FALL BIOMECHANICS AND HIP FRACTURE RISK

以其发生频率衡量，对生活质量和经济 髋部骨折是一个危机比例的公共卫生问题。 的 髋部骨折发病率随年龄呈指数增长， 已经证明，骨密度和强度的年龄依赖性降低导致 人们普遍认为，与年龄有关的骨质流失，或骨质疏松症， 髋部骨折发病率的最重要决定因素。 然而，有些人 表明，老年人福尔斯跌倒倾向的增加是由于 最重要的致病因素。 最近通过对福尔斯的监控 研究和尸体股骨的体外强度测试，我们已经表明， 从站立高度坠落时所能提供的能量是 体外髋关节骨折所需的能量。 此外，大多数跌倒者 髋部骨折的人会倒向一侧，直接落在髋部， 而不是用伸出的手来阻止坠落。 这些发现表明 除了跌倒的发生率增加外， 跌倒本身很可能主导髋部骨折的发生， 老人 虽然先前的研究已经确定了这些宿主和 引发福尔斯的环境因素，没有以前的工作集中在 跌倒力学在髋部骨折病因学中的作用 老人 我们假设反射介导的福尔斯（其中神经肌肉 响应机制处于活动状态）导致坠落配置和撞击 力，代表髋部骨折的风险显著降低， 与跛行福尔斯（其中神经肌肉反应机制 缺席）。 为了探索这一假设，我们将使用一个快速移动的 蹦床，以启动安全的福尔斯在年轻的成年志愿者。 运动学 反射介导的和跛行的福尔斯跌倒将使用高速视频进行监测： B）装有仪表的汽车碰撞假人;以及 （c）老年尸体标本。 我们的第二个假设是髋部撞击 从一个简单的非伤害性的， 实验 这个“骨盆释放”实验使我们能够描述 身体部分配置（有效质量）的综合影响， 通过确定弹簧常数覆盖髋关节的软组织， 系统的简单质量-弹簧-阻尼器模型的阻尼因子。 这 实验将在男性和女性志愿者中进行， 几种潜在撞击形态的年龄和体型范围 有肌肉活动和没有肌肉活动的情况下。 的预测准确性 然后，将评估坠落撞击速度实际值下的模型 尸体坠落测试 最后，提供一个理论框架， 理解和扩展实验福尔斯和 骨盆释放实验，我们将开发一系列的分析 坠落和撞击的模型。 这些将开始与简单的集中质量 表示，并扩展到两个和三个元素的铰接段。 我们还将采用一个15段的动态模型（最初为 汽车碰撞模拟）到坠落的研究。 模型预测 将通过与实验福尔斯和尸体进行比较来验证 影响，然后用来探索条件，如反应时间， 下肢力量下降，导致高风险的福尔斯跌倒， 老人 我们希望这些实验和分析研究， 力学，以导致更好地理解这些因素，导致 福尔斯跌倒时髋部骨折的高风险，因此设计更多 有效的干预策略，以减少髋关节的发病率不断上升 老年人骨折。

As measured by their frequency, influence on quality of life and economic cost, hip fractures are a public health problem of crisis proportions. The exponential increase with age in hip fracture incidence, coupled with demonstrated age-dependent reductions in bone density and strength have led to the widely held view that age-related bone loss, or osteoporosis, is the most important determinant of hip fracture incidence. However, some have suggested that the increased propensity for falls among the elderly is the most important etiologic factor. Recently, through falls surveillance studies and in-vitro strength tests of cadaveric femora, we have shown that the energy available in a fall from standing height is about sixteen times the energy required to fracture the hip in-vitro. Moreover, most fallers who fracture their hip fall to the side, land directly on the hip and do not use the outstretched hand to break the fall. These findings suggest that in addition to the increased incidence of falling, the mechanics of the fall itself may well dominate the occurrence of hip fracture in the elderly. While previous research has determined those host and environmental factors which initiate falls, no previous work has focused on the role of fall mechanics in the etiology of hip fracture among the elderly. We hypothesize that reflex-mediated falls (in which neuromuscular response mechanisms are active) result in fall configurations and impact forces which represent a significantly decreased risk for hip fracture when compared to limp falls (in which neuromuscular response mechanisms are absent). To explore this hypothesis we will use a rapidly displaced trampoline to initiate safe falls in young adult volunteers. Kinematics of reflex-mediated and limp falls will be monitored using high-speed video in: a) young adult volunteers; b) an instrumented automotive crash dummy; and c) elderly cadaveric specimens. Our second hypothesis is that hip impact forces resulting from a fall can be predicted from a simple non-injurious experiment. This "pelvis-release" experiment allows us to characterize the combined influence of body segment configuration (the effective mass) and soft tissues overlying the hip by determining the spring constants and damping factors for simple mass-spring-dashpot models of the system. This experiment will be conducted with male and female volunteers representing a range of ages and body types for several potential impact configurations and both with and without muscle activity. The predictive accuracy of the model at realistic values of fall impact velocity will then be evaluated using cadaver drop tests. Finally, to provide a theoretical framework for understanding and extending the results of both the experimental falls and the pelvis-release experiments, we will develop a series of analytical models for falling and impact. These will begin with simple lumped mass representations and extend to two- and three-element articulated segments. We will also adapt a 15-segment, dynamic model (developed originally for automotive crash simulations) to the study of falling. Model predictions will be validated by comparison to the experimental falls and to cadaver impacts, and then used to explore conditions such as reaction times and decreased lower extremity strength which lead to high-risk falls in the elderly. We expect these experimental and analytical studies of fall mechanics to lead to an improved understanding of those factors which lead to falls with a high risk of hip fracture and thus to the design of more effective intervention strategies to reduce the growing incidence of hip fractures among the elderly.