Background Seatbelt use, alone and in conjunction with an airbag, is associated with lower risk of mortality, blunt abdominal trauma and kidney injury in motor vehicle crashes (MVCs). However, the effect of these protective devices on risk of severe liver injury is not well characterised.
Methods This retrospective cohort study included patient admissions with liver injuries from MVCs from the National Trauma Data Bank (NTDB), collected from 2010 to 2015 in the USA. We examined associations between injury severity and seatbelt use and airbag presence individually and in the presence of additive interaction. Secondary outcomes were mortality, complications and discharge disposition.
Results We analysed 55 543 records from the National Trauma Data Bank. In adjusted analysis, seatbelt use alone was protective against severe (AAST VI or above) hepatic injury (risk ratio (RR) 0.79, 95% CI 0.75 to 0.84), while airbag presence alone was not (RR 1.05, 95% CI 0.8 to 1.12). The joint association of seatbelt use and airbag presence with injury severity was greater than seatbelts alone (RR 0.74, 95% CI 0.70 to 0.79), with 13% of the joint lower risk attributable to interaction (95% CI 3% to 24%). The adjusted mortality risk of those without protective devices (10.3%, n=2297) was nearly double that of patients who used a seatbelt in conjunction with a present airbag (5.3%, n=699, p<0.001).
Conclusions Seatbelts are associated with lower liver injury severity and are more protective with airbags present, while airbags without seatbelt use were not protective against severe injury among patients with liver injury.
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Contributors All authors envisioned and designed the study; interpreted the data; edited and approved the final manuscript. AR carried out statistical analysis and revised the manuscript. AR, BM and FDS composed the initial draft.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The National Trauma Data Bank is available to the public at a fee from the American College of Surgeons, at https://www.facs.org/quality-programs/trauma/ntdb.
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