Modeling Humans: Defining In Vivo Joint and Contact Characteristics

计算模型是系统研究损伤动力学、评估特定对象、环境和设备变量对冲击力和损伤的影响的有力工具。然而，这些模型的准确性取决于已知的接触和连接特性。虽然许多研究团队正在开发新的模型，以更好地代表组织，但大多数模型是使用几十年前发表的研究的实验数据建立的。很少有研究团队拥有准确测试和表征活体组织力学的工具和能力。为了推进我们的研究计划，开发人体损伤的计算模型，我们必须继续完善我们对人类关节和组织特征的知识，特别是量化跌倒或撞击时的关节反应，并测量体内组织的接触机制。使用我们开发的一种新工具，将精确的机械组织测试带到旁边，我们将能够评估活体人类受试者的软组织特征，并首次绘制出表面组织特征的变化以及姿势和肌肉激活的变化。使用这一新系统将能够应用更大的变形来更好地映射非线性组织行为，这对于理解损伤机制和损伤预防非常重要。这项研究计划的核心目标是开发新的人类影响计算模型。我们将通过三个研究目标来实现这一目标：1)表征和建模髋关节、膝部、足部、肩部、肘部、手部和头部的正常活体组织接触力学；2)建模手臂和腿部主动关节对扰动的响应；3)在人体刚体动力学模型中将组织接触定义与关节位置和激活相耦合。此外，我们将是第一个推导和实现对平衡扰动的反应性反应的条件模型。开发主动关节响应的计算表示并将这些响应耦合到组织接触特征的变化将提高复制撞击事件的计算方法的保真度，并提供对坠落受试者所采用的伤害预防策略的更好的机械理解。开发这些用于公共软件平台(Madymo)的建模方法将允许其他人在我们的结果的基础上进一步测试和改进这些新模型。

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.