van den Kroonenberg A J, Hayes W C, McMahon T A
Charles A. Dana Research Institute, Department of Orthopaedic Surgery, Beth Israel Hospital, Boston, MA, USA.
J Biomech Eng. 1995 Aug;117(3):309-18. doi: 10.1115/1.2794186.
Despite our growing understanding of the importance of fall mechanics in the etiology of hip fracture, previous studies have largely ignored the kinematics and dynamics of falls from standing height. Beginning from basic principles, we estimated peak impact force on the greater trochanter in a sideways fall from standing height. Using a one degree-of-freedom impact model, this force is determined by the impact velocity of the hip, the effective mass of that part of the body that is moving prior to impact, and the overall stiffness of the soft tissue overlying the hip. To determine impact velocity and effective mass, three different paradigms of increasing complexity were used: 1) a falling point mass or a rigid bar pivoting at its base; 2) two-link models consisting of a leg segment and a torso; and 3) three-link models including a knee. The total mechanical energy of each model before falling was equated to the total mechanical energy just prior to impact in order to estimate the hip impact velocity. In addition, the configuration of the model just before impact was used to estimate the effective mass. Our model predictions were compared with the results of an earlier experimental study with young subjects falling on a 10-inch thick mattress. Values from literature were used to estimate the soft tissue stiffness. For the models, predicted values for hip impact velocity and effective mass ranged from 2.47 to 4.34 m/s and from 15.9 to 70.0 kg, respectively. Predicted values for the peak force applied to the greater trochanter ranged from 2.90k to 9.99k N. Based on comparisons to the experimental falls, impact velocity and impact force were best predicted by a simple two-link model with the trunk at 45 degrees to the vertical at impact. A three-link model with a quadratic spring incorporated in the knee of the model was the best predictor of effective mass. Using our most accurate model, the peak impact force was 2.90k N for a 5th percentile female and 4.26k N for a 95th percentile female, thereby confirming the widely held perception that "the bigger they are, the harder they fall".
尽管我们对跌倒力学在髋部骨折病因中的重要性的理解不断加深，但以往的研究在很大程度上忽略了从站立高度跌倒的运动学和动力学。从基本原理出发，我们估算了从站立高度侧向跌倒时大转子上的峰值冲击力。使用单自由度冲击模型，该力由髋部的冲击速度、冲击前运动的身体部分的有效质量以及髋部上方软组织的整体刚度决定。为了确定冲击速度和有效质量，使用了三种不同复杂度递增的范例：1）一个落体质点或一个在其底部枢转的刚性杆；2）由腿部节段和躯干组成的双连杆模型；3）包括膝盖的三连杆模型。每个模型跌倒前的总机械能等于冲击前的总机械能，以估算髋部冲击速度。此外，冲击前模型的构型用于估算有效质量。我们的模型预测结果与一项早期针对年轻受试者在10英寸厚床垫上跌倒的实验研究结果进行了比较。使用文献中的值来估算软组织刚度。对于这些模型，髋部冲击速度和有效质量的预测值分别在2.47至4.34米/秒和15.9至70.0千克之间。施加在大转子上的峰值力的预测值在2.90k至9.99k牛顿之间。基于与实验性跌倒的比较，冲击速度和冲击力通过一个简单的双连杆模型能得到最佳预测，该模型在冲击时躯干与垂直方向成45度角。一个在膝盖处包含二次弹簧的三连杆模型是有效质量的最佳预测模型。使用我们最精确的模型，第5百分位女性的峰值冲击力为2.90k牛顿，第95百分位女性为4.26k牛顿，从而证实了人们普遍持有的看法，即“块头越大，摔得越狠”。
