Knee Implant Wear Modeling
Undergraduate Honor's Thesis
Dartmouth College
Fall 2011 - Spring 2012
Total knee arthroplasty (TKA) is a clinically successful solution for diminishing pain, restoring knee mobility, and treating advanced knee osteoarthritis by replacing the natural articulating surface of the knee with an implant. The number of revision surgeries and failed implants is significant due to the large volume of surgeries.
Wear of polyethylene due to the cyclic articulation of metal leads to osteolysis and the most common modes of implant failure. This explant study focused on identifying the predictors of backside volumetric wear rates for two DePuy knee systems, the PFC and the Sigma.
FEA model construction to test the wear rate hypothesis using finite element analysis complemented a statistical analysis of explant characteristics. Modeling common loading conditions for human knees and comparing the resultant stress distributions revealed that higher ketone peaks lead to large sliding displacements and lower stresses and contact areas than lower ketone peaks. I concluded that PFC implants failed due to poor conformity and high ketone peak, whereas only ketone peak drove failure in Sigma implants. Sigma implants failed with less wear than PFC implants due to particle generation with high functional biological activity, provoking a premature osteolysis response and causing implant failure.
