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

有许多基于工程的生物力学研究检查了与人体关节相关的各种因素，许多研究集中在植入物重建上。基本上，所有这些研究都在关节处采用了静态或循环载荷。然而，很少有关于动态载荷的影响，其中结构的时间依赖性（即粘弹性）特性，特别是骨和界面是重要的。在动态范围内引入载荷是合乎逻辑的，由于高速或撞击相关事件，将改变相对于静态或准静态加载情况下的载荷传递力学。随着关节重建后的个体变得越来越活跃，确定动态载荷对种植体设计和测试方案的影响非常重要。本研究旨在建立动态载荷对肩骨植入体载荷传递力学和应力状态的重要性。迄今为止，实验肩部测试采用尸体标本或替代泡沫模型的静态加载协议。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，优化我们对这种接头的理解和评估需要开发和应用先进的综合测试和建模方法，包括动态加载。本研究计划的短期目标是采用实验和计算方法：(i)确定动力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。该项目的长期目标是建立一个最先进的测试程序，允许对肩部进行广泛的先进研究，特别关注从低要求到高速（冲击）活动的模拟关节载荷。本文提出的工作将彻底改变对动态载荷影响的理解。这些研究还将确定惯性效应相关的运动阈值速度。这些进步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，这将导致重新起草ASTM植入物测试标准。此外，与动态载荷相关的一般发现将对所有其他种植体重建关节的测试产生影响。

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.