Finite element analysis of stress and wear characterization in total ankle replacements

• A characteristic axial force model for the ankle gait was developed.
• Linear viscoelastic parameters for UHMWPE were modeled during FEA.
• Deduced FEA models were used to determine the contact and sub-surface stresses.
• A new wear model was developed to predict the wear rate in the TARs.
• Determined optimization equations provide a basis for improving the life of TARs.

Total Ankle Arthroplasty is performed in order to reduce the pain and loss of ambulation in patients with various forms of arthritis and trauma. Although replacement devices fail by a number of mechanisms, wear in the polyethylene liner constitutes one of the dominating failure modes. This leads to instability and loosening of the implant. Mechanisms that contribute to wear in the liners are high contact and subsurface stresses that break down the material over time. Therefore, it is important to understand the gait that generates these stresses. Methods to characterize and decrease wear in Ohio Total Ankle Replacements (TARs) have been performed in this research. This research utilizes finite element analysis of Wright State University (WSU) patented TAR models. From the Finite element analysis (FEA) results, mathematical models of contact conditions and wear mechanics were developed. The maximum wear rate values obtained in the study (at 25.598 MPa, 3.74 mm3/year) and maximum surface Mises stress obtained with new optimization model (11.52 MPa) seem to be comparable with the maximum wear values obtained in other similar studies. These models were used to determine the best methods for wear characterization and reduction. Furthermore, optimization models were developed based on geometry of the implants. These equations optimize geometry, thus congruency and anatomical simulations for total ankle implants.

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