Xu Chun, Silder Amy, Zhang Ju, Hughes Julie, Unnikrishnan Ginu, Reifman Jaques, Rakesh Vineet
J Biomech Eng. 2016 Oct 1;138(10). doi: 10.1115/1.4034216.
Prior studies have assessed the effects of load carriage on the tibia. Here, we expand on these studies and investigate the effects of load carriage on joint reaction forces (JRFs) and the resulting spatiotemporal stress/strain distributions in the tibia. Using full-body motion and ground reaction forces from a female subject, we computed joint and muscle forces during walking for four load carriage conditions. We applied these forces as physiological loading conditions in a finite-element (FE) analysis to compute strain and stress. We derived material properties from computed tomography (CT) images of a sex-, age-, and body mass index-matched subject using a mesh morphing and mapping algorithm, and used them within the FE model. Compared to walking with no load, the knee JRFs were the most sensitive to load carriage, increasing by as much as 26.2% when carrying a 30% of body weight (BW) load (ankle: 16.4% and hip: 19.0%). Moreover, our model revealed disproportionate increases in internal JRFs with increases in load carriage, suggesting a coordinated adjustment in the musculature functions in the lower extremity. FE results reflected the complex effects of spatially varying material properties distribution and muscular engagement on tibial biomechanics during walking. We observed high stresses on the anterior crest and the medial surface of the tibia at pushoff, whereas high cumulative stress during one walking cycle was more prominent in the medioposterior aspect of the tibia. Our findings reinforce the need to include: (1) physiologically accurate loading conditions when modeling healthy subjects undergoing short-term exercise training and (2) the duration of stress exposure when evaluating stress-fracture injury risk. As a fundamental step toward understanding the instantaneous effect of external loading, our study presents a means to assess the relationship between load carriage and bone biomechanics.
先前的研究评估了负重对胫骨的影响。在此，我们拓展这些研究，并调查负重对关节反应力（JRFs）以及胫骨中由此产生的时空应力/应变分布的影响。利用一名女性受试者的全身运动和地面反作用力，我们计算了四种负重条件下行走过程中的关节力和肌肉力。我们将这些力作为生理负荷条件应用于有限元（FE）分析中，以计算应变和应力。我们使用网格变形和映射算法，从一名性别、年龄和体重指数匹配的受试者的计算机断层扫描（CT）图像中得出材料属性，并将其应用于有限元模型中。与无负重行走相比，膝关节JRFs对负重最为敏感，在背负30%体重（BW）的负荷时增加了26.2%（踝关节：16.4%，髋关节：19.0%）。此外，我们的模型显示，随着负重增加，内部JRFs不成比例地增加，这表明下肢肌肉功能进行了协调调整。有限元结果反映了空间变化的材料属性分布和肌肉参与对行走过程中胫骨生物力学的复杂影响。我们观察到，在蹬离期，胫骨前嵴和内表面存在高应力，而在一个行走周期中，高累积应力在胫骨的中后方面更为突出。我们的研究结果强化了以下必要性：（1）在对接受短期运动训练的健康受试者进行建模时，纳入生理上准确的负荷条件；（2）在评估应力性骨折损伤风险时，考虑应力暴露的持续时间。作为理解外部负荷即时效应的基本步骤，我们的研究提供了一种评估负重与骨骼生物力学之间关系的方法。
