Pull-Out Response of a Steel Post Inserted in a Pre-Drilled HDPE Cylinder: Analytical and Finite Element Analyses Using Pressure-Dependent Friction

Abstract

For the aim of fixing and stabilizing the Total Knee Arthroplasty (TKA) tibial component, pull-out strength of the post is one of the most important factors to be considered. The material properties of bone, coupled with the principal dimensions of bone/post assembly such as diameter, interference fit and implantation length, may affect the pull-out strength of the post fixation. In this study, a cylindrical stainless steel post inserted in a pre-drilled High Density Polyethylene (HDPE) cylinder with an initial interference fit was taken as a model to assess the contribution of post fixation to the initial stability of TKA tibial component. Pull-out experiments were carried out for different initial interference fits and implantation lengths. Under pull-out loading, the micro-slip initiation and propagation at the post/cylinder interface was found to be progressive and was modeled using Coulomb friction at the interface. In order to examine the experimental ultimate pull-out force results, an analytical model was developed. The analytical model was fitted to the experimental results by adjusting the friction coefficient for the considered ranges of initial interference fit and implantation length. It was found that friction coefficient depends on initial interference fit (Δr) as well as on the initial contact pressure (σ0). For the considered interference fit values Δr = 01 mm, Δr = 02 mm and Δr = 03 mm (σ₀ = 1362 MPa, σ₀ = 2724 MPa and σ₀ = 4086 MPa), the values of adjusted friction coefficient are 0.091, 0.067 and 0.058, respectively. Finite Element simulation was also carried out for the pull-out test using the ABAQUS program. It was found that numerical, analytical and experimental results are all in good agreement.