Courtney A C, Wachtel E F, Myers E R, Hayes W C
Department of Orthopaedic Surgery, Charles A. Dana Research Institute, Beth Israel Hospital and Harvard Medical School, Boston, Massachusetts 02215.
Calcif Tissue Int. 1994 Jul;55(1):53-8. doi: 10.1007/BF00310169.
Results from previous quasi-static mechanical tests indicate that femurs from elderly subjects fail in vitro at forces 50% below those available in a fall from standing height. However, bone is a rate-dependent material, and it is not known whether this imbalance is present at rates of loading which occur in a fall. Based on recent data on time to peak force and body positions at impact during simulated falls, we designed a high rate test of the femur in a loading configuration meant to represent a fall on the hip. We used elderly (mean age 73.5 +/- 7.4 (SD) years) and younger adult (32.7 +/- 12.8 years) cadaveric femurs to investigate whether (1) the strength, stiffness, and energy absorption capacity of the femur increases under high rate loading conditions; (2) elderly femurs have reduced strength, stiffness, and energy absorption capacity compared with younger adult femurs at this loading rate; and (3) densitometric and geometric measures taken at the hip correlate with the measured fracture loads. Femurs were scanned using dual-energy X-ray absorptiometry (DXA) and then tested to failure in a fall loading configuration at a displacement rate of 100 mm/second. The fracture load in elderly and younger adult femurs increased by about 20% with a 50-fold increase in displacement rate. However, energy absorption did not increase with displacement rate because of a twofold increase in stiffness at the higher loading rate.(ABSTRACT TRUNCATED AT 250 WORDS)
先前的准静态力学测试结果表明，老年受试者的股骨在体外承受的力比从站立高度跌落时所能产生的力低50% 时就会失效。然而，骨骼是一种与速率相关的材料，目前尚不清楚在跌落时出现的加载速率下这种不平衡是否存在。基于最近关于模拟跌落过程中达到峰值力的时间和撞击时身体姿势的数据，我们设计了一种股骨的高速率测试，其加载配置旨在模拟臀部着地的跌落。我们使用老年（平均年龄73.5±7.4（标准差）岁）和年轻成人（32.7±12.8岁）的尸体股骨来研究：（1）在高速率加载条件下，股骨的强度、刚度和能量吸收能力是否会增加；（2）在这种加载速率下，老年股骨与年轻成人股骨相比，其强度、刚度和能量吸收能力是否降低；（3）在髋部进行的骨密度和几何测量与测得的骨折负荷是否相关。使用双能X线吸收法（DXA）对股骨进行扫描，然后以100毫米/秒的位移速率在跌落加载配置下测试至失效。随着位移速率增加50倍，老年和年轻成人股骨的骨折负荷增加了约20%。然而，由于在较高加载速率下刚度增加了两倍，能量吸收并未随位移速率增加。（摘要截取自250词）
