Biomechanics and Injury Assessment of Head Impact Due to Falls

Head injury due to impact from falls represents a significant and growing problem. Due to an increasing incidence of fall related head injuries, there is significant concern regarding this important public health issue. Mitigation of head injuries due to falls requires a comprehensive understanding of the causes and the potential of head injuries in fall accidents. Injury prevention can include practices that promote fall reduction and development of high performance head protection devices. Therefore, to develop high performance protective headgear, a comprehensive database that provides the bounds and correlation between impact parameters is needed for estimating impact parameters based on fall conditions. This database is not currently available and there are currently no U.S. standards that exist specifically for design of protective headgear for falls. The aim of this dissertation was to fulfill the gap in the knowledge base that exists in this field by providing a database that gives an estimation of the head injury potential that may arise from falling and the bounds of the impact parameters; these parameters include force, peak linear and angular acceleration/velocity to the head due to an unprotected fall and prescribing reasonable criteria for design and evaluation of impact attenuation devices for falls. To ascertain these bounds—since it was not possible to assess the response of head impact due to human falling onto hard surfaces in the laboratory because of safety concerns—the pedestrian versions of a Hybrid III 5th percentile female and 50th percentile male anthropomorphic test dummy(ATD) were used. Several common fall scenarios were initiated from a frontal, sideward and backward orientation and the responses of the ATDs were quantified. A Vicon™ motion capture system was used to track the motion of the ATD during the fall. For verification, prior methods employed in other studies, including numerical simulations and cadaveric experiments were compared to the bounds obtained in this study. The effect of fall scenarios on head impact was also studied. In addition, in reconstruction of the real life fall incidents or head impact testing, some of the impact parameters are not available while the other impact parameters have been recorded or computed based upon eye-witness reports; video tape recorded or acquired sensor signals. Therefore, correlation between impact parameters were established and prediction intervals were obtained to provide bounds for estimation of the unavailable head impact parameters based on fall conditions and available impact parameters. These correlations can be used to develop simplified experimental procedures for testing of head protection devices and also improve real life fall incident reconstructions in forensic engineering. In addition, a concise review of head injury mechanisms and predictors was provided and head injury potentials in falls from diverse vantage points were assessed. Finally, the mass involved during head impact—the effective mass that expresses the contribution of the body during the event—was quantified and the effect of fall direction/type on the effective mass estimate was studied. The effective mass is a key parameter in the development of appropriate methodology to simulate falls more realistically. In summary, the studies performed for this dissertation dealt with different aspects of head impacts and injuries due to standing falls and provided further information on informed development of testing methods, standards, and how to more accurately reconstruct real life fall incidents and related head impacts