Session III - Injury Prevention

Thurs, 10/20/05 Injury Prevention, Paper #10, 4:16 pm

Air Bag Deployment Increases the Risk of Lower Extremity Injury

Justin S. Cummins, MD; Kenneth J. Koval, MD; Robert V. Cantu, MD;
Kevin F. Spratt, PhD; (n-all authors)
Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire, USA

Purpose: Although air bags have been reported to reduce passenger mortality by up to 30% in frontal collisions, air bags have also been reported as a cause of injury in motor vehicle collisions (MVCs). The purpose of this study was to evaluate a large cohort of patients involved in MVCs to determine the pattern of injuries associated with air bags to see if they increase the risk of injury.

Methods: Information on patients involved in MVCs from 1988 to 2004 was obtained from the National Trauma Data Bank (NTDB) Version 4.0. Patients were identified based on involvement in a MVC, as well as on the availability of complete abbreviated injury scale (AIS) scoring data. An occupant was considered injured if an AIS score of 2 or greater was recorded for one of the eight body regions, indicating an injury of at least moderate severity. The data was evaluated based on four groups of safety devices: seat belt and air bag deployed (SBAB), seat belt only (SBO), deployed air bag only (ABO), and no safety devices (NONE). Other variables considered were age, race, gender, driver or passenger status, injury severity score (ISS), and mortality. Logistic regression was used to calculate odds ratios and to adjust for the variables identified.

Results: A total of 35,609 patients met study inclusion criteria. 56% of the patients were male; 68% were drivers. Racial composition was 71% white, 18% black, 8% Hispanic, 3% Asian, and 1% unspecified. 2049 patients used SBAB, 15,720 used SBO, 947 used ABO, and 16,893 used NONE. Mortality rates were 3.32% for SBAB, 3.63% for SBO, 6.02% for ABO, and 6.23% for NONE. Patterns of injury location associated with seat belt and air bag use adjusted for all predictors are summarized in the table on the following page.

 SBAB vs. NONE

  SBO vs. NONE  ABO vs. NONE
 Body Region  Adjusted OR  99% CI  Adjusted OR  99% CI  Adjusted OR  99% CI
 Head  .36  .31 - .42  .45  .42 - .48 .79   .66 - .94
 Thorax  .67  .58 - .78  .80  .75 - .86  .76  .61 - .93
 Abdomen  .80  .66 -. 96  .92  .84 - .99  .96  .74 - 1.21
 Spine  .50  .40 - .60  .72  .67 - .78  .69  .54 - .89
 Upper Ext  1.04  .90 - 1.20  .81  .75 - .86  1.05  .85 - 1.28
 Lower Ext  1.36*  1.20-1.54  .87  .81 - .92  1.35*  1.13 - 1.61

Conclusion/Significance: In this cohort, seat belts with air bags or seat belts alone provided the greatest benefit to patients in mortality reduction. Air bag deployment alone did not significantly reduce mortality, and provided lesser degrees of protection for most body regions, and most notably significantly increased the risk of lower extremity injuries, even when seat belts were also in use (*). It might be worthwhile to consider underdash air bag deployment to reduce risk of lower extremity injury given the increased risk of lower extremity injury with current air bag deployment schemes.

If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.