Wimmer M A, Andriacchi T P
Biomechanics Section, Technical University Hamburg-Harburg, Germany.
J Biomech. 1997 Feb;30(2):131-7. doi: 10.1016/s0021-9290(96)00112-1.
Wear at the polyethylene tibial plateau in total knee arthroplasty (TKR) is one of the primary concerns with these devices. The artificial bearing of a TKR has to sustain large forces while allowing the mobility for normal motion, typically, rolling, gliding and rotation. The tractive forces during the rolling motion at the knee joint were analyzed to determine which factors cause these forces to increase in TKR. The implications of these tractive forces to polyethylene wear were considered. Traction forces were calculated using a model of the knee to evaluate the effect of variations in the coefficient of friction, gait characteristics, antagonistic muscle contraction and patellofemoral mechanics. The model was limited to the sagittal plane motion of the femur on the tibia. The input for the model was the shape of the articulating surface, coefficient of friction, contact path, muscle anatomy and gait kinetics common to patients with a total knee replacement. The generation of tractive forces on the tibial polyethylene plateau was highly dependent on the static and dynamic coefficient of friction between the femur and the tibia. A peak tractive force of approximately 0.4 body weight was calculated with a peak normal force of 3.3 body weight. Tractive rolling occurred during most of stance phase when the static coefficient was 0.2. Alterations in gait patterns had a substantial effect on the generation of tractive forces at the knee joint. When an abnormal gait pattern (often seen following TKR) was input to the model the posteriorly directed tractive force on the tibial surface was reduced. It was also found that variations in muscle contractions associated with antagonistic muscle activity as well as the angle of pull of the patellar tendon affected the magnitude of tractive forces. The results of the study suggest that there are feasible conditions following total knee replacement which can lead to tractive forces during rolling motion at the tibiofemoral articulation that should be considered in the analysis of factors leading to polyethylene damage in total knee replacement.
全膝关节置换术（TKR）中聚乙烯胫骨平台的磨损是这些装置的主要问题之一。TKR的人工关节面必须承受巨大的力量，同时还要保证正常活动所需的灵活性，通常包括滚动、滑动和旋转。分析膝关节滚动运动过程中的牵引力，以确定哪些因素会导致TKR中这些力增加。考虑了这些牵引力对聚乙烯磨损的影响。使用膝关节模型计算牵引力，以评估摩擦系数、步态特征、拮抗肌收缩和髌股力学变化的影响。该模型仅限于股骨在胫骨上的矢状面运动。模型的输入包括全膝关节置换患者常见的关节面形状、摩擦系数、接触路径、肌肉解剖结构和步态动力学。胫骨聚乙烯平台上牵引力的产生高度依赖于股骨与胫骨之间的静摩擦系数和动摩擦系数。计算得出，在正常力峰值为3.3倍体重时，牵引力峰值约为0.4倍体重。当静摩擦系数为0.2时，在大部分站立阶段都会发生牵引滚动。步态模式的改变对膝关节牵引力的产生有很大影响。当将异常步态模式（TKR后常见）输入模型时，胫骨表面向后的牵引力会降低。还发现，与拮抗肌活动相关的肌肉收缩变化以及髌腱的牵拉角度会影响牵引力的大小。研究结果表明，全膝关节置换术后存在一些可行的条件，可能导致胫股关节滚动运动期间产生牵引力，在分析全膝关节置换中导致聚乙烯损坏的因素时应予以考虑。
