Analysis and Development of Dynamic Loading Approaches for the Shoulder Implant-Bone Structure

已经有许多基于工程的生物力学研究来检验与人体关节相关的各种因素，其中许多集中在植入重建上。基本上，所有这些研究都在关节处采用了静态或循环加载。然而，关于动态载荷的影响，特别是骨和界面的时间依赖(即粘弹性)特性是显著的，关于动态载荷的影响还很少。假设由于高速或冲击相关事件而在动态范围内引入载荷将改变相对于静态或准静态载荷情况的载荷传递机制，这是合乎逻辑的。随着关节重建后的个体变得更加活跃，确定动态载荷对植入物设计和测试方案的影响是很重要的。本研究旨在明确动态载荷对肩部种植体骨构建中载荷传递机制和应力状态的重要性。到目前为止，试验性的肩部测试在身体标本或替代泡沫模型上使用静态加载方案。最近的一些系统使用简化的肌肉控制协议和/或机器人技术来产生手臂运动。然而，这些方法不能适应高速和惯性效应。此外，计算有限元模型通常不包括动态加载。因此，要优化我们对这种接头的理解和评估，就必须开发和应用先进的综合测试和建模方法，其中包括动态加载。该研究计划的短期目标是采用实验和计算方法：(I)确定动态活动对关节载荷的影响；(Ii)确定动态关节载荷对种植体-骨界面的影响。该计划的长期目标是制定一项最先进的测试计划，允许在肩部进行广泛的高级研究，特别是模拟从低需求活动到高速(冲击)活动的关节载荷。本文提出的工作必将彻底改变人们对动载影响的认识。这些研究还将确定与惯性效应相关的运动门槛速度。这些进展将为评估这些植入物的测试方法和标准奠定基础。理想情况下，这将导致ASTM植入物测试标准的重新起草。此外，与动态加载相关的一般发现将对所有其他植入物重建关节的测试具有指导意义。

There have been numerous engineering-based biomechanical studies examining various factors related to the human joint, many focused on implant reconstruction. Essentially all of these investigations have employed static or cyclic loading at the articulation. However, very little has been established with regard to the effect of dynamic loading, where the time-dependent (i.e. viscoelastic) properties of the construct, and in particular bone and the interfaces are significant. It is logical to postulate that the introduction of loading in the dynamic range, due to high-velocity or impact related events, will change the load transfer mechanics relative to the static or quasi-static loading case. As individuals following joint reconstruction are becoming more active, it is important to ascertain the influence of dynamic loading for implant design and testing protocols down the road. This research program is designed to establish the importance of dynamic loading on the load transfer mechanics and stress state in the implant-bone construct of the shoulder. To date, experimental shoulder testing employs static loading protocols on cadaver specimens or surrogate foam models. Some recent systems have produced arm motion using simplified muscle controlling protocols and/or robotics. However, these approaches do not accommodate for high velocity and inertial effects. Furthermore, computational finite-element modeling has not typically included dynamic loading. Hence, optimizing our understanding and evaluation of this joint necessitates the development and application of advanced comprehensive testing and modeling approaches that incorporate dynamic loading. The short-term objectives of this research program are to employ both experimental and computational approaches to: (i) determine the effect of dynamic activity on joint loads; (ii) determine the effect of dynamic joint loading on the implant-bone interface. The long-term objective of this program is to produce a state-of-the-art testing program that will permit a wide range of advanced research-based studies on the shoulder, with special interest in simulating joint loading for activities from low-demand to high-velocity(impact) activities. The work proposed herein will certainly revolutionize the understanding of the influence of dynamic loading. These studies will also establish the threshold velocities of motion where inertial effects become relevant. These advances will set the stage for testing methodologies and standards for the assessment of these implants. Ideally, this will lead to the re-drafting of the ASTM standards for implant testing. Furthermore, the general findings related to dynamic loading will have implications for the testing of all other implant reconstructed joints.