Dept of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia.
Dept of Mechanical Engineering, University of Melbourne, Victoria 3010, Australia.
J Biomech. 2021 Jun 23;123:110484. doi: 10.1016/j.jbiomech.2021.110484. Epub 2021 Apr 30.
We measured the moment arm of the knee-extensor mechanism as ten healthy young individuals performed six functional activities: level walking, downhill walking, stair ascent, stair descent, open-chain (non-weight-bearing) knee flexion, and open-chain knee extension. The moment arm of the knee-extensor mechanism was described by the moment arm of the patellar-tendon force, which acts to rotate the tibia about the instantaneous axis of rotation (screw axis) of the knee. A mobile biplane X-ray imaging system enabled simultaneous measurements of the three-dimensional movements of the femur, tibia and patella during each activity, from which the position and orientation of the screw axis and the patellar-tendon moment arm (PTMA) were determined. Mean PTMA across all activities and all participants remained nearly constant (~46 mm) from 0° to 70° of knee flexion and decreased by no more than 20% at higher flexion angles. The magnitude of the PTMA varied more substantially across individuals than across activities, indicating that the moment arm is more heavily influenced by differences in knee-joint geometry than muscle loading. Hence, PTMA measurements obtained for a given activity performed by one individual may be used with good confidence to describe the PTMA for any other activity performed by the same individual. Caution is advised when using PTMA measurements obtained from one individual to describe the moment arm in another individual even once the data are normalized by knee bone size, as the PTMA varied by as much as 13% from the mean across individuals.
我们测量了 10 位健康年轻个体在进行 6 种功能性活动时膝关节伸肌机制的力臂：水平行走、下坡行走、上楼梯、下楼梯、开链（非负重）膝关节屈曲和开链膝关节伸展。膝关节伸肌机制的力臂由髌腱力的力臂描述，它作用于使胫骨围绕膝关节的瞬时旋转轴（螺旋轴）旋转。一个移动的双平面 X 射线成像系统能够在每个活动中同时测量股骨、胫骨和髌骨的三维运动，从中确定螺旋轴和髌腱力臂（PTMA）的位置和方向。在所有活动和所有参与者中，平均 PTMA 在 0°至 70°的膝关节屈曲范围内几乎保持不变（约 46 毫米），在更高的屈曲角度下不超过 20%。个体之间的 PTMA 变化幅度比活动之间的变化幅度大得多，这表明力臂受膝关节几何形状差异的影响比肌肉负荷更大。因此，对于特定活动由一个个体获得的 PTMA 测量值可以被很好地用于描述同一个体进行的任何其他活动的 PTMA。即使通过膝关节骨大小对数据进行归一化，使用从个体获得的 PTMA 测量值来描述另一个个体的力臂时也需要谨慎，因为个体之间的 PTMA 变化幅度最大可达 13%。
