Modeling Humans: Defining In Vivo Joint and Contact Characteristics

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Computational models are powerful tools for systematically studying injury dynamics and evaluating the effects of specific subject, environmental and equipment variables on impact forces and injury. However, the accuracy of these models depends on known contact and joint characteristics. While many research teams are developing new models to better represent tissues, most are built using experimental data from studies published many decades ago. Few research teams have the tools and capacity to accurately test and characterize in vivo tissue mechanics. To advance our research program developing computational models of human injury we must continue to refine our knowledge of human joint and tissue characteristics particularly quantifying joint reactions during falls or impacts and measuring the contact mechanics of in vivo tissues. Using a new tool we developed to bring precision mechanical tissue testing to the beside we will be able to assess soft tissue characteristics in live human subjects and map changes in tissue characteristics across a surface and with changes in posture and muscle activation for the first time. Using this new system will be able to apply larger deformations to better map non-linear tissue behaviours, which are important for understanding injury mechanics and injury prevention. The core goal of this research program is to develop new computational models of human impact. We will achieve this through three research objectives; 1 ) characterizing and modeling normal in vivo tissue contact mechanics for the hip, knee, foot, shoulder, elbow, hand and head, 2) modeling active joint responses to perturbation for the arms and legs, and 3) coupling tissue contact definitions to joint position and activation in rigid body dynamic models of humans.This work is novel in experimentally measuring and defining computational models for contact characteristics of several live human tissues likely to be impacted during falls, injuries and activities of daily living. Further, we will be the first to derive and implement conditional models for reactive responses to balance perturbation. Developing computational representations of active joint responses and coupling those responses to changes in tissue contact characteristics will improve the fidelity of computational methods to replicate impact events and provide a better mechanistic understanding of injury prevention strategies employed by falling subjects. Developing these modeling methods for use in a common software platform (Madymo) will allow others to build on our results to further test and refine these new models.