Multiscale Contact Mechanics of Ankle Joint Implant: Comparison of Two Implant Models

This paper compares two different types of ankle implants. The first is the cylinder-cylinder configuration in conformal contact and the second involves a cylinder-flat in contact. The interaction of implant rough surfaces including both elastic and plastic deformations is included in the contact model. The tibia and the talus surfaces are treated as macroscopically conforming cylinders in the first model and flat-cylinder in the second model, containing micron-scale roughness. The derived equations relate contact force on the implant and the minimum mean surface separation of the rough surfaces. Based on the distribution of asperity heights, the force is expressed using statistical integral function of asperity heights over possible region of interaction of the roughness of the tibia and the talus implant surfaces. Closed-form approximate equation relating contact force and minimum separation is used to obtain hysteretic energy loss per cycle in a load-unload sequence applied to the implant.