Krevolin Janet L, Pandy Marcus G, Pearce John C
Department of Mechanical Engineering, University of Texas, Austin, TX 78712, USA.
J Biomech. 2004 May;37(5):785-8. doi: 10.1016/j.jbiomech.2003.09.010.
The moment arm of the knee-extensor mechanism is described by the moment arm of the patellar tendon calculated with respect to the screw axis of the tibia relative to the femur. The moment arm may be found once the line of action of the patellar tendon and the position and orientation of the screw axis are known. In this study, the orientation of the patellar tendon and the position and orientation of the finite screw axis of the tibia relative to the femur were calculated from measurements of the three-dimensional positions of the bones obtained from fresh cadaver specimens. Peak values of the patellar tendon moment arm ranged from 4-6 cm for the six knees tested; the moment arm was maximum near 45 degrees of knee flexion. The moment arm of the patellar tendon was nearly equal to the shortest (perpendicular) distance between the line of action of the patellar tendon and the axis of rotation of the knee at all flexion angles, except near full extension. Near full extension, the angle between the patellar tendon and the screw axis was significantly less than 90 degrees, and the magnitude of the moment arm was then less than the perpendicular distance between these two lines. The patellar tendon moment arm remained roughly constant across individuals when normalized by femoral condyle width, suggesting that anatomical differences play a large role in determining the moment arm of the extensor mechanism.
膝伸肌机制的力臂由髌腱相对于胫骨相对于股骨的螺旋轴计算得出的力臂来描述。一旦知道髌腱的作用线以及螺旋轴的位置和方向，就可以找到力臂。在本研究中，髌腱的方向以及胫骨相对于股骨的有限螺旋轴的位置和方向是根据从新鲜尸体标本获得的骨骼三维位置测量值计算得出的。所测试的六个膝关节的髌腱力臂峰值范围为4 - 6厘米；力臂在膝关节屈曲约45度时最大。除接近完全伸展外，在所有屈曲角度下，髌腱的力臂几乎等于髌腱作用线与膝关节旋转轴之间的最短（垂直）距离。接近完全伸展时，髌腱与螺旋轴之间的角度明显小于90度，此时力臂的大小小于这两条线之间的垂直距离。当以股骨髁宽度进行归一化时，髌腱力臂在个体间大致保持恒定，这表明解剖学差异在决定伸肌机制的力臂方面起很大作用。
