Dynamic stress response of the implant/cement interface: an axisymmetric analysis of a knee tibial component.
To determine the adverse effects on the implant/cement interface stresses caused by a dynamic load on the implant, an axisymmetric dynamic finite element analysis was performed for an idealized knee tibial component assuming perfect bonding at the interface. The component, consisting of a metal plate with a central stem, was subjected to a compressive load that varied with time as a terminated ramp function. At first, the reliability of the interface stress predictions was assessed by computing the effects of a number of method-related parameters, viz., the finite element mesh density, the assumed bone properties. Analysis was then performed considering the stem length, cement mantle thickness, and the type of implant metal as design variables. The analysis predicts high-frequency (600 Hz) stress oscillations of significant amplitude at those locations of the interface that are also subjected to high static stresses: near the stem-plate junction and the stem tip for normal stress, and at the stem tip for shear stress. However, the predicted stress amplitude has been found to be particularly sensitive to the assumed rise time of the input load function. With a rise time of 2.0 ms, an input condition considered to be severe enough to represent the most vigorous dynamic activity, the maximum stress augmentation, because of stress oscillations, is predicted to be less than 25%. In general, the design variables have been found to affect the static stresses much more than the dynamic ones. It has been concluded that for the cases studied, dynamic effects are relatively small and a static analysis is sufficient to characterize the interface stress condition.
Ahmed
A M
AM
Department of Mechanical Engineering, McGill University, Montreal, PQ, Canada.
Tissakht
M
M
Shrivastava
S C
SC
Chan
K
K
D000368:Aged; D001330:Electronic Data Processing; D006801:Humans; D007595:Joint Prosthesis; D007717:Knee / Q000033:anatomy & histology / Q000502:physiology; D007719:Knee Joint / Q000033:anatomy & histology / Q000502:physiology*; D008297:Male; D008433:Mathematics; D013314:Stress, Mechanical; D013977:Tibia / Q000033:anatomy & histology / Q000502:physiology