Biomechanical response of the pediatric abdomen, Part 2: injuries and their correlation with engineering parameters.

This paper describes the injuries generated during dynamic belt loading to a porcine model of the 6-year-old human abdomen, and correlates injury outcomes with measurable parameters. The test fixture produced transverse, dynamic belt loading on the abdomen of 47 immediately post-mortem juvenile swine at two locations (upper/lower), with penetration magnitudes ranging from 23% - 65% of the undeformed abdominal depth, with and without muscle tensing, and over a belt penetration rate range of 2.9 m/s - 7.8 m/s. All thoracoabdominal injuries were documented in detail and then coded according to the Abbreviated Injury Scale (AIS). Observed injuries ranged from AIS 1 to AIS 4. The injury distribution matched well the pattern of injuries observed in a large sample of children exposed to seatbelt loading in the field, with most of the injuries in the lower abdomen. Univariate and multiple regression models were used to assess mechanical predictors as injury criteria for maximum AIS 2+ and 3+ outcomes, including peak belt tension and posterior reaction force, abdominal penetration, penetration rate, the viscous criterion, and a newly proposed criterion, FCmax, which is the maximum of the instantaneous product of loading rate and normalized penetration. The Goodman-Kruskal Gamma (gamma) was used to assess each parameter's ability to discriminate between injurious and non-injurious tests. Injury risk functions were generated for both outcomes by fitting a 2-parameter Weibull distribution to the injury data using survival analysis. The best discriminators were peak belt tension (gamma = 0.86 and 0.83, p < 0.01), the work done by the deforming thorax (gamma = 0.86 and 0.74, p < 0.01), and abdominal penetration (gamma = 0.89 and 0.66, p < 0.02). Penetration rate was not a good discriminator (gamma = 0.34 and 0.52), and the consideration of penetration rate decreased the discrimination of the viscous criterion (gamma = 0.67 and 0.58) relative to penetration alone. FCmax was a better discriminator of injury than the viscous criterion (gamma = 0.70 and 0.76, p < 0.01), indicating that the loading rate may be more related to injury outcome than the penetration rate.