TRACTIVE FORCES DURING ROLLING MOTION OF THE KNEE - IMPLICATIONS FOR WEAR IN TOTAL KNEE REPLACEMENT

Wear at the polyethylene tibial plateau in total knee arthroplasty (TK R) is one of the primary concerns with these devices. The artificial b earing of a TKR has to sustain large forces while allowing the mobilit y for normal motion, typically, rolling, gliding and rotation. The tra ctive 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 consi dered. Traction forces were calculated using a model of the knee to ev aluate the effect of variations in the coefficient of friction,gait ch aracteristics, antagonistic muscle contraction and patellofemoral mech anics. 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 articulati ng surface, coefficient of friction, contact path, muscle anatomy and gait kinetics common to patients with a total knee replacement. The ge neration of tractive forces on the tibial polyethylene plateau was hig hly dependent on the static and dynamic coefficient of friction betwee n 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 stati c 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 mod el the posteriorly directed tractive force on the tibial surface was r educed. It was also found that variations in muscle contractions assoc iated with antagonistic muscle activity as well as the angle of pull o f the patellar tendon affected the magnitude of tractive forces. The r esults of the study suggest that there are feasible conditions followi ng total knee replacement which can lead to tractive forces during rol ling motion at the tibiofemoral articulation that should be considered in the analysis of factors leading to polyethylene damage in total kn ee replacement. Copyright (C) 1996 Elsevier Science Ltd.