Temperature modeling in a total knee joint replacement using patient- specific kinematics

This paper reports the implementation of a computer modeling approach that uses fluoroscopically measured motions of total knee replacements as inputs and predicts patient-specific implant temperature rises using computationally efficient dynamic contact and thermal analyses. The multibody dynamic simulations of two activities (gait and stair) were generated from the fluoroscopic data to predict contact pressure and slip velocity time histories for individual elements on the tibial insert surface. These time histories were used in a computational thermal analysis to predict average steady-state temperature rise due to frictional heating on each element. For the standard condition, which assumes an ultra-high molecular weight polyethylene (UHMWPE) tibial component and cobalt-chrome femoral component, 1Hz activity frequency, friction coefficient of 1⁄4 0:06; and convective heat transfer coefficient of h 1⁄4 30 ðW=ðm KÞÞ; the predicted maximum temperature rise on the medial compartment was 9.1 and 14 8C for continuous activities of gait and stair respectively. The sensitivity of the temperature rise to activity rate, heat partitioning to the femoral component, and convective heat transfer coefficient was explored. The model is extremely sensitive to the thermal properties of the femoral component and predicts order of magnitude changes in contact temperature with order of magnitude changes in thermal conductivity. A survey of thermal conductivity for current and proposed scratch resistant femoral component implant materials shows variations greater than an order of magnitude.