Abstract：
Fall-related hip fractures are a serious public health issue in older adults. As most mechanistic hip fracture risk prediction models incorporate tissue tolerance, test methods that can accurately characterize the fracture force of the femur (and factors that influence it) are imperative. While bone possesses viscoelastic properties, experimental characterization of rate-dependencies has been inconsistent in the whole-femur literature. The goal of this study was to investigate the influence of experimental paradigm on loading rate and fracture force (both means and variability) during mechanical tests simulating lateral fall loadings on the proximal femur. Six pairs of matched femurs were split randomly between two test paradigms: a \'lower rate\' materials testing system (MTS) with a constant displacement rate of 60 mm/s, and a hip impact test system (HIT) comprised of a custom-built vertical drop tower utilizing an impact velocity of 4 m/s. The loading rate was 88-fold higher for the HIT (mean (SD) = 2465.49 (807.38) kN/s) compared to the MTS (27.78 (10.03) kN/s) paradigm. However, no difference in fracture force was observed between test paradigms (mean (SD) = 4096.4 (1272.6) N for HIT, and 3641.3 (1285.8) N for MTS). Within-paradigm variability was not significantly different across paradigms for either loading rate or fracture force (coefficients of variation ranging from 0.311 to 0.361). Within each test paradigm, significant positive relationships were observed between loading rate and fracture force (HIT adjusted R2 = 0.833, p = 0.007; MTS adjusted R2 = 0.983, p < 0.0001). Overall, this study provides evidence that energy-based impact simulators can be a valid method to measure femoral bone strength in the context of fall-related hip fractures. This study motivates future research to characterize potential non-linear relationships between loading rate and fracture threshold at both macro and microscales.
摘要：
与跌倒相关的髋部骨折是老年人的严重公共卫生问题。由于大多数机械性髋部骨折风险预测模型都包含组织耐受性，能够准确表征股骨骨折力（及其影响因素）的测试方法势在必行。虽然骨骼具有粘弹性，在整个股骨文献中，速率依赖性的实验表征一直不一致。这项研究的目的是研究在模拟股骨近端横向跌落载荷的机械测试过程中，实验范式对载荷率和骨折力（均值和变异性）的影响。将六对匹配的股骨随机分为两个测试范例：一个“低速率”材料测试系统（MTS），其恒定位移速率为60mm/s，和髋部冲击测试系统(HIT),其包括利用4m/s的冲击速度的定制的垂直落塔。与MTS(27.78(10.03)kN/s)范例相比,HIT(平均值(SD)=2465.49(807.38)kN/s)的加载速率高88倍。然而,在试验范例之间没有观察到骨折力的差异(HIT的平均值(SD)=4096.4(1272.6)N,MTS为3641.3（1285.8）N）。对于加载速率或断裂力，范式内的变异性在范式之间没有显着差异（变异系数在0.311至0.361之间）。在每个测试范例中，在加载率和骨折力之间观察到显著的正相关(HIT调整R2=0.833,p=0.007;MTS调整R2=0.983,p<0.0001)。总的来说,这项研究提供的证据表明,在跌倒相关髋部骨折的情况下,基于能量的冲击模拟器可以成为测量股骨骨强度的有效方法.这项研究激发了未来的研究，以表征在宏观和微观尺度上加载速率和断裂阈值之间的潜在非线性关系。
