Pelvic Injuries and Mechanisms of Small Females in Different Postures in Frontal Impacts.

Abstract

Purpose: Determine the mechanisms of pelvis injuries via an analysis of temporal sequence of the pelvic acceleration and load responses of small females under reclined and upright postures in frontal impacts.

Methods: A secondary analysis of pre-existing NHTSA database sled tests under the two postures was conducted. Temporal responses were analyzed using data from pelvic accelerometers and inboard and outboard load cells attached to the lap belt. Pelvic injuries were scored using the Abbreviated Injury Scale (AIS). Three specimens were tested in each posture/group.

Results: The mean age, stature, total body mass, and body mass index of the six specimens were 80.3 years, 1.6 m, 41.3 kg, 17.0 kg/m², respectively. All three reclined specimens and two specimens in the upright groups sustained pelvic fractures. Injuries were more severe/unstable and greater in number in the reclined group. It should be noted that fractures in the posterior pelvic region (ring and other structural components such as sacrum) are considered as unstable injuries and coded at the AIS 4 level of severity. Temporal details and AIS scores are given in the body of the paper.

Conclusions: The attainment of peak pelvis vertical acceleration earlier than the peak lap belt loads in the reclined group suggests that the distal pelvic structures absorb the axial loading prior to the loading of the iliac wing. While a similar phenomenon occurred for the upright posture, timings were delayed. These results appear to indicate a dual mechanism of load transfer for pelvic fractures. The pre-angulation of the reclined pelvis anatomy is a critical factor for earlier pelvic loading, potentially influencing the severity and number of injuries, as determined by the temporal analysis of accelerations and loads. Because of the limitations in the sample size, the present findings should be considered as an initial first step in an understanding of the kinematics and injuries under reclined and upright postures. More samples with controlled variables should be sled-tested to reinforce the initial observations.