Dry and Wet Lubrication Analysis for Multi-Material Hip Assembly

Hip joint repair/replacement is one of the most thriving orthopedic surgical procedures in the human body. The group of patients undergoing hip replacement considerably includes young and physically active persons with varying movements thus requiring longer product life and ease of maintenance. Perfect lubrication in hip assembly ensures a low wear rate and better product life. The present work focuses on dry and wet lubrication analysis of complete implant assembly instead of an individual part. The assembly consists of a stem, head, liner and cup, each made of different materials like a ceramic femoral head mounted over a metallic femoral stem with a polyethylene liner and a metallic acetabular cup.  In this work, eight metal-materials are considered for stem/cup, three ceramic materials for the head and two polyethylene materials for the liner. The combinations of these materials are evaluated for various mechanical parameters. Dry (µ = 0.13) and wet (µ = 0.05) lubricating conditions between the liner and femoral head have been considered and their effects on the head, liner and cup have been evaluated for the optimization of Hip joint design. Fifty percent of re-surgery cases arise because of excessive wear out resulting in aseptic loosening of the femoral head and liner interface. Femoral head of size 28 mm diameter with 2 mm thick liner and 3 mm thick acetabular cup are modeled and are analyzed for axial pay load of 2.3 kN. The maximum von mises stress and total deformation for various material combinations of implant assembly have been compared to select the most suitable one for the arthroplasty implantation. The combination of CoCrMo – Ceramics – HXLPE – CoCrMo demonstrates minimum stress and deformation for all three parts i.e. femoral head, liner and acetabular cup under present loading and boundary conditions. ZTA is emerged as the preferred ceramic material for femoral head having a higher compressive strength.