41; 95% CI, 0.22-0.76). Near null associations were found for airbag-only (OR, 1.1; 95% CI, 0.68-1.76) and seatbelt-airbag-combined (OR, 0.97; 95% CI, 0.56-1.69).

CONCLUSION

The results of this study suggest that UE injuries may become more common as a result of MVCs as the proportion of airbags in motor vehicles increases.

Restraint Use and Lower Extremity Fractures in Frontal Motor Vehicle Collisions

BACKGROUND

Seat belts and air bags have been shown to significantly reduce morbidity and mortality following MVCs. Research suggests that restraint use does not protect against lower extremity fracture; however, no population-based studies of this association exist. The purpose of this study is to compare the effectiveness of combined seat belt and airbag restraint systems with airbag alone, seat belt alone, and no restraints with respect to incidence and location of lower extremity fractures.

METHODS

A retrospective analysis of front seat occupants involved in police-reported, tow-away frontal MVCs was conducted using data from the 1995 through 2000 National Automotive Sampling System (NASS). Incidence and relative risk (RR) of fracture to specific bony regions were measured according to seat belt use and airbag deployment.

RESULTS

Compared with unrestrained occupants, occupants restrained with airbag only had significantly higher risk for all types of lower extremity fractures whereas those occupants restrained with either seat belt only or seat belt and airbag had lower risk of fracture. The greatest difference was seen with tibia/fibula fractures in airbag only (RR, 2.14) but this trend continued to be significant with femur and pelvic fractures (RR, 1.13 and 1.23, respectively).

CONCLUSION

While airbags may reduce the risk of death when used alone or in combination with seat belts, the results of this study demonstrate that air bags increase the risk of lower extremity fractures when used as the sole method of passenger protection. Also, they may do so differentially according to skeletal region. This data strongly support the consideration of developing accessory knee bolster airbags to prevent the "submarining" or sliding under the airbag that may be responsible for this finding.

The association between occupant restraint systems and risk of injury in frontal motor vehicle collisions

BACKGROUND

An evaluation of seat belt use and airbag deployment, either alone or in combination, on risk of injury to specific body regions has yet to be completed.

METHODS

A retrospective cohort study of front seat occupants involved in police-reported, tow-away, frontal motor vehicle collisions using data from the 1995 through 2000 National Automotive Sampling System was conducted. Only vehicles with a change in velocity (delta-V) of >/= 15 km/h were included. Risk of injury (Abbreviated Injury Scale score >/= 2) to specific body regions was compared according to seat belt use and airbag deployment.

RESULTS

Compared with completely unrestrained occupants, those using a seat belt alone or in combination with an airbag had a reduced overall risk of injury (relative risk, 0.42 and 0.71, respectively); no association was observed for those restrained with an airbag only (relative risk, 0.98). This pattern of results was similar for specific body regions with the exception of the lower extremity, wherein a significantly increased risk was observed for airbag deployment alone.

CONCLUSION

Airbag deployment does not appear to significantly reduce the risk of injury either alone or in combination with seat belts. Airbag deployment without associated seat belt use may increase the risk of lower extremity injury.

Effect of air bags and restraining devices on the pattern of facial fractures in motor vehicle crashes

OBJECTIVE

To examine the relationship between the use of restraining devices and the incidence of specific facial fractures in motor vehicle crashes.

DESIGN

Retrospective analysis of patients with facial fractures following a motor vehicle crash.

SETTING

University of Alabama at Birmingham Hospital level I trauma center from 1996 to 2000.

PATIENTS

Of 3731 patients involved in motor vehicle crashes, a total of 497 patients were found to have facial fractures as determined by International Classification of Diseases, Ninth Revision (ICD-9) codes. Facial fractures were categorized as mandibular, orbital, zygomaticomaxillary complex (ZMC), and nasal.

RESULTS

Use of seat belts alone was more effective in decreasing the chance of facial fractures in this population (from 17% to 8%) compared with the use of air bags alone (17% to 11%). The use of seat belts and air bags together decreased the incidence of facial fractures from 17% to 5%.

CONCLUSIONS

Use of restraining devices in vehicles significantly reduces the chance of incurring facial fractures in a severe motor vehicle crash. However, use of air bags and seat belts does not change the pattern of facial fractures greatly except for ZMC fractures. Air bags are least effective in preventing ZMC fractures. Improving the mechanics of restraining devices might be needed to minimize facial fractures.