Polycarbonate-urethane coating can significantly improve talus implant contact characteristics

Talus implants can be utilized in cases of talus avascular necrosis and has been regarded as a promising treatment method. However, existing implants are made of stiff materials that directly oppose natural cartilage. The risk of long-term cartilage wear and bone fracture from the interaction between the cartilage and stiff implant surfaces has been documented in post-hemiarthroplasty of the hip, knee and ankle joints. The aim is to explore the effects of adding a layer of compliant material (polycarbonate-urethane; PCU) over a stiff material (cobalt chromium) in talus implants. To do so, we obtained initial ankle geometry from four cadaveric subjects in neutral standing to create the finite element models. We simulated seven models for each subject: three different types of talus implants, each coated with and without PCU, and a biological model. In total, we constructed 28 finite element models. By comparing the contact characteristics of the implant models with their respective biological model counterparts, our results showed that PCU coated implants have comparable contact area and contact pressure to the biological models, whereas stiff material implants without the PCU coating all have relatively higher contact pressure and smaller contact areas. These results confirmed that adding a layer of compliant material coating reduces the contact pressure and increases the contact area which in turn reduces the risk of cartilage wear and bone fracture. The results also suggest that there can be clinical benefits of adding a layer of compliant material coating on existing stiff material implants, and can provide valuable information towards the design of more biofidelic implants in the future.