INVESTIGATION OF THE RADIAL CLEARANCE INFLUENCE ON THE TRIBOLOGICAL BEHAVIOUR OF HARD-ON-SOFT HIP IMPLANTS BASED ON LUBRICATION AND MULTIBODY SIMULATION MODELS

The aim of this work 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 in silico analysis is conducted by taking advantage of the interaction between a multibody model and a lubrication one, both developed in Matlab (MathWorks, Portola Valley, CA) by the authors. The multibody model solves the inverse dynamics of the musculoskeletal mechanical system associated to the lower limb apparatus, elaborating the muscular actions and the joint reactions produced by the gait cycle kinematics input. The lubrication model is based on the numerical solution of the Reynolds equation: it is supplied by the hip joint loads and relative angular velocities obtained from the multibody simulation and it 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 is used to conduct a parametric analysis with respect to the implant radial clearance, in order to study its role in the framework of the prosthesis wear prediction during its design.