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With rising life expectancy, an increasing number of people needs implants to replace
their natural joints and needs them for a longer time. To avoid implant revisions, with
all the risks additional surgery brings, an increased life-time of implants is therefore
important. One of the limiting factors for more durable implants is wear.
Design and later admission of new implant models requires in-vitro experiments using
mechanical knee simulators with controlled environment conditions and a standardized
gait cycle. This is expensive and time consuming: prototypes need to be manufactured,
and a run in the simulator takes about three months.
Recreating the physical experiments in a computer simulation avoids these limitations
during the design cycle: instead of prototypes, only meshes have to be created and
numerical simulations take hours instead of months. We therefore present a software
knee simulator based on the Dune framework to simulate wear on total knee
replacements following the standardized test procedure described in ISO 14243-1. Our
model uses frictionless contact between elastic bodies using a dual mortar formulation.
For a single gait cycle, we use a quasi-static time discretization and compute the wear
using Archard’s law. On a second, larger time scale, we keep track of the local mass
loss and modify the implant geometry accordingly.
CAD data and experimental results were available for two different knee implant
models. Our simulation results using material constants from the literature are
comparable to the experimental results for both the total wear mass loss and its spatial
distribution.