Total Hip Replacement response to a variation of the radial clearance through in silico models

The in silico analysis is a powerful approach able to simulate via calculators a physical phenomenon, in order to, for example, conduct a parametric analysis during the design of a prosthesis. In the biomechanics and biotribology fields, a specific attention is paid to the design parameters (i.e., mechanical and geometrical) characterising the prosthetic implant which will replace an unhealthy synovial articulation: a tribological characterization of the artificial joint is actually needed, so that minimum wear and maximum duration are guaranteed. The aim of this chapter is to analyse the tribological response of an artificial hip joint made of Ultra High Molecular Weight PolyEthylene acetabular cup against ceramic femoral head to a variation of the implant radial clearance. The task is performed by taking advantage of two numerical models developed by the authors in Matlab computational environment: - a multibody model solving the inverse dynamics of musculoskeletal mechanical systems and elaborating the muscular actions and the joint reactions produced by a selected kinematics input, used for a lower limb apparatus moving following the gait cycle evolution; - a lubrication model based on the Reynolds equation numerical solution supplied by the hip joint loads and relative angular velocities coming from the multibody simulation, which elaborates the tribological quantities associated to the mixed elasto-hydrodynamic lubrication mode (fluid/contact pressure, surfaces’ separation, wear penetration depth, etc.). The whole computational tool obtained by the merging of the two models allowed us to collect information about the behaviour of interesting tribological quantities, with respect to a variation of the implant radial clearance, in order to study its role in the framework of the prosthesis wear prediction during its design.